Micelle fluidity

Micellar systems Internal microviscosity of micelles Fluidity and order parameters (e.g. bilayers of vesicles)... 

Ahngren, M., Loefroth, J.E. Determination of micelle aggregation numbers and micelle fluidities from time-resolved fluorescence quenching studies. J. Colloid Interface Sci. 1981, 87(2), 486 99. 

The influence of the membrane fluidity was investigated for several types of reaction. Proton abstraction by a hydrophobic hydroxamate (23) is facilitated in the presence of cationic micelles (Okahata et al., 1980). Dialkylammonium... 

The fluorescence polarization technique is a very powerful tool for studying the fluidity and orientational order of organized assemblies (see Chapter 8) aqueous micelles, reverse micelles and microemulsions, lipid bilayers, synthetic non-ionic vesicles, liquid crystals. This technique is also very useful for probing the segmental mobility of polymers and antibody molecules. Information on the orientation of chains in solid polymers can also be obtained. 

We should first emphasize that viscosity is a macroscopic parameter which loses its physical meaning on a molecular scale. Therefore, the term microviscosity should be used with caution, and the term fluidity can be alternatively used to characterize, in a very general way, the effects of viscous drag and cohesion of the probed microenvironment (polymers, micelles, gels, lipid bilayers of vesicles or biological membranes, etc.). 

MacKerell, Jr., A. D. (1995) Molecular dynamics simulation analysis of a sodium dodecyl sulfate micelle in aqueous solution decreased fluidity of the micelle hydrocarbon interior. J. Phys. Chem. 99, 1846-1855. 

Similarly, vesicular reactivity is dependent on bilayer fluidity and Arrhenius (or Eyring) plots for the decarboxylation of 6-NBIC show a break around Tm. " For the Kemp elimination in different bilayers, it was found that the bilayer for which kinetic data had been gathered below its was least effective as a catalyst. Ester hydrolysis has also been found to be faster above r. For the decarboxylation of 6-NBIC, the increase in catalytic efficiency was attributed to different aggregate surface dynamics based on the observation that vesicles above showed intermediate activation parameters between vesicles below and micelles. One could, of course, discuss causality here considering the fact that many of the bilayer... 

Keywords Fluorescence probing Hemimicelle Micellar fluidity Micelle Organized assemblies in solution and interfaces Polarity parameter Pyrene... 

The fluidity (nanoviscosity) in an organized surfactant assembly on soUds can be substantially different from that in the bulk aqueous phase and hence, the diffusional resistance experienced by the probe in the micelle will be considerably different from that faced in the bulk solution [ 145]. Measurement of the viscosity or fluidity of the interior of a micelle is based on measurement of fluorescence properties that depend on the mobihty of the probe in the interior. A commonly used method for such studies involves the intramoleciflar... 

Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of lOOA. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micro-polarity as a function of distance from the polar core of these Inverted micelles. Pyrene exclmer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively. 

Lateral Mobility(Fluidity) of Sulfonate A and B Micelles. The ratio of excimer to monomer fluorescence intensity of pyrene had previously been used to measure the fluidity of biological membranes (8). The ease of excimer formation was correlated with the fluidity of the membrane. The same principle may be applied to the measurement of fluidity in inverted micelles. To this end, we used three pyrene carboxylic acid probes of varying chain length PVA, PNA and... 

It can be seen that the excimer to monomer fluorescence intensity ratios for the same molar ratio of probe to sulfonate are much smaller in the sulfonate A system than in the sulfonate B system. For both sulfonates A and B, the intensity ratio tends to Increase with the chain length of the carboxylic acid. The variation is distinctly established for sulfonate B micelles, but less so for sulfonate A micelles. The results indicate that the internal fluidity of the micelles decreases from the edge of the polar core to the continuous hydrocarbon medium the gradient is steeper for sulfonate B. 

Lateral Mobility in Alkarylsulfonate Micelles. In order to make a valid comparison of fluidity between sulfonates A and B, the micellar sizes should be comparable. This condition is required so that equal population of pyrene moieties between the two sulfonate systems can be assumed. Alternatively, the requirements might be met if they have equal aggregation numbers. If the above-mentioned (See Section A under "Results") assumptions regarding polar core composition are reasonable, the condition for equal probe population between the two sulfonate micelles can still be reasonably approximated. 

Variation of lateral mobility (fluidity) and polarity gradient have been reasonably established in certain calcium alkarylsulfonate micelles using 1-pyrene carboxylic acid probes with varying alkyl chain lengths. The existence of a polarity gradient in an inverted micelle may be responsible for the creation of an oxygen concentration gradient. 

James Bayer. Would the authors define what they mean by ordered arrangement of micelles or degree of anistropy in semicokes, as related to rank and fluidity ... 

Penetration enhancers have different mechanisms of action depending on their physicochemical properties. Some examples of penetration enhancers and their mechanisms are bile salts (micellization and solubilization of epithelial lipids), fatty acids such as oleic acid (perturbation of intracellular lipids) [25,26], azone (l-dodecylazacycloheptan-2-one) (increasing fluidity of intercellular lipids), and surfactants such as sodium lauryl sulfate (expansion of intracellular spaces). The complete list of enhancers and their mechanism of actions are discussed in detail in Chapter 10. 

The inclusion of a surfactant in the suppository formulation may enhance the rectal absorption of drugs. The effect has been attributed to the formation of mixed micelles. It has been suggested that the presence of the micelle facilitates the incorporation of the lipid component of the mixed micelle into the biological membrane. This lipid then enhances the fluidity and permeability of the membrane to the poorly absorbed drug. It appears that the colorectal mucous membrane is more sensitive to the effects of mixed micelles than the gastrointestinal membrane of the small intestine. 

Chromatographic efficiency seems to be linked to the additive-to-surfactant concentration ratio in the micellar mobile phase. The plate numbers increase with this ratio but reach a maximum level (e.g., at pentanol/SDS = 6 and acetonitrile/CTAC= 12). - The organic solvent/surfactant ratio affects the exchange rates of the solute between micelle/stationary and aqueous phases. It also controls the extent of the surfactant coverage and the fluidity of the organic layer on the stationary phase. 

Emulsifiers are necessary to allow water and lipids to combine. A surfactant is an amphiphilic molecule that has affinities for fats as well as water and that can be incorporated into lamellar lipid structures (e.g. cell walls). Surfactants increase the fluidity of the lipid structures by partitioning into the lipid membranes, as their lateral interactions with the membrane-forming lipids reduce the force of their attractive interaction. The mobility of the membrane lipids increases considerably in a similar manner to when a liquid crystal is converted into a gel. Finally, lipids can be seen to micellize or simply dissolve. Membranes lose their relative impermeability. See Figure 5.16. 

DiaryIpropanes. Excimer formation with diarylpropanes in solution talces place intramolecularly, making this process independent of concentration (44). Therefore, these molecules, especially 1Py(3)1Py (45), have been used extensively to probe the fluidity of micelles and artificial and biological membranes (17-19,46-50). Here, they are expected to be convenient indicators of the degree of mobility freedom of adsorbed molecules. 

Lysophosphatidylcholine is a frequent product of oxidized phospholipid hydrolysis and shows structural similarities to its diacyl counterparts containing a short acyl chain in sn-2 position. Therefore, its cellular activities deserve particular attention, especially in the context of its cytotoxicity. The effects of phospholipid oxidation products and lyso-PC depend not only on their concentration but also on the cell type. Lyso-PC containing a long acyl chain in sn- position (e.g. C16 0, C18 0) is an amphiphilic phospholipid that is generated by phospholipase-catalyzed hydrolysis of phosphatidylcholine or extensive oxidation leading to loss of the entire sn-2 acyl chain. Its critical micellar concentration (CMC) is around 50 pM. It is easily taken up into lipid membranes and increases their fluidities . Above the CMC it forms micelles that destroy membrane integrity also by removal of proteins as shown in erythrocytes (Bierbaum et al., 1979 Colics and Chisholm, 2000). Lyso-PC exerts apoptotic effects in rVSMCs at concentrations below its CMC and induces necrotic cell death at concentrations above its CMC (Hsieh et al.,... 

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