Supramolecular Association in the System Water−Lysozyme−Lithium Perfluorononanoate

Abstract

Mixtures containing water, lysozyme (LYS), and a fluorinated surfactant (LiPFN) have been investigated in a wide range of protein-to-surfactant ratios. Depending on composition, sample consistency and coexistence of the different phases, different experimental methods were used. Volumetric, viscometric, surface tension, potentiometric (by a home-built ion-selective electrode), turbidity, optical polarizing microscopy, and 19F NMR experiments 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. Solutions, gel phases, and precipitates have been observed in the range investigated in more detail. Multiphase regions have also been observed. 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 amount of time. Its formation obeys a volume fraction statistics; the width of the gel phase, in fact, is controlled by the amount of protein−surfactant complex.

Supra-molecular Association and Polymorphic Behaviour In Systems Containing Bile Acid Salts

“…The dissolution kinetics is several hours long. Such behaviour is not unexpected and was observed in other water-protein-surfactant systems [118][119][120][121]. When the pH is lower that 5.0, the precipitate area is located between the concentration ranges pertinent to hepatic and colecystic bile, respectively [122].…”

Polymer–surfactant and protein–surfactant interactions

“…Gels were also observed in mixtures containing globular proteins (LYS and albumins) and oppositely charged surfactants [94][95][96][97][98][99][100][101]. General features of the phase diagrams for the above systems imply the presence of a tiny molecular solution, a wide precipitate area, a micellar region, and a gel phase at relatively high solute volume fractions.…”

“…NMR essentially focused on the interactions of fluorinated surfactants with synthetic homopolymers. More recently, 19 F NMR was used to investigate the interactions of proteins with fluorinated surfactants [99].…”

Rheological properties of protein–surfactant based gels

“…The occurrence of diluted solutions, protein-rich precipitates, and micelle-assisted redissolution of protein-surfactant complexes (PSCs), as well as gel formation, have been observed [21]. The whole phase behavior is controlled by temperature, pH, and medium ionic strength.…”