Oxidation of polythionates with chloramine-T

Summary Chloramine-T has been found to bring about the rupture of S-S link in polythionates in acid medium and oxidise all the sulphur present in the chain into sulphuric acid. Quantitative estimation of a polythionate may be made on the basis of this oxidation reaction.Our thanks are due to Prof. M. R. A. Rao for his interest in the work.     

Investigation of stepwise covalent synthesis on a surface yielding porphyrin-based multicomponent architectures

Porphyrins have been shown to be a viable medium for use in molecular-based information storage applications. The success of this application requires the construction of a stack of components ("electroactive surface/tether/charge-storage molecule/linker/electrolyte/top contact") that can withstand high-temperature conditions during fabrication (up to 400 degrees C) and operation (up to 140 degrees C). To identify suitable chemistry that enables in situ stepwise synthesis of covalently linked architectures on an electroactive surface, three sets of zinc porphyrins (22 altogether) have been prepared. In the set designed to form the base layer on a surface, each porphyrin incorporates a surface attachment group (triallyl tripod or vinyl monopod) and a distal functional group (e.g., pentafluorophenyl, amine, bromo, carboxy) for elaboration after surface attachment. A second set designed for in situ dyad construction incorporates a single functional group (alcohol, isothiocyanato) that is complementary to the functional group in the base porphyrins. A third set designed for in situ multad construction incorporates two identical functional groups (bromo, alcohol, active methylene, amine, isothiocyanato) in a trans configuration (5,15-positions in the porphyrin). Each porphyrin that bears a surface attachment group was found to form a good quality monolayer on Si(100) as evidenced by the voltammetric and vibrational signatures. One particularly successful chemistry identified for stepwise growth entailed reaction of a surface-tethered porphyrin-amine with a dianhydride (e.g., 3,3',4,4'-biphenyltetracarboxylic dianhydride), forming the monoimide/monoanhydride. Subsequent reaction with a diamine (e.g., 4,4'-methylene-bis(2,6-dimethylaniline)) gave the bis(imide) bearing a terminal amine. Repetition of this stepwise growth process afforded surface-bound oligo-imide architectures composed of alternating components without any reliance on protecting groups. Taken together, the ability to prepare covalently linked constructs on a surface without protecting groups in a stepwise manner augurs well for the systematic preparation of a wide variety of functional molecular devices.     

The role of top predator interference on the dynamics of a food chain model

In this paper, the effects of top predator interference on the dynamics of a food chain model involving an intermediate and a top predator are considered. It is assumed that the interaction between the prey and intermediate predator follows the Volterra scheme, while that between the top predator and its favorite food depends on Beddington–DeAngelis type of functional response. The boundedness of the system, existence of an attracting set, local and global stability of non-negative equilibrium points are established. Number of the bifurcation and Lyapunov exponent bifurcation diagrams is established. It is observed that, the model has different types of attracting sets including chaos. Moreover, increasing the top predator interference stabilizes the system, while increasing the normalization of the residual reduction in the top predator population destabilizes the system.     

Transformation of Terminal Diols of Cyclic and Acyclic Saccharides to Epoxides and Alkenes by Reaction with Triphenylphosphine,Imidazole and Iodine

ABSTRACT

Reaction of various terminal diols 1,4,6,8-12, derived from cyclic and acyclic monosaccharides, with 2 mol equivalents each of TPP-imidazole-I₂ between -8 °C and 15 °C in THF afforded the corresponding epoxides 2,5,7,13-17, respectively, with 4 mol equivalents each of TPP-imidazole-I₂ in toluene at reflux temperature the starting diols afforded the corresponding alkenes 3,18-24, respectively.     

Effect of the unexcited vapour region inside a heatpipe on the observation of UV diffuse bands in 337.1 nm excitation of Na2

We report on some interesting aspects of the strong influence of the unexcited vapour zone inside a heatpipe on the observation of 366.6 and 380.0 nm UV diffuse bands of sodium. For a smaller unexcited sodium vapor zone, only the 366.6 nm band is observed, while for larger unexcited volumes, both 366.6 and 380.0 nm bands can be identified. Partial reabsorption of the 366.6 nm band leading to Stokes emission as 380.0 nm band appears most likely. Reduced power dependences observed for the 366.6 nm band, an indication of the Amplified Spontaneous Emission (ASE) nature of the emission, support this analysis. A simple kinetic for the system is discussed. The results are quite general and suggest some caution in the interpretation of the data from a number of Laser-Induced Fluorescence (LIF) experiments currently being reported.     

Hepatitis C virus NS3 protease requires its NS4A cofactor peptide for optimal binding of a boronic acid inhibitor as shown by NMR

NMR spectroscopy was used to characterize the hepatitis C virus (HCV) NS3 protease in a complex with the 24 residue peptide cofactor from NS4A and a boronic acid inhibitor, Ac-Asp-Glu-Val-Val-Pro-boroAlg-OH. Secondary-structure information, NOE constraints between protease and cofactor, and hydrogen-deuterium exchange rates revealed that the cofactor was an integral strand in the N-terminal beta-sheet of the complex as observed in X-ray crystal structures. Based upon chemical-shift perturbations, inhibitor-protein NOEs, and the protonation state of the catalytic histidine, the boronic acid inhibitor was bound in the substrate binding site as a transition state mimic. In the absence of cofactor, the inhibitor had a lower affinity for the protease. Although the inhibitor binds in the same location, differences were observed at the catalytic site of the protease.     

Nonresonant third harmonic generation in thallium vapour

Feasibility of nonresonant third harmonic generation in thallium is investigated. The third order susceptibility, for driving frequencies in the visible region, is calculated and the phase matching with Ar as buffer gas is investigated. Other related quantities like coherence length, minimum pulse lengths required to get phase matching and power input requirements to achieve 50% conversion are also calculated.     

Diastereoselective aldol condensations of tin enolates with aldehydes

The reaction of tin enolates of cyclohexanone or propiophenone with benzaldehyde at ?78°C gives predominately the $\text{threo}$ aldol diastereomer.     

Relative vibrational transition probabilities in the (B 3 π g−A 3Σ u + ) system of nitrogen for Hulbert-Hirschfelder oscillator model

Hulbert-Hirschfelder (h-h) potential function has been used to obtain the relative vibrational transition probabilities for the observed bands of the first positive system of nitrogen molecule. The vibrational wavefunctions have been calculated by solving the Schrödinger equation by the method due to Langer, at low vibrational quanta and by thewkb method at high vibrational quanta. It is established that theh-h potential is superior to the often used Morse potential function for the transition under consideration.