JMR - Journal of Magnetic Resonance - up to January 2008

JMR - Journal of Magnetic Resonance - up to January 2008

Journal of Magnetic Resonance
Volume 190, Issue 1, January 2008, Pages 1-6
doi:10.1016/j.jmr.2007.09.016

Pre-SAT180, a simple and effective method for residual water suppression

Huaping Mo, and Daniel Raftery
Received 25 July 2007; revised 12 September 2007. Available online 25 September 2007.

Abstract

Water located outside the NMR detection coil experiences a reduced RF field intensity. This "faraway water" is known to be very difficult to suppress and often gives rise to a large residual solvent signal. Pre-SAT180 (Pre-Saturation with Adiabatic Toggling of 180 degree pulse inversion) is proposed to cancel the residual water contribution efficiently. Compared with several popular methods such as 1D NOESY with pre-saturation or 270° excitation, Pre-SAT180 has a number of advantages, including: full retention of signal intensity and selectivity, good phase properties, easy setup, and high tolerance to pulse missettings.

Keywords: Pre-SAT180; NMR; Water suppression; Pre-saturation; Metabolomics; Urine metabolomics

–

Journal of Magnetic Resonance
Volume 190, Issue 1, January 2008, Pages 135-141
doi:10.1016/j.jmr.2007.07.012

A Hall effect angle detector for solid-state NMR

Salvatore Mamone, André Dorsch, Ole G. Johannessen, Manoj V. Naik, P.K. Madhu and Malcolm H. Levitt
Received 27 June 2007. Available online 29 August 2007.

Abstract

We describe a new method for independent monitoring of the angle between the spinning axis and the magnetic field in solid-state NMR. A Hall effect magnetic flux sensor is fixed to the spinning housing, so that a change in the stator orientation leads to a change in the angle between the Hall plane and the static magnetic field. This leads to a change in the Hall voltage generated by the sensor when an electric current is passed through it. The Hall voltage may be measured externally by a precision voltmeter, allowing the spinning angle to be measured non-mechanically and independent of the NMR experiment. If the Hall sensor is mounted so that the magnetic field is approximately parallel to the Hall plane, the Hall voltage becomes highly sensitive to the stator orientation. The current angular accuracy is around 10 millidegrees. The precautions needed to achieve higher angular accuracy are described.

Keywords: Magic-angle spinning; Hall effect; NMR; Solid-state NMR

–

Journal of Magnetic Resonance
Volume 190, Issue 1, January 2008, Pages 165-170

doi:10.1016/j.jmr.2007.10.002

Proton-detected separated local field spectroscopy

Chin H. Wu and Stanley J. Opella
Received 8 August 2007; revised 29 September 2007. Available online 10 October 2007.

Abstract

PISEMO, a separated local field experiment that can be performed with either direct 15N (or 13C) detection or indirect 1H detection, is demonstrated on a single crystal of a model peptide. The 1H signals modulated by 1H–15N heteronuclear dipole–dipole couplings are observed stroboscopically in the windows of the multiple-pulse sequence used to attenuate 1H–1H homonuclear dipole–dipole couplings. 1H-detection yields spectra with about 2.5 times the signal to noise ratio observed with 15N-detection under equivalent conditions. Resolution in both the 15N chemical shift and 1H–15N heteronuclear dipole–dipole coupling dimensions is similar to that observed with PISEMA, however, since only on-resonance pulses are utilized, the bandwidth is better.

Keywords: PISEMA; PISEMO; Multiple-pulse; Double-resonance; Crystal

–

Journal of Magnetic Resonance
Volume 189, Issue 1, November 2007, Pages 104-113
doi:10.1016/j.jmr.2007.08.019.

Stripline probes for nuclear magnetic resonance

P.J.M. van Bentum, J.W.G. Janssen, A.P.M. Kentgens, J. Bart and J.G.E. Gardeniers
Received 20 July 2007; revised 24 August 2007. Available online 7 September 2007.

Abstract

A novel route towards chip integrated NMR analysis is evaluated. The basic element in the design is a stripline RF ‘coil' which can be defined in a single layer lithographic process and which is fully scalable to smaller dimensions. The sensitivity of such a planar structure can be superior to that of a conventional 3D helix. The basic properties, such as RF field strength, homogeneity and susceptibility broadening are discussed in detail. Secondary effects related to the thermal characteristics are discussed in simplified models. Preliminary NMR tests of basic solid and liquid samples measured at 600 MHz confirm the central findings of the design study. It is concluded that the stripline structure can be a valuable addition to the NMR toolbox; it combines high sensitivity with low susceptibility broadening and high power handling capabilities in a simple scalable design.

Keywords: NMR; Microcoils; Stripline; Microfluidics; High resolution NMR; Thin films; Wide-line NMR; RF coil design

–

Journal of Magnetic Resonance
Volume 189, Issue 1, November 2007, Pages 20-31
doi:10.1016/j.jmr.2007.06.017

Pursuing structure in microcrystalline solids with independent molecules in the unit cell using 1H–13C correlation data

James K. Harper, Mark Strohmeier and David M. Grant
Received 4 May 2007. Available online 14 August 2007.

Abstract

The 1H–13C solid-state NMR heteronuclear correlation (HETCOR) experiment is demonstrated to provide shift assignments in certain powders that have two or more structurally independent molecules in the unit cell (i.e. multiple molecules per asymmetric unit). Although this class of solids is often difficult to characterize using other methods, HETCOR provides both the conventional assignment of shifts to molecular positions and associates many resonances with specific molecules in the asymmetric unit. Such assignments facilitate conformational characterization of the individual molecules of the asymmetric unit and the first such characterization solely from solid-state NMR data is described. HETCOR offers advantages in sensitivity over prior methods that assign resonances in the asymmetric unit by 13C–13C correlations and therefore allows shorter average analysis times in natural abundance materials. The 1H–13C analysis is demonstrated first on materials with known shift assignments from INADEQUATE data (santonin and Ca(OAc)2 phase I) to verify the technique and subsequently is extended to a pair of unknown solids: (+)-catechin and Ca(OAc)2 phase II. Sufficient sensitivity and resolution is achieved in the spectra to provide assignments to one of the specific molecules of the asymmetric unit at over 54% of the sites.

Keywords: Heteronuclear correlation; Powders; Asymmetric unit

–

Journal of Magnetic Resonance
Volume 188, Issue 2, October 2007, Pages 246-259
doi:10.1016/j.jmr.2007.07.009

Determination of NMR interaction parameters from double rotation NMR

I. Hung, A. Wong, A.P. Howes, T. Anupõld, J. Past, A. Samoson, X. Mo, G. Wu, M.E. Smith, S.P. Brown and R. Dupree
Received 30 May 2007; revised 18 July 2007. Available online 3 August 2007.

Abstract

It is shown that the anisotropic NMR parameters for half-integer quadrupolar nuclei can be determined using double rotation (DOR) NMR at a single magnetic field with comparable accuracy to multi-field static and MAS experiments. The 17O nuclei in isotopically enriched l-alanine and OPPh3 are used as illustrations. The anisotropic NMR parameters are obtained from spectral simulation of the DOR spinning sideband intensities using a computer program written with the GAMMA spin-simulation libraries. Contributions due to the quadrupolar interaction, chemical shift anisotropy, dipolar coupling and J coupling are included in the simulations. In l-alanine the oxygen chemical shift span is 455 ± 20 ppm and 350 ± 20 ppm for the O1 and O2 sites, respectively, and the Euler angles are determined to an accuracy of ±5–10°. For cases where effects due to heteronuclear J and dipolar coupling are observed, it is possible to determine the angle between the internuclear vector and the principal axis of the electric field gradient (EFG). Thus, the orientation of the major components of both the EFG and chemical shift tensors (i.e., V33 and ?33) in the molecular frame may be obtained from the relative intensity of the split DOR peaks. For OPPh3 the principal axis of the 17O EFG is found to be close to the O–P bond, and the 17O–31P one-bond J coupling (1JOP = 161 ± 2 Hz) is determined to a much higher accuracy than previously.

Keywords: Solid-state NMR; Double rotation; Quadrupolar interaction; Chemical shift anisotropy; J-coupling; Dipolar coupling; Oxygen-17

–

Journal of Magnetic Resonance
Volume 188, Issue 2, October 2007, Pages 267-274
doi:10.1016/j.jmr.2007.06.015

Efficient cross polarization with simultaneous adiabatic frequency sweep on the source and target channels

Weng Kung Peng and Kazuyuki Takeda
Received 13 April 2007; revised 21 June 2007. Available online 3 August 2007.

Abstract

In this work, we propose a new and efficient heteronuclear cross polarization scheme, in which adiabatic frequency sweeps from far off-resonance toward on-resonance are applied simultaneously on both the source and target spins. This technique, which we call as Simultaneous ADIabatic Spin-locking Cross Polarization (SADIS CP), is capable of efficiently locking both the source and target spins with moderate power even in the presence of large spectral distribution and fast relaxation. It is shown that by keeping the time-dependent Hartmann–Hahn mismatch minimal throughout the mixing period, polarization transfer can be accelerated. Experiments are demonstrated in a powder sample of l-alanine.

Keywords: Cross polarization; Simultaneous adiabatic frequency sweep; Spin–lattice relaxation time in the rotating frame; Time-dependent Hartmann–Hahn mismatch

–

Journal of Magnetic Resonance
Volume 188, Issue 2, October 2007, Pages 311-321
doi:10.1016/j.jmr.2007.07.005

High-field 75As NMR study of arsenic oxysalts

Geoffrey M. Bowers and R. James Kirkpatrick
Received 18 June 2007; revised 16 July 2007. Available online 2 August 2007.

Abstract

Arsenic is an important environmental hazard, but there have been few NMR investigations of its molecular scale structure and dynamics, due principally to the large quadrupole moment of 75As and consequent large quadrupole couplings. We examine here the potential of existing, single-field solid-state NMR technology to investigate solids containing arsenate and arsenite oxyanions. The results show that current techniques have significant potential for arsenates that do not contain both protonated Click to view the MathML source groups and structural water molecules, but that the quadrupole couplings for the arsenites examined here are large enough that interpretation of the spectra is difficult, even at 21.1 T. Compounds that contain both structural H2O molecules and protonated arsenate groups do not yield resolvable signal, likely a result of T2 effects related to a combination of strong quadrupolar interactions and proton exchange. Spin-echo experiments at 11.7 and 14.1 T were effective for Li3AsO4 and CsH2AsO4, as were whole-pattern spikelet experiments for arsenate oxide (As2O5) at 17.6 and 21.1 T. The central transition resonance of Ca3(AsO4)2·8H2O is not, vert, similar6 MHz broad and required a non-conventional, histogram-style spikelet method at high field to improve acquisition efficiency. This approach reduces the acquisition time due to the sensitivity enhancement of the spikelet sequence and a reduction in the number of frequency increments required to map the resonance. Despite the large quadrupole couplings, we have identified a correlation between the 75As isotropic chemical shift and the electronegativity of the next-nearest neighbor cation in arsenate compounds.

Keywords: Arsenic; Histogram; QCPMG; Shielding; Solid-state nuclear magnetic resonance

–

Journal of Magnetic Resonance
Volume 188, Issue 1, September 2007, Pages 49-55
doi:10.1016/j.jmr.2007.06.003

Using chemical shift anisotropy to resolve isotropic signals in solid-state NMR

Matthew S. Ironside, Robin S. Stein and Melinda J. Duer
Received 27 March 2007; revised 6 June 2007. Available online 15 June 2007.

Abstract

A key problem in solid-state NMR is resolving overlapping isotropic signals. We present here a two-dimensional method which can enable sites with the same isotropic chemical shift to be distinguished according to their chemical shift anisotropy and asymmetry. The method involves correlating sideband spectra at different effective spinning rates using CSA-amplification pulse sequences. The resulting two-dimensional correlation pattern allows very accurate determination of the chemical shift principal values in addition to the recovery of parameters for two overlapping patterns which allows the resolution of overlapping signals.

Keywords: CSA recoupling; CSA-amplified PASS; Overlapping signals; Spinning sidebands; 31P NMR