Partition coefficient micelle/water

Oligomer properties drastically depend on their ethoxylation degree. For instance, oligomers may be compared from the value of their partition coefficient in a typical water-oil system, which is the ratio of the oligomer concentrations in water and oil at ambient temperature and in absence of micelle (fC = Cw/Co). It is found that for oligomers with EON = 3 and EON = 7 the partition coefficients between water and heptane at 25 °C are respectively 0.003 and 0.17 [11]. 

Hebrant et al, [151] investigated the transport of amino acids (p-iodopheny la la-nine and tryptophan) through AOT/isooctane reverse micelles, and the rates of transport were compared and analyzed in relation to partition coefficients between water and the AOT palisade layer. The rate of uptake of amino acids by the reverse micelles and the influence of the ionization states of the acids on the extent of transport were also presented. Enantioselective transport using chiral AOT was also attempted, but the rigidity of the interfacial film according to them is not sufficient for chiral recognition for enantiomeric enrichment. 

Herein Pa and Pb are the micelle - water partition coefficients of A and B, respectively, defined as ratios of the concentrations in the micellar and aqueous phase [S] is the concentration of surfactant V. ai,s is fhe molar volume of the micellised surfactant and k and k , are the second-order rate constants for the reaction in the micellar pseudophase and in the aqueous phase, respectively. The appearance of the molar volume of the surfactant in this equation is somewhat alarming. It is difficult to identify the volume of the micellar pseudophase that can be regarded as the potential reaction volume. Moreover, the reactants are often not homogeneously distributed throughout the micelle and... 

Table 5.2. Analysis using the pseudophase model partition coefficients for 5.2 over CTAB or SDS micelles and water and second-order rate constants for the Diels-Alder reaction of 5.If and 5.1g with 5.2 in CTAB and SDS micelles at 25 C.

Table 5.2 shows that the partition coefficients of 5.2 over SDS or CTAB micelles and water are similar. Comparison of the rate constants in the micellar pseudophase calculated using the... 

In contrast to SDS, CTAB and C12E7, CufDSjz micelles catalyse the Diels-Alder reaction between 1 and 2 with enzyme-like efficiency, leading to rate enhancements up to 1.8-10 compared to the reaction in acetonitrile. This results primarily from the essentially complete complexation off to the copper ions at the micellar surface. Comparison of the partition coefficients of 2 over the water phase and the micellar pseudophase, as derived from kinetic analysis using the pseudophase model, reveals a higher affinity of 2 for Cu(DS)2 than for SDS and CTAB. The inhibitory effect resulting from spatial separation of la-g and 2 is likely to be at least less pronoimced for Cu(DS)2 than for the other surfactants. 

Estimation is easier and less time-consuming because use is made of empirical relationships between the BCF and physicochemical properties of the compound, such as water solubility (S) [42-48], Km, (solid organic carbon/water partition coefficient) [48], Kmw (membrane water partition coefficient), iipw (liposome water partition coefficient) [49], critical micelle concentration (CMC) [45], steric factors, molecular weight [47,48], and others. The most common regression method is the estimation of BCF from the octanol-water partition coefficient (Kovl) [18,42,44-48,50,51],... 

Freshwater mammals such as heaver may leave odors on the surface of their ponds and olfactorily sample the water or layer of air immediately above it. Lipids on water may form micelles, small blobs of molecules (from Latin mica, a grain, crumb, morsel) that enhance evaporation into the air layer by increased chemical potential. Some seahirds hunt hy odor (e.g. Hutchison and Wenzel, 1980 Nevitt, 1999). They may respond to prey volatiles (from krill, squid, or fish) that rise to the water surface and evaporate into the air. The air-water equilibrium for dilute solutions can be expressed by using partition coefficients, relative volatility, or Henry s law (Thibodeaux, 1979). 

N Chen, Y Zhang, S Terabe, T Nakagawa. Effect of physicochemical properties and molecular structure on the micelle—water partition coefficient in micellar electrokinetic chromatography. J. Chromatogr. A 678 327-332 (1994). 

The Menger-Portnoy model is closely related to the Berezin model employing partition coefficients instead of equilibrium constants.For the case where only two pseudophases (bulk water and micelle) are considered, the partitioning of the reactant is given by the partition coefficient P. This leads to Equation (4) describing observed rate constants as a function of surfactant concentration. 

Here, k is the rate constant for hydrolysis in the Stern region, Fstem and Fmic are the volumes of the Stern region and of the micelle, respectively, AvS and Pm are the water-to-Stern region and water-to-micelle partition coefficients, respectively. Equation (6) shows that, for the assumptions described above, the micellar rate constant is given by the rate constant for the reaction in the Stern region, multiplied by a factor representing the distribution of the reactant within the micelle. Further subdivision of the micellar pseudophase is (mathematically) possible " " " but may not be warranted. 

Surfactants can act like lipids or emulsifiers in solubilizing flavor materials in surfactant micelles. Headspace analysis techniques were used to follow the release of several common dentifrice flavorants from a solution containing the surfactant sodium lauryl sulfate. Water/micelle partition coefficients were derived to describe the solubilization of the flavorants in tiie surfactant micelle (76). Initially, the flavor is solubilized in the surfactant micelle. As both the micelle and flavor concentration decrease on dilution, flavor compounds, which are highly soluble in the micelle, preferentially increase in the headspace [HGURE11]. 

Here km and kw are the second-order rate constants in the micellar pseudo-phase and the aqueous phase, respectively, Phrp and Prfc are the partition coefficients for HRP and RFc, respectively, between the micellar and aqueous phases (PA= [AJm/fA],, A = HRP or RFc), C is the total surfactant concentration without cmc (C = [surfactant] t-cmc), and V is the molar volume of micelles. Equation (39) simplifies assuming Phrp <3C 1 and PRFc 1. In fact, the hydrophilic enzyme molecule is expected to be in the aqueous phase, while hydrophobic, water-insoluble ferrocenes have a higher affinity to the micellar pseudo-phase. Taking also into account that relatively low surfactant concentrations are used, i.e., CV <5iC 1, Eq. (39) transforms into Eq. (40). 

Nystatin Micelle-Water Partition Coefficients and Pluronic Micelle Core Polarities as a Function of Pluronic and Temperature... 

The rate constant for the reentry is of the magnitude expected for a diffusion-controlled reaction as in Eq. (5.6). This means that the exit rate is determined by the partition coefficient of the solubilizate in its triplet state between the micelle and the aqueous solution. Table 5.2 shows the exit rate constants k for several systems. The water solubilities of the probes are also given to show the correlation between kt and the solubility in water. These studies give further support to the view that the micelle has a very dynamic structure, which makes it easy for the solubilizate to enter and leave the aggregate. 

El Tayar et al., using micelle-water (mw) partition coefficients determined on a polyoxyethylene(23)-lauryl ether column [31], found a significant correlation between log Pmw and the activity of a series of antiplatelet agents, but no correlation when using log Poet. or calculated [10] log P-values (CLOGP) parameters. 

C is the concentration of surfactant in the micellar form (i,e, the total surfactant concentration minus the CMC), and are the dimensionless solute partition coefficients between micelles and the bulk water and between the stationary phase and the bulk water, respectively. 

If the chemical is surface active, for example an alkyl benzene sulfonate used in detergents, it will form micelles above a critical micelle concentration (CMC). This is effectively a solubility limit for such substances and it is essential that the test conditions be below the CMC, otherwise the BCF will be underestimated. Finally it should be noted that actual concentrations in the water may differ considerably from nominal concentrations deduced by adding a known mass of chemical to a known volume of water, because much of the chemical may sorb to the walls of the tank and to pumps and filters. Further, substances of relatively high air-water partition coefficients will evaporate appreciably from solution especially as a result of aeration. For these reasons actual concentration measurements are essential, and nominal values should not be trusted. 

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