Cobalt(Iii) Essay

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Project SEED 2009 Research Report: Synthetic Studies of Light-induced Oxidation Manganese Porphyrins of Written by: Khadija Abubakar University of Memphis Department of Chemistry {'rtlrQ"# Khadfja Abubakar i lav leq Date *tf Lq/" Dr. Xuan Zhao "/-'" Date I Introduction The oxygen evolving complex (OEC), as found in photosystem II (PSII) of plants, is essential in the process of oxidizing water (H 2 O) to protons, electrons and dioxygen during the process of photosynthesis.1-3 The active site of the OEC in the homodimeric membrane protein is made up of oxygen, calcium and manganese. During photosynthesis, the chlorophylls in the homodimeric membrane protein absorb light to induce water oxidation and the release of dioxygen. Ruthenium polypyridine complexes, such as the one shown in Figure 1, have high molar absorptivity and photostability.4,5 They have N N N Ru II been used as artificial light-harvesting antennae for the N N 6-16 oxidation of manganese and iron complexes. The formation of a high valent Mn-O species has been suggested as a key intermediate during the oxygen N Figure 1. Ruthenium polypyridine evolution of photosystem II (PSII). Manganese prophyrin complexes have been shown to catalyze water oxidation through a highly reactive MnV=O as an active intermediate created by chemical oxidation.17,18 Photo-induced oxidation of MnII complex has been shown to lead to the generation of MnIV species.8 However, the light-induced generation of a high valent Mn-O species has been rare except by laser flash photolysis. 19-22 Since a high valent MnV=O species has been proposed as a critical intermediate in water splitting by the oxygen evolving center of PSII, the possibility of generating a light-induced Mn-O species in the presence of both photoactive chromophores and manganese

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