Crystal growth and structural investigation of A2BReO6 (A=Sr, Ba; B=Li, Na)

Single crystals of the double perovskite rhenates A₂BReO₆ (A=Sr, Ba; B=Li, Na) were grown out of molten hydroxide fluxes. Single crystals of orange/yellow Ba₂LiReO₆, Ba₂NaReO₆ and Sr₂LiReO₆ were solved in the cubic, Fm-3m space group with a=8.1214(11) Å, 8.2975(3) Å, and 7.9071(15) Å, respectively, while Sr₂NaReO₆ was determined to be monoclinic P2₁/n with a=5.6737(6) Å, b=5.7988(6) Å, c=8.0431(8) Å, and β=90.02(6) °. The cubic structure consists of a rock salt lattice of corner-shared ReO₆ and MO₆ (M=Li, Na) octahedra which, in the monoclinic structure, are both tilted and rotated. A discrepancy exists between the symmetry of Sr₂LiReO₆ indicated by the single-crystal refinement of flux-grown crystals (cubic, Fm-3m) and the symmetry indicated by the powder diffraction data collected on polycrystalline samples prepared by the ceramic method (tetragonal, I4/m). It is possible that the cubic crystals are a kinetic product that forms in small quantities at low temperatures, while the powder represents the more stable polymorph that forms at higher reaction temperature.     

Synthesis, structure and magnetic properties of A2MnB′O6 (A=Ca, Sr; B′=Sb, Ta) double perovskites

A₂MnB′O₆ (A=Ca, Sr; B=Sb, Ta) double perovskites have been synthesized and their structural and magnetic properties have been investigated. Rietveld refinement of the powder X-ray diffraction data for Sr₂MnSbO₆ indicated significant ordering of Mn and Sb at the B-site while all other phases showed mostly a random distribution of the B-site cations. X-ray absorption spectroscopic data established the presence of Mn in the 3+ and Sb/Ta in the 5+ oxidation states in all the phases. Magnetic susceptibility data indicated ferromagnetic correlations for all the A₂MnB′O₆ phases with Weiss temperatures varying from 64 to 107 K.     

Belamcandanes A and B,two unprecedented tricyclic-iridal triterpenoids from Belamcanda chinensis

Two unprecedented tricyclic-iridal triterpenoids, belamcandanes A–B (1–2), have been isolated from the rhizomes of Belamcanda chinensis. The structures of 1 and 2 were assigned by interpretation of spectroscopic data including NMR and MS, and their absolute configurations were assigned by ECD calculation. Compounds 1–2 possess a spiro[4,5]decane core structure and a α-terpineol moiety, representing the first example of tricyclic-iridal triterpenoids. The plausible biogenetic pathway for 1 and 2 is also proposed.     

Raman spectra of lanthanide sesquioxide single crystals: Correlation between A and B-type structures

Structures and Raman spectra of lanthanide sesquioxide single crystals with A-type trigonal structure (La₂O₃, Pr₂O₃, Nd₂O₃, Sm₂O₃) and B-type monoclinic structure (Sm₂O₃, Eu₂O₃, Gd₂O₃) are compared. The B form (C³_2h or $\text{C2}\text{m}\text{, Z = 6}$) derives from the A form (D³_3d or $\text{P}\text{3}\text{m1, Z = 1}$) by a slight lattice deformation, implying a splitting of D_3d and C_3v atomic positions into less symmetrical C_2h and C_s sites. This close structural relationship allows one to relate the Raman active modes of the B-type crystals to vibrations of the A-type crystals and to deduce an interpretation of the complex B-type spectra from those of the simpler A-type spectra. Furthermore, it is shown that the frequency of the modes which mainly involve metal-oxygen stretching motion increases with the lanthanide atomic number in the A and B series. This evolution is interpreted in terms of increasing compactness of the structure.     

Kadcoccilactones K-R, triterpenoids from Kadsura coccinea

Phytochemical investigation on the stems of Kadsura coccinea led to the isolation of 8 new triterpenoids, kadcoccilactones K-R (1-8), and 10 known analogues. Their structures were elucidated on the basis of extensive spectroscopic analysis. Compounds 1-3 characterized with an aromatic ring E in their molecules are rarely naturally occurred kadlongilactone derivatives. Moreover, all compounds were evaluated for their inhibitory activity against K562, Bel-7402, and A549 human tumor cells. Compounds 9 and 10 exhibited potent cytotoxicity against K562, Bel-7402, and A549 cell lines with IC₅₀ values less than 0.1, 0.1, and 1.0 μm, respectively.     

Order-disorder in In perovskites: The example of A(In2/3B″1/3)O3 (A=Ba, Sr; B″=W, U)

We describe the preparation and structural characterization of four In-containing perovskites from neutron powder diffraction (NPD) and X-ray powder diffraction (XRPD) data. Sr₃In₂B″O₉ and Ba(In_2/3B″_1/3)O₃ (B″=W, U) were synthesized by standard ceramic procedures. The crystal structure of the W-containing perovskites and Ba(In_2/3U_1/3)O₃ have been revisited based on our high-resolution NPD and XRPD data, while for the new U-containing perovskite Sr₃In₂UO₉ the structural refinement was carried out from high-resolution XRPD data. At room temperature, the crystal structure for the two Sr phases is monoclinic, space group P2₁/n, where the In atoms occupy two different sites Sr₂[In]_2d[In_1/3B″_2/3]_2cO₆, with a=5.7548(2) Å, b=5.7706(2) Å, c=8.1432(3) Å, β=90.01(1)° for B″=W and a=5.861(1) Å, b=5.908(1) Å, c=8.315(2) Å, β=89.98(1)° for B″=U. The two phases with A=Ba should be described in a simple cubic perovskite unit cell (S.G. Pm3¯m) with In and B″ distributed at random at the octahedral sites, with a=4.16111(1) Å and 4.24941(1) Å for W and U compounds, respectively.     

Structural determination of two new triterpenoids biotransformed from glycyrrhetinic acid by Mucor polymorphosporus

Five hydroxylated derivatives of glycyrrhetinic acid by Mucor polymorphosporus were isolated. Among them, 6β, 7β‐dihydroxyglycyrrhentic acid (2) and 27‐hydroxyglycyrrhentic acid (3) are new compounds. Their chemical structures were identified by spectral methods including 2D‐NMR. Copyright © 2009 John Wiley & Sons, Ltd.     

NQR study of ternary chalcogenides A3BX3, ABX2, and ABX where A = Cu,Ag, or TI, B = As or Sb,and X = S or Se

¹²¹Sb, ¹²³Sb, ⁷⁵As, ⁶³Cu, and ⁶⁵Cu NQR resonances are reported for CuSbSe₂, Tl₃SbSe₃, Tl₃SbS₃, Tl₃AsS₃, Tl₃AsSe₃, Ag₃AsSe₃, TlSbS₂, CuAsS, AgAsS, and Cu₅SbS₃I₂. Tl₃SbSe₃ is an incongruently melting compound not observed in an earlier phase-diagram study of the pseudobinary system Tl₂SeSb₂Se₃. For isostructural arsenic and antimony chalcogenides the ratio of ⁷⁵As to ¹²¹Sb quadrupole coupling constants is 0.42, and for the BX₃ group in binary or ternary corresponding pairs of sulfide and selenides the ratio of quadrupole coupling constants for ⁷⁵As or ¹²¹Sb is 0.83. A reversible phase transition was observed at 130 K for Ag₃AsSe₃. Unit cell parameters are reported for crystals of TlSbS₂ and Cu₅SbS₃I₂.     

Smectic E,C and A free radicals

Some new paramagnetic liquid crystals are described. Their mesophases have been identified, by isomorphism with known phases, as smectic mesophases of types S_E, S_C and S_A.     

Malyngic acid,a new fatty acid from Lyngbya majuscula

Malyngic acid, a major fatty acid in several varieties of the marine blue-green alga Lyngbya majuscula, has been determined to be 9(S),12(R),13(S)-trihydroxyoctadeca-10(E),15(Z)-dienoic acid from chemical and spectral data and by its conversion to 9(S),12(R),13(S)-trihydroxystearic acid and degradation to 2-deoxy-D-ribitol.     

The first A-nor-hippuristanol and two novel 4,5-secosuberosanoids from the Gorgonian Isis hippuris

The first A-nor-hippuristanol, A-nor-22-epi-hippurin-2α-carboxylic acid (1), and two 4,5-secosuberosane sesquiterpenoids, isishippuric acids A and B (2 and 3), have been isolated from the gorgonian coral Isis hippuris. Those structures were deduced by extensive 1D and 2D NMR studies. The structure of 1 was further supported by a single crystal X-ray diffraction analysis. Isishippuric acid B has been shown to exhibit potent cytotoxicity toward a limited panel of cancer cells.     

First examples of tetracyclic triterpenoids with a D:B-friedobaccharane skeleton. A tentative biosynthetic route

Baruol (1) and Leonal (2), first examples of tetracyclic triterpenes possessing a D:B-friedobaccharane skeleton, were isolated from Maytenus blepharodes and M. chiapensis, respectively. Their structures were established by spectroscopic analysis, molecular modeling studies and biogenetic background. The implication of the D:B-friedobaccharenyl cation in the biosynthetic route of baccharane and shionane skeletons is discussed. Baruol exhibited β-glucuronidase inhibitory activity, a target in the search for hepatoprotective agents.     

Tetracyclic triterpenoids from Melia azedarach, L.—III

From petroleum ether extracts of the bark of M. azedarach four novel tetracyclic triterpenoids have been isolated and characterized to be C₃₀ compounds of the euphane (20R) series. Previously known triterpenoids from Meliaceae have all been 20S compounds. Kulinone 1 is the first known euphane or tirucallane (20S) derivative oxygenated in the D ring; kulactone 2, kulolactone 3 and methyl kulonate 4 are additionally oxygenated in the side chain. Compounds 2 and 3 have a 2-oxa-trans-bicyclo[3,3,0]-octanone structure.     

Isothermal decomposition of ternary oxide AxByOz on an isobar—Stability of perovskite ABO3 (A = La,Sm, Dy; B = Mn,Fe) in a reducing atmosphere

The isothermal decomposition of any ternary oxide A_xB_yO_z on liberation of n moles of oxygen at a constant pressure is found to be driven by the mixing entropy ΔS_m = ?nRln P_O2 of the total entropy change ΔS = ΔS° + ΔS_m. The stability of A_xB_yO_z towards isothermal decomposition into a biphasic solid mixture is derived from the equilibrium condition $\text{ΔG1 = 0}$ as functions of standard changes ΔH° and ΔS°. Assuming ΔS° = 44n and calculating ΔH° in terms of lattice energies U(ABO₃) and U(A₂O₃), the stability of perovskites is given as a function of the ionic radius of the A³⁺ ion. The calculated stability agrees well with that observed. The effect of electronic entropy change ΔS_e on ΔS° is demonstrated for AFeO₃ (A = La, Sm, Dy).     

Phytolaccinic acid,a new triterpene from Phytolacca americana

The saponin from the berries of Phytolacca americana yielded one known and two new aglycones. One of the new aglycones was identified as desmethylphytolaccagenin 2, and the other as 3β, 23-dihydroxyolean-12-ene-28, 30-dioic acid-30-methyl ester 3.     

Stelliferins J-N, isomalabaricane-type triterpenoids from Okinawan marine sponge Rhabdastrella cf. globostellata

Five new isomalabaricane-type triterpenoids, stelliferins J-N (1-5), were isolated from Okinawan marine sponge Rhabdastrella cf. globostellata. The structures of 1-5 were elucidated from the spectroscopic data and chemical means including application of a modified Mosher’s method and an exciton chirality method.     

Synthesis and structure of a new family of phases, A2MGe5O12: A = Rb,Cs; M = Be,Mg, Co,Zn

A new family of eight germanate phases, A₂MGe₅O₁₂: A = Rb, Cs; M = Be, Mg, Co, Zn, has been synthesized. They are cubic with a in the range 13.7 to 14.0 Å, Z = 8, and space group $\text{I}\text{4}\text{3d}$. These phases, named the β phases, are isostructural with KBSi₂O₆ which has a structure related to that of pollucite, CsAlSi₂O₆. The structure of one, Rb₂ZnGe₅O₁₂, has been refined to an R value of 0.079 using X-ray powder diffraction data. Several of the new phases are polymorphic. Cs₂ZnGe₅O₁₂, Cs₂CoGe₅O₁₂, and Rb₂MgGe₅O₁₂ form low-temperature, δ polymorphs which have primitive cubic unit cells. Rb₂ZnGe₅O₁₂ forms a low-temperature, ε polymorph which is probably a tetragonal distortion of the β structure.     

Lannotinidines A-G, new alkaloids from two species of Lycopodium

Seven new Lycopodium alkaloids, lannotinidines A-G (1-7), have been isolated from the club moss Lycopodium annotinum and L. annotinum var. acrifolium. Stereochemistry of 1-7 was elucidated by combination of NOESY correlations and chemical transformation. Lannotinidines B-E (2-5) elevated NGF mRNA expression.     

Interference between A- and B-term resonance Raman scattering for totally symmetric modes

A resonance Raman scattering mechanism for totally symmetric modes is proposed, involving both A- and B-term contributions to the transition polarizability. It is shown how interference between A- and B-term scattering may give rise to an asymmetric excitation profile.