RESUMEN

The adsorption of dimers and trimers on triangular lattices is studied by combining theoretical modeling and Monte Carlo (MC) simulations. The thermodynamic process is analyzed through the behavior of the configurational entropy per site of the adsorbed phase as a function of the coverage. MC calculations, supplemented by the thermodynamic integration method, are performed in the grand canonical ensemble. The theoretical model used in the present study is called Cluster Approximation (CA), and it is based on exact calculation of states on finite cells. An efficient algorithm allows us to determine the detailed structure of the configuration space for m = l1 × l2 cells. From there, the thermodynamic properties can be obtained. Five systems are investigated, according to the size and shape of the molecule in the adsorbed state: (i) dimers, (ii) linear trimers, (iii) triangular trimers, (iv) 60°-angular trimers and (v) 120°-angular trimers on triangular lattices. Dimer and trimer are the simplest cases of a polyatomic adsorbate, containing all the properties of the multisite-occupancy adsorption and can be used to model several experimental systems. CA solutions are tested by comparison with MC simulations and previous data in the literature. Special interest is devoted to the calculation of the configurational entropy per site in the limit case of θ → 1 (full coverage), where some exact results are available. The theoretical formalism is also applied to model CH4 and CO2 clathrate hydrates. In these systems, a triangular lattice is used to simulate the substrate, and methane(carbon dioxide) molecules can be well represented by triangular(linear) trimers. The good qualitative agreement between simulation and analytical data supports the validity of the CA scheme to predict the behavior of a wide variety of multisite-adsorption models, for which theoretical solutions are very difficult to obtain.

RESUMEN

The aim of this study was to synthesize several small molecules of the type 5-nitroimidazole-sulfanyl and evaluate biological properties against the main Leishmania species that cause cutaneous leishmaniasis in Venezuela. Final compounds 4-7 were generated through simple nucleophilic substitution of 1-(2-chloroethyl)-2-methyl-5-nitroimidazole 3 with 2-mercaptoethanol, 1-methyl-2-mercaptoethanol, and 2-thyolacetic acid derivative. Compound 8 was synthesized via a coupling reaction between 7 and (S)-Methyl 2-amino-4-methylpentanoate hydrochloride. The inhibitory concentrations of (3, 4, 7, 8) against Leishmania (L.) mexicana and (V.) braziliensis in promastigotes and experimentally infected macrophages were determined by in vitro activity assays. Compounds 7 and 8 shown high activity against both species of Leishmania and were selected for the in vivo evaluation. Animals were infected with promastigotes of the two species and divided into four groups of ten (10) animals and a control group. Intralesional injection way was used for the treatment. The parasitological diagnostic after treatment was obtained by PCR using species specific oligonucleotides. The two Leishmania species were susceptible to compounds 7 and 8 in vivo assays. The results indicated that both compounds reduce significantly (96%) the size of the lesion and cure 63% of the mice infected with L (L) mexicana or L (V) braziliensis as was determined by PCR. The results are indicating that both compounds may represent an alternative treatment for these two Leishmania species.

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RESUMEN

El objetivo de este estudio fue realizar la caracterización fenotípica y conocer la distribución de las especies de Candida aisladas en 92 pacientes con candidemia (niños y adultos) internados en el Hospital Universitario de Maracaibo (Servicios UCI y No UCI), Edo. Zulia, Venezuela, de Marzo de 2000 a Septiembre de 2002. La identificación de las levaduras aisladas de los hemocultivos fue realizada mediante el uso de CHROMagar Candida y métodos tradicionales; en algunos casos se aplicó API 20C e ID32. Los resultados indican la presencia de C. albicans (33,7 por ciento) y Candida no albicans (66,3 por ciento): Candida tropicalis (30,4 por ciento), Candida parapsilosis (21,7 por ciento), Candida guilliermondii (5,4 por ciento), Candida pelliculosa (5,4 por ciento), Candida famata (2,2 por ciento) y Candida glabrata (1,1 por ciento). Entre los ni¤os (n= 70) internados en la UCI y servicios no UCI, predominaron aislamientos de C. parapsilosis y C. albicans respectivamente. Por otra parte, Candida tropicalis fue la levadura más frecuentemente aislada en adultos en los servicios evaluados. El predominio de Candida no albicans observado en este estudio, ha sido reportado en América Latina.

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