Abstract
The results of time-resolved fluorescence measurements of flavin mononucleotide (FMN) in rigid polyvinyl alcohol films (PVA) demonstrate that fluorescence intensity decays are strongly accelerated in the presence of fluorescent dimers and nonradiative energy transfer processes. The fluorescence decay originating both from H and J dimer states of FMN was experimentally observed for the first time. The mean fluorescence lifetimes for FMN dimers were obtained: = 2.66 ns (at λexc = 445 nm) and = 2.02 (at λexc = 487 nm) at λobs = 600 nm and T = 253 K from H and J state of dimers, respectively. We show that inhomogeneous orientational broadening of energy levels (IOBEL) affects the shape of the fluorescence decay and leads to the dependence of the average monomer fluorescence lifetime on excitation wavelength. IOBEL affected the nonradiative energy transfer and indicated that different flavin positioning in the protein pocket could (1) change the spectroscopic properties of flavins due to the existence of âblueâ and âredâ fluorescence centers, and (2) diminish the effectiveness of energy transfer between FMN molecules.
Highlights
With the increase in concentration, the fluorescence decays are accelerated. They are deviated from a single exponential character. This can be explained by the formation of flavin mononucleotide (FMN) dimers (D) with increasing concentration and nonradiative energy transfer (NET) from monomers (M) to dimers (D), preceded by energy migration between monomers [21] which arise with increasing concentration, too
The fluorescence decays for FMN in polyvinyl alcohol films (PVA) were performed at the observation of λobs = 600 nm, at the edge of the fluorescence band, to obtain the clear decays coming from dimers states
The examination of fluorescence decays clearly shows that NET processes and dimer formation with increasing concentration of FMN greatly shortens the fluorescence decay time of FMN samples in concentrations ranging from 6.9 Ă 10â4 M to 6.8 Ă 10â1 M
Summary
Light is a key environmental factor affecting the physiology and evolution of most organisms. An extra-cellular light signal is transformed into an intra-cellular response by a photoreceptor built of the protein fragment and a photopigment. Photoreceptor proteins bind riboflavins, which are chromophores of plants. The major flavinâriboflavin [1]âis synthesized by plants, fungi, and various bacteria, and is a flavin precursor (FMNâflavin mononucleotide, FADâflavin adenine dinucleotide, and RFâriboflavin). Flavins are important compounds that are present in many biological systems. They take part in cell energetic processes, where they play the role of electron and proton transporters (as coenzymes), as well as chromophores in photoreceptors sensitive to blue light [2,3]
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