Polymerization on the rocks: negatively-charged alpha-amino acids

Area of Science:

• Biogeochemistry
• Mineralogy
• Polymer Science

Background:

• Amino acids are fundamental building blocks of life.
• Minerals like hydroxylapatite and illite are abundant in geological and biological systems.
• Understanding the interactions between organic molecules and mineral surfaces is crucial for fields ranging from prebiotic chemistry to environmental science.

Purpose of the Study:

• To investigate the adsorption affinities of negatively charged amino acid oligomers on hydroxylapatite and illite.
• To determine how oligomer length affects adsorption strength.
• To explore the potential for mineral-mediated oligomer elongation.

Main Methods:

• Synthesis and characterization of oligomers of glutamic acid, aspartic acid, and O-phospho-L-serine.
• Adsorption experiments using hydroxylapatite and illite as mineral substrates.
• Analysis of adsorption strength and oligomer length using techniques such as chromatography and mass spectrometry.
• Incubation of adsorbed oligomers with activated monomers to assess elongation potential.

Main Results:

• Adsorption affinity increased with oligomer length for both hydroxylapatite and illite.
• Oligo-glutamic acids showed a four-fold increase in adsorption strength per added residue on hydroxylapatite, with long oligomers (>>7-mer) being tenaciously retained.
• Repeated incubation with activated monomers enabled the accumulation of oligo-glutamic acids of at least 45 units on both minerals.
• Oligo-aspartic acid and O-phospho-L-serine showed less effective elongation on hydroxylapatite, and minimal long oligomer accumulation on illite.

Conclusions:

• Mineral surfaces, particularly hydroxylapatite, can strongly bind and facilitate the elongation of specific negatively charged amino acid oligomers.
• The findings suggest a potential mechanism for the abiotic synthesis and concentration of peptides or related polymers on mineral surfaces in early Earth environments.
• The differential effectiveness of mineral substrates and amino acid types highlights the specificity of these prebiotic chemical processes.