Micelle ordering, relationship concentration

In a functional micelle in which the reactive group is fully deprotonated there is a 1 1 relationship between the concentrations of reactive nucleophile and micellar head group in the micellar pseudophase. If under these conditions the substrate is fully micellar bound, (5) or (6) take the very simple form (19). This rate constant, kM, can then be converted into the second-order rate constant, k in M 1s 1, estimating the volume element of reaction, VM, which can be assumed to be that of the micelle or of its Stem layer, and these second-order rate constants can be compared with reaction in water of a chemically similar, non-micellized, nucleophile. 

Anions will be separated by cationic micellar phases. Kirkbright and Mullins obtained the elution order T> N03 > Br > N02 > lOj with a 0.14 M cetyltrimethylammonium chloride (CTAC) micellar mobile phase and a C18 Spherisorb column [29]. This is the usual eluotropic order obtained with strong basic anion exclmngers. They showed that the ion retention decreased with the increase of both the ionic strength, p, and the surfactant concentration. Plots of 1/k vs. and 1/k vs. [CTAC] were linear. The first linear relationship is typical of ion-exchange mechanisms, the second plot means that the anion-micelle interaction obeys the Armstrong-Nome model for molecule-micelle partition. 

The two terms, one for the reaction in micelles (right hand side, first term) and water (right-hand side, second term of this equation are primarily composed of independently measurable or estimable constants, Xa, P, Fm, cmc, 2, Xa, and Xn and experimentally fixed concentrations, [St], [Nt], and [Xj]). Above the cmc, the second term rapidly diminishes, which is important for catalyzed reactions (most studies), but makes a significant contribution for inhibited reactions (not considered). The first term defines the relationships between k2 and [Sj] and [Xt].[Xt] = [St] because X is added as a counterion with surfactant and [Nt] is often small in comparison. The first term describes a maximum in k2 with increasing [St] because the numerator is first order and the denominator is second order in surfactant concentration. Figme 7 shows a simulated kinetic plot based on (15) (real data is seldom this uniform). It illustrates the effect of the added cationic surfactant on a reaction between the neutral substrate. A, an anionic reactant, N, and the anionic nonreactive counterion, X, with increasing [St] and the effect of increasing Xa on... 

There is little effect of micelles upon the rate of an intramolecular nucleophilic reaction. Micelles of hexadecyltrimethylammonium bromide catalyse, by factors of 10 —10, the arenesulphinate anion-induced hydrolysis of 4-tolylsulphonyl-methyl perchlorate. There is no relationship between the rate acceleration and hydro-phobicity of the sulphinate anion and catalysis is attributed to the concentration of the reactants in the micellar phase.The rate constants for the reaction of nucleophiles with carbonium ions and those for the addition of cyanide ion to the A -alkylpyridinium ions are similar in the micellar and aqueous phases, and the rate enhancement is due to the concentration of reactants in the micellar pseudophase. Similarly, although micellar catalysed dephosphorylation by nucleophiles may show rate enhancements of up to 4 x 10 -fold, the second-order rate constants may be slightly smaller in the micellar pseudophase lowing to its lower polarity. However, the reaction of fluoride ion with 4-nitrophenyldiphenyl phosphate is very rapid in micelles of cetyltrimethylammonium fluoride, but the rate constant continues to increase when the substrate is fully bound with increasing cetyltrimethylammonium fluoride or sodium fluoride. The failure of the micellar pseudophase model is also apparent in the reaction of hydroxide ion with 2,4-dinitrochlorobenzene. It is suggested that reaction occurs between reactants in the aqueous and micellar pseudophases and also between hydroxide ion in water and substrate in the micelle. ... 

The behaviour of sulphisoxazole in surfactant and glycol solutions has been studied in a series of papers [140,141]. In order to clarify the mechanism of the reduction in rectal absorption of this sulphonamide in the presence of PEG 4000 the effect of this compound on its physicochemical properties was examined. There is a linear relationship between the solubilities of sulphathiazole, sulphapyridine, and sulphisoxazole and the concentration of PEG 4000. The drugs apparently do not form complexes with the glycols it is thought that the reduction in activity is due to a depression of the concentration of the drug in rectal lipid. The effect of non-ionic surfactants is to reduce the absorption of the sulphonamides through solubilization in micelles [141]. Fig. 6.18 indicates the extent of solubilization in polysorbate 80 solutions. Values of apparent distri-... 

In Scheme 3.11, n is the additional number of detergent molecules that must associate with the catalytic micelle D S to completely inactivate it, and K is the association constant of this reversible process. The relationship between the second-order rate constant k2 for a bimolecular reaction in the presence of surfactant D and surfactant concentration [D] is derived in terms of Scheme 3.11, which follows Equation 3.65. ... 

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