Intramolecular Excited‐State Hydrogen Transfer in Rutin and Quercetin

Abstract

Steady‐state and time‐resolved optical spectroscopy techniques were employed to study the excited‐state intramolecular hydrogen transfer (ESIHT) in rutin, a flavonol that contains a disaccharide and is a natural product in plants. The results are compared with those of a similar natural compound, quercetin, which also has a flavonol structure. The fluorescence decay signal of the normal form of these two compounds is composed of three time components. The ESIHT rate in both compounds has a time constant of 70 fs or less. The ESIHT processes of both compounds show a distinctive kinetic isotope effect of 1.5 or more. The intermediate and long‐time components are about 300 fs and a few picoseconds, respectively, for both compounds. The amplitude of the intermediate component in rutin is twice that of quercetin. We explain this difference as arising from the hydrogen bonding of the glucose in rutin to the ESIHT active site.

Concentration-Dependent Fluorescence Emission of Quercetin

“…However, in Ref. [23] the FL spectrum of Q solution in methanol with the concentration of 50 µM have been shown. The excitation wavelength in that study was of 350 nm.…”

“…This is probably due to the fact that a different excitation wavelength (405 nm) was used in our study. Another possible reason for that discrepancy is that the measured solution of Q in the methanol [23] was relatively fresh and the Q molecules were yet not dissipated. Unfortunately, the data about the time between the solution preparation and its measurement was absent in that reference.…”

Charge Transfer in Proteins: In Celebration of Hemi Gutman's 80 th Birthday

“…A close insight into the chemistry of transfer reactions on the surface is provided by Simkovitch and Huppert, who discuss their recent studies of intramolecular excited-state hydrogen transfer on two flavonols. [14] Finally, three articles report on computational studies involving proteins. Ben-Tal and coworkers used computational analysis to discuss a problem related to the evolution of a protein domain.…”