Nanocomposites Based on Metal and Metal Sulfide Clusters Embedded in Polystyrene

Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SR)x, where R is a linear aliphatic hydrocarbon group, –CnH2n+1) undergo a thermolysis reaction at moderately low temperatures (close to 200 °C), which produces metal atoms or metal sulfide species and an organic by-product, disulfide (RSSR) or thioether (RSR) molecules, respectively. Alkane-thiolates are non-polar chemical compounds that dissolve in most techno-polymers and the resulting solid solutions can be annealed to generate polymer-embedded metal or metal sulfide clusters. Here, the preparation of silver and gold clusters embedded into amorphous polystyrene by thermolysis of a dodecyl-thiolate precursor is described in detail. However, this chemical approach is quite universal and a large variety of polymer-embedded metals or metal sulfides could be similarly prepared

Assembled Nanostructured Architectures Studied By Grazing Incidence X-Ray Scattering

In this chapter, we will focus on a specific X‐ray-based technique among those employed in surface science and which is especially suitable for the study of self‐assembled nanocrystals: Grazing Incidence Small Angle X‐ray Scattering (GISAXS). We will first introduce the main field of investigation considered herein, with basic notions of X‐ray scattering from surfaces, and then address basic concepts about GISAXS. Finally, we will describe a few relevant examples of studies, of nanostructured architectures, through ex situ and in situ experiments of grazing incidence X‐ray scattering. This manuscript is focused on the former, showing that they can be performed by using laboratory instruments. In situ investigations still need synchrotron radiation sources in most cases; therefore, only a few examples selected from the literature are reported here, for the sake of completeness. The experiments described are mainly performed in the small angle range, providing information on the size and shape of nanocrystals, together with their spatial arrangement. Both 2D and 3D architectures are considered. In particular, GISAXS measurements of 2D superlattices of nano‐octapods, performed both at a third generation synchrotron beamline and with a table‐top set‐up, are compared; the employed table‐top set‐up is described in a dedicated paragraph. Further examples of grazing incidence studies as performed by the authors with a table‐top set‐up are reported: a GISAXS study of 3D iron oxide nanocrystal superlattices, showing the importance of modelling in order to obtain structural information from data; a combined small/wide angle scattering (GISAXS/GIWAXS) study of 3D PbS nanocrystal superlattices; and a GIWAXS study of P3HT nanofibres, showing how the ordering at the molecular and atomic length scales can be obtained by exploring different angular ranges in the same grazing incidence geometry. Finally, selected examples of in situ GISAXS studies, performed with synchrotron radiation sources, are described

Functional nano-hydroxyapatite for applications in conservation of stony monuments of cultural heritage

Stone is one of the most durable construction materials used in historic buildings all over the world. However, over time, the stone can be subject to various degradation processes leading to physical and chemical modifications. Although these effects may be limited to the surface and negligible to the structural stability of the affected buildings, they can represent a major problem in decorative elements of artistic value, where any detail should be preserved [1]. The challenge for conservators and material scientists involved in stone conservation has always been to find a way to stop or delay the effects of these degradation processes. The basic principle of the patrimony is that the cultural heritage is an incalculable and integral legacy to our future: observing and knowing the past, will help next generations to better challenge the future. Thus, conservation of stone heritage is always a delicate and complex task, due to the multiple variables that have to be taken into account to identify the problems, and to define the necessary conservation actions and to select materials and best procedures to be used. The variety of factors to be analyzed includes the intrinsic stone properties (from geological features up to mechanical behavior), the state of conservation, the degradation mechanisms and the environmental factors. One of the most promising technology employed for lowering the previously described degradation processes, is that of nanomaterials, nowadays largely applied in the maintenance of the world cultural heritage, with the aim of improving the consolidation and protection treatments of damaged stone materials they are made of [2]. Such nanomaterials display important advantages that could solve many problems found in the traditional interventions, that often showed the serious bias of the lack the vital compatibility with the original substrate and a durable performance: application of nanotechnology in the cultural heritage conservation is characterized by the possibility to design consolidant products strongly compatible with the original stone substrate. Moreover, when particles have dimensions of about 100 nanometers, the material properties change significantly from those at larger scales. The nanoparticles must show: stability and sustained photoactivity; biological and chemical inactivity nontoxicity, as well as antimicrobial properties for lowering ecotoxicological impact on animals and plants [3]; low cost suitability towards visible or near UV light; high conversion efficiency and high quantum yield. In addition, these treatments can also have water repellent properties which favor this self-cleaning action and prevent the generation of damage caused by water. The most commonly used inorganic consolidant agents are the products based on Ca(OH)2 calcium hydroxide nanoparticles [4], due to their compatibility with a large part of the built and sculptural heritage. As well as other hydroxides (Mg(OH)2, Sr(OH)2), metal oxides (TiO2, ZnO), and metal nanoparticles (Au, Ag, Pt)) have been reported in the literature, focusing on their potential as consolidants on different artifacts of cultural heritage [2, 5]. But one of the most challenging nanomaterial is Ca10(PO4)6(OH)2 hydroxyapatite (HAP), already applied in a large variety of technological and biomedical applications, mainly due to its close relationship with mineral component of hard human tissues [6-7], and in cultural heritage conservation used for carbonate stone consolidation [2]. HAP can be applied for the consolidation of limestones, marbles and sandstones with different carbonate contents. This product is not introduced directly into stone material, but it comes from the reaction between phosphate ions from an aqueous solution of diammonium hydrogen phosphate applied to the stone and calcium ions coming from substrate. Among its advantages, HAP has a similar crystal structure and close lattice parameters of CaCO3 calcite, the main constituents of marbles and limestone. Thanks to its low viscous nature, this aqueous consolidant product is able to penetrate deeply into the stone, generating a significant improvement in mechanical properties of the same stone. The HAP has been tested as a protective treatment for marble against acid rain corrosion [8]. The study of compatibility and adaptability requires that the physical and chemical properties of both consolidator products and stone substrate are well known. Such a knowledge plays a very important role for the good outcome of the present project. Materials of interest, synthesized in our labs has been analysed by using: 1) X-ray diffraction (XRD), effective on crystalline materials and able to carry out information on chemical composition, size, shape and atomic structure, 2) small- and/or wide-angle scattering (SAXS/WAXS), powerful tool to investigate the domain of phosphate particles as a function of their optical properties; in the case of SAXS the technique can be applied to HAp nanoparticles characterization; 3) Fourier-Transform Infrared (FTIR) spectroscopy, reliable techniques for investigating hydroxyl anions and variations within anionic and cationic groups in the obtained materials; 4) scanning electron microscopy for checking morphologies of nanonparticles; 5) biological evaluation of the antimicrobial properties of obtained HAp materials, through direct contact and disc diffusion methods versus most common gram + and gram - bacteria present in human or animal biosystems 6) Laser Induced Breakdown Spectroscopy (LIBS), a non-destructive technique able to get quali-quantitative informations on museal artifacts. 1 - Pesce C., Moretto L.M., Orsega E.F., Pesce G.L., Corradi M., Weber J. Effectiveness and Compatibility of a Novel Sustainable Method for Stone Consolidation Based on Di-Ammonium Phosphate and Calcium-Based Nanomaterials. Materials 12 (2019) 3025. 2 - David, M.E., Ion, R.-M., Grigorescu, R.M., Iancu, L., Andrei, E.R. Nanomaterials Used in Conservation and Restoration of Cultural Heritage: An Up-to-Date Overview. Materials 13 (2020) 2064. 3 - Reyes-Estebanez, M., Ortega-Morales, B.O., Chan-Bacab, M., Granados-Echegoyen, C., Camacho-Chab, J.C., Pereanez-Sacarias J.E., Gaylarde C. Antimicrobial engineered nanoparticles in the built cultural heritage context and their ecotoxicological impact on animals and plants: a brief review. Heritage Science 6 (2018) 52. 4 - El Bakkari M, Bindiganavile V, Boluk Y. Facile Synthesis of Calcium Hydroxide Nanoparticles onto TEMPO-Oxidized Cellulose Nanofibers for Heritage Conservation. ACS Omega 4 (2019) 20606-20611. 5 - Dida B., Siliqi D., Baldassarre, F., Karaj D., Hasimi A., Kasemi V., Nika V., Vozga I. "Nanomaterialet per Konservimin e Trashegimise Kulturore", SHLBSH, Tirana (2020), ISBN 978-99943-2-468-2 6 - Rakovan J.R., Pasteris J.D. A technological gem: Materials, Medical, and Environmental Mineralogy of Apatite. Elements 11 (2015) 195-200. 7 - Baldassarre F., Altomare A., Corriero N., Mesto E., Lacalamita M., Bruno G., Sacchetti A., Dida B., Karaj D., Della Ventura G.D., Capitelli, F., Siliqi, D. Crystal Chemistry and Luminescence Properties of Eu-Doped Polycrystalline Hydroxyapatite Synthesized by Chemical Precipitation at Room Temperature. Crystals 10 (202) 250. 8 - Graziani G., Sassoni E., Franzoni E., Scherer G.W. Hydroxyapatite Coatings for Marble Protection: Optimization of Calcite Covering and Acid Resistance. Applied Surface Science 368 (2016) 241-257

Structural insights into the intracellular region of the human magnesium transport mediator CNNM4

The four member family of “Cyclin and Cystathionine β-synthase (CBS) domain divalent metal cation transport mediators”, CNNMs, are the least-studied mammalian magnesium transport mediators. CNNM4 is abundant in the brain and the intestinal tract, and its abnormal activity causes Jalili Syndrome. Recent findings show that suppression of CNNM4 in mice promotes malignant progression of intestinal polyps and is linked to infertility. The association of CNNM4 with phosphatases of the regenerating liver, PRLs, abrogates its Mg2+-efflux capacity, thus resulting in an increased intracellular Mg2+ concentration that favors tumor growth. Here we present the crystal structures of the two independent intracellular domains of human CNNM4, i.e., the Bateman module and the cyclic nucleotide binding-like domain (cNMP). We also derive a model structure for the full intracellular region in the absence and presence of MgATP and the oncogenic interacting partner, PRL-1. We find that only the Bateman module interacts with ATP and Mg2+, at non-overlapping sites facilitating their positive cooperativity. Furthermore, both domains dimerize autonomously, where the cNMP domain dimer forms a rigid cleft to restrict the Mg2+ induced sliding of the inserting CBS1 motives of the Bateman module, from a twisted to a flat disk shaped dimer.Gobierno Vasco PI2010-17, IE05-147, IE07-202Diputación Foral de Vizcaya 7/13/08/2006/11, 7/13/08/2005/14Ministerio de Ciencia e Innovación BFU2010-17857, CSD2008-00005Ministerio de Economía y Competitividad BFU2013-47531-R, BES-2014-068464, BFU2016-77408-R, BES-2017-08043

X-ray Characterization of Conformational Changes of Human Apo- and Holo-Transferrin

DGAPA-PAPIIT project No. 207922.Human serum transferrin (Tf) is a bilobed glycoprotein whose function is to transport iron through receptor-mediated endocytosis. The mechanism for iron release is pH-dependent and involves conformational changes in the protein, thus making it an attractive system for possible biomedical applications. In this contribution, two powerful X-ray techniques, namely Macromolecular X-ray Crystallography (MX) and Small Angle X-ray Scattering (SAXS), were used to study the conformational changes of iron-free (apo) and iron-loaded (holo) transferrin in crystal and solution states, respectively, at three different pH values of physiological relevance. A crystallographic model of glycosylated apo-Tf was obtained at 3.0 Å resolution, which did not resolve further despite many efforts to improve crystal quality. In the solution, apo-Tf remained mostly globular in all the pH conditions tested; however, the co-existence of closed, partially open, and open conformations was observed for holo-Tf, which showed a more elongated and flexible shape overall.DGAPA-PAPIIT project No. 207922

X-ray Diffraction: A Powerful Technique for the Multiple-Length-Scale Structural Analysis of Nanomaterials

During recent decades innovative nanomaterials have been extensively studied, aiming at both investigating the structure-property relationship and discovering new properties, in order to achieve relevant improvements in current state-of-the art materials. Lately, controlled growth and/or assembly of nanostructures into hierarchical and complex architectures have played a key role in engineering novel functionalized materials. Since the structural characterization of such materials is a fundamental step, here we discuss X-ray scattering/diffraction techniques to analyze inorganic nanomaterials under different conditions: dispersed in solutions, dried in powders, embedded in matrix, and deposited onto surfaces or underneath them

Conformational Flexibility of Proteins Involved in Ribosome Biogenesis: Investigations via Small Angle X-ray Scattering (SAXS)

The dynamism of proteins is central to their function, and several proteins have been described as flexible, as consisting of multiple domains joined by flexible linkers, and even as intrinsically disordered. Several techniques exist to study protein structures, but small angle X-ray scattering (SAXS) has proven to be particularly powerful for the quantitative analysis of such flexible systems. In the present report, we have used SAXS in combination with X-ray crystallography to highlight their usefulness at characterizing flexible proteins, using as examples two proteins involved in different steps of ribosome biogenesis. The yeast BRCA2 and CDKN1A-interactig protein, Bcp1, is a chaperone for Rpl23 of unknown structure. We showed that it consists of a rigid, slightly elongated protein, with a secondary structure comprising a mixture of alpha helices and beta sheets. As an example of a flexible molecule, we studied the SBDS (Shwachman-Bodian-Diamond Syndrome) protein that is involved in the cytoplasmic maturation of the 60S subunit and constitutes the mutated target in the Shwachman-Diamond Syndrome. In solution, this protein coexists in an ensemble of three main conformations, with the N- and C-terminal ends adopting different orientations with respect to the central domain. The structure observed in the protein crystal corresponds to an average of those predicted by the SAXS flexibility analysis

Table-top combined scanning X-ray small angle scattering and transmission microscopies of lipid vesicles dispersed in free-standing gel

A mm thick free-standing gel containing lipid vesicles made of 2-oleoyl-1-palmitoyl-sn-glycero-3- phosphocholine (POPC) was studied by scanning Small Angle X-ray Scattering (SAXS) and X-ray Transmission (XT) microscopies. Raster scanning relatively large volumes, besides reducing the risk of radiation damage, allows signal integration, improving the signal-to-noise ratio (SNR), as well as high statistical significance of the dataset. The persistence of lipid vesicles in gel was demonstrated, while mapping their spatial distribution and concentration gradients. Information about lipid aggregation and packing, as well as about gel density gradients, was obtained. A posteriori confirmation of lipid presence in well-defined sample areas was obtained by studying the dried sample, featuring clear Bragg peaks from stacked bilayers. The comparison between wet and dry samples allowed it to be proved that lipids do not significantly migrate within the gel even upon drying, whereas bilayer curvature is lost by removing water, resulting in lipids packed in ordered lamellae. Suitable algorithms were successfully employed for enhancing transmission microscopy sensitivity to low absorbing objects, and allowing full SAXS intensity normalization as a general approach. In particular, data reduction includes normalization of the SAXS intensity against the local sample thickness derived from absorption contrast maps. The proposed study was demonstrated by a room-sized instrumentation, although equipped with a high brilliance X-ray micro-source, and is expected to be applicable to a wide variety of organic, inorganic, and multicomponent systems, including biomaterials. The employed routines for data reduction and microscopy, including Gaussian filter for contrast enhancement of low absorbing objects and a region growing segmentation algorithm to exclude no-sample regions, have been implemented and made freely available through the updated in-house developed software SUNBIM

Photoconductivity of tellurium-poly(methyl methacrylate) in the ultraviolet–visible-near infrared range

Fine powders composed of tellurium grains of average size<10 nm were produced by dry vibration milling combined with liquid-phase sedimentation techniques, starting from polycrystalline powders with average grain diameter of ca. 30 μm. Nanocomposite films were obtained by binding the nanosized tellurium grains with poly (methyl methacrylate). Raman spectroscopy revealed that the films were based on the coexistence of tellurium and tellurium oxide crystalline phases due to a partial oxidation in air of the grains. The optical measurements of the fabricated material showed that the absorbance was nearly constant in the 310–2200 nm range and that a typical UV absorption peak of the nanostructured tellurium was centered at around 260 nm. An extensive characterization of the photoconductivity properties was carried out by illuminating the tellurium-poly(methyl methacrylate) films with white light or radiations of different spectral composition selected from the UV–Vis-NIR region. Data analysis has allowed to demonstrate that the photoresponse is closely related to the optical absorption and is independent of the spectral composition of the incident radiation in the wavelength range from 310 to 2200 nm, while the photocurrent increases linearly as a function of the optical power density over about three orders of magnitude