Thermodynamic, IR spectral and X-ray diffraction studies of the ����-cyclodextrin-para-aminobenzoic acid�� inclusion complex

The inclusion complex with stoichiometric composition 1:1 was formed as a result of intermolecular interactions between para-aminobenzoic acid and ??-cyclodextrin. The stability constant of ????-cyclodextrin-para-aminobenzoic acid?? inclusion complex at 289, 292 and 313 K was calculated by the Ketelar equation. The influence of temperature on the stability of ????-cyclodextrin-para-aminobenzoic acid?? inclusion complex was also examined, and thermodynamic parameters involved in the complex formation (??G, ??H, ??S) were calculated. Supramolecular complex formation between para-aminobenzoic acid and ??-cyclodextrin was confirmed by X-ray diffraction and IR spectroscopy studies.     

Structure and physical properties of ternary NaF–LiF–LnF3 (Ln = La,Nd) systems of eutectic compositions

Ternary NaF–LiF–LnF₃ (Ln = La, Nd) systems of eutectic compositions were studied by means of X-ray diffraction method in the solid and liquid states. It was found that the crystalline phases LiF, NaF and NaLnF₄ coexist in the solid state up to the melting temperatures. Above the melting point, a decrease in the nearest interatomic distances with a pronounced minimum has been observed, which correlates with the extreme behaviour of the temperature-dependent structure-sensitive physical properties of the investigated alloys.     

The shear modulus of the human vocal fold in a transverse direction

The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3g was applied to the epithelium, and the resultant displacement logged at a rate of 1kHz. Force measurement accuracy was 20microg and position measurement accuracy was 4microm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension.     

Direct chemical assembly of quaternary ammonium groups on a surface of highly dispersed silica

Direct assembly of quaternary ammonium groups onto a silica surface has been realized by use of many-stage chemical reactions. Adsorption of cholic acid in dependence on duration, equilibrium concentration, and pH solution onto a surface of silicas modified with quaternary ammonium groups has been studied. The main parameters of cholic acid adsorption have been calculated.     

Reverse Monte Carlo and Voronoi-Delaunay simulation and structure analysis for liquid metals

This paper discusses the applicability of the integrated reverse Monte Carlo and Voronoi-Delaunay approach to local structure analysis and medium-scale structure determination of liquid metals. The advantages of this approach are shown: generation of 3D structural models using experimental diffraction data and subsequent structure determination by atomic coordinate analysis.Original Russian Text Copyright © 2004 by A. S. Roik, V. P. Kazimirov, and V. E. SokolskiiTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 683–691, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Designing of the centers for adsorption of bile acids on a silica surface

Silicas chemically modified with attached aminopropyl, imidazolyl, and trimethylsilyl groups, with adsorptive and coordinative grafted hemin were synthesized. Adsorption of some bile acids on the surface of hydroxylated silica, synthesized siliceous adsorbents and cholestyramine has been studied. It was found that the main contribution to the total adsorption is caused by electrostatic attraction between anions of bile acids and positively charged sites of the surface of modified silica and also by dispersion interactions between steroid skeleton of bile acids and functional groups of modified silicon dioxides. It was established that the kinetic parameters of adsorption and adsorptive capacity for all investigated siliceous adsorbents exceed similar characteristics for cholestyramine. The best of synthesized adsorbents is hemin-containing adsorbent IX, and the sequence of increase in its adsorptive capacity in relation to bile acids corresponds to the following series: I < III < II, IV < VI < V < VIII < VII < IX.     

X-ray diffraction study of the structure of Al-Co melts

The structure of Al-Co melts with 0 at.%, 10 at.%, 18 at.%, 23.5 at.%, 26 at.%, 80.7 at.%, and 100 at.% Co has been studied by X-ray diffraction. Inverse Monte Carlo simulation using the experimental curves of the structural factor was employed to reconstruct the models of melts, analyzed by the Voronoi-Delaunay technique. The dependence of parameters that define short-and longer range ordering of atoms is nonmonotonous in the range 85–74 at.% Al and is extremal in the vicinity of a melt with 76.5 at.% Al. In the stated range of concentrations, the cobalt atoms basically lie at distances of ≈4.2 Å in the pentagonal rings of icosahedral type polytetrahedral clusters. Therefore one can speak about correlation in the character of atomic ordering in melts and corresponding periodic and quasiperiodic phases.     

Interaction of supramolecular centers of silica surface with aromatic amino acids

Surface grafting of β-cyclodextrin onto aminopropylsilica has been carried out under mild conditions using 1,1'-carbonyldiimidazole as an activator. The obtained β-cyclodextrin-silica has been characterized by means of chemical and IR spectral analysis. Adsorption of para-aminobenzoic and para-aminosalicylic acids onto the surface of hydroxylated silica, aminopropylsilica, and silica with chemically attached β-cyclodextrin moieties has been studied in relation to duration of contact, equilibrium concentration, and solution pH. Chemical immobilization of β-cyclodextrin onto silica surface improves adsorption parameters for aromatic amino acids. The well-known mathematical models for the kinetic and equilibrium adsorption processes have been used, and the main adsorption parameters have been calculated. Kinetic curves of aromatic amino acids adsorption correspond to the model of pseudo-second order reaction. The major contribution to the equilibrium adsorption of para-aminobenzoic and para-aminosalicylic acids onto β-cyclodextrin-containing silica is due to the formation of surface inclusion complexes between grafted oligosaccharide molecules and aromatic amino acids.     

Surface structure and adsorption properties of multiwalled carbon nanotubes

The pore structure, sorption parameters, and chemical composition of the surface of multiwalled carbon nanotubes synthesized by catalytic pyrolysis were determined. The dependences of the amount of cholic acid adsorbed by the nanotube surface on time, pH, and concentration of an equilibrium solution were studied. Physical adsorption of cholic acid is mainly the outcome of nonspecific interactions between the acid and the surface of the nanotubes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1712–1715, October, 2006.