Protein—surface interactions in the presence of polyethylene oxide

Protein—surface interactions in the presence of polyethylene oxide: II. Effect of protein size

The general concept of using the unique phase separation behavior of some surfactant micelle solutions as a means for extractive separation is outlined and described. Next, the specific micellar parameters and phase separation behavior of nonionic and zwitterionic charge-type surfactant solutions are summarized. In addition, the phase behavior of some derivatized B-cyclodextrin solutions is briefly described. The specific applications of such systems and their phase behavior for the extractive preconcentration, separation, and/or purification of metal chelates, biomaterials, and organic compounds are summarized and discussed. The potential use of affinity ligands in conjunction with the cloud-point approach for selective bioextractions is also mentioned. The experimental protocols, advantages, and limitations of the different cloud-point extraction techniques are outlined. The use of zwitterionic as opposed to nonionic surfactant media in such separations is compared and contrasted. In addition, ...

A Critical Review of Surfactant-Mediated Phase Separations (Cloud-Point Extractions): Theory and Applications

The adsorption of model proteins onto brush-coated surfaces can occur via two modes. Primary adsorption at the surface, where short range attraction is dominant, is important for small proteins and may be repressed by increasing the grafting density. Secondary adsorption, due to van der Waals attraction, occurs at the outer edge of the brush. Large rodlike proteins are likely to adsorb in this fashion. This mode may be repressed by increasing the brush thickness. The thermodynamics and kinetics of adsorption of model proteins are considered within a simple analytical theory distinguishing between the different adsorption mechanisms of small and big proteins.

Polymer Brushes that Resist Adsorption of Model Proteins: Design Parameters

Recent developments in the direct measurements of forces between surfaces in liquids at the angstrom resolution level are reviewed. The results reveal a rich variety of interactions and interaction potentials that depend on the nature of the surfaces and intervening liquids. These results also shed new insights into liquid structure adjacent to surfaces and the interactions occurrig in complex systems, with implications in many different areas of chemical physics, biology, and technology. The origin of some important fundamental interactions, such as repulsive "hydration" forces and attractive "hydrophobic" forces, are still not understood and offer a challenge for experimental and theoretical work in this area.

https://science.sciencemag.org/content/sci/241/4867/795.full.pdf

Forces between surfaces in liquids.

The force between two surfaces coated with pentaoxyethylene dodecyl ether, C12E5, and immersed in aqueous solution has been measured as a function of surface separation in the temperature range 15–37 °C. The surfaces were prepared by allowing the non-ionic surfactant to adsorb on to hydrophobised mica from the solution. At 15 °C the interaction is repulsive at all separations, but above 20 °C an attractive minimum appears at separations below ca. 4 nm. The attraction increases rapidly with temperature and is identified with the interaction that gives rise to the phase separation (‘clouding’) in micellar solutions of many non-ionic surfactants as well as in the poly-(ethylene oxide)–water system.The net interaction is composed of two large parts, one entropic that is attractive and one enthalpic that is repulsive. The two parts nearly cancel, making the net interaction repulsive at low temperatures but attractive at high. They apparently originate mainly from the hydration interactions between the oxyethylene head groups on one surface with those on the other, and are of the same order of magnitude as in pure poly(ethylene oxide)–water solutions.The thickness of the non-ionic surfactant layers increases with temperature, implying a decrease in surface area per head group. This indicates that the intralayer head-group interaction also becomes more attractive (or less repulsive) with temperature.

Roland Kjellander

Papers

Direct measurement of temperature-dependent interactions between non-ionic surfactant layers