Lipid-water partitioning

Typically lipids, chlorophyll, and phenolic acids can be separated by liquid-liquid partition. Lipids and chlorophyll can be removed from acetone-water extracts by chloroform while phenolic acids have higher affinities for ethyl acetate at a pH close to nentral and water. °°... 

The solubility-diffusion theory assumes that solute partitioning from water into and diffusion through the membrane lipid region resembles that which would occur within a homogeneous bulk solvent. Thus, the permeability coefficient, P, can be expressed as... 

The lipophilicity of a solute affects its permeability in lipid bilayers. Lipophilicity is usually expressed in terms of its partitioning between water and an organic solvent, such as olive oil [95], oleyl alcohol [96], ether [97], or octanol [98]. Partition coefficient (PC) of a compound is expressed as its concentration ratio between organic medium and water at equilibrium ... 

The topic of drug partitioning between water and lipids concerns chemical equilibria. For a monoprotic weak acid (and base), the partitioning equilibria may be represented as... 

In mixtures containing high lipid water ratios, HC1 will appreciably partition into solutions with pH <2.5, as will KOH when pH >11.5 [162,284]. General box diagrams reflecting these caveats have been discussed [275]. 

Seiler [250] proposed a way of estimating the extent of hydrogen bonding in solute partitioning between water and a lipid phase by measuring the so-called A log P parameter. The latter parameter is usually defined as the difference between the partition coefficient of a solute measured in the octanol-water system and that measured in an inert alkane-water suspension AlogP = log Kp oet — log Kp aik. 

Loidl-Stahlhofen, A. Hartmann, T. Schottner, M. Rohring, C. Brodowsky, H. Schmitt, J. Keldenich, J., Multilamellar liposome and solid-supported lipid membranes (TRAN-SIL) Screening of lipid-water partitioning toward a high-throughput scale, Pharm. Res. 

The simplest way to predict the lipid/ water partition coefficient, Kiw, of a drug is based on measurements of the surface pressure, ttd, of the drug as a function of its concentration in the aqueous subphase (Gibbs adsorption isotherm). The Gibbs adsorption isotherm provides the air/water partition coefficient, Kaw, and the cross-sectional area, Ad of the drug and allows calculation of the lipid/water partition coefficient, K]w, according to Eq. (6) [59] ... 

The presence of a transporter can be assessed by comparing basolateral-to-apical with apical-to-basolateral transport of substrates in polarized cell monolayers. If P-gp is present, then basolateral-to-apical transport is enhanced and apical-to baso-lateral transport is reduced. Transport experiments are in general performed with radioactively labeled compounds. Several studies have been performed with Caco-2 cell lines (e.g. Ref. [85]). Since Caco-2 cells express a number of different transporters, the effects measured are most probably specific for the ensemble of transporters rather than for P-gp alone. P-gp-specific transport has been assayed across confluent cell layers formed by polarized kidney epithelial cells transfected with the MDR1 gene [86], Figure 20.11 shows experimental data obtained with these cell lines. A rank order for transport called substrate quality was determined for a number of compounds [86]. The substrate quality is a qualitative estimate, but nevertheless allows an investigation of the role of the air/water (or lipid/water) partition coefficient, log Kaw, for transport as seen in Fig. 20.11(A). For most of the compounds, a linear correlation is observed between substrate quality and log Kaw- However, four compounds are not transported at all despite their distinct lipophilicity. A plot of the substrate quality as a function of the potential of a... 

Compounds with a high H-bond acceptor potential (EUh > 8) (e.g., cyclosporine A, SDZ PSC-833) act as competitive inhibitors, presumably because they occupy all H-bond donor sites of the transporter. Due to the strong interaction of these compounds with P-gp they are transported slowly, and this is reflected in a low rate of ATP hydrolysis. Many of these compounds exhibit high lipid/water partition coefficients and thus also low K, values. 

Tab. 20.2. Drug properties which influence the lipid/water partition coefficient, K w and the transporter binding constant, Kt.

Chiou, C. T. (1985) Partition coefficients of organic compounds in lipid-water systems and correlations with fish bioconcentration factors. Environ. Sci. Technol. 19, 57-62. 

I. Lipid-soluble drugs cross the membrane at a rate proportional to the concentration gradient across the membrane and the lipid water partition coefficient of the drug... 

Absorption of chemicals with widely differing characteristics can occur at different levels in the GI tract (Schranker, 1960 Hogben et al., 1959 Schranker et al., 1957). The two factors primarily influencing this regional absorption are (1) the lipid-water partition characteristics of the undissociated toxicant and (2) the dissociation constant (pLJ that determines the amount of toxicant in the dissociated form. 

The specific mechanisms by which mirex and chlordecone are transferred from the gut, lungs, or skin to the blood are not known. However, mirex is a highly stable, lipophilic compound that is resistant to metabolism. It has a high lipid water partition coefficient, so it partitions readily into fat and demonstrates a very high potential for accumulation in tissues. The preferential distribution of chlordecone to the liver rather than to the fat tissue is due to its association with plasma proteins. 

Toropov AA, Roy K (2004) QSPR modeling of lipid-water partition coefficient by optimization of correlation weights of local graph invariants. J. Chem. Inf. Comput. Sci. 44 179-186. 

Combining the equation for the diffusion coefficient with a Collander-type expression for the lipid-water partition coefficient resulted in an expression for calculating the permeability across the stratum corneum ... 

Einally, LDPE SPMDs with grass carp lipid were exposed for 21 d to 14C-2,2, 5,5 -TCB, 14c-3,3, 4,4 -TCB, i c-mirex and i c-fenvalerate, whereas SPMDs with triolein or lecithin were exposed to only " C-2,2, 5,5 -TCB. After 21 d, the largest mass fraction of these test chemicals ( " C-mirex was an exception) was in the triolein. The C-2,2, 5,5 -TCB log triolein-water partition coefficient was 6.01, whereas the " C-2,2, 5,5 -TCB partition coefficients for the grass carp lipid-water and lecithin-water systems were 30% and 35% lower, respectively. Comparison of these data to literature log AlowS of 2,2, 5,5 -TCB showed that the partition coefficients for the grass-carp lipid and the lecithin were not significantly different from median values reported for the log ATow of " C-2,2, 5,5 -TCB. However, the partition coefficient of 2,2, 5,5 -TCB in triolein and water in direct... 

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