Semipolar solute

However, it may also be possible that the buffer negatively influences the solubility of the drug and other excipients. Buffer salts can either increase or decrease the solubility of organic compounds in water. The effect depends on a combination of the polarity of the solute and of the salt. Nonpolar solutes are solubilized (salted in) by less polar organic salts and are desolubilized (salted out) by polar salts. Conversely, polar solutes are salted in by polar salts and salted out by organic salts. It was shown that for a semipolar solute such as ampicillin, strong electrolytes... 

It is important to realize that a discussion of solvent polarity is only useful when considered in relation to a particular solute. Thus, for a semipolar solute such as theophylline, pure ethanol might be considered nonpolar, but for a relatively non-polar solute such as hydrocortisone, ethanol might be considered semipolar. This concept is illustrated in Fig. 1. For nonpolar and polar solutes, solubility will continually decrease or increase, respectively, as solvent polarity increases. For semipolar solutes, solubility reaches a maximum at some intermediate solvent polarity. It should be noted that the reverse argument (i.e., solute polarity should be discussed relative to solvent polarity) is also valid. 

Semipolar solutes are generally solubilized by the polar regions of nonionic surfactants. The solute is absorbed into the polyoxyethylene mantle rather than the hydrocarbon core. The micellar partition coefficients of the semipolar solutes is also dependent upon... 

Applications The scientific literature on this relatively new approach is still quite limited. SPME-HPLC-MS is suitable for quantitation of polar and semipolar organic compounds from aqueous solutions. 

Fig. 1 Solubility vs. solvent polarity for polar, semipolar and non-polar solutes.

Various substituted 2-pyrazolin-5-ones react with metal salts with replacement of hydrogen and formation of semipolar bonds with electron donating atoms. The most important of these compounds are the metal complexes of 4-arylazo-2-pyrazolin-5-ones. These complexes are widely used in the dye industry to give desired properties to 4-arylazo-2-pyrazolin-5-one dyes. Although a large number of metal-dye complexes have been used in dyeing, only a few such compounds have been characterized and reported in the literature. Usually a solution of the azo compound and an appropriate salt such as cupric chloride or nickel sulfate are mixed in solution and heated.326 The reaction is... 

Solution formulations generally require a semipolar cosolvent to achieve dissolution, and these cosolvents are more susceptible to moisture uptake. Since the drug is molecularly dispersed, side groups are exposed which may be susceptible to rapid degradation. 

The solubility of semipolar and nonpolar solutes in water has been related to the term molecular surface area of the solute and some interfacial tension term. This model was later analyzed by various investigators in much greater detail. °... 

Reversed micelles stabilize a nanometer-sized aqueous environment within the surfactant aggregate, which is dispersed in a fully nonhydrous or a semipolar solvent. In this micellar core environment we may dissolve metal salt solutions that react to the extent of the available reactants. 

U.S. 6306805 (2001) Bratescu et al. (Stepan) Anionic-cationic bridging surfactant blends bridging surfactants selected from ethoxylated alkanolamide, semipolar nonionic, amphoteric, zwitterionic Clear solutions at a variety of concentrations in water impart cleaning, foaming, and conditioning properties to hair... 

Then it is assumed that in the case of binary mobile phases composed of one low-polar and one semipolar or high-polar solvent, the polar forces acting in that mobile phase on solute molecule are... 

To examine the influence of different concentrations of polar or semipolar solvent in the same dispersing medium (e.g., an aliphatic hydrocarbon) on solute retention, Eq. 34e can be given in a simplified form ... 

In the neighborhood of the semipolar interface the average orientation of the alkyl chains is characterized by an order parameter of S 0.65. Accordingly these lamellar phases are well suited to prepare highly ordered solutions of polar and amphiphilic molecules. 

Solubilization is the process of preparation of thermodynamically stable isotropic solution of a substance (normally insoluble or sparingly soluble in a given solvent) by incorporation of an additional amphiphiUc component(s) [27]. It is the incorporation of the compound (referred to as solubilizate or substrate) within micellar (L phase) or reverse micellar (L2 phase) system. Lipophilic (water insoluble) substances become incorporated in the (normal micelle) phase. Hydrophilic (water soluble) substances are incorporated in the L2 phase. The site of incorporation of the solubilizate is closely related to its structure, as illustrated in Fig. 2.22 nonpolar solubilizate in the hydrocarbon core semipolar or polar solubilizate oriented within the micelle (short or deep) [28]. 

---