UV-Induced Photodegradation of 2-Aminothiazole-4-Carboxylic Acid: Identification of New Carbodiimide Molecules

The UV-induced photolysis of 2-aminothiazole-4-carboxylic acid (ACA), a biologically active molecule, was studied using the infrared matrix isolation method. As the first step of photolysis, a decarboxylation reaction occurred. Subsequently, two main photolysis pathways of 2-aminothiazole were observed, during which a number of new molecules, including potential prebiotic carbodiimides or molecular complexes, were identified. The CS-CN bond cleavage path produced <i>N</i>-(1-sulfanylethen-2-yl)carbodiimide (fp1), <i>N</i>-(thiiran-2-yl)carbodiimide (fp3), <i>N</i>-(1-thioethan-2-yl)carbodiimide (fp2), <i>N</i>-(1-thioethan-1-yl)carbodiimide (fp4) and <i>N</i>-(1-thioethan-2-yl)cyanamide (fp33), which were identified for the first time. In this channel, additional disruption of the N-C bond produced cyanamide (fp27) and thiirene (fp28) and subsequent photoreactions generated carbodiimide (fp29) or ethynethiol (fp30). The CS-CC bond cleavage path occurred simultaneously and produced several new molecules: <i>N</i>'-ethynylcarbamimidothioic acid (fp14), <i>N</i>-ethynylcarbamimidothioic acid (fp17), <i>N</i>-ethenylidenecarbamimidothioic acid (fp18) and <i>N</i>-ethenylidenethiourea (fp15). In this channel, additional disruption of the N-C bond produced acetylene (fp23) and <i>N</i>-thiolcarbodiimide (fp26). Among the small molecules, <i>N</i>-thiolcarbodiimide and thiirene, as well as all molecular complexes, were observed for the first time.