Monday, January 10, 2011

Solid-State NMR

A practical guide for the setup of a 1H-31P-13C double cross-polarization (DCP) experiment

Publication year: 2010
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 13 December 2010
Wlodzimierz, Ciesielski , Hassan, Kassasir , Marek J., Potrzebowski
O-phospho-L-threonine is a convenient sample to setup a 1H-31P-13C double cross-polarization (DCP) Hartmann-Hahn match. The 1H-31P-13C technique is extremely sensitive to the rate of sample spinning. Both zero-quantum (ZQ) and double-quantum (DQ) cross-polarization operate at an average spinning rate (6–7 kHz). At higher spinning rates (10 kHz), the DQCP mechanism dominates and leads to a reduction of signal intensity, in particular for lower 31P rf field strength. The application of two shape pulses during the second cross-polarization greatly improves the signal to noise ratio allowing the recording of better quality spectra. 31P-13C SPECIFIC-CP (spectrally induced filtering in combination with cross-polarization) experiments can be carried out under ZQCP and DQCP condition if careful attention is paid to the choice of RF field amplitudes and carriers Ω. Application of 1D and 2D 1H-31P-13C experiments is demonstrated on model samples; disodium ATP hydrate and O-phospho-L-tyrosine.

Multinuclear NMR study of silica fiberglass modified with zirconia

Publication year: 2010
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 29 December 2010
O.B., Lapina , D.F, Khabibulin , V.V., Terskikh
Silica fiberglass textiles are emerging as uniquely suited supports in catalysis which offer unprecedented flexibility in designing advanced catalytic systems for chemical and auto industries. During manufacturing fiberglass materials are often modified with additives of various nature to improve glass properties. Glass network formers, such as zirconia and alumina, are known to provide the glass fibers with higher strength and to slow down undesirable devitrification processes. In this work multinuclear 1H, 23Na, 29Si, and 91Zr NMR spectroscopy was used to characterize the effect of zirconia on the molecular-level fiberglass structure. 29Si NMR results help in understanding why zirconia-modified fiberglass is more stable towards devitrification comparing with pure silica glass. Internal void spaces formed in zirconia-silica glass fibers after acidic leaching correlate with sodium and water distributions in the starting bulk glass as probed by 23Na and 1H NMR. These voids spaces are important for stabilization of catalytically active species in the supported catalysts. Potentials of high-field 91Zr NMR spectroscopy to study zirconia-containing glasses and similarly disordered systems are illustrated.

Kinetics of 1H→13C NMR cross-polarization in polymorphs and solvates of the antipsychotic drug olanzapine

Publication year: 2011
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 4 January 2011
Waclaw, Kolodziejski , Joanna, Herold , Marzena, Kuras , Irena, Wawrzycka-Gorczyca , Anna E., Koziol
The 1H→13C NMR cross-polarization (CP) was studied under magic-angle spinning at 7.5 kHz in various crystal forms of the antipsychotic drug olanzapine: two polymorphs (metastable I and stable II) and eight solvates containing organic solvent and water molecules. The CP kinetics followed the non-classical I-I*-S model, in which CP begins in a spin cluster of proximate abundant spins I* and rare spins S, then is controlled by spin diffusion of the abundant spins I from bulk to the I* spins of the spin cluster and finally is governed by spin-lattice relaxation of the abundant spins in the rotating frame. The corresponding CP kinetics parameters were determined and analyzed. It was demonstrated that the, λ and Tdf values (the CP time constant, the cluster composition parameter and the 1H spin-diffusion constant, respectively) were very useful to discriminate the functional groups, especially in the 3D parameter space. In order to conveniently analyze the large amount (1 7 5) of the collected CP parameters, the number of the observed variables was reduced using the principal component (PC) analysis. The 2D plot of PC2 vs. PC1 showed adequate separation of the CH3, CH2, CH and C cases (C stands for carbons without adjacent hydrogens). It was demonstrated that those cases were located along the PC1 axis in the order of increasing 1H-13C dipolar couplings: C32. Our study showed the I-I*-S model at work and established ranges of its parameters for various functional groups.

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