Probing\nthe Limits of Reactant Concentration and Volume\nin Primitive Polyphenyllactate Synthesis and Microdroplet Assembly\nProcesses

Polyester microdroplets have been investigated as primitive\nprotocell\nmodels that can exhibit relevant primitive functions such as biomolecule\nsegregation, coalescence, and salt uptake. Such microdroplets assemble\nafter dehydration synthesis of alpha-hydroxy acid (αHA) monomers,\ncommonly available on early Earth, via heating at mild temperatures,\nfollowed by rehydration in aqueous media. αHAs, in particular,\nare also ubiquitous in biology, participating in a variety of biochemical\nprocesses such as metabolism, suggesting the possible strong link\nbetween primitive and modern αHA-based processes. Although some\nprimitive αHA polymerization conditions have been probed previously,\nincluding monomer chirality and reaction temperature, relevant factors\npertaining to early Earth’s local environmental conditions\nthat would likely affect primitive αHA polymerization are yet\nto be fully investigated. Hence, probing the entire breadth of possible\nconditions that could promote primitive αHA polymerization is\nrequired to understand the plausibility of polyester microdroplet\nassembly on early Earth at the origin of life. In particular, there\nare numerous aqueous environments available on early Earth that could\nhave resulted in varying volumes and concentrations of αHA accumulation,\nwhich would have affected subsequent αHA polymerization reactions.\nSimilarly, there were likely varying levels of salt in the various\naqueous prebiotic solutions, such as in the ocean, lakes, and small\npools, that may have affected primitive reactions. Here, we probe\nthe limits of the dehydration synthesis and subsequent membraneless\nmicrodroplet (MMD) assembly of phenyllactic acid (PA), a well-studied\nαHA relevant to both biology and prebiotic chemistry, with respect\nto reactant concentration and volume and salinity through mass spectrometry-\nand microscopy-based observations. Our study showed that polymerization\nand subsequent microdroplet assembly of PA appear robust even at low\nreactant concentrations, smaller volumes, and higher salinities than\nthose previously tested. This indicates that PA-polyester and its\nmicrodroplets are very much viable under a wide variety of conditions,\nthus more likely participating in prebiotic chemistries at the origins\nof life.