Micelle ordering, relationship

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. 

Microemulsions are thermodynamically stable mixtures. The interfacial tension is almost zero. The size of drops is very small, and this makes the microemulsions look clear. It has been suggested that microemulsion may consists of bicontinuous structures, which sounds more plausible in these four-component microemulsion systems. It has also been suggested that microemulsion may be compared to swollen micelles (i.e., if one solubilizes oil in micelles). In such isotropic mixtures, short-range order exists between droplets. As found from extensive experiments, not all mixtures of water-oil-surfactant-cosurfactant produce a microemulsion. This has led to studies that have attempted to predict the molecular relationship. 

Furthermore, they studied the effect of radical desorption from the polymer particles on the particle number formed in Internal I of emulsion polymerization, using above equations, and showed that radical desorption leads to an increase in the number of particles. The reason fw this is that (I) The desorbed radicals reenter the micelles and take part in particle nu-cleation (2) Radical desorption decreases the particle growth rate and hence, results in a decrease in the rate of micelle consumption. This also increases the chance of radical entry into the micelles. They also showed that radical desorption brought about the change in the orders of particle number with respect to emulsifier and initiator according to the following relationship ... 

The fractional binding of counterions to ionic micelles is commonly denoted by the parameter /S. It follows that the corresponding micellar charge is l-fi [176]. Work on classic micellar systems such as dodecyl sulfate and octanoate show that this subject is highly complicated and as yet not fully understood [176-179]. In the presence of different counterions (such as the alkali ions Li", Na, K, Rb and Cs ), micellar size and shape, CMC values and CMT values of dodecyl sulfate are altered and do not follow the order of atomic number of the alkali ions in the periodic table nor their hydrated radius (P.J. Missel, G.B. Benedek and M.C. Carey, unpublished observations). Hydrated radius bears an inverse relationship to atomic radius, viz. (in A) Li (2.35), Na (1.85), (1.32), Cs+ (1.27) and Rb" (1.26). A... 

PHN, ACE, PYR, CHY, B[a]P, and benzo[e]pyrene were separated in a 50 mM borate buffer (pH 9) containing a mixture of 20 mM neutral methyl-(3-cyclodextrin (M(3CD) and 25 mM anionic sulfobutylether-(3-cyclodextrin (SB(3CD) at 30 kV and 30°C. " B[a]P and benzo[e]pyrene were successfully resolved with the other compounds in under 11 min in a 50-cm effective length of capillary without micelles in the mobile phase. The system was also less sensitive to temperature and separation potential. LIE detection with excitation at 325 nm at 2.5 mW from a He/Cd laser coupled to an optical fiber allowed for detection limits in the sub ppb range. The method described above was applied to the analysis of contaminated soil that had been extracted by supercritical CO2 for 20 min at 120°C and collected in methanol/DCM. ° Of the 16 EPA PAH mixtures, eleven compounds were detectable in the low ppb range. Ten of the eleven detectable compounds were measured in the soil extract. When compared to RP-HPLC, CE values were slightly lower but only six compounds were detected by HPLC-FLD. No direct relationship between PAH molecular size, polarity, or volatility with migration order was observed and B[b]F/B[k]F isomers were readily separated. 

Differences occur with regard to the three-dimensional arrangement of the non-aqueous phases. Most biological lipids consist of membranes, in which the molecules are predominantly arranged in bilayers. The lipid phase thus has a distinct structure and restricted spatial dimensions. Because the 1-octanol phase is a bulk phase, presumably with little or no structure, organic solutes may display different activity coefficients and partitioning behaviour in 1-octanol than in membranes. The more ordered a lipid phase is - in, for example, micelles and membranes - the more important becomes the entropy, resulting in non-linearity of the relationship between the respective partition coefficients and log... 

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... 

In addition to the adsorption process, in which the molecules reach the interface depending on their structure and relationship with the solvents, amphiphilic molecules show the tendency to organize and coordinate themselves into ordered sttuctures in water or solvent including the formation of aggregates such as micelles, liquid crystals (LCs), or bilayers. Such self-assembly phenomena can be described when the hydrophobic tails of surfactant molecules form a cluster to produce small aggregates, such as micelles, or large layered structures such as bilayers that are similar to a cell wall. ... 

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. ... 

Several authors have noted a relationship between the lipophilicity of the solubilizate, expressed as its partition coefficient between octanol and water, Pocianob its Saturation distribution between micelles and the aqueous phase. Rank-order correlations between the amount of substituted barbituric acid solubilized by polyoxyethylene stearates and their Poctanoi values have been reported by Ismail et al. [133]. Similarly the partition coefficients of several steroids between water and micelles of long-chain polyoxyethylene non-ionic surfactants have been correlated with their ether/water partition coefficients [145], Fig. 5.18 shows a linear relationship between the partition coefficient of a... 

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