title: Ultrafast transient mid IR to visible spectroscopy of fully reduced flavins.
abstract: The light sensing apparatus of many organisms includes a flavoprotein. In any spectroscopic analysis of the photocycle of flavoproteins a detailed knowledge of the spectroscopy and excited state dynamics of potential intermediates is required. Here we correlate transient vibrational and electronic spectra of the two fully reduced forms of flavin adenine dinucleotide (FAD): FADH(-) and FADH(2). Ground and excited state frequencies of the characteristic carbonyl modes are observed and assigned with the aid of DFT calculations. Excited state decay and ground state recovery dynamics of the two states are reported. Excited state decay occurs on the picosecond timescale, in agreement with the low fluorescence yield, and is markedly non single exponential in FADH(-). Further, an unusual 'inverse' isotope effect is observed in the decay time of FADH(-), suggesting the involvement in the radiationless relaxation coordinate of an NH or hydrogen bond mode that strengthens in the excited electronic state. Ground state recovery also occurs on the picosecond time scale, consistent with radiationless decay by internal conversion, but is slower than the excited state decay.
authors: School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK.
authors: Rui-Kun
authors: RK
authors: Zhao
authors: Andras
authors: A
authors: Lukacs
authors: Allison
authors: A
authors: Haigney
authors: Richard
authors: R
authors: Brust
authors: Gregory M
authors: GM
authors: Greetham
authors: Michael
authors: M
authors: Towrie
authors: Peter J
authors: PJ
authors: Tonge
authors: Stephen R
authors: SR
authors: Meech
mesh_terms: D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
chemical_list: D005182:Flavin-Adenine Dinucleotide