Evaluating Temperature Variations, Energy Fluctuations, and Pathways When Excitons Are Transferred in the FMO Complex

ABSTRACT The Fenna-Matthews-Olson protein of green sulphur bacteria is a model photosynthetic unit. Therein, coupled chromophores transfer energy from antennae to a reaction centre. Close to unit quantum yield efficiencies have been recorded and wave-like transfer also observed in the Fenna-Matthews-Olson complex. The protein also possesses a relatively simple structure. These features have meant that the complex has been the subject of many investigations. In this thesis, primary aims are the assessment of how dynamics in a Fenna-Matthews-Olson monomer are affected by a change in temperature and explicit inclusion (or exclusion) of intra-molecular vibrational modes following a characterization of important values. A genetic type algorithm was crucial in parameterizing equations of motion that described energy transfer. Excellent fits to Fenna-Matthews-Olson spectra at 77 K were obtained by this evolutionary algorithm, so confidence could be expressed in any subsequent results. In the absence of explicitly including vibrational modes, it is proposed that transport of excitation populations is greatly conditioned by fine details in the density of state distributions for excitonic states. Non-trivial energy transfer was observed in one set of simulations; occupation of low-energy states was clearly enhanced at physiological temperatures relative to low temperature. The ‘skew’ of energy distributions, entering into equations of motion via a random sampling technique, are seen as being crucial and these affect resonance conditions in trajectories. When non-resonant vibrational modes were explicitly included in simulations, inter-state beatings were strong although energy transfer was not perceptibly enhanced relative to when only resonant modes were incorporated. Finally, pathways through the complex depended on low energy states with transfer towards the reaction centre inhibited if chromophores in the low to intermediate part of the excitonic spectrum had large resonance gaps.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2015

Author dc:creator

• Gillis, Colm

Language dc:language

en