Chitooligosaccharides: Synthesis,characterization and applications

Chitosans with high degree of polymerization and molecular weight exhibit poor aqueous solubility which is an impediment in their applicability. The low molecular weight chitosans (LMWCs) and chitooligosaccharides (COSs) can be used to avoid this hurdle. The development of an efficient process for reducing the molecular weight of chitosan, without altering its chemical structure, is of great interest to produce tailormade chitosans of varying Degree of Acetylation (DAs) and Degree of Polymerization (DPs). The production of well-defined COS-mixtures, or even pure COS, is of great interest since these oligosaccharides are thought to have several interesting bioactivities and applications. For this proper delineation of their characteristics is needed. Hence it is our attempt to provide an overview of difffernt methods and techniques of their production and characterization. Several methods viz. depolymerization under the action of reagents, enzymes, high energy impact and combinations thereof have been employed to get COS by depolymerization of high molecular weight chitosans. Acid hydrolysis (hydrochloric, nitrous, phosphoric acid, hydrogen fluoride) and oxidative reductive depolymerization (mediated by peroxide, ozone, and persulfate) are important routes for synthesis of COSs. These oligomers can be produced from chitin or chitosan as a starting material by enzymatic conversions. For this, numbers of enzymes have been used. Depolymerization under high energy impact and recombinant approaches are also being tried for production of COSs. LMWC and COS, like parent chitosan, can be used for drug delivery and gene delivery. The efficient and productive processes are needed for separation of COSs into its components or mixture of defined characters. The characterization of COS can be carried out by chromatographic and spectroscopic techniques. Importantly COSs display an array of biological activities as antimicrobial, anticancer/antimetastatic, wound healing acceleration, immunostimulation, apoptosis induction or inhibiton, antioxidant, enzyme inhibiton, antihyperlipidemic, antidiabetic, chemoprevention, and many more. A few of the biological actions are reported only sporadically where as some are persistently taken up by the scientific fraternity to substantiate the claims and propose possible mechanisms of action. However there remains the disagreement of results on COS activities. The disagreements can arise due to poor and variable reporting of the properties of COS such as used in the studies as molecular weight, degree of acetylation, molecular weight distribution, and the pattern of N-acetylation etc. With production of COS of well defined characters it might be possible to understand the modes of actions of COS in better ways.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

Prediction of anti-HIV activity and cytotoxicity of pyrimidinyl and triazinyl amines: A QSAR study

A QSAR study on a series of pyrimidinyl and triazinyl amines was performed to explore the physico-chemical parameters responsible for their anti-HIV activity and cytotoxicity. Physico-chemical parameters were calculated using WIN CAChe 6.1. Stepwise multiple linear regression analysis was carried out to derive QSAR models which were further evaluated for statistical significance and predictive power by internal and external validation. The selected best QSAR models showed correlation coefficient R of 0.914 and 0.901, and cross-validated squared correlation coefficient Q ² of 0.685 and 0.691 for anti-HIV activity and cytotoxicity, respectively. The developed significant QSAR model indicates that hydrophobicity of the whole molecule plays an important role in the anti-HIV activity and cytotoxicity of pyrimidinyl and triazinyl amine derivatives. When hydrophobicity is increased, anti-HIV activity of the present series of compounds is decreased leading to high cytotoxicity.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Disparity in properties of 20-mol% Eu-doped ceria synthesized by different routes

Ce_0.8Eu_0.2O_2?δ was synthesized by conventional solid state route as well as wet chemical route (i.e. cation complexation, combustion method). The crystallite size obtained for cation complexation and combustion samples is 14 and 19 nm while their surface area is 11.70 and 29.63 m²g^?1 respectively. Cation complexation synthesized product lead to formation of agglomerates and hence the sintered sample showed porosity compared to combustion synthesized sample. However, despite high packing density the combustion synthesized sample showed lower grain boundary, total conductivity than cation complexation synthesized product due to the formation of siliceous film at the grain boundary.     

Development of tBu-phenyl Acetamide Appended Thiacalix[4]arene as “Turn-ON” Fluorescent Probe for Selective Recognition of Hg(II) Ions

Journal of Fluorescence - Herein, a novel N-(4-(tert-butyl)-phenyl)-2-chloroacetamide functionalized thiacalix[4]arene architecture, viz TCAN2PA has been synthesized and the sensing behaviour...