Phospholipid Amphiphiles

LB monolayers and Y-type bilayers lead us to bilayers, hemimicelles, and micelles (Fig. 4.12). A bilayer of phospholipid amphiphiles forms the cell wall, which surrounds each living cell (prokaryotic and eukaryotic) the ionic outer layers contact the bulk solution (blood, serum, etc.), while the... 

Figure 2 Illustrative lyotropic lipid-water phase diagram for phospholipid amphiphiles with transitions between the phase ranges driven by the water content. Hatched areas indicate two-phase regions (reproduced from (52) with permission from Elsevier).

Figure 9.1 (a) Cell membranes are composed primarily of phospholipid amphiphiles. (b) Cholesterol molecules act as... 

Figure 6. Complex lyotropic mesophase at interface of cholesterol (solid phase), phospholipid (amphiphile), and water (solvent)...

A new family of nanotubes derived from anionic gluco-phospholipidic amphiphiles has been reported recently (Figure lOg)." These compounds possess a double-tailed hydrophobic chain grafted through a phosphate linkage... 

The central role of biomembranes in cellular function underlines the importance of membrane research, an area that is by its very nature highly interdisciplinary and ranges from molecular biology to physical chemistry. At its core, however, is an essentially supramolecular interaction, the hydrophobic effect, which causes phospholipid amphiphiles to self-assemble into bilayers and then into complex closed compartments. The elegant self-assembly process that forms these remarkably large structures is an area of keen interest in its own right, but much recent study into self-assembled membranes aims to replicate the functions of biomembranes. Indeed, for cells, phospholipid bilayers are more than just delimiting boundaries they are... 

Although a variety of amphipathic molecules can be used to form the bilayer, the major lipidic components of liposomes are usually phospholipids, amphiphilic moieties with a hydrophilic head group and two hydrophobic chains. The phospholipid molecules form a closed bilayer... 

The attachment of pyrene or another fluorescent marker to a phospholipid or its addition to an insoluble monolayer facilitates their study via fluorescence spectroscopy [163]. Pyrene is often chosen due to its high quantum yield and spectroscopic sensitivity to the polarity of the local environment. In addition, one of several amphiphilic quenching molecules allows measurement of the pyrene lateral diffusion in the mono-layer via the change in the fluorescence decay due to the bimolecular quenching reaction [164,165]. 

Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

A typical biomembrane consists largely of amphiphilic lipids with small hydrophilic head groups and long hydrophobic fatty acid tails. These amphiphiles are insoluble in water (<10 ° mol L ) and capable of self-organization into uitrathin bilaycr lipid membranes (BLMs). Until 1977 only natural lipids, in particular phospholipids like lecithins, were believed to form spherical and related vesicular membrane structures. Intricate interactions of the head groups were supposed to be necessary for the self-organization of several ten thousands of... 

Phospholipids are amphiphilic compoimds with high surface activity. They can significantly influence the physical properties of emulsions and foams used in the food industry. Rodriguez Patino et al. (2007) investigated structural, morphological, and surface rheology of dipalmitoylpho-sphatidylcholine (DPPC) and dioleoyl phosphatidylcholine (DOPC) monolayers at air-water interface. DPPC monolayers showed structural polymorphisms at the air-water interface as a function of surface pressure and the pH of the aqueous phase (Fig. 6.18). DOPC monolayers showed a... 

One question addressed in the literature is the relationship between the angle of orientation of the adsorbed species within the monolayer and their amphiphilic character. The case of surfactants like fatty acids or phospholipids is deferred until Section VI, since the technique of choice is SFG in order to perform a surface vibrational study. Phenol deri-... 

There is a group of substances, in the presence of which significant changes in the surface tension of the ITIES were observed, which are also likely to influence the differential capacity of the ITIES correspondingly. These substances include various ionic and nonionic surfactants (Section IV.B.2) and amphiphilic phospholipids (Section IV.B.3) or affinity dyes. Attention has focused on phospholipids. 

Biomembranes mainly consists of phospholipid matrices, and the major component is phosphorylcholines (PC). PC is an amphiphile consisting of hydrophilic headgroup and hydrophobic long chains. In view of the amphiphilic feature of PC, we can divide hydrated lipid bilayers into the three zones, I, II, and III. The zone model, which has been used in a recent NMR study of DD [46-48], is illustrated in Fig. 2. 

Liposomes are formed due to the amphiphilic character of lipids which assemble into bilayers by the force of hydrophobic interaction. Similar assemblies of lipids form microspheres when neutral lipids, such as triglycerides, are dispersed with phospholipids. Liposomes are conventionally classified into three groups by their morphology, i.e., multilamellar vesicle (MLV), small unilamellar vesicle (SUV), and large unilamellar vesicle (LUV). This classification of liposomes is useful when liposomes are used as models for biomembranes. However, when liposomes are used as capsules for drugs, size and homogeneity of the liposomes are more important than the number of lamellars in a liposome. Therefore, "sized" liposomes are preferred. These are prepared by extrusion through a polycarbonate... 

Phospholipids or similar water-insoluble amphiphilic natural substances aggregate in water to form bilayer liquid crystals which rearrange when exposed to ultrasonic waves to give spherical vesicles. Natural product vesicles are also called liposomes. Liposomes, as well as synthetic bilayer vesicles, can entrap substances in the inner aqueous phase, retain them for extended periods, and release them by physical process. 

Two principal routes of passive diffusion are recognized transcellular (la —> lb —> lc in Fig. 2.7) and paracellular (2a > 2b > 2c). Lateral exchange of phospholipid components of the inner leaflet of the epithelial bilayer seems possible, mixing simple lipids between the apical and basolateral side. However, whether the membrane lipids in the outer leaflet can diffuse across the tight junction is a point of controversy, and there may be some evidence in favor of it (for some lipids) [63]. In this book, a third passive mechanism, based on lateral diffusion of drug molecules in the outer leaflet of the bilayer (3a > 3b > 3c), wih be hypothesized as a possible mode of transport for polar or charged amphiphilic molecules. 

The charge-state section highlighted the value of Bjerrum plots, with applications to 6- and a 30-pKa molecules. Water-miscible cosolvents were used to identify acids and bases by the slope in the apparent pKa/wt% cosolvent plots. It was suggested that extrapolation of the apparent constants to 100% methanol could indicate the pKa values of amphiphilic molecules embedded in phospholipid bilayers, a way to estimate pAi m using the dielectric effect. 

Phospholipids are amphiphilic substances i.e. their molecules contain both hydrophilic and hydrophobic groups. Above a certain concentration level, amphiphilic substances with one ionized or polar and one strongly hydrophobic group (e.g. the dodecylsulphate or cetyltrimethylammonium ions) form micelles in solution these are, as a rule, spherical structures with hydrophilic groups on the surface and the inside filled with the hydrophobic parts of the molecules (usually long alkyl chains directed radially into the centre of the sphere). Amphiphilic substances with two hydrophobic groups have a tendency to form bilayer films under suitable conditions, with hydrophobic chains facing one another. Various methods of preparation of these bilayer lipid membranes (BLMs) are demonstrated in Fig. 6.10. 

Hydrophilic carotenoids behave as typical amphiphiles. The contact angle of a water drop on a dry film of the phospholipid, 3.15, and its lifetime before spreading were signs of noticeable surfactant properties (Foss et al. 2005a). When amphiphiles are in contact with water, the molecules move to... 

Phospholipidosis is an excessive intracellular accumulation of phospholipids and drug, which is normally reversible after discontinuation of drug treatment. Currently, it is thought that phospholipidosis alone is not toxic per se, but because some compounds cause concurrent phospholipidosis and organ toxicity, avoidance of the issue in drug discovery projects seems prudent [74]. Fortunately, there are clear links between phospholipidosis and physical properties, especially lipophilicity, basicity, and amphiphilicity [75] which allow for good prediction of the risk. 

Sakai-Kato, K., Kato, M., Ishihara, K. and Toyo-oka, T. (2004) An enzyme immobilization method for integration of biofunctions on a microchip using a water-soluble amphiphilic phospholipid polymer having a reacting group. Lab on a Chip, 4, 4—6. 

Liposomes are artificial structures composed of phospholipid bilayers exhibiting amphiphilic properties (Chapter 22). In complex liposome morphologies, concentric spheres or sheets of lipid bilayers are usually separated by aqueous regions that are sequestered or compartmentalized... 

Figure 22.1 The amphiphilic nature of phospholipids in solution drives the formation of complex structures. Spherical micelles may form in aqueous solution, wherein the hydrophilic head groups all point out toward the surrounding water environment and the hydrophobic tails point inward to the exclusion of water. Larger lipid bilayers may form by similar forces, creating sheets, spheres, and other highly complex morphologies. In non-aqueous solution, inverted micelles may form, wherein the tails all point toward the outer hydrophobic region and the heads point inward forming hexagonal shapes.

Relatively little work on chiral assemblies was reported over the next 15 years until a resurgence in activity in the mid-1980s with nearly simultaneous reports of chiral morphologies in gluconamides,22 amino acid amphiphiles,23,24 and diacetylenic phospholipids 25,26 These systems will be discussed in... 

In this chapter, we have surveyed a wide range of chiral molecules that self-assemble into helical structures. The molecules include aldonamides, cere-brosides, amino acid amphiphiles, peptides, phospholipids, gemini surfactants, and biological and synthetic biles. In all of these systems, researchers observe helical ribbons and tubules, often with helical markings. In certain cases, researchers also observe twisted ribbons, which are variations on helical ribbons with Gaussian rather than cylindrical curvature. These structures have a large-scale helicity which manifests the chirality of the constituent molecules. 

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