Synthesis, physicochemical characterization and aquatic toxicity studies of anionic surfactants derived from amino and α-hydroxy acids

Abstract

Surfactants are extremely versatile ubiquitous compounds with a wide range of applications. Traditional surfactants are based on non-renewable sources, while the alternative surfactants from natural feedstock remain underexplored. In our work, we synthesized and characterized a library of bioderived compounds with different structural properties. Namely, amide and ester derivatives of C₁₀–C₁₆ fatty acids and amino or α-hydroxy acids, including methionine, aspartic, glutamic, malic and citric acid. To further elucidate the structure–property relationship, we also included iminodiacetic acid, a non-natural acid. The surfactant molecular structures varied in the number of carboxylic groups (one to three), the length of the hydrophobic chain and the type of linkage between the two parts of the molecule (ester, secondary or tertiary amide). The structural differences had a pronounced impact on their foaming properties, critical micelle concentration (CMC), and maximum tolerable concentration (MTC) in aquatic life, studied using zebrafish as model animals. The compounds exhibited a broad range of foaming properties across the whole pH range. Their respective CMC values spanned several orders of magnitude, and a linear relationship between the logarithm of CMC and the hydrophobic chain length was observed. Several compounds showed very high MTC values. The obtained results provide a basis for further development of bioderived surfactants and their use in different domains.