Abstract

Photosystem II, the water oxidising enzyme of photosynthesis, is in large part responsible for converting solar energy into the high energy chemicals that sustain life on the planet. Over time the excess energy stored has accumulated as the fossil fuels. This solar-driven enzyme also put the oxygen into the atmosphere and thus made the biosphere aerobic with all the associated repercussions for the planet (O2-based respiration, multicelluar life, UV screening by ozone etc). It is also one of very few catalysts known that is able to oxidise water with a low overpotential, i.e. at close to its thermodynamic optimum. As such it is the focus of much attention with a view to producing bio-inspired catalysts that have potential uses for more efficient (and sustainable) energy conversion processes: such as a) H2 production by electrolysis or by photolysis, and b) in electricity production in fuel cells. We have applied biophysical, biochemical and molecular biological methods to investigate the photochemistry and molecular enzymology of this remarkable enzyme. While understanding aspects of both structure and function ( particularly of the photochemical part) of the enzyme has advanced rapidly in recent years, some basic enymological questions remain to be answered. In parallel to the biochemical and biophysical studies, we (in association with the University of Paris at Orsay) also design, synthesize and study chemical models that are aimed at mimicking certain features of the water oxidising enzyme. Mn-based catalysts linked to photochemical charge separating systems have been constructed and characterised.