Electron-transfer reactions of cobalt(III) complexes. 1. The kinetic investigation of the reduction of various surfactant cobalt(III) complexes by iron(II) in surface active ionic liquids.

The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2](3+) (1), cis-[Co(dp)2(C12H25NH2)2](3+) (2), cis-[Co(trien)(C12H25NH2)2](3+) (3), cis-[Co(bpy)2(C12H25NH2)2](3+) (4) and cis-[Co(phen)2(C12H25NH2)2](3+) (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2'-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe(2+) ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ΔH(‡) and entropy of activation ΔS(‡)) of the reaction have been calculated which substantiate the kinetics of the reaction.

Synthesis, micellization behaviour, DNA/RNA binding and biological studies of a surfactant cobalt(III) complex with dipyrido[3,2-a:2',4'-c](6,7,8,9-tetrahydro)phenazine.

A new surfactant cobalt(III) complex, cis-[Co(dpqc)2(DA)2](ClO4)3, where dpqc = dipyrido[3,2-a:2',4'-c](6,7,8,9-tetrahydro)phenazine and DA = dodecylamine, has been synthesized and characterized by elemental analysis, UV-Visible, IR and NMR spectra. The critical micelle concentration (CMC) value of this surfactant cobalt(III) complex in aqueous solution was obtained from conductance measurements. The conductivity data (at 303, 308, 313, 318 and 323 K) were used for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG(0) m, ΔH(0) m and ΔS(0) m). Absorption, fluorescence, cyclic voltammetry, circular dichroism and viscosity experiments have been carried out to study the interaction of the surfactant cobalt(III) complex with DNA and RNA. The results suggest that the complex can bind to nucleic acids by intercalation via both the dpqc ligand and the long aliphatic chain of the complex into the base pairs of DNA/RNA. In vitro cytotoxicity experiments show that the surfactant cobalt(III) complex exhibits cytotoxic activity against the HepG2 (human hepatocellular liver carcinoma) tumor cell lines and found to be active.

Visible-light activation of the bimetallic chromophore-catalyst dyad: analysis of transient intermediates and reactivity toward organic sulfides.

In order to develop a new photocatalytic system, we designed a new redox-active module (5) to hold both a photosensitizer part, [Ru(II)(terpy)(bpy)X](n+) (where terpy = 2,2':6',2''-terpyridine and bpy = 2,2'-bipyridine), and a popular Jacobsen catalytic part, salen-Mn(III), covalently linked through a pyridine-based electron-relay moiety. On the basis of nanosecond laser flash photolysis studies, an intramolecular electron transfer mechanism from salen-Mn(III) to photooxidized Ru(III) chromophore yielding the catalytically active high-valent salen-Mn(IV) species was proposed. To examine the reactivity of such photogenerated salen-Mn(IV), we employed organic sulfide as substrate. Detection of the formation of a Mn(III)-phenoxyl radical and a sulfur radical cation during the course of reaction using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. This is the first report for the electron transfer reaction of organic sulfide with the photochemically generated salen-Mn(IV) catalytic center.