Phycobilisome is the key structure of the photosynthetic system of cyanobacteria and red algae.It can efficiently capture light energy and transfer it to the photosystem I/II and reaction center through protein skeleton localization of pigment molecules(bilins),so as to realize the conversion from light energy to chemical energy.The use of supramolecular assembly strategy to simulate the light capture and reaction center structure of photosynthetic bacteria or algae is of great significance for exploring new artificial photosynthetic systems.Its core is to construct an artificial skeleton to simulate apolipoprotein to control the spatial arrangement of pigment molecules,so as to realize the efficient coupling of light capture and light reaction.Phycobilisome is a typical natural photosynthetic assembly structure,which provides an important idea for the construction of a new supramolecular artificial photosynthetic system.Tian Jia,a researcher at the Shanghai Institute of organic chemistry,Chinese Academy of Sciences,is committed to building an artificial photosynthetic assembly system to achieve efficient conversion and storage of light energy to chemical energy.In 2023,he reported the first organic supramolecular artificial photosynthetic assembly constructed by imitating the pigment of photosynthetic purple bacteria for efficient CO2 reduction in aqueous phase at room temperature.
Recently,Tian Jia and his collaborators have made progress in the research on the construction of aqueous phase artificial photosynthetic assemblies using phycobilisomes for photocatalytic H2 production.The relevant research results,titled as bioinspired self-assembly of metaloporphyrins and polymers into hierarchical supramolecular nanostructures for enhanced photocatalytic H2 production in water,are published online in German Journal of Applied Chemistry.
Inspired by cyanobacterial phycobilisomes,the artificial assembly structure was realized by using polyelectrolyte PDDA to simulate protein skeleton and metalloporphyrins to simulate chromophore molecules.In water,cationic PDDA is co assembled with anionic metalloporphyrins with photosensitive and catalytic functions to form a one-dimensional photosynthetic assembly,thus simulating the rod antenna structure and catalytic center of phycobilisomes(Fig.1).The photosynthetic assembly structure can realize the photocatalytic production of H2 in aqueous phase,and its efficiency is more than 23 times higher than that of monomer molecules.Through the formation of nano assembly structure,the photostability of photosensitive and catalytic metalloporphyrins was significantly improved compared with the monomer structure.The photocatalytic mechanism was further studied by transient absorption spectra,fluorescence spectra and theoretical calculations(Fig.2).After illumination,the formation of metalloporphyrin cationic free radicals was observed by femtosecond transient absorption spectra,indicating that there may be a light induced electron transfer process;Theoretical calculations also support the formation of charge separated states between magnesium porphyrins and copper porphyrins through electron transfer.In addition,fluorescence and transient absorption spectra experiments support the existence of energy transfer process in photosynthetic assembly.Therefore,the photosensitive metalloporphyrin in the biomimetic assembly system can transfer the light energy from the photosensitizer to the photocatalytic center through the cooperative process of energy transfer and electron transfer,thus realizing the efficient photocatalytic proton reduction in aqueous phase to produce H2.By optimizing the photocatalytic conditions,the photocatalytic performance of the assembly was significantly better than that of other metalloporphyrin assembly systems.Under light,the hydrogen production rate and the number of conversions(ton)of this photosynthetic assembly could reach 51776μMol H-1 g-1 and 1299.This study not only deepened scientists'understanding of the structure and mechanism of photosynthesis of natural phycobilisomes,but also provided a new idea for the construction of biomimetic supramolecular photosynthetic assembly system in water phase.
The research work has been supported by the national key R&D plan,the National Natural Science Foundation of China,the Chinese Academy of Sciences and the Shanghai Municipal Commission of science and technology.
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Figure 1.schematic diagram of biomimetic photosynthetic assembly inspired by phycobilisomes
Figure 2.study on photocatalytic mechanism of biomimetic photosynthetic assembly
