Optical Studies of the coexistence curve of the n-heptane+nitrobenzene mixture near its consolute point measured by an optical method

We have measured the coexistence curve of the binary liquid mixture n-heptane+nitrobenzene near its consolute point using an optical method. In particular, the critical exponent beta describing the coexistence curve was measured for this system. Previous experimental values of beta for n-heptane+nitrobenzene were higher than the typical theoretically calculated value, an unusual, although not unique, occurrence. In an effort to study this discrepancy, we have used an improved experimental apparatus for our measurements. We have taken special care to minimize temperature gradients and maximize the temperature stability of our thermal control system. We have also exploited features of a known optical method to analyze, thoroughly, sources of systematic errors. We measured an apparent value of beta as 0.367+/- 0.006 and by a careful study of the known sources of error we find that they are not able to remove the discrepancy between the measured and the theoretical values of beta. We also measured the critical temperature of the system at Tc=291.80+/- 0.02 K (18.65 C).Comment: 21 pages, 8 figures, submitted to Physical Review B. Shrunk Experimental section, expanded Equilibration and Conclusion sections, eliminated a figure, added reference; 19 pages, 7 figures, resubmitted to PRB. Replaced Fig. 3, added separate simple text file with coexistence curve data (OPvsT.txt); resubmitted to PR

Lorentz-Lorenz Coefficient, Critical Point Constants, and Coexistence Curve of 1,1-Difluoroethylene

We report measurements of the Lorentz-Lorenz coefficient density dependence, the critical temperature, and the critical density, of the fluid 1,1-difluoroethylene. Lorentz-Lorenz coefficient data were obtained by measuring refractive index and density of the same fluid sample independently of one another. Accurate determination of the Lorentz-Lorenz coefficient is necessary for transformation of refractive index data into density data from optics-based experiments on critical phenomena of fluid systems done with different apparatus, with which independent measurement of the refractive indes and density is not possible. Measurements were made along the coexistence curve of the fluid and span the density range 0.01 to 0.80 g/cc. The Lorentz-Lorenz coefficient results show a stronger density dependence along the coexistence curve than previously observed in other fluids, with a monotonic decrease from a density of about 0.2 g/cc onwards, and an overall variation of about 2.5% in the density range studied. No anomaly in the Lorentz-Lorenz coefficient was observed near the critical density. The critical temperature is measured at Tc=(302.964+-0.002) K (29.814 C) and the measured critical density is (0.4195+-0.0018)g/cc.Comment: 14 pages, 6 figures, MikTeX 2.4, submitted to Physical Review

Altered deoxyribonucleotide pools in T-lymphoblastoid cells expressing the multisubstrate nucleoside kinase of Drosophila melanogaster

The multisubstrate nucleoside kinase of Drosophila melanogaster (Dm-dNK) can be expressed in human solid tumor cells and its unique enzymatic properties makes this enzyme a suicide gene candidate. In the present study, Dm-dNK was stably expressed in the CCRF-CEM and H9 T-lymphoblastoid cell lines. The expressed enzyme was localized to the cell nucleus and the enzyme retained its activity. The Dm-dNK overexpressing cells showed approximately 200-fold increased sensitivity to the cytostatic activity of several nucleoside analogs, such as the pyrimidine nucleoside analogs (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and 1-beta-d-arabinofuranosylthymine (araT), but not to the antiherpetic purine nucleoside analogs ganciclovir, acyclovir and penciclovir, which may allow this technology to be applied in donor T cells and/or rescue graft vs. host disease to permit modulation of alloreactivity after transplantation. The most pronounced effect on the steady-state dNTP levels was a two- to 10-fold increased dTTP pool in Dm-dNK expressing cells that were grown in the presence of 1 microm of each natural deoxyribonucleoside. Although the Dm-dNK expressing cells demonstrated dNTP pool imbalances, no mitochondrial DNA deletions or altered mitochondrial DNA levels were detected in the H9 Dm-dNK expressing cells

Mechanisms underlying activity of antiretroviral drugs in HIV-1-infected macrophages: New therapeutic strategies

Monocyte-derived macrophages (M/M) are considered the second cellular target of HIV-1 and a crucial virus reservoir. M/M are widely distributed in all tissues and organs, including the CNS, where they represent the most common HIV-infected cells. Differently from activated CD4+ T lymphocytes, M/M are resistant to the cytopathic effect of HIV and survive HIV infection for a long lime. Moreover, HIV-1 replication in M/M is a key pathogenetic event during the course of HIV-1 infection. Overall findings strongly support the clinical relevance of anti-HIV drugs in M/M. Nucleoside RT inhibitors (NRTIs) are more active against HIV in M/M than in CD4+ T lymphocytes. Their activity is further boosted by the presence of an additional monophosphate group (i.e., a phosphonate group, as in the case of Tenofovir), thus overcoming the bottleneck of the low phosphorylation ability of M/M. In contrast, the antiviral activity of non-NRTIs (not affecting the DNA chain elongation) in M/M is similar to that in CD4+ T lymphocytes. Protease inhibitors are the only clinically approved drugs acting at a late stage of the HIV lifecycle. They are able to interfere with HIV replication in HIV-1 chronically infected M/M, even if at concentrations greater than those observed in HIV-1 chronically infected CD4+ T lymphocytes. Finally, several new drugs have been shown to interfere efficiently with HIV replication in M/M, including entry inhibitors. A better understanding of the activity of the anti-HIV drugs in M/M may represent a key element for the design of effective anti-HIV chemotherapy. © Society for Leukocyte Biology

Conformational states of HIV-1 reverse transcriptase for nucleotide incorporation vs. pyrophosphorolysis – binding of foscarnet

HIV-1 reverse transcriptase (RT) catalytically incorporates individual nucleotides into a viral DNA strand complementing an RNA or DNA template strand; the polymerase active site of RT adopts multiple conformational and structural states while performing this task. The states associated are dNTP binding at the N site, catalytic incorporation of a nucleotide, release of a pyrophosphate, and translocation of the primer 3′-end to the P site. Structural characterization of each of these states may help in understanding the molecular mechanisms of drug activity and resistance and in developing new RT inhibitors. Using a 38-mer DNA template-primer aptamer as the substrate mimic, we crystallized an RT/dsDNA complex that is catalytically active, yet translocation-incompetent in crystals. The ability of RT to perform dNTP binding and incorporation in crystals permitted obtaining a series of structures: (I) RT/DNA (P-site), (II) RT/DNA/AZTTP ternary, (III) RT/AZT-terminated DNA (N-site), and (IV) RT/AZT-terminated DNA (N-site)/foscarnet complexes. The stable N-site complex permitted the binding of foscarnet as a pyrophosphate mimic. The Mg2+ ions dissociated after catalytic addition of AZTMP in the pretranslocated structure III, whereas ions A and B had re-entered the active site to bind foscarnet in structure IV. The binding of foscarnet involves chelation with the Mg2+ (B) ion and interactions with K65 and R72. The analysis of interactions of foscarnet and the recently discovered nucleotide-competing RT inhibitor (NcRTI) α-T-CNP in two different conformational states of the enzyme provides insights for developing new classes of polymerase active site RT inhibitors

Descripción de artrópodos epigeos en dos ambientes del Parque Nacional Talampaya, La Rioja, Argentina.

This Project studies the biodiversity composition of epigean artrhropods in two habitats of the Talampaya, National Park, La Rioja,Argentina. The two studied habitats are different in the composition and vegetational structure. The habitats were designed as follow: “Site A”: poor in organic matter with scare development and structure of the soil; “Site B”: is structured soil with morefloristic richness.The diversity of the epigean arthropods was considered using pit-fall trapping that gives good information about diversity of the epigean arthropods. Twenty pit-fall traps were put on each site according with the follow design: 4 traps arranged into 5 rows, separated each trap by 5 meters considering this distance between the rows and the traps. The traps were filled with a water solution with drops of detergent. The traps were active during 2 days on each season during one year, and revised three times by day: between 8:00-10:00AM; 2:00-4:00PM and 6:00-8:00PM. The statistical analysis was carried out using the software InfoStat 2004.Two thousand three hundred and eighty five epigean arthropods of 15 orders were collected at the Talampaya National Park. Both studied sites were different in the epigean arthropod composition community in species diversity, maybe this will be relationship with the variation of the vegetation structure and the soil composition of each sites. According with them, both habitats are important to conserve in theTalampaya National Park, La Rioja (Argentina), because the have a complementary fauna.Este proyecto estudia la biodiversidad y la composición de los artrópodos epigeos en dos ambientes aparentemente diferentes en cuanto a estructura y composición de la vegetación en el Parque Nacional Talampaya, La Rioja, Argentina. Los hábitat fueron designados como: “Sitio A” (pobre en materia orgánica con escaso desarrollo y estructura del suelo); y el “Sitio B” (con sueloestructurado con mayor riqueza florística).La diversidad fue considerada usando trampas de caída que proveen buena información sobre la diversidad de los artrópodos epigeos.Veinte trampas de caída fueron colocadas en cada sitio de acuerdo con el siguiente diseño: 4 trampas dispuestas en 5 filas, separadas cada trampa por 5 metros, considerando esta distancia entre las filas y las trampas. Las trampas fueron llenadas con una solución de agua y gotas de detergente, y estuvieron activas durante 2 días en cada estación a lo largo de un año, siendo revisadas tres veces al día: entre las 8:00-10:00AM; 2:00-4:00PM y 6:00-8:00PM. Los análisis estadísticos fueron realizados por medio del software InfoStat 2004.Dos mil trescientos ochenta y cinco artrópodos fueron colectados en el Parque Nacional Talampaya, correspondiente a 15 órdenes. Ambos sitios estudiados fueron diferentes en la composición de artrópodos epigeos en cuanto a la diversidad, posiblemente relacionado con la variación en la estructura de la vegetación y en la composición del suelo de cada sitio. De acuerdocon ello, ambos hábitats son importantes conservar en el Parque Nacional Talampaya, La Rioja (Argentina), debido a que ellos son complementarios en fauna