Prebiotic Synthesis and Isomerization in Interstellar Analog Ice: Glycinal, Acetamide, and Their Enol Tautomers

Abstract

Glycinal (HCOCH2NH2) and acetamide (CH3CONH2) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic rays. Glycinal and acetamide are accessed via barrierless radical‐radical reactions of vinoxy (⋅CH2CHO) and acetyl (⋅C(O)CH3), and then undergo keto‐enol tautomerization. Exploiting tunable photoionization reflectron time‐of‐flight mass spectroscopy and photoionization efficiency (PIE) curves, these results demonstrate fundamental reaction pathways for the formation of complex organics through non‐equilibrium ice reactions in cold molecular cloud environments. These molecules demonstrate an unconventional starting point for abiotic synthesis of organics relevant to contemporary biomolecules like polypeptides and cell membranes in deep space.

Kinetics of the tautomerization of thioimidic acids R−C(SH)NH → R−C(S)NH2: For R = H, F, HO, CN, NC, H2N, HC(O), HC(S), HC≡ C, CH3, CF3, H2C=CH, HOCH2, H2NCH2,CH3C(O), C2H5, (CH3)2CH, C6H5

“…Concrete examples in the literature do not abound but Marks et al. identified 66 H 2 C=C(OH)NH 2 as being formed, but not H 3 CC(OH)NH, from acetamide during the irradiation of ammonia–acetaldehyde ices by proxies of galactic cosmic rays (GCRs) which they mechanistically portray as: $$$$\begin{eqnarray*} &&\text{H}_3\text{CC(O)H} + \text{NH}_3 \xrightarrow {\text{GCR}} \text{CH}_3\text{C(O)}^\bullet + \text{NH}2^\bullet \\ & \longrightarrow & \text{H}_3\text{C}-\text{C(O)}-\text{NH}_2 \\ & \longrightarrow & \text{H}_2\text{C}=\text{C(OH)}-\text{NH}_2 \end{eqnarray*}$$$$However, as is the case for the O‐analog, the zero‐point corrected electronic energy barrier amounts to 286.0 kJ mol −1 for H 3 C‐C(S)NH 2 → H2C=CH(SH)NH2 which is considerably higher than the tautomerizations at issue here.…”

Peptide Bonds in the Interstellar Medium: Facile Catalytic Formation from Nitriles on Water–Ice Grains

“…14 Most recently Marks et al have carried out experiments involving acetaldehyde (ethanal) ammonia mixtures undergoing irradiation with simulated galactic cosmic rays. 15 The compounds arise, they suggest, as the result of barrierless radical−radical recombination reactions:…”

“…Most recently Marks et al have carried out experiments involving acetaldehyde (ethanal) ammonia mixtures undergoing irradiation with simulated galactic cosmic rays. 15 They report the formation of glycinal, HC(O)CH 2 NH 2 , and acetamide and their tautomers HC(OH)CHNH 2 and H 2 C=C(OH)NH 2 . The compounds arise, they suggest, as the result of barrierless radical–radical recombination reactions: …”