Dopamine: Acid-base properties and membrane penetration capacity.

Dopamine and 4 related compounds were studied by H NMR-pH titrations and a case-tailored evaluation method. The resulting acid-base properties of dopamine are quantified in terms of 3 macroscopic and 12 microscopic protonation constants and the concomitant 3 interactivity parameters. The species- and site-specific basicities are interpreted by means of inductive and shielding effects through various intra- and intermolecular comparisons. The site-specific basicities determined this way are key parameters for the prediction of pharmacokinetic behavior and receptor-binding at the molecular level.