Degree Type

Dissertation

Date of Award

1994

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

J. W. Petrich

Abstract

Time-resolved and steady-state fluorescence study of the biological optical probe, 7-azatryptophan, its chromophoric moiety 7-azaindole are performed in order to explain the observation that the fluorescence spectrum of 7-azaindole (7-azatryptophan) apparently consists of one band in water ([lambda][subscript]sp\max em = 386nm) whereas in alcohols the spectrum is bimodal (eg. for methanol, [lambda][subscript]sp\max em = 374, 505nm). Careful measurements of the fluorescence decay as a function of emission wavelength indicate a small amplitude of an ~70 ps decaying component at the bluer wavelength and a rising component of the same duration at the redder wavelengths. The small amplitude component, which comprises no more than 20% of the fluorescence decay, is attributed to excited-state tautomerization that is mediated by the solvent. The fluorescence emission maximum and lifetime of 7-azaindole is dominated by the 80% of the solute molecules that are blocked by unfavorable solvation from executing excited-state tautomerization;The proton inventory technique is used for the first time to investigate excited-sate proton transfer processes. The nonradiative pathways of the 7-azaindole, in methanol, ethanol, and water are examined. Results in methanol and ethanol demonstrate the involvement of two protons in the transition state for the excited-state double-proton transfer process. These data provide the first experimental evidence suggesting a concerted tautomerization of 7-azaindole in alcohols. The data in water are different from that in alcohols. The abstraction of N[subscript]1 hydrogen by water as a possible nonradiation decay process has been proposed. The solvation of 7-azaindole in water and alcohols is discussed generally;The fluorescence lifetime measurements of 7-azatryptophan as a function of pH and nonaqueous solvents are performed to explain the single exponential decay in water. The observation of such phenomenon is discussed in terms of nonradiative processes-proton transfer-that compete effectively with charge transfer from the excited-state 7-azaindole to the side chain groups and in terms of the dependence of the charge reaction on the excited-state energy of 7-azaindole. The potential for 7-azatryptophan as an optical probe of biological molecules is discussed.

DOI

https://doi.org/10.31274/rtd-180813-11140

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Yu Chen

Language

en

Proquest ID

AAI9424203

File Format

application/pdf

File Size

182 pages

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