胆汁酸盐-胆红素-钙离子三元复合物的构象性质

根据九种胆汁酸盐-胆红素-钙离子三元体系的UV和CD实验所见, 提出一种所形成的三元复合物的构象模型。利用PPP-SCF-CI-DV量子化学程序拟合有关的UV和CD谱, 研究三元复合物的构象性质。得到两类六种与光谱学实验符合的胆红素分子的最佳构象。利用它们可以解释九种胆汁酸盐-胆红素-钙离子三元复合物表现在园二色谱中的手性性质。     

A differential microcalorimetric study of whey proteins and their behaviour in oil-in-water emulsions

Oil-in-water emulsions (20% soya oil, 1% protein) have been prepared containing lysozyme or isolates of -lactalbumin and β-lactoglobulin from whey protein. The structural characteristics of these proteins adsorbed at an oil/water interface were determined by following their thermal transitions using differential scanning microcalorimetry. Thermograms of the proteins in the adsorbed state differed markedly from the corresponding transitions seen for the proteins in solution. This suggests that the proteins underwent substantial changes in secondary and tertiary structure upon adsorption. In general, for all the proteins studied, a net decrease in the total energy absorbed during denaturation was found when the proteins were in an adsorbed state. Both lysozyme and -lactalbumin were in part “surface denatured”, and they showed a certain degree of reversibility between solution and the adsorbed state. β-Lactoglobulin showed the highest degree of denaturation upon adsorption and the conformational change was irreversible.     

Synthesis and Structure of a 1,3-alternate-Thiacalix[4]arene diamide Derivative

A novel receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. The tetrathiacalix[4]arene diamide shows strong intramolecular hydrogen bonding. The binding behavior towards K⁺ and halides has been examined by ¹H NMR titration experiments.     

Polynitro-substitutedN-alkylalkaneimidoyl chlorides

The reaction of -fluorosubstituted polynitroalkylaldimines with HCl results in replacement of the fluorine atom by a chlorine atom. The hitherto unknown -chlorosubstituted polynitroalkylaldimines have been obtained, and their X-ray structural investigation has been performed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 440–443, March, 1994.     

Design considerations and computer modeling related to the development of molecular scaffolds and peptide mimetics for combinatorial chemistry

Summary A critical issue in drug discovery utilizing combinatorial chemistry as part of the discovery process is the choice of scaffolds to be used for a proper presentation, in a three-dimensional space, of the critical elements of structure necessary for molecular recognition (binding) and information transfer (agonist/ antagonist). In the case of polypeptide ligands, considerations related to the properties of various backbone structures (-helix, -sheets, etc.; , space) and those related to three-dimensional presentation of side-chain moieties (topography; (chi) space) must be addressed, although they often present quite different elements in the molecular recognition puzzle. We have addressed aspects of this problem by examining the three-dimensional structures of chemically different scaffolds at various distances from the scaffold to evaluate their putative diversity. We find that chemically diverse scaffolds can readily become topographically similar. We suggest a topographical approach involving design in chi space to deal with these problems.     

Comparative FT infrared study of structural changes occuring on dealumination of zeolite Na-Y with ethylenediaminetetraacetic or hydrochloric acid

IR lattice vibration spectra were used to monitor the changes in the structure of zeolite Na-Y upon its dealumination with ethylenediaminetetraacetic acid (EDTA) or with HCl. The terminal Si-O(H,Na) bonds thus formed (which are detectable by characteristic absorbance at v 900–950 cm^–1) are energetically less uniform when EDTA has been used as the dealuminating agent. This inhomogeneity is connected with the local deformations of zeolite structure which result in lowering the symmetry of silicon-oxygen tetrahedra. As a consequence, two novel bands appear at v 1090 cm^–1 and 1200 cm^–1 in addition to the fundamental absorption bands, v_as (TO₄) (T = Si, Al), at 1030 cm^–1 and 1145 cm^–1. A mechanism of dealumination is proposed, which takes into account the topochemical peculiarities involved in the chelation of the framework aluminum ions with EDTA.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskay, No. 2, pp. 284–287, February, 1993.     

Effects of solute-matrix interaction on monitoring the conformational changes of immobilized proteins by surface plasmon resonance sensor

A real-time and labeling-free surface plasmon resonance (SPR) sensor was used to monitor the conformational changes of immobilized globule proteins (RNase A and lysozyme) in chemical unfolding and refolding. The effects of chemical denaturants on the protein structures were investigated. The methodology in protein conformational study on the solid surface is refined through the theoretic calculations and the conformational information of native/denatured proteins in solution. Additionally, our observation illustrates that the ambient buffer solution is merit to influence the refractive index of immobilized protein films and directly be observed from the SPR resonance angle shifts.     

A configuration interaction study of phosphine using bonded functions

A computational study is made of the effect of basis set upon the energy, properties and inversion barrier of the phosphine molecule. The calculations are performed at both the SCF and CI level. The flexibility of the double zeta basis is discussed in the light of the results.     

Etude théorique par la méthode DFT des structures non-classiques des systèmes X2H2F2 (X=Si, Ge, Sn)

The structure and the relative stability of isomers of molecules X₂H₂F₂ (X=Si, Ge, Sn) have been studied using the density functional theory (DFT). We have determined the optimised structures of the substituted isomers. The XX bond have been studied and compared to that of the parent molecules: X₂H₄. It appears that, for the planar and trans ethylenic systems, the double bond character of the XX decreases when the hydrogen atoms are substituted by fluorine atoms. The most stable structure is shown to be the one where the two fluorine atoms are fixed on the same atom. The bridged structures are also studied.     

Possible conformations and relative stability of the 7-membered ring in 1α,5β,6,7α(H)-and 1β,5α,6,7α(H)-guai-11(13)-en-6,12-olides

Stereoisomers of 1,5,6,7(H)- and 1,5,6,7(H)-guai-11(13)-en-6,12-olides are calculated using molecular mechanics. The possibility of forming various conformations in the 7-membered ring is examined as a function of the fusion to the 5-membered C-ring. The effect of the methyl orientation on the conformation of the 7-membered ring and the relative stability of the conformers are discussed.Insitute of Phytochemistry, Karaganda, fax (3212)-43-37-73. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 54–56, January–February, 2000.