Angela Trapananti

Interaction of cisplatin with human superoxide dismutase.

cis-Diamminedichloroplatinum(II) (cisplatin) is able to interact with human superoxide dismutase (hSOD1) in the disulfide oxidized apo form with a dissociation constant of 37 ± 3 μM through binding cysteine 111 (Cys111) located at the edge of the subunit interface. It also binds to Cu(2)-Zn(2) and Zn(2)-Zn(2) forms of hSOD1. Cisplatin inhibits aggregation of demetalated oxidized hSOD1, and it is further able to dissolve and monomerize oxidized hSOD1 oligomers in vitro and in cell, thus indicating its potential as a leading compound for amyotrophic lateral sclerosis.

Melting of iron determined by X-ray absorption spectroscopy to 100 GPa

Significance There is a long-standing controversy over the melting curve of Fe at high pressure as determined from static laser heated diamond anvil cell and dynamic compression studies. X-ray absorption spectroscopy measurements are used here as a criterion to detect melting under pressure. Confronted with a diversity of obtained melting curves, this technique, used at such pressure and temperature conditions, is eligible to be at the forefront to probe Earths deep interior. Furthermore, the experiment reported here holds promise for addressing important issues related to the structure and phase diagram of compressed melts, such as the existence of structural complexity (polyamorphism) in the liquid phase or the extent of icosahedral ordering whose investigation has been limited until now to ambient conditions. Temperature, thermal history, and dynamics of Earth rely critically on the knowledge of the melting temperature of iron at the pressure conditions of the inner core boundary (ICB) where the geotherm crosses the melting curve. The literature on this subject is overwhelming, and no consensus has been reached, with a very large disagreement of the order of 2,000 K for the ICB temperature. Here we report new data on the melting temperature of iron in a laser-heated diamond anvil cell to 103 GPa obtained by X-ray absorption spectroscopy, a technique rarely used at such conditions. The modifications of the onset of the absorption spectra are used as a reliable melting criterion regardless of the solid phase from which the solid to liquid transition takes place. Our results show a melting temperature of iron in agreement with most previous studies up to 100 GPa, namely of 3,090 K at 103 GPa.

Insights into the cytotoxic activity of the phosphane copper(I) complex [Cu(thp)4][PF6]

The phosphane Cu(I) complex [Cu(thp)4][PF6], 1 (thp=tris(hydroxymethyl)phosphane) shows notable in vitro antitumour activity against a wide range of solid tumours. Uptake experiments performed in 1-treated colon cancer cells by atomic absorption spectrometry, reveal that the antiproliferative activity is consistent with the intracellular copper content. The solution chemistry of this agent, investigated by means of X-ray Absorption Spectroscopy and spectrophotometric titrations in aqueous media, indicates that 1 is labile giving coordinative unsaturated [Cu(thp)n]+ species (n=3 and 2) at micromolar concentrations. [Cu(thp)n]+ are reactive species that yield the mixed-ligand complex [Cu(thp)2(BCS)]- (BCS: bathocuproinedisulphonate(2-)) upon interaction with N,N-diimine. Analogously, [Cu(thp)n]+ interact with the methionine-rich peptide sequence (Ac-MMMMPMTFK-NH2; Pep1), relevant in the recruiting of physiological copper, giving [Cu(thp)(Pep1)]+ and [Cu(Pep1)]+ species. The formation of these adducts was assessed by electrospray mass spectrometry in the positive ion mode and validated by density functional theory investigations. The possibility to trans-chelate Cu(I) from pure inorganic [Cu(thp)n]+ assemblies into more physiological adducts represents a pathway that complex 1 might follow during the internalization process into cancer cells.

Reverse Monte Carlo refinement of molecular and condensed systems by x-ray absorption spectroscopy

We have developed a successful method for structural refinement, based on the reverse Monte Carlo (RMC) algorithm, that can be applied simultaneously to diffraction and x-ray absorption (XAS) data. The method is designed to study molecular and condensed systems incorporating all of the advances related to the application of modern multiple-scattering (MS) codes and the n-body expansion for XAS data-analysis (GNXAS). Convergence properties and the dependence of the structural model upon specific features of the XAS spectra and calculation parameters are discussed. Limitations and advances of the method are elucidated in the light of the structural sensitivity of the XAS technique.

Polymorphism and metastable phenomena in liquid tin under pressure

Polymorphism of substances under high pressures is observed and used to obtain materials with new physical properties. Here the authors present experimental results revealing phase transitions and structure of liquid tin at high pressure under metastable conditions using x-ray absorption spectroscopy and x-ray diffraction. They show that there is an abrupt change in the undercooling limit of liquid Sn above 2GPa, where nucleation takes place into the Sn-III metastable solid phase. The liquid local structure is found to be composed of tetrahedral and close-packed configurations. The latter are found to dominate at high pressure favoring crystallization to the Sn-III metastable solid phase.

Structural and Electrochemical Characterization of Zn1−xFexO—Effect of Aliovalent Doping on the Li+ Storage Mechanism

In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs), new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with varying dopant concentrations, potentially serving as anode for LIBs (Rechargeable lithium-ion batteries). The wurtzite structure of the Zn1−xFexO samples (with x ranging from 0 to 0.12) has been refined via the Rietveld method. Cell parameters change only slightly with the Fe content, whereas the crystallinity is strongly affected, presumably due to the presence of defects induced by the Fe3+ substitution for Zn2+. XANES (X-ray absorption near edge structure) data recorded ex situ for Zn0.9Fe0.1O electrodes at different states of charge indicated that Fe, dominantly trivalent in the pristine anode, partially reduces to Fe2+ upon discharge. This finding was supported by a detailed galvanostatic and potentiodynamic investigation of Zn1−xFexO-based electrodes, confirming such an initial reduction of Fe3+ to Fe2+ at potentials higher than 1.2 V (vs. Li+/Li) upon the initial lithiation, i.e., discharge. Both structural and electrochemical data strongly suggest the presence of cationic vacancies at the tetrahedral sites, induced by the presence of Fe3+ (i.e., one cationic vacancy for every two Fe3+ present in the sample), allowing for the initial Li+ insertion into the ZnO lattice prior to the subsequent conversion and alloying reaction.

In Situ X‐ray Absorption Fine Structure Spectroscopy of a Palladium Catalyst for the Direct Synthesis of Hydrogen Peroxide: Leaching and Reduction of the Metal Phase in the Presence of Bromide Ions

For the first time a Pd catalyst for the direct synthesis (DS) of H2O2 from H2 and O2 was investigated using in situ Pd K‐edge X‐ray absorption fine structure spectroscopy. The catalyst was loaded into a continuous reaction cell and fed at room temperature and pressure with a mixture of CO2, O2, H2 (86:10:4, v/v), and methanol. Pd and PdO phases are observed in similar and steady proportions (62 and 28 %, respectively). The same is found if the catalyst is either dry or treated with pure methanol only. With 10 ppm of NaBr in the reaction mixture both the Pd edge jump and the fraction of PdO decrease steadily during the DS. This shows that Br− ions promote both the leaching and the reduction of Pd in a monometallic DS catalyst. It also suggests that they are connected to each other and to the ability of Br− ions to promote Pd in the DS. An unprecedented mechanism of protection and remediation supported by Br− ions against the overoxidation of Pd is proposed and discussed in this context.

Local structure of liquid and undercooled liquid Cu probed by x-ray absorption spectroscopy.

In this work we report about a recent XAS (x-ray absorption spectroscopy) experiment aimed to study the local structure of liquid and undercooled copper, a typical close-packed liquid metal, under high-pressure conditions. In our study we have obtained new experimental data of liquid Cu under high pressure and high-temperature conditions using synchrotron radiation at the ESRF and a large-volume Paris-Edinburgh cell. We have studied the extension of the undercooling region as well as possible modifications of the local structure as a function of pressure, using XAS data-analysis. Liquid copper has been undercooled up to 300°C below the melting point at high pressures up to 3.3 GPa.

An Introduction to Differential EXAFS

Differential EXAFS (DiffEXAFS) is a novel technique for measuring atomic perturbations on a local scale that result from the modulation of a given sample property. Experiments conducted to date have revealed a sensitivity to such perturbations of the order of femtometres, two orders of magnitude more sensitive than is considered possible by conventional EXAFS techniques. Here, the concept behind DiffEXAFS is described, and experimental factors required to detect such a signal discussed.

Structure and atomic correlations in molecular systems probed by XAS reverse Monte Carlo refinement

The Reverse Monte Carlo (RMC) algorithm for structure refinement has been applied to x-ray absorption spectroscopy (XAS) multiple-edge data sets for six gas phase molecular systems (SnI2, CdI2, BBr3, GaI3, GeBr4, GeI4). Sets of thousands of molecular replicas were involved in the refinement process, driven by the XAS data and constrained by available electron diffraction results. The equilibrated configurations were analysed to determine the average tridimensional structure and obtain reliable bond and bond-angle distributions. Detectable deviations from Gaussian models were found in some cases. This work shows that a RMC refinement of XAS data is able to provide geometrical models for molecular structures compatible with present experimental evidence. The validation of this approach on simple molecular systems is particularly important in view of its possible simple extension to more complex and extended systems including metal-organic complexes, biomolecules, or nanocrystalline systems.