University of Kentucky
Producing Reactive Intermediates via Photodriven Electron Transfer
Institution
University of Kentucky
Faculty Advisor/ Mentor
Anne-Frances Miller; John Patrick Hoben
Abstract
Flavoenzymes are essential to all forms of life and make up a large portion of genomes, e.g. 0.25% Homo sapiens and 1.8% Escherichia coli. Flavoproteins are proteins that contain a flavin that may be covalently or non-covalently bound. Flavins are redox-active prosthetic groups; flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN), which are Vitamin B2 derivatives. The flavoprotein name reflects the fact that flavoenzymes are an intense yellow color because the flavin absorbs blue light. Understanding the mechanism by which flavin cofactors are photoexcited and transfer electrons is essential in harnessing flavoproteins for organic electronic applications, e.g. functionalized electrodes. After the initial photoexcitation of flavin, the fluorescence lifetime can be anywhere from 1 femtosecond to 100 nanoseconds until the excited state is quenched by electron transfer. Therefore, femtosecond transient absorption spectroscopy (TAS) was needed to study these extremely short lived excited states. To optimize the yield of electron transfer intermediates, a donor was needed to supply an electron to the vacancy that was formed by exciting the initial flavin group. With this electron hole filled, the flavin adopted an excited semiquinone state. We used fluorescence quenching to measure the efficiency of electron transfer to photoexcited flavins and screened an array of candidate electron donors to identify those with optimal efficiency and favourable dissociation constants. We learned temperature has a significant effect on fluorescence emission intensity in our systems of study. With a reliable way to produce flavin semiquinone, TAS can be utilized to understand the formation and decay of the semiquinone state.
Producing Reactive Intermediates via Photodriven Electron Transfer
Flavoenzymes are essential to all forms of life and make up a large portion of genomes, e.g. 0.25% Homo sapiens and 1.8% Escherichia coli. Flavoproteins are proteins that contain a flavin that may be covalently or non-covalently bound. Flavins are redox-active prosthetic groups; flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN), which are Vitamin B2 derivatives. The flavoprotein name reflects the fact that flavoenzymes are an intense yellow color because the flavin absorbs blue light. Understanding the mechanism by which flavin cofactors are photoexcited and transfer electrons is essential in harnessing flavoproteins for organic electronic applications, e.g. functionalized electrodes. After the initial photoexcitation of flavin, the fluorescence lifetime can be anywhere from 1 femtosecond to 100 nanoseconds until the excited state is quenched by electron transfer. Therefore, femtosecond transient absorption spectroscopy (TAS) was needed to study these extremely short lived excited states. To optimize the yield of electron transfer intermediates, a donor was needed to supply an electron to the vacancy that was formed by exciting the initial flavin group. With this electron hole filled, the flavin adopted an excited semiquinone state. We used fluorescence quenching to measure the efficiency of electron transfer to photoexcited flavins and screened an array of candidate electron donors to identify those with optimal efficiency and favourable dissociation constants. We learned temperature has a significant effect on fluorescence emission intensity in our systems of study. With a reliable way to produce flavin semiquinone, TAS can be utilized to understand the formation and decay of the semiquinone state.