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Biomedical subjects

P E Werner

Publications and source records attributed to P E Werner.

7 recordsLinked to original sources
PubMed2001

Structure of Nd10W22O81 from high-resolution electron microscopy and X-ray powder diffraction.

The crystal structure of Nd(10)W(22)O(81), neodymium tungstate, has been determined using a combination of high-resolution transmission electron microscopy and X-ray powder diffraction methods. The unit-cell dimensions determined from X-ray data are a = 3.8613 (1), b = 35.9431 (1), c = 21.8900 (1) A, V = 3038.05 A(3), Z = 2, space group Pbcm. The structure is built up of pentagonal columns (PCs) connected to ReO(3)-type fragments consisting of three octahedra, thus forming W(9)O(32) units. These units form 'pillars' along (a). These 'pillars' are joined by pairs of tilted octahedra (W(2)O(11) groups) to form corrugated layers perpendicular to (b). The Nd atoms are located in the space between these layers and form the only link between them. Interstitial O atoms are located between two of the Nd atoms. The formula Nd(10)W(22)O(81) can thus be alternatively given as Nd(5)W(11)O(39 + x) (x approximately 1.5), where x represents the interstitial O atoms. Nd(10)W(22)O(81) is a new type of PC structure.

Journal Article↗
PubMed2000

Structures and phase transitions of B-Ta2O5 and Z-Ta2O5: two high-pressure forms of Ta2O5.

A sample of Ta2O5, ditantalum pentaoxide, heat-treated in a "toroid"-type high-pressure chamber at P = 8 GPa and T = 1470 K, was studied by X-ray powder diffraction and high-resolution transmission electron microscopy (HRTEM). Two high-pressure modifications of Ta2O5, isostructural with B-Nb2O5 and Z-Nb2O5, were identified from the X-ray powder pattern. Both structures were refined by the Rietveld method from the X-ray diffraction data: B-Ta2O5, a = 12.7853 (4), b = 4.8537 (1), c = 5.5276 (2) A, beta = 104.264 (2)degrees, V = 332.45 A3, Z = 4, space group C2/c; Z-Ta2O5, a = 5.2252 (1), b = 4.6991 (1), c = 5.8534 (1) A, beta = 108.200 (2)degrees, V = 136.53 A3, Z = 2, space group C2. The Z-Ta2O5 modification is new. The Ta atoms are six-coordinated in B-Ta2O5 and seven-coordinated in Z-Ta2O5. The two structures are closely related, which makes an intergrowth and a transformation between them possible. An idealized model of the intergrowth structure has been given. The HRTEM study showed defect-rich B-Ta2O5 crystals, which could be interpreted as an intergrowth between the B-Ta2O5 and Z-Ta2O5 phases.

Microscopy, Electron↗
PubMed1992

Resolution and absolute stereochemistry of 6,7-dimethoxy-4-phenyl- 1,2,3,4-tetrahydroisoquinoline. The crystal structure of the R-hydrochloride salt form.

Stereospecific multistep synthesis and resolution of 6,7-dimethoxy-4- phenyl-1,2,3,4-tetrahydroisoquinoline (3) has been achieved from its racemic base. The absolute configurations of the optical antipodes converted into their hydrochloride salt forms have been determined by X-ray diffractometric analysis, thus permitting assignment of the antipodes as the (+)-(4R)-3 and (-)-(4S)-3 enantiomers. The crystal structures of the two enantiomers are related as mirror images and only the (4R)-3.HCl form has been fully determined by three-dimensional X-ray diffraction. In the solid state, the carbon atoms of the two methoxy groups deviate slightly from the benzene-ring plane and the chirally oriented phenyl substituent is almost perpendicularly tilted out of conjugation with the isoquinoline system. Examination of the enantiomers in several biochemical tests for 5-HT, NE and DA uptake inhibition-activity revealed an exclusive preference for the (4S)-enantiomer. These results are in accord with previous suggestions that the S-configurational state of the 4-phenyl substituent is important for biological activity.

Antidepressive Agents, Tricyclic↗