Monolayer membranes

Compression of the PS II membrane monolayer shows that the monolayer collapses at a relatively low surface pressure, at around 20mN/m. This can be attributed to the formation of a multilayered structure [8] and some of PS II membrane fragments diffuse into the subphase. This observation further indicates that PS II membranes can only marginally stay at the air-water interface and one must be very careful in choosing the experimental parameters. 

Membrane-Interaction (MI)-QSAR approach developed by Iyer et al. was used to develop predictive models of some organic compounds through BBB, and to simulate the interaction of a solute with the phospholipide-rich regions of cellular membranes surrounded by a layer of water. Molecular dynamics simulations were used to determine the explicit interaction of each test compound with the DMPC-water model (a model of dimyristoylphosphatidylcholine membrane monolayer, constructed using the software Material Studio according to the work done by van der Ploeg and Berendsen). Six MI-QSAR equations were constructed (Eqs. 74-79) ... 

Another mechanism of the transmembrane electron transfer in the system under discussion has been proposed by Khairutdinov and co-workers [60]. This mechanism assumes the two-quantum ionization of porphyrin dimer located in the inner membrane monolayer with the capture of the electron by MV2+ dication to be the primary redox photochemical process. However, this interpretation is based on the data obtained when studying vitreous suspensions of vesicles at 77 K, and further experiments seem to be needed to justify their applicability to liquid suspensions at ambient temperatures. 

Note, however that the concepts about the lipid membrane as the isotropic, structureless medium are oversimplified. It is well known [19, 190] that the rates and character of the molecular motion in the lateral direction and across the membrane are quite different. This is true for both the molecules inserted in the lipid bilayer and the lipid molecules themselves. Thus, for example, while it still seems possible to characterize the lateral movement of the egg lecithin molecule by the diffusion coefficient D its movement across the membrane seems to be better described by the so-called flip-flop mechanism when two lipid molecules from the inner and outer membrane monolayers of the vesicle synchronously change locations with each other [19]. The value of D, = 1.8 x 10 8 cm2 s 1 [191] corresponds to the time of the lateral diffusion jump of lecithin molecule, Le. about 10 7s. The characteristic time of flip-flop under the same conditions is much longer (about 6.5 hours) [19]. The molecules without long hydrocarbon chains migrate much more rapidly. For example for pyrene D, = 1.4x 10 7 cm2 s1 [192]. 

The appearance of electron transfer across membranes via electron exchange reactions seems to result from the necessity of overcoming the difficulties for an ion to pass through the highly hydrophobic region of the boundary which separates the two membrane monolayers. This boundary corresponds to the maximum of potential energy profile for the ion motion in the membrane (see Fig. 6b). If the ion could reach the top of the potential barrier, it would be able to diffuse with... 

Figure 8 Snapshot of a DPPC bilayer with a small concentration of DPPCs replaced with PyrPC probes, see Fig. 1 (26). One finds PyrPC probes (shown in dark grey) to penetrate (interdigitate) significantly into the opposing leaflet, thus causing perturbations in both membrane monolayers. Water is not shown for clarity.

Here, cu and C are the local mean curvatures of each of the two membrane monolayers, and nm denotes the bending rigidity of a single monolayer that is here assumed to be the same for each leaflet and for both lipid species. The spontaneous curvatures of the two leaflets, and cj are described as sums of the spontaneous curvatures of the pure lipid constituents weighted by their local compositions. This approximation has been previously validated [36,48]. 

The MI-QSAR method is receptor based, in effect the assumption made is that the phospholipid regions of a cellular membrane constitute the receptor. The receptor is usually constructed as a monolayer from the phospholipids that comprise the cell membrane of the system of interest for instance, a single dimyristoylphosphatidylcholine (MDPC) molecule is selected as the model phospholipid and an assembly of 25 DMPC molecules (5 x 5 x 1) in (x, y, z) directions, respectively, is used as the model membrane monolayer. 

Type of membrane Monolayer perfluorocarboxylic acid membrane (COOH) Multilayer membrane of perfluorocarboxylic and sulfonic acid by lamination or coating (C00H S03H) Multilayer membrane of perfluorocarboxylic and sulfonic acid by chemical treatment (COOH/SO3H)... 

In contrast to polymersomes, there are various models of planar membranes monolayers at the water-air interface, free-standing bilayers, and solid-supported membranes. The functionality of proteins in natural membranes strongly depends on their mobility in the matrix, and this is thus an essential prerequisite for artificial membranes to mimic the dynamic environment of biomembranes in order to serve as templates for biomolecules.Therefore, the building blocks forming a bio-inspired membrane need to possess high flexibility to compensate the hydrophobic mismatch between the size of the biomolecules, and the membrane thickness. Furthermore, a variety of membrane properties (thickness, polarity, and surface charge) have to be considered for the successful insertion/attach-ment of biomolecules. Decoration of polymer membranes with biomolecules, either on their surfaces or inside the bilayers, can be achieved by various approaches, such as physical adsorption, insertion, and covalent binding. Compared to physical immobilization of biomolecules on... 

The properties of monolayers of the cyclodepsipeptide, valinomydn (Fig. 4.12) have been the subject of recent investigations. Ries and Swift [105] have determined a molecular area of 3.70 nm from extrapolations of pressure-area isotherms for monolayers of valinomydn from which they infer a horizontal orientation of molecules within the monolayer. Mixtures of valinomydn and cholesterol (which has a vertical orientation in monolayers) have been investigated in view of their similarity to biological membranes and the possibility of their use as models for naturally occurring membranes. Monolayers of valinomydn are also of interest because of the ability of valinomycin to stimulate the transport of ions across mitochondrial and red blood cell membranes [106]. Several workers have studied the interaction of electrolytes with valinomycin monolayers [106-108]. These studies have shown a specific interaction of... 

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