Reinvestigation of the crystal structure of lautite, CuAsS

The crystal structure of the mineral lautite (copper arsenic sulfide), CuAsS, previously described as either centrosymmetric [Pnma; Marumo & Nowacki (1964 ▶). Schweiz. Miner. Petro. Mitt. 44, 439–454] or noncentrosymmetric [Pna21; Craig & Stephenson (1965 ▶). Acta Cryst. 19, 543–547], was reinvestigated by means of single-crystal X-ray diffraction. The centrosymmetric structural model reported previously was confirmed, although with improved precision for the atomic coordinates and inter­atomic distances. Lautite shows a sphalerite-derivative structure with a linking of Cu[AsS3], As[CuAs2S] and S[Cu3As] tetra­hedra. All atoms lie on special positions (Wyckoff position 4c, site symmetry m)

Twin-chain polymer networks loaded with nanostructured fluids for the selective removal of a non-original varnish from Picasso's "L'Atelier" at the Peggy Guggenheim Collection, Venice

Abstract This paper reports on the evaluation of a polyvinyl alcohol (PVA) "twin-chain" polymer network (TC-PN) combined with an oil-in-water nanostructured fluid (NSF) for the removal of a polyvinyl acetate (PVAc) varnish. Small Angle X-ray Scattering, Confocal Laser Scanning Microscopy, and Fluorescence Correlation Spectroscopy showed that the structure of the gel and the NSF are only minimally altered by loading the fluid into the gel. The NSF is partially free to diffuse through the network, but also interacts with the gel walls. During the cleaning, the dynamics of the fluid at the gel-substrate interface are controlled by the osmotic balance taking place among the interconnected pores. These features grant effective and controlled cleaning performances. The case study identified for this research is Pablo Picasso's The Studio (L'Atelier, 1928), one of the masterpieces in the Peggy Guggenheim Collection, Venice (PGC). In 1969 the oil painting, originally unprotected, was wax-lined and then varnished using a PVAc varnish. Over the years, the white shades of the painting have been compromised by the yellowing of the varnish and soiling of deposits. On painting mock-ups, the NSF-loaded hydrogels allowed the swelling and softening of PVAc varnish and wax layers, which were then removed with gentle mechanical action. Effective varnish and wax removal at the micron scale, and the absence of residues from the cleaning system (gel and NSF), were confirmed by Fourier Transform Infrared Spectroscopy (FTIR) 2D imaging. The effective and safe removal of the aged PVAc varnish and wax layer from the surface of the painting was then carried out using the same cleaning protocol successfully tested on the mock-ups, setting the NSF-loaded PVA TC-PNs as robust and reliable tools for the cleaning of sensitive works of art

Characterisation of (micro-)plastics in groundwater bodies: insights from Italian aquifers

Nowadays, microplastics (MPs) are considered as contaminants of emerging concern, since they are ubiquitously present in the majority of ecosystems. This research focuses on the chemical characterization of MPs in four Italian groundwater bodies, two karst caves, one in Piedmont and the other in Tuscany, and two saturated alluvial aquifers in Florence (Tuscany). Atmospheric depositions, infiltrations through soil and anthropic contribution, especially in touristic areas, can cause MPs penetration into groundwater bodies, posing a risk not only to groundwaters’ quality but also to biodiversity conservation in these sensitive ecosystems. A single water sample was collected from each sampling site, and, if necessary, an oxidative digestion step was performed to remove any organic matter that could interfere with subsequent analysis. Vacuum filtration was employed on each sample, followed by a preliminary observation using a stereomicroscope to assess colors and shapes. The chemical characterization was done by 2D imaging Fourier Transform Infrared Spectroscopy (FTIR). Every polymer found in each site was classified by shape, color and composition. This study was supported by National Recovery and Resilience Plan (PNRR), Mission 4, Component 2 “From Research to Enterprise”, funded by the European Union NextGenerationEU, CUP B83C22004820002

Acid washing effect on elemental and isotopic composition of whole beach arthropods: implications for food web studies using stables isotopes

Inorganic carbon removal through acidification is a common practice prior to isotopic analysis of macroinvertebrate samples. We have experimentally tested the effect of acidification on the elemental and isotopic composition of a range of beach arthropod species. Acidification resulted in a significant depletion of 7.7 % and 1.2 % in average for carbon and nitrogen, respectively. This highlights that acid washing affects other body compounds apart from carbonates. With a few exceptions, 13C and 15N showed no changes following the 1N HCl attack. Our results strongly suggest that samples with a presumable high CaCO3 content, result impoverished in 13C as a consequence of acidification, while those suspected to be carbonate-free are not significantly affected. Regarding 15N values, it seemed that only high carbonate species may be 15N impoverished when treated with HCl. It is recommended to acidify only carbonate-rich samples prior 13C analyses as a standard protocol.This study has been supported partially by funds of a bilateral programme between the CNR (Italy) and the CSIC (Spain), and partially by the EU-INCO project WADI (CT2005-15226)Peer reviewe

From 3D channelled frameworks to 2D layered structures in molecular salts of l-serine and dl-serine with oxalic acid

L-Serine and DL-serine have been treated with oxalic acid under different experimental conditions, e. g. crystallization from solution and slurry, kneading and dry mixing, yielding the molecular salts [L-serH](2)[ox]center dot 2H(2)O forms I and II, [L-serH][Hox] and [DL-serH](2)[ox]center dot 2H(2)O, all fully characterized by powder or single crystal X-ray diffractions; the relationship between the different crystal forms, relative thermal stability, dependence on relative humidity and possible interconversions have all been explored

Structural and Magnetic Properties of the {Cr(pybd)₃[Cu(cyclen)]₂}(BF₄)₄ Heteronuclear Complex

Heterotopic ligands containing chemically different binding centers are appealing candidates for obtaining heteronuclear metal complexes. By exploiting this strategy, it is possible to introduce different paramagnetic centers characterized by specific anisotropic magnetic properties that make them distinguishable when weakly magnetically coupled. This molecular approach has great potential to yield multi-spin adducts capable of mimicking logical architectures necessary for quantum information processing (QIP), i.e., quantum logic gates. A possible route for including a single-ion magnetic center within a finite-sized heterometallic compound uses the asymmetric (1-pyridyl)-butane-1,3-dione (pybd) ligand reported in the literature for obtaining Cr3+−Cu2+ metallo-cages. To avoid the formation of cages, we adopted the cyclen (1,4,7,10-tetraazacyclododecane) ligand as a “capping” agent for the Cu2+ ions. We report here the structural and magnetic characterization of the unprecedented adduct {Cr(pybd)3[Cu(cyclen)]2}(BF4)4, whose structure is characterized by a central Cr3+ ion in a distorted octahedral coordination environment and two peripheral Cu2+ ions with square-pyramidal coordination geometries. As highlighted by Continuous Wave Electron Paramagnetic Resonance (EPR) spectroscopy and Direct Current (DC) magnetometry measurements, this adduct shows negligible intramolecular magnetic couplings, and it maintains the characteristic EPR signals of Cr3+ and Cu2+ moieties when diluted in frozen solutions