Abstract
Ultraviolet (UV) irradiation is considered an energy source for the prebiotic chemical synthesis of life’s building blocks. However, it also results in photodegradation of biology-related organic compounds on early Earth. Thus, it is important to find a process to protect these compounds from decomposition by UV irradiation. Herein, pH effects on both the adsorption of peptides on montmorillonite (MMT) and the abilities of peptides to resist UV irradiation due to this adsorption were systematically studied. We found that montmorillonite (MMT) can adsorb peptides effectively under acidic conditions, while MMT-adsorbed peptides can be released under basic conditions. Peptide adsorption is positively correlated with the length of the peptide chains. MMT’s adsorption of peptides and MMT-adsorbed peptide desorption are both rapid-equilibrium, and it takes less than 30 min to reach the equilibrium in both cases. Furthermore, compared to free peptides, MMT-adsorbed peptides under acidic conditions are well protected from UV degradation even after prolonged irradiation. These results indicate amino acid/peptides are able to concentrate from aqueous solution by MMT adsorption under low-pH conditions (concentration step). The MMT-adsorbed peptides survive under UV irradiation among other unprotected species (storage step). Then, the MMT-adsorbed peptides can be released to the aqueous solution if the environment becomes more basic (releasing step), and these free peptides are ready for polymerization to polypeptides. Hence, a plausible prebiotic concentration–storage–release cycle of amino acids/peptides for further polypeptide synthesis is established.
Highlights
The origin of life remains an unsolved mystery, because none of us can go back to the time when life first emerged [1]
These results indicated adsorption of Phe2 on MMT was preferred under acidic conditions rather than basic conditions
We found that most of the samples could efficiently adsorbed on MMT at low pH values
Summary
The origin of life remains an unsolved mystery, because none of us can go back to the time when life first emerged [1]. In order to provide a reasonable explanation of the beginning of life, many scientists have made tremendous efforts to mimic prebiotic conditions (spark discharge, UV irradiation, shock waves, etc.) to investigate how the key components (amino acids, peptides, and nucleic acids) of living cells could have been produced [2]. In 1953, the Miller–Urey experiment confirmed that amino acids were formed by discharging a reducing atmosphere [3]. Amino acids have been found in meteorites, among other organic compounds [4]. Combining all these results, amino acids have been considered relatively abundant substrates on early Earth.
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