183W NMR

J. Am. Chem. Soc., ASAP Article 10.1021/ja0575934 S0002-7863(05)07593-1
Web Release Date: April 7, 2006

Copyright © 2006 American Chemical Society
A Strategy for the Analysis of Chiral Polyoxotungstates by Multinuclear (31P, 183W) NMR Spectroscopy Applied to the Assignment of the 183W NMR Spectra of 1-[P2W17O61]10- and 1-[YbP2W17O61]7-

Géraldine Lenoble, Bernold Hasenknopf, and René Thouvenot*

Contribution from the Université Pierre et Marie Curie - Paris 6, Institut de Chimie Moléculaire FR 2769, Laboratoire de Chimie Inorganique et Matériaux Moléculaires (UMR CNRS 7071), Case Courrier 42, 4 place Jussieu, 75252 Paris Cedex 05, France

rth@ccr.jussieu.fr
Received November 21, 2005

Abstract:

This paper describes the complete assignment of the 183W NMR spectra of the chiral polyoxometalates 1-[P2W17O61]10- and 1-[YbP2W17O61]7- in aqueous solution. These spectra display each 17 lines of equal intensity with a relatively narrow chemical shift distribution. The identification of signals is based on selective 31P-183W decoupling and recognition of particular sets of coupling constants for tungsten atoms around the lacunary site. Further assignment is obtained by 183W 2D-COSY NMR experiments. We demonstrate herewith a new way for the unambiguous assignment of 183W NMR spectra of polyoxotungstates without any symmetry elements or tungsten atoms in special positions. This way relies on the correlation of the magnitude of 2JW-W coupling constants with the geometry of oxo-bridges in polyoxotungstates. These results open the way to monitor interaction sites of chiral polyoxotungstates with organic ligands.

14N at high field

J. Am. Chem. Soc., ASAP Article 10.1021/ja0578597 S0002-7863(05)07859-5
Web Release Date: April 15, 2006

Copyright © 2006 American Chemical Society
Measuring Amide Nitrogen Quadrupolar Coupling by High-Resolution 14N/13C NMR Correlation under Magic-Angle Spinning

Zhehong Gan

National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310

gan@magnet.fsu.edu
Received November 30, 2005

Abstract:

The measurement of amide nitrogen 14N quadrupolar coupling by two-dimensional 14N/13C correlation experiment is presented with a natural abundant polypeptide. Directly bonded 14N/13C pairs are correlated through J and residual dipolar coupling under magic-angle spinning using a HMQC-type pulse sequence. The 14N quadrupolar coupling is measured from the isotropic second-order quadrupolar shift obtained by comparing the 14N peak positions with the 15N chemical shifts. The high spectral resolution and sensitivity through 13C detection make this method applicable to many organic, inorganic, and biological molecules for the measurement and the use of 14N quadrupolar coupling as a probe for molecular structure and dynamics.

NMR of metals, molecular clusters, zeolites

"NMR in metals, metal particles and metal cluster compounds" by van der Klink, J.J.; Brom, H.B. Prog. Nucl. Magn. Reson. Spectrosc. 2000, 36, 89.

Abstract:
A review with 243 refs. about the ways to deduce the electronic states of bulk metals, small metal particles, and the metal cores in metal cluster compds. by NMR. First, a theory of the NMR parameters is developed which is governed by the Fermi contact interaction between nuclear and electronic spins using the concept of nonlocal susceptibility. Going from mols. to solids and esp. metallic solids, the simple Korringa relation which connects the relaxation rates to the Knight shift and temp. has to be modified due to ferro- or antiferromagnetic interactions. NMR phenomena of alkali metals, noble metals (Cu, Ag, Au), and some transition metals (Cd, Mn, Pt, Pd) are treated. The consequences for the NMR linewidth and relaxation rates are discussed going from the bulk metal to small particles. Exptl. findings are presented for small particles of Cu, Ag, Pt, Rh, Pt-Pd alloys, zeolites, sodalites, clathrates, and metal cluster compds.

Chem. Eur. J., 77Se chemical shifts, experiment and theory

Andre, please check out....

Chemistry - A European Journal
Volume 12, Issue 14 , Pages 3829 - 3846

Orientational Effect of Aryl Groups on 77Se NMR Chemical Shifts: Experimental and Theoretical Investigations
Waro Nakanishi, Prof. 1 *, Satoko Hayashi, Dr. 1, Daisuke Shimizu 1, Masahiko Hada, Prof. 2
1Department of Material Science and Chemistry, Faculty of Systems Engineering, Wakayama University, 930 Sakaedani, Wakayama 640-8510, Japan, Fax: (+81) 73-457-8253
2Department of Chemistry, Faculty of Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji-shi, Tokyo 192-0397, Japan

Keywords
ab initio calculations • aryl selenides • NMR spectroscopy • orientational effects • selenium • substituent effects

Abstract
The orientational effect of p-YC6H4 (Ar) on (Se) is elucidated for ArSeR, based on experimental and theoretical investigations. The effect is examined in the cases in which SeCR in ArSeR is either in the Ar plane (pl) or is perpendicular to the plane (pd). 9-(Arylselanyl)anthracenes (1) and 1-(arylselanyl)anthraquionones (2) are employed to establish the effect in pl and pd, respectively. Large upfield shifts are observed for Y=NMe2, OMe, and Me, and large downfield shifts for Y=COOEt, CN, and NO2 in 1, relative to Y=H, as is expected. Large upfield shifts are brought by Y=NMe2, OMe, Me, F, Cl, and Br, and downfield shifts by Y=CN and NO2 in 2, relative to Y=H, with a negligible shift by Y=COOEt. Absolute magnetic shielding tensors of Se ((Se)) are calculated for ArSeR (R=H, Me, and Ph), assuming pl and pd, based on the DFT-GIAO method. Observed characters are well explained by the total (Se). Paramagnetic terms (p(Se)) are governed by (p(Se)xx+p(Se)yy), in which the direction of np(Se) (constructed by 4pz(Se)) is set to the z axis. The main interaction in pl is the np(Se)-(C6H4)-pz(Y) type. The Y dependence in pl occurs through admixtures of 4pz(Se) in (SeC6H4Y) and *(SeC6H4Y), modified by the conjugation, with 4px(Se) and 4py(Se) in (CSeX) and *(CSeX) (X=H or C) under a magnetic field. The main interaction in pd is the (CSeX)-(C6H4)-px(Y) type, in which SeX is nearly on the x axis. The Y dependence in pd mainly arises from admixtures of 4pz(Se) in np(Se) with 4px(Se) and 4py(Se) in modified *(CSeX), since np(Se) is filled with electrons. It is demonstrated that the effect of Y on p(Se) in the pl conformation is the same regardless of whether Y is an electron-donor or electron-acceptor, whereas for pd conformations the effect is greater when Y is an electron donor, as observed in 1 and 2, respectively. Contributions of each molecular orbital and each transition on p(Se) are evaluated, which enables us to recognize and visualize the effect clearly.

JACS, Vega: 51V NMR of Vanadium Chloroperoxidase

J. Am. Chem. Soc., 128 (15), 5190 -5208, 2006. 10.1021/ja060480f S0002-7863(06)00480-X

51V Solid-State Magic Angle Spinning NMR Spectroscopy of Vanadium Chloroperoxidase

Neela Pooransingh-Margolis, Rokus Renirie, Zulfiqar Hasan, Ron Wever, Alexander J. Vega, and Tatyana Polenova*

Contribution from the Brown Laboratories, Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, Van 't Hoff Institute for Molecular Sciences, Faculty of Science, University of Amsterdam, NieuweAchtergracht 129, 1018 WS Amsterdam, The Netherlands

Received January 20, 2006

Abstract:

We report 51V solid-state NMR spectroscopy of the 67.5-kDa vanadium chloroperoxidase, at 14.1 T. We demonstrate that, despite the low concentration of vanadium sites in the protein (one per molecule, 1 mol of vanadium spins in the entire sample), the spinning sideband manifold spanning the central and the satellite transitions is readily detectable. The quadrupolar and chemical shift anisotropy tensors have been determined by numerical simulations of the spinning sideband envelopes and the line shapes of the individual spinning sidebands corresponding to the central transition. The observed quadrupolar coupling constant CQ of 10.5 ± 1.5 MHz and chemical shift anisotropy of -520 ± 13 ppm are sensitive reporters of the geometric and electronic structure of the vanadium center. Density functional theory calculations of the NMR spectroscopic observables for an extensive series of active site models indicate that the vanadate cofactor is most likely anionic with one axial hydroxo- group and an equatorial plane consisting of one hydroxo- and two oxo- groups. The work reported in this manuscript is the first example of 51V solid-state NMR spectroscopy applied to probe the vanadium center in a protein directly. This approach yields the detailed coordination environment of the metal unavailable from other experimental measurements and is expected to be generally applicable for studies of diamagnetic vanadium sites in metalloproteins.

Cory's journals - march 2006

March 2006 articles from the journals that I am responsible for have been placed in their usual folder.

Happy Easter!

JACS - Volume 128, Issue 12

Cory's Comment: CP & symmetry-based recoupling to detect carbon-13 J-couplings.

Title: Accurate Measurements of 13C-13C J-Couplings in the Rhodopsin Chromophore by Double-Quantum Solid-State NMR Spectroscopy

Authors: Lyndon Emsley, Steven P. Brown, Richard C. D. Brown, Willem J. DeGrip, and Malcolm H. Levitt et al...

Page #: 3878

Abstract: A new double-quantum solid-state NMR pulse sequence is presented and used to measure one-bond 13C-13C J-couplings in a set of 13C2-labeled rhodopsin isotopomers. The measured J-couplings reveal a perturbation of the electronic structure at the terminus of the conjugated chain but show no evidence for protein-induced electronic perturbation near the C11-C12 isomerization site. This work establishes NMR methodology for measuring accurate 1JCC values in noncrystalline macromolecules and shows that the measured J-couplings may reveal local electronic perturbations of mechanistic significance.

JMR, Jerschow, selection of ordered 23Na signals via central transition

Journal of Magnetic Resonance
Volume 180, Issue 1 , May 2006, Pages 105-109

Selective detection of ordered sodium signals via the central transition

Jennifer Choy, Wen Ling and Alexej Jerschow

Chemistry Department, New York University, New York, NY 10003, USA

Abstract

Given the correlation between the concentrations of ordered 23Na and the onset of tissue disorders, the ability to select the signal from ordered 23Na over that of free 23Na is of particular importance and can greatly enhance the potential of 23Na-MRI as a diagnostic tool. Here, we describe a simple method that selectively detects the central transition of ordered sodium while minimizing the signal from free sodium. Our method relies upon the influence of the quadrupolar interaction on nutation frequencies and may also benefit solid-state imaging experiments. Both a liquid crystalline environment and a cartilage sample are used to demonstrate a clean separation between anisotropic and isotropic regions in the experiments.

Keywords: Nutation; Double-quantum filter; Sodium-MRI; Ordered sodium; Quadrupolar coupling; Cartilage imaging

JMR, Luis Smith, QPASS variation, 93Nb NMR

Journal of Magnetic Resonance
Volume 179, Issue 1 , March 2006, Pages 164-168
Communication

Site-selective QPASS for the isolation of large quadrupolar coupling environments

Luis J. SmithCorresponding Author Contact Information, E-mail The Corresponding Author and Christopher Seith

Carlson School of Chemistry and Biochemistry, Clark University, 950 Main Street, Worcester, MA 01610, USA

Abstract

Spectral editing of high spinning rate quadrupolar powder patterns observed using the QPASS experiment was achieved through the coupling of QPASS with the selective p/2-RAPT enhancement sequence. The resulting p/2-RAPT-QPASS sequence yields spectra that are dominated by the powder patterns form sites with large quadrupolar couplings thus reducing the overlap of patterns from multiple sites of different symmetry in a material. The 93Nb isotropic chemical shifts and quadrupolar coupling parameters were determined for the two niobium crystallographic sites in the layered KCa2Nb3O10. The asymmetric surface site in the structure was selectively enhanced and easily fit to second-order quadrupolar powder pattern with this method.

Keywords: Quadrupolar; QPASS; Spectral editing; 93Nb; RAPT

JMR, Dupree, 65Cu and 31P NMR

Journal of Magnetic Resonance
Volume 179, Issue 1 , March 2006, Pages 140-145
Communication

Solid-state 31P CP/MAS and static 65Cu NMR characterization of polycrystalline copper(I) dialkyldithiophosphate clusters

Daniela Rusanova, Willis Forsling, Oleg N. Antzutkin, Kevin J. Pike, 1 and Ray Dupree

Luleå University of Technology, Division of Chemistry, SE 971 87 Luleå, Sweden
University of Warwick, Department of Physics, Coventry CV4 7AL, UK

Abstract

Polycrystalline tetra-nuclear Cu4[S2P(O-i-C3H7)2]4, hexa-nuclear Cu6[S2P(OC2H5)2]6, and octa-nuclear Cu8[S2P(O-i-C4H9)2]6(S) complexes were synthesized and analyzed by means of solid-state 31P CP/MAS and 65Cu static NMR spectroscopy. The symmetries of the electronic environments around each P-site were estimated from the 31P chemical shift anisotropy (CSA) parameters, ?aniso and ?. The 65Cu chemical shift and quadrupolar splitting parameters obtained from the experimental 65Cu NMR spectra of the polycrystalline CuI-complexes are presented. A solid-state NMR approach for the elucidation of the stereochemistry of poly-nuclear Cu(I) dithiophosphate complexes, when the structural analysis of the systems by single-crystal X-ray diffraction is not readily available, is proposed.

Keywords: 31P CP/MAS NMR; Solid-state 65Cu NMR; Copper(I); Dialkyldithiophosphate

JMR, Levitt, Symmetry-based recoupling of 17O–1H spin pairs in MAS NMR

Symmetry-based recoupling of 17O–1H spin pairs in magic-angle spinning NMR

Jacco D. van Beek, 1, Ray Dupree and Malcolm H. Levitt

School of Chemistry, Southampton University, Highfield, Southampton, SO17 1BJ, UK
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK

Abstract

We have performed magic-angle-spinning solid-state NMR experiments in which protons are recoupled to oxygen-17 nuclei by applying a symmetry-based recoupling sequence at the proton Larmor frequency. Two-dimensional quadrupole-dipole correlation spectra are produced, in which the second-order quadrupolar shift of the oxygen-17 central transition is correlated with the recoupled heteronuclear dipole–dipole interaction. These spectra are sensitive to the relative orientation of the electric field gradient at the site of the oxygen-17 nucleus and the O–H internuclear vector. We also demonstrate experiments in which polarization is transferred from protons to oxygen-17, and show that oxygen-17 signals may be selected according to the protonation state of the oxygen site. We discuss the small observed value of the heteronuclear dipolar splitting in the central-transition oxygen-17 spectra.

Keywords: Solid-state NMR; Quadrupolar nuclei; Oxygen-17; Correlation spectroscopy; Symmetry-based recoupling; MAS; Brucite

Phyical Review Letters, Vol 96, Issue 10

Cory's Comment: sticking metallocenes in nanotubes...

Title: Tuning the Electrical Conductivity of Nanotube-Encapsulated Metallocene Wires

Authors: Victor M Garcia-Suarez, Jamie Ferrer, and Colin J. Lambert

Article #: 106804

Abstract: We analyze a new family of carbon nanotube-based molecular wires, formed by encapsulating metallocene molecules inside the nanotubes. Our simulations, which are based on a combination of nonequilibrium Green function techniques and density functional theory, indicate that these wires can be engineered to exhibit desirable magnetotransport effects for use in spintronics devices. The proposed structures should also be resilient to room-temperature fluctuations, and are expected to have a high yield.

Joel's ChemPhysChem Update

Quenching Echo Modulations in NMR Spectroscopy
Jens Dittmer adn Geoffrey Bodenhausen
ChemPhysChem (2006) 7(4),831.
Abstract:
In NMR spectroscopy, homonuclear scalar couplings normally lead to modulations of spin echoes that tend to interfere with the accurate determination of transverse relaxation rates by Carr–Purcell–Meiboom–Gill (CPMG) multiple refocusing experiments. Surprisingly, the echo modulations are largely cancelled when the refocusing pulses applied to the coupling partner deviate slightly from ideal p rotations due to tilted effective radio-frequency (RF) fields, even at offsets that are much smaller than the radio-frequency amplitude. Experiments and simulations illustrate these effects for two-spin IS systems containing donor and acceptor 15N nuclei I=ND and S=NA in RNA Watson–Crick base pairs with homonuclear scalar couplings JIS=2hJ(ND, NA) across the hydrogen bonds.

Fingerprints of Damped Quantum Rotation Observed in Solid-State Proton NMR Spectra.
P. Gutsche, H. Schmitt, U. Haberlen, T. Ratajczyk, and S. Symanski.
ChemPhysChem (2006) 7(4),884.
Abstract:
1H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acidwith all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency andtwo coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical.

Joel: JPCB Update

Interesting Article
Detecting Gas Hydrate Behavior in Crude Oil Using NMR
S. Gao, W. House,and W.G. Chapman
J.Phys.Chem.B (2006)110, 6549.
Abstract:
Because of the associated experimental difficulties, natural gas hydrate behavior in black oil is poorly understood despite its grave importance in deep-water flow assurance. Since the hydrate cannot be visually observed in black oil, traditional methods often rely on gas pressure changes to monitor hydrate formation and dissociation. Because gases have to diffuse through the liquid phase for hydrate behavior to create pressure responses, the complication of gas mass transfer is involved and hydrate behavior is only indirectly observed. This pressure monitoring technique encounters difficulties when the oil phase is too viscous, the amount of water is too small, or the gas phase is absent. In this work we employ proton nuclear magnetic resonance (NMR) spectroscopy to observe directly the liquid-to-solid conversion of the water component in black oil emulsions. The technique relies on two facts. The first, well-known, is that water becomes essentially invisible to liquid state NMR as it becomes immobile, as in hydrate or ice formation. The second, our recent finding, is that in high magnetic fields of sufficient homogeneity, it is possible to distinguish water from black oil spectrally by their chemical shifts. By following changes in the area of the water peak, the process of hydrate conversion can be measured, and, at lower temperatures, the formation of ice. Taking only seconds to accomplish, this measurement is nearly direct in contrast to conventional techniques that measure the pressure changes of the whole system and assume these changes represent formation or dissociation of hydrates - rather than simply changes in solubility. This new technique clearly can provide accurate hydrate thermodynamic data in black oils. Because the technique measures the total mobile water with rapidity, extensions should prove valuable in studying the dynamics of phase transitions in emulsions.

Multinuclear Solid-State High Resolution and 13C-{27Al} Double Resonance Magic-Angle Spinning NMR Studies on Aluminum Alkoxides.
A. Abraham, R. Prins, J.A. van Bokhoven, E.R.H. van Eck, A.P.M Kentgens.
J.Phys.Chem.B (2006)110, 6549.
Abstract:
A combination of 27Al magic-angle spinning (MAS)/multiple quantum (MQ)-MAS, 13C-1H CPMAS, and 13C-{27Al} transfer of population in double-resonance (TRAPDOR) nuclear magnetic resonance (NMR) were used for the structural elucidation of the aluminum alkoxides aluminum ethoxide, aluminum isopropoxide, and aluminum tertiarybutoxide. Aluminum alkoxides exist as oligomers with aluminum in different coordinations. High-resolution 27Al MAS NMR experiments with high-spinning speed distinguished the aluminum atoms in different environments. The 27Al MAS NMR spectrum gave well-resolved powder patterns with different coordinations. Z-filter MQ-MAS was performed to obtain the number and types of aluminum environments in the oligomeric structure. 13C-1H CPMAS chemical shifts resolved the different carbon species (-CH3, =CH2, =CH-, and =C=) in the structures. 13C-{27Al} TRAPDOR experiments were employed to obtain relative Al-C dipolar interactions and to distinguish between terminal and bridging alkoxides in the crystallographic structures. The complete characterization of selected aluminum alkoxides using advanced NMR methods has evidenced the tetrameric structure for aluminum isopropoxide and the dimeric structure for aluminum tertiary-butoxide, as reported in the literature, and proposed a polymeric structure for aluminum ethoxide.

Rob Posted Before
NMR Study of Strontium Binding by a Micaceous Mineral
G.M. Bowers, R. Ravella, S. Komarneni, and K.T. Mueller
J.Phys.Chem.B (2006)110, 7159.

Goward Paper
7Li NMR and Two-Dimensional Exchange Study of Lithium Dynamics in Monoclinic Li3V2(PO4)3
L.S. Cahill, R.P. Chapman, J.F. Britten, and G.R. Goward
J.Phys.Chem.B (2006)110, 7171.
Abstract:
High-resolution solid-state 7Li NMR was used to characterize the structure and dynamics of lithium ion transport in monoclinic Li3V2(PO4)3. Under fast magic-angle spinning (MAS) conditions (25 kHz), three resonances are clearly resolved and assigned to the three unique crystallographic sites. This assignment is based on the Fermi-contact delocalization interaction between the unpaired d-electrons at the vanadium centers and the lithium ions. One-dimensional variable-temperature NMR and two-dimensional exchange spectroscopy (EXSY) are used to probe Li mobility between the three sites. Very fast exchange, on the microsecond time scale, was observed for the Li hopping processes. Activation energies are determined and correlated to structural properties including interatomic Li distances and Li-O bottleneck sizes.

Little off topic but ever wonder how...
Modeling the Cycles of Growth and Detachment of Bubbles in Carbonated Beverages.
S. Uzel, M.A. Chappell, S.J. Payne.
J.Phys.Chem.B (2006)110, 7579.
Abstract:
In this paper, a model for the formation of bubbles in carbonated beverages is presented. It has previously been shown that bubbles form from cellulose fibers within such beverages and the passage of such bubbles from the fibers to the liquid surface has been modeled. A model is thus presented here that considers the process of formation, which is governed by diffusion through the fiber and bubble surfaces. The model comprises two stages, growth and detachment, and it is shown here that both play an important role. The latter process is found to occur over a much shorter time scale than the former, enabling the models to be partially decoupled. The total number of bubbles released from individual fibers over time is found to be approximated well by an exponential relationship, and the parameters in this relationship are presented for a range of different detachment angles and fiber sizes. It is found that bubble formation is promoted in narrow, long tubes, but that the time constant is solely determined by the rate of diffusion across the liquid surface. The surface tension is found to have minimal influence on the number of bubbles produced.

CPC, Haeberlen, 1H NMR investigation of non-classical motion of methyl groups - i.e., tunnelling

ChemPhysChem
Volume 7, Issue 4 , Pages 886 - 893
Fingerprints of Damped Quantum Rotation Observed in Solid-State Proton NMR Spectra
Peter Gutsche, Dr. 1, Heike Schmitt 1, Ulrich Haeberlen, Prof. Dr. 1 *, Tomasz Ratajczyk 2, Slawomir Szymanski, Prof. Dr. 2 *
1Max-Planck Institute for Medical Research, 69120 Heidelberg, Germany, Fax: (+) 49 6221 4856351
2Institute of Organic Chemistry, Polish Academy of Sciences, 01224 Warsaw, Poland, Fax: (+) 48 2263 26681

Keywords
methyl group • NMR spectroscopy • quantum rotation • rate processes • tunnelling

Abstract
1H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acid with all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency and two coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical.

Cory's journals - feb2006

Journal articles from February 2006 will be put in their usual place on Purcell by the end of today.

JMR, Yesinowski, 71Ga and 69Ga magnetization recovery experiments in GaN

Journal of Magnetic Resonance
Volume 180, Issue 1 , May 2006, Pages 147-161

Magnetization-recovery experiments for static and MAS-NMR of I = 3/2 nuclei

James P. Yesinowski
Chemistry Division, Naval Research Laboratory, Washington, DC 20375, USA

Abstract

Multifrequency pulsed NMR experiments on quadrupole-perturbed I = 3/2 spins in single crystals are shown to be useful for measuring spin–lattice relaxation parameters even for a mixture of quadrupolar plus magnetic relaxation mechanisms. Such measurements can then be related to other MAS-NMR experiments on powders. This strategy is demonstrated by studies of 71Ga and 69Ga (both I = 3/2) spin–lattice relaxation behavior in a single-crystal (film) sample of gallium nitride, GaN, at various orientations of the axially symmetric nuclear quadrupole coupling tensor. Observation of apparent single-exponential relaxation behavior in I = 3/2 saturation-recovery experiments can be misleading when individual contributing rate processes are neglected in the interpretation. The quadrupolar mechanism (dominant in this study) has both a single-quantum process (T1Q1) and a double-quantum process (T1Q2), whose time constants are not necessarily equal. Magnetic relaxation (in this study most likely arising from hyperfine couplings to unpaired delocalized electron spins in the conduction band) also contributes to a single-quantum process (T1M). A strategy of multifrequency irradiation with observation of satellite and/or central transitions, incorporating different initial conditions for the level populations, provides a means of obtaining these three relaxation time constants from single-crystal 71Ga data alone. The 69Ga results provide a further check of internal consistency, since magnetic and quadrupolar contributions to its relaxation scale in opposite directions compared to 71Ga. For both perpendicular and parallel quadrupole coupling tensor symmetry axis orientations small but significant differences between T1Q1 and T1Q2 were measured, whereas for a tensor symmetry axis oriented at the magic-angle (54.74°) the values were essentially equal. Magic-angle spinning introduces a number of complications into the measurement and interpretation of the spin–lattice relaxation. Comparison of 71Ga and 69Ga MAS-NMR saturation-recovery curves with both central and satellite transitions completely saturated by a train of 90° pulses incommensurate with the rotor period provides the simplest means of assessing the contribution from magnetic relaxation, and yields results for the quadrupolar mechanism contribution that are consistent with those obtained from the film sample.

Keywords: Quadrupolar NMR; Spin–lattice relaxation; Magic-angle spinning; Single crystal; Gallium nitride

JMR, Amoreux, Homogeneous broadenings in 2D solid-state NMR of half-integer quadrupolar nuclei

Journal of Magnetic Resonance
Volume 179, Issue 2 , April 2006, Pages 311-316
Communication

Homogeneous broadenings in 2D solid-state NMR of half-integer quadrupolar nuclei

J.P. Amoureux, J. Trébosc

UCCS, CNRS-8181, University of Lille-1, ENSCL Bâtiment C7, 59652 Villeneuve d’Ascq Cedex, France

Abstract

The question of the homogeneous broadening that occurs in 2D solid-state NMR experiments is examined. This homogeneous broadening is mathematically introduced in a simple way, versus the irreversible decay rates related to the coherences that are involved during t1 and t2. We give the pulse sequences and coherence transfer pathways that are used to measure these decay rates. On AlPO4 berlinite, we have measured the 27Al echo-type relaxation times of the central and satellite transitions on 1Q levels, so that of coherences that are situated on 2Q, 3Q, and 5Q levels. We compare the broadenings that can be deduced from these relaxation times to those directly observed on the isotropic projection of berlinite with multiple-quantum magic-angle spinning (MAS), or satellite-transition MAS. We show that the choice of the high-resolution method, should be done according to the spin value and the corresponding homogeneous broadening.

Keywords: Magic-angle spinning NMR; Quadrupolar nuclei; Multiple-quantum MAS; Satellite-transition MAS; High-resolution; Homogeneous broadening

JMR, Bain, 3rd order quadrupolar interactions

Journal of Magnetic Resonance
Volume 179, Issue 2 , April 2006, Pages 308-310

A simple proof that third-order quadrupole perturbations of the NMR central transition of half-integral spin nuclei are zero

Alex D. Bain

Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, Ont., Canada L8S 4M1

Abstract

It has been known for a long time that the third-order quadrupole corrections to transitions from mz = -n/2 to mz = +n/2 are zero in the NMR of half-integer nuclei. However, the derivation has relied on deriving the corrections to the energy levels through somewhat laborious calculations. Only when the transitions between the levels were calculated was it revealed that the corrections to the transition frequency were zero. In this paper, we use Liouville-space methods to work with the transitions directly. Application of a recently published [A.D. Bain, Exact calculation, using angular momentum, of combined Zeeman and quadrupolar interactions in NMR, Mol. Phys. 101 (2003) 3163–3175] selection rule for the quadrupole coupling leads to a very simple proof that third-order corrections to the central and other symmetrical transitions are zero. The simplicity of the proof suggests there is a fundamental symmetry involved.

Keywords: Quadrupolar nuclei; Perturbation theory; Second-order effects; Third-order effects; Solid-state NMR

JMR, spin-1/2-quadrupolar dipolar relaxation mechanism

Journal of Magnetic Resonance
Volume 179, Issue 2 , April 2006, Pages 250-262

Field-dependent nuclear relaxation of spins 1/2 induced by dipole–dipole couplings to quadrupole spins: LaF3 crystals as an example

Danuta Kruka, Oliver Lips

Institut für Festkörperphysik, TU Darmstadt, Hochschulstr. 6, 64289 Darmstadt, Germany
Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow, Poland

Abstract

A general theory of spin–lattice nuclear relaxation of spins I = 1/2 caused by dipole–dipole couplings to quadrupole spins S greater-or-equal, slanted 1, characterized by a non-zero averaged (static) quadrupole coupling, is presented. In multispin systems containing quadrupolar and dipolar nuclei, transitions of spins 1/2 leading to their relaxation are associated through dipole–dipole couplings with certain transitions of quadrupole spins. The averaged quadrupole coupling attributes to the energy level structure of the quadrupole spin and influences in this manner relaxation processes of the spin 1/2. Typically, quadrupole spins exhibit also a complex multiexponential relaxation sensed by the dipolar spin as an additional modulation of the mutual dipole–dipole coupling. The proposed model includes both effects and is valid for an arbitrary magnetic field and an arbitrary quadrupole spin quantum number. The theory is applied to interpret fluorine relaxation profiles in LaF3 ionic crystals. The obtained results are compared with predictions of the ‘classical’ Solomon relaxation theory.

Keywords: Nuclear relaxation; Quadrupole spins; Dipolar spins; Solid state; Ion dynamics

JMR, Tim Cross, PISEMA tensors

Journal of Magnetic Resonance
Volume 179, Issue 2 , April 2006, Pages 190-198

Intensity and mosaic spread analysis from PISEMA tensors in solid-state NMR

J.R. Quine, S. Achuthan, T. Asbury, R. Bertram, M.S. Chapmanc, J. Hue and T.A. Cross

Abstract

The solid-state NMR experiment PISEMA, is a technique for determining structures of proteins, especially membrane proteins, from oriented samples. One method for determining the structure is to find orientations of local molecular frames (peptide planes) with respect to the unit magnetic field direction, B0. This is done using equations that compute the coordinates of this vector in the frames. This requires an analysis of the PISEMA function and its degeneracies. As a measure of the sensitivity of peptide plane orientations to the data, we use these equations to derive a formula for the intensity function in the powder pattern. With this function and other measures, we investigate the effect of small changes in peptide plane orientations depending on the location of the resonances in the powder pattern spectrum. This gives us an indication of the change in lineshape due to mosaic spread and a way to interpret these in terms of an orientational error bar.

Keywords: PISEMA tensors; Solid-state NMR; Powder pattern intensity; Mosaic spread; Lineshapes

SSNMR; 7 mm MAS NMR probe to a single-crystal goniometer

Solid State Nuclear Magnetic Resonance
Volume 30, Issue 1 , July 2006, Pages 55-59

Hardware modification of a 7 mm MAS NMR probe to a single-crystal goniometer

Gábor Kovács and János Rohonczy
Department of General and Inorganic Chemistry, Institute of Chemistry, Eötvös Loránd University, Budapest, Hungary

Abstract

Tensorial terms of the Hamiltonian can be measured by solid-state single-crystal nuclear magnetic resonance (NMR) spectroscopy which requires a goniometer NMR probehead. Goniometer probes; however, are not standard parts of solid NMR spectrometers and are available only at a much higher price than magic-angle spinning (MAS) probeheads widely used in research. Due to requirements of MAS experiments, modern probeheads are designed for small ceramic rotors, which are 1–4 mm in diameter, to reach very high angular frequencies, so there are several older 7 mm MAS probeheads used rarely todays in NMR laboratories. In this paper, a simple method is presented how to rebuild step-by-step a 7 mm Bruker MAS probehead to be suitable for single-crystal spectroscopy. In the second part 31P chemical shift tensors of Na4P2O7·10H2O are determined to demonstrate the functionality of the rebuilt probehead.

Keywords: NMR; Single crystal; MAS probe; ASICS; Goniometer; Sodium pyrophosphate; Home-built probehead; Nuclear magnetic resonance; 31-P NMR; Crystal orientation

SSNMR, Duer, CSA-amplified PASS

Joel, Hiyam; please check out

Solid State Nuclear Magnetic Resonance
Volume 30, Issue 1 , July 2006, Pages 1-8

Applications of the CSA-amplified PASS experiment

Robin M. Orr and Melinda J. Duer
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK

Abstract

The recently reported CSA-amplified PASS experiment correlates the spinning sidebands at the true spinning frequency ?r with the spinning sidebands that would be obtained at the effective spinning frequency ?r/N, where N is termed the scaling factor. The experiment is useful for the measurement of small chemical shift anisotropies, for which slow magic-angle spinning frequencies, required to measure several spinning sidebands, can be unstable. We have experimentally evaluated the reliability of this experiment for this application. In particular we have demonstrated that large scaling factors of the order of N=27 may be used, whilst still obtaining accurate chemical shift sideband intensities at the effective spinning frequency from the F1 projection. Moreover, the sideband intensities are accurately obtained even in the presence of significant pulse imperfections. A second application of the CSA-amplified PASS experiment is the measurement of the chemical shift anisotropy of sites that experience homonuclear dipolar coupling, as may be found in uniformly labelled biological molecules, or for nuclei with a high natural abundance. The effects of homonuclear dipolar coupling on CSA-amplified PASS spectra has been investigated by numerical simulations and are demonstrated using uniformly 13C enriched l-histidine monohydrochloride monohydrate.

Keywords: Solid-state NMR; Magic-angle spinning; Chemical shift anisotropy; Recoupling; Homonuclear dipolar coupling