Oxido- and mixed-ligand peroxido complexes of niobium(V) as potent phosphatase inhibitors and efficient catalysts for eco-friendly styrene epoxidation.

The present study describes the facile synthesis and comprehensive characterization of new oxido and peroxidoniobium(V) complexes with biogenic ligands, maltol (malt) and deferiprone (def) in their co-ordination sphere, viz., [NbO(malt)3]2·9H2O (1), Na2[Nb(O2)3(malt)]·H2O (2) and Na2[Nb(O2)3(def)]·2H2O (3). The complexes were characterized using various analytical and spectroscopic techniques (FTIR, Raman, NMR, UV-visible, TGA, ICP-OES and elemental analysis). The charge neutral complex 1 was further characterized by single crystal XRD analysis, and the proposed structures of the peroxidoniobium (pNb) complexes 2 and 3 were validated by density functional theory (DFT) studies. A comparative investigation on the in vitro effect of the title compounds and a set of previously reported polymer-anchored peroxidoniobium complexes, [Nb(O2)3(sulfonate)2]3--PSS [PSS = poly(sodium 4-styrene sulfonate)] (5), [Nb2(O2)6(carboxylate)2]4--PA [PA = poly(sodium acrylate)] (6) and [Nb(O2)3(carboxylate)]2--PMA [PMA = poly(sodium methacrylate)] (7), on the activity of the model enzyme wheat thylakoid acid phosphatase has revealed that each of the compounds is an effective inhibitor of the enzyme (IC50 values varying within the range 1-64 µM). The results of the detailed enzyme kinetic study demonstrated that the compounds induce their inhibitory effect via distinct pathways. The oxidoniobium complex 1 as well as polymer-anchored pNb complexes acted as classical non-competitive inhibitors of ACP, whereas the monomeric pNb complexes emerged as mixed inhibitors of the enzyme (Kii > Ki). Notably, the complexes serve as excellent recyclable catalysts for selective styrene epoxidation with H2O2, affording 99% styrene conversion, ≥98% epoxide selectivity and a high turnover number of 1740 under eco-friendly solventless conditions.

Octahedral copper(ii)-diimine complexes of triethylenetetramine: effect of stereochemical fluxionality and ligand hydrophobicity on CuII/CuI redox, DNA binding and cleavage, cytotoxicity and apoptosis-inducing ability.

Octahedral copper(ii) complexes of the type [Cu(trien)(diimine)](ClO4)2 (1-4), where trien is triethylenetetramine and diimine is 2,2'-bipyridine (1), 1,10-phenanthroline (2), 5,6-dimethyl-1,10-phenanthroline (3), and 3,4,7,8-tetramethyl-1,10-phenanthroline (4), have been isolated. Single crystal X-ray structures of 1 and 2 reveal that the coordination geometry around Cu(ii) is tetragonally distorted octahedral. The stereochemical fluxionality of the complexes illustrates the observed trend in CuII/CuI redox potentials and DNA binding affinity (Kb: 1, 0.030 ± 0.002 < 2, 0.66 ± 0.01 < 3, 1.63 ± 0.10 < 4, 2.27± 0.20 × 105 M-1), determined using absorption spectral titration. All complexes effect oxidative DNA cleavage more efficiently than hydrolytic DNA cleavage. The bpy complex 1 with stereochemical fluxionality lower than its phen analogue 2 shows a higher cytotoxicity against both A549 lung (IC50, 3.3 µM) and MCF-7 human breast (IC50, 3.9 µM) cancer cells, and induces the generation of the highest amount of ROS in A549 cells. Complex 3 with a higher stereochemical fluxionality and higher ligand hydrophobicity exhibits a higher DNA binding and cleavage ability and higher cytotoxicity (IC50, 2.1 µM) towards MCF-7 cells. Complex 4 with a still higher stereochemical fluxionality displays the highest DNA binding and cleavage ability but a lower cytotoxicity towards both A549 and MCF-7 cell lines due to its tendency to form a five-coordinated complex with the uncoordinated amine group. Annexin V.Cy3 staining and immunoblot analysis demonstrate the mechanism of cell death caused by 1 and 2. The finding of the up-regulation of the pro-apoptotic Bax protein and down-regulation of PARP protein in western blot analysis confirms the induction of apoptosis by these complexes.

Growth arrest of lung carcinoma cells (A549) by polyacrylate-anchored peroxovanadate by activating Rac1-NADPH oxidase signalling axis.

Hydrogen peroxide is often required in sublethal, millimolar concentrations to show its oxidant effects on cells in culture as it is easily destroyed by cellular catalase. Previously, we had shown that diperoxovanadate, a physiologically stable peroxovanadium compound, can substitute H2O2 effectively in peroxidation reactions. We report here that peroxovanadate when anchored to polyacrylic acid (PAPV) becomes a highly potent inhibitor of growth of lung carcinoma cells (A549). The early events associated with PAPV treatment included cytoskeletal modifications, increase in GTPase activity of Rac1, accumulation of the reactive oxygen species, and also increase in phosphorylation of H2AX (γH2AX), a marker of DNA damage. These effects persisted even at 24 h after removal of the compound and culminated in increased levels of p53 and p21 together with growth arrest. The PAPV-mediated growth arrest was significantly abrogated in cells pre-treated with the N-acetylcysteine, Rac1 knocked down by siRNA and DPI an inhibitor of NADPH oxidase. In conclusion, our results show that polyacrylate derivative of peroxovanadate efficiently arrests growth of A549 cancerous cells by activating the axis of Rac1-NADPH oxidase leading to oxidative stress and DNA damage.

Phospholipase C-γ2 via p38 and ERK1/2 MAP kinase mediates diperoxovanadate-asparagine induced human platelet aggregation and sCD40L release.

OBJECTIVE: Redox imbalance either inside platelets or in their immediate surroundings prove detrimental to their physiologic functions during haemostasis. This study was therefore aimed to assess the effect of peroxide radicals on platelet functions and underlying signalling mechanisms using asparagine-conjugated diperoxovanadate (DPV-Asn). METHODS: Platelet aggregation, ATP secretion, TxB2 release, intra-platelet calcium mobilization, protein tyrosine phosphorylation, GPIIbIIIa activation by PAC1 labelling and sCD40L release (enzyme-linked immunosorbent assay) was monitored using various concentrations of DPV-Asn. Cell viability was assessed by Annexin V labelling, MTT assay, LDH leakage and mitochondrial membrane potential by JC-1. RESULTS: Platelet aggregation induced by DPV-Asn was chiefly regulated by dense granule secretion, thromboxane A2 (TxA2) generation, intra-platelet [Ca(2+)] influx, GPIIbIIIa activation and sCD40L release, which were significantly reduced in presence of U73122 (PLC inhibitor), aspirin (COX), SB203580 (p38 inhibitor), and PD98059 (ERK inhibitor). This was further corroborated by enhanced tyrosine phosphorylation of numerous platelet proteins including PLC-γ2, which apparently played a central role in transducing peroxide signals to regulate [Ca(2+)] influx and phosphorylation of p38 and ERK1/2 MAP kinase. DISCUSSION: Peroxide radicals critically regulate the thrombo-inflammatory functions of platelets via the PLCγ2-p38-ERK1/2-TxA2 pathway, which closely resembles the clinical scenario of various pathologies like hyperglycemia and atherosclerosis during which oxidative stress disrupts platelet functions.

Physical and biophysical characteristics of nanoscale tungsten oxide particles and their interaction with human genomic DNA.

Nanoscale tungsten oxide (WO3) particles were synthesized via a user-friendly solvothermal cum reduction route using sodium tungstanate (Na2WO4) and cetyl trimethyl ammonium bromide (C19H42NBr) as reactants. The X-ray diffraction and transmission electron microscopy studies have revealed monoclinic phase of WO3 with an average crystallite size of 40 nm and competitive crystallographic orientation along (002), (020), (200) planes. After extracting human genomic DNA from human blood by a standard protocol (Qiagen-Kit method), they were conjugated with nanoscale WO3 particles in varying molar concentrations. The biophysical interaction of DNA bound nanoparticles were characterized by Fourier transform infra-red spectroscopy, photoluminescence spectroscopy, agarose gel-electrophoresis and polymerase chain reaction. Understanding physical and biophysical aspects of unconjugated and DNA conjugated WO3 would provide scope for biosensing applications.

Polymer-anchored peroxo compounds of vanadium(V) and molybdenum(VI): synthesis, stability, and their activities with alkaline phosphatase and catalase.

We generated a series of new polymer-bound peroxo complexes of vanadium(V) and molybdenum(VI) of the type [VO(O(2))(2)(sulfonate)]-PSS [PSS = poly(sodium 4-styrene sulfonate)] (PV(3)), [V(2)O(2)(O(2))(4)(carboxylate)VO(O(2))(2)(sulfonate)]-PSSM [PSSM = poly(sodium styrene sulfonate-co-maleate)] (PV(4)), [Mo(2)O(2)(O(2))(4)(carboxylate)]-PA [PA = poly(sodium acrylate)] (PMo(1)), [MoO(O(2))(2)(carboxylate)]-PMA [PMA = poly(sodium methacrylate)] (PMo(2)), and [MoO(O(2))(2)(amide)]-PAm [PAm = poly(acrylamide)] (PMo(3)) by reacting V(2)O(5) (for PV(3) and PV(4)) or H(2)MoO(4) (for PMo(1), PMo(2), and PMo(3)) with H(2)O(2) and the respective water-soluble macromolecular ligand at pH 5-6. The compounds were characterized by elemental analysis (CHN and energy-dispersive X-ray spectroscopy), spectral studies (UV-vis, IR, (13)C NMR, (51)V NMR, and (95) Mo NMR), thermal (TGA) as well as scanning electron micrographs (SEM), and EDX analysis. It has been demonstrated that compounds retain their structural integrity in solutions of a wide range of pH values and are approximately 100 times weaker as substrate to the enzyme catalase relative to H(2)O(2), its natural substrate. The effect of the title compounds, along with previously reported compounds [V(2)O(2)(O(2))(4)(carboxylate)]-PA (PV(1)) and [VO(O(2))(2)(carboxylate)]-PMA (PV(2)) on rabbit intestine alkaline phosphatase (ALP) has been investigated and compared with the effect induced by the free diperoxometallates viz. Na[VO(O(2))(2)(H(2)O)] (DPV), [MoO(O(2))(2)(glycine)(H(2)O)] (DMo(1)), and [MoO(O(2))(2)(asparagine)(H(2)O)] (DMo(2)). It has been observed that although all the compounds tested are potent inhibitors of the enzyme, the polymer-bound and neat complexes act via distinct mechanisms. Each of the macromolecular compounds is a classical noncompetitive inhibitor of ALP. In contrast, the action of neat pV and heteroligand pMo compounds on the enzyme function is consistent with a mixed type of inhibition.

Vasomodulatory effect of novel peroxovanadate compounds on rat aorta: Role of rho kinase and nitric oxide/cGMP pathway.

The present study was undertaken to assess the role of reactive oxygen species (ROS) in rat aortic ring vasoreactivity and integrity by using various peroxovanadate (pV) compounds. All the pV compounds (1nM-300 µM) used in the present study exerted concentration-dependent contractions on endothelium intact rat aortic rings. All compounds with an exception of DPV-asparagine (DPV-asn) significantly altered vascular integrity as shown by diminished KCl responses. Phenylephrine (PE)-mediated contractions (3nM-300 µM) were unaltered in the presence of these compounds. Acetylcholine (Ach)-mediated relaxation in PE (1µM) pre-contracted rings was significantly reduced in presence of diperoxovanadate (DPV), poly (sodium styrene sulfonate-co-maleate)-pV (PSS-CoM-pV) and poly (sodium styrene 4-sulfonate)-pV (PSS-pV). However, no significant change in Ach-mediated responses was observed in the presence of poly (acrylate)-pV (PAA-pV) and DPV-asn. DPV-asn was thus chosen to further elucidate mechanism involved in peroxide mediated modulation of vasoreactivity. DPV-asn (30nM - 300 µM) exerted significantly more stable contractions, that was found to be catalase (100U/ml) resistant in comparison with H(2)O(2) (30nM-300 µM) in endothelium intact aortic rings. These contractile responses were found to be dependent on extracellular Ca(2+) and were significantly inhibited in presence of ROS scavenger N-acetylcysteine (100 µM). Intracellular calcium chelation by BAPTA-AM (10µM) had no significant effect on DPV-asn (30nM-300 µM) mediated contraction. Pretreatment of aortic rings by rho-kinase inhibitor Y-27632 (10µM) significantly inhibited DPV-asn-mediated vasoconstriction indicating role of voltage-dependent Ca(2+) influx and downstream activation of rho-kinase. The small initial relaxant effect obtained on addition of DPV-asn (30nM-1 µM) in PE (1 µM) pre-contracted endothelium intact rings, was prevented in the presence of guanylate cyclase inhibitor, methylene blue (10 µM) and/or nitric oxide synthase (NOS) inhibitor, l-NAME (100 µM) suggesting involvement of nitric oxide and cGMP. DPV-asn, like H(2)O(2), exerted a response of vasoconstriction in normal arteries and vasodilation at low concentrations (30nM-1 µM) in PE-pre contracted rings with overlapping mechanisms. These findings suggest usefulness of DPV-asn having low toxicity, in exploring the peroxide-mediated effects on various vascular beds. The present study also convincingly demonstrates role of H(2)O(2) in the modulation of vasoreactivity by using stable peroxide DPV-asn and warrants future studies on peroxide mediated signaling from a newer perspective.

Sub-optimal dose of Sodium Antimony Gluconate (SAG)-diperoxovanadate combination clears organ parasites from BALB/c mice infected with antimony resistant Leishmania donovani by expanding antileishmanial T-cell repertoire and increasing IFN-gamma to IL-10 ratio.

We demonstrate that the combination of sub-optimal doses of Sodium Antimony Gluconate (SAG) and the diperoxovanadate compound K[VO(O2)2(H2O)], also designated as PV6, is highly effective in combating experimental infection of BALB/c mice with antimony resistant (Sb(R)) Leishmania donovani (LD) as evident from the significant reduction in organ parasite burden where SAG is essentially ineffective. Interestingly, such treatment also allowed clonal expansion of antileishmanial T-cells coupled with robust surge of IFN-c and concomitant decrease in IL-10 production. The splenocytes from the treated animals generated significantly higher amounts of IFN-c inducible parasiticidal effector molecules like superoxide and nitric oxide as compared to the infected group. Our study indicates that the combination of sub-optimal doses of SAG and PV6 may be beneficial for the treatment of SAG resistant visceral leishmaniasis patients.

Kinetics of inhibition of rabbit intestine alkaline phosphatase by heteroligand peroxo complexes of vanadium(V) and tungsten(VI).

The present work was undertaken to examine and compare some biologically important properties of peroxo compounds of V(V) and W(VI) containing biogenic species as ancillary ligand. New anionic peroxovanadate(V) complex of the type Na[VO(O(2))(2)(triglycine)].3H(2)O (pV1) and a molecular peroxotungstate(VI) [WO(O(2))(2)(triglycine)].3H(2)O (pW1) were synthesized and characterized for the purpose and their stability in solution was ascertained. Studies on kinetics of inhibition of alkaline phosphatase activity by the newly synthesized compounds and series of dipeptide and amino acid containing peroxo complexes of vanadium and tungsten synthesized previously by us viz., Na[VO(O(2))(2)(gly-gly)(H(2)O)].H(2)O (gly-gly = glycyl-glycine), Na[VO(O(2))(2)(asn)].H(2)O (asn = asparagine), Na[VO(O(2))(2)(gln)].H(2)O (gln = glutamine), and [WO(O(2))(2)(gly-gly)(H(2)O)].3H(2)O, revealed that each of these species is a potent mixed-type inhibitor of the enzyme. Significant difference was noted between the peroxovanadium (pV) and peroxotungsten (pW) compounds in terms of their oxidant activity with reduced glutathione.

Mononuclear and dinuclear peroxotungsten complexes with co-ordinated dipeptides as potent inhibitors of alkaline phosphatase activity.

New molecular peroxotungstate(VI) complexes with dipeptides as ancillary ligands of the type, [WO(O(2))(2)(dipeptide)(H(2)O)].3H(2)O, dipeptide = glycyl-glycine or glycyl-leucine, have been synthesized and characterized by elemental analysis, spectral and physico-chemical methods including thermal analysis. The complexes contain side-on bound peroxo groups and a peptide zwitterion bonded to the metal centre unidentately through an O(carboxylate) atom. Investigations on certain biologically important key properties of these compounds and a set of dimeric compounds in analogous co-ligand environment, Na(2)[W(2)O(3)(O(2))(4)(dipeptide)(2)].3H(2)O, dipeptide = glycyl-glycine and glycyl-leucine, reported previously by us revealed interesting features of the compounds. Each of the compounds despite having a 7 co-ordinated metal centre exerts a strong inhibitory effect on alkaline phosphatase activity with a potency higher than that of the free dipeptide, tungstate or peroxotungstate. The compounds exhibit remarkable stability in solutions of acidic as well as physiological pH and are weaker as substrate to the enzyme catalase, compared to H(2)O(2). The mononuclear and dinuclear peroxotungsten compounds are efficient oxidants of reduced glutathione (GSH), a reaction in which only one of the peroxo groups of a diperoxotungsten moiety of the complexes was found to be active.

New oxo-bridged peroxotungsten complexes containing biogenic co-ligand as potent inhibitors of alkaline phosphatase activity.

Novel dinuclear peroxo complexes of tungsten with coordinated cystine of the type A(2)[W(2)O(3)(O(2))(4)(cystine)].4H(2)O, A = Na (1) or K (2) have been synthesized from the reaction of A(2)WO(4,)cysteine and 30% H(2)O(2)at pH 2.5. The synthesized compounds were characterized by elemental analysis, spectral and physico-chemical methods. The two W(VI) centres with side-on bound peroxo groups of the dinuclear complex species are bridged by an oxo group and a cystine ligand, formed from the oxidation of cysteine. Cystine occurring as zwitterion binds the metal centers of the complex ion through O(carboxylate) atoms leading to hepta co-ordination around each W(VI). The compounds exhibit high stability toward decomposition in solution of acidic as well as physiological pH and serve as weak substrates to catalase, undergoing degradation in presence of the enzyme at a rate much slower relative to H(2)O(2). The compounds efficiently oxidized GSH to GSSG, a reaction in which only two of the peroxide groups of the complex species were found to participate. The compounds induce strong inhibitory effect on alkaline phosphatase activity with a potency higher than that of the free cystine, tungstate, or peroxotungstate.

Peroxo-bridged divanadate as selective bromide oxidant in bromoperoxidation.

Diperoxovanadate is effective only in presence of free vanadate in vanadium-dependent bromoperoxidation at physiological pH. Peroxide in the form of bridged divanadate complex (VOOV-type), but not the bidentate form as in diperoxovanadate, is proposed to be the oxidant of bromide. In order to obtain direct evidence, peroxo-divanadate complexes with glycyl-glycine, glycyl-alanine and glycyl-asparagine as heteroligands were synthesized. By elemental analysis and spectral studies they were characterized to be triperoxo-divanadates, [V2O,(O2)3(peptide)3] x H2O, with the two vanadium atoms bridged by a peroxide and a heteroligand. The dipeptide seems to stabilize the peroxo-bridge by inter-ligand interaction, possibly hydrogen bonding. This is indicated by rapid degradation of these compounds on dissolving in water with partial loss of peroxide accompanied by release of bubbles of oxygen. The 51V-NMR spectra of such solutions showed diperoxovanadate and decavanadate (oligomerized from vanadate) as the products. Additional oxygen was released on treating these solutions with catalase as expected of residual diperoxovanadate. The solid compounds when added to the reaction mixtures showed transient, rapid bromoperoxidation reaction, but not oxidation of NADH or inactivation of glucose oxidase, the other two activities shown by a mixture of diperoxovanadate and vanadyl. This demonstration of peroxide-bridged divanadate as a powerful, selective oxidant of bromide, active at physiological pH, should make it a possible candidate of mimic in the action of vanadium in bromoperoxidase proteins.