Trapping internal water clusters and hydrogen-bonding networks in photosynthetic oxygen evolution

Abstract

To summarize the work presented in this thesis, I have investigated the structure and function of the internal hydrogen-bonding network in PSII in three different ways. In the first (Chapter 2), I used an infrared signal from a protonated water cluster in the S2 state of the OEC. When trapped at 190 K, solvent isotope exchange confirmed the spectral assignment to the internal water network. This signal then became a novel and effective probe of the effects of hydrogen bond disruption, calcium depletion and replacement, and pH change on the network. In the second (Chapter 3), I used EPR spectroscopy at 190 K to investigate the effects of these treatments on the EPR signal and decay rate of YZ radical. The radical was trapped in the S2 state and decayed by coupled proton and electron transfer through recombination with QA−. A correlation was discovered between the intensity of the protonated water cluster and conditions that altered YZ radical decay rates. In the third (Chapter 4), I used reaction induced FT-IR spectroscopy to obtain structural information concerning YZ radical and YZ singlet in the S2 state. Calcium depletion and replacement was employed. This third approach provides a new high-resolution method to define the structure of the radical and singlet state in the presence of an intact metal cluster.