DMSO Binding to the Uncharged Form of a Compound

It was found that the log 5/pH curves were altered in the presence of as little as 0.5% v/v DMSO, in that the apparent pKa values, pA pp, derived from log S versus pH [481], were different from the true pKa values by about one log unit. The pA pp values were generally higher than the true pKa values for weak acids (positive shift), and lower than those for weak bases (negative shift). This has been called 

Such a reaction can cause a shift in the apparent ionization constant. It was discovered that the A shift, when subtracted from the logarithm of the apparent (DMSO-distorted) solubility, S ( )PP, yields the true aqueous solubility constant  

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