We investigated the hydrothermal conversion of tetra-L-alanine in subcritical water at temperatures of 170, 200, and 230 °C and for batch holding times ranging from 0 to 90 min. We also examined the effects of pH by adjusting the initial pH of tetra-L-alanine solutions between 3.3 to 11.6. The initial pH of the tetra-L-alanine solution highly influenced the formation of products with cyclo(alanylalanyl) being the major product and dialanine and alanine being the minor products under acidic and near neutral conditions while basic conditions led to the formation of peptide chains that included various stereoisomers of tetraalanine, trialanine, and dialanine, and also alanine. Under acidic and near neutral initial pH conditions, tetra-L-alanine would undergo preferential hydrolysis at the interior peptide bond leading to the formation of dialanine, which subsequently, would undergo cyclodehydration to form cyclo(alanylalanyl). Under basic conditions, tetra-L-alanine underwent epimerization to form various stereoisomers, which would undergo hydrolysis at both exterior and interior peptide bonds leading to the formation of stereoisomers of both trialanine and dialanine, and also alanine. The formation of cyclo(alanylalanyl) was diminished under basic conditions. Under all initial pH conditions, the formation of alanine increased with increasing temperature and batch holding times. This presentation will further elucidate on the effects of experimental conditions (e.g., temperature, time, pH) on the reaction pathways, selectivity, and mechanisms of tetra-L-alanine conversion in subcritical water through the development of chemical kinetic model.

Hydrothermal Conversion of Peptides: Reaction Pathways, Kinetics, and Mechanistic Insights<i> </i>

256th National Meeting (2018)

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