Artificial photoenzymes

The model systems for enzymes activated by light can be called artificial photoenzymes . This expression comprises two important requirements, which must be fulfilled by system its activity should be triggered by light and it should behave like an artificial enzyme . The term artificial enzyme is very often used inappropriately and applied to any catalysts. The detailed explanation of this term, together with critical analysis of enzyme model systems, can be found in an excellent review by Kirby [35], In general, enzymes are more than just highly developed catalysts  

Usually mimetics of enzymes are not as sophisticated and their catalytic efficiency is taken into account as a main objective. The important feature of enzyme mimetics is an initial binding interaction between substrate and the catalyst, thus giving rise to Michaelis-Menten kinetics [35], Therefore for a model system to be called an artificial enzyme it should combine more than one of the key features identified for enzymes [35], For some systems it is difficult to decide if they can be considered as artificial photoenzymes or if they are just photocatalysts (described in Chapters 6, 7,10, and 21). It is not the purpose of this book to judge whether model systems can be called artificial photoenzymes or should be considered as just chemical photocatalysts. To get some feeling which type of model systems have been investigated we describe a few model systems that have claimed to have enzyme-like activity. 

There are several photocatalysts mimicking hydrogenase activity that are not based on metalloporphyrin systems. Among them there are mixed-valence complexes of rhodium or iridium, [41] as well as complex systems encompassing photosensitizers (eg ruthenium complexes) attached to a catalytic bimetallic centre [43], The design of more sophisticated systems approaches that of photosynthetic processes [44], 

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Photoactivated redox proteins will play important roles in the future development of artificial photosynthetic systems. The unique participation of the protein matrices in photoinduced charge separation and the possibility of implanting catalytic sites in the protein indicate that tailored photoenzymes will be important components for the light-driven synthesis of fuels and valuable chemicals, e.g., CO2 and N2 fixation and amino acid synthesis. The areas of bioelectronics and opto-bioelectronics represent exciting interdisciplinary ventures for chemists, biologists, physicists and materials scientists. The advances in these fields oflFer compelling opportunities for the development of electronic biomaterial-based devices. 

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