Enzyme-mimetic model compounds: conformational analysis and far-IR study of Cu(TAAB)2+

Many enzymes occurring in nature like superoxide dismutase are systems rather too big to be accessible for vibrational and quantum chemical investigations. Thus, enzyme-mimetic model compounds consisting of a biological active metal centre surrounded by a macrocyclic ligand are used to shed light on binding properties of the active metal centre. Far- and mid-range IR spectroscopic investigations and a conformational analysis with the semi-empirical ZINDO/1 method of superoxide dismutase-mimetic complex Cu[TAAB]2+ are performed (TAAB = [b,f,j,n][1,5,9,13]tetra-aza-cyclohexadecine (tetra-anhydroamino benzaldehyde)). A distorted tetrahedral copper(II) centre with slightly twisted phenyl subunits is determined as the most stable conformation. Calculated mid- and far-IR spectra are in good agreement with the experimental data and confirm the proposed structure. A harmonic normal-coordinate analysis is used to assign the vibrational modes of the observed spectra.