Photoregeneration of NADH Using Carbon-Containing TiO2

A novel photochemical approach for NADH regeneration, which employs visible light as a light source, carbon-containing TiO2, and [Cp*Rh(bpy)(H2O)]2+ as a catalyst, has been developed here. The carbon-containing TiO2 has a strong absorption toward visible light. [Cp*Rh(bpy)(H2O)]2+ shows high activity and selectivity toward 1,4-NADH. In the photoregeneration of NADH, the conversion is low and only achieves 25.83% at 31 (degree) C and pH 6.5 when using H2O as an electron donor. While under the same conditions using mercaptoethanol, the conversion achieves 74.30% and even reaches 94.29% in the presence of H2. Lower pH and higher temperature result in higher conversion and a higher reaction rate. The influence of the initial concentration of [Cp*Rh(bpy)(H2O)]2+ on NADH photoregeneration is much greater than that of the initial concentration of NAD+. The optimum conditions for NADH photoregeneration are determined to be a pH of 6.0, 37 (degree) C, a NAD+ initial concentration of 0.2 mM, and a [Cp*Rh(bpy)(H2O)]2+ initial concentration of 0.3~0.5 mM. The conversion achieves 63.98% under optimum conditions.