NOPR Collection:

The limited Frank's chiral amplification model

Tue, 01 Feb 1994 00:00:00 GMT

Title: The limited Frank's chiral amplification model Authors: Gutman, Ivan; Todorovic, Dragan; Vuckovic, Miroslav Abstract: Frank's law of mass action-based model of chiral amplification is modified so as to avoid the unlimited increase in the concentration of one enantiomer. The basic features of this limited Frank model could be established without knowing the actual form of the solution of the respective system of differential equations. The model predicts two distinct time-evolutions of the system, one leading to complete monochirality and the other resulting in a racemic final state. The conditions for each of the two possible terminations of the process are established; they depend on the ratio of two certain rate constants and are independent of the initial composition of the system. Page(s): 93-96

Raman spectral studies for solutions of dimethyl sulphoxide in the S = 0 stretching region

Tue, 01 Feb 1994 00:00:00 GMT

Title: Raman spectral studies for solutions of dimethyl sulphoxide in the S = 0 stretching region Authors: Sajeevkumar, V A; Sastry, M I S; Singh, Surjit Abstract: Raman spectra in the S=0 stretching region are reported for solutions of dimethyl sulphoxide (DMSO) in carbon tetrachloride (CCI₄), dichloromethane (CH₂Cl₂), chloroform (CHCI₃) and acetonitrile (CH₃CN). The bands have been analysed qualitatively as a function of the concentration of DMSO with respect to the change in the shape and integrated intensities. Raman spectra of solutions of DMSO in binary mixtures of polar solvents and CCI₄, keeping the concentration of DMSO constant and varying the concentration of polar solvent, show interesting regularities in the variation of the band shapes. In some cases the bands are further subjected to analysis such as second derivative, Fourier self deconvolution (FSD) and Gaussian band fitting for gaining further information on the band structures and the existence of different complexed species in solutions. The results are explained in terms of self-association of DMSO and its intermolecular interactions with polar solvents. Page(s): 97-103

Charge transfer intoteraction of picoline with iodine and acceptors- A spectroscopic study

Tue, 01 Feb 1994 00:00:00 GMT

Title: Charge transfer intoteraction of picoline with iodine and acceptors- A spectroscopic study Authors: Latha, J; Palaniappan, S; Sathyanarayan, D N Abstract: The interaction of 2-amino-6-methyl ridine, 2-picoline and 4-picoline as donors with iodine, 7,7',8, 8'-tetracyanoquinodimethane,2,3-dichlo -5,6-dicyano-1 ,4-benzoquinone, p-chloranil, o-chloranil, 2,4, 7- . trinitro-9-fluorenone and 2,4,5,7-tetranitro-9-fluorenone as acceptors has been studied by measuring visible and ultraviolet spectra. Infrared , electron paramagnetic and nuclear magnetic resonance spectra have also been obtained. Kinetic parameters have been derived. The results indicate that the charge transfer interaction occurs through the formation of free radicals which is followed by a slow reaction to give a diamagnetic product. However, with iodine, the charge transfer complex formation occurs without the formation of free radicals. The donor site is inferred to be the lone pair of electrones on the amino nitrogen of 2-amin -6-methylpyridine whereas for 2- and 4-picolines, the preferred site is lone pair of electrons on the pyridine nitrogen. Page(s): 104-110

Fluorescence quenching of a few aromatic amines by inorganic anions

Tue, 01 Feb 1994 00:00:00 GMT

Title: Fluorescence quenching of a few aromatic amines by inorganic anions Authors: Sarpal, Ranjit S; Dogra, Sneh K Abstract: Inorganic anions-induced fluorescence quenching of seven aromatic amines has been studied up to 0.1M concentration. The fluorescence intensities of all the aromatic amines (except aniline) remain unaffected when CI^- and SCN^-are used as quenchers, whereas sufficient decrease in the fluorescence intensities is noticed when Br^- and I^- are used as quenchers. Based on the results obtained in the case of aniline, the fluorescence quenching efficiency of the anions can be ordered as: SCN^- < Br^- < I^-. Observed results cannot be explained completely either by spin-orbit coupling interaction or by charge transfer mechanism, although the latter seems to be more appropriate as log kq cannot be correlated with the spin-orbit coupling constants of the quencher atom when aniline is considered. Page(s): 111-114