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.     

LC–DAD–ESI-MS–MS Separation and Chemical Characterization of the Inflammatory Fraction of the Roots of Euphorbia kansui

In China the roots of Euphorbia kansui T.N. Liou ex T.P. Wang, known as ‘kansui’, have been used for centuries as a herbal remedy for edema, ascites, and asthma. Kansui, has inflammatory and tumor-promoting toxicity, and other side-effects, however, which have seriously restricted its clinical application. In the work discussed in this paper a simple and rapid LC–DAD–ESI-MS–MS method has been established for separation and characterization of the main compounds in the toxic fraction of E. kansui roots. Twelve diterpene derivatives were identified in the inflammatory fraction of kansui: kansuinine C, kansuinine B, kansuinine A, kansuinine D, 5-O-benzoyl-20-deoxyingenol, kansuinine E, kansuiphorin C, 3-O-benzoyl-20-deoxyingenol, 3-O-(2′E,4′Z-decadienoyl)-5-O-acetylingenol, 3-O-(2′E,4′Z-decadienoyl)-20-deoxyingenol, 20-O-(2′E, 4′E-decadienoyl)ingenol, and 3-O-(2′E,4′Z-decadienoyl)-20-O-acetylingenol. The inflammatory fraction was separated on a C₁₈ reversed-phase column with a mobile phase gradient. The proposed method is a scientific and technical platform enabling the herbal medicine industry to perform quality control and ensure the safety of preparations that contain this class of poisonous diterpenoids.     

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.     

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.

Investigation of the presence of KCl in the structure and morphology of V-amylose–inclusion complexes

Amylose–fatty acid inclusion complexes were prepared using amylose extracted from pea starch and fatty acids with different chain length. To form the complexes, amylose, dissolved in aqueous alkaline solution (0.1 Ν ΚΟΗ), was mixed with fatty acid potassium soap solution and after neutralization the complex was obtained as precipitate. To investigate the structure and morphology of V-amylose–inclusion complexes, a series of techniques such as X-ray diffraction, SEM-microscopy combined with elemental microanalysis, Differential scanning calorimetry and Fourier transform infrared spectroscopy were employed. XRD analysis of complexes, revealed that the complexes displayed the typical V-form pattern, with an extra peak at 2θ?=?28.2°. To identify the origin of that peak the complexes were examined by SEM microscopy combined with elemental microanalysis. The results indicated that the peak was due to the presence of potassium chloride, formed during the preparation of the complexes. Washing the complexes with water was sufficient to remove the salt.     

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.     

LC–DAD and LC–ESI–MS Chromatographic Fingerprinting and Quantitative Analysis for Evaluation of the Quality of Huang-Lian-Jie-Du-Tang

LC–DAD coupled with electrospray tandem mass spectrometry (LC–ESI–MS–MS) has been used to evaluate the quality of the traditional Chinese medicine Huang-Lian-Jie-Du-Tang (HLJDT). Twenty-five chromatographic peaks were obtained from a C₁₈ analytical column by gradient elution with acetonitrile and formate buffer (containing 0.5% formic acid) at a flow rate of 1.0 mL min^?1. The linearity, precision, and accuracy of the data obtained were acceptable. Thirteen components were identified by ESI–MS, and seven of these were quantitatively analyzed by LC–DAD. The method was used to analyze ten batches of HLJDT, and both chromatographic fingerprints and quantitative data were used to evaluate the quality of the HLJDT. It was concluded that this LC–DAD–ESI–MS method enables more fully validated and complete evaluation and monitoring of the quality of HLJDT.     

Synthesis of functionalized and fused furans and pyrans from the Morita–Baylis–Hillman acetates of nitroalkenes

The Morita–Baylis–Hillman (MBH) acetates derived from nitroalkenes and ethyl glyoxylate have been transformed in one pot at room temperature to highly fused and functionalized furans and pyrans in good to excellent yield. The reaction involves a cascade Michael–oxa-Michael addition of β-dicarbonyl compounds to the MBH acetates in the presence of an amine base such as DABCO. An unusual switching of selectivity in the oxa-Michael addition from 5-exo-trig to 6-endo-trig was observed when the β-dicarbonyl compound was changed from acyclic or six-membered ring cyclic to five-membered ring cyclic system.     

Thermal characterization of the effect of fillers and ionic liquids on the vulcanization and properties of acrylonitrile–butadiene elastomer

Different thermal analysis techniques were used to study the effect of fillers and ionic liquids (ILs) on the vulcanization process, thermal and dynamic mechanical properties of acrylonitrile–butadiene elastomer (NBR). The products of the studies were composites of NBR filled with hydrotalcite, nanosized silica or carbon black. ILs such as 1-butyl-1-methylpyrrolidinium (BMpyrrolBF₄), 1-butyl-4-methylpyridinium (BMpyrBF₄) or 1-butyl-1-methylpiperidinium (BMpipBF₄) tetrafluoroborates were applied to improve the dispersion degree of the curatives and filler particles in the elastomer and to increase the efficiency of vulcanization. The differential scanning calorimetry results indicated that ILs reduced the vulcanization temperature of NBR compounds and increased the homogeneity of cross-link distribution in the elastomer network. NBRs filled with carbon black or silica exhibited similar thermal stabilities, whereas hydrotalcite reduced the temperature of thermal decomposition. The lowest mechanical loss factors were determined for vulcanizates filled with nanosized silica.

     

Prediction and experimental verification of the salt effect on the vapour–liquid equilibrium of water–ethanol–2-propanol mixture

Experimental vapour–liquid equilibria of water–ethanol–2-propanol saturated with NaNO₃, NaCl, KCl and containing 0.05 mol CH₃COOK/mol total solvent compared well with those predicted by Tan–Wilson and Tan–non-random two liquid (NRTL) models for multicomponent solvent–solute mixture using a set of solvent–solvent interaction parameters obtained from the regression of the vapour–liquid equilibrium of the solvent mixture without the dissolved solute and a set of solute–solvent interaction parameters calculated from the bubble points of the individual solvent components saturated or containing the same molar ratio of solute/total solvents as the mixture. The results also showed that a solvent component i is salted-in or out of the liquid phase relatively more than solvent component j would depend on whether A_sj/A_si (Tan–Wilson model) or exp(τ_is−τ_js) (Tan–NRTL model) is less or greater than 1. This is consistent with earlier publications on the effect of dissolved solutes (electrolytes and non-electrolytes) on the binary solvents mixtures. These findings confirmed that Tan–Wilson and Tan–NRTL models for multicomponent solvent–solute system can provide an accurate and rapid screening of electrolytes and non-electrolytes for their suitability in facilitating solvent separation by salt distillation of ternary solvent mixtures simply by determining the relative ratios of the solute–solvent interaction parameters from the respective bubble points of the solvent components containing the dissolved solute. The results also suggest that this may also be extended to other multicomponent solvent mixtures.     

Low-temperature synthesis and characterization of the Mn–Zn ferrite

Nanocrystalline ferrite with the composition: Mn_0.6Zn_0.4Fe₂O₄ was synthesized by two-stage route: the precipitation of Zn, Mn and Fe hydroxides from sulphates solution and the synthesis of a precursor by the sol–gel auto-combustion method. The ferrite powder obtained from the gel by ashing was sintered under air at a temperature of 720, 1150 and 1300 °C. The composition and morphology of the as-obtained phases were examined by ICP-AES, TG/DTA, XRD, FTIR, SEM and low-temperature nitrogen adsorption (BET). It was found that the spinel phase forms after gel combustion. The nanometric ferrite powder obtained as a result of the combustion is soft-agglomerated. The zinc content in the ferrite during ashing and auto-combustion is lower by about 21 mol% than the assumed one and the final product turn out to be Mn_0.68Zn_0.32Fe₂O₄.     

Sensitivity and stability of the Fricke–gelatin–xylenol orange gel dosimeter

Spectrophotometric measurements of the Fricke–gelatin–xylenol orange (FGX) gel dosimeter demonstrated reproducible linear dose response up to 25 Gy. However, oxidation processes continue post-irradiation, affecting the response of this dosimetry system. Additional oxygenation during preparation increases the sensitivity of the gel but does not improve the auto-oxidation stability of the dosimeter post-irradiation. A suitably stable gel composition that is recommended for radiotherapy dosimetry measurements contains 0.5 mM ferrous ammonium sulphate, 50 mM sulphuric acid, 0.15 mM xylenol orange and 3.0% by weight gelatin.     

Structural and spectroscopic investigations of the Eu–CDTA system

Two crystal structures of Eu^III complexes with CDTA (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetate), [C(NH₂)₃]₃[Eu₂(CDTA)₂(H₂O)₂]ClO₄ · 7H₂O (I) and [C(NH₂)₃][Eu(CDTA)(H₂O)] · 2.375H₂O (II), are presented. Both structures are polymeric and the central metal ions are eight-coordinate. The first coordination sphere of each Eu^III cation contains five carboxylate oxygen atoms, two nitrogen ones and a water molecule. For I, as well as for water solutions of the Eu^III–CDTA complex at various pH values, the spectroscopic (UV–Vis) properties were investigated.     

Phase diagram and crystal chemistry of the La–Ca–Co–O system

The phase diagram of the La–Ca–Co–O system at 885 °C in air has been determined. The system consists of two materials that have interesting thermoelectric properties, namely, the misfit layered thermoelectric oxide solid solution, (Ca,La)₃Co₄O₉, and Ca₃Co₂O₆ which consists of 1D chains of alternating CoO₆ trigonal prism and CoO₆ octahedra. The reported La₂CaO₄ and the Ca-doped (La,Ca)₂CoO_4−z phases were not found at 885 °C. As a result of the absence of these phases, the phase diagram is significantly different from that reported at 1100 °C. Small solid solution regions of (La_1−xCa_x)₂O_3−z (0 ≤ x ≤ 0.08), (Ca_1−xLa_x)₃Co₄O₉ (0 ≤ x ≤ 0.07), and (La_1−xCa_x)CoO_3−z (0 ≤ x ≤ 0.2) were established.     

Experimental investigation and thermodynamic modeling of the Au–Ge–Ni system

Abstract  

Phase equilibria in the Au–Ge–Ni ternary system were studied by means of scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry. The phase relations in the solid state at 600 °C as well as a vertical section at Au₇₂Ge₂₈–Ni were established. No ternary compound was found at 600 °C. On the basis of the experimental phase equilibria data, a thermodynamic model of the Au–Ge–Ni ternary system was developed using the CALPHAD method. Thermodynamically calculated phase diagrams are shown at 600 °C, in two vertical sections and the liquidus projection. Reasonable agreement between the calculations and the experimental results was achieved.     

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.     

Copper and zinc co-catalyzed synthesis of imidazoles via the activation of sp C–H and N–H bonds

An efficient and facile approach to synthesize imidazoles from amidines and arylketone via oxidative coupling of sp³ C–H bond and N–H bond is reported. This strategy exhibits high performance in terms of regioselectivity with moderate to high yields by using easily available materials, and provides an alternative method to synthesize multi-substituted imidazole skeletons.