Macroscopic protein adsorption

Protein function at solid-liquid interfaces holds a structural and a dynamic perspective [31]. The structural perspective addresses macroscopic adsorption, molecular interactions between the protein and the surface, collective interactions between the individual adsorbed protein molecules, and changes in the conformational and hydration states of the protein molecules induced by these physical interactions. Interactions caused by protein adsorption are mostly non-covalent but strong enough to cause drastic functional transformations. All these features are, moreover, affected by the double layer and the electrode potential at electrochemical interfaces. Factors that determine protein adsorption patterns have been discussed in detail recently, both in the broad context of solute proteins at solid surfaces [31], and in specific contexts of interfacial metalloprotein electrochemistry [34]. Some important elements that can also be modelled in suitable detail would be ... 

TIRF occupies a unique niche, providing a noninvasive method for studying protein adsorption in situ and in real time. The TIRF technique, as it is applied in our laboratory, has been used successfully to study both macroscopic and molecular aspects of protein adsorption. The present goal of this laboratory is to elucidate the interactions occurring when a protein adsorbs to a solid surface using the TIRF technique. It is hoped that, eventually, a complete, general description of the protein adsorption process will be attained. 

Samples, one half coated with SiOa and the other half with Ti02, were used for quantitative surface analysis after each of the siuface treatment steps (cleaning, self-assembly, and polymer and protein adsorption, section 2). These samples exhibit material contrast on a macroscopic scale and are discussed in section 3.1. Micropat-temed surfaces were subjected to identical siuface modification procedures and characterized qualitatively by imaging ToF-SIMS (section 3.2) and fluorescence microscopy (section 3.3) and were used in the cell experiments (section 3.4). In both types of samples, material contrast (on a macroscopic or microscopic scale, Figure la) is converted into contrast with respect to protein adhesion (Figure Ic) via a series of surface modification steps (self-assembly of DDP, adsorption of PLL-g-PEG section 2). 

An exact solution of the macroscopic flow can be obtained for the rotating risk, often used as an electrode in various electrochemical studies [78] and in colloid particle or protein adsorption experiments [79]. Although the velocity components are, in general, expressed in terms of complicated series expansions, for small separations from the disk when h < (where m is... 

KI Al-Malah, ed. A Macroscopic Model for Protein Adsorption Equilihrinm at Hydrophohic Solid-Water Interlaces, PhD dissertation, Oregon State University, Corvallis, 1993. 

Notwithstanding the undoubted presence of probably relatively small, but still non-negligible numbers of electron-acceptor sites, sudi as on clay f>arti-cles, large crystals, glass surfaces, etc., by macroscopic measurements (e.g., contact angle determination), only net electron-donicity is found (van Oss et al., 1997). By, e.g., protein-adsorption onto such mineral surfaces it could however be shown, that microscopically small, discrete electron-acceptor sites are active in the guise of plurivalent metal ions (van Oss et al., 1995a,b). 

Upon surface-thermodynamic analysis of protein adsorption onto hydrophilic surfaces such as silica or glass, based on the known surface properties of the hydrophilic protein as well as of the hydrophihc mineral substratum, one would arrive at the conclusion that the macroscopic-scale interactions in a neutral aqueous medium are so strongly repulsive that adsorption should not occur, cf. van Oss et al. (1995a). In spite of this prediction, protein adsorption onto hydrophilic glass, silica, etc. does take place, at neutral pH (MacRitchie, 1972 van Oss et al., 1995b). The mechanism of protein adsorption onto hydrophilic surfaces is quite different from that operative with... 

The adsorption of proteins from aqueous solutions onto hydrophobic surfaces has a simple and straightforward physico-chemical mechanism, based upon the global hydrophobic attraction between an apolar, or largely apolar surface and a hydrophilic polymer (such as a protein), driven by the polar free energy of cohesion of the surrounding water molecules cf. Chapter 9, section 9.1. Thus, the attraction between a protein molecule and a hydrophobic surface, immersed in water is appropriately designated as a macroscopic interaction. 

---