Prooxidant and antioxidant properties of human serum ultrafiltrates toward LDL: important role of uric acid

Oxidized LDL is present within atherosclerotic lesions, demonstrating a failure of antioxidant protection. A normal human serum ultrafiltrate of M-r below 500 was prepared as a model for the low M-r components of interstitial fluid, and its effects on LDL oxidation were investigated. The ultrafiltrate (0.3%, v/v) was a potent antioxidant for native LDL, but was a strong prooxidant for mildly oxidized LDL when copper, but not a water-soluble azo initiator, was used to oxidize LDL. Adding a lipid hydroperoxide to native LDL induced the antioxidant to prooxidant switch of the ultrafiltrate. Uric acid was identified, using uricase and add-back experiments, as both the major antioxidant and prooxidant within the ultrafiltrate for LDL. The ultrafiltrate or uric acid rapidly reduced Cu2+ to Cu+. The reduction of Cu2+ to Cu+ may help to explain both the antioxidant and prooxidant effects observed. The decreased concentration of Cu2+ would inhibit tocopherol-mediated peroxidation in native LDL, and the generation of Cu+ would promote the rapid breakdown of lipid hydroperoxides in mildly oxidized LDL into lipid radicals. The net effect of the low M-r serum components would therefore depend on the preexisting levels of lipid hydroperoxides in LDL.jlr These findings may help to explain why LDL oxidation occurs in atherosclerotic lesions in the presence of compounds that are usually considered to be antioxidants.

Synthesis, structure and magnetic characterisation of a new layered ammonium manganese(II) diphosphate hydrate, (NH4)(2)[Mn-3(P2O7)(2)(H2O)(2)]

A new layered ammonium manganese(II) diphosphate, (NH4)(2)[Mn-3(P2O7)(2)(H2O)(2)], has been synthesised under solvothermal conditions at 433 K in ethylene glycol and the structure determined at 293 K using single-crystal X-ray diffraction data (M-r = 584.82, monoclinic, space group P2(1)/a, a = 9.4610( 8), b = 8.3565( 7), c = 9.477(1) Angstrom, beta = 99.908(9) degrees, V = 738.07 Angstrom(3), Z = 2, R = 0.0351 and R-w = 0.0411 for 1262 observed data (I > 3(sigma(I))). The structure consists of chains of cis- and trans-edge sharing MnO6 octahedra linked via P2O7 units to form layers of formula [Mn3P4O14(H2O)(2)](2-) in the ab plane. Ammonium ions lie between the manganese-diphosphate layers. A network of interlayer and ammonium-layer based hydrogen bonding holds the structure together. Magnetic measurements indicate Curie - Weiss behaviour above 30 K with mu(eff) = 5.74(1) mu(B) and theta = -23(1) K, consistent with the presence of high-spin Mn2+ ions and antiferromagnetic interactions. However, the magnetic data reveal a spontaneous magnetisation at 5 K, indicating a canting of Mn2+ moments in the antiferromagnetic ground state. On heating (NH4)(2)[Mn-3(P2O7)(2)(H2O)(2)] in water at 433 K under hydrothermal conditions, Mn-5(HPO4)(2)(PO4)(2).4H(2)O, synthetic hureaulite, is formed.

Synthesis, structure, and redox states of homoleptic d-block metal complexes with bis-1,2,4-triazin-3-yl-pyridine and 1,2,4-triazin-3-yl-bipyridine extractants

it has been established that triazinyl bipyridines (hemi-BTPs) and bis-triazinyl pyridines (BTPs), ligands which are currently being investigated as possible ligands for the separation of actinides from lanthanides in nuclear waste, are able to form homoleptic complexes with first row transition metals such as cobalt(IT), copper(II), iron(II), manganese(II), nickel(II) and zinc(II). The metal complexes exhibit six-co-ordinate octahedral structures and redox states largely analogous to those of the related terpyridine complexes. The reactivity of the different redox states of cobalt bis-hemi-BTP complex in aqueous environments has been studied with two-phase electrochemistry by immobilisation of the essentially water-insoluble metal complexes on graphite electrodes and the immersion of this modified electrode in an aqueous electrolyte. It was found that redox potentials for the metal-centred reactions were pH-independent whereas the potentials for the ligand-centred reactions were strongly pH-dependent. The reductive degradation of these complexes has been investigated by computational methods. Solvent extraction experiments have been carried out for a range of metals and these show that cobalt(II) and nickel(II) as well as palladium(II), cadmium(II) and lead(II) were all extracted with the ligands 1e and 2c with higher distribution ratios that was observed for americium(III) under the same conditions. The implications of this result for the use of these ligands to separate actinides from nuclear waste are discussed. (c) 2005 Elsevier Ltd. All rights reserved.

Synthesis, structure and solution chemistry of mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes incorporating tridentate ONO donor hydrazone ligands

In the title family, the ONO donor ligands are the acetylhydrazones of salicylaidehyde (H2L1) and 2-hydroxyacetophenone (H2L2) (general abbreviation, H2L). The reaction of bis(acetylacetonato)oxovanadium(IV) with a mixture of tridentate H2L and a bidentate NN donor [e.g., 2,2'-bipyridine(bpy) or 1,10-phenanthroline(phen), hereafter B] ligands in equimolar ratio afforded the tetravalent complexes of the type [(VO)-O-IV(L)(B)]; complexes (1)-(4) whereas, if B is replaced by 8-hydroxyquinoline(Hhq) (which is a bidentate ON donor ligand), the above reaction mixture yielded the pentavalent complexes of the type [(VO)-O-V(L)(hq)]; complexes (5) and (6). Aerial oxygen is most likely the oxidant (for the oxidation of V-IV -> V-V) in the synthesis of pentavalent complexes (5) and (6). [(VO)-O-IV(L)(B)] complexes are one electron paramagnetic and display axial EPR spectra, while the [(VO)-O-V(L)(hq)] complexes are diamagnetic. The X-ray structure of [(VO)-O-V(L-2)(hq)] (6) indicates that H2L2 ligand is bonded with the vanadium meridionally in a tridentate dinegative fashion through its phenolic-O, enolic-O and imine-N atoms. The general bond length order is: oxo < phenolato < enolato. The V-O (enolato) bond is longer than V-O (phenolato) bond by similar to 0.07 angstrom and is identical with V-O (carboxylate) bond. H-1 NMR spectrum of (6) in CDCl3 solution indicates that the binding nature in the solid state is also retained in solution. Complexes (1)(4) display two ligand-field transitions in the visible region near 820 and 480 nm in DMF solution and exhibit irreversible oxidation peak near +0.60 V versus SCE in DMSO solution, while complexes (5) and (6) exhibit only LMCT band near 535 nm and display quasi-reversible one electron reduction peak near -0.10 V versus SCE in CH2Cl2 solution. The VO3+-VO2+ E-1/2 values shift considerably to more negative values when neutral NN donor is replaced by anionic ON donor species and it also provides better VO3+ binding via phenolato oxygen. For a given bidentate ligand, E-1/2 increases in the order: (L-2)(2-) < (L-1)(2-). (c) 2004 Elsevier B.V. All rights reserved.

Photochemical, photophysical and redox properties of novel fulgimide derivatives with attached 2,2 '-bipyridine (bpy) and [M(bpy)(3)](2+) (M = Ru and Os) moieties

Fulgimides monosubstituted with [M(bpy)(3)](2+) (M = Ru, Os; bpy = 2,2'-bipyridine) chromophore units and with a single bpy group were synthesized and investigated as components of conceivable dinuclear photochromic switches of luminescence. The E-, Z- and closed-ring (C) photoisomer forms of the bpy-bound fulgimide were successfully separated by semi-preparative HPLC. The same procedure failed, however, in the case of the [M(bpy)(3)](2+)-substituted fulgimides. Energy transfer from the excited photochromic unit to the metal-bpy centre competes with the fulgimide cyclization, reducing the photocyclization quantum yields by approximately one order of magnitude compared to the non-complexed fulgimide-bpy ligand (phi(EC) = 0.17, phi(EZ) = 0.071, phi(ZE) = 0.15 at lambda(exc) = 334 nm). The cycloreversion of the fulgimide-bpy ligand is less efficient (phi(CE) = 0.047 at lambda(exc) = 520 nm). The intensity of the (MLCT)-M-3-based luminescence of the metal-bpy chromophore (in MeCN, phi(deaer) = 6.6 x 10(-2) and tau(deaer) = 1.09 mu s for Ru; phi(deaer) = 6.7 x 10(-3) and tau(deaer) = 62 ns for Os) is not affected by the fulgimide photoconversion. These results and supporting spectro-electrochemical data reveal that the lowest triplet excited states of the photochromic fulgimide moiety in all its E-, Z- and closed-ring forms lie above the lowest 3MLCT levels of the attached ruthenium and osmium chromophores. The actual components are therefore unlikely to form a triad acting as functional switch of energy transfer from [Ru(bpy)(3)](2+) to [Os(bpy)(3)](2+) through the photochromic fulgimide bridge.

Micellar and surface properties of a poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) copolymer in aqueous solution

Critical micelle concentrations (cmc) of aqueous solutions of poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) were determined at several temperatures by surface tensiometry. Below the lower critical solution temperature (LCST), the low Delta(mic) H-0 determined can be assigned to the PMMA block being tightly coiled in the dispersed molecular state, so that the unfavorable interactions of hydrophobic entities with water are minimized. Above the LCST the cmc value was found to increase; an anomalous behavior that can be directly related to the micelle-globule transition of the hydrophilic block. Interestingly, above the LCST the surface tension of relatively concentrated solutions was found to depend weakly on temperature not following the usual strong decrease with temperature expected for aqueous solutions. (C) 2007 Elsevier Inc. All rights reserved.

Synthesis, spectroscopic and redox properties of some ruthenium(II) thiosemicarbazone complexes: structural description of four of these complexes

Sixteen neutral mixed ligand thiosemicarbazone complexes of ruthenium having general formula [Ru(PPh3)(2)L-2], where LH = 1-(arylidine)4-aryl thiosemicarbazones, have been synthesized and characterized. All complexes are diamagnetic and hence ruthenium is in the +2 oxidation state (low-spin d(6), S = 0). The complexes show several intense peaks in the visible region due to allowed metal to ligand charge transfer transitions. The structures of four of the complexes have been determined by single-crystal X-ray diffraction and they show that thiosemicarbazone ligands coordinate to the ruthenium center through the hydrazinic nitrogen and sulfur forming four-membered chelate rings with ruthenium in N2S2P2 coordination environment. In dichloromethane solution, the complexes show two quasi-reversible oxidative responses corresponding to loss of electron from HOMO and HOMO - 1. The E-0 values of the above two oxidations shows good linear relationship with Hammett substituents constant (sigma) as well as with the HOMO energy of the molecules calculated by the EHMO method. A DFT calculation on one representative complex suggests that there is appreciable contribution of the sulfur p-orbitals to the HOMO and HOMO - 1. Thus, assignment of the oxidation state of the metal in such complexes must be made with caution. (c) 2005 Elsevier B.V. All rights reserved.

Synthesis, structure and solution chemistry of quaternary oxovanadium(V) complexes incorporating hydrazone ligands

[VIVO(acac)(2)] reacts with an equimolar amount of benzoyl hydrazone of 2-hydroxyacetophenone (H2L1) or 5-chloro-2-hydroxyacetophenone (H2L2) in the presence of excess pyridine (py) in methanol to produce the quaternary [(VO)-O-V(L-1)(OCH3)(py)] (1) and [(VO)-O-V(L-2)(OCH3)(py)] (2) complexes, respectively, while under similar condition, the benzoyl hydrazones of 2-hydroxy-5-methylacetophenone (H2L3) and 2-hydroxy-5-methoxyacetophenone (H2L4) afforded only the methoxy bridged dimeric [(VO)-O-V(L-3/L-4)(OCH3)](2) complexes. The X-ray structural analysis of 1 and 2 indicates that the geometry around the metal is distorted octahedral where the three equatorial positions are occupied by the phenolate-O, enolate-O and the imine-N of the fully deprotonated hydrazone ligand in its enolic form and the fourth one by a methoxide-O atom. An oxo-O and a pyridine-N atom occupy two axial positions. Quaternary complexes exhibit one quasi-reversible one-electron reduction peak near 0.25 V versus SCE in CH2Cl2 and they decompose appreciably to the corresponding methoxy bridged dimeric complex in CDCl3 solution as indicated by their H-1 NMR spectra. These quaternary VO3+ complexes are converted to the corresponding V2O34+-complexes simply on refluxing them in acetone and to the VO2+-complexes on reaction with KOH in methanol. An equimolar amount of 8-hydroxyquinoline (Hhq) converts these quaternary complexes to the ternary [(VO)-O-V(L)(hq)] complexes in CHCl3. (C) 2009 Elsevier B. V. All rights reserved.

Synthesis, structure and solution chemistry of a family of dinuclear hydrazonato-vanadium(V) complexes with [OV(mu-O)VO](4+) core

Dinuclear trioxidic [{VOL}(2)mu-O] (1-4) complexes were synthesized from the reaction of [(VO)-O-IV(acac)(2)] with an equimolar amount of H2L [H2L is the general abbreviation of hydrazone ligands (H2L1-4) derived from the condensation of benzoyl hydrazine with either 2-hydroxyacetophenone or its para substituted derivatives] in acetone or CH2Cl2 or acetonitrile. These V2O3L2 complexes were also obtained from the reaction of VOSO4 with H2L in the presence of two equivalents sodium acetate in aqueous-methanolic (50% V/V) medium and also from the decomposition of [(VO)-O-IV(L)(bipy/phen)] complexes in CH2Cl2 Solution. Black monoclinic crystals of 2 and 4 with C2/c space group were obtained from the reaction of [(VO)-O-IV(acac)(2)], respectively, with H2L2 and H2L4 in acetone in which the respective ligands are bonded meridionally to vanadium in their fully deprotonated enol forms. The V-O bond lengths follow the order: V-O(oxo) < V-O(oxo-bridged) < V-O(phenolate) < V-O(enolate). Complexes (1-4) are diamagnetic exhibiting LMCT transition band near 380 nm in CH2Cl2 solution and they are electroactive displaying a quasi-reversible reduction peak in the 0.14-0.30 V versus SCE region. The and the reduction peak potential (E-p(c)) values show linear relationships with the Hammett constant (sigma) of the substituents in the hydrazone ligands. These dinuclear complexes are converted to the corresponding mononuclear cis dioxo complexes K(H2O)(+)[(VO2)-O-V(L)](-) (5-8) and mixed-ligand [(VO)-O-V(L)(hq)] complexes on reaction, respectively, with two equivalents KOH in methanol and two equivalents 8-hydroxyquinoline (Hhq) in CHCl3. Ascorbic acid reduces the dioxovanadium(V) complexes reversibly under aerobic condition. (C) 2008 Elsevier Ltd. All rights reserved.

Influence of counter anions on the structures and magnetic properties of trinuclear Cu(II) complexes containing a mu(3)-OH core and Schiff base ligands

Four trinuclear Cu(II) complexes, [(CuL1)(3)(mu(3)-OH)](NO3)(2) (1), [(CuL2)(3)(mu(3)-OH)](I)(2)center dot H2O (2), [(CuL3)(3)(mu(3)-OH)](I)(2) (3) and [(CuL1)(3)(mu(3)-OH)][(CuI3)-I-1] (4), where HL1 (8-amino-4-methyl-5-azaoct-3-en-2-one), HL2 [7-amino-4-methyl-5-azaoct-3-en-2-one] and HL3 [7-amino-4-methyl-5-azahept-3-en-2- one] are the three tridentate Schiff bases, have been synthesized and structurally characterized by X-ray crystallography. All four complexes contain a partial cubane core, [(CuL)(3)(mu(3)-OH)](2+) in which the three [CuL] subunits are interconnected through two types of oxygen bridges afforded by the oxygen atoms of the ligands and the central OH- group. The copper(II) ions are in a distorted square-pyramidal environment. The equatorial plane consists of the bridging oxygen of the central OH- group together with three atoms (N, N, O) from the Schiff base. The oxygen atom of the Schiff base also coordinates to the axial position of Cu(II) of another subunit to form the cyclic trimer. Magnetic susceptibilities have been determined for these complexes over the temperature range of 2-300 K. The isotropic Hamiltonian, H = -J(12)S(1)S(2) - J(13)S(1)S(3) - J(23)S(2)S(3) has been used to interpret the magnetic data. The best fit parameters obtained are: J = - 54.98 cm(-1) g = 2.24 for 1; J = - 56.66 cm(-1), g = 2.19 for 2; J = -44.39 cm(-1), g = 2.16 for 3; J = - 89.92 cm(-1), g = 2.25 for 4. The EPR data at low temperature indicate that the phenomenon of spin frustration occurs for complexes 1-3. (c) 2007 Elsevier B.V. All rights reserved.

Structural and spectroscopic properties of Ru(II) complexes of 4-(aryl)thiosemicarbazones of thiophen-2-carbaldehyde

Six Ru(II) complexes of formula [Ru(L)(2)(PPh3)(2)] have been prepared where LH = 4-(aryl)thiosemicarbazones of thiophen-2-carbaldehyde. X-ray crystal structures of five of the complexes are reported. In all the complexes ruthenium is six coordinate with a distorted octahedral cis-P-2, cis-N-2, trans-S-2 donor environment, and each of the two thiosemicarbazone ligands are coordinated in a bidentate fashion forming a four membered chelate ring. The complexes undergo a one-electron oxidation at similar to 0.5 V vs. Ag/AgCl. The EPR spectrum of the electrochemically oxidized solution at 100 K shows a rhombic signal, with transitions at g(1) = 2.27, g(2) = 2.00 and g(3) = 1.80. DFT calculations on one of the complexes suggest that there is 35% ruthenium and 17% sulfur orbital contribution to the HOMO. These results suggest that the assignment of metal atom oxidation states in these compounds is not unambiguous. (C) 2009 Elsevier Ltd. All rights reserved.

Electrochemical fabrication and electrocatalytic properties of nanostructured mesoporous platinum microelectrodes

Electrodeposition from a lyotropic liquid crystal template medium was used to produce nanostructured platinum microelectrodes with high specific surface area and high mass transport efficiency. Compared to polished and conventional platinized microelectrodes, well-ordered nanostructured platinum microelectrodes exhibited enhanced electrocatalytic properties for oxygen and ascorbic acid, whilst well-ordered nanostructured platinum microelectrodes offered improved electrocatalytic properties for oxygen reduction compared to disordered nanostructured platinum microelectrodes.

Synthesis, crystal structure and thermal studies of catena(L-glutamato)-aqua copper(II) monohydrate

The synthesis. crystal structure and thermal study of the blue catena-(L-glutamato)-aqua copper(II) monohydrate have been reported. The compound crystallizes in P2(1)2(1)2(1) space group and consists of a polymeric three-dimensional network of copper(II) which is coordinated with the amino nitrogen and the carboxylate oxygen Of L-glutamate, the side chain carboxylate oxygen of a neighbouring L-glutamate and the oxygen of a water molecule in the equatorial position. Weak coordination of two additional glutamate oxygen atoms to both the axial positions Completes a distorted octahedron. The crystal structure shows that the lattice water is stabilized by the formation of strong H-bonding network with the coordinated water molecule. Removal and reabsorption of the water molecule have been studied by thermal analysis.

Novel supramolecular network in tri- and mono-nuclear oxovanadium(V)-salicyl-hydroximate: Synthesis, structure and catalytic oxidation of hydrocarbons using H2O2 as terminal oxidant

oxovanadium(V) salicylhydroximate complexes, [VO(SHA)(H2O)]center dot 1.58H(2)O (1) and [V3O3(CSHA)(3) (H2O)(3)]center dot 3CH(3)COCH(3) (2) have been synthesized by reaction of VO43- with N-salicyl hydroxamic acid (SHAHS) and N-(5-chlorosalicyl) hydroxamic acid (CSHAH(3)), respectively, in methanol medium. Compound 1 on reaction with pyridine 2,6-dicarboxylic acid (PyDCH2) yields mononuclear complex [VO(SHAH(2))(PyDC)] (3). Treatment of compound 3 with hydrogen peroxide at low pH (2-3) and low temperature (0-5 degrees C) yields a stable oxoperoxovanadium(V) complex H[VO(O-2)(PyDC)(H2O)]center dot 2.5H(2)O (4). All four complexes (1-4) have been characterized by spectroscopic (IR, UV-Vis, V-51 NMR) and single crystal X-ray analyses. Intermolecular hydrogen bonds link complex 1 into hexanuclear clusters consisting of six {VNO5} octahedra surrounded by twelve {VNO5} octahedra to form an annular ring. While the molecular packing in 2 generates a two-dimensional framework hydrogen bonds involving the solvent acetone molecules, the mononuclear complexes 3 and 4 exhibit three-dimensional supramolecular architecture. The compounds 1 and 2 behave as good catalysts for oxygenation of benzylic, aromatic, carbocyclic and aliphatic hydrocarbons to their corresponding hydroxylated and oxygenated products using H2O2 as terminal oxidant; the process affords very good yield and turnover number. The catalysis work shows that cyclohexane is a very easily oxidizable substrate giving the highest turnover number (TON) while n-hexane and n-heptane show limited yield, longer time involvement and lesser TON than other hydrocarbons. (C) 2008 Elsevier Ltd. All rights reserved.

The influence of hydration on the tensile and compressive properties of avian keratinous tissues

Despite recent research exploring the elastic properties of avian keratins, data on failure properties are less common in the literature. In this paper we present data on the failure properties and moduli of both avian feather and claw keratin in tension and the modulus of claw keratin in compression. Increased water content acts to decrease stiffness and strength but to increase strain at failure. The modulus of claw did not differ significantly when tested under tension and compression.