NOPR Collection:

Synthesis, characterization and nuclease activity of copper(ll), nickel(II) and iron(II) complexes of 2-acetylpyridine oxime

Mon, 01 Jul 1996 00:00:00 GMT

Title: Synthesis, characterization and nuclease activity of copper(ll), nickel(II) and iron(II) complexes of 2-acetylpyridine oxime Authors: Kumbhar, Avinash; DamIe, Shirish; Kulkarni, Prasad; Srinivas, Duduka; Chatur, Vaishali Abstract: A few complexes of Cu(II), Ni(II) and Fe(II) with 2-acetylpyridine oxime have been synthesized and characterized by elemental analysis, IR, UV-vis spectroscopy, magnetic moments and cyclic voltammetry and their interactions with plasmid DNA are investigated. Page(s): 533-535

Microscopic origin of the chirality driven morphologies of the amphiphilic monolayers and bilayers

Mon, 01 Jul 1996 00:00:00 GMT

Title: Microscopic origin of the chirality driven morphologies of the amphiphilic monolayers and bilayers Authors: Nandi, Nilashis; Bagchi, Biman Abstract: It is widely known that the compressed monolayers and bilayers of chiral lipids or fatty acids form helical morphologies, while the corresponding racemic modification gives only flat platelets without twist. No molecular explanation of this phenomenon is yet available, although subtle interactions at the chiral centers have often been proposed as the driving force behind the morphology of the aggregate to form a particular shape. In the present study, the morphologies of the chiral amphiphilic assemblies have been predicted on the basis of an effective pair potential between the molecules, which depends on the relative sizes of the groups attached to the chiral centers, the orientation of the amphiphilic molecules and also on the distance between them. It is shown that for a pair of same kind of enantiomers, the minimum energy conformation favours a twist angle between them. This twist between the neighbouring molecules gives rise to the helicity of the aggregate. The present theory also shows from the molecular considerations that for a pair of mirror-image isomers (i.e. the racemic modification) the minimum energy conformation corresponds to the zero angle between the molecules, thus giving rise to flat platelets as observed in experiments. Another fascinating aspect of such chirality driven helical structures is that the sense (or the handedness) of the helix is highly specific about the chirality of the monomer concerned. The molecular theory shows, for the first time, that the sense of the helical structures in many cases is determined by the sizes of the groups attached to the chiral centers and the effective potential between them. The predicted senses of the helical structures are in complete agreement with the experimental results. Page(s): 536-545

Solution of the limited Frank's model of chiral amplification

Mon, 01 Jul 1996 00:00:00 GMT

Title: Solution of the limited Frank's model of chiral amplification Authors: Murphy, R D; EI-Agez, Taher M Abstract: A formal solution to the rate equation of the limited Frank's model discussed by Gutman and coworkers is obtained. Special cases displaying the two different types (monochiral and racemic) of end-state behaviour are solved explicitly. Page(s): 546-547

Nuclear magnetic resonance studies on interactions of halide ions with acetonitrile

Mon, 01 Jul 1996 00:00:00 GMT

Title: Nuclear magnetic resonance studies on interactions of halide ions with acetonitrile Authors: Jayaraj, A F Abstract: NMR spectra for ¹H and ¹³C nuclei of acetonitrile are reported for solutions of alkali metal and tetraalkylammonium halides. Chemical shifts and relaxation times for a series of concentrations at five temperatures between 25°C and 60°C are analyzed to gain an insight into the mode of anion-molecule interactions. The various salts considered include LiBr, LiI, NaI, tetrabutylammonium bromide (TBAB) and tetrabutylammonium iodide (TBAI). It is found that the chemical shift moves towards lower field on addition of the electrolyte and to higher fields on increasing the temperature of the system. An increase in the concentration of the electrolyte and a decrease in temperature increase the concentration of complexed species which is reflected in the measured chemical shifts. Earlier conclusions on the linear variation of the changes in the ¹H chemical shifts with concentration of the electrolytes are reviewed. The chemical shift data for solutions of tetrabutylammonium halides have been utilised for the determination of equilibrium constants for anion-molecule interactions and the values are found to be in the order I^- > Br^- which shows that the interactions are more of electrostatic type which depend on the extent of polarization of the charge on the halide ions. The relaxation times obtained from the line widths of ¹H, ¹³C and ⁸¹Br are analyzed on the basis of anion-molecular equilibria. Page(s): 548-556