Proteins colloidal particles

The most familiar type of electrokinetic experiment consists of setting up a potential gradient in a solution containing charged particles and determining their rate of motion. If the particles are small molecular ions, the phenomenon is called ionic conductance, if they are larger units, such as protein molecules, or colloidal particles, it is called electrophoresis. 

Kondo A and FllgashItanI K 1992 Adsorption of model proteins with wide variation In molecular properties on colloidal particles J. Colloid Interfaoe Sc/. 150 344-51... 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

Ultrafiltration (UF) is used for the separation and concentration of macromolecules and colloidal particles. Ultrafiltration membranes usually have larger pore sizes than RO membranes, typically 1 to 100 nanometer (nm). Operating pressures are generally low (30-100 psig). Applications include electropaints, gray water, emulsions, oily wastes, and milk, cheese, and protein processing. 

Sagvolden et al. [86] also combined the use of colloids with AFM force sensors to study adhesion. In their case, instead of attaching the colloid to the end of the AFM probe and applying a normal force, they approached the free colloids from side on, with the AFM cantilevered at an angle of approximately 30° to the surface normal. Thus, they applied a predominantly lateral force to the colloid particles. The colloids were coated with protein molecules, and their adhesion was studied against three nonbiological surfaces, consisting... 

The colloidal particles can be crystalline or constitnte an amorphons agglomeration of individual molecnles. The definition also includes nonaggregated large macromolecules such as proteins. An arbitrary distinction is made between hydrophobic colloids (sols) and hydrophilic colloids (gels), which depends on the degree and type of interaction with the aqneons solvent. 

An important technique for the qualitative and quantitative analysis of different macromolecular materiafs is based on the efectrophoretic separation of particfes having different transport vefocities (e.g., because they have different zeta potentiafs). This technique is used for the anafysis of proteins, pofysaccharides, and other naturally occurring substances whose molecular size approaches that of colloidal particles (for more details, see Section 30.3.4). It is an advantage of the electrophoretic method that mild experimental conditions can be used—dilute solutions with pH values around 7, room temperature, and so on—which are not destructive to the biological macromolecules. 

The sorbent materials are supplied as finely dispersed colloidal particles, whose surfaces are smooth. Some of their properties are presented in Table 3. The sorbents cover different combinations of hydrophobicity and sign of the surface charge. Thus, the model systems presented allow systematic investigation of the influences of hydrophobicity, electric charge, and protein structural stability on protein adsorption. 

Addition of the protein lysozyme to DC89PC dispersions resulted in the formation of conical tubules in ethanol-water solution.149 The scanning electron micrograph in Figure 5.37 shows that precipitate from this system is primarily composed of these cones, with a smaller number of cylinders. The cones exhibit more pronounced helical ridges on their exteriors than pure lipid cylinders, suggesting that protein selectively associates to the helical defects in a similar manner as the colloidal particles discussed above. 

Proteins often form gels at concentrations between 20 and 30 percent. Likewise the "gel concentration" for colloidal particles should be equivalent to a value for close-packed spheres between 60 and 75 percent. 

As a postdoctoral associate with Professor Michael J. Natan, the PI investigated plas-mon coupling between noble metal films and metal colloidal particles using SPR in both scanning and imaging mode. It was discovered that SPR signals due to protein-protein... 

The basic mechanism is that a polyphenol molecule with at least two binding sites attaches to two proteins and bridges them together. Additional polyphenol molecules attach this structure to additional protein molecules and eventually the complex grows so large that it is no longer soluble. At this point, it becomes a colloidal particle and scatters light. The... 

Transferrin plays a major role in the transport and cellular uptake of thorium (Peter and Lehmann 1981). Thorium can be displaced from transferrin by an excess of iron, but it is not known whether thorium and iron bind to the same sites on the transferrin molecule. It has also been determined that thorotrast (Th02 colloid) blocks the uptake of labelled protein by the RES in female rabbits and in both male and female rats (Hyman and Paldino 1967). The mechanism of the blockade is not clear. Sex differences were found in rabbits but not in rats. The particle size of the Thorotrast colloid influences its effect on the uptake of protein only particles larger than 1 pm will interfere with uptake of protein by the RES. 

Semenova, M.G., Chen, J., Dickinson, E., Murray, B.S., Whittle, M. (2001). Sticking of protein-coated particles in a shear field. Colloids and Surfaces B Biointerfaces, 22, 237-244. 

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