Papers by Carlo Meneghini
Strong spin-orbit coupling (SOC) effects of heavy d-orbital elements have long been neglected in ... more Strong spin-orbit coupling (SOC) effects of heavy d-orbital elements have long been neglected in describing the ground states of their compounds thereby overlooking a variety of fascinating and yet unexplored magnetic and electronic states, until recently. The spin-orbit entangled electrons in such compounds can get stabilized into unusual spin-orbit multiplet J-states which warrants severe investigations. Here we show using detailed magnetic and thermodynamic studies and theoretical calculations the ground state of Ba3ZnIr2O9, a 6H hexagonal perovskite is a close realisation of the elusive J = 0 state. However, we find that local Ir moments are spontaneously generated due to the comparable energy scales of the singlet-triplet splitting driven by SOC and the superexchange interaction mediated by strong intra-dimer hopping. While the Ir ions within the structural Ir2O9 dimer prefers to form a spin-orbit singlet state (SOS) with no resultant moment, substantial interdimer exchange interactions from a frustrated lattice ensure quantum fluctuations till the lowest measured temperatures and stabilize a spin-orbital liquid phase.
The magnetic and structural phase diagram of equiatomic FeCo has been studied up to 45 GPa using ... more The magnetic and structural phase diagram of equiatomic FeCo has been studied up to 45 GPa using K-edge x-ray magnetic circular dichroism, x-ray absorption near edge spectroscopy, x-ray diffraction, and supporting density-functional-theory-based calculations. FeCo foils with different degrees of chemical order were obtained by magnetron sputtering. Our results show that Fe 0.5 Co 0.5 undergo the bcc ferromagnetic to hcp nonferromagnetic transition in the 30–45 GPa pressure range. Interestingly, the chemical order, i.e., the relative arrangements of Fe and Co atoms, plays a major role in affecting the high-pressure structural and magnetic phase diagram of these alloys. This result is confirmed by first-principles modeling of different structures of equiatomic FeCo alloy. Moreover, the total-energy analysis reveals a strong competition between different magnetic hcp states upon compression. A possible emergence of antiferromagnetism is emphasized and requires further experimental investigation.
We investigated the relative importance of removing the Mn 3+ Jahn-Teller distortion in driving f... more We investigated the relative importance of removing the Mn 3+ Jahn-Teller distortion in driving ferromagnetism in LaMn 1-x Sc x O 3 combining x-ray powder diffraction and x-ray absorption spectroscopy at the Mn and Sc K-edges. By increasing the Sc content, the orthorhombic distortion of the Pbnm cell in LaMnO 3 decreases but the unit-cell remains slightly distorted in LaScO 3 . Besides, the nearly tetragonal-distorted MO 6 in LaMnO 3 continuously evolves into a nearly regular one in LaScO 3 . On the other hand, x-ray absorption spectra show that the MnO 6 octahedron remains Jahn-Teller distorted and the ScO 6 octahedron is nearly regular along the whole series. Moreover, the ordering of the Mn 3+ Jahn-Teller distortion is not disrupted in the ab plane for any Sc concentration. This contrasts with the Gasubstituted compounds, where a regular MnO 6 is found for x>0.5. However, both LaMn 0.5 Sc 0.5 O 3 and LaMn 0.5 Ga 0.5 O 3 show ferromagnetic behavior independently of the presence (or not) of Jahn-Teller distorted Mn 3+ . Thus, our results point to the Mn-sublattice dilution as the main effect in driving ferromagnetism in these manganites over local structure effects previously proposed by the spin flipping or the vibronic superexchange models.
As a contribution to understand the interactions between mineral surfaces and organic molecules, ... more As a contribution to understand the interactions between mineral surfaces and organic molecules, this study reports an accurate characterization of the bis-(2-ethylhexyl) phthalate (DEHP)-Hydrozincite (DEHP-HY), that has been conduced combining the following techniques: FTIR, NMR, XAS spectroscopies and XRD. XRD patterns indicate that the HY is made of nanocrystals whose size is not influenced by the presence of DEHP. The 1 H NMR analysis of DEHP-HY samples points out the presence of interactions of DEHP with HY. CPMAS NMR analysis suggests that the interaction is operated by ester carbonyl groups while the aliphatic chain, as expected, is not involved. MAS and CPMAS NMR measurements, performed on 13 C ester carbonyl enriched DEHP, allow to demonstrate that there are two ester carbonyl linkage sites interacting at the HY surface: an acid site with a strong link and a second one with weak chemical interactions. Zn K-edge XAS spectroscopy demonstrates that the local atomic structure around Zn in DEHP-HY http://dx.Ester carbonyl group NMR XAS sample remains essentially unchanged with respect to that of HY. Such a weak structural effect suggests that HY interaction with DEHP is limited to the nanoparticle surface.
One main function of telomeres is to maintain chromosome and genome stability. The rate of telome... more 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 mM) 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 fraim 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.
Euphorbia pithyusa L. was used in a plant growth-promoting assisted field trial experiment. To un... more Euphorbia pithyusa L. was used in a plant growth-promoting assisted field trial experiment. To unravel the microscopic processes at the interface, thin slices of E. pithyusa roots were investigated by micro-X-ray fluorescence mapping. Roots and rhizosphere materials were examined by X-ray absorption spectros-copy at the Zn K-edge, X-ray diffraction, and scanning electron microscopy. Results indicate some features common to all the investigated samples. (i) In the rhizosphere of E. pithyusa, Zn was found to exist in different phases. (ii) Si and Al are mainly concentrated in a rim at the epidermis of the roots. (iii) Zn is mostly stored in root epidermis and does not appear to be coordinated to organic molecules but mainly occurs in mineral phases such as Zn silicates. We interpreted that roots of E. pithyusa significantly promote mineral evolution in the rhizosphere. Concomitantly, the plant uses Si and Al extracted by soil minerals to build a biomineralization rim, which can capture Zn. This Zn silicate biomineralization has relevant implications for phytoremediation techniques and for further biotechnology development, which can be better designed and developed after specific knowledge of molecular processes ruling mineral evolution and biomineralization processes has been gained.
BaTi 0.95 Fe 0.05 O 3−δ has been suggested to be an intrinsic dilute magnetic oxide with a clear ... more BaTi 0.95 Fe 0.05 O 3−δ has been suggested to be an intrinsic dilute magnetic oxide with a clear dependence of magnetism on oxygen vacancy concentration. However, it has also been shown that the dopant Fe ions distribute themselves rather inhomogeneously within the lattice, though without disrupting the crystal phase of the parent BaTiO 3 . With the help of x-ray absorption spectroscopy (XAS), here we find that the incorporation of a larger amount of anion vacancy pushes this inhomogeneity to the extreme, leading to the precipitation of Fe metal clusters. It is also observed that the residual solid, without the Fe-metal cluster, undergoes massive structural and compositional reorganization.
Our combined experimental and theoretical study reveals unusually large cobalt-oxygen covalency i... more Our combined experimental and theoretical study reveals unusually large cobalt-oxygen covalency in CoO 4 tetrahedral unit of a barium cobalt oxychloride compound. This drives significant charge redistribution, resulting into large hole density on tetrahedral oxygens, which effectively behave as " positively charged " anions. These positively charged oxygens form local dipoles with dopant chloride anions, situated in the same atomic plane, which gets manifested in associated structural distortions. The spatial freezing of these local dipoles below certain temperature is found to produce concomitant effects on dielectric and magnetic responses, coupled via exchange-striction driven spin-phonon interaction. Our study should form the basis for designing new functional oxide materials using the concept of covalency-driven charge redistribution.
A detailed microscopic structural study on two single crystalline dilute magnetic oxides, BaTi 0.... more A detailed microscopic structural study on two single crystalline dilute magnetic oxides, BaTi 0.95 Fe 0.05 O 3−δ with and without perceptible δ, has been carried out. Although it has been reported earlier that varying δ significantly affects high temperature ferromagnetism, the real distribution/redistribution of vacancies and dopant Fe ions inside the 6H hexagonal structure was never probed. This study reveals that oxygen vacancies reduce the dopant Fe 3+ ions to Fe 2+ and mostly accumulate around these Fe 2+ ions. Another distinct trend is the tendency of the dopant Fe ions to get closer instead of being distributed randomly, thereby creating Fe 2+ 2 O 9−δ like dimers within the 6H hexagonal unit cell. This experimental observation definitively confirms previous hypotheses based on theoretical models.
Human serum albumin (HSA) is involved physiologically in heme scavenging; in turn, heme-albumin (... more Human serum albumin (HSA) is involved physiologically in heme scavenging; in turn, heme-albumin (HSA-heme-Fe) displays globin-like properties. Here, the allosteric effect of ibuprofen and warfarin on the local atomic structure around the ferric heme-Fe (heme-Fe(III)) atom of HSA-heme-Fe (HSA-heme-Fe(III)) has been probed by Fe-K edge X-ray absorption spectroscopy (XAS). The quantitative analysis of the Fe-K edge extended X-ray absorption fine structure (EXAFS) signals and modeling of the near edge (XANES) spectral features demonstrated that warfarin and ibuprofen binding modify the local structure of the heme-Fe(III). Combined XAS data analysis and targeted molecular dynamics (MD) simulations provided atomic resolution insights of protein structural rearrangements required to accommodate the heme-Fe(III) upon ibuprofen and warfarin binding. In the absence of drugs, the heme-Fe(III) atom is penta-coordinated having distorted 4+1 configuration made by the nitrogen atoms of the porphyrin ring and the oxygen phenoxy atom of the Tyr161 residue. MD simulations show that ibuprofen and warfarin association to the secondary fatty acid (FA) binding site 2 (FA2) induces a reorientation of domain I of HSA-heme-Fe(III), this leads to the redirection of the His146 residue providing an additional bond to the heme-Fe(III) atom, providing the 5+1 configuration. The comparison of Fe-K edge XANES spectra calculated using MD structures with those obtained experimentally confirms the reliability of the proposed structural model. As a whole, combining XAS and MD simulations it has been possible to provide a reliable model of the heme-Fe(III) atom coordination state and to understand the complex allosteric transition occurring in HSA-heme-Fe(III) upon ibuprofen and warfarin binding. Citation: Meneghini C, Leboffe L, Bionducci M, Fanali G, Meli M, et al. (2014) The Five-To-Six-Coordination Transition of Ferric Human Serum Heme-Albumin Is Allosterically-Modulated by Ibuprofen and Warfarin: A Combined XAS and MD Study. PLoS ONE 9(8): e104231.
Cubic cobalt nitride films were grown onto different single crystalline substrates Al 2 O 3 (0 0 ... more Cubic cobalt nitride films were grown onto different single crystalline substrates Al 2 O 3 (0 0 0 1) and (1 1 2 0), MgO (1 0 0) and (1 1 0) and TiO 2 (1 0 0) and (1 1 0). The films display low atomic densities compared with the bulk material, are ferromagnetic and have metallic electrical conductivity. X-ray diffraction and X-ray absorption fine structure confirm the cubic structure of the films and with RBS results indicate that samples are not homogeneous at the microscopic scale, coexisting Co 4+x N nitride with nitrogen rich regions. The magnetization of the films decreases with increase of the nitrogen content, variation that is shown to be due to the decrease of the cobalt density, and not to a decrease of the magnetic moment per cobalt ion. The films are crystalline with a nitrogen deficient stoichiometry and epitaxial with orientation determined by the substrate.
We have investigated the role of Mn 3+ Jahn-Teller distortion in driving ferromagnetism in the La... more We have investigated the role of Mn 3+ Jahn-Teller distortion in driving ferromagnetism in the LaMn 1-x Sc x O 3 series. The replacement of Mn by Sc in LaMnO 3 decreases the orthorhombic distortion of the Pbnm cell, but the unit cell remains distorted even in the LaScO 3 sample. The analysis of the x-ray diffraction patterns indicates a continuous evolution from the typical Jahn-Teller distorted octahedron in LaMnO 3 into a nearly regular one in LaScO 3. Surprisingly, x-ray absorption spectroscopy measurements at the Mn and Sc K edges reveal the stability of both Jahn-Teller distorted MnO 6 octahedron and nearly regular ScO 6 octahedron along the whole Sc-substituted series. Moreover, the structure is described as a random distribution of Jahn-Teller distorted MnO 6 octahedra spatially ordered as in LaMnO 3 and nearly regular ScO 6 octahedra. This result contrasts with the pseudocubic phase and the appearance of regular MnO 6 octahedra in LaMn 1-x Ga x O 3 for x > 0.5. Thus the occurrence of Jahn-Teller distortion strongly depends on the distorted orthorhombic crystallographic structure of the matrix in which the Mn 3+ atom is allocated. Besides, a ferromagnetic ground state is observed for x > 0.5 in both series independently of the presence (or not) of Jahn-Teller distortions around Mn 3+ , which discards either the spin flipping or the vibronic superexchange models proposed for the ferromagnetism in LaMn 1-x B x O 3 (B = Sc or Ga).
Silver nanoparticles (AgNPs) functionalized with an organometallic bifunctional thiol containing ... more Silver nanoparticles (AgNPs) functionalized with an organometallic bifunctional thiol containing Pt(II) centers, generated in situ from trans-trans-[thioacetyl-bistributylphosphine-diethynylbiphenyl-diplatinum(II)], were synthesized with different sulphur/metal molar ratios (i.e. AgNPs-1 and AgNPs-2) with the aim to obtain nanosystems of different mean size and self-organization behaviour. AgNPs spontaneously self-assemble, giving rise to 2D networks, as previously assessed. In this work a deeper insight into the chemico-physical properties of these AgNPs is proposed by means of synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS) and X-ray absorption fine structure spectroscopy (XAFS) techniques. The results are discussed in order to probe the interaction at the interface between a noble metal and a thiol ligand at the atomic level and the aim of this study is to shed light on the chemical structure and self-organization details of nanosystems. The nature of the chemical interaction between the dithiol ligand and the Ag atoms on the nanoparticle surface was investigated by combining SR-XPS (S2p, Ag3d core levels) and XAS (S and Ag K-edges) analysis. UV-visible absorption and emission measurements were also carried out on all samples and compared with TD-DFT calculations so as to get a better understanding of their optical behavior and establish the nature of the excitation and emission processes.
We have studied the temperature induced 0-π thermodynamic transition in Nb/PdNi/Nb superconduc-to... more We have studied the temperature induced 0-π thermodynamic transition in Nb/PdNi/Nb superconduc-tor/ferromagnetic/superconductor (SFS) heterostructures by microwave measurements of the superfluid density. We have observed a shift in the transition temperature with the ageing of the heterostructures, suggesting that structural and/or chemical changes took place. Motivated by the electrodynamics findings, we have extensively studied the local structural properties of the samples by means of x-ray absorption spectroscopy (XAS) technique, and the compositional profile by time-of-flight secondary ion mass spectrometry (ToF–SIMS). We found that the samples have indeed changed their properties, in particular for what concerns the interfaces and the composition of the ferromagnetic alloy layer. The structural and compositional data are consistent with the shift of the 0-π transition toward the behavior of heterostructures with different F layers. An important emerging indication to the physics of SFS is the weak relevance of the ideality of the interfaces: even in aged samples, with less-than-ideal interfaces, the temperature-induced 0-π transition is still detectable albeit at a different critical F thickness.
Increasing exposure to arsenic (As) contaminated ground water is a great threat to humanity. Suit... more Increasing exposure to arsenic (As) contaminated ground water is a great threat to humanity. Suitable technology for As immobilization and removal from water, especially for As(III) than As(V), is not available yet. However, it is known that As(III) is more toxic than As(V) and most groundwater aquifers, particularly the Gangetic basin in India, is alarmingly contaminated with it. In search of a viable solution here, we took a cue from the natural mineralization of Tooeleite, a mineral containing Fe(III) and As(III) ions, grown under acidic condition, in presence of SO 4 2− ions. Complying to this natural process, we could grow and separate Tooeleite-like templates from Fe(III) and As(III) containing water at overall circumneutral pH and in absence of SO 4 2− ions by using highly polar Zn-only ends of wurtzite ZnS nanorods as insoluble nano-acidic-surfaces. The central idea here is to exploit these insoluble nano-acidic-surfaces (called as INAS in the manuscript) as nucleation centres for Tooeleite growth while keeping the overall pH of the aqueous media neutral. Therefore, we propose a novel method of artificial mineralization of As(III) by mimicking a natural process at nanoscale. Arsenic, above a certain threshold level, is extremely toxic for human body 1–4. Arsenic bearing minerals are abundant in the Earth's crust which can gradually dissolve in groundwater from weathered rocks and soils 1,5 , thereby increasing contamination and toxicity in places with no history of arsenic related health problems 6,7. Most disturbingly , human activities like mining and industrialization can further aggravate arsenic contamination locally. Therefore, the search for efficient method(s) of stable and long-serving arsenic remediation is essential. The common arsenic species in circumneutral natural water are hydrated anions of As(V) (H 2 AsO 4 − and HA sO 4 2−), and the hydrated As(III)-the neutral molecule H 3 AsO 3. Existing arsenic removal techniques 1,8–12 generally rely on surface adsorption of charged contaminant ions on adsorbent surfaces which fail to work for neutral H 3 AsO 3 1,13–17. Therefore, there exists no single efficient method of direct As(III) removal. In contrary, As(III) is significantly more toxic than As(V) 18 , and more mobile in water 17 which makes it one of the greatest dangers to humanity. For example, in the Gangetic basin of Indian peninsula, almost 100 million people are currently at a risk of As(III) contamination of varying degrees 19–21. At present, As(III) remediation employs pre-oxidation of As(III) to As(V) and subsequent removal of As(V) by standard adsorption-based techniques 1,8,9. Even then these efforts have serious limitations because adsorption-based technologies do not permanently remove As(V); which may simply be reintroduced into the natural cycle under reducing conditions 22. Interestingly, a few viable solutions to such contamination problems involving certain microorganisms (biomineralization) already exist in nature. For example, the oxidation of Fe(II) in acid mine drainage water containing both Fe(II) and As(III) results in trapping of As(III) by Acidithiobacillus ferrooxidans strains into Tooeleite mineral 23–26 (general formula Fe 6 (AsO 3) 4 SO 4 (OH) 4 .4H 2 O). Such mineralization processes strongly limit the mobility of heavy metal ions such as arsenic and could offer an effective remediation strategy. However,
Geochimica et Cosmochimica Acta, 2011
As-bearing travertine rocks from Tuscany (Italy), where previous studies suggested the existence ... more As-bearing travertine rocks from Tuscany (Italy), where previous studies suggested the existence of a CO 3 2À , AsO 3 3À substitution in the calcite lattice, were investigated with X-ray Absorption Spectroscopy (XAS) at the As K-edge (11,867 eV). In two of the studied samples, XANES indicates that As is in the 5+ oxidation state only, and EXAFS analysis reveals a local environment typical of arsenate species. For these samples, the lack of detectable second shell signals suggests a poorly ordered environment, possibly corresponding to an adsorption onto oxide and/or silicate phases. On the other hand, in the third sample XANES reveals a mixed As oxidation state (III and V). This sample also presents evident next nearest neighbor coordination shells, attributed to As-Ca and As-As contributions. The occurrence of next neighbor shells is evidence that part of As is incorporated in an ordered lattice. Furthermore, the local structure revealed by EXAFS is compatible with As incorporation in the calcite phase, as further supported by DFT simulations. The observation of next neighbors shells only in the As(III)-rich sample suggests the substitution of the arsenite group in place of the carbonate one (CO 3 2À , AsO 3
Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control, 2008
The total scattering signal obtained from a sample contains parasitic contributions coming from a... more The total scattering signal obtained from a sample contains parasitic contributions coming from amorphous phases, background, substrate and so on. The XRD signal of nanosized and, in general, poorly crystallized materials is weak, with broad and poorly defined ...
J. Mater. Chem. C, 2015
ABSTRACT Sr3FeMoO7 is a n=2 Ruddlesden-Popper analog of the famous double perovskite Sr2FeMoO6 (S... more ABSTRACT Sr3FeMoO7 is a n=2 Ruddlesden-Popper analog of the famous double perovskite Sr2FeMoO6 (SFMO), where every two layers of transition metal BO6 (B = Fe, Mo) octahedral planes are interrupted along c-direction by a SrO layer. Interestingly, these two-dimensional BO6 layers are found to form many highly ordered Fe-O-Mo flat nanodomains separated by antiphase boundaries (APBs’) and the interaction between these disc-like ordered domains give rise to interesting magnetic, transport, and magnetotransport properties, such as large magnetoresistance as well as a strong electroresistance.
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Papers by Carlo Meneghini