Group region

The main peculiarity of solutions of reversed micelles is their ability to solubilize a wide class of ionic, polar, apolar, and amphiphilic substances. This is because in these systems a multiplicity of domains coexist apolar bulk solvent, the oriented alkyl chains of the surfactant, and the hydrophilic head group region of the reversed micelles. Ionic and polar substances are hosted in the micellar core, apolar substances are solubilized in the bulk apolar solvent, whereas amphiphilic substances are partitioned between the bulk apolar solvent and the domain comprising the alkyl chains and the surfactant polar heads, i.e., the so-called palisade layer [24],... 

For an explanation of reporter-group regions, see text.h C-5 of is also included in this region, for 4 only (see formulas 4-10). 

Figure 1 (Plate 1). A molecular view of a small section of a flat lipid bilayer generated by molecular dynamics simulations. The bilayers are composed of l-stearoyl-2-docosa-hexaenoyl-5M-g]ycero-3-phosphatidylcholine lipids, i.e. the sn 1 chain is 18 C atoms long and the sn2 chain has 22 carbons, including six cis double bonds. The hydrophobic core is in the centre of the picture, and the hydrated head-group regions are both on top and bottom of the view graph. The head group is zwitterionic and no salt has been added. From [102], Reproduced by permission of the American Physical Society. Copyright (2003)...

Alkanes and short alcohols actually partition into the interior of the membrane [171]. The well-shielded tetraphenylphosphonium (TPP+) and tetraphe-nylborate (TPB-) ions are also deeply intercalated into the lipid bilayer [6,169]. The binding site of TPB- is located somewhere below the head-group region in the vicinity of the ester groups, while the cation TPP+ binds a few tenths of a nanometre further outwards [6],... 

The number of organic substituents also influences interaction with lipid bilayers. Diphenyltin chloride causes disturbances of the hydrophobic region of the lipid bilayer, triphenyltin chloride adsorbs to the head-group region, and tetraphenyltin does not partition into the lipid bilayer [235-237]. Similar results were found for the butylated tins [238]. In addition, the mono-butyltin was homogeneously distributed within the lipid bilayer [238]. 

The properties of membranes commonly studied by fluorescence techniques include motional, structural, and organizational aspects. Motional aspects include the rate of motion of fatty acyl chains, the head-group region of the phospholipids, and other lipid components and membrane proteins. The structural aspects of membranes would cover the orientational aspects of the lipid components. Organizational aspects include the distribution of lipids both laterally, in the plane of the membrane (e.g., phase separations), and across the membrane bilayer (phospholipid asymmetry) and distances from the surface or depth in the bilayer. Finally, there are properties of membranes pertaining to the surface such as the surface charge and dielectric properties. Fluorescence techniques have been widely used in the studies of membranes mainly since the time scale of the fluorescence lifetime coincides with the time scale of interest for lipid motion and since there are a wide number of fluorescence probes available which can be used to yield very specific information on membrane properties. 

The motional characteristics of interest are typically those governed by the phospholipid fatty acyl chains and head-group region and the neutral lipid or protein components of membranes. Rotational motion can be subdivided into a structural component, the order or degree of orientational constraint,... 

The region at the surface of membranes and the underlying phospholipid head-group region are of particular interest since these regions can vary considerably with variations in the membrane phospholipid composition and under the influence of external molecules such as ions and hydrophobic molecules. The fluorescence anisotropy parameter tends to be less useful for examining this region since it is already intrinsically disordered and the... 

The results obtained on the doublelayer properties show that the studied monolayers may be represented by a two-capadtors-in-series model. One capacitor corresponds to the thiol head-group region of the monolayer and the second to the hydrocarbon phase. 

The two important areas for a preliminary examination of a spectrum are the regions 4000-1300 and 900-650 cm-1. The high-frequency portion of the spectrum is called the functional group region. The characteristic stretching frequencies for important functional groups such as OH, NH, and C=0 occur in this... 

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