Headgroups classes

An attractive class of low toxicity, biodegradable cationic lipids has been derived from the natural PCs, in which the zwitterionic headgroup of the PC is converted into a cation by esterification of the phosphate group (Fig. 3) [16-18]. 

Changes in headgroup composition lipid class. A commonly observed change in lipid composition during thermal acclimation is a shift in the relative amounts of different classes of lipids present in a membrane. Cold acclimation frequently leads to an increase in phospha-tidylethanolamine (PE) and a decrease in phosphatidylcholine (PC). Thus, the PC/PE ratio falls, as shown for phospholipids isolated from gills of rainbow trout (Oncorhynchus mykiss) acclimated initially to either 5°C or 20°C and, then, transferred to the reciprocal temperature (figure 7.26 Hazel and Carpenter, 1985). The PC/PE ratio falls rapidly in the trout transferred to 5°C, and rises even more quickly in the trout transferred to 20°C. Note, however, that the PC/PE ratios did not reach stable plateau values during the 28-day acclimation period. Rather, after the initial rise (20° C) or fall... 

Since the headgroup of PLs contains phosphate derivatives, it is apparent that 31P NMR became the method of choice in structural studies of this class of compounds. The NMR measurements provide information about the composition of PLs mixtures, phase of samples, their morphology and molecular dynamics.86... 

The class of compoimds most extensively studied at liquid surfaces by VSF is the alkyl ionic surfactants. The simplest type of these surfactants consists of a charged polar headgroup and a long hydrocarbon chain and represents typical surfactants used in commercial products and industrial processes. In a typical soap or detergent solution, if the concentration of surfactant is high enough, the surfactant molecules form micelles... 

The classihcation scheme of Papahadjopoulos et al. (32), appropriately modihed for type 3 proteins, is still of some use in studies of lipid-protein interactions, although some proteins, at least under certain conditions, do not fall neatly into any of these three categories. It seems that all naturally occurring membrane proteins studied to date interact with lipid bilayers by both hydrophobic and electrostatic interactions and that different membrane proteins differ only in the specihc types and relative magnitudes of these two general classes of interactions. It is also clear that the behavior exhibited by any particular membrane protein can depend on its conformation, method of reconstitution, and relative concentration, as well as on the polar headgroup and fatty acid composition of the lipid bilayer with which it is interacting (see Reference 17). 

Another class of phospholipids is the sphingofipids. A sphingofipid molecule has the phosphatidyl-based headgroup structure described above, but (in contrast to a common phospholipid molecule) contains a single fatty acid... 

Surfactants Two other classes of host molecule, with, however, flexible cavities, are amphiphilic micellar and vesicular assemblies. In a simple view, these molecules bear a hydrophilic headgroup (e.g., ionic, zwitter ionic, or non-ionic) and a hydrophobic tail (carbon hydrogen chain). Depending on the solvent environment they organize in 3-dimensional surface-active assemblies. For example, in aqueous solutions their alignment... 

The term bolaamphiphile [104, 105] describing the shape of this class of mesogens very pictorial it is related to the South American hurl weapon consisting of two stones or leather balls linked by a rope. Bolaamphiphiles consist of two hydrophilic headgroups at both ends of the lipophilic section of the molecules. 

The last two cubic phases have only recently been identified in systems based on gangliosides (a widespread class of natural glycolipids with unusual bull polar headgroups) [176] and in the water-C12EO12 system [164]. 

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