Hydrophilic - Lipophilic Balance

This stereospecific oxidation does not occur for all dioximes, probably due to isomerisation of the dioxime during the reaction or to different reaction mechanisms involved in the use of different oxidants. When the lipophilic-hydrophilic balance of the two furoxan isomers is appropriate, they are easily separated by chromatography or fractional crystallisation. For example, the synthesis of 4-hydroxymethyl-3-furoxancarboxamide (CAS 1609), one of the most promising furoxancarboxamide vasodilators (see later), passes through the intermediate formation of a mixture of the two isomeric methyl hydroxymethylfuroxancarboxylic esters, which can easily be separated by recrystallisation from isopropyl acetate [18]. 

In conclusion, by varying the number and kind of the attached substructures for exohedrally functionalized fullerenes the solubility in water can be fine-tuned. From a pharmacological point of view, a well-balanced arrangement of both hydrophilic and lipophilic behaviour is required in order to achieve favourable biodistribution. Amphiphilic monoadducts containing long lipophilic alkyl chains like 8 are promising candidates for potential medical applications. 

Analogous gel matrices of liquid crystalline lamellar phases can also be formed with nonionie mesogens, such as the combination of cetyl/stearyl alcohol and ethoxy-lated fatty alcohol, provided that the hydrophilic and lipophilic properties of the surfactant molecules are more or less balanced to favor the formation of lamellar structures. 

Some of these triiodinated compounds are orally active, i.e. they are absorbed from the gastrointestinal tract after oral administration and imaging of the biliary system is possible following this route of administration. Examples are iopanoic acid, iophenoxic acid and sodium ipodate. A prerequisite for oral absorption is a balance of relatively hydrophilic and lipophilic moieties in the molecule. Numerous investigations have been performed to establish structure-activity relationships for this class of compounds, e.g. by Archer and Hoppe [70, 71]. Sodium salts are better absorbed than the free acids [72]. 

Different surfactants are usually characterised by the solubility behaviour of their hydrophilic and hydrophobic molecule fraction in polar solvents, expressed by the HLB-value (hydrophilic-lipophilic-balance) of the surfactant. The HLB-value of a specific surfactant is often listed by the producer or can be easily calculated from listed increments [67]. If the water in a microemulsion contains electrolytes, the solubility of the surfactant in the water changes. It can be increased or decreased, depending on the kind of electrolyte [68,69]. The effect of electrolytes is explained by the HSAB principle (hard-soft-acid-base). For example, salts of hard acids and hard bases reduce the solubility of the surfactant in water. The solubility is increased by salts of soft acids and hard bases or by salts of hard acids and soft bases. Correspondingly, the solubility of the surfactant in water is increased by sodium alkyl sulfonates and decreased by sodium chloride or sodium sulfate. In the meantime, the physical interactions of the surfactant molecules and other components in microemulsions is well understood and the HSAB-principle was verified. The salts in water mainly influence the curvature of the surfactant film in a microemulsion. The curvature of the surfactant film can be expressed, analogous to the HLB-value, by the packing parameter Sp. The packing parameter is the ratio between the hydrophilic and lipophilic surfactant molecule part [70] ... 

The focus of this work was to determine if a glyco-peptide or a simple dextrinized, oxidized starch could be produced which would enhance the behavior of a starch-based polymer for spray dried flavoring production. Enhancement of a starch s lipophilic/hydrophilic balance was anticipated to maintain the polymer s film forming" and cohesive wall development during the spray drying process while improving its emulsifying/interfacial activity capabilities. 

Molecular Associations Considered from the Point of View of the Lipophilic-Hydrophilic Balance... 

The process of reabsorption depends on the lipophilic-hydrophilic balance of the molecule. Charged and ionized molecules are reabsorbed slowly or not at all. Reabsorption of acidic and basic metabolites is pH-dependent, an important property in detoxification processes in drug poisoning. Both passive and active carrier-mediated mechanisms contribute to tubular drug ieabsorplion. 

The HLB concept, introduced in Section 3.6.1 is probably the most useful approach to predicting the type of emulsion that will be stabilized by a given surfactant or surfactant formulation. The HLB concept was introduced [207,209] as an empirical scale that could be used to describe the balance of the size and strength of the hydrophilic and lipophilic groups on an emusifier molecule. Originally used to classify Imperial Chemical Industries non-ionic surfactant series of Spans and Tweens the HLB system has now been applied to many other surfactants, including ionics and amphoterics. 

A useful index for choosing surfactants for various applications is the hydrophilic-lipophilic balance (HLB), which is based on the relative percentage of hydrophilic-to-lipophilic groups in the surfactant molecule(s). Surfactants with a low HLB number normally form W/O emulsions, whereas those with a high HLB number form a O/W emulsion. A summary of the HLB range required for various purposes is given in Table I. 

Hydrophilic versus lipophilic balance (from -3, -4 kcal/mol water probe to -0.6, -0.8 kcal/mol dry probe)... 

To penetrate the cornea effectively, a drug must possess a balance of hydrophilic and lipophilic properties... 

Quinolizidine derivatives with a more or less extended and planar aromatic moiety displayed antimicrobial activity [256]. Similar compounds were prepared for testing against Mycobacterium tuberculosis, due to the growing concern for the upsurge of new cases of tuberculosis and of non-tuberculous mycobacterioses in the western world since 1986. Several quinolizidines (Q) bearing different aryl nuclei substituents (which changed both the electronic distribution and the lipophilic-hydrophilic balance of the molecule) were synthesised. Six of these synthesised compounds (Q1-Q6), Fig. (42), were highly active and it is reasonable to state that... 

In spite of many advances in the theory of stability of lyophobic colloids, resort has still to be made to an empirical approach to the choice of emulsifier, devised in 1949 by Griffin. In this system we calculate the hydrophile-lipophile balance (HLB) of surfactants, which is a measure of the relative contributions of the hydrophilic and lipophilic regions of the... 

According to Eqnation 9.3, solubilization shonld increase with decreasing interfacial tension y between the micelles and water. It is known that interfacial tension decreases as a surfactant s hydrophilic and lipophilic properties become more nearly balanced, for example, as salinity or hardness of the aqneons phase increases in the case of ionic surfactants. Solubilization increases nnder these conditions as well, so that the predicted trend is in qualitative agreement with experimental data. 

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