Background: The Ca-ATPase activity of the plasma membranes of several tissues of preeclamptic pregnant women is significantly reduced when compared with the values of normotensive pregnant women. This has been explained considering the raise in the level of lipid peroxidation of the plasma membranes with preeclampsia. In this work we studied the effect of lipid peroxidation of syncytiotrophoblast basal (fetal facing) plasma membranes from normotensive pregnant women, on their level of Ca-ATPase activity. Methods: The syncytiotrophoblast basal (fetal facing) plasma membranes from normotensive pregnant women were isolated and irradiated with ultraviolet (UV) light (254 nm). The membranes were then assayed for Ca-ATPase activity and lipid peroxidation by TBARS. Results: The UV irradiation raises the level of lipid peroxidation of the membranes, producing a concomitant inhibition of their Ca-ATPase activity. Presence of the antioxidant butylated hydroxytoluene during the UV irradiation of the membranes prevents increase in their level of lipid peroxidation and hence the inhibition of their Ca-ATPase activity. Conclusion: These results give a strong support to the hypothesis that the lowered Ca-ATPase activity already described for plasma membranes of several tissues of preeclamptic women is the consequence of the increased level of lipid peroxidation shown by these membranes.

The Na or /Ca2 or exchanger's family of membrane transporters is widely distributed in cells and tissues of the animal kingdom and constitutes one of the most important mechanisms for extruding Ca2 or from the cell. Two basic properties characterize them. 1) Their activity is not predicted by thermodynamic parameters of classical electrogenic countertransporters (dependence on ionic gradients and membrane potential), but is markedly regulated by transported (Na or and Ca2 or ) and nontransported ionic species (protons and other monovalent cations). These modulations take place at specific sites in the exchanger protein located at extra-, intra-, and transmembrane protein domains. 2) Exchange activity is also regulated by the metabolic state of the cell. The mammalian and invertebrate preparations share MgATP in that role; the squid has an additional compound, phosphoarginine. This review emphasizes the interrelationships between ionic and metabolic modulations of Na or /Ca2 or exchange, focusing mainly in two preparations where most of the studies have been carried out: the mammalian heart and the squid giant axon. A surprising fact that emerges when comparing the MgATP-related pathways in these two systems is that although they are different (phosphatidylinositol bisphosphate in the cardiac and a soluble cytosolic regulatory protein in the squid), their final target effects are essentially similar: Na or -Ca2 or -H or interactions with the exchanger. A model integrating both ionic and metabolic interactions in the regulation of the exchanger is discussed in detail as well as its relevance in cellular Ca-i(2 or ) homeostasis.

Body composition in birds was evaluated indirectly by O-18 and H-2 dilution. Body composition was determined by whole-body chemical analysis of eight adult roosters (Gallus gallus). In vivo measurements of total body water (TBW) were carried out using doubly labeled water ((H2O)-H-2-O-18). Estimated dilution spaces using both the plateau and intercept approaches were compared with the results obtained by carcass lyophilization. Both O-18 and H-2 slightly overestimated TBW compared with the results obtained by lyophilization, by and 2.2% or /- 1.9% and 5.7% or /- 0.2%, respectively; both differences were statistically significant (P < 0.01). The difference between these isotope estimations was significant (P < 0.001). However, isotope dilution spaces and P < 0.001 TBW were highly correlated. There was a strong inverse relationship between total body fat and TBW percentages (r(2) = 0.98, P < 0.0001). The relation between TBW and body protein 0.98 P < 0.0001 was significant. Water content in lean body mass (72.8%) obtained in our study was very close to that reported in mammals, demonstrating no fundamental difference in tissue water content between birds and mammals. Estimated body fat and protein values from isotopic dilution did not significantly differ from values obtained by direct chemical analysis (P > 0.05) except for body fat in the Pace and Rathbun approach (Table 3). Although estimation of TBW and body composition by isotope dilution is time consuming and expensive, deuterium offers a reliable and low-cost alternative compared with O-18. The advantage of in vivo estimation of TBW with isotopic dilution in combination with the regression approach is that it permits repeated measurements of body composition on the same birds under laboratory and free-living conditions.

MEK1/2 inhibitors like U0126 can potentiate or antagonize the antitumor activity of cytotoxic agents such as cisplatin, paclitaxel or vinblastine, depending on the drug or the target cells. We now investigated whether U0126, differentially regulates melanoma signaling in response to UV radiation or betulinic acid, a drug lethal against melanoma. This report shows that U0126 inhibits early response (ERK) kinase activation and cyclin A expression in wt p53 C8161 melanoma exposed to either UV radiation or betulinic acid. However, U0126 does not protect from UV damage, but counteracts betulinic acid-mediated apoptosis in the same cells. Protection from the latter drug by joint treatment with U0126 was also evident in wt p53 MelJuso melanoma and mutant p53 WM164 melanoma. The latter cells were the most responsive to betulinic acid, showing a selective decline in the cdk4 protein, without a comparable change in other key cell cycle proteins like cdc2, cdk2, cdk7 or cyclin A, prior to apoptosis-associated PARP fragmentation. Laser scanning cytometry also showed that betulinic acid induced a significant increase in chromatin condensation in WM164 melanoma irrespective of whether they were in adherent form or as multicellular spheroids. All these betulinic acid-induced changes were counteracted by U0126. Our data show for the first time that (a) cdk4 protein is an early target of betulinic acid-induced apoptosis and (b) unrestricted ERK signaling favours betulinic acid-induced apoptosis, but this is counteracted by U0126, partly through counteracting chromatin condensation and restoring Akt activation decreased by betulinic acid treatment.

A mesoscopic model for the liquid/vapor interface previously developed for nonpolar fluids [J. Phys. Chem. A 2003, 107, 875; 2003, 107, 883] is extended to the case of polar associated compounds. The interfacial energy is factorized in two terms: one corresponding to association depending on the hydrogen bonds density, the other corresponding to the nonpolar contribution. This last term is treated in the framework of the corresponding states formalism similar to the one used in the case of nonpolar fluids [J. Phys. Chem. B 2004, 108, 5951]. The model yields a generalized behavior of the association factor as a function of the dielectric constant for the treated fluids. The calculated surface tension shows a mean error of about 1% for seven compounds having different multivalent H-bond characters.

We studied the breeding biology of the Yellow-shouldered Parrot (Amazona barbadensis) on Margarita Island from March-August, 1990 to 1999. The timing of the different phases (egg-laying, hatching, fledging) was consistent over the years, except during 1998 when all phases were delayed. The average clutch size was 3.38 or /- 0.78 eggs per nest, with a range of one to five eggs per clutch, and most eggs survived until hatching (3.36 or /- 0.80 eggs per nest). Total clutch size and hatching success of this species on Margarita Island are among the highest in the genus Amazona, suggesting the Yellow-shouldered Parrot has a higher reproductive potential than other species of the genus. We detected interannual differences for some of the reproductive parameters, all in 1998, a year with an extreme drought. Egg losses totaled 20% and were caused by hatching failure, predation, and human disturbance. Forty-nine percent of nestlings were lost, mainly due to poaching. The number of fledglings per nesting pair averaged 1.27 or /- 1.61, but varied greatly among years. Thus, in relation to the average total clutch laid, each pair lost an average of 62% of its initial reproductive investment.

Since diethyl dithiocarbamate (DEDTC) forms complexes with either zinc or copper, and 8-hydroxyquinoline (8-OHQ) also complexes with copper, we now compared the cytotoxic activity of Cu[DEDTC](2), Zn[DEDTC](2) and Cu[8-OHQ](2). This report shows that at nanomolar levels, only copper-[DEDTC](2), suppresses proliferation and clonogenicity of SKBR3 human breast carcinoma, concurrently with induction of apoptosis-associated PARP fragmentation. Susceptibility to these agents was paralleled by reactive oxygen generation (ROS) and greater expression of anti-oxidant enzymes like MnSOD and catalase, with no comparable effect on Cu/Zn superoxide dismutase. The lethal effects of Cu[DEDTC](2) manifested when adding the two separate aqueous components or the preformed synthetic complexes in DMSO, was prevented by N-acetyl cysteine or glutathione, with no comparable protection afforded by non-thiol anti-oxidants like mannitol or DMSO. Exogenously added catalase also protected cells from Cu[DEDTC](2), suggesting that this complex may kill after the levels of superoxide anion [O-2(center dot-)] dismutated by MnSOD increase hydrogen peroxide-related stress. Cu[DEDTC](2) also induced p21WAF1, a cdk inhibitor usually not inducible in mutant p53 tumors like SKBR3 carcinoma, correlating with dephosphorylation of the Sp1 transcription factor. Concentrations of Cu[DEDTC](2) cytotoxic for SKBR3 carcinoma did not induce comparable damage versus normal diploid human WI-38 fibroblasts. In contrast to the cytotoxic effect of nM levels of Cu[DEDTC](2) against SKBRR3 cells, no response was seen in the same cells exposed to 20 mu M cis-platin. Since neither DEDTC bound to zinc, nor copper bound to 8-OHQ showed comparable cytotoxicity, our results suggest that the greater activity of copper-DEDTC reflects a specific structure-activity relationship for the active complex. Since Cu[DEDTC](2) shows more effectiveness than other metal-chelator complexes, it may be worth further investigation as an alternative to cancer therapies.

The genetic variability was studied in HIV-1 from Venezuelan patients with and without treatment, in order to evaluate the presence of polymorphisms and drug resistance mutations. Proviral DNA from peripheral blood mononuclear cells or viral RNA from plasma was extracted from the blood of 30 patients. Two regions from the polymerase gene, protease (Pr) and reverse transcriptase (RT) and one genomic fragment from the envelope (Env) gene were amplified and sequenced. All HIV-1 samples analyzed were classified as subtype B, without evidence of recombination. Although no primary protease mutations were detected, a high frequency of secondary mutations (86%, 19/22), associated to restoration of viral replicative fitness, was observed in strains circulating both in treated and non-treated patients. Resistance mutations to nucleoside RT inhibitors (NRTI) and non-nucleoside RT inhibitors (NNRTI) were detected in 35% (6/17) and 12% (2/17) of the viruses circulating in treated patients, respectively. Resistance mutations were also present in the virus infecting one antiretroviral naïve individual (7.7%), suggesting that local screening for resistant mutation in naïve patient might be important to minimize therapy failure. Future studies are warranted to assess the role of secondary mutation in the success of viral infection.

Commercially available iodine has played an important role in organic synthesis. This review discusses the versatile uses of iodine in different chemical transformations. Reactions include esterification, cycloaddition reaction, allylation of aldehydes, acetalization of carbonyl compounds, acylation of alcohols, synthesis of cyclic ethers and aromatization of a,ß-unsaturated ketones.

This contribution explores the interaction of the fibrous silicates, palygorskite, sepiolite and chrysotile with a wide range of organic agents. Infrared spectroscopy (IR) methods are essential for the characterization of solid surfaces and for the investigation of the kind of bonds formed between the surface of these silicates and the organic moieties. Thus, when sepiolite or palygorskite are treated, e.g., with polyurethanes, alcohols, isocyanates, amines or pyridines, specific Si-NH-C or Si-O-C bonds are derived from the linkage of the differently located OH groups in these fibrous silicates with the organic moieties. On the other hand, more stable, covalent Si-O-Si-C bondings are formed when the fibrous silicates, especially chrysotile, are reacted with heterofunctional silylating agents like chlorosilanes or ethoxysilanes carrying, alkyl, alkenyl or aryl groups. Such reactions may occur in the presence or absence of HCl. An absorption band at 960 cm-1-which we assigned to Si-OH groups-is detected only in the presence of HCl. The evolution of this band is related to the degree of grafting of the organic radicals with the silanol groups of the silicates. HCl-generated silanol groups are the main bridges for the coupling of organosilyl groups on chrysotile and other silicates by covalent bonding, leading the way to the preparation of interesting new materials, including fibrous sheet polymers.

Se presenta una síntesis biográfica de Gilberto Rodríguez (1929-2004), científico venezolano que se destacó de manera protagónica en el desarrollo de las ciencias ambientales y de la carcinología en Venezuela y América. Se incluye una lista de sus publicaciones científicas.

A biographical síntesis of the Venezuelan scientist Gilberto Rodríguez (1929-2004) is presented. He stands as a main actor in the development of the environmental sciences and carcinology in Venezuelan and America. A list of his scientific publications is included.

The Ca-ATPase activity of the plasma membranes of several tissues of preeclamptic pregnant women is significantly reduced when compared with the values of normotensive pregnant women. This has been explained considering the raise in the level of lipid peroxidation of the plasma membranes with preeclampsia. In this work we studied the effect of lipid peroxidation of syncytiotrophoblast basal (fetal facing) plasma membranes from normotensive pregnant women, on their level of Ca-ATPase activity. Methods: The syncytiotrophoblast basal (fetal facing) plasma membranes from normotensive pregnant women were isolated and irradiated with ultraviolet (UV) light (254 nm). The membranes were then assayed for Ca-ATPase activity and lipid peroxidation by TBARS. Results: The UV irradiation raises the level of lipid peroxidation of the membranes, producing a concomitant inhibition of their Ca-ATPase activity. Presence of the antioxidant butylated hydroxytoluene during the UV irradiation of the membranes prevents increase in their level of lipid peroxidation and hence the inhibition of their Ca-ATPase activity. Conclusion: These results give a strong support to the hypothesis that the lowered Ca-ATPase activity already described for plasma membranes of several tissues of preeclamptic women is the consequence of the increased level of lipid peroxidation shown by these membranes.

Populations of threatened taxa in captivity within their natural ranges can make important contributions to conservation, but these may be compromised by the inappropriate application of population management goals developed in other contexts. We conducted demographic, genetic, and population viability analyses on the captive population of Andean bears (Tremarctos ornatus) in Venezuela to investigate the management of within-range captive populations in general, and to better integrate this population into the conservation of Andean bears in particular. We found that although the present population is very small and not internally self-sustaining, incorporation of confiscated wild individuals has resulted in a low average number of generations in captivity and low inbreeding, with moderate gene diversity and a high probability of future population persistence. However, past imports from extra-range populations have been from over-represented lineages of unknown origin, which have mixed with under-represented Venezuelan ones, reducing the future value of the Venezuelan population as a source for founder stock. Our analyses indicate that the rate of incorporation of wild recruits is a major factor influencing proxy measures of conservation value, and distinguishing within- from extra-range populations. This implies that, contrary to conventional wisdom, internal self-sustainability can be a misguided goal in within-range populations, which furthermore may not be suitable destinations for surplus animals from captive populations elsewhere

We investigate the nonlinear oscillations of heat-conductive, viscous, liquid drops in vacuum with zero gravity, using smoothed particle hydrodynamics (SPH). The liquid drops are modeled as a van der Waals fluid in two dimensions so that the models apply to flat, disklike drops. Attention is focused on small- to large-amplitude oscillations of drops that are released from a static elliptic shape. We find that for small-amplitude motions the combined dissipative effects of finite viscosity and heat conduction induce rapid decay of the oscillations after a few periods, while for large-amplitude motions wave damping is governed by the action of both viscous dissipation and surface tension forces. The transition from periodic to aperiodic decay at Re similar to 1 as well as the quadratic decrease of the frequency with the initial aspect ratio at large Re are reproduced in good agreement with previous theoretical predictions and experimental results.

The isolation and biological activity of several sesquiterpenes classified as phytoalexin are described. The synthesis of these sesquiterpenes, are described. Several routes have been developed to synthesize a particular sesquiterpenes. The applications of several reagents and reactions can be observed.

Radon measurements were performed across two sections of the Avila fault near Caracas, Venezuela. The radon concentrations clearly showed the different tectonic features and lithology at the Tacamahaca and Spanish Trail sites. ²¹⁴Bi (U-cps) measurements also were related to the lithology. The passive radon method employed laboratory-made dosimeters with LR 115, type 2 celulose nitrate films as detectors. They were buried in the ground at 30 cm depth. While, the active radon method was performed with a Pylon radon measurement system with Lucas cells. The soil gas was also sampled at 30 cm depths, but for only one minute, which was sufficient to fill the 150 cm³ Lucas cells completely. The total radon counts were then separated into those corresponding to ²²²Rn (radon) and ²²⁰Rn (thoron) by a simple computer routine. A comparison of the active and passive methods for the Tacamahaca section over a three-month period showed that both methods could locate precisely the active fault trace.

The objective of the present work was to study the catalytic reformation of methane in presence of carbon dioxide on activated carbon-supported nickel and calcium catalysts. Results are very promising ones because they suggests that it is possible to transform methane on these catalysts by using mild reaction conditions.

A new species of freshwater crab Microthelphusa viloriai, from the Andean range of Venezuela is described and illustrated. The type species of the genus, M. rodriguezi is redescribed on the following examination of the single specimen so far known. Data on the geographical and altitudinal distribution of the species of Microthelphusa are also presented.

Se describe una nueva especie de las estribaciones de los Andes venezolanos, Microthelphusa viloriai, y se redescribe la especie tipo del género M. rodriguezi. Además se presentan datos sobre la distribución geográfica y altitudinal del género.

The problem of the self-interaction of a quasi-rigid classical particle with an arbitrary spherically symmetric charge distribution is completely solved up to the first order in the acceleration. No ad hoc assumptions are made. The relativistic equations of conservation of energy and momentum in a continuous medium are used. The electromagnetic fields are calculated in the reference frame of instantaneous rest using the Coulomb gauge; in this way the troublesome power expansion is avoided. Most of the puzzles that this problem has aroused are due to the inertia of the negative pressure that equilibrates the electrostatic repulsion inside the particle. The effective mass of this pressure is -U-e(3c(2)), where U-e is the electrostatic energy. When the pressure mass is taken into account the dressed mass m. turns out to be the 2 bare mass plus the electrostatic mass m = m(0) or U-e/c(2). It is shown that a proper mechanical behaviour requires that m(0) > U-e/3c(2). This condition poses a lower bound on the radius that a particle of a given bare mass and charge may have. The violation of this condition is the reason why the Lorentz-Abraham-Dirac formula for the radiation reaction of a point charge predicts unphysical motions that run away or violate causality. Provided the mass condition is met the solutions of the exact equation of motion never run away and conform to causality and conservation of energy and momentum. When the radius is much smaller than the wavelength of the radiated fields, but the mass condition is still met, the exact expression reduces to the formula that Rohrlich (2002 Phys. Lett. A 303 307) has advocated for the radiation reaction of a quasi-point charge.

Surficial sediments from 56 stations on the Orinoco Delta offshore zone were analyzed by x-ray fluorescence spectrometry for aluminum (Al), barium (Ba), calcium (Ca), chromium (Cr), copper (Cu), iron (Fe), hafnium (Hf), magnesium (Mg), manganese (Mn), sodium (Na), nickel (Ni), rubidium (Rb), silicon (Si), strontium (Sr), vanadium (V), zinc (Zn), and zirconium (Zr). The resulting compositional data set was subjected to factorial and cluster analysis. The results demonstrated that two different sedimentary environments could be distinguished: (1) fine-grained sediments with significantly higher concentrations of Al, Cr, Fe, Mn, Rb, V, and Zn, and (2) coarse-grained sediments with significantly higher concentrations of Ca, Hf, Sr, Zr, and Si. On the other hand, Ba, Cu, Mg, Na, and Ni show relatively homogeneous concentrations in the sediments studied. Our results suggest that the calcareous and coarse-grained quartz sand fringe is a transgressive and relict sediment from the last glacial. This fringe, which is parallel with the coastlines, occurs at between 80 and 170 meters of water depth. Presumably all the studied trace elements, except Sr, Hf, and Zr, are adsorbed on clays and/or are associated with oxide-oxyhydroxides of Fe-Mn. Strontium shows a good correlation with Ca, which suggests the presence of carbonates. The high degree of correlation between Zr and Hf suggests a common origin, probably associated with the presence of heavy minerals.The concentrations of the trace elements reported in this work are useful as reliable baselines and can be used for comparison in future sediment studies.

A systematic revision of the Pedaliodes praxia group is presented. It consists of three closely related species occurring in the uppermost cloud forests of the northern Andes in Colombia and Ecuador. Two new taxa, Pedaliodes puciula n. sp. and P. praxia buckleyi n. ssp., are described. Geographic distribution patterns are overviewed. Main ecological traits are discussed.

We solve the Klein-Gordon equation in the presence of a spatially one-dimensional cusp potential. The bound state solutions are derived and the antiparticle bound state is discussed.

We discuss the mechanism of production of positrons and electrons by a spatially homogeneous time-dependent electric field whose amplitude vanishes for large values of time. Using the Hamiltonian technique, we compute the density of particles created as a function of time. We show that, as the time parameter goes to infinity, the distribution of pair created by the electric field reduces to the result calculated via the Bogoliubov coefficients.

En este artículo se discute el mecanismo de producción de electrones y positrones debido a un campo eléctrico homogéneo y dependiente del tiempo cuya amplitud se anula para valores grandes del tiempo. Haciendo uso de la técnica de diagonalización del Hamiltoniano calculamos la densidad de partículas creadas como una función del tiempo. Se muestra que, cuando el tiempo tiende a infinito, la distribución de pares creados por el campo eléctrico se reduce al resultado obtenido a través de los coeficientes de Bogoliubov.

We solve the Klein-Gordon equation in the presence of a spatially one-dimensional Woods-Saxon potencial. The bound state solutions are derived. The pair creation mechanism and the antiparticle bound state are discussed.

Se resuelve la ecuación de Klein-Gordon para el potencial de Woods-Saxon unidimensional independiente del tiempo. Se derivan las soluciones para los estados ligados. Se discute la creación de pares y los estados ligados de antipartículas.

Emulsion stability simulations (ESS) are used to study the aggregation behavior of oil-in-water (O/W) emulsions composed of non-deformable drops. In the absence of a strong repulsive force (low surfactant concentration), the number of aggregates decreases along with the number of drops following the dynamics predicted by Smoluchowski for irreversible flocculation. During this initial stage, the drops coalesce as soon as they make contact and no stable flocs are formed. The polydispersity of the system increases while its interfacial area decreases. This behavior disfavors the formation of aggregates with the characteristic fractal dimensions exhibit by suspensions under diffusion limited cluster aggregation (DLCA) and reaction limited cluster aggregation (RLCA) regimes. Moreover, the increase of the surfactant surface excess due to the redistribution of surfactant molecules among the available interfaces progressively augments the repulsive force between the remaining drops. In the absence of surface deformation, coalescence stops once the total interfacial area of the emulsion can be stabilized with the available surfactant concentration. At this point, aggregation occurs. In this terminal stage the aggregation behavior is likely to be determined by the characteristics of the secondary minimum of the interaction potential. A high surfactant concentration in the initial system leads to very different results. It prevents coalescence making the drops behave as solid particles. In this case clusters with the fractal dimensions corresponding to the DLCA and RLCA regimes are observed.

A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)(2)-(NH4)(2)HPO4 and Ca(OH)(2)P2O5, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis. The transformations taking place during the first periods of milling are very different for both mixtures. However, prolonged milling, over nearly the same period, causes amorphization of both mixtures. DSC analysis of the milled powders showed the temperature of crystallization of hydroxyapatite and tricalcium phosphate (beta-TCP). Calcinations of all the different milled powders at 800 degrees C for 2 h, results in the formation of hydroxyapatite and beta-TCP.

Previous studies carried out in an endemic semiarid region northwest of Venezuela at Falcon State have shown a prevalence of 15.4/1000 of chromoblastomycosis following traumatisms with xenophile vegetation infected with Cladophialophora carrionii. We performed high-resolution DNA typing of human leukocyte antigen (HLA)-A, -B and -C and major histocompatibility complex class I chain related gene A (MICA) alleles and segregation analysis in 49 members of one extended family with 12 affected individuals, who have lived for approximately 70 years in this endemic zone. None of the alleles, haplotypes or genotypes is shared by all the patients. No deviation from the expected HLA haplotype distribution or association of chromoblastomycosis with HLA-A, -B and -C haplotypes was observed. Further, a haplotype-sharing transmission/disequilibria testing of 11 nuclear families did not give enough evidence to claim linkage (P = 0.398), suggesting that genes located in the short arm of chromosome 6 may not be relevant in the immune response toward infection with C. carrionii in this Venezuelan endemic zone. Deleted MICA alleles on HLA-B*4802 haplotypes were present among several members of the extended family, but only two of them were affected.

Interaction between killer cell immunoglobulin-like receptors (KIR) and cognate HLA class I ligands influences the innate and adaptive immune response to infection. The KIR family varies in gene content and allelic polymorphism, thereby, distinguishing individuals and populations. KIR gene content was determined for 230 individuals from three Amerindian tribes from Venezuela: the Yucpa, Bari and Warao. Gene-content haplotypes could be assigned to 212 individuals (92%) because only five different haplotypes were present-group A and four group B. Six different haplotype combinations accounted for > 80% of individuals. Each tribe has distinctive genotype frequencies. Despite few haplotypes, all 14 KIR genes are at high frequency in the three tribes, with the exception of 2DS3. Each population has an even frequency of group A and B haplotypes. Allele-level analysis of 3DL1/S1 distinguished five group A haplotypes and six group B haplotypes. The high frequency and divergence of the KIR haplotypes in the Amerindian tribes provide greater KIR diversity than is present in many larger populations. An extreme case being the Yucpa, for whom two gene-content haplotypes account for > 90% of the population. These comprise the group A haplotype and a group B haplotype containing all the KIR genes, except 2DS3, that typify the group B haplotypes. Here is clear evidence for balancing selection on the KIR system and the biological importance of both A and B haplotypes for the survival of human populations.

Whole blood samples from 74 unrelated healthy individuals were collected. The donors' sample included Venezuelan mestizos from various regions of the country, but mostly from the resident population of Caracas City. A Venezuelan mestizo is the offspring of a mating between a native Venezuelan and a person born in Europe, mainly in Spain.

The conversion of tetralone 1 to methylketone 7, a valuable intermediate of occidol 8, has been accomplished in four steps ( reduction, mesylation, cyanation, and Grignard reaction with methylmagnesium bromide).

The taxonomic limits of the neotropical montane satyrine genus Manerebia Staudinger are defined, with the names Penrosasa Brown and Posteuptychia Forster treated as junior subjective synonyms. The taxonomic history of the genus is discussed and the current knowledge on the distribution, ecology and behavior of all north Andean species is summarized. A species-level taxonomic review of north Andean Manerebia is presented that includes 23 species and 37 taxa. Of these, 10 new species and 13 new aubspecies are described here: M. germaniae n. sp., M. golondrina n. sp., M. magnifica n. sp., M. mammuthus n. sp., M. pervaga n. sp., M. pluviosa n. sp., M. prattorum n. sp., M. rufanalis n. sp., M. seducta n. sp., M. undulata n. sp., M. franciscae rodriguezi n.ssp., M. germaniae vitalei n. ssp., M. inderena antioquiana n. ssp., M. inderena clara n. ssp., M. inderena fina n. ssp., Minderena leaeniva n. ssp., M. inderena mirena n. ssp., M. inderena similis n. ssp., M. leaena gonzalezi n. ssp., M. rufanalis fernandina n. ssp., M. satura lamasi n. ssp., M. satura pauperata n. ssp., M. undulate milaena n. ssp. A lectotype is designated for M. leaena to stabilize future nomenclature and Penrosada lanassa f.neglecta is placed as subspecies of Manerebia ignilineata n. stat. Accounts are presented for each species, discussing identification, taxonomy and ecology, and listing known geographic and elevational range data. Adult speciments, drawings of male genitalia and distribution maps are figured for all taxa where possible and the location of type material is given.

Dry forest environments limit the number of species that can survive there. Antillean dry forests have low floristic diversity and stature, high density of small and medium-sized trees, and are among the least conserved of the tropical forests. Their canopies are smooth with no emergent trees and have high species dominance. Antillean dry forests occur mostly on limestone substrate, exposing them to more water strees and nutrient limitations than other dry forests. They also experience periodic hurricanes and antropogenic disturbances. Many of the attributes that allow plants to survive in the stressful environment of the dry forest also provide resilience to disturbance. We attribute the high resilience of Antillean dry forests to the diversity of life forms, a high resistance to wind, a high proportion of root biomass, high soil carbon and nutrient accumulation belowground, the ability of most tree species to resprout and high nutrient-use efficiency. However, opening the canopy, eroding the soil and removing root biomass decreases forest resilience and allows alien species invasion.

We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 parts per thousand. Growth and leaf area were affected by salinity higher than 10 parts per thousand. As salinity increased, the predawn leaf water potential (Psi(w)) and leaf osmotic potential (Psi(s)) decreased. Leaf Psi(w) was at least -0.32 MPa lower than the Psi(w) of solution. Na or and K or ions explained about 78 % of decrease in psi(s). K or tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 parts per thousand. Inversely, Na or concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate (P-N) and stomatal conductance (g(s)) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 parts per thousand; the intereellular CO2 concentration (C-i) followed the same trend. The P-N as a function of C-i showed that both the initial linear slope and upper plateau of the P-N vs. C-i curve were markedly affected by high salinity (40 and 55 parts per thousand).

While the amount of reactive nitrogen circulating at the global level has increased markedly in the last century, the effects of this increase are largely seen at the regional level due to interacting ecological and socio-economic factors. In contrast with most other regions of the world, Latin America and the Caribbean (LA-Ca) stand out due to the fact that the major input of reactive nitrogen (Nr) still occurs naturally via biological nitrogen fixation (BNF) in natural ecosystems as opposed to anthropogenic inputs of synthetic fertilizer, fossil fuel combustion and cropping with leguminous species. Largely due to economic reasons, the consumption of fertilizer N in the LA-Ca region is still low in comparison with the average consumption of the world. However, the fertilizer N consumption is increasing at a much faster rate than that in developed regions of the world, like USA and Canada. The Nr production through BNF in cultivated plants that. x nitrogen (C-BNF) is 5 times lower than that occurring naturally in Latin America, but is still equivalent to 16% of the world C-BNF. The cultivation of nitrogen-fixing crop species in the LA-Ca region is also increasing, almost entirely due to the expansion of soybean fields in the central and northern regions of Brazil and the Pampa region of Argentina. Other anthropogenic activities in the region that contribute to an increase in the circulation of reactive nitrogen include the impact of biomass burning and urbanization. In the last decade, an average of 47,000 km(2) per year of forests was burned in the LA-Ca region. The environmental impact of urban centers in the LA-Ca region has become very important, since an intense urbanization process is occurring in this region, at an intensity that far exceeds urban development in the northern hemisphere. The consequences of increased urbanization include increased emissions of NOx to the atmosphere due to the fossil fuel combustion, and the lack of sewage treatment facilities in most cities of the LA-Ca result in a large volume of untreated sewage discharged into surface waters, creating serious environmental problems. The combination of rapid urbanization and agricultural intensification in this region suggest that concern is warranted for the potential for increase in the circulation of reactive nitrogen in the very near future. At the same time, the opportunity still exists to mitigate some of the consequences of human impact on the nitrogen cycle in a region that still maintains a large fraction of its natural ecosystems intact.

We attempted to separate species of the genus Clusia according to the concentration of linear alkanes (C25 and C35), and the presence and diversity of terpenes in epicuticular wax extracts. We collected leaves of 15 Clusia species growing in mountain forests of Panama (Cerro Jefe 1007 m and Altos de Campana 800 m a.s.l.) and from cultivated plants at two lowland sites. Leaf surfaces were washed gently with hexane to extract epicuticular waxes, which were analyzed using gas chromatography and mass spectrometry. The predominant alkanes were C29, C31, and C33. In the extract the ratio C31/C29 was <= 1 in 6 of the 15 species analyzed: Clusia multiflora, Clusia peninsulae (Hammel ined.), Clusia stenophylla, Clusia liesneri, Clusia coclensis, and Clusia triflora. The concentrations of C29 and C33 were inversely related, the latter being above 10% in Clusia divaricata, Clusia pratensis, Clusia rosea, Clusia uvitana, and Clusia valerioi. Proportion of triterpenes was less than 5% in the species C. minor, C. pratensis, C. uvitana, C. rosea, Clusia cylindrica, C. divaricata, and C. valerioi. The rest contained squalene, and specific triterpenes such as beta-amyrine in C. liesneri, betuline in Clusia osseocarpa, taraxerol in C. stenophylla, and lupeol in C. multiflora. The variety of triterpenes was higher in Clusia liesneri (5) and C. multiflora (3). The results suggest that groups of species can be distinguished within the genus according to the presence of terpenes and ratios of linear alkanes. These groups overlap with those generated by other classifications using morphology and nuclear ribosomal DNA.

Savannas are the most common vegetation type in the tropics and subtropics, ranging in physiognomy from grasslands with scattered woody plants to woodlands with heterogeneous grass cover. Productivity and organic matter turnover in savannas are controlled by interactions between water and nutrient availability, and this basic environmental structure is modified by fire frequency and land management practices. We compared temperate and tropical savannas in order to understand the strength of nitrogen (N) limitation of productivity. American tropical and temperate savannas are N limited systems, and the N cycle differs according to the woody plant density, fire frequency, land use change, N deposition and N fixation. Grazing and conversion to pasture have been the predominant land-use changes in most savannas. In the Cerrado and the Llanos tropical savannas, intensified use of fire for pasture management is leading to decreased woody plant density. Oppositely, in the Chaco and North American temperate savannas,. re suppression and grazing are leading to increases in woody density. In addition, the higher soil P availability in the Gran Chaco and the higher N deposition in North American savannas may be contributing to increases of N cycling and net productivity rates. Some aspects of the N budget for savannas of the American continent are still unclear and require further analysis to determine rates of N fixation, and to understand how spatial and temporal soil heterogeneity control N fluxes through soil solution and into streams.

En el presente trabajo se describe una relación academia-gobierno-industria. El Instituto Venezolano de Investigaciones Científicas (IVIC), un instituto estatal de orientación académica, promovió una solución para un problema de salud pública mediante la creación de una planta de producción de derivados sanguíneos (PPDS); para ello estableció alianzas con el Estado venezolano que acogió el proyecto y se constituyó en financista del mismo, mientras que el IVIC aportaba su capital intelectual. Se creó una interfase empresarial (Quimbiotec, C.A.), posibilitándose el surgimiento de una empresa farmacéutica dentro de la cual se produjo un proceso de aprendizaje (learning by doing), el cual se relata de manera sucinta. La experiencia descrita muestra como la interacción academia-gobierno-industria, en el contexto latinoamericano puede dar ocasión a situaciones un tanto distintas a lo que acontece en el mundo desarrollado.

The present work describes a academy-government-industry relationship. The Venezuelan Institute of Scientific Investigations (IVIC), a state institute of academic orientation, promoted a solution for a problem of public health by means of the creation of a sanguine derivate production plant (PPDS); with that purpose IVIC settled down alliances with the Venezuelan State, who welcomed the project and was constituted in the project’s financier, while IVIC contributed with its intellectual capital. An industrial interface (Quimbiotec, C.A.) making the surfacing of a pharmaceutical industry possible, inside which a learning process (Learning by Doing) took place, related in a succinct way. The described experience shows how the academy-government-industry interaction, in the Latin American context can give occasion to situations a little different to what happens in the developed world.

El presente trabajo de investigación se evaluó la posibilidad de elaborar mermeladas a partir de la pulpa de los frutos de cardón dato (Stenocereus griseus) de las variedades Blanca y Roja. Para ello, se propuso desarrollar las formulaciones de dichas mermeladas y estudiar su estabilidad durante tres meses de almacenamiento a temperatura ambiente. Como primer paso se caracterizaron los frutos de ambas variedades, observándose que a pesar de la diferencia notable de color entre ambos, no hay diferencias estadísticamente significativas en su peso promedio, dimensiones y proporciones de pulpa, piel y semillas. Por otro lado, ambas pulpas presentaron valores altos de pH (5,2 en ambas variedades) y contenidos bajos de azúcares reductores (3,59 g/100g variedad Blanca y 2,23 g/100g variedad Roja), azúcares no reductores (0,75 g/100g variedad Blanca y 2,03 g/100g variedad Roja), pectina (0,14 g/100g variedad Blanca y 0,23 g/100g variedad Roja) y ácidos (7,67 g/100g variedad Blanca y 0,15 g/100g variedad Roja), debido a lo cual fue necesario añadir azúcar, pectina y ácido cítrico a la formulación de la mermelada. La primeras mermeladas elaboradas presentaron consistencia gomosa, lo cual se solucionó añadiendo el ácido desde el principio del proceso de elaboración en lugar de al final. Durante los tres meses de almacenamiento, las mermeladas tuvieron buena aceptación por parte de los panelistas, a pesar de ligeras fluctuaciones observadas durante el almacenamiento en el pH y contenidos de sólidos solubles y acidez total titulable.

This study aimed to examine the possibility of producing marmalades from the fruit pulp of the red and white varieties of cardón dato (Stenocereus griseus). We developed the formulations of the marmalades and evaluated their stability during three months of storage at room temperature. As first step, we characterized the fruits of the two color varieties, observing that despite the considerable difference between both color varieties, there were no significant differences in average weight, dimensions and proportion of pulp, skin and seeds. The pulp of the two color types had high pH (5,2) values and low contents of reductor sugars (3,59 g/100g white variety 2,23 g/100g red variety), non reductor sugars (0,75 g/100g white variety and 2,03 g/100g red variety), pectin (0,14 g/100g white variety and 0,23 g/100g red variety) and acids (7,67 g/100g white variety and 0,15 g/100g red variety). It is needed to include sugar, pectin, and citric acid in the marmalade formula. The first marmalades produced were gummy, a problem that we solved adding the acid from the beginning of the making process. During the three months of storage, the marmalades had good acceptance by the evaluators, this despite slight fluctuations observed in pH, solid contents, and acidity.

The effect of 0.1 wt% vanadium additions on the precipitation behavior and the mechanical properties of a commercial Al-6063 alloy were studied. A master alloy containing 3 wt% V was added during casting. The cast ingot was homogenized, extruded and cooled employing two different cooling modes: forced air and water. Further aging was carried out following the standard T5 and T6 treatments for alloys with and without vanadium. The microstructural characterization, mechanical properties, and fractografic study were carried out. The addition of 0.1% vanadium to Al-6063 alloy under T5 treatment, accelerates the precipitation kinetics of ß? and ß' phases. The alloys with and without vanadium under T6 show a similar behavior, the co-existence of ß' and ß? precipitation is observed in both alloys. In general, vanadium additions to Al 6063 have a detrimental effect on the mechanical properties, showing only a beneficial effect for certain specific conditions.

Se sintetizaron las zeolitas FAU, EMT y sus intercrecimientos empleando como templantes 15-crown-5, 18 -crown-6 y sus mezclas al 50%, respectivamente. Las muestras fueron caracterizadas por XRD, SEM-EDX, adsorción de N2, y TPD-NH3, todas las muestras obtuvieron altamente cristalinas. Los cristalitos de FAU están constitutitos por octaedros submicrométricos y los de EMT poseen una morfología de platos hexagonales de 2 a 5 µm. Las partículas de los intercrecimientos están formadas por placas hexagonales típicas de la estructura EMT, sobre cuyas caras hexagonales se observan cristales octaédricos de FAU producidos por intercrecimiento. La proporción de intercrecimiento se evaluó usando el programa DiFFaX, resultando en diferentes proporciones de intercrecimiento dependiendo de la relación molar de templante/Al2O3 y de las proporciones relativas de los templantes usados en el gel de síntesis. Para la relación molar de templante/Al2O3 = 0,70 se obtuvo 50% FAU/50% EMT con apilamientos tipo cluster, y para la relación molar de templante/Al2O3 = 0,30 se obtuvieron proporciones de intercrecimiento 12% FAU/ 88% EMT, tanto con apilamientos tipo cluster como apilamientos aleatorios. A estas zeolitas y sus intercrecimientos se les incorporó platino vía intercambio iónico en estado sólido, la dispersión del platino se determinó por TEM, obteniéndose partículas entre 4 y 10 nm para la mayoría de los catalizadores. Los catalizadores. Los catalizadores preparados a partir de las estructuras de intercrecimiento resultaron los más activos; sin embargo, todos los catalizadores resultaron activos en la conversión de pentano. La selectividad a isopentano fue de 82% independiente del tiempo de reacción, acidez, relación Pt/Al, dispersión del Pt. La estabilidad catalítica (actividad remanente a 10 min) disminuye en el orden: FAU EMT intercrecimiento.Zeolitas FAU, EMT and their intergrowths have been synthesized using 15-crown-5, 18-crown-6 and their mixture in proportion of 50% of each, respectively. The samples were characterized by the following techniques XRD, SEM-EDX, N2 adsorption and TPD-NH3, the samples obtained were all highly crystalline. The FAU samples were formed by octahedral submicrometric crystallites, EMT samples have hexagonal plate morphology of 2 to 5 µm. The intergrowth crystals are micrometric hexagonal plates through whose hexagonal faces intergrow the octahedral crystallites of FAU. The intergrowth proportion was evaluated by means of DiFFaX, resulting in different intergrowth proportions depending on the molar ratio of template /Al2O3 and relative template proportion used in the gel. For template /Al2O3 = 0,70 a 50% FAU/50% EMT intergrowth proportion was obtained, with stacking arranged as clusters and for template/ Al2O3 = 0.30 the intergrowth proportion was 12% FAU/88% EMT with both stacking arrangements as clusters and as random stackings. Platinum was incorporated to these zeolites and their intergrowths by solid ion exchange, the metal dispersion was evaluated by TEM. For most catalysts the platinum particles were between 4 and 10 nm. The intergrowth catalysts were the most active materials. However, the catalysts were all active for n-pentane conversion. The iso-pentane selectivity was 82% independent of time on stream, acidity, Pt/Al ratio, Pt dispersion. The catalytic stability (remaining acitivity at 10min) decreased in the following order: FAU EMT intergrowth.

Radiation is employed to sterilize composite materials used in the biomedical field. Due to the changes induced by radiation onto polymeric materials, it is important to study variations in their melt flow index (MFI), as well as in their mechanical and thermal properties. In this work, those previous parameters were determined in composites obtained via solution of a high-density polyethylene (HDPE) in decalin, with different amounts of hydroxyapatite (HA), varying from 10 to 30 parts per hundred, after being exposed to gamma radiation at absorbed doses between 25 and 100 kGy. After the irradiation, the MFI of HDPE dissolved in decalin and precipitated afterwards and without filler increased from 6 to 24 g/10 min at the highest absorbed doses. This behavior was also observed in composites with 10 pph of HA, being the increase less pronounced, specifically in the range between 50 and 100 kGy. Composites with 20 and 30 pph of HA showed a maximum MFI value at 50 kGy, which decreased at higher doses. This implies that the filler begin to exert an influence because it does not melt at the test temperature and consequently, it does not flow. It was observed that Young’s modulus increased with HA addition due to rigidity of the ceramic filler. Radiation did not significantly affect this tensile property. On the other hand, the tensile strength did not show significant variations at the different doses but the filler content did affect this property improving it. Finally, elongation at break showed a drastic decrease with filler addition. When the thermal behavior was studied it was noticed that crystallization and melting temperatures remained unchanged. Instead, crystallinity degree slightly increased in the composites, and a little decrease was obtained when they were irradiated.

Most of the University libraries in Venezuela were neglected entities with scattered funds and disorganized services during the 60s through the early 90s. University libraries were not structured as a system but libraries used to subscribe to sufficient serial publications prior to 1982 due to the strong currency. Each library was working to serve their users in a classical manner and without automation of library services. The aim of forming a national consortium is to share resources, create efficiency, cost savings, and to promote participation on the basis of mutual benefit.

The effect of steric interactions on the stability of oil-in-water emulsions is studied here by means of emulsion stability simulations (ESS). For this purpose, a new steric potential based on a modification of the one formerly proposed by Vincent et. al. [Colloids Surf. 18 (1986) 261] is employed. The parameters of the calculation correspond to hexadecane in water emulsions stabilized with nonylphenol ethoxylated surfactants of different chain lengths (NPEm). Stability ratios (W) were calculated using the half life time of the number of drops per unit volume of these systems. A functional relationship between W and the repulsive potential barrier, (?V), similar to the one previously found by Prieve and Ruckenstein for electrostatically stabilized suspensions [J. Colloid Interface Sci. 73 (1980) 539] was obtained. However, according to our simulations there exists a threshold for the stability of emulsions with respect to coalescence which is approximately located around 12.7k_BT.

Differences in mycotrophic growth and response to phosphorus (P) fertilization were studied in seedlings of two woody native species: Clusia minor L. and Clusia multiflora H.B.K. from a cloud montane forest of tropical America. Greenhouse investigation was undertaken to determine the relationships between mycorrhizal dependency of host species associated with P utilization and growth in two different soils contrasting in pH (acidic and neutral) and nutrient content. Four treatments were performed: sterilized soil; sterilized soil plus 375 mg/kg of triple superphosphate (TSP); sterilized soil inoculated with Scutellospora fulgida (20 g/pot); and sterilized soil plus S. fulgida and TSP, with 10 replications per treatment for the two species. Results showed that both Clusia species presented high growth response to increasing P availability, which indicates that the root morphology (magnolioid roots) of these species is not a limiting factor for the incorporation of P from soils. Plants inoculated with arbuscular mycorrhizal fungi (AMF) in acidic soil had significantly increased shoot and root biomass, leaf area and height, in comparison to the biomass of P-fertilized plants and nonmycorrhizal plants. In neutral soil, seedlings of C. minor and C. multiflora were negatively affected by inoculation with AMF. In contrast, a significant decrease in growth was observed when inoculated plants were compared with noninoculated plants on neutral soil. Results indicate that an increase in the availability of a limiting nutrient (P) can turn a balanced mutualistic relationship into a less balanced nonmutualistic one.

Con frecuencia la región del Delta del Orinoco es imaginada como un paisaje “prístino”,que ha experimentado muy pocos cambios en su geografia natural y humana. Sin embargo, durante el último siglo el Delta del Orinoco ha sufrido cambios muy radicales, con graves consecuencias para la ecología y para la distribución de las poblaciones locales. La descripción estándar del modo de vida Warao, basado en un presente etnográfico que no contempla estos cambios importantes, ha traído como consecuencia concepciones y políticas erradas en relación a programas asistenciales, de ordenamiento y uso del espacio, y de percepción por parte de agentes gubernamentales y público en general. En este ensayo se describen y analizan algunos de los cambios en el modo de vida, la distribución de las poblaciones y la composición de los grupos Warao del Delta a partir de los cambios ocurridos por factores tales como la introducción del llamado “Ocumo Chino” (Colocasia esculenta), y la construcción del dique en el caño Manamo, y se presenta una visión general de la ecología histórica del Delta.

En este trabajo se estudió el efecto de un pretratamiento de nitración con amoníaco a temperaturas entre 500 y 900°C, sobre la actividad de un catalizador comercial a base de óxido de Ni-Mo/Al2O3 (AERO HDS-3A). El catalizador nitrado fue caracterizado por XPS y medidas de área superficial por el método BET. Mediante XPS se determinó la presencia de Mo+2 y Mo0 en el catalizador nitrado a 700°C, como posibles especies activas. De igual manera se realizaron medidas de actividad HDS, observándose que la conversión de tiofeno se duplicó cuando el catalizador comercial fue sometido a nitración seguida de sulfuración-reducción «in situ».

In this work, it was studied the effect of a nitridation pretreatment with ammonia at temperatures between 500 and 900°C, on the activity of a commercial Ni-Mo/Al2O3 catalyst. The nitrided catalyst was characterized by XPS and BET surface area. The presence of Mo+2 and Mo0 in the catalyst nitrided at 700°C, as detected by XPS, could be related to the possible active species. Thiophene conversion was doubled when the commercial catalyst was nitrided followed by sulfidingreduction «in situ» pretreatment.

The present study investigates the n-butane oxidative dehydrogenation (ODH) using VMgO catalysts supported on SiO2 or promoted with different amounts of Gallium or Molybdenum. The Mg/V atomic ratio used for all catalysts was four. Experiments were performed in a fixed bed reactor within the temperature range of 480 to 540ºC and a residence time within the range of 6 to 50 (gcat min moltotal -1). The need for catalysts previously stabilized in order to avoid changes in behavior with time on run was demonstrated. The VMgO unsupported and unpromoted phase showed a good level of activity (conversions of ±30% at a contact time of 50 [gcat min moltotal -1] and a temperature of 540°C) with selectivities toward unsaturated hydrocarbons in the order of 90%. In order to increase the catalyst resistance to attrition, this active phase was supported on SiO2 (30% by weight). The activity and selectivity of this catalyst was somewhat lower than the observed on the unsupported phase but still interesting. The additions of molybdenum or gallium oxides with an atomic ratio (Mo/V or Ga/V) in the range 0.1 to 1.0 show instead to have mixed effects. Molybdenum promotes the selectivity toward butylenes but with a reduction in activity. Instead, gallium introduces a rather small effect.

En el presente estudio se investiga la Deshidrogenación Oxidativa (DHOX) de n-butano utilizando catalizadores de VMgO soportados en SiO2 o promovidos con diferentes cantidades de galio o molibdeno. La relación atómica Mg/V usada fue de cuatro para todos los catalizadores. Los experimentos se realizaron en un reactor de lecho fijo a temperaturas dentro del rango de 480 a 540ºC y con un tiempo de residencia que se varió entre 6 y 50 (gcat min moltotal -1). Se demuestra que para evitar cambios de comportamiento es necesario trabajar con catalizadores previamente estabilizados. La fase VMgO no soportada ni promovida presentó un buen nivel de actividad (conversiones de ±30% a un tiempo de contacto de 50 [gcat min moltotal -1] y una temperatura de 540ºC) con selectividades hacia hidrocarburos no saturados del orden del 90%. Con el objeto de aumentar la resistencia a la atrición del catalizador, esta fase activa se soportó sobre SiO2 (30% en peso). La actividad y la selectividad de este catalizador fueron algo menores a las observadas sobre la fase activa no soportada pero todavía interesante. La adición de óxidos de molibdeno o galio con relaciones atómicas (Mo/V o Ga/V) en el rango de 0.1 a 1.0 mostró efectos variados. El molibdeno promovió la selectividad hacia butenos pero con reducción de la actividad. En cambio el galio conduce tan solo a cambios menores.

The present work is part of an ongoing project aiming to a better understanding of the mechanisms of atomization on graphite furnace platforms used for electrothermal atomic absorption spectrometry (ETAAS). It reports the study of unused pyrolytic graphite coated platforms of commercial origin, as well as platforms thermally or thermo-chemically treated under simulated ETAAS analysis conditions. X-ray photoelectron spectroscopy (XPS) was employed to study the elements present at the surfaces of the platforms. New, unused platforms showed the presence of molybdenum, of unknown origin, in concentrations up to 1 at.%. Species in two different oxidations states (Mo6+ and Mo2+) were detected by analyzing the Mo 3d spectral region with high resolution XPS. The analysis of the C 1s region demonstrated the presence of several signals, one of these at 283.3 eV related to the presence of Mo carbide. The O 1s region showed also various peaks, including a signal that can be attributed to the presence of MoO3. Some carbon and oxygen signals were consistent with the presence of C=O and C—O— (probably C—OH) groups on the platforms surfaces. Upon thermal treatment up to 2900 8C, the intensity of the Mo signal decreased, but peaks due to Mo oxides (Mo6+ and Mo5+) and carbide (Mo2+) were still apparent. Thermo-chemical treatment with 3 vol.% HCl solutions and heating up to 2900 8C resulted in further diminution of the Mo signal, with complete disappearance of Mo carbide species. Depth profiling of unused platforms by Ar+ ion etching at increasing time periods demonstrated that, upon removal of several layers of carbonaceous material, the Mo signal disappears suggesting that this contamination is present only at the surface of the pyrolytic graphite platform.

In this work dimeric complexes, dioxo-m-oxo and oxo-bis (µ-oxo) of molybdenum, were theoretically modeled to try to understand reactivity for hydrocarbon oxidation. The first complex, dioxo (µ-oxo) thiocyanatomolybdenum (VI) bearing a 4,4'-di-ter-butyl-2,2'-bipyridine ligand (complex 1) in trans conformation exhibits a high oxidizing ability, giving as product a dimeric complex oxo-bis (µ-oxo) thiocyanatomolybdenum (V) with the same ligands (complex 2) in cis conformation. Calculations were perfomed by using CATIVIC, a parametric quantum chemistry method for catalytic reactions. Furthermore, new geometries were created, using the CATIVIC graphic interface, starting with complex 1 to transform it to cis conformation (complex 3). Molecular parameters for Mowere estimated from diatomic molecules and molecular properties, such as charges, interatomic distances, bond orders, and diatomic energies of selected bonds, and atomswere calculated for these complexes. In addition, LUMO characteristics were evaluated and discussed. Results suggest the feasibility of complex 1 transformation through a bridge Mo–O bond rotation to form complex 3 that is energetically less stable than complex 1 in 21 kcal/mol. Results of bond strength indicate a high lability of the bipyridine ligand and a high LUMO density of states in cis conformation. Preliminary steps of the mechanism for the formation of a highly active site that explains the oxidizing ability of complex 1 is given by considering the rotation through a bridging Mo–O bond to form a cis complex 3 and then a Mo–N bond breaking. Vacancy creation could be considered as a previous step to the formation of active sites for catalytic oxidation.

Background: Malignant hyperthermia is a pharmacogenetic disorder affecting humans, dogs, pigs, and horses. In the majority of human cases and all cases in animals, malignant hyperthermia has been associated with missense mutations in the skeletal ryanodine receptor (RyR1).

Methods: The authors used a “knock-in” targeting vector to create mice carrying the RyR1 R163C malignant hyperthermia mutation.

Results: Validation of this new mouse model of human malignant hyperthermia susceptibility includes (1) proof of transcription of the R163C allele and expression of ryanodine receptor protein in R163C heterozygous and R163C homozygous animals; (2) fulminant malignant hyperthermia episodes in R163C heterozygous mice after exposure to 1.25—1.75% halothane or an ambient temperature of 42°C characterized by increased rectal temperature, respiratory rate, and inspiratory effort, with significant blood biochemical changes indicating metabolic acidosis, ending in death and hyperacute rigor mortis; (3) intraperitoneal pretreatment with dantrolene provided 100% protection from the halothane-triggered fulminant malignant hyperthermia episode; (4) significantly increased sensitivity (decreased effective concentration causing 50% of the maximal response) of R163C heterozygous and homozygous myotubes to caffeine, 4-chloro-m-cresol, and K⁺-induced depolarization; (5) R163C heterozygous and homozygous myotubes have a significantly increased resting intracellular Ca²⁺ concentration compared with wild type; (6) R163C heterozygous sarcoplasmic reticulum membranes have a twofold higher affinity (K_d = 35.4 nm) for [³H]ryanodine binding compared with wild type (K_d = 80.1 nm) and a diminished inhibitory regulation by Mg²⁺.

Conclusions: Heterozygous R163C mice represent a valid model for studying the mechanisms that cause the human malignant hyperthermia syndrome.

SUMMARY This article presents the 2007 synthesis about the structure, history, activities, and explorations carried out by the Sociedad Venezolana de Espeleología (SVE) since its foundation 40 years ago. It includes summaries of Venezuela's main karst areas and caves, as well as the state of the knowledge in geospeleology, biospeleology, anthropospeleology, and notes on publications and cadastre. More information, including illustrations and the content of the latest bulletins, is available on the SVE website at www.sve-espeleologia.org.ve

RESUMEN El artículo es una síntesis de información para el 2007 sobre la estructura, historia, actividades y exploraciones efectuadas por la Sociedad Venezolana de Espeleología (SVE) desde su fundación, hace 40 años. Incluye resúmenes sobre las principales zonas kársticas y cavernas de Venezuela y el conocimiento actual en geoespeleología, bioespeleología, bioespeleología, antropoespeleología, publicaciones y catastro. Una información mas amplia, e ilustrada, junto al contenido de los últimos boletines está disponible en la página web de la SVE en www.sve-espeleologia.org.ve

---------------------------------------------------------------------------------------------------------

^{RESUMEN El fármaco antidiabético gliclazida (1) es fototóxico y fotolabil bajo condiciones aeróbicas y de luz UV-B. La irradiación de una solución buffer de 1 bajo atmósfera oxigenada produce dos fotoproductos. La fotoquímica de 1 involucra la ruptura del enlace S-N y C(O)-N de la unidad de urea. La lisis fotosensibilizada de eritrocitos por 1 fue determinada. Sin embargo los fotoproductos de la gliclazida no mostraron este efecto. La inhibición de este proceso en presencia de DABCO, GSH, confirman la posibilidad de la participación de radicales libres en la fotohemólisis. Además, mediante ensayos de peroxidación lipídica con ácido linoleico también se verificó la fototoxicidad in vitro de 1. La generación de oxígeno singlete durante la fotólisis de 1 fue descartada mediante los ensayos de histidina y de NaN3. En un estudio suplementario la habilidad de 1 de inhibir radicales libres o especies de oxígeno reactivas (OH, 1O2, H2O2) en sistemas libres de células fue investigado usando quimioluminescencia y los espectros de absorción.}

^{ABSTRACT The phototoxic antidiabetes drug gliclazide (1) is photolabile under aerobic conditions and UV-B light. Irradiation of a phosphate buffered solution of 1 under oxygen atmosphere produces two photoproducts. The photochemistry of 1 involves cleavage of the S-N and C(O)-N bonds of the urea unit. Red blood cell lysis photosensitized by 1 was demonstrated. Their photoproducts didn't show this effect. Inhibition of this process by addition of DABCO, GSH, confirmed the possibility of the participation of free radicals in the photoinduced hemolysis. Furthermore, in a lipid-photoperoxidation test with linoleic acid the in vitro phototoxicity of gliclazide was also verified. The generation of singlet oxygen during the photolysis of gliclazide was ruled out by means of the histidine and NaN3 assays. In a supplementary study the ability of 1 to inhibit free radical or reactive oxygen species (.OH, 1O2, H2O2) generated in cell-free systems was investigated using chemiluminescence and electronic absorption spectra.}

Blood stages of Plasmodium vivax induce the development of caveolae and caveola—vesicle complexes (CVC) in the membrane of their host erythrocyte. Caveolae are found in almost all types of cells and are involved in endogenous processes as calcium and cholesterol homeostasis, cell signalling, transporting, ligand internalization and transcytosis of serum components. Major structural components of caveolae are the proteins caveolins and flotillins. The functional role of caveolae in the P. vivax-infected erythrocyte is not properly understood. As these organelles have been shown to contain malaria antigens, it has been suggested that they are involved in the transport and release of specific parasite antigens from the infected erythrocyte and in the uptake of plasma proteins. Using specific antibodies to classical caveolae proteins and an immunolocalization approach, we found caveolin-2, caveolin-3, and flotillin-2 in the vesicle profiles and some CVC of P. vivax-infected erythrocytes. Caveolin-1—3 were not found in uninfected erythrocytes. This is the first report of identification and localization of caveolins in the CVC present in erythrocytes infected with P. vivax, thereby providing evidence of the role of this particular organelle in the protein-trafficking pathway that connect parasite-encoded proteins with the erythrocyte cytoplasm and the cell surface throughout the asexual blood cycle of vivax malaria parasite.

Se presenta una síntesis biográfica de Gilberto Rodrígues (1929- 2004), científico venezolano que se destacó de manera protagónica en el desarrollo de las ciencias ambientales y de la carcinología, en Venezuela y América. Se incluye una lista de sus publicaciones científicas.

A biographical synthesis of the venezuela scientist Gilberto Rodríguez (1929-2004) is presentd. He stands as a main actor in the develpment of the enviromental sciences and carcinología, en venezuela and America. A list of this scientific publitions is included.

Four new tungsten-oxo(VI) complexes have been synthesized, characterized spectroscopically and their molecular structure established by X-ray diffraction analysis. These bear identical environment as previously reported molybdenum-oxo(VI) complexes, which allowed direct comparison of their spectroscopic properties. Their capability as oxygen atom transfer agents was found to be significantly lower than their molybdenum analogs.

The iridium complexes [Ir(PBz₃)₂(COD)]PF₆ and [Ir(py)(PBz₃)(COD)]PF₆ are effective catalyst precursors for the homogeneous hydrogenation of N-(ß-naphthylmethylene)aniline (NßNA) to naphthalene-2-ylmethylphenylamine (PBz₃ = tribenzylphosphine; COD = 1,5-cyclooctadiene; py = pyridine). For comparative purposes, other iridium and rhodium catalysts modified with either PBz₃ or PPh₃ have been tested as catalysts for NßNA hydrogenation. A kinetic study of this reaction catalyzed by [Ir(PBz₃)₂(COD)]PF₆, [Ir(py)(PBz₃)(COD)]PF₆, and [Rh(PPh₃)₂(COD)]PF₆, together with in situ NMR experiments, has led us to propose catalytic cycles for the three precursors.

Rheological and thermal behavior of isotactic polypropylene (PP) and natural rubber (NR) blends were studied, with special reference to the type of vulcanization (dynamic and static). It was found that dynamic crosslinking of the NR phase increases the viscosity of the system, while it decreases crystallinity degree. Statically vulcanized blends show similar properties regardless curing time while dynamically vulcanized blends show enhanced properties if compared to the corresponding uncured blends.

The efficacy of melatonin, glutathione, serotonin, minocycline, lipoic acid and ascorbic acid in counteracting the toxicity of paraquat in Drosophila melanogaster was examined. Male Oregon wild strain flies were fed for 5 days with control food or food containing the test substance. They were transferred in groups of five to vials containing only filter paper soaked with 20 mM paraquat in 5% sucrose solution. Survival was determined 24 and 48 h later. All the substances assayed increased the survival of D. melanogaster. At equimolar concentrations (0.43 mM) melatonin was more effective than serotonin, lipoic acid and ascorbic acid. However, lower concentrations of glutathione (0.22 mM) and minocycline (0.05 mM) were as efficient as melatonin. The highest survival rate (38.6%) after 48 h of paraquat treatment was found with 2.15 mM of lipoic acid. No synergistic effect of melatonin with glutathione, serotonin, minocycline, lipoic acid and ascorbic acid was detected.

Fibrinogen Guarenas is a dysfibrinogenemia with a nonsense mutation at G4731T that causes an Aa-chain truncation at Ser 466. This abnormal fibrinogen is associated with a bleeding diathesis, severe in the proposita and mild in one brother, even though the fibrinogen levels in plasma are normal. All other family members are asymptomatic. Fibrinogens from the proposita and one family member, the mother of the proposita, both heterozygous for the mutation, were studied. Turbidity curves of fibrin polymerization showed that the lateral association of protofibrils was impaired and the maximum rate of polymerization was slightly diminished. The binding of albumin to fibrinogen was increased compared to control due to the presence of a free sulfhydryl group because of the missing disulphide bridge between Aa-Cys 442—472 in the mutated molecules. The abnormal fibrinogen formed much less a-polymer, and ?-dimer formation was delayed compared to the control. Plasminogen activation by t-PA in the presence of fibrin was decreased. When Guarenas clots were perfused with fibrinolytic enzymes, clot degradation was retarded. Clot structure studied by confocal 3D microscopy showed that the fibrin network was dense, made up of thin and highly branched fibers, which accounted for the decreased flow rates by buffer permeation and increased rigidity of the fibrin clots, measured using a torsion pendulum. It seems that the increased clot rigidity, decreased porosity, hypofibrinolysis and t-PA induced fibrinolysis, by itself are not necessarily associated with thrombotic disorders in dysfibrinogenemia

The theoretical studies of the gas-phase elimination of 2-substituted ethyl N,N-dimethylcarbamates (Z=CH₂Cl, C=CH, C=N) were performed using ab initio MP2/6-31G and MP2/6-31G(d) levels of theory. The gas phase elimination reaction of these carbamates yields N,N-dimethylcarbamic acid and the corresponding substituted olefin in a rate-determining step. The intermediate N,N-dimethylcarbamic acid is unstable and rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO₂ gas. The results of these calculations suggest a mechanism to be concerted, asynchronous, and a six-membered cyclic transition state structure. Plotting the relative theoretical rate coefficients against Taft's s* values gave an approximate straight line (?*=0.4057, r=0.9894 at 360 °C). The correlation between experimental log k_rel vs. theoretical log k_rel. for these 2-substituted ethyl N,N-dimethylcarbamates gave an approximate straight line (r=0.9715 at 360 °C), suggesting the same type of mechanism.

We present a simple example in which the importance of the inertial effects of stress is evident. The system is an insulating solid narrow disc whose faces are uniformly charged with charges of equal magnitude and opposite signs. The motion of the system in two different directions is considered. It is shown how the contributions to energy and momentum of the stress that develops inside the solid to balance the lectrostatic forces have to be added to the electromagnetic contributions to obtain the results predicted by the relativistic equivalence of mass and energy.

A series of azasterol derivatives, designed as potential inhibitorsof the ²⁴-sterol methyltransferase enzyme (24-SMT), were synthesizedand evaluated for their activities against parasitic protozoa.Values in the nanomolar range were obtained for 50% effectivedose against the Trypanosoma brucei subsp. rhodesiense bloodstreamform cultured in vitro. In order to investigate the mode ofaction, Trypanosoma brucei subsp. brucei 24-SMT was cloned andoverexpressed and compounds were assayed for inhibitory activity.None of the inhibitors tested appeared to be active againstthe enzyme. Sterol composition analysis showed that only cholestanetype sterols are present in membranes of bloodstream forms whileergosterol is a major component of procyclic sterol extracts.Interestingly, Northern blot analysis showed the presence of24-SMT mRNA in both the procyclic and the bloodstream formsof the parasite, although levels of mRNA were threefold lowerin the latter. Likewise, Western blot analysis and activitydeterminations evidenced the existence of active enzyme in bothforms of the parasite. We conclude that the designed compoundsact at sites other than 24-SMT in Trypanosoma brucei.

The Mycobacterium tuberculosis serine/threonine protein kinases are attractive potential drug targets, and protein kinase D (PknD) is particularly interesting, as it is autophosphorylated on 11 residues, binds proteins containing forkhead associated domains, and contains a ß-propeller motif that likely functions as an anchoring sensor domain. We created a pknD knockout of a clinical M. tuberculosis isolate, and found that on in vitro phosphorylation of cell wall fractions it lacked a family of phosphorylated polypeptides seen in the WT. Mass spectrometry identified the phosphorylated polypeptides as MmpL7, a transporter of the RND family. MmpL7 is essential for virulence, presumably because it transports polyketide virulence factors such as phthiocerol dimycocerosate (PDIM) to the cell wall. Phosphorylation of the MmpL family of transporters has not been previously described, but these results suggest that PknD, and perhaps other serine/threonine kinases, could regulate their critical role in the formation of the M. tuberculosis envelope.

Blood stages of Plasmodium vivax induce the development of caveolae and caveola—vesicle complexes (CVC) in the membrane of their host erythrocyte. Caveolae are found in almost all types of cells and are involved in endogenous processes as calcium and cholesterol homeostasis, cell signalling, transporting, ligand internalization and transcytosis of serum components. Major structural components of caveolae are the proteins caveolins and flotillins. The functional role of caveolae in the P. vivax-infected erythrocyte is not properly understood. As these organelles have been shown to contain malaria antigens, it has been suggested that they are involved in the transport and release of specific parasite antigens from the infected erythrocyte and in the uptake of plasma proteins. Using specific antibodies to classical caveolae proteins and an immunolocalization approach, we found caveolin-2, caveolin-3, and flotillin-2 in the vesicle profiles and some CVC of P. vivax-infected erythrocytes. Caveolin-1—3 were not found in uninfected erythrocytes. This is the first report of identification and localization of caveolins in the CVC present in erythrocytes infected with P. vivax, thereby providing evidence of the role of this particular organelle in the protein-trafficking pathway that connect parasite-encoded proteins with the erythrocyte cytoplasm and the cell surface throughout the asexual blood cycle of vivax malaria parasite.

Radiation is employed to sterilize composite materials used in the biomedical field. Due to the changes induced by radiation onto polymeric materials, it is important to study variations in their melt flow index (MFI), as well as in their mechanical and thermal properties. In this work, those previous parameters were determined in composites obtained via solution of a high-density polyethylene (HDPE) in decalin, with different amounts of hydroxyapatite (HA), varying from 10 to 30 parts per hundred, after being exposed to gamma radiation at absorbed doses between 25 and 100 kGy. After the irradiation, the MFI of HDPE dissolved in decalin and precipitated afterwards and without filler increased from 6 to 24 g/10 min at the highest absorbed doses. This behavior was also observed in composites with 10 pph of HA, being the increase less pronounced, specifically in the range between 50 and 100 kGy. Composites with 20 and 30 pph of HA showed a maximum MFI value at 50 kGy, which decreased at higher doses. This implies that the filler begin to exert an influence because it does not melt at the test temperature and consequently, it does not flow. It was observed that Young’s modulus increased with HA addition due to rigidity of the ceramic filler. Radiation did not significantly affect this tensile property. On the other hand, the tensile strength did not show significant variations at the different doses but the filler content did affect this property improving it. Finally, elongation at break showed a drastic decrease with filler addition. When the thermal behavior was studied it was noticed that crystallization and melting temperatures remained unchanged. Instead, crystallinity degree slightly increased in the composites, and a little decrease was obtained when they were irradiated.

The Venezuelan scorpion Tityus discrepans is known to cause human fatalities. We describe the first complete proteomic analysis of its venom. By HPLC 58 different fractions were obtained and 205 different components were identified by MS analysis. Components having molecular masses from 272 to 57 908 amu were found. Forty homogeneous components had their N-terminal amino acid sequence determined by Edman degradation, from which two new peptides named TdK2 and TdK3 (meaning T. discrepans (Td) K⁺ channel toxins 2 and 3) were fully characterized. The first contains 34 amino acid residues with a molecular mass of 3451 amu, and the second has 36 amino acids with 3832 amu. Both peptides are tightly bound by three disulfide bridges. TdK2 was shown to block reversibly the Shaker B K⁺-channel expressed heterologously in Sf9 cells. The systematic number assigned to TdK2 is -KTx-18.2 and that of TdK3 is -KTx-18.3. Comparative analysis of the amino acid sequences found suggests that this venom contains peptides highly similar to those that block K⁺ channels, as well as those that modify the gating mechanisms of Na⁺ channels, found in other scorpions. Additionally, peptides similar to defensins were also identified.

The new water soluble complex [HRu(CO)(CH₃CN)(TPPTS)₃]BF₄ (TPPTS = tris[(m-sulfonated)phenyl]phosphine P(m-C₆H₄SO₃Na)₃) has been synthesized by ligand exchange techniques from the corresponding PPh₃ derivative in a methoxyethanol–water mixture. The new complex was characterized by FTIR, UV–vis, and ¹H NMR and ³¹P {¹H} NMR spectroscopy and used as catalyst precursor for the aqueous biphasic hydroformylation of several olefins and their mixtures under moderate reaction conditions. The catalytic activity order found was: 1-hexene Greater than allylbenzene Greater than 2,3-dimethyl-1-butene Greater than styrene Greater than cyclohexene. The sulphur tolerance of this complex was also investigated using thiophene as a model molecule; it was found that the new complex maintains its activity when the thiophene concentration is below 500 ppm. The mercury test in independent experiments showed no interference of the Hg at all with the evolution of the reaction, demonstrating that the catalysis is performed by molecular species. The recyclable nature of the complex was demonstrated during 1-hexene hydroformylation where at the end of each catalytic reaction all the metal remains in the aqueous phase.

Anthropogenic actions are altering fluxes of nitrogen (N) in the biosphere at unprecedented rates. Efforts to study these impacts have concentrated in the Northern hemisphere, where experimental data are available. In tropical developing countries, however, experimental studies are lacking. This paper summarizes available data and assesses the impacts of human activities on N fluxes in Puerto Rico, a densely populated Caribbean island that has experienced drastic landscape transformations over the last century associated with rapid socioeconomic changes. N yield calculations conducted in several watersheds of different anthropogenic influences revealed that disturbed watersheds export more N per unit area than undisturbed forested watersheds. Export of N from urban watersheds ranged from 4.8 kg ha^-1 year^-1 in the Río Bayamón watershed to 32.9 kg ha^-1 year^-1 in the highly urbanized Río Piedras watershed and 33.3 kg ha^-1 year^-1 in the rural-agricultural Río Grande de Añasco watershed. Along with land use, mean annual runoff explained most of the variance in fluvial N yield. Wastewater generated in the San Juan Metropolitan Area receives primary treatment before it is discharged into the Atlantic Ocean. These discharges are N-rich and export large amounts of N to the ocean at a rate of about 140 kg ha^-1 year^-1. Data on wet deposition of inorganic N () suggest that rates of atmospheric N deposition are increasing in the pristine forests of Puerto Rico. Stationary and mobile sources of NO _x (NO+NO₂) and N₂O generated in the large urban centers may be responsible for this trend. Comprehensive measurements are required in Puerto Rico to quantitatively characterize the local N cycle. More research is required to assess rates of atmospheric N deposition, N fixation in natural and human-dominated landscapes, N-balance associated with food and feed trade, and denitrification.

We show that any string x_s,x_s+1,...,x_s+r (for any r) constitutes a set of statistically independent random variables given the generalized chaotic sequence x_n=cos [2p?zⁿ], where z is a typical real number. This result can be generalized to sequences of type x_n=P(zⁿ), where P(t) is a periodic function. We will discuss the relevance of this result to dynamical systems, real physical experiments, and new technological devices used in secure communications.

The theoretical studies on the elimination kinetics of 2-substituted ethyl N,N-dimethylcarbamates [(CH₃)₂NCOOCH₂CH₂Z, Z=CH₂C₆H₅, C₆H₅, C(CH₃)CH₂] in the gas phase were carried out using the ab initio MP2/6-31G and DFT RMPWP91/6-31G(d,p) levels of theory. These carbamates produce N,N-dimethylcarbamic acid and the corresponding substituted olefin in a rate determining step. On the basis of these calculations, the mechanism appears to be concerted, asynchronous, through a six-membered cyclic transition state structure. The acidity of the benzylic and allylic ß-hydrogen is believed to be responsible for faster elimination rates.

Paracoccidioides brasiliensis is the etiologic agent of paracoccidioidomycosis,a disease confined to Latin America and of marked importancein the endemic areas due to its frequency and severity. Thisspecies is considered to be clonal according to mycologicalcriteria and has been shown to vary in virulence. To characterizenatural genetic variation and reproductive mode in this fungus,we analyzed P. brasiliensis phylogenetically in search of crypticspecies and possible recombination using concordance and nondiscordanceof gene genealogies with respect to phylogenies of eight regionsin five nuclear loci. Our data indicate that this fungus consistsof at least three distinct, previously unrecognized species:S1 (species 1 with 38 isolates), PS2 (phylogenetic species 2with six isolates), and PS3 (phylogenetic species 3 with 21isolates). Genealogies of four of the regions studied stronglysupported the PS2 clade, composed of five Brazilian and oneVenezuelan isolate. The second clade, PS3, composed solely of21 Colombian isolates, was strongly supported by the -tubulingenealogy. The remaining 38 individuals formed S1. Two of thethree lineages of P. brasiliensis, S1 and PS2, are sympatricacross their range, suggesting barriers to gene flow other thangeographic isolation. Our study provides the first evidencefor possible sexual reproduction in P. brasiliensis S1, butdoes not rule it out in the other two species.

Blood stages of Plasmodium vivax induce the development of caveolae and caveola—vesicle complexes (CVC) in the membrane of their host erythrocyte. Caveolae are found in almost all types of cells and are involved in endogenous processes as calcium and cholesterol homeostasis, cell signalling, transporting, ligand internalization and transcytosis of serum components. Major structural components of caveolae are the proteins caveolins and flotillins. The functional role of caveolae in the P. vivax-infected erythrocyte is not properly understood. As these organelles have been shown to contain malaria antigens, it has been suggested that they are involved in the transport and release of specific parasite antigens from the infected erythrocyte and in the uptake of plasma proteins. Using specific antibodies to classical caveolae proteins and an immunolocalization approach, we found caveolin-2, caveolin-3, and flotillin-2 in the vesicle profiles and some CVC of P. vivax-infected erythrocytes. Caveolin-1—3 were not found in uninfected erythrocytes. This is the first report of identification and localization of caveolins in the CVC present in erythrocytes infected with P. vivax, thereby providing evidence of the role of this particular organelle in the protein-trafficking pathway that connect parasite-encoded proteins with the erythrocyte cytoplasm and the cell surface throughout the asexual blood cycle of vivax malaria parasite.

Litterfall and nutrient return were studied in a primary forest (tall forest), a slight fire-affected forest (medium forest with low abundance of charred residues) and a strong fire-affected forest (low forest with abundant burned trunks on the forest floor) in the Gran Sabana, Southern Venezuela. The purpose was to determine how old fire disturbances that affected the forest structure are affecting the return of organic matter and nutrients from the biomass to the soil surface. The results did not reveal significant differences (P Greater than 0.05) in annual litter production between tall forest (5.2Mg·ha-1·year-1) and medium forest (5.7Mg·ha-1·year-1), indicating that minor perturbations had not affected the canopy productivity. Annual litter production in low forest (3.9Mg·ha-1·year-1) was significantly lower than in tall and medium forests (P less than 0.05). The differences in the litter production of low forest compared to tall and medium forests were surprisingly small considering that low forest were largely degraded, with 74 and 79% less stem density, 91 and 90% less basal area,and 97 and 96% less aboveground biomass than tall and medium forests, respectively. This indicates that fire disturbances that considerably affected the structural attributes of the forests are not influencing substantially the canopy productivity. Inputs of nutrients were low in all the forest types with low rates of litterfall to the soil surface and low concentrations of nutrients in such litterfall. The annual input of N and P followed the same trend as the annual input of litterfall, while the annual inputs of Ca, K and Mg were very variable

The effects of the g-308 Asn!Lys substitution of fibrinogen Biceˆ tre II on clot formation, structure and properties were determined to elucidate the role of this part of the molecule in fibrin polymerization. This process was followed by measurement of turbidity, and the structure and biophysical characteristics of the clots were studied by permeation, scanning electron microscopy, and rheological techniques. Turbidity studies revealed an increased lag period and greater final turbidity for fibrin BII clots, indicating impaired oligomer formation. By permeation it was found that BII clots had greater network porosity, four times more than that of the control. The clot architecture visualized by scanning electron microscopy was similar to that of control clots with pore size and fiber diameter slightly increased. BII clots had a stiffness decreased by more than half, and an increased loss tangent, a measure of the inelastic deformation of the clot. All these results suggest a disruption of the proper alignment of fibrin monomers during oligomer formation. Consistent with these results, fibrin cross-linking by adding the physiological concentration of factor XIII to the purified protein showed that g and a chain cross-linking was impaired in BII clots. This amino acid substitution defines distinctive effects on the surface of the D:D interaction sites that are reflected in the clot structure and functional properties.

Rapid, accurate and inexpensive methods are essential to detect drug-resistant Mycobacterium tuberculosis and allow timely application of effective treatment and precautions to prevent transmission. The proportion method, the MTT and Alamar Blue redox methods, and the D29 mycobacteriophage assay, were compared for their ability to detect resistance to isoniazid and rifampicin. When tested against a panel of known M. tuberculosis strains, the redox methods and the D29 assay showed good sensitivity and specificity compared to the proportion method, suggesting that they could be useful alternatives for identifying multidrug resistance in M. tuberculosis.

This paper deals with the coordination homopolymerization of -undecenyl poly(styrene-block-isoprene) macromonomers. The synthesis of the macromonomers made use of an anionic living poly(styrene-block-isoprene) copolymer which is deactivated at low temperature by 11-bromo-1-undecene. The ability of these macromonomers to get involved in coordination homopolymerization in the presence of selected titanium catalysts was discussed. Special emphasis was given to the influence of polymerization temperature, macromonomer molar mass and concentration on the yield of homopolymerization and average degree of polymerization (DP_n). In the presence of the CGC-Ti/MAO catalyst, macromonomer conversion, determined by SEC, was between 35 to 52 wt.-%, and DP_n was between 5 to 14 depending upon the experimental conditions. However, as revealed by SEC/LS, the resulting comb-shaped polymers (PE-graft-(PI-block-PS), are characterized by sharp molar distributions. Increasing macromonomer molar mass, led to only a slight decrease of DP_n whereas conversion increased moderately. Other titanium catalysts such as CpTiCl₃/MAO and Cp*TiCl₃/MAO only caused macromonomer dimerization.

The importance of complement activation and naturally occurring anti-pig antibodies in the hyperacute rejection (HAR) observed in models of pig-to-human xenotransplantation is well established. To overcome this, much effort has been dedicated to preparing transgenic pigs by knocking out Gala(1-3)Gal expression in these animals, or knocking in the expression of human complement regulatory proteins (CRPs), such as CD59 or decay accelerating factor. A soluble form of another membrane CRP, complement receptor type 1 (CR1), has also been shown to inhibit complement activation. Here, we show that transfection of a pig endothelial cell line with a truncated form of human soluble complement receptor 1 (sCR1) almost completely protected these cells from complement-mediated lysis by human AB serum. Pigs genetically manipulated to express human sCR1 may represent an additional strategy to inhibit HAR of pig-to-human transplanted organs.

Ecosystems dominated by herbaceous plant communities are amongst the most diversified landscape units in the Guayana (Guiana) Shield region. This paper aims to present a synthetic overview of the wide array of herbaceous ecosystems found in the region in an attempt to furnish a more concrete baseline for a better understanding of the pattern of variation, and to clarify some of the differences that occur in the vegetation of the area.

We present a generalization of Koplienko-Neidhardt trace formula for pairs of Hilbert space operators (T , V ) with T contractive and V unitary such that T - V is a Hilbert-Schmidt operator. We extend the result to pairs of contractions and then, via Cayley transform, to pairs of maximal dissipative operators.

The homogeneous, unimolecular, gas-phase elimination kinetics of several heterocyclic carbamates was studied at the MP2/6-31G level of theory under the average experimental conditions for each substrate. The elimination products for these carbamates are the corresponding carbamic acid and isobutylene. The intermediate acids are unstable and decarboxylate at the reaction temperature. Calculated thermodynamic and kinetic parameters are in good agreement with the experimental values, displaying the same reactivity order observed experimentally. An increase in the electron-withdrawing effect of the substituent on the carbamate nitrogen, increases the elimination rate. Transition state structures are described as six-membered rings with some departure from planarity. NBO charge analysis reveals strong polarization at the O(ester) ^-C⁺ bond. Bond indexes and synchronicity parameters are consistent with a concerted polar type of mechanism with O(ester) ^-C⁺ bond breaking as the most important process.

We study the nature of the [Ti ii] and [Ni ii] emission from the so-called strontium filament found in the ejecta of ? Carinae. To this purpose, we employ multilevel models of the Ti ii and Ni ii systems, which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the Ti ii ion, for which no atomic data were previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of 10⁷ cm^-3 and a temperature around 6000 K. In analysing three observations with different slit orientations recorded between 2000 March and 2001 November, we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust—gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of ? Carinae. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of Ti is likely the result of selective photoevaporation of Ti-bearing grains. Some mechanisms for such a scenario are proposed.

Theoretical studies on the gas phase elimination of 2-substituted alkyl ethyl methylcarbonates were performed at the B3LYP/6-31G* and B3LYP/6-31+G** level of theory. The results of these calculations provide additional evidence that the mechanism of carbonates with a CH bond proceeds through a concerted nonsynchronous six-membered cyclic transition state to produce methylcarbonic acid and the corresponding olefin. The unstable intermediate, methylcarbonic acid, rapidly decomposes through a four-membered cyclic transition state to methanol and carbon dioxide. The correlation of the logarithm of theoretical rate coefficients against Hancock's steric parameters E gave an approximate straight line ( = 0.30, r = 0.996 at 400°C). An additional fact is that when experimental log k_re.l is plotted against the theoretical log k_re.l. for 2-alkyl ethyl methylcarbonates an approximate straight line (r = 0.997 at 400°C) is obtained.

Overexpression of EGF receptors and constitutive cyclin D1 expression are frequently associated with human squamous carcinomas.We have now investigated whether these parameters influence susceptibility to okadaic acid induced cell death in EGF-receptor overexpressing mutant p53 A431 human carcinoma. Exposure of these cells to 20 nM okadaic acid induced apoptosis-associated caspase 3 activation, DNA fragmentation, cleavage of Poly ADP-Ribose Polymerase (PARP), p53-independent expression of proapoptotic bax, and loss of proliferation-promoting cyclin D1. All these alterations were antagonized by concurrent addition of exogenous EGF. Ectopic overexpression of the cyclin D1 gene in A431 carcinoma conferred resistance to 20 nM okadaic acid irrespective of exogenous EGF, associated with a parallel induction of anti-apoptotic bcl-2. Treatment with a subtoxic concentration of a bispecific bcl-2/bcl xL antisense oligonucleotide cooperated with okadaic acid to down-regulate bcl-2 and sensitize cyclin D1-overexpressing cells to okadaic acid. Although EGF protects EGF-R proficient epithelial cells from diverse apoptotic stimuli through Mcl-1, this is the first report demonstrating that cyclin D1 overexpression provides an EGF independent protection from okadaic acid-induced cell death through induction of bcl-2. We also show that this anti-apoptotic effect of cyclin D1 overexpression, can be partly antagonized with antisense strategies that down-regulate anti-apoptotic bcl-2 family members.

MEK1/2 inhibitors like U0126 can potentiate or antagonize the antitumor activity of cytotoxic agents such as cisplatin, paclitaxel or vinblastine, depending on the drug or the target cells. We now investigated whether U0126, differentially regulates melanoma signaling in response to UV radiation or betulinic acid, a drug lethal against melanoma. This report shows that U0126 inhibits early response (ERK) kinase activation and cyclin A expression in wt p53 C8161 melanoma exposed to either UV radiation or betulinic acid. However, U0126 does not protect from UV damage, but counteracts betulinic acid-mediated apoptosis in the same cells. Protection from the latter drug by joint treatment with U0126 was also evident in wt p53 MelJuso melanoma and mutant p53 WM164 melanoma. The latter cells were the most responsive to betulinic acid, showing a selective decline in the cdk4 protein, without a comparable change in other key cell cycle proteins like cdc2, cdk2, cdk7 or cyclin A, prior to apoptosis-associated PARP fragmentation. Laser scanning cytometry also showed that betulinic acid induced a significant increase in chromatin condensation in WM164 melanoma irrespective of whether they were in adherent form or as multicellular spheroids. All these betulinic acid-induced changes were counteracted by U0126. Our data show for the first time that (a) cdk4 protein is an early target of betulinic acid-induced apoptosis and (b) unrestricted ERK signaling favours betulinic acid-induced apoptosis, but this is counteracted by U0126, partly through counteracting chromatin condensation and restoring Akt activation decreased by betulinic acid treatment

Methane flux measurements from the soil-grass system were made during the wet season in unperturbed plots and plots where standing dry and green Trachypogon sp. grasses were clipped to just above the soil surface. Results support the surprising discovery that vegetation emits methane. The results of this work allows to infer that the savanna dry/green mixture of grasses produce methane at a rate of ~10 ng m^-2 s^-1, which is in agreement with early published soil-grass system fluxes. An extrapolation of this flux to the global savanna produces an annual emission much lower than the CH₄ production recently suggested in the literature. On the other hand, during the wet season savanna soil consume CH₄ at a rate of ~4.7 ng m^-2 s^-1. Therefore, the tropical savanna soil-grass system would make a modest contribution to the global budget of methane.

An emulsion-based method was developed as an alternative for the introduction of oil-based samples into a graphite furnace to produce a more rapid, precise, and accurate method of analysis. The combination of emulsion sampling and electrothermal atomization for atomic absorption spectroscopy was developed and then applied to the determination of Ni and manganese in neem oil from Venezuela. The optimal concentration of neem oil in the emulsion was 30 and 4% for Ni and Mn, respectively, based on the metal concentration of the neem oil. The stability of the emulsion as a function of time was evaluated. The use of aqueous calibration solutions and the accuracy attained using this method make it attractive for the analysis of oil samples. The metal recovery was between 97 and 101%. Based on the emulsion method, the neem oil samples had 1.39 and 0.21 mg of Mn and Ni per kg of oil, respectively. The wet digestion method indicated a Mn and Ni concentration in the neem oil sample of 1.42 and 0.24 mg/kg, respectively.

Many examples of systems presenting self-limiting behaviour exist in nature: population dynamics, structure engineering, Townsend’s electron breakdown, nuclear decay in radioactive equilibrium, histeresis process, meteorological models, etcetera. Each case is treated, generally with a different theory, sometimes a phenomenological one. In this work, we call your attention to the advantages the use of a variational formulation should provide in the study of self-regulated systems, such as a unified description of the phenomena mentioned above, further comprehension of the internal structure and symmetries of the related equations, and the equilibria points obtained via the energy function. As a particular and useful case, we have the Lagrangean and Hamiltonian functions obtained from the logistic equation, studying some of its dynamical properties and applications.

We solve the Klein–Gordon equation in the presence of a spatially one–dimensional Woods–Saxon potential. The bound state solutions are derived. The pair creation mechanism and the antiparticle bound state are discussed.

Se resuelve la ecuación de Klein—Gordon para el potencial de Woods—Saxon unidimensional independiente del tiempo. Se derivan las soluciones para los estados ligados. Se discute la creación de pares y los estados ligados de antipartículas.

Electron paramagnetic resonance (EPR) was used to study the effect of aging on irradiated samples of high–density polyethylene (HDPE) blended with diethyl maleate (DEM) in different proportions. Initially, we synthesize the HDPE using bis–(cyclopentadienyl) zirconium dichloride and P–MAO. The funcionalization of the synthesized HDPE was carried out in a 10% weight/vol of polyethylene in decalin solution using different percentages of diethyl maleate (5, 10, 15 and 30% in weight). The samples were irradiated at 5, 15 and 30 kGy. An exponential decay in the total free radicals concentration was observed in the pure HDPE sample at the 15 and 30 kGy irradiation doses, as it was expected. For the 15 and 30 kGy irradiation doses the HDPE blended with 15 and 30% of DEM in decalin shows an increase in the total free radical concentrations as the storage time is increased. This behavior has been interpreted in terms of trapped free radicals.

Usando resonancia paramagnética electrónica (RPE), se estudia el efecto del envejecimiento sobre muestras irradiadas de polietileno de alta densidad (PEAD) mezclado con dietil maleato (DEM) en distintas proporciones. Inicialmente, se sintetizo el PEAD utilizando dicloruro de bis—(ciclopentadienil) zirconio y P—MAO. La funcionalización del PEAD sintetizado se realizó en una solución de 10% peso/volumen de polietileno en decalina, utilizando diferentes porcentajes de dietil maleato (5, 10, 15 y 30% en peso). Las muestras fueron irradiadas a 5, 15 y 30 kGy. El PEAD puro muestra un decaimiento de primer orden de la concentración total de radicales libres para 15 y 30 kGy, como es de esperarse. El PEAD mezclado con DEM y decalina a 15 y 30% de DEM y para las dosis de 15 y 30 kGy muestra, al transcurrir el tiempo, un incremento en la concentración de radicales libres totales. Este comportamiento lo hemos interpretado en términos de radicales libres atrapados.

A tchnique for simulating quantum dynamics in phase space is discussed. It makes use of ensembles of classical trajectories to approximate the distribution functions and their derivatives by implementing Adaptive Kernel Density Estimation. It is found to improve the accuracy and stability of the simulations compared to more conventional particle methods. Formulation of the method in higher dimensions is straightforward.