Lipophilic substances

Stability. Avermectins are highly lipophilic substances and dissolve in most organic solvents such as chloroform, methylene chloride, acetone, alcohols, toluene, cyclohexane, dimethylformamide, dimethyl sulfoxide, and tetrahydrofiiran. Thek solubiUty in water is correspondingly low, only 0.006-0.009 ppm (= mg/L). 

Important intermedia transfer mechanisms that must be considered where significant surface water contamination is expected include transfers to ground water where hydrogeology of the area indicates significant surface water-ground water exchange, transfers to biota where waters contaminated with lipophilic substances support edible biotic species, and transfer... 

Nondestructive Dection Using Other Physical Methods 43 Table 7. Nondestructive detection of lipophilic substances with water as detecting reagent. 

Lipophilic dyes in aqueous alcoholic solutions can be employed in an analogous manner [92, 93]. They are enriched at the zones of lipophilic substances, so that these appear deeply colored on a pale background. This does not apply to fatty acids with less than 12 C atoms [94]. 

Table 8. Employment of fluorescent substances for the nondestructive detection of lipophilic substances.

Treatment of the solvent-free chromatogram with iodine vapor or by dipping in or spraying with iodine solution (0.5 — 1%) is a rapid and economical universal method of detecting lipophilic substances. Molecular iodine is enriched in the chromatogram zones and colors them brown. 

Recently, 202 and 203 were found to significantly reduce the mutation frequency induced by BaP in vivo as well (00UP3). Previously, flie same group had pointed out that some genotoxic effects could result from UV irradiation of tryptophan, but this had not been attributed to lipophilic substances like 202 and 203 (94MI5). 

If / > 1 the structural change of the reference molecule affords a more lipophilic substance. / < 1 indicates that the hydrophilic character of the reference... 

Iodine is enriched to a greater extent in chromatogram zones coated with lipophilic substances than it is in a hydrophilic environment. Hence, iodine is only physically dissolved or adsorbed. Occasionally a chemical reaction also takes place, such as, for example, with estrone [19] (cf. Iodine Reagents ). In general it may be said that the longer the iodine effect lasts the more oxidations, additions or electrophilic substitutions are to be expected. 

In conclusion, delivery of liposome-encapsulated drugs in eye drops can improve the extent of uptake and the residence time compared to the free drug. In particular, lipophilic substances seem to benefit from this approach. The exact mechanism behind the improved biopharmaceutical behavior still has to be unraveled. Intra-vitreal injection of drug-containing liposomes increases the residence times of both hydrophilic and lipophilic drugs. 

FIGURE 5.23 Example of a two-dimensional development (plate turned by 180°), first development for removal of lipophilic substances and second development for separation. 

Grade extracts of different plants are often rich in lipophilic substances, such as plant oils, chlorophylls, and waxes and also highly polar components such as tannines or sugars. Because the complicated liquid-liquid extraction (LLE) procedures are... 

Although the absence of paracellular transport across the BBB impedes the entry of small hydrophilic compounds into the brain, low-molecular-weight lipophilic substances may pass through the endothelial cell membranes and cytosol by passive diffusion [7]. While this physical barrier cannot protect the brain against chemicals, the metabolic barrier formed by the enzymes from the endothelial cell cytosol may transform these chemicals. Compounds transported through the BBB by carrier-mediated systems may also be metabolized. Thus, l-DOPA is transported through the BBB and then decarboxylated to dopamine by the aromatic amino acid decarboxylase [7]. 

The vertical distribution of pollutants originates from water movements and sinking of organic particulate matter operating as carriers for lipophilic substances. PFOA enters ocean water exclusively in the surface level and instantaneously establishes... 

The photochemiluminiscence (PCL) assay was initially used by Popov and others (1987). Popov and Lewin (1994 1996) have extensively studied this technique to determine water-soluble and lipid-soluble antioxidants. The PCL assay measures the antioxidant capacity, toward the 02 radical, in lipidic and water phase. This method allows the quantification of both the antioxidant capacity of hydrophilic and/or lipophilic substances, either as pure compounds or complex matrices from different origin synthetic, vegetable, animal, human, etc. The PCL method is based on an approximately 1,000-fold acceleration of the oxidative reactions in vitro by the presence of an appropriate photosensitizer. The PCL is a very quick and sensitive method. Chua and others (2008) used this assay to determine the antioxidant potential of Cin-namomum osmophloeum, whereas Kaneh and Wang and others (2006) determined the antioxidant capacity of marigold flowers. The antioxidant activity of tree nut oil extracts was also assessed by this method (Miraliakbari and Shahidi 2008). 

Holton The bladder is designed so that substances aren t absorbed from it. When drugs are given through a catheter these are lipophilic substances that will cross epithelia readily. The kidney is designed to create water-soluble substances to be excreted. They tend to be ionized and will not readily be absorbed from the bladder. 

Table 4.6 gives a few representative values for Kow and Kp for non-polar organic substances on typical soil material and Table 4.7 gives estimates on typical retardation factors estimated for an aquifer. The data show that many non-polar organic substances, with the possible exception of very lipophilic substances such as hexachlorobenzene, are not markedly retarded in aquifers that contain little organic material (foe = 0.001 - 0.005). On the other hand, such substances are effectively retained in soils rich in organic carbon. 

The intercellular route is considered to be the predominantly used pathway in most cases, especially when steady-state conditions in the stratum corneum are reached. In case of intercellular absorption, substance transport occurs in the bilayer-structured, continuous, intercellular lipid domain within the stratum corneum. Although this pathway is very tortuous and therefore much longer in distance than the overall thickness of the stratum corneum, the intercellular route is considered to yield much faster absorption due to the high diffusion coefficient of most drugs within the lipid bilayer. Resulting from the bilayer structure, the intercellular pathway provides hydrophilic and lipophilic regions, allowing more hydrophilic substances to use the hydrophilic and more lipophilic substances to use the lipophilic route. In addition, it is possible to influence this pathway by certain excipients in the formulation. 

Ahlin, P, Kristi, J. and Sentjurc, M., EPR study of loading capacity of spin-labelled lipophilic substance in different SLN. Proc. Int. Symp. Control. Release Bioact. Mater, 25, 334-35, 1998. 

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