Multiple-scattering XAS calculations for the characterization of the binuclear (type 3) copper sites of hemocyanins and related model compounds

Abstract

Our previous studies on the met- and met-azido-Hc forms from Octopus vulgaris (mollusc) and Carcinus aestuarii (arthropod) at pH 7.5 and on some related binuclear models without X-ray diffraction have considered and resolved some fundamental aspects of their binuclear type-3 copper site (i.e. correct values of the Cu-Cu distances; apical distortion, when present, at the copper site; presence and type of bridging groups). In this contribution the multiple-scattering (MS) calculations performed in order to refine the EXAFS modulation of the absorption spectra are presented. It is only with a composite and advanced approach that some severe problems, mainly deriving from the presence of two absorbing atoms and from the fact that the metal-metal contribution in the absorption spectra overlaps with the Cu-His signals, have been overcome. Results are also presented which indicate the role of the MS calculations in the XANES edge region, and which show how it is possible to extract quantitative information from this zone of the spectrum in order to refine the structure of the site also in the case of a binuclear centre.

XAFS Study of the Ferro- and Antiferromagnetic Binuclear Copper(II) Complexes of Azomethine Based Tridentate Ligands

“…It is seen that all the spectra show the pre-edge feature A located between 8974 and 8976 eV which is related to the dipole forbidden 1s→3d transition and due to mixing of metal 3d and 4p orbitals. The position and the intensity of features B, C and D are typical for dipole 1s→4p+L transitions and appear in previously published spectra of copper complexes [2]. The splitting of the first derivative of the XANES spectra has been attributed to the tetragonal symmetry around the atom of the metal.…”

“…Different members of metalloproteins of the type-3 with binuclear copper sites are known: hemocyanins, tyrosinase, catechol oxidase with bridging oxygen atoms and cytochrome c oxidase with bridging sulfur atoms. In most of these, copper is ligated by histidine and cysteine amino acids [1,2].…”

X-Ray absorption spectroscopy quantitative analysis of biomimetic copper(ii) complexes with tridentate nitrogen ligands mimicking the tris(imidazole) array of protein centres

“…On the contrary, in this study a larger size of the cluster was chosen, considering both the powdered form of the samples that highlights the structural contributions and the structural characteristics of the 2-BB ligand in these complexes. Previous data obtained with the CONTINUUM code for the full MS cross-sections calculations 17 (and unpublished data), showed the need to use clusters including the entire ligand, to reproduce the experimental features linked to dominant contribution of the copper(II)-2-BB system within different geometries. The fine structural differences between the three compounds produce changes in the shape of the XANES region and using CONTINUUM it has been possible to exemplify them.…”

“…The fine structural differences between the three compounds produce changes in the shape of the XANES region and using CONTINUUM it has been possible to exemplify them. 17 À counter ion present in the crystal), which include atoms within a distance of B5.4 A ˚from the absorbing Cu centre (Fig. 1a).…”

Copper(II) Carboxylate Containing Paddle Wheel Structure: Synthesis and Crystal Structure

“…Different members of metalloproteins of the type-3 with binuclear copper sites are known: hemocyanins, tyrosinase, catechol oxidase with bridging oxygen atoms and cytochrome coxidase with bridging sulfur atoms. In most of these,copper is ligated by histidine and cysteine amino acids 11,12 .In this work, we report synthesis and crystal structure of binuclear Cu(II) complex containing 2-nitrobenzoic acid.The complex exhibited a paddlewheel structure.…”