Solutes bound micelles

NPY free in solution (black bars) and NPY bound micelles, to micelles (grey bars) (top), and (bottom) gener-... 

The effect of the micelles on the paramagnetic shifts of the heme was very clearly demonstrated [22] in NMR of labelled cyanide in [Fe(PP)(Ci"N)2]- and [Fe(PP)(py)(Ci N)] in different micelles as well as in the absence of micelles (Fig. 9). A pronounced systematic downfield shift of the bound cyanide signals is observed on going from a solution without micelles to SDS, to TX-lOO and to CTAB micellar solutions which is also the trend in increasing hydrophobicity. The signal is known to be extremely sensitive... 

Table II gives binding constants and partition coefficient values (P) calculated by the NLLSQ program using reported capacity factors for solutes bound to micelles. These values were determined on two different LC columns. One to one equations were used to obtain the binding constants (Equation 1). This table shows the ability of this particular NLLSQ routine to perform linear least square approximations. NLLSQ programs usually are less accurate at this. The mobile phase in this study was composed of solutions of sodium dodecylsufate (SDS). These binding constants were converted to partition coefficients by Equation 4.

Table II. Binding constants (K ) and partition coefficients (P ) using reported capacity factor n) for solutes bound to micelles on two different columns (SOS mobile phase with Cia reversed stationary phase and SDS mobile phase with alkyl nitr 11 stationary phase)...

Solutes bound to micelles, droplets, or interfacial regions can have D values > tenfold smaller than their D values in the corresponding homogeneous solvent. For abrogates with a single size distribution, where the equilibrium between the bound and the free solute is fast with respect to the timescale of the electrochemical experiment, D is given by a two-state model [4, 5] ... 

The stractural and functional complexity of biomembranes has ehal-lenged researehers to develop simpler artificial models to mimie their properties. Amphiphilic block copolymers are of particular interest, beeause of the dual environmental affinity that is associated with covalently bound hydrophobie and hydrophilic blocks. These strive to minimize their eontaet, and therefore drive self-assembly into assemblies with different arehi-teetures. Based on their chemical specificity, as for example the hydrophilie-to hydrophobie ratio, amphiphilic block copolymers can self-assemble in dilute aqueous solutions into micelles, vesicles, tubes, wire-like structures, nanopartieles, or planar membranes at water-air interfaces. Synthetic membranes have greater mechanical stability than phospholipids because of the higher moleeular weight (Mw) of amphiphilic block copolymers, and thus are thicker and stiffer than lipid bilayers. 

Solutes bound to micellar and microemulsion aggregates are in rapid equilibrium with free solute and aggregates. Rate constants for the exit of neutral solutes from ionic micelles are estimated at 10 -10 s ". Rates for recapture are near or at diffusion control. Rates of these processes are similar to equilibration rates between micelles and surfactant momomers. Solutes in micelles and microemulsions are most probably solubilized near the Stern layer or in the interfacial region. Hydrophilic or hydrophobic environments will be preferred depending on the properties of the particular solutie. There is little evidence for deep solute penetration into the core of the aggregate. Vesicles have much slower dynamics of solute equilibria. 

The cmc decreases with increasing chain length of the apolar groups, and is higher for ionic than for non-ionic or zwitterionic micelles. For ionic micelles it is reduced by addition of electrolytes, especially those having low charge density counterions (Mukerjee and Mysels, 1970). Added solutes or cosolvents which disrupt the three-dimensional structure of water break up micelles, unless the solute is sufficiently apolar to be micellar bound (Ionescu et al., 1984). 

This hypothesis is satisfactory for nucleophilic reactions of cyanide and bromide ion in cationic micelles (Bunton et al., 1980a Bunton and Romsted, 1982) and of the hydronium ion in anionic micelles (Bunton et al., 1979). As predicted, the overall rate constant follows the uptake of the organic substrate and becomes constant once all the substrate is fully bound. Addition of the ionic reagent also has little effect upon the overall reaction rate, again as predicted. Under these conditions of complete substrate binding the first-order rate constant is given by (8), and, where comparisons have been made for reaction in a reactive-ion micelle and in solutions... 

Firstly, the (negative) values of the NOE for residues of the unstructured N-terminus that do not interact with the DPC micelle surface are larger. This result is most probably due to increased saturation transfer from the water and results from increased exchange of amide protons at the used pH of 6.0 compared to that used in the absence of DPC (pH 3.1). Secondly, the values for residues from the C-terminal pentapeptide are negative in the case of NPY free in solution whereas they are positive in the micelle-bound form. This clearly indicates that the C-terminal pentapeptide is significantly rigidified upon binding to the micelle. The result is supported by the structure calculation that displays rather low RMSD values for that part... 

The 3 1 LDAO/SDS mixture becomes viscoelastic and rheo-pectic when a small amount of NaCl Is added. Its viscosity shows a reversible Increase with time of shearing at constant shear rate. The rheopectic behavior Is probably due to long thread-like micelles that are aligned parallel to the flow In weakly bound clusters, as In the case of cetyltrlmethyl ammonium bromide and monosubstituted phenol mixed solutions (21). 

The structure and properties of water soluble dendrimers, such as 46, is, in itself, a very promising area of research due to their similarity with natural micellar systems. As can be seen from the two-dimensional representation of 46 the structure contains a hydrophobic inner core surrounded by a hydrophilic layer of carboxylate groups (Fig. 12). However these dendritic micelles differ from traditional micelles in that they are static, covalently bound structures instead of dynamic associations of individual molecules. A number of studies have exploited this unique feature of dendritic micelles in the design of novel recyclable solubilization and extraction systems that may find great application in the recovery of organic materials from aqueous solutions [84,86-88]. These studies have also shown that dendritic micelles can solubilize hydrophobic molecules in aqueous solution to the same, if not greater, extent than traditional SDS micelles. The advantages of these dendritic micelles are that they do not suffer from a critical micelle concentration and therefore display solvation ability at nanomolar... 

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