Adsorption of macromolecules

The ability of some macromolecules to adsorb at interfaces is made use of in suspension and emulsion stabilisation (see Chapter 7). Gelatin, acacia, poly(vinyl alcohol) and proteins adsorb at interfaces. Sometimes such adsorption is unwanted, as in the case of insulin adsorption onto glass infusion bottles and poly(vinyl chloride) infusion containers and tubing used in giving sets. Adsorption of insulin to glass bottles and plastic i.v. tubing at slow rates of infusion is well documented. It 

The adsorption of macromolecules at interfaces may be the reason why molecules such as those of hyaluronic acid can act as biological lubricants in joint fluids. In healthy joints only 0.5 cm of synovial fluid is required to provide almost perfect lubrication in diseased joints there are sometimes faults in this system and some research has been aimed at producing synthetic substitutes for synovial fluid. 

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We also attempt to distinguish between surface physical chemistry and colloid and polymer physical chemistry. This distinction is not always possible, and clearly many of the features of physical chemistry of surfaces, such as the electrostatic interactions and adsorption of macromolecules, have a significant... 

Adsorption of macromolecules has been widely investigated both theoretically [9—12] and experimentally [13 -17]. In this paper our purpose was to analyze the probable structures of polymeric stationary phases, so we shall not go into complicated mathematical models but instead consider the main features of the phenomenon. The current state of the art was comprehensively summarized by Fleer and Lyklema [18]. According to them, the reversible adsorption of macromolecules and the structure of adsorbed layers is governed by a subtle balance between energetic and entropic factors. For neutral polymers, the simplest situation, already four contributor factors must be distinguished ... 

Protective Colloids. Another approach in preparing and stabilizing metal colloids is by adsorption of macromolecules on their surfaces. A wide variety of materials have been used including gummy gelatinous liquids,(J 0) albumin,(27) Icelandic moss,(28) latex,(22) polyvinylpyrrolidone, (29) antibodies, ( 30 ) carbowax 20M, ( 31 ) polyvinylpyridine, (31 ) and various polymer-water/oil-water mixtures.( 2) These studies clearly indicate that "steric stabilization of metal colloids is also important (along with electronic stabilization).(33)... 

Hogg, R. Mirville, R. J. "Adsorption of Macromolecules at Solid-Liquid Interfaces" presented at 56th Colloid and Surface Science Symposium, Blacksburg, VA (1982). 

Mineral segregation in industry relies heavily on the selective adsorption of macromolecules onto the surfaces of those minerals that have particular industrial applications. This selectivity is governed mainly by the surface chemistry of the mineral and the type of polymer used as a flocculant. " Effectiveness of flocculation depends upon the charge, concentration and molecular weight of the polymer, and also the pH and salt concentration of the clay suspension. The bonding between the anionic flocculant polyacrylamide (PAM) and clay mineral surfaces has been effectively reviewed recently by Hocking et al and the reader is referred to this should they require an in-depth literature review. For more information on general colloidal chemistry of clay suspensions the reader is referred to the review of Luckham and Rossi." ... 

FIGURE 16.7 Schematic representation of the surface (a) and interface (h) adsorption of macromolecules. The role of solvent strength is depicted. Note large changes of macromolecular conformation which accompany the adsorption process. 

Despite their distinct advantages, on-line SPE and column-switching proce-dures do not always represent ideal separation techniques. In many cases, only a small number of samples can be analyzed before contamination of the precolumn by proteins occurs. Alternative techniques that prevent the adsorption of macromolecules onto column packings and allow direct injection of sample extracts are those based on use of specific LC columns. Shielded hydrophobic phase (27), small pore reversed-phase (28), and internal surface reversed-phase (29, 30) columns can be used to elute proteins in the excluded volumes, allowing small... 

The adsorption of macromolecules is rarely an equilibrium process. Just as the properties of synthetic polymers are often dependent on non-equilibrium processes and relaxation phenomena30), so do the properties of adsorbed proteins depend on time, metastable states, and hysteresis processes. 

This review has surveyed the present status of theoretical and experimental studies on the adsorption of macromolecules, with particular reference to the determination of conformations of adsorbed macromolecules. No definitive experimental method is as yet available for this determination. At present, the conformation of adsorbed macromolecules can only be inferred from a comparison of experimental data of such properties as the adsorbed amount T, the fraction p of adsorbed trains and the thickness of the adsorbed layer with the existing theories formulated on various conformational models as depicted in Fig. X. 

We extend our description to adsorption at the solid-liquid interface. For many systems we can use the same models as for gas adsorption on a solid surface, we only have to replace the pressure P by the concentration c. The adsorption of macromolecules to surfaces is briefly discussed in Section 10.3.2. For macromolecules desorption is often negligible and thermodynamic equilibrium is only reached after a very long time, if at all. 

When the composite-matrix is formed with a polystyrene solution as a dispersion medium, the self-assembly of silica particles is influenced by the adsorption of macromolecules on their surface. During adsorption, both solitary macromolecules and their aggregates transfer simultaneously onto the adsorbent surface. Depending on solution concentration, not only the conformation of adsorbed molecules but also the number and size of macromolecular aggregates in the solution change on adsorption. This leads to the formation of complex-shaped structures, which are linked by a system of nonvalent interactions and consist of polymeric-inorganic blocks[8,14] this is of interest in the preparation of a nanostructured medium (polystyrene-silica gel) as a precomposite for the fabrication of carbon structures in a matrix of silica particles. 

Chang MJ, Joseph LB, Stephens RE, et al. 1990. Modulation of biological processes by mineral fiber adsorption of macromolecules in vitro. JEPTO 10 89-93. 

For our purposes, adsorption from solution is of more direct relevance than gas adsorption. Most, if not all, topics in the five volumes of FICS Involve one or more elements of it. In the present chapter, the basic elements will be introduced, restricting ourselves to low molecular weight, uncharged adsorbates and solid surfaces. Adsorption of charged species leads to the formation of electrical double layers, which will be treated in chapter 3. Adsorption at fluld/fluid Interfaces follows in Volume III. Adsorption of macromolecules will be Introduced in chapter 5. Between monomers, short oligomers, longer oligomers and polymers there is no sharp transition in the present chapter we shall go as far as non-ionic surfactants, but omit most of the association and micelle formation features, which will be addressed in a later Volume. There will be some emphasis on aqueous systems. 

The Sepharose-based DEAE CL-6B (Pharmacia) is also a very useful resin for ion exchange of high-mol wt proteins it has a very low nonspecific adsorption of macromolecules, good flow properties, and is relatively stable to changes in ionic strength and pH. Sephadex-based lERs tend to alter volume drastically as a result of changes in ionic strength... 

For monodisperse or unimodal dispersion systems (emulsions or suspensions), some literature (28-30) indicates that the relative viscosity is independent of the particle size. These results are applicable as long as the hydrodynamic forces are dominant. In other words, forces due to the presence of an electrical double layer or a steric barrier (due to the adsorption of macromolecules onto the surface of the particles) are negligible. In general the hydrodynamic forces are dominant (hard-sphere interaction) when the solid particles are relatively large (diameter >10 (xm). For particles with diameters less than 1 (xm, the colloidal surface forces and Brownian motion can be dominant, and the viscosity of a unimodal dispersion is no longer a unique function of the solids volume fraction (30). 

There are two methods of stabilization of lyophobic colloids electrostatic and polymeric. Electrostatic stabilization results from charge-charge repulsion, as discussed previously. Polymeric stabilization is achieved by the adsorption of macromolecules (lyophilic colloids) at the surface of a lyophobic colloid. Macromolecules of at least a few thousand molecular weight are required, as they must extend in space over... 

Colloidal properties that influence RES uptake are particle size, surface charge, surface hydrophobicity, and the adsorption of macromolecules onto the particle surface. The surface of colloidal particles can be altered to avoid RES uptake by adsorption or grafting of a hydrophilic polymer onto the surface of a particle and thereby creating an energy barrier to particle interaction (e.g., the non-ionic surfactant Tween 20 can be adsorbed).Both biological and synthetic polymers have been used for RES masking of colloidal particles, for example, albumin,immunoglobulin car-... 

A permeate flux declines in the presence of solute due to membrane fouling. A decrease in flux is a result of several phenomenons including adsorption of macromolecules to membrane surface involving pore blocking, concentration polarization, and formation of a gel-like cake layer within the membrane pores (50). Several models have been used to describe solute fouling, among them are hydraulic resistance, osmotic pressure, gel polarization, and film models (51,52). 

Electric fields can be used, for instance, to reduce fouling phenomena in systems involving electrically charged macromolecules (e.g., proteins). In microsystems used for capillary zone electrophoresis an external electric field applied across the capillary tube induces electrostatic repulsion between the macromolecules and the inner surface. The reduced adsorption of macromolecules enhances separation resolution and efficiency. 

Before dealing with the adsorption of biomolecules (proteins and nucleic acids) onto latex particles, we should recall certain aspects (which will not be defined here) of the adsorption of macromolecules on solid-liquid interfaces. Biomolecules are complex macromolecules in nature, which in... 

The adsorption from three-component solutions (n-hexane, benzene, and dioxane) on the hydroxylated silica surface was studied. The effect of the chemical properties of the SiC>2 surface and the nature of the solvent on the adsorption of polymers was investigated. The adsorption of macromolecules on nonporous and fairly large-pore silica is determined by their conformational transformations. The adsorption equilibrium is often established very slowly the process may take up to several months. 

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