Panel Discussion: How Well Do We Understand the Primary Event of Charge Separation

Abstract

We are asking the question “How well do we understand the primary event of charge separation” and I think the answer is: at some levels, very well, but at the mechanistic level, not so well. I think that the talks this morning give a good example of how there have been some spectacular progress, not only in the way we look at the reaction center, but also in introducing new and very necessary techniques to look at these systems. What I just want to comment on right now is what we don’t know, just to raise your consciousness about it. It’s true to say that of the six chlorophylls that are present in the reaction center, we really can only be sure of three of them. So we can only say, we know what half the components do. The other monomeric chlorophyll and the other Fe function is completely unknown. It is known that energy transfer to the dimer is very effective through this system. So it may be that: a route in for photons. The monomeric chlorophyll, whether it’s truly an intermediate that you can identify as a stable redox state, or just some kind of virtual state that the electron uses as a medium to get from chlorophyll to Fe, still remains to be seen. It would be very nice to know what the redox properties of these components are. In the equilibrium sense, we have no idea.