Structures and stabilities of Fe^2+/3+ complexes relevant to Alzheimer's disease: An ab initio study

Iron is one of the most abundant metals found in senile plaques of post mortem patients with Alzheimer's disease. However, the interaction mode between iron ions and β-amyloid peptide as well as their precise affinity is unknown. In this study we apply ab initio computational methodology to calculate binding energies of Fe2+/3+ with the His13-His14 sequence of Aβ, as well as other important ligands such as His6 and Tyr10. Calculations were carried out at the "MP2/6-311+G(2df,2p)"//B3LYP/6-31+G(d) level of theory and solvent effects included by the IEFPCM procedure. Several reaction paths for the binding of imidazole, phenol, and the His13-His14 fragment (modeled by N-(2-(1H-imidazol-4-yl)ethyl)-3-(1H-imidazol-4-yl)propanamide) were sequentially explored. The results show that the most stable complexes containing His13-His14 and phenolate of Tyr10 are the pentacoordinated [Fe 2+(O-HisHis)(PhO-)(H2O)]+ and [Fe3+(N-HisHis)(PhO-)(H2O)]+ compounds and that simultaneous coordination of tyrosine and His13-His14 to Fe2+/3+ is thermodynamically favorable in water at physiological pH. Computed Raman spectra confirm the conclusion obtained by Miura et al. (Biochemistry 2000, 39, 7024) that tyrosine is coordinated to Fe3+ but do not exclude coordination of imidazoles. Finally, calculations of standard reduction potentials indicate that phenol coordination reduces the redox activity of the iron/Aβ complexes. © 2011 American Chemical Society.