Composition,temperature and radiation induced changes in gamma irradiated AAAMPS copolymer

Effect of composition, temperature and radiation dose in gamma irradiated acrylamide-2-acrylamido-2-methyl propane sulphonic acid (AA) copolymer has been investigated by electron spin resonance (ESR) and fourier transform infrared (FTIR) techniques. ESR spectra of gamma irradiated AA copolymer have been recorded under different conditions. The observed ESR spectra are analysed by computer simulation techniques, to separate the constituent component spectra. Magnetic parameters employed to simulate the component spectra enabled the identification of corresponding free radicals. The AA copolymer with low acrylamide content composed of macroradicals of the type ?CH₂?CH?CH₂? and methyl radicals (CH₃) whereas the copolymer with high acryl amide content possess methyl radicals and radicals of the type ?CH₂?C(CONH₂)?CH₂?/CH₃?C?CH₃. Reasons for the variation in the formation of free radicals have been explained. The observed changes in ESR spectra of irradiated AA copolymer at higher temperatures are thought to be due to the recombination of free radicals. Formation of free radicals found to be enhanced with the increase in dose of irradiation. FTIR spectra of pure and irradiated copolymers have also confirmed the previous results.     

Chemical Profiling of an Indian Herbal Formula Using Liquid Chromatography Coupled with Electro Spray Ionization Mass Spectrometry

Amruthotharam kashayam is an important Ayurvedic formulation prepared using specified plant parts of Tinospora cordifolia, Terminalia chebula, and Zingiber officinale. The current study developed a rapid liquid chromatographic method coupled with electro spray ionization mass spectrometry for the identification of major phytoconstituents present in the formulation. Reverse phase high-pressure liquid chromatogram was developed as chemical fingerprint. The mass spectrum along with the MS/MS fragmentation on collision-induced dissociation led to the structural identification of separated compounds. Phenolic acids such as quinic acid, protocatechuic acid, gallic acid, and chebulic acid were identified in the formulation along with some flavonoids.     

Flexible organic crystals. Understanding the tractable co-existence of elastic and plastic bending

As an emerging class of flexible materials, mechanically bendable molecular crystals are broadly classified as elastic or plastic. Nevertheless, flexible organic crystals with mutually exclusive elastic and plastic traits, with contrasting structural requirements, co-existing under different stress settings are exceptional; hence, it is imperative to establish the concurring factors that beget this rare occurrence. We report a series of halogen-substituted benzil crystals showing elastic bending (within ∼2.45% strain), followed by elastoplastic deformation under ambient conditions. Under higher stress settings, they display exceptional plastic flexibility that one could bend, twist, or even coil around a capillary tube. X-ray diffraction, microscopy, and computational data reveal the microscopic and macroscopic basis for the exciting co-existence of elastic, elastoplastic, and plastic properties in the crystals. The layered molecular arrangement and the weak dispersive interactions sustaining the interlayer region provide considerable tolerance towards breaking and making upon engaging or releasing the external stress; it enables restoring the original state within the elastic strain. Comparative studies with oxalate compounds, wherein the twisted diketo moiety in benzil was replaced with a rigid and coplanar central oxalate moiety, enabled us to understand the effect of the anisotropy factor on the crystal packing induced by the C O⋯C tetral interactions. The enhanced anisotropy depreciated the elastic domain, making the oxalate crystals more prone to plastic deformation. Three-point bending experiments and the determined Young''s moduli further corroborate the co-existence of the elastic and plastic realm and highlight the critical role of the underlying structural elements that determine the elastic to plastic transformation. The work highlights the possible co-existence of orthogonal mechanical characteristics in molecular crystals and further construed the concurrent role of microscopic and macroscopic elements in attaining this exceptional mechanical trait.

Structural and mechanical studies of benzil and oxalate crystals highlight the microscopic and macroscopic basis for the co-existence of orthogonal mechanical traits and the elastic to plastic transformation under different stress settings.     

Spectroscopic characterization of porous nanohydroxyapatite synthesized by a novel amino acid soft solution freezing method

In this paper, we have reported a novel method to synthesize nanoporous hydroxyapatite (HAP) powders by freezing organic–inorganic soft solutions. The formation of porous and crystalline HAP nanopowder was achieved via calcining the samples at 600 °C followed by sintering at temperatures ranging from 900 °C to 1100 °C. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopic (SEM) techniques. The results showed the formation of a carbon free nanoporous hydroxyapatite powders due to the decomposition of organic template enclosing the precipitated HAP. It was also observed that the rapid grain growth with retainment of pores while the crystallinity of the HAP nanopowder increased with the increase in sintering temperature which is substantiated from the XRD and SEM results. Such organized porous materials can act as a better biomaterial for bone tissue engineering.     

Efficient organotin catalysts for urethanes: kinetic and mechanistic investigations

Dibenzyltin bis(2‐ethylhexanoate) 1 (4‐Y C₆H₄CH₂)₂Sn(OC(O)R¹)₂ [Y = H, 1a; MeO, 1b; Cl, 1c; Me, 1d; and R¹ = MeCH₂CH₂CH₂CH(Et) ] were synthesized either from the reaction of corresponding dibenzyltin dichlorides with silver 2‐ethylhexanoate or from the reaction of dibenzyltin oxides with 2‐ethylhexanoic acid. Compound 1a was further utilized as a catalyst for the reaction of mono‐ and di‐isocyanates [PhNCO, CH₃C₆H₃‐2,4‐(NCO)₂ and OCN(CH₂)₆NCO] with alcohols (primary, secondary, tertiary, cyclohexcyl, alkyl, allyl, benzyl and aryl) leading to the formation of the corresponding urethanes. The catalytic efficiencies of 1 vis‐à‐vis industrially known organotin catalysts have been determined through kinetic studies for the reaction of PhNCO and n‐BuOH at various temperatures. Compounds 1a, 1c and 1d show higher efficiency than dibutyltin bis(2‐ethylhexanoate). FTIR studies further provide mechanistic insights into the catalytic cycle, which comprises pre‐coordination of isocyanate to tin(IV), formation of stannyl carbamate and generation of dibenzyl(alkoxy)carboxylate as the active catalyst. Copyright © 2000 John Wiley & Sons, Ltd.     

Mean amplitudes of vibration as a tool for structural analysis of simple molecules

The use of mean amplitudes of vibration as a tool for structural analysis of simple molecules is presented. The results show that the equilibrium configuration of a molecule corresponds to minimum vibrational amplitude in the case of XY₂ bent symmetric type molecules.     

Molecular electrostatic charge models: A topographical approach

Electrostatic charge models for molecules have been developed by employing the critical topographical features of the molecular electrostatic potential (MESP ) as the “fitting” criterion. These models include one or more spherical Gaussians for incorporating the continuous electron-charge distribution in addition to the positive valued point charges representing the nuclei. The model parameters (point charges, the orbital exponents, and Gaussian centers) are optimized so as to mimic the extremal characteristics of the corresponding quantum chemical MESP . The test cases reported here include methane, ethylene, and methanol molecules. The charge models developed using the present method are seen to satisfactorily reproduce the ab initio MESP and its extremal features. © 1994 John Wiley & Sons, Inc.     

Comparison of energy interaction parameters for the complexation of Pr(III) with glutathione reduced (GSH) in absence and presence of Zn(II) in aqueous and aquated organic solvents using 4f-4f transition spectra as PROBE

The coordination chemistry of glutathione reduced (GSH) is of great importance as it acts as excellent model system for the binding of metal ions. The GSH complexation with metal ions is involved in the toxicology of different metal ions. Its coordination behaviour for soft metal ions and hard metal ions is found different because of the structure of GSH and its different potential binding sites. In our work we have studied two chemically dissimilar metal ions viz. Pr(III), which prefer hard donor site like carboxylic groups and Zn(II) the soft metal ion which prefer peptide-NH and sulphydryl groups. The absorption difference and comparative absorption spectroscopy involving 4f-4f transitions of the heterobimetallic Complexation of GSH with Pr(III) and Zn(II) has been explored in aqueous and aquated organic solvents. The variation in the energy parameters like Slater-Condon (F(K)), Racah (E(K)) and Lande (xi(4f)), Nephelauxetic parameter (beta) and bonding parameter (b(1/2)) are computed to explain the nature of complexation.     

Different channels of ·OH radical reaction with tryptophanol in aqueous solutions: A pulse radiolysis study

The pulse radiolysis technique has been employed to study the reaction of ·OH radical with tryptophanol (TPN). Reactions of specific one-electron oxidants like Br₂· - and N₃· and ·H atom were carried out to understand the contribution of different channels of · OH radical reaction with TPN. The studies were carried out in the pH range 3 to 10. One-electron oxidation of TPN (pH 3) produced radical cation absorbing at 570 nm. However, at higher pH, deprotonation of TPN cation radical takes place from N(1) position and indolyl radical absorbing at 520 nm with a p ^K a value of 3.6 is formed. Redox titration with TMPD, ABTS^2- and MV²⁺ was performed to determine the total yield of oxidizing and reducing radicals produced during ·OH reaction.     

Infra-red spectroscopic studies of solvent-solute interactions in parachlorophenol and thiophenol with tertiary amides

Hydrogen bonding of O-H ... O=C and S-H ... O=C type has been studied in parachlorophenol and thiophenol with dimethyl and diphenyl amides and from the equilibrium constants, variation in the integrated absorption intensities and frequency shifts, the strength of the interaction in these complexes is discussed. In these systems diphenyl amides form weaker H-bond compared to that with the corresponding dimethyl amides. In dimethyl amides, the interaction is in the order dimethyl acetamide > dimethyl propionamide > dimethyl formamide. Similar results are obtained with diphenyl amides.