Interactions of anionic detergents with

W. L. Mattice, "Conformational Changes Accompanying the Interaction of Anionic Detergents with Cationic Polypeptides", presented at the Amer. Chem. Soc. Mtg., Philadelphia, Aug. 1984. 

Interaction of Anionic Detergents with Cationic Residues in Polypeptides... 

The alkylamidopropyl betaines, as a rule, are compatible with the anionic detergents over a wide range of concentration. The simpler alkyl betaines show some incompatibilities with alkyl sulfates at concentrations at which the betaine s concentration is about one half that of sodium lauryl sulfate [15-17]. The nature of these incompatibilities is largely dependent on the nature of anionic species present. The pH of the system also plays a role in compatibility. At the pHs normally encountered in shampoos, a competitive reaction occurs between the presumed zwitterionic inner salt and the complex salt formation from the interaction of the anionic detergent with the quaternary nitrogen. 

Anionic Surfactants. PVP also interacts with anionic detergents, another class of large anions (108). This interaction has generated considerable interest because addition of PVP results in the formation of micelles at lower concentration than the critical micelle concentration (CMC) of the free surfactant the mechanism is described as a "necklace" of hemimicelles along the polymer chain, the hemimicelles being surrounded to some extent with PVP (109). The effective lowering of the CMC increases the surfactant s apparent activity at interfaces. PVP will increase foaming of anionic surfactants for this reason. 

Found that the anionic form of the Coomassie dye reacts primarily with arginine residues within the macro molecular protein. Coomassie dye reacts to a lesser extent with other basic amino acid residues (His, Lys) and aromatic residues (Try, Tyr, Phe) present in macromolecularproteins, but not with the free amino acids. Dye binding is attributed to van der Waals forces and hydrophobic interactions. The interference seen with bases, detergents, and other compounds can be explained by their effects upon the equilibrium between the three dye forms (cationic, neutral, anionic). 

The characteristic effect of surfactants is their ability to adsorb onto surfaces and to modify the surface properties. Both at gas/liquid and at liquid/liquid interfaces, this leads to a reduction of the surface tension and the interfacial tension, respectively. Generally, nonionic surfactants have a lower surface tension than ionic surfactants for the same alkyl chain length and concentration. The reason for this is the repulsive interaction of ionic surfactants within the charged adsorption layer which leads to a lower surface coverage than for the non-ionic surfactants. In detergent formulations, this repulsive interaction can be reduced by the presence of electrolytes which compress the electrical double layer and therefore increase the adsorption density of the anionic surfactants. Beyond a certain concentration, termed the critical micelle concentration (cmc), the formation of thermodynamically stable micellar aggregates can be observed in the bulk phase. These micelles are thermodynamically stable and in equilibrium with the monomers in the solution. They are characteristic of the ability of surfactants to solubilise hydrophobic substances. 

These observations have also found application in softergents. The harder the water, the more the cationic softener deposition from an anionic detergent [9], since the compression of electrical double layers leads to a reduction of the anionic-cationic interaction. The deposition from a nonionic detergent may drop from 100% to 50% [9] as the softener, becoming less soluble, tends to interact more strongly with the hardness-insensitive surfactant. 

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