Synthesis of amino acid surfactants bioinspired from melanin using ethyl protocatechuate

Abstract Amino acid surfactants are widely used in areas of life and industry. Biomimetic synthesis of a new type of amino acid surfactant was based on the melanogenesis using the natural substances ethyl protocatechuate. Ethyl protocatechuate was oxidized to o‐benzoquinone using silver oxide. The amino group of amino acids, including arginine, cysteine, glutamic acid, histidine, leucine, and threonine, was conjugated with o‐benzoquinone to synthesize melanin‐like amino acid surfactants. o‐Benzoquinone moiety behaved as hydrophobic part while amino acid residue served as hydrophilic head group. The critical micelle concentration of cysteine product was 1.18 mM. The melanin‐like amino acid surfactant showed excellent foamability, wettability, emulsification, solubilization, and dispersibility properties. Arginine product showed the longest foam half lifetime of 18 min; the wetting time of threonine product was 23 s; the emulsion delamination time of cysteine product was 1034 and 1940 s for liquid paraffin and soybean oil, respectively; threonine product had the most solubilization capacity of 9430 mL mol −1 of benzene; glutamic acid product showed the highest lime soap dispersing power value of 45.58%. It was the first invention for biomimetic synthesis of amino acid surfactant from aspect of both structure and route. Melanin‐like amino acid surfactant had promising potential in both fundamental research and industrial application.