Enzyme mimicking activity of the Ru(pic)₃ complex in the oxidation NADH coenzymes: kinetic and mechanistic studies

Abstract

Mimicking the enzymatic oxidation of NADH and obtaining mechanistic insight into the electron transfer reaction pertinent to the redox inter-conversion of NADH/NAD⁺ couple is a long-term challenge in biological and energy-related chemistry. The kinetics and mechanism of the oxidation of NADH by [Ru^III(pic)₃] (pic^– = picolinate anion) has been studied spectrophotometrically and kinetically in aqueous solution at pH 7.0 (MES buffer). The reaction was followed over time at 466 nm (metal to ligand charge transfer band of [Ru^II(pic)₃]^–). The rate of NADH oxidation was found to be first-order with respect to Ru(III)-complex concentration. The values of the observed rate constant (k_obs) increased linearly with increase in the concentration of NADH. The rate of the reaction was independent of the ionic strength of the reacting solution. Activation parameters (ΔH^≠ = 56 ± 1 kJ mol⁻¹ and ΔS^≠ = −65 ± 3 J.deg⁻¹mol⁻¹) were determined from the temperature dependence studies (15-35 °C) of the reaction. Kinetic data and activation parameters are interpreted in terms of a mechanism involving outer-sphere electron transfer.

[Ru^III(pic)₃] (pic⁻ = picolinate anion) effectively oxidizes NADH in an outer-sphere electron transfer pathway.

Keywords:

• Ruthenium-pic
• NADH Oxidation
• electron transfer
• kinetics
• mechanism

Disclosure statement

No potential conflict of interest was reported by the author(s).