Effects of oxidation on copper-binding properties of Aß1-16 peptide: a pulse radiolysis study.

The reaction of hydroxyl radicals ((•)OH) with Aß1-16 peptide was carried out using pulse radiolysis to understand the effect of oxidation of peptide on its copper-binding properties. This reaction produced oxidized, dimeric and trimeric Aß1-16 peptide species. The formation of these products was established with the help of fluorescence spectroscopy and mass spectrometry. The mass spectral data indicate that the major site of oxidation is at His6, while the site for dimerization is at Tyr10. Diethyl pyrocarbonate-treated Aß1-16 peptide did not produce any trimeric species upon oxidation with (•)OH. The quantitative chemical modification studies indicated that one of the three histidine residues is covalently modified during pulse radiolysis. The copper-binding studies of the oxidized peptide revealed that it has similar copper-binding properties as the unoxidized peptide. Further, the cytotoxicity studies point out that both oxidized and unoxidized Aß1-16 peptide are equally efficient in producing free radicals in presence of copper and ascorbate that resulted in comparable cell death.

Derivatization Ion Chromatography for the Determination of Monoethanolamine in Presence of Hydrazine in PHWR Steam-Water Circuits.

A simple, rapid and accurate method for the determination of monoethanolamine (MEA) in PHWR steam-water circuits has been developed. MEA is added in the feed water to provide protection against corrosion while hydrazine is added to scavenge dissolved oxygen. The quantitative determination of MEA in presence of hydrazine was accomplished using derivatization ion chromatography with conductometric detection in nonsuppressed mode. A Metrosep cation 1-2 analytical column and a Metrosep cartridge were used for cation separation. A mixture of 4 mM tartaric acid, 20% acetone and 0.05 mM HNO(3) was used as eluent. Acetone in the mobile phase leads to the formation of different derivatives with MEA and hydrazine. The interferences due Na(+) and NH(4) (+) were eliminated by adopting a simple pretreatment procedure employing OnGuard-H cartridge. The limit of detection limit of MEA was 0.1 µg mL(-1) and the relative standard deviation was 2% for the overall method. The recovery of MEA added was in the range 95%-102%. The method was applied to the determination of MEA in steam generator water samples.

Synthesis, characterization and redox chemistry of Ru(II) complexes of N-methyl pyridyl quinoxaline.

A series of metal complexes having the general formula [Ru(bpy)(n)(mebpq(+))(3-n)]((5-n)+) (n = 0, 1,2,3)(2,2'-bipyridine (bpy) and/or 2-(N-methylpyridyl)3-pyridyl quinoxaline (mebpq(+)) were synthesized and characterized by optical, elemental analysis, NMR and electrochemical methods. The absorption spectra of complexes have bands in the UV region (< or = 350 nm) consisting of an intense pi --> pi* transition due to the ligands (epsilon approximately 10(5) dm(3) mol(-1) cm(-1)) and in the visible region dominated by MLCT (dpi --> pi*). The emission intensity is the least when ruthenium is fully coordinated to mebpq(+) and it increased 50 fold on going to [Ru(bpy)(3)]Cl(2). Electrochemical data revealed that the Ru(II)/Ru(III) oxidation peaks are in the range 1.31 to 1.76 V and the sequential replacement of bpy by mebpq(+) resulted in the increase of the oxidation potential. The reactions of oxidizing and reducing radicals (OH, O(-), N(3) , Cl(2)(-) and e) with these complexes were studied by pulse radiolysis. The OH radical reacts with all complexes at diffusion controlled rates and the k values increased from 6.2 to 9.8 x 10(9) dm(3) mol(-1) s(-1) on going from [Ru(bpy)(3)]Cl(2) to [Ru(mebpq(+))(3)](PF(6))(5). The rates of reaction of e with Ru(II) complexes are high (k approximately 10(10) dm(3) mol(-1) s(-1)) and the reaction leads to the formation of the radical anion of the bipyridine in [Ru(bpy)(3)]Cl(2) and tertiary quinoxaline radical in mixed complexes containing mebpq(+). The underlying reaction mechanism is discussed.

Construction of copper halide networks within layered perovskites. Syntheses and characterization of new low-temperature copper oxyhalides.

The construction of two-dimensional (2D) copper halide networks within a variety of perovskite hosts by a low-temperature topochemical method is demonstrated. Ion exchange between some layered perovskite oxides of the type A'[An - 1(M,M')nO3n + 1] (A' = alkali metal, H, NH4; A = alkaline earth, rare earth, or Bi; M,M' = Nb, Ta, Ti; n = 2, 3) with CuX2 (X = Cl, Br) results in the oxyhalides (CuX)[An - 1(M,M')nO3n + 1]. Rietveld refinements from X-ray powder diffraction data show that the structures of these new copper oxyhalides contain edge-sharing CuO2X4 octahedra sandwiched between the M/M'O6 octahedra of the perovskite slabs. The compounds are low-temperature phases that decompose well below 700 degrees C. The copper oxyhalides exhibit antiferromagnetic ordering resulting from the magnetic exchange interactions within the planar Cu-X networks.

Spectrophotometric method for determination parts per million levels of cyclohexylamine in water.

UV-vis spectrophotometric method for the analysis of cyclohexylamine (CHA) in aqueous medium in the range of 0.3-20 ppm was developed by coupling CHA with sodium 1,2-naphthaquinone-4-sulphonate (NQS). At 470 nm a calibration slope of 0.028 OD ppm(-1) was observed. Minimum detection limit was 0.3 ppm with standard deviation of 0.1 ppm. Reagent concentration and solution pH for the analysis are optimised by studying its effect on absorbance at 470 nm. The method was applied to analyse CHA for evaluating the performance of ion exchange resin used in condensate purification plant (CPP) of power station where, CHA is used as all volatile treatment (AVT) reagent to inhibit steam generator (SG) corrosion. Structure of the adduct formed by coupling CHA with NQS is elucidated using NMR ((1)H and (13)C) and IR spectra, CHN analysis and mole ratio variation method.

Naturally occurring hydroxy napthoquinones and their iron complexes as modulators of radiation induced lipid peroxidation in synaptosomes.

The modulation of radiation induced lipid peroxidation in synaptosomes by iron (II) and iron (III) complexes of two naturally occurring and therapeutically relevant naphthoquinones viz. 5,hydroxy-1,4 naphthoquinone; juglone and 2,hydroxy-1,4 naphthoquinone; lawsone, have been studied. At lower concentrations the complexes enhance lipid peroxidation predominantly through redox cycling as observed for Fe(II)- juglonate while at higher concentrations the complexes tend to limit lipid peroxidation through fast recombinations.

Cytotoxic properties of iron-hydroxynaphthoquinone complexes in rat hepatocytes.

The mechanisms of toxicity to isolated rat hepatocytes of Fe(II) and Fe(III) complexes of two structurally related naphthoquinones have been studied. All complexes were found to show a dose-dependent toxicity which precedes cell death. Within the naphthoquinone series the order of toxicity is Fe(II) > parent naphthoquinone > Fe(III). The iron complexes of 5-OH-1,4 naphthoquinone (5-OH-1,4 NQ; Juglone) are more toxic than the iron complexes of 2-OH-1,4 naphthoquinone (2-OH-1,4 NQ; Lawsone) indicating that the mechanisms of toxicity are different. Electrochemical studies on these complexes shows that 5-OH-1,4 NQ facilitates formation of stable semiquinone species while 2-OH-1,4 NQ does not. The low redox potential of 2-OH-1,4 NQ makes it a poor substrate for metabolism by reductases.

Novel, quinone-thiosemicarbazone hybrid (QTSCHY) non-platinum antitumor agents: inhibition of DNA biosynthesis in P388 lymphocytic cells by coordinatively unsaturated copper(II) and iron(III) complexes of naphthoquinone thiosemicarbazones.

Coordinately unsaturated Cu(II) and Fe(III) complexes of the stoichiometry [Cu(L)Cl] and [Fe(L)Cl2], where L = tridentate anion of 2-hydroxy-1,4-naphthoquinone 1-thiosemicarbazone (2HNQTSC) and its 3-methyl derivative (3M2HNQTSC), were screened in vitro against P388 lymphocytic leukemia cells. Copper complexes were found to be more effective inhibitors of DNA synthesis than analogous Fe(III) compounds. The inhibitory activities are suggested to be related to Cu(II)-Cu(I) redox couple or nitrogen adduct formation.

Novel broad-spectrum metal-based antifungal agents. Correlations amongst the structural and biological properties of copper (II) 2-acetylpyridine N4-dialkylthiosemicarbazones.

Copper(II) complexes of the type [Cu(L)X], where L = tridentate anion of 2-acetylpyridine N4-diethyl thiosemicarbazone and X = C1 or Br, were screened against seven fungal strains pathogenic to man viz. Aspergillus niger, Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans, Tricophyton rubrum, Epidermophyton floccosum and Microsporum canis. The greater growth inhibition exhibited by the bromo complex can be explained on the basis of its lower Cu(II)/Cu(I) redox couple and greater covalent bonding. These compounds represent a novel class of metal-based antifungal agents which provide opportunities for a large number of synthetic variations for modulation of the activities.