Lipophilicity and hydrophobicity

Compounds with high values are of low polarity and are described as being lipophilic and hydrophobic. Compounds with high values are of high polarity and are hydrophilic. Although the partition coefficient between octanol and water is... 

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-... 

Lipophilicity is the measure of the partitioning of a compound between a lipidic and an aqueous phase [1]. The terms lipophilicity and hydrophobicity are often used inconsistently in the literature. Lipophilicity encodes most of the intramolecular forces that can take place between a solute and a solvent. Hydrophobicity is a consequence of attractive forces between nonpolar groups and thereby is a component of lipophilicity [2]. Lipophilicity is one of the most informative physicochemical properties in medicinal chemistry and since long successfully used in quantitative structure-activity relationship (QSAR) studies. Its... 

Cyclosporine is a very lipophilic and hydrophobic compound, making mandatory the use of lipid vehicles in order to obtain stable preparations for ex-... 

After surface modification, whiskers have much better lipophilic and hydrophobic properties, and the alkyl chains of OTS absorbed on the whisker surface are inclined while OTS usually is distributed unequally on the matrix surface. The self-assembly mechanism of OTS is as follows. First, Si-Cl bonds are changed to Si-OH bonds when OTS and trace water on the whisker surface are hydrolyzed. Then, Si-OH... 

Chem. Descrip. Water-based defoamer composed of lipophilic and hydrophobic surface act, agents... 

One of the most important characteristics of the emulsifier is its CMC, which is defined as the critical concentration value below which no micelle formation occurs. The critical micelle concentration of an emulsifier is determined by the structure and the number of hydrophilic and hydrophobic groups included in the emulsifier molecule. The hydrophile-lipophile balance (HLB) number is a good criterion for the selection of proper emulsifier. The HLB scale was developed by W. C. Griffin [46,47]. Based on his approach, the HLB number of an emulsifier can be calculated by dividing... 

Molecules consisting of polar and apolar moieties behave as amphiphiles they are simultaneously hydro- and lipophilic or hydrophilic and hydrophobic. Due to this... 

The stereoelectronic features produce actions at a distance by the agency of the recognition forces they create. These forces are the hydrophobic effect, and the capacity to enter ionic bonds, van der Waals interactions and H-bonding interactions. The most convenient and informative assessment of such recognition forces is afforded by computahon in the form of MIFs, e.g. lipophilicity fields, hydrophobicity fields, molecular electrostatic potentials (MEPs) and H-bonding fields (see Chapter 6) [7-10]. 

R.F. Rekker and R. Mannhold, Calculation of Lipophilicity. The Hydrophobic Fragmental Constant Approach. VCH, Weinheim, Germany, 1992. 

Figure 7.17 shows the asymmetry ratios of a series of compounds (acids, bases, and neutrals) determined at iso-pH 7.4, under the influence of sink conditions created not by pH, but by anionic surfactant added to the acceptor wells (discuss later in the chapter). The membrane barrier was constructed from 20% soy lecithin in dodecane. All molecules show an upward dependence on lipophilicity, as estimated by octanol-water apparent partition coefficients, log KdaA). The bases are extensively cationic at pH 7.4, as well as being lipophilic, and so display the highest responses to the sink condition. They are driven to interact with the surfactant by both hydrophobic and electrostatic forces. The anionic acids are largely indifferent... 

Lipophilicity and specific hydrophobic surface area were determined by using reversed-phase thin-layer chromatography for fused heterocyclic ring systems including five pyrido[2,iy][l,2,4]triazine derivatives <1998MI64>. 

Despite the diversity of analytical procedures, no valid selection of solely right methods exists. Depending on the problem, the nature of the free radicals themselves or the physicochemical properties of the test system such as composition and hydrophobicity of the medium, oxygen partial pressure, pH value, etc., are important as well [15-17], An adequate test system is characterized by the fact that with regard to size, lipophilicity, and reactivity the biological target substrate reacts with the most relevant radicals. 

Surfactants, sometimes called surface active agents or detergents, are amphiphilic materials which contain both apolar, hydrophobic (lipophilic) and polar, hydrophilic (lipophobic) groups (Hartley, 1948, 1977 Fendler and Fendler, 1975 Fendler, 1982 Lindman and Wennerstrom, 1980 Sudholter... 

The lipophilicity and specific hydrophobic surface area of 42 synthetic dyes were also measured on alumina-based RP-TLC layers as described above. The common and IUPAC names of the non-homologue series of synthetic dyes are compiled in Table 3.7. 

The lipophilicity and specific surface area of a similar set of synthetic dyes was also determined on an alumina-based RP-TLC stationary phase and the linear relationship between the two hydrophobicity parameters was calculated. The result of the calculation is depicted in Fig. 3.6. The good correlation between these physicochemical parameters indicated that from the chromatographic point of view these compounds behave as a homologous series of analytes, however, their chemical structures are markedly different [87],... 

---