Electron transfer reactions of tris(polypyridine)ruthenium(III) complexes with organic sulfides: importance of hydrophobic interaction

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.

Spectroscopic investigation on kinetics, thermodynamics and mechanism for electron transfer reaction of iron(III) complex with sulphur centered radical in stimulated biological system

Electron transfer reactions of biological organic sulphides with several metal ions to generate sulphide radical cations are a great concern in biochemical process. To understand the mechanism, a stimulated biological system having model compounds, iron(III)-bipyridyl complex with thio-diglycolic acid (TDGA) was investigated. Spectroscopic study reveals the kinetics and thermodynamics of the reaction in aqueous perchloric acid medium. The reaction follows first and fractional order of 0.412 with respect to [Fe(bpy)3](3+) and TDGA, respectively. The oxidation is insensitive to variation in [H(+)] but slightly decreases with increase in ionic strength ([I]). Addition of acrylamide, a radical scavenger has no effect on the rate of the reaction. The high negative value of ΔS(#) (-74.3±1.09 J K(-1) mol(-1)) indicates the complex formed has a definite orientation higher than the reactants. Based on the above results, a suitable reaction mechanism for this reaction is proposed.

Studies of interactions among cobalt(III) polypyridyl complexes, 6-mercaptopurine and DNA

The interactions between cobalt polypyridyl coordination compounds Co(L)(3)(3+)(L=1,10-phenanthroline(phen), and bipyridine(bpy)),6-mercaptopurine and calf thymus DNA have been investigated using electrochemical methods(cyclic voltammetry, differential pulse voltammetry), electronic absorption spectroscopy and viscosity measurements. Results indicate that there is an obvious interaction equilibrium between Co(L)(3)(3+), 6-mercaptopurine and DNA. The phenomena are investigated for the first time, and believed to be helpful to use the anticancer drugs more efficiently.

Micellar catalysis on the electron transfer reactions of iron(iii)-polypyridyl complexes with organic sulfides—importance of hydrophobic interactions

The oxidation of organic sulfides with iron(III)-polypyridyl complexes [Fe(NN)3]3+ proceeds through an electron transfer mechanism and an increase in the methanol content in the methanol-water mixture favors the reaction. The reaction is catalyzed by both the anionic surfactant, sodium dodecyl sulfate (SDS) and the cationic surfactant, cetyltrimethylammonium bromide (CTAB). The micellar catalysis in the presence of SDS is accounted for in terms of strong binding of the cationic oxidant with the anionic surfactant and the development of positive charge on sulfur center of substrate in the transition state. The micellar catalysis observed on the reaction involving a trication, [Fe(NN)3]3+, in the presence of CTAB indicates the importance of hydrophobic interaction between the micelle and hydrophobic ligand of [Fe(NN)3]3+. The micellar catalysis is explained in terms of a pseudophase ion exchange model.