The research, spearheaded by Mahendran Sithamparam of the Space Science Center (ANGKASA) at the Institute of Climate Change, National University of Malaysia, was co-supervised by ELSI's Specially Appointed Associate Professor Tony Z. Jia and ANGKASA Research Scientist Kuhan Chandru. Their investigation delved into the feasibility of polyester microdroplet formation under conditions more representative of early Earth environments. The study revealed that these microdroplets could emerge in high-salinity settings, at low aHA concentrations, and within small reaction volumes. These findings expand upon previous research that primarily examined their formation in high concentrations or within larger bodies of water such as coastal lakes or hot springs. The results suggest that polyester protocells might have been more widespread than initially assumed, potentially forming in confined settings such as rock pores or saline environments like briny pools or oceanic waters.
In 2019, this research team demonstrated that polyester microdroplets could be generated through a simple dehydration process. When heated to 80C, phenyllactic acid (PA), a type of aHA, transformed into a gel-like substance that, upon rehydration, formed membraneless droplets. In their latest study, researchers aimed to determine whether these microdroplets could assemble under more diluted or lower-volume conditions resembling those present on prebiotic Earth. "Previous laboratory studies typically utilized high initial concentrations and volumes of aHAs, often in the hundreds-of-millimolar or microliter range. However, such conditions may not accurately reflect prebiotic Earth, where reactants were likely far more dilute. Thus, we aimed to explore the limits of polymerization droplet assembly processes to determine their feasibility on early Earth," explained Jia.
To mimic more realistic conditions, the team reduced the concentration and volume of PA during synthesis and droplet formation experiments. They discovered that polyester microdroplets could still form with as little as 500 uL of 1 mM PA or 5 uL of 500 mM PA. This indicates that polyester microdroplets could have naturally emerged within confined spaces such as rock pores or under diluted conditions caused by environmental factors like flooding or precipitation.
To further assess real-world plausibility, the researchers simulated reactions in salinity levels comparable to those of ancient oceans. They introduced 1M NaCl, KCl, and MgCl2 into PA reactants, finding that polyester synthesis and microdroplet formation proceeded successfully in NaCl and KCl solutions but were inhibited in MgCl2. This suggests that polyester microdroplets were more likely to form in aqueous environments with specific salt compositions, particularly those enriched in NaCl and KCl but with lower MgCl2 levels. "The results of this study strongly indicate that polyester protocells were likely more prevalent on early Earth than previously assumed. Additionally, our findings will guide future experimental research into the formation and stability of these protocells under diverse conditions," stated Chandru. "These insights suggest that a wide array of primitive environments-including oceanic, freshwater, briny, and confined niches such as rock pores-could have facilitated the emergence of these protocells, both on Earth and potentially beyond."
Research Report:Probing the Limits of Reactant Concentration and Volume in Primitive Polyphenyllactate Synthesis and Microdroplet Assembly Processes
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