Study of the Reactivity of CH₃COOH^+• and COOH⁺ Ions with CH₃NH₂: Evidence of the Formation of New Peptide-like C(O)–N Bonds

Abstract

Acetamide, a small organic compound containing a peptide bond, was observed in the interstellar medium, but reaction pathways leading to the formation of this prebiotic molecule remain uncertain. We investigated the possible formation of a peptide-like bond from the reaction between acetic acid (CH 3 -COOH) and methylamine (CH 3 -NH 2 ) that were identified in the interstellar medium. From an experimental point of view, a quadrupole/ octopole/quadrupole mass spectrometer was used in combination with synchrotron radiation as a tunable source of VUV photons for monitoring the reactivity of selected ions. Acetic acid was photoionized, and the reactivity of CH 3 COOH +• as well as COOH + (produced from either acetic acid or formic acid) ions with neutral CH 3 NH 2 was further studied. With no surprise, charge transfer, proton transfer, and concomitant dissociation processes were found to largely dominate the reactivity. However, a C(O)−N bond formation process between the two reactants was also evidenced, with a weak cross section reaction. From a theoretical point of view, results concerning reactivity and barrier heights were obtained using density functional theory, with the LC-ωPBE range-separated functional in combination with the 6-311++G(d,p) Pople basis set and are in perfect agreement with the experimental data.

About the Formation of NH2OH+ from Gas Phase Reactions under Astrochemical Conditions

“…We have explored and presented a rather long list of possible gas-phase reactions whose outcome is either hydroxylamine or its cation. Hydroxylamine is an important pre-biotic molecule, together with molecules such as urea, ethanolaminem, and propylene oxide [ 35 ] (the only chiral molecule of the batch), whose detection shows how interstellar medium chemistry can bear a complex oxygen–nitrogen chemistry that is the necessary prelude to biochemistry [ 10 ].…”

“…In particular, G+0.693-0.027 appears to possess a very rich nitrogen chemistry with the synthesis of several pre-biotic chemical species such as urea [ 7 ]. The discovery of such molecules concentrated in a specific portion of the interstellar medium support hypotheses such as “RNA-world”, where the pre-biotic ingredients are supposed to be formed in space [ 8 , 9 , 10 , 11 ], especially those containing the biologically all-important N–O bond [ 12 ].…”

On the relevance of the electron density analysis for the study of micro-hydration and its impact on the formation of a peptide-like bond

“…This work also suggests that a C-N bound could be formed from acetic acid and methylamine taken in their fundamental states, in the presence of a small number of water molecules. Following a preliminary study using a mass spectrometer coupled with the synchrotron radiations, 92 we will further investigate this aspect from an experimental point of view.…”

“…The formation of such a peptide-like bond was experimentally observed between ionized acetic acid and methylamine taken separately and close to their fundamental state. 40 Because of the prebiotic and exobiological interest of this reaction, 41,42,43 it seems necessary to deepen the research on this kind of reaction, starting from neutral or ionized reagents, especially by determining the role that some water molecules could play on the reaction. Water plays indeed a major role in the chemistry of the interstellar medium.…”