Side chain effects in reactions of the potassium-tyrosine charge transfer complex

Fragmentation of transient negative ions of tyrosine formed, through electron transfer in collisions with neutral potassium atoms is presented in the collision energy range from 30 to 75 eV. At low collision energies the dominating side chain channel observed corresponds to the cleavage of the bond from the para-position of the phenyl ring to the beta-C of the remaining moiety, but cleavage of the C-alpha-C-beta, bond is also observed. Further fragments are formed through cleavage of the C-alpha bond to the carbonyl group, through decomposition of the carboxyl group or through significant decomposition of the backbone. The dehydrogenated molecular anion is also observed with appreciable intensity. These results are discussed in the context of earlier studies on dissociative electron attachment to tyrosine and other amino acids, as well as within the role of the side chain in electron induced decomposition of this aromatic amino acid. Stabilization of the temporary molecular anion in the transient collision complex is discussed and we argue that this may have significant influence on the branching ratios observed. (C) 2016 Published by Elsevier B.V.