Synthesis of Gemini Surfactants and Evaluation of Their Interfacial and Cytotoxic Properties: Exploring the Multifunctionality of Serine as Headgroup

Two series of novel cationic gemini surfactants based on the amino acid serine have been synthesized. These compounds contain long alkyl chains linked to the nitrogen atoms of the amino acid residues, as well as spacers interconnecting two carboxylic acid groups, through amide or ester bonds. The most efficient synthetic pathway was established; it involves the introduction of the spacers into the N,N-dialkylated monomeric precursors by peptide condensation methods with diamines or diols, with subsequent methylation and deprotection to yield the final target surfactants. The effects of molecular structure, type of spacer linkage, and spacer length on the interfacial and cytotoxic properties of these gemini surfactants are reported and discussed; studies on gemini surfactants with amine linkages and other relevant homologous compounds (conventional bis-quat gemini and monomeric surfactants) are also included. Overall, it is shown that cationic serine-based gemini surfactants have enhanced interfacial properties and low cytotoxicities, offering potential use in technical and biological applications.