9600925 Haddy The primary research goal is to characterize the oxidation state changes of the manganese cluster of the oxygen evolving complex (OEC) of higher plants in terms of energetics. This will be carried out by monitoring two electron paramagnetic resonance (EPR) signals, a multiline signal at g=2 and a broad signal at g=4, associated with one of the oxidation states, S2. In addition, the presence of an even spin EPR signal at g=4.8 associated with S1, the state preceding S2, will be confirmed using parallel mode detection and subsequently used to monitor S1. The specific research objectives include: confirmation that the state associated with the S2 signal at g=4 (designated S2-g=4) precedes the state associated with the S2 multiline signal (S2-mult); determination of the activation energy barriers between the states associated with S1 and S2-g=4, S2-g=4 and S2-mult, and S2-mult and S3, the state that follows S2; determination of the relative free energies of the states associated with S1, S2-g=4, and S2-mult; and investigation of the energy barriers and relative free energies in the presence of the inhibitor ammonia. To achieve these objectives, the magnitudes of the S2 signals and if present the S1 signal will be measured in a series of equilibrium and kinetics experiments performed over a range of illumination temperatures. The magnitudes will be related to the population in each state. The educational activities proposed are in accord with the Chemistry Department's current plans to develop a concentration or major in biochemistry. The education objectives include the development of: a one-semester biochemistry laboratory course; a series of lectures on biophysical topics to be given as part of the second semester introductory course; and a set of EPR experiments for use in undergraduate laboratories. The EPR experiments for undergraduates will include some that have applications in biochemistry and are not presently available in the chemical education literature. %%%
