Protocell-like Microspheres from Thermal Polyaspartic Acid

One of the most prominent amino acids to appear in monomer-generating origin-of-life experiments is aspartic acid. Hugo Schiff found in 1897 that aspartic acid polymerizes when heated to form polyaspartylimide which hydrolyzes in basic aqueous solution to form thermal polyaspartic acid which is a branched polypeptide. We recently reported at the ISSOL 2005 Conference that commercially made thermal polyaspartic acid forms microspheres when heated in boiling water and allowed to cool. In a new experiment we heated aspartic acid at 180°C for up to 100 h to form thermal polyaspartylimide which when heated in boiling water without addition of base hydrolyzed to form thermal polyaspartic acid which upon cooling formed microspheres. Thermal polyaspartic acid microspheres appear protocell-like in the sense of being prebiotically plausible lattices or containers that could eventually have been filled with just the right additions of primordial proteins, nucleic acids, lipids, and metabolites so as to constitute protocells capable of undergoing further chemical and biological evolution. Thermal polyaspartic acid microspheres are extremely simple models of protocells that are more amenable to precise quantitative experimental investigation than the proteinoid microspheres of Sidney W. Fox. We present here scanning electron microscope images of such thermal polyaspartic acid microspheres. Figure 1 shows thermal polyaspartic acid microspheres from l-aspartic acid heated at 180°C for 50 h, at a magnification of 3,500×. Figure 2 shows thermal polyaspartic acid microspheres from the same sample at a magnification of 7,000×. The thermal polyaspartic acid microspheres have a diameter of approximately 1 μm These images were viewed with a Hitachi S2460N scanning electron microscope at 20 kV acceleration voltage. Figure 1 Thermal polyaspartic acid microspheres from l-aspartic acid heated at 180°C for 50 h, at a magnification of 3,500×.

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Figure 2 Thermal polyaspartic acid microspheres from l-aspartic acid heated at 180°C for 50 h, at a magnification of 7,000×.

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Presented at: National Workshop on Astrobiology: Search for Life in the Solar System, Capri, Italy, 26 to 28 October, 2005.