Rienk van Grondelle (Department VU University Amsterdam, Amsterdam)

 

The Design of Photosynthesis

Photosynthesis is the process that plants, algae and photosynthetic bacteria use to store sunlight as chemical energy to be used by the cell for growth, maintenance, multiplication etc. The photosynthetic apparatus, a set of pigment-proteins, is associated to the photosynthetic membrane (in plants the thylakoid membrane). Two ultrafast events underlie the high quantum efficiency of photosynthesis: solar photons are absorbed by the protein bound pigments (chlorophylls, carotenoids) of the light-harvesting antenna, the energy is transferred among the antenna pigments on a femtosecond to picosecond timescale to the pigments of the photosynthetic reaction center. Upon excitation of the reaction center an ultrafast transmembrane charge separation is triggered. Plants and algae make do with two reaction centers, operating in series, while photosynthetic bacteria use a single reaction center. In contrast to plants and algae, the latter do not extract electrons from water. In this lecture I will illuminate some of the design principles of photosynthesis: the amazing pigment density, the role of excitons, the persistence of coherence, the engineering of ultrafast energy transfer vs. ultrafast charge separation, the uni-directionality of charge separation, the role of energetic disorder, the ability of the photosynthetic membrane to structurally and functionally reorganize itself on an ultrafast timescale, the interplay between photosynthesis and photoprotection. I will discuss which of those principles will be key to the design of a future artificial or biosynthetic ‘biosolar cell'.