Role of a Repeated Hexapeptide Motif GIHFAP Near C-terminus in Assembly, Stability, and Activity of “HCH Dehydrochlorinase LinA”

Enzyme “hexachlorocyclohexane (HCH) dehydrochlorinase LinA” mediates first step of aerobic microbial degradation of a chlorinated insecticide γ-HCH. The archetypal LinA-type1 consists of 156 amino acids that include a directly repeated hexapeptide motif GIHFAP at positions 141–146 and 148–153. Analysis of a series of LinA mutants, containing none, one, two, or three units of this repeated motif revealed that two units, as present in wild-type LinA, are required for its optimal activity and stability. Moreover, the presence of a bend in its secondary structure due to a proline residue that precedes the distal repeated unit contributes to enhanced LinA activity.     

Advances in arsenic speciation techniques

The present review describes the speciation techniques of arsenic. The principal advanced techniques discussed are gas chromatography, reversed-phase liquid chromatography, ion chromatography, capillary electrophoresis. Some other techniques are also mentioned. The extraction procedures of arsenic species from unknown samples are also discussed. Arsenic speciation is summarized in tabular form and optimizing parameters are also discussed.     

Accurate measurement of uranium isotope ratios in soil samples using thermal ionization mass spectrometry equipped with a warp energy filter

A chemical and mass-spectrometric procedure for uranium isotopic analysis using a thermal ionisation mass spectrometer equipped with a Wide Aperture Retardation Potential energy filter has been developed and applied to uranium isotopic measurements for various soil samples. Soil samples were digested using a microwave digestor. Uranium was isolated from soil samples by the chemical separation procedure based on the use of anion-exchange resin and UTEVA extraction chromatography column. The isotope ratios were measured for two certified reference materials by using a VG Sector 54-30 thermal ionisation mass spectrometer in dynamic mode with Faraday cup and Daly ion counting system. Replicates of standard reference materials showed excellent analytical agreement with established values supporting the reliability and accuracy of the method. Precision of the ²³⁵U/²³⁸U ratio was achieved by a correction factor of 0.22% amu as a function of ion-beam intensity with sample loads of around 250?ng of U. The resulting reproducibility for standards and soil samples was better than 0.2% at two standard deviations (SD). Uranium isotopic compositions have been determined in several reference soil samples such as Buffalo river sediment, NIST 2704, river sediment SRM 4350b and ocean sediment NIST-4357 and a Chernobyl soil sample. There was a significant deviation from the natural uranium in comparison with Chernobyl soil samples.     

Synthesis and structural studies of some copper-benzoate complexes

The reaction of CuCl₂·2H₂O with 3,5-diisopropylpyrazole (Pz^iPr2H) in the presence of sodium parafluorobenzoate (Na-p-FBz) resulted in the formation of an oxo-chloro-bridged tetranuclear complex [Cu₄(Pz^iPr2H)₄(μ-O)(μ-Cl)₆] 1, whereas the reaction of Cu(NO₃)₂·3H₂O with Pz^iPr2H in the presence of different benzoates gave [Cu(Pz^iPr2H)₂(μ-OCH₃)]₂(NO₃)₂ 2, [Cu(Pz^iPr2H)₃(NO₃)(p-ClBz)]·CH₃CN 3, [Cu(p-CH₃Bz)₂(Pz^iPr2H)]₂·2CH₃CN 4, [Cu(p-OCH₃Bz)₂(CH₃CN)]₂·4CH₃CN 5 and [Cu(p-CNBz)(CH₃CN)]₂ 6. Single-crystal X-ray diffraction studies confirmed these formulations. DNA binding studies for these complexes were performed by means of UV-visible absorption titration and viscosity measurements. Gel electrophoresis studies showed that hydroxyl radicals are involved in DNA cleavage in the presence of the complexes.     

Control of molecular architecture by hydrogen bonding: mononuclear versus dinuclear copper(II) complexes with tridentate N2O donor Schiff base isomers

Two isomeric Schiff bases, HL ¹  = 1-[(2-dimethylamino-ethylimino)-methyl]-naphthalen-2-ol and HL ²  = 1-[(2-ethylamino-ethylimino)-methyl]-naphthalen-2-ol, have been used to prepare copper(II) complexes in presence of thiocyanate. HL ¹ forms a mononuclear complex [Cu(L ¹ )NCS] with terminal thiocyanate, whereas the isomeric Schiff base HL ² , which is capable of hydrogen bonding, gives a dimeric complex, [Cu₂ (L ² ) ₂(NCS)₂], with double μ-1,1-NCS bridges. Both complexes are characterized by physico-chemical and spectroscopic methods as well as by single crystal X-ray diffraction studies.     

Thermoluminescence studies of UV-irradiated Y2O3:Eu3+ doped phosphor

The present paper reports thermoluminescence (TL) glow curves of Eu³⁺-doped Y₂O₃ phosphor with different ultraviolet (UV) exposure times. The glow peak shows second-order kinetics of Eu³⁺-doped Y₂O₃, and corresponding kinetic parameters were evaluated using the peak shape method. Calculations of trap depth were carried out using different methods. The kinetics order, activation energy, and frequency factor were calculated. The recorded glow curve shifts towards higher intensity with longer UV exposure. The heating rate used for recording TL was 3.0 °C s^?1. Particle size and structure were verified by X-ray diffraction (XRD) pattern and morphology by scanning electron microscopy (SEM) imaging.     

An efficient and facile synthesis of Zn(II) complexes with 2-substituted benzothiazoles and glycine- and alanine-based ligands having antifungal and antibacterial activities

We carried out an efficient and facile synthesis of Zn(II) complexes with heterocyclic ligands based on 2-substituted benzothiazole moieties, 2-(2′-hydroxynaphthyl)benzothiazole, 2-(2′-hydroxyphenyl)benzothiazole, and 2-(2′-merceptophenyl)benzothiazole, and amino acids, glycine and alanine, are reported and also examined for antifungal and antibacterial activities. Ligands and complexes were characterized by FTIR, ¹H NMR, and elemental analysis.     

Lanthanum Trifluoromethane-sulfonate‐Catalyzed Facile Synthesis of Per‐O‐acetylated Sugars and Their One‐Pot Conversion to S‐Aryl and O‐Alkyl/Aryl Glycosides†

Lanthanum trifluoromethanesulfonate‐catalyzed solvent‐free per‐O‐acetylation with stoichiometric acetic anhydride proceeds in high yield (95%–99%) to afford exclusively pyranose products as anomeric mixtures. Subsequent anomeric substitution employing borontrifluoride etherate and thiols or alcohols furnished the corresponding 1,2‐trans‐linked thioglycosides and O‐glycosides, respectively, in good to excellent overall yield (75%–85%). Alternatively, reaction of free sugars in neat alcohol employing the same catalyst at elevated temperature gives the corresponding 1,2‐cis‐linked O‐glycosides (along with 1,2‐trans‐linked glycosides as minor product) in good yield (73%–80%). Anomeric mixtures of compounds thus produced were characterized as their per‐O‐acetylated derivatives.      

Synthesis of Tetrasaccharide Repeating Unit of the K-Antigen from Klebsiella Type-16

Abstract

Starting from L-fucose, D-glucose and lactose, methyl O-[2,3-di-O-benzoyl-4, 6-O-(4-methoxybenzylidene)-β-D-glucopyranosyl]-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside and methyl O-(2,3,4,6-tetra-O-benzyl-β-D-galactopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-O-(methyl 2,3-di-O-benzoyl-β-D-glucopyranosyluronate)-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside were synthesized. Removal of protecting groups gave the tetrasaccharide repeating unit of the antigen from Klebsiella type-16 in the form of its methyl ester methyl glycoside.