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The design of solid-state materials whose properties and functions can be manipulated in a controlled manner by the application of electron beam irradiation is important in modern materials chemistry and physics. In this paper, we present a progress in the development of scalable electron beam irradiation platform to obtain innovative materials for technological and industrial applications, since one of the problems to be solved in this research area is the scalability of these new nanomaterials induced by electron beam irradiation (EBI). In particular, we focus on carbon structures due to its excellent and exciting properties applied in the technological area in the last years, where we show for the first time a new strategy for carbon allotropic transformation through the portable EBI. This new platform is particularly effective, fast, versatile, clean and easy-to-use, facilitating the preparation of many types of nanomaterials that cannot be obtained by conventional chemical and physical methods. The EBI on flat graphite pellets resulted in a covering of it surface with rod-like particles composed of different allotropic forms of carbon. Furthermore, the developed system allowed the implantation of the Fe as a catalytic material through steel sputtering of the high voltage acceleration anode during the EBI process. It was observed by HRTEM analyses that the rod-like particles are preferentially composed of highly oriented graphite in its bottom, polycrystalline graphite in its middle and magnetite nanoparticles in its top.

Herein, a novel silver and chromium nanostructured N-doped carbonaceous material has been synthesized by a biomass-annealing approach using readily available chitosan as a raw material. The resulting catalyst AgCr@CN-800 has been applied for the dehydrogenative coupling reaction of various silanes with different alcohols to obtain the corresponding silyl ethers under aerobic and mild conditions. Besides excellent activity and selectivity, the as-prepared catalyst exhibits good stability and reusability. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, and high-resolution transmission electron microscopy (TEM) in combination with careful examination of the structure with Cs-corrected high-angle annular dark-field scanning TEM revealed that the catalyst AgCr@CN-800 comprises Ag- and CrN-aggregated particles, as well as highly dispersed Ag–Nx and Cr–Nx sites embedded in N-doped graphitic structures. A comparative catalytic study using structure-related catalysts in combination with acid-leaching treatments has shown that the most active species are the Ag particles and that their activity is boosted by the presence of Cr-derived species. By in situ Raman spectroscopy experiments, it has been found that the dehydrogenative coupling of silanes with alcohols in the presence of catalyst AgCr@CN-800 takes place through an oxygen-assisted mechanism., The authors thank the financial support from MICIU/AEI/FEDER (PGC2018-094417-B-I00 and RTI2018-098237-B-C22) and Universitat Jaume I (UJI-A2019-16, UJI-B2019-30, and UJI-B2018-23). I.S. thanks the Spanish Ministerio de Economía, Industria y Competitividad (MINECO) for a postdoctoral “Juan de la Cierva-Incorporación” fellowship (IJCI-2016-30590), and the financial support from the “José Castillejo” Mobility Program (CAS19/00339) of the Ministerio de Ciencia, Innovación y Universidades (MICIU). S.M. acknowledges DGA/fondos FEDER (construyendo Europa desde Aragón) for funding the research group Platón (E31_17R). D.V.-E. thanks the MICIU for a FPU grant (FPU15/03011). E.L. and M.A. thank the financial support from FAPESP (2013/07296-2), CNPq (166281/2017-4), CAPES, and FINEP. The authors also thank the “Servei Central d’Instrumentació Científica (SCIC)” of the Universitat Jaume I, as well as Dr. G. Antorrena for technical support in XPS studies.

Summary Atomic-scale structure determination is crucial to the understanding of nanomaterial properties and development of new technologies. Although pair distribution function (PDF) analysis by neutrons and X-ray scattering profile has been used to study materials, electron diffraction can offer advantages to characterize the atomic structure of clusters, amorphous samples, and nanomaterials. Electrons have higher scattering power than X-rays, allowing the acquirement of PDF from electron diffraction (ePDF) for small sample amounts and with time-efficient data acquisition. Compared with synchrotron X-rays and neutrons as sources for PDF, the availability of electron microscopes worldwide is advantageous. Nowadays, with the rise of methodologies and specific software for ePDF data analysis, the scientific community can benefit from advanced transmission electron microscopy (TEM) structure determination integrating commonly available TEM analyses—size, distribution, shape, and high-resolution TEM atomic visualization—with ePDF atomic structure determination, both for bulk and surface configurations. Therefore, ePDF has the potential to become a routine and advanced characterization tool for nanomaterials science.

Copper indium sulfide quantum dots (QDs) have attracted substantial attention in recent years due to environmental issues and diverse applications. We report the synthesis and characterization of c...

International audience; Hard and strong transparent glass-ceramics (TGCs) can be used as cooktop plates, telescope mirrors, armor materials, and screens for smartphones and tablets. In this work, transparent glass-ceramics from the MgO-Al2O3-SiO2 (MAS) system were obtained after a refined heat-treatment protocol. The evolution in fracture toughness, KIC (Single Edge Precracked Beam), and Vickers hardness (H-V) were characterized as a function of the crystallization progress. The K-IC of the parent glass was 0.6 MPa m(1/2), whereas the TGC samples present values around 1.1 MPa m(1/2). The average glass hardness was 8.5 and PLUSMN; 0.8 GPa for loads of 0.6-5 N, whereas the H-V of the TGC samples varied from 9 to 10 GPa, for indentation loads ranging from 4.9 to 9.8 N. These results are discussed in light of our previous findings on the evolution of elastic modulus in the same glass-ceramics.

Multifunctional quantum dots (QDs) of Co3O4 were fabricated using cobalt II nitrate hexahydrate with tomato (Solanum lycopersicum L.) seed extract and were efficiently applied as a virucidal additive in cotton fabric. The low-dimensional semiconductor, exhibiting a quantum confinement regime along with charge carrier confinement, resulted in superior antiviral characteristics. The QDs were characterized by UV-visible spectrophotometry, high-resolution transmission electron microscopy, X-ray excited photoelectron spectrometry, Fourier transform infrared spectroscopy, and magnetic properties using a superconductor quantum interference device. Co3O4 QDs exhibit chirality, as evidenced by the magnetic circular dichroism spectrum in the spectral region in which the material absorbs. The high ferritin content in tomato seeds, as evidenced by electron paramagnetic resonance, suggested that this protein acts as a nanocage for the growth of Co3O4. Commercially purified horse spleen ferritin was equally efficient in producing Co3O4 QDs. Based on these results, it can be concluded that the multifunctional platform of Co3O4 QDs satisfactorily meets the requirements to be an efficient photocatalyst and exhibits the potential to be employed as a semiconductor textile-based to combat/ to prevent coronavirus disease as a sustainable personal protective clothing.

Lead halide perovskites have emerged as promising materials for light-emitting devices. Here, we report the preparation of colloidal CsPbBr3 nanoplatelets (3 × 4 × 23 nm3) experiencing a strong qua...

Made available in DSpace on 2022-04-28T19:47:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-02-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Ministerio de Ciencia, Innovación y Universidades Universitat Jaume I This work elucidates the morphology-photoluminescence (PL) emission relationships, based on experimental and calculated results, on β-Ag2MoO4 samples synthesized by microwave-assisted hydrothermal method. It was shown that the solvent (water and ammonia) and temperature (120, 130, 140, and 150 °C) play a crucial role in the morphology and PL emissions. A crystal structure model, composed by the local coordination of both Ag and Mo atoms at bulk and exposed surfaces, was built, and the possible mechanism along the synthesis progress was proposed and analyzed. This study provides an idea for the preparation and development of β-Ag2MoO4 based materials with desirable properties. CDMF Federal University of São Carlos, P.O. Box 676 Institute of Chemistry State University of Campinas, Campinas Universidade Estadual Paulista Laboratório Interdisciplinary de Eletroquímica e Cerâmica Department of Physics Federal University of São Carlos, P.O. Box 676 Department of Analytical and Physical Chemistry University Jaume I Brazilian Nanotechnology National Laboratory (LNNano)/CNPEM, Campinas Universidade Estadual Paulista Laboratório Interdisciplinary de Eletroquímica e Cerâmica CAPES: 001 CNPq: 142035/2017-3 FAPESP: 2013/07296-2 FAPESP: 2016/23891-6 FAPESP: 2017/26105-4 FAPESP: 2019/01732-1 CNPq: 305792/2020-2 Ministerio de Ciencia, Innovación y Universidades: PGC2018-094417-B-I00 Universitat Jaume I: UJI-B2019-30

CdTe/CdS core/shell quantum dots (QDs) are formed in aqueous synthesis via the partial decomposition of hydrophilic thiols, used as surface ligands. In this work, we investigate the influence of the chemical nature (functional group and chain length) of the used surface ligands on the shell formation. Four different surface ligands are compared: 3-mercaptopropionic acid, MPA, thioglycolic acid, TGA, sodium 3-mercaptopropanesulfonate, MPS, and sodium 2-mercaptoethanesulfonate, MES. The QD growth rate increases when the ligand aliphatic chain length decreases due to steric reasons. At the same time, the QDs stabilized with carboxylate ligands grow faster and achieve higher photoluminescence quantum yields compared to those containing sulfonate ligands. The average PL lifetime of TGA and MPA capped QDs is similar (≈20 ns) while in the case of MPS shorter (≈15 ns) and for MES significantly longer (≈30 ns) values are measured. A detailed structural analysis combining powder X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) indicates the existence of two novel regimes of band alignment: in the case of the mercaptocarboxylate ligands the classic type I band alignment between the core and shell materials is predominant, while the mercaptosulfonate ligands induce a quasi-type II alignment (MES) or an inverted type I alignment (MPS). Finally, the effect of the pH value on the optical properties was evaluated: using a ligand excess in solution allows achieving better stability of the QDs while maintaining high photoluminescence intensity at low pH.

Observation of relevant phenomena related with dynamical redox process in a plasmonic heterogeneous-photocatalyst system composed by silver nanoparticles (NPs) around and in contact with amorphous silver chloride NPs are reported by in situ transmission electron microscopy. During this process, nanobubbles are initially produced inside the silver chloride NPs, which immediately begin to move within the amorphous phase. Besides, silver atoms inside the silver chloride NPs start to migrate out the occupied volume leaving a space behind, which is filled by crystalline regions of silver chloride located between the pre-existing silver NPs. During the observation time, fast-nucleation, movement, growth, and fast-dissolution of silver NPs take place. Specific space correlation with silver mass loss (or gain) when a new NP is formed (or dissolved), was detected in different regions during the reaction. This mass loss (or gain) takes place on certain places of pre-existing silver NPs. All these phenomena were observed for a configuration comprising at least two silver NPs separated few nanometers apart by a silver chloride NP., Facultad de Ingeniería, Centro de Investigaciones Ópticas

Aim: This work is focused on obtaining degradable mesoporous silica nanoparticles (DMSNs) which are able to maintain their colloidal stability in complex biological media. Materials & methods: DMSNs were synthesized using different ratios of disulfide organosilane (degradable structural moiety) and further functionalized with sulfobetaine silane (SBS) to enhance colloidal stability and improve biological compatibility. Results: There was a clear trade-off between nanoparticle degradability and colloidal stability, since full optimization of the degradation process generated unstable particles, while enhancing colloidal stability resulted in poor DMSNs degradation. It was also shown that acidic pH improved particle degradation which is commonly triggered by reduction stimulus. Conclusion: A chemical composition window was found where DMSNs presented satisfactory colloidal stability in biologically relevant medium, meaningful degradation profiles and high biocompatibility.

Made available in DSpace on 2022-04-28T19:46:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-12-16 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Ministerio de Ciencia, Innovación y Universidades Universitat Jaume I In this study, we have demonstrated that Bi2S3 semiconductor under ultrasound behaves as a piezoelectric material, facilitating the transfer of electrons and holes, thus enabling the formation of oxidizing agents. In the presence of light, Bi2S3 showed no photocatalytic activity, resulting in Rhodamine B (RhB) degradation of 2.5%, while the ultrasound application led to a degradation of 40.6%. Herein, we propose a possible mechanism to explain this behavior based on the local charge polarization in [BiS7] clusters. LIEC – CDMF - Department of Chemistry Universidade Federal de São Carlos - UFSCar, P.O. Box 676 Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473 Institute of Chemistry - São Paulo State University - UNESP Departament de Química Inorgànica I Orgànica Universitat Jaume I (UJI) Department of Analytical and Physical Chemistry University Jaume I Brazilian Nanotechnology National Laboratory (LNNano)/CNPEM Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473 Institute of Chemistry - São Paulo State University - UNESP CNPq: 142035/2017-3 FAPESP: 2013/07296-2 Ministerio de Ciencia, Innovación y Universidades: PGC2018094417-B-I00 Universitat Jaume I: UJI-B2019-30

Recently, core–shell nanowires have been proposed as potential electrical connectors for nanoelectronics components. A promising candidate is Mn5Si3 nanowires encapsulated in an oxide shell, due to their low reactivity and large flexibility. In this work, we investigate the use of the one-step metallic flux nanonucleation method to easily grow manganese silicide single crystal oxide-protected nanowires by performing their structural and electrical characterization. We find that the fabrication method yields a room-temperature hexagonal crystalline structure with the c-axis along the nanowire. Moreover, the obtained nanowires are metallic at low temperature and low sensitive to a strong external magnetic field. Finally, we observe an unknown electron scattering mechanism for small diameters. In conclusion, the one-step metallic flux nanonucleation method yields intermetallic nanowires suitable for both integration in flexible nanoelectronics as well as low-dimensionality transport experiments.

A facile hydrothermal method to synthesize water-soluble copper indium sulfide (CIS) nanocrystals (NCs) at 150 &deg, C is presented. The obtained samples exhibited three distinct photoluminescence peaks in the red, green and blue spectral regions, corresponding to three size fractions, which could be separated by means of size-selective precipitation. While the red and green emitting fractions consist of 4.5 and 2.5 nm CIS NCs, the blue fraction was identified as in situ formed carbon nanodots showing excitation wavelength dependent emission. When used as light absorbers in quantum dot sensitized solar cells, the individual green and red fractions yielded power conversion efficiencies of 2.9% and 2.6%, respectively. With the unfractionated samples, the efficiency values approaching 5% were obtained. This improvement was mainly due to a significantly enhanced photocurrent arising from complementary panchromatic absorption.

Novel magnetic metals and metal oxides that use both the spin and charge of an electron offer exciting technological applications. Their discovery could boost research on functional nanoscale materials. Here, for the first time, we report the magnetization of α-Ag2WO4 under electron beam and femtosecond laser irradiation. The formation and growth of silver oxides (AgO, Ag2O, and Ag3O4) and Ag nanofilaments can be observed on the surface of α-Ag2WO4 crystals. These features were also present in the composition of an extruded material and could open new avenues for surface magnetism studies. In order to understand these results, we used first-principles density functional theory calculations. This allowed us to investigate several potential scenarios for controlling magnetic properties. The effect of electron addition on the crystalline structures of α-Ag2WO4, Ag3O4, Ag2O, and AgO has been analyzed in detail. The creation of Ag and O vacancies on these compounds was also analyzed. Based on structural and electronic changes at the local coordination site of Ag, a mechanism was proposed. The mechanism illustrates the processes responsible for the formation and growth of metallic Ag and the magnetic response to electron beam irradiation.

Made available in DSpace on 2020-12-12T01:25:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-06-01 Present theoretical and experimental work provides an in-depth understanding of the morphological, structural, electronic, and optical properties of hexagonal and monoclinic polymorphs of bismuth phosphate (BiPO4). Herein, we demonstrate how microwave irradiation induces the transformation of a hexagonal phase to a monoclinic phase in a short period of time and, thus, the photocatalytic performance of BiPO4. To complement and rationalize the experimental results, first-principles calculations have been performed within the framework of density functional theory. This was aimed at obtaining the geometric, energetic, and structural parameters as well as vibrational frequencies; further, the electronic properties (band structure diagram and density of states) of the bulk and corresponding surfaces of both the hexagonal and monoclinic phases of BiPO4 were also acquired. A detailed characterization of the low vibrational modes of both the hexagonal and monoclinic polymorphs is key to explaining the irreversible phase transformation from hexagonal to monoclinic. On the basis of the calculated values of the surface energies, a map of the available morphologies of both phases was obtained by using Wulff construction and compared to the observed scanning electron microscopy images. The BiPO4 crystals obtained after 16-32 min of microwave irradiation provided excellent photodegradation of Rhodamine B under visible-light irradiation. This enhancement was found to be related to the surface energy and the types of clusters formed on the exposed surfaces of the morphology. These findings provide details of the hexagonal-to-monoclinic phase transition in BiPO4 during microwave irradiation; further, the results will assist in the design of electronic devices with higher efficiency and reliability. Chemistry Department CDMF LIEC Federal University of São Carlos, P.O. Box 676 Instituto de Química de São Carlos Universidade de São Paulo, P.O. Box 780 CDMF LIEC Chemistry Institute of the Paulista State University UNESP, P.O. Box 1680 Department of Physical and Analytical Chemistry University Jaume i Physics Department Federal University of São Carlos, P.O. Box 676 Brazilian Nanotechnology National Laboratory, Rua Giuseppe Maximo Scolfa no. 10000 CDMF LIEC Chemistry Institute of the Paulista State University UNESP, P.O. Box 1680

In this work were synthesized highly luminescent carbon dots for use as fluorescence sensor for Cr(VI). Carbon dots (CDots) were prepared by pyrolysis of the mixture of molecular precursors as citric acid and reduced glutathione. Pyrolysis revealed to be a simple procedure that afforded CDots with a photoluminescence quantum yield of 69.4%, and particle size of about 2.5 nm. To explore the analytical potentiality of the nanomaterial produced, the CDots were applied as fluorescent sensors to determine Cr(VI) in water and soil samples. The interaction mechanism between CDots and Cr(VI) is associated with both inner filter effect and static quenching. After optimization of the main analytical parameters, the method showed a linear range of 0.10–12 μg mL −1 with limit of detection (LOD) of 0.03 μg mL −1 (pH 7), and recoveries of 90–105% and 99.5–107% for samples of water and soil, respectively. Thus, the method proved to be sensitive, fast and versatile for applications in different environmental samples.

In this paper we proposed the synthesis, characterization and application of magnetic restricted access carbon nanotubes (M-RACNTs) to smoothly capture Cu and Zn from Cu, Zn superoxide dismutase (Cu,Zn-SOD). Fe3O4 magnetic nanoparticles were incorporated on the external surface of carbon nanotubes. The obtained material was encapsulated with a chemically crosslinked bovine serum albumin (BSA) layer, resulting in the M-RACNTs. The BSA capsule acts as a biocompatible barrier that prevents the proteins binding on the M-RACNTs surface. In a pH higher than the isoelectric point of BSA, the proteins from the sample and from the BSA layer, are negatively charged, resulting in an exclusion mechanism by electrostatic repulsion. The characterization tests confirmed the presence of the Fe3O4 magnetic nanoparticles in the interior, and the BSA layer on the surface of the M-RACNTs. The kinetic and isotherm tests were carried out for the Cu and Zn sorption by M-RACNTs, and the results confirmed the fast mass transference rate, and the metal retention in monolayers (Sips model, Cu and Zn maximum adsorption capacities of about 65 mg g−1), respectively. M-RACNTs were able to remove 64 and 62% of Cu and Zn, respectively, from a 0.140 mol L−1 Cu,Zn-SOD aqueous solution, with only one magnetic dispersive solid phase extraction cycle. During this process, M-RACNTs retained less than 5% of the enzyme, attesting the efficiency of the BSA layer to prevent protein binding. The Cu,Zn-SOD submitted to the extraction lost about 15% of its activity, which was totally recovered when Cu and Zn were reincorporated in the enzyme structure by addiction of an aqueous solution of both metals. Thus, we are sure that the M-RACNTs are promising sorbents to obtain apoproteins from metalloproteins in biotechnological applications.

Dopant atoms can be incorporated into nanowires either via the vapor-liquid-solid mechanism through the catalyst droplet or by the vapor-solid growth on the sidewalls. Si is a typical n-type dopant for GaAs, but in nanowires it often suffers from a strongly amphoteric nature in the vapor-liquid-solid process. This issue can be avoided by using Te, which is a promising but less common alternative for n-type doping of GaAs nanowires. Here, we present a detailed investigation of Te-doped self-catalyzed GaAs nanowires. We use several complementary experimental techniques, such as atom probe tomography, off-axis electron holography, micro-Raman spectroscopy, and single-nanowire transport characterization, to assess the Te concentration, the free-electron concentration, and the built-in potential in Te-doped GaAs nanowires. By combing the experimental results with a theoretical model, we show that Te atoms are mainly incorporated by the vapor-liquid-solid process through the Ga droplet, which leads to both axial and radial dopant gradients due to Te diffusion inside the nanowires and competition between axial elongation and radial growth of nanowires. Furthermore, by comparing the free-electron concentration from Raman spectroscopy and the Te-atom concentrations from atom probe tomography, we show that the activation of Te donor atoms is 100% at a doping level of 4×1018cm-3, which is a significant result in terms of future device applications. acceptedVersion

‘Together we are stronger’ In this work, the preparation of the quaternary nanocomposite TiO2/CdS/rGO/Pt is reported along with its application, for the first time, as a catalyst for the photocatalytic reduction of carbon dioxide (CO2) to methane (CH4). TiO2/CdS nanoparticles and Pt nanoparticle-decorated reduced graphene oxide sheets (rGO/Pt) were synthesized separately and characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, UV-vis spectroscopy and photoelectrochemical experiments. Hydrocarbon samples were collected and analysed using gas chromatography (GC). After 5 hours of illumination under visible light, 0.11 μmol of CH4 was produced at an average production rate of 0.0867 μmol h−1, which is higher than the production of CH4 measured from the TiO2/CdS and the TiO2/CdS/Pt control samples. The photoelectrochemical experiments confirmed that the presence of rGO sheets in the nanocomposite enhanced the electrochemical and photocatalytic properties of the nanocomposite as a result of rapid electron transport and the inhibition of charge recombination.

In this work, we have synthesized CdTe quantum dots (QDs) dispersed in an aqueous medium at ambient temperature, and investigated their optical properties. Synthesis of CdTe QDs in the presence of simple amines removed the need for an additional energy source and inert atmosphere, in a simple and inexpensive experimental setup. The use of ammonia or hydrazine promoted nanoparticle growth by kinetic nanocrystal agglomeration in the initial growth stage. These weak electrolytes acted in the electrical double layer during the growth of the nanocrystals. A comparative study on the concentration of hydrazine in the reaction medium helped to investigate their role in nanocrystal growth. Substitution of hydrazine for ethylenediamine and other electrolytes like sodium chloride and ammonium chloride contributed to a better understanding of the mechanism that underlies the use of primary amines in the synthesis of CdTe. The synthesis conditions afforded the highest photoluminescence quantum yield for CdTe QDs prepared at room temperature (27.5%).

On the basis of tissue-specific enzyme activity and inhibition by catalytic products, Hans Krebs first demonstrated the existence of multiple glutaminases in mammals. Currently, two human genes are known to encode at least four glutaminase isoforms. However, the phylogeny of these medically relevant enzymes remains unclear, prompting us to investigate their origin and evolution. Using prokaryotic and eukaryotic glutaminase sequences, we built a phylogenetic tree whose topology suggested that the multidomain architecture was inherited from bacterial ancestors, probably simultaneously with the hosting of the proto-mitochondrion endosymbiont. We propose an evolutionary model wherein the appearance of the most active enzyme isoform, glutaminase C (GAC), which is expressed in many cancers, was a late retrotransposition event that occurred in fishes from the Chondrichthyes class. The ankyrin (ANK) repeats in the glutaminases were acquired early in their evolution. To obtain information on ANK folding, we solved two high-resolution structures of the ANK repeat-containing C-termini of both kidney-type glutaminase (KGA) and GLS2 isoforms (glutaminase B and liver-type glutaminase). We found that the glutaminase ANK repeats form unique intramolecular contacts through two highly conserved motifs; curiously, this arrangement occludes a region usually involved in ANK-mediated protein-protein interactions. We also solved the crystal structure of full-length KGA and present a small-angle X-ray scattering model for full-length GLS2. These structures explain these proteins' compromised ability to assemble into catalytically active supra-tetrameric filaments, as previously shown for GAC. Collectively, these results provide information about glutaminases that may aid in the design of isoform-specific glutaminase inhibitors.

The growing interest in magnetic nanowires (NWs) is connected to possibility of employing them for advanced applications in wide technological fields, such as data storage and biotechnology. In addition, NWs can be used as sensor devices for several applications, since they present high sensitivity to their environment. One of the major challenges when dealing with transport measurements in NWs is to trap them between electrodes, which allows electrical characterization and therefore fabrication of nanowire-based devices. Electrically neutral NWs can be deposited by dielectrophoresis (DEP) method, which requires the application of an alternating electric field between electrodes. In this work, Ni nanowires (NiNWs) fabricated by electrodeposition technique and properly dispersed in a dimethylformalmide (DMF) solution were deposited on top of Pt electrodes using the DEP method. The deposited NiNWs exhibit initially a Schottky-like current versus voltage behavior due to the high contact resistance between NiNW and electrode. Its reduction down to three orders of magnitude, reaching value less than the NiNW resistance, was achieved by depositing an ion beam-assisted 10 nm-thick Pt layer over the NWs extremities. Therefore, this method presents a suitable process of NWs deposition and electrical characterization. This can be used for investigation of electrical transport properties of individual NWs and fabrication of NWsbased devices, such as sensors and field-effect transistors. Especially for ferromagnetic NWs, one can use the present method for fabrication of magnetic field-effect transistors (MagFET).

Human hair has three main regions, the medulla, the cortex and the cuticle. An existing model for the cortex suggests that the α-keratin- based intermediate filaments (IFs) align with the hair’s axis, but are orientationally disordered in-plane. We found that there is a new region in the cortex near the cuticle’s boundary in which the IFs are aligned with the hair’s axis, but additionally, they are orientationally ordered in-plane due to the presence of the cuticle/hair boundary. Further into the cortex, the IF arrangement becomes disordered, eventually losing all in-plane orientation. We also find that in the cuticle, a key diffraction feature is absent, indicating the presence of the β-keratin rather than that of the α-keratin phase. This is direct structural evidence that the cuticle contains β-keratin sheets. This work highlights the importance of using a sub-micron x-ray beam to unravel the structures of poorly ordered, multi-phase systems.

B-type carbonate apatite samples were synthesized by wet chemical method and characterized by X-ray Fluorescence Spectrometry, X-ray Diffraction, Fourier Transformed Infrared Spectroscopy and High Resolution Transmission Electron Microscopy. The XRD and FTIR analysis confirmed the presence of one B-type carbonate apatite phase and the HRTEM images revealed the coexistence of amorphous and polycrystalline regions in the order of 2nm with the carbonate apatite structure. Second phases or precursors were not discovered.

"Bottom-up" methods to obtain nanocrystals usually result in metastable phases, even in processes carried out at room temperature or under soft annealing conditions. However, stable phases, often associated with anisotropic shapes, are obtained in only a few special cases. In this paper we report on the synthesis of two well-studied oxides-titanium and zirconium oxide-in the nanometric range, by a novel route based on the decomposition of peroxide complexes of the two metals under hydrothermal soft conditions, obtaining metastable and stable phases in both cases through transformation. High-resolution transmission electron microscopy analysis reveals the existence of typical defects relating to growth by the oriented attachment mechanism in the stable crystals. The results suggest that the mechanism is associated to the phase transformation of these structures.

In this work, we report the synthesis of titanium oxide nanocrystals, especially the rutile TiO 2 phase with nanorod morphology, by a method based on peroxotitanium complex decomposition. The results indicate that the anisotropic morphology reported for rutile TiO 2 nanocrystals is related to the oriented attachment process. Despite the predominance of rutile nanocrystals at longer treatment times, the nanocrystals were obtained also in the anatase type, according to the degradation time adopted. XANES results evidenced the absence of structural correlation between the peroxytitanium complex and phase evolution, and the coexistence of the two phases strongly suggests a correlation of the oriented attachment mechanism and the rutile phase stabilization.

Rapid variations of the environmental energy caused by ultrashort laser pulses have induced phase transitions in carbon allotropes, therefore bringing the promise of revealing new carbon phases. Here, by exposing polycrystalline graphite to 25 fs laser pulses at 4 J/cm2 fluence under standard air atmosphere, we demonstrated the synthesis of translucent micrometer-sized structures carrying diamond-like and onion-like carbon phases. Texturized domains of the diamond phase were also identified. Concerning different synthesized carbon forms, pulse superposition and singularities of the thermodynamical process, we pinpoint the synthesis mechanism by the laser-induced subsequent products energetically evolving to attain the diamond-like phase.

We report here an atomistic study of the mechanical deformation of AuxCu(1-x) atomic-size wires (NWs) by means of high resolution transmission electron microscopy (HRTEM) experiments. Molecular dynamics simulations were also carried out in order to obtain deeper insights on the dynamical properties of stretched NWs. The mechanical properties are significantly dependent on the chemical composition that evolves in time at the junction; some structures exhibit a remarkable de-alloying behavior. Also, our results represent the first experimental realization of mixed linear atomic chains (LACs) among transition and noble metals; in particular, surface energies induce chemical gradients on NW surfaces that can be exploited to control the relative LAC compositions (different number of gold and copper atoms). The implications of these results for nanocatalysis and spin transport of one-atom-thick metal wires are addressed., Comment: Accepted to Journal of Applied Physics (JAP)

This article reports on the growth of SnO nanobelts and dendrites by a carbothermal reduction process. The materials were synthesized in a sealed tube furnace at 1210 degrees C and at 1260 degrees C for 2 h, in a dynamic nitrogen atmosphere of 40 sccm. After synthesis, gray-black materials were collected downstream in the tube and the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The results showed that the gray-black materials were composed of nanobelts, which grew in the [110] direction of the orthorhombic structure of SnO. Some of the belts also presented dendritic growth. The dendrites grew in the (110) planes of the SnO structure, and no defects were observed at the junction between the nanobelts and the dendrites. A self-catalytic vapor-liquid-solid (VLS) process was proposed to explain the growth of the SnO nanobelts and dendrites.

A new analytical expression for the size-dependent bandgap of colloidal semiconductor nanocrystals is proposed within the framework of the finite-depth square-well effective mass approximation in order to provide a quantitative description of the quantum confinement effect. This allows one to convert optical spectroscopic data (photoluminescence spectrum and absorbance edge) into accurate estimates for the particle size distributions of colloidal systems even if the traditional effective mass model is expected to fail, which occurs typically for very small particles belonging to the so-called strong confinement limit. By applying the reported theoretical methodologies to CdTe nanocrystals synthesized through wet chemical routes, size distributions are inferred and compared directly to those obtained from atomic force microscopy and transmission electron microscopy. This analysis can be used as a complementary tool for the characterization of nanocrystal samples of many other systems such as the II-VI and III-V semiconductor materials., Comment: 9 pages, 5 figures

We prepared very high-coercivity cobalt ferrite nanoparticles synthesized by a combustion method and using short-time high-energy mechanical milling to increase strain and the structural defects density. The coercivity (HC) of the milled sample reached 3.75 kOe—a value almost five times higher than that obtained for the non-milled material (0.76 kOe). To investigate the effect of the temperature on the magnetic behavior of the milled sample, we performed a thermal treatment on the milled sample at 300, 400, and 600 °C for 30 and 180 min. We analyzed the changes in the magnetic behavior of the nanoparticles due to the thermal treatment using the hysteresis curves, Williamson-Hall analysis, and transmission electron microscopy. The thermal treatment at 600 °C causes decreases in the microstructural strain and density of structural defects resulting in a significant decrease in HC. Furthermore, this thermal treatment increases the size of the nanoparticles and, as a consequence, there is a substantial increase in the saturation magnetization (MS). The HC of the samples treated at 600 °C for 30 and 180 min were 2.24 and 1.93 kOe, respectively, and the MS of these same samples increased from 57 emu/g to 66 and 70 emu/g, respectively. The HC and the MS are less affected by the thermal treatment at 300 and 400 °C.

High-resolution synchrotron radiation Renninger scans (RS) have been used in the analysis of hybrid reflections in the InGaP/GaAs structure. Four-beam cases involving two Bragg (primary and secondary) and one Laue (secondary) reflections of the 002 Renninger scans for the GaAs substrate and the InGaP layer were analysed in detail. Different structures of asymmetry regarding the in-plane directions [110] and [1{\bar 1}0] were observed from the measurements of the same three families of four-beam cases, {1{\bar 1}}{\bar 1}/{1{\bar 1}}3, {20}0/{20}2 and {3{\bar 1}}{\bar 1}/{3{\bar 1}}3, at several φ positions. The comparison between the experimental and MULTX simulated scan clearly shows a marked asymmetry observed on the {20}0/{20}2 contributions. An asymmetric peak instead of the simulated dip appears due to the layer Laue secondary beam {20}0 crossing the layer/substrate interface to generate a hybrid peak. The break in the lattice coherence for this heterostructure is shown by the occurrence of an unexpected dip in the layer RS, which does not obey the mirror symmetry.

The phosphate-dependent transition between enzymatically inert dimers into catalytically capable tetramers has long been the accepted mechanism for the glutaminase activation. Here, we demonstrate that activated glutaminase C (GAC) self-assembles into a helical, fiber-like double-stranded oligomer and propose a molecular model consisting of seven tetramer copies per turn per strand interacting via the N-terminal domains. The loop 321LRFNKL326 is projected as the major regulating element for self-assembly and enzyme activation. Furthermore, the previously identified in vivo lysine acetylation (Lys311 in humans, Lys316 in mouse) is here proposed as an important down-regulator of superoligomer assembly and protein activation. Bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide, a known glutaminase inhibitor, completely disrupted the higher order oligomer, explaining its allosteric mechanism of inhibition via tetramer stabilization. A direct correlation between the tendency to self-assemble and the activity levels of the three mammalian glutaminase isozymes was established, with GAC being the most active enzyme while forming the longest structures. Lastly, the ectopic expression of a fiber-prone superactive GAC mutant in MDA-MB 231 cancer cells provided considerable proliferative advantages to transformed cells. These findings yield unique implications for the development of GAC-oriented therapeutics targeting tumor metabolism. Background: GAC supplies for increased metabolic needs of tumors because of exclusive localization and kinetic properties. Results: Higher than tetramer oligomers are the active form in in vitro and in cellular assays. Bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide disrupts oligomers. Conclusion: A novel molecular mechanism for GAC activation is proposed. Significance: The data affect the development of therapies targeting GAC in tumors, with emphasis on allosteric inhibitors.

Leishmania RNA Virus (LRV, Totiviridae) infect Leishmania cells and subvert mice immune response, probably promoting parasite persistence, suggesting significant roles for LRV in host-parasite interaction. Here we describe a new LRV1-4 purification protocol, enabling capsid visualization by negatively stained electron microscopy representing a significant contribution to future LRV investigations.

Cell division in bacteria is regulated by proteins that interact with FtsZ and modulate its ability to polymerize into the Z ring structure. The best studied of these regulators is MinC, an inhibitor of FtsZ polymerization that plays a crucial role in the spatial control of Z ring formation. Recent work established that E. coli MinC interacts with two regions of FtsZ, the bottom face of the H10 helix and the extreme C-terminal peptide (CTP). Here we determined the binding site for MinC on Bacillus subtilis FtsZ. Selection of a library of FtsZ mutants for survival in the presence of Min overexpression resulted in the isolation of 13 Min-resistant mutants. Most of the substitutions that gave rise to Min resistance clustered around the H9 and H10 helices in the C-terminal domain of FtsZ. In addition, a mutation in the CTP of B. subtilis FtsZ also produced MinC resistance. Biochemical characterization of some of the mutant proteins showed that they exhibited normal polymerization properties but reduced interaction with MinC, as expected for binding site mutations. Thus, our study shows that the overall architecture of the MinC-FtsZ interaction is conserved in E. coli and B. subtilis. Nevertheless, there was a clear difference in the mutations that conferred Min resistance, with those in B. subtilis FtsZ pointing to the side of the molecule rather than to its polymerization interface. This observation suggests that the mechanism of Z ring inhibition by MinC differs in both species.

A comprehensive study of pulsed nitriding in AISI H13 tool steel at low temperature (400{\deg}C) is reported for several durations. X-ray diffraction results reveal that a nitrogen enriched compound (Epsilon-Fe2-3N, iron nitride) builds up on the surface within the first process hour despite the low process temperature. Beneath the surface, X-ray Wavelength Dispersive Spectroscopy (WDS) in a Scanning Electron Microscope (SEM) indicates relatively higher nitrogen concentrations (up to 12 at.%) within the diffusion layer while microscopic nitrides are not formed and existing carbides are not dissolved. Moreover, in the diffusion layer, nitrogen is found to be dispersed in the matrix and forming nanosized precipitates. The small coherent precipitates are observed by High-Resolution Transmission Electron Microscopy (HR-TEM) while the presence of nitrogen is confirmed by electron energy loss spectroscopy (EELS). Hardness tests show that the material hardness increases linearly with the nitrogen concentration, reaching up to 14.5 GPa in the surface while the Young Modulus remains essentially unaffected. Indeed, the original steel microstructure is well preserved even in the nitrogen diffusion layer. Nitrogen profiles show a case depth of about ~43 microns after nine hours of nitriding process. These results indicate that pulsed plasma nitriding is highly efficient even at such low temperatures and that at this process temperature it is possible to form thick and hard nitrided layers with satisfactory mechanical properties. This process can be particularly interesting to enhance the surface hardness of tool steels without exposing the workpiece to high temperatures and altering its bulk microstructure., Comment: 16 pages, 12 figures, 65 references, in press