The thermodynamic microquantities of dissociation of L-3,4-dihydroxyphenylalanine (L-dopa) at an ionic strength of 0.2 mol/dm3 (KCl) were determined from the temperature-dependence of microconstants measured with a pH-spectrophotometric method. It was found that the microenthalpies relating to the same donor group depend only slightly on the protonation state of the other group. In a pH-spectrophotometric study of the manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II)L-dopa systems the microconstants for the formation of complexes with the same stoichiometric composition but different arrangements of the donor groups were determined. Taking into account the different bonding modes of the species, a quantitative equilibrium description was given for these metal ionL-dopa systems. It was found that the tendency to rearrangement from L-dopa complexes containing both amino acid-like and pyrocatechol-like bonding to species containing only (O,O) bonds varies with the metal ion: Cu(II) ∼ Zn(II) > Co(II) > Mn(II), Ni(II). It was demonstrated that in complexes with the same bonding mode the protonation state of the other group has practically no effect on the deprotonation of donor groups not coordinated to the metal ion.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry