OPTICAL ROTATORY DISPERSION OF SOME N-DECYL-N-N-DIMETHYLALANINE SALTS AND THEIR CRITICAL MICELLE CONCENTRATIONS

The optically active salts of N‐decyl‐NN‐dimethylalanine are shown to have anomalous optical rotatory dispersion curves and to not be fully ionized in aqueous solution. The position of the peak in the 225 to 230 mμ region varies with concentration of the surfactant as does the molecular rotation at a given wavelength. The positions of the peaks and the molecular rotations at these low wavelengths are pH sensitive. The change in molecular rotation with concentration enables the critical micelle concentrations of L and D N‐decyl‐NN‐dimethylalanine hydrobromides to be determined by optical rotatory dispersion measurements, the results agreeing well with the values calculated from the literature. The change in rotation on micelle formation appears to be due to a change in the degree of ionization of these weak acids, a fact which is confirmed by pH measurements on these solutions. 1968 Royal Pharmaceutical Society of Great Britain