Acidic ionizable moieties

Using 2NpOH and 2-naphthol-3,6-disulfonate [121] as excited-state proton emitters, a transient high proton concentration is achieved on the membrane surface. With bromocresol green dye adsorbed on the membrane serving as a pH indicator, it has been found that the protons first react with the acidic ionized moieties on the surface and then reach the strongest base on the surface by rapid exchange. 

In the current era neutral compounds are important simply because there are so many of them especially in screening collections made in automated chemistry for HTS. Other things being equal, a compound with an ionizable moiety is preferred to a neutral compound. By definition a neutral compound will not give an acid or basic pJCj value. Some essentially neutral compounds can form aqueous unstable salts. This most commonly occurs when an extremely poorly basic compound is dissolved in organic solvent and the salt is precipitatated, e.g. by bubbling in HCl gas. 

There has been intensive study of 1-hydropyridinyl radicals bearing one or more carboxylic acid substituents.72,195,198-202 In basic solution these radicals are anionic, but the charge is associated with the ionization of the acid functions and not with the radical moiety. Equilibrium and kinetic data have been reported for the acid ionizations 198-202 and the variation of persistence with structure discussed.195... 

Basic ionizable moieties (e.g. substituted amines) can be neutralized by a very large number of organic and inorganic acids (see Chapter 35). The salts obtained are also readily crystalhzed and usually show less surface-active properties... 

In most of acidic PE the ionizable moiety is the carboxylic group. Such is the case of carbomers (C, also known as carbopol or carboxyvinyl polymers), alginic acid (AA), hyaluronic acid (HA, also known as hyaluronan). Other acidic PE such as dextran sulfate, cellulose sulfate and nucleic acids are based on sulfate, or phosphoric ionizable groups. 

Ionized or charged organic moieties do not readily pass through the lipophilic cell membranes of the epithelial cells that line the GI tract. Thus more acidic molecules tend to be more readily absorbed from the stomach while more alkaline materials tend to be absorbed from the small intestine. This is because at the acidic pH of the stomach, acidic chemicals tend to be nonionized. More alkaline chemicals tend to be more ionized in the stomach and less ionized in the gut. The equilibrium reaction for acidic dissociation can be represented by this equation ... 

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