Innovative mechanochemical synthesis of lipopeptide surfactants through direct amidation of fatty esters: application to silk-derived amphiphilic lipopeptides

Abstract

The present work describes the development of a novel methodology for producing lipopeptides from fatty acid methyl esters and amino acids or peptides using mechanochemistry in basic conditions, and its use to prepare biobased surfactants from silk sericin protein. The experimental protocol was optimized with variable molar ratios and reaction times, on model amino acids, glycine, leucine, and serine. Lipoamino acids resulted in a significantly improved conversion rate, up to 99%, after an increase in the base and fatty ester ratio. The structures of the synthesized molecules were characterized with NMR and FTIR. The optimal experimental conditions for high conversion with no excess fatty acid ester were applied to produce sericin lipopeptides with three different lengths of hydrophobic part: 10, 12 and 14 carbons. The acylation rates of sericin peptides of 40–49% were obtained depending on fatty acid size. The surface activity of the silk lipopeptides produced was evaluated and showed a significant reduction in surface tension until ∼24 mN m⁻¹. The results of this study provide an efficient new strategy for the amidation of amino acids and peptides using mechanochemistry, presenting a promising alternative to the conventional Schotten–Baumann acylation reaction. The results also demonstrate the effectiveness of silk sericin lipopeptides for reduced surface tension, indicating their good potential as substitutes for conventional petroleum derived surfactants in different applications.