Carlo Meneghini

X-ray optics of a dynamical sagittal-focusing monochromator on the GILDA beamline at the ESRF

The performance of a dynamical sagittal-focusing monochromator for hard X-rays is described. It consists of a flat first crystal and a diamond-shaped ribbed second crystal which is clamped by its central rib and dynamically bent by applying a force on its two apices. The system has proved to perform very well on the GILDA beamline at the ESRF. The horizontal acceptance varies with energy and with focusing geometry as predicted theoretically; the total available horizontal fan of radiation (3.6 mrad) is in fact collected in the 1:3 geometry. The system is routinely run in a dynamical focusing mode for XAFS spectroscopy in the energy range 5-30 keV with Si(311) crystals, with a constant spot size FWHM ~1 mm on the sample and without degradation of energy resolution or reproducibility. Using simple geometrical considerations we calculate the variations of the horizontal profile of the reflected beam during rocking-curve scans in different focusing geometries and find them in agreement with observed ones. Not only is this is a practical aid in alignment but it illustrates the X-ray optics of sagittal focusing in an elegant way.

Multipurpose imaging-plate camera for in situ powder XRD at the GILDA beamline

An Imaging-Plate (IP) camera for X-ray powder diffraction (XRPD) experiments was installed on the synchrotron radiation beamline GILDA at the ESRF. The IP camera can be used in fixed data-collection mode of the whole diffraction rings, or in translation mode for time-dependent experiments. The apparatus is ideal for collecting medium to relatively high-resolution diffraction data from diluted or weakly scattering samples and to investigate in situ phase changes induced by temperature and/or chemical reactions. The possibility to rapidly collect several good quality diffraction patterns coupled with tunable beam energy allow for multiwavelength experiments such as anomalous XRPD.

Rietveld Refinement on X-Ray Diffraction Patterns of Bioapatite in Human Fetal Bones

Bioapatite, the main constituent of mineralized tissue in mammalian bones, is a calcium-phosphate-based mineral that is similar in structure and composition to hydroxyapatite. In this work, the crystallographic structure of bioapatite in human fetuses was investigated by synchrotron radiation x-ray diffraction (XRD) and microdiffraction ( micro -XRD) techniques. Rietveld refinement analyses of XRD and micro -XRD data allow for quantitative probing of the structural modifications of bioapatite as functions of the mineralization process and gestational age.

Oxidative stress induces persistent telomeric DNA damage responsible for nuclear morphology change in Mammalian cells.

One main function of telomeres is to maintain chromosome and genome stability. The rate of telomere shortening can be accelerated significantly by chemical and physical environmental agents. Reactive oxygen species are a source of oxidative stress and can produce modified bases (mainly 8-oxoG) and single strand breaks anywhere in the genome. The high incidence of guanine residues in telomeric DNA sequences makes the telomere a preferred target for oxidative damage. Our aim in this work is to evaluate whether chromosome instability induced by oxidative stress is related specifically to telomeric damage. We treated human primary fibroblasts (MRC-5) in vitro with hydrogen peroxide (100 and 200 µM) for 1 hr and collected data at several time points. To evaluate the persistence of oxidative stress-induced DNA damage up to 24 hrs after treatment, we analysed telomeric and genomic oxidative damage by qPCR and a modified comet assay, respectively. The results demonstrate that the genomic damage is completely repaired, while the telomeric oxidative damage persists. The analysis of telomere length reveals a significant telomere shortening 48 hrs after treatment, leading us to hypothesise that residual telomere damage could be responsible for the telomere shortening observed. Considering the influence of telomere length modulation on genomic stability, we quantified abnormal nuclear morphologies (Nucleoplasmic Bridges, Nuclear Buds and Micronuclei) and observed an increase of chromosome instability in the same time frame as telomere shortening. At subsequent times (72 and 96 hrs), we observed a restoration of telomere length and a reduction of chromosome instability, leaving us to conjecture a correlation between telomere shortening/dysfunction and chromosome instability. We can conclude that oxidative base damage leads to abnormal nuclear morphologies and that telomere dysfunction is an important contributor to this effect.

Eu doping in multiferroic BiFeO3 ceramics studied by Mossbauer and EXAFS spectroscopy

Bismuth ferrite ceramics (BiFeO(3)) are multifunctional materials classified as multiferroics for their special magnetic and electric properties that can be modified by substitutional doping at the Bi and/or Fe sites. Understanding the relation between magnetoelectric response and structural/electronic modification upon doping is a relevant issue. In this work, the structure of Eu-doped multiferroic systems (Bi(1-x)Eu(x)FeO(3), x = 0, 0.5, 0.1, 0.15) as well as the valence state of Fe and Eu ions have been investigated combining Mossbauer and x-ray absorption fine structure (XAFS) spectroscopy techniques. The Eu(3+) doping at the Bi site results in better magnetic properties. High temperature (57)Fe Mossbauer data and Fe K-edge XAFS results show that FeO(6) octahedron distortions reduce with Eu(3+) doping. It is conclusively shown that the observed magnetic properties in BiFeO(3) with chemical substitution (Eu) are mainly due to the structural distortions and not due to Fe multiple valence. (151)Eu Mossbauer measurements show that the Eu(3+)(Bi(3+)) site is magnetically inactive in BiFeO(3).

Structural study of a-Si1-xCx:H by exafs and x-ray scattering

We present a comprehensive study of short range order in a-Si 1-x C x :H using X-ray scattering and Si K-edge EXAFS. The X-ray scattering probes the total radial distribution function; by detailed fitting in R-space we measure short range order parameters around C and Si for the first and second shell. The C-C distances in first and second shell indicate that both carbidic and graphitic configurations are present. The coordination numbers indicate that there is a tendency to chemical order; at high C concentrations there is evidence for chemical order with phase separation. The EXAFS measurements probe local order in the Si-C alloy phase; there is clear evidence that even this phase is chemically ordered.

High Yield Synthesis of Pure Alkanethiolate-Capped Silver Nanoparticles

One-phase, one-pot synthesis of Ag(0) nanoparticles capped with alkanethiolate molecules has been optimized to easily achieve a pure product in quantitative yield. We report the synthesis of dodecanethiolate-capped silver particles and the chemophysical, structural, and morphologic characterization performed by way of UV-vis, (1)H NMR, and X-ray photoelectron (XPS) spectroscopies, X-ray powder diffraction (XRD) and X-ray absorption fine structure analysis (XFAS), electron diffraction and high-resolution transmission electron microscopy (HR-TEM), and scanning and transmission electron microscopy (SEM and TEM). Depending on the molar ratio of the reagents (dodecylthiosulphate/Ag(+)), the mean Ag(0) particle size D(XRD) is tuned from 4 to 3 nm with a narrow size distribution. The particles are highly soluble, very stable in organic solvents (hexane, toluene, dichloromethane, etc.), and resistant to oxidation; the hexane solution after one year at room temperature does not show any precipitation or formation of oxidation byproducts.

Identifying the structure of the active sites of human recombinant prolidase

In this paper we provide a detailed biochemical and structural characterization of the active site of recombinant human prolidase, a dimeric metalloenzyme, whose misfunctioning causes a recessive connective tissue disorder (prolidase deficiency) characterized by severe skin lesions, mental retardation and respiratory tract infections. It is known that the protein can host two metal ions in the active site of each constituent monomer. We prove that two different kinds of metals (Mn and Zn) can be simultaneously present in the protein active sites with the protein partially maintaining its enzymatic activity. Structural information extracted from X-ray absorption spectroscopy measurements have been used to yield a full reconstruction of the atomic environment around each one of the two monomeric active sites. In particular, as for the metal ion occupation configuration of the recombinant human prolidase, we have found that one of the two active sites is occupied by two Zn ions and the second one by one Zn and one Mn ion. In both dinuclear units a histidine residue is bound to a Zn ion.

Structure of bioapatite in human foetal bones: An X-ray diffraction study

Bioapatite is a calcium phosphate closely resembling the hydroxyapatite (Ca10(PO4)6(OH)) and is considered to be the major component of the mineralised part in mammalian bones. Even if bones are widely investigated, several aspects concerning the initial bone formation stages are unclear and need to be clarified. In this work advanced X-ray powder diffraction techniques have been exploited to get insights on the structural evolution of human bioapatite during the early stages of ossification processes.

The active site structure of tetanus neurotoxin resolved by multiple scattering analysis in X-Ray absorption spectroscopy.

A detailed study of the x-ray absorption spectrum of tetanus neurotoxin in the K-edge EXAFS region of the zinc absorber is presented that allows the complete identification of the amino acid residues coordinated to the zinc active site. A very satisfactory interpretation of the experimental data can be given if multiple scattering contributions are included in the analysis. Comparing the absorption spectrum of tetanus neurotoxin to that of two other structurally similar zinc-endopeptidases, thermolysin and astacin, in which the zinc coordination mode is known from crystallographic data, we conclude that in tetanus neurotoxin, besides a water molecule, zinc is coordinated to two histidines and a tyrosine.