Radical formation of amino acid precursors in interstellar regions? Ser, Cys and Asp

It is proposed that the glycine precursor NH2CH2CN may be synthesised in interstellar dust clouds by the radical combination reactions NH2˙ + ˙CH2CN → NH2CH2CN (ΔG = −302 kJ mol−1) and/or NH2CH2˙ + ˙CN → NH2CH2CN (ΔG = −414 kJ mol−1). All calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31+G(d) level of theory. This paper extends that concept to radical/radical coupling reactions to form Ser, Cys and Asp precursor nitriles. The hydrogen abstraction process NH2CH2CN + HO˙ → NH2˙CHCN + H2O (ΔG = −130 kJ mol−1) is suggested to precede the radical coupling reactions NH2˙CHCN + R˙ → NH2CHRCN (R˙ = ˙CH2OH, ˙CH2SH and ˙CH2CN) to form nitrile precursors of the amino acids Ser, Cys and Asp. These three reactions are all favourable (ΔG = −240, −227 and −223 kJ mol−1). The radical species ˙CH2NH2, ˙CH2OH, ˙CH2SH and ˙CH2CN are shown to be stable for the microsecond timeframe by a combination of theoretical calculations and the experimental mass spectrometric neutralization/reionization procedure.