Polymer-Anchored Peroxo Compounds of Vanadium(V) and Molybdenum(VI): Synthesis, Stability, and Their Activities with Alkaline Phosphatase and Catalase

Therapeutic Properties of Vanadium Complexes

Vanadium is a hard, silver-grey transition metal found in at least 60 minerals and fossil fuel deposits. Its oxide and other vanadium salts are toxic to humans, but the toxic effects depend on the vanadium form, dose, exposure duration, and route of intoxication. Vanadium is used by some life forms as an active center in enzymes, such as the vanadium bromoperoxidase of ocean algae and nitrogenases of bacteria. The structure and biochemistry of vanadate resemble those of phosphate, hence vanadate can be regarded as a phosphate competitor in a variety of biochemical enzymes such as kinases and phosphatases. In this review, we describe the biochemical pathways regulated by vanadium compounds and their potential therapeutic benefits for a range of disorders including type 2 diabetes, cancer, cardiovascular disease, and microbial pathology.

Oxoperoxovanadium Complexes of Hetero Ligands: X-Ray Crystal Structure, Density Functional Theory, and Investigations on DNA/BSA Interactions, Cytotoxic, and Molecular Docking Studies

Oxoperoxovanadium (V) complexes [VO (O)₂ (nf) (bp)] (1) and [VO (O)₂ (ox) (bp)] (2) based on 5-nitro-2-furoic acid (nf), oxine (ox) and 2, 2′ bipyridine (bp) bidentate ligands have been synthesized and characterized by FT-IR, UV-visible, mass, and NMR spectroscopic techniques. The structure of complex 2 shows distorted pentagonal-bipyramidal geometry, as confirmed by a single-crystal XRD diffraction study. The interactions of complexes with bovine serum albumin (BSA) and calf thymus DNA (CT-DNA) are investigated using UV-visible and fluorescence spectroscopic techniques. It has been observed that CT-DNA interacts with complexes through groove binding mode and the binding constants for complexes 1 and 2 are 8.7 × 10³ M⁻¹ and 8.6 × 10³ M⁻¹, respectively, and BSA quenching constants for complexes 1 and 2 are 0.0628 × 10⁶ M⁻¹ and 0.0163 × 10⁶ M⁻¹, respectively. The ability of complexes to cleave DNA is investigated using the gel electrophoresis method with pBR322 plasmid DNA. Furthermore, the cytotoxic effect of the complexes is evaluated against the HeLa cell line using an MTT assay. The complexes are subjected to density functional theory calculations to gain insight into their molecular geometries and are in accordance with the results of docking studies. Furthermore, based on molecular docking studies, the intermolecular interactions responsible for the stronger binding affinities between metal complexes and DNA are discussed.

Enhanced oxygen transfer over bifunctional Mo-based oxametallacycle catalyst for epoxidation of propylene

Activation of inert propylene to produce propylene oxide (PO) is critical, but still faces some challenges in realizing higher PO selectivity and productivity. Herein, a temperature-controlled phase transfer catalyst (MoOO·DMF) is prepared for the liquid-phase epoxidation of propylene with tert-butyl hydroperoxide (TBHP) as oxidant, which exhibit the selectivity of 90.6% and the productivity of 1286.42·h^-1 for PO (catalyst/propylene = 0.77 mol‰). Some experimental factors (solvent types, reaction temperature, contact time, the dosage of catalyst, TBHP and substrate) were investigated, and the reaction kinetics and thermodynamics are discussed. MoOO·DMF has the characteristic of both homogeneous and heterogeneous catalysts, which can be dissolved in the solvent at higher temperatures and separated from the solvent after reaction by lowering the temperature. Importantly, MoOO·DMF has a wonderful epoxidation performance for many olefins (e.g., light olefins, linear α-olefins, cyclic olefins and others). The mechanisms are proved by in-situ FT-IR, ESR and HRMS spectrum to be the selective oxygen transfer from tert-butyl peroxide radical and the MoOO bridge in MoOO·DMF to propylene. Density functional theory (DFT) calculations show that the MoOO bridge in catalyst is the key role for the activation of both the OH bond in TBHP and the CC bond in propylene, thus enhanced the epoxidation of propylene.

Tantalum(v) peroxido complexes as phosphatase inhibitors: a comparative study vis-a-vis peroxidovanadates

Peroxido Ta(v) complexes are found to be more effective as inhibitors of wheat thylakoid acid phosphatase vis-à-vis their V containing analogues. In addition, these compounds showed unique resistance towards degradation in the presence of catalase.

Ionic-liquid-modified CMK-3 as a support for the immobilization of molybdate ions (MoO42-): Heterogeneous nanocatalyst for selective oxidation of sulfides and benzylic alcohols

A nanometric carbon CMK-3 modified with octylimidazolium ionic liquid and MoO₄^2- as a new hybrid catalyst was synthesized. The study is the first to report a successful immobilization of MoO₄⁼ on the CMK-3/OctIm as a hybrid nanocatalyst. A variety of analytical methods were utilized to determine the properties of the structure and morphology of the synthesized nanocatalyst [CMK-3/Im/MoO₄^2-]. The analytical techniques were transmission electron microscopy (TEM), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP), X-ray diffraction (XRD), N₂ isotherms (BET), IR spectroscopy and thermogravimetric analysis (TGA). CMK-3/OctIm/MoO₄^2- hybrid catalyst demonstrated a considerable catalytic activity. It is a recyclable nanocatalyst that is utilized to chemoselectively oxidize different types of sulfides to the corresponding sulfoxides and benzylic alcohols to aldehydes using the green oxidant, hydrogen peroxide (H₂O₂) in high-yields. With a little leaching and variation in activity, it is possible to recover and reuse the catalyst frequently. A combination of molybdate anion and the CMK-3 order mesoporous carbon resulted in an improvement in the performance of catalysis and ease of separation for the reaction procedure.

Polymer immobilized tantalum(v)–amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

Polymer supported peroxotantalate based heterogeneous catalysts served as highly efficient, selective and recyclable catalysts for alkene epoxidation and sulfide oxidation with green oxidant aqueous H₂O₂ under mild reaction conditions.

In vitroexperiments and infrared spectroscopy analysis of acid and alkaline phosphatase inhibition by vanadium complexes

Two oxidovanadium complexes with 4-aminobenzoic acid and/or the peroxo anion as ligands were synthesized and characterized by elemental analysis, conductivity measurements, TGA/DTA,¹H NMR, EPR, FTIR, and UV/vis spectroscopies.

Solventless, selective and catalytic oxidation of primary, secondary and benzylic alcohols by a Merrifield resin supported molybdenum(vi) complex with H2O2 as an oxidant

Here, we have described the synthesis, characterization and catalytic activity of a dioxo-molybdenum(vi) complex supported on functionalized Merrifield resin (MR-SB-Mo). The functionalization of Merrifield resin (MR) was achieved in two-steps viz. carbonylation (MR-C) and Schiff base formation (MR-SB). The compounds, MR-C, MR-SB and MR-SB-Mo, were characterized at each step of the synthesis by elemental, SEM, EDX, thermal, BET and different spectroscopic analysis. The catalyst, MR-SB-Mo, efficiently and selectively oxidized a wide variety of alcohols to aldehydes or ketones using 30% H₂O₂ as an oxidant with reasonably good TOF (660 h⁻¹ in case of benzyl alcohol). The catalyst acted heterogeneously under solventless reaction conditions and did not lead to over oxidized products under optimized conditions. The catalyst afforded regeneration and can be reused for at least five reaction cycles without loss of efficiency and product selectivity. A reaction mechanism for the catalytic activity of MR-SB-Mo was proposed and a probable reactive intermediate species isolated.

Synthesis of a Merrifield resin supported dioxomolybdenum(vi) complex. The compound was well characterized and it catalysed the oxidation of alcohols to aldehydes or ketones with high TOF.

Portraying the role of halo ligands and the auxiliary part of ligands of mononuclear manganese(iii)-Schiff base complexes in catalyzing phospho–ester bond hydrolysis

The influences of the auxiliary part of ligands and halo ligands have been explored towards phosphatase like activity using a series of manganese(iii)-Schiff base complexes as catalysts.

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.

Peroxoniobium(v)-catalyzed selective oxidation of sulfides with hydrogen peroxide in water: a sustainable approach

Facile and selective transformation of thioethers to the corresponding sulfoxides or sulfones with 30% H₂O₂ has been achieved in an aqueous medium by using peroxoniobium(v) complexes as reusable catalysts.

Polyoxometalates as potent and selective inhibitors of alkaline phosphatases with profound anticancer and amoebicidal activities

The biological significance of polyoxometalates is well renowned owing to their anticancer, antiviral and antibiotic properties. Here another therapeutic aspect of polyoxometalates has been explored as alkaline phosphatase inhibitors along with the remarked anticancer and amoebicidal properties. Synthesis and inhibitory studies of a set of seven polyoxotungstates against two major isozymes of alkaline phosphatase i.e. tissue specific and tissue non-specific alkaline phosphatase revealed their promising activity as alkaline phosphatase inhibitors. All compounds exhibited alkaline phosphatase inhibitory potency in nanomolar ranges. For tissue specific alkaline phosphatase, Na(10)[H(2)W(12)O(42)]·27H(2)O (A6) was found to be the most potent inhibitor (K(i) value 313 ± 7 nM), while for tissue non-specific alkaline phosphatase Na(33)[H(7)P(8)W(48)O(184)]·92H(2)O (A3) showed the highest inhibition potency (K(i) values 135 ± 10 nM). Moreover cytotoxicity evaluation of these compounds against lung carcinoma cells and immortalized human corneal epithelial cells demonstrated their anticancer potential with no cytotoxic effects on normal human cell lines. All anticancer drugs result in an impaired immune system and such immunocompromised persons become vulnerable to opportunistic infections specially Acanthamoeba which causes granulomatous amoebic encephalitis (GAE) which almost always results in death. The exclusive property of our tested polyoxotungstates is their strong amoebicidal activity against Acanthamoeba. Hence the study reveals a new window towards cancer therapy with the combined control of elevated levels of alkaline phosphatase and granulomatous amoebic encephalitis in cancer patients.