Solution and solid state study of copper(II) ternary complexes containing amino acids of interest for brain biochemistry-2: Homocysteine with aspartate, glutamate or methionine

Alzheimer's disease is characterized by the loss of synapses and by the presence of extra-cellular amyloid beta-peptide (A beta) plaques, and it has been associated to copper metabolism. The plasma of patients with Alzheimer's disease presents higher levels of the amino acid homocysteine (hCys). In this study, three new ternary complexes of copper(II) with homocysteine and three amino acids of A beta (aspartate, glutamate or methionine) were studied both in solution (pH-potentiometry and UV-Vis) and in the solid state (CHNS, AAS, TGA, EPR, and FT-IR). Molar conductance and electrochemical (CV) measurements were carried out as well. The binary complex [Cu(hCys) 2] was also synthesized and characterized. For the ternary complexes, the values of the stability constants (log beta equal to 25.62 for CuAsphCys, 23.53 for CuGluhCys, and 18.61 for CuMethCys) are similar to those of the cysteine-containing ternary complexes CuAspCys and CuGluCys, recently reported by us, indicating a related N2OS coordination. The results found in the solid state are in agreement with the data found in solution studies whereby methionine, aspartic, and glutamic acids coordinate to copper(II) ion through the nitrogen atom of the amino group and one oxygen atom of the alpha-carboxylate group, and homocysteine coordinates through nitrogen and sulfur atoms. EPR data suggest that, in solution, the complexes are in a distorted tetrahedral geometry. (C) 2012 Elsevier B. V. All rights reserved.