On the polymorphism of aspirin.
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Aspirin↗
Biomedical subjects
Roland Boese
Publications and source records attributed to Roland Boese.
On the polymorphism of aspirin: crystalline aspirin as intergrowths of two "polymorphic" domains.
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Aspirin↗
Stereoselective preparation of six diastereomeric quatercyclopropanes from bicyclopropylidene and some derivatives.
Diastereomeric meso- and d,l-bis(bicyclopropylidenyl) (5) were obtained upon oxidation with oxygen of a higher-order cuprate generated from lithiobicyclopropylidene (4) in 50 and 31 % yield, respectively. Their perdeuterated analogues meso-[D(14)]- and d,l-[D(14)]-5 were obtained along the same route from perdeuterated bicyclopropylidene [D(8)]-3 (synthesized in six steps in 7.4 % overall yield from [D(8)]-THF) in 20.5 % yield each. Dehalogenative coupling of 1,1-dibromo-2-cyclopropylcyclopropane (6) gave a mixture of all possible stereoisomers of 1,5-dicyclopropylbicyclopropylidene 16 in 69 % yield, from which (Z)-cis-16 was separated by preparative gas chromatography (26 % yield). The crystal structure of meso-5 looks like a superposition of the crystal structures of two outer bicyclopropylidene units (3) and one inner s-trans-bicyclopropyl unit, whereas the two outer cyclopropyl moieties adopt a gauche orientation with respect to the cyclopropane rings at the inner bicyclopropylidene units in (Z)-cis-16. Birch reduction with lithium in liquid ammonia of meso-5 and d,l-5 gave two pairs of diastereomeric quatercyclopropanes trans,trans-(R*,S*,R*, S*)-17/cis,trans-(R*,S*,R*,R*)-18 and trans,trans-(R*,S*,S*,R*)-19/cis,trans-(R*,S*,S*,S*)-20 in 97 and 76 % yield, respectively, in a ratio 9:1 for every pair. The latter diastereomer was also obtained as the sole product by Birch reduction of (Z)-cis-16 in 96 % yield. Under the same conditions, tetradecadeuterio analogues trans,trans-[D(14)]-(R*,S*,R*,S*)-17/cis,trans-[D(14)]-(R*, S*,R*,R*)-18 (8:1) and trans,trans-[D(14)]-(R*,S*,S*,R*)-19/cis,trans-[D(14)]-(R*,S*,S*,S*)-20 (12:1) were prepared from meso-[D(14)]-5 and d,l-[D(14)]-5 in 37 and 63 % yield, respectively. Reduction of meso-5 with diimine gave the cis,cis-quatercyclopropane (S*,S*,R*,R*)-21 as the main product (58 % yield) along with the cis,trans-diastereomer (S*,S*,R*,S*)-18 (29 % yield). Thus, five of the six possible diastereomeric quatercyclopropanes were obtained from meso-5, d,l-5, and (Z)-cis-16. The X-ray crystal structure analyses of trans,trans-(R*,S*,R*,S*)-17 and cis,cis-(S*,S*,R*,R*)-21 revealed for the both an unusual conformation in which the central bicyclopropyl unit adopts an s-trans-(antiperiplanar) orientation with phi=180.0 degrees , and the two terminal bicyclopropyl moieties adopt a synclinal conformation with phi=49.8 and 72.0 degrees , respectively. In solution the vicinal coupling constants (3)J(H,H) in trans,trans-(R*,S*,R*,S*)-[D(14)]-17, trans,trans-(R*,S*,S*,R*)-[D(14)]-19, trans,cis-(R*,S*,R*,R*)-[D(14)]-18 and trans,cis-(R*,S*,S*,S*)-[D(14)]-20 were found to be 4.1, 4.7, 5.9 and 5.9 Hz, respectively. This indicates a predominance of the all-gauche conformer in (R*,S*,R*,S*)-17 and a decreasing fraction of it in this sequence of the other diastereomers.
Computer Simulation↗
Crystal structure and thermochemical reactivity of an unusual copper complex that contains copper in four different coordination geometries.
According to X-ray single-crystal structure analysis, {[Cu(II)(en)2]2[Cu(I)2(CN)6]}[Cu(II)(en)2]2[Cu(I)(CN)3]2.2H2O contains copper in four different coordination environments: trigonal planar, square planar, square pyramidal and tetrahedral. The different coordination geometries of copper were investigated by quantum chemical calculations of model compounds, thus allowing to tentatively assign the different CN-bands in the IR spectrum. The thermolysis led to sub-microm sized rod-like copper(II) oxide particles.
Copper↗
Toward an intimate understanding of the structural properties and conformational preference of oxoesters and thioesters: gas and crystal structure and conformational analysis of dimethyl monothiocarbonate, CH3OC(O)SCH3.
[structure: see text] The molecular structure and conformational properties of dimethyl monothiocarbonate, CH3OC(O)SCH3, have been studied in the gas phase by gas electron diffraction (GED) and vibrational spectroscopy and in the solid state by X-ray crystallography. The experimental investigations were supplemented by quantum chemical calculations at the B3LYP/6-311++G(3df,2p) and MP2/6-311++G(2df,p) levels of approximation. The gaseous molecule exhibits only one conformation having Cs symmetry with synperiplanar orientation of both the C-S and the C-O single bonds relative to the C=O double bond. The following skeletal geometric parameters were derived from the GED analysis (r(hl) values with 3sigma uncertainties): C=O = 1.203(4) A, C(sp(2))-O = 1.335(5) A, C(sp(3))-O = 1.437(5) A, C(sp(2))-S = 1.763(5) A, and C(sp(3))-S = 1.803(5) A; O=C-O = 125.9(8) degrees , O=C-S = 125.7(7) degrees , O-C-S = 108.4(9) degrees , and C-O-C = 113.4(15) degrees . The structure of a single crystal, grown by a miniature zone-melting procedure, was determined by X-ray diffraction analysis at a low temperature. The crystalline solid [monoclinic, P2(1)/n, a = 12.6409(9) A, b = 4.1678(3) A, and c = 19.940(1) A, beta = 98.164(1) degrees ] exists exclusively as molecules in the synperiplanar conformation and with geometrical parameters that agree with those of the molecule in the gas phase. The results are discussed in terms of anomeric and mesomeric effects and in terms of a natural bond orbital analysis.
Journal Article↗
((Fluoroformyl)imido)sulfuryl difluoride, FC(O)N=S(O)F2: structural, conformational, and configurational properties in the gaseous and condensed phases.
Structural, conformational, and configurational properties of the gaseous molecule ((fluoroformyl)imido)sulfuryl difluoride, FC(O)N=S(O)F(2), have been studied by vibrational spectroscopy (IR (gas) and Raman (liquid)) and quantum chemical calculations (HF, MP2, and B3LYP with 6-31+G* and 6-311+G* basis sets); in addition, the solid-state structure has been determined by X-ray crystallography. FC(O)N=S(O)F(2) exists in the gas phase as a mixture of a favored antiperiplanar-synperiplanar form (the S=O double bond antiperiplanar with respect to the C-N single bond, and the C=O group synperiplanar with respect to the S=N double bond) in equilibrium with less abundant antiperiplanar-antiperiplanar, synclinal-synperiplanar, and synclinal-antiperiplanar structures. The crystalline solid at 163 K (monoclinic, P2(1)/c, a = 5.1323(7) A, b = 15.942(2) A, c = 16.798(2) A, beta = 95.974(3) degrees , Z = 12) consists of three similar antiperiplanar-synperiplanar forms.
Journal Article↗
Synthon evolution and unit cell evolution during crystallisation. A study of symmetry-independent molecules (Z' > 1) in crystals of some hydroxy compounds.
A kinetically favoured crystal, with many molecules in the asymmetric unit, may be a fossil relic of the crystal nucleus of a more stable polymorph.
Journal Article↗
Alpha,beta-unsaturated ketoximes carrying a terminal pyridine or quinoline subunit as building blocks for supramolecular syntheses.
[Structure: see text]. The crystal structures of a new series of alpha,beta-unsaturated ketoximes, 8-14, carrying the terminal 4-pyridinyl, 3-pyridinyl, or 4-quinolinyl subunit have been investigated by X-ray structural analysis. The dominating intermolecular interaction in all structures, except 11, is the head-tail OH...N hydrogen bond between the oxime moiety and the nitrogen atom of the heterocyclic unit. This intermolecular interaction generates infinite chains, which are cross-linked by CH...O/N/Cl or CH...pi interactions. Compound 10 has been shown to adopt a double-helical structure in the crystalline state. Compound 11 represents the only case where the unexpected head-head NOH...N(OH) hydrogen bonds determine the crystal packing. Both hydrogen-bonding and aromatic interactions stabilize the crystal structures of 8-14.
Journal Article↗
3-Mercaptopropionic acid-nitrile imine adducts. An unprecedented cyclization into 1,3,4-thiadiazol-2(3H)-ones and -2(3H)-thiones.
3-Mercaptopropionic acid-nitrile imine acyclic adducts (6a-c) undergo cyclocondensation with 1,1'-carbonyldiimidazole to afford the respective 1,3,4-thiadiazol-2-(3H)-ones (7a-c). Corresponding 1,3,4-thiadiazol-2(3H)-thiones (8a-c) were likewise produced from 6a-cand 1,1'-thiocarbonyldiimidazole, with consequent elimination of the propionate moiety. The constitution of these heterocyclic products follows from analytical and spectral data and is confirmed by single crystal X-ray structure determination for 7b.
Journal Article↗
Self-assembly of nanoscale supramolecular truncated tetrahedra.
Two nanoscale truncated tetrahedra were synthesized via Pt(II)-mediated self-assembly. The first resulted from the reaction of 3 equiv of cis-Pt(PMe3)2(OTf)2 and 2 equiv of 1,3,5-tris(4-pyridylethynyl)benzene, giving a truncated tetrahedron with a diameter of approximately 25 A. The second, analogous structure was obtained by the self-assembly of cis-Pt(PMe3)2(OTf)2 and 1,3,5-tris(4-pyridyl-trans-ethenyl)benzene. These two truncated tetrahedra were crystallized after partially exchanging the counterion to cobalticarborane for the X-ray structural analysis.
Journal Article↗
Synthesis and supramolecular properties of molecular clips with anthracene sidewalls.
Novel molecular clips with anthracene sidewalls (1 a-c) were synthesized; they form stable host-guest complexes with a variety of electron-deficient aromatic and quinoid molecules. According to single-crystal structure analyses of clip 1 c and 1,2,4,5-tetracyanobenzene (TCNB) complex 14@1 b, the clips' anthracene sidewalls have to be compressed substantially during the complex formation to provide attractive pi-pi interactions between the aromatic guest molecule and the two anthracene sidewalls in the complex. The compression and expansion of aromatic sidewalls are calculated by molecular mechanics to be low-energy processes, so the energy required for compression of the anthracene sidewalls during complex formation is apparently overcompensated by the gain in energy resulting from the attractive pi-pi interactions. The finding that complexes of the clips 1 a-c are more stable than those of the corresponding clips 2 a-c can be explained in terms of the larger van der Waals contact surfaces of the anthracene sidewalls in 1 a-c (relative to the naphthalene sidewalls in 2 a-c). Color changes resulting from charge-transfer (CT) bands are observed in complex formation by 1 a-c: from colorless to red or purple with TCNB (14), and from yellow to green with 2,4,7-trinitro-9-fluorenone TNF (17). Independently, the host 1 b and guest 14 fluoresce from their respective excited singlet states, whilst in the complex 14@1 b the charge-transfer state quenches the higher-energy singlet states of the two components, and as a result luminescence is only observed from this new CT state. To the best of our knowledge, complex 14@1 b is the first example of CT luminescence from a host-guest complex. The binding constant determined for the formation of the TCNB complex 14@1 b from a UV/Vis titration experiment (Ka = 12 400 m(-1)) agrees well with the value (K(a) = 12 800 m(-1)) obtained by 1H NMR titration.
Anthracenes↗
Calcium sulfate hemihydrate is the inorganic mineral in statoliths of Scyphozoan medusae (Cnidaria).
Scyphomedusae use inorganic crystals (statoliths) for gravity sensing. The organs which contain the statoliths are called rhopalia. Rhopalia of five different species of the three different orders of the class Scyphozoa were studied with high-end solid-state chemical methods to elucidate the crystallographic nature of the biomineral: synchrotron powder diffraction, synchrotron single-crystal diffraction, synchrotron microtomography, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Each rhopalium contains a large number of statoliths in an ordered way. The statoliths of all species consist of calcium sulfate hemihydrate, a water-deficient phase. This is remarkable for sea-living organisms consisting mostly of water. The phylogenetic relationships within the class Scyphozoa are discussed.
Animals↗
Decomposition of triacetone triperoxide is an entropic explosion.
Both X-ray crystallography and electronic structure calculations using the cc-pVDZ basis set at the DFT B3LYP level were employed to study the explosive properties of triacetone triperoxide (TATP) and diacetone diperoxide (DADP). The thermal decomposition pathway of TATP was investigated by a series of calculations that identified transition states, intermediates, and the final products. Counterintuitively, these calculations predict that the explosion of TATP is not a thermochemically highly favored event. It rather involves entropy burst, which is the result of formation of one ozone and three acetone molecules from every molecule of TATP in the solid state.
Journal Article↗
Molecular recognition of carbohydrates with acyclic pyridine-based receptors.
The recognition capabilities of acyclic pyridine-based receptors toward monosaccharides were evaluated. Aminopyridine receptors based on the 2,4,6-trimethyl- or 2,4,6-triethylbenzene frame show high beta vs alpha binding selectivity in the recognition of glucopyranosides. Amidopyridine receptors, which are sterically less hindered at nitrogen, display high efficiency and an inverse selectivity. The 2-aminopyridine group has been established as a highly effective recognition group in the binding of monosaccharides. The factors influencing the binding properties of receptors 1-15, which differ in the nature and number of binding and spacer subunits used as the buildings blocks, are discussed.
Binding Sites↗
C6H4 valence bond isomers: a reactive bicyclopropenylidene.
[reaction: see text] The simple bicyclopropenylidene derivative 21b, stabilized by fusion into naphthalene, results from reaction of dimesitylcyclopropenone 20b with the 1-trimethylsilyl-1H-cyclopropa[b]naphthalenyl anion. Although unstable in air, the molecule survives ambient conditions long enough for separation and mass spectral characterization. Aerial oxidation of 21b leads to 2,3-dimesitylanthracene-1,4-dione 22b whose X-ray crystal structure has been determined. While diphenylcyclopropenone 20a does not give identifiable products, the di-tert-butyl analogue 20c gives quinone 22c but in lower yield.
Journal Article↗
Proton transfer and N(+)-H...S(-) hydrogen bonds in the crystal structure of 4-aminothiophenol.
4-Aminothiophenol exists as 4-ammonio-1-benzenethiolate in the solid and liquid state. The crystal structure is characterised by a tetrahedral beta-As type network which is the driving force for the proton transfer.
Journal Article↗
Gas hydrate single-crystal structure analyses.
The first single-crystal diffraction studies on methane, propane, methane/propane, and adamantane gas hydrates SI, SII, and SH have been performed. To circumvent the problem of very slow crystal growth, a novel technique of in situ cocrystallization of gases and liquids resulting in oligocrystalline material in a capillary has been developed. With special data treatment, termed oligo diffractometry, structural data of the gas hydrates of methane, acetylene, propane, a propane/ethanol/methane-mixture and an adamantane/methane-mixture were obtained. Cell parameters are in accord with reported values. Host network and guest are subject to extensive disorder, reducing the reliability of structural information. It was found that most cages are fully occupied by a guest molecule with the exception of the dodecahedral cage in the acetylene hydrate which is only filled to 60%. For adamantane in the icosahedral cage a disordered model is proposed.
Journal Article↗
Triphenyl(3,4,5-triiodophenyl)methane.
The crystal structure of the title compound, alternatively called 1,2,3-triiodo-5-(triphenylmethyl)benzene, C(25)H(17)I(3), is analysed in terms of I.I and I.pi interactions and the herring-bone T motif between phenyl groups. There are two molecules in the asymmetric unit, denoted A and B. Inversion-related A molecules are connected via an I.pi interaction (3.641 A, to a C-C bond mid-point) to form an I.pi dimer, and these dimers are connected through symmetry-independent B molecules via I.I [3.5571 (15) A] and I.pi (3.561 A, to a C-C bond mid-point) interactions.
Journal Article↗