The effect of constituent metal ions on the electrokinetics of chalcopyrite

Chalcopyrite in contact with water is thermodynamically unstable in the presence of oxygen. Oxidation of chalcopyrite may take place due to various factors, e.g., geological environment, mining/comminution, and storage. In this work oxidation of chalcopyrite has been investigated through interfacial electrokinetics. The characteristics of samples obtained from different geological locations as well as the effects of ageing and laboratory oxidation have been delineated. Variation of the solid-liquid ratio was found to have a significant effect on the zeta-potential characteristics of chalcopyrite. The role of constituent metal ions, namely copper and iron, has been studied in the absence and presence of externally added metal ions. The results indicated that the ratio of Cu/Fe on the surface of oxidized chalcopyrite determines the Stern layer potential and under appropriate solution chemistry conditions influences charge reversals. The mineral surfaces, thus, could be either copper-rich or iron-rich as reflected by a shift in pH(iep),,(s). The observed charge reversals have been explained on the basis of a model proposed by James and Healy. (C) 1997 Academic Press.

Synthesis and characterization of novel charge transfer complexes formed by N,N%-bis(ferrocenylmethylidene)-p-phenylenediamine and N-(ferrocenylmethylidene)aniline

N,N'-Bis(ferrocenylmethylidene)-p-phenylenediamine 1 and N-(ferrocenylmethylidene) aniline 2 are readily synthesized by Schiff base condensation of appropriate units. Iodine (I-2), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetrachloro-1,4-benzoquinone (CA), tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) form charge transfer complexes with 1 and 2. IR spectroscopy suggests an increase in the amount of charge transferred from the ferrocenyl ring to the oxidant in the order, I-2 < CA < TCNQ < TCNE approximate to DDQ. EPR spectra of the oxidized binuclear complexes are indicative of localized species containing iron- and carbon-centered radicals. The Mossbauer spectrum of the iodine oxidized complex of 1 reveals the presence of both Fe(III) and Fe(II) centers. Variable temperature magnetic and Mossbauer studies show that the ratio of Fe(III)/Fe(II) centers varies as a function of temperature. The larger Fe(II)/Fe(III) ratio at lower temperatures is best explained by a retro charge transfer from the iodide to the iron(III) metal center. There is negligible solvent effect on the formation of the iodine oxidized charge transfer complex of 1. (C) 1999 Elsevier Science S.A. All rights reserved.

Structural model for the Cu-B site of dopamine beta-hydroxylase: Crystal structure of a copper(II) complex showing N3OS coordination with an axial sulfur ligation

A copper(II) complex containing a NSO-donor Schiff base and NN-donor 2,2'-bipyridine has been prepared and structurally characterized. The square pyramidal complex with an axial sulfur ligation is a structural model for the CUB site of dopamine-hydroxylase in its oxidized form. The copper(II) complex is catalytically active in the oxidation of ascorbic acid by dioxygen mediated by a copper(I) species which is proposed to have a four-coordinate structure with a N3S coordination geometry.

The first bis(phosphine) monoxide (BPMO) complexes of copper(I)

Copper(l) complexes of bis(phosphine) monoxide ligands, bis(diphenylphosphino)ethane monoxide (dppeo) and bis(diphenylphosphino)methane monoxide (dppmo) have been prepared and characterized. One of the complexes with dppeo was characterized by X-ray crystal structure analysis confirming Cu(I) coordination to hard and soft donors. The stability of these complexes in solution was probed via spectroscopic and electrochemical studies. Copper(I) is more readily oxidized in the presence of the hard 0 donor ligands. In solution, they readily exchange the hard donor O, for soft ligands. Although copper(l) prefers soft ligands and is more stable towards oxidation in their presence, it coordinates to hard donors when there is electrostatic or an entropy driven advantage. (C) 2002 Elsevier Science Ltd. All rights reserved.

Low temperature synthesis of ferromagnetic (LaK)MnO3 from KCl, KBr and KI fluxes

Potassium doped lanthanum manganites have been synthesized from KCl, KBr and KI fluxes at 900, 850 and 750 °C respectively. While all the flux-grown oxides are ferromagnetic metals (Tc=290–330 K), the oxides grown from KCl and KBr fluxes crystallize in the rhombohedral structure and that synthesized from KI flux adopts the cubic structure. The enhancement in Tc correlates with the increasing tendency of the flux to get oxidized and decreasing melting points of the flux. Nearly stoichiometric (LaK)MnO3 with 33 % of Mn4+ concentration could be prepared at temperature as low as 750 °C. Composition of all the phases have been obtained from the chemical analysis of the elements present.

Severe wear of a near eutectic aluminium-silicon alloy

The severe wear of a near eutectic aluminium silicon alloy is explored using a range of electron microscopic, spectroscopic and diffraction techniques to identify the residually strained and unstrained regions, microcracks and oxidized regions in the subsurface. In severe wear the contact pressure exceeds the elastic shakedown limit. Under this condition the primary and eutectic silicon particles fragment drastically. The fragments are transported by the matrix as it undergoes incremental straining with each cyclic contact at the asperity level. The grains are refined from similar to 2000 nm in the bulk to 30 nm in the near surface region. A large reduction in the interparticle distance compared with that for a milder stage of wear gives rise to high strain gradients which contribute to an enhancement of the dislocation density. The resulting regions of very high strain in the boundaries of the recrystallized grains as well as within the subgrains lead to the formation of microvoidskracks. This is accompanied by the formation of brittle oxides at these subsurface interfaces due to enhanced diffusion of oxygen. We believe that the abundance of such microcracks in the near surface region, primed by severe plastic deformation, is what distinguishes a severe wear regime from mild wear. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Efficient synthesis of carbonyl compounds: oxidation of azides and alcohols catalyzed by vanadium pentoxide in water using tert-butylhydroperoxide

Catalytic amount of vanadium reagent with tert-butylhydroperoxide as the oxidant was found to be an excellent oxidizing agent in aqueous medium. Vanadium pentoxide with aq tert-butylhydroperoxide readily oxidizes primary benzylic azides to the corresponding acids and secondary benzylic azides to the corresponding ketones in excellent yields. Further, vanadium pentoxide and aq tert-butylhydroperoxide combination turned out to be an effective catalyst for the oxidation of alcohols. Using vanadium pentoxide and aq tert-butylhydroperoxide primary alcohols were oxidized to the corresponding acids, whereas secondary alcohols underwent a smooth transformation to furnish corresponding ketones in excellent yields. All the oxidations are performed in water. (C) 2011 Elsevier Ltd. All rights reserved.

Oleosin Is Bifunctional Enzyme That Has Both Monoacylglycerol Acyltransferase and Phospholipase Activities

In plants, fatty oils are generally stored in spherical intracellular organelles referred to as oleosomes that are covered by proteins such as oleosin. Seeds with high oil content have more oleosin than those with low oil content. However, the exact role of oleosin in oil accumulation is thus far unclear. Here, we report the isolation of a catalytically active 14 S multiprotein complex capable of acylating monoacylglycerol from the microsomal membranes of developing peanut cotyledons. Microsomal membranes from immature peanut seeds were solubilized using 8 M urea and 10 mM CHAPS. Using two-dimensional gel electrophoresis and mass spectrometry, we identified 27 proteins in the 14 S complex. The major proteins present in the 14 S complex are conarachin, the major allergen Ara h 1, and other seed storage proteins. We identified oleosin 3 as a part of the 14 S complex, which is capable of acylating monoacylglycerol. The recombinant OLE3 microsomes from Saccharomyces cerevisiae have been shown to have both a monoacylglycerol acyltransferase and a phospholipase A(2) activity. Overexpression of the oleosin 3 (OLE3) gene in S. cerevisiae resulted in an increased accumulation of diacylglycerols and triacylglycerols and decreased phospholipids. These findings provide a direct role for a structural protein (OLE3) in the biosynthesis and mobilization of plant oils.

Chromium Nanowires Grown Inside Lithographically Fabricated U-Trench Templates

Chromium nanowires of diameter 40-120 nm have been grown inside lithographically fabricated U-trench templates on oxidized silicon substrate by RF sputtering deposition technique. Under favourable experimental conditions, very long nanowires can be grown which depends on the trench length and surface homogeneity along the axis. Surface wettability control by the restricted supply of metal vapour is the key for the formation of nanowires. Diameter/depth ratio for the trench template is demonstrated to be crucial for the growth of nanowires.

A non-metal catalysed oxidation of primary azides to nitriles at ambient temperature

A novel non-metal catalyzed oxidation of organic azides to nitriles under solvent-free conditions is presented employing catalytic amounts of KI, and DABCO in aq. TBHP at room temperature. This nonmetal catalyzed oxidation of azides provides good selectivity as double and triple bonds were not oxidized under the present reaction conditions.

Redox modification of Akt mediated by the dopaminergic neurotoxin MPTP, in mouse midbrain, leads to down-regulation of pAkt

Impairment of Akt phosphorylation, a critical survival signal, has been implicated in the degeneration of dopaminergic neurons in Parkinson's disease. However, the mechanism underlying pAkt loss is unclear. In the current study, we demonstrate pAkt loss in ventral midbrain of mice treated with dopaminergic neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), when compared to ventral midbrain of control mice treated with vehicle alone. Thiol residues of the critical cysteines in Akt are oxidized to a greater degree in mice treated with MPTP, which is reflected as a 40% loss of reduced Akt. Association of oxidatively modified Akt with the phosphatase PP2A, which can lead to enhanced dephosphorylation of pAkt, was significantly stronger after MPTP treatment. Maintaining the protein thiol homeostasis by thiol antioxidants prevented loss of reduced Akt, decreased association with PP2A, and maintained pAkt levels. Overexpression of glutaredoxin, a protein disulfide oxidoreductase, in human primary neurons helped sustain reduced state of Akt and abolished MPP+-mediated pAkt loss. We demonstrate for the first time the selective loss of Akt activity, in vivo, due to oxidative modification of Akt and provide mechanistic insight into oxidative stress-induced down-regulation of cell survival pathway in mouse midbrain following exposure to MPTP.-Durgadoss, L., Nidadavolu, P., Khader Valli, R., Saeed, U., Mishra, M., Seth, P., Ravindranath, R. Redox modification of Akt mediated by the dopaminergic neurotoxin MPTP, in mouse midbrain, leads to down-regulation of pAkt. FASEB J. 26, 1473-1483 (2012). www.fasebj.org

Structure and Mechanistic Insights into Novel Iron-mediated Moonlighting Functions of Human J-protein Cochaperone, Dph4

J-proteins are obligate cochaperones of Hsp70s and stimulate their ATPase activity via the J-domain. Although the functions of J-proteins have been well understood in the context of Hsp70s, their additional co-evolved ``physiological functions'' are still elusive. We report here the solution structure and mechanism of novel iron-mediated functional roles of human Dph4, a type III J-protein playing a vital role in diphthamide biosynthesis and normal development. The NMR structure of Dph4 reveals two domains: a conserved J-domain and a CSL-domain connected via a flexible linker-helix. The linker-helix modulates the conformational flexibility between the two domains, regulating thereby the protein function. Dph4 exhibits a unique ability to bind iron in tetrahedral coordination geometry through cysteines of its CSL-domain. The oxidized Fe-Dph4 shows characteristic UV-visible and electron paramagnetic resonance spectral properties similar to rubredoxins. Iron-bound Dph4 (Fe-Dph4) also undergoes oligomerization, thus potentially functioning as a transient ``iron storage protein,'' thereby regulating the intracellular iron homeostasis. Remarkably, Fe-Dph4 exhibits vital redox and electron carrier activity, which is critical for important metabolic reactions, including diphthamide biosynthesis. Further, we observed that Fe-Dph4 is conformationally better poised to perform Hsp70-dependent functions, thus underlining the significance of iron binding in Dph4. Yeast Jjj3, a functional ortholog of human Dph4 also shows a similar iron-binding property, indicating the conserved nature of iron sequestration across species. Taken together, our findings provide invaluable evidence in favor of additional co-evolved specialized functions of J-proteins, previously not well appreciated.

Serine/Threonine/Tyrosine Protein Kinase Phosphorylates Oleosin, a Regulator of Lipid Metabolic Functions

Plant oils are stored in oleosomes or oil bodies, which are surrounded by a monolayer of phospholipids embedded with oleosin proteins that stabilize the structure. Recently, a structural protein, Oleosin3 (OLE3), was shown to exhibit both monoacylglycerol acyltransferase and phospholipase A(2) activities. The regulation of these distinct dual activities in a single protein is unclear. Here, we report that a serine/threonine/tyrosine protein kinase phosphorylates oleosin. Using bimolecular fluorescence complementation analysis, we demonstrate that this kinase interacts with OLE3 and that the fluorescence was associated with chloroplasts. Oleosin-green fluorescent protein fusion protein was exclusively associated with the chloroplasts. Phosphorylated OLE3 exhibited reduced monoacylglycerol acyltransferase and increased phospholipase A(2) activities. Moreover, phosphatidylcholine and diacylglycerol activated oleosin phosphorylation, whereas lysophosphatidylcholine, oleic acid, and Ca2+ inhibited phosphorylation. In addition, recombinant peanut (Arachis hypogaea) kinase was determined to predominantly phosphorylate serine residues, specifically serine-18 in OLE3. Phosphorylation levels of OLE3 during seed germination were determined to be higher than in developing peanut seeds. These findings provide direct evidence for the in vivo substrate selectivity of the dual-specificity kinase and demonstrate that the bifunctional activities of oleosin are regulated by phosphorylation.

Structure and mechanical properties of Ti-C films deposited using combination of pulsed DC and normal DC magnetron co-sputtering

Titanium-carbon (Ti-C) thin films of different compositions were prepared by a combination of pulsed DC (for Ti target) and normal DC (for graphite target) magnetron co-sputtering on oxidized silicon and fused quartz substrates. At 33.7 at.% of C content, pure hcp Ti transforms into fcc-TiC with a preferential orientation of (2 2 0) along with (1 1 1) and (2 0 0). A clear transformation in the preferential orientation from (2 2 0) to (1 1 1) has been observed when the C content was increased to 56 at.%. At 62.5 at.% of C, TiC precipitates in an amorphous carbon matrix whereas further increase in C leads to X-ray amorphous films. The cross-sectional scanning electron microscope images reveal that the films with low carbon content consists of columnar grains, whereas, randomly oriented grains are in an amorphous carbon matrix at higher carbon content. A dramatic variation was observed in the mechanical properties such as hardness, H, from 30 to 1 GPa and in modulus, E, from 255 to 25 GPa with varying carbon content in the films. Resistance to plastic deformation parameter was observed as 0.417 for films containing 62.5 at.% of C. Nanoscratch test reveals that the films are highly scratch resistant with a coefficient of friction ranging from 0.15 to 0.04. (C) 2012 Elsevier B.V. All rights reserved.

Growth of Polypyrrole-Horseradish Peroxidase Microstructures for H2O2 Biosensor

Conducting polymer microstructures for enzymatic biosensors are developed by a facile electrochemical route. Horseradish peroxide (HRP)-entrapped polypyrrole (PPy) films with bowl-shaped microstructures are developed on stainless steel (SS 304) substrates by a single-step process. Potentiodynamic scanning/cyclic voltammetry is used for generation of PPy microstructures using electrogenerated oxygen bubbles stabilized by zwitterionic surfactant/buffer N-2-hydroxyethylpiperazine N-2-ethanesulfonic acid as soft templates. Scanning electron microscopic images reveal the bowl-shaped structures surrounded by cauliflower-like fractal PPy films and globular nanostructures. Raman spectroscopy reveals the oxidized nature of the film. Sensing properties of PPy-HRP films for hydrogen peroxide (H2O2) are demonstrated. Electrochemical characterization of the sensor films is done by linear sweep voltammetry (LSV) and amperometry. LSV results indicated the reduction of H2O2 and linearity in response of the sensing film. The amperometric biosensor has a performance comparable to those in the literature with advantages of hard-template free synthesis procedure and a satisfactory sensitivity value of 12.8 mu A/(cm(2) . mM) in the range of 1-10 mM H2O2.