1 April 1992 Fluorescence studies with conformationally constrained tryptophan analogs: implications on the mechanisms of intramolecular quenching
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Abstract
The fluorescence properties of a set of tryptophan analogs, including several that are conformationally restricted, is reported. The conformationally restricted analogs include tetrahydrocarboline-3-carboxylic acid, 3-amino-3-carboxytetrahydrocarbazole, 3- aminotetrahydrocarbazole, and 3-carboxytetrahydrocarbazole. Steady-state and time-resolved measurements were made. The fluorescence decay of most of the conformationally restricted analogs is a bi-exponential. The fluorescence quantum yield and average lifetime of the restricted analogs is a bi-exponential. The fluorescence quantum yield and average lifetime of the restricted analogs are higher than the values for tryptophan and corresponding flexible tryptophan analogs. This indicates that the effective rate constant for intramolecular non- radiative (quenching) processes, knx, is smaller for the restricted tryptophan analogs than for the flexible analogs. For a series of flexible analogs, having a bifunctional side chain, there is synergism between the two functional groups (i.e., (alpha) -NH3+ and (alpha) -CO2- groups) in determining the effective knx. Potential mechanisms for intramolecular quenching mechanisms, which contribute to knx, include proton transfer from a side chain ammonium group to position four of the excited indole ring and charge transfer from the excited indole ring to a side chain acceptor group. By measuring the rate of photo-induced isotope exchange into position four of an analog's indole ring, we have estimated the contribution of proton transfer quenching to the total intramolecular quenching rate constant for several flexible tryptophan derivatives.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Maurice R. Eftink, D. Hu, and Y. W. Jia "Fluorescence studies with conformationally constrained tryptophan analogs: implications on the mechanisms of intramolecular quenching", Proc. SPIE 1640, Time-Resolved Laser Spectroscopy in Biochemistry III, (1 April 1992); doi: 10.1117/12.58198; https://doi.org/10.1117/12.58198
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