Structures and Stabilities of Fe2+/3+ Complexes Relevant to Alzheimer’s Disease: An ab Initio Study

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 115; no. 45; pp. 12523 - 12530
• Main Authors: Alí-Torres, Jorge, Rodríguez-Santiago, Luis, Sodupe, Mariona, Rauk, Arvi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.11.2011
• Subjects: Alzheimer Disease; Ferric Compounds - chemistry; Ferrous Compounds - chemistry; Models, Molecular; Molecular Structure; Quantum Theory; Thermodynamics
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp2026626

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 [Fe2+(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.