Chemistry

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In aqueous acidic media sodium azide and the orange-yellow title complex react quantitatively generating N2 gas along with a colourless solution of Ag+ ion and the ligand, ethylenebis(biguanide). The parent complex, [Ag(H2L)]3+, and one of its conjugate bases, [Ag(HL)]2+, participate in the reaction with N 3- as the kinetically reactive reductant. Ag+ has no catalytic effect. At 25.0 °C, I = 1.0 M (NaNO3), rate constants for the reactions [Ag(H2L)]3+ + N 3- and that for [Ag(HL)]2+ + N3 - are (12.3±0.5) and (3.8±0.6) M-1· S-1, respectively. The high rate constants along with the very low equilibrium constant (10-15 M-1) calculated for the first reaction strongly suggest inner-sphere redox mechanism. © Wiley-VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003.

World University root node

(SoNS) School of Natural Sciences

European Journal of Inorganic Chemistry

Kinetics of Oxidation of Azide by [Ethylenebis(biguanide)]silver(III) in Aqueous Acidic Media

The synthesis, characterization and physical properties of energetic azido binders were discussed. The energetic composites of glycidyl azide polymer (GAP)/nitroplasticizers and polyethylene glycol with HMX in various particle sizes were studied and compared with hydroxy terminated polybutadiene (HTPB) composites. The particle size of the oxidizer played an important role in determining the performance of the propellants. It was found that the flame structure of the GAP propellants was altered by the nature of the oxidizers.

Journal of Macromolecular Science - Polymer Reviews

Azido Polymers - Energetic Binders for Solid Rocket Propellants

The transferability of atomic and functional group properties is an implicit concept in chemistry. The work presented here describes the use of Transferable Atom Equivalents (TAE) to represent molecular electrostatic potential fields through the use of integrated atomic multipole moments that are associated with each TAE atom type used in the reconstruction. TAE molecular surface distributions of electrostatic potentials are compared with analytical ab initio and empirical (Gasteiger) partial charge reference models for several conformations of test peptides. Surface electrostatic potential distributions computed using TAE multiple representations were found to converge at the octopole level, with incremental improvement observed when hexadecapoles were included. Molecular electrostatic potential fields that were produced using the TAE method were observed to be responsive to conformational changes and to compare well with ab initio reference distributions, Generation of TAE atom types and their associated multipoles does not involve fitting to sample electrostatic potential fields, but rather utilizes integrated AIM atomic electron density distribution within representative chemical environments. The RECON program was used for TAE reconstruction. RECON is capable of processing 5000 drug-sized molecules or 25 proteins per minute per 1.7 GHz P4 Linux processor.

Journal of Computational Chemistry

Transferable atom equivalent multicentered multipole expansion method

The paper describes the synthesis of low molecular mass poly(allyl chloride) (PAC) (Mn = 856-3834 g mol-1) using Lewis acid (AlCl3, FeCl3, TiCl4) and Al powder. Branching in PAC was indicated on the basis of elemental analysis and 1H-NMR spectroscopy. Azidation of PAC could be carried out at 100°C by using NaN3 and DMSO as solvent. Curing of poly(allyl azide) (PAA) by cyclic dipolar addition reaction with EGDMA (ethylene glycol dimethacrylate, 5-45 phr) was investigated by differential scanning calorimetry and structure of cured polymer was confirmed by FTIR. A two-step mass loss was exhibited by uncured and cured PAA in nitrogen atmosphere. A mass loss of 20-28% (155-274°C) and 50-61% (330-550°C) was observed.

Journal of Thermal Analysis and Calorimetry

Thermal behaviour of poly(allyl azide)

Recent investigations have shown that the inclusion of hybrid shape/property descriptors together with 2D topological descriptors increases the predictive capability of QSAR and QSPR models. Property-Encoded Surface Translator (PEST) descriptors may be computed using ab initio or semi-empirical electron density surfaces and/or electronic properties, as well as atomic fragment-based TAE/RECON property-encoded surface reconstructions. The RECON and PEST algorithms also include rapid fragment-based wavelet coefficient descriptor (WCD) computation. These descriptors enable a compact encoding of chemical information. We also briefly discuss the use of the RECON/PEST methodology in a virtual high-throughput mode, as well as the use of TAE properties for molecular surface autocorrelation analysis.

Journal of Computer-Aided Molecular Design

New developments in PEST shape/property hybrid descriptors

This study examines the effect of different salt types on protein retention and selectivity in anion exchange systems. Particularly, linear retention data for various proteins were obtained on two structurally different anion exchange stationary-phase materials in the presence of three salts with different counterions. The data indicated that the effects are, for the most part, nonspecific, although various specific effects could also be observed. Quantitative structure retention relationship (QSRR) models based on support vector machine feature selection and regression models were developed using the experimental chromatographic data in conjunction with various molecular descriptors computed from protein crystal structure geometries. Star plots for each descriptor used in the final model were generated to aid in interpretation. The resulting QSRR models were predictive, with cross-validated r2 values of 0.9445, 0.9676, and 0.8897 for Source 15Q and 0.9561, 0.9876, and 0.9760 for Q Sepharose resins in the presence of three different salts. The predictive power of these models was validated using a set of test proteins that were not used in the generation of these models. Interpretation of the models revealed that particular trends for proteins and salts could be captured using QSRR techniques.

Analytical Chemistry

Prediction of the effect of mobile-phase salt type on protein retention and selectivity in anion exchange systems

Fulltext

Acta Crystallographica Section B: Structural Science

Erratum: Electron density study of 2H-chromene-2-thione (Acta Crystallographica Section B: Structural Science (2002) B58 (1011-1017))

A dendritic polyester based on pentaerythritol and 1,2,4 - benzenetricarboxylic acid anhydride followed by modification with glycidyl methacrylate was synthesised by using a divergent approach. The dendrimer (D-2) thus obtained had approximately eight double bonds. Several blends of D-2 with varying proportions of bismethacryloxy derivative of diglycidyl ether of bisphenol-A having styrene as a reactive diluent (VE resin) were prepared. The Brookfield viscosity of VE resin increased with an increase in D-2 content in the blends. Curing behaviour of these resins in the presence of AIBN was investigated by DSC. No significant change in curing exotherm was observed by addition of D-2 to the VE resin. Isothermal curing of resin samples in the presence of AIBN was done at 60 °C for 5 h and then at 150 °C for 90 mins. A significant improvement in char yield at 600 °C in nitrogen atmosphere was observed in samples containing D-2. Mechanical properties of glass fiber reinforced laminates with 31 ± 3% of resin content (w/w) were also determined. Smoke density of laminates increased with decrease in D-2 content in the resin, whereas only a marginal effect on limiting oxygen index was observed.

Materials Research Innovations

Thermal behaviour of dendritic methacrylated polyesters

A technique is presented for the highthroughput screening of ion-exchange displacers. Potential displacers were employed to displace proteins in parallel batch ion-exchange experiments. The percentage of protein displaced from a particular stationary phase was then used as a parameter to rank the displacers. By employing this technique, a large number of molecules possessing a range of affinities and properties could be rapidly evaluated. This data was then used together with traditional and electron density-based transferable atom equivalent (TAE) molecular descriptors computed for the displacer molecules to produce quantitative structure-efficacy relationship (QSER) models using a genetic algorithm/partial least squares (GA/PLS) regression approach. The QSER models were generated using a portion of the protein-displacement data, with the remainder serving as a test set. Descriptor selection and model building was accomplished using a genetic algorithm/partial least squares approach. The resulting models were found to have high-correlation coefficients and could be used to accurately predict the behavior of molecules not included in the training set. In addition, the models were employed to examine a virtual library of displacers based on modifications of neomycin to provide further insight into displacer design. The results presented here indicate that it may be possible to design displacers that can dramatically improve the effective selectivity of ion-exchange chromatographic materials. © 2002 Wiley Periodicals, Inc.

Biotechnology and Bioengineering

High-throughput screening and quantitative structure-efficacy relationship models of potential displacer molecules for ion-exchange systems

The charge-density distribution in 2H-chromene-2-thione (2-thiocoumarin), C9H6OS, has been determined from X-ray diffraction data measured at 90 K using a CCD detector, to a resolution of sinθ/λ &lt; 1.08 Å-1. A multipolar-atom density model was fitted against 6908 reflections with I &gt; 2σ(I) [R(F) = 0.021, wR(F) = 0.022, goodness of fit = 1.81] in order to generate the difference Fourier maps. The topological properties of the molecular electron density in terms of the bond critical points and the evaluation of the dipole moment show that the molecular dipole moment in the crystal is higher than the corresponding value derived from theoretical calculations.