Band-Shape Analysis of Delayed Slow-Passage ODMR in the Photoexcited Triplet State of Tryptophan

Abstract

Delayed slow passage optically detected magnetic resonance (ODMR) band shapes of the triplet state of tryptophan, lysyl-tryptophanyl-lysine, N-acetyl tryptophanamide, and ribonuclease T1 from A. oryzae (RNaseT1) in low-temperature aqueous glass are analyzed using data obtained from independent microwave-induced delayed phosphorescence (MIDP) measurements as fixed input parameters. This method which uses only the band center frequency, Gaussian width, overall amplitude, and baseline position as variables is compared with a previously employed empirical analysis (Wu, J. Q.; Ozarowski, A.; Davis, S. K.; Maki, A. H. J. Phys. Chem. 1996, 100, 11496) that requires many more variables. Comparable quality of fit is found for the new, more rigorous method for each band except for the Tx ↔ Tz (D−E) ODMR transition which (with the exception of RNaseT1) deviates systematically when using the fixed kinetic parameters. The quality of fit of this band becomes comparable to that of the multiparameter empirical method upon introduction of dispersion in kx, which assumes values between −1 and −2 s-1/GHz. The sign and magnitude of this dispersion are consistent with previous kinetic data. Band centers and widths are altered only slightly from those obtained by the earlier empirical analysis.