Bacterial photosynthetic enzymes as photochemical soft bio-materials

The sun initiated to shine roughly five billion years ago, and it is estimated that it will irradiate energy for another five billion years. Sun can hence be considered the sole renewable energy source. The ability to convert solar light energy into chemical energy is the fundamental feature of photosynthetic systems. Photosynthesis is the most important biological process, supplying Earth's biosphere with oxygen and food1. Today we have a quite deep knowledge of this natural process at a molecular level and many researches aim to develop bio-inspired artificial machineries for efficient energy conversion2. The complexity of the natural photosynthetic systems is difficult to reproduce in vitro; however, it is largely related to their living character and can be reduced in a biomimetic environment. The photochemical core of photosynthesis is represented by a specific transmembrane multi-subunit protein, known as the reaction center (RC), the sole photoenzyme in the biosphere converting solar energy into chemical energy3. Light induced electron transfer within the RC consists of a cascade of reactions leading to a charge separated state with an intrinsic long lifetime of 1-3 s. This feature makes the RC extremely attractive as it gives the system plenty of time for ancillary chemistry and electrochemistry to take place4. Although the RC energy conversion efficiency is close to unity, the direct light capture of the bare protein is intense in the UV and NIR regions and limited in the visible region, where solar irradiance is maximum. Our research group is deeply involved in efforts to extend the RC visible absorption cross-section, as well as in exploiting its unique features in bio-hybrid devices with applications in energy conversion and sensing. 1.Maróti, P.; Trotta, M., Artificial Photosynthetic Systems. In CRC Handbook of Organic Photochemistry and Photobiology, Third Edition - Two Volume Set, Griesbeck , A.; Oelgemöller, M.; Ghetti, F., Eds. CRC Press: 2012; pp 1289-1324. 2.Barber, J.; Tran, P. D., From natural to artificial photosynthesis. J R Soc Interface 2013, 10 (81), 20120984. 3.Blankenship, R. E., Molecular Mechanisms of Photosynthesis. Blackwell Science Ltd.: Oxford, 2002. 4.Mavelli, F.; Trotta, M.; Ciriaco, F.; Agostiano, A.; Giotta, L.; Italiano, F.; Milano, F., The binding of quinone to the photosynthetic reaction centers: kinetics and thermodynamics of reactions occurring at the QB-site in zwitterionic and anionic liposomes. Eur Biophys J 2014, 43 (6-7), 301-15.