Amino Acid Gemini Surfactant Salts

Gemini surfactant salts based upon amino acids with a suitable anionic surfactant (e.g., LAS) offer distinct advantages in numerous industrial and homecare applications owing to their strong amphiphilic character and affinity for interfacial adsorption. This often manifests in drastic reductions in interfacial tension, improved detergency, and antifoaming capabilities among others. While prior works have indeed explored derivatization of the essential amino acids to yield Gemini surfactants, this has almost exclusively been approached through the lens of covalent modification, requiring bespoke syntheses that are impractical for an industrial setting. Recently, however, non-covalent approaches between anionic surfactants and a suitable cationic diamine linker have emerged as an industrially scalable alternative to yielding Gemini behavior, but at the cost of highly toxic diamine starting materials. It is herein shown that the simple neutralization of the sulfonic acid group of anionic surfactants with the cationic center of the essential amino acids results in a non-covalent association that leads to improved interfacial tension reduction when compared to sodium salts of the anionic surfactant alone. Furthermore, conductivity studies reveal the correspondence of counterion binding strength and Gemini character with the strength of the association depending upon the nature of the cationic character in the amino acids. Thus, non-covalent Gemini surfactant salts employing amino acids show great promise in a breadth of industrial applications owing to their improved performance, ease of production, and compliance with environmental regulations.