Protein colloidal dispersion

KEY TERMS intermolecular forces proteins colloidal dispersion... 

To study gelation phenomena in globular proteins, colloid dispersions, etc., Baxter s adhesive hard sphere (AHS) system [38] is often used as a model system. Particles in the AHS system interact with each other through strongly attractive short-range square well potentials. 

Globular protein (Section 27 20) An approximately spheri cally shaped protein that forms a colloidal dispersion in water Most enzymes are globular proteins Glycogen (Section 25 15) A polysaccharide present in animals that IS denved from glucose Similar in structure to amy lopectin... 

Globular protein (Section 27.20) An approximately spherically shaped protein that forms a colloidal dispersion in water. Most enzymes are globular proteins. 

Layered materials are of special interest for bio-immobilization due to the accessibility of large internal and external surface areas, potential to confine biomolecules within regularly organized interlayer spaces, and processing of colloidal dispersions for the fabrication of protein-clay films for electrochemical catalysis [83-90], These studies indicate that layered materials can serve as efficient support matrices to maintain the native structure and function of the immobilized biomolecules. Current trends in the synthesis of functional biopolymer nano composites based on layered materials (specifically layered double hydroxides) have been discussed in excellent reviews by Ruiz-Hitzky [5] and Duan [6] herein we focus specifically on the fabrication of bio-inorganic lamellar nanocomposites based on the exfoliation and ordered restacking of aminopropyl-functionalized magnesium phyllosilicate (AMP) in the presence of various biomolecules [91]. 

C. Tribet, R. Audebert, J.-L. Popot (1997) Stabilisation of hydrophobic colloidal dispersions in water with amphiphilic polymers application to integral membrane proteins. Langmuir, 13 5570-5576... 

A colloid is defined as a non-crystalline substance consisting of ultra-microscopic particles, often of large single molecules, such as proteins, usually dispersed through a second substance, as in gels, sols and emulsion. 

Stains in the form of colloidal dispersions The need for highly sensitive detection methods for proteins after blotting (e.g., electroblotting, dot-blotting, slot blotting) applied to nitrocellulose or PYDF membranes drove scientists attention to develop new stains. It was discovered that the stains in the form of colloidal dispersions are suitable for such applications. The most commonly used colloidal stains are... 

Izmailova, V.N., Yampolskaya, G.P., Tulovskaya, Z.D. (1999). Development of Reh-binder s concept on structure-mechanical barrier in stability of dispersions stabilized with proteins. Colloids and Surfaces A Physicochemical and Engineering Aspects, 160, 89-106. 

Milks of most species contain more water than any other constituent. Certainly this is true of the milks consumed by humans. The other constituents are dissolved, colloidally dispersed, and emulsified in water. The dissolved solutes in bovine milk aggregate about 0.3 M and depress the freezing point by about 0.54°C (see Chapter 8). The activity of water in milk, aw, which is the ratio of its vapor pressure to that of air saturated with water, is about 0.993. A small amount of the water of milk is bound , o tightly by proteins and by the fat globule membrane that it does not function as a solvent for small molecules and ions. Water content is usually determined as loss in weight upon drying under conditions that minimize decomposition of organic constituents, e.g., 3 hr at 98-100°C (Horwitz 1980). 

Raw milk is a unique agricultural commodity. It contains emulsified globular lipids and colloidally dispersed proteins that may be easily modified, concentrated, or separated in relatively pure form from lactose and various salts that are in true solution. With these physical-chemical properties, an array of milk products and dairy-derived functional food ingredients has been developed and manufactured. Some, like cheese, butter, and certain fermented dairy foods, were developed in antiquity. Other dairy foods, like nonfat dry milk, ice cream, casein, and whey derivatives, are relatively recent products of science and technology. This chapter describes and explains the composition of traditional milk products, as well as that of some of the more recently developed or modified milk products designed to be competitive in the modern food industry. 

Milk appears to be homogeneous. But as Figure 4 shows, under a microscope you see that milk contains globules of fat and small lumps of the protein casein dispersed in a liquid called whey. Milk is actually a colloid, and not a solution. The particles of casein do not settle out after standing. 

Colloids can be broadly classified as those that are lyophobic (solvent-hating) and those that are lyophilic and hydrophilic. Surfactant molecules, because of their dual affinity for water and oil and their consequent tendency to associate into micelles, form hydrophilic colloidal dispersions in water. Proteins and gums also form lyophilic colloidal systems. Hydrophilic systems are dealt with in Chapters 8 and 11. Water-insoluble drugs in fine dispersion or clays and oily phases will form lyophobic dispersions, the principal subject of this chapter. While lyophilic dispersions (such as phospholipid vesicles and micelles) are inherently stable, lyophobic colloidal dispersions have a tendency to coalesce because they are thermodynamically unstable as a result of their high surface energy. 

The analysis of cow s milk shows it to be a mixture consisting of 78 per cent water and 12 per cent solid substances in solution or colloidal dispersion. Of this 12 per cent casein, the most important, belongs to a complex group of organic compounds called proteins a sugar (lactose), butter-fat, and small amounts of inorganic salts comprise the remainder. By addition of a small amount of acetic acid the dispersed protein is precipitated. By evaporation of the filtrate the crude sugar is obtained. 

Introduction. Proteins are substances produced by living matter which on enzymatic or acid hydrolysis yield amino acids. They are non-volatile and of high molecular weight, and form colloidal dispersions from which they may be precipitated by-heat, alcohol, various salts, and acids (tannic, picric, and phosphotungstic). Each protein has a minimum solubility at a characteristic pH which is called the iso-electric point. At this point the protein molecules exist as a regates and the solution has the maximum turbidity. The nature of the union of various amino acids in the protein molecule is not known. One theory assumes that the carboxyl of one amino acid unites with the amino group of another, thus ... 

In the second case treated by MacLeod a victim of morphinism and alcoholism was cured of addiction to both simultaneously by the use of great amounts of sodium bromide. The next case was that of a patient who used chloral habitually the patient was kept asleep for eight days by the use of sodium bromide. At the end of the treatment the sufferer was ctued. Chloral, being a well-known anesthetic, acts by agglomerating reversibly the protein colloids of the brain and of the sensory nerves the action of the sodium bromide in this case was to disperse the agglomerated protein particles in the same way that it acted to cure morphinism. This establishes an experimental parallelism between the action of morphine and chloral, and the action of sodium bromide in antagonizing them both. 

The migration of colloidally dispersed particles in a direct current field was reported as early as 1809. From then on the phenomenon received attention only every 30 or 50 years as an analytical method, culminating in 1948 when Arne Tiselius received the Nobel Prize for his experimentations, particularly electrophoretic separation of proteins. 

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