Abstract
With the aim to provide a general protocol to interpret electron paramagnetic resonance (EPR) spectra of paramagnetic copper(II) coordination compounds, density functional theory (DFT) calculations of spin Hamiltonian parameters g and A for fourteen Cu(II) complexes with different charges, donor sets, and geometry were carried out using ORCA software. The performance of eleven functionals was tested, and on the basis of the mean absolute percent deviation (MAPD) and standard deviation (SD), the ranking of the functionals for Az is: B3LYP > B3PW91 ~ B3P86 > PBE0 > CAM-B3LYP > TPSSh > BH and HLYP > B2PLYP > MPW1PW91 > ω-B97x-D >> M06; and for gz is: PBE0 > BH and HLYP > B2PLYP > ω-B97x-D > B3PW91~B3LYP~B3P86 > CAM-B3LYP > TPSSh~MPW1PW91 >> M06. With B3LYP the MAPD with respect to A z exp t l is 8.6% with a SD of 4.2%, while with PBE0 the MAPD with respect to g z exp t l is 2.9% with a SD of 1.1%. The results of the validation confirm the fundamental role of the second order spin-orbit contribution to Az. The computational procedure was applied to predict the values of gz and Az of the adducts formed by Cu(II) with albumin and two fragments of prion protein, 106–126 and 180–193.
Highlights
The coordination chemistry of copper has been extensively studied for its biological role [1,2,3,4], synthetic and catalytic applications [5,6,7], and recently, for its pharmacological action and the potential use of its compounds in medicine [8,9,10]
Many metal species play a fundamental role in bioinorganic chemistry, biochemistry, and medicine, including copper containing complexes
Several instrumental techniques are available for their characterization, but in the case of paramagnetic species, electron paramagnetic resonance (EPR) is the most used tool because the values of spin Hamiltonian parameters, gz and Az, depend mainly on the equatorial donors bound to the metal
Summary
The coordination chemistry of copper has been extensively studied for its biological role [1,2,3,4], synthetic and catalytic applications [5,6,7], and recently, for its pharmacological action and the potential use of its compounds in medicine [8,9,10]. Several papers have been published on the calculation of g and A values for Cu(II) complexes, but to the best of our knowledge the only systematic study is from Neese [34], who found a MAPD below 5% using B3LYP functional for 10 different species. He tested only B3LYP and BP86, and any comparison with other or more recent functionals is lacking.
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