COSMO‐RS Calculations of Partition Coefficients: Different Tools for Conformation Search

This work is encouraged by the growing interest and recent success of quantum mechanics‐based methods in modeling of thermodynamic properties in the field of chemical engineering and life sciences. Among those, the COSMO‐RS model has become one of the most popular methods to predict phase equilibria in complex bio‐related systems. Recently, we have shown that the quality of predictions of n‐octanol/water and micelle/water partition coefficients is improved when the weighted mixtures of conformers are used to represent molecules, thereby demanding that the conformation analysis is performed for each component of the system. In this paper, different methods for performing the conformational search are evaluated. Micelle/water partition coefficients of solutes from different homologous series in aqueous solutions of Triton X100 as well as the n‐octanol/water partitioning of three common drugs (aminopinicillanic acid, ampicillin, and penicillin G) are calculated and compared with experimental data. Conformational analysis is made by the HyperChem program for the molecules placed in vacuum as well as by using the molecular dynamics simulation in a solvent medium (n‐octanol and water). It is demonstrated that molecular dynamics simulation is a promising tool to conduct conformational analysis. Along with the possibility of providing the conformers for large surfactant and pharmaceutical molecules, the method accounts for the solvent in a realistic manner. The results for micelle/water partition coefficients illustrate that n‐octanol is a reasonable approximation for the “micelle‐like” medium in molecular dynamics (MD) simulations. Predicted n‐octanol/water partition coefficients of three penicillins are in a good agreement with literature data and values calculated by a common quantitative structure‐activity relationship (QSAR).     

A SAXS study of the structure of gels formed by mixtures of polyoxyalkylene triblock copolymers

Small‐angle X‐ray scattering was used to characterise aqueous micellar gels of triblock copolymers E₁₃₇S₁₈E₁₃₇, E₈₂S₉E₈₂, E₇₆S₅E₇₆, E₆₂P₃₉E₆₂, and of two mixtures: E₁₃₇S₁₈E₁₃₇ and E₆₂P₃₉E₆₂ (Mix 1) and E₈₂S₉E₈₂ and E₆₂P₃₉E₆₂ (Mix 2), each 50/50 wt%. E = oxyethylene, CH₂CH₂O; S = oxyphenylethylene, OCH₂CH(C₆H₅); and P = oxypropylene, OCH₂CH(CH₃). Within the concentration and temperature ranges investigated (30–40 wt% copolymer, 20–80 °C), spherical micelles of copolymers E₁₃₇S₁₈E₁₃₇, E₈₂S₉E₈₂ and E₆₂P₃₉E₆₂ packed into body‐centred cubic (BCC) structures. Gels of E₇₆S₅E₇₆ were stable only at high concentrations and low temperatures, and a 70 wt% copolymer solution at T = 30 °C formed a hexagonal gel consistent with cylindrical micelles. It is likely that the mixed copolymers would form two distributions of micelles, and more complex structures were expected. However, gels of Mix 2 had well‐ordered BCC structures, while the less ordered gels of Mix 1 were also best characterised as BCC. Copyright © 2006 Society of Chemical Industry     

A method for analytical monitoring of surface deposits on jackets of fuel elements of reactors with water heat carrier

A method of postreactor analytical monitoring of elemental composition of deposits on jackets of fuel elements from zirconium alloys based on chemical removal and subsequent quantitative analysis of deposited elements using inductively coupled plasma atomic emission spectroscopy (ICP-AES) is described. The choice of the method of chemical removal of deposits from jackets of fuel elements is substantiated; data on the composition of solution of chemical reagents and temperature-time regime of the procedure are presented. Devices for nondestructively obtaining detailed and precise information on element distribution in deposits along the fuel element height by means of a small length of the analyzed segment and the capability of sequential segment analysis along the whole fuel element length are developed. Advantages of ICP-AES application for analysis of elemental composition of deposits with allowance for the specific features of studies of irradiated reactor materials are considered. A method of quantitative analysis of deposits is developed, its metrological aspects are considered, and results of determination of some elements of deposits on jackets of fuel elements of the RBMK-1000 of the Leningrad Nuclear Power Plant are given.     

The mannose receptor mediates uptake of pathogenic and nonpathogenic mycobacteria and bypasses bactericidal responses in human macrophages

The mannose receptor (MR) is involved in the phagocytosis of pathogenic microorganisms. Here we investigated its role in the bactericidal functions of human monocyte-derived macrophages (MDMs), using (i) trimannoside-bovine serum albumin (BSA)-coated latex beads and zymosan as particulate ligands of the MR, and (ii) mannan and mannose-BSA as soluble ligands. We show that phagocytosis of mannosylated latex beads did not elicit the production of O2-. Zymosan, which is composed of alpha-mannan and beta-glucan, was internalized by the MR and a beta-glucan receptor, but the production of O2- was triggered only by phagocytosis through the beta-glucan receptor. Activation and translocation of Hck, a Src family tyrosine kinase located on lysosomes, has previously been used as a marker of fusion between lysosomes and phagosomes in human neutrophils. In MDMs, Hck was activated and recruited to phagosomes containing zymosan later than LAMP-1 and CD63. Phagosomes containing mannosylated latex beads fused with LAMP-1 and CD63 vesicles but not with the Hck compartment, and the kinase was not activated. We also demonstrate that the MR was unable to distinguish between nonpathogenic and pathogenic mycobacteria, as they were internalized at similar rates by this receptor, indicating that this route of entry cannot be considered as a differential determinant of the intracellular fate of mycobacteria. In conclusion, MR-dependent phagocytosis is coupled neither to the activation of NADPH oxidase nor to the maturation of phagosomes until fusion with the Hck compartment and therefore constitutes a safe portal of entry for microorganisms.     

Mastering the production of 08GDNFL steel fitting castings

Chemical and Petroleum Engineering -