Phase separation of poly(γ-benzyl L-glutamate) to liquid crystal and isotropic solution in various helicogenic solvents

Solvent effects on the phase separation of poly(-benzyl L-glutamate) to liquid crystal and isotropic solution have been observed in various helicogenic solvents. The temperature-composition phase diagrams have been determined for each solution. The critical concentrations, ₂ ^* , at which the phase separation occours have been compared in various solvents. In dimethylformamide in which the polymer is molecularly dispersed, the observed ₂ ^* value has agreed with that calculated by Flory's theory. In some solvents in which the polymer aggregates in a head-to-tail mode such as chloroform, the observed ₂ ^* values have been considerably small. It is assumed that the polymer aggregates behave as longer particles than the original particles. In dioxane in which the polymer aggregates highly both in a head-to-tail and a side-by-side modes, the ₂ ^* value has been a little larger than that in chloroform. In this case the relationship between the aggregation and the liquid crystal formation is so complicated that further investigation is necessary. In aromatic solvents such asm-cresol that dissolves the polymer almost molecularly, the ₂ ^* is smaller than that in dimethylformamide. Therefore, the intermolecular interactions between the phenyl groups in the side groups of the polymer and those in solvent molecules must be considered.The author is grateful to Mr. K. Sano and Mr. M. Watanabe for their observation of the liquid crystal formation.     

Molecular orbital studies on the conformation of GABA (γ-aminobutyric acid)

In distinction to Extended Hückel Theory which predicts as the most stable conformation of free zwitterionic GABA a totally extended form, PCILO and SCF ab initio studies show that the intrinsically preferred conformation of the isolated molecule is a highly folded one, resulting from strong interactions between the two charged ends. Computations are also carried out for hydrated GABA in the supermolecule approach allowing moreover for the flexibility of binding of some of the water molecules of the first hydration shell. They predict the coexistence in solution of a large number of conformations showing different degrees of folding (or extension), a result confirmed by recent NMR studies. This and a number of similar results show that we have to adapt our thinking on the role of conformations in pharmacological activity to this situation, which was frequently obscured by the more abundant results of X-ray crystallography yielding a single conformation.     

Solubility Study of Nimodipine Inclusion Complexation with α- and β-Cyclodextrin and some Substituted Cyclodextrins

The solubility of nimodipine was measured in aqueous solutions of the following cyclodextrins: -cyclodextrin (-CD), hydroxypropyl--CD (HP--CD), -cyclodextrin (-CD), random substituted methyl--CD (M--CD), three hydroxypropyl--CDs (HP--CD) with mutually different average degree of substitution, and hydroxypropyl--cyclodextrin (HP--CD). From the determined linear solubility diagrams the values of the binding constant K₁₁ of the inclusion complexes of nimodipine with the respective CDs were evaluated. The -CDs efficiently solubilized sparingly soluble nimodipine, the highest value of K₁₁ was found for M--CD (1680 M^-1), followed by -CD (550 M^-1) and HP--CDs, where the higher degree of substitution lowered K₁₁. Only slight solubilization of nimodipine was observed in the solutions of the -CDs and HP--CD.     

Interactions of proteins with uniform colloidal hematite and chromium hydroxide particles. I. Adsorption

The adsorption of ovalbumin, -globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and -globulin was greatest at their isoelectric points and differed little at 10^–2 and 10^–3 mol dm^–3 NaNO₃. The adsorption of lysozyme was strongly influenced by the ionic strength.The deposition of ovalbumin on hematite in the presence of Mg (NO₃)₂ was significantly greater than that with NaNO₃ under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg²⁺ to be specifically bound to the protein.The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of -globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.Supported by the NSF Grant CHE-9108420Part of a Ph.D. thesis     

Linear silver clusters in aqueous solution (clusterites): radiation-induced chemical synthesis and properties

The formation and properties of the products of the radiation-induced chemical reduction of silver ions in aqueous solutions containing sodium polyacrylate were investigated. The absorption spectra of these species exhibit a band at 290 mn and a band in the visible region. The latter shifts from 470 nm to -800 nm with time or after the addition of silver ions. The species obtained (clusterites) arc linear silver clusters bound to the carboxyl groups of the ion exchanger. The red shift of the visible band is due to the increase in their size. The mechanism of the formation and the structure of the clusterites are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1429–1435, June, 1996.     

Enantiomer differentiation in intramolecular carbon—hydrogen insertion reactions of racemic secondary alkyl diazoacetates catalyzed by chiral dirhodium(ii) carboxamidates

Highly efficient kinetic resolution of racemic secondary alkyl diazoacetates in intramolecular carbon-hydrogen insertion reactions has been achieved using chiral dirhodium(ii) carboxamidates. Products formed from catalytic diazo decomposition of racemic 2-octyl diazoacetate and, separately, its (2R)- and (2S)-enantiomeric forms, as well as bothcis- andtrans-2-methylcyclohexyl diazoacetates, have been systematically evaluated. Enantioselectivities up to 99 %ee have been obtained for -lactone formation. -Lactone production has been observed and, although minor with cyclohexyl diazoacetates, is the major insertion pathway for diazo decomposition of 2-octyl diazoacetate.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1798–1803, September, 1995.Financial support for this research from the National Institutes of Health (GM 46503) and the National Science Foundation of the United States is gratefully acknowledged. We thank D. A. Pierson for her preparation of 2-methylcyclohexyl diazoacetates and preliminary studies of their diazo decomposition and A. Melekhov from the Higher College of Chemistry for his preparation and catalytic studies of rac-2-octyl diazoacetate.     

The diagnonal multivariate natural exponential families and their classification

A natural exponential family (NEF)F in ? ⁿ ,n>1, is said to be diagonal if there existn functions,a ₁,...,a _n , on some intervals of ?, such that the covariance matrixV _F (m) ofF has diagonal (a ₁(m ₁),...,a _n (m _n )), for allm=(m ₁,...,m _n ) in the mean domain ofF. The familyF is also said to be irreducible if it is not the product of two independent NEFs in ? ^k and ? ^n-k , for somek=1,...,n?1. This paper shows that there are only six types of irreducible diagonal NEFs in ? ⁿ , that we call normal, Poisson, multinomial, negative multinomial, gamma, and hybrid. These types, with the exception of the latter two, correspond to distributions well established in the literature. This study is motivated by the following question: IfF is an NEF in ? ⁿ , under what conditions is its projectionp(F) in ? ^k , underp(x ₁,...,x _n )∶=(x ₁,...,x _k ),k=1,...,n?1, still an NEF in ? ^k ? The answer turns out to be rather predictable. It is the case if, and only if, the principalk×k submatrix ofV _F (m ₁,...,m _n ) does not depend on (m _k+1,...,m _n ).     

On the electrostatic and steric similarity of lactam compounds and the natural substrate for bacterial cell-wall biosynthesis

Summary Electrostatic and structural properties of a set of -lactam, -lactam and nonlactam compounds have been analyzed and compared with those of a model of the natural substrate d-alanyl-d-alanine for the carboxy- and transpeptidase enzymes. This first comparison of the electrostatic properties has been based on a distributed multipole analysis of high-quality ab initio wave functions of the substrate and potential antibiotics. The electrostatic similarity of the substrate and active compounds is apparent, and contrasts with the electrostatic properties of the noninhibitors. This has been quantified to give a reasonable correlation with the MIC (Minimum Concentration for Inhibition) and with kinetic data (k₂/K) in accordance with the model for interaction of the lactam compounds with dd-peptidase. These correlations provide a better prediction of antibacterial activity than purely structural criteria.