Amphiphatic Molecules

Lipophilic or amphiphatic molecules are fully solubilized by the bilayers and tend not to leak (e.g., Weiner, 1987 Van Bloois et al.,... 

Figure 5.3 Self-assembly of a vesicle. Water-soluble molecules can be entrapped inside, ionic molecules on the polar head groups of the surface, amphiphatic molecules in the hydrophobic bilayer, (cac critical aggregate concentration).

Membrane lipids are amphiphatic molecules they contain both a hydrophilic and a hydrophobic moiety. Molecules of this kind can lead to various types of interface. A natural example is the cellular membrane, a bilayer arrangement of such molecules, that marks the frontier between cells. The principal constituents of this membrane are lipids and proteins (Fig. 17.1). 

Lipids are building blocks of model and real membranes, which can be combined with proteins and some other important biomolecules to simulate real membranes. The simplest model is hence the self-assembly of only one component of the complex membrane, in this case the lipids. These mono-component lipidic models are often employed in studies as their interaction with small molecules mimics the actual relationship between the cell membrane and a substrate. A commonly employed amphiphatic lipid, dipalmitoyl phosphatidylcholine (DPPC) (Figure 4.6.2), has been widely used to construct these cell membrane motifs, due to its high content in animal cells, and thus its tendency to mimic a valid animal ceU. The supramolecular organization of these (a) DPPC amphiphatic molecules lead to a (b) Langmuir monolayer, (c) bilayer, (d) micelle, and (e) vesicle, which are the available levels of modeling to mimic the cellnlar membrane. 

From N. K. Adam s observation that many bipolar amphiphatic molecules form gaseous expanded films, it is evident that these nitroxide probe films, with the possible exception of 5-NS and 5-NS(Me), behave as typical bipolar amphiphatic films. The shift to lower areas/molecule for 5-NS and 5-NS (Me) shows that, as the oxazolidine ring moves closer to the primary polar group, the bipolar nature of the molecule diminishes. Thus the carboxyl group and oxazolidine ring for these compounds effectively constitute one polar group. 

Supported bilayer lipid membranes (s-BLMs) have been prepared from mixtures of natural phospholipids and synthetic amphiphatic molecules. Three classes of compounds have been immobilized into these s-BLMs as follows ... 

The bacteria apparently produce some kind of diffusible substance. Extracts from bacterial cultures were fractionated and a compound highly effective in inhibiting fungal growth was isolated. The pure compound was active on its own and it was shown to be a new substance, viscosinamide. The compound is a cyclic peptide Fig 5.2 with a lipid tail and has strong surfactant properties (amphiphatic molecule). The compound is similar to other compounds that have been shown to create holes in membranes. 

Certain amphiphatic molecules arrange themselves in discoidal bilayered structures known as bicelles. The bicelles have highly anisotropy magnetic susceptibility and thus the property to align themselves in the magnetic field with the plane normal perpendicular to the field [434]. This results in a uniaxial medium suitable for... 

Langmuir-Blodgett (LB) films are molecularly ordered layers of amphiphatic molecules on a solid support. The special, well-defined layer structure offers the potential of its use in fields such as electronics, microlithography, biosensors, and corrosion protection [1, 2, 3, 4, 5]. The stability of LB films under various conditions has been and still is a crucial issue in practical applications [6, 7, 8, 9, 10], although the possible change of LB layers in an aqueous environment has obtained less attention [11,12, 13, 14]. 

Amphiphatic A molecule possessing both polar and nonpolar moieties. 

Micelles of amphiphatic surfactant molecules in non-polar solvents have the reverse structure when compared with micelles in aqueous solvents. The polar... 

T he use of spin-label probes to investigate cell membrane structure and function clearly demonstrates the fluidity of membrane lipid structures (1,2,3,4) however, a spin-label probe sees only its immediate environment. Predictions (5, 6, 7, 8) and data (9, 10, 11, 12) show that the introduction, for example, of a substituted oxazolidine ring as part of a typical amphiphatic lipid molecule can also significantly perturb a normal lipid environment. Consequently, some quantitative observations that used spin-label techniques need revision while others may be reduced to the level of qualitative predictions. 

It is well known that the extent of topical tissue damage produced by a series of surface active compounds are in parallel with their in vitro hemolytic activities (9,10) Thus, it is reasonable to assume that the muscular tissue toxicity of amphiphatic CPZ occurs mainly through the membrane disruption of the muscular tissues. Recently, we reported that 3-CyD significantly protected the human erythrocytes against the membrane disruption elicited by the penetration of CPZ molecules into the cytoplasmic leaflet of the bilayer ( ). Therefore, the reduction in the muscular tissue toxicity of CPZ by 3-CyD may be explained by decrease in the affinity of CPZ to the tissue... 

The control of surface functionality by proper selection of the composition of the LB films and/or the self-assembling (amphiphatic) molecular systems can mimic many functions of a biologically active membrane. An informative comparison is that between inverted erythrocyte ghosts (Dinno et al., 1991 Matthews et al., 1993) and their synthetic mimics when environmental stresses are imposed on both systems. These model systems can assist in mechanistic studies to understand the functional alterations that result from ultrasound, EM fields, and UV radiation. The behavior of carrier molecules and receptor site functionality must be mimicked properly along with simulating disturbances in the proton motive force (PMF) of viable cells. Use of ion/electron transport ionomers in membrane-catalyst preparations is beneficial for programs such as electro-enzymatic synthesis and metabolic pathway emulation (Fisher et al., 2000 Chen et al., 2004). Development of new membranes used in artificial organs and advances in micelle reaction systems have resulted from these efforts. 

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