Mario Corti

Aggregative properties of gangliosides in solution

The aggregative properties of gangliosides in diluted aqueous solutions are discussed on the basis of simple and well-established thermodynamic concepts. Theoretical assumptions are compared with experimental data obtained, mainly by scattering techniques, on GM3, GM2, GM1, GD1a, GalNAc-GD1a, GD1b, GD1b lactone and GT1b gangliosides, all containing ceramide portions of similar composition, and on GM1 molecular species containing different well-defined ceramide structures. We also report on mixed aggregates with amphiphilic compounds and on the ganglioside aggregate-soluble protein interaction effects which give rise to very stable lipoproteic complexes of well-defined ganglioside-protein composition.

Laser-light scattering investigation of the micellar properties of gangliosides

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.

Light-scattering study on the micellar properties of a non-ionic surfactant

Abstract Aqueous solutions of Triton X-100 are investigated over a wide range of temperatures and concentrations by Rayleigh scattering of laser light. The measured temperature dependence of the micellar parameters is shown to be consistent with the hypothesis of critical concentration fluctuations.

Critical properties of nonionic micellar solutions

Solutions of the nonionic amphiphile n‐dodecyl octaoxyethylene glycol monoether (C12E8) in D2O and in salty H2O have been investigated by static and dynamic light scattering. It is found that the micellar properties are little influenced by the choice of the solvent, whereas the critical properties (in particular, the critical exponents γ and ν) show a marked solvent effect. The interpretation of the observed critical behavior in terms of first‐order correction‐to‐scaling contributions is discussed.

Light scattering measurements on gangliosides: dependence of micellar properties on molecular structure and temperature

Static and dynamic laser light scattering measurements on micellar aqueous solutions of gangliosides GM2, GM1, GD1a are reported. The aggregation number, the hydrodynamic radius and the micellar shape depend on the type of ganglioside and the unsaturation degree of the hydrocarbon chains. At a temperature of 25 degrees C the molecular weights of GM2, GM1 and GD1a are 740,000, 470,000 and 418,000 DA respectively. A significant decrease of micellar size with temperature has been found for saturated GM1 in the region 25 degrees-40 degrees C. The strong sensitivity of the micellar parameters to the ganglioside structure is explained by making reference to some simple model which takes into account geometrical packing considerations. By measuring the scattered light intensity at low ionic strength of the solution (0.1-30 mE) it was possible to evaluate the ganglioside micellar charge, 100 electronic units for GM2, 48 for GM1 and 60 for GD1a.

Nonionic micelles in mixed water-glycerol solvent

Abstract The aggregation properties of the nonionic amphiphile C 12 E 8 in water-glycerol mixtures are investigated at various glycerol volume fractions X by surface tension, light scattering, refractometry, and viscosimetry measurements. In the range 0 X X , and the aggregation number m decreases with X . For X > 0.4, the CMC grows considerably, and the Krafft temperature becomes larger than room temperature. The minimum of the cloud point curve decreases from 74°C at X = 0 to 43°C at X = 0.6.

Investigation of micelle formation in aqueous solution by laser-light scattering

Abstract The micellar properties of dilute solutions of two ionic detergents are investigated by quasielastic scattering of laser light. The interpretation of the results in terms of Tanfords theory shows that micelles have oblate ellipsoidal shape near the critical micelle concentration. Evidence for micelle polydispersity is presented, and an approximate evaluation of the spread of the size distribution function is given.

Aggregation properties of GM3 ganglioside (II3Neu5AcLacCer) in aqueous solutions

The aggregative properties of highly pure GM3 ganglioside in aqueous solution have been studied by static and dynamic laser light scattering measurements and fluorescence spectroscopy experiments performed by the use of a GM3 derivative containing the pyrene group at the end of the fatty acid moiety. GM3 ganglioside spontaneously aggregates as unilamellar vesicles, down to a concentration of 1.25 x 10(-8) M, showing molecular weight and hydrodynamic radius ranging from 15,000 to 30,000 kDa and from 350 to 470 A, respectively. GM3 vesicles are stable with dilution and can be stored at room temperature for some weeks without appreciable change.

Evidence for spontaneous segregation phenomena in mixed micelles of gangliosides.

A light scattering study of the effect of mixing in aqueous solution two gangliosides, GM2 and GT1b, having different hydrophilic headgroups and similar lipid moieties is presented. Mixed micelle formation with spatial segregation of one ganglioside with respect to the other was observed. It is also shown that segregation is a spontaneous phenomenon which is explainable only in terms of simple geometrical arguments, that is by the fact that the large headgroup of GT1b provides the lipidic core of the aggregate with a better shielding from water in the highly curved regions than the smaller headgroup of GM2 can do. This finding may be of help in understanding the behaviour of gangliosides in artificial and natural membranes.

Micelle structure in isotropic C12E8 amphiphile solutions

Solutions of n-dodecyloctaoxyethylene glycol monoether (C12E8) in D2O have been studied by static and dynamic neutron scattering as a function of temperature and concentration in the isotropic phase. Little variation in micelle size or shape is found throughout the range of conditions studied, which includes points close to the minimum of the consolution curve and points close to the boundary between the isotropic and the hexagonal phases.