Weak interactions in ternary copper(II) complexes with iodotyrosinates. Biological significance of the iodines in thyroid hormones

Structures and spectroscopic studies have been carried out on ternary copper(II) complexes, Cu(DA)(AA), with aromatic amino acids (AA = 3,5-diiodo-L-tyrosinate (L-I(2)tyr), 3-iodo-L-tyrosinate (L-Ityr), L-tyrosinate) and diamines (DA = 1,10-phenanthroline, 2,2'-bipyridine (bpy), 2-(aminomethyl)pyridine, histamine (hista), or ethylenediamine). The charge transfer (CT) absorption bands observed in the near UV region and the CD spectral magnitude anomaly observed in the d-d region indicated an effective aromatic ring stacking interaction between the side-chain phenol ring of AA and the aromatic diamine DA in the complexes in solution. Two complexes, [Cu(bpy)(L-Ityr)(H2O). NO3 . CH3OH . H2O (1) and [Cu(hista)(L-I(2)tyrO(-))(H2O)](2) . 2H(2)O (2), where O- represents the deprotonated form of the phenol hydroxyl group, were isolated as single crystals, and their structures were determined by X-ray analysis. Both 1 and 2 crystallized in the monoclinic space group P2(1), with a = 7.549(1) Angstrom, b = 11.431(1) Angstrom, c = 14.292(2) Angstrom, beta = 100.08(1)degrees, and Z = 2 for 1 and a = 9.9642(9) Angstrom, b = 15.825(1) Angstrom, c = 12.451(1) Angstrom, beta = 91.565(7)degrees, and Z = 2 for 2. The molecular structures of 1 and 2 revealed the intramolecular aromatic ring stacking between DA and the iodinated phenol ring of Ityr and I(2)tyrO(-), respectively, in correspondence with the solution spectral observations. The stacking with hista was found to be weaker than that with bpy from the interplanar distances in 1 and 2 and the CT band intensities in solution. The molecular and crystal structures revealed some intermolecular iodine-aromatic ring and iodine-oxygen interactions as well as some hydrogen bonds involving the phenol hydroxyl group.