Formation constants of bivalent metal ion complexes with diphenyl violuric acid and its higher analogues

Stability constants of transition-metal chelates of 1,3-disubstituted 5-hydroximino-hexahydropyrimidine-2,4,6-trione [diphenyl violuric acid (DPhVA) and di-o-,m-, andp-tolyl violuric acid (DiToVA)] have been determined in 75% dioxane (aqueous) at 30±1°C, in solutions containing an excess of the ligand at ionic strength 0.1M-NaClO₄. The order of formation constants found is: $$UO_2 > Cu > Ni \geqslant Fe > Co > Pb > Zn > Cd > Mn.$$ The stability influencing effects of donor π-bond (metal to ligand) has been demonstrated. The effects of electrophilic and nucleophilic centres within the ligand have been correlated to stability constants and acid dissociation constants.     

Toward <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> DXR inhibitor design: homology modeling and molecular dynamics simulations

Mycobacterium tuberculosis 1-deoxy-d-xylulose-5-phosphate reductoisomerase (MtDXR) is a potential target for antitubercular chemotherapy. In the absence of its crystallographic structure, our aim was to develop a structural model of MtDXR. This will allow us to gain early insight into the structure and function of the enzyme and its likely binding to ligands and cofactors and thus, facilitate structure-based inhibitor design. To achieve this goal, initial models of MtDXR were generated using MODELER. The best quality model was refined using a series of minimizations and molecular dynamics simulations. A protein–ligand complex was also developed from the initial homology model of the target protein by including information about the known ligand as spatial restraints and optimizing the mutual interactions between the ligand and the binding site. The final model was evaluated on the basis of its ability to explain several site-directed mutagenesis data. Furthermore, a comparison of the homology model with the X-ray structure published in the final stages of the project shows excellent agreement and validates the approach. The knowledge gained from the current study should prove useful in the design and development of inhibitors as potential novel therapeutic agents against tuberculosis by either de novo drug design or virtual screening of large chemical databases. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Free Radical Synthetic Protocol for Benzothiazoles via Ring Opening of Benzotriazole: A Two‐step Organic Chemistry Experiment for Undergraduate and Postgraduate Students

The utility and advantages of benzotriazole methodology have been described for the practical synthesis of benzothiazoles. The two‐step synthetic procedure includes nucleophilic acyl substitution followed by benzotriazole ring cleavage under the free radical condition and subsequent cyclization via elimination of molecular nitrogen (N₂). This protocol requires cheap and readily available reagents, and moreover easy to handle, thus can be used to teach undergraduate and postgraduate students about the importance of benzotriazole moiety in organic synthesis, ring cleavage chemistry, cyclization reactions, and use of industrial waste in free radical reactions. Students can also learn some important and common techniques useful in organic chemistry such as monitoring of organic reaction using thin‐layer chromatography and UV, microwave (MW) technique for the synthesis, and column chromatography for the product isolation and structure determination through NMR, MS, and IR spectral analysis of the pure compounds.     

A self-consistent density-functional approach to the structure of electric double layer: charge-asymmetric electrolytes

A self-consistent density-functional approach has been employed to study the structure of an electric double layer formed from a charge-asymmetric (2:l) electrolyte within the restricted primitive model which corresponds to charged hard sphere ions and a continuum solvent. The particle correlation due to hard-core exclusions is evaluated by making use of the universality of the density functionals and the correlation function of the uniform hard sphere fluid obtained through the integral equation theory with an accurate closure relation whereas mean spherical approximation is employed for the electrical contribution. Numerical results on the diffuse layer potential drop, ionic density profile, and the mean electrostatic potential near the electrode surface at several surface charge densities are found to be in quantitative agreement with the available simulation data.     

Experimentally Evaluating Equilibrium Stress in Uniaxial Tests

Many models use the equilibrium stress, also sometimes known as the back stress, in characterizing the response of both polymeric and non-polymeric materials. We study the characteristics of the equilibrium and show that the tangent modulus and local Poisson’s ratio at equilibrium both are rate independent for common modeling assumptions. This fact is used to propose a method based on uniaxial tension or compression to measure the equilibrium stress, and the associated point’s tangent modulus and local Poisson’s ratio. The method is based on cyclic loading and identification of similar states with vastly different loading rates. The method is used to characterize the equilibrium stress in glassy polycarbonate, and the results are studied in regard to the possible error for such a measurement. The method is faster than most other proposed methods for calculating the equilibrium stress, and provides additional measurements of parameters at equilibrium that are normally not obtained.     

Performance model of metallic concentric tube recuperator with counter flow arrangement

A performance model for counter flow arrangement in concentric tube recuperator that can be used to utilize the waste heat in the temperature range of 900–1,400°C is presented. The arrangement consists of metallic tubular inner and outer concentric shell with a small annular gap between two concentric shells. Flue gases pass through the inner shell while air passes through the annular gap in the reverse direction (counter flow arrangement). The height of the recuperator is divided into elements and an energy balance is performed on each elemental height. Results give necessary information about surface, gas and air temperature distribution, and the influence of operating conditions on recuperator performance. The recuperative effectiveness is found to be increased with increasing inlet gas temperature and decreased with increasing fuel flow rate. The present model accounts for all heat transfer processes pertinent to a counterflow radiation recuperator and provide a valuable tool for performance considerations.     

Spectroscopic assessment of biomolecular changes in Helicobacter pylori and Epstein–Barr virus co-infected gastric epithelial cells

Helicobacter pylori and Epstein–Barr Virus (EBV) are Group 1 carcinogens that can enhance gastric cancer progression. Bioactive substances extracted from plants can be effective therapeutic agents in cancer treatment. For example, Withania somnifera extract-WSE reduces the Gankyrin oncoprotein, which is upregulated in the presence of H. pylori and EBV. The various biochemical and metabolic changes upon 24 hrs post-infection followed by W. somnifera extract (WSE) treatment on gastric epithelial cells (AGS) can be studied using spectroscopic techniques. In the biomedical sciences, Raman and NMR spectroscopy have been extensively employed to interpret cellular alterations contributing to the onset of infection and the severity of gastric cancer. More specifically, alterations in cellular biochemical homeostasis are linked to the moieties of cholesterol, collagen, choline, carbohydrate, lipids, tyrosine, and phenylalanine. Further, we have found significantly elevated FWHM for carbohydrates, tumor associated protein, collagen, cholesterol, and cholesterol ester in the co-infection model. We also looked into the potential correlation between these molecules using molecular network analysis and found several related factors that can be modulated through biomolecular levels. These molecules are crucial in several physiological functions, including cell division, cell proliferation, apoptosis, necrosis, cell migration, and lipid transport. Our study paves the pathway to study H. pylori and EBV co-infection in human gastric epithelial cells and the therapeutic interventions of WSE in this scenario and highlights specific biomolecular alterations, which can be focused for further mechanistic investigations.     

Microwave‐assisted synthesis and diels–alder reactions of 1,3‐azaphospholo[5,1‐a]isoquinolines

The application of microwave technique has been extended successfully for the first time to the synthesis of a representative class of azaphospholes, viz. 1,3‐bis(alkoxycarbonyl)‐1,3‐azaphospholo[5,1‐a]isoquinolines ( 2 ), which occurs rapidly giving higher yields. Stereoselectivity is observed in the reaction with 2,3‐dimethyl‐1,3‐butadiene, and isoprene reacts regioselectively as well. 1‐Methyl‐3‐ethoxycarbonyl‐1,3‐azaphospholo[1,5‐a]pyridine ( 4 ) remains inert toward [2+4] cycloaddition. The nonoccurrence of the Diels–Alder reaction in the latter case has been supported by semiempirical PM3 calculations. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:560–563, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10193