Structures and properties of ternary copper(II) complexes with 4,5-dihydroxyphenylalanine or 2,4,5-trihydroxyphenylalanine and aromatic diamines

Structural and spectroscopic studies were carried out on ternary Cu(II) complexes, Cu(DA)(AA), with tyrosine derivatives having hydroxyl substituents (AA = 4,5-dihydroxyphenylalanine (dopa) or 2,4,5-trihydroxyphenylalanine (topa)) and aromatic diamines (DA=2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen)). The charge transfer (CT) absorption bands observed as difference absorption spectra in the near-UV region indicate an effective stacking interaction between DA and the side-chain aromatic ring of AA in the ternary Cu(II) complexes. Three complexes, [Cu(DL-topa)(bpy)(H2O)](+) (complex 1), [Cu(L-dopa)(phen)](+)[Cu(L-dopa)(CH3CH2CH2OH)(phen)](+) (complex 2), and [Cu(DL-dopa)(bpy)](+) (complex 3), were isolated as single crystals, and their structures were determined by X-ray analysis. The central Cu(II) ions in complexes 1 and 3 have square-pyramidal and square-planar geometries respectively. Complex 2 contains two independent molecules having each of the two geometries. All the molecular structures reveal intramolecular aromatic ring stacking between DA and AA in correspondence with the solution spectral observations. The stacking with the topa ring having three hydroxyl groups was found to be slightly stronger than that with the dopa ring having two hydroxyl groups, which is consistent with the more intense CT absorption bands of the topa complex compared with the dopa complex in aqueous solution. Moreover, the oxidative deamination of benzylamine with the ternary Cu(II) complex containing dopa or topa was investigated under aerobic conditions. (C) 1998 Elsevier Science S.A. All rights reserved.