Syntheses of 2‐(N‐2‐hydroxyalkyl‐N,N‐dimethylammonio)ethyl hydrogen phosphates and their physicochemical and antimicrobial properties

A series of new phosphate type of amphoterics having a 2‐hydroxyalkyl group as a hydrocarbon chain, 2‐(N‐2‐hydroxyalkyl‐N,N‐dimethylammonio)ethyl hydrogen phosphates (alkyl[R]:dodecyl, tetradecyl, hexadecyl), was synthesized and their physicochemical properties—isoelectric point, critical micelle concentration (CMCs), occupied area/molecule at interface and the change of free energy of micellization—and antimicrobial properties were investigated in comparison with those of sodium 2‐(N‐alkyl‐N‐methylamino)ethyl hydrogen phosphates. It was found that the CMCs and the occupied areas were observed to decrease due to a phosphobetaine moiety and a 2‐hydroxyethyl group. Solution properties of the binary system of SDS/2‐(N‐2‐hydroxytetradecyl‐N,N‐dimethylammonio)ethyl hydrogen phosphate in aqueous solutions were studied in terms of surface tension and pH value. On the other hand, it was observed that the Minimum inhibitory concentration (MICs) of 2‐(N‐2‐hydroxyhexadecyl‐N,N‐dimethylammonio)ethyl hydrogen phosphate against fungi were smaller than those of chlorhexidine digluconate.