Sintered and 3D-Printed Bulks of MgB2-Based Materials with Antimicrobial Properties.

Pristine high-density bulk disks of MgB2 with added hexagonal BN (10 wt.%) were prepared using spark plasma sintering. The BN-added samples are machinable by chipping them into desired geometries. Complex shapes of different sizes can also be obtained by the 3D printing of polylactic acid filaments embedded with MgB2 powder particles (10 wt.%). Our present work aims to assess antimicrobial activity quantified as viable cells (CFU/mL) vs. time of sintered and 3D-printed materials. In vitro antimicrobial tests were performed against the bacterial strains Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Enterococcus faecium DSM 13590, and Enterococcus faecalis ATCC 29212; and the yeast strain Candida parapsilosis ATCC 22019. The antimicrobial effects were found to depend on the tested samples and microbes, with E. faecium being the most resistant and E. coli the most susceptible.

Antimicrobial Activity of MgB2 Powders Produced via Reactive Liquid Infiltration Method.

We report for the first time on the antimicrobial activity of MgB2 powders produced via the Reactive Liquid Infiltration (RLI) process. Samples with MgB2 wt.% ranging from 2% to 99% were obtained and characterized, observing different levels of grain aggregation and of impurity phases. Their antimicrobial activity was tested against Staphylococcus aureus ATCC BAA 1026, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 10231. A general correlation is observed between the antibacterial activity and the MgB2 wt.%, but the sample microstructure also appears to be very important. RLI-MgB2 powders show better performances compared to commercial powders against microbial strains in the planktonic form, and their activity against biofilms is also very similar.

Bridging Solution and Solid-State Chemistry of Dicyanoaurate: The Case Study of Zn-Au Nucleation Units.

The behavior in solution of the dicyanoaurate anion in the presence of other metal centers has so far been little explored, despite its importance in material science. The design and synthesis of systems with controlled coordination behavior, using chelating ligands and ZnII, has allowed us to detect self-assembly and oligomerization in solution. This phenomenon has been studied with 13C and 1H NMR, absorption and emission UV-vis spectroscopy, ESI-MS, and XAS at both the Au L3-edge and Zn K-edge: all of these techniques confirm the presence of Au-Zn aggregation products. These fragments, resembling structural units in the solid state, reveal that coordination of dicyanoaurate to free sites around metal centers can occur at a lower concentration than those at which crystals start to form and at which aurophilic interactions are observed, forming the connection between solution species and solid-state architectures.

Direct-Write X-ray Nanopatterning: A Proof of Concept Josephson Device on Bi2Sr2CaCu2O8+δ Superconducting Oxide.

We describe the first use of a novel photoresist-free X-ray nanopatterning technique to fabricate an electronic device. We have produced a proof-of-concept device consisting of a few Josephson junctions by irradiating microcrystals of the Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide with a 17.6 keV synchrotron nanobeam. Fully functional devices have been obtained by locally turning the material into a nonsuperconducting state by means of hard X-ray exposure. Nano-XRD patterns reveal that the crystallinity is substantially preserved in the irradiated areas that there is no evidence of macroscopic crystal disruption. Indications are that O ions have been removed from the crystals, which could make this technique interesting also for other oxide materials. Direct-write X-ray nanopatterning represents a promising fabrication method exploiting material/material rather than vacuum/material interfaces, with the potential for nanometric resolution, improved mechanical stability, enhanced depth of patterning, and absence of chemical contamination with respect to traditional lithographic techniques.

Bimolecular Homolytic Substitutions at Nitrogen: An Experimental and Theoretical Study on the Gas-Phase Reactions of Alkyl Radicals with NF3.

The X-ray irradiation of binary mixtures of alkyl iodides R-I (R=CH3 , C2 H5 , or i-C3 H7 radicals) and NF3 produces R-NF2 and R-F. Based on calculations performed at the CCSD(T), MRCI(SD+Q), G3B3, and G3 levels of theory, the former product arises from a bimolecular homolytic substitution reaction (SH 2) by the alkyl radicals R, which attack the N atom of NF3 . This mechanism is consistent with the suppression of R-NF2 by addition of O2 (an efficient alkyl radical scavenger) to the reaction mixture. The R-F product arises from the attack of R to the F atom of NF3 , but additional contributing channels are conceivably involved. The F-atom abstraction is, indeed, considerably more exothermic than the SH 2 reaction, but the involved energy barriers are comparable, and the two processes are comparably fast.

Biostimulants derived from organic urban wastes and biomasses: An innovative approach.

We used humic and fulvic acids extracted from digestate to formulate nanohybrids with potential applications in agronomy. In order to obtain a synergic co-release of plant-beneficial agents, we functionalized with humic substances two inorganic matrixes: hydroxyapatite (Ca10(PO4)6(OH)2, HP) and silica (SiO2) nanoparticles (NPs). The former is a potential controlled-release fertilizer of P, and the latter has a beneficial effect on soil and plants. SiO2 NPs are obtained from rice husks by a reproducible and fast procedure, but their ability to absorb humic substances is very limited. HP NPs coated with fulvic acid are instead a very promising candidate, based on desorption and dilution studies. The different dissolutions observed for HP NPs coated with fulvic and humic acids could be related to the different interaction mechanisms, as suggested by the FT-IR study.

HgBrI: a possible tecton for NLO molecular materials?

Mixed mercury(II) halogenides have been known for a long time as good NLO (non-linear optic) materials. The NLO properties are due to the halogen disposition in the solid state and the electron distribution among the bonds formed by soft elements. We investigated the possibility of using HgBrI as a asymmetric tecton in the preparation of noncentrosymmetric crystalline compounds, by exploiting the coordinating power of Hg(II) toward N-donor ligands, and seven coordination complexes have been obtained. To unravel the nature of these complex systems we combined the data from different techniques: Raman spectroscopy, SC-XRD and Second Harmonic Generation, supported by a periodic DFT computational approach. In HgBrI crystalline products with low symmetry, the presence of substitutional disorder leads to a lack of the inversion center conferring NLO activity, which is absent in analogous complexes of Hg(II) halogenides. These results indicate HgBrI as an interesting tecton to obtain metallorganic NLO materials.

Metallophilic interactions in silver(I) dicyanoaurate complexes.

This manuscript reports four new gold(I)-silver(I) complexes with 2-(2-pyridyl)-1,8-naphthyridine (pyNP) and terpyridine (terpy) as ancillary ligands, having formulae [Ag(pyNP)(Au(CN)2)]2 (1), [Ag2Au2(µ-CN)2(CN)2(pyNP)2] (2), [Ag2Au(µ-CN)2(terpy)2][Au(CN)2] (3) and [Ag4Au4(µ-CN)8(terpy)2(py)] (4). Complexes 1 and 2 are structural isomers obtained from different solvents. The Au(CN)2- anion is not coordinated and establishes intramolecular Au⋯Ag,Ag interactions in 1. In contrast, it is monocoordinated to silver atoms via a CN fragment in compound 2 and no metallophilic interaction is observed. In compound 3, one Au(CN)2 anion bridges two Ag(terpy) fragments. In this complex an infinite array of gold atoms is found, exhibiting aurophilic interactions of 3.415 Å. In complex 4 the 3D architecture observed in the crystal packing is driven by Au⋯Au and Au⋯Ag metallophilic interactions. All compounds have been structurally and vibrationally characterized to better understand the crystal forces. In addition, a solution chemistry study in different solvents by ESI-MS spectrometry was performed to comprehend the speciation and solvent effects. Finally, DFT calculations were carried out to analyze the Ag⋯Au interactions and also the π-stacking interactions that are relevant in the crystal packing of some structures. Special attention has been paid to the bifurcated nature of the Au⋯Ag,Ag interactions in compound 1 that has been analyzed theoretically using the quantum theory of atoms-in-molecules (QTAIM) and the Natural Bond Orbital (NBO) computational tools.

Xenon-nitrogen chemistry: gas-phase generation and theoretical investigation of the xenon-difluoronitrenium ion F2N-Xe+.

The xenon-difluoronitrenium ion F(2)N-Xe(+) , a novel xenon-nitrogen species, was obtained in the gas phase by the nucleophilic displacement of HF from protonated NF(3) by Xe. According to Møller-Plesset (MP2) and CCSD(T) theoretical calculations, the enthalpy and Gibbs energy changes (ΔH and ΔG) of this process are predicted to be -3 kcal mol(-1) . The conceivable alternative formation of the inserted isomers FN-XeF(+) is instead endothermic by approximately 40-60 kcal mol(-1) and is not attainable under the employed ion-trap mass spectrometric conditions. F(2)N-Xe(+) is theoretically characterized as a weak electrostatic complex between NF(2)(+) and Xe, with a Xe-N bond length of 2.4-2.5 Å, and a dissociation enthalpy and free energy into its constituting fragments of 15 and 8 kcal mol(-1), respectively. F(2)N-Xe(+) is more fragile than the xenon-nitrenium ions (FO(2)S)(2)NXe(+), F(5)SN(H)Xe(+), and F(5)TeN(H)Xe(+) observed in the condensed phase, but it is still stable enough to be observed in the gas phase. Other otherwise elusive xenon-nitrogen species could be obtained under these experimental conditions.

Positive ion chemistry of SiH4/NF3 gaseous mixtures studied by ion trap mass spectrometry.

The positive ion chemistry occurring in silane/nitrogen trifluoride gaseous mixtures has been investigated by ion trap mass spectrometry. Reaction sequences and rate constants have been determined for the processes involving the primary ions SiH(n)(+) (n = 0-3) and NF(x)(+) (x = 1-3) and the secondary ions obtained from their reactions with SiH(4) and NF(3). The SiH(n)(+) efficiently react with NF(3) and undergo cascades of abstraction and scrambling reactions which form the fluorinated and perfluorinated cations SiHF(m)(+) (m = 1, 2), SiH(2)F(+) and SiF(x)(+) (x = 0-3). Fluorinated Si(2)- clusters such as Si(2)H(2)F(+), Si(2)H(3)F(+) and Si(2)H(5)F(+) were also observed. The reaction of both SiH(3)(+) and SiH(2)F(+) with NF(3) produces the elusive fluoronitrenium ion NHF(+). Any NF(x)(+) reacts with SiH(4) mainly by charge transfer. Additional ionic products are, however, observed which suggest intimate reaction complexes. Worth mentioning is the formation of SiNH(2)(+) from the reaction of both NF(+) and NHF(+) with SiH(4). The primary ions NF(2)(+) and SiH(2)(+) are also "sink" species in our observed chemistry.

Gas-phase ion chemistry of GeH(4)/B(2)H(6) mixtures.

The gas phase ion-molecule reactions in positively and negatively ionized germane/diborane mixtures have been studied by ion trap mass spectrometry. Reaction sequences and rate constants for the most interesting processes have been determined. In positive ionization, formation of Ge-B bonds exclusively occurs through condensation reactions of B(n)H(m)(+) ions with germane, followed by H(2) or BH(3) loss. No reactions of ions from germane with B(2)H(6) were observed under the experimental conditions used here. In negative ionization, the Ge(n)H(m)(-) (n = 1, 2) ion families react with diborane to yield the Ge(n)B(p)H(q)(-) (p = 1, 2) ions, again via dehydrogenation and BH(3) loss, while diborane anions proved to be unreactive. In both positive and negative ionization, Ge-B ions reach appreciable abundances. The present results afford fundamental information about the intrinsic reactivity of gas-phase ions and provide valuable indications about the first nucleation steps ultimately leading to amorphous Ge and B-doped semiconductor materials by chemical vapor deposition methods.

Maskless X-Ray Writing of Electrical Devices on a Superconducting Oxide with Nanometer Resolution and Online Process Monitoring.

X-ray nanofabrication has so far been usually limited to mask methods involving photoresist impression and subsequent etching. Herein we show that an innovative maskless X-ray nanopatterning approach allows writing electrical devices with nanometer feature size. In particular we fabricated a Josephson device on a Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide micro-crystal by drawing two single lines of only 50 nm in width using a 17.4 keV synchrotron nano-beam. A precise control of the fabrication process was achieved by monitoring in situ the variations of the device electrical resistance during X-ray irradiation, thus finely tuning the irradiation time to drive the material into a non-superconducting state only in the irradiated regions, without significantly perturbing the crystal structure. Time-dependent finite element model simulations show that a possible microscopic origin of this effect can be related to the instantaneous temperature increase induced by the intense synchrotron picosecond X-ray pulses. These results prove that a conceptually new patterning method for oxide electrical devices, based on the local change of electrical properties, is actually possible with potential advantages in terms of heat dissipation, chemical contamination, miniaturization and high aspect ratio of the devices.

Effect of Al and Ca co-doping, in the presence of Te, in superconducting YBCO whiskers growth.

High-Tc superconducting cuprates (HTSC) such as YBa2Cu3O7 - x (YBCO) are promising candidates for solid-state THz applications based on stacks of intrinsic Josephson junctions (IJJs) with atomic thickness. In view of future exploitation of IJJs, high-quality superconducting YBCO tape-like single crystals (whiskers) have been synthesized from Ca-Al-doped precursors in the presence of Te. The main aim of this paper is to determine the importance of the simultaneous use of Al, Te and Ca in promoting YBCO whiskers growth with good superconducting properties (Tc = 79-84 K). Further, single-crystal X-ray diffraction (SC-XRD) refinements of tetragonal YBCO whiskers (P4/mmm) are reported to fill the literature lack of YBCO structure investigations. All the as-grown whiskers have also been investigated by means of X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Our results demonstrate that the interplay of Ca, Te and Al elements is clearly necessary in order to obtain superconducting YBCO whiskers. The data obtained from SC-XRD analyses confirm the highly crystalline nature of the whiskers grown. Ca and Al enter the structure by replacing the Y and the octahedral coordinated Cu1 site, respectively, as in other similar orthorhombic compounds, while Te does not enter the structure of whiskers but its presence in the precursor is essential to the growth of the crystals.

Gas-phase ion chemistry in XH4--C3H4--ZH3 (X==Si, Ge; Z==N, P) mixtures.

The gas-phase ion chemistry of silane-allene-ammonia, germane-allene (or propyne)-ammonia (or phosphine) systems was studied by ion trap mass spectrometry. Reaction sequences were determined and rate constants were measured for the main processes observed. The mixture containing silane displays higher reactivity with respect to that with germane. Comparison with analogous systems provides useful information about the reactivity of different hydrocarbon molecules and the different affinities of silicon and germanium towards nitrogen and phosphorus. The most interesting product ions observed are those containing Si (or Ge), C and N (or P) elements together, as these ion species may be considered precursors of doped amorphous carbides, which are widely used in semiconductor devices.

Gas-phase ion chemistry of the allene-phosphine and silane-allene-phosphine systems.

The gas-phase ion chemistry of allene-phosphine and silane-allene-phosphine mixtures was studied by ion trap mass spectrometry. Rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. For the binary mixture, the highest yield of C- and P-containing ions is obtained with a 1 : 1 partial pressure ratio among the reagents. In the ternary mixture, formation of ion species containing Si, C and P together is mainly achieved in reactions of Si/P ions with allene, with a lower contribution from reactions of Si/C and C/P ions with phosphine and silane, respectively. The formation of ternary ion clusters is related to their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained by deposition from properly activated silane-allene-phosphine mixtures.

Gas-phase ion chemistry in the ternary silane-propyne-phosphine system.

The gas-phase ion chemistry of propyne-phosphine and silane-propyne-phosphine mixtures was studied by ion trap mass spectrometry. For the binary mixture, the effect of different partial pressures of the reagents on the yield of C and P-containing ions was evaluated. Reaction sequences and rate constants were determined and reaction efficiencies were calculated from comparison of experimental and collisional rate constants. In the ternary silane-propyne-phosphine systems, the reaction pathways leading to formation of Si(m)C(n)P(p)H(q) (+) ions were determined and the rate constants of the most important steps were measured. For some ion species, selected by double isolation procedures (MS/MS), the low ion abundances prevented determination of the reaction rate constants. Si, C and P-containing ions are mainly produced in reactions of Si(m)P(p)H(q) (+) ions with propyne, while the reactivity of the Si(m)C(n)H(q) (+) ions towards PH(3) and of the C(n)P(p)H(q) (+) ions towards SiH(4) is very low. The formation of hydrogenated Si--C--P ions is interesting for their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained in a single step, by deposition from properly activated silane-propyne-phosphine mixtures.

Gas-phase ion chemistry in the ternary SiH(4)-C(3)H(6)-PH(3) system.

Propene-phosphine and the silane-propene-phosphine gaseous mixtures were studied by ion trap mass spectrometry. For the binary mixture the variation of ion abundances under different partial pressures and the mechanisms of ion-molecule reactions are reported. Moreover, the rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-phosphine mixture the mechanisms of formation of Si(m)C(n)P(p)H(+)(s) ion clusters were elucidated, but the complexity of the system and the low abundances of the ions usually isolated by successive steps prevented the determination of rate constants. The hydrogenated ternary ions are mainly formed by reactions of Si(r)P(s)H(+)(t) ions with propene, whereas a minor contribution comes from reactions of Si(m)C(n)H(+)(p) ions with phosphine. The C(v)P(w)H(+)(z) ions show very low reactivity with silane. The formation processes of these species are discussed in relation to their possible role as precursors of amorphous silicon carbides doped with phosphorus obtained by deposition from properly activated silane-propene-phosphine mixtures.

Gas-phase ion chemistry in germane-propane and germane-propene mixtures.

Germane-propane and germane-propene gaseous mixtures were studied by ion trap mass spectrometry. Variations of ion abundances observed under different partial pressure ratios and mechanisms of ion-molecule reactions elucidated by multiple isolation steps are reported. In addition, the rate constants for the main reactions were experimentally determined and compared with the collisional rate constants to obtain the reaction efficiencies. The yield of ions containing both Ge and C atoms is higher in the germane-propene than in the germane-propane system. In the former mixture, chain propagation takes place starting from germane ions reacting with propene and proceeds with the formation of clusters such as Ge(2)C(4)H(n) (+) and Ge(3)CH(n) (+).

Gas-phase ion chemistry in the ternary SiH4-C3H6-NH3 system.

The gas-phase ion chemistry of propene-ammonia and silane-propene-ammonia mixtures was studied by ion trap mass spectrometry. As far as the binary mixture is concerned, the effect of different molar ratios of the reactants on the trend of ion species formed was evaluated, the ion-molecule reaction processes were identified and the rate constants for the main processes were measured. The results were compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-ammonia mixture the mechanisms of formation of Si(m)C(n)N(p)H(q)(+) clusters were elucidated and the rate constants of the most important steps were measured. For some species, selected by double isolation (MS/MS), the low abundance of the ions allowed us to determine the reaction paths but not the rate constants. Ternary ions are mainly formed by reactions of Si(m)C(n)H(q)(+) ions with ammonia, whereas a minor contribution comes from reactions of Si(m)N(p)H(q)(+) ions with propene. On the other hand, the C(n)N(p)H(q)(+) ions showed a very low reactivity and no step leading to ternary ion species was identified. The formation of hydrogenated ternary ions with Si, C and N has a basic importance in relation to their possible role as precursors of amorphous silicon carbides doped with nitrogen obtained by deposition from silane-propene-ammonia mixtures properly activated.

A quadrupole ion trap and Fourier transform ion cyclotron resonance concerted study of the kinetics of an ion/molecule association reaction: a chemometric approach.

The effects of different experimental parameters on rate constant measurements performed by mass spectrometry were investigated with a two-level fractional factorial design. This chemometric technique allows a study of the effects of selected factors and of their interactions on the response of an experiment by performing a limited number of analyses. The selected factors were: sample pressure, energy of the ionising electrons, reaction time and ionisation time. In this work, two mass spectrometric techniques were compared: Fourier transform ion cyclotron resonance (FT-ICR) and quadrupole ion trap (QIT) mass spectrometries. Experimental results were obtained from a study of a reaction system consisting of the condensation between triethylphosphite and its fragment ion (CH(3)CH(2)O)(2)P(+). Apparent bimolecular rate constants are clearly larger when determined by QIT than by FT-ICR, because of collisional stabilisation of the adduct ion by helium buffer gas introduced in the QIT spectrometer. However, the QIT rate constant extrapolated to zero helium pressure is almost identical to the FT-ICR value; this supports the conclusion regarding the buffer gas effect. Minor effects evidenced by the chemometric method were attributed to the sample pressure and to the reaction time.