The bioinorganic chemistry of Photosystem II watersplitting: An investigation of di-mu-oxo dimanganese model complexes

Natasha Keith
Yale University

The protein responsible for water-splitting in biological photosynthesis pathways, Photosystem II, manifests some unexplained behaviors when exposed to different dielectric environments. This project, in an attempt to elucidate these phenomena, investigates the behavior of model di-mu-oxo manganese complexes in solutions of varying dielectric. [Mn2(bipyridine)4](ClO4)3 was synthesized from a procedure by S. Cooper and M. Calvin (J. Am. Chem. Soc.; 1977; 99(20); 6623-6630), UV spectra with a UV Varian spectrometer were taken from the range of 500 to 1100 nm at room temperature in varying solvents (a 0.10 M bpy buffer, acetonitrile, and dichloromethane via counterion exchange with sodium pentafluoropropionate) and deconvoluted with Microcal Origins into gaussian components using the spectral assignments of D. Gamelin and E. Solomon (J. Am. Chem. Soc.; 1994; 116(6); 2392-2399). Unique deconvolutions could not be achieved with this method, so experimental methods for taking UV spectra at low temperatures from 60-85 K are being refined. Future studies are planned to draw conclusions about the nature of these compounds in different solvent dielectrics based on low temperature spectroscopy, and to extend the research to the exploration of intermediates in the O2-evolving reaction of Mn dimer complexes with oxidants the same low temperature UV spectroscopy techniques.