Fluorescence Quenching and Isotope Effect of Tryptophan

Abstract

The fluorescence spectra and quantum yields of trytophan (TRP) and several tryptophan derivatives in water and a polar glass have been measured over wide temperature ranges. For TRP, the wavelength of maximum emission shifts from 310 nm at 80°K to 355 nm at room temperature with almost all of the red shift occurring between 170° and 230°K, which is the temperature range where the glass softens. The successively more red-shifted spectra have no isoemissive wavelength, which supports the view that reorientation of several solvent molecules in the solvent shell of the excited TRP molecule and not a 1:1 exciplex is responsible for the red shift. The quantum yield remains constant until a temperature is reached at which solvent reorientation is virtually complete. Above that temperature, the quenching of the 355-nm emission can be fitted with a nonradiative de-excitation having an activation energy of 7 kcal/mole. A model for these spectral changes and quenching mechanism will be offered. In deuterated solvents, a large isotope effect of fluorescence yield of TRP has been reported. This effect is clearly not caused by proton transfer in the excited state since it is found to be virtually the same for TRP and 1-Me-TRP. At temperatures below those at which solvent reorientation occurs, the isotope effect vanishes, and above them it approaches an asymptotic value, the quenching activation energy being independent of the isotopic constitution of the solvent. The fluorescence of most proteins and hormones originates in their tryptophan residues. The quantum yields, isotope effects, and emission spectra of such polypeptides are compared with the corresponding parameters for solvated TRP.

Investigating the molecular and aggregated states of a drug molecule rutaecarpine using spectroscopy, microscopy, crystallography and computational studies

“…43,44 The radiative and non-radiative rate constants for rutaecarpine in molecular as well as aggregated states with the variation of water contents have also been estimated. 72,73 This has been clearly observed in the present case for the colloidal solution of rutaecarpine with the increase in temperature. For the solution of rutaecarpine in 35% v/v solution of DMSO and water, the radiative rate constant (k r ) is observed to be 1 Â 10 8 s À1 .…”

Fluorosolvatochromism of monomethyl indoles: further evidence in support of a new photophysical model for the indole chromophore

“…For the reasons exposed, we think that an interpretation of this behavior based on the model of Eisinger and Navon should be discarded and the model recently proposed by us should be also open up to a possible structural change or to a possible aggregation of the compound.…”

“…This situation is similar to that present for indole in ClB, which shifts bathochromically its spectrum by Δῦ = +917 cm −1 . This spectral behavior of 6‐MeIndole and of Indole is immediately explained by the model of Eisinger and Navon, based on a strong rearrangement of some solvent molecules leading to an emission from 1 L a state that may be blocked, preventing that these solvent molecules move themselves responding to the strong dipolar demand of the compounds.…”

Fluorescence study of the thyroxine‐dependent conformational changes in human serum transthyretin

“…The curves of thermal quenching of emission indicate the temperature dependence of the frequency of active collisions and therefore the dynamic mobility rate of protein structures surrounding the tryptophans [11]. Their nonradiative de-excitation rate is limited by the activation energy of quenching, E,, which can be calculated from the slope of the straight line obtained by plotting log (I/Q -1) versus 1/T, where Q is the fluorescence quantum yield of tryptophans and T is the absolute temperature [12].…”