Association of saponins in water and water-gelatine mixtures.

The solution properties of a commercial saponin obtained from Quillaja Bark (QBS), have been investigated in a wide range of experimental conditions in water and in the presence of moderate amounts of porcine skin gelatine, GEL. Saponins are surface active and form micelles at very low concentration. Significant changes in the solution dielectric properties are concomitant to micelle formation. The combination of thermodynamic, spectroscopic, transport and dielectric methods characterises the micelle formation, giving information on interactions between the components. NMR relaxation times, NMR self-diffusion and dielectric measurements were used. Micelle aggregation numbers, inferred from light scattering, indicate the formation of relatively large aggregates. No evidence for interactions between protein and surfactant was obtained. This is presumably due to the limited ionisation of acidic groups on the surfactant, which does not allow significant electrostatic binding with the protein

Equilibrium Between Phases in Water - Protein - Surfactant Systems

Phase diagrams relative to the systems water-lysozime-lithium perfluorononanoate (H2O-LYS-LiPFN), water-bovine serum albumin-sodium taurodeoxycholate (H2O-BSA-NaTDC), and water-gelatin-Quiilaja bark Saponin (H2O-GEL-QBS) have been drawn, at 25 degreesC. Solutions, gels, multiphase systems and solid particles dispersed in gel have been observed. In all cases the presence of protein-surfactant based gels has been observed. Ionic strength and, to a less extent, pH of the solvent medium reduce the width of the gel phase and are responsible for modifications in the equilibrium solution-disperse solid. Optical microscopy, surface tension, optical turbidity, ionic conductivity, emf, NMR, volumetric and viscosity data have been used to characterise the solution and the multiphase regions occurring in the aforementioned systems. Proper combination of the above findings allows drawing some preliminary hypotheses on the mechanisms responsible for the stability of protein-surfactant based gels

Supramolecular Association in the System Water – Lysozime - Lithium Perfluorononanoate

Mixts. contg. water, lysozyme (LYS), and a fluorinated surfactant (LiPFN) have been investigated in a wide range of protein-to-surfactant ratios. Depending on compn., sample consistency and coexistence of the different phases, different exptl. methods were used. Volumetric, viscometric, surface tension, potentiometric (by a home-built ion-selective electrode), turbidity, optical polarizing microscopy, and 19F NMR expts. were used. The results obtained from the above methods have been interpreted in terms of a combination of electrostatic and hydrophobic contributions to the stability of the different phases formed in the water-LYS-LiPFN system. Solns., gel phases, and ppts. have been obsd. in the range investigated in more detail. Multiphase regions have also been obsd. Such rich polymorphic behavior implies the existence of interactions between the protein and surfactant. The gel phase is presumably formed by interconnections between micelles and protein-surfactant complexes, held together by protein-bound micelles and forming, presumably, interconnected necklace structures. The overlapping of different protein-surfactant aggregates to form gels requires a significant amt. of time. Its formation obeys a vol. fraction statistics; the width of the gel phase, in fact, is controlled by the amt. of protein-surfactant complex