Micelle transport

Competition resulting in a decrease of global carotenoid absorption can occur at many steps of the digestion process, including the transfer of carotenoids into mixed micelles, transport across... 

Fig. 3 Micelle formation by the amphiphilic DNA-polymer conjugate resulting from the coupling of nucleotide sequences and poly(DjL-lactic-co-glycolic acid) in aqueous medium. Confocal image shows cellular uptake of rhodamine-labeled micelles transported within NIH3T3 mouse fibroblast cells [77] (figure adapted with permission of American Chemical Society)...

In another paper, written in collaboration with D. Whitehill, it was demonstrated that the addition of NaCl to multiple emulsions causes droplet shrinkage due to loss of internal water. Micelle transport seemed to be the primary mechanism. 

The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. 

The structure of cholic acid helps us understand how bile salts such as sodium tauro cholate promote the transport of lipids through a water rich environment The bot tom face of the molecule bears all of the polar groups and the top face is exclusively hydrocarbon like Bile salts emulsify fats by forming micelles m which the fats are on the inside and the bile salts are on the outside The hydrophobic face of the bile salt associates with the fat that is inside the micelle the hydrophilic face is m contact with water on the outside... 

Each concentration can be evaluated assuming no mass transport limitation and the usual priorities for the distribution of the emulsifier polymer particles > aqueous phase > micelles (12). The... 

The importance of the material exchange process can hardly be overemphasized since it is the mechanism whereby the equUibrium miceUar size and polydispersity are reached and maintained, the reversed micelles of ionic surfactants become charged, polar and amphiphilic solubilizates are transported, and hydrophilic reactants can come in... 

Some investigations have tested the ability of reversed micelles to act as efficient carriers of molecular species. Solutions of water-containing AOT-reversed micelles have been employed for the selective transport and the efficient separation of the two amino acids tryptophane and j9-iodophenylalanine [160]. 

Moreover, as a consequence of their transient character, a hierarchy of clusters in dynamic equilibrium that may differ in shape and size can be hypothesized [253], Mass, momentum, and charge transport within a cluster of reversed micelles is expected to be strongly enhanced as compared to that among isolated reversed micelles. It has been shown that the dynamics of a network of interacting reversed micelles is successfully described by a model developed by Cates [35,69,254],... 

Two system-dependent interpretative pictures have been proposed to rationalize this percolative behavior. One attributes percolation to the formation of a bicontinuous structure [270,271], and the other it to the formation of very large, transient aggregates of reversed micelles [249,263,272], In both cases, percolation leads to the formation of a network (static or dynamic) extending over all the system and able to enhance mass, momentum, and charge transport through the system. This network could arise from an increase in the intermicellar interactions or for topological reasons. Then all the variations of external parameters, such as temperature and micellar concentration leading to an extensive intermicellar connectivity, are expected to induce percolation [273]. 

The overall objective of this chapter is to review the fundamental issues involved in the transport of macromolecules in hydrophilic media made of synthetic or naturally occurring uncharged polymers with nanometer-scale pore structure when an electric field is applied. The physical and chemical properties and structural features of hydrophilic polymeric materials will be considered first. Although the emphasis will be on classical polymeric gels, discussion of polymeric solutions and nonclassical gels made of, for example, un-cross-linked macromolecular units such as linear polymers and micelles will also be considered in light of recent interest in these materials for a number of applications... 

The structure of these gel-like systems of micelles is very different from that of conventional electrophoresis media made from chemically and physically cross-linked polymers of polyacrylamide and agarose [75], The absence of chemical or physical cross-links in the Pluronic gel-like phases may allow a larger degree of freedom for macromolecular transport around the obstacles that make up the medium than occurs in conventional electrophoresis media. 

Historically, the absorption of lipid-soluble nutrients has been considered to be carrier-independent, with solutes diffusing into enterocytes down concentration gradients. This is true for some lipid-soluble components of plants (e.g. the hydroxytyrosol in olive oil Manna et al., 2000). However, transporters have been reported for several lipid-soluble nutrients. For example, absorption of cholesterol is partly dependent on a carrier-mediated process that is inhibited by tea polyphenols (Dawson and Rudel, 1999) and other phytochemicals (Park et al., 2002). A portion of the decreased absorption caused by tea polyphenols may be due to precipitation of the cholesterol associated with micelles (Ikeda et al., 1992). Alternatively, plant stanols and other phytochemicals may compete with cholesterol for transporter sites (Plat and Mensink, 2002). It is likely that transporters for other lipid-soluble nutrients are also affected by phytochemicals, although this has not been adequately investigated. 

A mechanism Is proposed by which water-insoluble plant lipids (sterols etc.) may act as allelochemicals via micelle formation with long-chain fatty acids. By this process plant lipid solubility and transport In the aqueous medium are enhanced. This might suggest a reevaluation of water-insoluble plant constituents such as sterols as potential allelopathic agents. 

The transport properties of the acids did not respond significantly to the presence of the sink. This may be because at pH 7.4 the acids are negatively charged, as are the phospholipid membranes and also the surfactant micelles electrostatic repulsions balanced out the attractive forces due to increased membrane lipophilicity. Lowered surface pH may also play a balancing role [457]. 

The method for creating acceptor sink condition discussed so far is based on the use of a surfactant solution. In such solutions, anionic micelles act to accelerate the transport of lipophilic molecules. We also explored the use of other sink-forming reagents, including serum proteins and uncharged cyclodextrins. Table 7.20 compares the sink effect of 100 mM (5-cyclodextrin added to the pH 7.4 buffer in the acceptor wells to that of the anionic surfactant. Cyclodextrin creates a weaker sink for the cationic bases, compared to the anionic surfactant. The electrostatic binding force between charged lipophilic bases and the anionic surfactant micelles... 

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