Nanobiocatalytic assemblies for artificial photosynthesis

Abstract

Solar energy has attracted a great deal of interest as a sustainable and environmentally acceptable energy source. In nature, green plants store solar energy in chemical fuels through natural photosynthesis, which occurs through a complex cascade of photo-induced electron transfer steps. This process is achieved by the photosynthetic units, highly sophisticated nanostructures, composed of chlorophyll aggregates, which serve as light-harvesting antennae, and catalytic metal clusters embedded within proteins. Thus, the utilization of solar energy through photo-induced electron transfer remains a target model for the development of artificial photosynthetic systems that utilize solar light as a sustainable and environmentally benign energy source. The key requirement in the design of artificial photosynthesis is an efficient and forward electron transfer between each photosynthetic component. In this thesis, nanobiocatalytic assemblies inspired from the photosynthetic units were studied for the development of artificial photosynthesis by means of efficient light harvesting and photo-induced electron transfer originated from the structure of nanobiocatalytic assemblies. Chapter 1 reviews the concept of biocatalyzed artificial photosynthesis through coupling redox biocatalysis with photocatalysis to mimic natural photosynthesis based on visible-light-driven regeneration of enzyme cofactors. In green plants, solar energy utilization is accomplished through a cascade of photo-induced electron transfer, which remains a target model for realizing artificial photosynthesis. Key design principles for reaction components, such as electron donors, photosensitizers, and electron mediators, are described for artificial photosynthesis involving biocatalytic assemblies. Recent research outcomes that serve as a proof of the concept are summarized and current issues are discussed to provide a future perspective. Chapter 2 describes Zn-containg porphyrin as a biomimetic light-har...