Thermal Decomposition and Prebiotic Formation of Adenosine Phosphates in Simulated Early-Earth Evaporative Settings

Adenosine nucleotides and polyphosphates play a significant role in biochemistry, from participating in the formation of genetic material to serving as metabolic energy currency. In this study, we examine the stability and decomposition rates of adenosine phosphates&mdash:5&prime:-AMP, 5&prime:-ADP, and 5&prime:-ATP (mentioned simply as AMP, ADP and ATP hereafter)&mdash:at temperatures of 22&ndash:25 &deg:C, 50&ndash:55 &deg:C, 70&ndash:75 &deg:C, and 85&ndash:90 &deg:C, at a pH of 4, over periods of 2 and 4 days, in both saltwater and ultrapure water, under unsealed and completely dried down conditions. We found that adenosine phosphates degrade rapidly under heat and dehydration, particularly at temperatures above 25 &deg:C. Among the three compounds, AMP is the most stable, maintaining its integrity between 22 and 55 &deg:C, whereas ATP begins to degrade at 22&ndash:25 &deg:C and ADP is completely decomposed at temperatures above this range. Decomposition rates were analyzed using quantitative 31P-NMR, based on the detection of various phosphorus-containing species. AMP primarily hydrolyzed into phosphate, pyrophosphate and even formed 2&prime:,3&prime:-cAMP. In contrast, the condensed adenosine phosphates (ADP and ATP) hydrolyzed to AMP, phosphate, pyrophosphate, triphosphate, 5&prime:-AMP and, in some cases, 2&prime:,3&prime:-cyclic adenosine monophosphate (2&prime:,3&prime:-cAMP). We also investigated the formation of these compounds in the presence of N-containing additives such as thiourea, urea, imidazole, and cyanamide at temperatures between 65 and 70 &deg:C. Among these, cyanamide and urea were particularly effective in promoting the synthesis of adenosine monophosphates (AMPs) from phosphate and adenosine. The major products observed were 2&prime:,3&prime:,5&prime:-AMPs and cyclic 2&prime:,3&prime:-AMPs. In some experiments, adenosine diphosphate (ADP) and dimeric nucleotide species were also detected. These findings suggest that moderately heated evaporating pools could facilitate the abiotic formation of AMPs. However, such environments would likely have been unsuitable for the long-term accumulation of these compounds due to continued degradation, though there would exist some level of these nucleotides at steady state.