Charged Lipid monolayers

The spread monolayers have provided much useful information about the role of charges at interfaces. In the case of an aqueous solution consisting of fatty acid or 

and NaCl, for example, the Gibbs equation [2.40] may be written as (Adamson and Gast, 1997 Birdi, 1989 Chattoraj and Birdi, 1984)  

It can be easily seen that the following will be valid  

It is also seen that following equation will be valid for this system  

This is the form of the Gibbs equation for an aqueous solution containing three different ionic species (e.g., R, Na, Cl). Thus, the more general form for solutions containing i number of ionic species would be 

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Aguilella, V., Mafe, S., and Manzanareas, J., Double layer potential and degree of dissociation in charged lipid monolayers, Chem. Phys. Lipids, 105 (2), 225 229, 2000. 

V. M. Aguilella, S. Mafe, and J. A. Manzanares, Ghent. Phys. Lipids, 105, 225 (2000). Double Layer Potential and Degree of Dissociation in Charged Lipid Monolayers. 

The enhancement of the electric field by about a factor of ten is not specifically related to the surfactant used, as it is also observed in the context of charged lipid monolayers at the air-water interface. Wurpel and co-workers used A-phage DNA bound to a cationic lipid monolayer at the air-water interface to study screening effects of counterions by detecting water signals in the OD stretching region at different concentrations. ... 

By preparing planar lipid monolayers or bilayers on hydrophobically derivatized or native hydrophilic glass, respectively, the adsorption equilibrium constants of a blood coagulation cascade protein, prothrombin, have been examined by TIRF on a surface that more closely models actual cell surfaces and is amenable to alterations of surface charge. It was found that membranes of phosphatidylcholine (PC) that contain some phosphatidyl-serine (PS) bind prothrombin more strongly than pure PC membranes/83... 

Fig. 3. Analysis of peptide-lipid interactions using ProteinChip arrays. Vesicles are absorbed to H50 ProteinChip arrays via interactions with C8 functional groups, creating a supported lipid monolayer on the chip surface (A, B). Samples are applied to the chip, incubated for 5 min (C), and washed to remove nonspecifically bound proteins (D). Matrix is added (E), and the array is introduced into the ProteinChip reader, where the laser is fired onto the chip surface. Peptides retained on the surface are finally resolved by TOF-MS, displaying mass-to-charge versus signal intensity (F, G). (Adapted from ProteinChip technology training course, Bio-Rad Laboratories.)...

Ultimately, sequestering charged lipids could potentially lead to a new stable state, in which bilayer bending forces favor membranes with local nonzero curvature. Moreover, the mechanism for coupling local lipid composition with membrane curvature may be complemented by a "local spontaneous curvature" mechanism [88], whereby the asymmetry between the spontaneous shapes of two monolayers is achieved by insertion of amphipathic N-terminal helices of certain BAR domains into the lipid polar head-groups region on one side of the membrane [7,88-95]. According to this mechanism, the insertion of an amphipathic... 

Similar adsorption behavior was observed at the air-solution interface, as shown recently for interactions of PNP with lipids at the air water interface, which were investigated by monolayer studies and tight reflection spectroscopy (Kozarac et al., 1989, in press). The nitrophenolate ion does not accumulate al the air-water interface as well as in the neutral lipid monolayer. Its attachment to these hydrophobic interfaces is mediated by electrostatic interaction with positively charged functional groups of hydrophobic surfactants. 

An indication of the role of electrostatic effects follows. The net charge on a -casein molecule at pH 7 is (— )13 (11), but Att and r are only slightly affected when, under given conditions, egg lecithin is replaced by lipids (e.g. phosphatidylserine, dicetyl phosphate, and arachidic acid) with a net negative charge. Electrostatic effects play a minor role in the interaction of /3-casein with insoluble lipid monolayers. A comparative series of experiments with lysozyme show some major effects. The results are summarized in Figure 6 where Att and r for lysozyme adsorbing to a variety of lipid monolayers at Cp1 = 5.6 X 10"5 % and... 

In order to elucidate the physicochemical properties of such a biological membrane interface, several model membrane systems (lipid monolayer, lipid bilayers, and protein-incorporated lipid model membrane systems) which mimic biological membrane interfaces have also been studied.In particular, many properties at the membrane surface are intimately related to the electrical potential originating from the fixed charge or electrical polarization of the membrane constitutents. 

Fig. 1. A schematic, cross-sectional view of a membrane. The head groups of the polar lipids are represented by ovals and the acyl chains by the wiggly lines. The integral proteins are shown as shaded areas and appear as single units embedded in both lipid monolayers, as aggregates of two subunits in one monolayer, or as single units traversing the bilayer. The hydrophilic regions of the proteins and lipids are represented as charges, (J) and 0. Thy hydrophobic regions are represented by the CHj and Q groups.

Fig. 5 Charge versus time curves following a series of potential steps from a fixed initial potential , = —0.250 V to final potentials E varying by —10 mV increments from —0.250 to —0.750 V on a mercury electrode coated with a lipid monolayer consisting of 57 mol%...

Lipophilic ions As a rule, lipophilic ions tend to permeate the lipid monolayer on the negative side of the region of the capacity minimum if cationic, and on the positive side if anionic. Such a permeation, which is due to electrostatic attraction for the charged electrode surface, causes a... 

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