Biotechnology for Biofuel Production and Optimization || Photobiohybrid Solar Conversion with Metalloenzymes and Photosynthetic Reaction Centers

摘要： Sunlight provides an abundant and sustainable supply of energy to the Earth's surface, at levels that far exceed the yearly human global energy demand. However, the intermittency and geographic variability of solar irradiation, combined with the need for storage, limits the ability to provide practical alternatives to use of conventional fossil fuels. To better utilize the available solar energy, current photovoltaic technologies must be integrated with conversion technologies that produce storable chemical energy (fuels) that are easily distributed to meet regional demand as needed. In biological photosynthesis, conversion of solar energy into chemical energy is accomplished by the water-splitting and CO2 fixation reactions. The molecular machinery of the natural system provides ideal models for the design and development of artificial solar-to-fuel systems. The theoretical limit of biological photosynthesis is ~12%, and under optimal conditions, efficiencies of 7% have been achieved; however, 1% is a more typical benchmark. Photosynthetic reactions rely on four key components which are integrated to act in concert as a highly functional energy transduction network: (i) the antenna, where photons are absorbed; (ii) the charge separation site, where high-energy excitons (electron-hole pairs) are separated into positive and negative charge carriers; (iii) the reduction catalyst, where electrons are utilized in a fuel-forming reaction (e.g., NAD+ → NADH formation used for CO2 fixation in photosynthesis); and (iv) the oxidation catalyst, where holes are utilized to drive an oxidation reaction (e.g., water oxidation by photosystem II during photosynthesis). Efforts are underway to translate photobiological design principles to develop artificial systems for solar fuel generation that circumvent or eliminate unwanted side reactions and attain higher efficiencies. These efforts include the development of photochemical devices, inorganic biomimetic and bioinspired catalysts and light-harvesting complexes, and organic hybrid materials for photo-driven fuel production. Here, we discuss research focused on the development of hybrid materials that incorporate artificial and natural molecular components into unified functional systems for light-harvesting and conversion into reduced chemical fuels.