Ivan K. Chu
University of Hong Kong, China
Title: Isomerization versus dissociation of phenylalanylglycyltryptophan radical cations
Biography
Biography: Ivan K. Chu
Abstract
Herein we report the propensity of radical migration and hence isomerization, or there lack of, in four tripeptide structures (FGW) that differ only in their initial radical locations: the π-system of Trp, the indole nitrogen, the α-carbon of Gly, and C-4 of the Phe ring. These radicals were generated by well-defined means and examined using tandem mass spectrometry. The π- and the N-radical centered on Trp interconvert after collisional activation; by contrast, the α-radical and the ζ-radical (on Phe) retain their distinctness even after collisional activation. Density functional calculations reveal a relatively low (31.1 kcal mol-1) barrier against interconversion between the π- and the N-radical, while interconversion between the α-radical and the ζ-radical exhibits much higher barriers, and these radicals will dissociate before they can interconvert. This study illustrates the intricate balance between radical migration and dissociation as exhibited by the four isomeric tripeptide radicals.