Low energy electron induced fragmentation of hot asparagine and aspartic acid molecules

Asparagine (Asn) and aspartic acid (Asp) are not only amino acids found in proteins but also building blocks for synthesis of eco-friendly polymers with techniques such those in which electrons play a role. In this contribution, we present a comparative study of dissociative electron attachment (DEA) to Asn and Asp under gas-phase conditions by means of DEA spectroscopy. In contrast to a number of amino acids studied so far, the formation of the dehydrogenated parent anion, (M - H)-, at about 1.2 eV from both investigated compounds is not the most intense dissociation channel. On the other hand, prominent negative ion resonances are observed peaking below 0.5 eV, resulting in the formation of fragment anions generated from a loss of a neutral -COOH group or neutral H2O2 molecule or leading to the production of HCOO- from both asparagine and aspartic acid. It should be stressed here that the surrogation of one hydroxyl group by an amino group in aspartic acid, which results in the formation of asparagine, sensitizes the latter compound for the loss of an entire neutral carboxyl group. Indeed, the formation of the (Asn - COOH)- anion from DEA to asparagine is more efficient by about an order of magnitude than the formation of the (Asp - COOH)- anion from DEA to aspartic acid.