A new dinuclear nickel(II) complex, [Ni(2)(LH(2))(H(2)O)(2)(OH)(NO(3))](NO(3))(3) (1), of an "end-off" compartmental ligand 2,6-bis(N-ethylpiperazine-iminomethyl)-4-methyl-phenolato, has been synthesized and structurally characterized. The X-ray single crystal structure analysis shows that the piperazine moieties assume the expected chair conformation and are protonated. The complex 1 exhibits versatile catalytic activities of biological significance, viz. catecholase, phosphatase, and DNA cleavage activities, etc. The catecholase activity of the complex observed is very dependent on the nature of the solvent. In acetonitrile medium, the complex is inactive to exhibit catecholase activity. On the other hand, in methanol, it catalyzes not only the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very difficult to oxidize, under aerobic conditions. UV-vis spectroscopic investigation shows that TCC oxidation proceeds through the formation of an intermediate. The intermediate has been characterized by an electron spray ionizaton-mass spectrometry study, which suggests a bidentate rather than a monodentate mode of TCC coordination in that intermediate, and this proposition have been verified by density functional theory calculation. The complex also exhibits phosphatase (with substrate p-nitrophenylphosphate) and DNA cleavage activities. The DNA cleavage activity exhibited by complex 1 most probably proceeds through a hydroxyl radical pathway. The bioactivity study suggests the possible applications of complex 1 as a site specific recognition of DNA and/or as an anticancer agent.

No abstract

No abstract

No abstract

3 ] (3), (where L 1 = 2,6-bis(N-ethylpyrrolidineiminomethyl)-4-methylphenolato, L 2 = 2,6-bis(N-ethylpiperidineiminomethyl)-4-methylphenolato and L 3 = 2,6-bis{N-ethyl-N-(3-hydroxypropyl iminomethyl)}-4-methylphenolato), have been synthesized and structurally characterized by X-ray single-crystal diffraction in addition to routine physicochemical techniques. Density functional theory calculations have been performed to understand the nature of the electronic spectra of the complexes. Complexes 1-3 when reacted with 4-nitrophenyl phosphate in 50:50 acetonitrile-water medium promote the cleavage of the O-P bond to form p-nitrophenol and smoothly convert 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) either in MeOH or in MeCN medium. Phosphatase-and catecholase-like activities were monitored by UV-vis spectrophotometry and the Michaelis-Menten equation was applied to rationalize all the kinetic parameters. Upon treatment with urea, complexes 1 and 0 ) derivatives, respectively, whereas 3 remains unaltered under same reaction conditions. IntroductionBimetallic cores are found to be present at the active sites of many metalloenzymes and play essential roles in biological systems. Structural exploration has pointed out that these active sites comprise of two (homo/hetero) transition metal ions in close proximity, and research had been extensively devoted to the synthesis of dinuclear coordination compounds in order to mimic these active centers [1][2][3][4]. A simple method to attain this goal is using compartmental ligands [5][6][7][8], in which at least one atom, acting as bridging donor, is shared by the metal centers [9]. Thus, complexes with compartmental ligands have received considerable attention for their unusual, although pre-ordered properties [7, 10-13]. Among the 3d metal ions, Ni II has been widely employed for its effectiveness as a templating agent in many syntheses and for the high stability of its complexes in solution [14]. Although nickel is recognized as an essential trace element for bacteria, plants, animals and also, recently, humans [15][16][17][18][19][20], the role of this metal in animal biochemistry remains unclear. To date, urease, glyoxylase I, acireductone dioxygenase, superoxide dismutase, methyl-CoM reductase, hydrogenase, carbon monoxide dehydrogenase and acetyl-CoA Electronic supplementary material The online version of this article (