Membranes repulsive interactions

McIntosh, T. J., Magid, A. D. and Simon, S. A. (1989). Cholesterol modifies the short-range repulsive interactions between phosphatidylcholine membranes,... 

Sometimes, thanks to the Donnan effect, by modifying the pH it is possible to retain in the reaction ambient molecules that otherwise would pass the membrane. In fact, some membranes can become electrically charged at acidic and alkaline pHs, then repulsive or attractive interactions between the substrate molecules and the membrane surface may occur if the charges are of the same or of different sign, respectively. Repulsive interactions increase rejection values, whereas attractive ones decrease them. 

Figure 6.14 The repulsive interaction between cationic head groups enforces large gaps between sulfur-bound monolayers on gold. Anions can pass such a membrane cations cannof. ...

Needham D, McIntosh TJ, Lasic DD (1992) Repulsive interactions and mechanical stability of polymer-grafted lipid membranes. Biochim Biophys Acta 1108 40-48... 

It is important to note that the lamellar phase is thus stabilized by the balance of a negative interfacial tension (of the free oil/water interface covered by an amphiphilic monolayer), which tends to increase the internal area, and a repulsive interaction between interfaces. The result, Eq. (48), indicates that the scattering intensity in a lamellar phase, with wave vector q parallel to the membranes, should have a peak at nonzero q for d > d due to the negative coefficient of the q term in the spectrum of Eq. (40). just as in the microemulsion phase. This effect should be very small for strongly swollen lamellar phases (in coexistence with excess oil and excess water), as both very small [96]. Very similar behavior has been observed in smectic liquid crystals (Helfrich-Hurault effect) [122]. Experimentally, the lamellar phase under an external tension can be studied with the surface-force apparatus [123,124] simultaneous scattering experiments have to be performed to detect the undulation modes. 

Most difficulties encountered with FlFFF are associated with the correct choice and installation of the membrane. Adsorption or repulsion of the sample can cause delayed or early elution, resulting in errors in size and MW, poor resolution, or low sample recovery. No doubt these problems will be reduced as a better understanding of membrane-sample interactions is obtained. 

There are different possibilities for how the forced translocation can be effected. For example, Milchev at al. [74, 75] studied the possibility that the monomer-membrane interaction is attractive on the tram side, while it is assumed to be repulsive on the cis side. Assuming that a few monomers of a chain have already passed through the pore and experience the favorable membrane-monomer interaction on the tram side, two questions that are asked are (1) How likely is it that the rest of the chain will follow from the cis to the tram side, depending on chain length N and the distance T/Tc — 1 from the adsorption transition that happens on the tram side at T = Tc (2) How does the time needed for complete translocation depend on these parameters ... 

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