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THE PHOTOLYSIS OF TRYPTOPHAN WITH 337.1 nm LASER RADIATION
Author(s) -
Borkman R. F.,
Hibbard L. B.,
Dillon James
Publication year - 1986
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1986.tb05585.x
Subject(s) - photodissociation , chemistry , tryptophan , photochemistry , absorption (acoustics) , fluorescence spectroscopy , analytical chemistry (journal) , fluorescence , chromatography , materials science , optics , biochemistry , physics , amino acid , composite material
— Aqueous solutions of L‐tryptophan were photolyzed by exposure to 337.1 nm radiation from a pulsed nitrogen laser. These data were compared with results for the 290 nm conventional‐source photolysis of tryptophan. The progress of photolysis was monitored by fluorescence analysis of tryptophan. UV absorption spectroscopy, HPLC, TLC, and proton NMR spectroscopy. The loss of Trp was observed to be first order for 290 nm photolysis but of mixed order for 337.1 nm photolysis. Five photolysis products were detected by TLC analysis, including: N‐formylkynurenine. kynurenine, tryptamine (detected after 290 nm photolysis but not 337.1 nm photolysis) and two unknown products. The tryptophan‐containing peptides N‐acetyl‐tryptophanamide (NATA) and tryptophylglycine (Trp‐Gly) were also observed to photolyze upon 337.1 nm laser radiation demonstrating that this phenomenon is not restricted to free tryptophan monomer. Since Trp is not ordinarily thought to absorb U V radiation at wavelengths as long as 337.1 nm. a number of experiments were performed in an effort to determine the mechanism of photolysis at this wavelength. Evidence is presented which indicates that the 337.1 nm laser photolysis of Trp does not result from two photon absorption, dielectric breakdown, or other laser‐specific processes. Instead. it is concluded that this photolysis results either from a very weak absorption tail extending to 337.1 nm in tryptophan itself or from a reaction involving an impurity sensitizer which absorbs the 337.1 nm radiation. The sensitizing impurity. if present, could not. however, be removed by preparative HPLC and could not be detected by TLC or fluorescence analysis.