Photochemical Steps in the Prebiotic Synthesis of Purine Precursors from HCN

Abstract

So much excitement: The mechanism for the photoconversion of the HCN tetramer into a precursor of purine nucleobases and nucleotides has been revealed by computational methods. Dissipation of the photoenergy in less than 2 ps eliminates the possibility of hot-ground-state reactions. Instead, a series of photoexcitations followed by internal conversion (IC) drives the reaction via an excited azetene

Prebiotic Chemistry of HCN Tetramerization by Automated Reaction Search

“…After the revolutionary experiments by Miller and Oró,t here were several studies of the mechanistic detailso ft hese reactions.I nar ecent computational study,t he Miller's experiment was successfully simulated by using Nanoreactor,a na bi nitio molecular dynamics package. [13] Barbatti's group studied the photochemical steps involvedi nt he formation of ap urine precursorf rom aH CN tetramer, [14] which provided support for the mechanisms proposed by Ferris and Orgel. [15] In this work, we were interested in events that led to formation of the HCN tetramer.M any of the mechanistic studies on the chemical evolution pathways consider HCN and HNCa s two fundamentalreactants.…”

“…Reactionp aths to [13][14][15][16] After analyzing the rearrangementr eactions leading to the three target molecules cis/trans-DAMN and AICN, we analyzed the trimerization and tetramerization reactions required to complete the route from the relevant dimer to the selected tetramers.…”

“…Three tetramers (13)(14)(15) were selected for mechanistic studies by using the component-based fingerprint methodd escribed above (see Theoretical and Computational Details).Afourth tetramer (16) was cognitively selected for its geometry,w hich could lead to cis-DAMN by asimple H-transfer reaction.…”

“…In a recent computational study, the Miller's experiment was successfully simulated by using Nanoreactor, an ab initio molecular dynamics package . Barbatti's group studied the photochemical steps involved in the formation of a purine precursor from a HCN tetramer, which provided support for the mechanisms proposed by Ferris and Orgel …”

“…The available studies on trimerization and tetramerization, and the corresponding trimeric and tetrameric structures, are fewer than those on dimers/dimerization. There are a few reports on the mechanisms of tetramerization and pentamerization of HCN to form purine precursor 4‐amino‐1 H ‐imidazole‐5‐carbonitrile (AICN) or cis / trans ‐2,3‐diaminomaleonitrile (DAMN) and adenine based on experimental studies . Many of the elementary reactions in these studies involve complex reaction steps that are rarely seen in laboratory chemical experiments, for example, rearrangement of C−CN to C−NC in the gas phase .…”