The crystal and molecular structures of 1,1′-divinyl-2,2′-biimidazolyl

The crystal and molecular structures of 1,1gif" alt="prime" align="BASELINE" BORDER="0">-divinyl-2,2gif" alt="prime" align="BASELINE" BORDER="0">-biimidazolyl (L) were determined by x-ray crystallographic analysis. It was established that the molecule of L has crystallographic symmetry 2 and a cisoid conformation with an angle of rotation of 128° between the imidazole rings. The length of the C²-C^{2gif" alt="prime" align="BASELINE" BORDER="0">} bond is increased to 1.485(11) Å compared with the length of the analogous bond in unsubstituted 2,2gif" alt="prime" align="BASELINE" BORDER="0">-biimidazolyl (1.423 Å). Localization of the N=C multiple bond is observed [1.297(9) Å]. The other N-C bonds of the ring are almost equalized (1.374 Å) and are close to the standard values for bonds of the C _sp ²-N type in imidazoles. The angle between the plane of the heterocycle and the plane passing through the atoms of the vinyl group amounts to 7°.N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow. Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1376–1380, June, 1992.     

Study of modified silicas by inverse gas chromatography part II: Influence of chain length on surface properties of silicas grafted withα−ω diols

Summary The surface properties of silicas modified with gif" alt="agr" align="BASELINE" BORDER="0">–gif" alt="ohgr" align="BASELINE" BORDER="0"> diols having between 4 and 16 carbon atoms were investigated by inverse gas chromatography. It is shown, that the value of the dispersive component of the surface energy does not change monotonously: a minimum value is recorded when the surface is covered by a monolayer of methylene groups. Further, when measuring the adsorption enthalpies of polar probes, an alternation of their gif" alt="Delta" align="BASELINE" BORDER="0">H values is observed: grafts having an odd number of carbon atoms systematically show higher gif" alt="Delta" align="BASELINE" BORDER="0">H values than the others. A trans-trans configuration of the grafted chains which allows optimum interactions is proposed, suggesting a preferential diesterification reaction of both terminal hydroxyl groups of odd diols.     

Moment characterization of localized orbitals

The parallel between orbital first and second electric moments and statistical first and second central moments is noted. Three measures of orbital spatial distribution in terms of their moments are proposed, and applied to the LMO's in a series of ten-electron hydrides. Consistent differences between bond and lone pair distributions are found. Using the statistical interpretation, for each LMO an gif" alt="ldquo" align="MIDDLE" BORDER="0">effectivegif" alt="rdquo" align="MIDDLE" BORDER="0"> solid angle around the central atom is postulated.     

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 gif" alt="ldquo" align="MIDDLE" BORDER="0">supermoleculegif" alt="rdquo" align="MIDDLE" BORDER="0"> 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: gif" alt="agr" align="BASELINE" BORDER="0">-cyclodextrin (gif" alt="agr" align="BASELINE" BORDER="0">-CD), hydroxypropyl-gif" alt="agr" align="BASELINE" BORDER="0">-CD (HP-gif" alt="agr" align="BASELINE" BORDER="0">-CD), gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin (gif" alt="beta" align="MIDDLE" BORDER="0">-CD), random substituted methyl-gif" alt="beta" align="MIDDLE" BORDER="0">-CD (M-gif" alt="beta" align="MIDDLE" BORDER="0">-CD), three hydroxypropyl-gif" alt="beta" align="MIDDLE" BORDER="0">-CDs (HP-gif" alt="beta" align="MIDDLE" BORDER="0">-CD) with mutually different average degree of substitution, and hydroxypropyl-gif" alt="gamma" align="MIDDLE" BORDER="0">-cyclodextrin (HP-gif" alt="gamma" align="MIDDLE" BORDER="0">-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 gif" alt="beta" align="MIDDLE" BORDER="0">-CDs efficiently solubilized sparingly soluble nimodipine, the highest value of K₁₁ was found for M-gif" alt="beta" align="MIDDLE" BORDER="0">-CD (1680 M^-1), followed by gif" alt="beta" align="MIDDLE" BORDER="0">-CD (550 M^-1) and HP-gif" alt="beta" align="MIDDLE" BORDER="0">-CDs, where the higher degree of substitution lowered K₁₁. Only slight solubilization of nimodipine was observed in the solutions of the gif" alt="agr" align="BASELINE" BORDER="0">-CDs and HP-gif" alt="gamma" align="MIDDLE" BORDER="0">-CD.     

The Reaction of Maleic and Phthalic Anhydrides with 2-Methylimidazole

The reaction of maleic anhydride with 2-methylimidazole in acetonitrile and DMF is accompanied by the appearance of strong absorption bands in the visible part of the spectrum due to the formation of molecular complexes. In acetonitrile the reaction proceeds by two routes via the formation of an amide and the molecular complex. Phthalic anhydride reacts with 2-methylimidazole to give amide but not to form molecular complexes.     

Ethyl 3,3-diamino-2-(2-p-tolylpyrimidin-4-yl)acrylate,a new representative of hetarylketene aminals

A new representative of hetarylketene aminals, ethyl 3,3-diamino-2-(2-p-tolylpyrimidin-4-yl)acrylate, was synthesized by the reaction ofp-toluamidine with the condensation product of dimethylformamide dimethyl acetal and the difluoroboron chelate of acetyl(ethoxycarbonyl)ketene (N-benzoyl)aminal. This synthesis is an example of pyrimidine ring assembly using the methodology based on transformations of chelate complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1638–1640, September, 1994.This research was partially supported by the International Science Foundation (Grant No. M5QOOO).     

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

The adsorption of ovalbumin, gif" alt="gamma" align="MIDDLE" BORDER="0">-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 gif" alt="gamma" align="MIDDLE" BORDER="0">-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 gif" alt="gamma" align="MIDDLE" BORDER="0">-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     

Molecular structure of potassium [N,N′-bis(salicylideneamino)nitroguanidonate-N,N′,-O,O′]nickel(ii), the product of condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni2+ ion template

The crystal structure of the product of the condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni²⁺ ion template, K[Ni(C₁₅H₁₀N₅O₄)] · DMF, has been studied. It was established that a planar Ni complex, consisting of isolated [NiL]^– anions and solvated [K⁺ · DMF] cations, is formed. The negative charge of the anion is localized mainly on the O atoms of the nitro group. The nitroguanidine fragment of the ligand occurs in the tautomeric form, which was not reported previously.Deceased in 1995Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2273–2277, September, 1996.     

Effect of hydrophobic amino acids on the conformational change of decapeptides in micellar environments

A series of peptides containing various hydrophobic amino acids [methionine (Met), leucine (Leu), norleucine (Nle), phenylalanine (Phe), 2-aminooctanoic acid (Aoc), and 2-aminodecanoic acid (Ade)] were synthesized and their conformations were studied using circular dichroism (CD) spectroscopy in different solvents such as water, methanol, and aqueous solution of ammonium tetradecanesulfonate. Peptides containing hydrophobic amino acids with linear side chains formed gif" alt="beta" align="MIDDLE" BORDER="0">-sheets in water and methanol. Electrostatic interaction between the charged side chain (lysine) and a micelle consisting of an anionic surfactant, ammonium tetradecanesulfonate, is necessary for the formation of gif" alt="agr" align="BASELINE" BORDER="0">-helices in micellar environments. The conformational transition from gif" alt="agr" align="BASELINE" BORDER="0">-helix to gif" alt="beta" align="MIDDLE" BORDER="0">-sheet structure required moderate hydrophobicity and linear side chains. This conformational transition depended on the surfactant concentration.