tailieunhanh - Biomimetics Learning from nature Part 3

Tham khảo tài liệu 'biomimetics learning from nature part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Photosynthetic energy conversion hydrogen photoproduction by natural and biomimetic systems 53 Fig. 2. The schematic view of the artificial photosynthetic system for production of hydrogen. P photosensitizer A electron acceptor D electron donor C electron carrier Catox catalyst for oxidation of water Catred catalyst for reduction of H . 2. Natural systems . Oxygenic organisms cyanobacteria and microalgae Photosynthesis involves a sequential chain of reactions that include light absorption charge separation water splitting electron transport reduction of NADP and creation of a proton gradient. Several major complexes are involved in the process of oxygenic photosynthesis Photosystem II PSII including water oxidation complex Photosystem I PSI cytochrome bõ f and ATP-synthase complexes Figure 1 . The detailed composition of the photosystems and electron transport intermediates from water to NADP are described in a number of papers see Chow 2003 Kruse et al. 2005b McEvoy and Brudvig 2006 Allakhverdiev et al. 2009 . Electrons are transferred from PSII to ferredoxin Fd through PSI. Normally Fd shuttles electrons to the enzyme ferredoxin-NADP-reductase that reduces NADP to NADPH an important source of electrons needed to convert CO2 into carbohydrates during the Calvin-Benson cycle. Here protons H outside the thylakoids are carried to the inner thylakoid space thus forming a proton gradient across the thylakoid membrane. Under anaerobic conditions hydrogenase nitrogenase can accept electrons from reduced Fd molecules and use them to reduce protons to molecular hydrogen H2 . In this case the photosynthetic reducing power can partition between at least two pathways CO2 reduction and H2 production. CO2 reduction requires ATP for using reductant from water whereas H2 production does not use ATP which is the desired pathway for renewable energy production. Under normal conditions the competition for electron donor favors the CO2 fixation pathway. However in the absence or .