Partition into lipid phases

Figure 2.6. The role of lipid membranes in drag distribution, a Structure of phosphatidylcholine (left), and schematic of a lipid bilayer (right). The hydrophobic interior phase represents the kinetic barrier to drag absorption and distribution. b Drag diffusion across lipid bilayers. Partition into the bilayer is the rate-limiting step. Hydrophilic drag molecules (left) will not efficiently partition into the hydrophobic phase and therefore can t get across the membrane easily. In contrast, hydrophobic molecules (right) will enter the membrane readily and therefore will cross the membrane more efficiently.

FIGURE 6.7 Phase separation in a iipid biiayer. This giant vesicie is composed of a single bilayer formed from three different lipids. Phase separation into two different lipid phases can be visualized using fluorescence labels. The red phase is the 1 phase, and we use a dye that does not partition into the Iq phase. Both phases can be visualized by using a different dye that partitions into both phases. 

For diprotic molecules, 12 different characteristic shift patterns have been identified for cases where two species may partition simultaneously into the lipid phase [347]. Three of these cases are shown in Fig. 4.8, picking familiar drug substances as examples. Once the approximate constants are obtained from Bjerrum analysis,... 

The molecular structure and conformation of an organic pollutant is a property which may affect adsorption onto a solid surface and/or partition into its organic lipid phase differently, thus hindering the expected correlation between KQM and K )W ... 

Hydrophobic pollutants such as PCBs often partition into lipid rather than into water. The K0w measures this partitioning. This coefficient provides an indication of the degree to which a pollutant accumulates into fatty tissues and any organic phase. This coefficient is especially useful for determining the release of PCBs from mineral oil transformer fluids, and Hawker and Connell [391] pro-... 

The distribution coefficient is the partition coefficient at a particular pH. The following equilibrium is often used to define D, with the assumption that only the unionized species partition into the oil or lipid phase ... 

Polyether antibiotics are hydrophobic compounds that are characterized chemically by their low polarities and their instability under acidic conditions. These antibiotics can be quantitatively extracted from the primary organic extract into carbon tetrachloride (393-395). When partitioning from a sodium chloride solution into an organic solvent, high yields have been achieved using dichloromethane (396, 397), carbon tetrachloride (391, 399), and chloroform (14, 398) as extraction solvents. In a different approach, water extracts containing lasalocid residues have been purified by partitioning into the mobile phase, which was a complex mixture of tetrahydrofuran, methanol, n-hexane, and ammonia (387, 389, 390, 392). To remove lipids, sample extracts have often been partitioned with n-hexane. 

The muscles were freed by gross dissection of extraneous tissue which was mainly fat and peripheral nerves, and then stored at -40°C. For an experiment, approximately 1 kg tissue was macerated by a meat grinder and homogenized in ten volumes of tetrahydrofuran 0.01 M KC1 (4 1, v/v), stirred for 3 hours, and filtered through a Buchner funnel. The extraction was repeated twice and the filtrates then combined and concentrated in a rotary evaporator. One liter of chloroform-methanol (2 1, v/v) was added to the lipid extract which has the appearance and consistency of syrup. Gangliosides were partitioned into the upper layer by the addition of 200 ml of water (11) and the lower layer extracted two additional times with theoretical upper phase containing 0.027% KC1. The combined upper layers were then concentrated and dialyzed exhaustively at 4°C with five changes of distilled water. 

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