Study and 3D modeling of the phase diagram of the Ag–Ge–Se system

In view of the contradictoriness of the literature data, phase equilibria in the Ag–Ge–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and an isothermal section at room temperature of the phase diagram were constructed, and so was the projection of the liquidus surface. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was shown that, in the system, a single ternary compound, Ag₈GeSe₆, forms, which undergoes congruent melting at 1175 K and a polymorphic transformation at 321 K. The formation of the compounds Ag₂GeSe₃ and Ag₈GeSe₅, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

Experimental Study and 3D Modeling of the Phase Diagram of the Ag–Sn–Se System

In connection with the contradictoriness of literature data, phase equilibria in the Ag–Sn–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and the isothermal section at room temperature of the phase diagram were constructed, and a projection of the liquidus surface was built. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was demonstrated that, in the system, two ternary compounds, Ag₈SnSe₆ and Ag_xSn_{2 – x}Se₂ (0.84 < x < 1.06), form. The former melts congruently at 1015 K and undergoes a polymorphic transformation at 355 K, and the latter melts with decomposition by a peritectic reaction at 860 K. The formation of the compound Ag₂SnSe₃, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a limited number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

Synthesis and characterization of SiO2–CrO3, SiO2–MoO3, and SiO2–WO3 mixed oxides produced using the non-hydrolytic sol–gel process

Silica-based mixed oxide xerogels, namely SiO₂–CrO₃, SiO₂–MoO₃, and SiO₂–WO₃, were prepared using the non-hydrolytic sol–gel process. The materials were synthesized using metal chloride:tetraethoxysilane (TEOS) molar ratios of 0.1:2; 0.2:2 and 0.4:2 for each metal chloride and 1:2 SiCl₄:TEOS molar ratio. All of the xerogels containing Cr, Mo or W had considerably greater surface areas than that of SiO₂. The small angle X-ray scattering experiments suggest that the surface roughness of the aggregates in SiO₂–CrO₃ is less than that of SiO₂–MoO₃ and SiO₂–WO₃. The morphological characteristics of the silica-based mixed oxide xerogels were not affected by the nature and amount of metal chloride employed in the synthesis. An irregular morphology was observed for SiO₂–CrO₃, SiO₂–MoO₃ and SiO₂–WO₃, but a lamellar structure was observed for SiO₂. X-ray photoelectron spectroscopy analysis suggests that tungsten species were preferentially distributed on the outmost part of the grain. The resulting particle diameter was shown to be lower for the mixed oxides compared to that of bare silica. Furthermore, the presence of metals (Cr, Mo and W) on silica caused a decrease in the size of the particles as the atomic radii of these metals increased. According to the Fourier transform infrared spectroscopy and Raman, Cr, Mo and W were incorporated within the silica framework.     

Thermodynamic and transport properties of the DyBr3–NaBr binary system

Phase equilibria in the DyBr₃–NaBr binary system were established from differential scanning calorimetry. This system exhibits incongruently melting compound Na₃DyBr₆ and one eutectic located at DyBr₃ molar fraction x = 0.409 (T = 711 K). Na₃DyBr₆ undergoes a solid–solid phase transition at 740 K and melts incongruently at 762 K. The specific conductivity of DyBr₃–NaBr liquid mixtures was measured over the whole composition range. Results obtained are discussed in term of possible complex formation.     

New ferroelectric and relaxor ceramics in the mixed oxide system NaNbO3–BaSnO3

New ferroelectric or relaxor ceramics were elaborated in the system Ba_1−xNa_xSn_1−xNb_xO₃ (BSNN) by solid-state reaction technique. The effect of cationic substitution of barium for sodium in the A sites and tin for niobium in the B sites in the NaNbO₃ perovskite lattice on symmetry and physical properties were investigated. Room temperature X-ray diffraction and dielectric permittivity in the temperature range from 80 to 600 K with frequencies from 0.1 to 200 kHz, respectively, were used. The material is relaxor with cubic symmetry when x<0.90 and becomes classical ferroelectric with a tetragonal cell when 0.90⩽x<1. Both T_C or T_m and the maximum of ε′_r decrease when BaSnO₃ is introduced in the lattice of NaNbO₃. The plot of T_m(f)/T_m (1 kHz) versus the logarithm of the frequency allows to determine the limit of composition between the ferroelectric and the relaxor state. Relaxor materials have been obtained at room temperature.     

Effect of cooling rate on the microstructure and solidification parameters of Mg–3Al–3Nd alloy

Journal of Thermal Analysis and Calorimetry - The effect of cooling rate on the microstructure and solidification parameters of Mg–3Al–3Nd alloy was investigated by thermal analysis....     

Adenine–Au and adenine–uracil–Au. Non-conventional hydrogen bonds of the anions and donator–acceptor properties of the neutrals

This is a study of adenine–Au and adenine–uracil–Au (neutral, anionic and cationic), applying the B3LYP density-functional approach. In these systems, the interaction is directly related to the charge; so that as the metal atomic charge increases, the bond strength also increases. Neutral molecules are weakly bonded, the interaction in the case of cations is mainly electrostatic and in the case of the anions, the extra electron is localized on the metal atom and consequently, non-conventional hydrogen bonds are formed. In the case of adenine–Au (anion), the H dissociation energy is similar to the electron dissociation energy, and therefore both reactions may be possible. Moreover, the Au anionic atom modifies the hydrogen bonds of the uracil–adenine base pair. This may be significant in the study of point mutations that may occur in the Watson–Crick dimmer of nucleic basis. The electron-donator properties of these compounds are analyzed with the aid of the donator–acceptor map (DAM), previously described. Adenine–Au, uracil–Au and adenine–uracil–Au are more effective electron donors, but poorer electron acceptors than adenine, uracil and adenine–uracil. If the electron acceptor properties of carotenoids such as β-carotene and astaxanthin are compared, there are indications that astaxanthin may act as an oxidant instead of an antioxidant with the uracil–adenine base pair. The oxidation of nucleic acid bases by carotenoids may have important consequences, as oxidative damage of DNA and RNA appears to be linked to cancer. This is something that demands further studies and for this reason, work concerning the reactivity of carotenoids with DNA-nitrogen bases is in progress.     

Phase Diagram of the AgNO3–CsNO3 System

The phase diagram of the binary AgNO₃–CsNO₃ system was constructed using differential thermal analysis (DTA) technique in the range 300–700 K. The apparatus is described briefly. The results exhibit a congruently melting compound CsNO₃·AgNO₃ (m.p.=453 K) characterized by two allotropic varieties and , an incongruently melting compound AgNO₃·CsNO₃ (m.p.=450 K) with three forms , and , two eutectics (16 mol% CsNO₃, 442 K and 32.5 mol% CsNO₃, 445 K) and a peritectic (38mol% CsNO₃, 450 K). The occurrence of the transitions of intermediates was confirmed by X-ray diffraction at variable temperatures. The phase diagram exhibits also two plateaus at 429 K and 435 K corresponding to the phase transitions of CsNO₃ and AgNO₃, respectively.This revised version was published online in November 2005 with corrections to the Cover Date.     

Hermann Jahn and Rudolf Renner of the Jahn–Teller and Renner–Teller effects

Vibronic interactions have received increasing attention in modern structural chemistry. Edward Teller played a pioneering role in understanding and describing them during the “molecular physics” period of his scientific career. Very little is known about the two scientists who contributed significantly to our knowledge about these effects and whose names have become associated with Teller’s. This Editorial is devoted to Hermann Jahn and Rudolf Renner and attempts to lift them out of oblivion by paying them tribute for their contributions.

Solvent-dependent Baylis–Hillman reactions for the synthesis of 3-benzyl-3-hydroxyoxindoles and benzo-δ-sultams

We have developed a solvent-dependent method for the preparation of novel benzo-δ-sultam and 3-benzyl-3-hydroxy-N-methyloxindole scaffolds. A variety of 3-(methoxy(phenyl)methyl)-1-methyl-1H-benzo-[c][1,2]thiazine 2,2-dioxides and 3-benzyl-3-hydroxy-1-methylindolin-2-ones were obtained in moderate to high yields via DBU-catalyzed Baylis–Hillman reaction of a number of (E)-N-(2-formylphenyl)-N-methyl-2-phenylethenesulfonamides in DMF and MeOH, respectively. The proof of the structures relies on analytical investigation and X-ray crystallography. Whereas reaction of (E)-N-(2-formylphenyl)-N-methyl-2-phenylethenesulfonamides in MeOH presumably proceeds through intramolecular Baylis–Hillman/dehydration, 3-hydroxy-N-methyloxindoles seem to have been generated via intramolecular Baylis–Hillman/1,3-H shift/oxidation/intramolecular cyclization tandem sequences in DMF.     

Structure and properties of glasses in the system Li2O–SnO–B2O3

Glasses in the system Li₂O–SnO–B₂O₃ system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B₂O₃ glasses exhibited relatively low glass-transition temperatures (T_g) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of T_g indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B₂O₃ binary system.     

Francis Bacon and the Art–Nature Distinction

Abstract

Commentators generally expound Bacon's position on the art–nature relationship in terms of how much it retained or departed from traditional conceptions. This paper argues that an appreciation of the Baconian meaning of the terms "art" and "nature" requires a close examination of his wider cosmogonical speculations. Bacon's cosmogonical account moves from a state of unbridled chaos to the relatively stable system for which the term "nature" is normally used. The fundamental principle lying at the heart of Baconian cosmogony is an enriched and appetitive matter: eternal, unchanging, and the plenipotentiary source of all things. Successive limitations of matter's absolute power produced a lazy and habitual nature, which Bacon labelled "nature free." To shift nature from this otiose condition, the Baconian operator recapitulates the original binding of matter. Bacon designated the systematic procedures of binding nature the science of magic. Magic is Bacon's human counterpart to the original cosmogonical process that gave rise to the current system of nature. In Bacon's cosmogony, all possible worlds unfold out of matter: the function of art is to shake out nature's hidden folds. Hence, the distinction between naturalia and artificialia maps on to the distinction between actual and potential. Nature free is without purpose, but art — nature bound — knowingly brings into being an alternative nature designed for human utility.     

Phase equilibria in the Sn–As–Ge and Sn–As–P systems

T–x diagrams of polythermal GeAs–SnAs, GeAs–Sn₄As₃ sections of the Sn–As–Ge system and Sn₄P₃–Sn₄As₃ section of the Sn–As–P system were constructed using the results of X-ray powder diffraction and differential thermal analyses. It was found that the section GeAs–Sn₄As₃ is not quasi-binary due to realization of four-phase peritectic transformation L + SnAs ? GeAs + Sn₄As₃ at the temperature of 834 K. The quasi-binary section GeAs–SnAs represents a phase diagram of the eutectic type with the following coordinates of eutectic reaction: temperature of the eutectic point is 840 K, and composition is 20 mol% GeAs. In the Sn–As–P system, the existence of the solid-solution range indicated as (Sn₄As₃) _x (Sn₄P₃)_1?x  was defined. The polythermal section Sn₄P₃–Sn₄As₃ is not quasi-binary due to the fact that in the composition range with a high content of tin arsenide discussed section intersects the peritectic part of the three-phase volume (L + SnAs + α) of the ternary diagram.     

Liquid–liquid equilibria in the system H3PO4–KCl–H2O–tri-n-butyl phosphate: experiments and modelling

The liquid–liquid equilibria of the system H₃PO₄–KCl–H₂O–TBP was studied experimentally in the concentration range 0–6 mol/kg. The obtained data were modelled using the Pitzer equation for the aqueous phase and the Sergievskii–Dannus relationship for the organic phase. A fairly good agreement was observed between the model and the experimental data.     

Phase equilibria in the solid state and colour properties of the CuO–In2O3 system

Phase equilibria up to solidus line in CuO?CIn₂O₃ system have been investigated using XRD and DTA/TG methods. According to the results, only one compound of the formula Cu₂In₂O₅ formed in the system studied. Its thermal stability was determined in the air and argon proving that the compound did not melt but underwent decomposition. The decomposition of Cu₂In₂O₅ in the air atmosphere began at 1080?°C, while in argon at 835?°C. Additional studies were undertaken to determine the hitherto unknown colour properties of samples representing the CuO?CIn₂O₃ system in the equilibrium state.     

Glass formation study within the TeO2–TlF and Tl2Te3O7–TlF systems

Large glassy domains have been observed at 800 °C within the TeO₂–TlF (from 7 to 65 mol% of TlF) and Tl₂Te₃O₇–TlF (from 0 to 75 mol% of TlF content) systems. The density, glass transition and crystallisation temperatures of glassy samples have been determined. The main features of a structural evolution within the TlF–TeO₂ glasses have been interpreted by analysing the relevant Raman spectra, and comparing them with those previously observed for the Tl₂O-TeO₂ system.     

Binding affinities in the SAMPL3 trypsin and host–guest blind tests estimated with the MM/PBSA and LIE methods

We have estimated affinities for the binding of 34 ligands to trypsin and nine guest molecules to three different hosts in the SAMPL3 blind challenge, using the MM/PBSA, MM/GBSA, LIE, continuum LIE, and Glide score methods. For the trypsin challenge, none of the methods were able to accurately predict the experimental results. For the MM/GB(PB)SA and LIE methods, the rankings were essentially random and the mean absolute deviations were much worse than a null hypothesis giving the same affinity to all ligand. Glide scoring gave a Kendall's τ index better than random, but the ranking is still only mediocre, τ = 0.2. However, the range of affinities is small and most of the pairs of ligands have an experimental affinity difference that is not statistically significant. Removing those pairs improves the ranking metric to 0.4-1.0 for all methods except CLIE. Half of the trypsin ligands were non-binders according to the binding assay. The LIE methods could not separate the inactive ligands from the active ones better than a random guess, whereas MM/GBSA and MM/PBSA were slightly better than random (area under the receiver-operating-characteristic curve, AUC = 0.65-0.68), and Glide scoring was even better (AUC = 0.79). For the first host, MM/GBSA and MM/PBSA reproduce the experimental ranking fairly good, with τ = 0.6 and 0.5, respectively, whereas the Glide scoring was considerably worse, with a τ = 0.4, highlighting that the success of the methods is system-dependent.     

HS–SPME–GC–MS for the Quantitation and Chiral Characterization of Camphor and Menthol in Creams

A GC–MS method is proposed for the analysis of camphor and menthol in “over-the-counter” (OTC) products. Sample preparation was achieved by head-space solid phase microextraction using a polydimethylsiloxane fibre. GC analysis was performed using a Phenomenex ZB-5 column and a temperature program was adopted. The method was validated by studying linearity (range 0.1–15.0% w/w), accuracy, reproducibility and sensitivity. Applications were directed to the determination of the active ingredients in four different OTC-products; the mean recoveries were in the ranges 91.30–99.74% and 94.34–102.89% for camphor and menthol, respectively and the LOD was in the order of 0.005% (w/w). Other important terpenoids (α- and β-pinene, 1,8-cineole, menthone, isomenthone, α-terpineole, t-cinnamaldehyde, eugenole) were identified by mass spectra and Kovats retention indices and quantified by peak area normalization to 100%. Further information for a comprehensive characterization of the OTC-products was achieved by the GC chiral analysis on a Cyclosil B capillary column.