Comparative Study of Interfacial and Biological Properties in d-Glycerate-Derived Surfactants

The effects of hydrophobic chain length on the interfacial and biological properties of diacyl d-glyceric acid (d-GA) sodium salts were evaluated based on interfacial tension analyses, dynamic light scattering (DLS), and antitrypsin activity. Of the four synthesized d-GA-derived surfactants [dihexanoyl d-GA sodium salt (diC6GA-Na), dioctanoyl d-GA sodium salt (diC8GA-Na), didecanoyl d-GA sodium salt (diC10GA-Na), and dilauroyl d-GA sodium salt (diC12GA-Na)], only those with C6, C8, and C10 acyl chains were investigated because diC12GA-Na were insoluble at room temperature. Together with our previous results, surface tensions at the critical micelle concentration (CMC) were 33.9 mN/m for diC6GA-Na, 25.5 mN/m for diC8GA-Na, and 27.9 mN/m for diC10GA-Na. Evaluation of assembly size via DLS and optical microscopy revealed that diC8GA-Na and diC10GA-Na formed large associates with average sizes ranging from 50 to 200 μm at concentrations 4–5 times greater than their CMC, whereas diC6GA-Na did not form such associates. In tryptic hydrolysis studies using N^α-benzoyl-dl-arginine-4-nitroanilide as a substrate, diC8GA-Na exhibited an inhibitory effect on trypsin (trypsin specific activity: 0.26 ± 0.045 U/mg-protein) greater than that of diC10GA-Na (0.39 ± 0.10 U/mg-protein), whereas diC6GA-Na did not show antitrypsin activity. These results show that diC8GA-Na was the most bioactive of the evaluated diacyl d-glycerate surfactants.