Softness Solubility, solvent effects

A varnish is often appHed on top of the paint layers. A varnish serves two purposes as a protective coating and also for an optical effect that enriches the colors of the painting. A traditional varnish consists of a natural plant resin dissolved or fused in a Hquid for appHcation to the surface (see Resins, natural). There are two types of varnish resins hard ones, the most important of which is copal, and soft ones, notably dammar and mastic. The hard resins are fossil, and to convert these to a fluid state, they are fused in oil at high temperature. The soft resins dissolve in organic solvents, eg, turpentine. The natural resin varnishes discolor over time and also become less soluble, making removal in case of failure more difficult (see Paint and FINNISH removers). Thus the use of more stable synthetic resins, such as certain methacrylates and cycHc ketone resins, has become quite common, especially in conservation practice. 

As has already been pointed out, the solubility properties of the anion, its lipophilicity, are extremely important for the dissolution of the complex in solvents of low polarity. Large and soft inorganic and, much more so, organic anions very strongly increase the solubility. Anion activation and cation transport processes both depend on such anion effects. 

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] ... 

Technically, the specificity of carbon dioxide in the fluid, and particularly the liquid, states makes it attractive as a solvent for hops. The volatile oil components dissolve readily in CO2 while the alpha acids, as components of the soft resin fraction, are soluble to a useful degree. (These components are soluble in non-polar solvents and carbon dioxide is effectively a non-polar solvent). Also the solubilities in this solvent of unwanted compounds with a molecular weight much in excess of about 400 are much lower than those of the compounds which it is desired to extract. 

As described in Sect. 2.1, bisnaphthalimido compoimds 14 and 15 (Fig. 4, Fig. 13) show cytotoxic effects but are usually insoluble in polar solvents. After improving the solubility by introduction of a polyamine chain of at least foin nitrogen atoms, bisnaphthalimido derivatives 14 and 15 exert strong dose- and time-dependent cytotoxic effects by inducing apoptosis [92]. Other polyamines that cause cytotoxic effects are based on spermidine metabolites, isolated from a soft coral [97,98[. 

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