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.     

Phenolic compounds,antioxidant activity and Cu,Zn, Cd and Pb content in wild and cultivated cranberries and blueberries

The aim of this study was to determine the content of Cu, Zn, Cd and Pb and the total polyphenol (TP) content as well as the total antioxidant capacity (TAC) in wild cranberries and blueberries collected from different localities of the Slovakia and to compare them with properties of six cranberry and six highbush blueberry cultivars obtained from the research centre. Compared with cultivated cranberries (Cu, Zn, Cd and Pb content: 0.642, 1.496, 0.015 and 0.050 mg/kg FM) in wild fruits, higher Cu (by 37%) and lower Zn, Cd and Pb (by 8%, 7% and 44% respectively) were determined using atomic absorption spectrometry method. In wild blueberries, higher Cu, Zn and Pb (by 16%, 209% and 80% respectively) and similar Cd contents were determined compared with cultivated fruits (Cu, Zn, Cd and Pb content: 0.483, 0.541, 0.003 and 0.055 mg/kg FM). The TP contents estimated by spectrophotometry using Folin–Ciocalteau reagent were in intervals 1405–3161 (cranberries) and 1300–3077 (blueberries) expressed as mg GAE/kg FM. While the average TP content determined in wild cranberries was by 31% lower than that in cultivated cranberries, in wild blueberries it was by 97% higher compared with highbush blueberry cultivars. The values of TAC determined by spectrophotometry method using 2,2-diphenyl-1-picrylhydrazyl were in range 20.67–22.22 (cranberries) and 14.03–24.79 (blueberries) expressed as mmol TE/kg FM. In wild cranberries and blueberries, the lower average TAC values compared with cultivated berries were determined (by 1% and 28%, respectively).     

LC-Multistage Mass Spectrometry for the Characterization of Poly(Butylene Adipate-co-Butylene Terephthalate) Copolyester

A comprehensive study using liquid chromatography electrospray ionization multistage mass spectrometry (LC-ESI MS ⁿ ) was performed to get detailed structural information on poly(butylene adipate-co-butylene terephthalate) co-polyester and its product of partial degradation. LC-MS and LC-MSⁿ identified the existence of cyclic structures in the original samples that disappear completely during the degradation. The occurrence of methanol transesterification in the degradation process was confirmed. MS² on the first ¹³C isotope peak helped to determine the elemental composition of the fragments and facilitated end group determination. The method can be used to provide an alternative for high mass accuracy MS² experiments. Sequence information was also revealed for certain copolymeric structures.     

Mobility of solid tert-butyl alcohol studied by deuterium NMR

The molecular mobility of solid deuterated tert-butyl alcohol (TBA) has been studied over a broad temperature range (103–283 K) by means of solid-state 2H NMR spectroscopy, including both line shape and anisotropy of spin–lattice relaxation analyses. It has been found that, while the hydroxyl group of the TBA molecule is immobile on the 2H NMR time scale (τC > 10(–5) s), its butyl group is highly mobile. The mobility is represented by the rotation of the methyl [CD3] groups about their 3-fold axes (C3 rotational axis) and the rotation of the entire butyl [(CD3)3-C] fragment about its 3-fold axis (C3′ rotational axis). Numerical simulations of spectra line shapes reveal that the methyl groups and the butyl fragment exhibit three-site jump rotations about their symmetry axes C3 and C3′ in the temperature range of 103–133 K, with the activation energies and preexponential factors E1 = 21 ± 2 kJ/mol, k(01) = (2.6 ± 0.5) × 10(12) s(–1) and E2 = 16 ± 2 kJ/mol, k(02) = (1 ± 0.2) × 10(12) s(–1), respectively. Analysis of the anisotropy of spin–lattice relaxation has demonstrated that the reorientation mechanism of the butyl fragment changes to a free diffusion rotational mechanism above 173 K, while the rotational mechanism of the methyl groups remains the same. The values of the activation barriers for both rotations at T > 173 K have the values, which are similar to those at 103–133 K. This indicates that the interaction potential defining these motions remains unchanged. The obtained data demonstrate that the detailed analysis of both line shape and anisotropy of spin–lattice relaxation represents a powerful tool to follow the evolution of the molecular reorientation mechanisms in organic solids.     

Morse index of a cyclic polygon

It is known that cyclic configurations of a planar polygonal linkage are critical points of the signed area function. In the paper we give an explicit formula of the Morse index for the signed area of a cyclic configuration. We show that it depends not only on the combinatorics of a cyclic configuration, but also on its metric properties.