A Biomimetic Manganese Model for Artificial Photosynthesis : Q-band Electron Paramagnetic Resonance Study of a Novel Mn2(II,III) Complex

• Main Author: Kiflemariam, Jordanos
• Format: Others
• Language: English
• Published: Linköpings universitet, Institutionen för teknik och naturvetenskap 2005
• Subjects: Photosynthesis; manganese; electron paramagnetic resonance; Molecular biophysics; Molekylär biofysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-4246

In natural oxygen-producing photosynthesis solar energy is stored as chemical energy, in carbohydrates, fats and amino acids, using water as electron source. The large transmembrane protein complex, PSII, is the key enzyme in the light-driven reactions. Water oxidation is accomplished by a triad in PSII in which the Mn-cluster plays an important role. In the artificial photosynthetic system, nature’s photosynthesis will be mimicked such that hydrogen, a sustainable energy source, can be produced from solar energy and water alone. Since water oxidiation requires the catalytic activity of a Mn-cluster in photosynthesis, different artificially constructed manganese complexes are investigated. The dinuclear ([Mn2(II,III)L(µ-OAc)2]ClO4), where L is the X-anion of 2-(N,N-Bis(2-methylpyridyl)aminomethyl)-6-(N-(3,5-ditert-butylbenzyl-2-hydroxy)-N-(pyridylmethyl)aminomethyl)-4-methylphenol, an unsymmetric ligand with two coordinating phenolate groups, has been studied. The two Mn-ions are linked via a mono-µ-oxo bridge and two acetate ligands. Q-band Electron Paramagnetic Resonance was conducted on the Unsymmetric Mn2(II,III) Complex. Aquired results show that the complex has a 2600 Gauss broad signal (11 400-14 000 Gauss) with 14-17 lines at g~2 and hyperfines of 120 Gauss. This is consistent with previous X-band studies. Q-band spectra of the Unsymmetric Mn(II,III) display increased hyperfine resolution compared to Qband spectra of the symmetric complex, Mn2(bpmp)(µ-OAC)2. This is noticeable since Unsymmetric Mn2(II,III) and Mn2 (bpmp)(µ-OAC)2 partly overlap in low-frequency experiments (X-band EPR). Further investigations are yet to be expected. Nevertheless, the conducted thesis study provides important knowledge in the futuristic goal of building an artificial super-complex.