General Stoichiometry Research Articles

Solid-state reaction synthesis and chemical stability studies in Nd-doped zirconolite-rich ceramics

In this study, Nd-bearing zirconolite-rich ceramics were prepared by solid-state reaction process using CaF2, ZrO2, Ti, TiO2, Fe2O3 and Nd2O3 as the raw materials. Neodymium was used as trivalent actinide surrogate and designed to substitute the Ca and Zr sites of zirconolite with general stoichiometry of Ca1−xZr1−xNd2xTi2O7 (0 ≤ x ≤ 0.3). Density of Fe-Nd-0 sample reaches a maximum value of 4.13 g/cm2 after being sintered at 1325 °C for 42 h. Three major phases, namely zirconolite, perovskite and pseudobrookite, are observed in all these samples. The EDX result shows that Nd2O3 can be successfully incorporated into the lattice structure of the prepared zirconolite-rich minerals and replace the Ca sites of zirconolite and perovskite with Fe3+ as the charge-compensating ion. Furthermore, the thermal conductivities are all in the range of 1.51–1.67 W/(m·K). The normalized elemental leaching rates of Ca and Nd in the Fe-Nd-0.2 sample keep in low values of 6.20 × 10−2 and 4.86 × 10−4 g/(m2·d) after 42 d.

Complex Portal - A Unifying Protein Complex Database

The EBI Complex Portal is a manually curated, unifying resource of macromolecular complexes from model organisms. Each entry has a unique and stable identifier and links participating molecule to their unique reference database (UniProt, ChEBI and RNAcentral). Each complex is annotated with information about their stoichiometry, topology and structural assembly, function, complex-centric Gene Ontology terms and evidence codes. Complexes are extensively cross-referenced to ChEMBL, EMDB, Experimental Factor Ontology, Intenz, MatrixDB, the PDB and Reactome. Bespoke visualisation tools for the general topology and stoichiometry, crystal structures, molecular reactions and gene expression data are provided. All data is open-source and available in PSI-MI xml2.5 and xml3.0 standard formats, MI-JSON and tab-delineated ComplexTAB format.

Atomic Layer Deposition of Rhenium–Aluminum Oxide Thin Films and ReOx Incorporation in a Metal–Organic Framework

Methyltrioxorhenium (ReO3Me) is introduced as the first rhenium atomic layer deposition (ALD) precursor and used to grow rhenium-aluminum oxide thin films in combination with trimethylaluminum (TMA-AlMe3). The growth rate of the smooth Re-Al oxide films, with general stoichiometry RexAlyO3x, has been monitored by in situ quartz crystal microbalance (QCM) and ex situ ellipsometry, and found to be 3.2 Å/cycle. X-ray photoelectron spectroscopy (XPS) revealed the mixed valent composition of the film with Re(III) species being the main component. In addition, ReO3Me has been successfully used to deposit rhenium oxide in NU-1000, a mesoporous zirconium-based metal-organic framework (MOF). The metalated MOF was found to retain porosity and crystallinity and to be catalytically active for ethene hydrogenation.

Influences of Cerium Addition on the Structural and Superconducting Properties with Pb and Pb-free Bi2Sr2Ca2Cu3Oδ System

In this study, the thermal, structural and superconducting properties with lead and lead-free cerium added Bi 2 Sr 2 Ca 2 Cu 3 O δ superconducting system have been investigated. Cerium-added superconductors with the general stoichiometry of Bi 2-x Pb x Sr 2 Ca 2 Cu 3 Ce y O δ (x = 0 and 0.4 and y = 0, 0.1, 0.2 and 0.4) were prepared by the conventional solid state synthesis technique. The materials are characterized by DTA/TGA, XRD, SEM, EDX and R-T measurements. Although the desired phase is the Bi-2223 phase in the manufactured materials, it is observed that Bi-2212 phase predominates in some materials. Especially while being the Bi-2212 phase in Pb-free samples, the main phase is relatively Bi-2223 phase in Pb containing samples. Consequently, critical temperature values have also decreased and transition behavior has been observed in two steps.

Synthesis, spectroscopic, and theoretical studies of tin(II) complexes with biologically active Schiff bases derived from amino acids

Abstract New tin(II) complexes of general stoichiometry [Sn(L)2] with bidentate ligand, derived from amino acids with isatin, 5-chloroisatin have been synthesized. It is characterized by elemental analyses, molar conductance measurements, and molecular weight determinations. Bonding of these complexes is discussed in terms of their UV-visible, infrared, and nuclear magnetic resonance (1H, 13C, and 119Sn NMR) spectroscopic studies. The ligands act as bidentate towards metal ions, via the azomethine nitrogen and deprotonated oxygen of the respective ligands. The bond length, bond angles, highest occupied molecular orbital, lowest unoccupied molecular orbital, chemical hardness, global softness, and the lowest energy model structure of the complexes have been determined by density functional theory (DFT) calculations at B3LYP/LanL2DZ level. A few representative ligands and their tin complexes have been screened for their antibacterial activities and found to be active in this respect.

Steady states and stability in metabolic networks without regulation

Metabolic networks are often extremely complex. Despite intensive efforts many details of these networks, e.g., exact kinetic rates and parameters of metabolic reactions, are not known, making it difficult to derive their properties. Considerable effort has been made to develop theory about properties of steady states in metabolic networks that are valid for any values of parameters. General results on uniqueness of steady states and their stability have been derived with specific assumptions on reaction kinetics, stoichiometry and network topology. For example, deep results have been obtained under the assumptions of mass–action reaction kinetics, continuous flow stirred tank reactors (CFSTR), concordant reaction networks and others. Nevertheless, a general theory about properties of steady states in metabolic networks is still missing. Here we make a step further in the quest for such a theory. Specifically, we study properties of steady states in metabolic networks with monotonic kinetics in relation to their stoichiometry (simple and general) and the number of metabolites participating in every reaction (single or many).Our approach is based on the investigation of properties of the Jacobian matrix. We show that stoichiometry, network topology, and the number of metabolites that participate in every reaction have a large influence on the number of steady states and their stability in metabolic networks. Specifically, metabolic networks with single-substrate–single-product reactions have disconnected steady states, whereas in metabolic networks with multiple-substrates–multiple-product reactions manifolds of steady states arise. Metabolic networks with simple stoichiometry have either a unique globally asymptotically stable steady state or asymptotically stable manifolds of steady states. In metabolic networks with general stoichiometry the steady states are not always stable and we provide conditions for their stability. In order to demonstrate the biological relevance we illustrate the results on the examples of the TCA cycle, the mevalonate pathway and the Calvin cycle.

Enhanced high-rate performance of manganese substituted Na3V2(PO4)3/C as cathode for sodium-ion batteries

Composites with general stoichiometry Na3V2−xMnx(PO4)3/C (0 ≤ x ≤ 0.7) have been evaluated as cathode materials in sodium-ion batteries. The sol-gel method here employed favors the formation of a homogeneously dispersed carbon conductive phase. XRD patterns show a limited solubility of Mn in the NASICON structure. The substitution of 0.3–0.5 manganese per formula unit promotes the formation of a homogeneous composite. XPS spectra evidence an effective substitution of V3+ by Mn3+. Galvanostatic cycling of sodium half-cell reveal a plateau at 3.4 V ascribable to the V4+/V3+ redox couple. A small and reversible plateau at ca. 3.85 V is also observed for x ≥ 0.3, and ascribed to the activation of the V5+/V4+ redox couple, according to XPS spectroscopy. Ex-situ XRD patterns NayV1.7Mn0.3(PO4)3 evidence the occurrence of a reversible two phase mechanism of sodium insertion. An optimized performance is achieved for Na3V1.7Mn0.3(PO4)3/C, reaching a capacity value of 104 mA h g−1 at C/2 and 92 mA h g−1 at 2C. It is ascribed to the optimal morphology, leading to low internal resistance and favorable electrode-electrolyte interphase.

Structural systematics of Ge substitution in primitive pyroxenes

Pyroxenes of general stoichiometry Mg(GexSi1−x)O3 were encountered in attempts to synthesise Ge-substituted talcs at 0.2 GPa, 650–700 °C. Orthopyroxenes (Pbca) of compositions x = 0.21, 0.30, and 0.34 were identified, and also a P21/c clinopyroxene of composition x = 0.63, and C2/c clinopyroxenes of compositions x = 0.91 and 1. End-member clinoenstatite MgSiO3-P21/c synthesised at 16 GPa, 1300 °C and transformed from C2/c was also included in the study. Crystal structure refinements using single-crystal XRD data showed that unit-cell parameters vary linearly with Si–Ge for the Pbca and P21/c pyroxenes, both of which have two symmetrically non-equivalent tetrahedral chains. Refinement of Si–Ge occupancies at tetrahedral sites showed that the two chains of all primitive pyroxenes have very different compositions, with XGe(TB) ≫ XGe(TA). This difference arises from the greater flexibility of the B-chain to rotate in response to tetrahedral expansion due to increasing Ge content. The TA-M2 shared polyhedral edge imposes significant constraints on the flexibility of the A-chain, which can accommodate much less Ge than the B-chain. Linear trends of cell parameters, site occupancies, and structural parameters for the primitive pyroxenes, when extrapolated to published data for MgGeO3–Pbca, extend across the entire Si–Ge join.

Synthesis, characterization and anti-fungal evaluation of Ni(II) and Cu(II) complexes with a derivative of 4-aminoantipyrine

Transition metal complexes of Ni(II) and Cu(II) metal ions with the general stoichiometry [M(L)X]X and [M(L)SO4], where M=Ni(II) and Cu(II), L=(1E)-N-((5-((E)-(2,3-dimethyl-1-phenyl-4-pyrazolineimino)methyl)thiophen-2-yl)methylene)-2,3-dimethyl-1-phenyl-4-pyrazolineamine and X=Cl−, NO3− and SO42−, have been synthesized and characterized. The synthesized ligand and metal complexes were characterized by 1H NMR, IR, mass spectrometry, UV–Vis spectra and EPR. In molecular modelling, the geometries of the Schiff's base and metal complexes were fully optimized with respect to the energy using the 6-31g(d,p) basis set. The nickel(II) complexes were found to have octahedral geometry, whereas the copper(II) complexes were of tetragonal geometry. The covalency factor (β) and orbital reduction factor (k) suggest the covalent nature of the complexes. To develop broad spectrum new molecules against seed-borne fungi, the minimum inhibitory concentration (MIC) of the ligand and its metal complexes was evaluated by the serial dilution method.

Phase evolution and microstructure studies on Nd3+ and Ce4+ co-doped zircon ceramics

A series compositions with general stoichiometry as Zr1−x−y(NdxCey)SiO4−x/2 (0≤x, y≤0.1) have been obtained by simultaneous substitution of Nd3+ and Ce4+ for Zr4+ in ZrSiO4 structure. The effects of Nd and Ce content on the phase evolution and microstructure of the ceramics were investigated systematically. The results show that the samples co-doped with total content of Nd3+ (x) and Ce4+ (y)<0.04 are single zircon phase. However, when the compositions co-doped with total content of Nd3+ (x) and Ce4+ (y)≥0.04 exhibit coexistence of zircon and (Nd,Ce)2Si2O7 phase. This demonstrates that the solubility of Nd3+ and Ce4+ in zircon structure is around 0.04mol per mol of zircon. In addition, it is found that the densities of the samples increase with increasing total content of Nd3+ and Ce4+. These results indicate that zircon ceramics are promising candidate for the immobilization of trivalent and tetravalent actinides.

Apparent kinetics of a gas–liquid–liquid system of Bunsen reaction with iodine-toluene solution for hydrogen production through H2S splitting cycle

A chemical splitting cycle of H2S to produce H2 for sustainable oil sands bitumen upgrading was recently developed in our research group which includes three reactions (Wang, H. Hydrogen production from a chemical cycle of H2S splitting. International Journal of Hydrogen Energy 2007; 32:3907–14):H2S + H2SO4 → S + SO2 + 2H2O (H2S Oxidation) (1)2H2O + I2+SO2 → H2SO4 + 2HI (Bunsen Reaction) (2)2HI → H2 + I2 (HI decomposition) (3)With iodine provided by iodine-toluene solution, the Bunsen reaction can be conducted at room temperature. Compared with the General Atomics stoichiometry and operation condition for the sulfur–iodine cycle, this modification can minimize or avoid problems such as side reactions, corrosion and iodine deposition. In addition, it reduces the unnecessary transportation of the excessive cycling agents in the cycle. This work studies the apparent reaction rate of the Bunsen reaction in a gas–liquid–liquid multiphase system resulted from the presence of toluene in a closed, fixed-volume batch reactor using the initial rate analysis method. The reaction rate was found to be the first order with respect to SO2 and I2, respectively. The temperature effect on the reaction rate showed activation energy of 6.02 kJ/mol, which suggests that the rate-controlling step of the Bunsen reaction in the gas–liquid–liquid system is the step of SO2 absorption into the liquid phases. The variation of operating conditions including toluene/water volume ratio, agitation speed, and temperature confirmed the mass transfer rate-limiting step.

Preparation and heavy-ion irradiation effects of Gd2CexZr2−xO7 ceramics

A number of compositions with the general stoichiometry of Gd2CexZr2−xO7 (0 ≤ x ≤ 2) ceramics have been synthesized and received irradiation tests at room temperature with Xe20+ ions in a broad fluence range.

Structural study of new cytotoxic heteroleptic Copper (II) complexes

The widespread success of Cisplatin in the treatment of several neoplasias has arisen the interest in coordination compounds as drugs for the treatment of cancer. In the search for new compounds with antitumor activity, copper coordination complexes are being studied by our group. This work presents the synthesis and structural characterization of four new copper complexes with general stoichiometry [Cu(L-dipeptide)(phen)]·nH2O and their cytotoxicity against tumor cell lines. Single crystal X-ray diffraction experiments show that the copper ion is situated in a distorted squared pyramidal environment. The phen ligand is perpendicular to the plane defined by the coordinated dipeptide, therefore exposed and potentially available for interaction with biological molecules, e.g. DNA. The availability of the phen ligand and the physico-chemical properties of the complexes are modulated by the dipeptide. Complementary techniques (elemental analysis, infrared and UV-vis spectroscopies) were used to further characterize the complexes in solid state and aqueous solution, confirming that the coordination is maintained in solution. Lipophilicity and DNA binding constants were also measured, being able to discriminate between the behavior of even the complexes containing the ala-phe and phe-ala dipeptide. All the complexes induce cell death in the cell lines of human cervical adenocarcinoma, human metastatic breast adenocarcinoma and human lung epithelial carcinoma. Among the six complexes studied, [Cu(ala-phe)(phen)] presents the lowest half maximal inhibitory concentration (IC50) values. In an attempt to increase the activity, studies are presently being carried out using 2,9-dimethyl-10-phenanthroline. X-ray diffraction studies on the latter show slight deviations in the coordination geometries and different results are expected in their biological activities. Acknoledgements: CSIC, CAPES-UdelaR, PEDECIBA.

Phase evolution and microstructural studies in CaZrTi2O7 (zirconolite)–Sm2Ti2O7 (pyrochlore) system

From the characterization of a series compositions with general stoichiometry as Ca 1− x Zr 1− x Sm 2 x Ti 2 O 7 (0.00 ≤ x ≤ 1.00), the phase evolution between zirconolite (CaZrTi 2 O 7 ) and pyrochlore type Sm 2 Ti 2 O 7 has been elucidated. All the compositions were prepared by high temperature solid state reaction and characterized by powder X-ray diffraction (XRD) and electron probe for microanalyses (EPMA). Three major phase fields, namely two layer (2-M) or four layer (4-M) monoclinic zirconolite and cubic pyrochlore structure types were observed in this system. In addition, a feeble amount of perovskite type phase is found to coexist with zirconolite phase. 4-M zirconolite phase is observed as single phase field at the composition with x = 0.30 and 0.35, while cubic pyrochlore phase is observed as single phase at the compositions with x ≥ 0.60. Further, the composition and microstructure of coexisting phases are verified by back scattered electron image and EPMA studies.

Synthesis, structural characterization and cytotoxic activity of ternary copper(II)–dipeptide–phenanthroline complexes. A step towards the development of new copper compounds for the treatment of cancer

In the search for new compounds with antitumor activity, coordination complexes with different metals are being studied by our group. This work presents the synthesis and characterization of six copper complexes with general stoichiometry [Cu(L-dipeptide)(phen)]·nH2O (were phen=1,10-phenanthroline) and their cytotoxic activities against tumor cell lines. To characterize these systems, analytical and spectroscopic studies were performed in solid state (by UV–visible, IR, X-ray diffraction) including the crystal structure of four new complexes (of the six complexes studied): [Cu(Ala-Phe)(phen)]·4H2O, [Cu(Phe-Ala)(phen)]·4H2O, [Cu(Phe-Val)(phen)]·4.5H2O and [Cu(Phe-Phe)(phen)]·3H2O. In all of them, the copper ion is situated in a distorted squared pyramidal environment. The phen ligand is perpendicular to the dipeptide, therefore exposed and potentially available for interaction with biological molecules. In addition, for all the studied complexes, structural information in solution using EPR and UV–visible spectroscopies were obtained, showing that the coordination observed in solid state is maintained. The lipophilicity, DNA binding and albumin interaction were also studied. Biological experiments showed that all the complexes induce cell death in the cell lines: HeLa (human cervical adenocarcinoma), MCF-7 (human metastatic breast adenocarcinoma) and A549 (human lung epithelial carcinoma). Among the six complexes, [Cu(Ala-Phe)(phen)] presents the lowest IC50 values. Taken together all these data we hypothesize that [Cu(Ala-Phe)(phen)] may be a good candidate for further studies in vivo.

High reversible sodium insertion into iron substituted Na1+xTi2−xFex(PO4)3

Current research trends on energy storage have given new impetus to the development of sodium-ion batteries. In this context, titanium phosphates with a NASICON-related structure are known to provide a stable crystal structure for sodium mobility. With adequate redox centers, these materials are studied here as attractive cathodes vs. sodium. Powdered solids of general stoichiometry Na1+xTi2−xFex(PO4)3 (0 ≤ x ≤ 0.8) were obtained and electrochemically tested. The structural modifications induced by the substitution of Ti4+ by Fe3+ were analyzed by X-ray diffraction revealing an anisotropic change of the unit cell parameters. A continuous voltage decrease is observed between 2.6 and 2.0 V in the iron containing samples, which was ascribed to the contribution of the Fe3+/Fe2+ redox couple, as determined by 57Fe Mössbauer spectroscopy. A detailed analysis of this region revealed the occurrence of local orderings of inserted sodium ions. The introduction of low contents of iron (x = 0.2) involved a capacity value of 130.2 mA h g−1 after the first discharge and a good capacity retention after an extended cycling. It was correlated to the low internal resistance values for this composition.

Phase Evolution and Microstructural Studies in CaZrTi2O7–Nd2Ti2O7 System

A series of compositions with general stoichiometry Ca1−xZr1−xNd2xTi2O7 has been prepared by high‐temperature solid‐state reaction of component oxides and characterized by powder X‐ray diffraction and electron probe for microanalyses (EPMA). The phase fields in CaZrTi2O7–Nd2Ti2O7 system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zirconolite, cubic perovskite, cubic pyrochlore, and monoclinic Nd2Ti2O7 structure types are observed in this system. The 4M‐polytype of zirconolite structure is stabilized by substitution of Nd3+ ion. The addition of Nd3+ ions form a cubic perovskite structure‐type phase and thus observed in all the compositions with 0.05 ≤ x ≤ 0.80. Cubic pyrochlore structure‐type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤ x ≤ 0.90. Only a subtle amounts of Ca2+ and Zr4+ are incorporated into the perovskite‐type Nd2Ti2O7 structure. EPMA analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have Nd3+‐rich compositions.

A Closer Look at the Relationships between College Students’ Cognitive Abilities and Problem Solving in Stoichiometry

Several cognitive abilities were investigated in order to determine whether they correlated with undergraduates’ ability to solve stoichiometry problems. The problems were analyzed and broken down into constituent sub-problems in stoichiometry. Students were given a series of tests to measure their cognitive abilities in working memory capacity, formal reasoning, cognitive development, and conceptual understanding of the particulate nature of matter and the mole concept. A mixed qualitative and quantitative approach was used to analyze students’ difficulties with stoichiometry problems. The investigation of the cognitive variables indicated that only formal reasoning ability and understanding of the mole concept were good predictors of students’ success in stoichiometry. Although understanding of the particulate nature of matter did not correlate with success in solving general stoichiometry problems, it was significantly correlated with writing and balancing chemical equations.

Tunable Ti4+/Ti3+ Redox Potential in the Presence of Iron and Calcium in NASICON-Type Related Phosphates as Electrodes for Lithium Batteries

Cathode materials with the general stoichiometry Li1.2+xTi1.9–xFexCa0.1(PO4)3 (0 ≤ x ≤ 0.4) and Li1+2xTi2–xCax(PO4)3 (0.1 ≤ x ≤ 0.5) were prepared by a sol–gel method followed by annealing at 750 °...

Synergistic Extraction of Cobalt(II) by Mixtures of Bis(2-Ethylhexyl)Phosphoric Acid and LIX 860

The extraction of Co(II) from 1.0 M KNO3 medium by mixtures of HDEHP (bis-2-ethylhexylphosphoric acid) and LIX 860 (5-dodecylsalicylaldoxime) dissolved in toluene has been studied. The effects of pH, metal, and extractant mixture concentrations on the extraction behavior have been examined. Synergistic extraction of the metal ion with the binary mixture of extractants has been found. Experimental results have been treated graphically and numerically by means of the Letagrop-Distr program and can be explained by assuming the extraction of two mixed complexes of general stoichiometry CoR2(HR)(HL) and CoR2(HR)(HL)3, HR being bis-2-ethylhexylphosphoric acid and HL standing for 5-dodecylsalicylaldoxime. The corresponding extraction constant values have also been determined.