Electrochemical and Electrogenerated Chemiluminescent Studies of a Trinuclear Complex, [((phen)(2)Ru(dpp))(2)RhCl2](5+), and Its Interactions with Calf Thymus DNA

Shijun Wang, University of Southern Mississippi
Jenifer Milam, University of Southern Mississippi
Andre C. Ohlin, University of Southern Mississippi
Eva Clark, University of Southern Mississippi

Abstract

The electrochemical behavior of a trinuclear ruthenium(H)containing complex, [((phen)(2)Ru(dpP))(2)RhCl2](5+) (where phen = 1,10-phenanthroline, dpp = 2,3-bis(2-pyridyl)pyrazine), was studied in acetonitrile (MeCN) and aqueous solutions. In MeCN containing 0.10 M tetran-butylammonium perchlorate (TBAP), the complex displayed a reversible, overlapping Ru-II/III redox process with E-1/2 = +1.21 V vs Ag/Ag+ (10 mM), an irreversible reduction of Rh-III/I at -0.73 V vs Ag/Ag+, and two quasi-reversible dpp/dpp(-) couples with E1/2 = -1.11 and -1.36 V vs Ag/Ag+ at a Pt electrode with a scan rate of 50 mV s(-1). In 0.20 M Tris buffer solution (pH 7.4), an irreversible, overlapping Ru-II/III oxidation at +1.48 V vs Ag/AgCl (3 M KCl), and an irreversible reduction of Rh-III/II at -0.78 V vs Ag/AgCl were observed at a glassy carbon electrode with a scan rate of 50 mV/s. Investigations on the electrogenerated chemiluminescence (ECL) of the complex revealed that 2-(dibutylamino) ethanol (DBAE) was superior to tri-n-propylamine (TPrA) as an ECL coreactant within their entire concentration range of 10-100 mM in MeCN, and in aqueous media, as low as 1.0 nM of the complex can be detected using TPrA coreactant ECL. A maximum ECL emission of 640 nm, which is about 55 run blue shift to its fluorescence, was observed in MeCN with DBAE as a coreactant. Interactions of the complex with calf thymus DNA (ctDNA) were conducted with a flow-cell based quartz-crystal microbalance, and a binding constant of 2.5 x 10(5) M-1 was calculated on the basis of the Langmuir isotherm equation.