Tetra(4-carboxyphenyl)porphyrin for efficient cofactor regeneration under visible light and its immobilization

Coenzyme regeneration is important for the industrial utilization of oxidoreductase. In this work, reduced nicotinamide adenine dinucleotide (NADH) was regenerated under visible light via a photosensitizer and an electron donor. First, several photosensitizers including 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), zinc porphyrin (ZnTCPP) and eosin Y (EY) with varied concentrations were compared. Next, using TCPP as the photosensitizer, the type and concentration of the electron donor, pH value and concentration of the buffer system for the reaction were optimized. Following that, TCPP was immobilized onto the surface of various supports for screening. Then, the immobilization conditions were optimized and the photocatalytic performance of silica-attached TCPP was studied. Lastly, the effect of a rhodium mediator on NADH regeneration was evaluated. The results show that the optimum concentration of TCPP, ZnTCPP and EY was 2, 1 and 4 mM, respectively, and the highest NADH yield of the TCPP system was 2.37 and 1.47 times those of the ZnTCPP and EY systems. With TCPP as the photosensitizer, triethanolamine was the most efficient electron donor and its appropriate concentration was 5 mM. The optimal pH value and concentration of the phosphate buffer was 7.0 and 0.05 M. Under these conditions, a high NADH yield of 81.5% was achieved after 60 min. For the supports examined, the thiol-containing silica microspheres coated with polydopamine and polyethyleneimine had the highest loading capacity of TCPP (9.15 mg per g-support). Via sensitization, the NADH yield was 9.64% after 90 min and was upgraded to 22.5% with the addition of the rhodium mediator.