Proteins colloidal systems

Oparin (64) lays emphasis on the part played by colloidal proteins in the origin of life. His sequence of events is simple forms of organic matter, primary proteins, colloidal systems, primary organisms, and highly evolved organisms. 

This recognition of proteins as macromolecules was staunchly advocated by Staudinger (1920 et seq.) in spite of vociferous opposition Organic molecules with more than forty C atoms do not exist. Purify your products. . . they will prove to be lower molecular weight substances. Even as late as 1938, Gorter maintained All of the reactions and interactions which we call life take place in colloidal systems. ... 

Fluid colloidal system of two or more components. (Gold Book online, 1972 entry [2].) Note Examples of colloidal sols are protein sols, gold sols, emulsions and surfactant solutions above their critical micelle concentrations. 

Colloids (Greek for glue-like) are a wide variety of systems consisting of finely divided particles or macromolecules (such as glue, gelatin, proteins, etc.) that are found in everyday life. In Table 1.1 examples of such typical colloidal suspensions are given. Further, colloidal systems are widespread in their occurrence, and have... 

For a colloidal system containing a mixture of different biopolymers, in particular a protein-stabilized emulsion containing a hydrocolloid thickening agent, it is evident that the presence of thermodynamically unfavourable interactions (A u > 0) between the biopolymers, which increases their chemical potentials (thermodynamic activity) in the bulk aqueous phase, has important consequences also for colloidal structure and stability (Antipova and Semenova, 1997 Antipova et al., 1997 Dickinson and Semenova, 1992 Dickinson et al., 1998 Pavlovskaya et al., 1993 Tsap-kina et al., 1992 Semenova et al., 1999a Makri et al., 2005 Vega et al., 2005 Semenova, 2007). 

B. Impact of Covalent Protein-Polysaccharide Conjugates on Structure and Stability of Colloidal Systems... 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

The methodological factors having a special influence on these tests of emulsifying properties are subdivision methods for the colloidal system, ratio of components (water protein oil), and the nature of the fat used. The second one is the most neglected of these influences and is usually chosen by the researcher at will. 

Chen, J. and Dickinson, E. 1995b. Protein/surfactant interfacial interactions. Part 2. Electrophoretic mobility of mixed protein + surfactant systems. Colloids Surf. A Physicochem. Engin. Aspects 100 267-277. 

The easiest model to treat theoretically is the sphere, and many colloidal systems do, in fact, contain spherical or nearly spherical particles. Emulsions, latexes, liquid aerosols, etc., contain spherical particles. Certain protein molecules are approximately spherical. The crystallite particles in dispersions such as gold and silver iodide sols are sufficiently symmetrical to behave like spheres. 

With polydispersed systems either a broadening of the boundary (in addition to that caused by diffusion) or the formation of distinct peaks representing the various fractions is observed. Sedimentation does not provide an unequivocal method for establishing the homogeneity of a colloidal system. For example, a mixture of serum albumin and haemoglobin is homogeneous with respect to sedimentation velocity but the two proteins are easily distinguished from each other by electrophoresis. 

This chapter reviews the wide range of colloidal systems amenable to investigation by FT - IR spectroscopy. Molecular level information about die interactions of amphiphilic substances in aggregates such as micelles, bilayers, and gels can be obtained and related to the appearance and stability of the various phases exhibited. The interactions of polymers, surfactants and proteins with interfaces, which substantially modify the solid - liquid or liquid - air interface in many important industrial and natural processes, can also be monitored using FT - IR. 

There are, however, colloidal systems, for which the above requirements are not fulfilled. For example, the surfaces of the proteins can have small radii, and their acidic and basic groups are not completely dissociated. In this case, the Verwey—Overbeek approach cannot be employed and the Langmuir—Deijaguin approximation is not accurate. 

The present article was stimulated by the recent experimental data on protein-covered latex colloidal systems immersed in various electrolyte solutions NaCl, NaNC>3, NaSCN and Ca(NOg)2, which showed strong specific anionic effects on the restabilization curves.1 In the opinion of Lopez-Leon et al.,1 the above polarization model for double layer/hydration forces could explain only some of their experiments, but not all of them. However, they assumed that at pH = 10 the adsorption of anions was negligible hence specific anion effects could not be predicted by their association with the positive sites of the surface. Furthermore, at pH = 4 they assumed the... 

The applications of colloid solutions are not restricted to paints and clay. They are also to be found in inks, mineral suspensions, pulp and paper making, pharmaceuticals, cosmetic preparations, photographic films, foams, soaps, micelles, polymer solutions and in many biological systems, for example within the cell. Many food products can be considered colloidal systems. For example, milk is an interesting mixture containing over 100 proteins, mainly large casein and whey proteins [6,7]. 

Picullel L, Halle B (1986) Water spin relaxation in colloidal systems. Part 2., 70 and 2H relaxation in protein solutions. J Chem Soc Faraday Trans I 82 401-414... 

It has been well known for a relatively long time that micellar, i.e. association colloidal, systems have a considerable effect on such indicator equilibria. Indeed, in the 1920 s and early 1930 s experiments were carried out in order to elucidate the so-called colloid or indicator error (Hartley, 1934 Hartley and Roe, 1940). In addition, the protein error was noted in investigations involving acid-base titrations in the presence of proteins (Sorensen, 1929 cf. Hartley, 1934). These errors are, of course, the consequence of micellization and the subsequent effects of micelles on equilibrium (34). The importance of many indicators in the dye, textile, and photographic industries, and the analytical utility of the shifts in indicator equilibria prompted much of the research in this area. 

Solubility, as well as the possibly related phenomenon of swelling, depends on the H bonding character of the solvent (or swelling agent). Indeed, the effect is not limited to proteins but also occurs for gelatin, cellulose, wood (1495), nylons, and probably for clays and other colloidal systems as well. Lloyd and co-workers discuss solubility and swelling of protein fibers (1250) (see, in fact, that entire discussion on swelling, 1252). 

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 chapter has dealt with the stability and stabilisation of colloidal systems and covered topics such as their formation and aggregation. If the particle size of a colloidal particle determines its properties (such as viscosity or fate in the body), then maintenance of that particle size throughout the lifetime of the product is important. The emphasis in the section on stability is understandable. Various forms of emulsions, microemulsions and multiple emulsions have also been discussed, while other chapters deal with other important colloidal systems, such as protein and polymer micro- and nanospheres and phospholipid and surfactant vesicles. 

Influent concentrations and residual concentrations of cationic surfactants, anionic surfactants, cationic polyelectrolyte, anionic polyelectrolyte, proteins, colloids, oxygen, ozone, detergents, suspended sohds, and so on, in the adsorptive bubble separation systems can be determined by the analytical methods reported in the literature (82,127-149). 

Enormous effort is spent on studying complex fluids, more-so than any of the previous topics reviewed above. These fluids include polymer solutions and melts, alkanes, colloidal systems, electrolytes, liquid crystals, micelles, surfactants, dendrimers and, increasingly, biological systems such as DNA and proteins in solution. There are therefore many specialist areas and it is impossible to review them all here. As such, we sample only a select few areas that reflect our own personal interests, and apologise to readers who have specific interests elsewhere. First, we briefly look over some simulations on colloidal systems, alkanes, dendrimers, biomolecular systems, etc, and will then... 

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