Lipids headgroups

On the basis of the h and C NMR, we have pictured the delivery site of BPA as illustrated in Fig. 15. There is trapped BPA between the lipid headgroup and hydrocarbon chain region most adjacent to the interface, with two methyl groups oriented toward inside... 

It is possible, however, that the electrochromic response of some styrylpyridi-nium probes, for example, RH421 (see Fig. 2), is enhanced by a reorientation of the dye molecule as a whole within the membrane. There is a steep gradient in polarity on going from the aqueous environment across the lipid headgroup region and into the hydrocarbon interior of a lipid membrane. Therefore, any small reorientation of a probe within the membrane is likely to lead to a change in its local polarity and hence a solvatochromic shift of its fluorescence excitation spectrum. Such a... 

Lee, K.-D., Hong, K. and Papahadjopoulos, D. (1992). Recognition of liposomes by cells in vitro binding and endocytosis mediated by specific lipid headgroups and surface charge density, Biochim. Biophys. Acta, 1103, 185-197. 

Water molecules are absent from the hydrophobic interior, but both the choline and the phosphate headgroups are fully solvated [41]. Similarly, the first hydration shell of the sulfate headgroup of SDS is formed rather by water molecules than by sodium ions. Because of hydration the charge density due to the lipid headgroups is overcompensated by the water dipoles, thereby reducing the transmembrane potential by 50-100 mV across the lipid water interface and resulting in a negative potential at the aqueous side [42]. 

Ortho ester lipids contain a pH-sensitive ortho ester linkage that causes lipid headgroup cleavage on exposure to the mildly acidic environment of the endosome... 

The charge on the liposomal surface is a property that has major effects on the stability, biodistribution, and cellular uptake of liposomes, and is governed by lipid headgroup composition and by pH. It can be monitored by micro electrophoresis (i.e., capillary zone electrophoresis), or by measurement of the zeta potential (Egorova, 1994). 

Dipolar Potential Anisotropy of lipid headgroup dipoles in organized membrane Electrostatic... 

The polar lipid headgroup zone contains the phospholipid and steroid phosphorus-nitrogen, carbonyl, hydroxyl and hydration water moieties which combine to establish a substantial dipolar potential. This positive potential is of a magnitude of several hundred millivolts across the membrane headgroup zone. In the membrane hydrocarbon interior, the electrostatic field must be at least 450 to 750 mV (14) and controls ion current across the interior as we 1 1 as possibly influencing selective ion adsorption to the membrane surface. 

The linker group that bridges the cationic lipid headgroup with the hydrocarbon moiety controls the biodegradability of a cationic amphiphile. Most of the linker bonds are ether, ester, or amide bonds (Fig. 1). Compounds with ether links generally render better transfection efficiency. However, they are more stable and may cause higher toxicity, while cationic lipids with ester links such as DOTAP are more biodegradable and less cytotoxic in cultured cells [28, 39]. Noteworthy,... 

The synthesis of the branched core of the lipid headgroups [24, 45] proceeds in the same manner as that of multiple antigenic peptides (MAPs) [50, 51 ] or polyethylene glycol-dendritic oligo-lysine block copolymers [52]. It starts from ornithine... 

The response range of the local environment to the excited Trp-probe is mainly within 10 A because the dipole-dipole interaction at 10 A to that at —3.5 A of the first solvent shell drops to 4.3%. This interaction distance is also confirmed by recent calculations [151]. Thus, the hydration dynamics we obtained from each Trp-probe reflects water motion in the approximately three neighboring solvent shells. About seven layers of water molecules exist in the 50-A channel, and we observed three discrete dynamic structures. We estimated about four layers of bulk-like free water near the channel center, about two layers of quasi-bound water networks in the middle, and one layer of well-ordered rigid water at the lipid interface. Because of lipid fluctuation, water can penetrate into the lipid headgroups, and one more trapped water layer is probably buried in the headgroups. As a result, about two bound-water layers exist around the lipid interface. The obtained distribution of distinct water structures is also consistent with —15 A of hydration layers observed by X-ray diffraction studies from White and colleagues [152, 153], These discrete water stmctures in the nanochannel are schematically shown in Figure 21, and these water molecules are all in dynamical equilibrium. 

Tiburu et al." investigated the influence of hCBi and hCB2/ G-protein-coupled receptors, on the dynamics of lipid headgroups and lipid acyl chains of the POPC bilayer. The authors described the reduction of the CSA width of 31P spectra in the lipid headgroups, which shows the local motions of this part. These disruptions result from the impact of hCBi and hCB2 peptides which can be either localised on the membrane surface or incorporated in hydrophobic core and leaves this lipid bilayer. 

The processes occurring within lipid membranes are very often pH-depen-dent and can be measured via 31P SS NMR. Chu et al.101 investigated the influence of sorbic acid on the DMPC membrane and compared the effects of the longer chain decanoic acid in different acid concentrations (pH). The line shape of the spectra was found to be typical for lipids in the lamellar phase. CSA values were obtained for different pH values and various amounts of peptide. The linewidth broadening after addition of sorbic or decanoic acids suggested a small impact on the dynamics of lipid headgroups (Figure 25). 

The phospholipid monolayers examined in this study were all saturated, symmetric, 1,2-diacyl-j -glycero-3-phosphate-based lipids. Four different lipid headgroups attached to the phosphate were examined choline, ethanolamine, glycerol and serine. Each lipid features a glycerol backbone, two saturated fatty acid chains and a phosphatidyl headgroup. 

The preliminary results just reported for DPPC/OA monolayers illustrate the way in which neutron reflectometry can be used to study the interaction of components in model membrane systems. In particular, the technique has been shown to be useful in the study of the water associated with lipid headgroups. Data analysis by the partial stmcture factor method offers the potential to study complex multicomponent membrane systems, which have more relevance to the behavior of biological membranes in vivo. 

Changes in pH modulate the lipid phase behavior as a consequence of protonation/deprotonation of the lipid headgroups, which results in a change of the surface charge of the membrane (77). They also modify the surface polarity and hydration. Typically, protonation decreases lipid hydration and increases the main transition temperature (53). The effects of pH titration on the chain-melting transition temperature of dimyristoyl phospholipids is illustrated in Fig. 3e, which shows that single protonation increases the melting transition temperature by about 5-15° C. 

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