Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 6, November 2006
pp. 369 - 383
Title: Operator formalisms: An overview
Author: Bain, Alex D.a
Affiliations: a. Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1
Keywords: operators; density matrix theory; spherical tensors; Cartesian tensors; single transition operators; quadrupolar echo; pulse sequences
Abstract (English):
Operator formalisms are mathematical recipes for simplifying the manipulations of the density matrix. Because the density matrix is a vital tool in describing and analyzing magnetic resonance experiments, many approaches have been developed. This article gives an overview of a number of different methods: spherical tensors, fictitious spin-1/2, single-transition operators, product operators, superspin methods, and others. In principle, they all must give the same answer, because an exact description of magnetic resonance phenomena is usually within reach. The choice of the formalism for the user, therefore, depends on various personal decisions. Among these decisions is the choice between spherical and Cartesian tensors, between Hilbert space and Liouville space, between commutators and matrix elements, and so on. We do not go into the details of any of the formalisms but rather try to compare their approaches at a fairly general level. The quadrupolar echo pulse sequence is used as an example of the application of the formalisms. The aim of this overview is to give readers enough of a picture so that they can make an intelligent choice for themselves. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 369–383, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 6, November 2006
pp. 384 - 409
Title: On the physical interpretation of density operators at the atomic scale: A thorough analysis of some simple cases
Author: Paniagua, Juan C.a
Affiliations: a. Departament de Química Física, Universitat de Barcelona, C. Martí i Franquès 1, E‐08028 Barcelona, Spain
Keywords: density operator; density matrix; coherences; phase coherence; physical interpretation
Abstract (English):
The physical meaning of the concepts underlying the density operator formalism are analyzed from different points of view. In particular, the diversity of ways of expressing the density operator of the simplest NMR sample is exploited to show that there are many molecular-scale physical pictures compatible with each macroscopic state, some of them being more useful than others for specific aims. Those corresponding to diagonal representations of the density matrix conform closely to classical-like pictures, which allow us to ignore the subtle effects of quantum interferences that are implicit in the concept of coherence. A widespread biconical picture that does not rely on a sound physical basis is shown to be quantitatively valid provided that ad hoc populations are chosen for the involved quantum states. The interpretation of the coefficients of the density operator expansion in terms of observable-related basis elements is discussed to show that the identification of these with the corresponding physical properties can be misleading in certain cases. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 384–409, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 5, September 2006
pp. 307 - 320
Title: A simple analytical model to describe dynamic magic-angle spinning experiments
Author: Hirschinger, Jérômea
Affiliations: a. Institut de Chimie, UMR 7177 CNRS, Université Louis Pasteur, BP 296, 67008 Strasbourg Cedex, France
Keywords: memory-function approach; Anderson-Weiss theory; magic-angle spinning; molecular motion; rotational-echo double-resonance (REDOR); solid-state NMR
Abstract (English):
A simple analytical method based on the memory-function approach and the Anderson-Weiss theory is presented for studying in a uniform way the spin dynamics in several NMR experiments performed under the conditions of magic-angle spinning (MAS). A series of 1H MAS spectra of adamantane serve as an example for a sample with homogeneous line broadening. A good agreement between experimental and calculated integral spinning sideband intensities for a spinning frequency ranging from 5 to 33 kHz is obtained using a sixth-order approximation of the theory. Moreover, this model, which is able to describe the NMR spectra in the presence of a rotationally diffusive isotropic and anisotropic Gaussian-Markoff process, allows the treatment of the combined effects of sample spinning and molecular motion. Finally, the application of MAS recoupling methods in the intermediate motional regime is examined by using the concept of refocusing pulses. It is shown that recoupling experiments such as rotational-echo double-resonance (REDOR) can still be applied in the presence of anisotropic molecular motion. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A, 28A: 307–320, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 5, September 2006
pp. 347 - 368
Title: The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations
Author: Stueber, Dirka
Affiliations: a. Department of Chemistry, Washington University, St. Louis, Missouri 60607‐7061
Keywords: NMR; nuclear magnetic shielding tensor; quantum mechanical shielding calculations; embedded ion method (EIM); intermolecular interactions; Ewald method; point charge arrays; electrostatic; crystal lattice effects
Abstract (English):
The nuclear magnetic shielding anisotropy of NMR active nuclei is highly sensitive to the nuclear electronic environment. Hence, measurements of the nuclear magnetic shielding anisotropy represent a powerful tool in the elucidation of molecular structure for a wide variety of materials. Quantum mechanical ab initio nuclear magnetic shielding calculations effectively complement the experimental NMR data by revealing additional structural information. The accuracy and capacity of these calculations has been improved considerably in recent years. However, the inherent problem of the limitation in the size of the systems that may be studied due to the relatively demanding computational requirements largely remains. Accordingly, ab initio shielding calculations have been performed predominantly on isolated molecules, neglecting the molecular environment. This approach is sufficient for neutral nonpolar systems, but leads to serious errors in the shielding calculations on polar and ionic systems. Conducting ab initio shielding calculations on clusters of molecules (i.e., including the nearest neighbor interactions) has improved the accuracy of the calculations in many cases. Other methods of simulating crystal lattice effects in shielding calculations that have been developed include the electrostatic representation of the crystal lattice using point charge arrays, full ab initio methods, ab initio methods under periodic boundary conditions, and hybrid ab initio/molecular dynamics methods. The embedded ion method (EIM) discussed here follows the electrostatic approach. The method mimics the intermolecular and interionic interactions experienced by a subject molecule or cluster in a given crystal in quantum mechanical shielding calculations with a large finite, periodic, and self-consistent array of point charges. The point charge arrays in the EIM are generated using the Ewald summation method and embed the molecule or ion of interest for which the ab initio shielding calculations are performed. The accuracy with which the EIM reproduces experimental nuclear magnetic shift tensor principal values, the sensitivity of the EIM to the parameters defining the point charge arrays, as well as the strengths and limitations of the EIM in comparison with other methods that include crystal lattice effects in chemical shielding calculations, are presented. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 347–368, 2006
Monday, February 26, 2007
JMR: Journal of Magnetic Resonance update to February 2007
Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 322-329
Title: Improved resolution in 13C solid-state spectra through spin-state-selection
Authors: Verel, Renéa; Manolikas, Theofanisa; Siemer, Ansgar B.a; Meier, Beat H.a
Affiliations: a. Physical Chemistry, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
Keywords: Solid-state NMR; Spin-state selection; High resolution
Abstract (English):
The application of a spin-state-selective coherence transfer experiment (INADEQUATE-SSS) to solid-state NMR spectroscopy is described. Two-dimensional 13C double-quantum/single-quantum spectra without J splittings in both dimensions lead to enhanced spectral resolution. The method is demonstrated to significantly improve the spectral resolution of the crowded C’–Ca region of two proteins.
Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 350-356
Title: Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation
Authors: Wickramasinghe, Nalinda P.a; Kotecha, Mrignayania; Samoson, Agob; Past, Jaanb; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, 845 W Taylor St., Chicago, IL 60607, USA
b. National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
Keywords: Solid-state NMR; Protein microcrystal; T1 relaxation; Paramagnetic doping; 13C CPMAS
Abstract (English):
We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T1 values can be reduced from 0.4–0.8s to 60–70ms for ubiquitin and lysozyme in D2O in the presence of 10mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T1 attained by paramagnetic doping provided sensitivity enhancements of 1.4–2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0–8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 1-14
Title: HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids
Authors: Amoureux, J.P.a; Trebosc, J.a; Wiench, J.b; Pruski, M.b
Affiliations: a. UCCS, CNRS-8181, ENSCL-USTL, Fr-59652 Villeneuve d’Ascq, France
b. Ames Laboratory, Iowa State University, Ames, IA 50011, USA
Keywords: Solid-state NMR; J-coupling; R-INEPT; HMQC; Quadrupolar nuclei; MAS; MQMAS; STMAS
Abstract (English):
Hetero-nuclear coherence transfers in HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids are analyzed. 1D and 2D schemes are considered under MAS for the general case of multi-spin systems SIn (n4), where S is an observed nucleus. These results are also discussed in the context of high-resolution schemes featuring MQMAS or STMAS. The theoretical predictions are verified experimentally in a series of 1D and 2D experiments performed at 9.4 and 18.8T.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 15-19
Title: Three-dimensional through-bond homonuclear–heteronuclear correlation experiments for quadrupolar nuclei in solid-state NMR applied to 27Al–O–31P–O–27Al networks
Authors: Deschamps, Michaëla; Massiot, Dominiquea
Affiliations: a. CRMHT-CNRS, 1D Avenue de la Recherche Scientifique, 45071 ORLEANS cedex 2, France
Keywords: 3D; J-coupling; Quadrupolar nuclei; Aluminium; Phosphate
Abstract (English):
We present here the first 3D homonuclear/heteronuclear correlation experiment applied to quadrupolar nuclei and making use of the sole scalar J-coupling. This experiment, based on the 2D-Homonuclear–Heteronuclear Single Quantum Correlation (H–HSQC) experiment, uses a relayed transfer from the 27Al central transition to neighbouring 31P spins and to the central transition of a second 27Al. It confirms the correlation map characterizing the two 27Al and the 31P NMR signatures of 27Al–O–31P–O–27Al chemically bonded molecular motifs.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 39-43
Title: 13C/14N heteronuclear multiple-quantum correlation with rotary resonance and REDOR dipolar recoupling
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: 13C/14N Correlation; HMQC; Dipolar recoupling; MAS; Rotary resonance; REDOR
Abstract (English):
A two-dimensional 13C/14N heteronuclear multiple quantum correlation (HMQC) experiment using dipolar recoupling under magic-angle spinning (MAS) is described. The experiment is an extension of the recent indirect 13C detection scheme for measuring 14N quadrupolar coupling under MAS. The recoupling allows the direct use of the much larger dipolar interaction instead of the small J and residual dipolar couplings for establishing 13C/14N correlations. Two recoupling methods are incorporated into the HMQC sequence, both applying rf only to the observed 13C spin. The first one uses the REDOR sequence with two p-pulses per rotor cycle. The second one uses a cw rf field matching the spinning frequency, known as rotary resonance. The effects of CSA, Formula Not Shown signal loss, MAS frequency and stability and t1-noise are compared and discussed.
Journal of Magnetic Resonance
Vol: 183, Issue: 2, December, 2006
pp. 235-241
Title: Rotary resonance echo double resonance for measuring heteronuclear dipolar coupling under MAS
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: Rotary resonance; R-REDOR; REDOR; MAS; Dipolar coupling
Abstract (English):
A rotary resonance echo double resonance (R-REDOR) experiment is described for measuring heteronuclear dipolar coupling under magic-angle spinning. Rotary resonance reintroduces both dipolar coupling and chemical shift anisotropy with an rf field matching the spinning frequency. The resonance effect from chemical shift anisotropy can be refocused with a rotary resonance echo. The R-REDOR experiment thus measures the dephasing of the rotary resonance echo from the heteronuclear dipolar coupling to determine the dipolar coupling constant. The rotary resonance experiment is suitable for measuring dipolar coupling with quadrupolar nuclei because it applies the recoupling rf only to the observed spin-1/2. The rotary resonance scheme has the advantages of a long Formula Not Shown and susceptible to spinning frequency fluctuation.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 68-76
Title: Polarization transfer from remote protons in 13C CP/MAS
Authors: Tripon, Carmena; Aluas, Mihaelab; Filip, Xeniaa; Filip, Claudiua
Affiliations: a. National Institute for R&D of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj, Romania
b. Physics Department, Babes-Bolyai University, Cluj, Romania
Keywords: Solid-state NMR; Cross-polarization; CP/MAS; Spin dynamics
Abstract (English):
An experimental procedure for CP/MAS polarization transfer from remote 1H nuclear spins is introduced, which is applicable to protonated carbons in organic solids. It is based on preparing a state of non-uniform polarization, where directly bonded 13C–1H nuclei are de-polarized prior to recording the CP buildup curve. This curve is then expected to quantify the polarization transfer from remote protons only. The ability of the cross-polarization/polarization-inversion (CPPI) sequence to generate an initial state suitable for remote 1H CP/MAS scheme is analyzed both theoretically and experimentally. Confining to aliphatic groups, it was found that complete de-polarization of bonded proton is possible in the case of CH, whereas for CH2 and CH3 moieties only a partial de-polarization can be achieved. The theoretical predictions have been verified in practice for the particular case of l-alanine. The significance of the results from fundamental, as well as practical point of view, is also discussed. In particular, it is shown that: (i) the coherent description of polarization transfer under CP/MAS, including 1H polarization redistribution, is valid over time-scales longer than commonly assumed in many treatments of cross-polarization, and (ii) the remote protons polarization transfer curve can be used in combination with the conventional CP/MAS curve to get additional structural and dynamical information in organic systems.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 123-133
Title: Bayesian and information theory analysis of MAS sideband patterns in spin 1/2 systems
Author: Sachleben, Joseph R.a
Affiliations: a. Department of Chemistry, Otterbein College, Westerville, OH 43081, USA
Keywords: Magic angle spinning; Errors; Bayesian analysis; Chemical shift tensor
Abstract (English):
Bayesian statistics and information theory are used to analyze the reliability of extracting chemical shift parameters from spinning sideband patterns of spin 1/2 systems. Efficient code has been written to calculate the two-dimensional posterior probability as a function of the chemical shift anisotropy, d, and the asymmetry parameter, , given the sideband intensities and the signal-to-noise ratio. This method has the advantage of assuming only that the noise in the sideband intensities is distributed as a Gaussian. It assumes nothing about the distribution of the values of parameters d and , which are shown in some cases to be highly non-Gaussian. The utility of Bayesian analysis is demonstrated on 1D slow-spinning MAS spectra and on sideband patterns extracted from 2D PASS spectra. Previous investigations have shown that there is an optimal range of spinning frequencies for determining d. In this study, information theory is used to determine the signal-to-noise ratio dependence of the entropy in d, , and total entropy in spinning sideband spectra. The entropy is a measure of the information content of a probability distribution. When the entropy is zero, there is perfect information on a system, while if it is infinite, there is no information on the system. It is found that for all values of and for signal-to-noise ratios in the range 50–1000, an entropy minimum in nd/nr occurs for values 1.5nd/nr3. In the same range of signal-to-noise ratios, the entropy in is a monotonically decreasing function of nd/nr. The global information content of a spinning sideband pattern (i.e., the total entropy) is dependent on the signal-to-noise ratio and has an optimal value at nd/nr2 at a signal-to-noise ratio of 50 and increasing to 2.5 for signal-to-noise ratios of 1000. Finally, the increase of information in a sideband pattern as a function of the number of sidebands used in the analysis is examined. Most of the information about d and is contained in the five central sidebands; i.e., sidebands -2 to 2.
Vol: 184, Issue: 2, February, 2007
pp. 322-329
Title: Improved resolution in 13C solid-state spectra through spin-state-selection
Authors: Verel, Renéa; Manolikas, Theofanisa; Siemer, Ansgar B.a; Meier, Beat H.a
Affiliations: a. Physical Chemistry, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
Keywords: Solid-state NMR; Spin-state selection; High resolution
Abstract (English):
The application of a spin-state-selective coherence transfer experiment (INADEQUATE-SSS) to solid-state NMR spectroscopy is described. Two-dimensional 13C double-quantum/single-quantum spectra without J splittings in both dimensions lead to enhanced spectral resolution. The method is demonstrated to significantly improve the spectral resolution of the crowded C’–Ca region of two proteins.
Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 350-356
Title: Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation
Authors: Wickramasinghe, Nalinda P.a; Kotecha, Mrignayania; Samoson, Agob; Past, Jaanb; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, 845 W Taylor St., Chicago, IL 60607, USA
b. National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
Keywords: Solid-state NMR; Protein microcrystal; T1 relaxation; Paramagnetic doping; 13C CPMAS
Abstract (English):
We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T1 values can be reduced from 0.4–0.8s to 60–70ms for ubiquitin and lysozyme in D2O in the presence of 10mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T1 attained by paramagnetic doping provided sensitivity enhancements of 1.4–2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0–8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 1-14
Title: HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids
Authors: Amoureux, J.P.a; Trebosc, J.a; Wiench, J.b; Pruski, M.b
Affiliations: a. UCCS, CNRS-8181, ENSCL-USTL, Fr-59652 Villeneuve d’Ascq, France
b. Ames Laboratory, Iowa State University, Ames, IA 50011, USA
Keywords: Solid-state NMR; J-coupling; R-INEPT; HMQC; Quadrupolar nuclei; MAS; MQMAS; STMAS
Abstract (English):
Hetero-nuclear coherence transfers in HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids are analyzed. 1D and 2D schemes are considered under MAS for the general case of multi-spin systems SIn (n4), where S is an observed nucleus. These results are also discussed in the context of high-resolution schemes featuring MQMAS or STMAS. The theoretical predictions are verified experimentally in a series of 1D and 2D experiments performed at 9.4 and 18.8T.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 15-19
Title: Three-dimensional through-bond homonuclear–heteronuclear correlation experiments for quadrupolar nuclei in solid-state NMR applied to 27Al–O–31P–O–27Al networks
Authors: Deschamps, Michaëla; Massiot, Dominiquea
Affiliations: a. CRMHT-CNRS, 1D Avenue de la Recherche Scientifique, 45071 ORLEANS cedex 2, France
Keywords: 3D; J-coupling; Quadrupolar nuclei; Aluminium; Phosphate
Abstract (English):
We present here the first 3D homonuclear/heteronuclear correlation experiment applied to quadrupolar nuclei and making use of the sole scalar J-coupling. This experiment, based on the 2D-Homonuclear–Heteronuclear Single Quantum Correlation (H–HSQC) experiment, uses a relayed transfer from the 27Al central transition to neighbouring 31P spins and to the central transition of a second 27Al. It confirms the correlation map characterizing the two 27Al and the 31P NMR signatures of 27Al–O–31P–O–27Al chemically bonded molecular motifs.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 39-43
Title: 13C/14N heteronuclear multiple-quantum correlation with rotary resonance and REDOR dipolar recoupling
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: 13C/14N Correlation; HMQC; Dipolar recoupling; MAS; Rotary resonance; REDOR
Abstract (English):
A two-dimensional 13C/14N heteronuclear multiple quantum correlation (HMQC) experiment using dipolar recoupling under magic-angle spinning (MAS) is described. The experiment is an extension of the recent indirect 13C detection scheme for measuring 14N quadrupolar coupling under MAS. The recoupling allows the direct use of the much larger dipolar interaction instead of the small J and residual dipolar couplings for establishing 13C/14N correlations. Two recoupling methods are incorporated into the HMQC sequence, both applying rf only to the observed 13C spin. The first one uses the REDOR sequence with two p-pulses per rotor cycle. The second one uses a cw rf field matching the spinning frequency, known as rotary resonance. The effects of CSA, Formula Not Shown signal loss, MAS frequency and stability and t1-noise are compared and discussed.
Journal of Magnetic Resonance
Vol: 183, Issue: 2, December, 2006
pp. 235-241
Title: Rotary resonance echo double resonance for measuring heteronuclear dipolar coupling under MAS
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: Rotary resonance; R-REDOR; REDOR; MAS; Dipolar coupling
Abstract (English):
A rotary resonance echo double resonance (R-REDOR) experiment is described for measuring heteronuclear dipolar coupling under magic-angle spinning. Rotary resonance reintroduces both dipolar coupling and chemical shift anisotropy with an rf field matching the spinning frequency. The resonance effect from chemical shift anisotropy can be refocused with a rotary resonance echo. The R-REDOR experiment thus measures the dephasing of the rotary resonance echo from the heteronuclear dipolar coupling to determine the dipolar coupling constant. The rotary resonance experiment is suitable for measuring dipolar coupling with quadrupolar nuclei because it applies the recoupling rf only to the observed spin-1/2. The rotary resonance scheme has the advantages of a long Formula Not Shown and susceptible to spinning frequency fluctuation.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 68-76
Title: Polarization transfer from remote protons in 13C CP/MAS
Authors: Tripon, Carmena; Aluas, Mihaelab; Filip, Xeniaa; Filip, Claudiua
Affiliations: a. National Institute for R&D of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj, Romania
b. Physics Department, Babes-Bolyai University, Cluj, Romania
Keywords: Solid-state NMR; Cross-polarization; CP/MAS; Spin dynamics
Abstract (English):
An experimental procedure for CP/MAS polarization transfer from remote 1H nuclear spins is introduced, which is applicable to protonated carbons in organic solids. It is based on preparing a state of non-uniform polarization, where directly bonded 13C–1H nuclei are de-polarized prior to recording the CP buildup curve. This curve is then expected to quantify the polarization transfer from remote protons only. The ability of the cross-polarization/polarization-inversion (CPPI) sequence to generate an initial state suitable for remote 1H CP/MAS scheme is analyzed both theoretically and experimentally. Confining to aliphatic groups, it was found that complete de-polarization of bonded proton is possible in the case of CH, whereas for CH2 and CH3 moieties only a partial de-polarization can be achieved. The theoretical predictions have been verified in practice for the particular case of l-alanine. The significance of the results from fundamental, as well as practical point of view, is also discussed. In particular, it is shown that: (i) the coherent description of polarization transfer under CP/MAS, including 1H polarization redistribution, is valid over time-scales longer than commonly assumed in many treatments of cross-polarization, and (ii) the remote protons polarization transfer curve can be used in combination with the conventional CP/MAS curve to get additional structural and dynamical information in organic systems.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 123-133
Title: Bayesian and information theory analysis of MAS sideband patterns in spin 1/2 systems
Author: Sachleben, Joseph R.a
Affiliations: a. Department of Chemistry, Otterbein College, Westerville, OH 43081, USA
Keywords: Magic angle spinning; Errors; Bayesian analysis; Chemical shift tensor
Abstract (English):
Bayesian statistics and information theory are used to analyze the reliability of extracting chemical shift parameters from spinning sideband patterns of spin 1/2 systems. Efficient code has been written to calculate the two-dimensional posterior probability as a function of the chemical shift anisotropy, d, and the asymmetry parameter, , given the sideband intensities and the signal-to-noise ratio. This method has the advantage of assuming only that the noise in the sideband intensities is distributed as a Gaussian. It assumes nothing about the distribution of the values of parameters d and , which are shown in some cases to be highly non-Gaussian. The utility of Bayesian analysis is demonstrated on 1D slow-spinning MAS spectra and on sideband patterns extracted from 2D PASS spectra. Previous investigations have shown that there is an optimal range of spinning frequencies for determining d. In this study, information theory is used to determine the signal-to-noise ratio dependence of the entropy in d, , and total entropy in spinning sideband spectra. The entropy is a measure of the information content of a probability distribution. When the entropy is zero, there is perfect information on a system, while if it is infinite, there is no information on the system. It is found that for all values of and for signal-to-noise ratios in the range 50–1000, an entropy minimum in nd/nr occurs for values 1.5nd/nr3. In the same range of signal-to-noise ratios, the entropy in is a monotonically decreasing function of nd/nr. The global information content of a spinning sideband pattern (i.e., the total entropy) is dependent on the signal-to-noise ratio and has an optimal value at nd/nr2 at a signal-to-noise ratio of 50 and increasing to 2.5 for signal-to-noise ratios of 1000. Finally, the increase of information in a sideband pattern as a function of the number of sidebands used in the analysis is examined. Most of the information about d and is contained in the five central sidebands; i.e., sidebands -2 to 2.
MRC: Magnetic Resonance in Chemitry - Update to February 2007
Magnetic Resonance in Chemistry
Vol: 45, Issue: 2, February 2007
pp. 118 - 122
Title: Structure of a paramagnetic supermicroporous silica-based material via a multinuclear solid-state NMR monitoring
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A & M University, P.O. Box 30012, College Station, Texas 77842‐3012, USA
Keywords: 29Si; 27Al; 1H; 13C MAS NMR; paramagnetic solids; T1 relaxation; porous materials
Abstract (English):
The paramagnetic Si/Al material doped with 19.8% (weight) of Mn2+ has been characterized by the 1H, 13C, 27Al, 29Si MAS NMR spectra and the 1H, 29Si T1MAS relaxation measurements as a gel dried at 130 °C and as samples calcined at 504, 540 and 650 °C. It has been demonstrated that in spite of strong paramagnetic effects, NMR monitoring in combination with 29Si T1 relaxation experiments can be successful for structural descriptions of porous materials. Copyright © 2007 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 45, Issue: 1, January 2007
pp. 5 - 23
Title: Structural elucidation of nitro-substituted five-membered aromatic heterocycles utilizing GIAO DFT calculations
Authors: Katritzky, Alan R.a; Akhmedov, Novruz G.a; Doskocz, Jacekb; Hall, C. Dennisa; Akhmedova, Rena G.a; Majumder, Sumana
Affiliations: a. Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611‐7200, USA
b. Faculty of Bioorganic Chemistry, Department of Chemistry, Wroclaw University of Technology, Wybrzeże Wyspiańkiego 27, 50‐370, Wroc3aw, Poland
Keywords: GIAO; long-range coupling constants; five-membered heterocycles; proton-coupled 13C NMR spectra
Abstract (English):
The GIAO (Gauge Including Atomic Orbitals) DFT (Density Functional Theory) method is applied at the B3LYP/6–31+G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311++G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311+G (2d,p)//B3LYP/6–31+G(d) and B3LYP/6–311++G(d,p)//B3LYP/6–311++G(d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants for 25 nitro-substituted five-membered heterocycles. Difference (1D NOE) spectra in combination with long-range gHMBC experiments were used as tools for the structural elucidation of nitro-substituted five-membered heterocycles. The assigned NMR data (chemical shifts and coupling constants) for all compounds were found to be in good agreement with theoretical calculations using the GIAO DFT method. The magnitudes of one-bond (1JCH) and long-range (nJCH, n > 1) coupling constants were utilized for unambiguous differentiation between regioisomers of nitro-substituted five-membered heterocycles. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 985 - 988
Title: 29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A&M University, College Station, Texas 77842‐3012, USA
Keywords: 29Si MAS NMR; T1 relaxation; microporous materials
Abstract (English):
The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1–6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2–4 with relatively small Mn2+ contents. Because the relaxation curves for 1–6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn2+ concentrations in terms of incorporation of the Mn2+ ions into the silica lattice when their concentration is small (£2.5 wt%). At higher concentrations, most of the manganese is located on the surface of the silica. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 989 - 1007
Title: Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac—[Ru(CO)3I3]-
Authors: Autschbach, Jochena; Zheng, Shaohuia
Affiliations: a. Department of Chemistry, 312 NSC, State University of New York at Buffalo, Buffalo, NY 14260‐3000, USA
Keywords: density functional theory; computational chemistry; ruthenium; solvent effects; relativistic effects
Abstract (English):
Solvent effects on the 99Ru NMR chemical shift of the complex fac—[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac—[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 10, October 2006
pp. 909 - 916
Title: 7Li and 13C solid-state NMR spectra of lithium cuprates
Authors: Jost, Steffena; Kühnen, Martina; Günther, Haralda
Affiliations: a. University of Siegen, FB 8, OC II, D‐57068 Siegen, Germany
Keywords: NMR; solid-state NMR; 7Li NMR; 13C NMR; quadrupole interaction; ion pairs; SIP; CIP; organolithium compounds
Abstract (English):
7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures—lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4-[tris(trimethylsilyl) methyl]2 cuprate (3)—have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, c(7Li), and the asymmetry parameters of the quadrupolar interactions, (7Li), as well as the 6, 7Li and 13C chemical shifts. The c(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 45, Issue: 2, February 2007
pp. 118 - 122
Title: Structure of a paramagnetic supermicroporous silica-based material via a multinuclear solid-state NMR monitoring
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A & M University, P.O. Box 30012, College Station, Texas 77842‐3012, USA
Keywords: 29Si; 27Al; 1H; 13C MAS NMR; paramagnetic solids; T1 relaxation; porous materials
Abstract (English):
The paramagnetic Si/Al material doped with 19.8% (weight) of Mn2+ has been characterized by the 1H, 13C, 27Al, 29Si MAS NMR spectra and the 1H, 29Si T1MAS relaxation measurements as a gel dried at 130 °C and as samples calcined at 504, 540 and 650 °C. It has been demonstrated that in spite of strong paramagnetic effects, NMR monitoring in combination with 29Si T1 relaxation experiments can be successful for structural descriptions of porous materials. Copyright © 2007 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 45, Issue: 1, January 2007
pp. 5 - 23
Title: Structural elucidation of nitro-substituted five-membered aromatic heterocycles utilizing GIAO DFT calculations
Authors: Katritzky, Alan R.a; Akhmedov, Novruz G.a; Doskocz, Jacekb; Hall, C. Dennisa; Akhmedova, Rena G.a; Majumder, Sumana
Affiliations: a. Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611‐7200, USA
b. Faculty of Bioorganic Chemistry, Department of Chemistry, Wroclaw University of Technology, Wybrzeże Wyspiańkiego 27, 50‐370, Wroc3aw, Poland
Keywords: GIAO; long-range coupling constants; five-membered heterocycles; proton-coupled 13C NMR spectra
Abstract (English):
The GIAO (Gauge Including Atomic Orbitals) DFT (Density Functional Theory) method is applied at the B3LYP/6–31+G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311++G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311+G (2d,p)//B3LYP/6–31+G(d) and B3LYP/6–311++G(d,p)//B3LYP/6–311++G(d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants for 25 nitro-substituted five-membered heterocycles. Difference (1D NOE) spectra in combination with long-range gHMBC experiments were used as tools for the structural elucidation of nitro-substituted five-membered heterocycles. The assigned NMR data (chemical shifts and coupling constants) for all compounds were found to be in good agreement with theoretical calculations using the GIAO DFT method. The magnitudes of one-bond (1JCH) and long-range (nJCH, n > 1) coupling constants were utilized for unambiguous differentiation between regioisomers of nitro-substituted five-membered heterocycles. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 985 - 988
Title: 29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A&M University, College Station, Texas 77842‐3012, USA
Keywords: 29Si MAS NMR; T1 relaxation; microporous materials
Abstract (English):
The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1–6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2–4 with relatively small Mn2+ contents. Because the relaxation curves for 1–6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn2+ concentrations in terms of incorporation of the Mn2+ ions into the silica lattice when their concentration is small (£2.5 wt%). At higher concentrations, most of the manganese is located on the surface of the silica. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 989 - 1007
Title: Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac—[Ru(CO)3I3]-
Authors: Autschbach, Jochena; Zheng, Shaohuia
Affiliations: a. Department of Chemistry, 312 NSC, State University of New York at Buffalo, Buffalo, NY 14260‐3000, USA
Keywords: density functional theory; computational chemistry; ruthenium; solvent effects; relativistic effects
Abstract (English):
Solvent effects on the 99Ru NMR chemical shift of the complex fac—[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac—[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 10, October 2006
pp. 909 - 916
Title: 7Li and 13C solid-state NMR spectra of lithium cuprates
Authors: Jost, Steffena; Kühnen, Martina; Günther, Haralda
Affiliations: a. University of Siegen, FB 8, OC II, D‐57068 Siegen, Germany
Keywords: NMR; solid-state NMR; 7Li NMR; 13C NMR; quadrupole interaction; ion pairs; SIP; CIP; organolithium compounds
Abstract (English):
7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures—lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4-[tris(trimethylsilyl) methyl]2 cuprate (3)—have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, c(7Li), and the asymmetry parameters of the quadrupolar interactions, (7Li), as well as the 6, 7Li and 13C chemical shifts. The c(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. Copyright © 2006 John Wiley & Sons, Ltd.
Progress in NMR - update to Jan. 30, 2007
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 50, Issue: 1, January 30, 2007
pp. 1-50
Title: NMR in chiral and achiral smectic phases: Structure, orientational order and dynamics
Authors: Domenici, Valentinaa; Geppi, Marcoa; Veracini, Carlo Albertoa
Affiliations: a. Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy
Keywords: Smectic; NMR; Carbon 13; Proton; Deuterium; Liquid crystals; Chirality; Relaxation
Abstract: No Abstract
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 49, Issue: 3-4, November 30, 2006
pp. 169-206
Title: The use of NMR spectroscopy to study tautomerism
Authors: Claramunt, R.M.a; López, C.a; Santa María, M.D.a; Sanz, D.a; Elguero, J.a
Affiliations: a. Departamento de Quı´mica Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey, 9, E-28040 Madrid, Spain
Keywords: NMR; Tautomerism; Prototropy; CPMAS NMR
Vol: 50, Issue: 1, January 30, 2007
pp. 1-50
Title: NMR in chiral and achiral smectic phases: Structure, orientational order and dynamics
Authors: Domenici, Valentinaa; Geppi, Marcoa; Veracini, Carlo Albertoa
Affiliations: a. Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy
Keywords: Smectic; NMR; Carbon 13; Proton; Deuterium; Liquid crystals; Chirality; Relaxation
Abstract: No Abstract
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 49, Issue: 3-4, November 30, 2006
pp. 169-206
Title: The use of NMR spectroscopy to study tautomerism
Authors: Claramunt, R.M.a; López, C.a; Santa María, M.D.a; Sanz, D.a; Elguero, J.a
Affiliations: a. Departamento de Quı´mica Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey, 9, E-28040 Madrid, Spain
Keywords: NMR; Tautomerism; Prototropy; CPMAS NMR
Solid-State NMR Update - October 2006
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 125-129
Title: 3-Methylglutaric acid as a 13C solid-state NMR standard
Authors: Barich, Dewey H.a; Gorman, Eric M.a; Zell, Mark T.b; Munson, Eric J.a
Affiliations: a. Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Ave., Lawrence, KS 66047, USA
b. Pfizer Global Research and Development, Analytical Research and Development, 2800 Plymouth Road, Ann Arbor, MI 48105, USA
Abstract (English):
The calibration of a solid-state NMR spectrometer requires setting the magic angle, setting the reference and decoupler frequencies, ensuring that the magnetic field is homogeneous across the sample volume, optimizing the signal-to-noise ratio, determining the p/2 pulse durations, and optimizing the Hartman–Hahn matching condition. Each task has one or more widely accepted standards, such as potassium bromide for setting the magic angle, adamantane for optimizing magnet homogeneity, and hexamethylbenzene or glycine for measuring the signal-to-noise ratio. We show that all of these tasks can be performed using 3-methylglutaric acid (MGA). In the case of high-powered decoupling, the CH2 and CH carbon peaks of MGA provide an opportunity to evaluate the decoupling in a manner that is superior to any of the commonly used standard compounds. Thus, MGA can be used as a single solid-state NMR standard compound to perform all calibration steps except for magnet shimming.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 130-134
Title: Decoupling residual dipolar coupling between 13C and14N spin pairs in CPMAS NMR
Authors: Orr, Robin M.a; Duer, Melinda J.a
Affiliations: a. University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
Abstract (English):
Decoupling of the residual dipolar coupling between 13C and14N nuclei is investigated experimentally in a triple resonance experiment. It is shown that pulsed decoupling can be used to give enhanced sensitivity and reduced line widths and the technique is illustrated using short peptides.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 162-170
Title: Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline g-glycine
Authors: Yamada, Kazuhikoa; Honda, Hisashib; Yamazaki, Toshioa; Yoshida, Mitsuruc
Affiliations: a. NMR Spectroscopy Team, RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama-shi, Kanagawa-ken 230-0045, Japan
b. International Graduate School of Arts and Sciences, Yokohama City University, 22-2 Seto, Kanawaza, Yokohama 236-0027, Japan
c. Analytical Science Division, National Food Research Institute, 2-1-12 Kannondai, Tsukuba 305-8642, Japan
Keywords: Solid-state 17O NMR; Chemical shielding tensor; Electric-field-gradient tensor; g-glycine
Abstract (English):
We report the first experimental determination of the carboxylate oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in polycrystalline g-glycine. Analysis of magic-angle spinning (MAS) and stationary 17O NMR spectra of [17O]-g-glycine obtained at 9.4, 14.1, 16.4, and 18.8T yields the magnitudes of the 17O EFG and CS tensors and the relative orientations between the two tensors. Extensive quantum chemical calculations at both the restricted Hartree–Fock and density functional levels have been performed to present the absolute tensor orientations in term of the molecular frame. We have demonstrated that 17O NMR tensor information could be unambiguously derived by the multiple field analyses of stationary 17O NMR spectra.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 171-181
Title: Vanadium-51 solid-state NMR electric field gradient tensors: A DFT-embedded ion and isolated cluster study of crystalline vanadium oxides
Author: Gee, Becky A.a
Affiliations: a. Department of Chemistry and Biochemistry, 1 University Plaza, Long Island University, Brooklyn Campus, Brooklyn, NY 11201, USA
Keywords: Vanadium-51; Nuclear magnetic resonance (NMR); Density functional theory (DFT); Embedded ion; Embedded cluster; Electric field gradient (EFG); Quadrupole coupling; Orthovanadates; Vanadium oxides
Abstract (English):
Density functional theory (DFT) calculations (6–311+G(2d,p)/B3LYP level of theory) of 51V electric field gradient (EFG) tensor elements are performed for embedded and isolated cluster models of orthovanadates. The structural models used to calculate the EFGs of 51V are (I) an isolated H4VO4+ cluster, (II) an isolated HnVO4n-3 cluster (n=number of next-neighbor cations) (III) an isolated orthovanadate anion, VO4-x, and (IV) a VO4-x ion embedded in a finite point-charge array whose electrostatic potential, at the embedded ion, is equivalent to that of the infinite lattice. For models III and IV, a charge x is assigned estimating the covalence of the system. Models III and IV provide results in good agreement with the experiment. Calculations, employing the embedded and isolated VO4-x models, are used to discuss site assignments for AlVO4. Correlations between quadrupole coupling parameters and deviations of the orthovanadate structure from ideal tetrahedral symmetry are shown.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 198-202
Title: First evidence of multiple Ca sites in amorphous slag structure: Multiple-quantum MAS NMR spectroscopy on calcium-43 at high magnetic field
Authors: Shimoda, Keijia; Tobu, Yasuhiroa; Kanehashi, Kojia; Nemoto, Takahirob; Saito, Kojia
Affiliations: a. Advanced Technology Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu 293-8511, Japan
b. JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
Abstract: No Abstract
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.
Vol: 30, Issue: 3-4, October, 2006
pp. 125-129
Title: 3-Methylglutaric acid as a 13C solid-state NMR standard
Authors: Barich, Dewey H.a; Gorman, Eric M.a; Zell, Mark T.b; Munson, Eric J.a
Affiliations: a. Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Ave., Lawrence, KS 66047, USA
b. Pfizer Global Research and Development, Analytical Research and Development, 2800 Plymouth Road, Ann Arbor, MI 48105, USA
Abstract (English):
The calibration of a solid-state NMR spectrometer requires setting the magic angle, setting the reference and decoupler frequencies, ensuring that the magnetic field is homogeneous across the sample volume, optimizing the signal-to-noise ratio, determining the p/2 pulse durations, and optimizing the Hartman–Hahn matching condition. Each task has one or more widely accepted standards, such as potassium bromide for setting the magic angle, adamantane for optimizing magnet homogeneity, and hexamethylbenzene or glycine for measuring the signal-to-noise ratio. We show that all of these tasks can be performed using 3-methylglutaric acid (MGA). In the case of high-powered decoupling, the CH2 and CH carbon peaks of MGA provide an opportunity to evaluate the decoupling in a manner that is superior to any of the commonly used standard compounds. Thus, MGA can be used as a single solid-state NMR standard compound to perform all calibration steps except for magnet shimming.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 130-134
Title: Decoupling residual dipolar coupling between 13C and14N spin pairs in CPMAS NMR
Authors: Orr, Robin M.a; Duer, Melinda J.a
Affiliations: a. University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
Abstract (English):
Decoupling of the residual dipolar coupling between 13C and14N nuclei is investigated experimentally in a triple resonance experiment. It is shown that pulsed decoupling can be used to give enhanced sensitivity and reduced line widths and the technique is illustrated using short peptides.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 162-170
Title: Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline g-glycine
Authors: Yamada, Kazuhikoa; Honda, Hisashib; Yamazaki, Toshioa; Yoshida, Mitsuruc
Affiliations: a. NMR Spectroscopy Team, RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama-shi, Kanagawa-ken 230-0045, Japan
b. International Graduate School of Arts and Sciences, Yokohama City University, 22-2 Seto, Kanawaza, Yokohama 236-0027, Japan
c. Analytical Science Division, National Food Research Institute, 2-1-12 Kannondai, Tsukuba 305-8642, Japan
Keywords: Solid-state 17O NMR; Chemical shielding tensor; Electric-field-gradient tensor; g-glycine
Abstract (English):
We report the first experimental determination of the carboxylate oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in polycrystalline g-glycine. Analysis of magic-angle spinning (MAS) and stationary 17O NMR spectra of [17O]-g-glycine obtained at 9.4, 14.1, 16.4, and 18.8T yields the magnitudes of the 17O EFG and CS tensors and the relative orientations between the two tensors. Extensive quantum chemical calculations at both the restricted Hartree–Fock and density functional levels have been performed to present the absolute tensor orientations in term of the molecular frame. We have demonstrated that 17O NMR tensor information could be unambiguously derived by the multiple field analyses of stationary 17O NMR spectra.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 171-181
Title: Vanadium-51 solid-state NMR electric field gradient tensors: A DFT-embedded ion and isolated cluster study of crystalline vanadium oxides
Author: Gee, Becky A.a
Affiliations: a. Department of Chemistry and Biochemistry, 1 University Plaza, Long Island University, Brooklyn Campus, Brooklyn, NY 11201, USA
Keywords: Vanadium-51; Nuclear magnetic resonance (NMR); Density functional theory (DFT); Embedded ion; Embedded cluster; Electric field gradient (EFG); Quadrupole coupling; Orthovanadates; Vanadium oxides
Abstract (English):
Density functional theory (DFT) calculations (6–311+G(2d,p)/B3LYP level of theory) of 51V electric field gradient (EFG) tensor elements are performed for embedded and isolated cluster models of orthovanadates. The structural models used to calculate the EFGs of 51V are (I) an isolated H4VO4+ cluster, (II) an isolated HnVO4n-3 cluster (n=number of next-neighbor cations) (III) an isolated orthovanadate anion, VO4-x, and (IV) a VO4-x ion embedded in a finite point-charge array whose electrostatic potential, at the embedded ion, is equivalent to that of the infinite lattice. For models III and IV, a charge x is assigned estimating the covalence of the system. Models III and IV provide results in good agreement with the experiment. Calculations, employing the embedded and isolated VO4-x models, are used to discuss site assignments for AlVO4. Correlations between quadrupole coupling parameters and deviations of the orthovanadate structure from ideal tetrahedral symmetry are shown.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 198-202
Title: First evidence of multiple Ca sites in amorphous slag structure: Multiple-quantum MAS NMR spectroscopy on calcium-43 at high magnetic field
Authors: Shimoda, Keijia; Tobu, Yasuhiroa; Kanehashi, Kojia; Nemoto, Takahirob; Saito, Kojia
Affiliations: a. Advanced Technology Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu 293-8511, Japan
b. JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
Abstract: No Abstract
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.
Subscribe to:
Posts (Atom)
