Photodissociation dynamics of tryptophan and the implication of asymmetric photolysis

Photodissociation of amino acid tryptophan in a molecular beam at wavelengths of 212.8 and 193 nm, corresponding to excitation to the second and third absorption bands, was investigated using multimass ion imaging techniques. The respective wavelengths also represent excitation to the edge of a positive circular dichroism band and the center of a negative circular dichroism band of L-tryptophan. Only one dissociation channel was observed at both photolysis wavelengths: C8NH6CH2CHNH2COOH -> C8NH6CH2 + CHNH2COOH. Dissociation rates were found to be 1.3 x 10(6) and 5 x 10(6) s(-1) at the respective wavelengths. Comparison to theoretical calculation indicates that dissociation occurs on the ground state after internal conversion. Implication of asymmetric photolysis is discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3474992]