Synthesis and crystal structure of hydrogen strontium paratungstate Sr<Subscript>4.5</Subscript>H[W<Subscript>12</Subscript>O<Subscript>40</Subscript>(OH)<Subscript>2</Subscript>] · 30H<Subscript>2</Subscript>O

The conditions for formation of individual isopolytungstates in solutions of the Sr(NO₃)₂-Na₂WO₄-HNO₃-H₂O system acidified to Z = ν(H⁺)/ν(WO ₄ ^2? ) = 1.29 were studied. The conditions of formation of strontium paratungstate B, strontium hydroheptatungstate, and hydrogen strontium paratungstate were determined. An X-ray diffraction study of single crystals of Sr_4.5H[W₁₂O₄₀(OH)₂] · 30H₂O was carried out. Selected crystallographic data for H₆₃O₇₂Sr_4.50W₁₂ are: M _r = 3815.99, monoclinic, space group P2₁/c, a = 11.41270(10) Å, b = 23.7575(3) Å, c = 12.4392(2) Å, β = 110.476(2)°, V = 3159.64(7) ų at T = 293 K, Z = 2, ρ = 4.011 g/cm³, F₀₀₀ = 3396, μ(MoK _α) = 25.635 mm^?1, ?14 ≤ h ≤ 14, ?30 ≤ k ≤ 30, ?16 ≤ l ≤ 16, R _F = 0.0430, wR ² = 0.1067 (R _F = 0.0506, wR ² = 0.1129), and S = 1.043.     

A transmission electron microscopy study of the effect of interfaces on bubble formation in He-implanted Cu-Nb multilayers

Magnetron sputtered thin films of Cu, Nb, and Cu-Nb multilayers with 2.5 and 5 nm nominal layer thickness were deposited on Si and implanted with 4He+ and 3He+ ions. Secondary ion mass spectroscopy and nuclear reaction analysis, respectively, were used to measure the 4He+ and 3He+ concentration profile with depth inside the films. Cross-sectional transmission electron microscopy was used to characterize the helium bubbles. Analysis of the contrast from helium bubbles in defocused transmission electron microscope images showed a minimum bubble diameter of 1.25 nm. While pure Cu and Nb films showed bubble contrast over the entire range of helium implantation, the multilayers exhibited bubbles only above a critical He concentration that increased almost linearly with decreasing layer thickness. The work shows that large amounts of helium can be trapped at incoherent interfaces in the form of stable, nanometer-size bubbles.     

Identification and differentiation of dragon's blood in works of art using gas chromatography/mass spectrometry

Dragon's blood is a common but non-specific name for red-coloured resins that are produced by various plants, particularly exudations from plant species belonging to the genera Dracaena and Daemonorops. Although dragon's blood is mentioned in historic sources as a colourant, it has hardly ever been identified in real artworks. This paper reports the identification and discrimination of dragon's blood produced by Dracaena cinnabari, Dracaena draco as well as Daemonorops draco and Daemonorops micracantha by means of gas chromatography/mass spectrometry (GC/MS) within the context of a routine analysis of binding media used in works of art. The detection of specific flavonoid marker compounds in both underivatised and methylated methanol extracts provided the first evidence for the use of dragon's blood from all four species in various works of art from the fifteenth to nineteenth centuries. Dragon's blood was mainly used as a red colourant in gold lacquers as well as translucent glazes and paints, e.g. in reverse-glass paintings (Hinterglasmalerei).     

Synthesis and structure of N-(hydroxyethyl)ethylenediammonium sulfite monohydrate

A reaction between sulfur(IV) oxide and aqueous N-(2-hydroxyethyl)ethylenediamine yields onium sulfite of composition (HOCH₂CH₂NH₂CH₂CH₂NH₃)SO₃ · H₂O, which has been characterized by X-ray diffraction, IR spectroscopy, and mass spectrometry. The three-dimensional structure of the salt is stabilized by numerous hydrogen bonds, such as NH…O and OH…O.     

Synthesis and structure of aminoguanidinium sulfite monohydrate

The reaction between sulfur(IV) oxide and an aqueous suspension of aminoguanidinium hydrocarbonate yields (CN₄H₇)₂SO₃ · H₂O, an “onium” sulfite, which has been characterized by X-ray diffraction and IR spectroscopy and mass spectrometry. The structure of the salt is stabilized by numerous H-bonds, such as NH…O, OH…O, and NH…N. The incorporation of pyramidal SO ₃ ^2? ions into the network of H-bonds is accompanied by the lowering of their symmetry in comparison with C _3v, thus complicating the IR spectra of the salt in the region where the vibrations of the anion appear.     

Activated sterically strained C=N bond in N-substituted p-quinone mono- and diimines: XIV. Reaction of some 3,5-dimethyl-1,4-benzoquinone monoimines with alcohols

Steric strain in the C=N-C fragment in 3,5-disubstituted N-acyl-1,4-benzoquinone monoimines, unlike their N-arylsulfonyl analogs, leads to increase of the C=N-C angle above 130° or twisting of the double C=N bond and loss of planarity of the quinoid ring. This structural transformation enhances the reactivity of the C=N bond so that 1,2-addition of alcohols becomes possible with formation of sterically unstrained cyclohexadienone structure with sp ³-hybridized C⁴ carbon atom.     

A round robin exercise in archaeometry: analysis of a blind sample reproducing a seventeenth century pharmaceutical ointment

Chemical analysis of ancient residues of pharmaceutical or cosmetic preparations such as balms or ointments is made problematic by the high complexity of these mixtures, composed of organic and inorganic materials. Consequently, a multi-analytical approach and special caution in the interpretation of the results are necessary. In order to contribute to the improvement of analytical strategies for the characterization of complex residues and to reconstruct ancient medical practices, a replica of a pharmaceutical formulation of the seventeenth century was prepared in the laboratory according to a historically documented recipe. In a round robin exercise, a portion of the preparation was analysed as a blind sample by 11 laboratories using various analytical techniques. These included spectroscopic, chromatographic and mass spectrometric methods. None of the laboratories was able to completely reconstruct the complex formulation, but each of them gave partial positive results. The round robin exercise has demonstrated that the application of a multi-analytical approach can permit a complete and reliable reconstruction of the composition. Finally, on the basis of the results, an analytical protocol for the study of residues of ancient medical and pharmaceutical preparations has been outlined.     

Nature of dual fluorescence in 2-(quinolin-2-yl)-3-hydroxychromone: Tuning between concurrent H-bond directions and ESIPT pathways

Synthesis of the quinoline-substituted 3-hydroxychromone is reported, spectral and fluorescent properties of the title compound are investigated in different solvents. The question of the possibility of the participation of the substituent heterocycle’s nitrogen atom in H-bond formation as well as in the ESIPT process is discussed. Quantum-chemical modeling provides evidence that the structure with an alternative H-bond to nitrogen is more energetically favorable and strongly prevails in solutions. However, our calculations together with the experimental data reveal that the excited species with the intramolecular N…HO hydrogen bond type undergoes rapid radiationless deactivation. This leads to a conclusion that the low-intensity dual-band fluorescence of the title compound in solutions originates from the traces of the conformation with the traditional “flavonol-like” H-bond to the carbonyl oxygen atom. A possibility to reversibly tune the direction of the intramolecular H-bond formation and thus regulate the ESIPT process pathway is demonstrated by the example of protonation/deprotonation of the title compound in a methylene chloride solution.