Search

Britholites are the lanthanide-silica-rich end-members of the apatite group, commonly studied for their optical properties. Here, we show ∼50-100 μm single crystals synthesized hydrothermally at 650-500 °C and 500-300 MPa composed of a solid solution between Ca 2 Pr 3 (SiO 4 ) 3 F-fluorbritholite and CaPr 4 (SiO 4 ) 3 O-oxybritholite, with a significant carbonate component substitution, via C 4+ replacing Si 4+ . Single-crystal X-ray diffraction and density functional theory computations show that a planar carbonate group occupies the face of a now-vacant silica tetrahedron. This modifies Pr-O bond lengths, diversifying lanthanide optical emission wavelengths. Our britholite was synthesized in geologically reasonable conditions and compositions, suggesting that carbonated oxybritholites could exist as yet-unrecognized natural minerals.

A simple method for the direct transformation of Sr-exchanged titanosilicate with the sitinakite structure (IONSIV) into ceramic material through cold pressing and subsequent sintering at 1100 °C for 4 h is presented. The temperature transformation of Sr-exchanged sitinakite showed the stages of recrystallization of the material with the formation of Sr-Ti phases matsubaraite (Sr 4 Ti 5 [Si 2 O 7 ] 2 O 8 ), jeppeite (SrTi 6 O 13 ), tausonite (SrTiO 3 ), and rutile. Leaching experiments showed the efficiency of fixation of Sr cations in a ceramic matrix; extraction into water does not exceed 0.01% and desorption in 1 M HNO 3 solution is only 0.19% within three days. The leaching rates of immobilized Sr demonstrate the structural integrity of the formed phases in the ceramic (2.8 × 10 -5 -1.0 × 10 -5 g/(m 2 ·day). The decrease in the crystallinity of the initial Na-sitinakite, which is achieved by reducing the synthesis temperature from 250 to 210 °C, does not affect the sorption capacity and the fixation of cations in the ceramic matrix. The obtained results confirm the prospect of using inexpensive precursors, titanium ore enrichment waste, for the synthesis of sorption materials.

Flexible crystal() structures, which exhibit() single-crystal()-to-single-crystal() (SCSC) transformations(), are attracting attention() in many applied aspects: magnetic() switches, catalysis, ferroelectrics and sorption. Acid treatment() for titanosilicate material() AM-4 and natural() compounds with the same structures led to SCSC transformation() by loss() Na + , Li + and Zn 2+ cations with large structural() changes (20% of the unit()-cell() volume()). The conservation() of crystallinity through complex() transformation() is possible due() to the formation() of a strong hydrogen bonding() system(). The mechanism() of transformation() has been characterized using single-crystal() X-ray() diffraction analysis(), powder() diffraction, Rietvield refinement, Raman spectroscopy and electron microscopy. The low migration() energy() of cations in the considered materials() is confirmed using bond()-valence and density() functional() theory() calculations, and the ion conductivity of the AM-4 family's materials() has been experimentally verified.

The possibility of plants growing on serpentine soils and the ability of serpentine minerals to accumulate significant amounts of metals was the basis for developing a method for using serpentine-containing materials to restore vegetation in areas with a high level of metal pollution. Serpentine-containing products obtained from phlogopite mining overburden (Kovdor, Murmansk region, Russia) with and without thermal activation were used in a field experiment on the remediation of industrially polluted peat soil. According to the geochemical mobility of the components, one of four fractions was allocated depending on the acidic (HCl) concentration of the solution used for the material treatment: readily mobile (0.001 mol/L), mobile (0.01 mol/L), potentially mobile (0.1 mol/L), and acid-soluble (1.0 mol/L). This study showed that the addition of serpentinites to peat soil changed the fraction composition. The most significant changes were noted for serpentinite components such as Ca and Mg: their concentrations increased 2-3 times even in the smallest portion of serpentine material. On the contrary, the contents of metals in the readily mobile fraction decreased 3-18, 3-23, 5-26, and 2-42 times for Cu, Ni, Fe, and Al, respectively. The main factor causing the decrease in metal mobility was the pH rise due to the release of Ca and Mg compounds into the soil solution. This study showed that the addition of serpentine-containing material at 25 vol.% to peat soil was sufficient to create a geochemical barrier with a stable-functioning vegetation cover. All serpentine-containing materials are recommended for the remediation of large industrially polluted areas.

Topological analysis of the heteropolyhedral MT framework (where M and T are octahedral and tetrahedral cations, respectively) in the eudialyte-type structure and its derivatives was performed based on a natural tiling analysis of the 3D cation. To analyze the migration paths of sodium cations in these structures, the Voronoi method was used. The parental eudialyte-type MT framework is formed by isolated ZO 6 octahedra, six-membered [M(1) 6 O 24 ] rings of edge-sharing M(1)O 6 octahedra, and two kinds of rings of tetrahedra, [Si 3 O 9 ] and [Si 9 O 27 ]. Different occupancies of M(2), M(3) and M(4) sites with variable coordination numbers by the additional Q, T* and M* cations, respectively, result in 12 different types of the MT framework. Based on the results of natural tilings calculations as well as theoretical analysis of migration paths, it is found that Na + ions can migrate through six- and seven-membered rings, while all other rings are too small for the migration. In eight types of MT frameworks, Na + -ion migration and diffusion is possible at ambient temperature and pressure, while in four other types cages are connected by narrow windows and, as a result, the Na + diffusion in them is complicated at ambient conditions because of the window diameter, but may be possible either at higher temperatures or under mild geological conditions for long periods of time.

A method of furo-annulation of 4-hydroxy-2-oxoquinoline-3-carboxylates with 3-arylazirines under Cu(II) catalysis was developed to synthesize a variety of 2,3-dihydrofuro[3,2- c]quinolones bearing a carbamate group at the C2 position. The reaction involves an azirine ring opening across the N-C2 bond and formation of a dihydrofuran ring with the inclusion of two azirine carbon atoms, accompanied by a shift of the ester group to the nitrogen. The discovered reaction is the first example of the use of 2 H-azirines for furo-annulation.

The TfOH-mediated reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-oles (CF₃-substituted diaryl propargyl alcohols) with arenes in CH₂Cl₂ afford 1,3-diaryl-1-CF₃-indenes in yields up to 84%. This new process for synthesis of such CF₃-indenes is complete at room temperature within one hour. The synthetic potential, scope, and limitations of this reaction were illustrated by more than 70 examples. The proposed reaction mechanism invokes the formation of highly reactive CF₃-propargyl cation intermediates that can be trapped at the two mesomeric positions by the intermolecular nucleophilic attack of an arene partner with a subsequent intramolecular ring closure., Competing Interests: The authors declare no conflict of interest.

Cu I -catalyzed cycloaddition (CA) of the ketonitrones, Ph 2 C=N + (R')O - (R' = Me, CH 2 Ph), to the disubstituted cyanamides, NCNR 2 (R = Me 2 , Et 2 , (CH 2 ) 4 , (CH 2 ) 5 , (CH 2 ) 4 O, C 9 H 10 , (CH 2 Ph) 2 , Ph(Me)), gives the corresponding 5-amino-substituted 2,3-dihydro-1,2,4-oxadiazoles (15 examples) in good to moderate yields. The reaction proceeds under mild conditions (CH 2 Cl 2 , RT or 45 °C) and requires 10 mol % of [Cu(NCMe) 4 ](BF 4 ) as the catalyst. The somewhat reduced yields are due to the individual properties of 2,3-dihydro-1,2,4-oxadiazoles, which easily undergo ring opening via N-O bond splitting. Results of density functional theory calculations reveal that the CA of ketonitrones to Cu I -bound cyanamides is a concerted process, and the copper-catalyzed reaction is controlled by the predominant contribution of the HOMO dipole -LUMO dipolarophile interaction (group I by Sustmann's classification). The metal-involving process is much more asynchronous and profitable from both kinetic and thermodynamic viewpoints than the hypothetical metal-free reaction., Competing Interests: The authors declare no competing financial interest.

Vesuvianite containing 5.85 wt% TiO 2 from an Alpine-cleft-type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, Pakistan, has been investigated by means of electron microprobe analyses, gas-chromatographic analysis of H 2 O, X-ray powder diffraction, single-crystal X-ray structure refinement, 27 Al NMR, 57 Fe Mössbauer spectroscopy, IR spectroscopy and optical measurements. Tetragonal unit-cell parameters are: a = 15.5326 (2), c = 11.8040 (2) Å, space group P4/nnc. The structure was refined to final R 1 = 0.031, wR 2 = 0.057 for 11247 I > 2σ(I). A general crystal-chemical formula of studied sample can be written as follows (Z = 2): [8-9] (Ca 17.1 Na 0.9 ) [8] Ca 1.0 [5] (Fe 2+ 0.44 Fe 3+ 0.34 Mg 0.22 ) [6] (Al 3.59 Mg 0.41 ) [6] (Al 4.03 Ti 2.20 Fe 3+ 1.37 Fe 2+ 0.40 ) (Si 18 O 68 ) [(OH) 5.84 O 2.83 F 1.33 ]. The octahedral site Y2 is Al-dominant and does not contain transition elements. Another octahedral site Y3 is also Al-dominant and contains Fe 2+ , Fe 3+ and Ti. The site Y1 is split into Y1a and Y1b predominantly occupied by Fe 2+ and Fe 3+ , respectively. The role of the Y1 site in the diversity of vesuvianite-group minerals is discussed.

Derivatives of phaeosphaeride A (PPA) were synthesised and characterised; then anti-cancer studies were carried out on the A549 cancer cell line. It was found that the acetyl derivative (compound 3) displayed comparable in vitro cytotoxicity to that of PPA (EC50=49±7 μM and EC50=46±5 μM, respectively), while chloroacetyl derivative 6 (EC50=33±7 μM) was found to have better efficacy towards the A549 cancer cell line., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A simple approach was developed for the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates from easily available compounds, 5-methoxyisoxazoles and phenacylimidazolium salts under hybrid Fe(II)/Et3N relay catalysis. The products were easily transformed into the corresponding 3-(5-methoxycarbonyl-1H-imidazol-3-ium-3-yl)pyrrol-1-ides, which in turn can be hydrolyzed under basic conditions into the corresponding betaines. A carbene tautomeric form of the 4-methoxycarbonyl-substituted imidazolylpyrrolides was trapped by reaction with sulfur affording the corresponding imidazolethiones under very mild conditions.

Thermal decomposition of a series of diazodicarbonyl compounds in the presence of α,β-unsaturated δ-amino esters and sodium hydride gives rise to a variety of nitrogenous heterocycles. The direction of these processes is highly dependent on the structure of the initial reagents giving rise to the formation of multi-functionalized 2-oxopiperidines, 5,6-dihydropyridin-2(1H)-ones or tetrahydroisoquinoline-1,6(2H,8aH)-diones. The reactions occur in domino processes involving the Wolff rearrangement of diazocarbonyl compounds, NaH-catalyzed anti-stereoselective intramolecular Michael addition to the α,β-unsaturated system of amino esters, and in some cases also cycloelimination and intramolecular Claisen condensation of the initial products formed.

The asymmetric unit of the title compound, C15H23NO5, contains two independent mol-ecules. Phaeosphaeride A contains two primary sections, an alkyl chain consisting of five C atoms and a cyclic system consisting of fused five- and six-membered rings with attached substituents. In the crystal, the mol-ecules form layered structures. Nearly planar sheets, parallel to the (001) plane, form bilayers of two-dimensional hydrogen-bonded networks with the hy-droxy groups located on the inter-ior of the bilayer sheets. The network is constructed primarily of four O-H⋯O hydrogen bonds, which form a zigzag pattern in the (001) plane. The butyl chains inter-digitate with the butyl chains on adjacent sheets. The crystal was twinned by a twofold rotation about the c axis, with refined major-minor occupancy fractions of 0.718 (6):0.282 (6).