Exploring electron dynamics in oxidized light harvesting complex 1 of Rhodobacter spharoides using electron paramagnetic resonance

The unique temperature dependent electron/hole transfer in LH1 ring is of special interest because this protein complex constitutes a type of molecular wire. The purpose of this work is to distill the true process behind electron dynamics in oxidized LH1, i.e. charge transport, by separating other possible dynamics through experiments. In addition, to understand the electron/hole transfer in LH1, it is important to determine the fundamental unit of the molecular building block that assembles LH1 from functional point of view. A dimeric form as suggested by alpha/&betaBChla2 subunit would result in different dynamics scale of electron delocalization in the LH1 because most likely the electron/hole would be localized in the subunit instead of actively transferred within LH1. Finally, to thoroughly comprehend the charge transport process in LH1, it is necessary to unveil the nature of the charge transport, the energy level of the radical cations and the chemistry that accompanies the process.;In this thesis, detergent isolated LH1 from Rb. spharoides was studied as the model system. Before going into results, the experimental procedure for this all the work in this thesis is presented in Chapter 2. Following the experimental procedure is the background theory of EPR and ENDOR in Chapter 3. To address the possible spin-spin interaction of paramagnetic ferricyanide and BChla radical cation, the reaction equilibrium property of ferricyanide and BChla was exploited such that the amount of ferricyanide was varied and the ratio of ferro-to-ferricyanide was controlled to fix the amount of BChla oxidized. Therefore for the same fraction oxidized LH1, the concentration of paramagnetic iron can vary greatly. The results are presented in Chapter 4.;Continuous wave ENDOR was used to answer the molecular building block of LH1 from functional point of view. The ENDOR technique is a more rigorous way to characterize the BChla radical cations in oxidized LH1. ENDOR spectra reveal the coupling strength between unpaired electron and its neighboring nuclei. By taking ENDOR at very low temperature where electron dynamics was believed to slow down significantly and comparing it with previous ENDOR study of monomeric BChla and the special pair in the RC would lead us to determine the fundamental unit that constructs the LH1 accurately. In addition to determining the basic unit of the molecular building block, ENDOR is also useful to describe the electron dynamics in LH1. Along with the chemistry of BChla oxidation, observing the magnitude changes of several ENDOR spectra of oxidized LH1 by different concentration of oxidant but under the same experimental conditions also provides insight about the nature of electron transfer that occurred in the ring that was claimed previously.