CW and pulsed EPR studies of manganese containing complexes and nanomaterials

• Main Author: Yeagle, Gregory Joseph
• Format: Dissertation
• Language: English
• Subjects: chemistry, biochemistry; chemistry, physical
• ISBN: 9780549666134; 0549666133

Continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) spectroscopy have been applied to study a variety of manganese containing biological and chemical systems: the oxygen evolving complex (OEC) of photosystem II (PSII), oxalate decarboxylase (OxDC), and tris(2,4-pentanedionato)manganese(III) which may be abbreviated as Mn(acac)3. Additionally, CW EPR studies of the surface defects sites on the anatase phase of titania (TiO2) are highlighted. The multifrequency electron spin-echo envelope modulation (ESEEM) studies of amino acid ligation to the tetranuclear manganese cluster of PSII were facilitated by construction of a Ka-band pulsed EPR spectrometer described in chapter 2 of this dissertation. The results from experiments performed on this spectrometer, in addition to experiments performed at X-, P, and Q-band microwave frequencies, provide detailed analysis of the hyperfine and nuclear quadrupolar coupling parameters for a single histidine imidazole nitrogen directly coordinated to the manganese cluster in the S2 state.
Parallel-mode CW EPR was applied to the Mn3+ form of the coordination complex Mn(acac)3. Through simulation of the parallel-mode EPR signal, in conjunction with high-frequency and -field EPR spectroscopic data, relevant spin Hamiltonian parameters were determined. The negative sign of the axial zero-field splitting parameter (D) shows that Mn(acac)3 exhibits a Jahn-Teller distortion as an axial (tetragonal) elongation.
Perpendicular- and parallel-mode X-band CW EPR was used to study the manganese dependent form of OxDC. These results show that while no manganese oxidation was observed during enzymatic turnover, formation of a tyrosine radical was detected.
Paramagnetic surface defect sites on TiO2 were studied by X-band CW EPR. Using a rhenium carbonyl complex as a probe molecule, a detailed description of the surface defect structure is described.