Structure and thermal characterisation of poly(arylene ether sulphone)s

Structurally different poly(arylene ether sulphone) (PES) copolymers were synthesized by reacting stoichiometric amount of dichlorodiphenyl sulphone (DCDPS) with bisphenols. The molar ratio of bisphenol-A and phenolphthalein (ESP)/hydroquinone (ESH)/resorcinol (ESR) was varied to prepare nine copolymer samples. Structural characterization was done by FT-IR and ¹H-NMR studies. The initial decomposition temperature as well as temperature of maximum rate of mass loss in ESR and ESH copolymers were similar and a marginal decrease in these decomposition temperatures were observed by increasing the isopropylidine units in the backbone. High char residue at 800°C was observed in polymers having high content of phthalein units.The paper was presented at Thermans 2004 held at Baroda, January 20–22, 2004.Reliance Industries Limited is gratefully acknowledged for creating a Chair at IIT Delhi (I. K. Varma) and Council of Scientific and Industrial Research for providing scholarship to one of the authors (R. T. S. Muthu Lakshmi).     

Titrimetric determination of mercaptans with potassium persulphate

Summary 2- and 3-Mercaptopropionic acids, thiomalic acid, 2-mercaptoethanol and propyl mercaptan have been determined by direct titration with potassium persulphate in the presence of iodide in acidic aqueous medium. These mercaptans react with the oxidant in 2 1 molar ratio forming corresponding disulphides. The reaction of thio-p-cresol, thioglycollic acid and thioacetic acid with persulphate is too slow to be followed titrimetrically. However, they are oxidised to disulphide when allowed to stand with excess persulphate for 2.0, 1.75 and 0.75 hours respectively. The reaction stoichiometry is not a function of time. 2- and 3-Mercaptopropionic acids, cysteamine hydrochloride, thiomalic acid, thioacetic acid and thioglycollic acid react with potassium persulphate in acidic medium in the presence of iodine cyanide which acts as preoxidiser and catalyst, in the molar ratio 1 3 forming corresponding sulphonic acids. As little as 0.50 mg of the mercaptan can be determined in 50 ml solution with ± 0.25 % error.

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Zusammenfassung Durch direkte Titration mit Kaliumpersulfat in Gegenwart von Jodid kann man in saurem Medium 2- und 3-Mercaptopropionsäure, Thiomalonsäure, 2-Mercaptoäthanol und Propylmercaptan bestimmen. Diese Thiole reagieren mit dem Oxydationsmittel im Molverhältnis 2 1 unter Disulfidbildung. Die Umsetzung von Thio-p-kresol, Thioglykolsäure und Thioessigsaure mit Persulfat verläuft für maßanalytische Zwecke zu langsam. Die genannten Verbindungen werden von überschüssigem Persulfat in 2,0, 1,75 bzw. 0,75 Stunden zu Disulfiden oxydiert. Die Stöchiometrie der Reaktionen ist zeitunabhängig. 2- und 3-Mercaptopropionsäure, Cysteaminchlorhydrat, Thiomalonsäure, Thioessigsäure und Thioglykolsäure reagieren mit Kaliumpersulfat in saurer Lösung in Gegenwart von Jodcyan, das als Voroxydationsmittel und Katalysator füngiert, im Molverhältnis 1 3 unter Bildung von Sulfonsäuren. Nur 0,25 mg Mercaptan in 50 ml Lösung sind mit ± 0,25% Fehler bestimmbar.

     

Pentacoordinated Cu(II)/Zn(II) complexes bearing macrocyclic skeleton: synthesis, spectroscopic and molecular structure optimization studies

2,6-Diacetylpyridine and 1,2-diaminoethane in the presence of copper(II) and zinc(II) chlorides containing a few drops of acetic acid were condensed into compositions [CuLH2]2.2HCl.H2O (1), [Cu2LPyz]2.2HCl.4CH3COCH3 (2) [CuZnLPyz]2.2HCl.2CH3COCH3.10H2O (3) and [ZnL'Cl]3.3HCl.3H2O (4) substantiated by elemental analyses, IR, UV-vis, 1H NMR and FAB mass spectral data. Demetallation of a Ni(II) complex (isolated as above) afforded macrocyclic skeleton LH4, whereas L' symbolizes a skeleton of the ligand containing only ethylenediamine and 2,6-diacetylpyridine. Molecular structure optimization using MM2 force field calculations for the complexes revealed distorted square pyramidal geometry around Cu(II) centers in complexes 1 and 2 and tetrahedral geometry around Cu(II) and Zn(II) centers with different degrees of distortion in complex 3 whereas three Zn(II) atoms (each in distorted square pyramidal geometry) attached via Cl bridges form a cyclic structure in complex 4. In complexes 1 and 2,Cu-Cu = 2.63-2.66 angstroms indicated the possibility of coupling between the two Cu(II) centers which has been supported by lower magnetic moment as well as ESR spectra showing half-field signal.     

Feasibility study of aqueous adsorption of Cr(VI) on titanium dioxide

Sorption of chromium radionuclide has been studied in the pH range of 1–10 on titanium dioxide from aqueous solutions. The adsorption isotherm obtained is of the Freundlich type. The kinetic study of adsorption and desorption of tagged chromate ions at different temperatures show that the adsorption process is exothermic innnature. Further, the feasibility of adsorption process is confirmed by calculating the thermodynamic parameters.     

Effect of pretreatment temperature on the acidity and aniline alkylation activity over HZSM-5

HZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 30–280 are pretreated at 773 K and 1173 K. The effect of pretreatment temperature on acidity measured by ammonia desorption and aniline alkylation activity over these zeolites in the entire SiO₂/Al₂O₃ ratio range studied is discussed.IICT Communication No.: 3399     

Adsorption of low level51Cr(VI) from aqueous solution by bismuth trioxide: Kinetic and IR study

Radiotracer technique has been used for the investigation of adsorption of chromium (VI) traces on bismuth trioxide from aqueous solution. The effect of pH (2–10), concentration of chromate solution (10^–6–10^–2M) and temperature (303–323 K) has been thoroughly investigated. The influence of certain foreign ions has also been studied. The calculated kinetic and thermodynamic parameters indicate the first order rate law, spontaneity and exothermic nature of the adsorption process. Further, IR studies have established the chemical interaction between the sorbate and sorbent and a possible mechanism of the sorption process based on ligand exchange has been proposed.     

Potential drug targets in Mycobacterium tuberculosis through metabolic pathway analysis

The emergence of multidrug resistant varieties of Mycobacterium tuberculosis has led to a search for novel drug targets. We have performed an insilico comparative analysis of metabolic pathways of the host Homo sapiens and the pathogen M. tuberculosis. Enzymes from the biochemical pathways of M. tuberculosis from the KEGG metabolic pathway database were compared with proteins from the host H. sapiens, by performing a BLASTp search against the non-redundant database restricted to the H. sapiens subset. The e-value threshold cutoff was set to 0.005. Enzymes, which do not show similarity to any of the host proteins, below this threshold, were filtered out as potential drug targets. We have identified six pathways unique to the pathogen M. tuberculosis when compared to the host H. sapiens. Potential drug targets from these pathways could be useful for the discovery of broad spectrum drugs. Potential drug targets were also identified from pathways related to lipid metabolism, carbohydrate metabolism, amino acid metabolism, energy metabolism, vitamin and cofactor biosynthetic pathways and nucleotide metabolism. Of the 185 distinct targets identified from these pathways, many are in various stages of progress at the TB Structural Genomics Consortium. However, 67 of our targets are new and can be considered for rational drug design. As a case study, we have built a homology model of one of the potential drug targets MurD ligase using WHAT IF software. The model could be further explored for insilico docking studies with suitable inhibitors. The study was successful in listing out potential drug targets from the M. tuberculosis proteome involved in vital aspects of the pathogen's metabolism, persistence, virulence and cell wall biosynthesis. This systematic evaluation of metabolic pathways of host and pathogen through reliable and conventional bioinformatic methods can be extended to other pathogens of clinical interest.     

Synthesis, spectroscopic characterization, electrochemical behaviour, reactivity and antibacterial activity of some transition metal complexes with 2-(N-salicylideneamino)-3-carboxyethyl-4,5-dimethylthiophene

Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with a potentially tridentate Schiff base, formed by condensation of 2-amino-3-carboxyethyl-4,5-dimethylthiophene with salicylaldehyde were synthesized and characterized on the basis of elemental analyses, molar conductance values, magnetic susceptibility measurements, UV-vis, IR, EPR and NMR spectral data, wherever possible and applicable. Spectral studies reveal that the free ligand exists in a bifunctionally hydrogen bonded manner and coordinates to the metal ion in a tridentate fashion through the deprotonated phenolate oxygen, azomethine nitrogen and ester carbonyl group. On the basis of electronic spectral data and magnetic susceptibility measurements, suitable geometry has been proposed for each complex. The EPR spectral data of the Cu(II) complex showed that the metal-ligand bonds have considerable covalent character. The Ni(II) complex has undergone facile transesterification reaction when refluxed in methanol for a lengthy period. X-ray diffraction studies of Cu(II) complex showed that the complex has an orthorhombic crystal lattice. In view of the biological activity of thiophene derivatives, the ligand and the complexes were subjected to antibacterial screening. It has been observed that the antibacterial activity of the ligand increased on chelation with metal ion.     

Single-shot fast spin-echo diffusion tensor imaging of the lumbar spine at 1.5 and 3 T

Diffusion tensor imaging (DTI) of the lumbar spine could improve diagnostic specificity. The purpose of this work was to determine the feasibility of and to validate DTI with single-shot fast spin-echo (SSFSE) for lumbar intervertebral discs at 1.5 and 3 T. Six normal volunteers were scanned with DTI-SSFSE using an eight- and a three-b-value protocol at 1.5 and 3 T, respectively. Apparent diffusion coefficient (ADC) values were computed and validated based on those obtained at 1.5 T from corresponding diffusion tensor scans using line scan diffusion imaging (LSDI), a technique that has been previously validated for use in the spine. Pearson correlation coefficients for LSDI and DTI-SSFSE ADC values were .88 and .89 for 1.5 and 3 T, respectively, with good quantitative agreement according to the Bland-Altman method. Results indicate that DTI-SSFSE is a candidate as a clinical sequence for obtaining diffusion tensor images of the lumbar intervertebral discs with scan times shorter than 4 min.