Photochemistry, photophysics and spectroscopy of redox states of flavins relevant to photoactive flavoproteins

There has been a tremendous interest in the study of flavins and their derivatives in order to gain information valuable for designing model compounds that can mimic the functions of flavoenzymes. This thesis aims a) to explore and enhance the knowledge about the behavior of the flavin cofactors in its different redox states b) to further study and develop the mechanism of BLUF domain protein. To achieve a better understanding of flavin behavior, we conducted a comparative study of excited state dynamics of different redox states of flavin cofactors in both aqueous solutions and protein. In this thesis, we present the systematic study of excited-state dynamics of the common flavin molecule: FAD and its fully reduced hydroquinones: FADH2 and FADH- together with its radical semiquinones: FADH● and FAD●- with the visible to mid-IR transient absorption spectroscopy. Ground and excited state frequencies of the characteristic carbonyl modes are observed and assigned with the aid of DFT calculations. Moreover, the stable neutral radical flavin has been prepared for study in aqueous solution, and both neutral and anionic radical states have been stabilized in the protein: flavodoxin and glucose oxidase. Ultrafast transient absorption measurements were performed in the visible and mid infrared region in order to characterize the excited and ground state‟s dynamics and vibrational spectra, and to probe the effect of the protein matrix on them. We also report our comprehensive studies of radiationless decay in reduced and radical flavins using ultrafast spectroscopy and temperature dependent fluorescence. Those model results are essential inputs to help us analyzing the flavin photo-kinetics in proteins and thus advance the knowledge of BLUF domain protein.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2012

Author dc:creator

• Zhao, Ruikun

Language dc:language

en