Aggregates protein-surfactant

In the case of the rather porous and flexible structure of sodium caseinate nanoparticles, the data show that the interaction with surfactants causes a tendency towards the shrinkage of the aggregates, most likely due to the enhanced cross-linking in their interior as a result of the protein-surfactant interaction. This appears most pronounced for the case of the anionic surfactants (CITREM and SSL) interacting with the sodium caseinate nanoparticles. Consistent with this same line of interpretation, a surfactant-induced contraction of gelatin molecules of almost 30% has been demonstrated as a result of interaction with the anionic surfactant a-olefin sulfonate (Abed and Bohidar, 2004). 

Pugnaloni, L.A., Ettelaie, R., Dickinson, E. (2003a). Growth and aggregation of surfactant islands during the displacement of an adsorbed protein monolayer a Brownian dynamics simulation study. Colloids and Surfaces B Biointerfaces, 31, 149-157. 

Specific formulation strategies need to be employed for macromolecule compounds. An excellent review of protein stability in aqueous solutions has been published by Chi et al. (92). In addition to solution stability of proteins and peptides, aerosolization may result in significant surface interfacial destabilization of these compounds if no additional stabilization excipients are added. This is due to the fact that protein molecules are also surface active and adsorb at interfaces. The surface tension forces at interfaces perturb protein structure and often result in aggregation (92). Surfactants inhibit interface-induced aggregation by limiting the extent of protein adsorption (92). 

It is widely believed that the unique properties of water are responsible for various physicochemical phenomena such as the aggregation of surfactants, the stability of biological membranes, the folding of nucleic acids and proteins, the binding of enzymes to substrates and more generally complex molecular associations in molecular recognition [6]. 

It can be seen that Eq. (2.157) is just the ordinary Langmuir equation in its generalised form (2.40) which follow rigorously from the analysis of chemical potentials of the components of a mixed monolayer. It was demonstrated that Pethica s equation provides the description of quite complicated systems, including the penetration of a soluble protein into the monolayer of insoluble phospholipids able to form 2D aggregates [155]. In another paper, the case of mixed layers composed of a soluble and a 2D aggregating insoluble surfactant is considered [156]. 

Evidence for surfactant aggregation into bilayers in protein-surfactant films was obtained by observing gel-to-liquid crystal-phase transitions by differential scanning calorimetry (DSC). This phase transition is related to the onset of fluidity of the hydrocarbon tails for surfactants arranged in bilayers [5-7]. Phase transition temperatures (T ) of Mb-surfactant films [19,24,25] were observed for all the surfactants in Fig. 2. For a given surfactant, values of films were within several °C of values for the corresponding vesicle dispersions. These results indicate that all of the surfactants are arranged in bilayers in the films. The presence of the protein does not seem to influence Tc in any consistent manner. 

The polarity of the protein-surfactant aggregates is lower than that of regular SDS micelles, as revealed by the shorter wavelength for maximum absorption by the probe. In this respect the behavior is similar to that of Polymer JR/SDS systems. 

A variety of fluorescence techniques were employed by Whitesides and Miller (138) to examine the interaction of gelatin and SDS, to determine the size of the aggregates within the protein/surfactant complexes. The interested reader is referred to their original paper. 

Finally, I introduce the naturally occurring protein surfactant originated from plants, called oleosin [75,76], In plant seeds, oils are stored in discrete organelles called oil bodies. Oil bodies are small spherical particles approximately 1 p,m in diameter. Notice in Fig. 14 the difference in size between plant oil bodies and mammalian lipoproteins (from approximately 10 nm to 80 nm in diameter) despite the similarity in structure. Each oil body has a core of triglycerides surrounded by a layer of phospholipids (Fig. 16) [76]. Oil bodies inside the cells of mature seeds or in isolated preparations are remarkably stable and do not aggregate or coalesce. This stability cannot be attained by only a layer of phospholipids. Seed oil bodies are stable because, in addition to the phospholipid layer, a layer of unique proteins, termed oleosin shields their surface. 

Ekwall and Baltcheffsky [265] have discussed the formation of cholesterol mesomorphous phases in the presence of protein-surfactant complexes. In some cases when cholesterol is added to these solutions a mesomorphous phase forms, e.g. in serum albumin-sodium dodecyl sulphate systems, but this does not occur in serum albumin-sodium taurocholate solutions [266]. Cholesterol solubility in bile salt solutions is increased by the addition of lecithin [236]. The bile salt micelle is said to be swollen by the lecithin until the micellar structure breaks down and lamellar aggregates form in solution the solution is anisotropic. Bile salt-cholesterol-lecithin systems have been studied in detail by Small and coworkers [267-269]. The system sodium cholate-lecithin-water studied by these workers gives three paracrystalline phases I, II, and III shown in Fig. 4.37. Phase I is equivalent to a neat-soap phase, phase II is isotropic and is probably made up of dodecahedrally shaped lecithin micelles and bile salts. Phase III is of middle soap form. The isotropic micellar solution is represented by phase IV. The addition of cholesterol in increasing quantities reduces the extent of the isotropic... 

There has been some preliminaiy chemical relaxation investigations of the kinetics of protein/surfactant systems.Both studies involved the bovine serumalbu-mine/SDS system and used the p-jmnp with conductivity detection. The introduction of the protein in the micellar solution of SDS was found to result in an increase of I/X2, a result similar to that obtained with regular pol5aners. This effect probably also reflects changes in the micelle size distribution curve. The surfactant aggregates bound to proteins are also smaller than in the absence of protein. 

Homogeneous biocatalysis in both fluorous biphasic and supercritical CO systems has been demonstrated [6]. By forming protein-surfactant complexes by hydrophobic ion pairing with a highly fluorinated anionic surfactant cytochrome c can be solubilized in perfluoromethylcyclohexane (PMFC) and in scCO. The secondary structure of the proteins within these ion-paired complexes has been shown to remain intact, and particle size analysis indicated that small aggregates of protein molecules surrounded by surfactant molecules are formed. The presence of the KDP (perfluoropolyether carboxylate surfactants) ion paired with a-chymotrypsin appears to enhance its catal)4ic activity as compared to that of the native enzyme in a fluorous biphasic system. The facile recycling of the a-chymotrypsin-KDP complex in a fluorous biphasic system has been demonstrated with retention of enzyme artivity over four reaction cycles. 

Micelles in water are described as spherical aggregates of a surfactant monomer27 30). They somewhat resemble to enzyme proteins in structures and functions, although the details are yet the subjects of recent controversies 29,30). There are numerous studies of micellar models of enzymes 28), but the examples of those of metalloenzymes are very few 31 37). In particular, there are no examples of micellar models of carboxypeptidase or carbonic anhydrase except ours 36,37). 

Recent development of the use of reversed micelles (aqueous surfactant aggregates in organic solvents) to solubilize significant quantities of nonpolar materials within their polar cores can be exploited in the development of new concepts for the continuous selective concentration and recovery of heavy metal ions from dilute aqueous streams. The ability of reversed micelle solutions to extract proteins and amino acids selectively from aqueous media has been recently demonstrated the results indicate that strong electrostatic interactions are the primary basis for selectivity. The high charge-to-surface ratio of the valuable heavy metal ions suggests that they too should be extractable from dilute aqueous solutions. 

Disperse systems can also be classified on the basis of their aggregation behavior as molecular or micellar (association) systems. Molecular dispersions are composed of single macromolecules distributed uniformly within the medium, e.g., protein and polymer solutions. In micellar systems, the units of the dispersed phase consist of several molecules, which arrange themselves to form aggregates, such as surfactant micelles in aqueous solutions. 

Although ionic surfactants are often associated with denaturation of proteins [104], the nonionic surfactant polysorbate 80 has been included in several marketed formulations and serves to inhibit protein aggregation. The mechanism may be the greater tendency of the surfactant molecules to align themselves at the liquid/ air interface, excluding the protein from the interface and inhibiting surface denaturation. 

Surfactants are well-known protein denaturants. However, when sufficiently dilute, some surfactants (e.g. polysorbate) exert a stabilizing influence on some protein types. Proteins display a tendency to aggregate at interfaces (air—liquid or liquid—liquid), a process that often promotes their denaturation. Addition of surfactant reduces surface tension of aqueous solutions and often increases the solubility of proteins dissolved therein. This helps reduce the rate of protein... 

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