Formation of adenosine from adenine and ribose under conditions of repeated wetting and drying in the presence of clay minerals

Abstract

Ribonucleic acid (RNA) was possibly the most important biopolymer in Earth’s early existence. However, the prebiotic synthesis of the nucleoside component of RNA is problematic. Here we report the formation of adenosine by subjecting a mixture of adenine and ribose to repeated wetting and drying from 40 to 80 °C in air, with or without the addition of clay minerals. Using liquid chromatography-mass spectrometry (LCMS) and 1H NMR spectroscopy, we were able to detect the formation of adenosine in the presence of kaolinite and Mg2+-exchanged montmorillonite at 70 °C. At this temperature adenosine was also formed in the absence of these minerals but none was detected in the presence of the raw (sodium-rich) montmorillonite. In all instances, only small amounts of adenosine were formed. On the other hand, a 12–13% yield of adenosine was measured in the presence of kaolinite at 60–80 °C, using the highly sensitive method of liquid chromatography coupled with tandem mass spectrometry (LCMS/MS). Kaolinite can apparently act as both a concentrating surface and a catalyst in the formation of adenosine from adenine and ribose although the underlying mechanism has yet to be established. The mild experimental conditions used here for nucleoside formation could plausibly obtain in some parts of the prebiotic Earth.