Luminescence and Raman Spectroscopic Characterization of Tyrosine Oxidized by Persulfate

Abstract

To gain insight into the photochemistry of oxidized amino acids, we have measured chemiluminescence and Raman spectra of persulfate oxidized tyrosine (POT). Chemiluminescence kinetics were obtained from a sealed capillary tube containing a basic POT solution. Excitation at 488.0 nm and monitoring emission at 633 nm produced a first-order rise and a second-order decay in intensity to steady-state levels. We collected steady-state emission spectra from a flow system excited by argon-ion and helium-neon laser radiation. The full-width at half-maximum, position, and intensity of fluorescence were measured. The full-width at half-maximum (3600 cm−1) was independent of excitation wavelength. At higher energy excitation, the emission maximum was independent of excitation line. At lower energy excitation, the emission maximum varied with the excitation line. The emission intensity dropped by a factor of 6 as the excitation wavelength was varied from 465.8 nm to 514.5 nm. Luminescence was also observed upon excitation at 632.8 nm of this compound dissolved in DMSO. Raman data, obtained from solid polymer suspended in a KBr pellet (rotating sample cell, 488.0 nm excitation, S cm−1 bandpass), revealed broad bands at 1385 cm−1, 1590–1615 cm−1, and 2930 cm−1 superimposed upon a weak fluorescent background. Upon ultraviolet laser excitation (363.8 nm, 5 mW power on the sample, 5 cm−1 bandpass), a single broad band appeared, centered at 1300 cm−1. The difference from visible excitation implies that resonance enhancement from an ultraviolet absorbing chromophore occurred.