• Akhil R Chakravarty

      Articles written in Journal of Chemical Sciences

    • Tribridged diruthenium complexes: A new structural motif

      Akhil R Chakravarty

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      Dinuclear complexes containing a (μ-oxo)bis(μ-carboxylato) diruthenium (III) core have been prepared by a novel synthetic route using metal-metal bonded diruthenium(II, III) tetracarboxylates as precursors. The complexes have been structurally characterized and they are redox active. The terminal ligands play an important role in tuning the electronic structure of the core. The stability of the core is found to be dependent on the size and π-acidic nature of the terminal ligandcis- to the μ-oxo ligand. The chemistry of such tribridged complexes is relatively new. The rapid growth of this chemistry is based on the discovery of similar core structures in several non-heme iron-and manganese-containing metalloproteins. The tribridged core presents a new structural motif in coordination chemistry. The chemistry of diruthenium complexes with a [Ru2(μ-O)(μ-O2CR)22+] core has been reviewed.

    • Copper complexes as chemical nucleases

      Akhil R Chakravarty Pattubala A N Anreddy Bidyut K Santra Anitha M Thomas

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      Redox active mononuclear and binuclear copper(II) complexes have been prepared and structurally characterized. The complexes have planar N-donor heterocyclic bases like 1,10-phenanthroline (phen), dipyridoquinoxaline (dpq) and dipyridophenazine (dppz) ligands that are suitable for intercalation to B-DNA. Complexes studied for nuclease activity have the formulations [Cu(dpq)2(H2O)] (ClO4)2.H2O (1), [CuL(H2O)2(μ-ox)](ClO4)2 (L = bpy,2; phen,3; dpq,4; and dppz,5) and [Cu(L)(salgly)] (L = bpy,6; phen,7; dpq,8; and dppz,9), where salgly is a tridentate Schiff base obtained from the condensation of glycine and salicylaldehyde. The dpq complexes are efficient DNA binding and cleavage active species. The dppz complexes show good binding ability but poor nuclease activity. The cleavage activity of thebis-dpq complex is significantly higher than thebis-phen complex of copper(II). The nuclease activity is found to be dependent on the intercalating nature of the complex and on the redox potential of the copper(II)/copper(I) couple. The ancillary ligand plays a significant role in binding and cleavage activity.

    • Effect of copper-sulphur bond on the DNA photo-cleavage activity of 2-(methylthio)ethylpyridine-2-carbaldimine copper(II) complexes

      Tarkeshwar Gupta Ashis K Patra Shanta Dhar Munirathinam Nethaji Akhil R Chakravarty

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      The binding and photo-induced DNA cleavage activity of a binary complex [CuL2](ClO4)2 (1) and the in situ generated ternary complexes [CuLB](ClO4)2 from 1 (B: 1,10-phenanthroline, phen, 2; dipyrido[3,2-d: 2′,3′-f]quinoxaline, dpq, 3) are studied, where L is a N2S-donor tridentate Schiff base 2- (methylthio)ethylpyridine-2-carbaldimine. Complex 1, structurally characterized by X-ray diffraction study, has six-coordinate meridional geometry showing CuN4S2 coordination. The Cu-N bond lengths are in the range of 1·968(3) to 2·158(4) Å. The Cu-S bond lengths of 2·599(2) and 2·705(2) Å are significantly long indicating weak covalent interaction between copper and sulphur atoms. The thiomethyl groups are cis to each other giving S-Cu-S angle of 75·82(5)°. The Cu-N(pyridyl) bond distances are longer than the Cu-N(imine) bonds. The complexes are redox active and display a quasi-reversible cyclic voltammetric response assignable to the Cu(II)/Cu(I) couple near 0·0 V vs SCE in DMF-Tris buffer (1: 4 v/v) using 0·1 M KCl as supporting electrolyte. Electronic spectra of the complexes show a d-d band in the range 630 to 700 nm in DMF along with higher energy charge transfer bands. While complex 1 is a poor binder to DNA, the ternary complexes show good DNA binding propensity. The photo-nuclease activity of 13 is studied using UV and visible wavelengths. The DNA cleavage activity at 365 nm follows the order: 3 > 2 > 1. The cleavage reaction involves the formation of singlet oxygen as the reactive species in a type-II process.

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