Synthesis, Characterization, Reactivity, and Catalytic Potential of Model Vanadium(IV, V) Complexes with Benzimidazole-Derived ONN Donor Ligands

Oxidovanadium(V) Schiff Base Complexes Derived from Chiral 3-amino-1,2-propanediol Enantiomers: Synthesis, Spectroscopic Studies, Catalytic and Biological Activity

Oxidovanadium(V) complexes, [(+)VOL1-5] and [(-)VOL1-5], with chiral tetradentate Schiff bases, which are products of monocondensation of S(‒)-3-amino-1,2-propanediol or R(+)-3-amino-1,2-propanediol with salicylaldehyde derivatives, have been synthesized. Different spectroscopic methods, viz. 1H and 51V NMR, IR, UV-Vis, and circular dichroism, as well as elemental analysis, have been used for their detailed characterization. Furthermore, the epoxidation of styrene, cyclohexene, and two monoterpenes, S(‒)-limonene and (‒)-α-pinene, using two oxidants, aqueous 30% H2O2 or tert-butyl hydroperoxide (TBHP) in decane, has been studied with catalytic amounts of all complexes. Finally, biological cytotoxicity studies have also been performed with these oxidovanadium(V) compounds for comparison with cis-dioxidomolybdenum(VI) Schiff base complexes with the same chiral ligands, as well as to determine the cytoprotection against the oxidative damage caused by 30% H2O2 in the HT-22 hippocampal neuronal cells in the range of their 10-100 μM concentration.

Synthesis, Spectroscopic Characterization, Catalytic and Biological Activity of Oxidovanadium(V) Complexes with Chiral Tetradentate Schiff Bases

New oxidovanadium(V) complexes, VOL1-VOL10, with chiral tetradentate Schiff bases obtained by monocondensation reaction of salicylaldehyde derivatives with 1S,2S-(+)-2-amino-1-(4-nitrophenyl)-1,3-propanediol. All complexes have been characterized using different spectroscopic methods, viz. IR, UV-Vis, circular dichroism, one- (1H, 51V) and two-dimensional (COSY, NOESY) NMR spectroscopy, and elemental analysis. Furthermore, the catalytic ability of all compounds in the epoxidation of styrene, cyclohexene, and its naturally occurring monoterpene derivatives, i.e., S(-)-limonene and (-)-α-pinene has also been studied, using two different oxidants, i.e., aqueous 30% H2O2 or tert-butyl hydroperoxide (TBHP). In addition, the biological properties of these chiral oxidovanadium(V) compounds, but also cis-dioxidomolybdenum(VI) complexes with the same chiral Schiff bases, were studied. Their cytotoxic and cytoprotective activity studies with the HT-22 hippocampal neuronal cells revealed a concentration-dependent effect in the range of 10-100 μM. Moreover, vanadium(V) complexes, in contrast to cis-dioxidomolybdenum(VI) compounds, demonstrated higher cytotoxicity and lack of cytoprotective ability against H2O2-induced cytotoxicity.

Polymer-Supported Dioxidovanadium(V) Complex-Based Heterogeneous Catalyst for Multicomponent Biginelli Reaction Producing Biologically Active 3,4-Dihydropyrimidin-2-(1H)-ones

Dioxidovanadium(V) complex [VVO2(sal-aebmz)] (1) (where Hsal-aebmz = Schiff base derived from the condensation of salicylaldehyde and 2-aminoethylbenzimidazole) has been immobilized on chloromethylated polystyrene (PS-Cl) cross-linked with divinylbenzene to obtain [VVO2(sal-aebmz)]@PS (2), a heterogeneous complex. Both complexes, after characterization, have been used as catalysts to explore a single pot multicomponent (benzaldehyde or its derivatives, urea and ethyl acetoacetate) Biginelli reaction producing biologically active 3,4-dihydropyrimidin-2-(1H)-one (DHPM)-based biomolecules under solvent-free conditions in the presence of H2O2 as a green oxidant. Various reaction conditions such as amounts of catalyst and oxidant, temperature, time, and solvent have been optimized to obtain the maximum yield of DHPMs. The polymer-immobilized complex has been found to show excellent catalytic activity, giving ca. 95% yield of DHPMs under the optimized reaction conditions selectively. Oxidant plays an important role in enhancing the yield of DHPMs.

Mononuclear/Binuclear [VIVO]/[VVO2] Complexes Derived from 1,3-Diaminoguanidine and Their Catalytic Application for the Oxidation of Benzoin via Oxygen Atom Transfer

Ligands H₄sal-dag (I) and H₄Brsal-dag (II) derived from 1,3-diaminoguanidine and salicylaldehyde or 5-bromosalicylaldehyde react with one or 2 mol equivalent of vanadium precursor to give two different series of vanadium complexes. Thus, complexes [V^IVO(H₂sal-dag) (H₂O)] (1) and [V^IVO(H₂Brsal-dag) (H₂O)] (2) were isolated by the reaction of an equimolar ratio of these ligands with [V^IVO(acac)₂] in MeOH. In the presence of K⁺/Cs⁺ ion and using aerially oxidized [V^IVO(acac)₂], the above reaction gave complexes [K(H₂O){V^VO₂(H₂sal-dag)}]₂ (3), [Cs(H₂O){V^VO₂(H₂sal-dag)}]₂ (4), [K(H₂O){VO₂(H₂Brsal-dag)}]₂ (5), and [Cs(H₂O){V^VO₂(H₂Brsal-dag)}]₂ (6), which could also be isolated by direct aerial oxidation of complexes 1 and 2 in MeOH in the presence of K⁺/Cs⁺ ion. Complexes [(H₂O)V^IVO(Hsal-dag)V^VO₂] (7) and [(H₂O)V^IVO(HBrsal-dag)V^VO₂] (8) were isolated upon increasing the ligand-to-vanadium precursor molar ratio to 1:2 under an air atmosphere. When I and II were reacted with aerially oxidized [V^IVO(acac)₂] in a 1:2 molar ratio in MeOH in the presence of K⁺/Cs⁺ ion, they formed [K(H₂O)₅{(V^VO₂)₂(Hsal-dag)}]₂ (9), [Cs(H₂O)₂{(V^VO₂)₂(Hsal-dag)}]₂ (10), [K₂(H₂O)₄{(V^VO₂)₂(Brsal-dag)}]₂ (11), and [Cs₂(H₂O)₄{(V^VO₂)₂(Brsal-dag)}]₂ (12). The structures of complexes 3, 4, 5, and 9 determined by single-crystal X-ray diffraction study confirm the mono-, bi-, tri-, and tetra-anionic behaviors of the ligands. All complexes were found to be an effective catalyst for the oxidation of benzoin to benzil via oxygen atom transfer (OAT) between DMSO and benzoin. Under aerobic condition, this oxidation also proceeds effectively in the absence of DMSO. Electron paramagnetic resonance and ⁵¹V NMR studies demonstrated the active role of a stable V(IV) intermediate during OAT between DMSO and benzoin.

Physicochemical, in-vitro therapeutic activity and biomolecular interaction studies of Mn(II), Ni(II) and Cu(II) complexes tethered with O2N2 ligand backbone

Two major health crisis of today's world are antimicrobial drug resistance and type II diabetes. To tackle them, there is an immediate requirement for the development of new and safer drugs and the present work is one such quest for novel and efficient drug candidates. We have developed three trace metal coordination compounds tethered with a reduced salen ligand {H₂(hpdbal)₂-an} (L), namely, a manganese-salan complex, [Mn^II(H₂O)₂{(hpdbal)₂-an}] (1), a nickel-salan complex, [Ni^II{(hpdbal)₂-an}] (2) and a copper-salan complex, [Cu^II{(hpdbal)₂-an}] (3). The compounds were characterized by elemental analysis, vibrational spectroscopy, electronic spectroscopy, thermogravimetric analysis, nuclear magnetic resonance and electron-paramagnetic resonance techniques. The compounds were evaluated for antimicrobial activity against seven pathogens (Escherichia coli, Klebsiella pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Cryptococcus neoformans) and antidiabetic activity by mimicking diabetic environment on the immortal human liver cancer cells, HepG2. Complexes 1 and 2 were additionally tested for their reactivity and stability in biological media mimic conditions. The nickel(II) salan complex (2) exhibited noteworthy antifungal activity against Candida albicans and the manganese(II) salan complex (1) induced increased glucose uptake by the insulin resistant cells. Both compounds were found to be stable when solution pH conditions were varied from 3 to 9. They exhibited strong affinity of binding towards a carrier protein, bovine serum albumin which was evaluated with the aid of multi-spectroscopic techniques.

In vitro apoptosis-induction, antiproliferative and BSA binding studies of a oxidovanadium(V) complex

In our ongoing efforts to develop novel trace metal complexes with therapeutically interesting properties, a neutral mono nuclear oxidomethoxidovanadium(V) complex, [V^VO(OCH₃)(hpdbal-sbdt)] (1) and a μ-O bridged dinuclear oxidovanadium(V) complex, [{V^VO(hpdbal-sbdt)}₂μ-O] (2) [H₂hpdbal-sbdt (I) is a tridentate and dibasic ONS^2- donor ligand obtained through the Schiff base reaction of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal) and S-benzyldithiocarbazate (Hsbdt)] have been synthesized and characterized by various analytical techniques such as TGA, EDS, ATR-IR, UV-Vis, CV, ¹H NMR, ¹³C NMR and ⁵¹V NMR. Single-crystal X-ray diffraction analysis of 1 confirms the coordination of phenolate oxygen, imine nitrogen and thioenolate sulfur of the ligand to the vanadium center with a distorted tetragonal-pyramidal geometry. The compound 2 triggered apoptotic and reproductive death of the cancer cells in vitro with 76% and 62% growth inhibition of human breast adenocarcinoma (MCF-7) and human lung carcinoma cells (A549) respectively. The compound 2 was found to be sufficiently stable over a wide window of physiological pH. The complex 2 was studied further for its interaction with a drug carrier protein BSA with the aid of spectroscopic techniques viz. fluorescence, temperature controlled UV-vis and deconvoluted IR techniques.

A novel biocompatible NiII tethered moiety as a glucose uptake agent and a hit against methicillin-resistant Staphylococcus aureus

In the efforts to develop a biocompatible transition metal complex as a drug alike for some of the prevailing non-communicable diseases (NCDs) and communicable diseases (CDs), a novel binuclear Ni^II compound [{Ni^II(hpdbal-sbdt)}₂] (2) has been synthesized by the reaction of Ni(OAc)₂.4H₂O and H₂hpdbal-sbdt (1) [1 is a dibasic tridentate ONS^2- donor Schiff base ligand obtained by the condensation of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal) and S-benzyldithiocarbazate (Hsbdt)]. Both ligand 1 and compound 2 were structurally characterized in the solid and solution state using various spectroscopic techniques like ATIR, ¹H NMR, ¹³C NMR, TGA, FESEM, EDS and CHNS analysis. The antidiabetic activity of H₂hpdbal-sbdt (1) and [{Ni^II(hpdbal-sbdt)}₂] (2) were assessed using 2-NBDG uptake assay. The assay results showed 85% and 95% of fluorescent glucose uptake by insulin resistant HePG2 cells treated with compounds 1 and 2 respectively. The 2-NBDG uptake by the cells treated with the compound 2 was observed to be comparable to the standard antidiabetic drug metformin. Compounds 1 and 2 were also tested against five bacterial and two fungi strains in order to evaluate pathogen killing activity. Compound 2 showed significant inhibitory action towards the methicillin-resistant Staphylococcus aureus (MRSA) strain with an MIC value of 2 μg/mL whereas the ligand 1 was found to be inactive. Furthermore, the interactive nature of compound 2 with a model serum carrier protein bovine serum albumin (BSA) was studied using a multi-spectroscopic approach which provided an insight into the nature and extent of binding, conformational changes and the quenching of amino acid residues of the protein.

A dioxidovanadium (V) complex of NNO-donor Schiff base as a selective inhibitor of protein tyrosine phosphatase 1B: Synthesis, characterization, and biological activities

A new dioxidovanadium (V) complex, VO₂(HPPCH) (1) (H₂PPCH = N'-picolinoylpyridin-1-ium-2-carbohydrazonate) has been synthesized and characterized by elemental analysis, IR, X-ray diffraction analysis and electrospray ionization mass spectra. Complex 1 crystallized in the monoclinic system with space group P2₁/c. It potently inhibited PTP1B with IC₅₀ of 0.13 μM, about 7, 15 and 125-fold stronger against PTP1B than over TCPTP, SHP-1 and SHP-2, displaying obvious selectivity against PTP1B. Western blotting analysis indicated that complex 1 effectively increased the phosphorylation of PTP1B substrates, especially the phosphorylation of IR/IGF 1R and IRS-1. It exhibited lower cytotoxicity than positive control VOSO₄. These results make complex 1 a promising candidate for novel anti-diabetic drug development.

Syntheses and characterization of monobasic tridentate Cu(ii) Schiff-base complexes for efficient oxidation of 3,5-di-tert-butylcatechol and oxidative bromination of organic substrates

Enhanced bifunctional catalytic activities are shown by monobasic tridentate Cu(ii) Schiff-base complexes.

Oxidation of phenyl propyne catalyzed by copper(II) complexes of a benzimidazolyl schiff base ligand: effect of acid/base, oxidant, surfactant and morphology

Copper(II) complexes with a new N-Substituted benzimidazolyl schiff base ligand are used as catalyst for the oxidation of 1-phenyl propyne. The oxidation is carried out under mild conditions using stoichiometric amounts of oxidant and catalytic amounts of Cu(II) complex as catalyst. Effect of acid/base, oxidant, morphology and surfactant has been studied. Two major products of phenyl propyne oxidation are the α-diketonic product and a terminal aldehyde. Diketone is the major product under acidic conditions while aldehyde formation is highest under basic conditions. The maximum conversion is found with the NO3(-) bound complex. GC-MS is used to find the percentage yields of products. SEM and PXRD of the reused complexes as catalyst suggest that morphology affects the catalytic efficiency.

A new metallate phase of V2O5 crystalline microstructure achieved in a facile route: synthesis, characterization, and measurement in catalytic reactions

Experiencing a series of complicated changes, abundant orange crystals of novel metallic phase of vanadium pentoxide were obtained by a mild chemical method, the formula of which is defined as [V3(μ3-O)2⋅(μ1-OH)⋅O5]⋅H2O. Differ from the synthesis methods of vanadium oxide published, we have adopted a simple solution method that mixed starting materials are refluxing in the system of ethanol-water under a relatively lower temperature. Symmetry of the crystals is Monoclinic, with cell unit dimensions: a=4.9978(10)Å, b=8.4273(17)Å, c=7.8669(16)Å, β=96.44(3)° and space group of P2₁/m. The structure of the complex was characterized by elemental analysis, IR, UV-vis spectroscopy and single-crystal diffraction analysis. Powder X-ray diffraction (PXRD) was used to detect the purity of the crystals, and crystal morphology was detected by the scanning electron microscope (SEM). In addition, in order to extend application of oxidovanadium complexes, bromination catalytic activity about the complex in a single-pot reaction of the conversion of phenol red to bromophenol blue in a mixed solution of H2O-DMF at a constant temperature of 30±0.5 °C with a buffer solution of NaH2PO4Na2HPO4 (pH=5.8) was evaluated firstly, indicating that the complex can be considered as a potential functional model of bromoperoxidase, in the meantime, we have conducted the bromination catalytic reaction to simulate and measure the changes in reaction process indirectly. Besides, catalytic oxidation activity of the complex is also evaluated in the oxidation of cyclohexane (Cy) and cyclopentane with hydrogen peroxide promoted under mild conditions, showing potential catalytic activity of the complex by comparing TON (total turnover number) ratios of CyO/CyOH (CyO is the abbreviation of cyclohexanone and CyOH represents cyclohexanol) in the oxidation results.

A novel one-dimensional chain built of vanadyl ions and pyrazine-2,5-dicarboxylate

Stand in line – a vanadium salt and a pyrazine ligand self-assemble to a linear coordination polymer.

Oxidovanadium(v) complexes of aroylhydrazones incorporating heterocycles: synthesis, characterization and study of DNA binding, photo-induced DNA cleavage and cytotoxic activities

The interaction of four neutral oxidovanadium(v) complexes with DNA and their cytotoxic activities have been reported.

Oxidovanadium(iv) and dioxidovanadium(v) complexes of hydrazones of 2-benzoylpyridine and their catalytic applications

V^V-polymer-supported compounds, their neat analogues and the corresponding peroxido-complexes are prepared and applied as catalyst precursors for the oxidation of isoeugenol.