scispace - formally typeset
Search or ask a question

Showing papers in "Acta Crystallographica in 1995"


Journal Article
TL;DR: In this article, the authors measured the electron-density image for small, naturally faced single crystals of synthetic calcite (CaCO 3 ), magnesite (MgCO 3 ) and mineral rhodochrosite(MnCO 3 ).
Abstract: Diffraction-deformation electron-density (Δp) images for small, naturally faced single crystals of synthetic calcite (CaCO 3 ), magnesite (MgCO 3 ) and mineral rhodochrosite (MnCO 3 ) were measured with focused λ = 0.7 and 0.9 A synchrotron (SR) X-radiation. Mo Kα (λ = 0.71073 A) structure factors were also measured for MnCO 3 . Lattice mode frequencies predicted from eigenvalues of T and L tensors for CO 3 rigid-group motion in these structures are close to spectroscopic values. High approximate Δp symmetry around the cations increases towards 6/mmm in the sequence CaCO 3 , MgCO 3 to MnCO 3 . The Δp topography near the CO 3 groups shows the influence of the cations, and correlates strongly with the refractive indices, as required for a cause and effect relationship between electron density and optical anisotropy. Aspherical electron density around the Mn atom can be attributed to the effect of a non-ideal octahedral crystal field on the 3d electron distribution. The relationship of the Δp topography near the Mn atom with that near the CO 3 group in MnCO 3 is consistent with magnetic interactions. Space group R3c, hexagonal, Z = 6, T= 295K : CaCO 3 , M r = 100.09, a = 4.988(2), c = 17.068(2) A, V = 367.8(3) A 3 , D x = 2.711 Mg m -3 , μ 0.7 = 1.93 mm -1 , F(000) = 300, R = 0.015, wR = 0.012, S = 3.0 for 437 unique reflections ; MgCO 3 , M r = 84.31, a = 4.632(1), c = 15.007 (2) A, V = 278.8 (2) A 3 , D x = 3.013 Mg m -3 , μ 0.9 = 0.99 mm -1 , F(000) = 252, R = 0.015, wR = 0.021, S = 4.34 for 270 unique reflections ; MnCO 3 , M r = 114.95, a = 4.772(3), c = 15.637 (3) A, V = 308.4 (4) A 3 , D x = 3.713 Mg m -3 , p 0.7 = 5.62 m -1 , F(000) = 330, R = 0.015, wR = 0.039, S = 3.38 for 386 unique reflections of the SR data set and a = 4.773 (1), c = 15.642(1) A, V = 308.6 (1) A 3 , D x = 3.711 Mg m -3 , μ(Mo Kα) = 5.86 mm -1 , R = 0.017, wR = 0.024, S = 2.79 for 368 unique Mo Kα reflections.

136 citations


Journal Article
TL;DR: In this paper, a series of non-macrocyclic ligands to FKBP12 have been synthesized, which are comparable in binding potency and peptidyl prolyl isomerase (PPIase) inhibition.
Abstract: We have synthesized a series of non-macrocyclic ligands to FKBP12 that are comparable in binding potency and peptidyl prolyl isomerase (PPIase) inhibition to FK506 itself. We have also solved the structure of one of these ligands in complex with FKBP12, and have compared that structure to the FK506-FKBP12 complex. Consistent with the observed inhibitory equipotency of these compounds, we observe a strong similarity in the conformation of the two ligands in the region of the protein that mediates PPIase activity. Our compounds, however, are not immunosuppressive. In the FKBP12-FK506 complex, a significant portion of the FK506 ligand, its 'effector domain', projects beyond the envelope of the binding protein in a manner that is suggestive of a potential interaction with a second protein, the calcium-dependent phosphatase, calcineurin, whose inhibition by the FKBP 12-FK506 complex interrupts the T-cell activation events leading to immunosuppression. In contrast, our compounds bind within the surface envelope of FKBP12, and induce significant changes in the structure of the FKBP12 protein which may also affect calcineurin binding indirectly.

14 citations


Journal Article
TL;DR: In this paper, the structure analysis of (1, 1'-ferrocenediyl)methylphenylsilane, [Fe(C 17 H 16 Si)], is the first such study of an unsymmetrically substituted silicon-bridged [1]ferrocenophane.
Abstract: The structure analysis of the title compound, (1, 1'-ferrocenediyl)methylphenylsilane, [Fe(C 17 H 16 Si)], is the first such study of an unsymmetrically substituted silicon-bridged [1]ferrocenophane. The strain present in this molecule results in a tilting of the cyclopentadienyl rings by 21.0 (2)° from being parallel

7 citations




Journal Article
TL;DR: In this paper, the title compound, C7H7N302S, was compared with diazoxide, an antihypertensive agent, from a structural and pharmacological point of view, and it was shown that the 4H (rather than 2H) tautomeric form is preferentially adopted by this pyridothiadiazine derivative in the solid state.
Abstract: The title compound, C7H7N302S, was prepared for comparison with diazoxide, an antihypertensive agent, from a structural and pharmacological point of view. The crystal structure determination shows that the 4H (rather than 2H) tautomeric form is preferentially adopted by this pyridothiadiazine derivative in the solid state.

Journal Article
TL;DR: The structure belongs to the monophosphate group and contains one type of PO 4 tetrahedra connected to one type MgO 6 octahedra by corner sharing.
Abstract: The structure belongs to the monophosphate group and contains one type of PO 4 tetrahedra connected to one type of MgO 6 octahedra by corner sharing. These PO 4 -MgO 6 groups are connected along the two shorter a and b axes to form two-dimensional zigzag sheets. Two sheets are connected along the longer c axis by two types of Na-O polyhedra. Pairs of PO 4 tetrahedra in the sheets are connected by H atoms situated at the centres of symmetry, forming short hydrogen bonds.