A. Congiu-Castellano

XANES study of iron displacement in the haem of myoglobin

The XANES (X‐ray absorption near edge structure) spectra of deoxy human adult haemoglobin (HbA) and myoglobin (Mb) have been measured at the wiggler beam line of the Frascati synchrotron radiation facility. The XANES are interpreted by the multiple scattering cluster theory. The variations in the XANES between HbA and Mb are assigned to changes in the Fe‐porphyrin geometry.

Increase of the Fe effective charge in hemoproteins during oxygenation process

The x-ray absorption near edge structure (XANES) spectra of hemoglobin and myoglobin have been measured at the wiggler beam line of the Frascati Synchrotron Radiation Facility. The energy shifts of the iron absorption jump edge and the chemical shifts of the bound excited state at threshold of 1s core excitations, going from deoxygenated to oxygenated form, are interpreted as evidence of some increase of the positive effective charge on the iron atom upon oxygenation.

Determination of CO and CN bond angles by X-ray absorption near edge structure in chelated protoheme in solution

Abstract X-ray absorption near edge structure (XANES) spectra of a model compound chelated protoheme methyl ester in solution reveal a linear Fe-C-N configuration and a bent Fe-C-O configuration, although there are no distal steric effects.

Aluminum site structure in serum transferrin and lactoferrin revealed by synchrotron radiation X-ray spectroscopy

The Al site structure of serum transferrin and lactoferrin is investigated using X-ray absorption near edge structure (XANES) spectroscopy. Al K-edge spectra in the mono- and dialuminum forms of the proteins have been recorded for the first time. Our results show that the aluminium ion is hexa-coordinated in an octahedral-like symmetry and that the monoaluminum form, where only the C-terminal binding site is saturated, has an increased structural distortion around the metal site.

Oxygen bonding in human hemoglobin and its isolated subunits: a XANES study.

The X-ray absorption near edge structure (XANES) spectra of the human adult and foetal hemoglobin, of the isolated alpha and beta chains, in the oxygenated forms, and of the oxymyoglobin and carp oxyhemoglobin have been measured at the wiggler beam line of the Frascati Synchrotron radiation facility. The bonding angle of oxygen molecule at the iron site in these hemoproteins in solution, has been measured using the multiple scattering theory for data analysis.

Constraints of T conformation of carp azide hemoglobin on Fe site structure

The iron site structure modifications induced by the transition from the quaternary R to T structure in ferric carp azide hemoglobin have been detected from analysis of multiple scattering resonances in the XANES (X‐ray absorption near edge structure) spectra. High signal‐to‐noise XANES spectra measured at the Frascati ‘wiggler’ synchrotron radiation facility reveal that the forces on the Fe active site, due to the transition from the R to T quaternary conformation, only induce the tilting of the porphyrin plane and probably also of the proximal histidine. The variation of the Fe‐N mean distance is not detected by XANES spectroscopy and therefore it is less than 0.01 Å.

Potential antitumor gold drugs: DFT and XANES studies of local atomic and electronic structure

Geometry structure optimization of the potential antitumor agent Au(bipy)(OH)2 was carried out by means of density functional theory simulations. The experimental Au L3-edge X-ray absorption near edge structure (XANES) spectrum of Au(bipy)(OH)2 was obtained. The theoretical Au L3-XANES spectra of the gold(III) complex Au(bipy)(OH)2 were simulated using both the self-consistent real-space full multiple scattering theory within the muffin-tin approximation for the potential shape and the full-potential finite difference method. The comparison of the theoretical spectra with the experimental XANES is discussed. The exact local atomic structure of gold complex Au(bipy)(OH)2 has been defined by two independent ab initio methods.

Iron and copper K-edge XAS study of serotransferrin and ovotransferrin

The active metal site structure of transferrin with iron and copper atoms is investigated using metal K-XANES. Theoretical analysis of experimental data has been performed on the basis of full multiple-scattering theory. This approach made it possible to study the origin of XANES fine details and to investigate the local structure around active metal sites. A deep insight into the local structure and electronic subsystem of Fe, Cu transferrins is obtained. For example, in the case of Cu substitution of Fe in the active centre, the best fit of theoretical spectra to experiment has been obtained for distances 3% smaller between the Cu atom and the nearest neighbours.

XANES of carboxy and cyanomet-myoglobin The role of the distal histidine in the bent Fe−C−O configuration

The ligand bonding geometry of carboxy-and cyanomet-myoglobin (MbCO and MbCN) has been measured by the XANES method (X-ray Absorption Near Edge Structure). A comparison between the ligand bonding geometry of carboxy- and cyanomet-myoglobin and of chelated protoheme methyl ester shows that the bent Fe−C−O configuration is the same in both systems. Therefore, we suggest that this configuration is not associated with any steric contraint imposed by the side chains of the aminoacid residues at the distal side of the heme pocket.