Tuesday, August 08, 2006

SSNMR journal update - Rob - Vol 30, i.2 Sept. 2006

Solid-State NMR:

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68

Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):

The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.


Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74

Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):

For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.


Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105

Title: Quantitative analysis of 17O exchange and Formula Not Shown relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):

The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).


Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123

Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):

Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.

No comments: