Dynamic fluorescence quenching, interaction

P. B. Contino and W. R. Laws, Rotamer-specific fluorescence quenching in tyrosinamide Dynamic and static interactions, J. Fluorescence 1, 5-13 (1991). 

How may these measured functions be related to the rate coefficients of reactions of the excited species It is useful to consider how the excitation arises and the various ways in which the excited species may dissipate its excess energy. Suppose A is excited to A which reacts with B to give products. There are two distinct mechanisms which may be considered for such a fluorescence quenching process. Before the transfer of energy from A to B is possible the species must form an encoimter complex in which the solvent cages of A and B have been sufficiently modified to allow significant chemical interaction between the two reactants. By the dynamic, or diffusional, pathway A is formed in comparative isolation from B, and the encounter complex is produced as a second step... 

In this chapter results of the picosecond laser photolysis and transient spectral studies on the photoinduced electron transfer between tryptophan or tyrosine and flavins and the relaxation of the produced ion pair state in some flavoproteins are discussed. Moreover, the dynamics of quenching of tryptophan fluorescence in proteins is discussed on the basis of the equations derived by the present authors talcing into account the internal rotation of excited tryptophan which is undergoing the charge transfer interaction with a nearby quencher or energy transfer to an acceptor in proteins. The results of such studies could also help to understand primary processes of the biological photosynthetic reactions and photoreceptors, since both the photoinduced electron transfer and energy transfer phenomena between chromophores of proteins play essential roles in these systems. 

The fluorescence quenching dynamics of excited state electron donors by various pyrimidine and 5,6-dihydropyrimidine substrates have been examined and found to obey the Rehm-Weller relationship." In addition, an unexpected difference was observed between the reduction potentials for the trans-syn and cis-syn diastereoisomers of dimethylthymine cyclobutane dimers, and this has been ascribed to a stereoelectronic effect in the cis-syn dimer anion radical resulting from an unfavourable charge-dipole interaction between the added electron and the O carbonyl group of the pyrimidine ring... 

This equation is traditionally used to quantify fluorescence quenching efficiency by additives at low concentrations that bind or otherwise interact with the fluorescent species, where the Stern-Volmer constant ( sv) is conventionally taken as a measure of the quenching efficiency, y, times the diffiision-lirmtod bimolecular rate for the dynamic quenching process. 

Previously, we have studied fluorescence quenching in unsolvated dye-derivatized biomolecules by performing measurements of fluorescence lifetime, intensity and emission spectrum as a function of temperature. These studies have identified that fluorescence quenching is dependent on conformational dynamics which lead to interactions between the dye and a Trp (Tryptophan) side chain in peptides [34,35] and small protein [36,37] structures. 

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