title: Vanadium complexes having [V(IV)O](2+) and [V(V)O(2)](+) cores with binucleating dibasic tetradentate ligands: Synthesis, characterization, catalytic and antiamoebic activities.
abstract: Binucleating hydrazones CH(2)(H(2)sal-bhz)(2) (I) and CH(2)(H(2)sal-fah)(2) (II), derived from 5,5'-methylbis(salicylaldehyde) and benzoylhydrazide or 2-furoylhydrazide, react with [V(IV)O(acac)(2)] to give dinuclear V(IV)O-complexes [CH(2){V(IV)O(sal-bhz)(H(2)O)}(2)] 1 and [CH(2){V(IV)O(sal-fah)(H(2)O)}(2)] 4, respectively. In the presence of KOH or CsOH.H(2)O, oxidation of 1 and 2 results in the formation of dioxidovanadium(v) complexes, K(2)[CH(2){V(V)O(2)(sal-bhz)}(2)].2H(2)O 2, K(2)[CH(2){V(V)O(2)(sal-fah)}(2)].2H(2)O 5, Cs(2)[CH(2){V(V)O(2)(sal-bhz)}(2)].2H(2)O 3 and Cs(2)[CH(2){V(V)O(2)(sal-fah)}(2)].2H(2)O 6. These complexes have also been prepared by aerial oxidation of in situ prepared oxidovanadium(iv) complexes 1 and 4. The compounds were characterized by IR, electronic, EPR, (1)H, (13)C and (51)V NMR spectroscopy, elemental analyses and thermogravimetric patterns. Single crystal X-ray analysis of 3 confirms the coordination of the ligand in the dianionic (ONO(2-)) enolate tautomeric form. The V(V)O(2)-complexes were used to catalyze the oxidative bromination of salicylaldehyde, therefore acting as functional models of vanadium dependent haloperoxidases, in aqueous H(2)O(2)/KBr in the presence of HClO(4) at room temperature. It is shown that the V(IV)O-complexes [CH(2){V(IV)O(sal-bhz)(H(2)O)}(2)] 1 and [CH(2){V(IV)O(sal-fah)(H(2)O)}(2)] 4 are catalyst precursors for the catalytic oxidation of organic sulfides using aqueous H(2)O(2). Plausible intermediates involved in these catalytic processes are established by UV-Vis, EPR and (51)V NMR studies. The vanadium complexes along with ligands I and II are also screened against HM1:1MSS strains of Entamoeba histolytica, the results showing that the IC(50) values of compounds 3 and 6 are lower than that of metronidazole. The toxicity studies against human cervical (HeLa) cancer cell line also showed that although compounds 3 and 6 are more toxic than metronidazole towards this cell line, the corresponding IC(50) values are relatively high, the cell viability therefore not being much affected.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247 667, India. rkmanfcy@iitr.ernet.in
authors.forename: Mannar R
authors.initials: MR
authors.lastname: Maurya
authors.forename: Aftab Alam
authors.initials: AA
authors.lastname: Khan
authors.forename: Amir
authors.initials: A
authors.lastname: Azam
authors.forename: Samir
authors.initials: S
authors.lastname: Ranjan
authors.forename: Neelima
authors.initials: N
authors.lastname: Mondal
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.forename: Fernando
authors.initials: F
authors.lastname: Avecilla
authors.forename: João Costa
authors.initials: JC
authors.lastname: Pessoa
mesh_terms: D000981:Antiprotozoal Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D006367:HeLa Cells; D006801:Humans; D006835:Hydrazones / Q000737:chemistry; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet; D014639:Vanadium / Q000737:chemistry*
chemical_list: D000981:Antiprotozoal Agents; D056831:Coordination Complexes; D006835:Hydrazones; D008024:Ligands; D014639:Vanadium