Thermogravimetry study of ion exchange and hydration in layered oxide materials

The behavior in aqueous solutions of the two types of layered perovskite-like structures, NaLnTiO₄ titanates (Ln?=?Nd, La) belonging to the family of Ruddlesden?CPopper phases and ANdTa₂O₇ tantalates (A?=?Na, Cs, H) belonging to the family of Dion?CJacobson phases, has been studied by means of thermogravimetric analysis and powder X-ray diffraction. In the case of NaLnTiO₄ compounds, the substitution of protons for sodium cations and the water intercalation into the interlayer space of the crystal structure were observed and proton-containing layered oxides with general formula H _x Na_1?x LnTiO₄·yH₂O (0.63?<?x?<?1, 0?<?y?<?0.74) have been obtained. Investigation on the hydration in layered tantalates ANdTa₂O₇ (A?=?H, Na, Cs) showed that NaNdTa₂O₇ and HNdTa₂O₇ form compounds intercalated by water molecules. Two steps of water intercalation were observed for NaNdTa₂O₇ and HNdTa₂O₇. Stable hydrated compounds HNdTa₂O₇·0.84H₂O, NaNdTa₂O₇·0.60H₂O, and NaNdTa₂O₇·1.35H₂O were synthesized.     

Linearized forward and inverse problems of the resonant ultrasound spectroscopy for the evaluation of thin surface layers

In this paper, linearized approximations of both the forward and the inverse problems of resonant ultrasound spectroscopy for the determination of mechanical properties of thin surface layers are presented. The linear relations between the frequency shifts induced by the deposition of the layer and the in-plane elastic coefficients of the layer are derived and inverted, the applicability range of the obtained linear model is discussed by a comparison with nonlinear models and finite element method (FEM), and an algorithm for the estimation of experimental errors in the inversely determined elastic coefficients is described. In the final part of the paper, the linearized inverse procedure is applied to evaluate elastic coefficients of a 310 nm thick diamond-like carbon layer deposited on a silicon substrate.     

Synthesis and cytotoxicity of silylalkylthio‐substituted N‐heterocycles and their hydroselenites

New hydroselenites of the different silylalkylthio‐substituted N‐heterocycles have been prepared by the reaction of selenium dioxide with N‐heterocycles in an aqueous medium. Their structure was confirmed by ¹H, ¹³C, and ⁷⁷Se NMR data. Most of these silylalkylthio‐substituted N‐heterocycles and their hydroselenites have an expressed cytotoxic activity on the MG‐22A (mouse hepatoma), HT‐1080 (human fibrosarcoma), B16 (mouse melanoma), and Neuro 2A (mouse neuroblastoma) cell lines. Some of the hydroselenites exhibit free‐radical protection simultaneously with a high cytotoxic effect. The substances studied were also active in vivoagainst sarcoma S‐180. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis and thermal transformations of spiro-fused N-phthalimidoaziridines

Oxidation of N-aminophthalimide in the presence of 2-arylideneinden-1,3-diones with electron-withdrawing substituents gives the corresponding 3-aryl-1-phthalimidospiro[aziridine-2,2′-indene]-1′,3′-diones in good yields. Heating these aziridines with standard dipolarophiles (N-phenylmaleimide, dimethyl acetylenedicarboxylate, maleate, and fumarate) leads, in most cases, to spiro[inden-2,2′-pyrrole] derivatives as products of 1,3-dipolar cycloaddition of the intermediate azomethine ylides with up to 70–95% yields in the case of N-phenylmaleimide. As is typical for 2-acylaziridines, the competing rearrangement into 2-aryl-4H-indeno[2,1-d][1,3]oxazol-4-ones prevails for less active dipolarophiles. Increasing the electron-releasing properties of the 3-aryl ring allows the observation of the push–pull effect of electron-donating and electron-withdrawing substituents on the ease of the three-membered ring-opening.     

Hexafluoropropylene Oxide–Alcohol: A Convenient System for Silica Dissolution

Abstract

A new method of silica dissolution is described. It involves the formation of a stable SiF₄ · n ROH complex (1, 1a) just from SiO₂ and anhydrous alcoholic HF generated in situ from commercially available hexafluoropropene oxide. Alcoholic SiF₄ complexes can be easily converted to different organosilicon compounds of the type SiF₄L₂ and (LH)₂SiF₆ [L = 1,10-phenantroline (2a), 2,2′-dipyridyl (2b), Me₂SO (2c), pyridine (2d), triethanolamine (3a)]. Different silica-containing compounds can be used in this strategy—silicagel, sand, alumosilicates, and even rice husk.

GRAPHICAL ABSTRACT     

Adamantane-bearing benzylamines and benzylamides: novel building blocks for supramolecular systems with finely tuned binding properties towards β-cyclodextrin

Novel building blocks for the synthesis of supramolecular components based on adamantane-bearing benzylamines were prepared. The binding properties of these amines and the corresponding acetamides towards β-cyclodextrin (β-CD) were studied using mass spectrometry, NMR spectrometry, isothermal titration calorimetry and semi-empirical calculations. It was found that all of the examined guests predominantly formed 1:1 inclusion complexes in an enthalpy-driven manner with association constants of the order of 10²–10³ M^? 1. Stronger binding to the β-CD cavity was observed for guests with a longer spacer between the adamantane and benzene moieties and/or a 1,4-disubstituted benzene ring.     

Online molecularly imprinted solid‐phase extraction coupled to liquid chromatography‐tandem mass spectrometry for the determination of hormones in water and sediment samples

The molecularly imprinted SPE directly coupled to RP LC‐MS/MS method has been developed and successfully validated for the determination of six hormones in water and sediment samples. The method is based on the use the home‐made column filled with a molecularly imprinted sorbent (imprinted against estrogens) that was used under nonaqueous conditions. Thus, its high selectivity could be utilized resulting in low matrix components’ coextraction. The method showed excellent recovery (92–105%) and satisfactory sensitivity (LOQs water: 1.9–4.0 ng/L; LOQs sediment: 0.2–0.5 ng/g). The intra‐ and interprecision for water and sediment was in the range of 4.0–6.0% and 4.4–7.6%, respectively. Finally, 20 water and sediment samples collected from the Svratka river were analyzed. Only estrone was quantified in eight water samples (4.4–7.1 ng/L); no analytes were found in sediment samples.     

Fluorescence properties of Ca2+-independent discharged obelin and its application prospects

Discharged obelin, a complex of coelenteramide and polypeptide, is a fluorescent protein produced from the photoprotein obelin, which is responsible for bioluminescence of the marine hydroid Obelia longissima. Discharged obelin is stable and nontoxic and its spectra are variable, and this is why it can be used as a fluorescent biomarker of variable color in vivo and in vitro. Here we examined light-induced fluorescence of Ca²⁺-independent discharged obelin (obtained without addition of Ca²⁺). Its emission and excitation spectra were analyzed under variation of the excitation wavelength (260–390 nm) and the emission wavelength (400–700 nm), as well as the 40 °C exposure time. The emission spectra obtained with excitation at 260–300 nm (tryptophan absorption region) included three peaks with maxima at 355, 498, and 660 nm, corresponding to fluorescence of tryptophan, polypeptide-bound coelenteramide, and a hypothetical indole–coelenteramide exciplex, respectively. The emission spectra obtained with excitation at 310–380 nm (coelenteramide absorption region) did not include the 660-nm maximum. The peak in the red spectral region (λ _max?=?660 nm) has not been previously reported. Exposure to 40 °C under excitation at 310–380 nm shifted the obelin fluorescence spectra to the blue, whereas excitation at 260–300 nm shifted them to the red. Hence, red emission and variation of the excitation wavelength form a basis for development of new medical techniques involving obelin as a colored biomarker. The addition of red color to the battery of known (violet to yellow) colors increases the potential of application of obelin.     

High‐Pressure Synthesis of Metal–Inorganic Frameworks Hf4N20⋅N2, WN8⋅N2, and Os5N28⋅3 N2 with Polymeric Nitrogen Linkers

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one‐step synthesis of metal–inorganic frameworks Hf₄N₂₀?N₂, WN₈?N₂, and Os₅N₂₈?3 N₂ via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf₄N₂₀, WN₈, and Os₅N₂₈) are built from transition‐metal atoms linked either by polymeric polydiazenediyl (polyacetylene‐like) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The high‐pressure reaction between Hf and N₂ also leads to a non‐centrosymmetric polynitride Hf₂N₁₁ that features double‐helix catena‐poly[tetraz‐1‐ene‐1,4‐diyl] nitrogen chains [?N?N?N=N?]_∞.     

The role of oxidizing radicals in neptunium speciation in γ-irradiated nitric acid

The irradiation of aqueous nitric acid solutions generates transient, reactive species that are known to oxidize neptunium. However, nitrous acid is also a long-lived product of nitric acid irradiation, which reduces neptunium. When we irradiated nitric acid solutions of neptunium and measured its speciation by UV/Vis spectroscopy, we found that at short irradiation times, oxidation of Np(V) to Np(VI) occurred due to reactions with radicals such as ^?OH, ^?NO₃ and ^?NO₂. However, at higher absorbed doses and after a sufficient amount of nitrous acid was produced, reduction of Np(VI) to Np(V) began to occur, eventually reaching an equilibrium distribution of these species depending on nitric acid concentration. Neptunium(IV) was not produced.