Binding to surfactant

It is known that interactions between ionic surfactants and polyions with the opposite charge lead to the formation of soluble colloidal complexes. The polyelectrolyte chain binds to surfactant molecules through Coulombic attractions, and the hydrophobic moieties of the surfactant molecules stabilize the complexes due to hydrophobic interactions in the aqueous solution (Morris and Jennings, 1976 Satake and Yang, 1976 Osica etal., 1977 Fendler, 1982 Hayakawa et al., 1983 Jonsson et al, 1998). 

Oakes J and Dixon S, Physical interactions of dyes in solution - influence of dye structure on aggregation and binding to surfactants/polymers . Rev. Prog. Color., 2004, 34, 110. 

Given the important role of silica oligomer binding to surfactants in this cooperative assembly formation route, significant effects on the structures formed are seen due to added salt. Early work by Ryoo et on MCM-41 formed in alkaline syntheses with cationic surfac-... 

Shapley, W. A., Bacskay, G. B., and Warr, G. G., Ab initio quantum chemical studies of the pKa s of hydroxybenzoic acids in aqueous solution with special reference to the hydrophobicity of hydroxybenzoates and their binding to surfactants, J. Phys. Chem. B, 102, 1938-1944 (1998). 

In all surfactant solutions 5.2 can be expected to prefer the nonpolar micellar environment over the aqueous phase. Consequently, those surfactant/dienophile combinations where the dienophile resides primarily in the aqueous phase show inhibition. This is the case for 5.If and S.lg in C12E7 solution and for S.lg in CTAB solution. On the other hand, when diene, dienophile and copper ion simultaneously bind to the micelle, as is the case for Cu(DS)2 solutions with all three dienophiles, efficient micellar catalysis is observed. An intermediate situation exists for 5.1c in CTAB or C12E7 solutions and particularly for 5.If in CTAB solution. Now the dienophile binds to the micelle and is slid elded from the copper ions that apparently prefer the aqueous phase. Tliis results in an overall retardation, despite the possible locally increased concentration of 5.2 in the micelle. 

Fonnation of a complex with a copper cation only further stimulates this behaviour. As a result, S.lg is almost completely bound to the micelles, even at low concentrations of Cu(DS)2. By contrast, the reaction of 5.1 f still benefits from an increasing surfactant concentration at 10 mM of Cu(DS)2. In fact, it is surprising that the reaction of this anionic compound is catalysed at all by an anionic surfactant. Probably it is the copper complex of 5.If, being overall cationic, that binds to the micelle. Not surprisingly, the neutral substrate S.lc shows intermediate behaviour. 

Gum arabic (gum acacia) is used as the lickable glue on stamps and envelopes, and as a flavor stabilizer (emulsifier) in soft drinks. It has components that bind to water, and components that bind to oils, making it an emulsifier but not a surfactant (because of the high molecular weight). 

Even chemisorption can take place in the binding of surfactants to particles if ionic surfactants are used as dispersants. Hence the properties of the surface are particularly enduring and specifically altered. These properties can be of... 

These esters of p-hydroxybenzoic acid have been used primarily to prevent growth of molds but in higher concentrations possess some weak antibacterial activity. Their effective use is limited by low aqueous solubility and by reports of stinging and burning sensations related to their use in the eye. They bind to a number of nonionic surfactants and polymers, thereby reducing their bioactivity. They are used in combination, with the methyl ester at 0.03-0.1% and the propyl ester at 0.01-0.02%. Parabens have also been shown to promote corneal absorption [140]. 

For ionizable lipophilic molecules, the right pH gradients can drive the solute in the acceptor compartment to the charged (impermeable) form the uncharged fraction is then further diminished in concentration by binding to the serum protein or surfactant, in the double-sink assay. 

Provided that equilibrium is maintained between the aqueous and micellar pseudophases (designated by subscripts W and M) the overall reaction rate will be the sum of rates in water and the micelles and will therefore depend upon the distribution of reactants between each pseudophase and the appropriate rate constants in the two pseudophases. Early studies of reactivity in aqueous micelles showed the importance of substrate hydropho-bicity in determining the extent of substrate binding to micelles for example, reactions of a very hydrophilic substrate could be essentially unaffected by added surfactant, whereas large effects were observed with chemically similar, but hydrophobic substrates (Menger and Portnoy, 1967 Cordes and Gitler, 1973 Fendler and Fendler, 1975). 

Two other general ways of treating micellar kinetic data should be noted. Piszkiewicz (1977) used equations similar to the Hill equation of enzyme kinetics to fit variations of rate constants and surfactant concentration. This treatment differs from that of Menger and Portnoy (1967) in that it emphasizes cooperative effects due to substrate-micelle interactions. These interactions are probably very important at surfactant concentrations close to the cmc because solutes may promote micellization or bind to submicellar aggregates. Thus, eqn (1) and others like it do not fit the data for dilute surfactant, especially when reactants are hydrophobic and can promote micellization. 

Residues of incompletely degraded surfactants can also enter the aquatic environment via WWTP effluents, and these can follow various fates. More hydrophobic species with low water solubilities are prone to bind to suspended particles or to sediments (see Chapter 6.2.1) [58-60] and in very rare cases may cross the water-gas phase boundary to enter the atmosphere [61]. 

Uptake occurs from the bioavailable fraction, which in almost all cases corresponds to the dissolved fraction. Sorption and binding to suspended solids, sediments, and DOM have a great effect on bioavailability [71,72] therefore the more hydrophobic surfactants tend to be less bioavailable. Thus, for the same initial concentration, the bioavailable fraction of C12LAS, compared with that of the Cn... 

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