The synthesis and structural characterization of two novel dioxomolybdenum(VI) (1) and dioxotungsten(VI) (2) complexes with 2-phenylacetylhydroxamic acid (PAHH) [M(O)2(PAH)2] [M = Mo, W] have been accomplished. The dioxomolybdenum(VI) and dioxotungsten(VI) moiety is coordinated by the hydroxamate group (-CONHO(-)) of the 2-phenylacetylhydroxamate (PAH) ligand in a bi-dentate fashion. In both the complexes the PAHH ligand is coordinated through oxygen atoms forming a five membered chelate. The hydrogen atom of N-H of the hydroxamate group is engaged in intermolecular H-bonding with the carbonyl oxygen of another coordinated hydroxamate ligand, thereby forming an extended 1D chain. The ligand as well as both the complexes exhibit the ability to protect from radiation induced damage both in CTDNA as well as in pUC19 plasmid DNA. As the damage to DNA is caused by the radicals generated during radiolysis, its scavenging imparts protection from the damage to DNA. To understand the mechanism of protection, binding affinities of the ligand and the complex with DNA were determined using absorption and emission spectral studies and viscosity measurements, whereby the results indicate that both the complexes and the hydroxamate ligand interact with calf thymus DNA in the minor groove. The intrinsic binding constants, obtained from UV-vis studies, are 7.2 × 10(3) M(-1), 5.2 × 10(4) M(-1) and 1.2 × 10(4) M(-1) for the ligand and complexes 1 and 2 respectively. The Stern-Volmer quenching constants obtained from a luminescence study for both the complexes are 5.6 × 10(4) M(-1) and 1.6 × 10(4) M(-1) respectively. The dioxomolybdenum(VI) complex is found to be a more potent radioprotector compared to the dioxotungsten(VI) complex and the ligand. Radical scavenging chemical studies suggest that the complexes have a greater ability to scavenge both the hydroxyl as well as the superoxide radicals compared to the ligand. The free radical scavenging ability of the ligand and the complexes was further established by EPR spectroscopy using a stable free radical, the DPPH, as a probe. The experimental results of DNA binding are further supported by molecular docking studies.
The synthesis and structural characterization of a novel oxoperoxovanadium(V) complex [VO(O(2))(PAH)(phen)] containing the ligands 2-phenylacetohydroxamic acid (PAHH) and 1,10-phenanthroline (phen) has been accomplished. The oxoperoxovanadium(V) complex was found to mimic both vanadate-dependent haloperoxidase (VHPO) activity as well as nuclease activity through effective interaction with DNA. The complex is the first example of a structurally characterized stable oxoperoxovanadium(V) complex with a coordinated bi-dentate hydroximate moiety (-CONHO(-)) from 2-phenylacetohydroximate (PAH). The oxoperoxovanadium(V) complex has been used as catalyst for the peroxidative bromination reaction of some unsaturated alcohols (e.g. 4-pentene-1-ol, 1-octene-3-ol and 9-decene-1-ol) in the presence of H(2)O(2) and KBr. The catalytic products have been characterized by GC-MS analysis and spectrophotometric methods. The DNA binding of this complex has been established with CT DNA whereas the DNA cleavage was demonstrated with plasmid DNA. The interactions of the complex with DNA have been monitored by electronic absorption and fluorescence emission spectroscopy. Viscometric measurements suggest that the compound is a DNA intercalator. The nuclease activity of this complex was confirmed by gel electrophoresis studies.
The two novel oxovanadium(V) complexes [VO(PyDC)(BHA)] (1) [PyDC = pyridine-2,6-dicarboxylate, BHA = benzohydroxamate] and [VO(PyDC)(BPHA)] (2) [BPHA = benzophenyl hydroxamate] were synthesized by successive addition of a methanolic solution of H2PyDC and the corresponding hydroxamic acid ligand to the aqueous solution of ammonium metavanadate (NH4VO3). The hydroxamic acid ligands were characterized by elemental analysis, IR, UV-vis and NMR studies whereas the complexes were characterized by IR, UV-vis, CHN, molar conductance, magnetic moment, mass and NMR spectroscopic methods. The structures of the complexes were determined by single crystal X-ray crystallography. The structures of both complexes reveal that vanadium(V) has distorted octahedral geometry. The bromoperoxidase activities of these complexes have been demonstrated through the activation of C-H bonds of phenol, o-cresol and p-cresol. The catalytic products have been characterized by GC-MS analysis which shows that good conversions have been achieved. So far as the catalytic efficiency of the complexes are concerned complex 2 is found to be superior to complex 1. Both the complexes were tested for DNA nuclease activity with pUC19 plasmid DNA. The results show that both of them exhibited nuclease activity against pUC19 circular plasmid DNA. The complexes produced both nicked coils and linear forms. In this case also it is observed that complex 2 shows better nuclease activity than complex 1.
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