DFT Study of L-Cysteine Fragmentation Route using a Novel Protocol

The analysis of amino acid fragmentation is promising in the search for living organisms in other planets, which could be investigated by just scanning for specific amino acid fragments in their upper atmosphere using advanced spectroscopy techniques. Motivated by this possibility, we develop here a Density Functional Theory (DFT)-based protocol to investigate the fragmentation of an essential constituent of cells: the L-cysteine amino acid. After determining the structural and energetics for neutral and single ionized conformers in good agreement with data available, we propose a novel protocol based upon the analysis of Wiberg bond order indices and Bader's Quantum Theory of Atoms in Molecules (QTAIM) theory. Our results indicate that the alpha carbon is the most favorable point of fragmentation for the CH2SH and COOH radicals after a cysteine molecule single ionization.