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1

Density functional theory (DFT) calculations of the proton nuclear magnetic resonance (NMR) spin-Hamiltonian parameters for serine  

International Nuclear Information System (INIS)

1H nuclear magnetic resonance spin-Hamiltonian parameters: chemical shifts ? and indirect spin–spin coupling constants J, have been calculated for serine, a brain metabolite. Serine molecules in the gas-phase as well as in solution in water have been investigated using density functional theory. Solvent and conformer effects as well as zero-point vibrational corrections have been taken into account. For the non-vibrating molecule, the best agreement is obtained when solvent and conformer effects are included. Zero-point vibrational corrections improve the agreement with experimental values, leading to a root mean square deviation of 0.05 ppm for chemical shifts and 0.7 Hz for spin–spin coupling constants

2

Density functional theory (DFT) calculations of the proton nuclear magnetic resonance (NMR) spin-Hamiltonian parameters for serine  

Science.gov (United States)

1H nuclear magnetic resonance spin-Hamiltonian parameters: chemical shifts ? and indirect spin-spin coupling constants J, have been calculated for serine, a brain metabolite. Serine molecules in the gas-phase as well as in solution in water have been investigated using density functional theory. Solvent and conformer effects as well as zero-point vibrational corrections have been taken into account. For the non-vibrating molecule, the best agreement is obtained when solvent and conformer effects are included. Zero-point vibrational corrections improve the agreement with experimental values, leading to a root mean square deviation of 0.05 ppm for chemical shifts and 0.7 Hz for spin-spin coupling constants.

Atieh, Z.; Allouche, A. R.; Graveron-Demilly, D.; Aubert-Frécon, M.

2011-11-01

3

Spin Hamiltonian effective parameters from periodic electronic structure calculations  

Energy Technology Data Exchange (ETDEWEB)

This paper presents and discusses a general procedure to extract spin Hamiltonian effective parameters from periodic calculations. The methodology is illustrated through representative examples of increasing complexity covering systems with three dimensional magnetic order or with a two dimensional magnetic structure. Some more complex systems are discussed where physical intuition based on the crystal structure of the system does not provide a reliable guide but where the present approach can be applied in a straightforward way.

Rivero, P; Moreira, I de Pr; Illas, F [Departamen de Quimica Fisica and Institut de Quimica Teorica i Computacional (IQTCUB), Universitat de Barcelona, MartI i Franques 1, E-08028 Barcelona (Spain)], E-mail: francesc.illas@ub.edu

2008-06-01

4

Density functional theory calculations of the nuclear magnetic resonance spin-Hamiltonian parameters for two polyamines of prostate tissue: spermidine and spermine  

International Nuclear Information System (INIS)

1H nuclear magnetic resonance (NMR) spin-Hamiltonian parameters: chemical shifts ? and spin–spin coupling constants J have been calculated for the two polyamines: spermidine and spermine present in prostate tissue. Molecules in the gas phase as well as in solution in water have been investigated using density functional theory calculations. From calculated ? and J values, NMR spectra have been simulated and compared to the experimental ones we acquired at 400 MHz for each polyamine in solution in D2O. From these comparisons, reliable NMR parameters are proposed for spermidine and spermine, among which the J constants were until now unknown for these two molecules

5

Spin-Hamiltonian parameters and defect structure for tetragonal Pr4+ centers in ZrSiO4 crystal  

International Nuclear Information System (INIS)

A complete diagonalization (of energy matrix) method (CDM) for 4f1 ions in tetragonal symmetry under an external magnetic field is applied to calculate the spin-Hamiltonian parameters (g factors g|| , gperpendicular and hyperfine structure constants A||, Aperpendicular) for Pr4+ ion at the tetragonally distorted dodecahedral (D2d) Zr4+ site in ZrSiO4 crystal. In the calculations, the crystal-field parameters used are acquired from the superposition model which enables correlation of the crystal-field parameters and hence the spin-Hamiltonian parameters with the defect structural data. The calculated spin-Hamiltonian parameters are in keeping with the experimental values and the defect structural data of the tetragonal Pr4+ center in ZrSiO4 crystal are obtained. The results are discussed.

6

Theoretical studies of spin-Hamiltonian parameters of Mo5+ ion doped in K2SnCl6 crystal  

International Nuclear Information System (INIS)

The spin-Hamiltonian (SH) parameters (g factors g//, g? and hyperfine structure constants A//, A? ) of K2SnCl6: Mo5+ (4d1) crystal are theoretically studied by the use of two microscopic spin-Hamiltonian (SH) methods, the high-order perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM) within the molecular orbital (MO) scheme. The contributions arising both from the crystal field and charge transfer excitations are taken into account. The investigations show that the charge transfer mechanism plays a decisive role in the understanding of the spin-Hamiltonian (SH) parameters for 4d1 ions in crystals with the strong coordinate covalence, especially for g//>g? which cannot be explained in the frame work of traditional crystal field approximation (CFA). The local defect structure around Mo5+ impurity ion center is determined to be D4h point group symmetry

7

Theoretical investigations of the local structure and the spin Hamiltonian parameters for Ti2+ in MgCl2  

International Nuclear Information System (INIS)

The local structure and spin Hamiltonian parameters (zero-field splitting and g factors) for Ti2+ in MgCl2 are theoretically studied using the perturbation formulas of these parameters for a 3d2 ion under trigonally distorted octahedra. The contributions from the dynamical Jahn–Teller effect, the configuration interactions and the ligand orbital and spin–orbit coupling interactions are quantitatively involved based on the cluster approach in a uniform way. The chlorine polyhedron around the impurity Ti2+ is found to transform from a slightly compressed octahedron in pure MgCl2 to a slightly elongated one, characterized by the local angular decrease of 0.3° related to the host bond angle 54.78° due to the Jahn–Teller effect. The calculated spin Hamiltonian parameters based on the above trigonal elongation show good agreement with the experimental data. The results are discussed

8

A density functional study of the electronic structure and spin Hamiltonian parameters of mononuclear thiomolybdenyl complexes.  

Science.gov (United States)

The electron paramagnetic resonance spin Hamiltonian parameters of mononuclear thiomolybdenyl complexes based upon the tris(pyrazolyl)borate ligand, together with their molybdenyl analogues, are calculated using density functional theory. The electronic g matrix and 95Mo hyperfine matrix are calculated as second-order response properties from the coupled-perturbed Kohn-Sham equations. The scalar relativistic zero-order regular approximation (ZORA) is used with an all-electron basis and an accurate mean-field spin-orbit operator which includes all one- and two-electron terms. The principal values and relative orientations of the g and A interaction matrices obtained from the experimental spectra in a previous EPR study are compared with those obtained from unrestricted Kohn-Sham calculations at the BP86 and B3LYP level, and the latter are found to be in good quantitative agreement. A quasi-restricted approach is used to analyze the influence of the various molecular orbitals on g and A. In all complexes the ground state magnetic orbital is dX2-Y2-based and the orientation of the A matrix is directly related to the orientation of this orbital. The largest single contribution to the orientation of the g matrix arises from the spin-orbit coupling of the dYZ-based lowest-unoccupied molecular orbital into the ground state. A number of smaller, cumulative charge-transfer contributions augment the d-d contributions. A comparison of the theoretical EPR parameters obtained using both crystallographic and gas-phase geometry-optimized structures of Tp*MoO(bdt) (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, bdt = 1,2-benzenedithiolate) suggests a correspondence between the metal-dithiolate fold angle and the angle of noncoincidence between g and A. PMID:17305330

Drew, Simon C; Young, Charles G; Hanson, Graeme R

2007-04-01

9

On the non-standard rhombic spin Hamiltonian parameters derived from Moessbauer spectroscopy and magnetism-related measurements  

International Nuclear Information System (INIS)

The orthorhombic standardization of spin Hamiltonian parameters is increasingly adopted in the electron magnetic resonance area. The aim of this paper is to elucidate the ramifications of orthorhombic standardization for other spectroscopic and magnetic techniques, which also employ the spin Hamiltonian formalism. This is illustrated by examples derived from the Moessbauer spectroscopy, magnetic moments and magnetic susceptibility, photoinduced changes of magnetization, and other magnetism-related measurements. Implications of standardization in the studies of magnetic ordering, Haldane gap for integer spin systems, the macroscopic quantum tunnelling of magnetization, specific heat measurements, the spin wave theory, and inelastic neutron scattering are also discussed. Several sets of the non-standard zero-field splitting (ZFS) parameters for transition ions at orthorhombic symmetry sites, expressed in various notations and units, are standardized. Calculations are performed using the computer package CST, which yields the standardized ZFS parameter sets. The results are presented in a unified way in the extended Stevens notation bkq and units of cm-1 together with the conventional D and E parameters, which prevail in the studies dealt with in this paper. This enables a direct comparison with the available data for similar ion/host systems. The standardization reveals several inconsistencies in interpretation of the experimental data o interpretation of the experimental data obtained by various techniques

10

Modeling of crystal field and spin-Hamiltonian parameters for Ti{sup 3+}:MgO  

Energy Technology Data Exchange (ETDEWEB)

The aim of this paper is to model the crystal field parameters (CFPs) and spin-Hamiltonian parameters (g factors g{sub ||}, g{sub ?} and hyperfine structure constants A{sub ||}, A{sub ?}) for the Ti{sup 3+}:MgO system. The CFPs were modeled in the frame of superposition model of the crystal field theory, based on ab initio supercell calculations of Ti{sup 3+}:MgO geometry and crystal field parameter 10Dq. The obtained values were used to simulate the energy levels scheme, by diagonalizing the full energy matrix of the Hamiltonian. The EPR parameters have been calculated from both the complete diagonalization method and the perturbation theory method. All the obtained results (optical and EPR) were compared with experimental data and a good agreement is observed.

Barb, A.M.; Gruia, A.S.; Avram, C.N., E-mail: acalin@physics.uvt.ro

2013-12-01

11

Theoretical studies of the local structure and spin Hamiltonian parameters for Rh2+:ZnWO4  

Science.gov (United States)

By establishing the perturbation formulas of the spin Hamiltonian parameters (anisotropic g factors and hyperfine structure constants) for a rhombically compressed 4d7 cluster, the EPR spectra and local structure are theoretically investigated for Rh2+:ZnWO4. Due to the Jahn-Teller effect, the impurity center shows slight axial compression of about 0.002 nm along the Z-axis and the perpendicular angular variation of about 6° for the planar impurity-ligand bonds. These lattice deformations transform the significant elongation (by about 0.031 nm) of host Zn2+ site into slight compression in the impurity center. The local distortion of the Jahn-Teller nature is discussed.

Ding, Chang-Chun; Wu, Shao-Yi; Kuang, Min-Quan; Cheng, Yong-Kun; Zhang, Li-Juan

2014-10-01

12

Investigations on the spin Hamiltonian parameters for Yb3+ ion in Bi2Sr2YCu2O8  

International Nuclear Information System (INIS)

Highlights: • The EPR spectra are studied for the two orthorhombic Yb3+ centers in Bi2Sr2YCu2O8. • The contributions due to the admixtures of various states are taken into account. • The spin Hamiltonian parameters show good agreement with experimental data. -- Abstract: Many theoretical and experimental works have been done to understand the several characteristics of the Bi2Sr2YCu2O8. Since the electron paramagnetic resonance (EPR) is a powerful tool to analyze the electronic and magnetic properties of paramagnetic impurities in compounds, studies on the above EPR parameters would be helpful to the investigations of the characteristics for the superconductors. In this paper, EPR parameters anisotropic g factors gx, gy, gz, and the hyperfine structure constants Ax, Ay and Az of the two orthorhombic Yb3+ centers in Bi2Sr2YCu2O8 are theoretically studied from the perturbation formulas of these parameters for a 4f13 ion in orthorhombic symmetry. In these formulas, the contributions due to the admixtures of various states are taken into account, and the orthorhombic field parameters are obtained from the superposition model and the local structure of the impurity Yb3+ ion occupying the host Bi3+ site. The calculated EPR parameters are reasonable agree with the observed values

13

Theoretical investigations of the local structure and the spin Hamiltonian parameters for Ti{sup 2+} in MgCl{sub 2}  

Energy Technology Data Exchange (ETDEWEB)

The local structure and spin Hamiltonian parameters (zero-field splitting and g factors) for Ti{sup 2+} in MgCl{sub 2} are theoretically studied using the perturbation formulas of these parameters for a 3d{sup 2} ion under trigonally distorted octahedra. The contributions from the dynamical Jahn–Teller effect, the configuration interactions and the ligand orbital and spin–orbit coupling interactions are quantitatively involved based on the cluster approach in a uniform way. The chlorine polyhedron around the impurity Ti{sup 2+} is found to transform from a slightly compressed octahedron in pure MgCl{sub 2} to a slightly elongated one, characterized by the local angular decrease of 0.3° related to the host bond angle 54.78° due to the Jahn–Teller effect. The calculated spin Hamiltonian parameters based on the above trigonal elongation show good agreement with the experimental data. The results are discussed.

Zhang, Zhi-Hong, E-mail: zhihongzhang723@gmail.com [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Wu, Shao-Yi [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China); Hu, Xian-Fen; Kuang, Min-Quan [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2013-07-15

14

Theoretical calculations of spin-Hamiltonian parameters for the rhombic-like Mo5+ centers in KTiOPO4 crystal  

International Nuclear Information System (INIS)

The spin-Hamiltonian parameters (g factors gi and hyperfine structure constants Ai, were i=x, y and z) for Mo5+ ion occupying the Ti(1) site with approximately rhombic symmetry in KTiOPO4 crystal are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, not only the contribution due to the conventional crystal-field (CF) mechanism, but also those due to the charge-transfer (CT) mechanism are included. The six calculated spin-Hamiltonian parameters with four adjustable parameters are in reasonable agreement with the experimental values. The calculations show that for more accurate calculations of spin-Hamiltonian parameters of the high valence dn ions (e.g., Mo5+ considered here) in crystals, the contribution from CT mechanism, which is ignored in the conventional crystal field theory, should be taken into account. The reasonable crystal field energy levels of Mo5+ in KTiOPO4 are also predicted from calculations

15

Theoretical calculations of spin-Hamiltonian parameters for the rhombic-like Mo{sup 5+} centers in KTiOPO{sub 4} crystal  

Energy Technology Data Exchange (ETDEWEB)

The spin-Hamiltonian parameters (g factors g{sub i} and hyperfine structure constants A{sub i}, were i=x, y and z) for Mo{sup 5+} ion occupying the Ti(1) site with approximately rhombic symmetry in KTiOPO{sub 4} crystal are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, not only the contribution due to the conventional crystal-field (CF) mechanism, but also those due to the charge-transfer (CT) mechanism are included. The six calculated spin-Hamiltonian parameters with four adjustable parameters are in reasonable agreement with the experimental values. The calculations show that for more accurate calculations of spin-Hamiltonian parameters of the high valence d{sup n} ions (e.g., Mo{sup 5+} considered here) in crystals, the contribution from CT mechanism, which is ignored in the conventional crystal field theory, should be taken into account. The reasonable crystal field energy levels of Mo{sup 5+} in KTiOPO{sub 4} are also predicted from calculations.

Yang, Mei [School of Physics and Electronic Engineering, Mianyang Normal University, Mianyang 621000 (China); Research Center of Laser Fusion, CAEP, Mianyang 621900 (China); Wen-Chen, Zheng, E-mail: zhengwc1@163.com [Department of Material Science, Sichuan University, Chengdu 610064 (China); Hong-Gang, Liu [Department of Material Science, Sichuan University, Chengdu 610064 (China)

2013-12-01

16

Theoretical calculations of spin-Hamiltonian parameters for the (MoOX5)2- (X=Cl, Br) metallic complexes in solution or frozen-glass  

Science.gov (United States)

The spin-Hamiltonian parameters (g factors g//, g? and hyperfine structure constants A//, A?) of the (MoOX5)2- (X=Cl, Br) metallic complexes in solution or frozen-glass are calculated from the high-order perturbation formulas based on the two-mechanism model. In these formulas, the contributions to spin-Hamiltonian parameters due to both the widely-applied crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (which is neglected in CF theory) are taken into account, and the needed CF and CT energy levels are obtained from the optical spectra. The calculated results with two adjustable parameters are in reasonable agreement with the experimental values. The calculations show that (i) the relative importance of CT mechanism in (MoOBr5)2- metallic complexes is larger than that in (MoOCl5)2- ones because of the stronger covalence of Mo5+-Br- combination, and (ii) in both (MoOCl5)2- and (MoOBr5)2- metallic complexes, the contributions to spin-Hamiltonian parameters due to CT mechanism should also be taken into account because of the high valence state of Mo5+ ion.

Mei, Yang; Zheng, Wen-Chen; Zhang, Lin; Chen, Bo-Wei

2014-11-01

17

Spin-Hamiltonian parameters and local structures of the tetragonal (CrO4)3- clusters in Cr5+-doped KDP-type crystals  

Science.gov (United States)

The spin-Hamiltonian parameters (g factors g//, g? and hyperfine structure constants A//, A?) of tetragonal (CrO4)3- clusters in Cr5+-doped KDP-type crystals KH2PO4, KD2PO4, NH4H2PO4, ND4D2PO4, KH2AsO4, KD2AsO4 and NH4AsO4 are calculated from the high-order perturbation formulas based on the two-mechanism model for the elongated d1 tetrahedral clusters in crystals with the ground state |d>. In the model, the contributions to spin-Hamiltonian parameters from both the crystal field (CF) mechanism and the charge-transfer (CT) mechanism (the latter is neglected in the widely-applied CF theory) are included. On the basis of the calculated values and by taking account of the small admixture of the first excited state |d> to the ground state |d> due to the vibrational motion of ligands (this dynamic effect leads a twinkling elongated tetrahedron to become a compressed one), all the calculated spin-Hamiltonian parameters are in reasonable agreement with the experimental values. The difficulty in the explanation of spin-Hamiltonian parameters by using the conventional static contributions for these Cr5+-doped KDP-type crystals are overcome, and the impurity-induced static local structures of (CrO4)3- clusters (which are different from the corresponding ones in the host crystals) in KDP-type crystals are estimated. The results are discussed.

Mei, Yang; Peng, Ren-Ming; Wei, Cheng-Fu; Zheng, Wen-Chen

2014-05-01

18

Theoretical studies of spin-Hamiltonian parameters of Mo{sup 5+} ion doped in K{sub 2}SnCl{sub 6} crystal  

Energy Technology Data Exchange (ETDEWEB)

The spin-Hamiltonian (SH) parameters (g factors g{sub //}, g{sub ?} and hyperfine structure constants A{sub //}, A{sub ?} ) of K{sub 2}SnCl{sub 6}: Mo{sup 5+} (4d{sup 1}) crystal are theoretically studied by the use of two microscopic spin-Hamiltonian (SH) methods, the high-order perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM) within the molecular orbital (MO) scheme. The contributions arising both from the crystal field and charge transfer excitations are taken into account. The investigations show that the charge transfer mechanism plays a decisive role in the understanding of the spin-Hamiltonian (SH) parameters for 4d{sup 1} ions in crystals with the strong coordinate covalence, especially for g{sub //}>g{sub ?} which cannot be explained in the frame work of traditional crystal field approximation (CFA). The local defect structure around Mo{sup 5+} impurity ion center is determined to be D{sub 4} {sub h} point group symmetry.

Fang, Wang, E-mail: mailfangwang@163.com; Yang, Da-Xiao; Chen, Heng-Jie; Tang, Hai-Yan

2013-11-15

19

Theoretical studies of the spin Hamiltonian parameters for the two tetragonal Cu2+ centers in the calcined catalysts CuO-ZnO  

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Full Text Available The spin Hamiltonian parameters for the two Cu2+ centers A1 and A2 in the calcined catalysts CuO-ZnO are theoretically investigated using the high order perturbation formulas of these parameters for a 3d9 ion in tetragonally elongated octahedra. In the above formulas, the tetragonal field parameters Ds and Dt are determined from the superposition model, by considering the relative axial elongation of the oxygen octahedron around the Cu2+ due to the Jahn-Teller effect. Based on the calculations, the relative elongation ratios of about 5% and 3% are obtained for the tetragonal Cu2+ centers A1 and A2, respectively. The theoretical spin Hamiltonian parameters are in good agreement with the observed values for both systems. The larger axial elongation in center A1 is ascribed to the more significant low symmetrical (tetragonal distortion of the Jahn-Teller effect. The local structures characterized by the above axial elongations are discussed.

Z.H. Zhang

2011-06-01

20

Semi-empirical and ab initio DFT modeling of the spin-Hamiltonian parameters for Fe6+: K2MO4 (M = S, Cr, Se)  

Science.gov (United States)

In this paper we calculated the spin-Hamiltonian parameters (g factors {{g}||}, {{g}\\bot } and zero field splitting parameter D) for Fe6+ ions doped in K2MO4 (M = S, Cr, Se) crystals, taking into account the actual site symmetry of the Fe6+ impurity ion. The suggested method is based on the successful application of two different approaches: the crystal field theory (CFT) and density functional based (DFT). Within the CFT model we used the cluster approach and the perturbation theory method, based on the crystal field parameters, which were calculated in the superposition model. Within the DFT approach the calculations were done at the self-consistent field (SCF) by solving the coupled perturbed SCF equations. Comparison with experimental data shows that the obtained results are quite satisfactory, which proves applicability of the suggested calculating technique.

Avram, N. M.; Brik, M. G.; Andreici, E.-L.

2014-09-01

 
 
 
 
21

A study of the spin-Hamiltonian parameters for the trigonal Sm3+ center in La2Mg3(NO3)(12)·24H2O crystal.  

Science.gov (United States)

This paper reports a theoretical calculation of spin-Hamiltonian parameters (g factors g//, g? and hyperfine structure constants 147A//, 147A?, 149A//, 149A?) for 147Sm3+ and 149Sm3+ isotopes in the trigonal La3+ site of La2Mg3(NO3)(12)·24H2O crystal from a diagonalization (of energy matrix) method. In the method, the Hamiltonian concerning the energy matrix includes the Zeeman and hyperfine interaction terms and so there is no perturbation calculation in it. The crystal-field parameters in the energy matrix are calculated using the superposition model, in which the structural data of 12-fold coordinated site rather than those of the incorrect 6-fold coordinated site given in the previous paper are applied. The calculated results are in reasonable agreement with the experimental results. The results are discussed. PMID:21030293

Yang, Wei-Qing; Zheng, Wen-Chen; Liu, Hong-Gang

2011-01-01

22

Studies of the spin-Hamiltonian parameters and defect structures for Gd3+ ions in zircon-structure silicates MSiO4 (M=Zr, Hf, Th).  

Science.gov (United States)

The spin-Hamiltonian parameters (g factors g?, g? and zero-field splittings b2(0), b4(0), b4(4), b6(0), b6(4)) for 4f7 ion Gd3+ at the tetragonal M4+ site of zircon-structure silicates MSiO4 (M=Zr, Hf, Th) are calculated from a diagonalization (of energy matrix) method. The Hamiltonian concerning this energy matrix contains the free-ion, crystal-field interaction and Zeeman interaction terms and the 56×56 energy matrix is constructed by considering the ground multiplet 8S7/2 and the excited multiplets 6L7/2 (L=P, D, F, G, H, I). The defect structures of Gd3+ centers in the three MSiO4 crystals are yielded from the calculation. The results are discussed. PMID:21665526

Yang, Wei-Qing; Zheng, Wen-Chen

2011-09-01

23

Investigations of the spin-Hamiltonian parameters and defect structures for Gd3+ ions in YMO4 (M=V, P, As) crystals  

International Nuclear Information System (INIS)

A 56×56 energy matrix containing the ground multiplet 8S7/2 and the excited multiplets 6L7/2 (where L=P, D, F, G, H, I) for 4f7 ion Gd3+ at a tetragonal crystal field and under an external magnetic field is constructed. By diagonalizing the energy matrix, the spin-Hamiltonian parameters (g factors g?, g? and zero-field splittings b20, b40, b44, b60, b64) for Gd3+ ion at the tetragonal Y3+ site of YMO4 (M=V, P, As) crystals are calculated. The calculated results are in reasonable agreement with the experimental values. The defect structures of Gd3+ centers in YMO4 crystals are estimated from the calculation. The results are discussed.

24

Theoretical investigations of the spin-Hamiltonian parameters and local structural distortion of Fe3+: ZnAl2O4 crystals  

Science.gov (United States)

The relations between the spin-Hamiltonian (SH) parameters and the structural parameters of the Fe3+ ions in Fe3+: ZnAl2O4 crystals have been established by means of the microscopic spin Hamiltonian theory and the superposition model (SPM). On the basis of this, the local structure distortion, the second-order zero-field splitting (ZFS) parameter D, the fourth-order ZFS parameter (a-F), and the Zeeman g-factors g factors: g//, g?, and ?g(=g// - g?) for Fe3+ ions in Fe3+: ZnAl2O4 crystals, for the first time taking into account the electronic magnetic interactions, i.e. the spin-spin (SS), the spin-other-orbit (SOO), and the orbit-orbit (OO) interactions, besides the well-known spin-orbit (SO) interaction, are theoretically investigated using complete diagonalization method (CDM). This investigation reveals that the local structure distortion effect plays an important role in explaining the spectroscopic properties of Fe3+ ions in Fe3+: ZnAl2O4 crystals. The theoretical second-order ZFS parameter D, the fourth-order ZFS parameter (a-F), and the Zeeman g-factors: g//, g?, and ?g of the ground state for Fe3+ ion in Fe3+: ZnAl2O4 crystals yield a good agreement with experiment findings by taking into account the lattice distortions: ?R = 0.0191 nm and ?? = 0.076°. In conclusion, our research shows that there is a slight local structure distortion for Fe3+ ions in Fe3+: ZnAl2O4 crystals, but the site of Fe3+ still retains D3d symmetry. On the other hand, it is found for Fe3+ ions in Fe3+: ZnAl2O4 crystals that the SO mechanism is the most important one, whereas the contributions to the SH parameters from other four mechanisms, including the SS, SOO, OO, and SO?SS?SOO?OO mechanisms are not appreciable, especially for the ZFS parameter D.

Yang, Zi-Yuan

2014-10-01

25

Investigations of the spin-Hamiltonian parameters and tetragonal distortions due to Jahn-Teller effect for the monovalent d9 (Ni+, Pd+, Pt+) impurity centers in AgCl crystals  

International Nuclear Information System (INIS)

Research highlights: ? The spin-Hamiltonian parameters of md9 ions Ni+, Pd+ and Pt+ substituting for the Ag+ ions in AgCl crystals are calculated. Especially for 4d9 ion Pd+ and 5d9 ion Pt+, the related study is very scarce. ? The calculation is using the high-order perturbation formulas based on cluster approach. The cubic chlorine octahedron in the host AgCl distorts into the tetragonally-elongated octahedron in the md9 impurity center owing to the Jahn-Teller effect. ? The tetragonal elongation is obtained from the calculation of spin-Hamiltonian parameters. - Abstract: When the monovalent md9 ions Ni+ (3d9), Pd+ (4d9) and Pt+(5d9) substitute for the Ag+ ions in AgCl crystal, the cubic chlorine octahedron surrounding Ag+ in the host AgCl crystal distorts into the tetragonally elongated octahedron in the md9 impurity center owing to the Jahn-Teller effect. The spin-Hamiltonian parameters (g factors g||, gperpendicular and hyperfine structure constants A||, Aperpendicular ) of the tetragonal md9 centers in AgCl are calculated from the high-order perturbation formulas based on the cluster approach, in which the admixture between d orbitals of dn ion and p orbitals of ligand ion viaion and p orbitals of ligand ion via covalence effect are taken into account. From the calculations, the spin-Hamiltonian parameters of these tetragonal md9 centers in AgCl are explained reasonably and the tetragonal distortions (characterized by the tetragonal elongation ?R = R|| - Rperpendicular, where R|| and Rperpendicular denote the metal-ligand distances parallel with and perpendicular to the tetragonal axis) of these centers due to Jahn-Teller effect are obtained. The results are discussed.

26

Theoretical studies of the spin Hamiltonian parameters and local structures for the tetragonal Cu{sup 2+} and Ni{sup 3+} centers in Mg{sub 2}TiO{sub 4}  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Spin Hamiltonian parameters and local structures are analyzed for the impurity Cu{sup 2+} and Ni{sup 3+} centers in Mg{sub 2}TiO{sub 4}. Black-Right-Pointing-Pointer Ligand orbital and spin-orbit coupling contributions are included from the cluster approach due to moderate covalency. Black-Right-Pointing-Pointer Ligand octahedra experience relative elongations along C{sub 4} axis due to Jahn-Teller effect. - Abstract: The local structures of the two impurity Cu{sup 2+} (and Ni{sup 3+}) centers with low spin (S = 1/2) in Mg{sub 2}TiO{sub 4} are theoretically studied by using the perturbation formulas of the spin Hamiltonian parameters for 3d{sup 9} (and 3d{sup 7}) ions in tetragonally elongated octahedra. In these formulas, the tetragonal field parameters are quantitatively determined using the superposition model and the local structures of the impurity Cu{sup 2+} (and Ni{sup 3+}) centers, and the ligand orbital and spin-orbit coupling contributions are included on the basis of the cluster approach in view of moderate covalency for the studied systems. The [CuO{sub 6}]{sup 10-} and [NiO{sub 6}]{sup 9-}clusters on the substitutional Mg{sup 2+} site are found to suffer relative elongations by about {Delta}Z{sub Cu} ( Almost-Equal-To 3.2%) and {Delta}Z{sub Ni} ( Almost-Equal-To 0.7%) for the impurity Cu{sup 2+} and Ni{sup 3+} centers, respectively, along the C{sub 4} axis due to the Jahn-Teller effect. The calculated spin Hamiltonian parameters based on the above Jahn-Teller elongations show good agreement with the observed values. The results are discussed.

Zhang, Hua-Ming, E-mail: huamingzhang66@gmail.com [Key Laboratory of Nondestructive Testing, Ministry of Education, Nanchang Hangkong University, Nanchang 330063 (China); Wan, Xiong; Zhang, Zhi-Ming [Key Laboratory of Nondestructive Testing, Ministry of Education, Nanchang Hangkong University, Nanchang 330063 (China)

2013-02-05

27

Theoretical analysis of the spin Hamiltonian parameters in Co(II)S4 complexes, using density functional theory and correlated ab initio methods.  

Science.gov (United States)

A systematic Density Functional Theory (DFT) and multiconfigurational ab initio computational analysis of the Spin Hamiltonian (SH) parameters of tetracoordinate S = 3/2 Co((II))S(4)-containing complexes has been performed. The complexes under study bear either arylthiolato, ArS(-), or dithioimidodiphosphinato, [R(2)P(S)NP(S)R'(2)](-) ligands. These complexes were chosen because accurate structural and spectroscopic data are available, including extensive Electron Paramagnetic Resonance (EPR)/Electron Nuclear Double Resonance (ENDOR) studies. For comparison purposes, the [Co(PPh(3))(2)Cl(2)] complex, which was thoroughly studied in the past by High-Field and Frequency EPR and Variable Temperature, Variable Field Magnetic Circular Dichroism (MCD) spectroscopies, was included in the studied set. The magnitude of the computed axial zero-field splitting parameter D (ZFS), of the Co((II))S(4) systems, was found to be within ~10% of the experimental values, provided that the property calculation is taken beyond the accuracy obtained with a second-order treatment of the spin-orbit coupling interaction. This is achieved by quasi degenerate perturbation theory (QDPT), in conjunction with complete active space configuration interaction (CAS-CI). The accuracy was increased upon recovering dynamic correlation with multiconfigurational ab initio methods. Specifically, spectroscopy oriented configuration interaction (SORCI), and difference dedicated configuration interaction (DDCI) were employed for the calculation of the D-tensor. The sign and magnitude of parameter D was analyzed in the framework of Ligand Field Theory, to reveal the differences in the electronic structures of the investigated Co((II))S(4) systems. For the axial complexes, accurate effective g'-tensors were obtained in the QDPT studies. These provide a diagnostic tool for the adopted ground state configuration (±3/2 or ±1/2) and are hence indicative of the sign of D. On the other hand, for the rhombic complexes, the determination of the sign of D required the SH parameters to be derived along suitably constructed symmetry interconversion pathways. This procedure, which introduces a dynamic perspective into the theoretical investigation, helped to shed some light on unresolved issues of the corresponding experimental studies. The metal hyperfine and ligand super-hyperfine A-tensors of the C(2) [Co{(SPPh(2))(SP(i)Pr(2))N}(2)] complex were estimated by DFT calculations. The theoretical data were shown to be in good agreement with the available experimental data. Decomposition of the metal A-tensor into individual contributions revealed that, despite the large ZFS, the observed significant anisotropy should be largely attributed to spin-dipolar contributions. The analysis of both, metal and ligand A-tensors, is consistent with a highly covalent character of the Co-S bonds. PMID:21848258

Maganas, Dimitrios; Sottini, Silvia; Kyritsis, Panayotis; Groenen, Edgar J J; Neese, Frank

2011-09-19

28

Theoretical investigations of the spin Hamiltonian parameters and local structures for the tetragonal V{sup 3+} and Ti{sup 2+} centers in MgO and CaO  

Energy Technology Data Exchange (ETDEWEB)

The spin Hamiltonian parameters (zero-field splitting D, g factor and hyperfine structure constant) and the local structures for MgO:V{sup 3+}, CaO:V{sup 3+} and CaO:Ti{sup 2+} are theoretically investigated from the perturbation formulas of these parameters for 3d{sup 2} ions under tetragonally distorted octahedra. The contributions from the dynamical Jahn-Teller effect, the configuration interactions and the ligand orbital and spin-orbit coupling interactions are quantitatively taken into account based on the cluster approach in a uniform way. The ligand octahedra are found to suffer the relative elongations of about 1.5%, 4.4% and 4.6% for MgO:V{sup 3+}, CaO:V{sup 3+} and CaO:Ti{sup 2+}, respectively, along the C{sub 4} axis due to the dynamical Jahn-Teller effect. The calculated spin Hamiltonian parameters based on the above local tetragonal elongations show reasonable agreement with the experimental data for all the systems. The results are discussed.

Zhang Zhihong, E-mail: zhihongzhang723@gmail.com [Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Wu Shaoyi [Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054 (China); International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China); Kuang Minquan; Hu Xianfen [Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2013-01-01

29

Supersymmetric analysis of a spin Hamiltonian model  

International Nuclear Information System (INIS)

The intertwining method has been applied to the effective potential of the spin Hamiltonian H=-?Sz2-BSx. The supersymmetric partner potentials, some of which are singular, are obtained by using low-lying states of this potential. Applying the intertwining method successively, hierarchy of effective potentials has been established. Supersymmetric partner of the transformed spin Hamiltonian's effective potential has also been constructed

30

Investigations of the spin-Hamiltonian parameters and tetragonal compression due to the static Jahn-Teller effect for Cr5+ center in cubic SrTiO3 crystal  

International Nuclear Information System (INIS)

By using the distortion model that the tetragonal site symmetry of Cr5+ in cubic phase of SrTiO3 originates from the static Jahn-Teller effect, the spin-Hamiltonian parameters (g factors g||, gperpendicular and hyperfine structure constants A||, Aperpendicular) of this tetragonally compressed Cr5+ center in SrTiO3 are calculated from the high-order perturbation formulas based on a two-mechanism model. In the model, not only the contribution to spin-Hamiltonian parameters due to the crystal-field mechanism, but also that due to the charge-transfer mechanism (which is omitted in the extensively used crystal-field theory) are included. The calculated results are in reasonable agreement with the experimental values. The tetragonal compression (characterized by ?R=Rperpendicular-R||, where Rperpendicular and R|| denote the metal-ligand distances perpendicular to and parallel with the C4 axis) of Cr5+ center is also obtained from the calculation. The results (including the tetragonal compression and the relative importance of the charge-transfer mechanism) are discussed.

31

Investigations of the spin-Hamiltonian parameters and the tetragonal distortion due to Jahn-Teller effect for Cu2+ in trigonal CsCdCl3 and CsMgCl3 crystals  

International Nuclear Information System (INIS)

The complete high-order perturbation formulas based on a two-mechanism [i.e., crystal-field (CF) and charge-transfer (CT) mechanisms, the latter is neglected in the widely-used CF theory] model for the spin-Hamiltonian (SH) parameters (g factors g||, gperpendicular and the hyperfine structure constants A||, Aperpendicular) of d9 ions in tetragonal symmetry with the ground state |dx2-y2> are established. These formulas are used to the calculations of SH parameters for the tetragonal Cu2+ centers in trigonal CsCdCl3 and CsMgCl3 crystals. Form the calculations, these SH parameters are reasonably explained and the tetragonal distortions of the Cu2+ centers due to Jahn-Teller effect in both crystals are obtained. The results (including the tetragonal distortion and the relative importance of CT mechanism) are discussed.

32

Supersymmetric analysis of a spin Hamiltonian model  

Energy Technology Data Exchange (ETDEWEB)

The intertwining method has been applied to the effective potential of the spin Hamiltonian H=-{gamma}S{sub z}{sup 2}-BS{sub x}. The supersymmetric partner potentials, some of which are singular, are obtained by using low-lying states of this potential. Applying the intertwining method successively, hierarchy of effective potentials has been established. Supersymmetric partner of the transformed spin Hamiltonian's effective potential has also been constructed.

Demircioglu, B. [Saraykoey Nuclear Research and Training Center, Saraykoey /Ankara (Turkey); Bilge Ocak, S. [Saraykoey Nuclear Research and Training Center, Saraykoey/Ankara (Turkey)]. E-mail: semamuzo@yahoo.com; Kuru, S. [Department of Physics, Ankara University, Faculty of Science, 06100 Tandogan/Ankara (Turkey)

2006-04-17

33

Theoretical studies of the spin-Hamiltonian parameters of the oxycation MoO3+ in (NH4)2MoOCl5 and K2MoOF5 single crystals  

Science.gov (United States)

Theoretical formulae for the spin-Hamiltonian (SH) parameters (g tensor g//, g? and hyperfine structure A tensor A//, A?) of the ground state of oxycation MoO3+ in [MOX5]2- (M=Mo5+, Cr4+, V3+, X=F-, Cl- or Br- ) complexes are derived by the high-order perturbation method within the frame of molecular orbital (MO) scheme. In those formulae, the contributions to the SH parameters arising both from the crystal field (CF) and charge transfer (CT) excitations are taken into account, which are derived up to the third and second order, respectively. Those formulae are applied to calculate the SH of the oxycation MoO3+ in (NH4)2MoOCl5 and K2MoOF5 single crystals by the best match method, and the calculated results are in good agreement with the experimental data. The investigations show that the charge transfer mechanism play a decisive role in the understanding for the SH parameters for 4d1 ions in crystals with the strong coordinate covalence, especially for anomalously experimental results g//>g? which cannot be explained by the traditional CF approximation alone. The MO coefficients are determined and the results are discussed.

Fang, Wang; Chen, Heng-Jie; Tan, Ren-Bing; Yang, Wen-Yan; Tang, Hai-Yan

2014-10-01

34

Sum-over-states based multireference ab initio calculation of EPR spin Hamiltonian parameters for transition metal complexes. A case study.  

Science.gov (United States)

The recently developed spectroscopy oriented multireference configuration interaction variant (SORCI) is applied to the problem of the prediction of electron paramagnetic resonance parameters in transition metal complexes within a sum-over-states (SOS) framework. The prototypical complex [Cu(NH(3))(4)](2+) is taken as an example in order to test the validity and convergence properties of several computational approximations. The results show that the SORCI method affords accurate results for the g-tensor, the metal dipolar hyperfine coupling (HFC), the spin-orbit coupling contribution to the metal HFC and the isotropic and dipolar ligand HFCs. Accurate prediction of the isotropic metal HFC is challenging and requires flexible basis sets in the core region together with explicit inclusion of the core electrons and high-lying core-like virtual orbitals in the CI. Comparison of SORCI and density functional theory (DFT) results reveals that the latter are far off experiment (g-tensor) or achieve reasonable results only through a fortunate cancellation of large errors (metal HFC). The ligand HFC is overestimated by DFT owing to overly covalent bonding which leads to too much spin transfer on to the ligands. PMID:15366053

Neese, Frank

2004-10-01

35

Investigations of the spin-Hamiltonian parameters and tetragonal distortion due to the Jahn-Teller effect for Cu(H2O)62+ clusters in C(NH2)3Al(SO4)2.6H2O: Cu2+ crystal  

International Nuclear Information System (INIS)

When Cu2+ ion occupies the trigonal Al3+ (II) site in guanidinium aluminium sulphate hexahydrate (GASH) (C(NH2)3Al(SO4)2.6H2O) crystals, the trigonal Al(H2O)63+ octahedron in the host GASH crystal changes to the tetragonally-elongated Cu(H2O)62+ octahedron in the impurity center due to the Jahn-Teller effect. The tetragonal distortion (characterized by ?R=Rparallel -Rperpendicular, where Rparallel and Rperpendicular represent the metal-ligand distances parallel with and perpendicular to the C4 axis) of this Cu(H2O)62+ cluster is studied by calculating its spin-Hamiltonian parameters (g factors gparallel , gperpendicular and hyperfine structure constants Aparallel and Aperpendicular) from two theoretical methods, the complete diagonalization (of energy matrix) method (CDM) and the perturbation theory method (PTM). Both methods are based on the cluster approach in which the admixture between the d orbitals of 3dn ion and the p orbitals of ligand ion is considered. The calculated results show that both methods can be used to calculate the spin-Hamiltonian parameters and to determine the structure of 3d9 clusters in crystals. These results are discussed. are discussed.

36

Gravitational spin Hamiltonians from the S matrix  

CERN Document Server

We utilize generalized unitarity and recursion relations combined with effective field theory(EFT) techniques to compute spin dependent interaction terms for inspiralling binary systems in the post newtonian(PN) approximation. Using these methods offers great computational advantage over traditional techniques involving feynman diagrams, especially at higher orders in the PN expansion. As a specific example, we reproduce the spin-orbit interaction up to 2.5 PN order as also the leading order $S^2$(3PN) hamiltonian for an arbitrary massive object. We also obtain the unknown $S^3$(3.5PN) spin hamiltonian for an arbitrary massive object in terms of its low frequency linear response to gravitational perturbations, which was till now known only for a black hole. Furthermore, we derive the missing $S^4$ Hamiltonian at leading order(4PN) for an arbitrary massive object and establish that a minimal coupling of a massive elementary particle to gravity leads to a black hole structure. Finally, the Kerr metric is obtain...

Vaidya, Varun

2014-01-01

37

Studies of the tetragonal distortion due to Jahn-Teller effect for the Cu2+ centres in trigonal ZnMF6.6H2O (M=Si,Ti,Zr) crystals from the calculations of spin-Hamiltonian parameters  

International Nuclear Information System (INIS)

The spin-Hamiltonian (SH) parameters (g -factors g parallel, g perpendicular to and hyperfine structure constants A parallel, A perpendicular to) of the tetragonal Cu(H2O)62+ centres (which are caused by the static Jahn-Teller effect) in trigonal ZnMF6.6H2O (M=Si,Ti,Zr) crystals are calculated from two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM). In the calculations, the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the SH parameters with the tetragonal distortion (characterized by ?R=R parallel -R perpendicular to, where R parallel and R perpendicular to denote the metal-ligand distances parallel with and perpendicular to the tetragonal axis) of Cu(H2O)62+ centres. The calculated SH parameters from both methods are in reasonable agreement with the experimental values, suggesting that both PTM and CDM can explain satisfactorily the SH parameters of 3d9 ions in crystals. The tetragonal distortion of the Cu(H2O)62+ centres in ZnMF6.6H2O crystals are also obtained from the calculations. (copyright 2009 WILEY-VCH Vealculations. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

38

On Spin Hamiltonian fits to Moessbauer spectra of high-spin Fe(II) porphyrinate systems  

Energy Technology Data Exchange (ETDEWEB)

Fits to Moessbauer spectra of high-spin iron(II) porphyrinates have been applied to the Fe(II) model compounds octaethylporphyrin(1,2-dimethylimidazole) and tetra-paramethoxyporphyrin(1,2-dimethylimidazole). Moessbauer spectra have been measured on these compounds at 4.2 K in large applied fields. Spin Hamiltonians were used for fitting both the electronic and nuclear interactions. The fits are done by adjusting the Hamiltonian parameters to simultaneously minimize the total {chi}{sup 2} for three different applied fields. In order to get best fits, the EFG tensor need to be rotated relative to the ZFS tensor. A comparative sensitivity analysis of their Spin Hamiltonian parameters has also been done on the ZFS parameters D, and the EFG asymmetry parameter {eta}. The best fits suggest that both systems definitely have a negative quadrupole splitting, and that largest EFG component is tilted far from the z-axis of the ZFS tensor, which is likely to be near the heme normal.

Schulz, Charles E., E-mail: cschulz@knox.edu [Knox College, Department of Physics (United States); Hu Chuanjiang, E-mail: scheidt.1@nd.edu; Scheidt, W. Robert [University of Notre Dame, Department of Chemistry and Biochemistry (United States)

2006-06-15

39

On Spin Hamiltonian fits to Moessbauer spectra of high-spin Fe(II) porphyrinate systems  

International Nuclear Information System (INIS)

Fits to Moessbauer spectra of high-spin iron(II) porphyrinates have been applied to the Fe(II) model compounds octaethylporphyrin(1,2-dimethylimidazole) and tetra-paramethoxyporphyrin(1,2-dimethylimidazole). Moessbauer spectra have been measured on these compounds at 4.2 K in large applied fields. Spin Hamiltonians were used for fitting both the electronic and nuclear interactions. The fits are done by adjusting the Hamiltonian parameters to simultaneously minimize the total ?2 for three different applied fields. In order to get best fits, the EFG tensor need to be rotated relative to the ZFS tensor. A comparative sensitivity analysis of their Spin Hamiltonian parameters has also been done on the ZFS parameters D, and the EFG asymmetry parameter ?. The best fits suggest that both systems definitely have a negative quadrupole splitting, and that largest EFG component is tilted far from the z-axis of the ZFS tensor, which is likely to be near the heme normal.

40

Electronic origins of NMR parameters  

International Nuclear Information System (INIS)

The Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful tool for the understanding of many theoretical aspects of molecular physics. In this work, many of these aspects as well as its applications will be discussed. (A.C.A.S.)

 
 
 
 
41

The Spin Hamiltonian Effective Approach to the Vibronic Effects-Selected Cases  

Science.gov (United States)

Here we propose and apply the use of spin Hamiltonian for the effective analytic description and fit to the computed spectrum of correspondingly selected states as a strategy to describe the potential energy surfaces and related vibronic effects in terms of physically meaningful valence bond picture. In order to achieve numerical precision and a physically consistent parameterization we introduced here new terms to the spin Hamiltonian, equated in the intercentric biquadratic form, invested with the meaning of interbond interaction, avoiding the artifact of large next nearest neighbor direct spin coupling constants in the numerical fit. This model was applied for prototypic vibronic cases: (i) the Jahn-Teller effect H3 molecule regarded as a spin-frustration topology and (ii) the bond length alternation vs. homogeneity in conjugated hydrocarbons (C4H4 and C6H6) as manifestation vs. silence, respectively, of a pseudo-Jahn-Teller effect involving states effectively described by the spin Hamiltonian.

Cimpoesu, F.; Hirao, K.; Stanica, N.; Chihaia, V.

42

Noether's theorem and low symmetry aspects concerning the crystal (ligand) field Hamiltonians and spin Hamiltonians  

Science.gov (United States)

This review presents a concise summary of major findings arising from our recent studies concerning the symmetry properties of crystal/ligand field (CF/LF) Hamiltonians and spin Hamiltonians (SHs). First we provide a bird's-eye view of these studies. Then we overview (i) the pertinent basic concepts and notations, (ii) the algebraic symmetry (AS) of Hamiltonians for continuous rotational symmetry (CRS) cases, and (iii) the concepts of the rotational invariants and moments of CF Hamiltonians. This enables a new look from the point of view of the Noether's theorem on the properties of CF/LF Hamiltonians and SHs invariant under CRS, i.e. hexagonal II, tetragonal II, trigonal II, monoclinic, and triclinic ones. An important theorem and a conjecture on the conserved quantities stipulated by Noether's theorem for the Hamiltonians in question formulated by us helps to elucidate the interrelationships and deeper meaning of the concepts involved. Implications of the existence of the conserved quantities for interpretation of experimental CF parameter (CFP) datasets are encapsulated in five corollaries. These considerations reveal that the feasibility of determination of CFPs from fitting experimental spectra and the reduction of the existing higher-order rotational invariants for hexagonal type II and cubic symmetry require reinterpretation. This novel approach enables adoption of better fitting strategies utilizing welldefined conserved quantities, which are invariant under CRS. The advantages of this approach are illustrated using the CFP datasets reported in literature for RE3+ (4fN) ions in LiYF4. This review deals also with the fundamental intricate aspects, hitherto not fully understood, concerning the CF Hamiltonians for the 'low symmetry' cases, including the CRS cases as well as orthorhombic ones. This includes: (1) selection of the axis systems, (2) types of CF parameters and their properties, (3) introduction of a new notion of a nominal axis system for the fitted CFP datasets, (4) implications of the Noether's theorem and the AS of CF Hamiltonians, (5) correlation properties among CFP datasets, (6) the rotational degrees of freedom and the reduction of the number of independent CFPs, and (7) extension of the multiple correlated fitting technique. Clarification of these intricate aspects enables us to provide a general framework aimed at achieving an increased compatibility and reliability of CFP datasets for transition ions at low symmetry sites in crystals. The usefulness of this framework is illustrated by reanalysis of the CFP datasets for Nd3+ (Pr3+ ) in NdGaO3 (PrGaO3) and RNiO3.

Rudowicz, C.; Qin, J.

2006-02-01

43

Understanding visual map formation through vortex dynamics of spin Hamiltonian models  

CERN Document Server

We introduce a general method for cerebral cortical map generation and apply it to pattern formation in orientation and ocular dominance columns of the brain. From a known cortical structure, we build spin Hamiltonian models with long-range interactions of the Mexican hat type. These Hamiltonian models allow a coherent interpretation of the diverse phenomena in the map formation in the visual cortex with the help of relaxation dynamics of spins. In particular, we predict various phenomena of self-organization in orientation and ocular map formation including the pinwheel annihilation and its dependency on the columnar wave vector and boundary conditions.

Cho, M W; Cho, Myoung Won; Kim, Seunghwan

2003-01-01

44

Dynamic spin Hamiltonian formalism and Moessbauer study of spin-lattice relaxation of paramagnetic Fe3+(6S) ions  

International Nuclear Information System (INIS)

In a crystal field potential the 6S state of a paramagnetic 57Fe3+ (3d5, 6S) ion splits into three Kramers spin doublets Ssub(z) = +- 5/2, +- 3/2, and +- 1/2 and each doublet produces its own Moessbauer magnetic hyperfine spectrum at low temperatures as a result of the slow spin relaxation rate. These Moessbauer hyperfine spectra are used to study the temperature dependence of Fe3+ spin lattice relaxation rate falling in the region 106 to 109 s -1. The dynamic spin Hamiltonian formalism is utilised to explicitly calculate the spin-lattice relaxation rate of the three Kramers doublets for one-phonon and two-phonon processes in different temperature regions. It is further assumed that the various modes of acoustic phonon propagation are direction independent, the phonon spectrum is of Debye type, and the dynamic crystal field parameters are very similar to the static ones. It is found that for Fe3+ ions the one-phonon relaxation process is most dominant and the theoretical results are in a very good agreement with the experimental observations. These calculations may be equally applicable to other S-state paramagnetic ions. (author)

45

Higher-order Zeeman and spin terms in the electron paramagnetic resonance spin Hamiltonian; their description in irreducible form using Cartesian, tesseral spherical tensor and Stevens' operator expressions  

International Nuclear Information System (INIS)

In setting up a spin Hamiltonian (SH) to study high-spin Zeeman and high-spin nuclear and/or electronic interactions in electron paramagnetic resonance (EPR) experiments, it is argued that a maximally reduced SH (MRSH) framed in tesseral combinations of spherical tensor operators is necessary. Then, the SH contains only those terms that are necessary and sufficient to describe the particular spin system. The paper proceeds then to obtain interrelationships between the parameters of the MRSH and those of alternative SHs expressed in Cartesian tensor and Stevens operator-equivalent forms. The examples taken, initially, are those of Cartesian and Stevens' expressions for high-spin Zeeman terms of dimension BS3 and BS5. Starting from the well-known decomposition of the general Cartesian tensor of second rank to three irreducible tensors of ranks 0, 1 and 2, the decomposition of Cartesian tensors of ranks 4 and 6 are treated similarly. Next, following a generalization of the tesseral spherical tensor equations, the interrelationships amongst the parameters of the three kinds of expressions, as derived from equivalent SHs, are determined and detailed tables, including all redundancy equations, set out. In each of these cases the lowest symmetry, 1-bar Laue class, is assumed and then examples of relationships for specific higher symmetries derived therefrom. The validity of a spin Hamiltonian containing mixtures of terms from the three expressions is co of terms from the three expressions is considered in some detail for several specific symmetries, including again the lowest symmetry. Finally, we address the application of some of the relationships derived here to seldom-observed low-symmetry effects in EPR spectra, when high-spin electronic and nuclear interactions are present.

46

A long-wave action of spin Hamiltonians and the inverse problem of the calculus of variations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We suggest a method of derivation of the long-wave action of the model spin Hamiltonians using the non-linear partial differential equations of motions of the individual spins. According to the Vainberg's theorem the set of these equations are (formal) potential if the symmetry analysis for the Frechet derivatives of the system is true. The case of Heisenberg (anti)ferromagnets is considered. It is shown the functional whose stationary points are described by the equations c...

Bostrem, I. G.; Ovchinnikov, A. S.; Egorov, R. F.

2003-01-01

47

Derivation of spin Hamiltonians from the exact Hamiltonian: Application to systems with two unpaired electrons per magnetic site  

Science.gov (United States)

The foundations and limits of S=1/2 and S=1 spin Hamiltonians for systems with two unpaired electrons in two well-defined orbitals per site are discussed by merging accurate ab initio calculations in binuclear systems with the effective Hamiltonian theory. It is shown that, beyond the usual JijSi.Sj terms, the effective spin Hamiltonian necessarily introduces four-body spin operators in the S=1/2 case and biquadratic terms in the S=1 formalism. The order of magnitude of these additional terms can be rationalized from a quasidegenerate perturbation theory expansion starting from a Hubbard-type Hamiltonian. This permits to discuss the physical mechanisms governing the reduction from the all electron Hamiltonian to the spin-only Hamiltonians and the conditions under which a further reduction from a spin Hamiltonian to the simplest Heisenberg-Dirac-Van Vleck form is possible. The overall discussion is illustrated by numerical calculations of the magnetic coupling between two Ni2+ cations in the K2NiF4 perovskite and between triply bonded carbon atoms in poly-ynes.

Moreira, I. De; Suaud, N.; Guihéry, N.; Malrieu, J. P.; Caballol, R.; Bofill, J. M.; Illas, F.

2002-10-01

48

Superexchange interaction between lanthanide f1 ions. Spin-Hamiltonian calculations for the 90 deg. and 180 deg. f1-f1 superexchange  

International Nuclear Information System (INIS)

Exchange interaction between two lanthanide or actinide ions of f1 configuration bridged by common diamagnetic ligands is theoretically studied using a modified version of the superexchange theory developed in this paper. Exchange spin Hamiltonians were calculated for the M2L10 and M2L11 dimers serving as models of the 90 deg. and 180 deg. f1-f1 superexchange, respectively. Spin-orbit coupling and crystal field splitting of the f1 configuration (resulting in the ?7 ground Kramers doublet and the effective spin S=1/2 of the metal ion), virtual transfers of electrons of the type 4f1(A) - 4f1(B) ? 4f0(A) - 4f1(B)5d1(B) via ns(L) and np(L) valent orbitals of the bridging ligands, and exchange pathways in these dimers are considered in detail. The f1-f1 superexchange is found to be extremely anisotropic and very sensitive to the geometry of the dimer. The spin Hamiltonian of the M2L10 dimer is H=JxSAxSBx+JySAySBy+JzSAzSBz, where the exchange parameters are rationalized in terms of J?? and J?? parameters referring, respectively, to the ?-? and ?-? pathways of the 4f(A)?np(L)?5d(B) s of the 4f(A)?np(L)?5d(B) electron transfers, Jx=2J?? - J??, Jy=J??+J?? and Jz=-J??+J??. The J?? and J?? values are analytically expressed through and overlap integrals, orbital energies and intra-ionic Slater parameters. Exchange interaction between f1 ions in the M2L11 dimer is described by an antiferromagnetic Ising Hamiltonian H = vertical bar J?? vertical bar SAzSbz, where the z axis connects two metal ions. Unusual magnetic properties of MUO3 (M = Li, Na, K and Rb) and Li3UO4 oxides involving U5+(5f1) ions and BaPrO3 distorted perovskite are discussed in the light of these theoretical results. (author)

49

Quantum model of a solid-state spin qubit: Ni cluster on a silicon surface by the generalized spin Hamiltonian and X-ray absorption spectroscopy investigations  

CERN Document Server

We present here the quantum model of a Ni solid-state electron spin qubit on a silicon surface with the use of a density functional scheme for calculation of the exchange integrals in the non-collinear spin configurations in the generalized spin Hamiltonian (GSH) with the anisotropic exchange couplings parameters linking the nickel ions with a silicon substrate. In this article we offer the model of the quantum solid-state N-spin qubit based on the studying of the spin structure and the spin-dynamics simulations of the 3d-metal Ni clusters on a silicon surface. The solution of the problem of the entanglement between a spin states in N-spin systems is becoming more interesting when considering clusters or molecules with a spectral gap in their density of states. For quantifying the distribution of the entanglement between the individual spin eigenvalues (modes) in the spin structure of the N-spin system we use the density of entanglement. We have studied the Rabi oscillations to evaluate the N-spin qubits syst...

Farberovich, Oleg V; Soldatov, Alexander V

2014-01-01

50

Influence of non-bonded parameters on the quality of NMR structures: A new force field for NMR structure calculation  

International Nuclear Information System (INIS)

The effects of different non-bonded parameters of force fields for NMR structure calculation on the quality of the resulting NMR solution structures were investigated using Interleukin 4 as a model system. NMR structure ensembles were calculated with an ab initio protocol using torsion angle dynamics. The calculations were repeated with five different non-bonded energy functions and parameters. The resulting ensembles were compared with the available X-ray structures, and their quality was assessed with common structure validation programs. In addition, the impact of torsion angle restraints and dihedral energy terms for the sidechains and the backbone was studied. The further improvement of the quality by refinement in explicit solvent was demonstrated. The optimal parameters, including those necessary for water refinement, are available in the new version of the PARALLHDG force field

51

Synthesis of some isoxazolines and evaluation of carbon-13 NMR substituent parameters for 5-methyl substitution  

International Nuclear Information System (INIS)

Some isoxazolines substituted at C-5 with phenyl and methoxycarbonyl groups have been synthesised and characterised. Carbon-13 NMR methyl substituent parameters for methyl substitution at C-5 carbon in these compounds have been evaluated. (author). 14 refs., 2 tabs

52

Limitations of the Giant Spin Hamiltonian in Explaining Magnetization Tunneling in a Single-Molecule Magnet  

CERN Document Server

EPR studies of a Ni4 single-molecule magnet yield the zero-field-splitting (zfs) parameters, D, B40 and B44, based on a giant spin approximation (GSA) with S = 4. Experiments on an isostructural Ni-doped Zn4 crystal establish the Ni(II) ion zfs parameters. The 4th-order zfs parameters in the GSA arise from the interplay between the Heisenberg interaction, Js1.s2, and the 2nd-order single-ion anisotropy, giving rise to mixing of higher lying states into the S = 4 state. Consequently, J directly influences the zfs in the ground state, enabling its direct determination by EPR.

Wilson, A; Yang, E C; Nakano, M; Hendrickson, D N; Hill, S

2006-01-01

53

Structure simulation with calculated NMR parameters - integrating COSMOS into the CCPN framework.  

Science.gov (United States)

The Collaborative Computing Project for NMR (CCPN) has build a software framework consisting of the CCPN data model (with APIs) for NMR related data, the CcpNmr Analysis program and additional tools like CcpNmr FormatConverter. The open architecture allows for the integration of external software to extend the abilities of the CCPN framework with additional calculation methods. Recently, we have carried out the first steps for integrating our software Computer Simulation of Molecular Structures (COSMOS) into the CCPN framework. The COSMOS-NMR force field unites quantum chemical routines for the calculation of molecular properties with a molecular mechanics force field yielding the relative molecular energies. COSMOS-NMR allows introducing NMR parameters as constraints into molecular mechanics calculations. The resulting infrastructure will be made available for the NMR community. As a first application we have tested the evaluation of calculated protein structures using COSMOS-derived 13C C? and C? chemical shifts. In this paper we give an overview of the methodology and a roadmap for future developments and applications. PMID:22942007

Schneider, Olaf; Fogh, Rasmus H; Sternberg, Ulrich; Klenin, Konstantin; Kondov, Ivan

2012-01-01

54

NMR observation of quadrupolar order parameter in NpO2  

International Nuclear Information System (INIS)

We report O17 NMR measurements in a single crystal of NpO2. We have observed oscillatory spin-echo decay for certain O sites below T0=26K. These spin-echo oscillations are well understood in terms of an axially symmetric electric field gradient created by a longitudinal triple-q antiferro-quadrupolar ordering. In the present work, we show that direct observation of the quadrupolar order parameters is possible by means of NMR

55

Practical Model Fitting Approaches to the Direct Extraction of NMR Parameters Simultaneously from All Dimensions of Multidimensional NMR Spectra  

International Nuclear Information System (INIS)

A maximum likelihood (ML)-based approach has been established for the direct extraction of NMR parameters (e.g., frequency, amplitude, phase, and decay rate) simultaneously from all dimensions of a D-dimensional NMR spectrum. The approach, referred to here as HTFD-ML (hybrid time frequency domain maximum likelihood), constructs a time-domain model composed of a sum of exponentially-decaying sinusoidal signals. The apodized Fourier transform of this time-domain signal is a model spectrum that represents the 'best fit' to the equivalent frequency-domain data spectrum. The desired amplitude and frequency parameters can be extracted directly from the signal model constructed by the HTFD-ML algorithm. The HTFD-ML approach presented here, as embodied in the software package CHIFIT, is designed to meet the challenges posed by model fitting of D-dimensional NMR data sets, where each consists of many data points (108 is not uncommon) encoding information about numerous signals (up to 105 for a protein of moderate size) that exhibit spectral overlap. The suitability of the approach is demonstrated by its application to the concerted analysis of a series of ten 2D 1H-15N HSQC experiments measuring 15N T1 relaxation. In addition to demonstrating the practicality of performing maximum likelihood analysis on large, multidimensional NMR spectra, the results demonstrate that this parametric model-fitting approach provides more accurate amplitude and frequency estimates than those obtude and frequency estimates than those obtained from conventional peak-based analysis of the FT spectrum. The improved performance of the model fitting approach derives from its ability to take into account the simultaneous contributions of all signals in a crowded spectral region (deconvolution) as well as to incorporate prior knowledge in constructing models to fit the data

56

NMR  

International Nuclear Information System (INIS)

For the interpretation of NMR images, it is important to recognize the effect of tissue specific parameters on the image contrast. In this study, we prepared T1, T2-sensitivity (total relaxation sensitivity) map as a means of presentation of the correlation between T1, T2 change and signal intensity change of various tissues. Ratio between fractional rate changes of each relaxation time against entire relaxation time and those of signal intensity against entire signal intensity; (? intensity/intensity)/(? relaxation time/relaxation time), are measured respectively by means of logarithmic differentiation, by which the sensitivity of each T1 and T2 (S (int., T1) and, S (int., T2)) was calculated. The summation of respective relaxation sensitivity was designated as total relaxation sensitivity (S. total (int., T1, T2)). The resulting S. total (int., T1, T2) is classified into seven different color indices according to its value. The classified S. total are plotted on T1 axis (T1; 0< T1<1,000 msec) and T2 axis (T2; 0< T2<200 msec). We present T1, T2-sensitivity map under the pulse sequence which applied frequently on Asahi Mark-J system. The classified S. total express generally the degree of dependence of respective relaxation time and we discuss about the precaution and limitation of T1, T2-sensitivity map application. (author)

57

NMR and FTIR characterization of petroleum residues: structural parameters and correlations  

International Nuclear Information System (INIS)

Heavy petroleum residues can be used as raw materials in the production of various carbon products, notably isotropic and anisotropic pitches and different types of coke. The chemical characterization of these residues, and carbon materials in general, is a challenge that has to be addressed in order to allow the adequate optimization of production processes. In this study, petroleum residues of different refineries were studied by NMR, FTIR and elemental analysis. Optimum parameters were determined for NMR analysis and diffuse reflectance spectroscopy (DRIFTS), a technique that is usually applied to solid materials but was shown to yield good quality spectra for these samples. Correlations were found between NMR and FTIR results for the aromaticity index, a structural parameter widely used in the study of mesophase formation in pitches, as well as between C/H ratios and the aromaticity index. Other structural parameters of interest were also obtained. (author)

58

First-principles calculation of the 17O NMR parameters of a calcium aluminosilicate glass.  

Science.gov (United States)

We have computed the (17)O NMR parameters of an amorphous calcium aluminosilicate (CAS) from first-principles. The atomic coordinates of a CAS glass of composition (CaO)(0.21)(Al(2)O (3))(0.12)(SiO (2))(0.67) were obtained by quenching a liquid to room temperature by the means of ab initio molecular-dynamics simulations of the Car-Parrinello type. The structure of the glass is found to be overall in good agreement with diffraction experiments. Some excess nonbridging O (NBO) atoms are found and are compensated by tricluster O atoms, i.e., by 3-fold coordinated O atoms to 4-fold coordinated Al or Si atoms. The glass coordinates were used to compute the (17)O NMR parameters using GGA-DFT and a correction of the Ca 3d orbital energy. The chemical shifts and the electric field gradients were obtained with the gauge including projector augmented-wave (GIPAW) and the projector augmented-wave (PAW) methods, respectively. The simulated 2D-3QMAS NMR spectrum of the CAS glass is in very good agreement with the available experimental data, notably because it takes into account the disorder present in the glass. This agreement further validates our CAS glass model. We show that the oxygen triclusters are not visible in a 2D-3QMAS NMR (17)O spectrum since their NMR parameters overlap with those of the Al-O-Si, Si-O-Si, or Al-O-Al sites. Finally, correlations between the structural characteristics and the values of the NMR parameters are extracted from the calculation with the aim of helping the interpretation of NMR spectra of glasses of similar compositions. PMID:16851665

Benoit, Magali; Profeta, Mickaël; Mauri, Francesco; Pickard, Chris J; Tuckerman, Mark E

2005-04-01

59

Determination of orientational order parameters from 2H NMR spectra of magnetically partially oriented lipid bilayers.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The partial orientation of multilamellar vesicles (MLVs) in high magnetic fields is known to affect the shape of 2H NMR spectra. There are numerical methods for extracting either the orientational order parameters of lipid molecules for a random distribution of domain orientations in the sample, or the distribution of orientations for a known set of spectral anisotropies. A first attempt at determining the orientational order parameters in the presence of an unknown nonrandom distribution of ...

Scha?fer, H.; Ma?dler, B.; Sternin, E.

1998-01-01

60

NMR observation of quadrupolar order parameter in NpO{sub 2}  

Energy Technology Data Exchange (ETDEWEB)

We report O17 NMR measurements in a single crystal of NpO{sub 2}. We have observed oscillatory spin-echo decay for certain O sites below T{sub 0}=26K. These spin-echo oscillations are well understood in terms of an axially symmetric electric field gradient created by a longitudinal triple-q antiferro-quadrupolar ordering. In the present work, we show that direct observation of the quadrupolar order parameters is possible by means of NMR.

Tokunaga, Y. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)]. E-mail: tokunaga.yo@jaea.go.jp; Aoki, D. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Homma, Y. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Kambe, S. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Sakai, H. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Ikeda, S. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Fujimoto, T. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Walstedt, R.E. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Yasuoka, H. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Shiokawa, Y. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Yamamoto, E. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Nakamura, A. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)

2007-03-15

 
 
 
 
61

Pharmacokinetic analysis of sparse in vivo NMR spectroscopy data using relative parameters and the population approach.  

Science.gov (United States)

NMR spectroscopy in vivo when applied to studying drugs and their metabolites usually measures relative concentration in a tissue over time. Only ratios of clearance and volume parameters can be estimated from these data. Low drug dosages (relative to the sensitivity of in vivo NMR) or rapid drug elimination create the additional problem of data sparsity where a pharmacokinetic model cannot be fitted individually. We have investigated whether relative and absolute pharmacokinetic parameters can be estimated from such data by applying a population model. The data analysed were relative concentrations of 5-fluorouracil (FU) and of the sum of its catabolites alpha-fluoro-beta-ureido-propanoic acid (FUPA) and alpha-fluoro-beta-alanine (FBAL) in the liver, as monitored in 16 cancer patients by [19F]-NMR spectroscopy during and after a 10-min intravenous infusion of 650 mg FU.m-2. The "structural" part of the population model was a non-linear, two-compartment model featuring one FU compartment with volume VFU, a saturable clearance of FU by conversion into the catabolites where CL = vmax/(kM+CFU), a catabolite compartment with volume Vcat, and a concentration-independent clearance of the catabolites, CLcat. The parameters actually fitted were: gamma, vmax, kM.VFU, Vcat/VFU, and CLcat/Vcat where gamma is a proportionality factor relating the NMR signal intensity of FU to the amount of FU in the body and, therefore, has no purely pharmacokinetic interpretation. All parameters were checked for random interindividual variation: gamma and vmax were also tested for inter-occasion variation. The program system NONMEM was used for model fitting.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7859808

Port, R E; Schlemmer, H P; Bachert, P

1994-01-01

62

Low-field NMR logging sensor for measuring hydraulic parameters of model soils  

Science.gov (United States)

SummaryKnowing the exact hydraulic parameters of soils is very important for improving water management in agriculture and for the refinement of climate models. Up to now, however, the investigation of such parameters has required applying two techniques simultaneously which is time-consuming and invasive. Thus, the objective of this current study is to present only one technique, i.e., a new non-invasive method to measure hydraulic parameters of model soils by using low-field nuclear magnetic resonance (NMR). Hereby, two model clay or sandy soils were respectively filled in a 2 m-long acetate column having an integrated PVC tube. After the soils were completely saturated with water, a low-field NMR sensor was moved up and down in the PVC tube to quantitatively measure along the whole column the initial water content of each soil sample. Thereafter, both columns were allowed to drain. Meanwhile, the NMR sensor was set at a certain depth to measure the water content of that soil slice. Once the hydraulic equilibrium was reached in each of the two columns, a final moisture profile was taken along the whole column. Three curves were subsequently generated accordingly: (1) the initial moisture profile, (2) the evolution curve of the moisture depletion at that particular depth, and (3) the final moisture profile. All three curves were then inverse analyzed using a MATLAB code over numerical data produced with the van Genuchten-Mualem model. Hereby, a set of values ( ?, n, ?r and ?s) was found for the hydraulic parameters for the soils under research. Additionally, the complete decaying NMR signal could be analyzed through Inverse Laplace Transformation and averaged on the 1/ T2 space. Through measurement of the decay in pure water, the effect on the relaxation caused by the sample could be estimated from the obtained spectra. The migration of the sample-related average with decreasing saturation speaks for a enhancement of the surface relaxation as the soil dries, in concordance with results found by other authors. In conclusion, this low-field mobile NMR technique has proven itself to be a fast and a non-invasive mean to investigate the hydraulic behavior of soils and to explore microscopical aspect of the water retained in them. In the future, the sensor should allow easy soil moisture measurements on-field.

Sucre, Oscar; Pohlmeier, Andreas; Minière, Adrien; Blümich, Bernhard

2011-08-01

63

Surface-induced order parameter distortion in superfluid ³He-B measured by nonlinear NMR.  

Science.gov (United States)

The B phase of superfluid 3He is a three-dimensional time-reversal invariant topological superfluid, predicted to support gapless Majorana surface states. We confine superfluid 3He into a thin nanofluidic slab geometry. In the presence of a weak symmetry-breaking magnetic field, we have observed two possible states of the confined 3He-B phase manifold, through the small tipping angle NMR response. Large tipping angle nonlinear NMR has allowed the identification of the order parameter of these states and enabled a measurement of the surface-induced gap distortion. The results for two different quasiparticle surface scattering boundary conditions are compared with the predictions of weak-coupling quasiclassical theory. We identify a textural domain wall between the two B phase states, the edge of which at the cavity surface is predicted to host gapless states, protected in the magnetic field. PMID:24476290

Levitin, Lev V; Bennett, Robert G; Surovtsev, Evgeny V; Parpia, Jeevak M; Cowan, Brian; Casey, Andrew J; Saunders, John

2013-12-01

64

Sensitivity of the NMR density matrix to pulse sequence parameters: A simplified analytic approach  

Science.gov (United States)

We present a formalism for the analysis of sensitivity of nuclear magnetic resonance pulse sequences to variations of pulse sequence parameters, such as radiofrequency pulses, gradient pulses or evolution delays. The formalism enables the calculation of compact, analytic expressions for the derivatives of the density matrix and the observed signal with respect to the parameters varied. The analysis is based on two constructs computed in the course of modified density-matrix simulations: the error interrogation operators and error commutators. The approach presented is consequently named the Error Commutator Formalism (ECF). It is used to evaluate the sensitivity of the density matrix to parameter variation based on the simulations carried out for the ideal parameters, obviating the need for finite-difference calculations of signal errors. The ECF analysis therefore carries a computational cost comparable to a single density-matrix or product-operator simulation. Its application is illustrated using a number of examples from basic NMR spectroscopy. We show that the strength of the ECF is its ability to provide analytic insights into the propagation of errors through pulse sequences and the behaviour of signal errors under phase cycling. Furthermore, the approach is algorithmic and easily amenable to implementation in the form of a programming code. It is envisaged that it could be incorporated into standard NMR product-operator simulation packages.

Momot, Konstantin I.; Takegoshi, K.

2012-08-01

65

Exact two-component relativistic theory for NMR parameters: general formulation and pilot application.  

Science.gov (United States)

The previously proposed exact two-component (X2C) relativistic theory of nuclear magnetic resonance (NMR) parameters [Q. Sun, W. Liu, Y. Xiao, and L. Cheng, J. Chem. Phys. 131, 081101 (2009)] is reformulated to accommodate two schemes for kinetic balance, five schemes for magnetic balance, and three schemes for decoupling in a unified manner, at both matrix and operator levels. In addition, three definitions of spin magnetization are considered in the coupled-perturbed Kohn-Sham equation. Apart from its simplicity, the most salient feature of X2C-NMR lies in that its diamagnetic and paramagnetic terms agree individually with the corresponding four-component counterparts for any finite basis. For practical applications, five approximate schemes for the first order coupling matrix X(10) and four approximate schemes for the treatment of two-electron integrals are introduced, which render the computations of X2C-NMR very much the same as those of approximate two-component approaches. PMID:23145715

Sun, Qiming; Xiao, Yunlong; Liu, Wenjian

2012-11-01

66

NMR and FTIR characterization of petroleum residues: structural parameters and correlations  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Resíduos pesados de petróleo podem ser usados como matéria-prima na produção de diversos materiais de carbono, como piches, isotrópicos e anisotrópicos, e diferentes tipos de coque. A caracterização química destes resíduos, e de materiais de carbono em geral, é um desafio que deve ser abordado para [...] que se possa otimizar adequadamente estes processos de produção. Neste trabalho, resíduos de petróleo de diferentes refinarias foram analisados por RMN, FTIR e análise elementar. Parâmetros de análise foram otimizados para a técnica de RMN e espectroscopia no infravermelho por refletância difusa, uma técnica geralmente aplicada a materiais sólidos, mas que gerou espectros de boa qualidade para estas amostras. Correlações foram encontradas entre os índices de aromaticidade por RMN e FTIR, um parâmetro largamente usado no estudo da formação da mesofase, bem como entre a razão C/H e o índice de aromaticidade. Outros parâmetros estruturais de interesse também foram determinados. Abstract in english Heavy petroleum residues can be used as raw materials in the production of various carbon products, notably isotropic and anisotropic pitches and different types of coke. The chemical characterization of these residues, and carbon materials in general, is a challenge that has to be addressed in orde [...] r to allow the adequate optimization of production processes. In this study, petroleum residues of different refineries were studied by NMR, FTIR and elemental analysis. Optimum parameters were determined for NMR analysis and diffuse reflectance spectroscopy (DRIFTS), a technique that is usually applied to solid materials but was shown to yield good quality spectra for these samples. Correlations were found between NMR and FTIR results for the aromaticity index, a structural parameter widely used in the study of mesophase formation in pitches, as well as between C/H ratios and the aromaticity index. Other structural parameters of interest were also obtained.

Alexandre T., Castro.

67

Thermal and solvent effects on NMR spectroscopy parameters of a prototypical Chagas disease drug  

International Nuclear Information System (INIS)

Full text. Hydrogen bonds in liquids can be of crucial importance for solvent effects in spectroscopy. We have herein computed the nuclear magnetic spin-spin coupling constants (SSCC) involving 15N and 1H nuclei motivated by the relevance of these couplings for the indirect detection of the 15N chemical shifts. Such nJ(N,H) couplings are now also taken as probes for obtaining structural information in proteins. In this work, we focus on the J-couplings; a complete analysis of the NMR spectral data for the compounds studied can be found in previous papers. Thermal and solvent effects on the SSCCs of metronidazole (1) were studied computationally with appropriate quantum-chemical methods. Metronidazole may serve as a model compound to investigate the influence of solvent molecules on the NMR spin-spin coupling constants in heterocyclic rings. We find a hydrogen bond between 1 and a solvent water molecule that is associated with a bond critical point between the imidazole N-3 atom and a water H atom. AIM analysis indicates this hydrogen bond to be mainly electrostatic in nature. Simple static SSCC calculations in vacuo underestimate the nJ(N-3,H) coupling constants because of the neglect of hydrogen bonding. PCM-based treatments perform reasonably well because of the electrostatic character of the hydrogen bond. For more reliable predictions, it is important to take into account the dynamics of the system and to include nearby solvent molecules explicitly. The reduction of the hyperconjugative interactions involving the sigma CH bond or the sigma *CH antibond (with the coupling nucleus H) that is found in solution appears to be correlated to the reduction of coupling pathways in the imidazole ring. Since nuclear spin orientation information is transferred electronically to the other nuclei in the molecule, experimentally determined J-couplings directly reflect the nature of the chemical bond involved.106,107 Unlike most other NMR properties, which can be understood on the basis of semiclassical physics, J-coupling is a purely quantum- mechanical phenomenon. The present results provide evidence that hyperconjugative effects in solute molecules are not due to changes in geometric parameters upon solvation, but arise from the direct response of the electronic wave function to the presence of the solvent, which can be represented by discrete molecules and/or the dielectric bulk. We believe that our findings may be helpful to rationalize the relation between NMR parameters and the interactions in hydrogen-bonded complexes. Further applications along these lines are in progress. (author)

68

Thermal and solvent effects on NMR spectroscopy parameters of a prototypical Chagas disease drug  

Energy Technology Data Exchange (ETDEWEB)

Full text. Hydrogen bonds in liquids can be of crucial importance for solvent effects in spectroscopy. We have herein computed the nuclear magnetic spin-spin coupling constants (SSCC) involving 15N and 1H nuclei motivated by the relevance of these couplings for the indirect detection of the 15N chemical shifts. Such nJ(N,H) couplings are now also taken as probes for obtaining structural information in proteins. In this work, we focus on the J-couplings; a complete analysis of the NMR spectral data for the compounds studied can be found in previous papers. Thermal and solvent effects on the SSCCs of metronidazole (1) were studied computationally with appropriate quantum-chemical methods. Metronidazole may serve as a model compound to investigate the influence of solvent molecules on the NMR spin-spin coupling constants in heterocyclic rings. We find a hydrogen bond between 1 and a solvent water molecule that is associated with a bond critical point between the imidazole N-3 atom and a water H atom. AIM analysis indicates this hydrogen bond to be mainly electrostatic in nature. Simple static SSCC calculations in vacuo underestimate the nJ(N-3,H) coupling constants because of the neglect of hydrogen bonding. PCM-based treatments perform reasonably well because of the electrostatic character of the hydrogen bond. For more reliable predictions, it is important to take into account the dynamics of the system and to include nearby solvent molecules explicitly. The reduction of the hyperconjugative interactions involving the sigma CH bond or the sigma {sup *}CH antibond (with the coupling nucleus H) that is found in solution appears to be correlated to the reduction of coupling pathways in the imidazole ring. Since nuclear spin orientation information is transferred electronically to the other nuclei in the molecule, experimentally determined J-couplings directly reflect the nature of the chemical bond involved.106,107 Unlike most other NMR properties, which can be understood on the basis of semiclassical physics, J-coupling is a purely quantum- mechanical phenomenon. The present results provide evidence that hyperconjugative effects in solute molecules are not due to changes in geometric parameters upon solvation, but arise from the direct response of the electronic wave function to the presence of the solvent, which can be represented by discrete molecules and/or the dielectric bulk. We believe that our findings may be helpful to rationalize the relation between NMR parameters and the interactions in hydrogen-bonded complexes. Further applications along these lines are in progress. (author)

NONE

2011-07-01

69

Cholesterol in oriented bilayers: Determination of order parameters by proton detected local field NMR spectroscopy  

Science.gov (United States)

Cholesterol order parameters are usually determined by deuterium NMR using specifically deuterated cholesterol. We demonstrate herein that the same information may be obtained from the C-H dipolar couplings using 2D experiments correlating 13C chemical shifts and H-C dipolar couplings (PDLF spectroscopy) which we have performed for the first time on oriented lipid bilayers. The order parameters of C4-Ha and C4-He vectors calculated from this experiment are in agreement with those previously determined on the same sample from deuterium NMR. This experiment opens the way to the simultaneous determination of order parameters of all C-H vectors without the need of specific labeling. La détermination des paramètres d'ordre du cholestérol dans une bicouche lipidique est possible par RMN du deutérium après synthèse de cholestérol spécifiquement marqué. Nous montrons dans cet article que la même information peut être extraite à partir des constantes de couplage dipolaire C-H à l'aide d'expériences 2D de corrélation déplacement chimique 13C - couplage dipolaire 13C-H, appelées PDLF, qui ont été réalisées pour la première fois sur des bicouches lipidiques orientées. Les paramètres d'ordre des vecteurs C4-Ha et C4-He issus de cette expérience sont en accord avec ceux déterminés précédemment, sur le même échantillon, par RMN du deutérium. Cette approche permet d'envisager la détermination en une seule expérience des couplages dipolaires de tous les vecteurs C-H sans avoir recours au marquage spécifique.

Massou, S.; Tropis, M.; Milon, A.

1999-10-01

70

Investigation of interaction parameters in mixed micelle using pulsed field gradient NMR spectroscopy.  

Science.gov (United States)

Pulsed field gradient NMR spectroscopy was used to determine the partitioning of surfactant between monomeric and micellar forms in a mixed CTAB (hexadecyltetramethylammonium bromide) and Triton X-100 [p-(1,1,3-tetramethylbutyl)polyoxyethylene] system. In addition, potentiometric and surface tension measurements were used to determine the free concentration of ionic surfactant and the critical micelle concentration (CMC) of mixtures of n-alkyltrimethylammonium bromide (C(n)TAB, n=12, 14, 16, 18) and Triton X-100. Regular solution theory cannot describe the behavior of the activity coefficient and the excess Gibbs free energy of mixtures of ionic and nonionic surfactants. To overcome these shortcomings, we developed a new model that combines Van Laar expressions and the theory of nonrandom mixing in mixed micelles. The Van Laar expressions contain an additional parameter, rho, which reflects differences in the size of the components of the mixture. Nonrandom mixing theory was introduced to describe nonrandom mixing in mixed micelles. This effect was modeled by a packing parameter, P*. The proposed model provided a good description of the behavior of binary surfactant mixtures. The results indicated that head group size and packing constraints are important contributors to nonideal surfactant behavior. In addition, the results showed that as the chain length of the C(n)TAB molecule in C(n)TAB/Triton X-100 mixtures was increased, the head group size parameter remained constant, but the interaction and packing parameters increased. Increase of the temperature caused an increase in the interaction parameter beta and a decrease in the packing parameter (P*). PMID:15797433

Gharibi, H; Javadian, S; Sohrabi, B; Behjatmanesh, R

2005-05-01

71

Polarization propagators: A powerful theoretical tool for a deeper understanding of NMR spectroscopic parameters  

Science.gov (United States)

Magnetic molecular spectroscopic properties, like NMR J-coupling and magnetic shielding ?, have been studied by non-relativistic quantum methods since their discovery. When they were found to depend strongly on relativistic effects in molecules containing heavy atoms, this started a new area of intensive research into the development of methods that include such effects. In most cases non-relativistic concepts were extended to the new field though keeping the previous non-relativistic point of view. Quantum mechanics can be formulated by two different formal approaches. Molecular physics and quantum chemistry were developed mostly within the Schrödinger or Heisenberg approaches. The path integral formalism of Feynman is less well known. This may be the reason why propagators are not broadly known in this field of research. Polarization propagators were developed in the early 1970s. Since that time they have been successfully applied to calculate NMR spectroscopic parameters. They are special theoretical devices from which one can do a deep analysis of the electronic mechanisms that underly any molecular response property from basic theoretical elements, like molecular orbitals, electronic excitation energies, coupling pathways, entanglement, contributions within different levels of theory, etc. All this is obtained in a natural way in both regimes: relativistic and non-relativistic. Its relativistic generalization in the early 1990s and the finding of a quantum electrodynamic (QED)-based theory for them, has given us the opportunity to improve our understanding of the physics behind such parameters. In this paper we give a presentation of polarization propagators that start in non-relativistic quantum physics and end up with the introduction of QED effects. The same and powerful basic quantum ideas are applied throughout this review, so that coherence and beauty arise in a natural way. We will give a new understanding that comes from the three levels of theory: non-relativistic, relativistic and QED. We will be cautious to highlight what one can learn when working in any of these regimes, being aware that the same concepts may have different meanings. Starting with a general overview of polarization propagators we develop both the theory and applications in each of the three levels mentioned above. We show how some of the most subtle properties of the NMR spectroscopic parameters can be explained in a simple and beautiful way: the sign of J, the Karplus rule, cooperative effects, diamagnetic and paramagnetic contributions; we also show new rules that appear within the relativistic regime and the way previously valid rules within the non-relativistic theory are broken. We highlight the fact that within the relativistic theory of polarization propagators the whole set of electronic mechanisms that appears within the NR regime and within its quasi-relativistic extension is unified. Furthermore the usual notion of diamagnetism and paramagnetism are now nonsense as such because they arise only after as an approximation from expressions which include a unique type of electronic (electron-positron) mechanism.

Aucar, Gustavo A.; Romero, Rodolfo H.; Maldonado, Alejandro F.

72

Evaluation of fractal parameters of percolation model objects and natural porous media by means of NMR microscopy  

Science.gov (United States)

Noninvasive NMR microscopy permits one to image the three-dimensional pore space of porous materials filled with a fluid. The binary representation of the geometrical structure is analysed with regard to fractal properties. The flow pattern of percolating liquids in the presence of a stationary pressure gradient can be visualized with the aid of NMR velocity mapping. The pore space maintaining the transport (the backbone) can thus be distinguished from dead ends. The fractal parameters of the backbone turned out to be different from those of the whole pore space. Reconstructed two- or three-dimensional objects based on site-percolation or continuous swiss-cheese models above the percolation threshold are compared with natural materials. The ingress of light water into a gel made with heavy water can also be visualized using NMR microscopy. The mean-squared displacement determined in this way in the site percolation model object indicates anomalous behavior.

Klemm, A.; Müller, H.-P.; Kimmich, R.

73

Investigations of the Local Structure and the EPR Parameters for the Tetragonal Ni+ Center in SrF2  

Directory of Open Access Journals (Sweden)

Full Text Available The local structure and the spin Hamiltonian parameters g factors g// and g? and the hyperfine structure constantsA// and A? of a tetragonal Ni+ center in SrF2 are investigated, using the high order perturbation formulas for a 3d9ion in tetragonally elongated octahedra. According to these studies, the impurity Ni+ is found to locate at thedistance of about 0.36 Å from the nearest fluorine plane. The obtained spin Hamiltonian parameters agree wellwith the experimental data.

Ji-zi Lin

2010-10-01

74

Improved determination of FID signal parameters in low-field NMR  

Science.gov (United States)

In this work, novel methods are suggested for assessing signal parameters of the free induction decay (FID) in nuclear magnetic resonance (NMR) experiments. The FID signal was recorded in a microtesla field and analysed to determine its relaxation time, amplitude, Larmor frequency and phase. The challenge was posed by the narrow line width, whose related effects were investigated through simulations, also. The developed methods give a new view on FID signal estimation in microtesla as well as lower and higher fields. It is shown that the transverse relaxation time of a sample can be accurately determined in the frequency domain by other means than the Lorentz peak half width. Also, with some realistic approximations, a simple functional form for the power spectrum Lorentz peak shape is proposed. As shown in this work, the inspection of the power spectrum instead of the absorption and dispersion Lorentzians is advantageous in the sense that the waveform is independent of the FID phase. The automatic and efficient methods presented in this work incorporate an integral exponential fit, the fit of the power spectrum Lorentz peak and two ways to determine the FID phase. When there are sufficiently many data points in the Lorentz peak, the power spectrum Lorentz peak shape fit provides a quick, simple and accurate way of determining the amplitude, relaxation time and Larmor frequency of the FID. In the measurements of this work, however, the narrow line width led to establishing a more applicable method which is based on the exponential decay of the Lorentz peak with a temporally moving power spectrum window.

Dabek, Juhani; Nieminen, Jaakko O.; Vesanen, Panu T.; Sepponen, Raimo; Ilmoniemi, Risto J.

2010-07-01

75

Reparameterization of RNA ? Torsion Parameters for the AMBER Force Field and Comparison to NMR Spectra for Cytidine and Uridine  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A reparameterization of the torsional parameters for the glycosidic dihedral angle, ?, for the AMBER99 force field in RNA nucleosides is used to provide a modified force field, AMBER99?. Molecular dynamics simulations of cytidine, uridine, adenosine, and guanosine in aqueous solution using the AMBER99 and AMBER99? force fields are compared with NMR results. For each nucleoside and force field, 10 individual molecular dynamics simulations of 30 ns each were run. For cytidine with AMBER99? ...

Yildirim, Ilyas; Stern, Harry A.; Kennedy, Scott D.; Tubbs, Jason D.; Turner, Douglas H.

2010-01-01

76

The dependence of the spin-Hamiltonian parameters of the [Ti(OH 2) 6] 3+ cation on the mode of water co-ordination  

Science.gov (United States)

Single crystal X-band EPR spectra of Ti(III) doped C( NH2) 3MIII( SO4) 2·6 H2O ( Gu[ MIII: Ti] SH, MIII= GaIII, AlIII) collected at ˜1.9 K, are presented. Principal g values for Gu[Ga:Ti]SH and Gu[Al:Ti]SH of g?˜0.965, g?˜0, and g?˜0.984, g?˜0, respectively, are derived. The values of g? are significantly less than that previously reported for Cs[Ga:Ti]SH ( g?˜1.161) and this work is principally concerned with accounting for the difference. Analytical expressions are derived for the first-order Jahn-Teller coupling coefficients between the states comprising the 2T g (T h) ground term and the twisting librations of the coordinating water molecules, in the framework of the Angular Overlap Model (AOM); and, values of g? computed by numerical diagonalisation of the vibronic Hamiltonian. On the basis of differences in the mode of water co-ordination alone, g? is calculated to increase from 0.965 (Gu[Ga:Ti]SH) to ˜1.10 (Cs[Ga:Ti]SH), in fair agreement with experiment. The EPR spectra of Gu[Ga:Ti]SH contain well-resolved proton superhyperfine structure. The magnitude of the superhyperfine coupling constant far exceeds that inferred from the EPR spectrum of Cs[Ga:Ti]SH, and this too is rationalised in terms of the different stereochemistries of the [Ti(OH 2) 6] 3+ cation in the two crystal systems.

Carver, Graham; Bendix, Jesper; Tregenna-Piggott, Philip L. W.

2002-09-01

77

Optimal control design of NMR and dynamic nuclear polarization experiments using monotonically convergent algorithms.  

Science.gov (United States)

Optimal control theory has recently been introduced to nuclear magnetic resonance (NMR) spectroscopy as a means to systematically design and optimize pulse sequences for liquid- and solid-state applications. This has so far primarily involved numerical optimization using gradient-based methods, which allow for the optimization of a large number of pulse sequence parameters in a concerted way to maximize the efficiency of transfer between given spin states or shape the nuclear spin Hamiltonian to a particular form, both within a given period of time. Using such tools, a variety of new pulse sequences with improved performance have been developed, and the NMR spin engineers have been challenged to consider alternative routes for analytical experiment design to meet similar performance. In addition, it has lead to increasing demands to the numerical procedures used in the optimization process in terms of computational speed and fast convergence. With the latter aspect in mind, here we introduce an alternative approach to numerical experiment design based on the Krotov formulation of optimal control theory. For practical reasons, the overall radio frequency power delivered to the sample should be minimized to facilitate experimental implementation and avoid excessive sample heating. The presented algorithm makes explicit use of this requirement and iteratively solves the stationary conditions making sure that the maximum of the objective is reached. It is shown that this method is faster per iteration and takes different paths within a control space than gradient-based methods. In the present work, the Krotov approach is demonstrated by the optimization of NMR and dynamic nuclear polarization experiments for various spin systems and using different constraints with respect to radio frequency and microwave power consumption. PMID:18532824

Maximov, Ivan I; Tosner, Zden?k; Nielsen, Niels Chr

2008-05-14

78

Aziridine nitrogen inversion by dynamic NMR: activation parameters in a fused bicyclic structure.  

Science.gov (United States)

The nitrogen inversion of a N-phenyl aziridine fused to a succinimide ring is influenced by the presence of a phenyl ring in the succinimide moiety. The endo invertomer is favored, showing an unsymmetrical equilibrium in variable (1)H NMR studies. PMID:24125572

de Loera, Denisse; Liu, Fang; Houk, K N; Garcia-Garibay, Miguel A

2013-11-15

79

Structural investigations of ?-CaAlF5 by coupling powder XRD, NMR, EPR and spectroscopic parameter calculations  

International Nuclear Information System (INIS)

?-CaAlF5 was synthesized by solid-state reaction. The precise structure was refined from X-ray powder diffraction data in the monoclinic space group P21/c with lattice constants a=5.3361A, b=9.8298A, c=7.3271A, and ?=109.91o (Z=4). The structure exhibits isolated chains of AlF63- octahedra sharing opposite corners.19F and 27Al solid state NMR spectra were recorded using MAS and SATRAS techniques. An EPR spectrum was recorded for ?-CaAlF5:Cr3+. The experimental spectra were simulated in order to extract the NMR and EPR parameter values. Five fluorine sites and one low symmetry aluminium site were found in agreement with the refined structure. These parameters were calculated using empirical and ab-initio methods. The agreement obtained between the calculated 19F chemical shift values, 27Al quadrupolar parameters, Cr3+ EPR fine structure parameters and the experimental results demonstrates the complementarity of XRD, magnetic resonance experiments and theoretical methodologies

80

NMR paramagnetic relaxation of the spin 2 complex Mn(III)TSPP: a unique mechanism.  

Science.gov (United States)

The S = 2 complex, manganese(III) meso-tetra(4-sulfonatophenyl)porphine chloride (Mn(III)TSPP) is a highly efficient relaxation agent with respect to water protons and has been studied extensively as a possible MRI contrast agent. The NMR relaxation mechanism has several unique aspects, key among which is the unusual role of zero-field splitting (zfs) interactions and the effect of these interactions on the electron spin dynamics. The principal determinant of the shape of the R1 magnetic relaxation dispersion (MRD) profile is the tetragonal 4th-order zfs tensor component, B4(4), which splits the levels of the m(S) = +/-2 non-Kramers doublet. When the splitting due to B4(4) exceeds the Zeeman splitting, the matrix elements of (S(z)) are driven into coherent oscillation, with the result that the NMR paramagnetic relaxation enhancement is suppressed. To confirm the fundamental aspects of this mechanism, proton R1 MRD data have been collected on polyacrylamide gel samples in which Mn(III)TSPP is reorientationally immobilized. Solute immobilization suppresses time-dependence in the electron spin Hamiltonian that is caused by Brownian motion, simplifying the theoretical analysis. Simultaneous fits of both gel and solution data were achieved using a single set of parameters, all of which were known or tightly constrained from prior experiments except the 4th-order zfs parameter, B4(4), and the electron spin relaxation times, which were found to differ in the m(S) = +/-1 and m(S) = +/-2 doublet manifolds. In liquid samples, but not in the gels, the B4(4)-induced splitting of the m(S) = +/-2 non-Kramers doublet is partially collapsed due to Brownian motion. This phenomenon affects the magnitudes of both B4(4) and electron spin relaxation times in the liquid samples. PMID:16833659

Schaefle, Nathaniel; Sharp, Robert

2005-04-21

 
 
 
 
81

Quantifying Lipari-Szabo modelfree parameters from 13CO NMR relaxation experiments  

International Nuclear Information System (INIS)

r data indicate that the SCO2 order parameters rapport on slower, and sometimes different, motions than the 15N relaxation order parameters. The CO local correlation times correlate well with the calmodulin's secondary structure

82

Reparameterization of RNA ? Torsion Parameters for the AMBER Force Field and Comparison to NMR Spectra for Cytidine and Uridine  

Science.gov (United States)

A reparameterization of the torsional parameters for the glycosidic dihedral angle, ?, for the AMBER99 force field in RNA nucleosides is used to provide a modified force field, AMBER99?. Molecular dynamics simulations of cytidine, uridine, adenosine, and guanosine in aqueous solution using the AMBER99 and AMBER99? force fields are compared with NMR results. For each nucleoside and force field, 10 individual molecular dynamics simulations of 30 ns each were run. For cytidine with AMBER99? force field, each molecular dynamics simulation time was extended to 120 ns for convergence purposes. Nuclear magnetic resonance (NMR) spectroscopy, including one-dimensional (1D) 1H, steady-state 1D 1H nuclear Overhauser effect (NOE), and transient 1D 1H NOE, was used to determine the sugar puckering and preferred base orientation with respect to the ribose of cytidine and uridine. The AMBER99 force field overestimates the population of syn conformations of the base orientation and of C2?-endo sugar puckering of the pyrimidines, while the AMBER99? force field’s predictions are more consistent with NMR results. Moreover, the AMBER99 force field prefers high anti conformations with glycosidic dihedral angles around 310° for the base orientation of purines. The AMBER99? force field prefers anti conformations around 185°, which is more consistent with the quantum mechanical calculations and known 3D structures of folded ribonucleic acids (RNAs). Evidently, the AMBER99? force field predicts the structural characteristics of ribonucleosides better than the AMBER99 force field and should improve structural and thermodynamic predictions of RNA structures. PMID:20463845

2010-01-01

83

Relating pore-scale geometric controls on NMR and SIP parameters for improved petrophysical models of synthetic sand-clay mixtures  

Science.gov (United States)

The microgeometry of porous geologic materials controls a wide range of key hydraulic parameters, such as permeability. Non-invasive geophysical methods have shown promise in mapping these properties in-situ over laterally extensive areas. Two near-surface geophysical techniques, nuclear magnetic resonance (NMR) and spectral induced polarization (SIP), demonstrate distinct relationships with porosity, grain size, and surface area. Permeability is also thought to be related to these physical properties suggesting that NMR and SIP can be used to estimate permeability. However, SIP lacks a universally accepted model and NMR is insensitive to anisotropy and pore-connectivity. Additionally, geochemical factors alter NMR and SIP measurements in non-unique manners. In this study, we performed a series of laboratory experiments on well-controlled sand-clay mixtures in order to constrain the geometric controls on measureable NMR and SIP responses in porous media. We combined the geophysical data to formulate better petrophysical models of key hydraulic parameters than would be possible using each method separately. NMR and SIP measurements were performed on different brine saturated mixtures of Ottawa sand and kaolin. Independent measurements were made to estimate the specific surface area, porosity, grain size distribution, and permeability for each sand-clay mixture. Additionally, the brine conductivity was varied in order to test the sensitivity of the NMR and SIP measurements to pore-fluid chemistry as well as determine the true electrical formation factor of the samples. Empirical relationships were first established between each physical property and the measured geophysical parameters using regression analysis. The resulting relationships form the foundation for future mechanistic permeability models that incorporate joint NMR and SIP measurements.

Osterman, G. K.; Keating, K.; Slater, L. D.; Binley, A. M.

2013-12-01

84

Theoretical investigations of spin Hamilton parameters and Knight shifts for rhombic and tetragonal CuGeO3  

International Nuclear Information System (INIS)

The spin Hamiltonian parameters (g factors and hyperfine structure constants) and the Knight shifts for Cu2+ in the spin-Pierels compound CuGeO3 of rhombic and tetragonal phases are theoretically investigated from the high order perturbation formulas of these parameters for a 3d9 ion under rhombically and tetragonally elongated octahedra in a uniform way. The approximately linear relationships between Knight shifts and g factors are found, i.e., Ki/(gi?gs)=Kj/(gj?gs) (with i, j=x, y and z; gs?2.0023). The theoretical results show good agreement with the observed values, and the improvements are achieved by adopting the fewer adjustable parameters as compared with the previous treatments. The anisotropies of the g factors and the Knight shifts are attributed to the local rhombic and tetragonal elongations of the Cu2+ sites. The studies in this work would be helpful to establish complete physical scheme for uniform investigations on EPR and NMR spectroscopic behaviours of Cu2+ (or other similar 3d9 ions) in compounds

85

The effects of some parameters on the calculated 1H NMR relaxation times of cell water  

International Nuclear Information System (INIS)

The effect of some parameters on the longitudinal and transverse relaxation times is calculated and a comparison between the calculated relaxation times with the results of different measurements is made. (M.S.)

86

NMR and NQR parameters of the SiC-doped on the (4,4) armchair single-walled BPNT: a computational study.  

Science.gov (United States)

The structural properties, NMR and NQR parameters in the pristine and silicon carbide (SiC) doped boron phosphide nanotubes (BPNTs) were calculated using DFT methods (BLYP, B3LYP/6-31G) in order to evaluate the influence of SiC-doped on the (4,4) armchair BPNTs. Nuclear magnetic resonance (NMR) parameters including isotropic (CS(I)) and anisotropic (CS(A)) chemical shielding parameters for the sites of various (13)C, (29)Si, (11)B, and (31)P atoms and quadrupole coupling constant (C ( Q )), and asymmetry parameter (? ( Q )) at the sites of various (11)B nuclei were calculated in pristine and SiC- doped (4,4) armchair boron phosphide nanotubes models. The calculations indicated that doping of (11)B and (31)P atoms by C and Si atoms had a more significant influence on the calculated NMR and NQR parameters than did doping of the B and P atoms by Si and C atoms. In comparison with the pristine model, the SiC- doping in Si(P)C(B) model of the (4,4) armchair BPNTs reduces the energy gaps of the nanotubes and increases their electrical conductance. The NMR results showed that the B and P atoms which are directly bonded to the C atoms in the SiC-doped BPNTs have significant changes in the NMR parameters with respect to the B and P atoms which are directly bonded to the Si atoms in the SiC-doped BPNTs. The NQR results showed that in BPNTs, the B atoms at the edges of nanotubes play dominant roles in determining the electronic behaviors of BPNTs. Also, the NMR and NQR results detect that the Fig. 1b (Si(P)C(B)) model is a more reactive material than the pristine and the Fig. 1a (Si(B)C(p)) models of the (4,4) armchair BPNTs. PMID:21625895

Baei, Mohammad T; Sayyad-Alangi, S Zahra; Moradi, Ali Varasteh; Torabi, Parviz

2012-03-01

87

NMR order parameters calculated in an expanding reference frame: identifying sites of short- and long-range motion  

International Nuclear Information System (INIS)

NMR order parameters are calculated from molecular dynamics computer simulations of ubiquitin and the apo (Ca2+-free) state of calbindin D9k. Calculations are performed in an expanding reference frame so as to discriminate between the effects of short- and long-range motions. This approach reveals that the dominant contributions to the order parameters are short-range. Longer-range contributions are limited to specific sites, many of which have been recognized in previous studies of correlated motions. These sites are identified on the basis of an effective reorientational number, neff. Not only does this parameter identify sites of short- and long-range motion, it also provides a way of evaluating the separability condition that is key to the Lipari-Szabo model-free method. When analyzed in conjunction with the Prompers-Brüschweiler separability index, the neff values indicate that longer-range motions play a more prominent role in apo calbindin than they do in ubiquitin.

88

Effects of substituents on the NMR features of basic bicyclic ring systems of fluoroquinolone antibiotics and the relationships between NMR chemical shifts, molecular descriptors and drug-likeness parameters.  

Science.gov (United States)

In the present study, the NMR spectroscopic features of trovafloxacin (TVA) mesylate, pefloxacin (PFX) mesylate dihydrate and ciprofloxacin (CIP) hydrochloride monohydrate were studied in DMSO-d6 solution with the aim of investigating the effects of substituents and the type of salt on the NMR parameters of basic bicyclic fluoroquinolone and fluoronaphthyridone ring systems. For this purpose, the 1H- and 13C- one- and two-dimensional homo- and heteronuclear NMR methods were used. The analysis of 1H- and 13C-NMR spectra confirmed the structures of investigated fluoroquinolone salts. Relationships between 1H- and 13C-NMR chemical shifts of fluoronaphthyridone and fluoroquinolone ring systems, calculated molecular descriptors (MDs) and drug-likeness scores (DLSs), computed for monoprotonic cations of investigated fluoroquinolone salts (TVAH+, PFXH+ and CIPH+), were also explored. The topological polar surface area (TPSA), the parameter of lipophilicity (miLogP), the relative molecular mass (Mr) and the volume (V) of computed molecular descriptors (MDs), as well as the G protein-coupled receptor ligand-likeness (GPCR ligand-ls), the ion channel ligand-likeness (ICL-ls), the kinase inhibitor-likeness (KI-ls) and the nuclear receptor ligand-likeness (NRL-ls) were used in this study. The 1H-NMR chemical shifts of protons in COOH, H5 and NHn+, as well as 13C-NMR chemical shifts of C4, C5 and C11 shown to be good parameters in exploration of property-property and property-drug-likeness relationships for investigated fluoroquinolone salts. Thus, collinear relationships of 1H-NMR chemical shifts of protons in COOH, H5 and NHn+ with TPSA and miLogP, as well as with GPCR ligand-ls, KI-ls and NRL-ls were revealed (?, ppm H in COOH vs. TPSA, R = -0.9421; ?, ppm H in COOH vs. NRL-ls, R = -0.9216; ?, ppm H5 vs. miLogP, R = 0.9962; ?, ppm H5 vs. KI-ls, R = 0.9969; ?, ppm NHn+vs. TPSA, R = -0.9875 and ?, ppm NHn+vs. NRL-ls, R = -0.9948). The collinearities between, 13C-NMR chemical shifts of C4, C5 and C11 with KI-ls and NRL-ls, as well as with TPSA, miLogP, Mr and V were also revealed (?, ppm C4 vs. TPSA, R = 0.9964; ?, ppm C4 vs. miLogP, R = 0.9487; ?, ppm C4 vs.Mr, R = 0.9629; ?, ppm C4 vs. KI-ls, R = 0.9461; ?, ppm C4 vs. NRL-ls, R = 0.9996; ?, ppm C5 vs. miLogP, R = 0.9994; ?, ppm C5 vs. KI-ls, R = 0.9990; ?, ppm C5 vs. NRL-ls, R = 0.9510; ?, ppm C11 vs. TPSA, R = -0,9958; ?, ppm C11 vs. NRL-ls, R = -0.9994 and ?, ppm C11 vs. KI-ls, R = -0.9481). PMID:21134860

Taka?, Milena Jadrijevi?-Mladar

2010-09-01

89

Compact NMR  

Energy Technology Data Exchange (ETDEWEB)

Nuclear Magnetic Resonance (NMR) spectroscopy is the most popular method for chemists to analyze molecular structures, while Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic tool for medical doctors that provides high-contrast images of biological tissue. In both applications, the sample (or patient) is positioned inside a large, superconducting magnet to magnetize the atomic nuclei. Interrogating radio-frequency pulses result in frequency spectra that provide the chemist with molecular information, the medical doctor with anatomic images, and materials scientist with NMR relaxation parameters. Recent advances in magnet technology have led to a variety of small permanent magnets to allow compact and low-cost instruments. The goal of this book is to provide an introduction to the practical use of compact NMR at a level nearly as basic as the operation of a smart phone.

Bluemich, Bernhard; Haber-Pohlmeier, Sabina; Zia, Wasif [RWTH Aachen Univ. (Germany). Inst. fuer Technische und Makromolekulare Chemie (ITMC)

2014-06-01

90

Compact NMR  

International Nuclear Information System (INIS)

Nuclear Magnetic Resonance (NMR) spectroscopy is the most popular method for chemists to analyze molecular structures, while Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic tool for medical doctors that provides high-contrast images of biological tissue. In both applications, the sample (or patient) is positioned inside a large, superconducting magnet to magnetize the atomic nuclei. Interrogating radio-frequency pulses result in frequency spectra that provide the chemist with molecular information, the medical doctor with anatomic images, and materials scientist with NMR relaxation parameters. Recent advances in magnet technology have led to a variety of small permanent magnets to allow compact and low-cost instruments. The goal of this book is to provide an introduction to the practical use of compact NMR at a level nearly as basic as the operation of a smart phone.

91

Exact NMR simulation of protein-size spin systems using tensor train formalism  

Science.gov (United States)

We introduce a new method, based on alternating optimization, for compact representation of spin Hamiltonians and solution of linear systems of algebraic equations in the tensor train format. We demonstrate the method's utility by simulating, without approximations, a N15 NMR spectrum of ubiquitin—a protein containing several hundred interacting nuclear spins. Existing simulation algorithms for the spin system and the NMR experiment in question either require significant approximations or scale exponentially with the spin system size. We compare the proposed method to the Spinach package that uses heuristic restricted state space techniques to achieve polynomial complexity scaling. When the spin system topology is close to a linear chain (e.g., for the backbone of a protein), the tensor train representation is more compact and can be computed faster than the sparse representation using restricted state spaces.

Savostyanov, D. V.; Dolgov, S. V.; Werner, J. M.; Kuprov, Ilya

2014-08-01

92

Lattice parameter and 195Pt NMR knight shift measurements in CePt 2- xRh x system  

Science.gov (United States)

The results of the X-ray diffraction and 195Pt NMR studies on CePt 2- xRh x suggest that the valency of Ce changes continuously from 3+ towards 4+ in this pseudobinary alloy as the value of x is increased.

Sampathkumaran, E. V.; Gupta, L. C.; Vijayaraghavan, R.

1983-02-01

93

Possibility of using computers to estimate the correlation between the paramagnetic shifts induced by lanthanides in the NMR spectra and the structural parameters of a lanthanide-substrate system  

International Nuclear Information System (INIS)

The present work examines the possibility of using computers to estimate the correlation between the paramagnetic shifts induced by lanthanides in the NMR spectra abnd the structural parameters of a lanthanide-substrate system

94

NMR imaging of plants  

International Nuclear Information System (INIS)

The basic possibility to use NMR imaging for non-invasive investigation of plants as well as the influence of the NMR parameters spin density and spin-spin relaxation time T2 on the image contrast is demonstrated. The numerical calculation of the spatial distribution of the pure NMR parameters points to the possibility of drawing conclusions concerning the physical and chemical state of the biological system. The experiments were performed on a commercial NMR spectrometer using a home-made accessory unit. (author)

95

Multiple quantum NMR of spin-carrying molecules in nanopores: high order corrections to the two-spin/two-quantum Hamiltonian  

CERN Document Server

This paper is devoted to the multiple-quantum (MQ) NMR spectroscopy in nanopores filled by a gas of spin-carrying molecules (s=1/2) in the strong external magnetic field. It turned out that the high symmetry of the spin system in nanopores yields a possibility to overcome the problem of the exponential growth of the Hilbert space dimension with an increase in a number of spins and to investigate MQ NMR dynamics in systems consisting of several hundreds of spins. We investigate the dependence of the MQ coherence intensities on their order (the profile of the MQ coherence intensities) for the spin system governed by the standard MQ NMR Hamiltonian (the nonsecular two-quantum/two-spin Hamiltonian) together with the second order correction of the average Hamiltonian theory. It is shown that the profile depends on the value of this correction and varies from the exponential to the logarithmic one.

Doronina, Sergei I; Felâ??dmana, Edward B; Zenchuka, Alexander I

2010-01-01

96

NMR Spectroscopy  

Science.gov (United States)

Quiz questions from the organic chemistry question bank provide students with an excellent opportunity to review key concepts. These questions pertain to Nuclear magnetic resonance (NMR) spectroscopy and include topics such as: Chemical Shift, Proton NMR, and Carbon NMR.

Reich, Ieva

2008-03-25

97

Correlation of tryptophan fluorescence intensity decay parameters with sup 1 H NMR-determined rotamer conformations: (tryptophan sup 2 )oxytocin  

Energy Technology Data Exchange (ETDEWEB)

While the fluorescence decay kinetics of tyrosine model compounds can be explained in terms of heterogeneity derived from the three ground-state {chi}{sup 1} rotamers, a similar correlation has yet to be directly observed for a tryptophan residue. In addition, the asymmetric indole ring might also lead to heterogeneity from {chi}{sup 2} rotations. In this paper, the time-resolved and steady-state fluorescence properties of (tryptophan{sup 2})oxytocin at pH 3 are presented and compared with {sup 1}H NMR results. According to the unrestricted analyses of individual fluorescence decay curves taken as a function of emission wavelength-independent decay constants, only three exponential terms are required. In addition, the preexponential weighting factors (amplitudes) have the same relative relationship (weights) as the {sup 1}H NMR-determined {chi}{sup 1} rotamer populations of the indole side chain. {sup 15}N was used in heteronuclear coupling experiments to confirm the rotamer assignments. Inclusion of a linked function restricting the decay amplitudes to the {chi}{sup 1} rotamer populations in the individual decay curve analyses and in the global analysis confirms this correlation. According to qualitative nuclear Overhauser data, there are two {chi}{sup 2} populations.

Ross, J.B.A.; Schwartz, G.P.; Laws, W.R. (Mount Sinai, New York, NY (United States)); Wyssbrod, H.R.; Porter, R.A. (Univ. of Louisville, KY (United States)); Michaels, C.A. (Swarthmore Coll., PA (United States))

1992-02-18

98

Microscopic access to long-range diffusion parameters of the fast lithium ion conductor Li7BiO6 by solid state 7Li stimulated echo NMR.  

Science.gov (United States)

Li self-diffusion in rhombohedral Li7BiO6, being a promising basic material for cathodes of rechargeable ion batteries, is studied by means of 7Li stimulated echo NMR. Using the pulse sequence introduced by Jeener and Broekaert, a spin-alignment echo is created whose amplitude decay is recorded as a function of mixing time. The so-obtained two-time correlation functions follow stretched exponential behavior and lead to decay rates which can be identified directly with microscopic Li motional correlation rates (tau(-1)). Using a jump distance of about 0.2 nm, this results in a diffusion coefficient (D) of about 0.5 x 10(-16) m(2) s(-1) at 294 K. The activation energy turned out to be 0.53(3) eV which is in very good agreement with recently obtained results by means of dc-conductivity measurements probing long-range diffusion parameters. This shows that stimulated echo NMR, due to its inherent time scale, gives microscopic access to long-range transport. The prefactor tau(0)(-1) of the corresponding Arrhenius law lies in the typical range of phonon frequencies, tau(0)(-1) = 3 x 10(12) s(-1). PMID:17625829

Wilkening, Martin; Mühle, Claus; Jansen, Martin; Heitjans, Paul

2007-08-01

99

From micro to macro: access to long-range Li+ diffusion parameters in solids via microscopic (6,?7) Li spin-alignment echo NMR spectroscopy.  

Science.gov (United States)

The development of highly conductive solids is a rapidly growing research area in materials science. In particular, the study of Li-ion conductors is driven by the ambitious effort to design powerful lithium-ion batteries. A deeper understanding of Li dynamics in solids requires the availability of a large set of complementary techniques to probe Li self-diffusion on different length and time-scales. We report on (7)Li as well as (6)Li spin-alignment echo (SAE) nuclear magnetic resonance (NMR) spectroscopy, which is capable of probing long-range diffusion parameters from a microscopic, that is, atomic-scale, point of view. So far, variable-temperature SAE NMR spectroscopy has been applied to a number of polycrystalline and glassy Li-ion conductors. The materials investigated serve as model systems to unravel the interesting features of the technique in determining reliable Li jump rates and hopping activation energies. In particular, the latter are compared with those probed by macroscopic techniques such as dc-conductivity measurements that are sensitive to long-range translational motions. PMID:21954143

Wilkening, Martin; Heitjans, Paul

2012-01-16

100

NMR espectroscopic parameters of HX and Si (Sn)X4 (X = H, F, Cl, Br and I) and SnBr4?nIn model compounds  

International Nuclear Information System (INIS)

Graphical abstract: Optimized fully relativistic calculations of NMR J-couplings (HBr, HI), chemical shifts (Si, Sn) and absolute shielding for reference compounds of heavy atoms (Si, Sn) are given. Highlights: ? In this article we show a procedure to get accurate NMR ?Ref of Si and Sn. ? Calculations of ? on more than three heavy-atom-containing molecules are given. ? Our results are closer to ?exp than previous calculations for SnX4 (X = H, Cl, Br, I). ? Optimized basis sets were considered for full R and NR calculations of NMR J and ?. ? Relativistic effects enlarge electron correlation effects on J-couplings. - Abstract: The NMR spectroscopic parameters are largely influenced by relativistic effects. They are highly dependent on the electronic behavior inside the spatial regions occupied by nuclei. Full relativistic calculations of indirect nuclear spin–spin couplings at random phase level of approach (RPA) in the title compounds with reoptimized Dyall cVTZ basis sets are given. A comparison with the results of calculations with other basis sets that are mostly used within the non-relativistic (NR) domain is presented. We analyzed the dependence of that couplings with the speed of light over the whole range of values, from the full relativistic to the NR regimes. Within this last regime, calculations at the second-order level of approach (SOPPA) indicated that electron correlation effects may not be as important for nuclear magnetic shieldings, but they must be included with care for J-coupling calculations. From these calculations, we determined that relativity enlarges the electron correlation effects of the J-couplings of HBr and HI. Because the results of nuclear magnetic shielding calculations within polarization propagators at the RPA level were reliable, we were able to show a new and easy procedure to obtain absolute nuclear magnetic shieldings on reference compounds for both Si and Sn nuclei: ?[Si (CH3)4] = 421.28 ± 29.33 ppm and ?[Sn (CH3)4] = 3814.96 ± 79.12 ppm. They were obtained from experimental chemical shifts and accurate nuclear magnetic shielding calculations on different molecular systems.

 
 
 
 
101

Improved determination of spin density T1 and T2 from a three-parameter fit to multiple-delay-multiple-echo (MDME) NMR images  

International Nuclear Information System (INIS)

A method is presented for simultaneously determining values of relative hydrogen spin density Nsub(r), T1 and T2 from a single set of NMR image intensities acquired in a short imaging time. Multiple-echo data are collected at multiple delays in virtually the same imaging time used to obtain T1 and a T2-weighted Nsub(r) from a separate saturation recovery (SR) T1 measurement. All three parameters are then determined by a three-parameter fit of a derived signal intensity equation to these multiple-delay-multiple-echo (MDME) data, providing an inherent correction of Nsub(r) for T1 and T2 weighting without the use of sequences with Tsub(D)>5T1, and without further data collection for a separate T2 measurement. It also provides an effective reduction in the noise of the separate T2 measurement. A three-parameter fit to MDME data appears to be superior to the separate T1 and T2 measurements currently used to determine all three parameters. Calculations performed on CrCl3 solutions produced T1 values from 21 ms to 3.4s, T2 values from 6 to 714 ms, and standard errors as low as 0.33%, with a net imaging time of the order of that required for routine low-noise signal intensity imaging. (author)

102

Moving NMR  

Science.gov (United States)

Initiated by the use of NMR for well logging, portable NMR instruments are being developed for a variety of novel applications in materials testing and process analysis and control. Open sensors enable non-destructive testing of large objects, and small, cup-size magnets become available for high throughput analysis by NMR relaxation and spectroscopy. Some recent developments of mobile NMR are reviewed which delineate the direction into which portable NMR is moving.

Blümich, Bernhard; Casanova, Federico; Danieli, Ernesto; Gong, Qingxia; Greferath, Marcus; Haber, Agnes; Kolz, Jürgen; Perlo, Juan

2008-12-01

103

Conformational stability, vibrational and NMR analysis, chemical potential and thermodynamical parameter of 3-tert-butyl-4-hydroxyanisole.  

Science.gov (United States)

The FT-IR and FT-Raman spectra of 3-tert-butyl-4-hydroxyanisole (TBHA) molecule have been recorded in the region 4000-400cm(-1) and 3500-100cm(-1), respectively. Optimized geometrical structure, harmonic vibrational frequencies has been computed by B3LYP level using 6-31G (d,p) and 6-311+G (d,p) basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analyzed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The Mulliken charges, the natural bonding orbital (NBO) analysis, the first-order hyperpolarizability of the investigated molecule were computed using DFT calculations. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and analyzed. The isotropic chemical shift computed by (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the TBHA calculated using the gauge invariant atomic orbital (GIAO) method also shows good agreement with experimental observations. PMID:25173520

Balachandran, V; Karpagam, V; Revathi, B; Kavimani, M; Santhi, G

2015-01-25

104

Study of correlations in molecular motion by multiple quantum NMR  

Energy Technology Data Exchange (ETDEWEB)

Nuclear magnetic resonance is a very useful tool for characterizing molecular configurations through the measurement of transition frequencies and dipolar couplings. The measurement of spectral lineshapes, spin-lattice relaxation times, and transverse relaxation times also provide us with valuable information about correlations in molecular motion. The new technique of multiple quantum nuclear magnetic resonance has numerous advantages over the conventional single quantum NMR techniques in obtaining information about static and dynamic interactions of coupled spin systems. In the first two chapters, the theoretical background of spin Hamiltonians and the density matrix formalism of multiple quantum NMR is discussed. The creation and detection of multiple quantum coherence by multiple pulse sequence are discussed. Prototype multiple quantum spectra of oriented benzene are presented. Redfield relaxation theory and the application of multiple quantum NMR to the study of correlations in fluctuations are presented. A specific example of an oriented methyl group relaxed by paramagnetic impurities is studied in detail. The study of possible correlated motion between two coupled methyl groups by multiple quantum NMR is presented. For a six spin system it is shown that the four-quantum spectrum is sensitive to two-body correlations, and serves a ready test of correlated motion. The study of the spin-lattice dynamics of orienting or tunneling methyl groups (CH/sub 3/ and CD/sub 3/) at low temperatures is presented. The anisotropic spin-lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules, is investigated, and the NMR spectrometers and other experimental details are discussed.

Tang, J.H.

1981-11-01

105

Exchange parameters of bcc solid 3He  

International Nuclear Information System (INIS)

Using the spin Hamiltonian, in which two-spin interactions up to third neighbors and two kinds of large folded and planar cyclic four-spin exchange terms are included, spin wave spectrum of uudd and pseudoferromagnetic (PF) phase of bcc solid 3He in finite magnetic field has been calculated. The necessary conditions for the exchange parameters to explain the first order phase transition from uudd to PF at magnetic field of about 0.4T and high temperature experimental results have been obtained within a framework of a three-parameter model. By a calculation using a mean field approximation, the new phase, double spiral spin configuration has been found, and the possibility of the appearance of this phase near T/sub N/ are discussed. 10 references, 5 figures

106

Benford distributions in NMR  

CERN Document Server

Benford's Law is an empirical law which predicts the frequency of significant digits in databases corresponding to various phenomena, natural or artificial. Although counter intuitive at the first sight, it predicts a higher occurrence of digit 1, and decreasing occurrences to other larger digits. Here we report the Benford analysis of various NMR databases and draw several interesting inferences. We observe that, in general, NMR signals follow Benford distribution in time-domain as well as in frequency domain. Our survey included NMR signals of various nuclear species in a wide variety of molecules in different phases, namely liquid, liquid-crystalline, and solid. We also studied the dependence of Benford distribution on NMR parameters such as signal to noise ratio, number of scans, pulse angles, and apodization. In this process we also find that, under certain circumstances, the Benford analysis can distinguish a genuine spectrum from a visually identical simulated spectrum. Further we find that chemical-sh...

Bhole, Gaurav; Mahesh, T S

2014-01-01

107

Quantitative NMR  

Science.gov (United States)

This site features a learning module focused on principles and practice of NMR for quantitative analysis, an application less commonly associated with the technique than is structure determination. Links to simulation packages are included.

Korir, Albert K.; Larive, Cynthia K.

2011-07-18

108

NMR Animations  

Science.gov (United States)

This site features animated tutorials on NMR with sufficient depth to be useful to the non NMR savvy. The animations are accompanied by short descriptions so that the processes displayed can be understood by the viewer. This site goes beyond just showing precession. There are nice animations showing the effect of different pulses, including composite pulses on the magnetization, the effects of magnetic gradient pulses to measure diffusion and do coherence pathway selection.

2011-07-26

109

NMR tutorial  

Science.gov (United States)

This site provides an entry-level introduction to NMR in a text and figures format. The site also contains example structure elucidation problems using NMR, IR and MS data complete with hints and answers. Although the molecules included are somewhat simple, the examples do a good job of illustrating the structure elucidation process. The site also has data for several more complex structure determination problems.

Bogdal, Dariusz

2011-07-19

110

Structure determination and analysis of helix parameters in the DNA decamer d(CATGGCCATG)2 comparison of results from NMR and crystallography.  

Science.gov (United States)

The solution structure of the DNA decamer (CATGGCCATG)2 has been determined by NMR spectroscopy and restrained molecular dynamic and distance geometry calculations. The restrainted data set includes interproton distances and torsion angles for the deoxyribose sugar ring which were obtained by nuclear Overhauser enhancement intensities and quantitative simulation of cross-peaks from double quantum filtered correlation spectroscopy. The backbone torsion angles were constrained using experimental data from NOE cross-peaks, 1H-1H and 1H-31P-coupling constants. The NMR structure and the crystal structure of the DNA decamer deviates from the structure of the canonical form of B-DNA in a number of observable characteristics. Particularly, both structures display a specific pattern of stacking interaction in the central GGC base triplet. Furthermore, a specific local conformation of the TG/CA base-pair step is present in NMR and crystal structure, highlighting the unusually high flexibility of this DNA duplex part. The solution structure of the TG/CA base-pair step obtained by our high resolution NMR study is characterized by a positive roll angle, whereas in crystal this base-pair step tends to adopt remarkably high twist angles. PMID:9878363

Dornberger, U; Flemming, J; Fritzsche, H

1998-12-18

111

Optimisation of NMR dynamic models II. A new methodology for the dual optimisation of the model-free parameters and the Brownian rotational diffusion tensor  

International Nuclear Information System (INIS)

onstrate the importance of this new procedure the NMR relaxation data of the Olfactory Marker Protein (OMP) of Gitti R et al. (2005) Biochem 44(28), 9673-9679 is reanalysed. The result is that the dynamics for certain secondary structural elements is very different from those originally reported

112

Targeted and nontargeted wine analysis by (1)h NMR spectroscopy combined with multivariate statistical analysis. Differentiation of important parameters: grape variety, geographical origin, year of vintage.  

Science.gov (United States)

The authenticity, the grape variety, the geographical origin, and the year of vintage of wines produced in Germany were investigated by (1)H NMR spectroscopy in combination with several steps of multivariate data analysis including principal component analysis (PCA), linear discrimination analysis (LDA), and multivariate analysis of variance (MANOVA) together with cross-validation (CV) embedded in a Monte Carlo resampling approach (MC) and others. A total of about 600 wines were selected and carefully collected from five wine-growing areas in the southern and southwestern parts of Germany. Simultaneous saturation of the resonances of water and ethanol by application of a low-power eight-frequency band irradiation using shaped pulses allowed for high receiver gain settings and hence optimized signal-to-noise ratios. Correct prediction of classification of the grape varieties of Pinot noir, Lemberger, Pinot blanc/Pinot gris, Müller-Thurgau, Riesling, and Gewürztraminer of 95% in the wine panel was achieved. The classification of the vintage of all analyzed wines resulted in correct predictions of 97 and 96%, respectively, for vintage 2008 (n = 318) and 2009 (n = 265). The geographic origin of all wines from the largest German wine-producing regions, Rheinpfalz, Rheinhessen, Mosel, Baden, and Württemberg, could be predicted 89% correctly on average. Each NMR spectrum could be regarded as the individual "fingerprint" of a wine sample, which includes information about variety, origin, vintage, physiological state, technological treatment, and others. PMID:23682581

Godelmann, Rolf; Fang, Fang; Humpfer, Eberhard; Schütz, Birk; Bansbach, Melanie; Schäfer, Hartmut; Spraul, Manfred

2013-06-12

113

NMR GHZ  

CERN Document Server

We describe the creation of a Greenberger-Horne-Zeilinger (GHZ) state of the form |000>+|111> (three maximally entangled quantum bits) using Nuclear Magnetic Resonance (NMR). We have successfully carried out the experiment using the proton and carbon spins of trichloroethylene, and confirmed the result using state tomography. We have thus extended the space of entangled quantum states explored systematically to three quantum bits, an essential step for quantum computation.

Laflamme, R; Zurek, W H; Catasti, P; Mariappan, S V S

1998-01-01

114

Selective averaging for high-resolution solid-state NMR spectroscopy of aligned samples.  

Science.gov (United States)

Solid-state NMR experiments benefit from being performed at high fields, and this is essential in order to obtain spectra with the resolution and sensitivity required for applications to protein structure determination in aligned samples. Since the amount of rf power that can be applied is limited, especially for aqueous protein samples, the most important pulse sequences suffer from bandwidth limitations resulting from the same spread in chemical shift frequencies that aids resolution. SAMPI4 is a pulse sequence that addresses these limitations. It yields separated local field spectra with narrower and more uniform linewidths over the entire spectrum than the currently used PISEMA and SAMMY experiments. In addition, it is much easier to set up on commercial spectrometers and can be incorporated as a building block into other multidimensional pulse sequences. This is illustrated with a two-dimensional HETCOR experiment, where it is crucial to transfer polarization from the amide protons to their directly bonded nitrogens over a wide range of chemical shift frequencies. A quantum-mechanical treatment of the spin Hamiltonians under high-power rf pulses is presented which gives the scaling factor for SAMPI4 as well as the durations of the rf pulses to achieve optimal decoupling. PMID:17074522

Nevzorov, Alexander A; Opella, Stanley J

2007-03-01

115

NMR spectroscopy  

International Nuclear Information System (INIS)

The book reviews the applications of NMR-spectroscopy in medicine and biology. The first chapter of about 40 pages summarizes the history of development and explains the chemical and physical fundamentals of this new and non-invasive method in an easily comprehensible manner. The other chapters summarize diagnostic results obtained with this method in organs and tissues, so that the reader will find a systematic overview of the available findings obtained in the various organ systems. It must be noted, however, that ongoing research work and new insight quite naturally will necessitate corrections to be done, as is the case here with some biochemical interpretations which would need adjustment to latest research results. NMR-spectroscopy is able to measure very fine energy differences on the molecular level, and thus offers insight into metabolic processes, with the advantage that there is no need of applying ionizing radiation in order to qualitatively or quantitatively analyse the metabolic processes in the various organ systems. (orig./DG) With 40 figs., 4 tabs

116

Spin Hamiltonian for which quantum hall wavefunction is exact  

International Nuclear Information System (INIS)

A Hamiltonian is introduced for which the spin-1/2 quantum liquid wavefunction proposed by Kalmeyer and Laughlin is the exact ground state. An explicit proof is given that this state is a doubly degenerate spin singlet. The excitation spectrum of the Hamiltonian is calculated variationally and a case is made for the presence of an energy gap. The spin-1 collective mode, calculated in the single-mode approximation, is shown to have a large energy that is minimized at the Brillouin zone corner. The spin-0 collective mode behaves similarly but has lower overall energy. Wavefunctions for the neutral spin-1/2 excitations are shown to form an exact spin doublet. The energy of a pair of such excitations increases or decreases logarithmically with separation depending on the total spin. When widely separated, the excitations possess an internal 2-fold degree of freedom, a Brillouin zone that is half the linear dimension of the full zone, and a mass comparable to that of the collective modes. copyright Academic Press, Inc. 1989

117

Ground states of unfrustrated spin Hamiltonians satisfy an area law  

Energy Technology Data Exchange (ETDEWEB)

We show that ground states of unfrustrated quantum spin-1/2 systems on general lattices satisfy an entanglement area law, provided that the Hamiltonian can be decomposed into nearest-neighbor interaction terms that have entangled excited states. The ground state manifold can be efficiently described as the image of a low-dimensional subspace of low Schmidt measure, under an efficiently contractible tree-tensor network. This structure gives rise to the possibility of efficiently simulating the complete ground space (which is in general degenerate). We briefly discuss 'non-generic' cases, including highly degenerate interactions with product eigenbases, using a relationship to percolation theory. We finally assess the possibility of using such tree tensor networks to simulate almost frustration-free spin models.

Beaudrap, Niel de; Eisert, Jens [Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam (Germany); Osborne, Tobias J, E-mail: jense@qipc.or [Institute for Advanced Study Berlin, 14193 Berlin (Germany)

2010-09-15

118

Microscopic Li self-diffusion parameters in the lithiated anode material Li4 + xTi5O12 (0 Li solid state NMR.  

Science.gov (United States)

The microscopic Li diffusion parameters in the lithiated spinel Li4 + xTi5O12, which is on its way to become a commercially used anode material in Li ion batteries, are probed for the first time via nuclear magnetic resonance spectroscopy. PMID:18046468

Wilkening, Martin; Iwaniak, Wojciech; Heine, Jessica; Epp, Viktor; Kleinert, Alexandra; Behrens, Malte; Nuspl, Gerhard; Bensch, Wolfgang; Heitjans, Paul

2007-12-21

119

NMR imaging of the eye, orbita, and optic nerve  

International Nuclear Information System (INIS)

Starting from an introduction into the physico-technical bases of NMR imaging, the book gives an overview of characteristic NMR findings for the most important diseases of the eye, orbita, and optic nerve, attributing special importance to the choice of suitable diagnostical parameters and instructive image material. The rank of NMR imaging as compared to other imaging techniques is discussed; guidelines for employing NMR imaging in ophthalmology conclude the book. (orig.) With 352 figs., 7 tabs

120

1H and 13C{1H} NMR spectral parameters of sulfur mustards, nitrogen mustards, and lewisites: computing and predicting of reference spectra for chemical identification.  

Science.gov (United States)

The (1)H and (13)C{(1)H} chemical shifts and (1)H spin-spin couplings of sulfur mustards, nitrogen mustards, and lewisites scheduled in the Chemical Weapons Convention, and those of bis(2-chloromethyl)disulfide, were determined in CDCl(3), CD(2)Cl(2), and (CD(3))(2)CO. Accurate parameters of this kind of series can be used for evaluating the current molecular modeling programs and the chemical shift and coupling constant prediction possibilities of the programs. Several prediction tests were made with commercial programs, and the results are reported here. PMID:22374852

Haapaniemi, Esa; Mesilaakso, Markku

2012-03-01

 
 
 
 
121

Ligand-receptor Interactions by NMR Spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Today NMR spectroscopy is a method of choice for elucidation of interactions between biomolecules and the potential ligands. Knowledge on these interactions is an essential prerequisite for the rational drug design. The most important contribution of NMR to drug design a few years ago was the 3D structure determination of proteins. Besides delivering the 3D structures of the free proteins as a raw material for the modeling studies on ligand binding, NMR can directly yield valuable experimental data on the biologically important protein-ligand complexes. In addition to X-ray diffraction, NMR spectroscopy can provide information on the internal protein dynamics ordynamics of intermolecular interactions. Changes in NMR parameters allow us to detect ("SAR by NMR" and quantitatively determine binding affinities (titration, diffusion NMR experiments, etc. of potential ligands. Also, it is possible to determine the binding site and conformations of ligands, receptors and receptor-ligand complexes with the help of NMR methods such as tr-NOESY. Epitopes or functional groups responsible for binding of ligands to the receptor can be identified by employing STD or WaterLOGSY experiments. In this review are described some of the most frequent NMR methods for the characterization of the interactions between biomolecules and ligands, together with their advantages and disadvantages.

Novak. P.

2008-04-01

122

Fundamentals of NMR  

Science.gov (United States)

This e-text presents an introduction to the fundamentals of NMR covering magnetic resonance, pulsed NMR, relaxation, chemical shift, spin-spin coupling, the nuclear Overhauser effect and chemical exchange. The document may be downloaded in PDF format.

James, Thomas L.

2011-03-30

123

Ligand screening using NMR.  

Science.gov (United States)

NMR has proven to be an invaluable technique for identifying and characterizing ligand interactions with biomolecules. NMR-based detection of ligand binding to protein targets is described. Specifically, the use of the WaterLOGSY NMR experiment to screen mixtures of compounds from a fragment library for binding to influenza H5 hemagglutinin is detailed. PMID:24590726

Ramirez, Benjamin E; Antanasijevic, Aleksandar; Caffrey, Michael

2014-01-01

124

NMR studies of multiphase flows II  

Energy Technology Data Exchange (ETDEWEB)

NMR techniques for measurements of spatial distribution of material phase, velocity and velocity fluctuation are being developed and refined. Versions of these techniques which provide time average liquid fraction and fluid phase velocity have been applied to several concentrated suspension systems which will not be discussed extensively here. Technical developments required to further extend the use of NMR to the multi-phase flow arena and to provide measurements of previously unobtainable parameters are the focus of this report.

Altobelli, S.A.; Caprihan, A.; Fukushima, E. [Lovelace Institutes, Albuquerque, NM (United States)] [and others

1995-12-31

125

NMR and NQR parameters of ethanol crystal  

CERN Document Server

Electric field gradients and chemical shielding tensors of the stable monoclinic crystal phase of ethanol are computed. The projector-augmented wave (PAW) and gauge-including projector-augmented wave (GIPAW) models in the periodic plane-wave density functional theory are used. The crystal data from X-ray measurements, as well as the structures where either all atomic, or only hydrogen atom positions are optimized in the density functional theory are analyzed. These structural models are also studied by including the semi-empirical Van der Waals correction to the density functional theory. Infrared spectra of these five crystal models are calculated.

Milinkovic, M

2012-01-01

126

An introduction to biological NMR spectroscopy.  

Science.gov (United States)

NMR spectroscopy is a powerful tool for biologists interested in the structure, dynamics, and interactions of biological macromolecules. This review aims at presenting in an accessible manner the requirements and limitations of this technique. As an introduction, the history of NMR will highlight how the method evolved from physics to chemistry and finally to biology over several decades. We then introduce the NMR spectral parameters used in structural biology, namely the chemical shift, the J-coupling, nuclear Overhauser effects, and residual dipolar couplings. Resonance assignment, the required step for any further NMR study, bears a resemblance to jigsaw puzzle strategy. The NMR spectral parameters are then converted into angle and distances and used as input using restrained molecular dynamics to compute a bundle of structures. When interpreting a NMR-derived structure, the biologist has to judge its quality on the basis of the statistics provided. When the 3D structure is a priori known by other means, the molecular interaction with a partner can be mapped by NMR: information on the binding interface as well as on kinetic and thermodynamic constants can be gathered. NMR is suitable to monitor, over a wide range of frequencies, protein fluctuations that play a crucial role in their biological function. In the last section of this review, intrinsically disordered proteins, which have escaped the attention of classical structural biology, are discussed in the perspective of NMR, one of the rare available techniques able to describe structural ensembles. This Tutorial is part of the International Proteomics Tutorial Programme (IPTP 16 MCP). PMID:23831612

Marion, Dominique

2013-11-01

127

Validation of quantitative NMR.  

Science.gov (United States)

NMR is by definition a quantitative spectroscopic tool because the intensity of a resonance line is directly proportional to the number of resonant nuclei (spins). This fact enables, in principle, a precise determination of the amount of molecular structures and, hence, of substances in solids as well as liquids. With the increase of sensitivity due to stronger and stronger static magnetic fields including improved electronics the detection limits have been pushed down significantly. However, the lack of a precise protocol that considers and controls the aspects of both the measurement procedure as well as the spectra processing and evaluation is responsible for the fact that quantitative investigations of identical samples in various laboratories may differ severely (deviations up to 90% relative to gravimetric reference values). Here, a validated protocol for quantitative high resolution 1H-NMR using single pulse excitation is described that has been confirmed by national and international round robin tests. It considers all issues regarding linearity, robustness, specificity, selectivity and accuracy as well as influences of instrument specific parameters and the data processing and evaluation routines. This procedure was tested by the investigation of three different 5-model-compound mixtures. As a result of the round robin tests using the proposed protocol it was found that the maximum combined measurement uncertainty is 1.5% for a confidence interval of 95%. This applies both for the determination of molar ratios and of the amount fractions of the various components. Further, the validation was extended to purity determinations of substances as shown for 1,8-epoxy-p-menthane (cineole). PMID:15893442

Malz, F; Jancke, H

2005-08-10

128

NMR: concepts, methods and applications. 2. edition  

International Nuclear Information System (INIS)

Since its discovery in 1945, the nuclear magnetic resonance (NMR) has been the object of spectacular developments. These developments concern the structural study of more and more complex and bigger molecules and the production of images. One of the applications of image production is the NMR imaging which has a considerable impact in medicine. Taking into consideration the variety of its experimental and methodological aspects and the range of its applications which is still growing up, NMR has become an entire discipline. This second edition takes stock of the most recent methods and concepts of NMR (multi-pulse and multi-dimensional techniques, signal processing) but also of the more traditional aspects like the structure of spectra and the dynamical parameters. The basic knowledge is presented in an accessible style and the complementary knowledge (mathematics, quantum mechanics) can be found on the Internet. (J.S.)

129

Development of Halbach magnet for portable NMR device  

Energy Technology Data Exchange (ETDEWEB)

Nuclear magnetic resonance (NMR) has enormous potential for various applications in industry as the on-line or at-line test/control device of process environments. Advantage of NMR is its non-destructive nature, because it does not require the measurement probe to have a contact with the tested media. Despite of the recent progress in this direction, application of NMR in industry is still very limited. This is related to the technical and analytical complications of NMR as a method, and high cost of NMR analyzers available at the market. However in many applications, NMR is a very useful technique to test various products and to monitor quantitatively industrial processes. Fortunately usually there is no need in a high-field superconducting magnets to obtain the high-resolution spectra with the detailed information on chemical shifts and coupling-constant. NMR analyzers are designed to obtain the relaxation parameters by measuring the NMR spectra in the time domain rather than in frequency domain. Therefore it is possible to use small magnetic field (and low frequency of 2-60 MHz) in NMR systems, based on permanent magnet technology, which are specially designed for specific at-line and on-line process applications. In this work we present the permanent magnet system developed to use in the portative NMR devices. We discuss the experimental parameters of the designed Halbach magnet system and compare them with results of theoretical modelling.

Dogan, N; Topkaya, R; Subasi, H; Yerli, Y; Rameev, B, E-mail: ndogan@gyte.edu.t [Gebze Institute of Technology, 41400 Gebze/Kocaeli (Turkey)

2009-03-01

130

Liquid-Liquid extraction and NMR  

International Nuclear Information System (INIS)

This paper offers an overview of the possibilities for the use of NMR techniques in solvent extraction studies for new extraction systems (monoamides, malonamides and picolinamides) and tri-n-butylphosphate (TBP) properties investigations. We have used NMR spectroscopy with monoamides to identify the structural parameters that control monoamide selectivity and efficiency. Distances between the carbon atoms of the monoamide ligands and the lanthanides(lII) or actinides(IV) metallic centres were determined through the analysis of the 13C T1 NMR relaxation time data. The conformational data obtained by NMR measurements related to lanthanide nitrate monoamide solvates were then compared with the corresponding distribution coefficients. Dynamic information on the extractant were also obtained and gave an indication of the time scale of different motions in liquid phases as well as the influence of a metal ion in the media. From 1H, 2H and 13C NMR spectra analyses, extractants in organic phases show some weak interactions such as malonamide dimer formations. These were observed for diluted benzenic solutions but for more concentrated solutions, micellar formation were observed. This may explain: decantation problems and the large amount of extracted water observed. Nitric acid extraction mechanisms can be also determined by NMR. The case of the picolinamide extractants, analysed from 1H and 13C NMR from 1H and 13C NMR spectra is a good example. A relatively straightforward mechanism results of this and protonation sites are determined. 31P NMR was found useful for practical and basic research dealing with the hydrolytic and radiolytic degradations of the TBP : each organophosphorus TBP degradation product was identified and quantified. A chemical exchange between dibutylphosphoric acid (HDBP) and DBP:Zr(NO3)4 system was pointed out and allows us to understand the original Zr(IV) property that induces demixion of HDBP from aqueous nitric solutions. (authors)

131

Understanding NMR Spectroscopy  

Science.gov (United States)

This site provides links to a series of PDF files that represent chapters of an e-text on the basics of NMR. While many other textbooks on NMR are available, the chief merit of this one is that it has a nice chapter on the NMR instrumentation (ch. 5) which should be accessible to undergraduates. The text also provides a relatively mathematics-free or maybe more accurately Dirac bracket notation-free introduction to 1-D and 2-D (COSY and NOESY) experiments that would be appreciated by advanced undergraduates or beginning graduate students involved in undergraduate research experiences using NMR.

Keeler, James

2011-04-15

132

A method for determining NMR log signal intensity  

International Nuclear Information System (INIS)

NMR log signal is very weak and the signal intensity directly decides success or failure of sonde design. At the same time, the signal intensity renders parameters for electron circuit. Based on NMR theory and mutual inductance idea, the paper presents a new method for determining signal intensity that is important for sonde design and electron circuit design. (authors)

133

NMR Spectroscopy - Theory  

Science.gov (United States)

This web site begins with a simple quantum description of NMR and proceeds to introduce resonance absorption, relaxation, chemical shifts, and scalar couplings. This site will be useful for advanced undergraduate students needing a description of NMR that is more detailed than that given in most introductory Organic texts.

Lord, J. R.

2011-06-30

134

Lectures on pulsed NMR  

International Nuclear Information System (INIS)

These lectures discuss some recent developments in pulsed NMR, emphasizing fundamental principles with selected illustrative applications. Major topics covered include multiple-quantum spectroscopy, spin decoupling, the interaction of spins with a quantized field, adiabatic rapid passage, spin temperature and statistics of cross-polarization, coherent averaging, and zero field NMR. 32 refs., 56 figs

135

Lectures on pulsed NMR  

International Nuclear Information System (INIS)

These lectures discuss some recent developments in pulsed NMR, emphasizing fundamental principles with selected illustrative applications. Major topics covered include multiple-quantum spectroscopy, spin decoupling, the interaction of spins with a quantized field, adiabatic rapid passage, spin temperature and statistics of cross-polarization, coherent averaging, and zero field NMR. 55 figs

136

Optimization and practical implementation of ultrafast 2D NMR experiments  

Directory of Open Access Journals (Sweden)

Full Text Available Ultrafast 2D NMR is a powerful methodology that allows recording of a 2D NMR spectrum in a fraction of second. However, due to the numerous non-conventional parameters involved in this methodology its implementation is no trivial task. Here, an optimized experimental protocol is carefully described to ensure efficient implementation of ultrafast NMR. The ultrafast spectra resulting from this implementation are presented based on the example of two widely used 2D NMR experiments, COSY and HSQC, obtained in 0.2 s and 41 s, respectively.

Luiz H. K. Queiroz Júnior

2013-01-01

137

Optimization and practical implementation of ultrafast 2D NMR experiments  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Ultrafast 2D NMR is a powerful methodology that allows recording of a 2D NMR spectrum in a fraction of second. However, due to the numerous non-conventional parameters involved in this methodology its implementation is no trivial task. Here, an optimized experimental protocol is carefully described [...] to ensure efficient implementation of ultrafast NMR. The ultrafast spectra resulting from this implementation are presented based on the example of two widely used 2D NMR experiments, COSY and HSQC, obtained in 0.2 s and 41 s, respectively.

Luiz H. K., Queiroz Júnior; Antonio G., Ferreira; Patrick, Giraudeau.

138

Experimental studies on permeability by a pulsed NMR method  

International Nuclear Information System (INIS)

The experimental data on the determination of permeability of sandstones saturated with a fluid by pulsed nuclear magnetic resonance method (NMR) are presented. The modernization of a standard pulsed NMR spectrometer operating according to the spin echo method is briefly described. The data obtained make it possible to conclude the necessity of further development of theoretical representations on the relation between NMR parameters of a fluid contained in rock and rock permeability. In this case the increase of the accuracy determination of the rock permeability by pulsed NMR method is assumed

139

Basics of NMR  

Science.gov (United States)

Dr. Joseph Hornak of the Rochester Institute of Technology presents this high quality hypertextbook for in-depth coverage of the physics and technique behind Nuclear Magnetic Resonance (NMR) (For Dr. Hornak's Basics of MRI, see the August 4, 1999 Scout Report for Science & Engineering). The material is presented in a detailed and clear manner without over simplifying the concepts. Chapters include "The Mathematics of NMR," "Spin Physics," "NMR Spectroscopy," "Fourier Transforms," "Pulse Sequences," and much more. A chapter on "NMR Hardware" offers an overview of components (like the superconducting magnet and various coils) used in most NMR systems. The "Practical Considerations" chapter emphasizes spectroscopic techniques. With the screen split into two separate frames, explanatory graphics can be viewed alongside the text. A glossary and a list of symbols are also included in this carefully produced textbook.

Hornak, Joseph P.

140

NMR logging apparatus  

Energy Technology Data Exchange (ETDEWEB)

Technologies including NMR logging apparatus and methods are disclosed. Example NMR logging apparatus may include surface instrumentation and one or more downhole probes configured to fit within an earth borehole. The surface instrumentation may comprise a power amplifier, which may be coupled to the downhole probes via one or more transmission lines, and a controller configured to cause the power amplifier to generate a NMR activating pulse or sequence of pulses. Impedance matching means may be configured to match an output impedance of the power amplifier through a transmission line to a load impedance of a downhole probe. Methods may include deploying the various elements of disclosed NMR logging apparatus and using the apparatus to perform NMR measurements.

Walsh, David O; Turner, Peter

2014-05-27

 
 
 
 
141

Solid state NMR  

Energy Technology Data Exchange (ETDEWEB)

This series presents critical reviews of the present position and future trends in modern chemical research. Short and concise reports on chemistry. Each written by the world renowned experts. Still valid and useful after 5 or 10 years. More information as well as the electronic version of the whole content available at: springerlink.com. Dipolar Recoupling, by Niels Chr. Nielsen, Lasse A. Strassoe and Anders B. Nielsen. - Solid-State NMR Techniques for the Structural Determination of Amyloid Fibrils, by Jerry C. C. Chan. - Solid-State {sup 19}F-NMR of Peptides in Native Membranes, by Katja Koch, Sergii Afonin, Marco Ieronimo, Marina Berditsch and Anne S. Ulrich. - Probing Quadrupolar Nuclei by Solid-State NMR Spectroscopy: Recent Advances, by Christian Fernandez and Marek Pruski. - Solid State NMR of Porous Materials Zeolites and Related Materials, by Hubert Koller and Mark Weiss. - Solid-State NMR of Inorganic Semiconductors, by James P. Yesinowski.

Chan, Jerry C.C. (ed.) [National Taiwan Univ., Taipei (China). Dept. of Chemistry

2012-07-01

142

Solid state NMR  

International Nuclear Information System (INIS)

This series presents critical reviews of the present position and future trends in modern chemical research. Short and concise reports on chemistry. Each written by the world renowned experts. Still valid and useful after 5 or 10 years. More information as well as the electronic version of the whole content available at: springerlink.com. Dipolar Recoupling, by Niels Chr. Nielsen, Lasse A. Strassoe and Anders B. Nielsen. - Solid-State NMR Techniques for the Structural Determination of Amyloid Fibrils, by Jerry C. C. Chan. - Solid-State 19F-NMR of Peptides in Native Membranes, by Katja Koch, Sergii Afonin, Marco Ieronimo, Marina Berditsch and Anne S. Ulrich. - Probing Quadrupolar Nuclei by Solid-State NMR Spectroscopy: Recent Advances, by Christian Fernandez and Marek Pruski. - Solid State NMR of Porous Materials Zeolites and Related Materials, by Hubert Koller and Mark Weiss. - Solid-State NMR of Inorganic Semiconductors, by James P. Yesinowski.

143

A high-resolution technique for multidimensional NMR spectroscopy.  

Science.gov (United States)

In this paper, a scheme for estimating frequencies and damping factors of multidimensional nuclear magnetic resonance (NMR) data is presented, multidimensional NMR data can be modeled as the sum of several multidimensional damped sinusoids. The estimated frequencies and damping factors of multidimensional NMR data play important roles in determining protein structures. In this paper we present a high-resolution subspace method for estimating the parameters of NMR data. Unlike other methods, this algorithm makes full use of the rank-deficiency and Hankel properties of the prediction matrix composed of NMR data. Hence, it can estimate the signal parameters under low signal-to-noise ratio (SNR) by using a few data points. The effectiveness of the new algorithm is confirmed by computer simulations and it is tested by experimental data. PMID:9444842

Li, Y; Razavilar, J; Liu, K J

1998-01-01

144

A review of oxygen-17 solid-state NMR of organic materials--towards biological applications.  

Science.gov (United States)

17O solid state NMR of organic materials is developing rapidly. This article provides a snapshot of the current state of development of this field. The NMR techniques and enrichment protocols that are driving this progress are outlined. The (17)O parameters derived from solid-state NMR experiments are summarized and the structural sensitivity of the approach to effects such as hydrogen bonding highlighted. The prospects and challenges for (17)O solid-state NMR of biomolecules are discussed. PMID:15388187

Lemaître, V; Smith, M E; Watts, A

2004-01-01

145

NMR study of NpFeGa{sub 5}  

Energy Technology Data Exchange (ETDEWEB)

We report a {sup 69}Ga NMR study of the antiferromagnet NpFeGa{sub 5}. In the paramagnetic state, hyperfine parameters such as NMR shift, electric field gradient and hyperfine coupling constant have been determined for the two crystallographically inequivalent Ga sites. These parameters are found to have a similar magnitude to those of UNiGa{sub 5} and UPtGa{sub 5}.

Kambe, S. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan)]. E-mail: kambe@popsvr.tokai.jaeri.go.jp; Homma, Y. [IMR, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Tokunaga, Y. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Sakai, H. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Aoki, D. [IMR, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yamamoto, E. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Nakamura, A. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Shiokawa, Y. [IMR, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Walstedt, R.E. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan)

2005-04-30

146

?-NMR sample optimization  

CERN Document Server

During my summer student programme I was working on sample optimization for a new ?-NMR project at the ISOLDE facility. The ?-NMR technique is well-established in solid-state physics and just recently it is being introduced for applications in biochemistry and life sciences. The ?-NMR collaboration will be applying for beam time to the INTC committee in September for three nuclei: Cu, Zn and Mg. Sample optimization for Mg was already performed last year during the summer student programme. Therefore sample optimization for Cu and Zn had to be completed as well for the project proposal. My part in the project was to perform thorough literature research on techniques studying Cu and Zn complexes in native conditions, search for relevant binding candidates for Cu and Zn applicable for ß-NMR and eventually evaluate selected binding candidates using UV-VIS spectrometry.

Zakoucka, Eva

2013-01-01

147

Applications of NMR in biological metabolic research  

International Nuclear Information System (INIS)

The nuclear magnetic resonance has become a powerful means of studying biological metabolism in non-invasive and non-destructive way. Being used to study the metabolic processes of living system in normal physiological conditions as well as in molecular level, the method is better than other conventional approaches. Using important parameters such as NMR-chemical shifts, longitudinal relaxation time and transverse relaxation time, it is possible to probe the metabolic processes as well as conformation, concentration, transportation and distribution of reacting and resulting substances. The NMR spectroscopy of 1H, 31P and 13C nuclei has already been widely used in metabolic researches

148

NMR of peroxide borofluoric compounds. Hydroperoxofluoroborates  

International Nuclear Information System (INIS)

Using the method of 1H and 19F NMR reactions between sodium, potassium and ammonium hydroxotrifluoroborates and hydrogen peroxide are studied. Mono-, di-, and trihydroperoxofluoroborates, stable in solutions, have been found for the first time, their NMR parameters and rate constants of formation reactions being determined. The high yield of boron complexes (75%) in the first moment after MBF3OH dissolution in H2O2 solutions is used for their separation from the solution using the method of cation substitution with the formation of less soluble compounds

149

Renal transplant NMR  

International Nuclear Information System (INIS)

The preliminary results of NMR evaluation of renal transplants (Txs) are reported including correlation with nuclear medicine (NM) and ultrasound (US). Thirteen Txs (8 cadaver (Cd), 5 living related doner (LRD) in 13 patients (6M, 7F) ranging in age from 25-47 (x 35) were evaluated by NM (32), NMR (15) and US (5). Clinical diagnoses included: rejection (8), ATN (2), infarction (1), and normal (2). Of the 8 patients with rejection (5) Cd; 3 LRD) pathologic proof was obtained in 3. An experimental 0.12 T resistive magnet (GE) was used with a partial saturation technique with repetition time (TR) of 143 and 286 msec to provide T1 weighting. T2 weighted information was obtained with a spin echo technique with echo times (TE) of 20, 40, 60 and 80 msec. The NMR appearance of normal Txs consisted of a uniform signal intensity (Tx> pelvic musculature), well-defined internal architecture with good cortical medullary differentiation and normal appearing vessels. The NMR appearance of abnormal transplants consisted of a heterogeneous or overall decrease in signal intensity (kidney muscle) with poor cortical medullary differentiation with or without a halo of decreased signal intensity. Although NMR was able to differentiate normal from abnormal, it was unable to clearly discriminate between ATN and rejection. Advantages of NMR included the ability to demonstrate regional anatomy, vasculature, post operative fluid collections and hematomas, and associated avascular necrosis of the hips

150

Soils, Pores, and NMR  

Science.gov (United States)

Within Cluster A, Partial Project A1, the pore space exploration by means of Nuclear Magnetic Resonance (NMR) plays a central role. NMR is especially convenient since it probes directly the state and dynamics of the substance of interest: water. First, NMR is applied as relaxometry, where the degree of saturation but also the pore geometry controls the NMR signature of natural porous systems. Examples are presented where soil samples from the Selhausen, Merzenhausen (silt loams), and Kaldenkirchen (sandy loam) test sites are investigated by means of Fast Field Cycling Relaxometry at different degrees of saturation. From the change of the relaxation time distributions with decreasing water content and by comparison with conventional water retention curves we conclude that the fraction of immobile water is characterized by T1 low-field and ultra-fast pulse imaging. Also first results on the imaging of soil columns measured by SIP in Project A3 are given. Haber-Pohlmeier, S., S. Stapf, et al. (2010). "Waterflow Monitored by Tracer Transport in Natural Porous Media Using MRI." Vadose Zone J.: submitted. Haber-Pohlmeier, S., S. Stapf, et al. (2010). "Relaxation in a Natural soil: Comparison of Relaxometric Imaging, T1 - T2 Correlation and Fast-Field Cycling NMR." The Open Magnetic Resonance Journal: in print. Pohlmeier, A., S. Haber-Pohlmeier, et al. (2009). "A Fast Field Cycling NMR Relaxometry Study of Natural Soils." Vadose Zone J. 8: 735-742. Stingaciu, L. R., A. Pohlmeier, et al. (2009). "Characterization of unsaturated porous media by high-field and low-field NMR relaxometry." Water Resources Research 45: W08412

Pohlmeier, Andreas; Haber-Pohlmeier, Sabina; Haber, Agnes; Sucre, Oscar; Stingaciu, Laura; Stapf, Siegfried; Blümich, Bernhard

2010-05-01

151

Probing surface interactions by combining NMR cryoporometry and NMR relaxometry  

Science.gov (United States)

To further expand on the understanding of surface interactions at the liquid/solid interface on pore walls, the nuclear magnetic resonance (NMR) techniques of cryoporometry and relaxometry have been combined. The combination of these techniques allows variations in NMR relaxation parameters from pore surface to volume ratio changes and from surface interaction changes to be distinguished. By studying a range of sol-gel silicas from two different sources, it was noted that the relaxation time measurements were not consistent with the pore diameters determined by cryoporometry and N2 gas adsorption. Instead distinctly different relaxivity constants were determined for each absorbate in each of the two brands of silica. It was clear that the relaxation times were modified by more than just the pore geometry. Independent experiments on the two brands of silica suggested that the relaxometry results were heavily influenced by the concentration of paramagnetic relaxation centres in the silica gels. The strength of surface interaction, and hence surface affinity, was seen to depend on the liquid in the pores. Using this difference in surface affinities, binary mixtures of alkanes placed in sol-gel silicas were separated via preferential absorption and their components identified using cryoporometry, whereas the components could not be distinguished in the bulk liquid.

Mitchell, J.; Stark, S. C.; Strange, J. H.

2005-06-01

152

Earth’s field NMR flow meter: Preliminary quantitative measurements  

Science.gov (United States)

In this paper we demonstrate the use of Earth’s field NMR (EF NMR) combined with a pre-polarising permanent magnet for measuring fast fluid velocities. This time of flight measurement protocol has a considerable history in the literature; here we demonstrate that it is quantitative when employing the Earth’s magnetic field for signal detection. NMR signal intensities are measured as a function of flow rate (0-1 m/s) and separation distance between the permanent magnet and the EF NMR signal detection. These data are quantitatively described by a flow model, ultimately featuring no free parameters, that accounts for NMR signal modulation due to residence time inside the pre-polarising magnet, between the pre-polarising magnet and the detection RF coil and inside the detection coil respectively. The methodology is subsequently demonstrated with a metallic pipe in the pre-polarising region.

Fridjonsson, Einar O.; Stanwix, Paul L.; Johns, Michael L.

2014-08-01

153

Earth's field NMR flow meter: preliminary quantitative measurements.  

Science.gov (United States)

In this paper we demonstrate the use of Earth's field NMR (EF NMR) combined with a pre-polarising permanent magnet for measuring fast fluid velocities. This time of flight measurement protocol has a considerable history in the literature; here we demonstrate that it is quantitative when employing the Earth's magnetic field for signal detection. NMR signal intensities are measured as a function of flow rate (0-1m/s) and separation distance between the permanent magnet and the EF NMR signal detection. These data are quantitatively described by a flow model, ultimately featuring no free parameters, that accounts for NMR signal modulation due to residence time inside the pre-polarising magnet, between the pre-polarising magnet and the detection RF coil and inside the detection coil respectively. The methodology is subsequently demonstrated with a metallic pipe in the pre-polarising region. PMID:25033240

Fridjonsson, Einar O; Stanwix, Paul L; Johns, Michael L

2014-08-01

154

NMR studies of oriented molecules  

Energy Technology Data Exchange (ETDEWEB)

Deuterium and proton magnetic resonance are used in experiments on a number of compounds which either form liquid crystal mesophases themselves or are dissolved in a liquid crystal solvent. Proton multiple quantum NMR is used to simplify complicated spectra. The theory of nonselective multiple quantum NMR is briefly reviewed. Benzene dissolved in a liquid crystal are used to demonstrate several outcomes of the theory. Experimental studies include proton and deuterium single quantum (..delta..M = +-1) and proton multiple quantum spectra of several molecules which contain the biphenyl moiety. 4-Cyano-4'-n-pentyl-d/sub 11/-biphenyl (5CB-d/sub 11/) is studied as a pure compound in the nematic phase. The obtained chain order parameters and dipolar couplings agree closely with previous results. Models for the effective symmetry of the biphenyl group in 5CB-d/sub 11/ are tested against the experimental spectra. The dihedral angle, defined by the planes containing the rings of the biphenyl group, is found to be 30 +- 2/sup 0/ for 5DB-d/sub 11/. Experiments are also described for 4,4'-d/sub 2/-biphenyl, 4,4' - dibromo-biphenyl, and unsubstituted biphenyl.

Sinton, S.W.

1981-11-01

155

(29)Si NMR in LC-NMR analysis of silicones.  

Science.gov (United States)

It is demonstrated using a practical example that indirect detection of (29)Si NMR signals is sufficiently sensitive in LC-NMR stop-flow arrangement to analyze mixtures of siloxane polymers. New cryogenic probes with better signal-to-noise ratio will turn this version of LC-NMR into a routine method for analysis of siloxane polymers. PMID:16261506

Blechta, Vratislav; Sýkora, Jan; Hetflejs, Jirí; Sabata, Stanislav; Schraml, Jan

2006-01-01

156

Fluid-Rock Characterization and Interactions in NMR Well Logging  

Energy Technology Data Exchange (ETDEWEB)

The objective of this report is to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. The advances made in the understanding of NMR fluid properties are summarized in a chapter written for an AAPG book on NMR well logging. This includes live oils, viscous oils, natural gas mixtures, and the relation between relaxation time and diffusivity. Oil based drilling fluids can have an adverse effect on NMR well logging if it alters the wettability of the formation. The effect of various surfactants on wettability and surface relaxivity are evaluated for silica sand. The relation between the relaxation time and diffusivity distinguishes the response of brine, oil, and gas in a NMR well log. A new NMR pulse sequence in the presence of a field gradient and a new inversion technique enables the T{sub 2} and diffusivity distributions to be displayed as a two-dimensional map. The objectives of pore morphology and rock characterization are to identify vug connectivity by using X-ray CT scan, and to improve NMR permeability correlation. Improved estimation of permeability from NMR response is possible by using estimated tortuosity as a parameter to interpolate between two existing permeability models.

George J. Hirasaki; Kishore K. Mohanty

2005-09-05

157

Prediction of peak overlap in NMR spectra  

Energy Technology Data Exchange (ETDEWEB)

Peak overlap is one of the major factors complicating the analysis of biomolecular NMR spectra. We present a general method for predicting the extent of peak overlap in multidimensional NMR spectra and its validation using both, experimental data sets and Monte Carlo simulation. The method is based on knowledge of the magnetization transfer pathways of the NMR experiments and chemical shift statistics from the Biological Magnetic Resonance Data Bank. Assuming a normal distribution with characteristic mean value and standard deviation for the chemical shift of each observable atom, an analytic expression was derived for the expected overlap probability of the cross peaks. The analytical approach was verified to agree with the average peak overlap in a large number of individual peak lists simulated using the same chemical shift statistics. The method was applied to eight proteins, including an intrinsically disordered one, for which the prediction results could be compared with the actual overlap based on the experimentally measured chemical shifts. The extent of overlap predicted using only statistical chemical shift information was in good agreement with the overlap that was observed when the measured shifts were used in the virtual spectrum, except for the intrinsically disordered protein. Since the spectral complexity of a protein NMR spectrum is a crucial factor for protein structure determination, analytical overlap prediction can be used to identify potentially difficult proteins before conducting NMR experiments. Overlap predictions can be tailored to particular classes of proteins by preparing statistics from corresponding protein databases. The method is also suitable for optimizing recording parameters and labeling schemes for NMR experiments and improving the reliability of automated spectra analysis and protein structure determination.

Hefke, Frederik [Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance (Germany); Schmucki, Roland [F. Hoffmann-La Roche AG (Switzerland); Guentert, Peter, E-mail: guentert@em.uni-frankfurt.de [Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance (Germany)

2013-06-15

158

NMR contribution to the actinides chemistry in aqueous solution  

International Nuclear Information System (INIS)

Multi-nuclei NMR utilization, for actinides aqueous solutions studies, give data on the formed complexes. With the NMR parameters, such as chemical displacements, it is possible to accede to the complex structure, to the determination of the equilibrium constants and so to follow the whole chemical equilibriums occurring in aqueous solutions, with the mi-height width of the NMR signals: to the ligand-metal exchange speed, and with the Sz component of the total magnetization of the electronic spin: to some data on the actinides paramagnetic effects. (A.B.). 6 refs., 3 figs

159

On the use of ultracentrifugal devices for sedimented solute NMR  

Energy Technology Data Exchange (ETDEWEB)

We have recently proposed sedimented solute NMR (SedNMR) as a solid-state method to access biomolecules without the need of crystallization or other sample manipulation. The drawback of SedNMR is that samples are intrinsically diluted and this is detrimental for the signal intensity. Ultracentrifugal devices can be used to increase the amount of sample inside the rotor, overcoming the intrinsic sensitivity limitation of the method. We designed two different devices and we here report the directions for using such devices and the relevant equations for determining the parameters for sedimentation.

Bertini, Ivano, E-mail: ivanobertini@cerm.unifi.it [University of Florence, Center for Magnetic Resonance (CERM) (Italy); Engelke, Frank [Bruker Biospin GmbH (Germany); Gonnelli, Leonardo [University of Florence, Center for Magnetic Resonance (CERM) (Italy); Knott, Benno [Bruker Biospin GmbH (Germany); Luchinat, Claudio, E-mail: luchinat@cerm.unifi.it [University of Florence, Center for Magnetic Resonance (CERM) (Italy); Osen, David [Bruker Biospin GmbH (Germany); Ravera, Enrico [University of Florence, Center for Magnetic Resonance (CERM) (Italy)

2012-10-15

160

On the use of ultracentrifugal devices for sedimented solute NMR  

International Nuclear Information System (INIS)

We have recently proposed sedimented solute NMR (SedNMR) as a solid-state method to access biomolecules without the need of crystallization or other sample manipulation. The drawback of SedNMR is that samples are intrinsically diluted and this is detrimental for the signal intensity. Ultracentrifugal devices can be used to increase the amount of sample inside the rotor, overcoming the intrinsic sensitivity limitation of the method. We designed two different devices and we here report the directions for using such devices and the relevant equations for determining the parameters for sedimentation.

 
 
 
 
161

Fluid-Rock Characterization and Interactions in NMR Well Logging  

Energy Technology Data Exchange (ETDEWEB)

The objective of this project was to characterize the fluid properties and fluid-rock interactions which are needed for formation evaluation by NMR well logging. NMR well logging is finding wide use in formation evaluation. The formation parameters commonly estimated were porosity, permeability, and capillary bound water. Special cases include estimation of oil viscosity, residual oil saturation, location of oil/water contact, and interpretation on whether the hydrocarbon is oil or gas.

Hirasaki, George J.; Mohanty, Kishore K.

2003-02-10

162

Solid state NMR study of cumbaru flour  

International Nuclear Information System (INIS)

The polysaccharide obtained by seed of Dipteryx alata Vog, has been characterised by 13C solid state, using the basic routine techniques, like MAS and CPMAS and by the proton spin-lattice relaxation time in the rotating frame parameter (T1H?). Knowing that the chemical structure and molecular dynamic are extremely necessary route to obtain information on the polysaccharides, this work contributes to the classification of the seed containing in the cumbaru fruit to get response on its application. To obtain the initial responses for our purposes some solid state NMR techniques were chosen. The CPMAS 13C NMR spectrum of the polysaccharide was investigated to know if it has some crystallinity. The MAS 13C NMR spectrum showed the presence of domains with distinct molecular mobility, because these domains will differ basically in the distribution size and chain packing. The variable contact time experiment was used to analyse the distribution form of 13C decays, which give us more information about sample heterogeneity. The T1H?Hr values were obtained from the variable contact time and by delayed contact time experiment, because these parameter indicate the order of polysaccharides. From the values of this parameter, we found that this polysaccharide is completely non-ordered. (author)

163

A Review of the Principles and Applications of the NMR Technique for Near-Surface Characterization  

Science.gov (United States)

This paper presents a comprehensive review of the recent advances in nuclear magnetic resonance (NMR) measurements for near-surface characterization using laboratory, borehole, and field technologies. During the last decade, NMR has become increasingly popular in near-surface geophysics due to substantial improvements in instrumentation, data processing, forward modeling, inversion, and measurement techniques. This paper starts with a description of the principal theory and applications of NMR. It presents a basic overview of near-surface NMR theory in terms of its physical background and discusses how NMR relaxation times are related to different relaxation processes occurring in porous media. As a next step, the recent and seminal near-surface NMR developments at each scale are discussed, and the limitations and challenges of the measurement are examined. To represent the growth of applications of near-surface NMR, case studies in a variety of different near-surface environments are reviewed and, as examples, two recent case studies are discussed in detail. Finally, this review demonstrates that there is a need for continued research in near-surface NMR and highlights necessary directions for future research. These recommendations include improving the signal-to-noise ratio, reducing the effective measurement dead time, and improving production rate of surface NMR (SNMR), reducing the minimum echo time of borehole NMR (BNMR) measurements, improving petrophysical NMR models of hydraulic conductivity and vadose zone parameters, and understanding the scale dependency of NMR properties.

Behroozmand, Ahmad A.; Keating, Kristina; Auken, Esben

2014-09-01

164

Some exercises in quantitative NMR imaging  

International Nuclear Information System (INIS)

The articles represented in this thesis result from a series of investigations that evaluate the potential of NMR imaging as a quantitative research tool. In the first article the possible use of proton spin-lattice relaxation time T1 in tissue characterization, tumor recognition and monitoring tissue response to radiotherapy is explored. The next article addresses the question whether water proton spin-lattice relaxation curves of biological tissues are adequately described by a single time constant T1, and analyzes the implications of multi-exponentiality for quantitative NMR imaging. In the third article the use of NMR imaging as a quantitative research tool is discussed on the basis of phantom experiments. The fourth article describes a method which enables unambiguous retrieval of sign information in a set of magnetic resonance images of the inversion recovery type. The next article shows how this method can be adapted to allow accurate calculation of T1 pictures on a pixel-by-pixel basis. The sixth article, finally, describes a simulation procedure which enables a straightforward determination of NMR imaging pulse sequence parameters for optimal tissue contrast. (orig.)

165

Proton NMR imaging in experimental ischemic infarction  

International Nuclear Information System (INIS)

Proton nuclear magnetic resonance (NMR) images depict the distribution and concentration of mobile protons modified by the relaxation times T1 and T2. Using the steady-state-free-precession (SSFP) technique, serial coronal images were obtained sequentially over time in laboratory animals with experimental ischemic infarction. Image changes were evident as early as 2 hours after carotid artery ligation, and corresponded to areas of ischemic infarction noted pathologically. Resulting SSFP images in experimental stroke are contrasted to inversion-recovery NMR images in an illustrative patient with established cerebral infarction. Bulk T1 and T2 measurements were made in vitro in three groups of gerbils: normal, those with clinical evidence of infarction, and those clinically normal after carotid ligature. Infarcted hemispheres had significantly prolonged T1 and T2 (1.47 +/- .12 sec, 76.0 +/- 9.0 msec, respectively) when compared to the contralateral hemisphere (T1 . 1.28 +/- .05 sec, T2 . 58.7 +/- 3.9 msec) or to the other two groups. These data suggest that changes in NMR parameters occur and can be detected by NMR imaging as early as two hours after carotid artery ligation

166

Modeling NMR parameters by DFT methods as an aid to the conformational analysis of cis-fused 7a(8a)-methyl octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines.  

Science.gov (United States)

The energies of the preferred conformations of four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were investigated by DFT methods. Following geometry optimization at the B3LYP/6-31G(d,p) level, both the proton chemical shifts and the vicinal coupling constants between H-4a and the H-4 and H-5 protons were calculated at the B3LYP/cc-pVTZ level and compared to the previously experimentally measured values. The agreement between the calculated and the experimental chemical shifts was found to be good. Similarly, the agreement between the calculated and the experimental vicinal coupling constants was also found to be good, thus providing a methodology for determining the conformational equilibria of such systems that is comparable in many respects to experimental approaches such as variable-temperature NMR or to the use of model coupling constant values, when available, from analogous compounds. PMID:12683833

Tähtinen, Petri; Bagno, Alessandro; Klika, Karel D; Pihlaja, Kalevi

2003-04-16

167

NMR of buried interfaces  

International Nuclear Information System (INIS)

We employ Xe-NMR to investigate surface phenomena by adsorbing hyperpolarized 129Xe onto a helium-cooled single crystal and studying the electronic interactions of substrate and adsorbate. The high nuclear spin polarization of the adsorbed Xe-film could be transferred to buried interfaces within the substrate (which then would be accessible for further NMR experiments) via dipolar distant-field transfer. Such a transfer can be achieved by applying two rf-frequencies at the same time using a double resonant probe, integrated into an UHV system. Furthermore, an inhomogeneous magnetic structure of the Xe-film is needed, which could be provided by a geometrically structured sample in the ?m range. Here, we present the development of the double resonant probe and first experiments.

168

NMR of buried interfaces  

Energy Technology Data Exchange (ETDEWEB)

We employ Xe-NMR to investigate surface phenomena by adsorbing hyperpolarized {sup 129}Xe onto a helium-cooled single crystal and studying the electronic interactions of substrate and adsorbate. The high nuclear spin polarization of the adsorbed Xe-film could be transferred to buried interfaces within the substrate (which then would be accessible for further NMR experiments) via dipolar distant-field transfer. Such a transfer can be achieved by applying two rf-frequencies at the same time using a double resonant probe, integrated into an UHV system. Furthermore, an inhomogeneous magnetic structure of the Xe-film is needed, which could be provided by a geometrically structured sample in the {mu}m range. Here, we present the development of the double resonant probe and first experiments.

Schmitt, Anuschka; Buschmann, Matthias; Kastelik, Richard; Potzuweit, Alexander; Jaensch, Heinz [Fachbereich Physik, Philipps-Universitaet Marburg, D-35032 Marburg (Germany)

2011-07-01

169

NMR, water and plants  

International Nuclear Information System (INIS)

This thesis describes the application of a non-destructive pulsed proton NMR method mainly to measure water transport in the xylem vessels of plant stems and in some model systems. The results are equally well applicable to liquid flow in other biological objects than plants, e.g. flow of blood and other body fluids in human and animals. The method is based on a pulse sequence of equidistant ? pulses in combination with a linear magnetic field gradient. (Auth.)

170

NMR chemical shift imaging  

International Nuclear Information System (INIS)

Chemical shift imaging combines the spatial information provided by a conventional nuclear magnetic resonance (NMR) image with the chemical shift spectral information provided by NMR spectroscopy. In order to preserve the chemical shift information and provide a spatial map simultaneously, new NMR imaging methods have been developed. In general, these methods have taken two forms: (a) three-dimensional techniques which add an extra axis of information--chemical shift spectral data--to a planar (2-D) image; and (b) two-dimensional techniques which, in certain circumstances, allow one to use techniques only slightly different from conventional ones to obtain high-resolution images of particular chemical shift species. Each of these methods offers unique challenges to the imager, as well as special advantages. In particular, three-dimensional techniques offer the opportunity to visualize the chemical shift spectra explicitly, while two-dimensional techniques allow for rapid imaging times and high spatial resolution. Most of the work in chemical shift imaging to date has focused on 1H, 31P, and 23Na. The high concentration of water and lipids in biological tissue has made the proton especially amenable to study, and the ability to sample other proton-containing compounds (such as lactate) in the face of high concentration lipid and water is now being explored. The potential use of chemical shift imaging techniques in the research and cliniaging techniques in the research and clinical settings is currently under investigation. 60 references

171

Nitrogen NMR spectroscopy  

International Nuclear Information System (INIS)

This report provides a full survey of the nitrogen NMR literature that has been published from late 1980 to the end of 1983. During this time the applications of nitrogen NMR have continued to increase and the number of publications relating to it has burgeoned. Advances have been made in both the experimental and theoretical aspects of the subject. Both the /sup 14/N and /sup 15/N isotopes are commonly studied; the former in situations where either the quadrupolar relaxation rate is small, in order to provide relatively narrow signals and thus reliable nuclear shielding results, or where the factors responsible for quadrupole interactions are the main interest of the investigation. The /sup 15/N nucleus, of lower natural abundance, has sharper NMR signals which are capable of yielding nuclear shielding, spin-spin coupling and relaxation data. The less efficient nuclear relaxation processes, such as those arising from dipole-dipole, chemical shielding anisotropy or spin-rotation interactions, normally control /sup 15/N relaxation

172

Applications of Unilateral NMR in Nondestructive Testing  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Für die Messung mit NMR-Spektroskopie wird eine Probe in der Regel vorbereitet, gemessen und anschließend entsorgt. In dem Fall, dass Probe nicht zerstört werden darf, gewinnt die Relaxationsanalyse bei niedrigen Feldern, i.e. die niedrig-auflösende NMR, an Bedeutung. Für große Proben ist die unilaterale NMR mit inhomogenen Feldern die Methode der Wahl. Unilaterale NMR oder inside-out NMR ist eine etablierte Technik der niedrig-auflösende NMR. Die NMR-MOUSE(Mobile Universal Surface Exp...

Sharma, Shatrughan

2004-01-01

173

NMR in biology and medicine  

International Nuclear Information System (INIS)

This volume explores the applications of NMR in basic biological research and in clinical diagnosis. The contributors highlight the capabilities of NMR as a tool for studying living organisms at the molecular and cellular levels and detecting abnormalities in various organ systems. Included are solid-state and high-resolution NMR studies of the molecular structure and dynamic interactions of lipids, proteins, and nucleic acids. The latest developments in NMR zeugmatographic imaging and in musculoskeletal and cardiovascular magnetic resonance imaging are detailed. Concluding chapters review the uses of in vivo NMR spectroscopy to study energy metabolism and cellular biochemistry. Emphasis is placed on in vivo NMR spectroscopy studies that elucidate normal metabolic functions and their pathological disturbances

174

Study of a Conformational Equilibrium of Lisinopril by HPLC, NMR, and DFT  

Science.gov (United States)

The isomerization of lisinopril has been investigated using chromatographic, NMR spectroscopic, and theoretical calculations. The NMR data, particularly the NOEDIFF experiments, show that the major species that was eluted first is the trans form. The proportion was 77% and 23% for the trans and cis, respectively. The thermodynamic parameters (?H, ?S, and ?G) were determined by varying the temperature in the NMR experiments. The interpretations of the experimental data were further supported by DFT/B3LYP calculations. PMID:24707291

Bouabdallah, Sondes; Ben Dhia, Med Thaieb; Driss, Med Rida

2014-01-01

175

DNA oligonucleotide conformations: high resolution NMR studies  

International Nuclear Information System (INIS)

The present work describes a DNA double-helix model, which is well comparable with the models derived from fibre-diffraction studies. The model has a mononucleotide repeat with torsion angles in accordance with average geometries as derived from 1H NMR studies. Special attention was paid to reduce the number of short H-H nonbonding contacts, which are abundantly present in the 'classical' fibre-diffraction models. Chapter 3 describes the first complete assignment of a 1H NMR spectrum of a DNA tetramer, d(TAAT). Preliminary conformational data derived from the spectral parameters recorded at 27 0C are given. A more detailed analysis employing temperature-dependence studies is given in Chapter 4. (Auth.)

176

Some nitrogen-14 NMR studies in solids  

International Nuclear Information System (INIS)

The first order quadrupolar perturbation of the 14N NMR spectrum yields information regarding the static and dynamic properties of the surrounding electronic environment. Signal to noise problems caused by long 14N longitudinal relaxation times (T1) and small equilibrium polarizations are reduced by rotating frame cross polarization (CP) experiments between 14N and 1H. Using quadrupolar echo and CP techniques, the 14N quadrupolar coupling constants (e2qQ/h) and asymmetry parameters (eta) have been obtained for a variety of tetraalkylammonium compounds by observation of their quadrupolar powder patterns at various temperatures. For choline chloride and iodide the 14N NMR powder patterns exhibit the effects of anisotropic molecular motion, while choline bromide spectra show no such effects

177

Some nitrogen-14 NMR studies in solids  

Energy Technology Data Exchange (ETDEWEB)

The first order quadrupolar perturbation of the /sup 14/N NMR spectrum yields information regarding the static and dynamic properties of the surrounding electronic environment. Signal to noise problems caused by long /sup 14/N longitudinal relaxation times (T/sub 1/) and small equilibrium polarizations are reduced by rotating frame cross polarization (CP) experiments between /sup 14/N and /sup 1/H. Using quadrupolar echo and CP techniques, the /sup 14/N quadrupolar coupling constants (e/sup 2/qQ/h) and asymmetry parameters (eta) have been obtained for a variety of tetraalkylammonium compounds by observation of their quadrupolar powder patterns at various temperatures. For choline chloride and iodide the /sup 14/N NMR powder patterns exhibit the effects of anisotropic molecular motion, while choline bromide spectra show no such effects.

Pratum, T.K.

1983-11-01

178

Summary of Miniature NMR Development  

International Nuclear Information System (INIS)

The effort in this project has been in 3 distinct directions: (1) First, they focused on development of miniature microfabricated micro-coil NMR detectors with maximum Signal-to-Noise (SNR) ratio. (2) Secondly, they focused on design of miniature micro-coil NMR detectors that have minimal effect on the NMR spectrum distortions. (3) Lastly they focused on the development of a permanent magnet capable of generating fields on the order of 1 Tesla with better than 10 ppm uniformity

179

NMR and nuclear fuel reprocessing  

International Nuclear Information System (INIS)

31P NMR is useful for the study of the hydrolytic and radiolytic degradation of tributylphosphate (TBP), extractant used for nuclear fuel reprocessing. Each degradation product can be easily identified and measured. NMR can also be used to study the behaviour of technetium, (99Tc), a fission product which able to cause problems in the implementation of the process. N, N-dialkylamides are alternative extractants to TBP for fuel reprocessing. Their extracting properties can also be studied using NMR. An NMR conformational analysis helps us to understand the behaviour of these new molecules. (authors). 5 refs., 3 figs., 1 tab

180

NMR at low magnetic fields  

Science.gov (United States)

NMR provides outstanding information in chemistry and in medicine. But the equipment is expensive as high-field magnets are employed. Low-field NMR works with inexpensive permanent magnets. Until recently these did not provide fields sufficiently homogeneous for spectroscopy and were mostly used for relaxation measurements. Relaxation can also be measured outside the magnet, and small mobile NMR devices have been developed for non-destructive testing of large objects. Today small stray-field magnets and small magnets with homogeneous fields are available for relaxation analysis, imaging, and spectroscopy. Their availability is believed to be essential for shifting NMR analysis from a specialist's tool to a convenience tool.

Blümich, Bernhard; Casanova, Federico; Appelt, Stephan

2009-08-01

 
 
 
 
181

Transformer-coupled NMR probe  

Science.gov (United States)

In this study, we propose an NMR probe circuit that uses a transformer with a ferromagnetic core for impedance matching. The ferromagnetic core provides a strong but confined coupling that result in efficient energy transfer between the sample coil and NMR spectrometer, while not disturbing the B1 field generated by the sample coil. We built a transformer-coupled NMR probe and found that it offers comparable performance (loss low-field mobile NMR applications of multi-frequency operation, such as imaging, relaxation, and diffusion measurements, as well as NQR.

Utsuzawa, Shin; Mandal, Soumyajit; Song, Yi-Qiao

2012-03-01

182

Phenomenological simulation and density functional theory prediction of 57 Fe Mössbauer parameters: application to magnetically coupled diiron proteins  

Science.gov (United States)

The use of phenomenological spin Hamiltonians and of spin density functional theory for the analysis and interpretation of Mössbauer spectra of antiferromagnetic or ferromagnetic diiron centers is briefly discussed. The spectroscopic parameters of the hydroxylase component of methane monooxygenase (MMOH), an enzyme that catalyzes the conversion of methane to methanol, have been studied. In its reduced diferrous state (MMOH Red ) the enzyme displays 57Fe Mössbauer and EPR parameters characteristic of two ferromagnetically coupled high spin ferrous ions. However, Mössbauer spectra recorded for MMOH Red from two different bacteria, Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b, display slightly different electric quadrupole splittings (? E Q ) in apparent contradiction to their essentially identical active site crystallographic structures and biochemical functions. Herein, the Mössbauer spectral parameters of MMOH Red have been predicted and studied via spin density functional theory. The somewhat different ? E Q recorded for the two bacteria have been traced to the relative position of an essentially unbound water molecule within their diiron active sites. It is shown that the presence or absence of the unbound water molecule mainly affects the electric field gradient at only one iron ion of the binuclear active sites.

Rodriguez, Jorge H.

2013-04-01

183

Phenomenological simulation and density functional theory prediction of {sup 57}Fe Moessbauer parameters: application to magnetically coupled diiron proteins  

Energy Technology Data Exchange (ETDEWEB)

The use of phenomenological spin Hamiltonians and of spin density functional theory for the analysis and interpretation of Moessbauer spectra of antiferromagnetic or ferromagnetic diiron centers is briefly discussed. The spectroscopic parameters of the hydroxylase component of methane monooxygenase (MMOH), an enzyme that catalyzes the conversion of methane to methanol, have been studied. In its reduced diferrous state (MMOH{sub Red}) the enzyme displays {sup 57}Fe Moessbauer and EPR parameters characteristic of two ferromagnetically coupled high spin ferrous ions. However, Moessbauer spectra recorded for MMOH{sub Red} from two different bacteria, Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b, display slightly different electric quadrupole splittings ({Delta}E{sub Q}) in apparent contradiction to their essentially identical active site crystallographic structures and biochemical functions. Herein, the Moessbauer spectral parameters of MMOH{sub Red} have been predicted and studied via spin density functional theory. The somewhat different {Delta}E{sub Q} recorded for the two bacteria have been traced to the relative position of an essentially unbound water molecule within their diiron active sites. It is shown that the presence or absence of the unbound water molecule mainly affects the electric field gradient at only one iron ion of the binuclear active sites.

Rodriguez, Jorge H., E-mail: jhrodrig@purdue.edu [Purdue University, Department of Physics (United States)

2013-04-15

184

A pulsed NMR spectrometer  

International Nuclear Information System (INIS)

A pulsed NMR spectrometer working at 12.4 MHz constructed in the laboratory is described. The spectrometer produces phase coherent rf pulses of amplitude 300 volts peak-to-peak. Solid state devices such as transistors and integrated circuits have been used in the construction of the spectrometer. A digital double box-car signal averager developed in the laboratory has been employed in this spectrometer for data processing. Using this spectrometer preliminary measurements on spin-lattice relaxation times have been made in water. (author)

185

NMR Spectroscopy in Ionic Liquds  

Science.gov (United States)

Today, NMR spectroscopy is the most important analytical tool for synthetically working chemists. This review describes the development of NMR spectroscopic methods for use in ionic liquid media and the state-of-the art in terms of routine analytics as well as modern advanced techniques.

Giernoth, Ralf

186

Nuclear magnetic resonance (NMR) tomography  

International Nuclear Information System (INIS)

A brief survey of the working principle of the NMR technique in diagnostical medicine is given. Its clinical usefulness for locating tumors, diagnosing various other diseases, such as some mental illnesses and multiple sclerosis, and its possibilities for studying biochemical processes in vivo are mentioned. The price of NMR image scanners and the problems of the strong magnetic field around the machines are mentioned

187

NMR imaging of the kidney  

International Nuclear Information System (INIS)

NMR imaging was performed in 18 patients suffering from various renal disorders. 2 scanners were used, a 0.14T resistive prototype system and the superconducting Gyroscan S5. NMR imaging proved to be a very sensitive technique. Tumours as small as 5-10 mm were detected. Solid tumours and cysts could be distinguished. As a result of the excellent contrast resolution and tissue differentiation NMR imaging appears to be very accurate in the staging of renal cell carcinoma. Blood vessels within a tumour may be visible as little black dots. Because of their short T1 hemorrhagic cysts can be differentiated from simple cysts. Further prospective follow-up studies are required before a definite statement can be made as to the value of NMR imaging in diffuse parenchymal disease. Calcifications were not detected. NMR imaging does not seem to be any more specific as to tissue characterisation than other imaging modalities

188

Fundamentals of Protein NMR Spectroscopy  

CERN Document Server

NMR spectroscopy has proven to be a powerful technique to study the structure and dynamics of biological macromolecules. Fundamentals of Protein NMR Spectroscopy is a comprehensive textbook that guides the reader from a basic understanding of the phenomenological properties of magnetic resonance to the application and interpretation of modern multi-dimensional NMR experiments on 15N/13C-labeled proteins. Beginning with elementary quantum mechanics, a set of practical rules is presented and used to describe many commonly employed multi-dimensional, multi-nuclear NMR pulse sequences. A modular analysis of NMR pulse sequence building blocks also provides a basis for understanding and developing novel pulse programs. This text not only covers topics from chemical shift assignment to protein structure refinement, as well as the analysis of protein dynamics and chemical kinetics, but also provides a practical guide to many aspects of modern spectrometer hardware, sample preparation, experimental set-up, and data pr...

Rule, Gordon S

2006-01-01

189

Structural Biology: Practical NMR Applications  

CERN Document Server

This textbook begins with an overview of NMR development and applications in biological systems. It describes recent developments in instrument hardware and methodology. Chapters highlight the scope and limitation of NMR methods. While detailed math and quantum mechanics dealing with NMR theory have been addressed in several well-known NMR volumes, chapter two of this volume illustrates the fundamental principles and concepts of NMR spectroscopy in a more descriptive manner. Topics such as instrument setup, data acquisition, and data processing using a variety of offline software are discussed. Chapters further discuss several routine stategies for preparing samples, especially for macromolecules and complexes. The target market for such a volume includes researchers in the field of biochemistry, chemistry, structural biology and biophysics.

Teng, Quincy

2005-01-01

190

NMR of bent-core nematogens: a mini-review.  

Science.gov (United States)

This review focuses on two of our studied bent-core liquid crystals 2-methyl-3-[4-(4-octylbenzoyloxy)-benzylidene]-amino-benzoic acid 4-(4-dodecylphenylazo)-phenyl ester A131, and a shape-persistent fluorenone mesogen, F1a by means of temperature-dependent (13) C NMR spectra and deuterium NMR spectra, respectively. Orientational order parameters, molecular packing, and/or conformations in the nematic phases or nematic glass can be extracted from the observed NMR spectra. These will be discussed in terms of certain motional models. In particular, F1a has been found to form a biaxial nematic glass. The derived orientational order parameters would put the biaxial system of phase symmetry lower than orthorhombic. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24975632

Figueirinhas, João L; Dong, Ronald Y

2014-10-01

191

Protein NMR Structures Refined without NOE Data.  

Science.gov (United States)

The refinement of low-quality structures is an important challenge in protein structure prediction. Many studies have been conducted on protein structure refinement; the refinement of structures derived from NMR spectroscopy has been especially intensively studied. In this study, we generated flat-bottom distance potential instead of NOE data because NOE data have ambiguity and uncertainty. The potential was derived from distance information from given structures and prevented structural dislocation during the refinement process. A simulated annealing protocol was used to minimize the potential energy of the structure. The protocol was tested on 134 NMR structures in the Protein Data Bank (PDB) that also have X-ray structures. Among them, 50 structures were used as a training set to find the optimal "width" parameter in the flat-bottom distance potential functions. In the validation set (the other 84 structures), most of the 12 quality assessment scores of the refined structures were significantly improved (total score increased from 1.215 to 2.044). Moreover, the secondary structure similarity of the refined structure was improved over that of the original structure. Finally, we demonstrate that the combination of two energy potentials, statistical torsion angle potential (STAP) and the flat-bottom distance potential, can drive the refinement of NMR structures. PMID:25279564

Ryu, Hyojung; Kim, Tae-Rae; Ahn, SeonJoo; Ji, Sunyoung; Lee, Jinhyuk

2014-01-01

192

Statistical filtering for NMR based structure generation  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract The constitutional assignment of natural products by NMR spectroscopy is usually based on 2D NMR experiments like COSY, HSQC, and HMBC. The difficulty of a structure elucidation problem depends more on the type of the investigated molecule than on its size. Saturated compounds can usually be assigned unambiguously by hand using only COSY and 13C-HMBC data, whereas condensed heterocycles are problematic due to their lack of protons that could show interatomic connectivities. Different computer programs were developed to aid in the structural assignment process, one of them COCON. In the case of unsaturated and substituted molecules structure generators frequently will generate a very large number of possible solutions. This article presents a "statistical filter" for the reduction of the number of results. The filter works by generating 3D conformations using smi23d, a simple MD approach. All molecules for which the generation of constitutional restraints failed were eliminated from the result set. Some structural elements removed by the statistical filter were analyzed and checked against Beilstein. The automatic removal of molecules for which no MD parameter set could be created was included into WEBCOCON. The effect of this filter varies in dependence of the NMR data set used, but in no case the correct constitution was removed from the resulting set.

Junker Jochen

2011-08-01

193

Introduction to the conformational investigation of peptides and proteins by using two-dimensional proton NMR experiments  

International Nuclear Information System (INIS)

This report presents the elementary bases for an initiation to the conformational study of peptides and proteins by using two-dimensional proton NMR experiments. First, some general features of protein structures are summarized. A second chapter is devoted to the basic NMR experiments and to the spectral parameters which provide a structural information. This description is illustrated by NMR spectra of peptides. The third chapter concerns the most standard two-dimensional proton NMR experiments and their use for a conformational study of peptides and proteins. Lastly, an example of NMR structural investigation of a peptide is reported

194

Identification and MS-assisted interpretation of genetically influenced NMR signals in human plasma.  

Science.gov (United States)

Nuclear magnetic resonance spectroscopy (NMR) provides robust readouts of many metabolic parameters in one experiment. However, identification of clinically relevant markers in (1)H NMR spectra is a major challenge. Association of NMR-derived quantities with genetic variants can uncover biologically relevant metabolic traits. Using NMR data of plasma samples from 1,757 individuals from the KORA study together with 655,658 genetic variants, we show that ratios between NMR intensities at two chemical shift positions can provide informative and robust biomarkers. We report seven loci of genetic association with NMR-derived traits (APOA1, CETP, CPS1, GCKR, FADS1, LIPC, PYROXD2) and characterize these traits biochemically using mass spectrometry. These ratios may now be used in clinical studies. PMID:23414815

Raffler, Johannes; Römisch-Margl, Werner; Petersen, Ann-Kristin; Pagel, Philipp; Blöchl, Florian; Hengstenberg, Christian; Illig, Thomas; Meisinger, Christa; Stark, Klaus; Wichmann, H-Erich; Adamski, Jerzy; Gieger, Christian; Kastenmüller, Gabi; Suhre, Karsten

2013-01-01

195

Quantitative calibration of radiofrequency NMR Stark effects.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) Stark responses can occur in quadrupolar nuclei for an electric field oscillating at twice the usual NMR frequency (2?(0)). Calibration of responses to an applied E field is needed to establish nuclear spins as probes of native E fields within material and molecular systems. We present an improved approach and apparatus for accurate measurement of quadrupolar Stark effects. Updated values of C(14) (the response parameter in cubic crystals) were obtained for both (69)Ga and (75)As in GaAs. Keys to improvement include a modified implementation of voltage dividers to assess the 2?(0) amplitude, |E|, and the stabilization of divider response by reduction of stray couplings in 2?(0) circuitry. Finally, accuracy was enhanced by filtering sets of |E| through a linear response function that we established for the radiofrequency amplifier. Our approach is verified by two types of spectral results. Steady-state 2?(0) excitation to presaturate NMR spectra yielded C(14) = (2.59 ± 0.06) × 10(12) m(-1) for (69)Ga at room-temperature and 14.1 T. For (75)As, we obtained (3.1 ± 0.1) × 10(12) m(-1). Both values reconcile with earlier results from 77 K and below 1 T, whereas current experiments are at room temperature and 14.1 T. Finally, we present results where few-microsecond pulses of the 2?(0) field induced small (tens of Hz) changes in high-resolution NMR line shapes. There too, spectra collected vs |E| agree with the model for response, further establishing the validity of our protocols to specify |E|. PMID:22047309

Tarasek, Matthew R; Kempf, James G

2011-10-01

196

Flow units from integrated WFT and NMR data  

Energy Technology Data Exchange (ETDEWEB)

Reliable and continuous permeability profiles are vital as both hard and soft data required for delineating reservoir architecture. They can improve the vertical resolution of seismic data, well-to-well stratigraphic correlations, and kriging between the well locations. In conditional simulations, permeability profiles are imposed as the conditioning data. Variograms, covariance functions and other geostatistical indicators are more reliable when based on good quality permeability data. Nuclear Magnetic Resonance (NMR) logging and Wireline Formation Tests (WFT) separately generate a wealth of information, and their synthesis extends the value of this information further by providing continuous and accurate permeability profiles without increasing the cost. NMR and WFT data present a unique combination because WFTs provide discrete, in situ permeability based on fluid-flow, whilst NMR responds to the fluids in the pore space and yields effective porosity, pore-size distribution, bound and moveable fluid saturations, and permeability. The NMR permeability is derived from the T{sub 2}-distribution data. Several equations have been proposed to transform T{sub 2} data to permeability. Regardless of the transform model used, the NMR-derived permeabilities depend on interpretation parameters that may be rock specific. The objective of this study is to integrate WFT permeabilities with NMR-derived, T{sub 2} distribution-based permeabilities and thereby arrive at core quality, continuously measured permeability profiles. We outlined the procedures to integrate NMR and WFT data and applied the procedure to a field case. Finally, this study advocates the use of hydraulic unit concepts to extend the WFT-NMR derived, core quality permeabilities to uncored intervals or uncored wells.

Kasap, E.; Altunbay, M.; Georgi, D.

1997-08-01

197

NMR-tomography of the heart  

International Nuclear Information System (INIS)

The NMR-tomography as a non-invasive imaging process is examined regarding to the value to answer clinical issues. This method allows an evaluation of qualitative, quantitative, morphological and functional parameters. The diagnostic use on the heart shows early myocardial changes, thrombosis, changes in the dynamics of the left ventricle (EDV, ESV, EF), the quantitative wall movement and the blood flow in a shunt defect. The placed value of echocardiography, myocardial scintigraphy and coronary angiography in the diagnosis of acquired valvular heart disease, myocardial perfusion and coronary heart disease is not lowered by the above mentioned method. (orig.)

198

APSY-NMR with proteins: practical aspects and backbone assignment  

International Nuclear Information System (INIS)

Automated projection spectroscopy (APSY) is an NMR technique for the recording of discrete sets of projection spectra from higher-dimensional NMR experiments, with automatic identification of the multidimensional chemical shift correlations by the dedicated algorithm GAPRO. This paper presents technical details for optimizing the set-up and the analysis of APSY-NMR experiments with proteins. Since experience so far indicates that the sensitivity for signal detection may become the principal limiting factor for applications with larger proteins or more dilute samples, we performed an APSY-NMR experiment at the limit of sensitivity, and then investigated the effects of varying selected experimental parameters. To obtain the desired reference data, a 4D APSY-HNCOCA experiment with a 12-kDa protein was recorded in 13 min. Based on the analysis of this data set and on general considerations, expressions for the sensitivity of APSY-NMR experiments have been generated to guide the selection of the projection angles, the calculation of the sweep widths, and the choice of other acquisition and processing parameters. In addition, a new peak picking routine and a new validation tool for the final result of the GAPRO spectral analysis are introduced. In continuation of previous reports on the use of APSY-NMR for sequence-specific resonance assignment of proteins, we present the results of a systematic search for suitable combinations of a minimal number of four- and five-dimensional APSY-NMR experiments that can provide the input for algorithms that generate automated protein backbone assignments

199

Two dimensional solid state NMR  

International Nuclear Information System (INIS)

This thesis illustrates, by discussing some existing and newly developed 2D solid state experiments, that two-dimensional NMR of solids is a useful and important extension of NMR techniques. Chapter 1 gives an overview of spin interactions and averaging techniques important in solid state NMR. As 2D NMR is already an established technique in solutions, only the basics of two dimensional NMR are presented in chapter 2, with an emphasis on the aspects important for solid spectra. The following chapters discuss the theoretical background and applications of specific 2D solid state experiments. An application of 2D-J resolved NMR, analogous to J-resolved spectroscopy in solutions, to natural rubber is given in chapter 3. In chapter 4 the anisotropic chemical shift is mapped out against the heteronuclear dipolar interaction to obtain information about the orientation of the shielding tensor in poly-(oxymethylene). Chapter 5 concentrates on the study of super-slow molecular motions in polymers using a variant of the 2D exchange experiment developed by us. Finally chapter 6 discusses a new experiment, 2D nutation NMR, which makes it possible to study the quadrupole interaction of half-integer spins. 230 refs.; 48 figs.; 8 tabs

200

Carbon-13 NMR studies of liquid crystals  

International Nuclear Information System (INIS)

High resolution, proton decoupled 13C nmr are observed for a series of neat nematic liquid crystals, the p-alkoxyazoxybenzenes, and a smectic-A liquid crystal, diethylazoxydibenzoate in a magnetic field of 23 kG. The (uniaxial) order parameters S = less than P2(costheta) greater than are found to be about 0.4 and 0.9 for the nematic and smectic-A phase respectively at the clearing points. The order parameter increases with decreasing temperature in the nematic phase but is constant, or nearly so, with temperature in the smectic-A phase. In the nematic series studied, the ordering exhibits an even-odd alternation along the series and qualitative agreement with a recent theory due to Marcelja is found. In both phases, the spectra show that the molecule rotates rapidly about its long axis. Tentative conclusions about molecular conformational motion and 14N spin relaxation are presented for both nematic and smectic-A phases. In the smectic-A phase, the sample is rotated about an axis perpendicular to H0 and the resulting spectra are dicusssed. The theory of observed chemical shifts in liquid crystals is discussed and equations are derived which relate the nmr spectra of liquid-crystals to the order parameters. A model for the smectic-C phase due to Luz and Meiboom and Doane is described and lineshapes are determined on the basis of this model for special cases. The dependence of the order parameters on the molecular potential which give rise to the various degrees of order in the different liquid crystalline phases is examined. To a good approximation the functional dependence of the order parameters on the molecular potential is shown to be a simple one in the limit of small tilt angle in the smectic-C phase

 
 
 
 
201

Optimal strategies for obtaining the minimal NMR data set  

International Nuclear Information System (INIS)

The NMR image is dependent on multiple tissue parameters: relaxation times T1 and T2, hydrogen density and flow. A minimal data set allows for the calculation of these fundamental parameters with sufficient accuracy to be diagnostically useful. Factors contributing to the choice of this data set are presented. This minimal set allows the calculation of late echo images data accumulated at short values of TE with excellent visualization of pathology

202

Spin Hamiltonian of the Highly Frustrated Gd3Ga5O12 Garnet Antiferromagnet  

CERN Document Server

Gadolinium Gallium Garnet (GGG) is a fascinating magnetic material that displays an ordered phase in an applied magnetic field, but lacks long-range order and shows spin glass behavior in zero field. We investigate GGG in the zero field regime using a variational mean-field theory approach. We reproduce the spin liquid like correlations and the positions of sharp peaks seen in powder neutron diffraction measurements on GGG. Contrary to the current belief, our results speak in favor of a scenario where GGG is on the verge of developing true conventional long-range magnetic order in zero magnetic field.

Yavorskii, T; Gingras, M J P; Yavors'kii, Taras; Enjalran, Matthew; Gingras, Michel J.P.

2005-01-01

203

Understanding Visual Map Formation through Vortex Dynamics of Spin Hamiltonian Models  

Science.gov (United States)

The pattern formation in orientation and ocular dominance columns is one of the most investigated problems in the brain. From a known cortical structure, we build spinlike Hamiltonian models with long-range interactions of the Mexican hat type. These Hamiltonian models allow a coherent interpretation of the diverse phenomena in the visual map formation with the help of relaxation dynamics of spin systems. In particular, we explain various phenomena of self-organization in orientation and ocular dominance map formation including the pinwheel annihilation and its dependency on the columnar wave vector and boundary conditions.

Cho, Myoung Won; Kim, Seunghwan

2004-01-01

204

Tuning the spin Hamiltonian of NENP by external pressure a neutron scattering study  

CERN Document Server

We report an inelastic neutron scattering study of antiferromagnetic spin dynamics in the Haldane chain compound Ni(C2H8N2)2NO2ClO4 (NENP) under external hydrostatic pressure P = 2.5 GPa. At ambient pressure, the magnetic excitations in NENP are dominated by a long-lived triplet mode with a gap which is split by orthorhombic crystalline anisotropy into a lower doublet centered at 2.5meV. With pressure we observe appreciable shifts in these levels, which move to $\\Delta_\\perp{\\rm(2.5GPa)} \\approx$ 1.45 meV and $\\Delta_\\parallel(2.5GPa) perpendicular to the chain was measured here for the first time, and can be accounted for by an interchain exchange J'_c approximately 3e-4*J which changes only slightly with pressure. Since the average gap value $\\Delta_H\\approx$ 1.64 meV remains almost unchanged with P, we conclude that in NENP the application of external pressure does not affect the intrachain coupling J appreciably, but does produce a significant decrease of the single-ion anisotropy constant from D/J = 0.16...

Zaliznyak, Yu A; Broholm, C L; Reich, D H; Reich, Daniel H.

1997-01-01

205

NMR characterization of thin films  

Science.gov (United States)

A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

Gerald, II, Rex E. (Brookfield, IL); Klingler, Robert J. (Glenview, IL); Rathke, Jerome W. (Homer Glen, IL); Diaz, Rocio (Chicago, IL); Vukovic, Lela (Westchester, IL)

2008-11-25

206

Optical pumping and xenon NMR  

International Nuclear Information System (INIS)

Nuclear Magnetic Resonance (NMR) spectroscopy of xenon has become an important tool for investigating a wide variety of materials, especially those with high surface area. The sensitivity of its chemical shift to environment, and its chemical inertness and adsorption properties make xenon a particularly useful NMR probe. This work discusses the application of optical pumping to enhance the sensitivity of xenon NMR experiments, thereby allowing them to be used in the study of systems with lower surface area. A novel method of optically-pumping 129Xe in low magnetic field below an NMR spectrometer and subsequent transfer of the gas to high magnetic field is described. NMR studies of the highly polarized gas adsorbed onto powdered samples with low to moderate surface areas are now possible. For instance, NMR studies of optically-pumped xenon adsorbed onto polyacrylic acid show that xenon has a large interaction with the surface. By modeling the low temperature data in terms of a sticking probability and the gas phase xenon-xenon interaction, the diffusion coefficient for xenon at the surface of the polymer is determined. The sensitivity enhancement afforded by optical pumping also allows the NMR observation of xenon thin films frozen onto the inner surfaces of different sample cells. The geometry of the thin films results in interesting line shapes that are due to the bulk magnetic susceptibility of xenon. Experiments are also described that combine optical pumping with optical detection for high sensitivity in low magnetic field to observe the quadrupoler evolution of 131 Xe spins at the surface of the pumping cells. In cells with macroscopic asymmetry, a residual quadrupolar interaction causes a splitting in the 131Xe NMR frequencies in bare Pyrex glass cells and cells with added hydrogen

207

Optical pumping and xenon NMR  

Energy Technology Data Exchange (ETDEWEB)

Nuclear Magnetic Resonance (NMR) spectroscopy of xenon has become an important tool for investigating a wide variety of materials, especially those with high surface area. The sensitivity of its chemical shift to environment, and its chemical inertness and adsorption properties make xenon a particularly useful NMR probe. This work discusses the application of optical pumping to enhance the sensitivity of xenon NMR experiments, thereby allowing them to be used in the study of systems with lower surface area. A novel method of optically-pumping {sup 129}Xe in low magnetic field below an NMR spectrometer and subsequent transfer of the gas to high magnetic field is described. NMR studies of the highly polarized gas adsorbed onto powdered samples with low to moderate surface areas are now possible. For instance, NMR studies of optically-pumped xenon adsorbed onto polyacrylic acid show that xenon has a large interaction with the surface. By modeling the low temperature data in terms of a sticking probability and the gas phase xenon-xenon interaction, the diffusion coefficient for xenon at the surface of the polymer is determined. The sensitivity enhancement afforded by optical pumping also allows the NMR observation of xenon thin films frozen onto the inner surfaces of different sample cells. The geometry of the thin films results in interesting line shapes that are due to the bulk magnetic susceptibility of xenon. Experiments are also described that combine optical pumping with optical detection for high sensitivity in low magnetic field to observe the quadrupoler evolution of 131 Xe spins at the surface of the pumping cells. In cells with macroscopic asymmetry, a residual quadrupolar interaction causes a splitting in the {sup 131}Xe NMR frequencies in bare Pyrex glass cells and cells with added hydrogen.

Raftery, M.D.

1991-11-01

208

Optical pumping and xenon NMR  

Energy Technology Data Exchange (ETDEWEB)

Nuclear Magnetic Resonance (NMR) spectroscopy of xenon has become an important tool for investigating a wide variety of materials, especially those with high surface area. The sensitivity of its chemical shift to environment, and its chemical inertness and adsorption properties make xenon a particularly useful NMR probe. This work discusses the application of optical pumping to enhance the sensitivity of xenon NMR experiments, thereby allowing them to be used in the study of systems with lower surface area. A novel method of optically-pumping [sup 129]Xe in low magnetic field below an NMR spectrometer and subsequent transfer of the gas to high magnetic field is described. NMR studies of the highly polarized gas adsorbed onto powdered samples with low to moderate surface areas are now possible. For instance, NMR studies of optically-pumped xenon adsorbed onto polyacrylic acid show that xenon has a large interaction with the surface. By modeling the low temperature data in terms of a sticking probability and the gas phase xenon-xenon interaction, the diffusion coefficient for xenon at the surface of the polymer is determined. The sensitivity enhancement afforded by optical pumping also allows the NMR observation of xenon thin films frozen onto the inner surfaces of different sample cells. The geometry of the thin films results in interesting line shapes that are due to the bulk magnetic susceptibility of xenon. Experiments are also described that combine optical pumping with optical detection for high sensitivity in low magnetic field to observe the quadrupoler evolution of 131 Xe spins at the surface of the pumping cells. In cells with macroscopic asymmetry, a residual quadrupolar interaction causes a splitting in the [sup 131]Xe NMR frequencies in bare Pyrex glass cells and cells with added hydrogen.

Raftery, M.D.

1991-11-01

209

Deriving NMR surface relaxivities, pore size distributions and water retention curves by NMR relaxation experiments on partially de-saturated rocks  

Science.gov (United States)

Nuclear magnetic resonance (NMR) is a method used over a wide field of geophysical applications to non-destructively determine transport and storage properties of rocks and soils. In NMR relaxometry signal amplitudes correspond directly to the rock's fluid (water, oil) content. On the other hand the NMR relaxation behavior, i.e. the longitudinal (T1) and transverse (T2) NMR relaxation times, can be used to derive pore sizes and permeability as it is linearly linked to the pore's surface-to-volume-ratio and physiochemical properties of the rock-fluid interface by the surface relaxivity ?_s This parameter, however, is dependent on the type and mineral constituents of the investigated rock sample and thus has to be determined and calibrated prior to estimating pore sizes from NMR relaxometry measurements. Frequently used methods to derive surface relaxivity to calibrate NMR pore sizes comprise mercury injection, pulsed field gradients (PFG-NMR) or grain size analysis. This study introduces an alternative approach to jointly estimate NMR surface relaxivity and pore radii distributions using NMR relaxation data obtained from partially de-saturated rocks. In this, inverse modeling is carried on a linked Young Laplace equation for capillary bundles and the Brownstein and Tarr equations. Subsequently, this approach is used to predict water retention curves of the investigated rocks. The method was tested and validated on simulated and laboratory transverse NMR data. Calculated inverse models are generally in a good agreement with results obtained from mercury injection and drainage measurements. Left: Measured and predicted water retention (pF) curves. Center: NMR relaxometry data, fit and error. Right: Mercury injection data (HgPor, dashed line) and jointly derived pore radii distributions and surface relaxivity by joint inverse modelling

Mohnke, O.; Nordlund, C. L.; Klitzsch, N.

2013-12-01

210

Practical applications of NMR in civil engineering  

Digital Repository Infrastructure Vision for European Research (DRIVER)

By studying Hydrogen Nuclear Magnetic Resonance (1H-NMR) signals of water in porous materials, it is possible to determine their properties of water storage and transport. Besides, NMR studies can provide detailed information about the porous microstructure (porosity, pore-size distribution) of these materials. This approach is used in geophysical applications of NMR (e.g. for subsoil investigations), whereas a special NMR instrumentation ("NMR logging" tool) is lowered down into a drilled bo...

Wolter, B.; Kohl, F.; Surkowa, N.; Dobmann, G.

2003-01-01

211

NMR imaging methods  

International Nuclear Information System (INIS)

A method is described for producing an image representative of nuclear spin density data, employing nuclear magnetic resonance performed by a species of nuclei in a test object to be sampled. The method includes: (a) placement of a phantom object containing NMR-observable nuclei in a constant magnetic field oriented in a direction parallel to a first axis; (b) application of a radiofrequency excitation pulse to excite spins of the nuclei in the phantom object; (c) application of first and second linear magnetic field gradients along mutually orthogonal second and third axes lying in a first plane passing through the phantom object, during which application the spins of the nuclei evolve; (d) application of a refocusing pulse to produce a spin echo; (e) detection of the spin echo in the absence of the first and second magnetic field gradients; (f) conversion of the spin echo into a first set of electrical signals; (g) repetition of steps (b)-(f) wherein the amplitudes of the first and second magnetic field gradients are successively varied for each application, thereby producing a multiplicity of sets of electrical signals; (h) processing of the electrical signals to obtain a correction data set reflecting the deviation of the constant magnetic field from homogeneity in the first plane; (i) storage of the data correction set in the memory of a computer

212

AUREMOL: Automatic protein structure determination from NMR data  

International Nuclear Information System (INIS)

Several approaches to the problem of automated protein structure determination from NMR data exist. The concept for automation is a molecule centred approach where all of the available a priori information is used to eliminate as many free parameters as possible and reduce the amount of information and experimental data. Using a starting structure and as much additional information as possible, like predicted chemical shifts and backbone torsion angles, the assignment and the structure itself are refined in an iterative process. Therefore we are developing AUREMOL, which goal is the reliable and automatic structure determination of biological macro molecules such as proteins from NMR data. In AUREMOL included modules are RELAX, which uses complete relaxation formalism to calculate a simulated NOESY NMR spectrum, SIBASA (simulated based sequential assignment), which bases on simulated annealing to determine the chemical shifts of these signals, KNOWNOE, REFINE, which calculates intermolecular distances from a NOESY spectrum and the structure evaluation RFAC.

213

Spectrometer with direct NMR detection in a rotating coordinate system  

International Nuclear Information System (INIS)

A spectrometer with direct NMR detection in efficient magnetic field in a rotating coordinate system (rcs) during nuclear spin system irradiation by strong high-frequency field is described. The detection is carried out at comparatively low frequency in the 10-100 kHz range using the inductance coil oriented parallel to constant magnetic field. The concrete spectrometer parameters are presented as applied to 1H and 19F NMR of solids under ''magic'' angle conditions. The spectrometer permits to obtain the NMR frequency spetrum in rcs, lateral and longitudinal relaxation curves in rcs and double-rotating coordinate system, echo signals in rcs, The detection is continuous and is carried out in one pass. With respect to the spectra resolution in solids the spectrometer is by two-three order in excess of traditional wide-line spectrometers with continuous irradiation

214

Timescales in NMR: relaxation phenomena in relation with molecular reorientation  

International Nuclear Information System (INIS)

An overview of one fundamental aspect of molecular dynamics, NMR relaxation and its relationship with molecular reorientation, is presented: after a brief survey of techniques other than NMR (infrared absorption, Raman and Rayleigh light scattering, inelastic neutron scattering, fluorescence depolarization, computerized molecular dynamics), molecular motions are described: overall motions of rigid systems (sphere, ellipsoid, J and M extended models, Fokker-Planck-Langevin model), molecules with fast internal motions. NMR relaxation parameters and their experimental determination are then reviewed: theoretical background, measurements (specific relaxation rates under monoexponential decay or recovery, cross relaxation rates, cross-correlation spectral densities). Relaxation mechanisms and applications are also described: reduced spectral densities, dipolar interactions, chemical shift anisotropy, scalar relaxation of the second kind, spin-rotation). 8 fig., 3 tab., 118 ref

215

Ligand screening by saturation-transfer difference (STD) NMR spectroscopy.  

Energy Technology Data Exchange (ETDEWEB)

NMR based methods to screen for high-affinity ligands have become an indispensable tool for designing rationalized drugs, as these offer a combination of good experimental design of the screening process and data interpretation methods, which together provide unprecedented information on the complex nature of protein-ligand interactions. These methods rely on measuring direct changes in the spectral parameters, that are often simpler than the complex experimental procedures used to study structure and dynamics of proteins. The goal of this review article is to provide the basic details of NMR based ligand-screening methods, with particular focus on the saturation transfer difference (STD) experiment. In addition, we provide an overview of other NMR experimental methods and a practical guide on how to go about designing and implementing them.

Krishnan, V V

2005-04-26

216

Variable-temperature NMR and conformational analysis of Oenothein B  

Energy Technology Data Exchange (ETDEWEB)

Oenothein B is a dimeric hydrolyzable tannin with a wide range of biological activities, such as antitumour, anti-inflammatory and antiviral. Its nuclear magnetic resonance (NMR) at room temperature show duplications and broadening of signals. Experiments of 1D and 2D NMR at lower temperatures were useful for the complete NMR assignments of all hydrogens and carbons. The 3D structure of the most stable conformer was determined for the first time by nuclear Overhauser effect spectroscopy (NOESY) experiment (-20 deg C) and density functional theory (DFT)(B3LYP/6-31G)/ polarizable continuum model (PCM) quantum chemical calculations. The favoured conformation showed a highly compacted geometry and a lack of symmetry, in which the two valoneoyl groups showed distinct conformational parameters and stabilities. (author)

Santos, Suzana C.; Carvalho, Ariadne G.; Fortes, Gilmara A.C.; Ferri, Pedro H.; Oliveira, Anselmo E. de, E-mail: suzana.quimica.ufg@hotmail.com [Universidade Federal de Goias (UFGO), Goiania, GO (Brazil). Instituto de Quimica

2014-02-15

217

Medical applications of NMR imaging and NMR spectroscopy with stable isotopes. Summary  

International Nuclear Information System (INIS)

The current status of NMR imaging and NMR spectroscopy are summarized. For the most part examples from the March 1983 Puerto Rico symposium are used to illustrate the utility of NMR in medicine. 18 refs., 5 figs

218

Medical applications of NMR imaging and NMR spectroscopy with stable isotopes. Summary  

Energy Technology Data Exchange (ETDEWEB)

The current status of NMR imaging and NMR spectroscopy are summarized. For the most part examples from the March 1983 Puerto Rico symposium are used to illustrate the utility of NMR in medicine. 18 refs., 5 figs.

Matwiyoff, N.A.

1983-01-01

219

Application of Solution NMR Spectroscopy to Study Protein Dynamics  

Directory of Open Access Journals (Sweden)

Full Text Available Recent advances in spectroscopic methods allow the identification of minute fluctuations in a protein structure. These dynamic properties have been identified as keys to some biological processes. The consequences of this structural flexibility can be far?reaching and they add a new dimension to the structure-function relationship of biomolecules. Nuclear Magnetic Resonance (NMR spectroscopy allows the study of structure as well as dynamics of biomolecules in a very broad range of timescales at atomic level. A number of new NMR methods have been developed recently to allow the measurements of time scales and spatial fluctuations, which in turn provide the thermodynamics associated with the biological processes. Since NMR parameters reflect ensemble measurements, structural ensemble approaches in analyzing NMR data have also been developed. These new methods in some instances can even highlight previously hidden conformational features of the biomolecules. In this review we describe several solution NMR methods to study protein dynamics and discuss their impact on important biological processes.

Christoph Göbl

2012-03-01

220

Electronic Properties of Catalyst Nanoparticles Revealed by Solid State NMR  

Science.gov (United States)

Solid state NMR has emerged as a powerful local probe to investigate the surface physics of nanoparticle catalysts. We present the ^195Pt and ^13C NMR (of adsorbed CO) results on nanoparticles of Pt and Pt-Ru alloy. The surface atoms in nanoparticles give rise to a separate peak in the ^195Pt NMR spectrum that reflects the changes in the local density of states (LDOS) at these sites as a result of boundary effects. ^195Pt NMR spectrum of Pt-Ru alloy suggests that the surface of these nanoparticles is enriched with Pt atoms. Analysis of the ``slow-beat'' pattern observed in the spin echo decay indicates that the indirect spin-spin coupling between Pt nuclei (mediated via the s-type conduction electrons) is unaffected by alloying. ^13C NMR parameters of adsorbed CO obtained from CO saturated electrolytic medium reveals that the addition of Ru to Pt lowers the LDOS at the Pt atoms and weakens the Pt-CO adsorption bond. This electronic alteration is suggested to play a significant role in the improved catalytic performance of Pt-Ru alloy nanoparticles in fuel cell applications.

Babu, Panakkattu; Kim, Hee Soo; Wieckowski, Andrzej; Oldfield, Eric

2004-03-01

 
 
 
 
221

Permeability Prediction for Low Porosity Rocks by Mobile NMR  

Science.gov (United States)

Estimating permeability from NMR well logs or mobile NMR core scanner data is an attractive method as the measurements can be performed directly in the formation or on fresh cores right after drilling. Furthermore, the method is fast and non-destructive. Compared to T 1 relaxation times, commonly measured T 2 distributions are influenced by external and internal magnetic field gradients. We performed two-dimensional T 1 and T 2 relaxation experiments on samples of Rhaetian sandstone, a rock with low porosity and small pore radii, using a mobile NMR core scanner which operates within a nearly homogeneous static magnetic field. Because small pore sizes are associated with high internal magnetic field gradients, standard methods from NMR logging in the oil industry cannot be applied for accurate permeability prediction. Therefore, a new model theory was developed, which describes the pore radius dependence of the surface relaxivity ? 2 by both an analytical and a more practical empirical equation. Using corrected ? 2 values, permeability can be predicted accurately from the logarithmic mean of the T 2 distribution and the physically based Kozeny-Carman equation. Additional core plug measurements of structural parameters such as porosity, permeability, specific inner surface area and pore radius distributions supported the NMR results.

Pape, H.; Arnold, J.; Pechnig, R.; Clauser, C.; Talnishnikh, E.; Anferova, S.; Blümich, B.

2009-07-01

222

NMR relaxation times of trabecular bone-reproducibility, relationships to tissue structure and effects of sample freezing  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) spectroscopy provides a potential tool for non-invasive evaluation of the trabecular bone structure. The objective of this study was to determine the reproducibility of the NMR relaxation parameters (T2, Carr-Purcel-T2, T1?) for fat and water and relate those to the structural parameters obtained by micro-computed tomography (?CT). Especially, we aimed to evaluate the effect of freezing on the relaxation parameters. For storing bone samples, freezing is the standard procedure during which the biochemical and cellular organization of the bone marrow may be affected. Bovine trabecular bone samples were stored at -20 0C for 7 days and measured by NMR spectroscopy before and after freezing. The reproducibility of NMR relaxation parameters, as expressed by the coefficient of variation, ranged from 3.1% to 27.9%. In fresh samples, some correlations between NMR and structural parameters (Tb.N, Tb.Sp) were significant (e.g. the relaxation rate for T2 of fat versus Tb.Sp: r = -0.716, p < 0.01). Freezing did not significantly change the NMR relaxation times but the correlations between relaxation parameters and the ?CT structural parameters were not statistically significant after freezing, suggesting some nonsystematic alterations of the marrow structure. Therefore, the use of frozen bone samples for NMR relaxation studies may provide inferior information about the trabecular bone structure.

223

NMR relaxation times of trabecular bone-reproducibility, relationships to tissue structure and effects of sample freezing  

Energy Technology Data Exchange (ETDEWEB)

Nuclear magnetic resonance (NMR) spectroscopy provides a potential tool for non-invasive evaluation of the trabecular bone structure. The objective of this study was to determine the reproducibility of the NMR relaxation parameters (T{sub 2}, Carr-Purcel-T{sub 2}, T{sub 1}{rho}) for fat and water and relate those to the structural parameters obtained by micro-computed tomography ({mu}CT). Especially, we aimed to evaluate the effect of freezing on the relaxation parameters. For storing bone samples, freezing is the standard procedure during which the biochemical and cellular organization of the bone marrow may be affected. Bovine trabecular bone samples were stored at -20 {sup 0}C for 7 days and measured by NMR spectroscopy before and after freezing. The reproducibility of NMR relaxation parameters, as expressed by the coefficient of variation, ranged from 3.1% to 27.9%. In fresh samples, some correlations between NMR and structural parameters (Tb.N, Tb.Sp) were significant (e.g. the relaxation rate for T{sub 2} of fat versus Tb.Sp: r = -0.716, p < 0.01). Freezing did not significantly change the NMR relaxation times but the correlations between relaxation parameters and the {mu}CT structural parameters were not statistically significant after freezing, suggesting some nonsystematic alterations of the marrow structure. Therefore, the use of frozen bone samples for NMR relaxation studies may provide inferior information about the trabecular bone structure.

Prantner, Viktoria; Isaksson, Hanna; Nissi, Mikko J; Jurvelin, Jukka S [Department of Physics and Mathematics, University of Eastern Finland, PO Box 1627, 70211 Kuopio (Finland); Naervaeinen, Johanna; Groehn, Olli H J [Department of Neurobiology, A I Virtanen Institute for Molecular Sciences, University of Eastern Finland, PO Box 1627, 70211 Kuopio (Finland); Lammentausta, Eveliina [Department of Diagnostic Radiology, Oulu University Hospital, PO Box 50, 90029 OYS, Oulu (Finland); Avela, Janne, E-mail: hanna.isaksson@uef.f [Department of Biology of Physical Activity, University of Jyvaeskylae, PO Box 35, 40014 Jyvaeskylae (Finland)

2010-12-07

224

Pulsed zero field NMR of solids and liquid crystals  

Energy Technology Data Exchange (ETDEWEB)

This work describes the development and applications to solids and liquid crystals of zero field nuclear magnetic resonance (NMR) experiments with pulsed dc magnetic fields. Zero field NMR experiments are one approach for obtaining high resolution spectra of amorphous and polycrystalline materials which normally (in high field) display broad featureless spectra. The behavior of the spin system can be coherently manipulated and probed in zero field with dc magnetic field pulses which are employed in a similar manner to radiofrequency pulses in high field NMR experiments. Nematic phases of liquid crystalline systems are studied in order to observe the effects of the removal of an applied magnetic field on sample alignment and molecular order parameters. In nematic phases with positive and negative magnetic susceptibility anisotropies, a comparison between the forms of the spin interactions in high and low fields is made. High resolution zero field NMR spectra of unaligned smectic samples are also obtained and reflect the symmetry of the liquid crystalline environment. These experiments are a sensitive measure of the motionally induced asymmetry in biaxial phases. Homonuclear and heteronuclear solute spin systems are compared in the nematic and smectic phases. Nonaxially symmetric dipolar couplings are reported for several systems. The effects of residual fields in the presence of a non-zero asymmetry parameter are discussed theoretically and presented experimentally. Computer programs for simulations of these and other experimental results are also reported. 179 refs., 75 figs.

Thayer, A.M.

1987-02-01

225

Pulsed zero field NMR of solids and liquid crystals  

International Nuclear Information System (INIS)

This work describes the development and applications to solids and liquid crystals of zero field nuclear magnetic resonance (NMR) experiments with pulsed dc magnetic fields. Zero field NMR experiments are one approach for obtaining high resolution spectra of amorphous and polycrystalline materials which normally (in high field) display broad featureless spectra. The behavior of the spin system can be coherently manipulated and probed in zero field with dc magnetic field pulses which are employed in a similar manner to radiofrequency pulses in high field NMR experiments. Nematic phases of liquid crystalline systems are studied in order to observe the effects of the removal of an applied magnetic field on sample alignment and molecular order parameters. In nematic phases with positive and negative magnetic susceptibility anisotropies, a comparison between the forms of the spin interactions in high and low fields is made. High resolution zero field NMR spectra of unaligned smectic samples are also obtained and reflect the symmetry of the liquid crystalline environment. These experiments are a sensitive measure of the motionally induced asymmetry in biaxial phases. Homonuclear and heteronuclear solute spin systems are compared in the nematic and smectic phases. Nonaxially symmetric dipolar couplings are reported for several systems. The effects of residual fields in the presence of a non-zero asymmetry parameter are discussed theoretically and presented experimentally. Computer programs for simulations of these and other experimental results are also reported. 179 refs., 75 figs

226

Experimental studies of NMR logging irreducible water saturation  

International Nuclear Information System (INIS)

54 sandstone rock samples are selected from Xujiahe Formation in Sichuan Basin for experimental nuclear magnetic resonance (NMR) measurements. Irreducible water saturation is determined through methods of T2 spectrum area ratio, weighing, SBVI, unified T2cutoff and comprehensive statistical parameter model. Contrast analysis of the five methods reveals that bound water saturation can be established on the basis of weighing method and T2 spectrum area ratio method, and that two methods of unified T2 cutoff value and comprehensive parameter statistical model are better than SBVI method, and can be used to determine Irreducible water saturation model of Xujiahe Formation in Sichuan Basin. According to mercury intrusion capillary pressure measurements, all the application conditions of irreducible water saturation derived from NMR experiments are studied. The studies suggest that as to rock samples the permeability of which is greater than 1 x 10-4 ?m2, displacing force of 0.6897 MPa can drive all movable water, and that irreducible water saturation derived from NMR experiments is the proper one. While for rock samples with permeability less than 1 x 10-4 ?m2, displacing force of 0.6897 MPa can't drive all movable water, and irreducible water saturation derived from NMR experiments can only be the one under certain driving conditions. (authors)

227

Quantitative chemical analysis by NMR  

International Nuclear Information System (INIS)

This paper reports that nuclear magnetic resonance (NMR) spectroscopy offers several important advantages as a technique for quantitative chemical analysis, including the ease with which multicomponent mixtures can be analyzed, the nondestructive nature of NMR, and the direct proportionality of the integrated resonance intensity (I) and concentration (C) of nuclei giving the resonance: I = kC. With proper attention to experimental conditions, the proportionality constant is the same for all resonances in a spectrum. Thus NMR differs substantially from chromatographic methods and from together spectroscopic methods, which require a predetermined response factor for each compound being determined. Relative concentrations can be obtained directly from relative resonance intensities while absolute concentrations can be obtained by adding a known concentration of another compound as an internal intensity standard

228

NMR studies of actinide dioxides  

Energy Technology Data Exchange (ETDEWEB)

{sup 17}O NMR measurements have been performed on a series of the actinide dioxides, UO{sub 2}, NpO{sub 2} and PuO{sub 2}. Although the {sup 17}O NMR spectra in these materials are similar at higher temperatures, the low-temperature spectra present are significantly different. In UO{sub 2} we have observed a wide spectrum, forming a rectangular shape below T{sub N}=30 K. In NpO{sub 2}, on the other hand, the spectra broaden rather gradually and exhibit a two-peak structure below T{sub 0}=26 K. In PuO{sub 2}, neither spectrum broadening nor splitting has been observed. We show that these NMR spectra clearly indicate the different nature of the low-temperature magnetic ground states in these actinide compounds.

Tokunaga, Y. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)], E-mail: tokunaga.yo@jaea.go.jp; Sakai, H.; Fujimoto, T.; Kambe, S.; Walstedt, R.E.; Ikushima, K.; Yasuoka, H. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Aoki, D.; Homma, Y. [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Haga, Y.; Matsuda, T.D.; Ikeda, S.; Yamamoto, E.; Nakamura, A. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Shiokawa, Y. [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Nakajima, K.; Arai, Y. [Department of Nuclear Energy System, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Onuki, Y. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Department of Physics, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

2007-10-11

229

NMR studies of actinide dioxides  

International Nuclear Information System (INIS)

17O NMR measurements have been performed on a series of the actinide dioxides, UO2, NpO2 and PuO2. Although the 17O NMR spectra in these materials are similar at higher temperatures, the low-temperature spectra present are significantly different. In UO2 we have observed a wide spectrum, forming a rectangular shape below TN=30 K. In NpO2, on the other hand, the spectra broaden rather gradually and exhibit a two-peak structure below T0=26 K. In PuO2, neither spectrum broadening nor splitting has been observed. We show that these NMR spectra clearly indicate the different nature of the low-temperature magnetic ground states in these actinide compounds

230

A web-based database for EPR centers in semiconductors  

International Nuclear Information System (INIS)

We develop a web-based database system for electron paramagnetic resonance (EPR) centers in semiconductors. This database is available to anyone at http://www.kc.tsukuba.ac.jp/div-media/epr/. It currently has more than 300 records of the spin-Hamiltonian parameters for major known EPR centers. One can upload own new records to the database or can use simulation tools powered by EPR-NMR(C). Here, we describe the features and objectives of this database, and mention some future plans

231

Recent advances in NMR imaging  

International Nuclear Information System (INIS)

Proton NMR signals may be obtained from the human body in such a way as to produce two-dimensional images of anatomical slices. The NMR signal is mapped in the selected slice by application of field gradients which provide spatial encoding. Over the past twelve years the method has been developed to provide excellent NMR image which are useful in clinical practice. Its introduction into major hospitals is proceeding rapidly with a dozen commercial companies supplying the market, and over two hundred whole-body systems currently installed worldwide. As a method of medical imaging NMR has the advantages that it uses no ionizing radiation, that it gives sections in transverse, coronal and sagittal planes with equal ease, and that good tissue and pathological contrast are provided through relaxation time differences, using T/sub 1/-weighted and T/sub 2/-weighted images. Paramagnetic agents are being used to improve contrast of lesions in images. Special receiver coils and surface coils have been developed for improved imaging of selected parts of the body. Efficient use of time is achieved by the multi-echo/multi-slice procedure enabling images to be obtained in an average of a few seconds. Using special techniques real-time imaging is possible. Magnetic field strengths in use range from 0.02 to 2 Tesla. In vivo NMR spectroscopy using H/sup 1/, C/sup 13/ and P/sup 31/ provides an additional source of clinical information. Current trends suggest that before very long wholetrends suggest that before very long whole-body NMR systems will be found in all major hospitals

232

NMR velocity mapping and RHEO-NMR in complex liquids  

International Nuclear Information System (INIS)

By using the NMR technique, we have determined the velocity distribution and the rate of strain in a micelle solution (cetylpyridinium chloride and sodium salicylate) below and above a critical shear rate and have studied the isotropic and stress-induced ordered nematic phases in a micelle solution CTAB/D2O in a cylindric Couette cell.

233

A SENSITIVE NMR THERMOMETER FOR MULTINUCLEI FT NMR  

Science.gov (United States)

A pernicious problem in multinuclei FT NMR is accurate measurement of sample temperature. This arises from several factors including widespread use of high-power decoupling, large sample tubes (with potentially large temperature gradients across the sample volume), and lack of su...

234

Radiofrequency and magnet technology in medical NMR  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) is briefly described, particularly its rf and magnet aspects. Particular attention is given to the duplexer, the rf coils, and new kinds of magnets for remote sensing NMR

235

Push-through Direction Injectin NMR Automation  

Science.gov (United States)

Nuclear magnetic resonance (NMR) and mass spectrometry (MS) are the two major spectroscopic techniques successfully used in metabolomics studies. The non-invasive, quantitative and reproducible characteristics make NMR spectroscopy an excellent technique for detection of endogeno...

236

NMR Analysis of 2-(2?, 3?-dihydro-1?H-inden-1?-yl-1H-indene  

Directory of Open Access Journals (Sweden)

Full Text Available 1H, 13C and two dimensional NMR analyses were applied to determine the NMR parameters of 2-(2?,3?-dihydro-1?H-inden-1?-yl-1H-indene. The chemical shifts of all the H- and C-atoms, as well as the appropriate coupling constants were determined and the complete NMR resonance assignments of the molecule are given. The predicted patterns of the four different H atoms of the two methylene groups of the indane structural element coincided completely with the complex patterns in the NMR spectra.

PETER SPITELLER

2001-12-01

237

The CCPN data model for NMR spectroscopy: development of a software pipeline.  

Science.gov (United States)

To address data management and data exchange problems in the nuclear magnetic resonance (NMR) community, the Collaborative Computing Project for the NMR community (CCPN) created a "Data Model" that describes all the different types of information needed in an NMR structural study, from molecular structure and NMR parameters to coordinates. This paper describes the development of a set of software applications that use the Data Model and its associated libraries, thus validating the approach. These applications are freely available and provide a pipeline for high-throughput analysis of NMR data. Three programs work directly with the Data Model: CcpNmr Analysis, an entirely new analysis and interactive display program, the CcpNmr FormatConverter, which allows transfer of data from programs commonly used in NMR to and from the Data Model, and the CLOUDS software for automated structure calculation and assignment (Carnegie Mellon University), which was rewritten to interact directly with the Data Model. The ARIA 2.0 software for structure calculation (Institut Pasteur) and the QUEEN program for validation of restraints (University of Nijmegen) were extended to provide conversion of their data to the Data Model. During these developments the Data Model has been thoroughly tested and used, demonstrating that applications can successfully exchange data via the Data Model. The software architecture developed by CCPN is now ready for new developments, such as integration with additional software applications and extensions of the Data Model into other areas of research. PMID:15815974

Vranken, Wim F; Boucher, Wayne; Stevens, Tim J; Fogh, Rasmus H; Pajon, Anne; Llinas, Miguel; Ulrich, Eldon L; Markley, John L; Ionides, John; Laue, Ernest D

2005-06-01

238

NMR STUDIES OF THE STRUCTURE OF GLASS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Over the past 25 years, wide-line Nuclear Magnetic Resonance (NMR) techniques have been used successfully to study the structure of glasses on an atomic scale [1]. Analysis of the quadrupolar structure in NMR spectra of borate glasses has yielded quantitative determinations of the relative numbers of boron atoms in various oxygen environments. After a brief discussion of the relevant as ects of NMR theory, this paper will present some of the most recent studies : B11 NMR in sodium borosilicat...

Bray, P.; W.

1982-01-01

239

{sup 9}Be-NMR studies of the heavy-Fermion superconductor UBe{sub 13}  

Energy Technology Data Exchange (ETDEWEB)

Field-angle dependence of {sup 9}Be-NMR measurements has been carried out for a single crystal UBe{sub 13} in the temperature range of 0.35-1.5K. For H parallel [001], we observed that {sup 9}Be-NMR spectra consisted of 10 lines; one line comes from a Be(I) site located in the cubic symmetry, while nine lines come from Be(II) sites located in the lower symmetry. From the field angle dependence of the NMR spectra, we determined NQR parameters such as the nuclear quadrupole frequency ({nu}{sub Q}{approx}84kHz)and the asymmetry parameter ({eta}{approx}0.21). In the superconducting state, we found that {sup 9}Be-NMR Knight shift for H parallel [001] does not change at all. This result is consistent with the spin-triplet pairing state in UBe{sub 13}.

Tou, H. [Department of Quantum Matter, AdSM, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8530 (Japan) and Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530 (Japan)]. E-mail: tou@hiroshima-u.ac.jp; Tsugawa, N. [Department of Quantum Matter, AdSM, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8530 (Japan); Sera, M. [Department of Quantum Matter, AdSM, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8530 (Japan); Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530 (Japan); Haga, Y. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Onuki, Y. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043 (Japan)

2007-03-15

240

Magic-angle-spinning NMR  

International Nuclear Information System (INIS)

Magic-angle-spinning NMR is a very powerful technique which allows high-resolution spectra to be obtained from solids, even when the sample is microcrystalline or amorphous. The principles of the technique are described and examples given of its usefulness in many areas of chemistry with special stress being laid on aluminosilicate catalysts. (orig.)

 
 
 
 
241

Computer Simulation of NMR Spectra.  

Science.gov (United States)

Describes a PASCAL computer program which provides interactive analysis and display of high-resolution nuclear magnetic resonance (NMR) spectra from spin one-half nuclei using a hard-copy or monitor. Includes general and theoretical program descriptions, program capability, and examples of its use. (Source for program/documentation is included.)…

Ellison, A.

1983-01-01

242

Concretes damaging: the NMR lights  

International Nuclear Information System (INIS)

The damaging of cement-based materials (concrete, mortars, etc..) is a major concern for applications like road salting or wastes confinement. The NMR study of the calcium hydrate silicates (CHS) of concretes allows to determine the causes of their damaging: de-cohesion of CHS chains, hydration of alkaline ions. Short note. (J.S.)

243

High resolution solid state N.M.R. - theory and applications  

International Nuclear Information System (INIS)

The subject is reviewed under the headings: introduction; N.M.R. parameters; problems with solids; improving sensitivity; narrowing the lines; shortening of relaxation times; choosing the equipment - essential features; N.M.R. of catalytic materials -bulk and surface studies (silicon (characterization of silicious materials - silica and aluminosilicates; surface species -silica and zeolites; chemically bound species - silica); aluminium (alumina; zeolites; natural aluminosilicates); phosphorus; miscellaneous nuclei; metals); N.M.R. of adsorbed species and chemical reactions at the surface (carbon; hydrogen). (U.K.)

244

63Cu and 65Cu NMR study on an amorphous Ni-Cu-P alloy  

International Nuclear Information System (INIS)

63Cu and 65Cu NMR spectra were recorded on an amorphous Ni-Cu-P alloy using the point-by-point spin echo technique and the spin-lattice relaxation times were measured by the 180 deg pulse-spin echo and the saturation comb-spin echo sequences. The results were compared with the corresponding parameters of the 31P NMR spectrum. It was concluded that the quadrupole broadening is the dominant factor in the NMR spectra of both Cu isotopes and the Korringa-type mechanism is responsible for the nuclear spin-lattice relaxation. (author)

245

An AMBER/DYANA/MOLMOL Phosphorylated Amino Acid Library Set and Incorporation into NMR Structure Calculations  

International Nuclear Information System (INIS)

Protein structure determination using Nuclear Magnetic Resonance (NMR) requires the use of molecular dynamics programs that incorporate both NMR experimental and implicit atomic data. Atomic parameters for each amino acid type are encoded in libraries used by structure calculation programs such as DYANA and AMBER. However, only a few non-standard amino acid library sets are included in these programs or the molecular visualization program MOLMOL. Our laboratory is calculating the phosphorylated and non-phosphorylated states of peptides and proteins using NMR methods. To calculate chemically correct structures, we have extended the available molecular libraries for these programs to include the modified amino acids phosphoserine, phosphothreonine, and phosphotyrosine

246

Structure determination of aligned samples of membrane proteins by NMR spectroscopy.  

Science.gov (United States)

The paper briefly reviews the process of determining the structures of membrane proteins by NMR spectroscopy of aligned samples, describes the integration of recent developments in the interpretation of spectra of aligned proteins and illustrates the application of these methods to the trans-membrane helical domain of a protein. The emerging methods of interpreting the spectral parameters from aligned samples of isotopically labeled proteins provide opportunities for simultaneously assigning the spectra and determining the structures of the proteins, and also for comparing the results from solid-state NMR experiments on completely aligned samples with those of solution NMR experiments on weakly aligned samples. PMID:14745796

Nevzorov, Alexander A; Mesleh, Michael F; Opella, Stanley J

2004-02-01

247

17O NMR relaxation studies of oxide superconductors  

International Nuclear Information System (INIS)

In this study, solid state nuclear magnetic resonance (NMR) spectroscopy is used to investigate the structural, electronic, and dynamical properties of a variety of high temperature oxide superconductors and metal carbonyls adsorbed on metal oxide surface. The first five chapters describe the 17O Knight shift, nuclear spin lattice and spin-spin relaxation measurements carried out on a large number of cuprate, bismuthate and plumbate superconductors. After briefly reviewing the basic theory of the NMR parameters of metals in the normal and superconducting states, a detailed 17O NMR study of YBa2Cu3O7-x, is described in Chapter 2. Chapter 3 contains a comparative study of Tl2Ba2CaCu2O8+x, Bi2Sr2CaCu2O8+x, YBa2Cu3O7-x, and La1.85Sr0.15CuO4 are compared to the theoretical model of Monien, Millis, and Pines of an antiferromagnetic Fermi liquid state. In Chapter 4, it is shown that the normal state nuclear spin lattice relaxation behavior of the copper-free superconductors can be accounted for by a simple p conduction band model. The 17O NMR results for the different families of oxide superconductors are summarized in Chapter 5. The 17O NMR parameters of the bismuthate and plumbate superconductors show these materials to be weakly metallic oxides se materials to be weakly metallic oxides with T1T values which are consistent with a BCS-like relationship between the electronic density of states and Tc. The normal state of the cuprate superconductors display properties consistent with the presence of magnetic interactions and their T1T values show little variation with Tc

248

Estimation of the average aromatic cluster size based on solid-state NMR; Sekitan no kotai NMR sokutei ni yoru hokozoku kurasuta heikin saizu no suitei  

Energy Technology Data Exchange (ETDEWEB)

Measurements of solid-state NMR of eight Argonne Premium Coal Samples were conducted to estimate the average aromatic cluster size in these coals. Firstly, the carbon distribution was obtained from SPE/MAS {sup 13}C-NMR. Secondary, {sup 1}H-CRAMPS NMR spectra gave the hydrogen aromaticity of coal. Combination use of the hydrogen aromaticity and elemental analysis data could afford the amount of tertiary aromatic carbon. The parameter of X{sub b}, the mole fraction of aromatic bridgehead carbons in all aromatic carbons, could be derived from above NMR data and elemental analysis of coal. X{sub b} is directly correlated to the number of aromatic carbon atoms per aromatic cluster, C. In this study, the value of C varied from 10 (corresponding to the size of naphthalene) for Beulah-Zap and Wyodak coals to 23 (corresponding to the size of coronene) for Pocahontas No.3 coal. (author)

Kidena, K.; Murata, S.; Nomura, M. [Osaka Univ., Osaka (Japan) Department of Molecular Chemistry; Artok, L. [Izmir Inst. of Tech., Imzir (Turkey)

1999-11-20

249

Bone marrow NMR imaging and scintigraphy in AIDS patients  

International Nuclear Information System (INIS)

The examinations were carried out in order to ascertain whether bone marrow abnormalities can be detected in AIDS patients by means of magnetic resonance imaging or scintiscanning. In 16 of the 19 patients the NMR image and/or the scintiscan distinctly revealed bone marrow abnormalities, but there was no exact correlation to be found to immunological parameters, the peripheral blood picture, or the clinical stage of the HIV infection. (orig.)

250

NMR analysis, protonation equilibria and decomposition kinetics of tolperisone.  

Science.gov (United States)

The rate constants of spontaneous and hydroxide-catalyzed decomposition and the tautomer-specific protonation constants of tolperisone, a classical muscle relaxant were determined. A solution NMR method without any separation techniques was elaborated to quantitate the progress of decomposition. All the rate and equilibrium constants were determined at four different temperatures and the activation parameters were calculated. The molecular mechanism of decomposition is proposed. PMID:19577875

Orgován, Gábor; Tihanyi, Károly; Noszál, Béla

2009-12-01

251

X-ray and NMR tomography - medical equipment applied in petroleum research  

International Nuclear Information System (INIS)

Results from short, preliminary studies are presented where X-ray and Nuclear Magnetic Resonance (NMR) tomography are applied to form pictures from drill core samples. X-ray tomography may be utilized to determine the density of dry core samples containing fluids. This method is thus well suited for flow studies in porous media. NMR tomography offers the possibility to study fundamental fluid/rock parameters like wettability, but the method has to be further developed and tested

252

Interface contributions to the spin-orbit interaction parameters of electrons at the (001) GaAs/AlGaAs interface  

Science.gov (United States)

One-body mechanisms of spin splitting of the energy spectrum of 2D electrons in a one-side doped (001) GaAs/Al x Ga1 - x As quantum well have been studied theoretically and experimentally. The interfacial spin splitting has been shown to compensate (enhance) considerably the contribution of the bulk Dresselhaus (Bychkov-Rashba) mechanism. The theoretical approach is based on the solution of the effective mass equation in a quasi-triangular well supplemented by a new boundary condition at a high and atomically sharp hetero-barrier. The model takes into account the spin-orbit interaction of electrons with both bulk and interfacial crystal potential having C 2 v symmetry, as well as the lack of inversion symmetry and nonparabolicity of the conduction band in GaAs. The effective 2D spin Hamiltonian including both bulk and interface contributions to the Dresselhaus (?BIA) and Rashba (?SIA) constants has been derived. The analytical relation between these constants and the components of the anisotropic nonlinear g-factor tensor in an oblique quantizing magnetic field has been found. The experimental approach is based, on one hand, on the detection of electron spin resonance in the microwave range and, on the other hand, on photoluminescence measurements of the nonparabolicity parameter. The interface contributions to ?BIA and ?SIA have been found from comparison with the theory.

Devizorova, Zh. A.; Shchepetilnikov, A. V.; Nefyodov, Yu. A.; Volkov, V. A.; Kukushkin, I. V.

2014-09-01

253

Polymers under mechanical stress- an NMR investigation  

International Nuclear Information System (INIS)

Low-field NMR using permanent magnets in Halbach arrangements permit NMR investigation without the limits present in high-field NMR. The lower field in conjunction with confined stray field permit the application of NMR, in particular relaxation NMR in a stretching apparatus and a rheometer. Crystalline and amorphous fraction of semi-crystalline polymers are distinguished by their transverse relaxation times. Upon mechanical load the relaxation times of the amorphous fraction changes as seen in in-situ measurements on polypropylene rods. During the formation of a neck the crystalline fraction becomes more prominent.

254

NMR spectroscopic in vitro assay using hyperpolarization  

DEFF Research Database (Denmark)

An in vitro assay method which comprises the use of an assay reagent containing at least one NMR active nucleus, and hyperpolarising at least one NMR active nucleus of the assay reagent; and analysing the assay reagent and/or the assay by NMR spectroscopy and/or NMR imaging. The assay reagent may contain an artificially high concentration of an NMR active nucleus. Keyword: hyperpolarization comprising nuclear magnetic resonance spectroscopic in vitro assay laboratory techniques, spectrum analysis techniques,Biochemistry and Molecular Biophysics,10060, Biochemistry studies - General,Methods and Techniques

Knox, Peter; Cook, Neil

2009-01-01

255

11B NMR studies of some rare earth hexaborides  

International Nuclear Information System (INIS)

The electrical and magnetic properties of rare earth hexaborides are neither well understood nor their inter-relationship clear. Earlier work indicated that they behave like metallic conductors. However, the observed Knight shifts of 11B resonance in these compounds were very small e.g. approximately + 0.02% in LaB6. This small shift implies that the conduction electrons at the Fermi surface do not have appreciable s character. So one may expect an anisotropic magnetic interaction from the conduction electrons in such substances. Earlier NMR work reported the quadrupolar interaction parameter but unfortunately the evaluation of magnetic interaction parameter was inaccurate. As such in the present work, a systematic NMR investigation of nusub(Q), Ksub(iso) and Ksub(aniso) shift parameters in LaB6 and SmB6 have been undertaken and for analysing the second-order quadrupolar split line, the method of Jones et al has been followed. Interestingly, 11B resonances were easily detected in the powdered samples as such and no skin depth problems were encountered, as in a conducting sample. In earlier NMR investigations the finely powdered borides were suspended in oil on the assumption that they were conducting samples. (auth.)

256

All-atom molecular dynamics simulations using orientational constraints from anisotropic NMR samples  

International Nuclear Information System (INIS)

Orientational constraints obtained from solid state NMR experiments on anisotropic samples are used here in molecular dynamics (MD) simulations for determining the structure and dynamics of several different membrane-bound molecules. The new MD technique is based on the inclusion of orientation dependent pseudo-forces in the COSMOS-NMR force field. These forces drive molecular rotations and re-orientations in the simulation, such that the motional time-averages of the tensorial NMR properties approach the experimentally measured parameters. The orientational-constraint-driven MD simulations are universally applicable to all NMR interaction tensors, such as chemical shifts, dipolar couplings and quadrupolar interactions. The strategy does not depend on the initial choice of coordinates, and is in principle suitable for any flexible molecule. To test the method on three systems of increasing complexity, we used as constraints some deuterium quadrupolar couplings from the literature on pyrene, cholesterol and an antimicrobial peptide embedded in oriented lipid bilayers. The MD simulations were able to reproduce the NMR parameters within experimental error. The alignment of the three membrane-bound molecules and some aspects of their conformation were thus derived from the NMR data, in good agreement with previous analyses. Furthermore, the new approach yielded for the first time the distribution of segmental orientations with respect to the membrane and the order parametpect to the membrane and the order parameter tensors of all three systems

257

Xenon NMR of phase biaxiality in liquid crystals.  

Science.gov (United States)

Biaxial thermotropic nematic liquid crystals would be of great importance in liquid crystal display technology. Less than a decade ago, such liquid crystals were suggested. The biaxiality of the phases was confirmed using (2)H NMR spectroscopy of deuterated probe molecules. The spectra were collected from a sample rotating around an axis perpendicular to the external magnetic field, resulting in a two-dimensional powder pattern. We have proposed an alternate technique that is based on the second order quadrupole shift detectable in (131)Xe NMR spectra of dissolved xenon. The method has many advantages, such as the NMR spectra are taken from a static sample and the (131)Xe quadrupole coupling tensor is extremely sensitive to the symmetry of the phase. In the present study, we report results obtained on a 600-MHz NMR spectrometer. Together with the data of our earlier study, they confirm that the asymmetry parameter of the (131)Xe quadrupole coupling tensor in the nematic phase of a ferroelectric liquid crystal is 0.85 and in the smectic A phase ca 0.62, indicating significant phase biaxiality. PMID:24771455

Jokisaari, Jukka; Zhu, Jianfeng

2014-10-01

258

Low field NMR in aerogel-confined superfluid ^3He  

Science.gov (United States)

The superfluid states of bulk liquid ^3He were convincingly identified through their longitudinal and transverse NMR spectra. The order parameters of the superfluid phases of ^3He confined within aerogel have generally been assumed to be identical to those in bulk liquid. While that identification has not been contradicted by experimental data, it has not yet been tested as carefully as in bulk. Fomin has suggested that the A-like phase in aerogel could be an axiplanar state, distinct from the bulk axial state. We have tested the identification by studying low-field NMR which is more sensitive to the distinction between the candidate states. Using the dc SQUID based NMR detection system developed in our laboratory over many years we have studied both longitudinal and transverse resonance spectra in 99.5% porosity aerogel in magnetic fields of 1-4 mT, an order of magnitude lower than previous NMR work. Our work shows qualitative features similar to those found in higher magnetic fields. While we were unable to resolve the longitudinal resonance, transverse resonance measurements exhibit a characteristic field- and temperature-dependence.

Du, Yuliang; Bozler, H. M.; Gould, C. M.

2008-03-01

259

Recognition of lumbar disk herniation with NMR  

International Nuclear Information System (INIS)

Fifteen nuclear magnetic resonance (NMR) studies of 14 patients with herniated lumbar intervertebral disks were performed on the UCSF NMR imager. Computed tomographic (CT) scans done on a GE CT/T 8800 or comparable scanner were available at the time of NMR scan interpretation. Of the 16 posterior disk ruptures seen at CT, 12 were recognized on NMR. Diminished nucleus pulposus signal intensity was present in all ruptured disks. In one patient, NMR scans before and after chymopapain injection showed retraction of the protruding part of the disk and loss of signal intensity after chemonucleolysis. Postoperative fibrosis demonstrated by CT in one patient and at surgery in another showed intermediate to high signal intensity on NMR, easily distinguishing it from nearby thecal sac and disk. While CT remains the method of choice for evaluation of the patient with suspected lumbar disk rupture, the results of this study suggest that NMR may play a role in evaluating this common clinical problem

260

Efficient design of multituned transmission line NMR probes: the electrical engineering approach.  

Science.gov (United States)

Transmission line-based multi-channel solid state NMR probes have many advantages regarding the cost of construction, number of RF-channels, and achievable RF-power levels. Nevertheless, these probes are only rarely employed in solid state-NMR-labs, mainly owing to the difficult experimental determination of the necessary RF-parameters. Here, the efficient design of multi-channel solid state MAS-NMR probes employing transmission line theory and modern techniques of electrical engineering is presented. As technical realization a five-channel ((1)H, (31)P, (13)C, (2)H and (15)N) probe for operation at 7 Tesla is described. This very cost efficient design goal is a multi port single coil transmission line probe based on the design developed by Schaefer and McKay. The electrical performance of the probe is determined by measuring of Scattering matrix parameters (S-parameters) in particular input/output ports. These parameters are compared to the calculated parameters of the design employing the S-matrix formalism. It is shown that the S-matrix formalism provides an excellent tool for examination of transmission line probes and thus the tool for a rational design of these probes. On the other hand, the resulting design provides excellent electrical performance. From a point of view of Nuclear Magnetic Resonance (NMR), calibration spectra of particular ports (channels) are of great importance. The estimation of the ?/2 pulses length for all five NMR channels is presented. PMID:21316931

Frydel, J A; Krzystyniak, M; Pienkowski, D; Pietrzak, M; de Sousa Amadeu, N; Ratajczyk, T; Idzik, K; Gutmann, T; Tietze, D; Voigt, S; Fenn, A; Limbach, H H; Buntkowsky, G

2011-01-01

 
 
 
 
261

Isotope alternation system: two-level, NMR-controlled rapid switching  

International Nuclear Information System (INIS)

In the sequential transmission method of normalization in AMS the magnetic parameters of the accelerator must be alternated between their values for the lighter and the heavier isotopes with as little loss of time as possible. Rapid changing of these parameters has been effected through a combination of computer control and nuclear magnetic resonance (NMR) search and lock control

262

Measurements of Boar Spermatozoa Motility Using PFG NMR Method  

International Nuclear Information System (INIS)

The evaluation of spermatozoa motility, viability and morphology is an essential parameter in the examination of sperm quality and in the establishment of correlations between sperm quality and fertility. Until now, assessment of sperm quality has been based on subjective evaluation of parameters, such as motility and viability, and on objective parameters, such as semen concentration and morphology abnormalities. When subjective optical microscopic evaluation was used in humans and animals, variations of 30 to 60% have been reported in the estimation of the motility parameters of the same ejaculates. To overcome this variability, different systems have been proposed such as turbidimetry, laser-Doppler spectroscopy, and photometric methods. Other accurate techniques, such as flow cytometry, which allows the evaluation of concentration, and cellulose-acetate/nitrate filter measure only a single semen parameter. The more recent track semen analysis system, based on individual spermatozoon evaluation, offers an accurate calculation of different semen parameters. Although some interesting results have already been obtained, many questions remain, which have to be answered to allow for further development in veterinary medicine, clinical fertility settings, physiological, and toxicology research activities. Pulsed field gradient nuclear magnetic resonance (PFG NMR) techniques have been presented demonstrating the potential to study flow and transport processes in complex s flow and transport processes in complex systems. By PFG NMR, the molecular displacement can be measured that occurs during a time interval D, between two consecutive magnetic field gradient pulses. In this poster we present the results of PFG-NMR obtained for a number of samples of boar spermatozoa with varying motility and discuss whether this method can be useful for fast and reliable spermatozoa motility evaluation. (author)

263

Electromagnetically Induced Transparency with NMR  

Science.gov (United States)

Atomic, molecular and optical physics and quantum computing have a deep relationship, which we illustrate with an experimental study of electromagnetically induced transparency (EIT) in NMR. Recent results [1] illustrate how EIT can be used for light storage, and possibly as a memory for quantum states. Here, we demonstrate EIT operating at radiofrequency wavelengths, using the spin-7/2 nuclear quadrupole moment of Cesium and NMR quantum computation techniques. However, in contrast to the usual EIT experiment, we infer the transparency behavior by observing the spins instead of the transmitted electromagnetic radiation. We also provide alternative explanation of EIT as being an instance of quantum bang-bang control. References: 1. C. Liu, Z. Dutton, C. H. Behroozi, L. Vestergaard Hau, Nature 409, 490 (2001).

Son, Hyungbin; Kota, Murali; Chuang, Isaac; Steffen, Matthias; Judeinstein, Patrick

2003-03-01

264

NMR-based milk metabolomics  

DEFF Research Database (Denmark)

Milk is a key component in infant nutrition worldwide and, in the Western parts of the world, also in adult nutrition. Milk of bovine origin is both consumed fresh and processed into a variety of dairy products including cheese, fermented milk products, and infant formula. The nutritional quality and processing capabilities of bovine milk is closely associated to milk composition. Metabolomics is ideal in the study of the low-molecular-weight compounds in milk, and this review focuses on the recent nuclear magnetic resonance (NMR)-based metabolomics trends in milk research, including applications linking the milk metabolite profiling with nutritional aspects, and applications which aim to link the milk metabolite profile to various technological qualities of milk. The metabolite profiling studies encompass the identification of novel metabolites, which potentially can be used as biomarkers or as bioactive compounds. Furthermore, metabolomics applications elucidating how the differential regulated genes affects milk composition are also reported. This review will highlight the recent advances in NMR-based metabolomics on milk, as well as give a brief summary of when NMR spectroscopy can be useful for gaining a better understanding of how milk composition is linked to nutritional or quality traits.

Sundekilde, Ulrik; Larsen, Lotte Bach

2013-01-01

265

NMR probes HTGR fuel synthesis  

International Nuclear Information System (INIS)

Schemes for the synthesis of microspherical nuclear fuel particles of uranium dioxide using the sol-gel process were developed by scientists at Oak Ridge National Laboratory and General Atomics for use in high temperature gas cooled reactors (HTGR). When coated with ceramic layers of pyrolytic carbon and silicon carbide, the microspherical particle retains volatile fission products very effectively. Researchers at Savannah River have developed a new method using carbon-13 and oxygen-17 nuclear magnetic resonance (NMR) for monitoring particle fuel manufacture by this synthesis process. NMR is an electromagnetic method developed in the 1950s based upon the quantized nuclear spin properties of nuclei with non-zero nuclear magnetic moments. Early examples of highly sensitive nuclei included hydrogen-1, carbon-13, fluorine-19 and phosphorus-31. Modern NMR methods based upon Fourier-Transform signal accumulation, homogenous-field superconducting magnets and modern computers have extended the method to a much longer list of useful nuclei of interest to the nuclear industry including deuterium, tritium, lithium-7, boron-10 and -11, nitrogen-14 and -15, oxygen-17, sodium-23 and caesium-133. (Author)

266

Scalable NMR spectroscopy with semiconductor chips.  

Science.gov (United States)

State-of-the-art NMR spectrometers using superconducting magnets have enabled, with their ultrafine spectral resolution, the determination of the structure of large molecules such as proteins, which is one of the most profound applications of modern NMR spectroscopy. Many chemical and biotechnological applications, however, involve only small-to-medium size molecules, for which the ultrafine resolution of the bulky, expensive, and high-maintenance NMR spectrometers is not required. For these applications, there is a critical need for portable, affordable, and low-maintenance NMR spectrometers to enable in-field, on-demand, or online applications (e.g., quality control, chemical reaction monitoring) and co-use of NMR with other analytical methods (e.g., chromatography, electrophoresis). As a critical step toward NMR spectrometer miniaturization, small permanent magnets with high field homogeneity have been developed. In contrast, NMR spectrometer electronics capable of modern multidimensional spectroscopy have thus far remained bulky. Complementing the magnet miniaturization, here we integrate the NMR spectrometer electronics into 4-mm(2) silicon chips. Furthermore, we perform various multidimensional NMR spectroscopies by operating these spectrometer electronics chips together with a compact permanent magnet. This combination of the spectrometer-electronics-on-a-chip with a permanent magnet represents a useful step toward miniaturization of the overall NMR spectrometer into a portable platform. PMID:25092330

Ha, Dongwan; Paulsen, Jeffrey; Sun, Nan; Song, Yi-Qiao; Ham, Donhee

2014-08-19

267

Advanced NMR technology for bioscience and biotechnology  

Energy Technology Data Exchange (ETDEWEB)

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). NMR plays critical roles in bioscience and biotechnology in both imaging and structure determination. NMR is limited, however, by the inherent low sensitivity of the NMR experiment and the demands for spectral resolution required to study biomolecules. The authors addressed both of these issues by working on the development of NMR force microscopy for molecular imaging, and high field NMR with isotope labeling to overcome limitations in the size of biomolecules that can be studied using NMR. A novel rf coil design for NMR force microscopy was developed that increases the limits of sensitivity in magnetic resonance detection for imaging, and the authors demonstrated sub-surface spatial imaging capabilities. The authors also made advances in the miniaturization of two critical NMR force microscope components. They completed high field NMR and isotope labeling studies of a muscle protein complex which is responsible for regulating muscle contraction and is too large for study using conventional NMR approaches.

Hammel, P.C.; Hernandez, G.; Trewhella, J.; Unkefer, C.J. [Los Alamos National Lab., NM (US); Boumenthal, D.K. [Univ. of Utah, Salt Lake City, UT (US); Kennedy, M.A. [Pacific Northwest National Lab., Richland, WA (US); Moore, G.J. [Wayne State Univ., Detroit, MI (US)

1998-11-01

268

Complete 1H NMR spectral analysis of ten chemical markers of Ginkgo biloba.  

Science.gov (United States)

The complete and unambiguous (1)H NMR assignments of ten marker constituents of Ginkgo biloba are described. The comprehensive (1)H NMR profiles (fingerprints) of ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, bilobalide, quercetin, kaempferol, isorhamnetin, isoquercetin, and rutin in DMSO-d(6) were obtained through the examination of 1D (1)H NMR and 2D (1)H,(1)H-COSY data, in combination with (1)H iterative full spin analysis (HiFSA). The computational analysis of discrete spin systems allowed a detailed characterization of all the (1)H NMR signals in terms of chemical shifts (?(H)) and spin-spin coupling constants (J(HH)), regardless of signal overlap and higher order coupling effects. The capability of the HiFSA-generated (1)H fingerprints to reproduce experimental (1)H NMR spectra at different field strengths was also evaluated. As a result of this analysis, a revised set of (1)H NMR parameters for all ten phytoconstituents was assembled. Furthermore, precise (1)H NMR assignments of the sugar moieties of isoquercetin and rutin are reported for the first time. PMID:22730238

Napolitano, José G; Lankin, David C; Chen, Shao-Nong; Pauli, Guido F

2012-08-01

269

NMR in natural products: understanding conformation, configuration and receptor interactions.  

Science.gov (United States)

Covering: up to 2011. Natural products are of tremendous importance in both traditional and modern medicine. For medicinal chemistry natural products represent a challenge, as their chemical synthesis and modification are complex processes, which require many, often stereo-selective, synthetic steps. A prerequisite for the design of analogs of natural products, with more accessible synthetic routes, is the availability of their bioactive conformation. Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray crystallography are the two techniques of choice to investigate the structure of natural products. In this review, I describe the most recent advances in NMR to study the conformation of natural products either free in solution or bound to their cellular receptors. In chapter 2, I focus on the use of residual dipolar couplings (RDC). On the basis of a few examples, I discuss the benefit of complementing classical NMR parameters, such as NOEs and scalar couplings, with dipolar couplings to simultaneously determine both the conformation and the relative configuration of natural products in solution. Chapter 3 is dedicated to the study of the structure of natural products in complex with their cellular receptors and is further divided in two sections. In the first section, I describe two solution-state NMR methodologies to investigate the binding mode of low-affinity ligands to macromolecular receptors. The first approach, INPHARMA (Interligand Noes for PHArmacophore Mapping), is based on the observation of interligand NOEs between two small molecules binding competitively to a common receptor. INPHARMA reveals the relative binding mode of the two ligands, thus allowing ligand superimposition. The second approach is based on paramagnetic relaxation enhancement (PRE) of ligand resonances in the presence of a receptor containing a paramagnetic center. In the second section, I focus on solid-state NMR spectroscopy as a tool to access the bioactive conformation of natural products in complex with macromolecular receptors. PMID:22456471

Carlomagno, Teresa

2012-05-01

270

NMR metabolomics for assessment of exercise effects with mouse biofluids  

Energy Technology Data Exchange (ETDEWEB)

Exercise modulates the metabolome in urine or blood as demonstrated previously for humans and animal models. Using nuclear magnetic resonance (NMR) metabolomics, the present study compares the metabolic consequences of an exhaustive exercise at peak velocity (Vp) and at critical velocity (Vc) on mice. Since small-volume samples (blood and urine) were collected, dilution was necessary to acquire NMR spectra. Consequently, specific processing methods were applied before statistical analysis. According to the type of exercise (control group, Vp group and Vc group), 26 male mice were divided into three groups. Mice were sacrificed 2 h after the end of exercise, and urine and blood samples were drawn from each mouse. Proton NMR spectra were acquired with urine and deproteinized blood. The NMR data were aligned with the icoshift method and normalised using the probabilistic quotient method. Finally, data were analysed with the orthogonal projection of latent-structure analysis. The spectra obtained with deproteinized blood can neither discriminate the control mice from exercised mice nor discriminate according to the duration of the exercise. With urine samples, a significant statistical model can be estimated when comparing the control mice to both groups, Vc and Vp. The best model is obtained according to the exercise duration with all mice. Taking into account the spectral regions having the highest correlations, the discriminant metabolites are allantoin, inosine and branched-chain amino acids. In conclusion, metabolomic profiles assessed with NMR are highly dependent on the exercise. These results show that urine samples are more informative than blood samples and that the duration of the exercise is a more important parameter to influence the metabolomic status than the exercise velocity. (orig.)

Le Moyec, Laurence; Mille-Hamard, Laurence; Breuneval, Carole; Petot, Helene; Billat, Veronique L. [Universite Evry Val d' Essonne, UBIAE INSERM U902, Evry Cedex (France); Triba, Mohamed N. [Universite Paris 13, CSPBAT UMR 7244, Bobigny (France)

2012-08-15

271

Deducing relative permeability of tight gas rocks from NMR measurements  

Science.gov (United States)

As the economic production of hydrocarbons from unconventional sources, such as tight gas, is getting more and more important, understanding the differences in petrophysical behavior compared to conventional fields is crucial. The prediction of key reservoir parameters in low-permeability gas systems therefore needs new approaches in laboratory methods. Our research aims at predicting transport and storage properties such as gas/water content and relative permeability on based Nuclear Magnetic Resonance (NMR) measurements. NMR (at full water saturation) is sensitive to porosity and pore size distribution. Thus the method is commonly used to estimate the absolute permeability of rocks. At partial saturation the conventional capillary pore models used for NMR interpretation fail to predict the water distribution in the pore system because they do not account for the water trapped in corners or attached to the inner surface as a wetting film. Therefore, they shouldn't be applied for relative permeability calculation. We used a bundle of capillaries with equilateral triangle-cross-sections to simulate water distribution and transport both for drainage and imbibition as well as the corresponding NMR relaxometry responses. The triangular pore shape was chosen because of the tri- and multi-angular shaped pores caused by secondary clay growth in the pores and observed by SEM (scanning electron microscopy). In contrast to the commonly used tubular pore models this alternative approach accounts for residual water e.g. in corner meniscii. For model validation we used pore throat size distributions obtained from mercury porosimetry as well as from SEM images to calculate both NMR response and permeability. The calculated results correlate well with laboratory measurements carried out on tight gas rocks.

Jorand, R.; Klitzsch, N.; Mohnke, O.; Clauser, C.; Schleifer, N.; de Wijn, B.

2011-12-01

272

A conformational NMR analysis of methymycin aglycones: complete and unambiguous assignments of stereochemically diverse glycosylated methymycin analogs by 1D and 2D NMR techniques and molecular modeling.  

Science.gov (United States)

The (1)H and (13)C NMR spectra of 10-deoxymethynolide (1), 8.9-dihydro-10-deoxymethynolide (2) and its glycosylated derivatives (3-9) were analyzed using gradient-selected NMR techniques, including 1D TOCSY, gCOSY, 1D NOESY (DPFGSENOE), NOESY, gHMBC, gHSQC and gHSQC-TOCSY. The NMR spectral parameters (chemical shifts and coupling constants) of 1-9 were determined by iterative analysis. For the first time, complete and unambiguous assignment of the (1)H NMR spectrum of 10-deoxymethynolide (1) has been achieved in CDCl(3), CD(3)OD and C(6)D(6) solvents. The (1)H NMR spectrum of 8,9-dihydro-10-deoxymethynolide (2) was recorded in CDCl(3), (CD(3))(2)CO and CD(3)OD solutions to determine the conformation. NMR-based conformational analysis of 1 and 2 in conjugation with molecular modeling concluded that the 12-membered ring of the macrolactones may predominantly exist in a single stable conformation in all solvents examined. In all cases, a change in solvent caused only small changes in chemical shifts and coupling constants, suggesting that all glycosylated methymycin analogs exist with similar conformations of the aglycone ring in solution. PMID:23364799

Akhmedov, Novruz G; Gannett, Peter M; Wu, Bulan; Cummings, Matthew M; Train, Brian C

2013-03-01

273

1H HR-MAS NMR and S180 cells: metabolite assignment and evaluation of pulse sequence  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Ressonância magnética nuclear de ¹H de alta resolução com giro no ângulo mágico (HR-MAS NMR) é uma técnica empregada na avaliação de células e tecidos intactos. Entretanto, parâmetros bem estabelecidos de NMR são cruciais para a obtenção de resultados confiáveis. A fim de discutir as principais etap [...] as envolvidas na otimização das análises de HR-MAS NMR, este artigo avaliou diferentes sequências de pulsos e parâmetros de NMR usando células de sarcoma 180 (S180). O completo assinalamento dos metabólitos de S180 é também apresentado para auxiliar estudos futuros. Abstract in english High resolution magic angle spinning ¹H nuclear magnetic resonance spectroscopy (HR-MAS NMR) is a useful technique for evaluation of intact cells and tissues. However, optimal NMR parameters are crucial in obtaining reliable results. To identify the key steps for the optimization of HR-MAS NMR param [...] eters, we assessed different pulse sequences and NMR parameters using sarcoma 180 (S180) cells. A complete assignment of the metabolites of S180 is given to assist future studies.

Aline L. de, Oliveira; Bruno César B., Martinelli; Luciano M., Lião; Flávia C., Pereira; Elisangela P., Silveira-Lacerda; Glaucia B., Alcantara.

1135-11-01

274

A new inversion method for (T2, D) 2D NMR logging and fluid typing  

Science.gov (United States)

One-dimensional nuclear magnetic resonance (1D NMR) logging technology has some significant limitations in fluid typing. However, not only can two-dimensional nuclear magnetic resonance (2D NMR) provide some accurate porosity parameters, but it can also identify fluids more accurately than 1D NMR. In this paper, based on the relaxation mechanism of (T2, D) 2D NMR in a gradient magnetic field, a hybrid inversion method that combines least-squares-based QR decomposition (LSQR) and truncated singular value decomposition (TSVD) is examined in the 2D NMR inversion of various fluid models. The forward modeling and inversion tests are performed in detail with different acquisition parameters, such as magnetic field gradients (G) and echo spacing (TE) groups. The simulated results are discussed and described in detail, the influence of the above-mentioned observation parameters on the inversion accuracy is investigated and analyzed, and the observation parameters in multi-TE activation are optimized. Furthermore, the hybrid inversion can be applied to quantitatively determine the fluid saturation. To study the effects of noise level on the hybrid method and inversion results, the numerical simulation experiments are performed using different signal-to-noise-ratios (SNRs), and the effect of different SNRs on fluid typing using three fluid models are discussed and analyzed in detail.

Tan, Maojin; Zou, Youlong; Zhou, Cancan

2013-02-01

275

Automated NMR relaxation dispersion data analysis using NESSY  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Proteins are dynamic molecules with motions ranging from picoseconds to longer than seconds. Many protein functions, however, appear to occur on the micro to millisecond timescale and therefore there has been intense research of the importance of these motions in catalysis and molecular interactions. Nuclear Magnetic Resonance (NMR relaxation dispersion experiments are used to measure motion of discrete nuclei within the micro to millisecond timescale. Information about conformational/chemical exchange, populations of exchanging states and chemical shift differences are extracted from these experiments. To ensure these parameters are correctly extracted, accurate and careful analysis of these experiments is necessary. Results The software introduced in this article is designed for the automatic analysis of relaxation dispersion data and the extraction of the parameters mentioned above. It is written in Python for multi platform use and highest performance. Experimental data can be fitted to different models using the Levenberg-Marquardt minimization algorithm and different statistical tests can be used to select the best model. To demonstrate the functionality of this program, synthetic data as well as NMR data were analyzed. Analysis of these data including the generation of plots and color coded structures can be performed with minimal user intervention and using standard procedures that are included in the program. Conclusions NESSY is easy to use open source software to analyze NMR relaxation data. The robustness and standard procedures are demonstrated in this article.

Gooley Paul R

2011-10-01

276

NMR: concepts, methods and applications. 2. edition; La RMN: concepts, methodes et applications. 2. edition  

Energy Technology Data Exchange (ETDEWEB)

Since its discovery in 1945, the nuclear magnetic resonance (NMR) has been the object of spectacular developments. These developments concern the structural study of more and more complex and bigger molecules and the production of images. One of the applications of image production is the NMR imaging which has a considerable impact in medicine. Taking into consideration the variety of its experimental and methodological aspects and the range of its applications which is still growing up, NMR has become an entire discipline. This second edition takes stock of the most recent methods and concepts of NMR (multi-pulse and multi-dimensional techniques, signal processing) but also of the more traditional aspects like the structure of spectra and the dynamical parameters. The basic knowledge is presented in an accessible style and the complementary knowledge (mathematics, quantum mechanics) can be found on the Internet. (J.S.)

Canet, D.; Boubel, J.C. [Nancy-1 Univ., Lab. de Methodologie RMN, 54 (France); Canet Soulas, E. [Universite Claude Bernard, CNRS, Lab. CREATIS, 69 - Lyon (France)

2002-07-01

277

Heterogeneous solution NMR signal amplification by reversible exchange.  

Science.gov (United States)

A novel variant of an iridium-based organometallic catalyst was synthesized and used to enhance the NMR signals of pyridine in a heterogeneous phase by immobilization on polymer microbead solid supports. Upon administration of parahydrogen (pH2) gas to a methanol mixture containing the HET-SABRE catalyst particles and the pyridine, up to fivefold enhancements were observed in the (1)H?NMR spectra after sample transfer to high field (9.4?T). Importantly, enhancements were not due to any residual catalyst molecules in solution, thus supporting the true heterogeneity of the SABRE process. Further significant improvements may be expected by systematic optimization of experimental parameters. Moreover, the heterogeneous catalyst is easy to separate and recycle, thus opening a door to future potential applications varying from spectroscopic studies of catalysis, to imaging metabolites in the body without concern of contamination from expensive and potentially toxic metal catalysts or accompanying organic molecules. PMID:24889730

Shi, Fan; Coffey, Aaron M; Waddell, Kevin W; Chekmenev, Eduard Y; Goodson, Boyd M

2014-07-14

278

Low-frequency NMR with a non-resonant circuit  

Science.gov (United States)

Nuclear magnetic resonance typically utilizes a tuned resonance circuit with impedance matching to transmit power and receive signal. The efficiency of such a tuned coil is often described in terms of the coil quality factor, Q. However, in field experiments such as in well-logging, the circuit Q can vary dramatically throughout the depth of the wellbore due to temperature or fluid salinity variations. Such variance can result in erroneous setting of NMR circuit parameters (tuning and matching) and subsequent errors in measurements. This paper investigates the use of a non-resonant transmitter to reduce the circuit sensitivity on Q and demonstrates that such circuits can be efficient in delivering power and current to the coil. We also describe a tuned receiver circuit whose resonant frequency can be controlled digitally. Experimental results show that a range of common NMR experiments can be performed with our circuits.

Hopper, Timothy; Mandal, Soumyajit; Cory, David; Hürlimann, Martin; Song, Yi-Qiao

2011-05-01

279

Baseline Correction for NMR Spectroscopic Metabolomics Data Analysis  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background We propose a statistically principled baseline correction method, derived from a parametric smoothing model. It uses a score function to describe the key features of baseline distortion and constructs an optimal baseline curve to maximize it. The parameters are determined automatically by using LOWESS (locally weighted scatterplot smoothing regression to estimate the noise variance. Results We tested this method on 1D NMR spectra with different forms of baseline distortions, and demonstrated that it is effective for both regular 1D NMR spectra and metabolomics spectra with over-crowded peaks. Conclusion Compared with the automatic baseline correction function in XWINNMR 3.5, the penalized smoothing method provides more accurate baseline correction for high-signal density metabolomics spectra.

Rocke David M

2008-07-01

280

Saliva metabolomics by NMR for the evaluation of sport performance.  

Science.gov (United States)

The paper reports preliminary results of a study in order to verify that saliva is a bio-fluid sensitive to metabolite variations due to stress and fatigue in soccer athletes, and possibly, to identify potential markers of test of performance. Saliva samples of fourteen professional soccer players were collected before and after the stressful physical activity of the level 1 Yo-Yo intermittent recovery test and, also, physiological parameters were evaluated. The NMR spectra of saliva offer a metabolites profiling which was analyzed by Principal Component Analysis as a blind test. The results of NMR pre and post test shows that it was possible to cluster the best and the worst performing athletes and that the role of the actual player may be diagnosed by a different cluster of metabolites profile. Thus saliva can be considered a biofluid metabolically sensitive to the induced physical stress and, in the future, deeper investigated to monitor the performances in athletes. PMID:24176749

Santone, C; Dinallo, V; Paci, M; D'Ottavio, S; Barbato, G; Bernardini, S

2014-01-01

 
 
 
 
281

NMR analysis and site-specific protonation constants of streptomycin.  

Science.gov (United States)

Streptomycin, the classical aminoglycoside antibiotic, generally considered the most basic drug compound was characterized in terms of protonation macro- and microconstants. ¹H NMR-pH and ¹H-¹³C HSQC-pH titrations were carried out on streptomycin and streptidine, a symmetrical constituent compound of reduced complexity to monitor the proton-binding processes of the basic sites. Accurate, undistorted, electrodeless pH measurement was ensured by a new set of in tube indicators. The microscopic protonation constants of the two guanidino groups of streptomycin were calculated by evaluating the various NMR-pH data and transferring the pair-interactivity parameter from streptidine to streptomycin. Inherent guanidino basicities fall in the range of 13.03-13.39 log k units, which drop to 12.48-12.85 upon protonation of the other site. pH-dependent distribution of the major microspecies and charge-related biological consequences are provided. PMID:22079046

Orgován, Gábor; Noszál, Béla

2012-02-01

282

Applications of NMR in Dairy Research  

Digital Repository Infrastructure Vision for European Research (DRIVER)

NMR is a robust analytical technique that has been employed to investigate the properties of many substances of agricultural relevance. NMR was first used to investigate the properties of milk in the 1950s and has since been employed in a wide range of studies; including properties analysis of specific milk proteins to metabolomics techniques used to monitor the health of dairy cows. In this brief review, we highlight the different uses of NMR in the dairy industry.

Maher, Anthony D.; Rochfort, Simone J.

2014-01-01

283

Applications of NMR in Dairy Research  

Directory of Open Access Journals (Sweden)

Full Text Available NMR is a robust analytical technique that has been employed to investigate the properties of many substances of agricultural relevance. NMR was first used to investigate the properties of milk in the 1950s and has since been employed in a wide range of studies; including properties analysis of specific milk proteins to metabolomics techniques used to monitor the health of dairy cows. In this brief review, we highlight the different uses of NMR in the dairy industry.

Anthony D. Maher

2014-03-01

284

Multiple quantum NMR dynamics in pseudopure states  

International Nuclear Information System (INIS)

We investigate numerically the multiple quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by dipole-dipole interactions in the case of the pseudopure initial state. Simulations of the MQ NMR with real molecular structures such as six dipolar-coupled proton spins of benzene, hydroxyl proton chains in calcium hydroxyapatite, and fluorine chains in calcium fluorapatite open the way to experimental NMR testing of the obtained results. It was found that multiple-spin correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.

285

Multiple quantum NMR dynamics in pseudopure states  

Science.gov (United States)

We investigate numerically the multiple quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by dipole-dipole interactions in the case of the pseudopure initial state. Simulations of the MQ NMR with real molecular structures such as six dipolar-coupled proton spins of benzene, hydroxyl proton chains in calcium hydroxyapatite, and fluorine chains in calcium fluorapatite open the way to experimental NMR testing of the obtained results. It was found that multiple-spin correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.

Furman, G. B.

2009-01-01

286

NMR studies of isotopically labeled RNA  

Energy Technology Data Exchange (ETDEWEB)

In summary, the ability to generate NMR quantities of {sup 15}N and {sup 13}C-labeled RNAs has led to the development of heteronuclear multi-dimensional NMR techniques for simplifying the resonance assignment and structure determination of RNAs. These methods for synthesizing isotopically labeled RNAs are only several years old, and thus there are still relatively few applications of heteronuclear multi-dimensional NMR techniques to RNA. However, given the critical role that RNAs play in cellular function, one can expect to see an increasing number of NMR structural studies of biologically active RNAs.

Pardi, A. [Univ. of Colorado, Boulder, CO (United States)

1994-12-01

287

NMR exposure sensitizes tumor cells to apoptosis.  

Science.gov (United States)

NMR technology has dramatically contributed to the revolution of image diagnostic. NMR apparatuses use combinations of microwaves over a homogeneous strong (1 Tesla) static magnetic field. We had previously shown that low intensity (0.3-66 mT) static magnetic fields deeply affect apoptosis in a Ca2+ dependent fashion (Fanelli et al., 1999 FASEBJ., 13;95-102). The rationale of the present study is to examine whether exposure to the static magnetic fields of NMR can affect apoptosis induced on reporter tumor cells of haematopoietic origin. The impressive result was the strong increase (1.8-2.5 fold) of damage-induced apoptosis by NMR. This potentiation is due to cytosolic Ca2+ overload consequent to NMR-promoted Ca2+ influx, since it is prevented by intracellular (BAPTA-AM) and extracellular (EGTA) Ca2+ chelation or by inhibition of plasma membrane L-type Ca2+ channels. Three-days follow up of treated cultures shows that NMR decrease long term cell survival, thus increasing the efficiency of cytocidal treatments. Importantly, mononuclear white blood cells are not sensitised to apoptosis by NMR, showing that NMR may increase the differential cytotoxicity of antitumor drugs on tumor vs normal cells. This strong, differential potentiating effect of NMR on tumor cell apoptosis may have important implications, being in fact a possible adjuvant for antitumor therapies. PMID:16528477

Ghibelli, L; Cerella, C; Cordisco, S; Clavarino, G; Marazzi, S; De Nicola, M; Nuccitelli, S; D'Alessio, M; Magrini, A; Bergamaschi, A; Guerrisi, V; Porfiri, L M

2006-03-01

288

NMR on alkali-doped C60  

International Nuclear Information System (INIS)

In order to unravel the electronic and structural properties of Rb3C60 and K4C60 13C and 87Rb pulsed NMR spectroscopy was applied. The following results were obtained: The 87Rb NMR line shift is found to be temperature dependent for all three lines observed and can be interpreted in terms of a small hyperfine coupling of the conduction electrons to the Rb nuclear spins. It is also shown that 87Rb NMR is a sensitive probe to structural changes. From 13C NMR we obtained information on the dynamics of C60 and on the hyperfine coupling. (orig.)

289

Advance reservoir evaluation by using NMR logging  

International Nuclear Information System (INIS)

Based on brief explanation of the measurement principle for nuclear magnetic resonance (NMR) logging, this paper illustrates the importance of NMR logging in reservoir evaluation through typical case examples. These case examples include: Reservoir characterization and productivity evaluation by using NMR logging, determination of reservoir porosity in complex lithology, identification of oil, water and gas zones under complex reservoir conditions where resistivity log data give poor indication, guiding the implementation of completion and drilling programs, etc. Excellent application results indicate that NMR logging has its special features and advantages in comparison with conventional logging techniques. It is a very practical and very promising logging technology

290

Field Experiment Provides Ground Truth for Surface NMR Measurement  

Science.gov (United States)

Effective and sustainable long-term management of fresh water resources requires accurate information about the availability of water in groundwater aquifers. Proton Nuclear Magnetic Resonance (NMR) can provide a direct link to the presence of water in the pore space of geological materials through the detection of the nuclear magnetization of the hydrogen nuclei (protons) in the pore water. Of interest for groundwater applications is the measurement of the proton-NMR relaxation time constant, referred to as T2. This parameter is sensitive to the geometry of the water-filled pore space and can be related to the hydraulic conductivity. NMR logging instruments, which have been available since the 1980’s, provide direct measurements of T2 in boreholes. Surface NMR (SNMR) is a non-invasive geophysical method that uses a loop of wire on the surface to probe the NMR properties of groundwater aquifers to a depth of ~100 m, without the need for the drilling of boreholes. SNMR provides reliable measurements of a different NMR time constant referred to as T2*, that is related to, but not necessarily equivalent to, T2. The relationship between T2* and T2 is likely to depend upon the physical environment and the composition of the sampled material. In order to advance the use of SNMR as a non-invasive means of characterizing groundwater aquifers, we must answer the fundamental question: When probing a groundwater aquifer, what information is provided by T2*, the time constant measured with SNMR? Our approach was to conduct a field experiment in Nebraska, in an area underlain by the Quaternary Alluvium and Tertiary Ogallala aquifers. We first used SNMR to obtain a 1D profile of T2* to a depth of ~60 m. We then drilled a well inside the area of the SNMR loop, to a depth of ~150 m, and used the drill cuttings to describe the composition of the geologic material at the site. The borehole was kept open for 2 days to acquire logging NMR T2 measurements over the total depth. Three months later, borehole NMR T2 measurements were repeated with a second instrument; and logging measurements were made of the ambient magnetic field. Comparison of the three measurements of NMR relaxation show that T2* at this site is affected by inhomogeneity in the background magnetic field; this effect is most pronounced in sand and gravel units where dephasing, rather than surface relaxation, dominates the NMR response. When the borehole T2 measurements are transformed to T2*, by incorporating a term to account for this effect, we find good agreement between the two forms of measurement over the investigated depth range. The ability to ground truth the SNMR measurement has advanced our understanding of the time constant measured by SNMR, T2*, and its relationship to pore-scale properties. This is a critical step in developing SNMR as a reliable geophysical method for evaluation of groundwater resources.

Knight, R. J.; Abraham, J. D.; Cannia, J. C.; Dlubac, K. I.; Grau, B.; Grunewald, E. D.; Irons, T.; Song, Y.; Walsh, D.

2010-12-01

291

rNMR: open source software for identifying and quantifying metabolites in NMR spectra.  

Science.gov (United States)

Despite the extensive use of nuclear magnetic resonance (NMR) for metabolomics, no publicly available tools have been designed for identifying and quantifying metabolites across multiple spectra. We introduce here a new open source software tool, rNMR, which provides a simple graphics-based method for visualizing, identifying, and quantifying metabolites across multiple one- or two-dimensional NMR spectra. rNMR differs from existing software tools for NMR spectroscopy in that analyses are based on regions of interest (ROIs) rather than peak lists. ROIs contain all of the underlying NMR data within user-defined chemical shift ranges. ROIs can be inspected visually, and they support robust quantification of NMR signals. ROI-based analyses support simultaneous views of metabolite signals from up to hundreds of spectra, and ROI boundaries can be adjusted dynamically to ensure that signals corresponding to assigned atoms are analyzed consistently throughout the dataset. We describe how rNMR greatly reduces the time required for robust bioanalytical analysis of complex NMR data. An rNMR analysis yields a compact and transparent way of archiving the results from a metabolomics study so that it can be examined and evaluated by others. The rNMR website at http://rnmr.nmrfam.wisc.edu offers downloadable versions of rNMR for Windows, Macintosh, and Linux platforms along with extensive help documentation, instructional videos, and sample data. PMID:19821464

Lewis, Ian A; Schommer, Seth C; Markley, John L

2009-12-01

292

Access to NMR Spectroscopy for Two-Year College Students: The NMR Site at Trinity University  

Science.gov (United States)

Students at two-year colleges and small four-year colleges have often obtained their exposure to NMR spectroscopy through "canned" spectra because the cost of an NMR spectrometer, particularly a high-field spectrometer, is prohibitive in these environments. This article describes the design of a NMR site at Trinity University in which spectral…

Mills, Nancy S.; Shanklin, Michael

2011-01-01

293

NMR of small platinum particles  

International Nuclear Information System (INIS)

195Pt NMR lineshapes as well as relaxation data are presented in three different samples of platinum metal particles (46%, 26%, and 15% dispersion) supported on alumina. The electronic properties of these particles are very much different from that of bulk Pt metal. A prominent peak in the lineshape has been identified as a surface resonance which arises from Pt nuclei on the surface of the Pt particles. We find that these surface Pt atoms are non-metallic when coated with adsorbed molecules

294

Permanent magnet NMR imaging apparatus  

International Nuclear Information System (INIS)

An NMR apparatus is described having a desired imaging volume for imaging of biological tissue, the apparatus comprising bias means for generating a bias field, means for generating gradient fields, and radio frequency means for applying a pulse of electromagnetic radiation to the biological tissue and for detecting the resultant signals emitted from the tissue. The bias means consists of dipole ring magnets, each dipole ring magnet comprising segments, each segment comprising an oriented, anisotropic permanent magnet material arranged in a ring so that there is a substantially continuous ring of permanent magnet material

295

PEP parameters  

International Nuclear Information System (INIS)

This note is a compilation of PEP parameters as they stand as of this date. PEP parameters have been modified too often for us to state that this list is complete or final; however, since construction of PEP hardware has begun the parameters must of necessity become more frozen in. This compilation is incomplete for most of the technical components, including only those parameters required for beam dynamics and beam parameter calculations. A more detailed compilation is being prepared as an update of the Conceptual Design Report. 6 tabs. 1 fig

296

NMR of metal ions: biochemical investigations--introduction  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) of metalloproteins is briefly discussed, and a summary of the properties of several NMR active nuclei is given. In addition, the use of these NMR properties in solving biochemical problems is presented

297

Hypothesis driven assessment of an NMR curriculum  

Science.gov (United States)

The goal of this project was to develop a battery of assessments to evaluate an undergraduate NMR curriculum at Penn State University. As a chemical education project, we sought to approach the problem of curriculum assessment from a scientific perspective, while remaining grounded in the education research literature and practices. We chose the phrase hypothesis driven assessment to convey this process of relating the scientific method to the study of educational methods, modules, and curricula. We began from a hypothesis, that deeper understanding of one particular analytical technique (NMR) will increase undergraduate students' abilities to solve chemical problems. We designed an experiment to investigate this hypothesis, and data collected were analyzed and interpreted in light of the hypothesis and several related research questions. The expansion of the NMR curriculum at Penn State was funded through the NSF's Course, Curriculum, and Laboratory Improvement (CCLI) program, and assessment was required. The goal of this project, as stated in the grant proposal, was to provide NMR content in greater depth by integrating NMR modules throughout the curriculum in physical chemistry, instrumental, and organic chemistry laboratory courses. Hands-on contact with the NMR spectrometer and NMR data and repeated exposure of the analytical technique within different contexts (courses) were unique factors of this curriculum. Therefore, we maintained a focus on these aspects throughout the evaluation process. The most challenging and time-consuming aspect of any assessment is the development of testing instruments and methods to provide useful data. After key variables were defined, testing instruments were designed to measure these variables based on educational literature (Chapter 2). The primary variables measured in this assessment were: depth of understanding of NMR, basic NMR knowledge, problem solving skills (HETCOR problem), confidence for skills used in class (within the hands-on NMR modules), confidence for NMR tasks (not practiced), and confidence for general science tasks. Detailed discussion of the instruments, testing methods and experimental design used in this assessment are provided (Chapter 3). All data were analyzed quantitatively using methods adapted from the educational literature (Chapter 4). Data were analyzed and the descriptive statistics, independent t-tests between the experimental and control groups, and correlation statistics were calculated for each variable. In addition, for those variables included on the pretest, dependent t-tests between pretest and posttest scores were also calculated. The results of study 1 and study 2 were used to draw conclusions based on the hypothesis and research questions proposed in this work (Chapter 4). Data collected in this assessment were used to answer the following research questions: (1) Primary research question: Is depth of understanding of NMR linked to problem solving skills? (2) Are the NMR modules working as intended? Do they promote depth of understanding of NMR? (a) Will students who complete NMR modules have a greater depth of understanding of NMR than students who do not complete the modules? (b) Is depth of understanding increasing over the course of the experiment? (3) Is confidence an intermediary between depth of understanding and problem solving skills? Is it linked to both variables? (4) What levels of confidence are affected by the NMR modules? (a) Will confidence for the NMR class skills used in the modules themselves be greater for those who have completed the modules? (b) Will confidence for NMR tasks not practiced in the course be affected? (c) Will confidence for general science tasks be affected? (d) Are different levels of confidence (class skills, NMR tasks, general science tasks) linked to each other? Results from this NMR curriculum assessment could also have implications outside of the courses studied, and so there is potential to impact the chemical education community (section 5.2.1). In addition to providing reliable testing instrume

Cossey, Kimberly

298

New techniques in NMR spectroscopy  

International Nuclear Information System (INIS)

In 1989, Soerensen introduced a method, the unitary bound, for calculating the maximum efficiencies of coherence transfer processes in NMR. This thesis applies this method to quadrupolar nuclei, an area not investigated by Soerensen. In doing so, several questions are raised, and answered, as to the implications of the unitary bound for coherence transfer processes in all areas of NMR. These include discussions of when such processes can be reversed without loss of signal and when sequential coherence transfer steps can be carried out with both steps having the maximum efficiency. One area of NMR of quadrupolar nuclei which has attracted some interest over the past few years has been the selective excitation of 23Na nuclei in ordered environments. This was hinted at by Jaccard et al. in 1986 and demonstrated in biological systems by Eliav et al. in 1992, who achieved the selective excitation using a double-quantum filtration (DQF) experiment. The following year, Kemp-Harper and Wimperis demonstrated that the Jeener-Broekaert experiment could be used to achieve the same selectivity through excitation of quadrupolar order. The unitary bound shows that neither of these experiments achieve the maximum coherence transfer efficiency. This thesis sets out to improve upon the efficiency of these two experiments. Two multiple-pulse experiments are investigated. One seeks to improve upon the efficiency of the Jeener-Broekaert experiment for spin I = 3/2 nuclei by 33% to achieve the unitary bound efficiency. The other seeks to improve the efficiency of the selective DQF experiment by 41% to achieve the bound for spin I= 3/2 nuclei. 23Na NMR spectra of cartilage and a lyotropic liquid crystal are presented which show that, although the new version of the Jeener-Broekaert experiment achieves no greater efficiency in practical application than the original, the new DQF experiment produces up to half of the expected improvement in efficiency. Alternative techniques to the Jeener-Broekaert experiment for exciting and detecting quadrupolar order are the well-known methods of ADRF and ARRF. Furthermore, these methods promise to be broadband with respect to the quadrupolar splitting. The application of these techniques to quadrupolar nuclei is investigated theoretically and it is proved that they will achieve the unitary bound coherence transfer efficiencies for any quadrupolar nucleus. ADRF and ARRF pulse shapes are derived for spins I = 1 and I = 3/2 and applied to 2H and 23Na NMR of cartilage and liquid crystals. Although the desired improvements in sensitivity are not observed in practice, the broadband nature of these methods is demonstrated. The use of an adiabatic frequency-swept pulse train to excite second-rank double-quantum coherence is also investigated, both theoretically and using computer simulations. (author)

299

NMR Spectroscopy and Its Value: A Primer  

Science.gov (United States)

Nuclear magnetic resonance (NMR) spectroscopy is widely used by chemists. Furthermore, the use of NMR spectroscopy to solve structures of macromolecules or to examine protein-ligand interactions is popular. Yet, few students entering graduate education in biological sciences have been introduced to this method or its utility. Over the last six…

Veeraraghavan, Sudha

2008-01-01

300

Using Cloud Storage for NMR Data Distribution  

Science.gov (United States)

An approach using Google Groups as method for distributing student-acquired NMR data has been implemented. We describe how to configure NMR spectrometer software so that data is uploaded to a laboratory section specific Google Group, thereby removing bottlenecks associated with printing and processing at the spectrometer workstation. Outside of…

Soulsby, David

2012-01-01

 
 
 
 
301

NMR is getting ever more efficient  

International Nuclear Information System (INIS)

NMR (nuclear magnetic resonance) tomography is losing its reputation as a rather exotic examination method. For years, this method has been restricted to specific areas of indication; however, its range of application is broadening today. NMR imaging of i.e. the heart function, vascular system or bones provide valuable help in diagnosis by now - especially if conventional methods fall short. (orig.)

302

NMR studies on irradiated lecithin systems  

International Nuclear Information System (INIS)

By means of NMR and u.v. spectroscopy we have examined the radiation damage of liposomes under different experimental conditions including addition of a nitro compound as an effector with the aim of minimizing irradiation effects. Some NMR spectroscopic results were derived from partially relaxed spectra. This method seems to be useful for the detection of different radiation effects. (author)

303

2D NMR studies of biomolecules  

International Nuclear Information System (INIS)

The work described in this thesis comprises two related subjects. The first part describes methods to derive high-resolution structures of proteins in solution using two-dimensional (2-D) NMR. The second part describes 2-D NMR studies on the interaction between proteins and DNA. (author). 261 refs.; 52 figs.; 23 tabs

304

NMR imagery. Non-medical uses  

International Nuclear Information System (INIS)

This work deals with the non-medical uses of the nuclear magnetic resonance imagery (NMR I). After having determined the characteristics of the non-medical NMR I, the author describes some uses in the fields of polymer and composite materials. The crystal structures of these materials have been determined and the solvents diffusion in polymers, ceramics and rocks has been studied. Some chemical uses of the NMR I are given and more particularly the study of anisotropic polymerization reactions as photo polymerization reactions. The defects of diluents and plasticizers and the propergol distribution in rockets solid fuels have been analyzed by NMR I. The absorbed hydrogen in palladium has also been characterized and some aspects of the chromatography processes have been followed by NMR I. (O.L.). 37 refs., 9 figs., 2 tabs

305

Image reconstruction by NMR Fresnel diffractive imaging technique  

International Nuclear Information System (INIS)

A new approach to MR angiography, the NMR diffractive imaging technique, has been investigated. The expression for NMR signals obtained in the NMR diffractive imaging technique is similar to the equation for Fresnel diffraction in light waves or sound waves. Therefore, it is possible to reconstruct an image focusing on any plane in the depth direction from data scanned two-dimensionally by changing an imaging parameter in the reconstruction step. To support this imaging technique, a coil system composed of six coils was designed. Experiments were performed using an ultra-low-field MRI scanner to acquire two-dimensional data in the proposed technique. Even though blurred images outside the focus are superimposed on the image in the focal plane, the three-dimensional distribution of the object can be recognized by moving the focal plane in the depth direction. To obtain supplemental information for the object, acquiring images from different angles is helpful for recognizing the spatial distribution of the object more precisely. Although the image obtained contains blurred images outside the focus the proposed imaging technique is expected to be useful in MR fast angiography. (author)

306

High resolution NMR microscopy of plants and fungi.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) microscopy is a completely noninvasive technique that can be used to acquire images with high spatial resolution through opaque objects such as plant organs and tissue parts. The image contrast can be chosen to represent the anatomical details or to visualize the spatial distribution of a range of physico-chemical parameters such as the apparent diffusion constant of water or the velocity of water flow within plants in vivo. In addition, images can be generated which show the spatial distribution of metabolites. Furthermore, it is possible to detect chemical compounds labelled with the stable isotope (13)C and to generate images showing the spatial distribution of the (13)C label in the intact plant. The ability to monitor water flow and transport of (13)C-labelled tracer in intact plants with NMR microscopy favours the use of this technique in the investigation of long-distance transport processes in plants. A short introduction into the technical principles of NMR microscopy is provided and the problems associated with applications to plants are summarized. The potential of the technique is explained with applications to Zinnia elegans plants, wheat grains and Brassica napus siliques. PMID:15102065

Köckenberger, W; De Panfilis, C; Santoro, D; Dahiya, P; Rawsthorne, S

2004-05-01

307

NMR studies of molecules in liquid crystals and graphite  

Energy Technology Data Exchange (ETDEWEB)

NMR experiments to measure proton dipole couplings were performed on a series of n-alkanes (n-hexane through n-decane) dissolved in nematic liquid crystals. Computer modeling of the experimental NMR-spectra was done using several different models for intermolecular interactions in these systems. The model of Photinos et al. was found to be best in describing the intermolecular interactions in these systems and can provide a statistical picture of the conformation and orientation of the alkane molecules in their partially-oriented environment. Order parameters and conformational distributions for the alkanes can be calculated from the modeling. The alkanes are found to have conformational distributions very much like those found in liquid alkanes. Proton NMR spectra of tetrahydrofuran (THF) intercalated in two graphite intercalation compounds were also measured. Computer simulations of these spectra provide a picture of THF in the constrained environment between the graphene layers where the THF is oriented at a particular angle, can translate and rotate freely, but does not appear to pseudorotate.

Rosen, M.E.

1992-06-01

308

KAIS resistive NMR-CT and its clinical application  

International Nuclear Information System (INIS)

This paper contains the results of clinical studies with 0.1 and 0.15 Tesla KAIS NMR tomograph which was developed by Korean Advanced Institute of Science. A variety of imaging modes such as saturation recover (SR), spin echo (SE), and inversion recovery (IR) as well as echo and repetition times were applied. Clinical imagings were performed on 22 patients with diseases of brain (15 cases), cervical spine (2 cases), chest (2 cases), pancreas (2 cases), and kidney (1 case). In SR imaging, we have obtained images strongly dependent on the hydrogen nuclei density. SE with long echo time and IR are effective for T2 and T1 dependent images, respectively. Results of clinical NMR imaging are presented and compared with X-CT and the other radiological examinations. Obtained results appear promising and with further examinations along with parameter adjustment, it is expected that the NMR imaging will not only substitute many conventional diagnostic methods such as X-ray CT but also be useful for the early detection of tumor and other lesions not obtainable with other modalities

309

Xe-129 NMR of xenon dissolved in biological media.  

Science.gov (United States)

The high solubility and large chemical shift of ^129Xe in various tissues makes it an ideal, non-invasive probe for pathological conditions such as cancer or atherosclerosis. To this end, we report NMR measurements of lineshapes, chemical shifts, and relaxation times of ^129Xe dissolved in the following biological tissues in vitro: heart, muscle, sinew, stomach(R.K. Mazitov, K. M. Enikeev, et al., Dokl. Akad. Nauk) 365, 396 (1999)., and the white and yolk of egg. NMR measurements of xenon dissolved in olive and sunflower oils are also reported. Tissues weighing 160--250 mg, not exposed to freezing, were studied in a 11.75 T field at the ^129Xe resonance frequency of 138.4 MHz; the pressure of xenon in the sealed-sample ampoules was ~20 bar. The influence of drugs and water content on tissues was studied. No xenon-water clathrates(J.A. Ripmeester and D.W. Davidson, J. Mol. Struct. ) 75, 67 (1981). were observed in the tissues, even at the high pressures used. The aim of this study is to establish possible correlations between the NMR parameters of dissolved xenon and the state of the tissue.

Mazitov, R. K.; Kuzma, N. N.; Happer, W.; Driehuys, B.; Merrill, G. F.

2002-03-01

310

NMR study of the alkaline isomerization of fefficytochrome c  

International Nuclear Information System (INIS)

The pH-induced isomerization of horse heart cytochrome c has been studied by 1H NMR. We find that the transition occuring in D2O with a pKa measuresd as 9.5 ± 0.1 is from the native species to a mixture of two basic forms which have very similar NMR spectra. The heme methyl peaks of these two forms have been assigned by 2D exchange NMR. The forward rate constant (native to alkaline cytochrome c) has a value of 4.0 ± 0.6 s-1 at 27 deg C and is independent of pH; the reverse rate constant is pH-dependent. The activation parameters are ?H 12.8 ± 0.8 kcal-mol1, ?S = -12.9 ± 2.0 e.u. for the forward reaction and ?H = 6.0 ± 0.3 kcal-mol-1, ?S = - 35.1 ± 1.3 e.u. for the reverse reaction (Ph = 9.28). ?H and ?S for the isomerization are 6.7 ± 0.6 kcal-mol-1 and 21.9 ± 1.0 e.u., respectively. (author). 26 refs.; 5 figs

311

Classification of Italian honeys by 2D HR-NMR.  

Science.gov (United States)

The importance of honey has been recently increased because of its nutrient and therapeutic effects, but the adulteration of honey in terms of botanical origin has increased, too. The floral origin of honeys is usually determined using melisso-palynological analysis and organoleptic characteristics, but the application of these techniques requires some expertise. A number of papers have confirmed the possibility of characterizing honey samples by selected chemical parameters. In this study high-resolution nuclear magnetic resonance (HR-NMR) and multivariate statistical analysis methods were used to identify and classify honeys of five different floral sources. The 71 honey samples (robinia, chestnut, citrus, eucalyptus, polyfloral) were analyzed by HR-NMR using both 1H NMR and heteronuclear multiple bond correlation spectroscopy (HMBC). Spectral data were analyzed by application of unsupervised and supervised pattern recognition and multivariate statistical techniques such as principal component analysis (PCA) and general discriminant analysis (GDA). The use of 1H-(13)C HMBC coupled with appropriate statistical analysis seems to be an efficient technique for the classification of honeys. PMID:18205311

Lolli, Massimo; Bertelli, Davide; Plessi, Maria; Sabatini, Anna Gloria; Restani, Cinzia

2008-02-27

312

NMR relaxometry as a versatile tool to study Li ion dynamics in potential battery materials.  

Science.gov (United States)

NMR spin relaxometry is known to be a powerful tool for the investigation of Li(+) dynamics in (non-paramagnetic) crystalline and amorphous solids. As long as significant structural changes are absent in a relatively wide temperature range, with NMR spin-lattice (as well as spin-spin) relaxation measurements information on Li self-diffusion parameters such as jump rates and activation energies are accessible. Diffusion-induced NMR relaxation rates are governed by a motional correlation function describing the ion dynamics present. Besides the mean correlation rate of the dynamic process, the motional correlation function (i) reflects deviations from random motion (so-called correlation effects) and (ii) gives insights into the dimensionality of the hopping process. In favorable cases, i.e., when temperature- and frequency-dependent NMR relaxation rates are available over a large dynamic range, NMR spin relaxometry is able to provide a comprehensive picture of the relevant Li dynamic processes. In the present contribution, we exemplarily present two recent variable-temperature (7)Li NMR spin-lattice relaxation studies focussing on Li(+) dynamics in crystalline ion conductors which are of relevance for battery applications, viz. Li(7) La(3)Zr(2)O(12) and Li(12)Si(7). PMID:22364761

Kuhn, A; Kunze, M; Sreeraj, P; Wiemhöfer, H D; Thangadurai, V; Wilkening, M; Heitjans, P

2012-04-01

313

Sensitivity and resolution enhancement of oriented solid-state NMR: application to membrane proteins.  

Science.gov (United States)

Oriented solid-state NMR (O-ssNMR) spectroscopy is a major technique for the high-resolution analysis of the structure and topology of transmembrane proteins in native-like environments. Unlike magic angle spinning (MAS) techniques, O-ssNMR spectroscopy requires membrane protein preparations that are uniformly oriented (mechanically or magnetically) so that anisotropic NMR parameters, such as dipolar and chemical shift interactions, can be measured to determine structure and orientation of membrane proteins in lipid bilayers. Traditional sample preparations involving mechanically aligned lipids often result in short relaxation times which broaden the (15)N resonances and encumber the manipulation of nuclear spin coherences. The introduction of lipid bicelles as membrane mimicking systems has changed this scenario, and the more favorable relaxation properties of membrane protein (15)N and (13)C resonances make it possible to develop new, more elaborate pulse sequences for higher spectral resolution and sensitivity. Here, we describe our recent progress in the optimization of O-ssNMR pulse sequences. We explain the theory behind these experiments, demonstrate their application to small and medium size proteins, and describe the technical details for setting up these new experiments on the new generation of NMR spectrometers. PMID:24160761

Gopinath, T; Mote, Kaustubh R; Veglia, Gianluigi

2013-11-01

314

Analysis of porous media and objects of cultural heritage by mobile NMR  

Energy Technology Data Exchange (ETDEWEB)

Low-field NMR techniques are used to study porous system, from simple to complex structures, and objects of cultural heritage. It is shown that NMR relaxometry can be used to study the fluid dynamics inside a porous system. A simple theoretical model for multi-site relaxation exchange NMR is used to extract exchange kinetic parameters when applied on a model porous systems. It provides a first step towards the study of more complex systems, where continuous relaxation distributions are present, such as soil systems or building materials. Moisture migration is observed in the soil systems with the help of 1D and 2D NMR relaxometry methods. In case of the concrete samples, the difference in composition makes a significant difference in the ability of water uptake. The single-sided NMR sensor proves to be a useful tool for on-site measurements. This is very important also in the case of the cultural heritage objects, as most of the objects can not be moved out of their environment. Mobile NMR turns out to be a simple but reliable and powerful tool to investigate moisture distributions and pore structures in porous media as well as the conservation state and history of objects of cultural heritage.

Haber, Agnes

2012-11-01

315

Bituminous ore characterization by integrating low-field NMR with density and particle size distribution measurements  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) imaging is often used to determine the content of oil sands ore. However, it is difficult for current NMR spectrometers to differentiate bitumen spectra and clay-bound water signals. This paper provided details of a novel method for determining the fluid and solids content of oil sands using low-field NMR. The method involved the integration of a density measurement to an NMR algorithm combined with laboratory oil sands evaluations. Thawed raw oil sands samples were weighed and injected with nitrogen to calculate the gas occupied volume. An independent solid content estimate was made by measuring both the weight and the bulk density of an ore sample. The sample was then placed into an NMR spectrometer and exposed to different CPMG parameters. Bitumen and water content were determined using the NMR algorithm. Particle size distribution analysis using Dean-Stark extraction showed that the method correlated with the fast relaxation components of water spectra in both oil sands and water-saturated sand extracted from the ore. A vacuum saturation step was then followed by a centrifugal desaturation of the sand to irreducible saturation. The method was then tested with samples of 4 Athabasca oil sands. It was concluded that use of the new method will accelerate core analysis times

316

Analysis of porous media and objects of cultural heritage by mobile NMR  

International Nuclear Information System (INIS)

Low-field NMR techniques are used to study porous system, from simple to complex structures, and objects of cultural heritage. It is shown that NMR relaxometry can be used to study the fluid dynamics inside a porous system. A simple theoretical model for multi-site relaxation exchange NMR is used to extract exchange kinetic parameters when applied on a model porous systems. It provides a first step towards the study of more complex systems, where continuous relaxation distributions are present, such as soil systems or building materials. Moisture migration is observed in the soil systems with the help of 1D and 2D NMR relaxometry methods. In case of the concrete samples, the difference in composition makes a significant difference in the ability of water uptake. The single-sided NMR sensor proves to be a useful tool for on-site measurements. This is very important also in the case of the cultural heritage objects, as most of the objects can not be moved out of their environment. Mobile NMR turns out to be a simple but reliable and powerful tool to investigate moisture distributions and pore structures in porous media as well as the conservation state and history of objects of cultural heritage.

317

Full differentiation and assignment of boron species in the electrolytes Li2B6O9F2 and Li2B3O4F3 by solid-state 11B NMR spectroscopy  

International Nuclear Information System (INIS)

sub>F3. Highlights: ? Characterisation of title compounds by solid-state 11B NMR spectroscopy. ? Sub-spectra of boron species separated by evaluation of 3QMAS spectra. ? Isotropic chemical shift and quadrupolar interaction parameters determined. ? Full boron assignment based on NMR parameters and response to 19F decoupling.

318

Dynamic NMR studies of molecular motions and order in calamitic and discotic liquid crystals  

Science.gov (United States)

This dissertation reports a study of three kinds of liquid crystals using modern solid state NMR techniques: chiral rod-like liquid crystals, bent-core mesogens and disc-like liquid crystals. The properties and structures of liquid crystals are first introduced in Chapter 1. To understand the principles of different NMR phenomena, quantum mechanical theory is adopted to study different nuclear spin interactions and NMR techniques in Chapter 2. In the next part of this dissertation (Chapter 3-6), 2H NMR methods are used to investigate the dynamics and structures of some liquid crystal phases. This is first done using the spin relaxation study. The parameters obtained from the model simulation can describe the molecular motion and internal dynamics in the fast motion region. Secondly, we investigate the dynamic process of discotic mesophases and unwound smectic C* phase using the line shape simulation study. 2D 2H NMR exchange experiments are then performed to study the jump process in TGBA* phase and SmC* phase. The above investigation has demonstrated some powerful NMR methods for the dynamic study of liquid crystals. The third part of the dissertation (Chapter 7-9) is concerned with 13C NMR techniques. After we introduce the quantum theory of different pulse sequences, theoretical models are presented to fit observations such as chemical shifts and dipolar splittings. Moreover high resolution liquid 13C NMR experiments are introduced to study some bent-core molecules. They are useful to assist the carbon peak assignments of these molecules. The structure and ordering information of liquid crystals can be determined in their mesophases. Finally, a brief summary of the dissertation is given in the last chapter.

Zhang, Jing

319

29Si MAS NMR of zeolites  

International Nuclear Information System (INIS)

The isotropic 29Si chemical shift in silicates and aluminosilicates is related to the number and type of tetrahedrally bound atoms in the second coordination sphere of the silicon atom. By means of a simple semi-empirical quantum-chemical model, paramagnetic screening constants ?* for 29Si, which correlates weel with the experimental chemical shifts. Theoretical considerations demonstrate that increasing silicon net charges cause high-field shifts of the central silicon atom of the SiO4 tetrahedron. The net charge on the silicon is determined by the effective (orbital) electronegativities of the oxygen atoms in the four Si-O bonds of the SiO4 tetrahedron, which depend on the type of T (Si, Al, none) in the Si-O-T connection, and the degree of oxygen s-hydridization, Q. Since effective electronegativity is generally higher for bridging than for non-bridging oxygens, and similarly for O-Si than for O-Al, the theoretical treatment provides a direct expanation of the highfield shifts experimentally observed for the formation of Si-O-T connections and of the low-fields shifts for replacement of Si with Al. Moreover, since the oxygen s-hybridization is directly related to the Si-O-T bond angle and the Si-O distance, the empirically derived correlations between the chemical shifts and the latter structure parameters can be rationalized. Some recent applications of the relationships between structure parameters and 29 Si chemical shifts in deriving detailed information on the structure of selected zeolite types, and in the interpretation of 29Si NMR spectra, are discussed. Finally, the close analogy in the relations between 27Al and 31P chemical shifts, and in the corresponding T-O-T bond angles in aluminophosphates, is considered. (author). 24 refs.; 5 figs.; 1 tab

320

Synthesis, IR and NMR spectral correlations in some symmetrical diimines  

Directory of Open Access Journals (Sweden)

Full Text Available A series of diimines have been synthesized by coupling of diamine with substituted benzaldehydes. The purities of these diimines were checked by their analytical and spectroscopic data. The spectral frequencies ?CN (cm-1, NMR chemical shifts (?, ppm of C-H and C=N of these diimines have been correlated with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis. From the results of statistical analysis, the effect of substituents on the above spectral data has been studied. DOI: http://dx.doi.org/10.4314/bcse.v28i1.9

G. Thirunarayanan

2014-01-01

 
 
 
 
321

The visualization of pannus in rheumatoid arthritis using NMR imaging  

International Nuclear Information System (INIS)

The knee joints of 15 patients afflicted with rheumatoid arthritis were investigated using the method of nmr imaging. Parameters of investigation were the spin-echo and fast-field-echo sequences as well as the MR signal behaviour of proliferative synovial changes following intravenous administration of gadolinium dtpa. Pannus having formed on the articular surfaces or beneath the articular cartilages was distinguishable from other changes on the basis of the increased signal intensities to be observed after gadolinium dtpa had been given. (orig./GD)

322

Autodyne detector for acoustic NMR  

International Nuclear Information System (INIS)

A high-sensitivity circuit for investigating direct acoustic nuclear magnetic resonance is described. The circuit contains an autodyne, an acoustic resonator, a calibrator, and a rectifier. To increase the generation stability, the circuit uses parametric negative feedback from the rectifier output to the autodyne amplifier. The autodyne uses a differential amplifier assembled on field transistors and acting as an amplifier and summator simultaneously. Besides, both halves of the amplifier have a capacitive current coupling, which reduces the noise level and increases the stability of circuit operation. The circuit described was used to determine the coefficient of resonance absorption of ultrasound by the nuclear-spin system of 75As. During the measurements the power introduced into the specimen was equal to 1 ?w. The circuit can readily be adapted for investigating the ordinary NMR

323

A HTS dc SQUID-NMR: fabrication of the SQUID and application to low-field NMR for fruit quality detection  

Science.gov (United States)

Superconducting Quantum Interference Devices (SQUIDs) have made the detection of low-field (LF) and ultra-low field nuclear magnetic resonance (ULF-NMR) a reality. The latter has been proven to be a potential tool for non-destructive quality testing of horticultural products, amongst many other applications. High-Temperature Superconductor (HTS) dc SQUIDS are likely to allow for the development of not only low-cost NMR systems but also prototypes that are mobile and easily maintainable. A HTS dc SQUID was manufactured on an YBCO thin film, using a novel laser based lithography method. The lithography was implemented by a new laser system developed in-house, as a model of low-cost lithography systems. The junctions of the dc SQUID were tested and displayed normal I-V characteristics in the acceptable range for the application. In order to determine the viability of low-field NMR for non-destructive quality measurement of horticultural products, a commercial HTS dc SQUID-NMR system was used to measure quality parameters of banana during ripening. The trend of color change and sugar increase of the banana during ripening were the most highly correlated attributes to the SQUID-NMR measured parameter, average T1 (spin-lattice relaxation time). Further studies were done, that involved processing of the NMR signal into relaxation time resolved spectra. A spectral signature of banana was obtained, where each peak is a T1 value corresponding to a proton pool, and is reported here. These results will potentially lead to deeper understanding of the quality of the samples under study.

Isingizwe Nturambirwe, J. Frédéric; Perold, Willem J.; Opara, Linus U.

2014-06-01

324

Variable-temperature 17O NMR studies allow quantitative evaluation of molecular dynamics in organic solids.  

Science.gov (United States)

We report a comprehensive variable-temperature solid-state (17)O NMR study of three (17)O-labeled crystalline sulfonic acids: 2-aminoethane-1-sulfonic acid (taurine, T), 3-aminopropane-1-sulfonic acid (homotaurine, HT), and 4-aminobutane-1-sulfonic acid (ABSA). In the solid state, all three compounds exist as zwitterionic structures, NH(3)(+)-R-SO(3)(-), in which the SO(3)(-) group is involved in various degrees of O···H-N hydrogen bonding. High-quality (17)O NMR spectra have been obtained for all three compounds under both static and magic angle spinning (MAS) conditions at 21.1 T, allowing the complete set of (17)O NMR tensor parameters to be measured. Assignment of the observed (17)O NMR parameters to the correct oxygen sites in the crystal lattice was achieved with the aid of DFT calculations. By modeling the temperature dependence of (17)O NMR powder line shapes, we have not only confirmed that the SO(3)(-) groups in these compounds undergo a 3-fold rotational jump mechanism but also extracted the corresponding jump rates (10(2)-10(5) s(-1)) and the associated activation energies (E(a)) for this process (E(a) = 48 ± 7, 42 ± 3, and 45 ± 1 kJ mol(-1) for T, HT, and ABSA, respectively). This is the first time that SO(3)(-) rotational dynamics have been directly probed by solid-state (17)O NMR. Using the experimental activation energies for SO(3)(-) rotation, we were able to evaluate quantitatively the total hydrogen bond energy that each SO(3)(-) group is involved in within the crystal lattice. The activation energies also correlate with calculated rotational energy barriers. This work provides a clear illustration of the utility of solid-state (17)O NMR in quantifying dynamic processes occurring in organic solids. Similar studies applied to selectively (17)O-labeled biomolecules would appear to be very feasible. PMID:22877150

Kong, Xianqi; O'Dell, Luke A; Terskikh, Victor; Ye, Eric; Wang, Ruiyao; Wu, Gang

2012-09-01

325

Effect of Secondary Echo Signals in Spin-Systems with a Large Inhomogeneous Broadening of NMR Line  

CERN Document Server

The possibility of comparatively simple and fast determination of characteristic relaxation parameters T1, T2 and T3 for nuclear spin-systems with strong Larmor and Rabi inhomogeneous broadenings of NMR lines using the secondary echo signal effect was experimentally shown. Resides, this method gives opportunity to obtain a valuable infomation on the inhomogeneous NMR broadening which reflects the character of magnetic field microscopic destribution in such systems, as example, multidomain magnetics and superconductors.

Chigvinadze, J G; Sharimanov, Y G; Sharimanov, Yu.G.

2003-01-01

326

The NMR line shape of magneto-active nanoclusters in moveable nano-containers with self-similar stochastic dynamics  

International Nuclear Information System (INIS)

NMR line shape of isolated spin clusters in moving nanocontainers with self-similar correlation law was calculated. It was shown that taking into account self-similarity in stochastic dynamics of pores leads to new shapes of NMR lines which differ from traditional shapes of Gauss and Lorentz types. Fractal dimension of spatial-temporal ensemble can serve as convenient fitting parameter for experimental data interpretation.

327

NMR study of the ma?etic metals cobalt and nickel in the paramagnetic and ferromagnetic states  

International Nuclear Information System (INIS)

Results of NMR measurements in the 3d - electron transition metals nickel and cobalt are presented. Measurements were performed in the paramagnetic and ferromagnetic states, as close as possible, experimentally to the Curie transition temperature Tsub(c). It is shown that NMR is a powerful tool to study the behavior of magnetic metals. The developed experimental technique enables measurements in an extended temperature range in metals with strongly temperature dependent parameters. (B.G.)

328

Effect of Secondary Echo Signals in Spin-Systems with a Large Inhomogeneous Broadening of NMR Line  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The possibility of comparatively simple and fast determination of characteristic relaxation parameters T1, T2 and T3 for nuclear spin-systems with strong Larmor and Rabi inhomogeneous broadenings of NMR lines using the secondary echo signal effect was experimentally shown. Resides, this method gives opportunity to obtain a valuable infomation on the inhomogeneous NMR broadening which reflects the character of magnetic field microscopic destribution in such systems, as exampl...

Chigvinadze, J. G.; Mamniashvili, G. I.; Sharimanov, Yu G.

2003-01-01

329

CoNSEnsX: an ensemble view of protein structures and NMR-derived experimental data  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background In conjunction with the recognition of the functional role of internal dynamics of proteins at various timescales, there is an emerging use of dynamic structural ensembles instead of individual conformers. These ensembles are usually substantially more diverse than conventional NMR ensembles and eliminate the expectation that a single conformer should fulfill all NMR parameters originating from 1016 - 1017 molecules in the sample tube. Thus, the accuracy of dynamic conformational ensembles should be evaluated differently to that of single conformers. Results We constructed the web application CoNSEnsX (Consistency of NMR-derived Structural Ensembles with eXperimental data allowing fast, simple and convenient assessment of the correspondence of the ensemble as a whole with diverse independent NMR parameters available. We have chosen different ensembles of three proteins, human ubiquitin, a small protease inhibitor and a disordered subunit of cGMP phosphodiesterase 5/6 for detailed evaluation and demonstration of the capabilities of the CoNSEnsX approach. Conclusions Our results present a new conceptual method for the evaluation of dynamic conformational ensembles resulting from NMR structure determination. The designed CoNSEnsX approach gives a complete evaluation of these ensembles and is freely available as a web service at http://consensx.chem.elte.hu.

Perczel András

2010-10-01

330

Assessment of structural changes of human teeth by low-field nuclear magnetic resonance (NMR)  

Science.gov (United States)

A technique of low-field pulsed proton nuclear magnetic resonance (NMR) spin relaxation is described for assessment of age-related structural changes (dentin and pulp) of human teeth in vitro. The technique involves spin-spin relaxation measurement and inversion spin-spin spectral analysis methods. The spin-spin relaxation decay curve is converted into a T2 distribution spectrum by a sum of single exponential decays. The NMR spectra from the extracted dentin-portion-only and dental pulp-cells-only were compared with the whole extracted teeth spectra, for the dentin and pulp peak assignments. While dentin and pulp are highly significant parameters in determining tooth quality, variations in these parameters with age can be used as an effective tool for estimating tooth quality. Here we propose an NMR calibration method—the ratio of the amount of dentin to the amount of pulp obtained from NMR T2 distribution spectra can be used for measuring the age-related structural changes in teeth while eliminating any variations in size of teeth. Eight teeth (third molars) extracted from humans, aged among 17-67 years old, were tested in this study. It is found that the intensity ratio of dentin to pulp sensitively changes from 0.48 to 3.2 approaching a linear growth with age. This indicates that age-related structural changes in human teeth can be detected using the low-field NMR technique.

Ni, Qingwen; Chen, Shuo

2010-01-01

331

Assessment of structural changes of human teeth by low-field nuclear magnetic resonance (NMR)  

International Nuclear Information System (INIS)

A technique of low-field pulsed proton nuclear magnetic resonance (NMR) spin relaxation is described for assessment of age-related structural changes (dentin and pulp) of human teeth in vitro. The technique involves spin–spin relaxation measurement and inversion spin–spin spectral analysis methods. The spin–spin relaxation decay curve is converted into a T2 distribution spectrum by a sum of single exponential decays. The NMR spectra from the extracted dentin-portion-only and dental pulp-cells-only were compared with the whole extracted teeth spectra, for the dentin and pulp peak assignments. While dentin and pulp are highly significant parameters in determining tooth quality, variations in these parameters with age can be used as an effective tool for estimating tooth quality. Here we propose an NMR calibration method—the ratio of the amount of dentin to the amount of pulp obtained from NMR T2 distribution spectra can be used for measuring the age-related structural changes in teeth while eliminating any variations in size of teeth. Eight teeth (third molars) extracted from humans, aged among 17–67 years old, were tested in this study. It is found that the intensity ratio of dentin to pulp sensitively changes from 0.48 to 3.2 approaching a linear growth with age. This indicates that age-related structural changes in human teeth can be detected using the low-field NMR technique

332

Application of chemometrics to low-field H-1 NMR relaxation data of intact fish flesh  

DEFF Research Database (Denmark)

The possibilities for application of low-field H-1 nuclear magnetic resonance (NMR) as a rapid method for simultaneous assessment of basic quality parameters in fish were explored. In a first experiment, 200 salmon (Salmo salar) samples mapping the variation over an entire fish were measured by NMR and subsequently analysed for oil or water content by standard chemical methods. In a second experiment, 58 differently thawed cod (Gadus morhua) samples were measured by NMR and subsequently analysed for water-holding capacity. Correlations between chemical data and NMR data were evaluated using partial least squares (PLS) regression on complete relaxation curves and compared with conventional regression models on exponential fitting parameters. Predictions on an independent test set were superior for the PLS regression models, with optimal prediction errors of 12 g kg(-1), 6 g kg(-1) and 3.9% for oil and water content in fresh salmon flesh and water-holding capacity in thawed cod flesh respectively. Thus rapid, non-invasive low- field NMR can be used to simultaneously determine both oil and water content of fish flesh. Furthermore, it can predict water- holding capacity of cod flesh, with an R-2 of 0.9 over the range 30-90%, as determined by a centrifuge test. (C) 1999 Society of Chemical Industry

Jepsen, Signe Munk

1999-01-01

333

Numerical simulation of ( T 2, T 1) 2D NMR and fluid responses  

Science.gov (United States)

One-dimensional nuclear magnetic resonance (1D NMR) logging technology is limited for fluid typing, while two-dimensional nuclear magnetic resonance (2D NMR) logging can provide more parameters including longitudinal relaxation time ( T 1) and transverse relaxation time ( T 2) relative to fluid types in porous media. Based on the 2D NMR relaxation mechanism in a gradient magnetic field, echo train simulation and 2D NMR inversion are discussed in detail. For 2D NMR inversion, a hybrid inversion method is proposed based on the damping least squares method (LSQR) and an improved truncated singular value decomposition (TSVD) algorithm. A series of spin echoes are first simulated with multiple waiting times ( T W s) in a gradient magnetic field for given fluid models and these synthesized echo trains are inverted by the hybrid method. The inversion results are consistent with given models. Moreover, the numerical simulation of various fluid models such as the gas-water, light oil-water, and vicious oil-water models were carried out with different echo spacings ( T E s) and T W s by this hybrid method. Finally, the influences of different signal-to-noise ratios (SNRs) on inversion results in various fluid models are studied. The numerical simulations show that the hybrid method and optimized observation parameters are applicable to fluid typing of gas-water and oil-water models.

Tan, Mao-Jin; Zou, You-Long; Zhang, Jin-Yan; Zhao, Xin

2012-12-01

334

Nuclear magnetic resonance (NMR) tomography - parametric T2 imaging (spin-spin-relaxation)  

International Nuclear Information System (INIS)

The relaxation times T1 and T2 are essential parameters for tissue differentiation in NMR-Tomography. With respect to these criteria, potentially available information is not sufficiently utilized by current imaging methods. This disadvantage can be overcome by means of a parametrical method which is demonstrated for the production of T2 images. (orig.)

335

An NMR Study of Isotope Effect on Keto-Enol Tautomerization: A Physical Organic Chemistry Experiment  

Science.gov (United States)

Isotope substitution often affects the rate of an organic reaction and can be used to reveal the underlying mechanism. A series of experiments that use (super 1)H NMR to determine primary and secondary isotope effects, activation parameters, and the regioselectivity of butanone enolization are described.

Atkinson, D.; Chechik, V.

2004-01-01

336

Probing porous media with gas diffusion NMR  

Science.gov (United States)

We show that gas diffusion nuclear magnetic resonance (GD-NMR) provides a powerful technique for probing the structure of porous media. In random packs of glass beads, using both laser-polarized and thermally polarized xenon gas, we find that GD-NMR can accurately measure the pore space surface-area-to-volume ratio, S/V rho, and the tortuosity, alpha (the latter quantity being directly related to the system's transport properties). We also show that GD-NMR provides a good measure of the tortuosity of sandstone and complex carbonate rocks.

Mair, R. W.; Wong, G. P.; Hoffmann, D.; Hurlimann, M. D.; Patz, S.; Schwartz, L. M.; Walsworth, R. L.

1999-01-01

337

Resistive NMR of brain stem gliomas  

Energy Technology Data Exchange (ETDEWEB)

The NMR and CT findings in 22 patients with primary brain stem tumors were compared to determine the value of each study in identifying, and delineating the extent and relationships of the tumor to brain anatomy. NMR was found to be distinctly superior to CT in showing involvement of the medulla and upper cervical cord. NMR eliminates the need for intrathecal enhanced metrizamide CT, and in the future should be the only initial diagnostic test needed for the evaluation of intrinsic brain stem tumors.

Zimmerman, R.A.; Bilaniuk, L.T.; Samuel, L.; Johnson, M.H.; Grossman, R.I.; Goldberg, H.I.; Packer, R.; Sutton, L.

1985-01-01

338

Scalar operators in solid-state NMR  

Energy Technology Data Exchange (ETDEWEB)

Selectivity and resolution of solid-state NMR spectra are determined by dispersion of local magnetic fields originating from relaxation effects and orientation-dependent resonant frequencies of spin nuclei. Theoretically, the orientation-dependent resonant frequencies can be represented by a set of irreducible tensors. Among these tensors, only zero rank tensors (scalar operators) are capable of providing high resolution NMR spectra. This thesis presents a series of new developments in high resolution solid-state NMR concerning the reconstruction of various scalar operators motion in solid C{sub 60} is analyzed.

Sun, Boqin

1991-11-01

339

The NMR response of heterogeneous systems  

International Nuclear Information System (INIS)

This paper discusses the problem of modeling the NMR correlation functions in dynamically heterogeneous (liquid-solid) systems. It is shown that the mere presence of solid surfaces causes the appearance of solid-like features in the NMR response of the liquid even if its dynamics are not directly affected by the surfaces. Some of these topological or indiret surface effects are of the same kind as the recently explored low-dimensionality effects. In the water-protein systems, many features of the NMR response appear due to the indirect surface effects instead of the presence of bonded water. (orig.)

340

Determination of flow using NMR techniques  

International Nuclear Information System (INIS)

Evaluation of normal and abnormal blood flow patterns can be done with NMR imaging techniques, derived from differences in intrinsic NMR phenomena of static and moving tissue. Several techniques have been evaluated in this regard: Time-in-flight, phase shift, selective excitation, and orthogonal refocusing pulses. Each technique has advantages which will be discussed. It is also possible that evaluation of tissue perfusion will be possible using NMR techniques. Definition of vascular disease processes may also be possible based on blood flow information

 
 
 
 
341

Introduction to some basic aspects of NMR  

International Nuclear Information System (INIS)

The principal interactions are reviewed that are experienced by nuclear spins making magnetic resonance feasible and which disturb it in a way that gives access to the properties of bulk matter. The interactions leading to NMR include Zeeman interaction, dipole-dipole interactions, and exchange interactions. Spin-lattice relaxation relevant to NMR is revisited next. It is followed by an overview of spin temperature. Finally, the care of periodic Hamiltonian is discussed in detail as another contribution to NMR. (R.P.) 48 refs., 12 figs

342

NMR imaging of the brain: initial impressions  

International Nuclear Information System (INIS)

An NMR imaging system designed and built by Thorn-EMI Ltd was installed at Hammersmith Hospital in March 1981. In the first year of operation 180 patients and 40 volunteers have had cranial examinations and initial impressions bases on this experience are presented. Patients with a wide variety of neurological diseases have been studied to provide a basis for diagnostic interpretation, to define distinctive features, and to evaluate different types of scanning sequences. NMR imaging appears to be of considerable value in neurological diagnosis and has a number of advantages over CT. The detailed evaluation of NMR imaging will require much more work but the initial results are very promising

343

On electrophoretic NMR. Exploring high conductivity samples  

Science.gov (United States)

The performance of a new electrophoretic NMR (eNMR) method that uses a Carr-Purcell-Meiboom-Gill echo train with repeated electric field reversal is investigated. We show that this pulse sequence, with acronym CPMGER, yields strongly reduced artifacts from convective flow effects caused by the simultaneous presence of electroosmotic and thermal driving forces. We demonstrate the achieved improvements in various aqueous solutions. Ultimately, the method can be used for obtaining electrophoretic mobilities by eNMR without relying on uncharged reference molecules, otherwise a significant limitation for electrophoretic experiments performed with nuclei other than 1H.

Bielejewski, Micha?; Giesecke, Marianne; Furó, István

2014-06-01

344

Solid-state NMR of polymers  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) spectroscopy has emerged as one of the most important methods for the solid-state characterisation of polymers. The popularity of NMR is due to the fact that many molecular level features can be measured from the NMR spectra, including the polymer chain conformation, the morphology and the dynamics. The spectral features and relaxation times are affected by local interactions, so they provide information about the structure of polymers on a length scale (2-200 A) that is difficult to measure by other methods. In favourable cases, the NMR experiments provide a molecular-level explanation for the transitions observed by differential scanning calorimetry (DSC) and other methods, and the NMR properties can often be related to the bulk properties. Solid-state NMR has long been of interest in polymer science, and the first solid-state NMR studies of polymers were reported approximately a year after the discovery of nuclear resonance in bulk matter. It was reported in this initial study that the proton line width for natural rubber at room temperature is more like that of a mobile liquid than of a solid, but that the resonance broadens near the glass transition temperature (Tg). This was recognised as being related to a change in chain dynamics above and below the Tg. NMR methods developed rapidly after these initial observations, first for polymers in solution and, more recently, for polymers in the solid-state. Solid-state NMR studies of polymers were developed more slowly than their solution-state counterparts because solid-state NMR requires more specialised equipment. Solid-state NMR is now such an important tool that most modern spectrometers are capable of performing these studies. The interest in the NMR of solid polymers is due in part to the fact that most polymers are used in the solid state, and in many cases the NMR properties can be directly related to the macroscopic properties. Polymers have restricted mobility in solids, for example, and the chemical shifts can be directly related to the chain conformation. Solid-state NMR is also an efficient way to monitor the reactivity of polymers, since chemical changes often result in large spectral changes. The relaxation times in solids depend not only on the chain dynamics, but also on the morphology over a length scale of 20-200 A. NMR has been extensively used to measure the length scale of mixing in blends and multiphase polymers, and the domain sizes in semicrystalline polymers. Solid-state NMR methods have been greatly expanded with the introduction of multi-dimensional NMR. These studies have led to a molecular level understanding of the dynamics traditionally observed by dielectric and dynamic-mechanical spectroscopy, and a better understanding of the relationship between polymer morphology and macroscopic properties

345

Calculation of NMR parameters for bridging oxygens in H3T—O—T'H3 linkages (T, T'=Al, Si, P), for oxygen in SiH3O-, SiH3OH and SiH3OMg+ and for bridging fluorine in H3SiFSiH{3/+}  

Science.gov (United States)

Variations in the 17O nuclear quadrupole coupling constant, NQCC, and the 17O NMR shielding constant, ?O, are evaluated for bridging oxygens in H3T-O-T'H3 linkages (with T, T'=Al, Si, P), and for nonbridging O in SiH3O-, SiH3OH and SiH3OMg+ and the 19F NMR shielding constant, ?F, is evaluated for bridging F in H3SiFSiH{3/-}using Hartree-Fock methods with large, flexible Gaussian basis sets. Trends in 17O NQCC as a function of T and T' identity agree with experiment but the value for the Si-O-Al case is underestimated, indicative of neglected contributions from charge compensating cations. For H3SiOSiH3 the decrease in NQCC over the range from 180° to 140° is substantial but somewhat slower than the variation of -cosNMR spectra for this species.

Tossell, J. A.; Lazzeretti, Paolo

1988-08-01

346

NMR Analysis of Unknowns: An Introduction to 2D NMR Spectroscopy  

Science.gov (United States)

A study combined 1D (one-dimensional) and 2D (two-dimensional) NMR spectroscopy to solve structural organic problems of three unknowns, which include 2-, 3-, and 4-heptanone. Results showed [to the first power]H NMR and [to the thirteenth power]C NMR signal assignments for 2- and 3-heptanone were more challenging than for 4-heptanone owing to the…

Alonso, David E.; Warren, Steven E.

2005-01-01

347

NMR study of platinum catalysts  

Science.gov (United States)

The author reports on studies by his group of the 195Pt NMR of several samples of Pt supported on alumina at frequencies ranging from 9 to 74 MHz, and at 77 and 4.2 K, using spin-echoes at fixed frequency. The samples were prepared by Dr. John Sinfelt of the Exxon Research Laboratory, who has characterized their dispersions chemically as 46%, 26%, and 15% for samples 1, 2, and 3 respectively. The NMR spectra are exceedingly broad, extending from the value characteristic of bulk metallic Pt to a value characteristic of diamagnetic Pt compounds (a range of 4.5 kG at 74 MHz). The detailed shapes vary drastically with average particle size, and exhibit structure which depends on the chemical treatment of the Pt surface. The spin-spin and spin-lattice relaxation times T2 and T1 respectively, vary across the absorption line but, for a given surface treatment, and at a given position on the absorption line, T1 and T2 are the same in all three samples. In sample 3, there is a sharp peak at the position of the 195Pt resonance in bulk metal, but it is missing in the samples of smaller particle size. In samples exposed to the air or to hydrogen, there is a strong peak near the normal position of the 195Pt resonance in diamagnetic compounds which we believe arises from the surface layer of Pt atoms since its area relative to the total absorption line agrees with Sinfelt's chemical determination of the sample dispersion and since the peak disappears when the surface is cleaned chemically. When the surface is covered, the electrons of the surface platinum atoms are tied up in chemical bonds (i.e., are non-metallic) since the surface peak occurs at the position characteristic of 195Pt in diamagnetic compounds, possesses a long T1, and has T1 whose temperature and magnetic field dependence differ drastically from T1 in metals.

Slichter, Charles P.

1981-05-01

348

NMR studies on UPt 3  

Science.gov (United States)

A complete set of the 195Pt Knight-shift (KS) data on the superconducting (SC) state in UPt 3 identified the spin structure of the Cooper pair corresponding to the multiple SC phases. UPt 3 was acclaimed as the first odd-parity superconductor including a non-unitary pairing state characterized by the two-component d vector like db+ idc at low T and low H [H. Tou et al., Phys. Rev. Lett. 77 (1996) 1374; 80 (1998) 3129]. We have shed further light on these novel results through a comparison with the singlet even-parity anisotropic superconductors CeCu 2Si 2 and UPd 2Al 3. In the singlet pairing state, the fractional decrease in KS below T c, ?K obs is independent of the crystal direction. We have found that ? ?obs=( NA? B/ Ahf)? Kobs where Ahf is the hyperfine coupling constant, is in good agreement with spin susceptibilities ??el calculated from an enhanced electronic specific heat ?el and ?nmr from the quasiparticle Korringa relation T1TKs2=const. This gives direct evidence that the ?s of heavy quasiparticles in CeCu 2Si 2 and UPd 2Al 3 is rather isotropic and decreases to zero as T?0 due to the Cooper-pair formation. On the other hand in UPt 3, the ? ?obsb, cs along the b- and c-axis in the non-unitary-pairing state (B phase) are two orders of magnitude smaller than ??el and ?nmr. These anomalously small values for ? ?obsb, cs may suggest either that the spin degree of freedom in the B phase is not perfectly locked to the a-axis or that ?s is not enhanced although ?el is. The latter is theoretically pointed out by Ikeda and Miyake [J. Phys. Soc. Japan 66 (1997) 3714] to be possible if 5f electrons in the non-Kramerse singlet ground state for 5f 2 are hybridized with conduction electrons. We need further effort towards coherent understanding of a microscopic mechanism leading to the occurrence of the odd-parity superconductivity in UPt 3.

Kitaoka, Y.; Tou, H.; Ishida, K.; Kimura, N.; ?nuki, Y.; Yamamoto, E.; Haga, Y.; Maezawa, K.

2000-06-01

349

NMR studies of cerebral metabolism in vivo  

International Nuclear Information System (INIS)

The nature and extent of the potential synergism between PET and NMR methods is not yet well appreciated in the biomedical community. The long-range interest of medical neurobiology will be well served by efforts of PET and NMR scientists to follow each others' work so that opportunities for productive interchange can be efficiently exploited. Appreciation of the synergism by the rest of the biomedical community will follow naturally. PET is said by the people doing it to be still in its infancy, for they are more concerned with advancing their discipline than with admiring its already impressive achievements. On the scale of the same developmental metaphor, many NMR methods for studying the living human brain are still in utero. The best way to provide the reader a sense of the current status and future course of NMR research in medical neurobiology is by discussion of published in vivo studies. Such a discussion, adapted from another article is what follows

350

195Pt NMR--theory and application.  

Science.gov (United States)

This critical review highlights the progress in (195)Pt NMR over the last 25 years. In particular, some of the recent applications of (195)Pt NMR in catalytic and mechanistic studies, intermetallics and drug binding studies are discussed. (195)Pt NMR chemical shifts obtained from both theoretical studies and experiments are presented for Pt(0), Pt(II), Pt(III) and Pt(IV) complexes. (195)Pt coupling with various nuclei (viz. coupling constants) have also been collected in addition to data on (195)Pt relaxation. The latest developments in the theoretical knowledge and experimental advances have made (195)Pt NMR into a rich source of information in many fields. (164 references.). PMID:17387413

Still, Brett M; Kumar, P G Anil; Aldrich-Wright, Janice R; Price, William S

2007-04-01

351

NMR and optical studies of piezoelectric polymers  

International Nuclear Information System (INIS)

Progress is reported in several areas dealing with piezoelectric (electroactive) polymers (mostly vinylidene fluoride, trifluoroethylene, copolymers, PVF2) and liquid crystals. Optical studies, neutron scattering, NMR, thermal, theory and modeling were done

352

Nuclear magnetic resonance (NMR) theory and applications  

International Nuclear Information System (INIS)

Over the past years, techniques of nuclear magnetic resonance (NMR) have developed into several areas of applications. The relaxation times and the proton density have been measured and applied under various conditions to study the state of water in tissues and natural products. The fat and water content as well as their distribution have been determined by NMR methods. The shifts of the ATP spectral peaks may be applied to determine the functional state of an organ. In recent years a more significant innovation has emerged. The NMR signals, through mathematical manipulation have been successfully transformed into magnetic Resonance Images. It is very likely that, with the present rapid progress in instrumentation and computer engineering the magnetic resonance imaging (MRI) may supercede, in every aspect, those imaging modalities in current use. This paper describes briefly the theory of NMR and its applications in industries and medicine. Emphasis is given to the relationship between the relaxation times and the physical phenomena observed

353

NMR studies on irradiated lecithin systems  

International Nuclear Information System (INIS)

By means of NMR and UV spectroscopy we have examined the radiation damage of liposomes under different experimental conditions including an addition of a nitro compound as an effector with the aim to minimize the irradiation effects. (author)

354

NMR and optical studies of piezoelectric polymers  

Energy Technology Data Exchange (ETDEWEB)

Progress is reported in several areas dealing with piezoelectric (electroactive) polymers (mostly vinylidene fluoride, trifluoroethylene, copolymers, PVF[sub 2]) and liquid crystals. Optical studies, neutron scattering, NMR, thermal, theory and modeling were done.

Schmidt, V.H.; Tuthill, G.F.

1993-01-01

355

Concentration measurements of sucrose and sugar surfactants solutions by using the 1H NMR ERETIC method.  

Science.gov (United States)

The ERETIC method has been used to determine precise concentrations of aqueous solutions of sucrose and sugar surfactants, namely octyl glucoside and fatty acid sucrose esters by (1)H NMR spectroscopy. The effects of NMR tuning, acquisition parameters, and spectrum processing on the measurement have been assessed in these particular cases. The linearity upholds over the whole concentration range, with both sucrose and octyl glucoside, whatever the physicochemical phenomena occurring, either an increasing viscosity or the micellization of the surfactant. For sucrose solutions, an accuracy of 2% is measured for concentrations between 0.1 and 200 mmol/L, which is consistent with literature data. PMID:16697992

Molinier, Valérie; Fenet, Bernard; Fitremann, Juliette; Bouchu, Alain; Queneau, Yves

2006-08-14

356

Wheat flour enzymatic amylolysis monitored by in situ (1)H NMR spectroscopy.  

Science.gov (United States)

Starch enzymatic degradation caused by endogenous hydrolases is studied by in situ NMR spectroscopy on a set of hard and soft wheat flours. The results obtained by two different techniques (HR-MAS and (1)H NMR in solution) are analyzed in terms of a Michaelis-Menten kinetic phenomenological model taking into account the presence of endogenous enzymes and their eventual inactivation. The parameters resulting from the best fit of all experimental data to the kinetic model equations are submitted to a multivariate statistical analysis to assess the role of the oligosaccharides release in distinguishing between hard and soft wheats. PMID:14969537

Amato, Maria E; Ansanelli, Giuliana; Fisichella, Salvatore; Lamanna, Raffaele; Scarlata, Giuseppe; Sobolev, Anatoli P; Segre, Annalaura

2004-02-25

357

31P NMR knights shifts in the UPY (Y = S, Se, Te) compounds  

International Nuclear Information System (INIS)

Nuclear magnetic resonance of 31P measurements have been made for UPY (where Y = S, Se and Te) compounds. The resonance lines show the effect of anisotropic Knight shifts. In the UPS, the NMR data indicate an axial symmetry of the phosphorus environment whereas for UPSe and UPTe the symmetry is lower than the axial one. The result for UPSe disagrees with earlier structural studies. An analysis of NMR spectra indicates that both the asymmetry parameter epsilon and the isotropic component of the Knight shift increase with the increase of atomic weight of the Y element. (orig.)

358

NMR study of UPt 2Sn  

Science.gov (United States)

The 119Sn and 195Pt Knight shifts are anisotropic and exhibit Curie-Weiss-like temperature behavior above TN = 60 K, indicating the localized nature of 5f electrons. The 119Sn NMR is observable down to 4.2 K in spite of disappearance of the 195Pt NMR below TN. This suggests a spin structure which results in a cancellation of the transferred hyperfine fields at a Sn site.

Kojima, K.; Iwasaki, H.; Takabatake, T.; Fujii, H.; Hihara, T.

1993-05-01

359

Mobile NMR for rock porosity and permeability  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Als nicht-invasives Verfahren bietet die kernmagnetische Resonanz (engl. Nuclear magnetic resonance, NMR) unter anderem die Möglichkeit Gesteinsformationen hinsichtlich ihrer hydraulischen Fließeigenschaften zu charakterisieren. Im Rahmen dieser Arbeit wurden drei verschiedene mobile NMR-Geräte angewendet, um die Porosität und Permeabilität an ausgewählten Bohrkernen mit Durchmessern bis zu 60 mm zu bestimmen. Neben der Anwendung im Labor, eignen sich die handlichen Sensoren auch für d...

Arnold, Juliane

2007-01-01

360

Applications of field gradients in NMR  

International Nuclear Information System (INIS)

This chapter introduces the necessity for field NMR gradients when studying translational diffusion in solution. A related topic is NMR imaging where molecular mobility is a prime necessity for signal detection (flow-sensitive techniques, pulsed gradient spin echo experiment, displacement imaging). Imaging applications to chemistry and biochemistry are discussed: localized spectroscopy and micro-imaging of fluid inclusions in solid materials. 20 fig., 1 tab., 70 ref

 
 
 
 
361

H NMR Studies of Eukaryotic Cytochrome c  

Digital Repository Infrastructure Vision for European Research (DRIVER)

H NMR resonance assignments in the spectra of horse, tuna, Neurmpora crassa and Candida krusei cyto-chromes c are described. Assignments have been made using NMR double-resonance techniques in conjunction with electron-exchange experiments, spectral comparison of related proteins, and consideration of the X-ray structure of tuna cytochrome c. Resonances arising from 11 residues of horse cytochrome c have been assigned.

Boswell, Andrew P.; Eley, Crispin G. S.; Moore, Geoffrey R.; Robinson, Martin N.; Williams, Glyn; Williams, Robert J. P.; Neupert, Walter; Hennig, Bernd

1982-01-01

362

Pore geometry of sandstone derived from pulsed field gradient NMR  

Science.gov (United States)

Several parameters of pore geometry are needed for estimating permeability which is a key parameter for the characterization of reservoir sandstones. Powerful techniques for probing the pore space are the self-diffusion and the relaxation time NMR methods. However, the quality of results depends on the petrophysical model which underlies the interpretation of measurements. We applied the pulsed field gradient nuclear magnetic resonance (PFG-NMR) technique and measured time-dependent self-diffusion coefficients, D(?), of water in anhydrite cemented sandstones with low porosity and high tortuosity. The conventional method of fitting data with a function (Padé approximation) of the surface-to-volume ratio and the tortuosity yielded uncertain results. As part of a novel approach, we developed a numerical simulation code based on physical principles and a fractal pore space model. We compared our method with the Padé approximation and tested with data from the literature. For porous media with low tortuosity values and simple geometry such as randomly packed glass beads, both methods are in good agreement and give similar results. In sedimentary rocks, however, the new method of calculation is able to determine more accurate details of the pore geometry. However, its main advantage occurs in porous media with fractal geometry or with constricted pores, where the D(?)/ D0 curves deviate from the characteristic shape that is found for randomly packed glass beads.

Pape, Hansgeorg; Tillich, Joachim E.; Holz, Manfred

2006-03-01

363

33S NMR cryogenic probe for taurine detection  

Science.gov (United States)

With the goal of a S33 nuclear magnetic resonance (NMR) probe applicable to in vivo NMR on taurine-biological samples, we have developed the S33 NMR cryogenic probe, which is applicable to taurine solutions. The NMR sensitivity gain relative to a conventional broadband probe is as large as 3.5. This work suggests that improvements in the preamplifier could allow NMR measurements on 100 ?M taurine solutions, which is the level of sensitivity necessary for biological samples.

Hobo, Fumio; Takahashi, Masato; Maeda, Hideaki

2009-03-01

364

95Mo nuclear magnetic resonance parameters of molybdenum hexacarbonyl from density functional theory: appraisal of computational and geometrical parameters.  

Science.gov (United States)

Solid-state (95)Mo nuclear magnetic resonance (NMR) properties of molybdenum hexacarbonyl have been computed using density functional theory (DFT) based methods. Both quadrupolar coupling and chemical shift parameters were evaluated and compared with parameters of high precision determined using single-crystal (95)Mo NMR experiments. Within a molecular approach, the effects of major computational parameters, i.e. basis set, exchange-correlation functional, treatment of relativity, have been evaluated. Except for the isotropic parameter of both chemical shift and chemical shielding, computed NMR parameters are more sensitive to geometrical variations than computational details. Relativistic effects do not play a crucial part in the calculations of such parameters for the 4d transition metal, in particular isotropic chemical shift. Periodic DFT calculations were tackled to measure the influence of neighbouring molecules on the crystal structure. These effects have to be taken into account to compute accurate solid-state (95)Mo NMR parameters even for such an inorganic molecular compound. PMID:21960056

Cuny, Jérôme; Sykina, Kateryna; Fontaine, Bruno; Le Pollès, Laurent; Pickard, Chris J; Gautier, Régis

2011-11-21

365

NMR profiling of transgenic peas.  

Science.gov (United States)

A high throughput proton nuclear magnetic resonance spectroscopy method for the metabolite fingerprinting of plants was applied to genetically modified peas (Pisum sativum) to determine whether biochemical changes, so called 'unintended effects', beyond those intended by incorporation of a transgene, were detectable. Multivariate analysis of 1H NMR (nuclear magnetic resonance) spectra obtained from uniformly grown glasshouse plants revealed differences between the transgenic and control group that exceeded the natural variation of the plants. When a larger data set of six related transgenic lines was analysed, including a null segregant in addition to the wild-type control, multivariate analysis showed that the distribution of metabolites in the transgenics was different from that of the null segregant. However, the profile obtained from the wild-type material was diverse in comparison with both the transgenics and the null segregant, suggesting that the primary cause of the observed differences was that the transformation process selects for a subset of individuals able to undergo the transformation and selection procedures, and that their descendants have a restricted variation in metabolite profile, rather than that the presence of the transgene itself generates these differences. PMID:17166140

Charlton, Adrian; Allnutt, Theo; Holmes, Stephen; Chisholm, James; Bean, Samantha; Ellis, Noel; Mullineaux, Phil; Oehlschlager, Sarah

2004-01-01

366

NMR study of hydride systems  

International Nuclear Information System (INIS)

The hydrides of thorium (ThH2, Th4H15 and Th4D15) and the intermetallic compound system (Zr(Vsub(1-x)Cosub(x))2 and its hydrides were investigated using the nuclear magnetic resonance (NMR) technique. From the results for the thorium hydride samples it was concluded that the density of states at the Fermi level n(Esub(f)) is higher in Th4H15 than in ThH2; there is an indirect reaction between the protons and the d electrons belonging to the Th atoms in Th4H15; n(E) has a sharp structure near Esub(f). It was also found that the hydrogen diffusion mechanism changes with temperature. From the results for the intermetallic compound system conclusions were drawn concerning variations in the electronic structure, which explain the behavior of the system. In hydrogen diffusion studies in several samples it was found that Co atoms slow the diffusion rate. Quadrupole spectra obtained at low temperatures show that the H atoms preferably occupy tetrahedral sites formed by three V atoms and one Z atom. (H.K.)

367

Moderne Entwicklung der NMR (Nuclear Magnetic Resonance)  

Science.gov (United States)

Die NMR-Spektroskopie kann sich altersmäßig nicht mit den Annalen der Physik messen; sie entstand vor rd. 45 Jahren. Ihre Entwicklung wurde und wird durch unterschiedliche Erfahrungen, Erkenntnisse und Techniken bestimmt; sie zeigt, daß auch heute noch die Fortschritte von Spezialgebieten Impulse aus weiten Bereichen der Physik, der Naturwissenschaften und Technik beziehen. In entsprechender Weise machen Spezialzeitschriften das Erscheinen allgemeiner Fachzeitschriften nicht überflüssig. Diese Zusammenhänge sollen an einigen Beispielen der NMR demonstriert werden.Translated AbstractModern Development of NMR (Nuclear Magnetic Resonance)The age of NMR-spectroscopy is not comparable with that of the Annalen der Physik; NMR was established only about 45 years ago. Its development was promoted by different experience, knowledge and techniques; it shows that also in these days the progress of a special topic depends on stimulations by other parts of physics, of natural and technical science. In an analogous way general scientific journals are not made superfluous by the existence of special papers. These relations are demonstrated with some examples in NMR.

Lösche, Artur

368

14N NMR in AIN and BN  

International Nuclear Information System (INIS)

Full text: The metal nitrides AlN and BN are industrially and scientifically important materials. Aluminium nitride (AlN) is the industrially preferred material for semiconductor device heat sinks, and a starting material for many lightweight high toughness non-oxide ceramics. Boron nitride (BN) is a light weight insulator, with many high temperature applications. Theoretically, AlN and BN form part of a set of simple binary (4-4, 3-5, 2-6 and 1-7) compounds which have been repeatedly used to test theories of ionicity. Further, the non-cubic members of the set provide extra parameters, viz the electric field gradient (q) at the atomic sites, to constrain electronic structure calculations. These electric field gradients are conveniently measured by the nuclear quadrupole coupling constants (Cq e2qQ/h). Despite the 99% abundance of 14N, no value for 14Cq in AlN and BN has been reported. This suggests that Cq for each must be too high to be conveniently detected by quadrupole perturbed NMR and too low to be easily measured by NQR. However Cq is not the problem; the difficulty lies in the magnitude of T1. For AlN the 14N relaxation time turns out to be 1080 seconds at room temperature; the value in BN appears to be considerably longer. Such long T1 are surprising since efficient quadrupolar relaxation via indirect phonon Raman processes is expected. Additional dataman processes is expected. Additional data is given for the Cq values at the Al and B sites. Data is also included for other (mainly wurtzite) binary compounds for which Cq is known at each atomic site

369

Molecular dynamics of solid cortisol studied by NMR  

Science.gov (United States)

Polycrystalline cortisol (hydrocortisone; 11?,17?,21-trihydroxy-4-preg- nene-3,20-dione; C21H30O5) has been investigated by continuous and pulse proton NMR methods between 78 and 400 K at Larmor frequencies of 7, 25 and 60 MHz. A reduced value of second moment was found above 90 K and is ascribed to reorientation of two methyl groups. A single asymmetric minimum was found in the temperature dependence of the spin-lattice relaxation times and this also is attributed to reorientation of two methyl groups. The asymmetry suggests an asymmetric distribution of correlation times of the motion. Using the Cole-Davidson distribution, the best computer fit yields the following parameters characterizing the motion: Ea = 11?8 ± 0?1 kJ mol-1, ?0 = 4?6 ± 0?4) x 10-13s, distribution parameter ? = 0?62.

Andrew, E. R.

370

Quantitative Analysis of STD-NMR Spectra of Reversibly Forming Ligand-Receptor Complexes  

Science.gov (United States)

We describe our work on the quantitative analysis of STD-NMR spectra of reversibly forming ligand-receptor complexes. This analysis is based on the theory of complete relaxation and conformational exchange matrix analysis of saturation transfer (CORCEMA-ST) effects. As part of this work, we have developed two separate versions of the CORCEMA-ST program. The first version predicts the expected STD intensities for a given model of a ligand-protein complex, and compares them quantitatively with the experimental data. This version is very useful for rapidly determining if a model for a given ligand-protein complex is compatible with the STD-NMR data obtained in solution. It is also useful in determining the optimal experimental conditions for undertaking the STD-NMR measurements on a given complex by computer simulations. In the second version of the CORCEMA-ST program, we have implemented a torsion angle refinement feature for the bound ligand within the protein binding pocket. In this approach, the global minimum for the bound ligand conformation is obtained by a hybrid structure refinement protocol involving CORCEMA-ST calculation of intensities and simulated annealing refinement of torsion angles of the bound ligand using STD-NMR intensities as experimental constraints to minimize a pseudo-energy function. This procedure is useful in refining and improving the initial models based on crystallography, computer docking, or other procedures to generate models for the bound ligand within the protein binding pocket compatible with solution STD-NMR data. In this chapter we describe the properties of the STD-NMR spectra, including the dependence of the intensities on various parameters. We also describe the results of the CORCEMA-ST analyses of experimental STD-NMR data on some ligand-protein complexes to illustrate the quantitative analysis of the data using this method. This CORCEMA-ST program is likely to be useful in structure-based drug design efforts.

Krishna, N. Rama; Jayalakshmi, V.

371

Low Field NMR of Water in Soils. A Case of Study.  

Science.gov (United States)

The evolution of water in soils is a physical phenomenon of importance in soil science and climatology. While most investigations of soil moisture are performed inside large superconducting magnets in the laboratory, it is advantageous to do such investigations with mobile NMR equipment in the field. As a part of a DFG-funded interdisciplinary project (TR32), this work establishes preliminary results from the use of mobile NMR to measure moisture in soil columns. To demonstrate the ability of the NMR technique to follow the drying process of water in soils, daily moisture measurements were performed with a mobile NMR endoscope on three different types of soil (silt, sand, and a natural soil) during an one-step outflow experiment. The soils were packed in columns approximately one meter high. The NMR measurements were cross-validated by repetitive measurements of the mass drift due to the drying process. The NMR-endoscope exhibits a cylindrical geometry incorporating the principle of the u-shaped NMR-MOUSE. It could be raised and lowered inside a plastic tube (1 mm thick) in the soil column similar to a wire-line logging tool. Working with a frequency of 8.73 MHz, the sensitive volume has a depth of 2 mm, avoiding any boundary effects that might arise due to the tube wall. For the purpose of quantitative analysis, the water evolution (described by the Richards Equation) was modelled with the Hydrus1D Program, taking into account the boundary conditions under which the experiments were carried out. Out of these simulations, an assessment of the hydraulic parameters (Ks, ?, n and l of the Van Genuchten model) of the soil is achieved. Experimental aspects such as the optimization of the endoscope, the statistical uncertainty, and the noise shielding are discussed as well.

Sucre, O.; Pohlmeier, A.; Casanova, F.; Blümich, B.

2009-04-01

372

Solid-state NMR in the analysis of drugs and naturally occurring materials.  

Science.gov (United States)

This article presents some of the solid-state NMR (SSNMR) techniques used in the pharmaceutical and biomedical research. Solid-state magic angle spinning (MAS) NMR provides structural information on powder amorphous solids for which single-crystal diffraction structures cannot be obtained. NMR is non-destructive; the powder sample may be used for further studies. Quantitative results can be obtained, although solid-state NMR spectra are not normally quantitative. As compared with other techniques, MAS NMR is insensitive and requires a significant amount of the powder sample (2-100mg) to fill the 1.3-7 mm ZrO2 rotor. This is its main drawback, since natural compounds isolated from plants, microorganisms or cell cultures are difficult to obtain in quantities higher than a few milligrams. Multinuclear MAS NMR routinely uses (1)H and (13)C nuclei, less frequently (15)N, (19)F, (31)P, (77)Se, (29)Si, (43)Ca or (23)Na. The article focuses on the pharmaceutical applications of SSNMR, the studies were aimed to control over manufacturing processes (e.g. crystallization and milling) investigation of chemical and physical stability of solid forms both as pure drug and in a formulated product. SSNMR is used in combination with some other analytical methods (DSC, XRD, FT-IR) and theoretical calculations of NMR parameters. Biologically active compounds, such as amino acids and small peptides, steroids and flavonoids were studied by SSNMR methods (part 4) providing valuable structural information. The SSNMR experiments performed on biopolymers and large natural products like proteins, cellulose and lipid layers are commented upon briefly in part 5. PMID:24173236

Paradowska, Katarzyna; Wawer, Iwona

2014-05-01

373

Crystal field parameters for Yb3+ ions at orthorhombic centers in garnets-Revisited  

International Nuclear Information System (INIS)

The major purpose of this paper is to clarify the deficiencies identified in the recent paper by Liu et al. (J. Lumin. 130 (2010) 103) as well as to reanalyze the available data and provide corrected results for the orthorhombic crystal field parameters (CFPs) for selected rare-earth ions in garnets. It appears that Liu et al., when utilizing the computer package for standardization of CFPs, have inadvertently confused the properties of CFPs expressed in the Wybourne notation with those in the extended Stevens operator notation. This confusion has led to misinterpretations concerning the orthorhombic standardization transformations and incorrect labeling of the CFP sets as supposedly 'standardized' for Yb3+, Pr3+, Nd3+, and Er3+ ions in various garnets. These deficiencies have prompted us to reconsider the CFP sets determined earlier by matching the experimental data, i.e. the orthorhombic spin Hamiltonian parameters (g factors, gi, and hyperfine structure constants, Ai; i=x, y, z) and available optical spectral band positions, with the theoretical data calculated using the complete diagonalization method. To further verify the correctness of the present results the CFPs for orthorhombic Yb3+ centers in Yb3Al5O12 and Yb3Ga5O12 garnets are calculated using the superposition model (SPM), which requires adoption of a well-defined symmetry-adapted axis system (SAAS). Hence, the SPM calculations enable reanalysis of available CFP sets based on the correct standardization procedure and establishing the correspondence between the SAAS and the 'nominal' axis systems assigned to fitted CFP sets. Using the proper SAAS and general transformations of the axis systems, the relations between the calculated gi and/or Ai values and the respective principal values determined by EPR experiments can be established. The consistent methodology utilized here may be helpful for proper reanalysis of spectroscopic data for rare-earth and transition-metal ions at orthorhombic symmetry sites in various crystals. - Highlights: ? Problems due to mixing up of CFP properties in Wybourne and Stevens notations clarified. ? Superposition model analysis carried out for Yb3+ in YbAG and YbGG. ? Usefulness of CFP standardization and multiple correlated fitting technique shown. ? Principal axis used in EPR correlated with the axis used in SPM analysis. ? Present methodology can be applied to other RE3+ ions doped into garnets.

374

Determination of standard sample purity using the high-precision 1H-NMR process.  

Science.gov (United States)

This paper discusses the technique for high-precision quantification using (1)H-NMR to determine the purity of analytical standard samples. The procedure described is based on the use of internal reference samples in an (1)H NMR experiment in our laboratories. The sample preparation and all relevant NMR parameters were optimized for minimum uncertainty. The validation of accuracy and precision was performed by comparing different certified reference materials. It was shown that the high-precision measurement is applicable even for relatively small sample amounts down to 2.5 mg. The relative combined uncertainty of measurement was found to be 0.15%. Two different approaches for uncertainty calculation were compared; a complete uncertainty budget was calculated. PMID:22327969

Schoenberger, Torsten

2012-04-01

375

27Al NMR/NQR studies of YbAl3C3  

International Nuclear Information System (INIS)

The phase transition at T*=80 K in YbAl3C3 has been studied by 27Al nuclear quadrupole resonance (NQR) measurement and nuclear magnetic resonance (NMR) measurement up to 30T. The NQR and NMR spectra reveal clear anomalies just below T*, which provides the first microscopic evidence for symmetry lowering in the low-temperature phase below T*. The transition is characterized by marked changes in the 27Al-NQR frequencies ?Q's without significant changes in the lattice parameters. The field dependence of the transition is also investigated. The NMR line exhibits field-induced rapid broadening below T*, which almost vanishes in zero field. Moreover, we found that T* increases by 10 K at 30T. These unique magnetic properties are consistent with the scheme that the microscopic mechanism underlying the phase transition involves Yb-4f electrons rather than the scheme of a simple structural phase transition. (author)

376

Identifying Stereoisomers by ab-initio Calculation of Secondary Isotope Shifts on NMR Chemical Shieldings  

Directory of Open Access Journals (Sweden)

Full Text Available We present ab-initio calculations of secondary isotope effects on NMR chemical shieldings. The change of the NMR chemical shift of a certain nucleus that is observed if another nucleus is replaced by a different isotope can be calculated by computing vibrational corrections on the NMR parameters using electronic structure methods. We demonstrate that the accuracy of the computational results is sufficient to even distinguish different conformers. For this purpose, benchmark calculations for fluoro(2-2Hethane in gauche and antiperiplanar conformation are carried out at the HF, MP2 and CCSD(T level of theory using basis sets ranging from double- to quadruple-zeta quality. The methodology is applied to the secondary isotope shifts for 2-fluoronorbornane in order to resolve an ambiguity in the literature on the assignment of endo- and exo-2-fluoronorbornanes with deuterium substituents in endo-3 and exo-3 positions, also yielding insight into mechanistic details of the corresponding synthesis.

Karl-Heinz Böhm

2014-04-01

377

Optically detected NMR of optically hyperpolarized 31P neutral donors in 28Si  

CERN Document Server

The electron and nuclear spins of the shallow donor 31P are promising qubit candidates invoked in many proposed Si-based quantum computing schemes. We have recently shown that the near-elimination of inhomogeneous broadening in highly isotopically enriched 28Si enables an optical readout of both the donor electron and nuclear spins by resolving the donor hyperfine splitting in the near-gap donor bound exciton transitions. We have also shown that pumping these same transitions can very quickly produce large electron and nuclear hyperpolarizations at low magnetic fields, where the equilibrium electron and nuclear polarizations are near zero. Here we show preliminary results of the measurement of 31P neutral donor NMR parameters using this optical nuclear hyperpolarization mechanism for preparation of the 31P nuclear spin system, followed by optical readout of the resulting nuclear spin population after manipulation with NMR pulse sequences. This allows for the observation of single-shot NMR signals with very hi...

Steger, M; Yang, A; Saeedi, K; Hayden, M E; Thewalt, M L W; Itoh, K M; Riemann, H; Abrosimov, N V; Becker, P; Pohl, H -J

2010-01-01

378

Molecular mobility in Medicago truncatula seed during early stage of germination: Neutron scattering and NMR investigations  

Science.gov (United States)

First hours of Medicago truncatula (MT) seeds germination were investigated using elastic incoherent neutron scattering (EINS) and nuclear magnetic resonance (NMR), to follow respectively how macromolecular motions and water mobility evolve when water permeates into the seed. From EINS results, it was shown that there is an increase in macromolecular mobility with the water uptake. Changes in NMR relaxation parameters reflected microstructural changes associated with the recovery of the metabolic processes. The EINS investigation of the effect of temperature on macromolecular motions showed that there is a relationship between the amount of water in the seeds and the effect of freezing-thawing cycle. The NMR relaxometry results obtained at 253 K allowed establishing possible link between the freezing of water molecules tightly bound to macromolecules and their drastic motion restriction around 250 K, as observed with EINS at the highest water content.

Falourd, Xavier; Natali, Francesca; Peters, Judith; Foucat, Loïc

2014-01-01

379

NMR search for polymorphic phase transformations in chlorpropamide form-A at high pressures.  

Science.gov (United States)

The high-pressure effects on chlorpropamide (C10H13ClN2O3S) form-A have been studied by 1H NMR spectroscopy at high pressures up to 800 MPa in the temperature range 90-300 K. A study of the NMR second moment and spin-lattice relaxation time has been completed by a calculation of the steric hindrances for molecular reorientations and simulations of the second moment of the NMR line by the Monte-Carlo method, which enabled a precise description of molecular dynamics in the compound studied. Reorientations of the methyl group, oscillations and reorientations of the chlorophenyl ring and reorientations of the propyl group have been revealed and respective activation parameters extracted. No phase transformation of the compound form-A has been detected. PMID:18623194

Wasicki, J; Kozlenko, D P; Pankov, S E; Bilski, P; Pajzderska, A; Hancock, B C; Medek, A; Nawrocik, W; Savenko, B N

2009-04-01

380

NMR Studies on the Internal Structure of High-Tc Superconductors and Other Anorganic Compounds  

International Nuclear Information System (INIS)

Spatially-resolved NMR is used to probe internal structures in highly correlated superconductors of optimally-doped Tl2Ba2CuO6+? (Tc 85 K) and a heavy fermion superconductor CeCoIn5 (Tc = 2.3 K). The characteristic change of the properties of 205Tl-NMR in the vortex state provides a clear evidence of the antiferromagnetic order in the vortex cores below 20 K in Tl2Ba2CuO6+?. We also obtain anomalous 115In-NMR spectra of CeCoIn5, which provides a microscopic evidence for the occurrence of a spatially-modulated superconducting order parameter expected in a Fulde-Ferrel-Larkin-Ovchinnkov (FFLO) state.

 
 
 
 
381

Solid state NMR studies and density functional theory (DFT) calculations of conformers of quercetin.  

Science.gov (United States)

This work presents the first comparative analysis of two crystallographic modifications of quercetin (3,3',4',5,7-penta-hydroxyflavone). The existence of dihydrate and unhydrated forms of quercetin in the solid state is confirmed by several experimental techniques e.g. X-ray diffraction of powders, DSC, TGA, and NMR. Our studies allow an understanding of the complexity of quercetin samples obtained from different sources. A PASS-2D experiment is employed to establish principal values of 13C chemical shift tensors for both modifications. Solid state NMR spectroscopy and DFT GIAO calculations provide unique information about NMR shielding and electron density distribution for different conformers. It has been concluded that changes of conformation and hydrogen bonding pattern have great influence on bond order parameters of quercetin. Theoretical calculations and experimental data do not exclude the existence of the syn conformer of quercetin, which so far was not considered in the condensed phase. PMID:15305212

Olejniczak, Sebastian; Potrzebowski, Marek J

2004-08-21

382

A new method to construct reservoir capillary pressure curves using NMR log data and its application  

Science.gov (United States)

By analyzing hundreds of capillary pressure curves, the controlling factors of shape and type of capillary pressure curves are found and a novel method is presented to construct capillary pressure curves by using reservoir permeability and a synthesized index. The accuracy of this new method is verifi ed by mercury-injection experiments. Considering the limited quantity of capillary pressure data, a new method is developed to extract the Swanson parameter from the NMR T 2 distribution and estimate reservoir permeability. Integrating with NMR total porosity, reservoir capillary pressure curves can be constructed to evaluate reservoir pore structure in the intervals with NMR log data. An in-situ example of evaluating reservoir pore structure using the capillary pressure curves by this new method is presented. The result shows that it accurately detects the change in reservoir pore structure as a function of depth.

Liang, Xiao; Wei, Zhang

2008-06-01

383

NMR Structural Study of the Prototropic Equilibrium in Solution of Schiff Bases as Model Compounds  

Directory of Open Access Journals (Sweden)

Full Text Available An NMR titration method has been used to simultaneously measure the acid dissociation constant (pKa and the intramolecular NHO prototropic constant ?KNHO on a set of Schiff bases. The model compounds were synthesized from benzylamine and substituted ortho-hydroxyaldehydes, appropriately substituted with electron-donating and electron-withdrawing groups to modulate the acidity of the intramolecular NHO hydrogen bond. The structure in solution was established by 1H-, 13C- and 15N-NMR spectroscopy. The physicochemical parameters of the intramolecular NHO hydrogen bond (pKa, ?KNHO and ??G° were obtained from 1H-NMR titration data and pH measurements. The Henderson–Hasselbalch data analysis indicated that the systems are weakly acidic, and the predominant NHO equilibrium was established using Polster–Lachmann ?-diagram analysis and Perrin model data linearization.

David Ortegón-Reyna

2013-12-01

384

Orientational ordering studies of fluorinated thermotropic liquid crystals by NMR spectroscopy.  

Science.gov (United States)

Fluorinated calamitic thermotropic liquid crystals represent an important class of materials for high-tech applications, especially in the field of liquid crystal displays. The investigation of orientational ordering in these systems is fundamental owing to the dependence of their applications on the anisotropic nature of macroscopic optical, dielectric, and visco-elastic properties. NMR spectroscopy is the most powerful technique for studying orientational order in liquid crystalline systems at a molecular level thanks to the possibility of exploiting different anisotropic observables (chemical shift, dipolar couplings, and quadrupolar coupling) and nuclei ((2)H, (13)C, and (19)F). In this paper, the basic theory and NMR experiments useful for the investigation of orientational order on fluorinated calamitic liquid crystals are reported, and a review of the literature published on this subject is given. Finally, orientational order parameters determined by NMR data are discussed in comparison to those obtained by optical and dielectric anisotropy measurements. PMID:25042970

Calucci, Lucia; Geppi, Marco; Urban, Stanislaw

2014-10-01

385

A new de-noising method of NMR FID signals based on wavelet transform  

International Nuclear Information System (INIS)

Taking aim at the de-noising of clinical NMR FID signals, the paper analyzes the wavelet transform characteristic of available signals and noises separately based on wavelet transform technology. With the principles of three de-noising methods wavelet-based, wavelet transform modulus maxima, threshold shrinkage, and translation invariance. Effective solutions for selecting method of wavelet basis function, optimized thresholding function and wavelet decomposing parameters are put forward, so as the distinguishing method between signals and noises. Taking brain gliomas as an example, the paper implements effective experimental solutions based on the wavelet transform de-noising technology. About 30 clinical NMR data obtained from the NMR devices have been de-noised to provide high quality data and validated the new method. (authors)

386

EPR OF Mn2+ IMPURITIES IN CALCITE: A DETAILED STUDY PERTINENT TO MARBLE PROVENANCE DETERMINATION  

DEFF Research Database (Denmark)

We demonstrate that the electron paramagnetic resonance spectrum of Mn2+ impurities in calcite, and therefore also in marble, may be accurately reproduced by a traditional spin Hamiltonian formalism. The success of such a treatment, however, very much depends on the spin Hamiltonian parameters having the correct signs as well as magnitudes. We present data that determine the sign of the axial anisotropy parameter and thereby facilitate future quantum mechanical characterizations of marble electron paramagnetic resonance spectra that supplement provenance determination.

Laursen, Ib

2009-01-01

387

Quantitative on-line high-resolution NMR spectroscopy in process engineering applications.  

Science.gov (United States)

In many technical processes, complex multicomponent mixtures have to be handled, for example, in reaction or separation equipment. High-resolution NMR spectroscopy is an excellent tool to study these mixtures and gain insight in their behavior in the processes. For on-line studies under process conditions, flow NMR probes can be used in a wide range of temperature and pressure. A major challenge in engineering applications of NMR spectroscopy is the need for quantitative evaluation. Flow rates, recovery times, and other parameters of the on-line NMR experiments have to be optimized for this purpose. Since it is generally prohibitive to use deuterated solvents in engineering applications, suitable techniques for field homogenization and solvent signal suppression are needed. Two examples for the application of on-line NMR spectroscopic experiments in process engineering are presented, studies on chemical equilibria and reaction kinetics of the technically important system formaldehyde-water-methanol and investigations on reactive gas absorption of CO(2) in aqueous solutions of monoethanolamine. PMID:12733025

Maiwald, Michael; Fischer, Holger H; Kim, Young-Kyu; Hasse, Hans

2003-04-01

388

Spin Choreography: Basic Steps in High Resolution NMR (by Ray Freeman)  

Science.gov (United States)

There are three orientations that NMR courses may take. The traditional molecular structure course focuses on the interpretation of spectra and the use of chemical shifts, coupling constants, and nuclear Overhauser effects (NOE) to sort out subtle details of structure and stereochemistry. Courses can also focus on the fundamental quantum mechanics of observable NMR parameters and processes such a spin-spin splitting and relaxation. More recently there are courses devoted to the manipulation of nuclear spins and the basic steps of one- and two-dimensional NMR experiments. Freeman's book is directed towards the latter audience. Modern NMR methods offer a myriad ways to extract information about molecular structure and motion by observing the behavior of nuclear spins under a variety of conditions. In Freeman's words: "We can lead the spins through an intricate dance, carefully programmed in advance, to enhance, simplify, correlate, decouple, edit or assign NMR spectra." This is a carefully written, well-illustrated account of how this dance is choreographed by pulse programming, double resonance, and gradient effects. Although well written, this book is not an easy read; every word counts. It is recommended for graduate courses that emphasize the fundamentals of magnetic resonance. It is not a text on interpretation of spectra.

Minch, Michael J.

1998-02-01

389

AEM and NMR: Tools for the Future of Groundwater Management  

Science.gov (United States)

Within the world, understanding groundwater resources and their management are growing in importance to society as groundwater resources are stressed by drought and continued development. To minimize conflicts, tools and techniques need to be applied to support knowledge-based decisions and management. Airborne electromagnetic (AEM) surveys provide high-quality subsurface data not available from any other source for building the complex hydrogeologic frameworks needed by water-resource managers for effective groundwater management. Traditionally, point data, such as borehole logs, borehole geophysics, surface geophysics, and aquifer tests were interpolated over long distances to create hydrogeologic frameworks. These methods have enjoyed a long history of being the best available technology to inform our understanding of groundwater and how it moves. The AEM techniques proivde pathway for geoscientists to follow to develop more accurate descriptions of the hydrogeological framework. However, the critical and challenging measurements in characterizing aquifers include effective porosity and hydraulic conductivity. These parameters are not reliable derived from AEM. Typically, values for effective porosity and hydraulic conductivity are derived by lithological comparisons with published data; direct measurements of hydraulic conductivity acquired by a few constant head aquifer tests or slug tests; and expensive and time consuming laboratory measurements of cores which can be biased by sampling and the difficulty of making measurements on unconsolidated materials. Aquifer tests are considered to be the best method to gather information on hydraulic conductivity but are rare because of cost and difficult logistics. Also they are unique in design and interpretation from site to site. Nuclear Magnetic Resonance (NMR) can provide a direct measurement of the presence of water in the pore space of aquifer materials. Detection and direct measurement is possible due to the nuclear magnetization of the hydrogen (protons) in the water. These measurements are the basis of the familiar MRI (magnetic resonance imaging) in medical applications. NMR is also widely used in logging applications within the petroleum industry. Effective porosity values were derived directly from the borehole and surface NMR data, and hydraulic conductivity values were calculated using empirical relationships calibrated and verified with few laboratory permeameter and aquifer tests. NMR provides measurements of the effective porosity and hydraulic conductivity at a resolution not possible using traditional methods. Unlike aquifer tests, NMR logs are not unique in design and are applied in similar fashion from borehole to borehole providing a standard way of measuring hydraulic properties. When the hydraulic properties from the NMR are integrated with hydrogeological framework interpretations of AEM data large areas can be characterized. This allows a much more robust method for conceptualizing groundwater models then simply using previously published data for assigning effective porosity and hydraulic conductivity. Examples from the North Platte River Basin in Nebraska and the Murray Darling Basin of Australia illustrate that borehole and surface NMR allows superior, rapid measurements of the complexities of aquifers within when integrated with AEM.

Abraham, J. D.; Cannia, J. C.; Lawrie, K.

2012-12-01

390

Determination of relative natural isotopic abundance of 2H using NMR spectroscopy and application in food analysis  

International Nuclear Information System (INIS)

The basic relations are defined for determining the content of deuterium in compound CXHP. Hydrogen atoms 1H and 2H are distributed among the individual diastereotopic points in the molecule which is either monodeuterized or non deuterized. The SNIF-NMR parameter is derived from these assumptions. Procedures are presented for preparing samples for NMR experiments. For measuring NMR spectra of 2H the effects are considered of relaxation times and the total time of measurement. Relaxation times of deuterium in small molecules are of the order of 1 second. The possibilities are shown of using 2H NMR spectroscopy for the study of deuterium transfer during chemical and biochemical reactions, for the determination of isotope purity, the determination of the origin of the sample and for the surveillance of technological processes. Examples of the applications are given. (E.S.). 3 figs., 8 tabs., 42 refs

391

Use of NMR and NMR Prediction Software to Identify Components in Red Bull Energy Drinks  

Science.gov (United States)

A laboratory experiment designed as part of an upper-level undergraduate analytical chemistry course is described. Students investigate two popular soft drinks (Red Bull Energy Drink and sugar-free Red Bull Energy Drink) by NMR spectroscopy. With assistance of modern NMR prediction software they identify and quantify major components in each…

Simpson, Andre J.; Shirzadi, Azadeh; Burrow, Timothy E.; Dicks, Andrew P.; Lefebvre, Brent; Corrin, Tricia

2009-01-01

392

New methods for the correction of 31P NMR spectra in in vivo NMR spectroscopy  

International Nuclear Information System (INIS)

The new methods for the correction of 31P NMR spectra in vivo NMR spectroscopy have been performed. A method for the baseline correction of the spectra which represents a combination of time-domain and frequency-domain has been discussed.The method is very fast and efficient for minimization of base line artifacts of biological tissues impact

393

NMR line width of 12B in Pt detected by ?-NMR  

International Nuclear Information System (INIS)

NMR spectra of 12B in Pt (fcc) metal were observed by use of the ?-NMR detection method. A sharp single line was observed by use of an annealed Pt foil for the implantation medium. The dipolar broadening has been determined to be 332 ± 30 Hz (HWHM). (orig.)

394

NMR-CT of craniocerebral trauma  

International Nuclear Information System (INIS)

The rapid development of NMR imaging has been documented by many recent reports, but there have been fewer clinical studies. We applied NMR-CT to craniocerebral disease from July, 1983; our preliminary results are presented here. The device operates with a main magnetic field of 0.1T produced by the surrounding magnet. The data-accumulating time for protons and the T1 image was 4 minutes, while that of the IR image was 2 minutes. X-ray CT was performed with GE CT/T. Six patients with craniocerebral traumas were imaged with both NMR-CT and X-ray CT on the same day. A proton image, a T1 image, and an IR image were obtained and then compared with the image of the X-ray CT. All of the pathological changes in the brain were made visible by the NMR-CT. In some cases, the NMR-CT was more useful than the X-ray CT in demonstrating craniocerebral traumas. The advantages of the NMR-CT over the X-ray CT were as follows: a) the absence of bone artifacts, and b) important information for diagnosis could be obtained by measuring the T1 value. However, very small lesions were not clearly visible, and the data-accumulating time was longer than in the case of the X-ray CT. Much more clinical evaluation is required, but NMR-CT seems to be becoming a very important technique for craniocerebral traumas. (author)

395

Characterization of heroin samples by 1H NMR and 2D DOSY 1H NMR.  

Science.gov (United States)

Twenty-four samples of heroin from different illicit drug seizures were analyzed using proton Nuclear Magnetic Resonance ((1)H NMR) and two-dimensional diffusion-ordered spectroscopy (2D DOSY) (1)H NMR. A careful assignment and quantification of (1)H signals enabled a comprehensive characterization of the substances present in the samples investigated: heroin, its main related impurities (6-acetylmorphine, acetylcodeine, morphine, noscapine and papaverine) and cutting agents (caffeine and acetaminophen in nearly all samples as well as lactose, lidocaine, mannitol, piracetam in one sample only), and hence to establish their spectral signatures. The good agreement between the amounts of heroin, noscapine, caffeine and acetaminophen determined by (1)H NMR and gas chromatography, the reference method in forensic laboratories, demonstrates the validity of the (1)H NMR technique. In this paper, 2D DOSY (1)H NMR offers a new approach for a whole characterization of the various components of these complex mixtures. PMID:24378299

Balayssac, Stéphane; Retailleau, Emmanuel; Bertrand, Geneviève; Escot, Marie-Pierre; Martino, Robert; Malet-Martino, Myriam; Gilard, Véronique

2014-01-01

396

New NMR well logging/fracture mapping technique with possible application of SQUID NMR detection  

Energy Technology Data Exchange (ETDEWEB)

A new method for making NMR measurements has been developed that potentially can receive NMR signals from a precise distance into the geologic formation. It is based on the production of a toroidal region of homogeneous radial magnetic field near the mid-plane between two magnets arranged axially so their fields oppose between them. NMR signals have been detected from such a region in the laboratory. Preliminary data have been extrapolated to the projected performance of a logging tool using superconducting magnets. The presence of cryogenic temperatures required for these magnets may make signal detection using SQUIDs a logical consideration. Preliminary comparison of normal and SQUID NMR detection shows that near the borehole (<18 in.) standard NMR detection is probably superior; at greater distances SQUID detection may be advantageous. Directional detection of the signal may allow fractures near the wellbore to be mapped. Use of SQUID detection may be useful for this application.

Jackson, J.A.

1981-01-01

397

Nuclear magnetic resonance apparatus having semitoroidal rf coil for use in topical NMR and NMR imaging  

Science.gov (United States)

An improved nuclear magnetic resonance (NMR) apparatus for use in topical magnetic resonance (TMR) spectroscopy and other remote sensing NMR applications includes a semitoroidal radio-frequency (rf) coil. The semitoroidal rf coil produces an effective alternating magnetic field at a distance from the poles of the coil, so as to enable NMR measurements to be taken from selected regions inside an object, particularly including human and other living subjects. The semitoroidal rf coil is relatively insensitive to magnetic interference from metallic objects located behind the coil, thereby rendering the coil particularly suited for use in both conventional and superconducting NMR magnets. The semitoroidal NMR coil can be constructed so that it emits little or no excess rf electric field associated with the rf magnetic field, thus avoiding adverse effects due to dielectric heating of the sample or to any other interaction of the electric field with the sample.

Fukushima, Eiichi (Los Alamos, NM); Roeder, Stephen B. W. (La Mesa, CA); Assink, Roger A. (Albuquerque, NM); Gibson, Atholl A. V. (Bryan, TX)

1986-01-01

398

CHARMM36 all-atom additive protein force field: validation based on comparison to NMR data.  

Science.gov (United States)

Protein structure and dynamics can be characterized on the atomistic level with both nuclear magnetic resonance (NMR) experiments and molecular dynamics (MD) simulations. Here, we quantify the ability of the recently presented CHARMM36 (C36) force field (FF) to reproduce various NMR observables using MD simulations. The studied NMR properties include backbone scalar couplings across hydrogen bonds, residual dipolar couplings (RDCs) and relaxation order parameter, as well as scalar couplings, RDCs, and order parameters for side-chain amino- and methyl-containing groups. It is shown that the C36 FF leads to better correlation with experimental data compared to the CHARMM22/CMAP FF and suggest using C36 in protein simulations. Although both CHARMM FFs contains the same nonbond parameters, our results show how the changes in the internal parameters associated with the peptide backbone via CMAP and the ?1 and ?2 dihedral parameters leads to improved treatment of the analyzed nonbond interactions. This highlights the importance of proper treatment of the internal covalent components in modeling nonbond interactions with molecular mechanics FFs. PMID:23832629

Huang, Jing; MacKerell, Alexander D

2013-09-30

399

Variable-temperature NMR and conformational analysis of oenothein B  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Oenoteína B é um tanino hidrolisável dimérico com um amplo espectro de atividades biológicas, tais como antitumoral, anti-inflamatória e anti-viral. Seus espectros de ressonância magnética nuclear (RMN) à temperatura ambiente apresentam duplicações e alargamento de sinais. Experimentos de RMN uni e [...] bidimensionais a baixas temperaturas foram úteis no assinalamento de todos os sinais de hidrogênios e carbonos sem a necessidade de derivatização. A estrutura tridimensional do confôrmero mais estável foi determinada pela primeira vez através do experimento de espectroscopia de efeito nuclear Overhauser (NOESY) (-20 ºC) e cálculos computacionais usando métodos de teoria do funcional de densidade (DFT) (B3LYP/6-31G) e modelo contínuo polarizado (PCM). A conformação mais favorecida apresentou uma geometria altamente compactada e sem simetria, onde os dois grupos valoneoila mostraram diferentes parâmetros conformacionais e estabilidades. Abstract in english Oenothein B is a dimeric hydrolysable tannin with a wide range of biological activities, such as antitumour, anti-inflammatory and antiviral. Its nuclear magnetic resonance (NMR) at room temperature show duplications and broadening of signals. Experiments of 1D and 2D NMR at lower temperatures were [...] useful for the complete NMR assignments of all hydrogens and carbons. The 3D structure of the most stable conformer was determined for the first time by nuclear Overhauser effect spectroscopy (NOESY) experiment (-20 ºC) and density functional theory (DFT)(B3LYP/6-31G)/ polarizable continuum model (PCM) quantum chemical calculations. The favoured conformation showed a highly compacted geometry and a lack of symmetry, in which the two valoneoyl groups showed distinct conformational parameters and stabilities.

Suzana C., Santos; Ariadne G., Carvalho; Gilmara A. C., Fortes; Pedro H., Ferri; Anselmo E. de, Oliveira.

2014-02-01

400

Theoretical NMR correlations based Structure Discussion  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract The constitutional assignment of natural products by NMR spectroscopy is usually based on 2D NMR experiments like COSY, HSQC, and HMBC. The actual difficulty of the structure elucidation problem depends more on the type of the investigated molecule than on its size. The moment HMBC data is involved in the process or a large number of heteroatoms is present, a possibility of multiple solutions fitting the same data set exists. A structure elucidation software can be used to find such alternative constitutional assignments and help in the discussion in order to find the correct solution. But this is rarely done. This article describes the use of theoretical NMR correlation data in the structure elucidation process with WEBCOCON, not for the initial constitutional assignments, but to define how well a suggested molecule could have been described by NMR correlation data. The results of this analysis can be used to decide on further steps needed to assure the correctness of the structural assignment. As first step the analysis of the deviation of carbon chemical shifts is performed, comparing chemical shifts predicted for each possible solution with the experimental data. The application of this technique to three well known compounds is shown. Using NMR correlation data alone for the description of the constitutions is not always enough, even when including 13C chemical shift prediction.

Junker Jochen

2011-07-01

 
 
 
 
401

Nuclear magnetic resonance (NMR): principles and applications  

International Nuclear Information System (INIS)

The basis for the phenomenon of nuclear magnetic resonance (NMR) is the ability of certain nuclei possessing both intrinsic angular momentum or ''spin'' I and magnetic moment to absorb electromagnetic energy in the radio frequency range. In principle, there are approximately 200 nuclei which may be investigated using the NMR technique. The NMR spectrum consists of intensity peaks along an axis calibrated in terms of the steady magnetic field or the frequency of the radiofrequency electromagnetic radiation. Analysis of the number, spacing, position and intensity of the lines in an NMR spectrum consists of intensity peaks along an axis calibrated in terms of the steady magnetic field or the frequency of the radiofrequency electromagnetic radiation. Analysis of the number, spacing, position and intensity of the lines in an NMR spectrum provides a variety of qualitative and quantitative analytical applications. The most obvious applications consist of the measurements of nuclear properties, such as spin number and nuclear magnetic moment. In liquids, the fine structure of resonance spectra provides a tool for chemical identification and molecular structure analysis. Other applications include the measurements of self-diffusion coefficients, magnetic fields and field homogeneity, inter-nuclear distances, and, in some cases, the water content of biological materials. (author)

402

Mobile NMR for analysis of polyethylene pipes  

International Nuclear Information System (INIS)

NMR relaxometry is a suitable tool to determine the morphology of semi-crystalline polymers by its ability to discriminate between rigid, mostly crystalline and soft, usually amorphous material. The NMR-MOUSE (nuclear magnetic resonance mobile universal surface explorer) was explored in this work to supply morphological data of poly(ethylene) pipes nondestructively. PE-100 pipes were investigated in the new state, after squeezing them flat, and after annealing well below the glass temperature. Furthermore, the change in morphology induced by a pressure load from the inside and a point load from the outside was investigated as a function of depth, and the morphology change across a welding line was imaged. A shear-band was detected by destructive high-field NMR imaging in an area of severe deformation of a pipe, where an anomalous depths profile was observed by the NMR-MOUSE. These results demonstrate that the NMR-MOUSE is a suitable tool for non-destructive state assessment of polymer pipes on the basis of laboratory reference data. (author)

403

Rotational dynamics in a crystalline molecular gyroscope by variable-temperature 13C NMR, 2H NMR, X-ray diffraction, and force field calculations.  

Science.gov (United States)

A combination of solid-state 13C CPMAS NMR, 2H NMR, X-ray-determined anisotropic displacement parameters (ADPs), and molecular mechanics calculations were used to analyze the rotational dynamics of 1,4-bis[3,3,3-tris(m-methoxyphenyl)propynyl]benzene (3A), a structure that emulates a gyroscope with a p-phenylene group acting as a rotator and two m-methoxy-substituted trityl groups acting as a stator. The line shape analysis of VT 13C CPMAS and broad-band 2H NMR data were in remarkable agreement with each other, with rotational barriers of 11.3 and 11.5 kcal/mol, respectively. The barriers obtained by analysis of ADPs obtained by single-crystal X-ray diffraction at 100 and 200 K, assuming a sinusoidal potential, were 10.3 and 10.1 kcal, respectively. A similar analysis of an X-ray structure solved from data acquired at 300 K suggested a barrier of only 8.0 kcal/mol. Finally, a rotational potential calculated with a finite cluster model using molecular mechanics revealed a symmetric but nonsinusoidal potential that accounts relatively well for the X-ray-derived values and the NMR experimental results. It is speculated that the discrepancy between the barriers derived from low and high-temperature X-ray data may be due to an increase in anharmonicity, or to disorder, at the higher temperature values. PMID:17243820

Khuong, Tinh-Alfredo V; Dang, Hung; Jarowski, Peter D; Maverick, Emily F; Garcia-Garibay, Miguel A

2007-01-31

404

Ceramide-lipid interactions studied by MD simulations and solid-state NMR.  

Science.gov (United States)

Ceramides play a key modulatory role in many cellular processes, which results from their effect on the structure and dynamics of biological membranes. In this study, we investigate the influence of C16-ceramide (C16) on the biophysical properties of DMPC lipid bilayers using solid-state NMR and atomistic molecular dynamics (MD) simulations. MD simulations and NMR measurements were carried out for a pure DMPC bilayer and for a 20% DMPC-C16 mixture. Calculated key structural properties, namely area per lipid, chain order parameters, and mass density profiles, indicate that C16 has an ordering effect on the DMPC bilayer. Furthermore, the simulations predict that specific hydrogen-bonds form between DMPC and C16 molecules. Multi-nuclear solid-state NMR was used to verify these theoretical predictions. Chain order parameters extracted from (13)C(1)H dipole couplings were measured for both lipid and ceramide and follow the trend suggested by the MD simulations. Furthermore, (1)H-MAS NMR experiments showed a direct contact between ceramide and lipids. PMID:24882733

Dutagaci, Bercem; Becker-Baldus, Johanna; Faraldo-Gómez, José D; Glaubitz, Clemens

2014-10-01

405

Towards beyond-1 GHz solution NMR: Internal 2H lock operation in an external current mode  

Science.gov (United States)

We have commenced a project to develop a beyond-1 GHz solution NMR spectrometer using a HTS coil. Due to a small residual resistance present in the HTS conductor and joint resistance between conductors, a stable persistent current sufficient for NMR measurements is unlikely. Therefore, a current has to be supplied to the HTS coil from an external power supply. The ripple of an external power supply causes a field fluctuation which must be stabilized. In this study we show results of NMR measurements using a 500-600 MHz NMR in such an external current mode: the field fluctuations are stabilized by an internal 2H lock. The field fluctuation from the external power supply comprises a major field fluctuation component at low frequencies, 0.003-0.005 Hz, and superimposed minor field ripples at 2 Hz and 50 Hz. The former limits the time interval of the internal 2H lock, while the latter generates sidebands in the NMR spectrum. Sideband and baseline noise are controlled by appropriate selection of the feedback loop parameters of the lock. The quality of the 1D-solution NMR spectra observed in external current mode is equivalent to that obtained in persistent current mode. However, if the feedback loop time is as short as the gradient pulse width, refocusing of the NMR signal is lost and NMR peaks disappear. The 2D-NOESY and the 2D-HSQC spectra of ubiquitin in an external current mode have been acquired. The quality of the 2D spectra is equivalent to those obtained in persistent current mode; i.e. the internal 2H lock operates stably over an experimental time interval of 40-50 min. To realize a beyond-1 GHz NMR spectrometer, further investigations must be made of (i) the long term stability of a DC power supply, (ii) the enhancement of the compensation field limit for the internal 2H lock, (iii) the extension of the helium refill time interval, and (iv) a method to correct the field homogeneity in the external current mode.

Yanagisawa, Yoshinori; Nakagome, Hideki; Hosono, Masami; Hamada, Mamoru; Kiyoshi, Tsukasa; Hobo, Fumio; Takahashi, Masato; Yamazaki, Toshio; Maeda, Hideaki

2008-06-01

406

Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds.  

Science.gov (United States)

Two hexanuclear niobium halide cluster compounds with a [Nb6X12](2+) (X=Cl, Br) diamagnetic cluster core, have been studied by a combination of experimental solid-state NMR/NQR techniques and PAW/GIPAW calculations. For niobium sites the NMR parameters were determined by using variable Bo field static broadband NMR measurements and additional NQR measurements. It was found that they possess large positive chemical shifts, contrary to majority of niobium compounds studied so far by solid-state NMR, but in accordance with chemical shifts of (95)Mo nuclei in structurally related compounds containing [Mo6Br8](4+) cluster cores. Experimentally determined ?iso((93)Nb) values are in the range from 2,400 to 3,000 ppm. A detailed analysis of geometrical relations between computed electric field gradient (EFG) and chemical shift (CS) tensors with respect to structural features of cluster units was carried out. These tensors on niobium sites are almost axially symmetric with parallel orientation of the largest EFG and the smallest CS principal axes (Vzz and ?33) coinciding with the molecular four-fold axis of the [Nb6X12](2+) unit. Bridging halogen sites are characterized by large asymmetry of EFG and CS tensors, the largest EFG principal axis (Vzz) is perpendicular to the X-Nb bonds, while intermediate EFG principal axis (Vyy) and the largest CS principal axis (?11) are oriented in the radial direction with respect to the center of the cluster unit. For more symmetrical bromide compound the PAW predictions for EFG parameters are in better correspondence with the NMR/NQR measurements than in the less symmetrical chlorine compound. Theoretically predicted NMR parameters of bridging halogen sites were checked by (79/81)Br NQR and (35)Cl solid-state NMR measurements. PMID:24581866

Peri?, Berislav; Gautier, Régis; Pickard, Chris J; Bosio?i?,