Design and engineering of artificial photosynthesis in biocatalytic assemblies

Abstract

Mimicking the natural photosynthesis is an attractive way for achieving a new form of renewable energy by utilizing solar light. During the photosynthetic process, photon energy is absorbed by dye-sensitized photosystems and stored as chemical energy, which is then used for the synthesis of carbohydrates through Calvin cycle. It is subsequently regenerated by a recycling process between light and dark reactions. For artificial photosynthesis, the photo-induced electron transfer reaction should occur with a manmade light harvesting antenna that can fulfill the role of photosystems in natural photosynthesis. The efficient regeneration of nicotinamide and flavin cofactor is critical for the conversion of solar energy into fine chemicals since the oxidoreductase, working as a counterpart of the Calvin cycle, requires a stoichiometric amount of cofactors as redox equivalents. Therefore, in order to develop an artificial photosynthetic system, it is important to identify an efficient means of photo-induced electron transfer, especially in the visible light range. Oxidoreductases can catalyze difficult redox reactions that conventional chemical catalysts are unable to catalyze. Despite the capability of oxidoreductases to catalyze complex reactions, they require a stoichiometric amount of cofactors that have two contrary states (i.e., oxidized vs. reduced). Numerous efforts have been made for the in situ regeneration of cofactors, such as nicotinamide adenine dinucleotide (NADH), from its consumed counterparts towards the practical application of oxidoreductases in industrial biosynthesis. While conventional cofactor regeneration methods, such as the use of second enzymes or chemical electrodes, have such drawbacks as catalyst instability, low specific activity, and limited applications, the photochemical route to cofactor regeneration is at its infancy, providing an opportunity to utilize clean and abundant solar energy. A few studies report on the photochemical reg...