Single-crystal X-ray Experiments Research Articles

Lancifodilactone F: A Novel Nortriterpenoid Possessing a Unique Skeleton from Schisandra lancifolia and Its Anti-HIV Activity

[structures: see text] Lancifodilactone F (1), possessing an unprecedented rearranged pentanortriterpenoid backbone derived from cycloartane, was isolated from the leaves and stems of Schisandra lancifolia (Rehd. et Wils) A. C. Smith. Its structure was established by comprehensive NMR and MS spectroscopic analysis, coupled with single-crystal X-ray experiment. Compound 1 exerted minimal cytotoxicity against C8166 cells (CC50 > 200 microg/mL) and showed anti-HIV activity with EC50 = 20.69 +/- 3.31 microg/mL and a selectivity index > 6.62.

The crystal data and stability of calcite III at high pressures based on single-crystal X-ray experiments

Single-crystal X-ray experiments have been performed for calcite, calcite II, and calcite III at 300 K and pressures up to 4.1 GPa. The volume decrease from calcite to calcite II is estimated to be 0.54 cm3/mol (1.5 %) at 1.5 GPa, which compares well with the value 0.48 cm3/mol in the calcite to calcite II transition at 1.4 GPa reported previously based on piston-cylinder volume-compression experiments. The crystal data of calcite III have been determined using single-crystal X-ray analyses at 300 K and pressures between 2.3 and 4.1 GPa. The calcite III crystal is found to be monoclinic with the space group either C2, Cm, or C2/m from the systematic absence of reflections, and with the refined cell parameters of a = 8.707(7), b = 9.315(6), c = 6.154(4) A, and β = 115.18(2)° at 2.3 GPa. These crystal data of calcite III at 2.3 GPa yield a density of 2.94 g/cm3 for Z = 8, which is much less than the previously estimated densities, ranging from 3.11 to 3.28 g/cm3 at pressures from 1.9 to 2.9 GPa, using powder X-ray analyses based on orthorhombic structural models for calcite III, but is generally consistent with the reported data by the piston-cylinder experiments. Thus the present study reveals the density of calcite III is substantially less than that of aragonite (3.02 g/cm3 at 2.3 GPa), indicating that calcite III is metastable with respect to aragonite at high pressures.

Unusual Sesquiterpene Lactones from Ligularia virgaurea spp. oligocephala.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Unusual Sesquiterpene Lactones from Ligularia virgaurea spp. oligocephala

[structure: see text] [structure: see text] Sesquiterpene lactones, ligulolide A (1) and 6beta,8alpha-dihydroxy-1-oxoeremophila-7(11),9(10)-diene-12,8-olide (2), were isolated from Ligularia virgaurea spp. oligocephala. Their structures were established by analysis of one- and two-dimensional NMR data. The relative stereostructures were determined on the basis of NOESY and single-crystal X-ray experiments. 1 represents a novel sesquiterpene carbon framework, and a possible biosynthetic process is proposed. 2 is a novel eremophilane-type sesquiterpene.

A comparison of the ring conformational properties of two derivatives prepared from the same diene diacetate precursor.

Results of single-crystal X-ray experiments performed for the title compounds, (1S,2R,3S,4R,5R)-4-benzyloxy-2-[1-(benzyloxy)allyl]-5-hydroxymethyl-2,3,4,5-tetrahydrofuran-3-ol, C(22)H(26)O(5), (I), and (3R,5S,6S,7S,8S)-3,6-bis(benzyloxy)-5-iodomethyl-2,3,4,5-tetrahydrofuro[3,2-b]furan-2-one, C(21)H(21)IO(5), (II), demonstrate that the tetrahydrofuran ring that is common to both structures adopts a different conformation in each molecule. Structural analyses of (I) and (II), which were prepared from the same precursor, indicate that their different conformations are caused by hydrogen-bonding interactions in the case of (I) and the presence of a fused bicyclic ring system in the case of (II). Density functional theory calculations on simplified analogs of (I) and (II) are also presented.

Two New Guaianolides and a New Daucene Derivative fromSinodielsia yunnanensis

From the roots and rhizomes of Sinodielsia yunnanensis, three new sesquiterpenes were isolated and their structures were established as 5alpha,6beta- H-1(10),3,7(11)-guaiatrien-12,6alpha-olide ( 1), 5alpha,6beta,7beta- H-1(10),3-guaiadien-12,6alpha-olide ( 2) and 5beta-hydroxy-10alpha- O-angeloyl-3-oxodauc-8-ene ( 3) by means of spectroscopic analyses and single-crystal X-ray experiment (for compound 1).

Chemistry of a novel family of tridentate alkoxy tin(II) clusters.

The chemical interconversions observed for a novel family of trihydroxymethyl ethane (THME-H(3)) ligated Sn(II) compounds have been determined using single-crystal X-ray and (119)Sn NMR experiments. (mu-THME)(2)Sn(3) (1) was isolated from the reaction of 3 equiv of [Sn(NR(2))(2)](2) (R = SiMe(3)) with 4 equiv of THME as a unique trinuclear species capped above and below the plane of Sn atoms by two THME ligands. Upon reaction with "Sn(NR(2))(2)", compound 1 rearranged to yield another novel molecule [(mu-THME)Sn(2)(NR(2))](2) (2). Compound 2 could also be formed directly from the stoichiometric mixture of THME-H(3) and [Sn(NR(2))(2)](2). Further studies revealed that 1 would also rearrange in the presence of Sn(OR)(2) to form [(mu-THME)Sn(2)(mu-OR)](2) [OR = OMe (3), OCH(2)Me (4), OCH(2)CH(Me)CH(2)CH(3) (5), OCH(2)CMe(3) (6, ONep), OC(6)H(5) (7, not structurally characterized), OC(6)H(4)Me-3 (8), OC(6)H(4)Me-2 (9), OC(6)H(3)(Me)(2)-2,6 (10), OC(6)H(3)(CHMe(2))(2)-2,6 (11). Additionally, 3-11 could by synthesized from the reaction of 2 and the appropriate H-OR. (119)Sn solution NMR studies of 2-11, in THF-d(8), indicate that an equilibrium between the parent complex and its disassociation products (1 and the free parent Sn alkoxy or amide precursor) exists at room temperature. This is a likely reason behind the ease of interconversion observed for 1. The generality of this exchange was further verified through the reaction of 1 with [Ti(mu-ONep)(ONep)(3)](2), which led to the isolation of (mu-ONep)(2)Sn(3)(mu-THME)(2)Ti(ONep)(2) (12). For 12, the solid-state structure was maintained in solution with no indication of an equilibrium.

A New Family of Supramolecular Complexes with 3D Cationic Hg/Z Frameworks, SnX3− Guest Anions (Z = P, As, Sb; X = Cl, Br, I): Crystal Structures and Host−Guest Interactions

Five new inorganic supramolecular complexes, [Hg6P4Cl3](SnCl3) (I), [Hg6As4Cl3](SnCl3)Hg0.13 (II), [Hg6As4Br3](SnBr3) (III), [Hg6Sb4I3](SnI3)Hg0.16 (IV), and [Hg7P4Br3](SnBr3) (V), have been prepared and their structures determined by X-ray single crystal experiments. They all crystallize in the cubic space group P213 (No 198) with Z = 4, and unit cell parameters a = 11.865(1) (I), 12.233(1) (II), 12.383(1) (III), 13.285(2) (IV), and 12.490(1) A (V). The crystal structures of these compounds are composed of the 3D positively charged frameworks [Hg6Z4X3]+ (I−IV) or [Hg7P4Br3]+ (V), with SnX3− anions trapped in the larger cavities of the frameworks (X = Cl, Br, I; Z = P, As, Sb). In the structures of II and IV the smaller cavities are partly filled by mercury atoms. The structures of I−V and of previously reported [Hg7As4I3](SnI3) (VI) are discussed with respect to the matching and mutual adjusting of the host frameworks and guest anions. A comparison of the observed and calculated (ab initio, RHF level) geometry of the SnX3− anions is used to analyze the weak host−guest interactions.

Crystal structures of 2- and 3-cyanopyridine

The crystals of 2- and 3-cyanopyridine isomers have been obtained by a sublimation method. The crystal structures of both isomers have been determined on the basis of low-temperature X-ray single crystal experiments and compared, also in relation to 4-cyanopyridine. In 2-cyanopyridine the nitrogen atom of the CN group, whereas in 3- the N-ring atom, is involved in the shortest intermolecular contact. In both cases, the hydrogen bond type interactions are rather of a weak nature, but they are important for developing of the polymeric chains.

The lack of C2 molecular symmetry in (1R,2R,3S,6S)-3,6-dibenzyloxycyclohex-4-ene-1,2-diol.

The results of a single-crystal X-ray experiment and density functional theory calculations performed for the title compound, C20H22O4, demonstrate that the lowest energy conformation of this molecule does not contain C2 molecular symmetry.

%Variable-Temperature Studies of Order/Disorder Transitions in the Thiourea Pyridinium Halide Crystals by XRD and Solid-State 2H NMR

Variable-temperature single-crystal X-ray experiments have been performed on the thiourea pyridinium chloride, bromide, and iodide inclusion compounds. Two phases were found for the chloride, three for the bromide, and two for the iodide. As previously reported for the bromide, at room-temperature all three halides were found to form orthorhombic crystals in space group Cmcm. For each compound, the pyridinium cation is disordered in the square cross section thiourea channels. On cooling, the chloride undergoes a phase change between 200 and 230 K to give an orthorhombic form in Pbca with the a axis doubled and the pyridinium ions partially ordered. The bromide undergoes a phase change between 170 and 165 K to a partially ordered form in space group Cmc21 with the a axis tripled. A second phase change occurs between 140 and 150 K to a fully ordered phase in space group P21cn with cell dimensions approximately the same as the room-temperature form. The iodide undergoes a single-phase transition at 120−130 K to a fully ordered form isomorphous with the low-temperature form of the bromide. The phase transitions have also been studied by VT 2H NMR of the perdeuteriopyridinium salts. These data have been correlated with the XRD data and with models for the motion of the pyridinium cation.

High-Resolution Powder Diffractometry to Study the Phase Transition of h-BaTiO3

High-resolution powder diffraction experiments of hexagonal BaTiO3 were performed at BL02B1 of SPring-8 to determine the symmetry and the lattice form in the low temperature phases. The best resolution achieved was 0.0085° as FWHM even for the powder diffraction. The symmetry of the lowest ferroelectric phase was determined to be a monoclinic associated with small distortion. The deviation from 120° was only 0.05°. The intermediate phase was orthorhombic as was reported. Based on these analysis, both results on the high-resolution X-ray single crystal experiments performed at the home laboratory and the high-resolution powder neutron scattering experiments performed at JRR3M were interpreted.

Phase transitions of modulated Co-åkermanite, Ca2CoSi2O7

Abstract This paper deals with X-ray single crystal experiments of modulated cobalt åkermanite at temperatures between 30 K and 600 K. The primary objective of these investigations was to study the predicted lock-in phase transition into a commensurate low temperature phase. Upon cooling the phase transition occurs at 160 K, provided that the time for thermodynamic equilibration at each temperature step is guaranteed. The low temperature phase turns out to be incommensurate with a modulation wavelength of 3.086(6) · a 0. This is very close to the predicted commensurate value of 3 · a 0 The standard deviations of the q-values are small enough to determine this low temperature phase as significantly incommensurate. A fourier synthesis of the complementary structure (as a 3-fold superstructure) reveals a tetragonal displacement pattern of the cobalt-atoms at low temperatures. The second order phase transition to the parent structure occurs at 498(1) K. It is characterized by a critical exponent β = 0.31(1)°.

Two New Cubic Structures of Mercury Arsenidehalides

Crystal structures of Hg4As2Br3(I) and Hg7.4As4Cl6(II), which was prepared for the first time, have been refined based on the X-ray single crystal experiments. Both phases crystallize in the cubic space groupPa3. Crystal data: I,a= 12.610(1),Z= 8,R1= 0.0602; II,a= 12.178(1),Z= 4,R1= 0.0584. Characteristic of both structures are the As2Hg6octahedra having an As–As separation of ca. 2.38 Å. Such octahedra share vertices with AsHg4tetrahedra in I, while in II they compose a perovskite-like three-dimensional network by sharing all vertices. Part of the mercury atoms in II have no neighbors up to 3.53 Å and are considered to possess a zero oxidation state. An idealized path for the I to II structure transformation, which is based on the difference of halogen radii, is suggested.

Zirconium niobium phosphide (Zr6.45Nb4.55P4), a new mixed-transition-metal phosphide structure

A new structure which is similar to that of many known binary early-transition-metal phosphides, sulfides, and selenides has been found in the ternary Zr-Nb-P system. The compound Zr[sub 6.45]Nb[sub 4.55]P[sub 4] was synthesized using high-temperature techniques and characterized through X-ray single-crystal experiments. The space group is Immm with lattice parameters a = 15.917 (1) [angstrom], b = 9.5684 (9) [angstrom], and c = 3.5892 (3) [angstrom]. Bond order calculations revealed the approximate metal site occupancies and anomalous scattering allowed refinement of the metal site occupancies. 21 refs., 1 fig., 4 tabs.

New complex oxides in RBaThCuO systems ( R = LaGd)

The new complex oxides R 2Ba 1.33Th 0.67Cu 3O 8+ δ ( R = La, Pr) and La 0.67Ba 1.33 R 2− x Th x Cu 3O 8+ δ ( R = NdGd, x = 0.5, 0.67) were synthesized. These compounds have a similar structure to the Ce-223 high- T c oxides. The oxygen content (or δ) was varied over a wide range after annealing at high oxygen pressure (up to 90 atm). Unit cell parameters and δ values for all the new phases were determined. The resistivities of these semiconducting compounds obey the law ϱ = ϱ o T − α . A single crystal of Nd 2Ba 1.5Th 0.5Cu 3− x Al x O 8+ δ ( x = 0.3, δ = 0.8) was obtained and its structure was determined by X-ray single-crystal experiment (tetragonal system, space group I4 mmm , a = 3.9057(5) Å, c = 28.569(4) Å, Z = 2).