Lipophilic, definition

Fig. 12.1 The popular definition of lipophilicity. (A) A chemical is lipophilic if it dissolves much more easily in lipids than in...

A comparahve analysis of coefficients and descriptors clarifies the relationship between lipophilicity and hydrophobicity (Y in Eq. 4 is the molar volume which assesses the solute s capacity to elicit nonpolar interactions (i.e. hydrophobic forces) which, as also clearly stated in the International Union of Pure and Applied Chemistry definitions [3] are not synonyms but, when only neutral species are concerned, may be considered as interchangeable. In the majority of partitioning systems, the lipophilicity is chiefly due to the hydrophobicity, as is clearly indicated by the finding that the product of numerical values of the descriptors V and of the coefficient v is larger in absolute value than the corresponding product of other couples of descriptors/coefficients [9]. This explains the very common linear rela-... 

Note that the lipophilicity parameter log P is defined as a decimal logarithm. The parabolic equation is only non-linear in the variable log P, but is linear in the coefficients. Hence, it can be solved by multiple linear regression (see Section 10.8). The bilinear equation, however, is non-linear in both the variable P and the coefficients, and can only be solved by means of non-linear regression techniques (see Chapter 11). It is approximately linear with a positive slope (/ ,) for small values of log P, while it is also approximately linear with a negative slope b + b for large values of log P. The term bilinear is used in this context to indicate that the QSAR model can be resolved into two linear relations for small and for large values of P, respectively. This definition differs from the one which has been introduced in the context of principal components analysis in Chapter 17. 

Many pharmacologically active organic chemicals fonnd in natnre are alkaloids. In general, these componnds contain one or more nitrogen atoms, which in turn impart some basicity to the molecnle. Well-known alkaloid examples are caffeine, cocaine, codeine, ephedrine, morphine, nicotine, qninine, and scopolamine. Heroin is derived from morphine by a chemical modification that increases lipophilicity, making the heroin molecnle inherently more pharmacologically potent than morphine. The exhibition of its basic properties by an alkaloid (Aik) involves (by definition) the acceptance of a proton H+ according to ... 

These methods were developed to avoid the definition and parameterization of numerous fragments or atomic types and to allow the prediction of lipophilicity for stereoisomers or conformers. Only a selection of methods are highlighted here, since an excellent extensive review was recently published [34]. 

By definition, the fraction that enters the circulatory system is eliminated by extrarenal mechanisms (usually metabolism by the liver and other tissues) and is derived by the difference from renal excretion that is, 1 — Fg. The excretory organs are able to eliminate polar compounds such as tetracycline and tylosin more efficiently than compounds that are highly soluble in lipids (i.e., lipophilic) such as metronidazole, erythromycin, clindamycin, and trimethoporin. Thus, the highly lipophilic compounds will not be eliminated until they are metabolized to more polar intermediates. 

Knowledge of the pKa value is crucial for analyzing both lipophilicity and solubility of ionizable compounds, as discussed above. Ionization equilibria also affect several toxicokinetic parameters, such as intestinal absorption, membrane permeability, protein binding, and metabolic transformations. Therefore, much research has been invested in developing both experimental and computational tools for pKa determination. Experimentally, two high-throughput methods exist spectral gradient analysis and capillary electrophoresis. However, the most definitive methods are still... 

Amphetamines are definitely drugs which have been and are abused. Notice that the organic modifications in the fundamental amphetamine structure are to make the compound more lipophilic and so speed its delivery to the CNS as well as heighten the stimulant and euphoric effect. Therapeutic doses of amphetamines range from 5 to 10 mg for a maximum of 60 mg per day while abusive doses may be as high as 500-1000 mg every 2-3 hours. The side effects of abuse include tolerance, addiction, malnutrition, heart arrthymias, and... 

Further studies are required to unravel this mystery of how the methoxy substitutions and the a, p-unsaturated p-diketone moiety actually influence conformational changes, lipophillicity, electron density distribution, and redox properties of curcuminoids. Correlating these physicochemical properties with the unique pleiotropic effects of curcuminoids is a rewarding exercise. Such studies would definitely provide proper reasoning in understanding these markedly different antioxidant, antitumor, and anti-inflammatory activities of natural curcuminoids from turmeric. 

The chemical feature definitions described in the following sections are all categorized into hydrogen bond interactions, which are described as layer 3 features, and also into charge interactions and lipophilic interactions, which are represented as level 4 features. All current layer 4 features are represented as points with a tolerance radius forming a sphere, whereas layer 3 features are represented by vectors. The chemical feature definitions are specified in Daylight SMARTS notation [37] (listed in detail in Table 6.2) and directly imported into... 

Studies on structure-activity relationships between herbicides and homologous series of surfactants indicate that definite relationships exist between the herbicide and surfactant structure for maximum herbicide penetration. The length of the molecular chains (either hydrophilic or lipophilic) of a surfactant molecule appears to have considerable influence on herbicide penetration, and the surfactant concentration also influences this process markedly. 

Table 1 summarizes the relation between the hydrophilic-lipophilic balance (HLB) of surfactants and their ability to form concentrated emulsions. Because the continuous phase is that phase in which the surfactant is soluble, it is expected from the definition of HLB [17,18] that surfactants with low HLB values are oil-soluble and can therefore generate w/o concentrated emulsions, while those with high HLB values are water-soluble and can lead to o/w concentrated emulsions. Span 20, whose HLB is 8.6, can generate both w/o and o/w concentrated emulsions. 

In this expression, he divides the number of calories generated on the lipophile side of the surfactant by the number of calories generated by the hydrophile side of the surfactant. The amount of calories reflects or implies a proportional amount of swelling of the hydrophile and the lipophile, i.e., the greater number of calories on the lipophile side, the more tendency there is to form an oil in water type of emulsion. This definition of the C.E.R. (or Cohesive Energy Ratio) parameter leads to a direct expression which ties HLB to the Cohesive Energy Density parameter directly. The expression is ... 

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