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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

Superposition model analysis of the spin Hamiltonian parameters of two Gd3+ doped thorium dichalcogenides  

International Nuclear Information System (INIS)

The spin Hamiltonian parameters of Gd3+ in a single crystal of Thorium disulfide (ThS2) are analysed by means of the superposition model, in its most general form of a two exponents power law. In fact, the approximated one exponent power law is not suitable for this compound, where the ion-ligand distances show a quite large spread. The results of the analysis are then applied to the case of Gd3+ doped Thorium oxysulfide (ThOS), where the fitting of the experimental data is possible only assuming some distortion of the ligand cage. (orig.)

3

Spin-Hamiltonian parameters of Gd3+ ion in the room temperature tetragonal phase of BaTiO3  

International Nuclear Information System (INIS)

The spin-Hamiltonian parameters (g factors g verticalstrokeverticalstroke, g perpendicularto, and zero-field splittings b20, b40, b44, b60, b64) of the 4f7 Gd3+ ion in the tetragonal phase of a BaTiO3 crystal are calculated through the diagonalization (of energy matrix) method based on the one-electron crystal field mechanism. In the calculations, the crystal field parameters are estimated from the superposition model with the structural data of the studied crystal. It is found that by using three adjustable intrinsic parameters anti Ak(R0) (k = 2, 4, 6) in the superposition model, the seven calculated spin-Hamiltonian parameters are in good agreement with the experimental values, suggesting that the diagonalization method based on one-electron crystal field mechanism is effective in the studies of spin-Hamiltonian parameters for 4f7 ions in crystals.

4

Modeling of crystal field and spin-Hamiltonian parameters for Ti3+:MgO  

International Nuclear Information System (INIS)

The aim of this paper is to model the crystal field parameters (CFPs) and spin-Hamiltonian parameters (g factors g||, g? and hyperfine structure constants A||, A?) for the Ti3+:MgO system. The CFPs were modeled in the frame of superposition model of the crystal field theory, based on ab initio supercell calculations of Ti3+: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

5

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

6

Research on the spin-Hamiltonian parameters and defect structure for Ni{sup +} ion in CdS  

Energy Technology Data Exchange (ETDEWEB)

The spin-Hamiltonian parameters (g factors g{sub //}, g{sub ?} and hyperfine structure constants A{sub //}, A{sub ?}) for Ni{sup +} in the trigonally-distorted tetrahedral Cd{sup 2+} site of CdS are calculated from the complete diagonalization (of energy matrix) method with the suitable parameters. In the method, the contributions to spin-Hamiltonian parameters from both the spin-orbit parameters of central d{sup n} ion and ligands are contained and the interactions among all the ground and excited states are considered. The calculated results show reasonable agreement with the experimental values. The defect structure of Ni{sup +} center, which is similar to those of other 3d{sup n} centers in CdS, is obtained from the calculation.

Zheng, Wen-Chen, E-mail: zhengwc1@163.com [Department of Material Science, Sichuan University, Chengdu 610064 (China); International Center for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China); He, Lv [Department of Physics, Zhejiang Normal University, Jinhua 321004 (China); Li, Wei; Liu, Hong-Gang [Department of Material Science, Sichuan University, Chengdu 610064 (China)

2013-03-01

7

Density Functional Theory of Crystal Field Quasiparticle Excitations and the Ab Initio Calculation of Spin Hamiltonian Parameters  

International Nuclear Information System (INIS)

We show, by carefully examining the change of total energy in constrained variational calculations using the local spin density approximation, that crystal field excitations in normal rare earths are quasiparticles composed of a 4f excitation plus its associated cloud of shielding conduction electrons. Total energy calculations, which properly exclude the self-interaction of the nonspherical part of the 4f densities, are then used to calculate crystal field energies and the corresponding spin Hamiltonian parameters of TmSb and PrSb, accurately from first principles. copyright 1997 The American Physical Society

8

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

Energy Technology Data Exchange (ETDEWEB)

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 b{sub k}{sup q} and units of cm{sup -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 obtained by various techniques.

Rudowicz, C.Z. E-mail: apceslaw@cityu.edu.hk; Madhu, S.B.; Khasanova, N.M.; Galeev, Akhmet

2001-06-01

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

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

11

Spin-Hamiltonian parameters and defect structure for the tetragonal Mo5+ center in the reduced BaTiO3:Mo crystal  

International Nuclear Information System (INIS)

The spin-Hamiltonian parameters (g factors g?, g? and hyperfine structure constants A?, A?) of the tetragonal Mo5+ center in reduced BaTiO3:Mo crystal with low temperature phase are calculated from the high-order perturbation formulas based on the two-mechanism model for d1 ions in octahedral clusters with the ground state 2B2 (|dxy?). In the model, both the contributions to spin-Hamiltonian parameters from the crystal-field (CF) mechanism and that from the charge-transfer (CT) mechanism (which is neglected in the widely-used crystal field theory) are considered. The calculated results are in reasonably agreement with the experimental values. The calculations show that for the spin-Hamiltonian parameters of BaTiO3:Mo5+, the relative importances of CT mechanism |QCT/QCF| are about 17%, 9%, 7% and 7% for Q=?g?, ?g?, A?(2), and A?(2) (where ?g=g?ge, ge?2.0023, the g factor of free electron), respectively. It appears that for the high valence state dn ion clusters in crystals, the precise and complete calculations of spin-Hamiltonian parameters should take both the CF and CT mechanisms into account. The tetragonally-compressed distortion of (MoO6)7? octahedral clusters in the low-temperature rhombohedral phase of BaTiO3 caused by the static Jahn–Teller effect is also acquired from the calculations. The results are discussed. - Highlights: • Spin-Hamiltonian parameters of Mo5+ in rhombohedral BaTiO3 are calculated. • The calculation is based on the two (CF and CT)-mechanism model. • Contribution due to the charge-transfer mechanism should be considered. • Calculation confirms the defect model and obtains the defect structural data

12

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

13

Spin-Hamiltonian parameters of Gd{sup 3+} ion in the room temperature tetragonal phase of BaTiO{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

The spin-Hamiltonian parameters (g factors g {sub vertical} {sub stroke} {sub vertical} {sub stroke}, g {sub perpendicular} {sub to}, and zero-field splittings b{sub 2}{sup 0}, b{sub 4}{sup 0}, b{sub 4}{sup 4}, b{sub 6}{sup 0}, b{sub 6}{sup 4}) of the 4f{sup 7} Gd{sup 3+} ion in the tetragonal phase of a BaTiO{sub 3} crystal are calculated through the diagonalization (of energy matrix) method based on the one-electron crystal field mechanism. In the calculations, the crystal field parameters are estimated from the superposition model with the structural data of the studied crystal. It is found that by using three adjustable intrinsic parameters anti A{sub k}(R{sub 0}) (k = 2, 4, 6) in the superposition model, the seven calculated spin-Hamiltonian parameters are in good agreement with the experimental values, suggesting that the diagonalization method based on one-electron crystal field mechanism is effective in the studies of spin-Hamiltonian parameters for 4f{sup 7} ions in crystals.

Yang, Wei-Qing [Southwest Jiaotong Univ., Chengdu (China). Key Laboratory of Advanced Technologies of Materials; University of Electronic Science and Technology of China, Chengdu (China). State Key Laboratory of Electronic Thin Films and Integrated Devices; Zheng, Wen-Chen [Sichuan Univ., Chengdu (China). Dept. of Material Science

2014-10-15

14

Studies of the spin-Hamiltonian parameters and defect structures for the tetragonal and cubic Yb3+ centers in AgCl crystal.  

Science.gov (United States)

The spin-Hamiltonian parameters, g factors and hyperfine structure constants, for the tetragonal and cubic Yb(3+) centers in AgCl crystal are calculated from the complete diagonalization (of energy matrix) method. The calculations are based on the defect models that the tetragonal Yb(3+) center is formed by the substitutional Yb(3+) associated with two nearest Ag(+) vacancy (V(Ag)) along and axes (i.e., C(4) axis) owing to charge compensation and in cubic Yb(3+) center the two compensators V(Ag) are remote. From the calculations, the spin-Hamiltonian parameters of both Yb(3+) centers in AgCl are explained reasonably, the signs of hyperfine structure constants A(i)((171)Yb(3+)) and A(i)((173)Yb(3+)) are suggested, the above defect models of both Yb(3+) centers are confirmed and their defect structures are determined. PMID:21964239

Wen-Chen, Zheng; Hong-Gang, Liu; Ping, Su; Yu-Guang, Yang

2011-12-15

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

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

17

Studies on the local angular distortion and spin Hamiltonian parameters for the trigonal Co{sup 2+} center in MgCl{sub 2}  

Energy Technology Data Exchange (ETDEWEB)

The local angular distortion and spin Hamiltonian parameters (g factor g {sub vertical} {sub stroke} {sub vertical} {sub stroke}, g {sub perpendicular} {sub to} and the hyperfine structure constants) for the trigonal Co{sup 2+} center in MgCl{sub 2} are theoretically studied by diagonalizing the 6 x 6 energy matrix of ground {sup 4}T{sub 1} state for a trigonally distorted octahedral 3d{sup 7} cluster. Based on the cluster approach, the contributions from the admixtures of various J (= 1/2, 3/2, 5/2) states and the ligand orbital and spin-orbit coupling interactions are taken into account in a uniform way. The local impurity-ligand bond angle in the Co{sup 2+} center is found to be about 3.44 larger than the host metal-ligand bond angle in the pure crystal due to substitution of smaller Mg{sup 2+} by bigger Co{sup 2+}, inducing a further compressed ligand octahedron. The calculated spin Hamiltonian parameters using the above local angular distortion are in good agreement with the experimental data. The present studies on the local structure and the spin Hamiltonian parameters for Co{sup 2+} in MgCl{sub 2} are tentatively extended to a more general case by comparing the relevant impurity behaviours for Co{sup 2+} in various trigonal environments.

Hu, Xian-Fen [University of Electronic Science and Technology of China, Chengdu (China). School of Physical Electronics; Southwest University of Science and Technology of China, Mianyang (China). School of Science; Wu, Shao-Yi; Kuang, Min-Quan; Li, Guo-Liang [University of Electronic Science and Technology of China, Chengdu (China). School of Physical Electronics

2014-10-15

18

Studies on the local angular distortion and spin Hamiltonian parameters for the trigonal Co2+ center in MgCl2  

International Nuclear Information System (INIS)

The local angular distortion and spin Hamiltonian parameters (g factor g verticalstrokeverticalstroke, g perpendicularto and the hyperfine structure constants) for the trigonal Co2+ center in MgCl2 are theoretically studied by diagonalizing the 6 x 6 energy matrix of ground 4T1 state for a trigonally distorted octahedral 3d7 cluster. Based on the cluster approach, the contributions from the admixtures of various J (= 1/2, 3/2, 5/2) states and the ligand orbital and spin-orbit coupling interactions are taken into account in a uniform way. The local impurity-ligand bond angle in the Co2+ center is found to be about 3.44 larger than the host metal-ligand bond angle in the pure crystal due to substitution of smaller Mg2+ by bigger Co2+, inducing a further compressed ligand octahedron. The calculated spin Hamiltonian parameters using the above local angular distortion are in good agreement with the experimental data. The present studies on the local structure and the spin Hamiltonian parameters for Co2+ in MgCl2 are tentatively extended to a more general case by comparing the relevant impurity behaviours for Co2+ in various trigonal environments.

19

Local structure distortion and spin Hamiltonian parameters for Cr3+?VZn tetragonal defect centre in Cr3+ doped KZnF3 crystal  

International Nuclear Information System (INIS)

The quantitative relationship between the spin Hamiltonian parameters (D, g?, ?g) and the crystal structure parameters for the Cr3+?VZn tetragonal defect centre in a Cr3+:KZnF3 crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr3+?VZn tetragonal defect centre in the KZnF3 crystal are systematically investigated using the complete diagonalization method. It is found that the VZn vacancy and the differences in mass, radius and charge between the Cr3+ and the Zn2+ ions induce the local lattice distortion of the Cr3+ centre ions in the KZnF3 crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor ?g. We find that the ligand F? ion along [001] and the other five F? ions move towards the central Cr3+ by distances of ?1 = 0.0121 nm and ?2 = 0.0026 nm, respectively. Our approach takes into account the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It is found that for the Cr3+ ions in the Cr3+:KZnF3 crystal, although the spin—orbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

20

Theoretical study of the spin Hamiltonian parameters of vanadium ions V{sup 2+} in CsMgX{sub 3} (X=Cl,Br,I)  

Energy Technology Data Exchange (ETDEWEB)

The spin Hamiltonian g factors and the hyperfine structure constants for V{sup 2+} in CsMgX{sub 3} (X=Cl,Br,I) are theoretically studied by using the perturbation formulas of these parameters for a 3d{sup 3} ion in octahedral symmetry, based on the cluster approach. In such formulas, the contributions from the s-orbitals of the ligands were usually neglected. Here they are taken into account. The theoretical results (particularly the g factor for CsMgI{sub 3}) show a significant improvement compared with those in absence of the ligand s-orbital contributions in the previous studies. (orig.)

Gao Xiu-Ying; Wei Wang-He; Yan Wei-Zi [Dept. of Applied Physics, Univ. of Electronic Science and Technology of China, Chengdu (China); Wu Shao-Yi [Dept. of Applied Physics, Univ. of Electronic Science and Technology of China, Chengdu (China); International Center for Materials Physics, Chinese Academy of Sciences, Shenyang (China)

2005-03-01

21

Theoretical study of the spin Hamiltonian parameters of vanadium ions V2+ in CsMgX3 (X=Cl,Br,I)  

International Nuclear Information System (INIS)

The spin Hamiltonian g factors and the hyperfine structure constants for V2+ in CsMgX3 (X=Cl,Br,I) are theoretically studied by using the perturbation formulas of these parameters for a 3d3 ion in octahedral symmetry, based on the cluster approach. In such formulas, the contributions from the s-orbitals of the ligands were usually neglected. Here they are taken into account. The theoretical results (particularly the g factor for CsMgI3) show a significant improvement compared with those in absence of the ligand s-orbital contributions in the previous studies. (orig.)

22

Theoretical investigations of the local structures and spin Hamiltonian parameters for the trigonal Co2+ centers in LiNbO3 and LiTaO3  

International Nuclear Information System (INIS)

The local structures and spin Hamiltonian parameters (g factors gparallel, gperpendicular and the hyperfine structure constants) for the trigonal Co2+ centers in LiNbO3 and LiTaO3 are theoretically studied from diagonalization of the 6 x 6 energy matrix within 4T1 ground state for a 3d7 ion under trigonal symmetry. The contributions from the admixtures of various J (=1/2, 3/2, 5/2) states and the ligand orbitals and spin-orbit coupling interactions, which were usually ignored in the previous studies, are taken into account in this work. From the calculations, the impurity Co2+ is found not to occupy exactly the host Li+ site but to undergo an off-center displacement 0.06 A (or 0.03 A) away from the oxygen octahedron center in LiNbO3 (or LiTaO3). The theoretical spin Hamiltonian parameters based on the above local structures show good agreement with the experimental data. The various contributions to these parameters are also discussed

23

Studies of the spin-Hamiltonian parameters and the defect structure for Cu2+ at the rhombic Be2+ site of beryl crystal  

International Nuclear Information System (INIS)

The spin-Hamiltonian (SH) parameters (g factors gi and hyperfine structure constants Ai, where i=x, y, z) for Cu2+ at the rhombic Be2+ site of beryl (Be3Al2Si6O18) crystals are calculated from both the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM). The two methods are based on the cluster approach and so both the contribution to the SH parameters from the spin-orbit coupling parameters of central dn ion and that of ligand ion are included. The calculated results from the two theoretical methods are in reasonable agreement with the experimental values, suggesting that both methods are effective for the studies of SH parameters of 3d9 ion in rhombic symmetry. The defect structural data (which are unlike the corresponding data in the host beryl crystal) of the rhombic Cu2+ center in beryl are also acquired from the calculations. 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

Investigation on the spin Hamiltonian parameters and the local structures for Cu{sup 2+} centers in sodium phosphate and heavy metal fluoride glasses  

Energy Technology Data Exchange (ETDEWEB)

The spin Hamiltonian parameters (the anisotropic g factors g {sub parallel}, g {sub perpendicular} {sub to} and hyperfine structure constants A {sub parallel}, A {sub perpendicular} {sub to}) for the Cu{sup 2+} sites in sodium phosphate glasses Na{sub 2}O - 9P{sub 2}O{sub 5} and heavy metal fluoride glasses 60ZrF{sub 4} - 5LaF{sub 3} - 20BaF{sub 2} - 15NaF are theoretically investigated by using the high (fourth-) order perturbation formulas of these parameters for a 3d{sup 9} ion in tetragonally elongated octahedra. In these formulas, the contributions to the g factors from the tetragonal distortion, characterized by the tetragonal field parameters Ds and Dt, are taken into account by considering the relative axial elongation of the ligand octahedron around the Cu{sup 2+} due to the Jahn-Teller effect. According to the calculations, the ligand octahedra around Cu{sup 2+} are suggested to suffer about 12% and 18% relative elongation along the C{sub 4}-axis for the studied Na{sub 2}O - 9P{sub 2}O{sub 5} and 60ZrF{sub 4} - 5LaF{sub 3} - 20BaF{sub 2} - 15NaF glasses, respectively. The local structures characterized by the above axial elongations are discussed. (orig.)

Zhang, Hua-Ming; Wan, Xiong; Zhang, Zhi-Min [Nanchang Hangkong Univ. (China). Key Laboratory of Nondestructive Testing

2012-06-15

26

Spin Hamiltonian parameters and local structures for Co2+ ions in calcite-type trigonal carbonates MCO3 (M=Co, Cd and Ca)  

International Nuclear Information System (INIS)

From the perturbation formulas based on the cluster approach for 3d7 ion in trigonal octahedral sites of crystals, the spin Hamiltonian parameters (g factors gparallel, gperpendicular and hyperfine structure constants Aparallel, Aperpendicular) for Co2+ in calcite-type MCO3 (M=Co, Cd, Ca) crystals are calculated. In the calculations, for CoCO3 crystal, the structural data of pure crystal are used, whereas for the Co2+-doped CdCO3 and CaCO3 crystals, the local structural data caused by the impurity-induced local lattice relaxation are considered. The calculated results show good agreement with the observed values obtained from electron paramagnetic and antiferromagnetic resonance experiments. The difficulty shown in the previous paper related to the gperpendicular value of CoCO3 obtained from the change of the g factor as a function of the crystallographic data (i.e., the unit cell parameters) a0 and ?0 of pure MCO3 crystals is removed

27

Studies on the spin Hamiltonian parameters and local angular distortions for the tetragonal Cu2+ centers in the ZnX (X=O and S) nanocrystals  

Science.gov (United States)

The spin Hamiltonian parameters (g factors and hyperfine structure constants) and local structures are theoretically studied for the tetragonal Cu2+ centers in the ZnX (X=O and S) nanocrystals from the perturbation formulas of these parameters for a 3d9 ion in tetragonally distorted tetrahedra. The ligand orbital and spin-orbit coupling contributions are considered in view of strong covalency. Due to the Jahn-Teller effect, the local Cu2+?X2- bond angles between the four equivalent impurity-ligand bonds and the four-fold axis are found to be about 2.47° and 1.68° larger than that (?54.74°) for an ideal tetrahedron. This induces tetragonally compressed [CuX4]6- clusters on tetrahedral substitutional Zn2+ sites, different from the assignments (i.e., Cu2+ on tetragonally elongated octahedral and tetrahedral substitutional sites in the ZnO and ZnS nanocrystals, respectively) in the previous works. The calculated g factors for both systems and the parallel component of the hyperfine structure constants for the ZnS:Cu2+ nanocrystals based on the above local angular distortions are in good agreement with the observed values. The validity of the present assignments for the local structures of the Cu2+ centers is analyzed.

Li, Guo-Liang; Wu, Shao-Yi; Zhang, Zhi-Hong; Ding, Chang-Chun; Hu, Xian-Fen

2015-01-01

28

Modeling local structure using crystal field and spin Hamiltonian parameters: the tetragonal FeK3+-OI2- defect center in KTaO3 crystal  

International Nuclear Information System (INIS)

The local structure and the spin Hamiltonian (SH) parameters, including the zero-field-splitting (ZFS) parameters D and (a+2F/3), and the Zeeman g factors g|| and gperpendicular, are theoretically investigated for the FeK3+-OI2- center in KTaO3 crystal. The microscopic SH (MSH) parameters are modeled within the framework of the crystal field (CF) theory employing the CF analysis (CFA) package, which also incorporates the MSH modules. Our approach takes into account the spin-orbit interaction as well as the spin-spin and spin-other-orbit interactions omitted in previous studies. The superposition model (SPM) calculations are carried out to provide input CF parameters for the CFA/MSH package. The combined SPM-CFA/MSH approach is used to consider various structural models for the FeK3+-OI2- defect center in KTaO3. This modeling reveals that the off-center displacement of the Fe3+ ions, ?1(Fe3+), combined with an inward relaxation of the nearest oxygen ligands, ?2(O2-), and the existence of the interstitial oxygen OI2- give rise to a strong tetragonal crystal field. This finding may explain the large ZFS experimentally observed for the FeK3+-OI2- center in KTaO3. Matching the theoretical MSH predictions with th the theoretical MSH predictions with the available structural data as well as electron magnetic resonance (EMR) and optical spectroscopy data enables predicting reasonable ranges of values of ?1(Fe3+) and ?2(O2-) as well as the possible location of OI2- ligands around Fe3+ ions in KTaO3. The defect structure model obtained using the SPM-CFA/MSH approach reproduces very well the ranges of the experimental SH parameters D, g|| and gperpendicular and importantly yields not only the correct magnitude of D but also the sign, unlike previous studies. More reliable predictions may be achieved when experimental data on (a+2F/3) and/or crystal field energy levels become available. Comparison of our results with those arising from alternative models existing in the literature indicates considerable advantages of our method and presumably higher reliability of our predictions.

29

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

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

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

32

Investigations on the spin Hamiltonian parameters for Yb{sup 3+} ion in Bi{sub 2}Sr{sub 2}YCu{sub 2}O{sub 8}  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • The EPR spectra are studied for the two orthorhombic Yb{sup 3+} centers in Bi{sub 2}Sr{sub 2}YCu{sub 2}O{sub 8}. • 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 Bi{sub 2}Sr{sub 2}YCu{sub 2}O{sub 8}. 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 g{sub x}, g{sub y}, g{sub z}, and the hyperfine structure constants A{sub x}, A{sub y} and A{sub z} of the two orthorhombic Yb{sup 3+} centers in Bi{sub 2}Sr{sub 2}YCu{sub 2}O{sub 8} are theoretically studied from the perturbation formulas of these parameters for a 4f{sup 13} 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 Yb{sup 3+} ion occupying the host Bi{sup 3+} site. The calculated EPR parameters are reasonable agree with the observed values.

Dong, Hui-Ning, E-mail: donghn@163.com; Dong, Meng-Ran; Li, Jin-Jin; Liu, Jun

2013-10-15

33

Green commutator functions for a spin hamiltonian  

International Nuclear Information System (INIS)

All the Green commutator functions (GCF) for the Heisenberg spin hamiltonian (HSH) have been calculated in the Hartree-Fock (HF) approximation. It is shown that the Tjablik transverse GCF corresponds to the HF approximation only in the longitudinal HSH part and for obtaining the longitudinal GCF with the same accuracy that the Tjablik transverse GCF, it as necessary to go on to the HF approximation only in the transverse HSH part

34

Mean-field theory of antiferromagnetic spin Hamiltonian with four spin interactions for bcc lattice  

International Nuclear Information System (INIS)

An antiferromagnetic spin Hamiltonian with four spin interactions for bcc lattice is investigated on the assumption of four sublattices within the mean-field approximation. Phase diagrams are calculated in the parameter space for zero field. They possess a weak ferromagnetic phase. The effects of the magnetic field on the model are discussed in detail. The susceptibility of the antiferromagnetic phase becomes dependent on temperature in contrast to the usual cases. There is the case where the susceptibility of the SCAF perpendicular phase in the magnetic field on the spin plane can become much larger than the perpendicular susceptibility of this phase. On the basis of these results we examine to what extent this model can be compatible with the recent experimental results obtained in solid 3He. The magnitudes of exchange integrals are determined so as to fit to low-temperature behavior as well as high-temperature behavior of solid 3He. For these parameter values, it is shown that the paramagnetic phase undergoes a second-kind transition into the AF phase. In this phase the susceptibility increases more rapidly with lowering temperature than the extrapolation of the high-temperature Curie-Weiss law, and it shows a sudden drop to a nearly constant value from a peak value at T sub(c1), where this phase makes a first-kind transition to the SCAF parallel phase contrary to the case of Hetherington and Willard. This behavior is qualitatively similar to This behavior is qualitatively similar to that of the solid 3He. (author)

35

Large transverse field tunnel splittings in the Fe_8 spin Hamiltonian  

OpenAIRE

The spin Hamiltonian that describes the molecular magnet Fe$_8$ has biaxial symmetry with mutually perpendicular easy, medium, and hard magnetic axes. Previous calculations of the ground state tunnel splittings in the presence of a magnetic field along the hard axis are extended, and the meaning of the previously discovered oscillation of this splitting is further clarified.

Garg, Anupam

1999-01-01

36

Nuclear charge-distribution effects on the NMR spectroscopy parameters.  

Science.gov (United States)

We present here a systematic study about the influence of the size and type of nuclear charge-distribution models (Gaussian and point-like) on the NMR spectroscopic parameters, the nuclear magnetic shielding ? and the indirect nuclear spin J-coupling. We found that relativistic effects largely enhance the nuclear charge-distribution effects (NChDE) on those parameters being them quite sensitive to the nuclear model adopted for calculations. Results for two rare gas atoms (Kr, Rn) and few molecular systems like HX, (X = Br, I, At), CH(4), SnH(4), SnIH(3), SnI(2)H(2), and PbIH(3) are presented. J-couplings are more sensitive than shieldings in both, relativistic and non-relativistic (NR) regimes. The highest effect (close to 11% of variation in relativistic calculations with that two different nuclear models) is observed for J(Pb-I) in PbIH(3). A similar effect is found for J(Pb-H) in the same molecule, close to 9%. The NChDE for ?(Sn) in SnI(4-n)H(n) with n = 1, 2 is as large as few ppm (between 3 and 8.56 ppm). For J(Sn-H) in this set of molecules, it goes from 37 Hz for SnH(4) to 54 Hz for SnI(2)H(2). Furthermore, we found that the vicinal NChDE is very small though not zero. For (1)J(Sn-H) in SnIH(3), the NChDE of iodine is close to 2 Hz (0.1%). We also studied the NChDE on the ground state electronic energies of atoms and molecules. We found that these effects are only important within the relativistic regime but not within the NR one. They are in good agreement with previous works. PMID:22713039

Maldonado, Alejandro F; Giménez, Carlos A; Aucar, Gustavo A

2012-06-14

37

Theoretical and experimental investigation of the 1H NMR spectrum of putrescine  

Science.gov (United States)

Chemical shifts ? and spin-spin coupling constants J have been calculated for the putrescine molecule, a polyamine present in prostate tissue, through a DFT/B3LYP/6-311++G(d,p)/PCM/(GIAO) approach, which has been shown to be accurate in previous work. From ? and J values, calculated for the first time for the isolated and the solvated putrescine, the 1H NMR spectra have been simulated. Comparisons between the calculated and the experimental NMR spectra at 400 MHz show a good agreement and allow to propose reliable values for the NMR spin Hamiltonian parameters of putrescine to be used as good starting values for further quantitation methods of metabolites in prostate tissue.

Allouche, A. R.; Graveron-Demilly, D.; Fauvelle, F.; Aubert-Frécon, M.

2008-12-01

38

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

39

Modeling Ne-21 NMR parameters for carbon nanosystems.  

Czech Academy of Sciences Publication Activity Database

Ro?. 51, ?. 10 (2013), s. 676-681. ISSN 0749-1581 R&D Projects: GA ?R GAP208/11/0105; GA MŠk(CZ) LH11033 Grant ostatní: AV ?R(CZ) M200551205 Institutional support: RVO:61388963 Keywords : Ne-21 NMR * GIAO NMR * molecular modeling * carbon nanostructures Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.559, year: 2013

Kupka, T.; Nieradka, M.; Kaminský, Jakub; Stobinski, L.

2013-01-01

40

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

41

Derivation of the spin Hamiltonians for Fe in MgO  

Science.gov (United States)

A method to calculate the effective spin Hamiltonian for a transition metal impurity in a non-magnetic insulating host is presented and applied to the paradigmatic case of Fe in MgO. In the first step we calculate the electronic structure employing standard density functional theory (DFT), based on generalized gradient approximation (GGA), using plane waves as a basis set. The corresponding basis of atomic-like maximally localized Wannier functions is derived and used to represent the DFT Hamiltonian, resulting in a tight-binding model for the atomic orbitals of the magnetic impurity. The third step is to solve, by exact numerical diagonalization, the N electron problem in the open shell of the magnetic atom, including both effects of spin–orbit and Coulomb repulsion. Finally, the low energy sector of this multi-electron Hamiltonian is mapped into effective spin models that, in addition to the spin matrices S, can also include the orbital angular momentum L when appropriate. We successfully apply the method to Fe in MgO, considering both the undistorted and Jahn–Teller (JT) distorted cases. Implications for the influence of Fe impurities on the performance of magnetic tunnel junctions based on MgO are discussed.

Ferrón, A.; Delgado, F.; Fernández-Rossier, J.

2015-03-01

42

ESR and NMR study of mixed yttrium-lutetium-aluminum garnets  

International Nuclear Information System (INIS)

ESR of Mo3+ ions and NMR of 27Al nuclei is investigated in mixed single crystals of yttrium-lutetium-aluminium garnets (Ysub(1-x)Lusub(x))3Al5O12, where 0 3+ and 27Al compared with Y3Al5O12 and Lu3Al5O12 single crystals are revealed associated with symmetry and crystalline field parameter changes at isomorphous substitution of Y3+ ions in the rare-earth sublattice of the garnet by those of Lu3+. Symmetry, nearest coordination, and parameters of spin-Hamiltonians are estimated concerning all of Mo3+ and 27Al centres in (Ysub(1-x)Lusub(x))3Al5O12 at x < 0.15. (author)

43

Numerical Analysis of the EPR Spectrum of a Ni4 Single-Molecule Magnet through Direct Diagonalization of the Four-Spin Hamiltonian  

Science.gov (United States)

EPR studies have established the Giant Spin (GS) Hamiltonian parameters, D, B4^0 and B4^4, for members of the [Ni(hmp)(ROH)X]4 (R = Me, Et, etc., and X = Cl and Br) family of single-molecule magnets.^1 Four S = 1 Ni^II ions, aligned on corners of a cubic core, couple ferromagnetically creating a spin S = 4 ground state. Experiments on an isostructural Ni/Zn alloy established single-ion di and ei parameters, as well as the orientations of the local magnetic axes.^1 A numerical model utilizing matrix diagonalization has simulated EPR spectra for the coupled S = 1 Ni^II ions using parameters from the Ni/Zn studies. Fourth order anisotropy parameters in the giant spin model arise from the isotropic Heisenberg coupling, JS1.S2, and quadratic single-ion anisotropy in the four-spin Hamiltonian. Heisenberg coupling causes higher energy states to influence the S = 4 ground state addressed in the GS model. Matching the lowest nine energies of the four-spin model to those of the GS model allows direct spectroscopic determination of J. ^1E.-C. Yang et al., Inorg. Chem. 44, 3827-3836 (2005).

Wilson, Anthony; Hill, Steve

2006-03-01

44

?-NMR  

Science.gov (United States)

The ?-NMR facility at ISAC is constructed specifically for experiments in condensed matter physics with radioactive ion beams. Using co-linear optical pumping, a 8Li + ion beam having a large nuclear spin polarisation and low energy (nominally 30 keV) can be generated. When implanted into materials these ions penetrate to shallow depths comparable to length scales of interest in the physics of surfaces and interfaces between materials. Such low-energy ions can be decelerated with simple electrostatic optics to enable depth-resolved studies of near-surface phenomena over the range of about 2-200 nm. Since the ?-NMR signal is extracted from the asymmetry intrinsic to beta-decay and therefore monitors the polarisation of the radioactive probe nuclear magnetic moments, this technique is fundamentally a probe of local magnetism. More generally though, any phenomena which affects the polarisation of the implanted spins by, for example, a change in resonance frequency, line width or relaxation rate can be studied. The ?-NMR program at ISAC currently supports a number of experiments in magnetism and superconductivity as well as novel ultra-thin heterostructures exhibiting properties that cannot occur in bulk materials. The general purpose zero/low field and high field spectrometers are configured to perform CW and pulsed RF nuclear magnetic resonance and spin relaxation experiments over a range of temperatures (3-300 K) and magnetic fields (0-9 T).

Morris, Gerald D.

2014-01-01

45

Quadrupole coupling parameters and structural aspects of crystalline and amorphous solids by NMR and NQR  

International Nuclear Information System (INIS)

NMR and NQR techniques were combined to obtain the quadrupole coupling constant (Qcc) and asymmetry parameter (?) and extract structural information for several borate, gallate, and metavanadate compounds and glasses. 71Ga and 69Ga NMR was used to study crystalline ?-Ga2O3 and several gallate glasses. Quadrupole parameters were acquired for GaO6 and GaO4 units in ?-Ga2O3 by the computer simulation of the NMR powder patterns. A sensitive CW NQR spectrometer was built to detect NQR resonances below 2 MHz. The spectrometer includes a modified Robinson oscillator-detector, a new bi-symmetric square wave Zeeman modulator and a computerized data acquisition system. 51V (I = 7/2) NQR resonances below 850 kHz were detected for several metavanadates at both room temperature and liquid nitrogen temperature. Two methods, Zeeman perturbed NQR powder pattern and 10B NQR, can be employed to obtain both Qcc and ?. With a double coil tank circuit design, pure 11B NQR was used to determine the fraction of borons in BO3 and BO4 configurations in hydrated zinc borates. 11B NMR and NQR were also used to study lead borate glasses

46

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

47

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

48

NMR Principles  

OpenAIRE

The basic theory behind NMR spectroscopy is described. The various NMR parameters that can be obtained from NMR spectra are explained, including the chemical shift, spin-spin coupling, and relaxation. Some explanation of the theory of how NMR is detected is also presented. © 1999 Elsevier Ltd All rights reserved.

Hore, Pj

2010-01-01

49

Determination and first principles calculations, using the PAW/GIPAW method, of NMR parameters in inorganic fluorides  

OpenAIRE

This thesis focuses on the determination and the modeling, by the PAW/GIPAW (Gauge Including Projector Augmented Waves) method, of NMR parameters in inorganic fluorides. In the first part, a correlation between experimental 19F isotropic chemical shift (diso) and calculated 19F isotropic shieldings (siso) of binary fluorides with obvious assignments is established that allows to predict 19F NMR spectra with a good accuracy. The quadrupolar parameters of these fluorides are also determined and...

Biswal, Mamata

2013-01-01

50

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

51

The influence of NH 3 -attaching on the NMR parameters in the zigzag BN nanotube  

Science.gov (United States)

Two models of (10, 0) boron nitride nanotubes (BNNTs), perfect and Ammonia-attached, were studied in order to evaluate the influence of NH 3-attaching on the B-11 and N-15 nuclear magnetic resonance in the (10, 0) boron-nitride nanotube (BNNT) for the first time. At first, based on density functional theory (DFT) each of the structures was optimized using B3LYP/6-31G (d) model chemistry. At the next step, the chemical-shielding (CS) tensors were calculated using the B3LYP/6-31G (d, p) level of theory in both of the relaxed forms and were converted to experimentally measurable nuclear magnetic resonance (NMR) parameters, i.e. chemical-shielding isotropic (CSI) and chemical-shielding anisotropic (CSA). Our calculation revealed that in the NH 3-attached BNNT (the most stable model) the B atom chemically bonded to the NH 3 molecule has the largest chemical-shielding isotropic (CSI) and the smallest chemical-shielding anisotropic (CSA) values among the other boron nuclei. Additionally, the NMR parameters of those nuclei directly bonded to the boron dramatically change while those of the other B nuclei remain almost unchanged.

Zahedi, Ehsan; Bodaghi, Ali; Seif, Ahmad; Boshra, Asadollah

2011-02-01

52

First-principles calculation of NMR parameters using the gauge including projector augmented wave method: a chemist's point of view.  

OpenAIRE

First-principles calculations of NMR parameters in solids are of crucial importance in chemistry and materials science. The acquisition of a high-resolution spectrum, however, does come with a cost, that is, the suppression of all anisotropies. The interactions that affect NMR spectra are inherently anisotropic and can be represented mathematically by second- and fourth-rank tensors. A third approach is to employ electronic structure techniques that model extended solids using periodic bounda...

Bonhomme, C.; Gervais, C.; Babonneau, F.; Coelho, C.; Pourpoint, F.; Azai?s, T.; Ashbrook, Se; Griffin, Jm; Yates, Jr; Mauri, F.; Pickard, Cj

2012-01-01

53

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 lvent 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)

54

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

55

The effects of fast molecular motions and nuclear delocalisation on NMR parameters.  

Czech Academy of Sciences Publication Activity Database

Brno : Masaryk University, 2014 - (Novotný, J.; Foroutan-Nejad, C.; Marek, R.). C3 ISBN 978-80-86441-45-0. [NMR Valtice. Central European NMR Meeting /29./. 27.4.-30.4.2014, Valtice] Institutional support: RVO:61388963 Keywords : NMR spectroscopy * DFT molecular dynamics * nuclear quantum effects Subject RIV: CF - Physical ; Theoretical Chemistry

Dra?ínský, Martin; Hodgkinson, P.

56

Non-Linear Problems in NMR: Application of the DFM Variation of Parameters Method  

Science.gov (United States)

This Dissertation introduces, develops, and applies the Dirac-McLachlan-Frenkel (DFM) time dependent variation of parameters approach to Nuclear Magnetic Resonance (NMR) problems. Although never explicitly used in the treatment of time domain NMR problems to date, the DFM approach has successfully predicted the dynamics of optically prepared wave packets on excited state molecular energy surfaces. Unlike the Floquet, average Hamiltonian, and Van Vleck transformation methods, the DFM approach is not restricted by either the size or symmetry of the time domain perturbation. A particularly attractive feature of the DFM method is that measured data can be used to motivate a parameterized trial function choice and that the DFM theory provides the machinery to provide the optimum, minimum error choices for these parameters. Indeed a poor parameterized trial function choice will lead to a poor match with real experiments, even with optimized parameters. Although there are many NMR problems available to demonstrate the application of the DFM variation of parameters, five separate cases that have escaped analytical solution and thus require numerical methods are considered here: molecular diffusion in a magnetic field gradient, radiation damping in the presence of inhomogeneous broadening, multi-site chemical exchange, and the combination of molecular diffusion in a magnetic field gradient with chemical exchange. The application to diffusion in a gradient is used as an example to develop the DFM method for application to NMR. The existence of a known analytical solution and experimental results allows for direct comparison between the theoretical results of the DFM method and Torrey's solution to the Bloch equations corrected for molecular diffusion. The framework of writing classical Bloch equations in matrix notation is then applied to problems without analytical solution. The second example includes the generation of a semi-analytical functional form for the free precession and spin echo signals for a single, radiation damped, symmetric, inhomogenously broadened line. Although an analytical solution for the dynamics of the radiation damped single isochromat with and without homogeneous broadening is well known, the corresponding case involving symmetric inhomogeneous broadening has escaped solution to date. Although, an analytical theorem was developed to describe the tip angle |??|of the on resonance central vector of the inhomogeneous distribution due to the cumulative effect of radiation damping feedback, no insight into the magnetization dynamics during radiation damping are offered. Several trial functions were optimized with the DFM approach to obtain semi-analytical estimates of the free precession and spin echo signals with symmetric inhomogeneous broadening for the first time. The effect of inhomogeneous distribution function asymmetry in addition to sample demagnetization can also be treated using this approach. Initial results describing multi-site chemical exchange will be presented. It will be shown that the simplest trial function leads to the original treatment by Meiboom. The concept of multi-site exchange is then expanded to a continuum of exchange by proposing a chemical shift distribution where amplitude is proportional to shift probability. As an example, a symmetric Gaussian distribution is used to reproduce the expected result of mimicking diffusion effects on relaxation times. Finally the DFM method is applied to the composite problem of molecular diffusion in a magnetic field gradient with chemical exchange. The modeling of biologically relevant ion channels, which originally motivated this work, is treated as a two site exchange problem where ions in solution have a much higher diffusion coefficient than bound ions. Simulations for both the application of static magnetic field gradients and RF magnetic field gradients are presented.

Erker, Jay Charles

57

Isotropic chemical shifts and quadrupolar parameters of oxygen-17 using dynamic-angle spinning NMR  

International Nuclear Information System (INIS)

Several oxygen-17-enriched silicates were studied using dynamic-angle spinning (DAS) NMR spectroscopy at two magnetic field strengths. The DAS method averages second-order quadrupolar interactions by reorienting a sample about a time-dependent axis, thereby yielding high-resolution spectra for half-odd integer spin quadrupolar nuclei such as oxygen-17. A narrow spectral line is observed for each distinct oxygen site in a powdered sample at the sum of the isotropic chemical shift and the field-dependent isotropic second-order quadrupolar shift. Using equations for the total shift observed at two field strengths, the chemical shift is uniquely determined together with a product of the quadrupolar coupling constant (CQ = e2qQ/h) and the quadrupolar asymmetry parameter (?). For one silicate, the authors demonstrate a computer program that uses the isotropic shifts and quadrupolar products as constraints and provides simulations of overlapped magic-angle spinning line shapes. In this way the quadrupolar parameters, CQ and ?, are determined separately for each crystallographic site. The silicates studied include the discrete orthosilicates larnite (Ca2SiO4) and forsterite (Mg2SiO4), as well as diopside (CaMgSi2O6), wollastonite (CaSiO3), and clinoenstatite (MgSiO3), which are minerals composed of chains of silicon-oxygen tetrahedra. 49 refs., 2 figs., 2-oxygen tetrahedra. 49 refs., 2 figs., 2 tabs

58

Marshall-positive SU (N ) quantum spin systems and classical loop models: A practical strategy to design sign-problem-free spin Hamiltonians  

Science.gov (United States)

We consider bipartite SU (N ) spin Hamiltonians with a fundamental representation on one sublattice and a conjugate to fundamental on the other sublattice. By mapping these antiferromagnets to certain classical loop models in one higher dimension, we provide a practical strategy to write down a large family of SU (N ) symmetric spin Hamiltonians that satisfy Marshall's sign condition. This family includes all previously known sign-free SU (N ) spin models in this representation and in addition provides a large set of new models that are Marshall positive and can hence be studied efficiently with quantum Monte Carlo methods. As an application of our idea to the square lattice, we show that in addition to Sandvik's Q term, there is an independent nontrivial four-spin R term that is sign free. Using numerical simulations, we show how the R term provides a new route to the study of quantum criticality of Néel order.

Kaul, Ribhu K.

2015-02-01

59

General order parameter based correlation analysis of protein backbone motions between experimental NMR relaxation measurements and molecular dynamics simulations.  

Science.gov (United States)

Internal backbone dynamic motions are essential for different protein functions and occur on a wide range of time scales, from femtoseconds to seconds. Molecular dynamic (MD) simulations and nuclear magnetic resonance (NMR) spin relaxation measurements are valuable tools to gain access to fast (nanosecond) internal motions. However, there exist few reports on correlation analysis between MD and NMR relaxation data. Here, backbone relaxation measurements of (15)N-labeled SH3 (Src homology 3) domain proteins in aqueous buffer were used to generate general order parameters (S(2)) using a model-free approach. Simultaneously, 80 ns MD simulations of SH3 domain proteins in a defined hydrated box at neutral pH were conducted and the general order parameters (S(2)) were derived from the MD trajectory. Correlation analysis using the Gromos force field indicated that S(2) values from NMR relaxation measurements and MD simulations were significantly different. MD simulations were performed on models with different charge states for three histidine residues, and with different water models, which were SPC (simple point charge) water model and SPC/E (extended simple point charge) water model. S(2) parameters from MD simulations with charges for all three histidines and with the SPC/E water model correlated well with S(2) calculated from the experimental NMR relaxation measurements, in a site-specific manner. PMID:25600810

Liu, Qing; Shi, Chaowei; Yu, Lu; Zhang, Longhua; Xiong, Ying; Tian, Changlin

2015-02-13

60

71Ga NMR of reference GaIV, GaV, and GaVI compounds by MAS and QPASS, extension of gallium/aluminum NMR parameter correlation.  

Science.gov (United States)

We report new measurements of NMR parameters for 71Ga in gallium bearing oxide reference compounds, ranging from perfectly ordered systems to disordered crystalline structures and their aluminate counterparts. Static, MAS, and QPASS spectra are obtained at magnetic fields ranging from 7.0 to 18.8 T. With these results we enhance the previously established correlation between isotropic chemical shifts of 71Ga and 27Al and propose a correlation between gallium and aluminum electric field gradients (EFG). This correlation shows that the EFG at 71Ga sites are generally three times greater than those at equivalent 27Al sites. PMID:10672940

Massiot, D; Vosegaard, T; Magneron, N; Trumeau, D; Montouillout, V; Berthet, P; Loiseau, T; Bujoli, B

1999-12-01

61

Modeling NMR and EPR parameters in the metal-organic framework Cu3(BTC)2  

International Nuclear Information System (INIS)

In the last decade metal-organic frameworks (MOF) have been the subject of intensive research activity due to their tunable porous structure promoting interesting properties and applications. A very powerful tool for characterization of the complex chemical and electronic structure of these nanoporous materials is magnetic resonance spectroscopy. The interpretative and analytical power of the applied NMR and EPR experimental techniques can be significantly enhanced by supplying a reliable theoretical treatment of the underlying spectroscopic parameters. We report on the application of density functional theory (DFT) for computing the magnetic resonance properties of Cu3(BTC)2(H2O)3 (BTC=benzene 1,3,5-tricarboxylate). The ADF 2008 code with Slater basis sets incorporating relativistic corrections has been used for geometry optimization of the MOF building block. We have performed gas phase calculations modeling both the ground singlet and the excited triple state of the Cu(II) ions from the paddle-wheel unit. The nuclear shielding tensors of C and H forming the BTC linkers, as well as the ESR g- and A-tensors of the Cu(II) ions in the paddle-wheel have been calculated and compared to experimental results from the literature.

62

Isotropic chemical shifts and quadrupolar parameters of oxygen-17 using dynamic-angle spinning NMR  

Energy Technology Data Exchange (ETDEWEB)

Several oxygen-17-enriched silicates were studied using dynamic-angle spinning (DAS) NMR spectroscopy at two magnetic field strengths. The DAS method averages second-order quadrupolar interactions by reorienting a sample about a time-dependent axis, thereby yielding high-resolution spectra for half-odd integer spin quadrupolar nuclei such as oxygen-17. A narrow spectral line is observed for each distinct oxygen site in a powdered sample at the sum of the isotropic chemical shift and the field-dependent isotropic second-order quadrupolar shift. Using equations for the total shift observed at two field strengths, the chemical shift is uniquely determined together with a product of the quadrupolar coupling constant (C{sub Q} = e{sup 2}qQ/h) and the quadrupolar asymmetry parameter ({eta}). For one silicate, the authors demonstrate a computer program that uses the isotropic shifts and quadrupolar products as constraints and provides simulations of overlapped magic-angle spinning line shapes. In this way the quadrupolar parameters, C{sub Q} and {eta}, are determined separately for each crystallographic site. The silicates studied include the discrete orthosilicates larnite (Ca{sub 2}SiO{sub 4}) and forsterite (Mg{sub 2}SiO{sub 4}), as well as diopside (CaMgSi{sub 2}O{sub 6}), wollastonite (CaSiO{sub 3}), and clinoenstatite (MgSiO{sub 3}), which are minerals composed of chains of silicon-oxygen tetrahedra. 49 refs., 2 figs., 2 tabs.

Mueller, K.T.; Baltisberger, J.H.; Wooten, E.W.; Pines, A. [Lawrence Berkeley Laboratory, CA (United States)

1992-08-20

63

First-principles investigation of the relation between structural and NMR parameters in vitreous GeO2.  

OpenAIRE

NMR parameters of (73)Ge and (17)O in vitreous GeO(2) and quartz GeO(2), including the isotropic shifts, the quadrupole coupling constants C(Q), and the electric-field-gradient asymmetry parameters ?, are determined through density functional calculations. Clear correlations are established between (73)Ge shifts and the mean of the four neighboring Ge-O-Ge bond angles, and between C(Q) and ? parameters of (17)O and the local Ge-O-Ge angle. Available experimental data for C(Q) and the corres...

Kibalchenko, M.; Yates, Jr; Pasquarello, A.

2010-01-01

64

Microscopic spin Hamiltonian approaches for 3d8 and 3d2 ions in a trigonal crystal field - perturbation theory methods versus complete diagonalization methods  

International Nuclear Information System (INIS)

In this paper, we critically review the existing microscopic spin Hamiltonian (MSH) approaches, namely the complete diagonalization method (CDM) and the perturbation theory method (PTM), for 3d8(3d2) ions in a trigonal (C3v, D3, D3d) symmetry crystal field (CF). A new CDM is presented and a CFA/MSH computer package based on our crystal-field analysis (CFA) package for 3dN ions is developed for numerical calculations. Our method takes into account the contribution to the SH parameters (D, gparallel and gperpendicular to) from all 45 CF states for 3d8(3d2) ions and is based on the complete diagonalization of the Hamiltonian including the electrostatic interactions, the CF terms (in the intermediate CF scheme) and the spin-orbit coupling. The CFA/MSH package enables us to study not only the CF energy levels and wavefunctions but also the SH parameters as functions of the CF parameters (B20, B40 and B43 or alternatively Dq, ? and ?') for 3d8(3d2) ions in trigonal symmetry. Extensive comparative studies of other MSH approaches are carried out using the CFA/MSH package. First, we check the accuracy of the approximate PTM based on the 'quasi-fourth-order' perturbation formulae developed by Petrosyan and Mirzakhanyan (PM). The present investigations indicate that the PM formulae for the g-factors (gparallelrmulae for the g-factors (gparallel and gperpendicular to) indeed work well, especially for the cases of small v and ?' and large Dq, whereas the PM formula for the zero-field splitting (ZFS) exhibits serious shortcomings. Earlier criticism of the PM approach by Zhou et al (Zhou K W, Zhao S B, Wu P F and Xie J K 1990 Phys. Status Solidi b 162 193) is then revisited. Second, we carry out an extensive comparison of the results of the present CFA/MSH package and those of other CDMs based on the strong- and weak-CF schemes. The CF energy levels and the SH parameters for 3d2 and 3d8 ions at C3v symmetry sites in several crystals are calculated and analysed. Our investigations reveal serious inconsistencies in the CDM results of Zhou et al and Li (Li Y 1995 J. Phys.: Condens. Matter 7 4075) based on the strong-CF scheme for Ni2+ ions in LiNbO3 crystals. The correctness of our CFA/MSH package is verified by comparing our results with the predictions of Ma et al (Ma D P, Ma N, Ma X D and Zhang H M 1998 J. Phys. Chem. Solids 59 1211, Ma D P, Ma X D, Chen J R and Liu Y Y 1997 Phys. Rev. B 56 1780) and Macfarlane (Macfarlane R M 1964 J. Chem. Phys. 40 373) for ?-Al2O3:V3+(3d2) and MgO:Ni2+(3d8). It appears that the two independent approaches show perfect agreement with our approach, unlike those of Zhou et al and Li, which turn out to be unreliable. Our results reveal that the contributions to the ZFS parameter from the higher excited states cannot be neglected; also, the ZFS parameter is very sensitive to slight changes of the crystal structure. Hence our CFA/MSH package, which takes into account the contributions to the ZFS parameter from the higher excited states, can provide reliable results and proves to be a useful tool for the studies of the effect of the lattice distortions, defects and structural disorder on the spectroscopic properties of 3d2 and 3d8 ions at trigonal symmetry sites in crystals. (author)

65

Effects of Quantum Nuclear Delocalisation on NMR Parameters from Path Integral Molecular Dynamics.  

Czech Academy of Sciences Publication Activity Database

Ro?. 20, ?. 8 (2014), s. 2201-2207. ISSN 0947-6539 Grant ostatní: Seventh Framework Programme of the European Union(XE) FP7-299242 People Institutional support: RVO:61388963 Keywords : density functional calculations * isotope effects * NMR spectroscopy * nuclear delocalisation * path integral molecular dynamics Subject RIV: CC - Organic Chemistry Impact factor: 5.696, year: 2013

Dra?ínský, Martin; Hodgkinson, P.

2014-01-01

66

The effects of fast molecular motions and nuclear delocalisation on NMR parameters.  

Czech Academy of Sciences Publication Activity Database

Santiago : -, 2014. OP039. [WATOC 2014. Congress of the World Association of Theoretical and Computational Chemists /10./. 05.10.2014-10.10.2014, Santiago] R&D Projects: GA ?R GA13-24880S Institutional support: RVO:61388963 Keywords : NMR spectroscopy * molecular dynamics * DFT calculations Subject RIV: CF - Physical ; Theoretical Chemistry

Dra?ínský, Martin; Hodgkinson, P.

67

Calculations of Solid-State NMR Parameters of Isocytosine and Sesquiterpene Lactones.  

Czech Academy of Sciences Publication Activity Database

Ireland : University College Dublin, 2012. s. 243-243. [EUROMAR 2012. Magnetic Resonance Conference. 01.07.2012-05.07.2012, Dublin] Institutional research plan: CEZ:AV0Z40550506 Keywords : NMR * solid-state * DFT calculations * crystal packing Subject RIV: CC - Organic Chemistry

Dra?ínský, Martin; Bud?šínský, Miloš; Warzajtis, B.; Rychlewska, U.

68

Ab initio DFT study of bisphosphonate derivatives as a drug for inhibition of cancer: NMR and NQR parameters.  

Science.gov (United States)

DFT computations were carried out to characterize the (17)Oand (2)H electric field gradient, EFG, in various bisphosphonate derivatives. The computations were performed at the B3LYP level with 6-311++G (d,P) standard basis set. Calculated EFG tensors were used to determine the (17)O and (2)H nuclear quadrupole coupling constant, ? and asymmetry parameter, ?. For better understanding of the bonding and electronic structure of bisphosphonates, isotropic and anisotropic NMR chemical shieldings were calculated for the (13)C, (17)O and (31)P nuclei using GIAO method for the optimized structure of intermediate bisphosphonates at B3LYP level of theory using 6-311++G (d, p) basis set. The results showed that various substituents have a strong effect on the nuclear quadrupole resonance (NQR) parameters (?, ?) of (17)O in contrast with (2)H NQR parameters. The NMR and NQR parameters were studied in order to find the correlation between electronic structure and the activity of the desired bisphosphonates. In addition, the effect of substitutions on the bisphosphonates polarity was investigated. Molecular polarity was determined via the DFT calculated dipole moment vectors and the results showed that substitution of bromine atom on the ring would increase the activity of bisphosphonates. PMID:21633790

Aghabozorg, Hussein; Sohrabi, Beheshteh; Mashkouri, Sara; Aghabozorg, Hamid Reza

2012-03-01

69

Ab initio 27Al NMR chemical shifts and quadrupolar parameters for Al2O3 phases and their precursors  

Science.gov (United States)

The gauge-including projector augmented wave (GIPAW) method, within the density functional theory (DFT) generalized gradient approximation (GGA) framework, is applied to compute solid state NMR parameters for 27Al in the ?, ?, and ? aluminium oxide phases and their gibbsite and boehmite precursors. The results for well established crystalline phases compare very well with available experimental data and provide confidence in the accuracy of the method. For ?-alumina, four structural models proposed in the literature are discussed in terms of their ability to reproduce the experimental spectra also reported in the literature. Among the considered models, the Fd3¯m structure proposed by Paglia [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.71.224115 71, 224115 (2005)] shows the best agreement. We attempt to link the theoretical NMR parameters to the local geometry. Chemical shifts depend on coordination number but no further correlation is found with geometrical parameters. Instead, our calculations reveal that, within a given coordination number, a linear correlation exists between chemical shifts and Born effective charges.

Ferreira, Ary R.; Küçükbenli, Emine; Leitão, Alexandre A.; de Gironcoli, Stefano

2011-12-01

70

New program for computation of the thermodynamic, spectral, and NMR relaxation parameters of coordination compounds in complex systems  

International Nuclear Information System (INIS)

A new approach providing a direct calculations of equilibrium constants, parameters of the chemical exchange reactions, and spectral characteristics of complexes on the basis of data of several methods including pH-potentiometry, multi-wavelength electronic spectroscopy, and NMR relaxation within a single computer program was proposed and realized in the program STALABS. Application of the STALABS program has been demonstrated on the example of investigation of the complex nickel(II) - L-histidine system by joint usage of the above three methods.

71

Calculation of NMR-relaxation parameters for flexible molecules from molecular dynamics simulations  

International Nuclear Information System (INIS)

Comparatively small molecules such as peptides can show a high internal mobility with transitions between several conformational minima and sometimes coupling between rotational and internal degrees of freedom. In those cases the interpretation of NMR relaxation data is difficult and the use of standard methods for structure determination is questionable. On the other hand, in the case of those system sizes, the timescale of both rotational and internal motions is accessible by molecular dynamics (MD) simulations using explicit solvent. Thus a comparison of distance averages (-6>-1/6 or -3>1/3) over the MD trajectory with NOE (or ROE) derived distances is no longer necessary, the (back)calculation of the complete spectra becomes possible. In the present study we use two 200 ns trajectories of a heptapeptide of ?-amino acids in methanol at two different temperatures to obtain theoretical ROESY spectra by calculating the exact spectral densities for the interproton vectors and the full relaxation matrix. Those data are then compared with the experimental ones. This analysis permits to test some of the assumptions and approximations that generally have to be made to interpret NMR spectra, and to make a more reliable prediction of the conformational equilibrium that leads to the experimental spectrum

72

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

73

NMR : nuclear magnetic resonance  

International Nuclear Information System (INIS)

This book gives description of principles of NMR for example macroscopic magnetization, devices and sample processing, NMR spectrum such as chemical shift, decoupling, interpretation of spectrum, and pulse NMR including parameters of pulse NMR. It also adds polarization transfer experiment such as SPT, INEPT, DEPT, CIDNP, 2D NMR experiment including chemical shift correlation, J-resolved experiment, indirect detection and pulsed field gradient experiment, selective excitation experiment, and NOE for instance the Solomon equations, dipolar coupling, NOE applications.

74

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.

Maximov, Ivan I.; Tošner, Zden?k; Nielsen, Niels Chr.

2008-05-01

75

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

76

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.)

77

Calculated 13C NMR relaxation parameters for a restricted internal diffusion model. Application to methionine relaxation in dihydrofolate reductase  

International Nuclear Information System (INIS)

13C NMR relaxation parameters, T1, T2, and NOE, have been calculated based on a model assuming internal rotational diffusion subject to boundary conditions limiting the range of motion. Numerical results are presented as a function of diffusion coefficients D0 and D/sub i/ and angle ? defined as in the free internal rotation calculation, as well as 2theta, the allowed range of motion. Relaxation times vary from values expected in the absence of internal motion to values slightly below those calculated using the free internal rotation model as the range is increased from 0 to 3600. The discrepancy in the latter comparison arises from the boundary condition preventing diffusion from 180+ to 180-. Changes in T2 are typically monotonic or nearly monotonic as a function of theta; however, changes in T1 and NOE values are markedly nonmonotonic for D0 approx. 6 s-1 and for certain values of D/sub i/. Criteria for the applicability of the present calculations to the analysis of 13C NMR relaxation data obtained in studies of macromolecules undergoing restricted internal motion have been suggested. The results have been generalized to the case of multiple internal rotations, specifically for the problem of one free and one restricted diffusional process. In general, two types of rotation are not commutative. This model has been applnot commutative. This model has been applied to relaxation data recently obtained for the methionine methyl resonances of specifically 13C-labeled dihydrofolate reductase obtained from S. faecium. The results indicate that the data can be readily explained by assuming rapid free internal diffusion about the S--CH3 bond and restricted internal diffusion about the CH2--S bond of methionine, such that for the broadest resonances the motional range is restricted to approx. 900 and for the sharpest resonances the range is >1800. Restriction of the motion allows a significantly better fit of data than a model based on two free internal rotations

78

Detecting pyramidal state of the glycosidic nitrogen in 8-oxo-2'-deoxyguanosine; theoretical study of 15N NMR parameters.  

Czech Academy of Sciences Publication Activity Database

Brno : Masaryk University, 2014 - (Novotný, J.; Foroutan-Nejad, C.; Marek, R.). C7 ISBN 978-80-86441-45-0. [NMR Valtice. Central European NMR Meeting /29./. 27.4.-30.4. 2014 , Valtice] R&D Projects: GA ?R GA13-27676S Institutional support: RVO:61388963 Keywords : hOGG1 enzyme * OxoG * NMR Subject RIV: CF - Physical ; Theoretical Chemistry

Šebera, Jakub; Dra?ínský, Martin; Nencka, Radim; Trantírek, L.; Tanaka, Y.; Sychrovský, Vladimír

79

Calculated /sup 13/C NMR relaxation parameters for a restricted internal diffusion model. Application to methionine relaxation in dihydrofolate reductase  

Energy Technology Data Exchange (ETDEWEB)

/sup 13/C NMR relaxation parameters, T/sub 1/, T/sub 2/, and NOE, have been calculated based on a model assuming internal rotational diffusion subject to boundary conditions limiting the range of motion. Numerical results are presented as a function of diffusion coefficients D/sub 0/ and D/sub i/ and angle ..beta.. defined as in the free internal rotation calculation, as well as 2theta, the allowed range of motion. Relaxation times vary from values expected in the absence of internal motion to values slightly below those calculated using the free internal rotation model as the range is increased from 0 to 360/sup 0/. The discrepancy in the latter comparison arises from the boundary condition preventing diffusion from 180/sup +/ to 180/sup -/. Changes in T/sub 2/ are typically monotonic or nearly monotonic as a function of theta; however, changes in T/sub 1/ and NOE values are markedly nonmonotonic for D/sub 0/ approx. < 10/sup 6/ s/sup -1/ and for certain values of D/sub i/. Criteria for the applicability of the present calculations to the analysis of /sup 13/C NMR relaxation data obtained in studies of macromolecules undergoing restricted internal motion have been suggested. The results have been generalized to the case of multiple internal rotations, specifically for the problem of one free and one restricted diffusional process. In general, two types of rotation are not commutative. This model has been applied to relaxation data recently obtained for the methionine methyl resonances of specifically /sup 13/C-labeled dihydrofolate reductase obtained from S. faecium. The results indicate that the data can be readily explained by assuming rapid free internal diffusion about the S--CH/sub 3/ bond and restricted internal diffusion about the CH/sub 2/--S bond of methionine, such that for the broadest resonances the motional range is restricted to approx. 90/sup 0/ and for the sharpest resonances the range is >180/sup 0/. Restriction of the motion allows a significantly better fit of data. 5 figures, 1 table.

London, R.E.; Avitabile, J.

1978-11-08

80

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

81

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.

82

Zero-Field Anisotropic Spin Hamiltonians in First-Row Transition Metal Complexes: Theory, Models and Applications  

OpenAIRE

Magnetic anisotropy is responsible for the slow relaxation of the magnetization in single molecule magnets. The main goal of this work is to understand the factors that govern local and intersite anisotropies in polynuclear compounds. For this purpose, correlated relativistic calculations are performed in mono- and bi-nuclear species. The main degrees of freedoms of the two-step state-interaction ab initio method have been optimized in order to obtain anisotropic parameters in good agreement ...

Maurice, Re?mi

2011-01-01

83

Magnetic resonanse imaging in otorhinolaryngology. With special reference to the influence of factors upon NMR parameters and differential diagnosis of otorhinolaryngic lesions  

Energy Technology Data Exchange (ETDEWEB)

MRI diagnosis for malignant tumors are made possible by direct comparison to the results obtained by the brain and it seems possible to differentiate malignant tumors from other benign lesions. Cystic lesions, and mycotic sinusitis sometimes resemble malignant tumors in MR Image. In the present report, we investigated the relationships between the biochemical contents of cystic lesions and NMR-parameters to clarify why some inflammatory lesions appeared similar to malignant tumors in MRI. The variation of relaxation time depends upon the amount of protein in the cystic contents and the amount of glucose affects the relaxation time. We conclude that NMR-parameters are useful for the differential diagnosis of malignant tumors, cystic lesions and mycositic sinusitis by using the multiple variation analysis.

Inamura, Naoki; Hashimoto, Sho; Kawase, Tetsuaki; Takeyama, Minoru; Takasaka, Tomonori

1987-07-01

84

Dft Study on 4(5)-Imidazole-Carbaldehyde-N(5)-Phenylthiosemicarbazone (Imtph): Nmr Shielding Tensors, Thermodynamic Parameters, Nbo Analysis, Molecular Electrostatic Potential (Mep), Homo and Lumo Studies  

OpenAIRE

The density functional theory (DFT) calculations at the level of B3LYP/6-31G was carried out on the structure 4(5)-Imidazole-carbaldehyde-N(5)-phenylthiosemicarbazone (ImTPh) in gas phase using Gaussian 03. Dipole moment (Debye), energy of structure formation (HF; kcal/mol) and point group, NMR parameters such as isotropic shielding (?iso) and anisotropic shielding (?aniso), ?11, ?22 and ?33 obtained. Also thermodynamic properties and natural bond orbitals (NBO) were calculated. Besides,...

Masoome Sheikhi; Mohammad Mahmoodi Hashemi; Majid Monajjemi

2014-01-01

85

Determination of spin Hamiltonians from projected single reference configuration interaction calculations. I. Spin 1/2 systems.  

Science.gov (United States)

The most reliable wave-function based treatments of magnetic systems usually start from a complete active space self-consistent field calculation of the magnetic electrons in the magnetic orbitals, followed by extensive and expensive configuration interaction (CI) calculations. This second step, which introduces crucial spin polarization and dynamic correlation effects, is necessary to reach reliable values of the magnetic coupling constants. The computational cost of these approaches increases exponentially with the number of unpaired electrons. The single-determinantal unrestricted density functional Kohn-Sham calculations are computationally much simpler, and may provide reasonable estimates of these quantities, but their results are strongly dependent on the chosen exchange-correlation potential. The present work, which may be seen as an ab initio transcription of the unrestricted density functional theory technique, returns to the perturbative definition of the Heisenberg Hamiltonian as an effective Hamiltonian, and proposes a direct estimate of its diagonal energies through single reference CI calculations. The differences between these diagonal terms actually determine the entire Heisenberg Hamiltonian. The reference determinants must be vectors of the model space and the components on the other vectors of the model space are cancelled along the iterative process. The method is successfully tested on a series of bicentric and multicentric spin 12 systems. The projected single reference difference dedicated CI treatment is both accurate and of moderate cost. It opens the way to parameter-free calculations of large spin assemblies. PMID:20687632

Monari, A; Maynau, D; Malrieu, J-P

2010-07-28

86

Single-crystal and powder electron-nuclear double resonance of RbCl:O-2: A comparison between the spin Hamiltonian parameters obtained from both experiments  

Science.gov (United States)

In this work a single-crystal ENDOR study of RbCl:O-2 is presented. The angular variation of two sets of 85Rb and 87Rb ENDOR transitions is investigated. The corresponding superhyperfine (SHF) and nuclear-quadrupole coupling tensors are determined. These ENDOR results can be explained only by assuming a monovacancy model, i.e., O-2 replacing a single Cl- ion. The linewidth of the EPR signals is shown to be determined by the Rb SHF interaction. The corresponding powder ENDOR study of RbCl:O-2 is also presented. The powder ENDOR spectra could be simulated using the single-crystal data. Finally, from this simulation procedure a fitting program is derived to obtain information from powder ENDOR spectra of analogous systems.

van Doorslaer, S.; Callens, F.; Maes, F.; Boesman, E.

1995-05-01

87

Theoretical investigations of spin Hamilton parameters and Knight shifts for rhombic and tetragonal CuGeO{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

The spin Hamiltonian parameters (g factors and hyperfine structure constants) and the Knight shifts for Cu{sup 2+} in the spin-Pierels compound CuGeO{sub 3} of rhombic and tetragonal phases are theoretically investigated from the high order perturbation formulas of these parameters for a 3d{sup 9} 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., K{sub i}/(g{sub i}?g{sub s})=K{sub j}/(g{sub j}?g{sub s}) (with i, j=x, y and z; g{sub s}?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 Cu{sup 2+} sites. The studies in this work would be helpful to establish complete physical scheme for uniform investigations on EPR and NMR spectroscopic behaviours of Cu{sup 2+} (or other similar 3d{sup 9} ions) in compounds.

Kuang, Min-Quan, E-mail: mqkuang@yeah.net [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; Song, Bo-Tao [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2013-05-15

88

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

Science.gov (United States)

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.

Kuang, Min-Quan; Wu, Shao-Yi; Hu, Xian-Fen; Song, Bo-Tao

2013-05-01

89

Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules  

Science.gov (United States)

Using a recently proposed equation for NMR nuclear magnetic shielding for molecules with unpaired electrons [A. Soncini and W. Van den Heuvel, J. Chem. Phys. 138, 021103 (2013)], equations for the temperature (T) dependent isotropic shielding for multiplets with an effective spin S equal to 1/2, 1, 3/2, 2, and 5/2 in terms of electron paramagnetic resonance spin Hamiltonian parameters are derived and then expanded in powers of 1/T. One simplifying assumption used is that a matrix derived from the zero-field splitting (ZFS) tensor and the Zeeman coupling matrix (g-tensor) share the same principal axis system. The influence of the rhombic ZFS parameter E is only investigated for S = 1. Expressions for paramagnetic contact shielding (from the isotropic part of the hyperfine coupling matrix) and pseudo-contact or dipolar shielding (from the anisotropic part of the hyperfine coupling matrix) are considered separately. The leading order is always 1/T. A temperature dependence of the contact shielding as 1/T and of the dipolar shielding as 1/T2, which is sometimes assumed in the assignment of paramagnetic chemical shifts, is shown to arise only if S ? 1 and zero-field splitting is appreciable, and only if the Zeeman coupling matrix is nearly isotropic (?g = 0). In such situations, an assignment of contact versus dipolar shifts may be possible based only on linear and quadratic fits of measured variable-temperature chemical shifts versus 1/T. Numerical data are provided for nickelocene (S = 1). Even under the assumption of ?g = 0, a different leading order of contact and dipolar shifts in powers of 1/T is not obtained for S = 3/2. When ?g is not very small, dipolar and contact shifts both depend in leading order in 1/T in all cases, with sizable contributions in order 1/Tn with n = 2 and higher.

Martin, Bob; Autschbach, Jochen

2015-02-01

90

Initial clinical attempts of tissue characterisation in NMR-tomography by a quantitative assessment of proton density and the relaxation parameters T1, T2  

International Nuclear Information System (INIS)

The NMR parameters (proton density, relaxation times T1 and T2) have been assessed by Carr-Purcell-Meiboom-Gill (CPMG) spin echo sequences. A computer assisted analysis of the data of 21 patients with cerebral tumours allowed a classification of tumour tissue in different tumours. The use of quantitative procedures for tissue characterisation allows the differentiation of benign and malignant brain tissue by characteristic colour coding demonstrating morphological details like tumour, edema and necrosis as well as indicating the histological types of the tumours of the central nervous system. (orig.)

91

Dft Study on 4(5-Imidazole-Carbaldehyde-N(5-Phenylthiosemicarbazone (Imtph: Nmr Shielding Tensors, Thermodynamic Parameters, Nbo Analysis, Molecular Electrostatic Potential (Mep, Homo and Lumo Studies  

Directory of Open Access Journals (Sweden)

Full Text Available The density functional theory (DFT calculations at the level of B3LYP/6-31G was carried out on the structure 4(5-Imidazole-carbaldehyde-N(5-phenylthiosemicarbazone (ImTPh in gas phase using Gaussian 03. Dipole moment (Debye, energy of structure formation (HF; kcal/mol and point group, NMR parameters such as isotropic shielding (?iso and anisotropic shielding (?aniso, ?11, ?22 and ?33 obtained. Also thermodynamic properties and natural bond orbitals (NBO were calculated. Besides, the frontier molecular orbital (FMO analysis and the molecular electrostatic potential (MEP of the compound were investigated by theoretical calculations.

Masoome Sheikhi

2014-03-01

92

Study of correlations in molecular motion by multiple quantum NMR  

International Nuclear Information System (INIS)

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 (CH3 and CD3) 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

93

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

94

Thallium-205 NMR determination of the thermodynamic parameters for the binding of monovalent and divalent cations to gramicidin A and C incorporated into model phospholipid membranes: An equilibrium study  

International Nuclear Information System (INIS)

Thermodynamic parameters have been determined for the binding of monovalent and divalent cations to gramicidin A and C incorporated in lyso-?-phosphatidylcholine dispersions. The thermodynamic analyses used equilibrium constants derived from the analysis of Tl-205 NMR chemical shifts using a one-site binding model of the gramicidin channel. Initial experiments determined the thermodynamic parameters of the Tl+ ion binding to gramicidin A. Next, the competitive binding-Tl-205 NMR technique was used to obtain the thermodynamic parameters for the binding of Li+, Na+, K+, Rb+, Cs+, NH4+ and Ag+ cations to gramicidin A. A similar experiment for the binding of the Li+, Na+, K+ and Rb+ cations to gramicidin C was performed. Similar experiments determined the thermodynamic parameter for the Cd++, Mg++, Ca++, Sr++ and Ba++ cations. Thermodynamic parameters have also been determined for the binding of the Tl+ ion to gramicidin A incorporated into dimyristoylphosphatidylcholine vesicles using Tl-205 NMR spectroscopy

95

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

96

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

97

Molecular modeling and experimental studies on structure and NMR parameters of 9-benzyl-3,6-diiodo-9H-carbazole  

DEFF Research Database (Denmark)

A combined experimental and theoretical study has been performed on 9-benzyl-3,6-diiodo-9H-carbazole. Experimental X-ray (100.0 K) and room-temperature 13C NMR studies were supported by advanced density functional theory (DFT) calculations. The non relativistic structure optimization was performed and the 13C nuclear magnetic shieldings were predicted at the relativistic level of theory using the Zeroth Order Regular Approximation (ZORA). The changes in the benzene and pyrrole rings compared to the unsubstituted carbazole or the parent molecules were discussed in terms of aromaticity changes using the harmonic oscillator model of aromaticity (HOMA) and the nucleus independent chemical shift (NICS) indexes. Theoretical relativistic calculations of chemical shifts of carbons C3 and C6, directly bonded to iodine atoms, produced a reasonable agreement with experiment (initial deviation from experiment of 41.57 ppm dropped to 5.6 ppm). A good linear correlation between experimental and theoretically predicted structural and NMR parameters was observed.

Radula-Janik, Klaudia; Kupka, Teobald

2015-01-01

98

Order-parameter collective modes in 3He-A and their effect on nuclear magnetic resonance (NMR) and ultrasonic attenuation  

International Nuclear Information System (INIS)

A generalization of our previous microscopic theory is used to derive the spin and density correlation functions for the Anderson--Brinkman--Morel (ABM) state. The coupling of the 18 fluctuation components of the order parameter due to the nuclear dipole interaction is taken into accountrigorously. The results are valid for arbitary temperature, frequency, wave number (with q parallel to the anisotropy axis), and magnetic field. Damping by pari-breaking processes is calculated explicity; however, quasiparticle collisions are neglected. The frequencies of the clapping modes that couple to spin, and the frequencies of the flapping modes that couple to density, are found to split in a magnetic field. Near T/sub c/ the linewidth of the clapping mode and, at low T, the linewidth of the normal-flapping mode become small while the linewidth of the super-flapping mode is broad at all temperatures. The linewidth of the transverse NMR and the ultrasound attenuation coefficient, considered as functions of temperature, exhibit pronounced peaks at low temperatures. These arise from a coupling, induced by the dipole interaction, between spin or density fluctuations and the normal-flapping mode. Our results for the linewidth and line shift of the longitudinal NMR at low temperatures due to orbital effects are in agreement with results of Combescot

99

On the influence of vibrational modes and intramolecular isomerization processes on the NMR parameters of bullvalene: A Feynman path integral - ab initio investigation  

International Nuclear Information System (INIS)

The absolute isotropic shieldings and chemical shifts at the 13C and 1H nuclei of bullvalene have been theoretically studied under the conditions of thermal equilibrium. For temperatures T ? 400 K the present Monte Carlo simulations predict a bare vibrational nuclear dynamics. T values > 400 K allow the superposition of vibrational modes and an intramolecular isomerization, i.e. the so-called Cope rearrangement. This result can be correlated with the 'slow' and 'fast' isomerization regime of bullvalene. In the slow regime nuclear magnetic resonance (NMR) measures four different 13C and 1H signals, a splitting that is in line with the molecular C3v symmetry at the minimum of the potential energy surface (PES). In the fast regime only a single signal for the 13C and 1H nuclei is measured by NMR indicating that all bullvalene carbons and protons are equivalent in the NMR time-scale. To derive the NMR parameters of bullvalene we have combined the Feynman path integral quantum Monte Carlo (PIMC) formalism with a tight-binding (TB) Hamiltonian and the Gauge including atomic orbital (GIAO) approach in an ab initio Hartree-Fock formulation. The TB model has been used to calculate the ground state PES, the free energy barrier of the Cope rearrangement, the statistical weight of the nuclear configurations in thermal equilibrium as well as the radial distribution functions of the nuclei. The vibrationn functions of the nuclei. The vibrational modes in a highly anharmonic potential cause an elongation of all bond lengths in thermal equilibrium. This leads to a topology dependent deshielding of the bullvalene nuclei. The T dependence of the deshielding is characteristic for dominating zero-point fluctuations for all temperatures studied. The GIAO based chemical shifts at the 13C and 1H nuclei are compared with experiment. The PIMC - ab initio approach leads to theoretical results of good quality. The T gradient of the 13C and 1H chemical shifts can be reproduced qualitatively by the present PIMC - ab initio approach

100

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

CERN Document Server

We introduce a new method, based on alternating optimization, for compact representation of spin Hamiltonian, and solution of linear systems in the tensor train format. We demonstrate its utility by simulating, without significant approximations, a 15N NMR spectrum of ubiquitin --- 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 system size. We compare the proposed method to the Spinach package that uses heuristic restricted state space (RSS) techniques to achieve polynomial complexity scaling. When the spin system topology is close to a linear chain (e.g. for backbone of a protein), the tensor train representation of a Hamiltonian is more compact and can be computed faster than the sparse representation using the RSS.

Savostyanov, D V; Werner, J M; Kuprov, Ilya

2014-01-01

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

Smoothed acyl chain orientational order parameter profiles in dimyristoylphosphatidylcholine-distearoylphosphatidylcholine mixtures: a 2H-NMR study.  

OpenAIRE

The accommodation of chain-length mismatch in liquid crystal phase bilayers was examined by using deuterium nuclear magnetic resonance to obtain smoothed orientational order parameter profiles for acyl chains of both components in binary lipid mixture bilayers. Mixtures of dimyristoylphosphatidylcholine (DMPC) and distearoylphosphatidylcholine (DSPC) covering a range of compositions were prepared with either DSPC acyl chains or DMPC acyl chains perdeuterated. Orientational order parameters in...

Lu, D.; Vavasour, I.; Morrow, M. R.

1995-01-01

103

Assignment of the (13)C NMR spectrum by correlation to dipolar coupled proton-pairs and estimation of order parameters of a thiophene based liquid crystal.  

Science.gov (United States)

Materials with widely varying molecular topologies and exhibiting liquid crystalline properties have attracted considerable attention in recent years. (13)C NMR spectroscopy is a convenient method for studying such novel systems. In this approach the assignment of the spectrum is the first step which is a non-trivial problem. Towards this end, we propose here a method that enables the carbon skeleton of the different sub-units of the molecule to be traced unambiguously. The proposed method uses a heteronuclear correlation experiment to detect pairs of nearby carbons with attached protons in the liquid crystalline core through correlation of the carbon chemical shifts to the double-quantum coherences of protons generated through the dipolar coupling between them. Supplemented by experiments that identify non-protonated carbons, the method leads to a complete assignment of the spectrum. We initially apply this method for assigning the (13)C spectrum of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl oriented in the magnetic field. We then utilize the method to assign the aromatic carbon signals of a thiophene based liquid crystal thereby enabling the local order-parameters of the molecule to be estimated and the mutual orientation of the different sub-units to be obtained. PMID:25429708

Reddy, Y Jayasubba; Ramanathan, K V

2015-01-14

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

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.

106

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

107

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.

108

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

109

NMR analysis of proteins structure  

International Nuclear Information System (INIS)

The nuclear magnetic resonance (NMR) analysis of proteins aims at determining the 3-D folding of the polypeptide chain. Because of the high number of nuclei observed in the samples, the NMR protein spectra are extremely complex. The different steps of the structure determination are: the preparation of the samples, the acquisition and processing of the NMR signal, the analysis and attribution of spectra, and the calculation of the coordinates of the atoms using the NMR spectra parameters. Content: 1 - proteins and peptides (composition and structure, secondary, tertiary and quaternary structure); 2 - NMR of proteins in solution (characteristics, structures determination, homonuclear experiments, heteronuclear experiments, proteins with a size higher than 20 kDa, intermolecular interactions, stability factors, internal molecular dynamics); 3 - structures calculation (calculation framework, distance geometry, molecular dynamics and simulated annealing, quality of the structure obtained). (J.S.)

110

Characterizing ions in solution by NMR methods  

OpenAIRE

NMR experiments performed under the effect of electric fields, either continuous or pulsed, can provide quantitative parameters related to ion association and ion transport in solution.  Electrophoretic NMR (eNMR) is based on a diffusion pulse-sequence with electric fields applied in the form of pulses. Magnetic field gradients enable the measurement of the electrophoretic mobility of charged species, a parameter that can be related to ionic association. The effective charge of the tetrameth...

Giesecke, Marianne

2014-01-01

111

27Al NMR study on CeRu2Al10 single crystal. 1. Determination of the NQR parameters for five non-equivalent Al sites in the paramagnetic region  

International Nuclear Information System (INIS)

We performed 27Al (I=5/2) NMR measurements in CeRu2Al10 single crystal by rotating the crystal axes against applied field in the paramagnetic region. The angle dependence of the resonance peaks for each of the five nonequivalent Al site allows us to determine the NQR parameters (?Q and ?) as well as the direction of the maximal principal axis of the electric field gradient (EFG), including the Al(2) site not detected by the NQR experiment due to the smaller ?Q than the lower limit of the measurement, with the aid of the results of zero-field 27Al NQR measurement and band calculation. The NQR parameters are in agreement with those obtained by 27Al NQR measurements. Both NQR parameters and the direction of the maximal principal axis of the EFG show excellent agreement with those obtained by the band calculation except for those in the Al(2) site. (author)

112

Mechanical analogues of spin Hamiltonians and dynamics  

Science.gov (United States)

Bloch et al. mapped the precession of the spin-half in a magnetic field of variable magnitude and direction to the rotations of a rigid sphere rolling on a curved surface utilizing SU(2)-SO(3) isomorphism. This formalism is extended to study the behaviour of spin-orbit interactions and the mechanical analogy for Rashba-Dresselhauss spin-orbit interaction in two dimensions is presented by making its spin states isomorphic to the rotations of a rigid sphere rolling on a ring. The change in phase of spin is represented by the angle of rotation of sphere after a complete revolution. In order to develop the mechanical analogy for the spin filter, we find that perfect spin filtration of down spin makes the sphere to rotate at some unique angles and the perfect spin filtration of up spin causes the rotations with certain discrete frequencies.

Kaur, Harjeet; Jain, Sudhir R.; Malik, Sham S.

2014-01-01

113

An Introduction to Biological NMR Spectroscopy*  

OpenAIRE

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 ...

Marion, Dominique

2013-01-01

114

Imaging quantum confinement with optical and POWER (perturbations observed with enhanced resolution) NMR.  

Science.gov (United States)

The nanoscale distributions of electron density and electric fields in GaAs semiconductor devices are displayed with NMR experiments. The spectra are sensitive to the changes to the nuclear-spin Hamiltonian that are induced by perturbations delivered in synchrony with a line-narrowing pulse sequence. This POWER (perturbations observed with enhanced resolution) method enhanced resolution up to 10(3)-fold, revealing the distribution of perturbations over nuclear sites. Combining this method with optical NMR, we imaged quantum-confined electron density in an individual AlGaAs/GaAs heterojunction via hyperfine shifts. Fits to the coherent evolution and relaxation of nuclei within a hydrogenic state established one-to-one correspondence of radial position to frequency. Further experiments displayed the distribution of photo-induced electric field within the same states via a quadrupolar Stark effect. These unprecedented high-resolution distributions discriminate between competing models for the luminescence and support an excitonic state, perturbed by the interface, as the dominant source of the magnetically modulated luminescence. PMID:19104070

Kempf, James G; Miller, Michael A; Weitekamp, Daniel P

2008-12-23

115

DFT study of NH{sub 3} adsorption on the (5,0), (8,0), (5,5) and (6,6) single-walled carbon nanotubes. Calculated binding energies, NMR and NQR parameters  

Energy Technology Data Exchange (ETDEWEB)

Behavior of a single NH{sub 3} molecule adsorbed on external surface of H-capped (5,5), (6,6), (5,0), and (8,0) single-walled carbon nanotubes (SWCNTs) is studied via DFT calculations. Binding energies clearly exhibit adsorption dependence on tube diameter. {sup 13}C, {sup 15}N and {sup 1}H chemical shielding tensors are calculated at the B3LYP level using GIAO method. NMR calculations reveal that {sup 13}C chemical shielding of (8,0) is more sensitive to NH{sub 3} adsorption compared to (5,5), (6,6) and (5,0) tubes. {sup 15}N and {sup 1}H chemical shielding correlate noticeably with diameter of the nanotubes. {sup 14}N and {sup 2}H nuclear quadrupole coupling constants, C{sub Q}, and asymmetry parameter, eta, reveal the remarkable effect of NH{sub 3} adsorption on electronic structure of the SWCNTs.

Shirvani, Bahram B.; Beheshtian, Javad; Esrafili, Mehdi D. [Department of Chemistry, Tarbiat Modares University, P.O. Box: 14115-175, Tehran (Iran, Islamic Republic of); Hadipour, Nasser L., E-mail: hadipour@modares.ac.i [Department of Chemistry, Tarbiat Modares University, P.O. Box: 14115-175, Tehran (Iran, Islamic Republic of)

2010-03-15

116

DFT study of NH3 adsorption on the (5,0), (8,0), (5,5) and (6,6) single-walled carbon nanotubes. Calculated binding energies, NMR and NQR parameters  

International Nuclear Information System (INIS)

Behavior of a single NH3 molecule adsorbed on external surface of H-capped (5,5), (6,6), (5,0), and (8,0) single-walled carbon nanotubes (SWCNTs) is studied via DFT calculations. Binding energies clearly exhibit adsorption dependence on tube diameter. 13C, 15N and 1H chemical shielding tensors are calculated at the B3LYP level using GIAO method. NMR calculations reveal that 13C chemical shielding of (8,0) is more sensitive to NH3 adsorption compared to (5,5), (6,6) and (5,0) tubes. 15N and 1H chemical shielding correlate noticeably with diameter of the nanotubes. 14N and 2H nuclear quadrupole coupling constants, CQ, and asymmetry parameter, ?, reveal the remarkable effect of NH3 adsorption on electronic structure of the SWCNTs.

117

Optical NMR  

International Nuclear Information System (INIS)

Full text: Coherent pulse techniques at radio frequencies have proved invaluable for the study of structure and interactions in solid state systems. Equivalent techniques have never been successfully applied in the visible region of the spectrum. This is because even with the narrowest optical lines the very intense variable delay and duration optical pulses are not available from any laser source. In the present work a different approach has been taken and this is to manipulate the optical line to produce a sharp feature and with the sharp feature it is possible to make the required measurements with modest powers available from CW lasers. For the work a specially stabilized laser has been developed and has been used to demonstrate the first pulsed NMR measurements at optical frequencies

118

Vibrational spectra, NBO analysis, first order hyperpolarizabilities, thermodynamic functions and NMR chemical shielding anisotropy (CSA) parameters of 5-nitro-2-furoic acid by ab initio HF and DFT calculations  

Science.gov (United States)

In this work, FT-IR and FT-Raman spectra are recorded on the solid phase of 5-nitro-2-furoic acid (abbreviated as NFA) in the regions 4000-400 cm-1 and 3500-100 cm-1 respectively. The geometrical parameters, vibrational assignments, HOMO-LUMO energies and NBO calculations are obtained for the monomer and dimer of NFA from HF and DFT (B3LYP) with 6-311++G (d, p) basis set calculations. Second order perturbation energies and electron density (ED) transfer from filled lone pairs of Lewis base to unfilled Lewis acid sites of NFA are discussed on the basis of NBO analysis. Intermolecular hydrogen bonds exist through COOH groups; give the evidence for the formation of dimer entities in the title molecule. The theoretically calculated harmonic frequencies are scaled by common scale factor. The observed and the calculated frequencies are found to be in good agreement. The thermodynamic functions were obtained for the range of temperature 100-1000 K. The polarizability, first hyperpolarizability, anisotropy polarizability invariant has been computed using quantum chemical calculations. The chemical parameters were calculated from the HOMO and LUMO values. The NMR chemical shielding anisotropy (CSA) parameters were also computed for the title molecule.

Balachandran, V.; Rajeswari, S.; Lalitha, S.

2013-09-01

119

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

120

Annual reports on NMR spectroscopy  

CERN Document Server

The protean nature of the applications of NMR is regularly reflected in Annual Reports on NMR Spectroscopy. Volume 24 is no exception, and it is an ineluctable fact that all areas of science appear to benefit upon submission to the blandishments of NMR. The examples provided here encompass solid state NMR, solid state NMR imaging, NMR studies of interfaces, NMR investigations of cells and organisms, 199 Mercury NMR, and some applications of NMR to the area of coal science.

Webb, Graham A

1992-01-01

121

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.

122

Spectroscopic (FT-IR, FT-Raman and UV-Visible) investigations, NMR chemical shielding anisotropy (CSA) parameters of 2,6-Diamino-4-chloropyrimidine for dye sensitized solar cells using density functional theory  

Science.gov (United States)

The molecular structure, geometry optimization, vibrational frequencies of organic dye sensitizer 2,6-Diamino-4-chloropyrimidine (DACP) were studied based on Hartree-Fock (HF) and density functional theory (DFT) using B3LYP methods with 6-311++G(d,p) basis set. Ultraviolet-Visible (UV-Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the UV-Visible regions were assigned based on TD-DFT calculation. The absorption bands are assigned to transitions. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer DACP is due to an electron injection process from excited dye to the semiconductor's conduction band. The observed and the calculated frequencies are found to be in good agreement. The energies of the frontier molecular orbitals (FMOS) have also been determined. The chemical shielding anisotropic (CSA) parameters are calculated from the NMR analysis, Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis.

Gladis Anitha, E.; Joseph Vedhagiri, S.; Parimala, K.

2015-02-01

123

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

2013-01-01

124

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

125

11B NMR spectroscopy  

International Nuclear Information System (INIS)

This paper covers developments in 11B NMR spectroscopy subsequent to a previous review in this series. In addition, it serves to complement the preceding chapter. As in previous years, a major use of 11B has been archival - that is, use for routine characterization of new compounds - although considerable efforts to elucidate correlations between structure and NMR parameters continue. However, some significant trends may be noted. First, availability of high-field spectrometers with multinuclear capability as well as software for sophisticated data manipulation is increasingly common, and, with these instruments, lack of chemical-shift dispersion in the face of relatively large linewidths presents much less of a problem than previously when complex polyboron compounds are to be characterized. Coupled with this, potent separation techniques, exemplified by thin-layer, high-pressure and ion-exchange chromatography, are able to unravel complex mixtures and make pure compounds available for study. Use of X-ray crystallographic facilities with which to structurally characterize compounds whose spectra are reported is today almost routine. Less routine is an appreciation of the fact that one crystal teased from a reaction mixture is not necessarily representative of the system from which it was extracted; use of X-ray powder-diffraction analysis to test this hypothesis is to be encouraged. Thus inability to separate mixtures, to secure high-resolution arate mixtures, to secure high-resolution spectra and structural data are of decreasing importance in boron chemistry, leaving, perhaps, as the rate-limiting factors, creativity and the propensity to select for detailed study systems that offer new, significant and fundamental insights into the chemistry of boron and of the elements to which it bonds

126

NMR and NQR parameters of ethanol crystal  

Science.gov (United States)

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.

Milinkovi?, M.; Bilalbegovi?, G.

2012-04-01

127

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

128

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

129

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)

130

Teaching NMR Using Online Textbooks  

OpenAIRE

Nuclear magnetic resonance (NMR) spectroscopy has almost become an essential analytical tool for the chemist. High-resolution one- and multi-dimensional NMR, timedomain NMR, and NMR microscopy are but a few of the NMR techniques at a chemist's disposal to determine chemical structure and dynamics. Consequently, even small chemistry departments are finding it necessary to provide students with NMR training and experience in at least some of these techniques. The hands-on experience is readily ...

Hornak, Joseph P.

1999-01-01

131

Optimization and practical implementation of ultrafast 2D NMR experiments  

Energy Technology Data Exchange (ETDEWEB)

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. (author)

Queiroz Junior, Luiz H. K., E-mail: professorkeng@gmail.com [Universidade Federal de Sao Carlos (UFSC), SP (Brazil). Departamento de Quimica; Universidade Federal de Goias (UFGO), Goiania, GO (Brazil). Inst. de Quimica; Ferreira, Antonio G. [Universidade Federal de Sao Carlos (UFSC), SP (Brazil). Departamento de Quimica; Giraudeau, Patrick [Universite de Nantes (France). CNRS, Chimie et Interdisciplinarite: Synthese, Analyse, Modelisation

2013-09-01

132

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

133

?-NMR and ?-NQR spectrometer  

International Nuclear Information System (INIS)

The ?-NMR and ?-NQR spectrometer has been established for the first time in China. The lifetime, magnetic moment and polarization of 12B were measured with it. The experimental results show that reliability of this newly established ?-NMR and ?-NQR spectrometer

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

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.

136

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

137

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.

138

Rapid prediction of multi-dimensional NMR data sets  

Energy Technology Data Exchange (ETDEWEB)

We present a computational environment for Fast Analysis of multidimensional NMR DAta Sets (FANDAS) that allows assembling multidimensional data sets from a variety of input parameters and facilitates comparing and modifying such 'in silico' data sets during the various stages of the NMR data analysis. The input parameters can vary from (partial) NMR assignments directly obtained from experiments to values retrieved from in silico prediction programs. The resulting predicted data sets enable a rapid evaluation of sample labeling in light of spectral resolution and structural content, using standard NMR software such as Sparky. In addition, direct comparison to experimental data sets can be used to validate NMR assignments, distinguish different molecular components, refine structural models or other parameters derived from NMR data. The method is demonstrated in the context of solid-state NMR data obtained for the cyclic nucleotide binding domain of a bacterial cyclic nucleotide-gated channel and on membrane-embedded sensory rhodopsin II. FANDAS is freely available as web portal under WeNMR (http://www.wenmr.eu/services/FANDAShttp://www.wenmr.eu/services/FANDAS).

Gradmann, Sabine; Ader, Christian [Utrecht University, Faculty of Science, Bijvoet Center for Biomolecular Research (Netherlands); Heinrich, Ines [Max Planck Institute for Molecular Physiology, Department of Physical Biochemistry (Germany); Nand, Deepak [Utrecht University, Faculty of Science, Bijvoet Center for Biomolecular Research (Netherlands); Dittmann, Marc [Max Planck Institute for Molecular Physiology, Department of Physical Biochemistry (Germany); Cukkemane, Abhishek; Dijk, Marc van; Bonvin, Alexandre M. J. J. [Utrecht University, Faculty of Science, Bijvoet Center for Biomolecular Research (Netherlands); Engelhard, Martin [Max Planck Institute for Molecular Physiology, Department of Physical Biochemistry (Germany); Baldus, Marc, E-mail: m.baldus@uu.nl [Utrecht University, Faculty of Science, Bijvoet Center for Biomolecular Research (Netherlands)

2012-12-15

139

Annual reports on NMR spectroscopy  

International Nuclear Information System (INIS)

Volume 10 of Annual Reports on NMR Spectroscopy consists of accounts covering three main areas of molecular science: NMR of living systems is covered for the first time in this series; various aspects of Boron NMR are dealt with in two, largely complementary chapters; the third area reported on is that of NMR studies of alkali anions in nonaqueous solvents

140

Silver and Gold NMR  

OpenAIRE

Silver and gold, together with copper, form the transition metal group IB elements in the periodic table and possess very different nuclear magnetic resonance (NMR) spectroscopic properties. While there is only one gold isotope (197Au), which has a spin of 3/2 and therefore a quadrupole moment, silver occurs in two isotopic forms (109Ag and 109Au), both of which have a spin 1/2 and similar NMR spectroscopic properties. The unfavorable properties of g...

Zangger, Klaus; Armitage, Lan M.

1999-01-01

141

Benford distributions in NMR  

OpenAIRE

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-d...

Bhole, Gaurav; Shukla, Abhishek; Mahesh, T. S.

2014-01-01

142

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 ths, and associated avascular necrosis of the hips

143

NMR studies of cation transport across membranes  

International Nuclear Information System (INIS)

23Na NMR Studies of cation transport across membranes were conducted both on model and biological membranes. Two ionophores, the carrier monensin and the channel-former gramicidin, were chosen to induce cation transport in large unilamellar phosphatidylcholine vesicles. The distinction between the NMR signals arising from the two sides of the membrane was achieved by the addition of an anionic paramagnetic shift reagent to the outer solution. The kinetics of the cation transport across the membrane was observed simultaneously monitoring the changes in the 23Na NMR signals of both compartments. Two mathematical models were developed for the estimation of the transport parameters of the monensin- and gramicidin-induced cation transport. The models were able to fit the experimental data very well. A new method for the estimation of the volume trapped inside the vesicles was developed. The method uses the relative areas of the intra- and extravesicular NMR signals arising from a suspension of vesicles bathed in the same medium they contain, as a measure for the relative volumes of these compartments. Sodium transport across biological membranes was studied by 23 NMR, using suspensions of cultured nerve cells. The sodium influx through voltage-gated channels was studied using the channel modifier batrachotoxin in combination with scorpion toxin

144

Teaching NMR Using Online Textbooks  

Directory of Open Access Journals (Sweden)

Full Text Available Nuclear magnetic resonance (NMR spectroscopy has almost become an essential analytical tool for the chemist. High-resolution one- and multi-dimensional NMR, timedomain NMR, and NMR microscopy are but a few of the NMR techniques at a chemist's disposal to determine chemical structure and dynamics. Consequently, even small chemistry departments are finding it necessary to provide students with NMR training and experience in at least some of these techniques. The hands-on experience is readily provided with access to state-of-the-art commercial spectrometers. Instruction in the principles of NMR is more difficult to achieve as most instructors try to teach NMR using single organic or analytical chemistry book chapters with static figures. This paper describes an online textbook on NMR spectroscopy called The Basics of NMR (http://www.cis.rit.edu/htbooks/nmr/ suitable for use in teaching the principles of NMR spectroscopy. The book utilizes hypertext and animations to present the principles of NMR spectroscopy. The book can be used as a textbook associated with a lecture or as a stand-alone teaching tool. Conference participants are encouraged to review the textbook and evaluate its suitability for us in teaching NMR spectroscopy to undergraduate chemistry majors.

Joseph P. Hornak

1999-12-01

145

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

146

Annual reports on NMR spectroscopy  

CERN Document Server

This collection of reports demonstrate the extensive purview of NMR and its applications. The pellucid presentations provided include accounts on application of NMR spectroscopy to sciences and technologies of glassand ceramics; high-resolution solid-state NMR studies on ceramics; NMR studies of zeolite; NMR studies of higher-order structures of solid polymers; and organic thin films. Taken together with reviews in other volumes of this series, the present accountsably demonstrate that NMR is facile princeps when it comes to problem solving in most areas of science, including the medical sciences.

Webb, Graham A

1994-01-01

147

NMR for medical applications  

International Nuclear Information System (INIS)

The new NMR imaging technique very rapidly met with great approval in the medical field, and the growing variety and frequency of applications meanwhile has led to aspects of safety of patients and personnel being given more attention than hitherto. The problems to be studied for this purpose are closely connected with the biological and biochemical effects of strong magnetic fields. The information presented in the document refers to results obtained by animal experiments for the study of magnetic field-induced biological effects. The contributions are original lectures presented to a conference organised by the German Society for Medical Physics, at Frankfurt/Main, on April 19, 1985, under the subject theme 'Topics on physical principles, technical aspects and biological effects of NMR for medical applications'. The lectures explain both fundamentals of NMR imaging and latest research results; the information is intended for engineers and physicians alike. (DG)

148

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

149

Natural abundance 17O NMR study of 2- and 4-substituted benzoyl chlorides  

Science.gov (United States)

Natural abundance 17O NMR chemical shift data for 17 ortho and para benzoyl chlorides recorded in acetonitrile at 75°C are reported. 17O NMR data for the para substituted benzoyl chlorides are correlated with 17O NMR data for similarly substituted acetophenones and methyl benzoates. The 17O NMR signals for ortho isomers are downfield ( ca 30 ppm) from their para isomers; the downfield shifts are consistent with torsion angle change. The 17O NMR data for the para isomers gave good correlations with ? + constants and with dual substituent parameters (DSP).

Boykin, David W.

150

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

151

International symposium on NMR spectroscopy  

International Nuclear Information System (INIS)

The publication consists of 32 papers and presentations from the field of NMR spectroscopy applications submitted to the International Symposium on NMR Spectroscopy held at Smolenice between 29 Sep and 3 Oct, 1980. (B.S.)

152

Prediction of peak overlap in NMR spectra  

International Nuclear Information System (INIS)

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 ction 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.

153

THz Dynamic Nuclear Polarization NMR  

OpenAIRE

Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140- 600...

Nanni, Emilio A.; Barnes, Alexander B.; Griffin, Robert G.; Temkin, Richard J.

2011-01-01

154

Annual reports on NMR spectroscopy  

International Nuclear Information System (INIS)

This volume consists of one review on nitrogen NMR. The account relates to the literature published between 1981 and 1984 and serves to both update and expand upon those presented in earlier volumes of this series, the most recent of which was Volume 11B. CONTENTS: Nuclear Magnetic Resonance of Cyclophosphazene; Sulphur-33 NMR Spectroscopy; and Dynamic NMR Spectrocopy in Inorganic and Organometallic Chemistry

155

NMR Studies of Purines.  

Czech Academy of Sciences Publication Activity Database

Vol. 82. Oxford : Academic Press, 2014 - (Webb, G.), s. 59-113 ISBN 978-0-12-800184-4 R&D Projects: GA ?R GA13-24880S Institutional support: RVO:61388963 Keywords : NMR spectroscopy * purines * DFT calculations * chemical shifts Subject RIV: CC - Organic Chemistry

Dra?ínský, Martin; Pohl, Radek

156

NMR crystallography of polylactide.  

Czech Academy of Sciences Publication Activity Database

Prague : Institute of Macromolecular Chemistry AS CR, v. v. i, 2013. s. 60. ISBN 978-80-85009-77-4. [European Symposium on Polymer Spectroscopy /19./ - ESOPS19. Prague Meeting on Macromolecules /77./. 07.07.2013-11.07.2013, Prague] Institutional support: RVO:61389013 Keywords : NMR crystallography * polylactide Subject RIV: CD - Macromolecular Chemistry

Czernek, Ji?í

157

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

158

Quantum spin Hamiltonians for the SU(2)k WZW model  

International Nuclear Information System (INIS)

We propose to use null vectors in conformal field theories to derive model Hamiltonians of quantum spin chains and the corresponding ground state wavefunction(s). The approach is quite general, and we illustrate it by constructing a family of Hamiltonians whose ground states are the chiral correlators of the SU(2)k WZW model for integer values of the level k. The simplest example corresponds to k = 1 and is essentially a nonuniform generalization of the Haldane–Shastry model with long-range exchange couplings. At level k = 2, we analyse the model for N spin 1 fields. We find that the Renyi entropy and the two-point spin correlator show, respectively, logarithmic growth and algebraic decay. Furthermore, we use the null vectors to derive a set of algebraic, linear equations relating spin correlators within each model. At level k = 1, these equations allow us to compute the two-point spin correlators analytically for the finite chain uniform Haldane–Shastry model and to obtain numerical results for the nonuniform case and for higher-point spin correlators in a very simple way and without resorting to Monte Carlo techniques

159

On domain wall boundary conditions for the XXZ spin Hamiltonian  

DEFF Research Database (Denmark)

In this note, we derive the spectrum of the infinite quantum XXZ spin chain with domain wall boundary conditions. The eigenstates are constructed as limits of Bethe states for the finite XXZ spin chain with quantum sl(2) invariant boundary conditions.

Orlando, Domenico; Reffert, Susanne

2009-01-01

160

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 samples (Haber-Pohlmeier et al. 2010). Third, relaxometric information forms the basis of understanding magnetic resonance imaging (MRI) results. The general difficulty of imaging in soils are the inherent fast T2 relaxation times due to i) the small pore sizes, ii) presence of paramagnetic ions in the solid matrix, and iii) diffusion in internal gradients. The last point is important, since echo times can not set shorter than about 1ms for imaging purposes. The way out is either the usage of low fields for imaging in soils or special ultra-short pulse sequences, which do not create echoes. In this presentation we will give examples on conventional imaging of macropore fluxes in soil cores (Haber-Pohlmeier et al. 2010), and the combination with relaxometric imaging, as well as the advantages and drawbacks of 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

161

45scandium NMR investigations in aqueous solutions  

International Nuclear Information System (INIS)

45Sc NMR chemical shifts, linewidths, and longitudinal relaxation rates have been measured in aqueous solutions on scandium chloride and sulphate as a function of the appropriate acid. A common typical behaviour of these parameters without sudden changes has been observed. Also signals in the basic range have been obtained. H2O-D2O solvent isotope effects on Larmor frequency and relaxation rates are presented. (orig.)

162

Annual reports on NMR spectroscopy  

CERN Document Server

Commencing with Volume 21, the aim of this series is to produce a larger number of, relatively short but, timely and authoritative reviews. These will concentrate, in particular, on areas of NMR where recent progress, and developments, are of special interest and will reflect the many NMR developments occurring in the primary scientific literature. The present volume demonstrates the advances which can be made by the application of NMR techniques in many diverse areas of chemistry. Of particular significance is the account of Graphics-Aided NMR which will become an inprotant development in the use of NMR spectroscopy.

Webb, Graham A

1989-01-01

163

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.)

164

Benchmarking NMR experiments: A relational database of protein pulse sequences  

Science.gov (United States)

Systematic benchmarking of multi-dimensional protein NMR experiments is a critical prerequisite for optimal allocation of NMR resources for structural analysis of challenging proteins, e.g. large proteins with limited solubility or proteins prone to aggregation. We propose a set of benchmarking parameters for essential protein NMR experiments organized into a lightweight (single XML file) relational database (RDB), which includes all the necessary auxiliaries (waveforms, decoupling sequences, calibration tables, setup algorithms and an RDB management system). The database is interfaced to the Spinach library ( http://spindynamics.org), which enables accurate simulation and benchmarking of NMR experiments on large spin systems. A key feature is the ability to use a single user-specified spin system to simulate the majority of deposited solution state NMR experiments, thus providing the (hitherto unavailable) unified framework for pulse sequence evaluation. This development enables predicting relative sensitivity of deposited implementations of NMR experiments, thus providing a basis for comparison, optimization and, eventually, automation of NMR analysis. The benchmarking is demonstrated with two proteins, of 170 amino acids I domain of ?X?2 Integrin and 440 amino acids NS3 helicase.

Senthamarai, Russell R. P.; Kuprov, Ilya; Pervushin, Konstantin

2010-03-01

165

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.)

166

Bayesian reconstruction of projection reconstruction NMR (PR-NMR).  

Science.gov (United States)

Projection reconstruction nuclear magnetic resonance (PR-NMR) is a technique for generating multidimensional NMR spectra. A small number of projections from lower-dimensional NMR spectra are used to reconstruct the multidimensional NMR spectra. In our previous work, it was shown that multidimensional NMR spectra are efficiently reconstructed using peak-by-peak based reversible jump Markov chain Monte Carlo (RJMCMC) algorithm. We propose an extended and generalized RJMCMC algorithm replacing a simple linear model with a linear mixed model to reconstruct close NMR spectra into true spectra. This statistical method generates samples in a Bayesian scheme. Our proposed algorithm is tested on a set of six projections derived from the three-dimensional 700 MHz HNCO spectrum of a protein HasA. PMID:25218584

Yoon, Ji Won

2014-11-01

167

Jointly deriving NMR surface relaxivity and pore size distributions by NMR relaxation experiments on partially desaturated rocks  

Science.gov (United States)

Nuclear magnetic resonance (NMR) relaxometry is a geophysical method widely used in borehole and laboratory applications to nondestructively infer transport and storage properties of rocks and soils as it is directly sensitive to the water/oil content and pore sizes. However, for inferring pore sizes, NMR relaxometry data need to be calibrated with respect to a surface interaction parameter, surface relaxivity, which depends on the type and mineral constituents of the investigated rock. This study introduces an inexpensive and quick alternative to the classical calibration methods, e.g., mercury injection, pulsed field gradient (PFG) NMR, or grain size analysis, which allows for jointly estimating NMR surface relaxivity and pore size distributions using NMR relaxometry data from partially desaturated rocks. Hereby, NMR relaxation experiments are performed on the fully saturated sample and on a sample partially drained at a known differential pressure. Based on these data, the (capillary) pore radius distribution and surface relaxivity are derived by joint optimization of the Brownstein-Tarr and the Young-Laplace equation assuming parallel capillaries. Moreover, the resulting pore size distributions can be used to predict water retention curves. This inverse modeling approach—tested and validated using NMR relaxometry data measured on synthetic porous borosilicate samples with known petrophysical properties (i.e., permeability, porosity, inner surfaces, pore size distributions)—yields consistent and reproducible estimates of surface relaxivity and pore radii distributions. Also, subsequently calculated water retention curves generally correlate well with measured water retention curves.

Mohnke, O.; Hughes, B.

2014-06-01

168

Automatic maximum entropy spectral reconstruction in NMR.  

Science.gov (United States)

Developments in superconducting magnets, cryogenic probes, isotope labeling strategies, and sophisticated pulse sequences together have enabled the application, in principle, of high-resolution NMR spectroscopy to biomolecular systems approaching 1 megadalton. In practice, however, conventional approaches to NMR that utilize the fast Fourier transform, which require data collected at uniform time intervals, result in prohibitively lengthy data collection times in order to achieve the full resolution afforded by high field magnets. A variety of approaches that involve nonuniform sampling have been proposed, each utilizing a non-Fourier method of spectrum analysis. A very general non-Fourier method that is capable of utilizing data collected using any of the proposed nonuniform sampling strategies is maximum entropy reconstruction. A limiting factor in the adoption of maximum entropy reconstruction in NMR has been the need to specify non-intuitive parameters. Here we describe a fully automated system for maximum entropy reconstruction that requires no user-specified parameters. A web-accessible script generator provides the user interface to the system. PMID:17701276

Mobli, Mehdi; Maciejewski, Mark W; Gryk, Michael R; Hoch, Jeffrey C

2007-10-01

169

Lyotropic mesophases studied by 31P-NMR  

International Nuclear Information System (INIS)

The 31P-NMR is a powerful method to study liquid crystalline systems. Information about the phase states is obtained by only ''a look'' if the screening tensor of the anisotropy of chemical shift is known. The line shapes indicate also very simply mixed and transition states. If the screening tensor is known detailed information about dynamical and conformation states can be obtained. Finally the 31P-NMR can give valuable insight into very complex systems as biological systems. Liquid crystalline mesophases and their properties (structure, dynamical processes) are studied by different physical methods as X-ray-, neutron- and light-scattering, NMR etc. Each method is based on special parameters which are sensitive to certain properties. Each method yields therefore only information about these properties. If the molecules forming liquid-crystalline mesophases contain 31P-atoms the 31P-NMR can be used as a powerful physical technique. (author)

170

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.)

171

Fully automated system for pulsed NMR measurements  

Energy Technology Data Exchange (ETDEWEB)

A system is described which places many of the complex, tedious operations for pulsed NMR experiments under computer control. It automatically optimizes the experiment parameters of pulse length and phase, and precision, accuracy, and measurement speed are improved. The hardware interface between the computer and the NMR instrument is described. Design features, justification of the choices made between alternative design strategies, and details of the implementation of design goals are presented. Software features common to all the available experiments are discussed. Optimization of pulse lengths and phases is performed via a sequential search technique called Uniplex. Measurements of the spin-lattice and spin-spin relaxation times and of diffusion constants are automatic. Options for expansion of the system are explored along with some of the limitations of the system.

Cantor, David Milton

1977-01-01

172

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

173

NMR study of the magnetization of superfluid helium-3-boron and NMR of superfluid helium-3 in aerogel  

Science.gov (United States)

Pulsed NMR measurements of superfluid 3He confined in 98.2% porosity silica aerogel are reported. The aerogel suppressed the superfluid transition temperature TC and the order parameter magnitude from their bulk values in qualitative agreement with impurity scattering models. Magnetization measurements showed that the superfluid is an equal spin pairing state (ESP). The superfluid exhibited positive NMR frequency shifts with similar temperature dependence to those of the bulk A-phase, only smaller. TC was independent of the magnetic field for H wcp) theory at TAB for most pressures and fields. The Ginzburg-Landau strong-coupling parameter gz/( gz)wcp was determined from NMR results to equal 1.00 +/- 0.03 for all pressures. Combinations of the Ginzburg-Landau beta-parameters are reported that are consistent with this observation.

Haard, Thomas Michael

174

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 NQR.

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

2012-03-01

175

NMR studies of fast-ion conductors  

International Nuclear Information System (INIS)

NMR principles are reviewed, and NMR techniques which are likely to give a major contribution to studies of fast ion transport in solids are discussed. The NMR correlation function is defined, and examples are given and discussed

176

A combined ??Se NMR and molecular dynamics contribution to the structural understanding of the chalcogenide glasses.  

Science.gov (United States)

Solid-state (77)Se NMR measurements, first-principles molecular dynamics and DFT calculations of NMR parameters were performed to gain insight into the structure of selenium-rich GexSe(1-x) glasses. We recorded the fully-relaxed NMR spectra on natural abundance and 100% isotopically enriched GeSe4 samples, which led us to reconsider the level of structural heterogeneity in this material. In this paper, we propose an alternative procedure to initialise molecular dynamics runs for the chalcogenide glasses. The (77)Se NMR spectra calculated on the basis of the structural models deduced from these simulations are consistent with the experimental spectrum. PMID:25050418

Sykina, Kateryna; Bureau, Bruno; Le Pollès, Laurent; Roiland, Claire; Deschamps, Michaël; Pickard, Chris J; Furet, Eric

2014-09-01

177

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

178

Annual reports on NMR spectroscopy  

CERN Document Server

The current extent of applications of NMR spectroscopy to molecular problems is indicated by the diversity of the reviews presented in this volume. Dr. H.W.E. Rattle reports on NMR of amino acids, peptides, and proteins, which brings his account in Volume 11A up to date.

Webb, Graham A

1985-01-01

179

Annual reports on NMR spectroscopy  

CERN Document Server

This book is part of a series on spectroscopy, and covers NMR studiesof isolated spin-pairs in the solid state, the oxidation state dependence of transition metal shieldings, the Cinderella nuclei, nuclear spin relaxation in organic systems, solutions of macromolecules and aggregates and the NMR of coals and coal products. Related titlesare volumes 20, 21 and 22 in the series.

1991-01-01

180

NMR spektroskopie peptid? v roztoku.  

Czech Academy of Sciences Publication Activity Database

Praha : Ústav makromolekulární chemie AV ?R, v. v. i, 2011. s. 10. [Workshop on Solid-State NMR and Computational Methods /5./. 05.12.2011, Praha] R&D Projects: GA MŠk 2B08021 Institutional research plan: CEZ:AV0Z40500505 Keywords : NMR * neurotoxin Subject RIV: CB - Analytical Chemistry, Separation

Svobodová, Jana

181

11B nutation NMR study of powdered borosilicates  

International Nuclear Information System (INIS)

In this work, we applied the 1D 11B nutation NMR method for the analysis of the local structural environments in powdered borosilicates (SiO2-B2O3). Spin dynamics during a rf irradiation for spin I=3/2 was analytically calculated with a density matrix formalism. Spectral simulation programs were written in MATLAB on a PC. Two borosilicates prepared by the sol-gel process at different stabilization temperature were used for the 1D 11B nutation NMR experiment. The 11B NMR parameters, quadrupole coupling constants (e2qQ/h) and asymmetry parameters (?), for each borosilicate were extracted from the nonlinear least-squares fitting. The effects of heat treatments on the local structures of boron sites in borosilicates were discussed

182

Solid-state NMR study of halogen-bonded adducts.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) spectroscopy offers unique insights into halogen bonds. NMR parameters such as chemical shifts, quadrupolar coupling constants, J coupling constants, and dipolar coupling constants are in principle sensitive to the formation and local structure of a halogen bond. Carrying out NMR experiments on halogen-bonded adducts in the solid state may provide several advantages over solution studies including (1) the absence of solvent which can interact with halogen bond donor sites and complicate spectral interpretation, (2) the lack of a need for single crystals or even long-range crystalline order, and (3) the potential to measure complete NMR interaction tensors rather than simply their isotropic values. In this chapter, we provide an overview of the NMR interactions and experiments which are relevant to the study of nuclei which are often found in halogen bonds (RX···Y) including (13)C, (35/37)Cl, (79/81)Br, (127)I, (77)Se, and (14/15)N. Experimental examples based on iodoperfluorobenzene halides, bis(trimethylammonium)alkane diiodide, and selenocyanate complexes, as well as haloanilinium halides, are discussed. Of particular interest is the sensitivity of the isotropic chemical shifts, the chemical shift tensor spans, and the halide nuclear electric quadrupolar coupling tensors to the halogen bond geometry in such compounds. Technical limitations associated with the NMR spectroscopy of covalently-bonded halogens are underlined. PMID:24760615

Bryce, David L; Viger-Gravel, Jasmine

2015-01-01

183

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

184

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

185

Two-dimensional NMR spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Written for chemists and biochemists who are not NMR spectroscopists, but who wish to use the new techniques of two-dimensional NMR spectroscopy, this book brings together for the first time much of the practical and experimental data needed. It also serves as information source for industrial, academic, and graduate student researchers who already use NMR spectroscopy, but not yet in two dimensions. The authors describe the use of 2-D NMR in a wide variety of chemical and biochemical fields, among them peptides, steroids, oligo- and poly-saccharides, nucleic acids, natural products (including terpenoids, alkaloids, and coal-derived heterocyclics), and organic synthetic intermediates. They consider throughout the book both the advantages and limitations of using 2-D NMR.

Croasmun, W.R.; Carlson, R.M.K.

1987-01-01

186

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

187

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

188

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

189

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

190

NMR flow tube for online NMR reaction monitoring.  

Science.gov (United States)

In this paper we describe the development of a 5 mm NMR flow tube that can be used in a standard 5 mm NMR probe, enabling the user to conduct experiments on flowing samples or, more specifically, on flowing reaction mixtures. This enables reaction monitoring or kinetic experiments to be conducted by flowing reaction mixtures from a reaction vessel to detection in the coil area of the NMR, without the need for a specialized flow NMR probe. One of the key benefits of this flow tube is that it provides flexibility to be used across a range of available spectrometers of varying magnetic field strengths with a standard 5 mm probe setup. The applicability of this flow tube to reaction monitoring is demonstrated using the reaction of p-phenylenediamine and isobutyraldehyde to form the diimine product. PMID:25375410

Foley, David A; Bez, Eckhard; Codina, Anna; Colson, Kimberly L; Fey, Michael; Krull, Robert; Piroli, Don; Zell, Mark T; Marquez, Brian L

2014-12-16

191

Annual reports on NMR spectroscopy  

CERN Document Server

Over recent years, no other technique has grown to such importance as that of NMR spectroscopy. It is used in all branches of science where precise structural determination is required and where the nature of interactions and reactions in solution is being studied. Annual Reports on NMR Spectroscopy has established itself as a means for the specialist and non-specialist alike to become familiar with new applications of the technique in all branches of chemistry, including biochemistry, and pharmaceutics. This volume focuses on theoretical aspects of NMR nuclear shielding and on applications of

Webb, Graham A; McCarthy, M J

1995-01-01

192

NMR measurement of pore structure  

Energy Technology Data Exchange (ETDEWEB)

An attempt was made to pursue {sup 129}Xe NMR as a pore measurement technique. Samples studied were synthetic imogolite (tubular aluminosilicate with gibbsite structure), sodium Y-zeolite, and an aerogel and a xerogel. Gases used were normal Xe, {sup 13}CO{sub 2}, and {sup 15}N{sub 2}. Although a completely general NMR technique for measuring pore size distributions may not be possible, information about molecular motion and interactions can be obtained, because NMR is sensitive to short range interactions (1 nm or less) and to molecular dynamics in the range 10{sup {minus}2} to 10{sup {minus}6}s.

Earl, W.L. [Los Alamos National Lab., NM (United States); Kim, Yong-Wah [Los Alamos National Lab., NM (United States)]|[New Mexico Univ., Albuquerque, NM (United States). Center for Microengineered Ceramics; Smith, D.M. [New Mexico Univ., Albuquerque, NM (United States). Center for Microengineered Ceramics

1993-05-31

193

NMR measurement of pore structure  

Energy Technology Data Exchange (ETDEWEB)

An attempt was made to pursue [sup 129]Xe NMR as a pore measurement technique. Samples studied were synthetic imogolite (tubular aluminosilicate with gibbsite structure), sodium Y-zeolite, and an aerogel and a xerogel. Gases used were normal Xe, [sup 13]CO[sub 2], and [sup 15]N[sub 2]. Although a completely general NMR technique for measuring pore size distributions may not be possible, information about molecular motion and interactions can be obtained, because NMR is sensitive to short range interactions (1 nm or less) and to molecular dynamics in the range 10[sup [minus]2] to 10[sup [minus]6]s.

Earl, W.L. (Los Alamos National Lab., NM (United States)); Kim, Yong-Wah (Los Alamos National Lab., NM (United States) New Mexico Univ., Albuquerque, NM (United States). Center for Microengineered Ceramics); Smith, D.M. (New Mexico Univ., Albuquerque, NM (United States). Center for Microengineered Ceramics)

1993-05-31

194

Dynamic NMR of nano- and microstructured materials  

International Nuclear Information System (INIS)

The fast technological advancement which took place over the past few decades sustained the development of various categories of advanced polymeric, composite and porous materials, with complex physical and chemical properties determined by their structure and dynamics at nano- and micrometer levels. This brought forth the necessity of combining different methods of analysis, which cover multiple length scales, in order to allow for a comprehensive characterization and a valid prediction of a material's macroscopic behaviour. The purpose of this work was to characterize the structure and dynamics of various types of nano- and micro structured systems, such as silane crosslinked poly(ethylene), cement-in-polymer dispersion with different compositions or model and natural porous media, using a combination of nuclear magnetic resonance (NMR) methods that provide relevant information on different length scales of interest. Data processing and interpretation was facilitated by self-made computational procedures and mathematical models. The different subjects approached in this work are briefly presented in Chapter 1 (Introduction) and discussed in detail further on in an order according to the length scale of the motion probed. In Chapter 2 proton NMR wideline spectroscopy is used to obtain information on the phase composition, molecular mobility and domain sizes of crosslinked poly(ethylene) (PE), a polymer commonly used in a broad range of applications, from day-to-day life basic commodities like water and sewage pipes, to insulating coatings for medium and high voltage wires. Due to its industrial importance, this type of PE has been previously characterized using a variety of methods. The novelty brought by this study is the quantitative analysis of the spin diffusion (SD) coefficients and domain sizes of different phases by a dedicated software developed for solving the spin diffusion equations for a lamellar morphology, using as input data extracted from NMR double quantum filtered SD experiments and including a series of bonds for and minimizing uncertainties in the estimation of essential parameters. Recently developed cement-in-polymer dispersions (c/p) with different compositions and cement to polymer ratios are investigated in Chapters 3 and 4, by a vast array of NMR techniques, that probe, on different length scales, the structure of the investigated specimens, as well as the dynamics of water transport inside the materials. Chapter 3 presents the results obtained using multinuclear solid state magic angle spinning NMR to probe, at nanometer level, the structure of cement-in-polymer dispersions. The hydration effects and crystallization of the inorganic matrix are probed by 29Si NMR while the chemical reactions of the organic phase are quantified by 13C cross-polarization; the results are correlated with data offered by other analysis techniques. The study of hydrated c/p is continued in Chapter 4, where proton NMR imaging is employed to obtain information about the microstructural changes which take place upon exposure to water at different temperatures. The water transport in the c/p matrix is monitored on line and the hydration phenomenon, together with information about the physical suffered by the samples are discussed with regard to polymer type, amount and curing conditions. A simple mathematical model of diffusion in a cylindrical system, involving time dependent diffusion coefficients and variable surface concentrations, is used to predict the manner in which the water amount inside the organic/cementitious pastes evolves in time. Further on, the effects of diffusive and advective transport in model and natural porous media are systematically investigated in Chapters 5 and 6. NMR exchange relaxometry is known as a very powerful tool for probing the structure and dynamics of fully or partially hydrated porous systems, but, until know, no information existed on how the effects of slow advective transport - a phenomenon of considerable interest for different branches of science and industry - are reflected i

195

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

196

NMR of superfluid 3He in anisotropic aerogel  

CERN Document Server

We report on orientation of the order parameter in the 3He-A and 3He-B phases caused by aerogel anisotropy. In 3He-A we have observed relatively homogeneous NMR line with an anomalously large negative frequency shift. We can attribute this effect to an orientation of orbital momentum along the axis of density anisotropy. The similar orientation effect we have seen in 3He-B. We can measure the A-phase Leggett frequency, which shows the same energy gap suppression as in the B-phase. We observe a correlation of A - B transition temperature and NMR frequency shift.

Kunimatsu, T; Izumina, K; Matsubara, A; Sasaki, Y; Kubota, M; Ishikawa, O; Mizusaki, T; Bunkov, Yu M; Bunkov, Yu.M.

2006-01-01

197

NMR spectroscopy of muscle proteins  

International Nuclear Information System (INIS)

Author reviews various experimental techniques used for study of the structure of muscle proteins. Difficulties of application of NMR are described. Studies of the influence of Ca2+ on flexibility of actin polymer are presented

198

Compact orthogonal NMR field sensor  

Science.gov (United States)

A Compact Orthogonal Field Sensor for emitting two orthogonal electro-magnetic fields in a common space. More particularly, a replacement inductor for existing NMR (Nuclear Magnetic Resonance) sensors to allow for NMR imaging. The Compact Orthogonal Field Sensor has a conductive coil and a central conductor electrically connected in series. The central conductor is at least partially surrounded by the coil. The coil and central conductor are electrically or electro-magnetically connected to a device having a means for producing or inducing a current through the coil and central conductor. The Compact Orthogonal Field Sensor can be used in NMR imaging applications to determine the position and the associated NMR spectrum of a sample within the electro-magnetic field of the central conductor.

Gerald, II, Rex E. (Brookfield, IL); Rathke, Jerome W. (Homer Glen, IL)

2009-02-03

199

The inherent accuracy of 1H NMR spectroscopy to quantify plasma lipoproteins is subclass dependent.  

Science.gov (United States)

Proton NMR spectroscopy as a means to quantify lipoprotein subclasses has received wide clinical interest. The experimental part is a fast routine procedure that contrasts favourably to other lipoprotein measurement protocols. The difficulties in using (1)H NMR, however, are in uncovering the subclass specific information from the overlapping data. The NMR-based quantification has been evaluated only in relation to biochemical measures, thereby leaving the inherent capability of NMR rather vague due to biological variation and diversity among the biochemical experiments. Here we will assess the use of (1)H NMR spectroscopy of plasma per se. This necessitates data for which the inherent parameters, namely the shapes and areas of the (1)H NMR signals of the subclasses are available. This was achieved through isolation and (1)H NMR experiments of 11 subclasses--VLDL1, VLDL2, IDL, LDL1, LDL2, LDL3, HDL(2b), HDL(2a), HDL(3a), HDL(3b) and HDL(3c)--and the subsequent modelling of the spectra. The subclass models were used to simulate biochemically representative sets of spectra with known subclass concentrations. The spectral analyses revealed 10-fold differences in the quantification accuracy of different subclasses by (1)H NMR. This finding has critical significance since the usage of (1)H NMR methodology in the clinical arena is rapidly increasing. PMID:16730730

Ala-Korpela, Mika; Lankinen, Niko; Salminen, Aino; Suna, Teemu; Soininen, Pasi; Laatikainen, Reino; Ingman, Petri; Jauhiainen, Matti; Taskinen, Marja-Riitta; Héberger, Károly; Kaski, Kimmo

2007-02-01

200

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

201

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

202

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.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

2010-06-15

203

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

204

Distinguishing Individual Lipid Headgroup Mobility and Phase Transitions in Raft-Forming Lipid Mixtures with 31P MAS NMR  

OpenAIRE

A model membrane system composed of egg sphingomyelin (SM), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and cholesterol was studied with static and magic angle spinning 31P NMR spectroscopy. This model membrane system is of significant biological relevance since it is known to form lipid rafts. 31P NMR under magic angle spinning conditions resolves the SM and DOPC headgroup resonances allowing for extraction of the 31P NMR parameters for the individual lipid components. The isotropic che...

Holland, Gregory P.; Mcintyre, Sarah K.; Alam, Todd M.

2006-01-01

205

Evaluation of abdominal aortic aneurysms with NMR imaging  

International Nuclear Information System (INIS)

Seven patients (5 male and 2 female, age range from 50 to 88) with angiographic proven abdominal aortic aneurysms were evaluated with NMR imaging (1.5 K gauss system) of the abdomen. Images were obtained in transverse, coronal and saggital planes with three radiofrequency pulse sequences [saturation recovery (SR), inversion recovery (IR), and spin echo (SE)]. All of the aneurysms were identified as to site and relative size with NMR images. The lumen in which there was flowing blood was always dark (low intensity), whereas the aneurysmal area which contained presumed clot was brighter (high intensity) on SR images. Although the size, location and relationship to other blood vessels was best demonstrated on aortography, NMR images provided similar information in all cases. NMR images correctly demonstrated thrombus in six cases. The authors conclude that NMR imaging provides a clear delineation of the anatomy of abdominal aortic aneurysms. In addition it can provide information concerning tissue type, i.e., it distinguished clot from moving blood. It may be possible in the future to further characterize atherosclerotic and other pathological changes in vessel architecture by using various pulse sequences and timing parameters to provide in vivo histological typing

206

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

207

Determination of the three-dimensional structure for weakly aligned biomolecules by NMR spectroscopy  

International Nuclear Information System (INIS)

The key achievements and the potential of NMR spectroscopy for weakly aligned biomolecules are considered. Due to weak alignment, it becomes possible to determine a number of NMR parameters dependent on the orientation of biomolecules, which are averaged to zero in usual isotropic media. The addition of new orientational constraints to standard procedures of 3D structure determination markedly increases the achievable accuracy. The possibility of structure determination for biomolecules using only orientation-dependent parameters without invoking other NMR data is discussed. The methods of orientation, experimental techniques, and calculation methods are systematised. The main results obtained and the prospects of using NMR spectroscopy of weakly aligned systems to study different classes of biomolecules and to solve various problems of molecular biology are analysed. Examples of biomolecules whose structures have been determined using orientation-dependent parameters are given. The bibliography includes 508 references.

208

Bootstrap calibration and uncertainty estimation of downhole NMR hydraulic conductivity estimates in an unconsolidated aquifer.  

Science.gov (United States)

Characterization of hydraulic conductivity (K) in aquifers is critical for evaluation, management, and remediation of groundwater resources. While estimates of K have been traditionally obtained using hydraulic tests over discrete intervals in wells, geophysical measurements are emerging as an alternative way to estimate this parameter. Nuclear magnetic resonance (NMR) logging, a technology once largely applied to characterization of deep consolidated rock petroleum reservoirs, is beginning to see use in near-surface unconsolidated aquifers. Using a well-known rock physics relationship-the Schlumberger Doll Research (SDR) equation--K and porosity can be estimated from NMR water content and relaxation time. Calibration of SDR parameters is necessary for this transformation because NMR relaxation properties are, in part, a function of magnetic mineralization and pore space geometry, which are locally variable quantities. Here, we present a statistically based method for calibrating SDR parameters that establishes a range for the estimated parameters and simultaneously estimates the uncertainty of the resulting K values. We used co-located logging NMR and direct K measurements in an unconsolidated fluvial aquifer in Lawrence, Kansas, USA to demonstrate that K can be estimated using logging NMR to a similar level of uncertainty as with traditional direct hydraulic measurements in unconsolidated sediments under field conditions. Results of this study provide a benchmark for future calibrations of NMR to obtain K in unconsolidated sediments and suggest a method for evaluating uncertainty in both K and SDR parameter values. PMID:24520904

Parsekian, A D; Dlubac, K; Grunewald, E; Butler, J J; Knight, R; Walsh, D O

2015-01-01

209

In vivo applications of NMR to medicine  

Science.gov (United States)

This article describes the two in vivo applications of nuclear magnetic resonance (NMR) to medicine, namely NMR imaging and localized NMR spectroscopy. A brief outline of the principles of NMR for spins I = {1}/{2}, is followed by an account of NMR image formation using protons. The question of tissue discrimination is dealt with during a discussion of nuclear relaxation, before the phenomenon of chemical shielding is described, together with illustrations of the usefulness of 31P and 13C NMR spectra obtained in vivo.

Allen, Peter S.

210

Precise measurements of NMR shifts  

International Nuclear Information System (INIS)

A novel technique is developed for precise measurement of NMR signals. The experimental arrangement for precise measurement of NMR shifts is described. An accuracy of 8x10-5 parts per million is attained for specimens with an external etalon, and 2x10-5 parts in million for specimens with an internal etalon. This is about 100 times better than the resolution of commercial NMR spectrometers. The high accuracy is achieved by thermostabilizing the specimen with temperature stabilization to within 0.01 deg C. A control of the stability of the NMR line shape and the circuit for automatic fine adjustment of the modulating generator were also employed. This high accuracy in shift measurements make possible measurements of the magnetic susceptibility of substances in solution with an accuracy which is 100 times better than that of the Evans NMR technique. Moreover, contanct and pseudocontact shifts which are strongly masked by exchange processes can be recorded. Finally, weak temperature dependences of chemical shifts and of the spin-spin coupling constants can be measured. This opens some new possibilities in the investigation of the structure of metal-containing macromolecules (enzymes, nucleic, acids) or coordinate complexes and of processes involving intramolecular and intermolecular interactions

211

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

212

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)

213

Advanced NMR characterization of zeolite catalysts  

Science.gov (United States)

The program discussed in this report is a two-year two-phase joint UOP-University of Illinois study of the application of improved high resolution solid state nuclear magnetic resonance (NMR) techniques to the characterization of zeolite catalysts. During the first phase of this program very pure, and in some cases isotopically enriched faujasites will be prepared and studied by magic angle sample spinning NMR (MASS NMR) and variable engine sample spinning NMR (VASS NMR) on 500 and 360 MHz (proton frequency) NMR spectrometers. The NMR techniques that will be emphasized are the measurement and analysis of the (17)O NMR properties, (27)Al NMR intensity quantitation, and (27)Al and (29)Si NMR relaxation rates. During the second phase of this program these NMR techniques will be used to study the effects of impurity concentration, dealumination treatments and cation exchange on the NMR properties of faujasites. The initial emphasis of this program during Phase I is on the preparation and measurement of the NMR properties of (17)O enriched Na-Y faujasties.

Welsh, L. B.

1985-04-01

214

NMR crystallography: the use of chemical shifts  

Science.gov (United States)

Measurements of chemical shifts obtained from magic-angle spinning NMR spectra (together with quantum mechanical computations of shielding) can provide valuable information on crystallography. Examples are given of the determination of crystallographic asymmetric units, of molecular symmetry in the solid-state environment, and of crystallographic space group assignment. Measurements of full tensor components for 199Hg have given additional coordination information. The nature of intermolecular hydrogen bonding in cortisone acetate polymorphs and solvates is obtained from chemical shift information, also involving measurement of the full tensor parameters. The resulting data have been used as restraints, built into the computation algorithm, in the analysis of powder diffraction patterns to give full crystal structures. A combination of quantum mechanical computation of shielding and measurement of proton chemical shifts (obtained by high-speed MAS) leads to the determination of the position of a proton in an intermolecular hydrogen bond. A recently-developed computer program specifically based on crystallographic repetition has been shown to give acceptable results. Moreover, NMR chemical shifts can distinguish between static and dynamic disorder in crystalline materials and can be used to determine modes and rates of molecular exchange motion.

Harris, Robin K.

2004-10-01

215

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

216

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

217

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...

218

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...

219

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

Energy Technology Data Exchange (ETDEWEB)

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.

Craft, John W.; Legge, Glen B. [University of Houston, Department of Biology and Biochemistry (United States)], E-mail: glegge@uh.edu

2005-09-15

220

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

221

An NMR database for simulations of membrane dynamics.  

Science.gov (United States)

Computational methods are powerful in capturing the results of experimental studies in terms of force fields that both explain and predict biological structures. Validation of molecular simulations requires comparison with experimental data to test and confirm computational predictions. Here we report a comprehensive database of NMR results for membrane phospholipids with interpretations intended to be accessible by non-NMR specialists. Experimental ¹³C-¹H and ²H NMR segmental order parameters (S(CH) or S(CD)) and spin-lattice (Zeeman) relaxation times (T(1Z)) are summarized in convenient tabular form for various saturated, unsaturated, and biological membrane phospholipids. Segmental order parameters give direct information about bilayer structural properties, including the area per lipid and volumetric hydrocarbon thickness. In addition, relaxation rates provide complementary information about molecular dynamics. Particular attention is paid to the magnetic field dependence (frequency dispersion) of the NMR relaxation rates in terms of various simplified power laws. Model-free reduction of the T(1Z) studies in terms of a power-law formalism shows that the relaxation rates for saturated phosphatidylcholines follow a single frequency-dispersive trend within the MHz regime. We show how analytical models can guide the continued development of atomistic and coarse-grained force fields. Our interpretation suggests that lipid diffusion and collective order fluctuations are implicitly governed by the viscoelastic nature of the liquid-crystalline ensemble. Collective bilayer excitations are emergent over mesoscopic length scales that fall between the molecular and bilayer dimensions, and are important for lipid organization and lipid-protein interactions. Future conceptual advances and theoretical reductions will foster understanding of biomembrane structural dynamics through a synergy of NMR measurements and molecular simulations. PMID:21134351

Leftin, Avigdor; Brown, Michael F

2011-03-01

222

19F and 199Hg NMR of trimeric perfluoro- ortho-phenylenemercury  

Science.gov (United States)

19F and 199Hg high-resolution solution NMR spectra were acquired for cyclic trimeric perfluoro- ortho-phenylenemercury. Even with the high superconducting magnetic fields currently available, the 19F spectrum was not interpretable with a simple first-order analysis. Spectroscopic parameters for chemical shift and scalar coupling interactions in the NMR spectra were extracted from four- and five-spin simulations. Differential line widths in the 19F spectrum result from scalar coupling to the 199Hg.

Taylor, R. E.; Gabbaï, François P.

2007-08-01

223

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

224

Area per lipid and acyl length distributions in fluid phosphatidylcholines determined by (2)H NMR spectroscopy.  

OpenAIRE

Deuterium ((2)H) NMR spectroscopy provides detailed information regarding the structural fluctuations of lipid bilayers, including both the equilibrium properties and dynamics. Experimental (2)H NMR measurements for the homologous series of 1, 2-diacyl-sn-glycero-3-phosphocholines with perdeuterated saturated chains (from C12:0 to C18:0) have been performed on randomly oriented, fully hydrated multilamellar samples. For each lipid, the C-D bond order parameters have been calculated from de-Pa...

Petrache, H. I.; Dodd, S. W.; Brown, M. F.

2000-01-01

225

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

226

Baseline Correction for NMR Spectroscopic Metabolomics Data Analysis  

OpenAIRE

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 distortio...

Rocke David M; Xi Yuanxin

2008-01-01

227

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.

228

Investigation of structural information for boron-rich solids and aluminates via NMR and NQR studies  

International Nuclear Information System (INIS)

Along with NMR, Nuclear Quadrupole Resonance (NQR) has become important recently for obtaining structural information from oxide glasses. The NQR studies prove in this thesis that they provide more accurate structural information than the NMR studies have done. This study presents boron and aluminum NMR, and NQR studies for some borate glasses and compounds, icosahedral boron-rich solids, some crystalline aluminosilicates. Various borates were employed to acquire structural information as well as to determine the quadrupole parameters (the quadrupole coupling constant Qcc and the asymmetry parameter ?) using NQR under a guidance of NMR or vice versa. By NQR a previously unknown boron site was observed for vitreous Li2O·B2O3. The NMR and NQR studies were performed on some icosachedral boron-rich solids: ?-rhombohedral boron (B12), ?-boron (B105) and boron carbide (B12C3). Three different forms of crystalline aluminosilicate (Al2SiO5) were studied by NQR. The NQR study yielded more accurate values of the quadrupole parameters for 27Al than the previous NMR single crystal study did

229

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

230

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.)

231

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

232

Profiling formulated monoclonal antibodies by (1)H NMR spectroscopy.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) is arguably the most direct methodology for characterizing the higher-order structure of proteins in solution. Structural characterization of proteins by NMR typically utilizes heteronuclear experiments. However, for formulated monoclonal antibody (mAb) therapeutics, the use of these approaches is not currently tenable due to the requirements of isotope labeling, the large size of the proteins, and the restraints imposed by various formulations. Here, we present a new strategy to characterize formulated mAbs using (1)H NMR. This method, based on the pulsed field gradient stimulated echo (PGSTE) experiment, facilitates the use of (1)H NMR to generate highly resolved spectra of intact mAbs in their formulation buffers. This method of data acquisition, along with postacquisition signal processing, allows the generation of structural and hydrodynamic profiles of antibodies. We demonstrate how variation of the PGSTE pulse sequence parameters allows proton relaxation rates and relative diffusion coefficients to be obtained in a simple fashion. This new methodology can be used as a robust way to compare and characterize mAb therapeutics. PMID:24006877

Poppe, Leszek; Jordan, John B; Lawson, Ken; Jerums, Matthew; Apostol, Izydor; Schnier, Paul D

2013-10-15

233

ELISE NMR: experimental liquid sealing of NMR samples.  

Science.gov (United States)

We present a simple, generally applicable approach to prevent sample evaporation when working at elevated temperatures in high resolution NMR. It consists of experimentally sealing the NMR sample by a second liquid (Experimental Liquid Sealing, ELISE). For aqueous samples, we identified the mineral oil commonly used in PCR application as the best candidate, because it contains only a very limited amount of water-soluble contaminants, is stable over time and heat resistant. The procedure does not interfere with shim settings, and is compatible with a wide variety of samples, including oligosaccharides and proteins. For chloroform samples, a simple drop of water allows to efficiently seal the sample, avoiding solvent evaporation even over lengthy time periods. PMID:16709462

Wieruszeski, Jean-Michel; Landrieu, Isabelle; Hanoulle, Xavier; Lippens, Guy

2006-08-01

234

A detailed study of the magnetism of chiral {Cr?M} rings: an investigation into parametrization and transferability of parameters.  

Science.gov (United States)

Compounds of general formula [Cr7MF3(Etglu)(O2C(t)Bu)15(Phpy)] [H5Etglu = N-ethyl-d-glucamine; Phpy = 4-phenylpyridine; M = Zn (1), Mn (2), Ni (3)] have been prepared. The structures contain an irregular octagon of metal sites formed around the penta-deprotonated Etglu(5-) ligand; the chirality of N-ethyl-d-glucamine is retained in the final product. The seven Cr(III) sites have a range of coordination environments, and the divalent metal site is crystallographically identified and has a Phpy ligand attached to it. By using complementary experimental techniques, including magnetization and specific heat measurements, inelastic neutron scattering, and electron paramagnetic resonance spectroscopy, we have investigated the magnetic features of this family of {Cr7M} rings. Microscopic parameters of the spin Hamiltonian have been determined as a result of best fits of the different experimental data, allowing a direct comparison with corresponding parameters found in the parent compounds. We examine whether these parameters can be transferred between compounds and compare them with those of an earlier family of heterometallic rings. PMID:24968057

Garlatti, Elena; Albring, Morten A; Baker, Michael L; Docherty, Rebecca J; Mutka, Hannu; Guidi, Tatiana; Garcia Sakai, Victoria; Whitehead, George F S; Pritchard, Robin G; Timco, Grigore A; Tuna, Floriana; Amoretti, Giuseppe; Carretta, Stefano; Santini, Paolo; Lorusso, Giulia; Affronte, Marco; McInnes, Eric J L; Collison, David; Winpenny, Richard E P

2014-07-01

235

Microcoil NMR spectroscopy: a novel tool for biological high throughput NMR spectroscopy.  

Science.gov (United States)

Microcoil NMR spectroscopy is based on the increase of coil sensitivity for smaller coil diameters (approximately 1/d). Microcoil NMR probes deliver a remarkable mass-based sensitivity increase (8- to 12-fold) when compared with commonly used 5-mm NMR probes. Although microcoil NMR probes are a well established analytical tool for small molecule liquid-state NMR spectroscopy, after spectroscopy only recently have microcoil NMR probes become available for biomolecular NMR spectroscopy. This chapter highlights differences between commercially available microcoil NMR probes suitable for biomolecular NMR spectroscopy. Furthermore, it provides practical guidance for the use of microcoil probes and shows direct applications for structural biology and structural genomics, such as optimal target screening and structure determination, among others. PMID:18542883

Hopson, Russell E; Peti, Wolfgang

2008-01-01

236

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)

237

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

238

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

239

NMR metabolomics for assessment of exercise effects with mouse biofluids.  

Science.gov (United States)

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. PMID:22706325

Le Moyec, Laurence; Mille-Hamard, Laurence; Triba, Mohamed N; Breuneval, Carole; Petot, Hélène; Billat, Véronique L

2012-08-01

240

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

241

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

242

Development and Characterization of NMR Measurements for Polymer Gel Dosimetry  

Science.gov (United States)

Polymer gel dosimeters are systems of water, gelatin, and monomers which form polymers upon irradiation. The gelatin matrix retains dose distribution in 3D form, facilitating truly integrated measurements of complex dose plans for radiation therapy. Polymer gels have two proton pools coupled by exchange: free solvent protons and bound polymerized macromolecular protons. Measuring magnetization transfer (MT) and relaxation affords useful insights into particle rigidity and chemical exchange effects on relaxation in polymer gels. Polymer gel dose response has been previously quantified with several techniques, most often in terms of MRI parameters, usually at field strengths of 1.5 T and below. The research described here investigates the dose response of a revised MAGIC gel dosimeter via both high-field imaging and simpler nuclear magnetic resonance (NMR) spectroscopy. This includes both transverse and longitudinal relaxation rates (R2 and R1) and quantitative MT parameters. We investigated estimating polymer molecular weight for a given applied dose using the Rouse model and R2 data from the imaging study. Finally, we began development of NMR methods for studying dose response, requiring adaption of NMR experiments to accommodate for radiation damping.

Kwong, Zachary; Whitney, Heather

2012-03-01

243

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

244

The fluorescence properties and NMR analysis of protopine and allocryptopine  

Energy Technology Data Exchange (ETDEWEB)

The fluorescence properties of protopine and allocryptopine in aqueous and organic environments are described for the first time. The fluorescence of alkaloids and their pH-dependent interconversion to cationic forms (transannular interaction) were studied using steady-state and time-resolved fluorescence techniques. For the analysis of tricyclic base and cis/trans tetracyclic cations of the alkaloids, NMR and X-ray crystallography were used. - Highlights: {yields} We describe fundamental fluorescence characteristics of alkaloids protopine and allocryptopine. {yields} We analyzed the pH-dependent transitions and cis/trans isomerization. {yields} These two alkaloids can be better distinguished by their fluorescence decay characteristics. {yields} The fluorescence parameters are related to the NMR and crystallographic structural data.

Kubala, Martin, E-mail: mkubala@prfnw.upol.c [Department of Biophysics, Faculty of Science, Palacky University, tr. 17. listopadu 12, CZ-77146 Olomouc (Czech Republic); Vacek, Jan [Department of Medical Chemistry and Biochemistry, Faculty of Medicine and Dentistry, Palacky University, Hnevotinska 3, CZ-77515 Olomouc (Czech Republic); Popa, Igor [Department of Inorganic Chemistry, Faculty of Science, Palacky University, tr. 17. listopadu 12, CZ-77146 Olomouc (Czech Republic); Janovska, Marika [Department of Biophysics, Faculty of Science, Palacky University, tr. 17. listopadu 12, CZ-77146 Olomouc (Czech Republic); Kosina, Pavel; Ulrichova, Jitka [Department of Medical Chemistry and Biochemistry, Faculty of Medicine and Dentistry, Palacky University, Hnevotinska 3, CZ-77515 Olomouc (Czech Republic); Travnicek, Zdenek [Department of Inorganic Chemistry, Faculty of Science, Palacky University, tr. 17. listopadu 12, CZ-77146 Olomouc (Czech Republic); Simanek, Vilim [Department of Medical Chemistry and Biochemistry, Faculty of Medicine and Dentistry, Palacky University, Hnevotinska 3, CZ-77515 Olomouc (Czech Republic)

2011-07-15

245

Equilibrium Constant Determination by NMR. Advantages of Lineshape Analysis  

International Nuclear Information System (INIS)

Equilibrium constant for a reaction of complex formation can be determined by analysis of NMR spectra. Chemical shifts of species engaged in the reaction are population-weighted averages of chemical shifts of individual forms i.e. free and complexed. This is the truth, however, only in the limit where the exchange is very fast compared to the chemical shift difference. If the exchange is not fast enough, then signals bear residual broadening coming from the exchange, and their apparent maxima are shifted to the direction of higher populated form. Use of averaged chemical shifts taken directly from such spectrum may lead, therefore, to substantial systematic errors in equilibrium constant estimation. In order to overcome these difficulties the full NMR lineshape analysis is required. We show advantages of the latter technique extracting both the kinetic and thermodynamic parameters from spectra of complexes formed by both camphor enantiomers with alphacyclodextrin. (author)

246

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

247

An Inversion Recovery NMR Kinetics Experiment  

OpenAIRE

A convenient laboratory experiment is described in which NMR magnetization transfer by inversion recovery is used to measure the kinetics and thermochemistry of amide bond rotation. The experiment utilizes Varian spectrometers with the VNMRJ 2.3 software, but can be easily adapted to any NMR platform. The procedures and sample data sets in this article will enable instructors to use inversion recovery as a laboratory activity in applied NMR classes and provide research students with a conveni...

Williams, Travis J.; Kershaw, Allan D.; Li, Vincent; Wu, Xinping

2011-01-01

248

Quality Assessment of Protein NMR Structures  

OpenAIRE

Biomolecular NMR structures are now routinely used in biology, chemistry, and bioinformatics. Methods and metrics for assessing the accuracy and precision of protein NMR structures are beginning to be standardized across the biological NMR community. These include both knowledge-based assessment metrics, parameterized from the database of protein structures, and model vs. data assessment metrics. On line servers are available that provide comprehensive protein structure quality assessment rep...

Rosato, Antonio; Tejero, Roberto; Montelione, Gaetano T.

2013-01-01

249

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

250

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.)

251

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

252

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

253

NMR, DNP and EPR spectrometers  

International Nuclear Information System (INIS)

One of the great problems concerning NMR tomography for the obtention of images of objects which are millimeters long is the low sensitivity of the technique. Aiming to reduce this inconvenience, the dynamic nuclear polarization (DNP) technique was used for both solids and liquids. Theoretically, the DNP technique is 659 times more sensitive, however, in practical work the gains have been significantly lower than that. This discrepancy is due to difficulties in the operation, in addition to those related to special design of the equipment. This work presents an alternative for such difficulties

254

Short recovery time NMR probe  

International Nuclear Information System (INIS)

A NMR probe for low frequency and short recovery time is presented in this work. The probe contains the tuning circuit, diode expanders and quarter wavelength networks to protect the receiver from both the amplifier noise and the coil ringing following the transmitter power pulse. It also possesses a coil damper which is activated by of non active components. The probe performance shows a recovery time of about of 15?s a sensitive Q factor reduction and an increase of the signal to noise ratio of about 68% during the reception at a work frequency of 2 MHz. (author)

255

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

256

An Inexpensive High-Throughput NMR Tube Cleaning Apparatus  

OpenAIRE

Large scale Nuclear Magnetic Resonance (NMR) tube cleaning is currently a bottleneck in high throughput NMR ligand affinity screens. Expensive alternatives include discarding the NMR tubes after a single use (~$2 to $8/tube), using commercial NMR tube cleaners (~$15K) or abandoning NMR tubes for flow probe technology (~$75K). Instead, we describe a relatively inexpensive (~$400) and easily constructed apparatus that can clean 180 NMR tubes an hour while using a modest amount of solvent. The a...

Zhang, Bo; Hodgson, James; Hancock, Walter; Powers, Robert

2011-01-01

257

The eNMR platform for structural biology  

OpenAIRE

The e-NMR project is a European cooperation initiative that aims at providing the bio-NMR user community with a software platform integrating and streamlining the computational approaches necessary for the analysis of bio-NMR data. The e-NMR platform is based on a Grid computational infrastructure. A main focus of the current implementation of the e-NMR platform is on streamlining structure determination protocols. Indeed, to facilitate the use of NMR spectroscopy in t...

Bonvin, A. M. J. J.; Rosato, A.; Wassenaar, T. A.

2010-01-01

258

NMR imaging of soft tissue tumors  

Energy Technology Data Exchange (ETDEWEB)

Preliminary findings on NMR imaging of 30 soft tissue tumors demonstrated the indispensable value of this examination (particularly when a surface antenna is used) for preoperative investigation and diagnosis of tumoral recurrence when compared with other radiologic techniques. The possible potential of NMR imaging for characterization of tissues, apart from lipoma or liposarcoma, cannot be evaluated at the present time.

Laval-Jeantet, M.: Tobolsk, F.; Delepine, N.; Delepine, G.; Roger, B.; Cabanis, E.A.

1986-05-01

259

NMR imaging of soft tissue tumors  

International Nuclear Information System (INIS)

Preliminary findings on NMR imaging of 30 soft tissue tumors demonstrated the indispensable value of this examination (particularly when a surface antenna is used) for preoperative investigation and diagnosis of tumoral recurrence when compared with other radiologic techniques. The possible potential of NMR imaging for characterization of tissues, apart from lipoma or liposarcoma, cannot be evaluated at the present time

260

NMR studies of the structure of glasses  

International Nuclear Information System (INIS)

Earlier continuous wave (CW) NMR studies of chemical bonding and structure in glasses are summarized. Examples are given of this use of the quadrupolar interaction and chemical shift to obtain structural information. New NMR data and analyses are presented for alkali borate and gallate glasses. Extensions to other elements (e.g. molybdenum, lanthanum) are suggested. 44 refs. (author)

261

Large NMR signals and polarization asymmetries  

International Nuclear Information System (INIS)

A large modulation in the series Q-meter can lead to nonlinear NMR signals and asymmetric polarization values. With a careful circuit analysis the nonlinearity can be estimated and corrections to polarization can be determined as a function of the strength of the modulation. We describe the recent LAMPF polarized proton target experiment, its NMR measurement and corrections to the measured polarizations

262

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)

263

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

264

Early history of NMR at Los Alamos  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) spectroscopy has developed into an important research tool in chemistry. More recently, NMR imaging and in vivo spectroscopy promise to produce a revolution in medicine and biochemistry. Early experiments at Los Alamos led to DOE programs involving stable isotopes of importance to biology and to medicine. These events are briefly recounted. 2 refs

265

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

266

Enzyme dynamics from NMR spectroscopy.  

Science.gov (United States)

Conspectus Biological activities of enzymes, including regulation or coordination of mechanistic stages preceding or following the chemical step, may depend upon kinetic or equilibrium changes in protein conformations. Exchange of more open or flexible conformational states with more closed or constrained states can influence inhibition, allosteric regulation, substrate recognition, formation of the Michaelis complex, side reactions, and product release. NMR spectroscopy has long been applied to the study of conformational dynamic processes in enzymes because these phenomena can be characterized over multiple time scales with atomic site resolution. Laboratory-frame spin-relaxation measurements, sensitive to reorientational motions on picosecond-nanosecond time scales, and rotating-frame relaxation-dispersion measurements, sensitive to chemical exchange processes on microsecond-millisecond time scales, provide information on both conformational distributions and kinetics. This Account reviews NMR spin relaxation studies of the enzymes ribonuclease HI from mesophilic (Escherichia coli) and thermophilic (Thermus thermophilus) bacteria, E. coli AlkB, and Saccharomyces cerevisiae triosephosphate isomerase to illustrate the contributions of conformational flexibility and dynamics to diverse steps in enzyme mechanism. Spin relaxation measurements and molecular dynamics (MD) simulations of the bacterial ribonuclease H enzymes show that the handle region, one of three loop regions that interact with substrates, interconverts between two conformations. Comparison of these conformations with the structure of the complex between Homo sapiens ribonuclease H and a DNA:RNA substrate suggests that the more closed state is inhibitory to binding. The large population of the closed conformation in T. thermophilus ribonuclease H contributes to the increased Michaelis constant compared with the E. coli enzyme. NMR spin relaxation and fluorescence spectroscopy have characterized a conformational transition in AlkB between an open state, in which the side chains of methionine residues in the active site are disordered, and a closed state, in which these residues are ordered. The open state is highly populated in the AlkB/Zn(II) complex, and the closed state is highly populated in the AlkB/Zn(II)/2OG/substrate complex, in which 2OG is the 2-oxoglutarate cosubstrate and the substrate is a methylated DNA oligonucleotide. The equilibrium is shifted to approximately equal populations of the two conformations in the AlkB/Zn(II)/2OG complex. The conformational shift induced by 2OG ensures that 2OG binds to AlkB/Zn(II) prior to the substrate. In addition, the opening rate of the closed conformation limits premature release of substrate, preventing generation of toxic side products by reaction with water. Closure of active site loop 6 in triosephosphate isomerase is critical for forming the Michaelis complex, but reopening of the loop after the reaction is (partially) rate limiting. NMR spin relaxation and MD simulations of triosephosphate isomerase in complex with glycerol 3-phosphate demonstrate that closure of loop 6 is a highly correlated rigid-body motion. The MD simulations also indicate that motions of Gly173 in the most flexible region of loop 6 contribute to opening of the active site loop for product release. Considered together, these three enzyme systems illustrate the power of NMR spin relaxation investigations in providing global insights into the role of conformational dynamic processes in the mechanisms of enzymes from initial activation to final product release. PMID:25574774

Palmer, Arthur G

2015-02-17

267

sup 1 sup 1 B nutation NMR study of powdered borosilicates  

CERN Document Server

In this work, we applied the 1D sup 1 sup 1 B nutation NMR method for the analysis of the local structural environments in powdered borosilicates (SiO sub 2 -B sub 2 O sub 3). Spin dynamics during a rf irradiation for spin I=3/2 was analytically calculated with a density matrix formalism. Spectral simulation programs were written in MATLAB on a PC. Two borosilicates prepared by the sol-gel process at different stabilization temperature were used for the 1D sup 1 sup 1 B nutation NMR experiment. The sup 1 sup 1 B NMR parameters, quadrupole coupling constants (e sup 2 qQ/h) and asymmetry parameters (eta), for each borosilicate were extracted from the nonlinear least-squares fitting. The effects of heat treatments on the local structures of boron sites in borosilicates were discussed.

Woo, A J; Han, D Y

1998-01-01

268

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

269

NMR and MRI apparatus and method  

Science.gov (United States)

Nuclear magnetic resonance (NMR) signals are detected in microtesla fields. Prepolarization in millitesla fields is followed by detection with an untuned dc superconducting quantum interference device (SQUID) magnetometer. Because the sensitivity of the SQUID is frequency independent, both signal-to-noise ratio (SNR) and spectral resolution are enhanced by detecting the NMR signal in extremely low magnetic fields, where the NMR lines become very narrow even for grossly inhomogeneous measurement fields. Additional signal to noise benefits are obtained by use of a low noise polarization coil, comprising litz wire or superconducting materials. MRI in ultralow magnetic field is based on the NMR at ultralow fields. Gradient magnetic fields are applied, and images are constructed from the detected NMR signals.

Clarke, John; Kelso, Nathan; Lee, SeungKyun; Moessle, Michael; Myers, Whittier; McDermott, Robert; ten Haken, Bernard; Pines, Alexander; Trabesinger, Andreas

2007-03-06

270

NMR imaging of the brain: current status and perspectives  

International Nuclear Information System (INIS)

Recent developments in NMR imaging of the brain are summarised and preliminary results from cranial examination of 230 patients and 60 volunteers at Hammersmith Hospital are discussed. An NMR scanner is described and three pulse sequences which produce images with varying dependence on the basic imaging parameters proton density, T1 and T2 are outlined. The first of these pulse sequences, Repeated Free Induction Decay, produces images which demonstrate changes in proton density although these have limited diagnostic utility. The second sequence, Inversion-recovery, produces images which depend on T1. These show a high level of grey white matter contrast giving considerable anatomical detail. In addition pathological changes such as infarction, haemorrhage, demyelination and malignancy produce changes in T1 enabling lesions to be localised. The third sequence, Spin-echo, produces images dependent on T2. Whilst these display little grey-white matter contrast they frequently highlight pathological changes in the brain. Images of these three basic types can also be produced in transverse coronal and sagittal planes. Although much more work remains to be done, NMR imaging appears likely to play a major role in neurological diagnosis within the foreseeable future

271

Crystallinity and compositional changes in carbonated apatites: Evidence from 31P solid-state NMR, Raman, and AFM analysis  

OpenAIRE

Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and 31P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse 31P NMR linewidth and inverse Raman PO43? ?1 bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3–10.3 wt% CO32? range investigated. Comparison...

Mcelderry, John-david P.; Zhu, Peizhi; Mroue, Kamal H.; Xu, Jiadi; Pavan, Barbara; Fang, Ming; Zhao, Guisheng; Mcnerny, Erin; Kohn, David H.; Franceschi, Renny T.; Holl, Mark M. Banaszak; Tecklenburg, Mary M. J.; Ramamoorthy, Ayyalusamy; Morris, Michael D.

2013-01-01

272

Contribution of first-principles calculations to multinuclear NMR analysis of borosilicate glasses  

International Nuclear Information System (INIS)

Boron-11 and silicon-29 NMR spectra of xSiO2-(1-x)B2O3 glasses (x= 0. 40, 0. 80 and 0. 83) have been calculated using a combination of molecular dynamics (MD) simulations with density functional theory (DFT) calculations of NMR parameters. Structure models of 200 atoms have been generated using classical force fields and subsequently relaxed at the PBE-GGAlevel of DFT theory. The gauge including projector augmented wave (GIPAW) method is then employed for computing the shielding and electric field gradient tensors for each silicon and boron atom. Silicon-29 MAS and boron-11 MQMAS NMR spectra of two glasses (x = 0. 40 and 0. 80) have been acquired and theoretical spectra are found to well agree with the experimental data. For boron-11, the NMR parameter distributions have been analysed using a Kernel density estimation (KDE) approach which is shown to highlight its main features. Accordingly, a new analytical model that incorporates the observed correlations between the NMR parameters is introduced. It significantly improves the fit of the B-11 MQMAS spectra and yields, therefore, more reliable NMR parameter distributions. A new analytical model for a quantitative description of the dependence of the silicon-29 and boron-11 isotropic chemical shift upon the bond angles is proposed, which incorporates possibly the effect of SiO2-B2O3 intermixing. Combining all the above procedures, we show how distributio above procedures, we show how distributions of Si-O-T and B-O-T (T= Si, B) bond angles can be estimated from the distribution of isotropic chemical shift of silicon-29 and boron-11, respectively. (authors)

273

Characterization of coke by MAS 13C-NMR  

International Nuclear Information System (INIS)

The molecular architecture of coke is difficult to determine. Nuclear magnetic resonance spectroscopy allows one to understand the chemical environment or types of hydrogen and carbon in the sample. It is also possible to estimate the proportion of atoms in the various environments. Here, liquid-state and solid-state NMR have been used to characterize different series of feedstocks and coke samples. Liquid phase 13C NMR was used to analyse feeds and products separated by HPLC (PEW) in fractions called aliphatics, mono-, di-, tri-, and polyaromatics. An internal lock with deuterated chloroform was used due to the small amount of material present in each fraction. The NMR analysis gives the aromaticity and gives a nice correlation with the results obtained by GC/MS (average no of C-atoms in each fraction, chainlength, no. of substituents etc.). Structural features were gained by comparison of different fractions, while differences were seen, when feed and product were compared. For liquid samples, a model has been proposed in which the feed is supposed to be described as a mixture of six model compounds. Results concerning three series of feedstocks and the structural paramaters deduced from 13C and 1H NMR spectra are discussed and compared with the experimental data obtained from elemental analysis. In the solid state, by using Cross Polarization (CP) and Magic Angle Spinning (MAS), it is possible to obtain information on different carble to obtain information on different carbon structural types. Structural parameters, such as the aromaticity fa or the H/C ratio can be evaluated with a good reliability. (AB) (23 refs.)

274

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

275

Median Modified Wiener Filter for nonlinear adaptive spatial denoising of protein NMR multidimensional spectra.  

Science.gov (United States)

Denoising multidimensional NMR-spectra is a fundamental step in NMR protein structure determination. The state-of-the-art method uses wavelet-denoising, which may suffer when applied to non-stationary signals affected by Gaussian-white-noise mixed with strong impulsive artifacts, like those in multi-dimensional NMR-spectra. Regrettably, Wavelet's performance depends on a combinatorial search of wavelet shapes and parameters; and multi-dimensional extension of wavelet-denoising is highly non-trivial, which hampers its application to multidimensional NMR-spectra. Here, we endorse a diverse philosophy of denoising NMR-spectra: less is more! We consider spatial filters that have only one parameter to tune: the window-size. We propose, for the first time, the 3D extension of the median-modified-Wiener-filter (MMWF), an adaptive variant of the median-filter, and also its novel variation named MMWF*. We test the proposed filters and the Wiener-filter, an adaptive variant of the mean-filter, on a benchmark set that contains 16 two-dimensional and three-dimensional NMR-spectra extracted from eight proteins. Our results demonstrate that the adaptive spatial filters significantly outperform their non-adaptive versions. The performance of the new MMWF* on 2D/3D-spectra is even better than wavelet-denoising. Noticeably, MMWF* produces stable high performance almost invariant for diverse window-size settings: this signifies a consistent advantage in the implementation of automatic pipelines for protein NMR-spectra analysis. PMID:25619991

Cannistraci, Carlo Vittorio; Abbas, Ahmed; Gao, Xin

2015-01-01

276

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.)

277

Toward a description of the conformations of denatured states of proteins. Comparison of a random coil model with NMR measurements  

OpenAIRE

A strategy is proposed to describe the backbone conformations sampled in denatured states of proteins. Main chain dihedral angle distributions are extracted from the protein data base and used to predict NMR parameters such as coupling constants and NOE intensities. A simple model in which each residue samples its ?,? distribution noncooperatively has been found to reproduce many of the features of experimental NMR data for hen egg-white lysozyme denatured in 8 M urea at low pH. This model ...

Fiebig, Km; Schwalbe, H.; Buck, M.; Smith, Lj; Dobson, Cm

1996-01-01

278

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

OpenAIRE

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

279

NMR of superfluid 3He in anisotropic aerogel  

OpenAIRE

We report on orientation of the order parameter in the 3He-A and 3He-B phases caused by aerogel anisotropy. In 3He-A we have observed relatively homogeneous NMR line with an anomalously large negative frequency shift. We can attribute this effect to an orientation of orbital momentum along the axis of density anisotropy. The similar orientation effect we have seen in 3He-B. We can measure the A-phase Leggett frequency, which shows the same energy gap suppression as in the B-...

Kunimatsu, T.; Sato, T.; Izumina, K.; Matsubara, A.; Sasaki, Y.; Kubota, M.; Ishikawa, O.; Mizusaki, T.; Bunkov, Yu M.

2006-01-01

280

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; Pedersen, H.T.

1999-01-01

281

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

282

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

283

Preprocessing of NMR metabolomics data.  

Science.gov (United States)

Abstract Metabolomics involves the large scale analysis of metabolites and thus, provides information regarding cellular processes in a biological sample. Independently of the analytical technique used, a vast amount of data is always acquired when carrying out metabolomics studies; this results in complex datasets with large amounts of variables. This type of data requires multivariate statistical analysis for its proper biological interpretation. Prior to multivariate analysis, preprocessing of the data must be carried out to remove unwanted variation such as instrumental or experimental artifacts. This review aims to outline the steps in the preprocessing of NMR metabolomics data and describe some of the methods to perform these. Since using different preprocessing methods may produce different results, it is important that an appropriate pipeline exists for the selection of the optimal combination of methods in the preprocessing workflow. PMID:25738209

Euceda, Leslie R; Giskeødegård, Guro F; Bathen, Tone F

2015-05-01

284

High-resolution NMR imaging of mandibular joints, with special emphasis on soft tissue imaging  

International Nuclear Information System (INIS)

NMR imaging is the technique finally allowing good imaging of the soft tissue parts of the mandibular joint without recourse to surgery or ionizing radiation. Surface coils yield high-resolution images, and proper selection of tomographic parameters achieves excellent tissue contrast data without the use of positive or negative contrast media. (orig.)

285

Stereochemistry of tropane N-oxide derivatives studied by experimental and theoretical NMR.  

Czech Academy of Sciences Publication Activity Database

Frankfurt am Main : Cuvillier Verlag Göttingen, 2011. s. 279-279. [EUROMAR 2011. Magnetic Resonance Conference. 21.08.2011-25.08.2011, Frankfurt am Main] Institutional research plan: CEZ:AV0Z40550506 Keywords : stereochemistry * calculation of the NMR parameters * DFT GIAO Subject RIV: CC - Organic Chemistry

Pohl, Radek; Dra?ínský, Martin; Slav?tínská, Lenka; Bud?šínský, Miloš

286

Parameter Estimation  

DEFF Research Database (Denmark)

In this chapter the importance of parameter estimation in model development is illustrated through various applications related to reaction systems. In particular, rate constants in a reaction system are obtained through parameter estimation methods. These approaches often require the application of optimisation techniques coupled with dynamic solution of the underlying model. Linear and nonlinear approaches to parameter estimation are investigated. There is also the application of maximum likelihood principles in the estimation of parameters, as well as the use of orthogonal collocation to generate a set of algebraic equations as the basis for parameter estimation.These approaches are illustrated using estimations of kinetic constants from reaction system models.

Sales-Cruz, Mauricio; Heitzig, Martina

2011-01-01

287

Orientational order of two fluoro- and isothiocyanate-substituted nematogens by combination of 13C NMR spectroscopy and DFT calculations.  

Science.gov (United States)

Orientational order properties of two nematogens containing a fluoro- and isothiocyanate-substituted biphenyl moiety have been investigated by means of (13)C NMR spectroscopy. (13)C NMR spectra acquired on static samples under high-power (1)H-decoupling allowed both (13)C chemical shift anisotropies and (13)C-(19)F couplings to be measured. These data were used to determine the local principal order parameter and biaxiality for the different rigid fragments of the molecules. To this aim, advanced DFT methods for the calculation of geometrical parameters and chemical shift tensors were used. The orientational order parameters obtained by NMR have been critically compared with those obtained by dielectric spectroscopy. Trends of order parameters with temperature have been analyzed in terms of both mean field theory and the empirical Haller equation. PMID:24605890

Calucci, Lucia; Carignani, Elisa; Geppi, Marco; Macchi, Sara; Mennucci, Benedetta; Urban, Stanislaw

2014-03-27

288

Setting the anomeric effect against steric effects in simple acyclic acetals. Non-anomeric non-classical conformations. An n.m.r. and molecular mechanics investigation  

DEFF Research Database (Denmark)

N.m.r. parameters for a series of simple aliphatic acetals indicate that the preferred conformation changes from the anomeric one found in formaldehyde dimethyl acetal (formal), to a new one whose structure is suggested by molecular mechanics calculations.

Anderson, J. Edgar; Heki, Katsuhiko

1987-01-01

289

NMR data handbook for biomedical applications  

International Nuclear Information System (INIS)

The text is divided into 10 chapters, each of which covers a specific block of material and has its own references. The volume is meant to serve as a laboratory handbook and a desk reference, containing basic NMR theory, useful formulae and physical constants, and compiled data from the NMR literature. The volume attempts to cover the development of biological NMR through several decades of in vitro experiments that have laid the groundwork for and pointed to profitable areas of investigation for new in vivo techniques

290

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

291

Graphical programming for pulse automated NMR experiments  

Energy Technology Data Exchange (ETDEWEB)

We describe a software program designed to control a broadband pulse Nuclear Magnetic Resonance (NMR) spectrometer used in zero-field NMR studies of magnetic metals. The software is written in the graphical language LabVIEW. This type of programming allows modifications and the inclusion of new routines to be easily made by the non-specialist, without changing the basic structure of the program. The program corrects for differences in the gain of the two acquisition channels [U (phase) and V (quadrature)], and automatic baseline subtraction. We present examples of measurements of NMR spectra, spin-echo decay (T{sub 2}), and quadrupolar oscillations, performed in magnetic intermetallic compounds. (author)

Belmonte, S.B. [Universidade do Estado, Rio de Janeiro, RJ (Brazil); Oliveira, I.S.; Guimaraes, A.P. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)

1999-01-01

292

The characterisation of polymers using pulsed NMR  

International Nuclear Information System (INIS)

Broad line pulsed NMR is applied to obtain information on radiation-induced polymer changes and other aspects of polymer science based on the interpretation of spin-spin relaxation curves. Calculations are made to determine the molecular weight, the crosslink density of simple, low molecular weight, flexible polymers. For higher molecular weight polymers, a conclusion can be drawn on the concentrations of entangled and crosslinked units by means of pulsed NMR. Some typical applications of the technique are illustrated by the examples of polyethylenes, rubbers, filled polymeric systems and aqueous polyethylene oxide solutions. The morphology of polymers can be followed by pulsed NMR. (V.N.)

293

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

294

Graphical programming for pulse automated NMR experiments  

International Nuclear Information System (INIS)

We describe a software program designed to control a broadband pulse Nuclear Magnetic Resonance (NMR) spectrometer used in zero-field NMR studies of magnetic metals. The software is written in the graphical language LabVIEW. This type of programming allows modifications and the inclusion of new routines to be easily made by the non-specialist, without changing the basic structure of the program. The program corrects for differences in the gain of the two acquisition channels [U (phase) and V (quadrature)], and automatic baseline subtraction. We present examples of measurements of NMR spectra, spin-echo decay (T2), and quadrupolar oscillations, performed in magnetic intermetallic compounds. (author)

295

Graphical programming for broadband pulse NMR spectroscopy  

International Nuclear Information System (INIS)

In a broadband pulsed nuclear magnetic resonance (NMR) spectrometer we often need to sweep the excitation frequency over a wide range, and acquire the spin echo components in quadrature for further spectral analysis. Computer languages such as C or Pascal have been traditionally applied to the development of software control of laboratory equipment, and consequently, the automatization of NMR experiments. However, the use of graphical languages have proved to be a flexible and convenient way for experiment and data acquisition control. In our application we use the graphical language Labview for the automatic control of a broadband pulse NMR spectrometer, dedicated to the study of magnetic metal systems. (author)

296

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

297

NMR Analog of Bell's Inequalities Violation Test  

CERN Document Server

In this paper we present an analog of a Bell's inequalities violation test for N qubits to be performed in a nuclear magnetic resonance (NMR) quantum computer. To demonstrate our scheme, we implemented the first simulation of the violation of Clauser, Horne, Shimony and Holt (CHSH) inequality using a two qubit NMR system and compared the results to those of a photon experiment. The experimental results are well described by both, a Local Realistic Hidden Variables model, developed for NMR, and Quantum Mechanics theory. Our scheme can be used to simulate or predict results for different Bell's inequalities tests, with distinct configurations and larger number of qubits.

Souza, A M; Teles, J; deAzevedo, E R; Bonagamba, T J; Oliveira, I S; Sarthour, R S

2007-01-01

298

Structural investigations of substituted indolizine derivatives by NMR studies  

International Nuclear Information System (INIS)

Owing to the increasing importance of indolizine heterocycles in the field of biology and pharmacology we have synthesized and investigated the obtained heterocycles by NMR techniques. In order to investigate the substituent effects on the spectroscopic properties, a series of indolizine derivatives were studied by 1H-NMR, 13C-NMR and 2D NMR (GCOSY, GHMBC and GHMQC spectra). (authors)

299

The Corset Effect, Field-Cycling NMR Relaxometry, Transverse NMR Relaxation, Field-Gradient NMR Diffusometry, and Incoherent Neutron Scattering  

OpenAIRE

The corset effect is an experimentally established dynamic confinement phenomenon first observed by field-cycling NMR relaxometry and transverse NMR relaxation in polymer melts in pores with dimensions ranging from a few nanometers up to 0.06 micrometers or even more. The techniques employed are specifically sensitive to rotational fluctuations of polymer segments. It will be shown that neutron scattering and other methods probing translational fluctuations are not suitable ...

Kimmich, Rainer; Fatkullin, Nail

2010-01-01

300

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

301

ADAPT-NMR Enhancer: complete package for reduced dimensionality in protein NMR spectroscopy  

OpenAIRE

Summary: ADAPT-nuclear magnetic resonance (ADAPT-NMR) offers an automated approach to the concurrent acquisition and processing of protein NMR data with the goal of complete backbone and side chain assignments. What the approach lacks is a useful graphical interface for reviewing results and for searching for missing peaks that may have prevented assignments or led to incorrect assignments. Because most of the data ADAPT-NMR collects are 2D tilted planes used to find peaks in 3...

Lee, Woonghee; Bahrami, Arash; Markley, John L.

2012-01-01

302

Validation of quantitative 1H NMR method for the analysis of pharmaceutical formulations  

International Nuclear Information System (INIS)

The need for effective and reliable quality control in products from pharmaceutical industries renders the analyses of their active ingredients and constituents of great importance. This study presents the theoretical basis of ¹H NMR for quantitative analyses and an example of the method validation according to Resolution RE N. 899 by the Brazilian National Health Surveillance Agency (ANVISA), in which the compound paracetamol was the active ingredient. All evaluated parameters (selectivity, linearity, accuracy, repeatability and robustness) showed satisfactory results. It was concluded that a single NMR measurement provides structural and quantitative information of active components and excipients in the sample. (author)

303

Grape juice quality control by means of ¹H nmr spectroscopy and chemometric analyses  

Scientific Electronic Library Online (English)

Full Text Available This work shows the application of ¹H NMR spectroscopy and chemometrics for quality control of grape juice. A wide range of quality assurance parameters were assessed by single ¹H NMR experiments acquired directly from juice. The investigation revealed that conditions and time of storage should be r [...] evised and indicated on all labels. The sterilization process of homemade grape juices was efficient, making it possible to store them for long periods without additives. Furthermore, chemometric analysis classified the best commercial grape juices to be similar to homemade grape juices, indicating that this approach can be used to determine the authenticity after adulteration.

Caroline Werner Pereira da Silva, Grandizoli; Francinete Ramos, Campos; Fabio, Simonelli; Andersson, Barison.

1227-12-01

304

29Si NMR and hidden order in URu2Si2.  

Science.gov (United States)

Below T(N) approximately 17 K the 29Si NMR line in URu2Si2 exhibits a previously unobserved field-independent nearly isotropic contribution to the linewidth, which increases to approximately 12 G as T-->0. We argue that this feature does not arise from static freezing of the U-spin magnetization, but is due to coupling between 29Si spins and a hidden order parameter. We discuss time-reversal symmetry-breaking orbital antiferromagnetism and indirect nuclear spin-spin interactions as possible coupling mechanisms. Further NMR experiments and theoretical calculations are suggested. PMID:11690437

Bernal, O O; Rodrigues, C; Martinez, A; Lukefahr, H G; MacLaughlin, D E; Menovsky, A A; Mydosh, J A

2001-11-01

305

Parameter libraries  

International Nuclear Information System (INIS)

Full text: Recommendations for future parameter libraries: 1. The existing parameter library should be updated, extended and corrected regularly based on the latest measurements, evaluations and theoretical studies by international collaborations (through CRPs or other activities). What parts of the parameter library to be updated and corrected should be taken into account in setting up the activity. 2. New parameters should be added according to the new mechanisms or approaches introduced in the nuclear reaction model code and the updated results from nuclear theory studies. 3. Information on the range of parameters, especially for nuclear reaction model parameters used for covariance evaluations and sensitivity studies of nuclear data should be recommended. The information which can be used for this purpose should be considered based on the nuclear reaction models such like OM, DWBA, H-F and exciton model, etc. which are popular in the nuclear reaction model codes. 4. The model parameters (global and local) and related information for the unstable nuclei model calculations should be recommended and the uncertainties from the parameters for the model calculations of unstable nuclei should be studied and analyzed. 5. If some parameter systematics could be provided, it would help the nuclear data evaluators and nuclear data users to perform the model calculations. 6. CRPs and collaborations should be considered to address the above items. (author)bove items. (author)

306

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

307

Epitope mapping by solution NMR spectroscopy.  

Science.gov (United States)

Antibodies play an ever more prominent role in basic research as well as in the biotechnology and pharmaceutical sectors. Characterizing their epitopes, that is, the region that they recognize on their target molecule, is useful for purposes ranging from molecular biology research to vaccine design and intellectual property protection. Solution NMR spectroscopy is ideally suited to the atomic level characterization of intermolecular interfaces and, as a consequence, to epitope discovery. Here, we illustrate how NMR epitope mapping can be used to rapidly and accurately determine protein antigen epitopes. The basic concept is that differences in the NMR signal of an antigen free or bound by an antibody will identify epitope residues. NMR epitope mapping provides more detailed information than mutagenesis or peptide mapping and can be much more rapid than X-ray crystallography. Advantages and drawbacks of this technique are discussed together with practical considerations. Copyright © 2015 John Wiley & Sons, Ltd. PMID:25726811

Bardelli, M; Livoti, E; Simonelli, L; Pedotti, M; Moraes, A; Valente, A P; Varani, L

2015-06-01

308

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

309

A 2H NMR study on biosynthesis  

International Nuclear Information System (INIS)

A 2H NMR study on griseofulvin reports evidence of participation of medium water into the methlyl group of chain-starter, with use of various kinds of acetate precursors, as a result of hydrogen exchange. (Auth.)

310

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)

311

A new laboratory approach to shale analysis using NMR relaxometry  

Science.gov (United States)

Low-field nuclear magnetic resonance (LF-NMR) relaxometry is a non-invasive technique commonly used to assess hydrogen-bearing fluids in petroleum reservoir rocks. Measurements made using LF-NMR provide information on rock porosity, pore-size distributions, and in some cases, fluid types and saturations (Timur, 1967; Kenyon et al., 1986; Straley et al., 1994; Brown, 2001; Jackson, 2001; Kleinberg, 2001; Hurlimann et al., 2002). Recent improvements in LF-NMR instrument electronics have made it possible to apply methods used to measure pore fluids to assess highly viscous and even solid organic phases within reservoir rocks. T1 and T2 relaxation responses behave very differently in solids and liquids; therefore the relationship between these two modes of relaxation can be used to differentiate organic phases in rock samples or to characterize extracted organic materials. Using T1-T2 correlation data, organic components present in shales, such as kerogen and bitumen, can be examined in laboratory relaxometry measurements. In addition, implementation of a solid-echo pulse sequence to refocus T2 relaxation caused by homonuclear dipolar coupling during correlation measurements allows for improved resolution of solid-phase protons. LF-NMR measurements of T1 and T2 relaxation time distributions were carried out on raw oil shale samples from the Eocene Green River Formation and pyrolyzed samples of these shales processed by hydrous pyrolysis and techniques meant to mimic surface and in-situ retorting. Samples processed using the In Situ Simulator approach ranged from bitumen and early oil generation through to depletion of petroleum generating potential. The standard T1-T2 correlation plots revealed distinct peaks representative of solid- and liquid-like organic phases; results on the pyrolyzed shales reflect changes that occurred during thermal processing. The solid-echo T1 and T2 measurements were used to improve assessment of the solid organic phases, specifically kerogen, thermally degraded kerogen, and char. Integrated peak areas from the LF-NMR results representative of kerogen and bitumen were found to be well correlated with S1 and S2 parameters from Rock-Eval programmed pyrolysis. This study demonstrates that LFNMR relaxometry can provide a wide range of information on shales and other reservoir rocks that goes well beyond porosity and pore-fluid analysis.

Washburn, Kathryn E.; Birdwell, Justin E.

2013-01-01

312

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

313

NMR mechanisms in gel dosimetry  

Science.gov (United States)

Nuclear magnetic resonance was critical to the development of gel dosimetry, as it established the potential for three dimensional dosimetry with chemical dosimeter systems through magnetic resonance imaging [1]. In the last two decades MRI has served as the gold standard for imaging, while NMR relaxometry has played an important role in the development and understanding of the behaviour of new gel dosimetry systems. Therefore, an appreciation of the relaxation mechanisms determining the NMR behaviour of irradiated gel dosimeters is important for a full comprehension of a considerable component of the literature on gel dosimetry. A number of excellent papers have presented this important theory, this brief review will highlight some of the salient points made previously [1-5]. The spin relaxation of gel dosimeters (which determines the dose dependence in most conventional MR imaging) is determined principally by the protons on water molecules in the system. These water protons exist in different environments, or groups (see Figure 1): on bulk water, on water hydrating the chemical species that are being modified under irradiation, and on water hydrating the gel matrix used to spatially stabilize the dosimeter (e.g., gelatin, agarose, etc). The spin relaxation depends on the inherent relaxation rate of each spin group, that is, on the relaxation rate which would be observed for the specific group if it were isolated. Also, the different water environments are not isolated from each other, and the observed relaxation rate also depends on the rate of exchange of magnetization between the groups, and on the fraction of protons in each group. In fact, the water exchanges quickly between the environments, so that relaxation is in what is usually termed the fast exchange regime. In the limit of fast exchange, the relaxation of the water protons is well characterized by a single exponential and hence by a single apparent relaxation rate. In irradiated gel dosimeters this observed rate is a function of the absorbed dose. In this review I will first develop the fast exchange model for the spin lattice relaxation Fricke gel dosimeter system, as this is conceptually the simpler system. Fundamental concepts such as relaxivity (which specifies the ability of some species to enhance the relaxation of water protons) and chemical yield will be presented. The linear dose relationship for Fricke gel dosimeters, and the reduced dose sensitivity of Fricke dosimeters containing chelators, will be explained. The model will then be extended to the spin-spin relaxation of polymer gel systems and the main differences discussed. The reasons for the enhanced dose sensitivy and dynamic range for spin-spin (R2) rather than spin-lattice (R1) relaxation will be presented.

Schreiner, L. J.

2009-05-01

314

NMR Analog of Bell's Inequalities Violation Test  

OpenAIRE

In this paper we present an analog of the Bell's inequalities violation test for $N$ qubits to be performed in a nuclear magnetic resonance (NMR) quantum computer. This can be used to simulate or predict results for different Bell's inequalities tests, with distinct configurations and larger number of qubits. To demonstrate our scheme, we implemented a simulation of the violation of Clauser, Horne, Shimony and Holt (CHSH) inequality using a two qubit NMR system and compared ...

Souza, A. M.; Magalhaes, A.; Teles, J.; Deazevedo, E. R.; Bonagamba, T. J.; Oliveira, I. S.; Sarthour, R. S.

2007-01-01

315

Recent advances in SQUID NMR techniques  

International Nuclear Information System (INIS)

A discussion of the techniques used for performing a variety of magnetic resonance experiments using a SQUID is presented. In particular, measurements of the nuclear magnetism of liquid 3He in the temperature range 1.2 K to 2 mK in magnetic fields of 3.7 to 309 Oe using pulsed NMR, c-w NMR, adiabatic fast passage, and static susceptibility using the same detection system are discussed

316

Statistical filtering for NMR based structure generation  

OpenAIRE

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...

Junker Jochen

2011-01-01

317

Copper trafficking in biology: an NMR approach  

OpenAIRE

Copper ions are essential for living organisms because they are involved in several fundamental biological processes. Biomolecules interacting with copper ions have to be characterized as such, when bound to the metal ion, and when they interact with other biomolecules or substrates. The characterization is both structural and dynamic. In this context, NMR is a preferred tool of investigation because it allows shedding light on what happens in solution. Here, the NMR contribution to the coppe...

Banci, Lucia; Bertini, Ivano; Ciofi-baffoni, Simone

2009-01-01

318

Modern NMR spectroscopy: a guide for chemists  

International Nuclear Information System (INIS)

The aim of the authors of Modern NMR Spectroscopy is to bridge the communication gap between the chemist and the spectroscopist. The approach is nonmathematical, descriptive, and pictorial. To illustrate the ideas introduced in the text, the authors provide original spectra obtained specially for this purpose. Examples include spectroscopy of protons, carbon, and less receptive nuclei of interest to inorganic chemists. The authors succeed in making high-resolution NMR spectroscopy comprehensible for the average student or chemist

319

Frontiers of NMR in Molecular Biology  

Energy Technology Data Exchange (ETDEWEB)

NMR spectroscopy is expanding the horizons of structural biology by determining the structures and describing the dynamics of blobular proteins in aqueous solution, as well as other classes of proteins including membrane proteins and the polypeptides that form the aggregates diagnostic of prion and amyloid diseases. Significant results are also emerging on DNA and RNA oligomers and their complexes with proteins. This meeting focused attention on key structural questions emanating from molecular biology and how NMR spectroscopy can be used to answer them.

NONE

1999-08-25

320

Annual Reports on NMR Spectroscopy. Volume 58  

OpenAIRE

A novel NMR technique for imaging materials exhibiting extremely short T2 relaxation times is described and some examples of its application to materials of scientific and industrial interest are presented. The technique employs continuous wave (CW) radiofrequency irradiation of the sample together with continual detection, and thus the experimental deadtime inherent in pulsed techniques is effectively eliminated. The mechanisms which broaden the NMR linewidths of materials in the solid state...

Fagan, Andrew John

2005-01-01

321

Scalable NMR Spectroscopy with Semiconductor Chips  

OpenAIRE

Conventional nuclear magnetic resonance (NMR) spectrometers—the electronic brain that orchestrates and monitors nuclear spin motions—are bulky, expensive, thus, not scalable. In this thesis, we report on scalable 4-mm2 silicon spectrometer chips that perform a broad range of two-dimensional NMR spectroscopy—e.g., correlation spectroscopy, J-resolved spectroscopy, and heteronuclear quantum coherence spectroscopy—as well as one-dimensional spectroscopy and relaxometry. I...

Ha, Dongwan

2014-01-01

322

Theoretical NMR correlations based Structure Discussion  

OpenAIRE

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 ...

Junker Jochen

2011-01-01

323

The Quiet Renaissance of Protein NMR  

OpenAIRE

From roughly 1985 through the start of the new millennium, the cutting edge of solution protein nuclear magnetic resonance (NMR) spectroscopy was to a significant extent driven by the aspiration to determine structures. Here we survey recent advances in protein NMR that herald a renaissance in which a number of its most important applications reflect the broad problem-solving capability displayed by this method during its classical era during the 1970s and early 80s. “Without receivers f...

Barrett, Paul J.; Chen, Jiang; Cho, Min-kyu; Kim, Ji-hun; Lu, Zhenwei; Mathew, Sijo; Peng, Dungeng; Song, Yuanli; Horn, Wade D.; Zhuang, Tiandi; So?nnichsen, Frank D.; Sanders, Charles R.

2013-01-01

324

Exploiting periodic first-principles calculations in NMR spectroscopy of disordered solids.  

Science.gov (United States)

Much of the information contained within solid-state nuclear magnetic resonance (NMR) spectra remains unexploited because of the challenges in obtaining high-resolution spectra and the difficulty in assigning those spectra. Recent advances that enable researchers to accurately and efficiently determine NMR parameters in periodic systems have revolutionized the application of density functional theory (DFT) calculations in solid-state NMR spectroscopy. These advances are particularly useful for experimentalists. The use of first-principles calculations aids in both the interpretation and assignment of the complex spectral line shapes observed for solids. Furthermore, calculations provide a method for evaluating potential structural models against experimental data for materials with poorly characterized structures. Determining the structure of well-ordered, periodic crystalline solids can be straightforward using methods that exploit Bragg diffraction. However, the deviations from periodicity, such as compositional, positional, or temporal disorder, often produce the physical properties (such as ferroelectricity or ionic conductivity) that may be of commercial interest. With its sensitivity to the atomic-scale environment, NMR provides a potentially useful tool for studying disordered materials, and the combination of experiment with first-principles calculations offers a particularly attractive approach. In this Account, we discuss some of the issues associated with the practical implementation of first-principles calculations of NMR parameters in solids. We then use two key examples to illustrate the structural insights that researchers can obtain when applying such calculations to disordered inorganic materials. First, we describe an investigation of cation disorder in Y2Ti(2-x)Sn(x)O7 pyrochlore ceramics using (89)Y and (119)Sn NMR. Researchers have proposed that these materials could serve as host phases for the encapsulation of lanthanide- and actinide-bearing radioactive waste. In a second example, we discuss how (17)O NMR can be used to probe the dynamic disorder of H in hydroxyl-humite minerals (nMg2SiO4·Mg(OH)2), and how (19)F NMR can be used to understand F substitution in these systems. The combination of first-principles calculations and multinuclear NMR spectroscopy facilitates the investigation of local structure, disorder, and dynamics in solids. We expect that applications will undoubtedly become more widespread with further advances in computational and experimental methods. Insight into the atomic-scale environment is a crucial first step in understanding the structure-property relationships in solids, and it enables the efficient design of future materials for a range of end uses. PMID:23402741

Ashbrook, Sharon E; Dawson, Daniel M

2013-09-17

325

Uniform procedure of (1)H NMR analysis of rat urine and toxicometabonomics Part II: comparison of NMR profiles for classification of hepatotoxicity.  

Science.gov (United States)

A procedure of nuclear magnetic resonance (NMR) urinalysis using pattern recognition is proposed for early detection of toxicity of investigational compounds in rats. The method is applied to detect toxicity upon administration of 13 toxic reference compounds and one nontoxic control compound (mianserine) in rats. The toxic compounds are expected to induce necrosis (bromobenzene, paracetamol, carbon tetrachloride, iproniazid, isoniazid, thioacetamide), cholestasis (alpha-naphthylisothiocyanate (ANIT), chlorpromazine, ethinylestradiol, methyltestosterone, ibuprofen), or steatosis (phenobarbital, tetracycline). Animals were treated daily for 2 or 4 days except for paracetamol and bromobenzene (1 and 2 days) and carbon tetrachloride (1 day only). Urine was collected 24 h after the first and second treatment. The animals were sacrificed 24 h after the last treatment, and NMR data were compared with liver histopathology as well as blood and urine biochemistry. Pathology and biochemistry showed marked toxicity in the liver at high doses of bromobenzene, paracetamol, carbon tetrachloride, ANIT, and ibuprofen. Thioacetamide and chlorpromazine showed less extensive changes, while the influences of iproniazid, isoniazid, phenobarbital, ethinylestradiol, and tetracycline on the toxic parameters were marginal or for methyltestosterone and mianserine negligible. NMR spectroscopy revealed significant changes upon dosing in 88 NMR biomarker signals preselected with the Procrustus Rotation method on principal component discriminant analysis (PCDA) plots. Further evaluation of the specific changes led to the identification of biomarker patterns for the specific types of liver toxicity. Comparison of our rat NMR PCDA data with histopathological changes reported in humans and/or rats suggests that rat NMR urinalysis can be used to predict hepatotoxicity. PMID:17420222

Schoonen, Willem G E J; Kloks, Cathelijne P A M; Ploemen, Jan-Peter H T M; Smit, Martin J; Zandberg, Pieter; Horbach, G Jean; Mellema, Jan-Remt; Thijssen-Vanzuylen, Carol; Tas, Albert C; van Nesselrooij, Joop H J; Vogels, Jack T W E

2007-07-01

326

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

327

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

328

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.)

329

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)

330

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)

331

63,65Cu NMR Method in a Local Field for Investigation of Copper Ore Concentrates  

Science.gov (United States)

To choose the most efficient method and ore beneficiation flow diagram, it is important to know physical and chemical properties of ore concentrates. The feasibility of application of the 63,65Cu nuclear magnetic resonance (NMR) method in a local field aimed at studying the properties of copper ore concentrates in the copper-iron-sulfur system is demonstrated. 63,65Cu NMR spectrum is measured in a local field for a copper concentrate sample and relaxation parameters (times T1 and T2) are obtained. The spectrum obtained was used to identify a mineral (chalcopyrite) contained in the concentrate. Based on the experimental data, comparative characteristics of natural chalcopyrite and beneficiated copper concentrate are given. The feasibility of application of the NMR method in a local field to explore mineral deposits is analyzed.

Gavrilenko, A. N.; Starykh, R. V.; Khabibullin, I. Kh.; Matukhin, V. L.

2015-01-01

332

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

333

A simulated annealing approach for solving zeolite crystal structures from two-dimensional NMR correlation spectra.  

Science.gov (United States)

An improved NMR crystallography strategy is presented for determining the structures of network materials such as zeolites from just a single two-dimensional (2D) NMR correlation spectrum that probes nearest-neighbor interactions, combined with the unit cell parameters and space group information measured in a diffraction experiment. The correlation information contained within a 2D spectrum is converted into a "connectivity matrix" which is incorporated into a cost function whose minimum is searched for using a simulated annealing algorithm. The algorithm was extensively tested on over 150 zeolite frameworks from the International Zeolite Association database of zeolite structures and shown to be very robust and efficient in reconstructing the structures from connectivity information. The structure determination of the pure silica zeolites ITQ-4, Ferrierite, and Sigma-2 from experimental 2D (29)Si double-quantum NMR spectra and powder X-ray diffraction data using this improved approach is also presented. PMID:25466355

Brouwer, Darren H; Horvath, Matthew

2015-02-01

334

Probing acid-amide intermolecular hydrogen bonding by NMR spectroscopy and DFT calculations  

Science.gov (United States)

Benzene carboxylic acids and benzamide act as their self-complement in molecular recognition to form inter-molecular hydrogen bonded dimers between amide and carboxylic acid groups, which have been investigated by 1H, 13C and 15N NMR spectroscopy. Extensive NMR studies using diffusion ordered spectroscopy (DOSY), variable temperature 1D, 2D NMR, established the formation of heterodimers of benzamide with benzoic acid, salicylic acid and phenyl acetic acid in deuterated chloroform solution. Association constants for the complex formation in the solution state have been determined. The results are ascertained by X-ray diffraction in the solid state. Intermolecular interactions in solution and in solid state were found to be similar. The structural parameters obtained by X-ray diffraction studies are compared with those obtained by DFT calculations.

Chaudhari, Sachin Rama; Suryaprakash, N.

2012-05-01

335

DFT calculation of structures and NMR chemical shifts of simple models of small diameter zigzag single wall carbon nanotubes (SWCNTs).  

Science.gov (United States)

Linearly conjugated benzene rings (acenes), belt-shape molecules (cyclic acenes) and model single wall carbon nanotubes (SWCNTs) were fully optimized at the unrestricted level of density functional theory (UB3LYP/6-31G*). The models of SWCNTs were selected to get some insight into the potential changes of NMR chemical shift upon systematic increase of the molecular size. The theoretical NMR chemical shifts were calculated at the B3LYP/pcS-2 level of theory using benzene as reference. In addition, the change of radial breathing mode (RBM), empirically correlated with SWCNT diameter, was directly related with the radius of cyclic acenes. Both geometrical and NMR parameters were extrapolated to infinity upon increase in the studied systems size using a simple two-parameter mathematical formula. Very good agreement between calculated and available experimental CC bond lengths of acenes was observed (RMS of 0.0173 Å). The saturation of changes in CC bond lengths and (1)H and (13)C NMR parameters for linear and cyclic acenes, starting from 7-8 conjugated benzene rings, was observed. The (13)C NMR parameters of individual carbon atoms from the middle of ultra-thin (4,0) SWCNT formed from 10 conjugated cyclic acenes differ by about 130 ppm from the corresponding open end carbon nuclei. PMID:21815210

Kupka, Teobald; Stachów, Micha?; Nieradka, Marzena; Stobi?ski, Leszek

2011-09-01

336

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.

337

Early non-destructive biofouling detection in spiral wound RO Membranes using a mobile earth's field NMR  

KAUST Repository

We demonstrate the use of Earth\\'s field (EF) Nuclear Magnetic Resonance (NMR) to provide early non-destructive detection of active biofouling of a commercial spiral wound reverse osmosis (RO) membrane module. The RO membrane module was actively biofouled to different extents, by the addition of biodegradable nutrients to the feed stream, as revealed by a subtle feed-channel pressure drop increase. Easily accessible EF NMR parameters (signal relaxation parameters T1, T2 and the total NMR signal modified to be sensitive to stagnant fluid only) were measured and analysed in terms of their ability to detect the onset of biofouling. The EF NMR showed that fouling near the membrane module entrance significantly distorted the flow field through the whole membrane module. The total NMR signal is shown to be suitable for non-destructive early biofouling detection of spiral wound membrane modules, it was readily deployed at high (operational) flow rates, was particularly sensitive to flow field changes due to biofouling and could be deployed at any position along the membrane module axis. In addition to providing early fouling detection, the mobile EF NMR apparatus could also be used to (i) evaluate the production process of spiral wound membrane modules, and (ii) provide an in-situ determination of module cleaning process efficiency.

Vogt, S.J.

2015-04-20

338

Multi-probe magnetometer for the spatial and temporal analysis of the field of magnets used in NMR imaging  

International Nuclear Information System (INIS)

The spatial and temporal analysis of the magnetic field of magnets used in NMR is realised by a NMR multi-probe magnetometer whose orders are managed by a PC. The interface between the PC and the magnetometer call fact to a general-purpose acquisition card piloted by a program developed under Labview. After excitation of the selected probe, a NMR signal is acquired by the card, treated by the PC, and characteristic parameters of the temporal evolution of the signal frequency are extracted by parametric identification. One deduces the temporal evolution of the field to the place of the probe. A line of the space is swept by selecting successively probes, whose totality can also displace inside the magnet to change the line to explore. The equipment has been developed to analyse the drift of the gradients of field in a cryogenic magnet at 2 Tesla used in experimental NMR. (authors)

339

NMR probing of structural peculiarities in ionic solutions close to critical point.  

Science.gov (United States)

(1)H, (23)Na, (35)Cl, (79)Br, and (81)Br NMR chemical shifts (delta) and signal half widths (Delta(12)) have been measured in aqueous electrolyte mixtures [tetrahydrofuran/H(2)ONaCl and 3-methylpyridine (3MP)H(2)ONaBr] at different mass fractions of salt (X) in the one-phase region, close to their lower critical solution points (T(CL)). Discontinuous changes in slope of delta=f(X) and Delta(12)=f(X) have been found in (23)Na and (81)Br NMR spectra of 3MP/water/NaBr solution at X approximately 0.1 and T=301 K. The dependency of (1)H NMR signals of 3MP is continuous over the whole investigated range of X=0.002-0.2, whereas changes in the slope of H(2)O chemical shifts are hardly noticeable. In the two-phase region, i.e., at T>T(CL), a doubling of all NMR signals has been observed. The sensitivity of NMR parameters depends more on composition of solution for anions (Cl(-) and Br(-)) than for cations (Na(+)). A very strong relaxation effect for (81)Br nuclei with relaxation rates reaching 14 000 s(-1) was observed. The results are interpreted in terms of ion-molecular clustering and changes in coherency of dipole configurations of water molecules during supramolecular restructuring of solutions. PMID:16375485

Balevicius, Vytautas; Gdaniec, Zofia; Fuess, Hartmut

2005-12-01

340

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

341

NMR techniques in the study of cardiovascular structure and functions  

International Nuclear Information System (INIS)

The chapter titles of this book are: Introduction to NMR Techniques;Theory of NMR Probe Design;Overview of Magnetic Resonance Imaging to Study the Cardiovascular System;Vascular Anatomy and Physiology Studied with NMR Techniques;Assessment of Myocardial Ischemia and Infarction by Nuclear Magnetic Resonance Imaging;The Use of MRI in Congenital Heart Disease;Cardiomyopathies and Myocarditis Studied with NMR Techniques;Determination of Myocardial Mechanical Function with Magnetic Resonance Imaging Techniques;Determination of Flow Using NMR Techniques;The Use of Contrast Agents in Cardiac MRI;Can Cardiovascular Disease Be Effectively Evaluated with NMR Spectroscopy? NMR Studies of ATP Synthesis Reactions in the Isolated Heart;Studies of Intermediary Metabolism in the Heart by 13C NMR Spectroscopy;23Na and 39K NMR Spectroscopic Studies of the Intact Beating Heart;and Evaluation of Skeletal Muscle Metabolism in Patients with Congestive Heart Failure Using Phosphorus Nuclear Magnetic Resonance

342

Gallium doped in armchair and zigzag models of boron phosphide nanotubes (BPNTs): A NMR study  

International Nuclear Information System (INIS)

The electrical properties and NMR parameters of the pristine and Ga-doped structures of two representative (8, 0) zigzag and (4, 4) armchair of boron phosphide nanotubes (BPNTs) have been investigated. The structural geometries of above nanotubes have been allowed to relax by optimization and then the isotropic and anisotropic chemical shielding parameters (CSI and CSA) of 11B and 31P have been calculated based on DFT theory. The results reveal that the influence of Ga-doping was more significant on the geometries of the zigzag model than the armchair one. The difference of band gap energies between the pristine and Ga-doped armchair BPNTs was larger than the zigzag model. Significant differences of NMR parameters of those nuclei directly contributed to the Ga-doping atoms have been observed.

343

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

344

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

345

Computational techniques for the simulation and evaluation of hydrogen NMR imaging methods  

International Nuclear Information System (INIS)

Nuclear Magnetic Resonance Imaging of protons has become an imaging modality of proven diagnostic utility. The efficacy of the technique lies in the dependence of the NMR signal intensity on multiple parameters. The signal will depend on the intrinsic properties of the tissue, i.e., hydrogen density N(H), and the parameters characterizing relaxation, T1 and T2 and acquisition parameters, i.e., the interval between excitations, TR, and the delay between excitation and signal readout, TE. These multiple dependences provide the flexibility and therefore the potential of NMR imaging as well as the complexity involved in understanding and optimizing imaging methods. This dissertation describes techniques for evaluating the impact of these variables on image signal intensity and contrast. The NMR signal intensity is modeled for spin echo and inversion recovery imaging protocols by finding the solution to the Bloch equations under the boundary conditions imposed by the sequence. These equations describe the motion of the bulk magnetization in response to magnetic stimulations. The models are used to generate contour maps which illustrate the functional behavior of the response as two or more parameters change. These maps can be used to predict the useful imaging regime for best contrast between the tissue of interest and its surrounding background tissue. With an acquired set of data sufficient to extract hydrogen density and relaxation information, it is possible to calculaion information, it is possible to calculate images at new acquisition parameters

346

Application of site-specific natural isotope fractionation (SNIF-NMR) of hydrogen to the characterization of European beers  

International Nuclear Information System (INIS)

More than one hundred samples of European beers have been investigated by the new SNIF-NMR method which is based on 2H NMR at the natural abundance level and enables site-specific natural isotope fractionation factors in ethanol to be determined. The relative (R) and absolute (D/H)sub(i) parameters are shown to be characteristic of the country where the beers are brewed and the observed variations are explained in terms of cereal composition, water resource, and manufacturing processing (fermentation, yeast, temperature cycle). These new parameters find analytical and mechanistic applications in the identification of a beer and in the investigation of a fermentation process. (author)

347

Optimization of CPMG sequences for NMR borehole measurements  

Directory of Open Access Journals (Sweden)

Full Text Available Nuklear Magnetic Resonance (NMR can provide key information such as porosity and permeability for hydrological characterization of geological material. Especially the NMR transverse relaxation time T2 is used to estimate permeability since it reflects a pore-size dependent relaxation process. The measurement sequence (CPMG usually used consists of several thousands of electromagnetic pulses to densely record the relaxation process. These pulses are equidistantly spaced by a time constant ?. In NMR borehole applications the use of CPMG sequences for measuring the transverse relaxation time T2 is limited due to requirements on energy consumption. It is state of the art to conduct at least two sequences with different echo spacings (? for recording fast and slow relaxing processes that correspond to different pore-sizes. For the purpose to reduce the amount of energy used for conducting CPMG sequences and to obtain both, slow and fast, decaying components within one sequence we tested the usage of CPMG sequences with an increasing ? and a decreasing number of pulses. A synthetic study as well as laboratory measurements on samples of glass beads and granulate of different grain size spectra were conducted to evaluate the effects of of an increasing ? spacing, e.g. an enhanced relaxation due to diffusion processes. The results are showing broadened T2 distributions if the number of pulses is decreasing and the mean grain size is increasing, which is mostly an effect of a significantly shortened acquisition time. The shift of T2 distributions to small decay times in dependence of the ? spacing and the mean grain size distribution is observable. We found that it is possible to conduct CPMG sequences with an increased ? spacing. According to the acquisition time and enhanced diffusion the sequence parameters (number of pulses and ?max has to be chosen carefully. Otherwise the underestimated relaxation time (T2 will lead to misinterpretations.

M. Ronczka

2012-07-01

348

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

349

Measuring the contrast-enhancement in the skin and subcutaneous fatty tissue with the NMR-Mouse registered: a feasibility study  

International Nuclear Information System (INIS)

Purpose: the NMR-Mouse registered is an open and mobile sensor for measuring NMR relaxation parameters in organic matters. T1-measurements of the subcutaneous fatty tissue and the skin are reported. Material and method: for the first time, the NMR-Mouse registered was employed to measure the signal recovery following saturation of the skin and the subcutaneous fatty tissue of three patients, before and after administering a contrast agent. Results: despite a low signal-to-noise ratio, changes in the relaxation behaviour of the skin could be detected. Malignant tissue exhibits faster signal recovery than scar tissue and healthy tissue, which only show a small difference. Conclusions: changes in the relaxation behavior can be monitored with the NMR-Mouse registered. Before the clinical use of the NMR-Mouse, sensitivity, sensor mounting device, and sensor tuning must be improved. Further investigations need to be performed on a statistically relevant number of patients. (orig.)

350

BOOK REVIEW: NMR Imaging of Materials  

Science.gov (United States)

Magnetic resonance imaging (MRI) of materials is a field of increasing importance. Applications extend from fundamental science like the characterization of fluid transport in porous rock, catalyst pellets and hemodialysers into various fields of engineering for process optimization and product quality control. While the results of MRI imaging are being appreciated by a growing community, the methods of imaging are far more diverse for materials applications than for medical imaging of human beings. Blümich has delivered the first book in this field. It was published in hardback three years ago and is now offered as a paperback for nearly half the price. The text provides an introduction to MRI imaging of materials covering solid-state NMR spectroscopy, imaging methods for liquid and solid samples, and unusual MRI in terms of specialized approaches to spatial resolution such as an MRI surface scanner. The book represents an excellent and thorough treatment which will help to grow research in materials MRI. Blümich developed the treatise over many years for his research students, graduates in chemistry, physics and engineering. But it may also be useful for medical students looking for a less formal discussion of solid-state NMR spectroscopy. The structure of this book is easy to perceive. The first three chapters cover an introduction, the fundamentals and methods of solid-state NMR spectroscopy. The book starts at the ground level where no previous knowledge about NMR is assumed. Chapter 4 discusses a wide variety of transformations beyond the Fourier transformation. In particular, the Hadamard transformation and the 'wavelet' transformation are missing from most related books. This chapter also includes a description of noise-correlation spectroscopy, which promises the imaging of large objects without the need for extremely powerful radio-frequency transmitters. Chapters 5 and 6 cover basic imaging methods. The following chapter about the use of relaxation and spectroscopic methods to weight or filter the spin signals represents the core of the book. This is a subject where Blümich is deeply involved with substantial contributions. The chapter includes a lot of ideas to provide MR contrast between different regions based on their mobility, diffusion, spin couplings or NMR spectra. After describing NMR imaging methods for solids with broad lines, Blümich spends time on applications in the last two chapters of the book. This part is really fun to read. It underlines the effort to bring NMR into many kinds of manufacturing. Car tyres and high-voltage cables are just two such areas. Elastomeric materials, green-state ceramics and food science represent other interesting fields of applications. This part of the book represents a personal but nevertheless extensive compilation of modern applications. As a matter of course the MOUSE is presented, a portable permanent-magnet based NMR developed by Blümich and his co-workers. Thus the book is not only of interest to NMR spectroscopists but also to people in material science and chemical engineering. The bibliography and indexing are excellent and may serve as an attractive reference source for NMR spectroscopists. The book is the first on the subject and likely to become the standard text for NMR imaging of materials as the books by Abragam, Slicher and Ernst et al are for NMR spectroscopy. The purchase of this beautiful book for people dealing with NMR spectroscopy or medical MRI is highly recommended. Ralf Ludwig

Blümich, Bernhard

2003-09-01

351

NMR spectra simulation for quantum computing  

International Nuclear Information System (INIS)

Full text: Pulse NMR is one of the most serious candidates as an experimental technique for implementing quantum algorithms. To the present date, this technique is in fact the only one where full demonstrations of quantum algorithms implementations have been carried out, in spite of various technical difficulties. On NMR quantum computers, gates and subroutines are encoded as radiofrequency pulse sequences. A 'program output' is read directly on the measured spectra. On this work we simulate NMR spectra and show their evolution during algorithms implementations for two and three qubits systems. We will focus on Grover search, Quantum Fourier Transform, Shor factorization and Teleportation algorithms. Calculated spectra are compared to experimental data extracted from the literature. The main difficulties associated to the use of NMR to quantum computing, such as the exponential decrease of the signal upon increasing the number of qubits could, in principle, be partially removed by using ferromagnetic materials. However, broad NMR linewidths in these materials can mask logical operation. Some simulations are also presented to illustrate this point. (author)

352

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

353

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)

354

Mobile NMR for Analysis of Polyethylene Pipes  

Science.gov (United States)

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.

Blümich, B.; Casanova, F.; Buda, A.; Kremer, K.; Wegener, T.

2006-07-01

355

NMR methodologies in the analysis of blueberries.  

Science.gov (United States)

An NMR analytical protocol based on complementary high and low field measurements is proposed for blueberry characterization. Untargeted NMR metabolite profiling of blueberries aqueous and organic extracts as well as targeted NMR analysis focused on anthocyanins and other phenols are reported. Bligh-Dyer and microwave-assisted extractions were carried out and compared showing a better recovery of lipidic fraction in the case of microwave procedure. Water-soluble metabolites belonging to different classes such as sugars, amino acids, organic acids, and phenolic compounds, as well as metabolites soluble in organic solvent such as triglycerides, sterols, and fatty acids, were identified. Five anthocyanins (malvidin-3-glucoside, malvidin-3-galactoside, delphinidin-3-glucoside, delphinidin-3-galactoside, and petunidin-3-glucoside) and 3-O-?-l-rhamnopyranosyl quercetin were identified in solid phase extract. The water status of fresh and withered blueberries was monitored by portable NMR and fast-field cycling NMR. (1) H depth profiles, T2 transverse relaxation times and dispersion profiles were found to be sensitive to the withering. PMID:24668393

Capitani, Donatella; Sobolev, Anatoly P; Delfini, Maurizio; Vista, Silvia; Antiochia, Riccarda; Proietti, Noemi; Bubici, Salvatore; Ferrante, Gianni; Carradori, Simone; De Salvador, Flavio Roberto; Mannina, Luisa

2014-06-01

356

Structural fidelity and NMR relaxation analysis in a prototype RNA hairpin.  

Science.gov (United States)

RNA hairpins are widespread and very stable motifs that contribute decisively to RNA folding and biological function. The GTP1G2C3A4C5U6U7C8G9G10U11G12C13C14 construct (with a central UUCG tetraloop) has been extensively studied by solution NMR, and offers and excellent opportunity to evaluate the structure and dynamical description afforded by molecular dynamics (MD) simulations. Here, we compare average structural parameters and NMR relaxation rates estimated from a series of multiple independent explicit solvent MD simulations using the two most recent RNA AMBER force fields (ff99 and ff10). Predicted overall tumbling times are ?20% faster than those inferred from analysis of NMR data and follow the same trend when temperature and ionic strength is varied. The Watson-Crick stem and the "canonical" UUCG loop structure are maintained in most simulations including the characteristic syn conformation along the glycosidic bond of G9, although some key hydrogen bonds in the loop are partially disrupted. Our analysis pinpoints G9-G10 backbone conformations as a locus of discrepancies between experiment and simulation. In general the results for the more recent force-field parameters (ff10) are closer to experiment than those for the older ones (ff99). This work provides a comprehensive and detailed comparison of state of the art MD simulations against a wide variety of solution NMR measurements. PMID:25805858

Giamba?u, George M; York, Darrin M; Case, David A

2015-05-01

357

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?, Marko; Grbi?, Mihael S; Požek, Miroslav

2014-01-01

358

Solution conformation and dynamics of a tetrasaccharide related to the LewisX antigen deduced by NMR relaxation measurements  

International Nuclear Information System (INIS)

1H-NMR cross-relaxation rates and nonselective longitudinal relaxation times have been obtained at two magnetic fields (7.0 and 11.8 T) and at a variety of temperatures for the branched tetrasaccharide methyl 3-O-?-N-acetyl-galactosaminyl-?-galactopyranosyl-(1?4)[3-O-?-fucosyl] -glucopyranoside (1), an inhibitor of astrocyte growth. In addition, 13C-NMR relaxation data have also been recorded at both fields. The 1H-NMR relaxation data have been interpreted using different motional models to obtain proton-proton correlation times. The results indicate that the GalNAc and Fuc rings display more extensive local motion than the two inner Glc and Gal moieties, since those present significantly shorter local correlation times. The13C-NMR relaxation parameters have been interpreted in terms of the Lipari-Szabo model-free approach. Thus, order parameters and internal motion correlation times have been deduced. As obtained for the1H-NMR relaxation data, the two outer residues possess smaller order parameters than the two inner rings. Internal correlation times are in the order of 100 ps. The hydroxymethyl groups have also different behaviour,with the exocyclic carbon on the glucopyranoside unit showing the highestS2. Molecular dynamics simulations using a solvated system have also been performed and internal motion correlation functions have been deduced from these calculations. Order parameters these calculations. Order parameters and interproton distances have been compared to those inferred from the NMR measurements. The obtained results are in fair agreement with the experimental data

359

Analytical solution of the time-dependent Bloch NMR flow equations: a translational mechanical analysis  

Science.gov (United States)

Various biological and physiological properties of living tissue can be studied by means of nuclear magnetic resonance techniques. Unfortunately, the basic physics of extracting the relevant information from the solution of Bloch nuclear magnetic resource (NMR) equations to accurately monitor the clinical state of biological systems is still not yet fully understood. Presently, there are no simple closed solutions known to the Bloch equations for a general RF excitation. Therefore the translational mechanical analysis of the Bloch NMR equations presented in this study, which can be taken as definitions of new functions to be studied in detail may reveal very important information from which various NMR flow parameters can be derived. Fortunately, many of the most important but hidden applications of blood flow parameters can be revealed without too much difficulty if appropriate mathematical techniques are used to solve the equations. In this study we are concerned with a mathematical study of the laws of NMR physics from the point of view of translational mechanical theory. The important contribution of this study is that solutions to the Bloch NMR flow equations do always exist and can be found as accurately as desired. We shall restrict our attention to cases where the radio frequency field can be treated by simple analytical methods. First we shall derive a time dependant second-order non-homogeneous linear differential equation from the Bloch NMR equation in term of the equilibrium magnetization M0, RF B1( t) field, T1 and T2 relaxation times. Then, we would develop a general method of solving the differential equation for the cases when RF B1( t)=0, and when RF B1( t)?0. This allows us to obtain the intrinsic or natural behavior of the NMR system as well as the response of the system under investigation to a specific influence of external force to the system. Specifically, we consider the case where the RF B1 varies harmonically with time. Here the complete motion of the system consists of two parts. The first part describes the motion of the transverse magnetization My in the absence of RF B( t) field. The second part of the motion described by the particular integral of the derived differential equation does not decay with time but continues its periodic behavior indefinitely. The complete motion of the NMR flow system is then quantitatively and qualitatively described.

Awojoyogbe, O. B.

2004-08-01

360

Protein dielectric constants determined from NMR chemical shift perturbations.  

Science.gov (United States)

Understanding the connection between protein structure and function requires a quantitative understanding of electrostatic effects. Structure-based electrostatic calculations are essential for this purpose, but their use has been limited by a long-standing discussion on which value to use for the dielectric constants (?(eff) and ?(p)) required in Coulombic and Poisson-Boltzmann models. The currently used values for ?(eff) and ?(p) are essentially empirical parameters calibrated against thermodynamic properties that are indirect measurements of protein electric fields. We determine optimal values for ?(eff) and ?(p) by measuring protein electric fields in solution using direct detection of NMR chemical shift perturbations (CSPs). We measured CSPs in 14 proteins to get a broad and general characterization of electric fields. Coulomb's law reproduces the measured CSPs optimally with a protein dielectric constant (?(eff)) from 3 to 13, with an optimal value across all proteins of 6.5. However, when the water-protein interface is treated with finite difference Poisson-Boltzmann calculations, the optimal protein dielectric constant (?(p)) ranged from 2 to 5 with an optimum of 3. It is striking how similar this value is to the dielectric constant of 2-4 measured for protein powders and how different it is from the ?(p) of 6-20 used in models based on the Poisson-Boltzmann equation when calculating thermodynamic parameters. Because the value of ?(p) = 3 is obtained by analysis of NMR chemical shift perturbations instead of thermodynamic parameters such as pK(a) values, it is likely to describe only the electric field and thus represent a more general, intrinsic, and transferable ?(p) common to most folded proteins. PMID:24124752

Kukic, Predrag; Farrell, Damien; McIntosh, Lawrence P; García-Moreno E, Bertrand; Jensen, Kristine Steen; Toleikis, Zigmantas; Teilum, Kaare; Nielsen, Jens Erik

2013-11-13

361

NMR studies of equilibriums in electrolytes  

Energy Technology Data Exchange (ETDEWEB)

In this article, the formation constants of ionic pairs in salt-low molecular weight analogs of PEO (glyme, diglyme, triglyme) systems are estimated using NMR spectroscopy. The results from {sup 7}Li, {sup 11}B and {sup 19}F NMR titration are compared and the role of the nuclei studied is discussed. It is shown that even in the solvents of very similar coordination (in terms of the donor and acceptor number values) and dielectric properties, the ionic pair formation constant depends on solvent used. The role of the solvent is discussed in terms of effects related to ion agglomerate formation, non-covalent interactions between ions and liquid matrix as well as the number of interacting centers present in the molecules of the solvent. The discrepancies between the results obtained using various nuclei NMR as well as discrepancies between ion pair formation constant calculated for different experimental regimes are also analyzed.

Plewa-Marczewska, A.; Kalita, M.; Marczewski, M. [Polymer Ionics Research Group, Warsaw University of Technology, Chemical Faculty, Noakowskiego 3, PL-00664 Warsaw (Poland); Siekierski, M., E-mail: alex@ch.pw.edu.p [Polymer Ionics Research Group, Warsaw University of Technology, Chemical Faculty, Noakowskiego 3, PL-00664 Warsaw (Poland)

2010-01-25

362

Determination of solid fat content by NMR  

International Nuclear Information System (INIS)

To establish a standard method for determing solid fat content, the NMR method was tested at six laboratories and the results were examined for collaboration. Two types of instruments, pulse NMR and wide-line NMR were used. Standard deviation in results at six laboratories was less than 1.5 for the step wise method, but more than 1.5 for the rapid method. The standard deviation in results at a single laboratory was much less than either of these cases. No significant difference could be observed in the values obtained using both instruments. Solid fat content values measured for a mixture of fully hydrogenated rapeseed and rapeseed oil agreed well with the percentage of solid by weight. (author)

363

Nonclassical correlation in NMR quadrupolar systems  

CERN Document Server

The existence of quantum correlation (as the one revealed by the quantum discord) other than entanglement and its role in quantum information processing (QIP) is a current subject of discussion. Particularly, it has been suggested that this nonclassical correlation may provide the computational speedup for some quantum algorithms. In this sense bulk nuclear magnetic resonance (NMR) has been successfully used as a test bench for many QIP implementations, although it has also been continuously criticized about not presenting entanglement in most of the systems used so far. In this article we report a theoretical and experimental study on the dynamics of quantum and classical correlations in a NMR quadrupolar system. We present a method for computing the correlations from experimental NMR deviation-density matrices and show that, given the action of the nuclear spin environment, the relaxation produces a monotonic time decay in the correlations. Although the experimental realizations were done in a specific quad...

Soares-Pinto, D O; Auccaise, R; Fanchini, F F; deAzevedo, E R; Maziero, J; Bonagamba, T J; Serra, R M

2010-01-01

364

Deuterium NMR, induced and intrinsic cholesteric lyomesophases  

International Nuclear Information System (INIS)

Induced and intrinsic cholesteric lyotropic mesophases were studied. Induced cholesteric lyomesophases based on potassium laurate (KL) system, with small amounts of cholesterol added, were studied by deuterium NMR and by polarizing microscopy. Order profiles obtained from deuterium NMR of KL perdenderated chains in both induced cholesteric and normal mesophases were compared. The intrinsic cholesteric lyotropic mesophases were based on the amphiphile potassium N-lauroyl serinate (KLNS) in the resolved levo form. The study of the type I intrinsic cholesteric mesophase was made by optical microscopy under polarized light and the type II intrinsic cholesteric lyomesophase was characterized by deuterium NMR. The new texture was explained by the use of the theory of disclinations developed for thermotropic liquid crystals, specially for cholesteric type. (M.J.C.)

365

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

366

Spin Hamiltonian for the quantum Hall state in a ladder geometry  

Science.gov (United States)

The first calculation of the true ground state of the parent Hamiltonian proposed by Laughlin [Laughlin, Ann. Phys. 191, 163 (1989)] for the m=2 fractional quantum Hall state on a torus is presented. Laughlin’s model is generalized to the case of a system in a ladder geometry and rewritten in terms of familiar spin-spin interactions, demonstrating that the model corresponds to a long-range Heisenberg Hamiltonian with an additional four-site interaction. The exact diagonalization of the Hamiltonian is performed to extract the energies, correlation functions, sublattice magnetization, and overlap with the quantum Hall state. Our results confirm the recent work showing that the model is not exact [Schroeter, Ann. Phys. 310, 155 (2004)] and also show it to be not without merit: the overlap between the quantum Hall (QH) state and exact ground state approaches the significant value of 0.83 in the limit that the ladder becomes infinitely long.

Kapit, E.; Luitel, P.; Schroeter, D. F.

2006-02-01

367

Spin-Hamiltonian for the Quantum Hall State in a Ladder Geometry  

Science.gov (United States)

The first calculation of the true ground state of the parent-Hamiltonian proposed by Laughlin [R. B. Laughlin, Ann. Phys. 191, 163 (1989)] for the m=2 Fractional Quantum Hall state on a torus is presented. Laughlin's model is generalized to the case of a system in a ladder geometry and rewritten in terms of familiar spin-spin interactions, demonstrating that the model corresponds to a long-range Heisenberg Hamiltonian with an additional four-site interaction. The exact diagonalization of the Hamiltonian is performed to extract the energy, correlation functions, sub-lattice magnetization, and overlap with the Quantum Hall state. Our results confirm the recent work showing that the model is not exact [D. F. Schroeter, Ann. Phys. 310, 155 (2004)] and also show it to be not without merit: the overlap between the QH state and exact ground state approaches the significant value of 0.83 in the limit that the ladder becomes infinitely long.

Kapit, Eliot

2005-03-01

368

Effective chiral-spin Hamiltonian for odd-numbered coupled Heisenberg chains  

International Nuclear Information System (INIS)

An L x ? system of odd number of coupled Heisenberg spin chains is studied using a degenerate perturbation theory, where L is the number of coupled chains. An effective chain Hamiltonian is derived explicitly in terms of two spin half degrees of freedom of a closed chain of L sites, valid in the regime the inter-chain coupling is stronger than the intra-chain coupling. The spin gap has been calculated numerically using the effective Hamiltonian for L = 3,5,7,9 for a finite chain up to ten sites. It is suggested that the ground state of the effective Hamiltonian is correlated, by examining various variational trial states for the effective-spin chain Hamiltonian. (author). 11 refs, 1 fig., 1 tab

369

High field NMR in low dimensional quantum antiferromagnets  

International Nuclear Information System (INIS)

We present high field NMR studies of the field induced magnetic ordering in a few quasi-1D quantum antiferromagnets. Cu2(C5H12N2)2Cl4 (Cu(Hp)Cl) has for long been considered as the archetype of a strong coupling spin-ladder system. We show that it can be well understood in the framework of a spin-ladder with a staggered Dzyaloshinskii-Moriya (DM) interaction on the rungs. CuBr4(C5H12N)2 (BPCB) is made of regular spin-ladders (without DM interaction) weakly coupled together. Its phase diagram between the two quantum critical field Hc1 and Hc2 is fully dominated by the H dependence of the Luttinger liquid parameters of the ladders. We also briefly report the NMR evidence for the existence of an unconventional quantum ground state in the 1/3 magnetization plateau in the frustrated diamond chain compound Cu3(CO3)2(OH)2 (azurite)

370

Determination of dipole coupling constants using heteronuclear multiple quantum NMR  

International Nuclear Information System (INIS)

The problem of extracting dipole couplings from a system of N spins I = 1/2 and one spin S by NMR techniques is analyzed. The resolution attainable using a variety of single quantum methods is reviewed. The theory of heteronuclear multiple quantum (HMQ) NMR is developed, with particular emphasis being placed on the superior resolution available in HMQ spectra. Several novel pulse sequences are introduced, including a two-step method for the excitation of HMQ coherence. Experiments on partially oriented [1-13C] benzene demonstrate the excitation of the necessary HMQ coherence and illustrate the calculation of relative line intensities. Spectra of high order HMQ coherence under several different effective Hamiltonians achievable by multiple pulse sequences are discussed. A new effective Hamiltonian, scalar heteronuclear recoupled interactions by multiple pulse (SHRIMP), achieved by the simultaneous irradiation of both spin species with the same multiple pulse sequence, is introduced. Experiments are described which allow heteronuclear couplings to be correlated with an S-spin spreading parameter in spectra free of inhomogeneous broadening

371

31Phosphorus NMR studies of renal membrane phospholipids  

International Nuclear Information System (INIS)

A research program was undertaken in order to study the effects of toxin-induced acute renal failure and streptozotozin-induced diabetes mellitus on the organization and motion of phospholipids in kidney membranes. The method of study included 31P NMR and computer simulated lineshape analyses and apparent lipid diffusion rate measurements. These were performed with selected tissue samples and disease models, and the results were compared with those of healthy renal tissues in order to identify changes associated with the diseased state. A new selective-excitation NMR pulse sequence was developed in which a portion of the lipid molecules were excited with a series of short equally-spaced RF pulses. As the position of the molecules changed on the membrane by lateral diffusion, the shape of the hole was seen to change. Experimental spectra were compared with calculated lineshapes in order to obtain estimates of useful molecular parameters including relation times and lateral lipid diffusion rates. The lineshape calculations were based on a solution to the Bloch equations for complex magnetization components with exchange terms added for diffusion

372

A practical implicit solvent potential for NMR structure calculation  

Science.gov (United States)

The benefits of protein structure refinement in water are well documented. However, performing structure refinement with explicit atomic representation of the solvent molecules is computationally expensive and impractical for NMR-restrained structure calculations that start from completely extended polypeptide templates. Here we describe a new implicit solvation potential, EEFx (Effective Energy Function for XPLOR-NIH), for NMR-restrained structure calculations of proteins in XPLOR-NIH. The key components of EEFx are an energy term for solvation energy that works together with other nonbonded energy functions, and a dedicated force field for conformational and nonbonded protein interaction parameters. The initial results obtained with EEFx show that significant improvements in structural quality can be obtained. EEFx is computationally efficient and can be used both to fold and refine structures. Overall, EEFx improves the quality of protein conformation and nonbonded atomic interactions. Moreover, such benefits are accompanied by enhanced structural precision and enhanced structural accuracy, reflected in improved agreement with the cross-validated dipolar coupling data. Finally, implementation of EEFx calculations is straightforward and computationally efficient. Overall, EEFx provides a useful method for the practical calculation of experimental protein structures in a physically realistic environment.

Tian, Ye; Schwieters, Charles D.; Opella, Stanley J.; Marassi, Francesca M.

2014-06-01

373

NMR-based metabolomics of mammalian cell and tissue cultures  

International Nuclear Information System (INIS)

NMR spectroscopy was used to evaluate growth media and the cellular metabolome in two systems of interest to biomedical research. The first of these was a Chinese hamster ovary cell line engineered to express a recombinant protein. Here, NMR spectroscopy and a quantum mechanical total line shape analysis were utilized to quantify 30 metabolites such as amino acids, Krebs cycle intermediates, activated sugars, cofactors, and others in both media and cell extracts. The impact of bioreactor scale and addition of anti-apoptotic agents to the media on the extracellular and intracellular metabolome indicated changes in metabolic pathways of energy utilization. These results shed light into culture parameters that can be manipulated to optimize growth and protein production. Second, metabolomic analysis was performed on the superfusion media in a common model used for drug metabolism and toxicology studies, in vitro liver slices. In this study, it is demonstrated that two of the 48 standard media components, choline and histidine are depleted at a faster rate than many other nutrients. Augmenting the starting media with extra choline and histidine improves the long-term liver slice viability as measured by higher tissues levels of lactate dehydrogenase (LDH), glutathione and ATP, as well as lower LDH levels in the media at time points out to 94 h after initiation of incubation. In both models, media components and cellular metabolites are measured over time and correlated wis are measured over time and correlated with currently accepted endpoint measures.

374

Deriving rock transport properties from NMR relaxation experiments on partially de-saturated rocks using an inverse modelling approach based on the triangular pore model  

Science.gov (United States)

Nuclear magnetic resonance (NMR) is a method used over a wide field of geophysical applications e.g. petrophysics, logging or hydrogeology, to non-destructively and quickly determine transport and storage properties of rocks and soils. Measured NMR amplitudes indicate the rock's fluid content, whereas the NMR relaxation rates are used to derive pore size distributions and permeability as they are related to physiochemical properties of the rock-fluid interface, i.e. surface relaxivity. The aim of this work is to utilize triangular pore shapes in the inverse modeling of NMR relaxation data in order to better predict the water retention curves. Therefore, an inverse modeling scheme (Mohnke et al.; this conference) to derive NMR surface relaxivity along with pore radii distributions are determined has been adapted on the basis of triangular pore bundle models. . This approach then offers the advantage of having the triangular pores be partially saturated, thus accounting for a residual water content trapped in pore corners during drainage and imbibition (Tuller and Or, 2001). Additionally, besides the trapped water the presence of a water film at the pore walls is accounted for in the modeled and inverted NMR relaxation time distributions and thus allows to more accurately describe laboratory measurement results. Numerical parameter studies were carried out to assess the influence of pore shapes and contact angles on both, transport and NMR properties. Inverse models derived from laboratory NMR data on partially saturated reservoir rocks are in a good agreement with measured water retention data.

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

2013-12-01

375

Applications of NMR spectroscopy to xenobiotic metabolism  

International Nuclear Information System (INIS)

Recent years have seen high field NMR spectrometers become commonplace in research laboratories. At the same time, major advances in methodology for structural analysis have occurred, particularly notable among these being the development of two-dimensional spectroscopic techniques. Many applications have been made of NMR spectroscopy in the study of xenobiotic metabolic processes. This deals with two specific applications which have been made in the author's laboratory and involve mechanistic studies of the reactions of the carcinogens ethylene dibromide and aflatoxin with DNA

376

Development of a small NMR probe  

International Nuclear Information System (INIS)

In two-dimensional (2D) systems, it is possible to exactly match a static and a radiofrequency (RF) magnetic field. An arbitrary angle can be put between two fields, and this angle is constant everywhere in the space. Moreover, the modulus of the fields are linked by a proportionality factor. This result is based on the easy-axis rotation theorem and the amperian current model of permanent magnets. It is useful in portable nuclear magnetic resonance (NMR) applications, where a RF magnetic field perpendicular and correlated to a static magnetic field is needed. A small NMR probe based on this principle was developed

377

NMR in attendance on complex flows  

International Nuclear Information System (INIS)

This paper describes the pulsed gradient NMR methods used to follow the displacements of a fluid particle inside flows in dispersed media (porous media, two phase flow, fluidized beds, sedimentation etc..). The basic principles of the NMR are recalled first, then the experimental apparatus is described and the method used is illustrated with examples of experimental results obtained in dispersed media: molecular diffusion, Poiseuille flow in pipes, two-phase flows (water-air, water-freon 113) and flow in porous media. (J.S.)

378

NMR detection with an atomic magnetometer  

OpenAIRE

We demonstrate detection of NMR signals using a non-cryogenic atomic magnetometer and describe several novel applications of this technique. A water free induction decay (FID) signal in a 0.5 $\\mu$T field is detected using a spin-exchange-relaxation-free K magnetometer and the possibility of using a multi-channel magnetometer for 3-D MRI requiring only a single FID signal is described. We also demonstrate detection of less than $10^{13}$ $^{129}$Xe atoms whose NMR signal is ...

Savukov, I. M.; Romalis, M. V.

2004-01-01

379

New Designs for NMR Core Scanning  

Science.gov (United States)

Within the last ten years, mobile magnetic resonance has moved from the oil field to many new areas of application. While the focus of mobile NMR in the past was on single-sided or inside-out NMR, the advent of tube-shaped Halbach magnets has introduced the conventional outside-in NMR concept to mobile NMR where the object is inside a magnet. Our Halbach magnet is constructed from small magnet blocks at light weight and low cost with a magnetic field sufficiently homogeneous. To automatize NMR measurements, the Halbach magnet is mounted on a sliding table to scan long core sections without human interaction. In homogeneous magnetic fields, the longitudinal relaxation time T1 and even the transverse relaxation time T2 are proportional to the pore diameters of rocks. Hence, the T1 and T2 signals map the pore-size distribution of the studied rock cores. For fully saturated samples the integral of the distribution curve is proportional to porosity. The porosity values from NMR measurements with the Halbach magnet are used to estimate permability. The Halbach magnet can be used for certain sample geometries in combination with exchangeable radio frequency (rf) coils with different diameters from 24 mm up to 80 mm. To measure standard Ocean Drilling Program (ODP)/Integrated Ocean Drilling Program (IODP) cores, which have a standard diameter of 60 mm and are split lengthwise after recovery, we use a surface figure-8 rf coil with an inner diameter of 60 mm. Besides 1D T2 measurements, we perform relaxation-relaxation correlation experiments, where T1 and T2 are measured in parallel. In this way, the influence of diffusion on the shape of the T2 distribution function is probed. A gradient coil system was designed to perform Pulsed Field Gradients (PFG) experiments. As the gradient coils restrict the axial access to the magnet, only cylindrical core plugs with 20 mm in diameter can be analysed by PFG NMR methods. The homogeneity of the magnetic field in the sensitive volume of 20 mm length and height is sufficient for conventional PFG experiments. Hence, in a next step we will measure tortuosity and investigate pore anisotropies by PFG NMR.

Bluemich, B.; Anferova, S.; Talnishnikh, E.; Arnold, J.; Clauser, C.

2006-12-01

380

"In-plant" NMR: Analysis of the Intact Plant Vesicularia dubyana by High Resolution NMR Spectroscopy.  

Science.gov (United States)

We present here the concept of "in-plant" NMR and show that high-resolution NMR spectroscopy is suitable for the analysis of intact plants and can be used to follow the changes in the intraorganismal molecular composition over long time periods. The NMR-based analysis of the effect of different concentrations of heavy water on the aquatic plant Vesicularia dubyana revealed that due to the presence of specific adaptive mechanisms this plant can sustain the presence of up to 85% of D2O. However, it dies in 100% heavy water. PMID:25759953

Kutyshenko, Viktor P; Beskaravayny, Peter; Uversky, Vladimir N

2015-01-01

381

Fast automated protein NMR data collection and assignment by ADAPT-NMR on Bruker spectrometers  

OpenAIRE

ADAPT-NMR (Assignment-directed Data collection Algorithm utilizing a Probabilistic Toolkit in NMR) supports automated NMR data collection and backbone and side chain assignment for [U-13C, U-15N]-labeled proteins. Given the sequence of the protein and data for the orthogonal 2D 1H-15N and 1H-13C planes, the algorithm automatically directs the collection of tilted plane data from a variety of triple-resonance experiments so as to follow an efficient pathway toward the probabilistic assignment ...

Lee, Woonghee; Hu, Kaifeng; Tonelli, Marco; Bahrami, Arash; Neuhardt, Elizabeth; Glass, Karen C.; Markley, John L.

2013-01-01

382

Perspectives in enzymology of membrane proteins by solid-state NMR.  

Science.gov (United States)

Membrane proteins catalyze reactions at the cell membrane and facilitate thetransport of molecules or signals across the membrane. Recently researchers have made great progress in understanding the structural biology of membrane proteins, mainly based on X-ray crystallography. In addition, the application of complementary spectroscopic techniques has allowed researchers to develop a functional understanding of these proteins. Solid-state NMR has become an indispensable tool for the structure-function analysis of insoluble proteins and protein complexes. It offers the possibility of investigating membrane proteins directly in their environment, which provides essential information about the intrinsic coupling of protein structure and functional dynamics within the lipid bilayer. However, to date, researchers have hardly explored the enzymology of mem-brane proteins. In this Account, we review the perspectives for investigating membrane-bound enzymes by solid-state NMR. Understanding enzyme mechanisms requires access to kinetic parameters, structural analysis of the catalytic center, knowledge of the 3D structure and methods to follow the structural dynamics of the enzyme during the catalytic cycle. In principle, solid-state NMR can address all of these issues. Researchers can characterize the enzyme kinetics by observing substrate turnover within the membrane or at the membrane interphase in a time-resolved fashion as shown for diacylglycerol kinase. Solid-state NMR has also provided a mechanistic understanding of soluble enzymes including triosephosphate isomerase (TIM) and different metal-binding proteins, which demonstrates a promising perspective also for membrane proteins. The increasing availability of high magnetic fields and the development of new experimental schemes and computational protocols have made it easier to determine 3D structure using solid-state NMR. Dynamic nuclear polarization, a key technique to boost sensitivity of solid-state NMR at low temperatures, can help with the analysis of thermally trapped catalytic intermediates, while methods to improve signal-to-noise per time unit enable the real-time measurement of kinetics of conformational changes during the catalytic cycle. PMID:23745719

Ullrich, Sandra J; Glaubitz, Clemens

2013-09-17

383

Molecular Interactions Studied by Electrophoretic and Diffusion NMR  

OpenAIRE

Even though electrophoretic NMR (eNMR) experiments may provide unique chemical information and have been performed for three decades, the technique is still rarely applied, mainly because several experimental sources of artifacts have to be controlled to achieve accurate results. In this thesis, new experimental setups and protocols for accurate and precise eNMR experiments are presented. These include a novel eNMR sample cell, a radiofrequency filter and methods to suppress bulk flow effects...

Hallberg, Fredrik

2010-01-01

384

SPE-NMR metabolite sub-profiling of urine  

OpenAIRE

NMR-based metabolite profiling of urine is a fast and reproducible method for detection of numerous metabolites with diverse chemical properties. However, signal overlap in the (1)H NMR profiles of human urine may hamper quantification and identification of metabolites. Therefore, a new method has been developed using automated solid-phase extraction (SPE) combined with NMR metabolite profiling. SPE-NMR of urine resulted in three fractions with complementary and reproducible sub-profiles. The...

Jacobs, D. M.; Spiesser, L.; Garnier, M.; Roo, N.; Dorsten, F.; Hollebrands, B.; Velzen, E.; Draijer, R.; Duynhoven, J. P. M.

2012-01-01

385

Pulsed NMR for the determination of the nuclear polarization  

International Nuclear Information System (INIS)

The polarization in polarized solid targets is usually measured by a continuous wave nuclear magnetic resonance system (CW-NMR). This technique reaches its limits for small and wide signals. The pulsed NMR technique is usually used in nuclear physics and medicine, because of its higher performance and sensitivity compared to the CW-NMR. First tests and linearity measurements of the detection system of our new pulsed NMR will be presented

386

Constraining 17O and 27Al NMR spectra of high-pressure crystals and glasses: New data for jadeite, pyrope, grossular, and mullite  

Science.gov (United States)

The 17O NMR spectra of glasses quenched from melts at high pressure are often difficult to interpret due to overlapping peaks and lack of crystalline model compounds. High-pressure aluminosilicate glasses often contain significant amounts of [5]Al and [6]Al, thus these high-pressure glasses must contain oxygen bonded to high-coordinated aluminum. The 17O NMR parameters for the minerals jadeite, pyrope, grossular, and mullite are presented to assist interpretation of glass spectra and to help test quantum chemical calculations. The 17O NMR parameters for jadeite and grossular support previous peak assignments of oxygen bonded to Si and high-coordinated Al in high-pressure glasses as well as quantum chemical calculations. The oxygen tricluster in mullite is very similar to the previously observed tricluster in grossite (CaAl4 O7) and suspected triclusters in glasses. We also present 27Al NMR spectra for pyrope, grossular, and mullite.

Kelsey, K.E.; Stebbins, J.F.; Du, L.-S.; Hankins, B.

2007-01-01

387

Bomb parameters  

International Nuclear Information System (INIS)

The reconstruction of neutron and gamma-ray doses at Hiroshima and Nagasaki begins with a determination of the parameters describing the explosion. The calculations of the air transported radiation fields and survivor doses from the Hiroshima and Nagasaki bombs require knowledge of a variety of parameters related to the explosions. These various parameters include the heading of the bomber when the bomb was released, the epicenters of the explosions, the bomb yields, and the tilt of the bombs at time of explosion. The epicenter of a bomb is the explosion point in air that is specified in terms of a burst height and a hypocenter (or the point on the ground directly below the epicenter of the explosion). The current reassessment refines the energy yield and burst height for the Hiroshima bomb, as well as the locations of the Hiroshima and Nagasaki hypocenters on the modern city maps used in the analysis of the activation data for neutrons and TLD data for gamma rays. (J.P.N.)

388

Solution conformation and dynamics of a tetrasaccharide related to the Lewis{sup X} antigen deduced by NMR relaxation measurements  

Energy Technology Data Exchange (ETDEWEB)

{sup 1}H-NMR cross-relaxation rates and nonselective longitudinal relaxation times have been obtained at two magnetic fields (7.0 and 11.8 T) and at a variety of temperatures for the branched tetrasaccharide methyl 3-O-{alpha}-N-acetyl-galactosaminyl-{beta}-galactopyranosyl-(1{sup {yields}}4)[3-O-{alpha}-fucosyl] -glucopyranoside (1), an inhibitor of astrocyte growth. In addition, {sup 13}C-NMR relaxation data have also been recorded at both fields. The {sup 1}H-NMR relaxation data have been interpreted using different motional models to obtain proton-proton correlation times. The results indicate that the GalNAc and Fuc rings display more extensive local motion than the two inner Glc and Gal moieties, since those present significantly shorter local correlation times. The{sup 13}C-NMR relaxation parameters have been interpreted in terms of the Lipari-Szabo model-free approach. Thus, order parameters and internal motion correlation times have been deduced. As obtained for the{sup 1}H-NMR relaxation data, the two outer residues possess smaller order parameters than the two inner rings. Internal correlation times are in the order of 100 ps. The hydroxymethyl groups have also different behaviour,with the exocyclic carbon on the glucopyranoside unit showing the highestS{sup 2}. Molecular dynamics simulations using a solvated system have also been performed and internal motion correlation functions have been deduced from these calculations. Order parameters and interproton distances have been compared to those inferred from the NMR measurements. The obtained results are in fair agreement with the experimental data.

Poveda, Ana [Universidad Autonoma de Madrid, Servicio Interdepartamental de Investigacion (Spain); Asensio, Juan Luis; Martin-Pastor, Manuel; Jimenez-Barbero, Jesus [Instituto de Quimica Organica, CSIC, Grupo de Carbohidratos (Spain)

1997-07-15

389

The potential of NMR for the evaluation of fetal development  

International Nuclear Information System (INIS)

Contrast in NMR images depends not only on the specific nucleus concentration but also on the rate at which the magnetization of an ensemble of atomic nuclei returns to an equilibrium state after being disturbed - NMR relaxation time is least at equilibrium, greatest at states far from equilibrium. Consequently NMR may reveal thermodynamic divisions of disease at states near and far from equilibrium. (Auth.)

390

Superoxygenated Water as an Experimental Sample for NMR Relaxometry  

Science.gov (United States)

The increase in NMR relaxation rates as a result of dissolved paramagnetic species on the sample of superoxygenated drinking water is demonstrated. It is concluded that oxygen content in NMR samples is an important issue and can give rise to various problems in the interpretation of both spectroscopic and NMR imaging or relaxation experiments.

Nestle, Nikolaus; Dakkouri, Marwan; Rauscher, Hubert

2004-01-01

391

Optically pumped NMR in semiconductor InP  

International Nuclear Information System (INIS)

We have performed optically pumped NMR measurements on iron doped InP. A circularly polarized laser light pumps up the polarizations of electron spins, which are transferred to the nuclear spins via hyperfine couplings resulting in a significantly enhanced NMR signal. The enhancement of 31P NMR signal strongly depends on the temperature and the helicity of the laser light

392

Genetic algorithms and solid state NMR pulse sequences  

CERN Document Server

The use of genetic algorithms for the optimisation of magic angle spinning NMR pulse sequences is discussed. The discussion uses as an example the optimisation of the C7 dipolar recoupling pulse sequence, aiming to achieve improved efficiency for spin systems characterised by large chemical shielding anisotropies and/or small dipolar coupling interactions. The optimised pulse sequence is found to be robust over a wide range of parameters, requires only minimal a priori knowledge of the spin system for experimental implementations with buildup rates being solely determined by the magnitude of the dipolar coupling interaction, but is found to be less broadbanded than the original C7 pulse sequence. The optimised pulse sequence breaks the synchronicity between r.f. pulses and sample spinning.

Bechmann, Matthias; Sebald, Angelika

2013-01-01

393

Hyperfine interaction in USi3: 29Si NMR study  

International Nuclear Information System (INIS)

The 29Si Knight shifts and nuclear spin-lattice relaxation rates (1/T1) in USi3 have been measured in the temperature range T=5-294 K. It was found that the relaxation rate was proportional to the temperature with T1T=19 (s K), while an isotropic part of the Knight shift, Kiso=0.217%, and its axial component, Kax=0.017%, were temperature independent.Whereas the macroscopic characteristics of USi3 are mainly due to uranium 5f electrons behaviour, the microscopic 29Si NMR parameters (Kiso, Kax and T1T) result from the 29Si nuclei-Si 3p electron states coupling. It occurs via the orbital and dipolar mechanisms and is responsible for a large Korringa constant enhancement. (orig.)

394

Substituents effects on the hydrogen-1 NMR spectra of meta- and para- substituted diaryldi-?-lactones  

International Nuclear Information System (INIS)

In a preliminary investigation, NMR chemical shifts of various lignan dilactones have been examined to study the effect of different aromatic substituents. To this point, Hammett plots have given linear correlations between the 1H NMR chemical shifts of the hydrogens in the flurofuran rings of para-substituted diaryldi-?-lactones and their ? Hammett substituent constants, whereas with meta-substituted dilactones only a poor correlation was observed. Additionally, the equations derived from these data were used to calculate the ?p parameter for the benzyloxy group which gave an average value of -0.15. The electronic parameters so obtained will be taken into account in subsequent enzymatic transformations regarding trends observed with either substrate analog or inhibitors. (author)

395

Shape-independent model (SHIM) approach for studying aggregation by NMR diffusometry.  

Science.gov (United States)

NMR diffusometry has been gaining wide popularity in various areas of applied chemistry for investigating diffusion and complexation processes in solid and aqueous phases. To date, the application of this method to study aggregation phenomena proceeding beyond the dimer stage of assembly has been restricted by the need for a priori knowledge of the aggregates' shape, commonly difficult to know in practice. We describe here a comprehensive analysis of aggregation parameter-dependency on the type and shape selected for modeling assembly processes, and report for the first time a shape-independent model (designated the SHIM approach), which may be used as an alternative in cases when information on aggregates' shapes is unavailable. The model can be used for determining equilibrium aggregation parameters from self-diffusion NMR data including equilibrium self-association constant and changes in enthalpy, ?H, and entropy, ?S. PMID:25770533

Hernandez Santiago, Adrian A; Buchelnikov, Anatoly S; Rubinson, Maria A; Yesylevskyy, Semen O; Parkinson, John A; Evstigneev, Maxim P

2015-03-14

396

Clinical application and evaluation of the diagnostic significance of NMR-tomography  

International Nuclear Information System (INIS)

Aim of the project was the clinical application and evaluation of the diagnostic significance of NMR-tomography. About 3 000 patients have been examined especially with diseases of the brain. In 75% of all cases pathological findings could be detected. A subgroup of these patients was used for comprehensive studies with regard to tissue characterization based on the calculation of relaxation time parameters. With methods of image processing and classification techniques we tried to get a clear correlation between combined NMR-parameters and human tissue types. The results show that this procedure is able to improve the detectibility and the association to finding groups and tumorgradings in certain cases. (orig./ECB) With 134 refs., 17 tabs., 86 figs

397

Demixing of severely overlapping NMR spectra through multiple-quantum NMR.  

Science.gov (United States)

We introduce an NMR method to help in the analysis of complex mixtures. The spectra of molecular fragments are obtained as the traces of a correlation spectrum of the regular (1)H NMR spectrum on one dimension with the one of the highest possible (1)H multiple-quantum (MaxQ) order. As this latter is a function of the number of distinguishable protons in a given molecular fragment, the analysis of a series of multiple-quantum spectra is required to achieve a complete assignment. This MaxQ NMR approach is likely to perform best in the case of signals concentrated in a very narrow frequency range, which is a challenging situation commonly encountered in many relevant analytical problems such as the characterization of extraction fractions (oil, plants, tissues), biological fluids, or environmentally relevant samples. As a demonstration, we apply the MaxQ NMR analysis to a mixture of 11 poly- and monocyclic aromatic hydrocarbons. PMID:20329747

Manjunatha Reddy, G N; Caldarelli, Stefano

2010-04-15

398

Patient alignment system for NMR studies  

International Nuclear Information System (INIS)

A patient alignment system useful with an NMR system is described for acquiring NMR data in the course of a scan of a predetermined volume of a patient. The NMR system includes a magnet for producing a polarizing magnetic field within a magnet bore sized for receiving the patient volume, and a patient transport system in general longitudinal alignment with the magnet bore. The patient transport system is capable of positioning the patient volume for scanning in an advanced position in the active region of the magnetic field centered approximately at the isocenter and for retrieving the patient volume to a staged position substantially out of the active region of the magnetic field. The patient alignment system comprises: a first assembly including at least one energy source capable of projecting in use a first visible pattern on the surface of a patient; first means for detecting the position of the patient transport system when the first visible pattern is aligned with a patient anatomical reference point in the staged position prior to performing the NMR scan; and a second assembly including at least one energy source means capable of projecting in use a second visible pattern lying substantially in a horizontal plane on a surface of a patient

399

The bar coil for NMR tomograph  

International Nuclear Information System (INIS)

The bar coil (bi-planar) for the NMR tomograph, designed for medical diagnostics, has been described. The tests of coil shown that it generates good homogenous magnetic field in a big volume what results in improving of the signal-to-noise ratio

400

Strukturní charakterizace glukan? 13 C NMR spectroscopy.  

Czech Academy of Sciences Publication Activity Database

Ro?. 99, ?. 9 (2005), s. 668. ISSN 0009-2770. [Struktura a biologické ú?inky polysacharid? a jejich derivát?. 11.11.2005, Praha] R&D Projects: GA ?R(CZ) GA525/05/0273 Keywords : solid state 13C NMR * cellulose * chitin Subject RIV: GM - Food Processing

Sp?vá?ek, Ji?í

2005-01-01

401

Kvantitativní 31P NMR spektroskopie huminových kyselin.  

Czech Academy of Sciences Publication Activity Database

Ro?. 99, - (2005), s. 236-245. ISSN 0009-2770 R&D Projects: GA ?R(CZ) GA206/02/1504 Institutional research plan: CEZ:AV0Z6066911 Keywords : 31P NMR spectroscopy * humic acids Subject RIV: EH - Ecology, Behaviour Impact factor: 0.445, year: 2005

Novák, František; Hrabal, R.; Bartošová, I.; Kal?ík, Ji?í

2005-01-01

402

Multinuclear NMR spectroscopy in the gas phase  

Science.gov (United States)

Nuclear magnetic resonance (NMR) of some nuclei (e.g. 1H, 13C, 19F, 29Si or 31P, I=1/2) gives strong signals which allow analytical studies of gaseous compounds. The other magnetic nuclei have low natural abundance or/and contain an electric quadrupole moment and their NMR signals are rather weak. In our laboratory we have developed new experimental techniques, which permit us to monitor several micrograms of chemical compounds in gaseous matrices. Applying this approach we have observed magnetic shielding of various nuclei, including 17O and 33S at the natural abundance, in the gas phase as a function of density. Density-dependent spin-spin couplings were also found for many chemical compounds. It has been shown that NMR gas-phase studies can easily be extended on molecules, which exhibit strong intermolecular interactions and are liquids at room temperature. All the latter NMR experimental results obtained for gaseous matrices are reviewed in this paper.

Jackowski, K.

2006-04-01

403

SQUID detected NMR in microtesla magnetic fields  

Science.gov (United States)

We have built an NMR system that employs a superconducting quantum interference device (SQUID) detector and operates in measurement fields of 2-25 ?T. The system uses a pre-polarizing field from 4 to 30 mT generated by simple room-temperature wire-wound coils that are turned off during measurements. The instrument has an open geometry with samples located outside the cryostat at room-temperature. This removes constraints on sample size and allows us to obtain signals from living tissue. We have obtained 1H NMR spectra from a variety of samples including water, mineral oil, and a live frog. We also acquired gradient encoded free induction decay (FID) data from a water-plastic phantom in the ?T regime, from which simple projection images were reconstructed. NMR signals from samples inside metallic containers have also been acquired. This is possible because the penetration skin depth is much greater at the low operating frequencies of this system than for conventional systems. Advantages to ultra-low field NMR measurements include lower susceptibility artifacts caused by high strength polarizing and measurement fields, and negligible line width broadening due to measurement field inhomogeneity, reducing the burden of producing highly homogeneous fields.

Matlachov, Andrei N.; Volegov, Petr L.; Espy, Michelle A.; George, John S.; Kraus, Robert H.

2004-09-01

404

NMR and Ms studies of miscellaneous hydrodisulfides  

International Nuclear Information System (INIS)

Syntheses of five alkyl and arylalkyl hydrodisulfides were designed, and three hydrodisulfides were newly obtained. Methyl and ethyl hydrodisulfides as well as the three were subjected to nmr spectroscopic analysis, and the date were compared with those of thiols and other hydrodisulfides. Ms spectra of representative hydrodisulfides were also measured. (author)

405

NMR Proton relaxation and magnetic resonance imaging  

OpenAIRE

The work in this thesis has been performed in order to give a description of the behavior of the relaxation characteristics of tissue as a function of various intrinsic and extrinsic variables. NMR proton relaxation time measurements were performed on human and animal tissues, on macromolecular solutions, and on specific model systems. ... Zie: Summary

Kamman, Richard Leonard

1987-01-01

406

Pharmacological studies of cerebral edema by NMR  

International Nuclear Information System (INIS)

Wistar male rats have been orally administered 2 mg.kg-1j-1 of triethyltin (TET) chloride for 5 consecutive days. The results was a cerebral edema which constituted a reproducible and useful experimental model for pharmacological screening of drugs used in ageing. Water content modifications and clinical behaviour for 11 days from the beginning of experiment have been linked to T1 and T2 proton relaxation times measured by nuclear magnetic resonance (1H-NMR). The observation of 3 central nervous system structures, which differ in white matter content, has lead to the conclusion that NMR is a more sensitive technique to follow up the edema evolution than the water content measurement alone; it has also allowed to discriminate intra from extra-cellular edema (osmotic and TET edema), and has proved the action of two drugs which are used in aging process treatment on the TET edema (dihydroergotoxine 2x10 mg.kg-1j-1 and (-) eburnamonine 2x50 mg.kg-1j-1). In the future the mastery of this technology will be used to study other nuclei (Na, K, P) which will bring more physiopathological informations and to pharmacological investigations of the brain by NMR tomography or focalised NMR

407

Hyperpolarized NMR Probes for Biological Assays  

Directory of Open Access Journals (Sweden)

Full Text Available During the last decade, the development of nuclear spin polarization enhanced (hyperpolarized molecular probes has opened up new opportunities for studying the inner workings of living cells in real time. The hyperpolarized probes are produced ex situ, introduced into biological systems and detected with high sensitivity and contrast against background signals using high resolution NMR spectroscopy. A variety of natural, derivatized and designed hyperpolarized probes has emerged for diverse biological studies including assays of intracellular reaction progression, pathway kinetics, probe uptake and export, pH, redox state, reactive oxygen species, ion concentrations, drug efficacy or oncogenic signaling. These probes are readily used directly under natural conditions in biofluids and are often directly developed and optimized for cellular assays, thus leaving little doubt about their specificity and utility under biologically relevant conditions. Hyperpolarized molecular probes for biological NMR spectroscopy enable the unbiased detection of complex processes by virtue of the high spectral resolution, structural specificity and quantifiability of NMR signals. Here, we provide a survey of strategies used for the selection, design and use of hyperpolarized NMR probes in biological assays, and describe current limitations and developments.

Sebastian Meier

2014-01-01

408

Visualizing transient dark states by NMR spectroscopy.  

Science.gov (United States)

Myriad biological processes proceed through states that defy characterization by conventional atomic-resolution structural biological methods. The invisibility of these 'dark' states can arise from their transient nature, low equilibrium population, large molecular weight, and/or heterogeneity. Although they are invisible, these dark states underlie a range of processes, acting as encounter complexes between proteins and as intermediates in protein folding and aggregation. New methods have made these states accessible to high-resolution analysis by nuclear magnetic resonance (NMR) spectroscopy, as long as the dark state is in dynamic equilibrium with an NMR-visible species. These methods - paramagnetic NMR, relaxation dispersion, saturation transfer, lifetime line broadening, and hydrogen exchange - allow the exploration of otherwise invisible states in exchange with a visible species over a range of timescales, each taking advantage of some unique property of the dark state to amplify its effect on a particular NMR observable. In this review, we introduce these methods and explore two specific techniques - paramagnetic relaxation enhancement and dark state exchange saturation transfer - in greater detail. PMID:25710841

Anthis, Nicholas J; Clore, G Marius

2015-02-01

409

Responsibilities of NMR application in research  

International Nuclear Information System (INIS)

NMR investigations in clinical and/or scientific studies may be covered by different radiation protection regulations and legal liability responsibilities. The following topics are discussed: incidental findings, applicability to the situation in radiological hospitals, explicit abandonment of probands/patients, liability of the clinic, liability with respect to contrast agent administration, creation of additional imaging, attendance of radiologists, information requirements.

410

NMR analysis of a fluorocarbon copolymer  

International Nuclear Information System (INIS)

Vinylidene fluoride (VF2) can be copolymerized with chlorotrifluoroethylene (CTFE) in an aqueous emulsion using a peroxide chain initiator. The physical properties of the resulting fluorocarbon polymer depend on the ratio of VF2 to CTFE and the randomness of the copolymerization. When CTFE and VF are polymerized in an approximately 3:1 mole ratio, the resulting polymer is soluble in acetone (and other solvents) at room temperature. Using proton and fluorine-19 NMR, the mole ratio of CTFE to VF2, the emulsifier (perfluorodecanoate) concentration, and the randomness of copolymerization can be determined. A trifluorotoluene internal standard is added to a d6-acetone solution of the fluoropolymer. Proton NMR is used to determine the amount of VF2. Fluorine-19 NMR is used to measure the amount of emulsifier and the randomness of copolymerization. Each analysis requires about 5 minutes, and is quite precise, with relative standard deviations from 3 to 10% (10 replicates analyzed). In addition, the results from NMR analyses agree well with wet chemical analyses. 4 refs., 3 figs., 3 tabs

411

A Primer of Fourier Transform NMR.  

Science.gov (United States)

Fourier transform nuclear magnetic resonance (NMR) is a new spectroscopic technique that is often omitted from undergraduate curricula because of lack of instructional materials. Therefore, information is provided to introduce students to the technique of data collection and transformation into the frequency domain. (JN)

Macomber, Roger S.

1985-01-01

412

NMR study of GdPb2  

International Nuclear Information System (INIS)

Pb NMR results in GdPb2 have revealed that most parts of GdPb2 are not a coexisting compound of superconductivity and antiferromagnetic ordering, but a mixture of a superconducting Pb (or Pb-rich) region and an antiferromagnetic Gd compound (or metal). Some structural models for the Gd-Pb system are proposed. ((orig.))

413

NMR imaging: its potential clinical impact  

International Nuclear Information System (INIS)

Nuclear magnetic resonance, a developing technique for visualizing soft tissue pathology that is inaccessible to any modality utilizing ionizing radiation, seems likely to eventually outdistance CT scanning in clinical usefulness. In the near future, NMR, now in its infancy, should complement CT scanning and be increasingly used in probing hematologic and metabolic processes

414

Crystallinity and compositional changes in carbonated apatites: Evidence from {sup 31}P solid-state NMR, Raman, and AFM analysis  

Energy Technology Data Exchange (ETDEWEB)

Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and {sup 31}P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse {sup 31}P NMR linewidth and inverse Raman PO{sub 4}{sup 3?}?{sub 1} bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3–10.3 wt% CO{sub 3}{sup 2?} range investigated. Comparison with bone powder crystallinities showed agreement with values predicted by NMR and Raman calibration curves. Carbonate content was divided into two domains by the {sup 31}P NMR chemical shift frequency and the Raman phosphate ?{sub 1} band position. These parameters remain stable except for an abrupt transition at 6.5 wt% carbonate, a composition which corresponds to an average of one carbonate per unit cell. This near-binary distribution of spectroscopic properties was also found in AFM-measured particle sizes and Ca/P molar ratios by elemental analysis. We propose that this transition differentiates between two charge-balancing ion-loss mechanisms as measured by Ca/P ratios. These results define a criterion for spectroscopic characterization of B-type carbonate substitution in apatitic minerals. - Graphical abstract: Carbonated apatite shows an abrupt change in spectral (NMR, Raman) and morphological (AFM) properties at a composition of about one carbonate substitution per unit cell. Display Omitted - Highlights: • Crystallinity (XRD), particle size (AFM) of carbonated apatites and bone mineral. • Linear relationships among crystallinity, {sup 31}P NMR and Raman inverse bandwidths. • Low and high carbonated apatites use different charge-balancing ion-loss mechanism.

McElderry, John-David P.; Zhu, Peizhi [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Mroue, Kamal H. [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Department of Biophysics, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Xu, Jiadi [Department of Biophysics, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Pavan, Barbara [Department of Chemistry and Science of Advanced Materials Program, Central Michigan University, Mt. Pleasant, MI 48859 (United States); Fang, Ming [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Zhao, Guisheng; McNerny, Erin; Kohn, David H.; Franceschi, Renny T. [School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Holl, Mark M.Banaszak [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Tecklenburg, Mary M.J., E-mail: mary.tecklenburg@cmich.edu [Department of Chemistry and Science of Advanced Materials Program, Central Michigan University, Mt. Pleasant, MI 48859 (United States); Ramamoorthy, Ayyalusamy [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Department of Biophysics, University of Michigan, Ann Arbor, MI 48109-1055 (United States); Morris, Michael D. [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055 (United States)

2013-10-15

415

Crystallinity and compositional changes in carbonated apatites: Evidence from 31P solid-state NMR, Raman, and AFM analysis  

International Nuclear Information System (INIS)

Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and 31P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse 31P NMR linewidth and inverse Raman PO43??1 bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3–10.3 wt% CO32? range investigated. Comparison with bone powder crystallinities showed agreement with values predicted by NMR and Raman calibration curves. Carbonate content was divided into two domains by the 31P NMR chemical shift frequency and the Raman phosphate ?1 band position. These parameters remain stable except for an abrupt transition at 6.5 wt% carbonate, a composition which corresponds to an average of one carbonate per unit cell. This near-binary distribution of spectroscopic properties was also found in AFM-measured particle sizes and Ca/P molar ratios by elemental analysis. We propose that this transition differentiates between two charge-balancing ion-loss mechanisms as measured by Ca/P ratios. These results define a criterion for spectroscopic characterization of B-type carbonate substitution in apatitic minerals. - Graphical abstract: Carbonated apatite shows an abrupt change in spectral (NMR, Raman) and morphological (AFM) properties at a composition of about one carbonate substitution per unit cell. Display Omitted - Highlights: • Crystallinity (XRD), particle size (AFM) of carbonated apatites and bone mineral. • Linear relationships among crystallinity, 31P NMR and Raman inverse bandwidths. • Low and high carbonated apatites use different charge-balancing ion-loss mechanism

416

Dynamics of reassembled thioredoxin studied by magic angle spinning NMR: snapshots from different time scales.  

Science.gov (United States)

Solid-state NMR spectroscopy can be used to probe internal protein dynamics in the absence of the overall molecular tumbling. In this study, we report (15)N backbone dynamics in differentially enriched 1-73(U-(13)C,(15)N)/74-108(U-(15)N) reassembled thioredoxin on multiple time scales using a series of 2D and 3D MAS NMR experiments probing the backbone amide (15)N longitudinal relaxation, (1)H-(15)N dipolar order parameters, (15)N chemical shift anisotropy (CSA), and signal intensities in the temperature-dependent and (1)H T(2)'-filtered NCA experiments. The spin-lattice relaxation rates R(1) (R(1) = 1/T(1)) were observed in the range from 0.012 to 0.64 s(-1), indicating large site-to-site variations in dynamics on pico- to nanosecond time scales. The (1)H-(15)N dipolar order parameters, , and (15)N CSA anisotropies, delta(sigma), reveal the backbone mobilities in reassembled thioredoxin, as reflected in the average = 0.89 +/- 0.06 and delta(sigma) = 92.3 +/- 5.2 ppm, respectively. From the aggregate of experimental data from different dynamics methods, some degree of correlation between the motions on the different time scales has been suggested. Analysis of the dynamics parameters derived from these solid-state NMR experiments indicates higher mobilities for the residues constituting irregular secondary structure elements than for those located in the alpha-helices and beta-sheets, with no apparent systematic differences in dynamics between the alpha-helical and beta-sheet residues. Remarkably, the dipolar order parameters derived from the solid-state NMR measurements and the corresponding solution NMR generalized order parameters display similar qualitative trends as a function of the residue number. The comparison of the solid-state dynamics parameters to the crystallographic B-factors has identified the contribution of static disorder to the B-factors. The combination of longitudinal relaxation, dipolar order parameter, and CSA line shape analyses employed in this study provides snapshots of dynamics and a new insight on the correlation of these motions on multiple time scales. PMID:19736935

Yang, Jun; Tasayco, Maria Luisa; Polenova, Tatyana

2009-09-30

417

NMR Constraints Analyser: a web-server for the graphical analysis of NMR experimental constraints  

OpenAIRE

Nuclear magnetic resonance (NMR) spectroscopy together with X-ray crystallography, are the main techniques used for the determination of high-resolution 3D structures of biological molecules. The output of an NMR experiment includes a set of lower and upper limits for the distances (constraints) between pairs of atoms. If the number of constraints is high enough, there will be a finite number of possible conformations (models) of the macromolecule satisfying the data. Thus, the more constrain...

Heller, Davide Martin; Giorgetti, Alejandro

2010-01-01

418

Proton NMR studies on Megasphaera elsdenii flavodoxin: structure elucidation by 2D-NMR and implications.  

OpenAIRE

1H NMR techniques have been applied for a thorough study of the uncrystallizable Megasphaera elsdenii flavodoxin in its three redox states. The aim of the research project described in this thesis was to obtain answers regarding questions concerning the redox potential regulation of FMN by the protein and the observed activation barrier occurring between the oxidized and one-electron reduced redox states of the protein. Detailed information about the structure of the, from a NMR point of view...

Mierlo, C. P. M.

1990-01-01

419

Dynamic nuclear polarization surface enhanced NMR spectroscopy.  

Science.gov (United States)

Many of the functions and applications of advanced materials result from their interfacial structures and properties. However, the difficulty in characterizing the surface structure of these materials at an atomic level can often slow their further development. Solid-state NMR can probe surface structure and complement established surface science techniques, but its low sensitivity often limits its application. Many materials have low surface areas and/or low concentrations of active/surface sites. Dynamic nuclear polarization (DNP) is one intriguing method to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude. In a DNP experiment, the large polarization of unpaired electrons is transferred to surrounding nuclei, which provides a maximum theoretical DNP enhancement of ?658 for (1)H NMR. In this Account, we discuss the application of DNP to enhance surface NMR signals, an approach known as DNP surface enhanced NMR spectroscopy (DNP SENS). Enabling DNP for these systems requires bringing an exogeneous radical solution into contact with surfaces without diluting the sample. We proposed the incipient wetness impregnation technique (IWI), a well-known method in materials science, to impregnate porous and particulate materials with just enough radical containing solution to fill the porous volume. IWI offers several advantages: it is extremely simple, provides a uniform wetting of the surface, and does not increase the sample volume or substantially reduce the concentration of the sample. This Account describes the basic principles behind DNP SENS through results obtained for mesoporous and nanoparticulate samples impregnated with radical solutions. We also discuss the quantification of the overall sensitivity enhancements obtained with DNP SENS and compare that with ordinary room temperature NMR spectroscopy. We then review the development of radicals and solvents that give the best possible enhancements today. With the best polarizing mixtures, DNP SENS enhances sensitivity by a factor of up to 100, which decreases acquisition time by five orders of magnitude. Such enhancement enables the detailed and expedient atomic level characterization of the surfaces of complex materials at natural isotopic abundance and opens new avenues for NMR. To illustrate these improvements, we describe the successful application of DNP SENS to characterize hybrid materials, organometallic surface species, and metal-organic frameworks. PMID:23517009

Rossini, Aaron J; Zagdoun, Alexandre; Lelli, Moreno; Lesage, Anne; Copéret, Christophe; Emsley, Lyndon

2013-09-17

420

93Nb- and 27Al-NMR/NQR studies of the praseodymium based PrNb2Al20  

Science.gov (United States)

We report a study of 93Nb- and 27Al-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) in a praseodymium based compound PrNb2Al20. The observed NMR line at around 3 T and 30 K shows a superposition of typical powder patterns of one Nb signal and at least two Al signals. 93Nb-NMR line could be reproduced by using the previously reported NQR frequency ?Q ? 1.8MHz and asymmetry parameter ? ? 0 [Kubo T et al 2014 JPS Conf. Proc. 3 012031]. From 27Al-NMR/NQR, NQR parameters are obtained to be ?Q,A ? 1.53 MHz, and ?A ? 0.20 for the site A, and ?Q,B ? 2.28 MHz, and ?B ? 0.17 for the site B. By comparing this result with the previous 27Al-NMR study of PrT2Al20 (T = Ti, V) [Tokunaga Y et al 2013 Phys. Rev. B 88 085124], these two Al site are assigned to the two of three crystallographycally inequivalent Al sites.

Kubo, Tetsuro; Kotegawa, Hisashi; Tou, Hideki; Higashinaka, Ryuji; Nakama, Akihiro; Aoki, Yuji; Sato, Hideyuki

2015-03-01

421

Multiparametric optimization of (31)P NMR spectroscopic analysis of phospholipids in crude tissue extracts. 2. Line width and spectral resolution.  

Science.gov (United States)

The quality of NMR spectra in general and of spectra to be used for analysis of compound mixtures in particular is essentially defined by two basic parameters: signal-to-noise ratio and spectral resolution. The latter is determined by signal dispersion (chemical shift differences) and line widths. The present study focuses on multiparametric optimization of spectral resolution in (31)P NMR spectra of phospholipids from brain tissue extracts. This report presents, for the first time, a systematic and comprehensive study of phospholipid (31)P NMR line widths as a function of four experimental parameters: (i) extract concentration, (ii) concentration of a chelating agent, (iii) pH of the aqueous component of the solvent system, and (iv) temperature of the NMR measurement. Theoretical underpinnings of observed line width variations (transversal relaxation effects) are briefly discussed. In conjunction with an analogous, concurrently published report on chemical shift effects in the same tissue extract system, this multiparametric line width study provides a complete set of methodological guidelines for (i) generating well-defined tissue extracts, and (ii) choosing matched and optimized measurement conditions for highly reproducible and well-resolved (31)P NMR spectra of brain phospholipids. This study also offers a comprehensive database and a strategy for rational and efficient optimization of phospholipid spectra from other tissue extracts. PMID:20443551

Lutz, Norbert W; Cozzone, Patrick J

2010-07-01

422

NMR Constraints Analyser: a web-server for the graphical analysis of NMR experimental constraints.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) spectroscopy together with X-ray crystallography, are the main techniques used for the determination of high-resolution 3D structures of biological molecules. The output of an NMR experiment includes a set of lower and upper limits for the distances (constraints) between pairs of atoms. If the number of constraints is high enough, there will be a finite number of possible conformations (models) of the macromolecule satisfying the data. Thus, the more constraints are measured, the better defined these structures will be. The availability of a user-friendly tool able to help in the analysis and interpretation of the number of experimental constraints per residue, is thus of valuable importance when assessing the levels of structure definition of NMR solved biological macromolecules, in particular, when high-quality structures are needed in techniques such as, computational biology approaches, site-directed mutagenesis experiments and/or drug design. Here, we present a free publicly available web-server, i.e. NMR Constraints Analyser, which is aimed at providing an automatic graphical analysis of the NMR experimental constraints atom by atom. The NMR Constraints Analyser server is available from the web-page http://molsim.sci.univr.it/constraint. PMID:20513646

Heller, Davide Martin; Giorgetti, Alejandro

2010-07-01

423

OPENCORE NMR: open-source core modules for implementing an integrated FPGA-based NMR spectrometer.  

Science.gov (United States)

A tool kit for implementing an integrated FPGA-based NMR spectrometer [K. Takeda, A highly integrated FPGA-based nuclear magnetic resonance spectrometer, Rev. Sci. Instrum. 78 (2007) 033103], referred to as the OPENCORE NMR spectrometer, is open to public. The system is composed of an FPGA chip and several peripheral boards for USB communication, direct-digital synthesis (DDS), RF transmission, signal acquisition, etc. Inside the FPGA chip have been implemented a number of digital modules including three pulse programmers, the digital part of DDS, a digital quadrature demodulator, dual digital low-pass filters, and a PC interface. These FPGA core modules are written in VHDL, and their source codes are available on our website. This work aims at providing sufficient information with which one can, given some facility in circuit board manufacturing, reproduce the OPENCORE NMR spectrometer presented here. Also, the users are encouraged to modify the design of spectrometer according to their own specific needs. A home-built NMR spectrometer can serve complementary roles to a sophisticated commercial spectrometer, should one comes across such new ideas that require heavy modification to hardware inside the spectrometer. This work can lower the barrier of building a handmade NMR spectrometer in the laboratory, and promote novel and exciting NMR experiments. PMID:18374613

Takeda, Kazuyuki

2008-06-01

424

Calculations of NMR properties for sI and sII clathrate hydrates of carbon dioxide  

Science.gov (United States)

Nuclear shielding and spin-spin coupling constants (intra- and intermolecular) have been calculated for cages forming sI and sII clathrate hydrates of carbon dioxide (for all atoms of host and guest molecules). Structures of 512, 51262 and 51264 cages have been constructed using neutronographic data and DFT/B3LYP calculations conducted with HuzIII-su3 basis set for NMR parameters determination. Based on those results it is possible to discriminate between CO2 molecules residing in each type of the cage. The analysis of NMR parameters calculated for water molecules is focused on their dependence on geometry of the molecular environment. It is possible to connect changes in NMR parameters with types of H-bond patterns present in cages of hydrates and the strength of H-bonds formed. Moreover, our results show that topologically differentiable water molecules forming cages are characterized by distinct NMR parameters, for example 17O shielding constants for water molecules of different topologies differ by 1.6 and 2.1 ppm for cages 51262 and 51264, respectively. This observation could be confirmed experimentally.

Siuda, Pawe?; Sadlej, Joanna

2014-03-01

425

Inadequate-1D and dynamic NMR of mesoion 3-phenyl-1-thio-2,3,4-triazole-5-methylides  

International Nuclear Information System (INIS)

The chemical shifts and coupling constants have been measured in series of mesoionic triazoles by means of inadequate atoms and dynamic NMR techniques. The electronic structure and other parameters of C5-C6 chemical bond in different derivatives of mesoionic 3-phenyl-1-thio-2,3,4-triazole-5 methyls have been determined

426

Toward cardiac electrophysiological mapping based on micro-Tesla NMR: a novel modality for localizing the cardiac reentry  

Directory of Open Access Journals (Sweden)

Full Text Available Matching the proton magnetic resonance frequency to the frequency of a periodic electrophysiological excitation of myocardium enables direct localization of the cardiac reentry by magnetic resonance imaging techniques. The feasibility of this new idea has been demonstrated by conducting a numerical simulation based on a realistic heart model and experimental parameters in SQUID-based micro-Tesla NMR.

Kiwoong Kim

2012-06-01

427

Solid state NMR of biopolymers and synthetic polymers  

International Nuclear Information System (INIS)

Solid state NMR has been invaluable in evaluating the structure, phase separation, and dynamics of polymers. Because polymers are generally used in the solid state, solid state NMR is especially powerful because it provides information about the materials in their native state. This review gives a general overview of solid state NMR, concentrating on solid state 13 C and 2 H NMR. It then focuses on two examples: the biopolymer spider silka and the engineering material polyurethane. It illustrates how solid state NMR can provide new information about synthetic and bio-polymers. (author)

428

Automated Microflow NMR: Routine Analysis of Five-Microliter Samples  

OpenAIRE

A microflow CapNMR probe double-tuned for 1H and 13C was installed on a 400-MHz NMR spectrometer and interfaced to an automated liquid handler. Individual samples dissolved in DMSO-d6 are submitted for NMR analysis in vials containing as little as 10 ?L of sample. Sets of samples are submitted in a low-volume 384-well plate. Of the 10 ?L of sample per well, as with vials, 5 ?L is injected into the microflow NMR probe for analysis. For quality control of chemical libraries, 1D NMR spectra a...

Jansma, Ariane; Chuan, Tiffany; Geierstanger, Bernhard H.; Albrecht, Robert W.; Olson, Dean L.; Peck, Timothy L.

2005-01-01

429

Squid detected NMR and MRI at ultralow fields  

Science.gov (United States)

Nuclear magnetic resonance (NMR) signals are detected in microtesla fields. Prepolarization in millitesla fields is followed by detection with an untuned dc superconducting quantum interference device (SQUID) magnetometer. Because the sensitivity of the SQUID is frequency independent, both signal-to-noise ratio (SNR) and spectral resolution are enhanced by detecting the NMR signal in extremely low magnetic fields, where the NMR lines become very narrow even for grossly inhomogeneous measurement fields. MRI in ultralow magnetic field is based on the NMR at ultralow fields. Gradient magnetic fields are applied, and images are constructed from the detected NMR signals.

Clarke, John (Berkeley, CA); Pines, Alexander (Berkeley, CA); McDermott, Robert F. (Monona, WI); Trabesinger, Andreas H. (London, GB)

2008-12-16

430

75As NMR-NQR study in superconducting LiFeAs  

Science.gov (United States)

We report results of 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments as well as 7Li NMR on different samples of self flux grown LiFeAs and 5% Co doped LiFeAs single crystals, and a polycrystalline LiFeAs sample. We were able to distinguish the samples by their slightly different quadrupole frequencies, ?Q, which is a direct measure of the electric field gradient (EFG) at the As site. Interestingly, samples with a large quadrupole frequency appear to show a different Knight shift and spin lattice relaxation in the superconducting state from those with a lower ?Q, yet all the samples are clearly superconducting. For sample S1 which has the largest ?Q, we find constant Knight shift 𝒦 across Tc for a certain direction of the magnetic field and a peculiar upturn of the NQR spin lattice relaxation rate (T1T)-1 below Tc. In contrast, samples with a lower ?Q exhibit the expected behavior for a singlet superconductor: a drop of 𝒦 and (T1T)-1 for both NMR and NQR below Tc. Our results show that already tiny changes in stoichiometry uncovered by slightly different NQR frequencies lead to very different behavior of the NMR parameters in the superconducting state of LiFeAs. Different possibilities will be discussed which may explain the contrasting behavior.

Baek, S.-H.; Grafe, H.-J.; Hammerath, F.; Fuchs, M.; Rudisch, C.; Harnagea, L.; Aswartham, S.; Wurmehl, S.; van den Brink, J.; Büchner, B.

2012-05-01

431

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

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Neutron scattering and NMR approaches were used to characterize seed germination. • A parallel between macromolecular motions and water dynamics was established. • Freezing/thawing cycle revealed a hysteresis connected to the seed hydration level. - Abstract: 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 [UR1268 Biopolymères Interactions Assemblages, INRA, F-44316 Nantes (France); Natali, Francesca [CNR-IOM-OGG, c/o Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9 (France); Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9 (France); Peters, Judith [Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9 (France); Université Joseph Fourier UFR PhITEM, BP 53, 38041 Grenoble Cedex 9 (France); Institut de Biologie Structurale, 41 rue Jules Horowitz, 38027 Grenoble Cedex 1 (France); Foucat, Loïc, E-mail: Loic.Foucat@nantes.inra.fr [UR1268 Biopolymères Interactions Assemblages, INRA, F-44316 Nantes (France)

2014-01-15

432

Non-destructive characterization of materials by single-sided NMR  

Energy Technology Data Exchange (ETDEWEB)

The experiments conducted in this work demonstrate the efficiency and sensitivity of single-sided NMR for investigating macromolecular materials on large time and length scales. Elastomers can readily be characterized by unilateral NMR of protons in terms of a variety of parameters, which correlate with the overall molecular mobility. In this way information about the cross-link density, state of cure and strain, the effects of aging and product heterogeneity can obtained. For these purposes, the NMR-MOUSE was used to optimize product development and to monitor product and production quality on-line. The sensor is also suitable for nondestructive probing of the mechanical deformation in cross-linked elastomers. A special magnet design that fits a stress-strain device has been used for complementary investigation of a series of different rubber stripes during mechanical testing. The profile NMR-MOUSE was found to be a unique tool for the characterization of changes induced by the UV irradiation in natural rubber. The aging profiles were interpreted for the first time based on a novel model in which the radiation absorption coefficient depends on the depth in the sample. (orig.)

Goga, Nicolae-Octavian

2007-08-20

433

Bayesian deconvolution and quantification of metabolites in complex 1D NMR spectra using BATMAN.  

Science.gov (United States)

Data processing for 1D NMR spectra is a key bottleneck for metabolomic and other complex-mixture studies, particularly where quantitative data on individual metabolites are required. We present a protocol for automated metabolite deconvolution and quantification from complex NMR spectra by using the Bayesian automated metabolite analyzer for NMR (BATMAN) R package. BATMAN models resonances on the basis of a user-controllable set of templates, each of which specifies the chemical shifts, J-couplings and relative peak intensities for a single metabolite. Peaks are allowed to shift position slightly between spectra, and peak widths are allowed to vary by user-specified amounts. NMR signals not captured by the templates are modeled non-parametrically by using wavelets. The protocol covers setting up user template libraries, optimizing algorithmic input parameters, improving prior information on peak positions, quality control and evaluation of outputs. The outputs include relative concentration estimates for named metabolites together with associated Bayesian uncertainty estimates, as well as the fit of the remainder of the spectrum using wavelets. Graphical diagnostics allow the user to examine the quality of the fit for multiple spectra simultaneously. This approach offers a workflow to analyze large numbers of spectra and is expected to be useful in a wide range of metabolomics studies. PMID:24853927

Hao, Jie; Liebeke, Manuel; Astle, William; De Iorio, Maria; Bundy, Jacob G; Ebbels, Timothy M D

2014-01-01

434

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

International Nuclear Information System (INIS)

Highlights: • Neutron scattering and NMR approaches were used to characterize seed germination. • A parallel between macromolecular motions and water dynamics was established. • Freezing/thawing cycle revealed a hysteresis connected to the seed hydration level. - Abstract: 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

435

An efficient spectra processing method for metabolite identification from 1H-NMR metabolomics data.  

Science.gov (United States)

The spectra processing step is crucial in metabolomics approaches, especially for proton NMR metabolomics profiling. During this step, noise reduction, baseline correction, peak alignment and reduction of the 1D (1)H-NMR spectral data are required in order to allow biological information to be highlighted through further statistical analyses. Above all, data reduction (binning or bucketing) strongly impacts subsequent statistical data analysis and potential biomarker discovery. Here, we propose an efficient spectra processing method which also provides helpful support for compound identification using a new data reduction algorithm that produces relevant variables, called buckets. These buckets are the result of the extraction of all relevant peaks contained in the complex mixture spectra, rid of any non-significant signal. Taking advantage of the concentration variability of each compound in a series of samples and based on significant correlations that link these buckets together into clusters, the method further proposes automatic assignment of metabolites by matching these clusters with the spectra of reference compounds from the Human Metabolome Database or a home-made database. This new method is applied to a set of simulated (1)H-NMR spectra to determine the effect of some processing parameters and, as a proof of concept, to a tomato (1)H-NMR dataset to test its ability to recover the fruit extract compositions. The implementation code for both clustering and matching steps is available upon request to the corresponding author. PMID:23525538