Hydrated headgroup

Fig. 7 (a) A comparison of the TE of DOTAP/DOPC/Chol-DNA complexes (black squares) and DOTAP/DOPC/PC-cholesterol-DNA complexes (gray bowties). The replacement of DOPC with PC-cholesterol, which has a similarly hydrated headgroup, fails to increase TE. (b) The chemical structures of cholesterol and PC-cholesterol. Reprinted with permission from [27]. Copyright 2009 American Chemical Society... 

Figure 1 Cartoon of the surfactant unimer distribution in aqueous solution and the spontaneous self-assembly of surfactant unimers into spherical micelles just above the cmc. The two sets of arrows represent the concept of dynamic equilibrium in which the exchange rates of unimer between the air/water interface and micelles are equal. The cross section of the spherical micelle shows the core region containing the tails, the interfacial region containing hydrated headgroups (and a fraction of the counterions for ionic micelles, not shown), and the surrounding aqueous region. Such iconic images of micelles are unrealistic because experiments show that micelles are fluids and the tails are almost randomly distributed, and headgroups move at near diffusion-controlled rates that do not define a smooth surface.

These results are depicted in Figure 20.4. The lipids in the SOPC/SM monolayer are initially randomly distributed, at least on the macroscopic length scales of the optical microscope (panel A). Cleavage of the phosphocholine headgroup from SM by SMase generates ceramide, a lipid with a small, weakly hydrated headgroup (panel B). Compared to POPC with a mean molecular area of 70 [53], the area of... 

Sodium octanoate (NaO) forms reversed micelles not only in hydrocarbons but also in 1-hexanol/water. The hydration of the ionogenic NaO headgroups plays an important role in this case too. For this reason Fujii et al. 64) studied the dynamic behaviour of these headgroups and the influence of hydration-water with l3C and 23Na NMR measurements. Below w0 = [H20]/[NaO] 6 the 23Na line-width... 

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. 

Considering only the lipid phase as the transport pathway for the peptide, as the solute enters and diffuses across the membrane it will encounter a number of different microenvironments. The first is the aqueous membrane interface (Fig. 23). In this region, the hydrated polar headgroups of the membrane phospholipids separate the aqueous phase from the apolar membrane interior. It has been shown that this region is capable of satisfying up to 70% of the hydrophobic effect... 

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]. 

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