Influence of the side chain in the structure and fragmentation of amino acids radical cations

Adrià Gil, Silvia Simon, Luis Rodríguez-Santiago, Juan Bertrán, Mariona Sodupe

Research output: Contribution to journalArticleResearchpeer-review

37 Citations (Scopus)

Abstract

The conformational properties of ionized amino acids (Gly, Ala, Ser, Cys, Asp, Gln, Phe, Tyr, and His) have been theoretically analyzed using the hybrid B3LYP and the hybridmeta MPWB1K functional as well as with the post-Hartree Fock CCSD(T) level of theory. As a general trend, ionization is mainly localized at the -NH2 group, which becomes more planar and acidic, the intramolecular hydrogen bond in which -NH2 acts as proton donor being strengthened upon ionization. For this reason, the so-called conformer IV(+) becomes the most stable for nonaromatic amino acid radical cations. Aromatic amino acids do not follow this trend because ionization takes place mainly at the side chain. For these amino acids for which ionization of the side chain prevails over the -NH2 group, structures lll(+) and ll(+) become competitive. The Cα-X fragmentations of the ionized systems have also been studied. Among the different decompositions considered, the one that leads to the loss of COOH• is the most favorable one. Nevertheless, for aromatic amino acids fragmentations leading to R• or R+ start being competitive. In fact, for His and Tyr, results indicate that the fragmentation leading to R+ is the most favorable process. © 2007 American Chemical Society.
Original languageEnglish
Pages (from-to)2210-2220
JournalJournal of Chemical Theory and Computation
Volume3
Issue number6
DOIs
Publication statusPublished - 1 Nov 2007

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