Solidity, phospholipid monolayers

Kim K, Kim C, Byun Y. Biostability and biocompatibility of a surface-grafted phospholipid monolayer on a solid substrate. Biomaterials 2004, 25, 33-41. 

FIGURE 2.10. Representative spectra of dipalmitoyl phospholipid monolayers at the CCU/D2O interface under the ssp polarization scheme showing the methyl and methylene symmetric stretch (a) DPPC, (b) DPPE, (c) DPPG, (d) DPPS. Spectra of the monolayers are shown in solid squares. Spectra of the monolayers with halothane are shown with solid triangles. The lines ate fits to the data. From Ref. [62]. 

Fig. 9. CD spectra of the wild type E. coli LamB synthetic signal peptide in phospholipid monolayers. The experiment was carried out as described in Figs. 7 and 8. The solid line spectrum was obtained for films spread at pressures below the peptide s critical pressures of insertion, and the broken line spectrum for films spread above the peptide s critical pressure of insertion. Hence, the former represents inserted plus adsorbed peptide, and the latter is from adsorbed peptide only. Experimental details are reported in Briggs et al. (1986). Copyright 1986 by the American Association for the Advancement of Science.

Immobilized artificial membranes (lAM) are solid membrane mimetics that are covalently bound to the surface of a silica chromatographic support to generate a phospholipid monolayer. lAM chromatography can be applied to measure membrane partitioning of a given compound or to predict bile salt-membrane interactions they may also be used in studies on transcellular absorption. Artificial membranes appear to be well correlated with 1-octanol/water partition coefficients however, since the latter can be well predicted in silico, the real value of AIMs is the ability to study complex molecules or extracts, where in silico prediction is poor. I AM can also be applied to generate large data sets, that in turn can be applied to train and, therefore, improve in silico models by an extensive data input [41]. 

C.A. Helm, H. Mohwald, K. Kjaer, and J. Als-Nielsen, Phospholipid monolayers between fluid and solid states, Biophvs. T. 52 381 (1987). 

DOrc monolayers, due to the unsaturation, i.e. kinks of the alkyl chains, are in the liquid expanded phase, which is a fluid phase at all film pressures FI [3,13,15]. At 21 °C and T1 >25 mN m DPPC monolayers are in the solid analogous phase [3,13,16], which is highly incompressible and condensed [13,16]. Shah and Schulman [13] show that the effect of cholesterol on either saturated or unsaturated phospholipids is strikingly different. Cholesterol increases the surface elasticity, the dilational and the shear viscosity of unsaturated phospholipid monolayers [3,13,14,17]. In saturated monolayers cholesterol disturbs the order between phospholipid molecules fluidifying the solid monolayer [13,14,18] and lowering its shear viscosity [18]. Pure cholesterol monolayers are liquid [13] and have very low surface shear viscosities which are hardly detectable [18]. 

S-layer-stabilized solid-supported lipid membranes have also been fabricated as follows (Figure 15) [21], After compressing a phospholipid monolayer on a Langmuir trough into the... 

A decrease in occupied area of the head group results in an increase in packing density of the molecules (45) exhibits only an expanded phase, (46) both a liquid and a solid-like phase, and (47) forms only a condensed film. Monolayer properties of many natural phospholipids and synthetic amphiphiles are described in the literature37 38. Especially the spreading behaviour of diacetylenic phospholipids at the gas-water interface was recently described by Hupfer 120). 

The HBM consists of two differing leaves normally generated on a gold or silica surface. The lower leaf is a fixed long chain alkyl self-assembled monolayer covalently bound to a solid support while the upper leaf is a phospholipid mono-layer [82, 83]. This type of bilayer may show increased stability due to the covalent nature of the lower leaf fixation however it would present a system further removed in structure from the biological condition given this fixed nature and more limited fluidity [84]. 

Since the solidity or fluidity of the bilayer membrane is likely to depend on the alkyl chain interactions and consequently their length, an understanding of the relationship between chain order and chain length for tightly packed monolayers of phospholipids are important. As an example of how VSFS can be employed to study phospholipids at a liquid surface, a series of saturated symmetric chain phosphatidylcholines (PCs) were examined at the air/water and CCfr/water interfaces [49]. At the air/D20 interface, chain order within the monolayer was found to increase as the length of the chains increased (Figure 2.9a) under conditions of constant phospholipid head group area. 

Figure 2.10 shows the methylene and methyl symmetric stretch region of the spectrum for each headgroup before (solid squares) and after (solid triangles) the exposure of the monolayer to halothane. For each spectrum shown, there is a small increase in the overall intensity when halothane is present. This increase occurs across the entire spectrum for each of the phospholipids smdied. We believe that the small change in intensity... 

There are many cases in which other techniques have been applied to biphasic systems in order to establish the nature of mixing. For example, fluorescence microscopy of DPPC monolayers containing 2% of a fluorescent probe have shown the coexistence of solid and fluid phases of DPPC at intermediate pressures (Weis, 1991). Similar results have been achieved with a variety of other phospholipids using the same technique (Vaz et al., 1989). The recent application of laser light scattering to this area (Street et al., unpublished data) has yet to produce any conclusive evidence, but the future for this particular technique is also promising. It also provides information about the viscoelastic properties of the monolayer and how these are affected by the inclusion of penetration enhancers. 

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