ABSTRACT
Gemini (dimeric) surfactants are defined as surfactants that are made up of two amphiphilic moieties connected at the level of, or close to, the head groups by a spacer group. In the past 15 years, many different types of gemini surfactant have been synthesized due to their unique properties in aqueous solution. At first, however, studies on the catalysis of chemical reactions by micelles of cationic dimeric surfactants and on the use of these surfactants as bactericidal and fungicidal agents were reported some 30 years ago. It might have been recognized at that time that cationic surfactants showed unique micelle-forming and surface-adsorbing properties when connecting them two by two to generate dimeric surfactants. Thus, in 1971, Bunton et al. [1] reported the synthesis of dimeric cationic surfactants with an alkylene or 2-butynylene spacer group and their use in micelle catalysis. In 1985-1986, Devinsky et al. [2,3] reported on the relationship between the structure and surface activity of four series of cationic dimeric surfactants and on their high antimicrobial activity. Later, unique properties concerning not only surface activity but also molecular aggregation were evidenced. Currently, the relationship between structure and properties of dimeric surfactants has been fully evidenced for anionic as well as cationic gemini surfactants. The activity in the synthesis of these surfactants has shifted from simple gemini surfactants to multi-armed gemini, polyionic gemini, trimeric, tetrameric, and oligomeric surfactants, as well as in developing new kinds of hydrophilic group, hydrophobic chain, spacer, and counterion. Recently, gemini surfactants have attracted much attention as potential agents in gene therapy, and their properties as vehicle for gene delivery into cells (transfection) were reported.
