Pathways for the Formation of Formamide, a Prebiotic Biomonomer: Metal-Ions in Interstellar Gas-Phase Chemistry

Abstract

The chemistry occurring in the interstellar medium (ISM) is an active area of contemporary research. New aspects of interstellar chemistry are getting unraveled regularly. In this context, the role of metal-ions in the chemistry occurring in the ISM is not well-studied so far. Herein, we highlight the role of metal-ions in interstellar chemistry. For this purpose, we choose the problem of gas-phase formamide formation in interstellar molecular clouds. Formamide is a key biomonomer and contains the simplest peptide [−(CO)–NH−] linkage. With its two electronegative atoms (“O” and “N”), it provides an excellent platform to probe the role of the metal-ions. The metal-ions chosen are Na+, K+, Al+, Mg+, and Mg2+all of them present in the ISM. The metal-ions are studied in three different forms as bare positively charged ions, as hydrated metal-ions co-ordinated with a molecule of water, and when the metal-ions are part of a neutral covalent molecule. With the aid of electronic structure calculations [CCSD­(T) and DFT methods], we study different gas-phase pathways which result in the generation of interstellar formamide. Throughout our study, we find that metal-ions lower the barriers (with Mg+, Mg++, and Al+ offering maximal stabilization of the transition states) and facilitate the reactions. The chemical factors influencing the reactions, how we consider the putative conditions in the ISM, the astrochemical implications of this study, and its connection with terrestrial prebiotic chemistry and refractory astrochemistry are subsequently presented. Based on our results, we also recommend the detection of two new closed-shell molecules, NH2CH2OH (aminomethanol) and CH2NH2 + (iminium ion), and two open-shell molecules, CONH2 (carbamyl radical) and HCONH (an isomer of carbamyl radical), in the ISM.

Possible Role of Metal-Ions in the Chemistry of Prochirality and the Origin of Chirality in the Interstellar Medium

“…In this section, we shall first present our computational results for the interstellar formation of ethylene oxide, followed by that of propylene oxide. Throughout, consistent with our protocol followed in earlier works, , subsequent analysis is based on zero-point corrected quantum chemical energies and not free-energies. This is done to avoid any assumption based on the prevalence of Boltzmann distributions, which may not always be valid in all parts of the ISM.…”

“…In fact, we did not consider the chemistry of other main group elements such as Na + , K + in this work, given the nature of the barriers, when they were proposed to mediate the formation of other iCOMs . However, just as Woon has rightly pointed out very recently, we opine that a huge trove of new chemistry in the ISM is expected to come out by investigating the role of metal-ion mediated generation of iCOMs in the ISM including both main-group as well as transition metals. Interstellar prochirality and chirality: Propylene is a prochiral molecule.…”

“…The bare ions in this study could plausibly be obtained by cosmic ray irradiations of the neutral molecules, which first are thought to undergo excitation, followed by ionization. Water molecules are also abundantly present in the ISM, and they may bind with the electropositive metal-ions with their electronegative oxygen end. Yet, liquid water does not exist in any region of the ISM. , Given the very low number density in the ISM, we chose only one water molecule to model the hydrated metal-ion in the ISM, as was done in our earlier work too . As in turns out, the hydrated metal-ions render the pathway to be maximally feasible. Our finding that the reactions are barrierless even with neutral metal-bearing molecules is both chemically and astrochemically important.…”

Icy Grain Mantle Surface Astrochemistry of MgNC: The Emergence of Metal Ion Catalysis Studied via Model Ice Cluster Calculations

“…More than half a decade passed between the discovery of a new but unknown radical species in 1986 by Cernicharo et al and the experimental work of Kawaguchi et al and supporting theoretical work of Ishii et al which demonstrated that the unidentified molecule was MgNC. In addition to the further detections of Mg-containing compounds enumerated previously, various experimental, theoretical, and modeling studies have appeared in the following next three decades. − Work continues, with recent theoretical efforts to characterize magnesacylopropane, c-MgC 2 H 2 , and to elucidate gas phase routes to formamide mediated by Mg + , Mg 2+ , and other metal ions . However, all of the cited prior efforts focused exclusively on gas phase processes.…”

“…33−60 Work continues, with recent theoretical efforts to characterize magnesacylopropane, 60 c-MgC 2 H 2 , and to elucidate gas phase routes to formamide mediated by Mg + , Mg 2+ , and other metal ions. 58 However, all of the cited prior efforts focused exclusively on gas phase processes. In the present work, the chemistry of MgNC adsorbed onto an ice surface is explored.…”