Gabriela Weber

Crystallization of proteins under microgravity

For the crystallization of proteins under microgravity conditions, a Chinese re‐entry system was used, in which 101 experiments of 25 different biological macromolecules were accommodated. From the results obtained we conclude that under microgravity conditions crystal growth can only be expected under those crystallization conditions which also permit crystal growthon earth. A number of space‐grown crystals were larger in size and of a better quality in their ability to diffract X‐rays than the corresponding ground control crystals grown at the Chinese launch site. However, the space‐grown crystals have not reached the X‐ray diffraction quality of the crystals obtained under optimal conditions in the home laboratories.

(β-Cyclodextrin)2·KI7·9 H2O. Spatial fitting of a polyiodide chain to a given matrix

Abstractα-Cyclodextrin, a torus shaped molecule with a 5 Å wide central cavity, forms a number of deep green, blue and black crystals when complexed with iodine/metal iodide. In contrast, β-cyclodextrin, having a 6 Å cavity produces only one type of reddish-brown crystal, no matter what metal iodide is used. The complex (β-cyclodextrin)2 ·KI7·9H2O displays space groupP21 (pseudo-C2) with cell constantsa=19.609(5),b=24.513(7),c=15.795(6)Å, β=109.50(2)°,Z=4. The crystal structure was solved inC2 on the basis of 3022 absorption corrected CuKα (Ni-filter) X-ray intensities and refined by full matrix least squares toR=17%. This relatively highR-factor is due to many weak reflections (pseudo-C2) and considerable disorder exhibited by water and iodine. In the complex, β-cyclodextrin adopts a ‘round’ shape with O(2)...O(3) interglucose hydrogen bonds formed and all O(6) hydroxyls pointing away from the cavity. Two molecules are arranged head-to-head to produce a dimer, and dimers are stacked such that a slightly zigzagged cylinder with a 6 Å-wide cavity is formed. In the cavity described by each dimer, an I7− ion composed of I2·I3−·I2 units is located, with I2 and I3− perpendicular to each other. K+ ions and 9 H2O molecules are found in interstices between the β-cyclodextrin cylinders. This zigzag polyiodide contrasts with the linear form observed in the 5 Å wide α-cyclodextrin channels. It explains differences in color of the crystals and suggests that β-cyclodextrin polyiodide is not a good model for blue starch-iodine.

Versatility of the cyclic ligand 5,8,11-trioxa-2,14-dithia[15] (2,6)-pyridinophane: with copper(II) chloride

Abstract Colourless crystal of the Ba complex (1), C 15 H 23 NO 3 S 2 ·Ba(SCN) 2 ·H 2 O, Mr = 601.0, are triclinic, P 1 , a = 9.449(3), b = 14.710(4), c = 10.090(4) A, α = 113.41(6), β = 106.89(7), γ = 74.15(6)°, Z = 2, D c = 1.647, D o = 1.65 g cm −3 . The structure was refined to R = 0.054 for 5565 independent diffractometer data. Dark green needles of the Cu complex (2), C 15 H 23 NO 3 S 2 ·CuCl 2 , Mr = 463.9, are also triclinic, P 1 , a = 7.912(4), b = 8.793(5), c = 15.082(7) A, α = 92.79(9), β = 101.75(8), γ = 66.56(9)°, Z = 2, D c = 1.636, D o = 1.615 g cm −3 . This structure was refined to R = 0.095 using 2954 unique data. As is reflected by torsion angles, there is significantly more ring strain in the complexation of the ‘non-fitting’ cation Cu 2+ than in the complexation of the ‘ideal-fitting’ Ba 2+ cation. The latter is held in the centre of the cavity of the ligand and nine-fold coordinated to all the six hetero atoms of the ligand, to one water molecule, and to two − NCS anions. With the much smaller Cu 2+ cation, however, the ligand adopts a folded conformation leaving the Cu 2+ coordination geometry relatively undistorted from a regular square pyramid. This is formed by the three neighbouring hetero atoms S, N, S of the ligand and two Cl − anions; oxygen atoms of the ligand are not involved in obvious interactions.

Carbonyl oxygen coordinated to potassium in a monomeric and a dimeric crown ether complex: The crystal structure of [18] ·KNCS

Abstract Colourless crystals of the title compound, M r = 469.61, are monoclinic, P 2 1 /c, a = 21.631(9), b = 9.170(4), c = 23.746(9) A, β = 93.48(5)°, U = 4701.5 A 3 , D c = 1.327 Mg m −3 for Z = 8. The structure was solved by direct methods and refined to R = 0.058 for 4850 diffractometer data. There are two independent ion pairs per asymmetric unit. In complex A the cation is additionally coordinated to the five ether O atoms (mean distance 2.92 A) of the macrocycle, to the carbonyl O at 3.049(2) A and to a symmetry related second >CO at 2.846(2) A, thus giving rise to a dimer via linkages. The monomeric complex B is characterised by a relatively short >CO··K + contact of 2.587(2) A and three strong (mean distance 2.73 A) and two weak (mean distance 3.14 A) K + ··O(ether) interactions.

Synchrotron light on ribosomes: The development of crystallographic studies of bacterial ribosomal particles

Table o f

cis-trans-Configuration of α-Azidochalkones

Abstract The two stereoisomeric α-azidochalkones (1,3-diaryl-2-azidopropenones) are selectively obtain-able, depending on the temperature, by condensation of aldehydes with a-azidocarbonyl compounds. For the higher melting point compound the trans configuration is proved by single crystal X-ray analysis of its triphenyl-phosphazeno derivative. Analogous isomers may now be characterised from their 1H NMR parameters.

X-Ray Structure Analysis and Spectroscopic Data of the Antibiotic 8-(Dichloroacetyl)-5-hydroxy-2,7-dimethyl-1,4-naphthoquinone from the Fungus Mollisia sp.*

Abstract Mass spectra, X-ray data and high resolution 13C and 1H NMR spectra of 8-(dichloroacetyl)-5-hydroxy-2,7-dim ethyl-1,4-naphthoquinone are reported. The antibiotic active com pound was isolated from the fungus Mollisia sp.

A 1:1 Host-Guest Complex between 1,4,7,10,13,16-Hexaoxacyclooctadecane ('18-crown-6') and m-Nitroaniline: Mere Stoicheiometry or a Genuine 1:1 Adduct ?

Abstract The stoicheiometrically 1:1 adduct of 1,4,7,10,13,16-hexaoxa-cyclooctadecane with m-nitroaniline, C18H30N2O8, Mr = 402.45, crystallises from toluene in red-orange prisms, (probable) space group P1̄, a = 801.8(3), b = 920.4(3), c = 1403.3(4) pm, α = 80.40(4), β = 79.79(4), γ = 85.95(3)°, V = 1.07910 nm3 , Z = 2, dcalc. = 1.238 Mgm-3 . Structure refinement converged at R = 0.060 (Rw = 0.002) for 2915 diffractometer data.

Structural Change of a Line ar Polyether upon Complex Formation. 1.11-Bis(2-acetylaminophenoxy)-3.6.9-trioxaundecane and its KSCN Complexa

The title compound (1) was crystallized as free ligand and as its (1 · KSCN)2 · H2O complex. Crystallographic data are, for the former: space group C 2/c, a = 31.110(9), b = 4.608(4), c = 17.188(6) Å, β = 105.27(8)°, Z = 2, Dm = 1.25 gem-3; for the latter: space group P21, a = 11.044(3), b = 18.310(4), c = 14.485(4) Å, β = 97.49(2)°, Z = 4, Dm = 1.27 gem-3. Crystal structures were solved by direct methods using X-ray diffraktometer data and least squares refinements converged at 10.8% for 1 and at 7.6% for (1 · KSCN)2 · H2O. The free ligand (1) is S-shaped and, upon K+-complexation, changes signs of some gauche O-C-C-O torsion angles while C-C-O-C angles remain trans. In (1 · KSCN)2 · H2O, there are two complex molecules 1 A · KSCN · H2O (I) and 1 B · KSCN (II). The ligands are wrapped circularly around K+ and coordinated with only four of the five polyether oxygens. K+ interacts further with H2O in (I) and with N of SCN- in II and, in both complexes, with acetylamino oxygen of adjacent 1. The latter interaction leads to polymeric structures not observed previously for similar complexes.