tives and their quaternary ammonium salts. The results for A series of long-chain piperazine derivatives, N-alkyl-Nthe antimicrobial activities of some piperazine derivatives methyl piperazine and their amphiphilic salts, N-alkyl-N-ethyland the polymers prepared from the polymerizable amphi-N-methyl piperazinium bromide, and the related N-alkyl-N,Nphilic piperazine derivatives are to be reported later. dimethyl piperazinium bromide were synthesized and characterized by 1 H and 13 C NMR and FTIR spectroscopy. Under the MATERIALS AND METHODS experimental conditions used, the NMR data showed unequivocally that quaternarization of N-alkyl-N-methyl piperazine by Piperazine, N-methyl piperazine, and N,N-dimethyl piperthe reaction with ethyl bromide occurred exclusively at the nitroazine were obtained from Aldrich. n-Bromoalkanes were gen atom bearing the methyl group due to the steric hindrance of obtained from Fluka (Switzerland).
the long-chain alkyl group attached to the other nitrogen atom. Critical micelle concentration (cmc) and surface-active properties Melting Points and Refractive Indexes of the amphiphiles were investigated. Plots of surface tension, g, against log concentration were presented. At cmc, the number of The melting points or melting behaviors of some commolecules adsorbed at the air-water interface was found to depounds were investigated by differential scanning calorimecrease with increasing chain length. This was attributed to the try (DSC). A Perkin-Elmer DSC-7 was used. The instruincrease in electrostatic repulsion within the adsorption layer as ment was calibrated against cyclohexane and indium at a suggested by Lunkenheimer et al. (Colloids Surf. A 101, 197
heating rate of 10 K/min using nitrogen as the purge gas.