The electronic spectroscopy of tyrosine and phenylalanine analogs in a supersonic jet: Acidic analogs

Abstract

Fluorescence excitation spectra of the origin regions of 3-(4-hydroxyphenyl) propionic acid, 3-(4-methoxyphenyl) propionic acid, and hydrocinnamic acid have been measured in a supersonic jet. Power dependence studies reveal the existence of one, one, and two conformers, respectively. The dispersed emission spectra of these molecules were measured and analysis of the region of the spectrum near the electronic origin confirms our conformer assignments. Molecular modeling calculations are used to propose the most reasonable structures for these conformers. The fluorescence lifetimes of the conformers of these molecules were measured. The fluorescence decays of hydrocinnamic acid were found to be single exponential and the lifetimes of its two conformers are 67 ± 6 and 76 ± 5 nsec. The fluorescence decay of 3-(4-methoxyphenyl) propionic acid was also found to be single exponential and the lifetime of its conformer is 15 ± 3 nsec. In the case of 3-(4-hydroxyphenyl) propionic acid only an upper limit of 10 nsec can be given to its conformer lifetime because of our limited time resolution. This work serves as a basis for interpreting the more complicated spectroscopy of the amino acids tyrosine and phenylalanine. © 1991.