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The micellar properties of gangliosides in water solutions were investigated by quasielastic light scattering measurements. GM1 and GD1a gangliosides were isolated from calf brain, purified to more than 99% and dissolved in 0.025 M Tris--HCl buffer (pH 6.8) at 37 degrees C. The average intensity of scattered light and the intensity correlation function were measured by an apparatus including a 5145 A argon laser and a real-time digital correlator. The scattered intensity data allowed the derivation of an upper limit to the critical micelle concentration (c0) and the evaluation of the molecular weight (M) of the micelle. The intensity correlation function gave the diffusion coefficient D, and hence the hydrodynamic radius RH, and also contained information on the polydispersity of the sample. We find co less than 1 x 10(-6) M for both GM1 and GD1a, M = 532000 +/- 50000 and RH = 63.9 +/- 2 A for GM1, and M = 417000 +/- 40000 and RH = 59.5 +/- 2 A for GD1a. The mixture 3:1 of the two gangliosides gave intermediate values for all examined parameters. The presence of cations, within the physiological concentration range, and, in particular of Ca2+, did not influence significantly the values of co and the main features of the micelle.

Frequency resolved electric birefringence measurements were made on dilute aqueous suspensions of charged, rodlike latex particles. Ionic amphiphile adsorption was used to vary the particle charge as described in the first paper of this series [J. Chem. Phys. 103, 8228 (1995)]. Using the high frequency part of the birefringence spectra, the electric polarizability is computed from the Kerr constant following the approach set out in the second paper of the series [J. Chem. Phys. 109, 6905 (1998)]. Then, the polarizability spectra were interpreted with our extended Maxwell-Wagner model [J. Chem. Phys. 113, 6974 (2000), preceding paper]. Theory and experiment are in good agreement. The procedure provides a new and simple way to extract the particle charge from birefringence data. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recent frequency resolved electric birefringence experiments on dilute suspensions of charged, ellipsoidal particles reveal new relaxation features in the MHz frequency range. Such behavior can be explained in terms of surface transport processes. Here we develop a model for the electric polarizability of spheroidal particles by combining features of electrokinetic and Maxwell-Wagner theories. The model accurately depicts the high frequency features and relates them to the colloidal properties of the polyelectrolyte. Using the model, particle charge can be extracted from electric birefringence measurements. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]