Ionization constants of catechols and catecholamines.

Catecholamines can appear in different charged states: as positive, negative and zwitterion and as zero-charged molecule. The microscopic ionization constants of ten catecholamines were determined spectrophotometrically. For each charged state the fraction of total catecholamine at pH = 7.85 was calculated from the microscopic ionization constants. Some attention is given to the interpretation of the differences between the fractions of corresponding charged states.