TY - JOUR A1 - Jäger, Christian A1 - Welzel, T. A1 - Meyer-Zaika, W. A1 - Epple, M. T1 - A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatite JF - Magnetic resonance in chemistry N2 - Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30-50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. KW - NMR KW - H-1 KW - P-31 KW - Biomineralization KW - Hydroxyapatite KW - Calcium phosphate KW - Nanoparticles PY - 2006 DO - https://doi.org/10.1002/mrc.1774 SN - 0749-1581 SN - 1097-458X VL - 44 IS - 6 SP - 573 EP - 580 PB - Wiley CY - Chichester AN - OPUS4-12366 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, T. A1 - Dai, Z. A1 - Drexler, H.-J. A1 - Baumann, W. A1 - Jäger, Christian A1 - Pfeifer, Dietmar A1 - Heller, D. T1 - Novel contributions to the mechanism of the enantioselective hydrogenation of dimethyl itaconate with rhodium complexes JF - Chemistry - A European journal KW - Enantioselective Hydrogenation KW - Rhodium-Phosphor-Complex KW - Powder Diffractometry KW - Hr- and Solid State NMR-Spectroscpy KW - Asymmetric catalysis KW - Hydrogenation KW - Kinetics KW - Reaction mechanisms KW - Rhodium PY - 2008 DO - https://doi.org/10.1002/chem.200800389 SN - 0947-6539 SN - 1521-3765 VL - 14 IS - 15 SP - 4469 EP - 4471 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-18368 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lutz, W. A1 - Kurzhals, R. A1 - Sauerbeck, S. A1 - Toufar, H. A1 - Buhl, J.-C. A1 - Gesing, T. A1 - Altenburg, Wolfgang A1 - Jäger, Christian T1 - Hydrothermal stability of zeolite SAPO-11 JF - Microporous and mesoporous materials N2 - The hydrothermal stability of SAPO-11 was studied in water of autogenous pressure as function of the temperature. SAPO-11 remained crystalline up to 190 °C. Thereby, it was observed, parent as well as hydrothermally treated samples showed similarities to the isotypic structure of zeolite AlPO-11 called here AELdry. After fully hydration of the samples, AELdry changed completely into a hydrated AELwet structure of another framework symmetry. The transition from calcined to hydrated state was reversible for both the parent and the hydrothermally treated samples. 27Al and 31P NMR MAS spectra showed a single resonance typical for AlPO4 type tetrahedra for the calcined parent and hydrothermally treated samples. Upon hydration, the single AlPO4 resonance signal split into three different signals as is the case for the corresponding 31P signals. By means of NH3-TPD measurement a loss of acidity was detected after the hydrothermal treatment as follows from a framework desilication. Nitrogen and water adsorption decreased systematically. At 210 °C a non-zeolitic, non-porous phase was irreversibly formed. The XRD pattern of this phase shows resemblance to a synthetic aluminium phosphate of the tridymite structure type. KW - Zeolite KW - Silicoaluminophosphate KW - SAPO-11 KW - Hydrothermal stability KW - Phase transformation PY - 2010 DO - https://doi.org/10.1016/j.micromeso.2009.08.003 SN - 1387-1811 SN - 1873-3093 VL - 132 IS - 1-2 SP - 31 EP - 36 PB - Elsevier CY - Amsterdam AN - OPUS4-21131 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Riedel, Jens A1 - Hoekstra, S. A1 - Jäger, W. A1 - Gilijamse, J.J. A1 - van de Meerakker, S.Y.T. A1 - Meijer, G. T1 - Accumulation of Stark-decelerated NH molecules in a magnetic trap JF - The European physical journal D N2 - Here we report on the accumulation of ground-state NH molecules in a static magnetic trap. A pulsed supersonic beam of NH (a1Δ) radicals is produced and brought to a near standstill at the center of a quadrupole magnetic trap using a Stark decelerator. There, optical pumping of the metastable NH radicals to the X3Σ- ground state is performed by driving the spin-forbidden A3Π ← a1Δ transition, followed by spontaneous A → X emission. The resulting population in the various rotational levels of the ground state is monitored via laser induced fluorescence detection. A substantial fraction of the groundstate NH molecules stays confined in the several milliKelvin deep magnetic trap. The loading scheme allows one to increase the phase-space density of trapped molecules by accumulating packets from consecutive deceleration cycles in the trap. In the present experiment, accumulation of six packets is demonstrated to result in an overall increase of only slightly over a factor of two, limited by the trap-loss and reloading rates. KW - Cold matter KW - Stark deceleration KW - Trapping of polar molecules KW - NH KW - High resolution spectroscopy KW - Fluorescence KW - Radical PY - 2011 DO - https://doi.org/10.1140/epjd/e2011-20082-7 SN - 1434-6060 VL - 65 IS - 1-2 SP - 161 EP - 166 PB - Springer CY - Berlin AN - OPUS4-25050 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jeromenok, J. A1 - Böhlmann, W. A1 - Jäger, Christian A1 - Weber, J. T1 - Carbon dioxide adsorption in Betulin-based micro- and macroporous polyurethanes JF - ChemistryOpen N2 - Separation of CO2. Microporous polyurethane networks were prepared based on a renewable resource. Betulin, extracted from birch bark, is used as a structure-directing diol monomer in A3-B2 monomers. The resulting microporous networks show very promising CO2/N2 selectivities. The state of adsorbed CO2 is analyzed by in situ NMR spectroscopy, and pure physisorption is proven. The preparation of monolithic materials is demonstrated as well. KW - Carbon dioxide KW - Gas adsorption KW - Microporous polymers KW - Renewable resources KW - Solid state NMR spectroscopy PY - 2013 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-304431 DO - https://doi.org/10.1002/open.201200045 SN - 2191-1363 VL - 2 IS - 1 SP - 17 EP - 20 PB - Wiley-VCH-Verl. CY - Weinheim AN - OPUS4-30443 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -