Effect of the addition of electrolytes on the partition coefficients, activity coefficients, and acid dissociation constants of carnitine and its acetyl and propionyl derivatives.

The partition coefficients, P, between n-octanol and water of carnitine, acetylcarnitine, propionylcarnitine, and tetraethylammonium pentacyanopropenides have been determined spectrophotometrically at 20 degrees C. The value of P increases upon addition of electrolytes, the increase produced by LiCl being particularly high. The carnitine cations are 'salted-out' by electrolytes as shown by the variation of their 'single-ion' activity coefficients (relative to that of the tetraethylammonium ion) with electrolyte concentration. These cations are appreciably more hydrated than the reference tetraethylammonium ion. The considered carnitine cations are at least one pKa (where Ka is the acid dissociation constant) unit more acidic than butanoic acid in water at 25 degrees C. Electrolyte addition somewhat increases the pKa of these cationic acids.