EPR STUDY OF COMPLEX-FORMATION BETWEEN COPPER(II) IONS AND SYMPATHOMIMETIC AMINES IN AQUEOUS-SOLUTION

The complex formation between sympathomimetic amines (SA): adrenaline (AD), noradrenaline (NA), dopamine (DA), ephedrine (ED) and p-tyramine (pTA), and Cu(II) ion in aqueous solution has been studied by X-band EPR at room temperature. Excepting pTA, all investigated SA yielded tw o types of complexes in different pH domains. All complexes presented a g(parallel to) > g(perpendicular to) relationship, consistent with a ligand field having a distorted octahedral symmetry, i.e. hexacoordin ation of Cu(II). The covalence coefficient calculated from the isotrop ic g and A values has shown strong ionic sigma-type ligand bonds. A st ructural model with the Cu(II) ion bound by four catecholic O(hydroxy) atoms for the low pH complexes of AD, NA, and DA is proposed. For the high pH complexes of the former compounds as well as for both ED comp lexes, we suppose Cu(II) bound by two N (amino) and two O (hydroxy) at oms. The spectra are consistent to water binding on the longitudinal o ctahedron axis in all compounds excepting the high pH complex of ED, w here OH- ions are bound. Possible implications for the SA-cell recepto rs interactions are discussed.