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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

2011-11-01

2

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

International Nuclear Information System (INIS)

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

2009-10-01

3

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

International Nuclear Information System (INIS)

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

2009-06-01

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

2013-12-01

5

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

International Nuclear Information System (INIS)

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

2013-07-15

6

Theoretical investigations of the spin Hamiltonian parameters and local angular variations for the trigonal V3+ centers in alum compounds  

Science.gov (United States)

The spin Hamiltonian parameters (zero-field splittings D, g factors g // and g ?) for V3+ in the alum compounds are theoretically studied using the perturbation formulas for these parameters for a 3d2 ion in the trigonally distorted octahedra. The contributions from the dynamical Jahn-Teller effect, the configuration interactions and the ligand orbital and spin-orbit coupling interactions are considered from the cluster approach in a uniform way. The angles in the deformed octahedra around V3+ ions are increased by 1.1°-2.7°, as compared with those ones for the host. The theoretical spin Hamiltonian parameters based on the above angular variations and the related effects show good agreement with the experimental data, which reveal that these effects (especially the Jahn-Teller effect) can bring forward significant influences on the spin Hamiltonian parameters, and should be taken into account in electron paramagnetic resonance (EPR) analysis. The contributions from the configuration interactions and the ligand orbital and spin-orbit coupling interactions are quantitatively involved from the cluster approach in a uniform way. The results are discussed.

Zhang, Zhi-Hong; Wu, Shao-Yi; Hu, Xian-Fen; Kuang, Min-Quan

2014-04-01

7

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

8

Theoretical studies of the Spin Hamiltonian Parameters for the orthorhombic Pr4+ ion in SrCeO3 crystal  

International Nuclear Information System (INIS)

The perturbation formulae of the Spin Hamiltonian Parameters (EPR parameters anisotropic gyromagnetic factors gx, gy, gz and hyperfine structure constants Ax, Ay, Az) for the lowest Kramers doublet of 2F5/2 of 4f1 ion in orthorhombic symmetry are established. In these formulae, the contributions of the covalence effects, the admixture between J = 5/2 and J = 7/2 states as well as the second-order perturbation are all included. The crystal field parameters for the studied Pr4+ center are calculated from the superposition model and the crystal structure data. Based on the perturbation equations and related parameters, the g factors gx, gy, gz and hyperfine structure constants Ax, Ay, Az for orthorhombic Pr4+ ion in SrCeO3 are calculated. The results are in reasonable agreement with the observed values. The results are discussed

2008-02-28

9

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-12-01

10

Investigations of the spin-Hamiltonian parameters for Ta4+ ions in LiTaO3 crystal  

International Nuclear Information System (INIS)

The spin-Hamiltonian parameters (g factors g|| , gperpendicular and hyperfine structure constants A|| , Aperpendicular) of Ta4+ ion (which is produced by a self-trapped electron at the Ta5+ site) in LiTaO3 crystal are calculated from three theoretical methods, the complete diagonalization (of energy matrix including Zeeman interaction and hyperfine interaction) method (CDM), the first-order perturbation formulas related to 2T2 state and the third-order perturbation formulas. From the calculations, it is found that only the calculated results using the CDM show good agreement with the experimental values, but those using the rest two methods do not. The causes are discussed. The defect structure of Ta4+ defect in LiTaO3 is also obtained from the calculations. The result is coincident with the expectation based on the electrostatic interaction and electron cloud overlap.

2009-05-27

11

Investigations on the spin Hamiltonian parameters for Gd3+ in YBa2Cu3O6+x  

International Nuclear Information System (INIS)

The spin Hamiltonian parameters [zero-field splittings (ZFSs) b20, b22, b40, b44, b60, b64 and the g factors] for the orthorhombic Gd3+ center in YBa2Cu3O6+x are theoretically investigated from the superposition model formulas for the ZFSs and the approximation formula of the g factors including admixture of the ground 8S7/2 and the excited 6L7/2 (L=P,D,F,G) states via the spin-orbit coupling interactions, respectively. The large anisotropy of the g factors in the (a,b) plane, originated from the anisotropy of spin susceptibility, is illustrated by the effective spin-orbit coupling coefficients ?' in the a and b principle axis directions. The calculated ZFSs and the g factors show reasonable agreement with the observed values

2005-08-01

12

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

International Nuclear Information System (INIS)

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

2013-10-15

13

Calculations of spin Hamiltonian parameters and analysis of trigonal distortions in LiSr(Al,Ga)F6:Cr3+ crystals  

International Nuclear Information System (INIS)

The effective spin-Hamiltonian (SH) parameters (zero-field splitting D and g factors g -parallel and g -perpendicular ) for Cr3+ ions in LiSr(Al,Ga)F6 crystals are calculated from the complete high-order perturbation formulae for a d3 ion. Parameters of trigonal crystal field acting on the Cr3+ ion are calculated. The magnitude of trigonal distortion of the [CrF6]3- clusters is related to the experimental measurements of the spin-Hamiltonian parameters in the considered systems. Since in both crystals gparallel perpendicular , [CrF6]3- clusters undergo an axial compression along the C3 axis. Experimental values of the hyperfine structure constants Aparallel and Aperpendicular are used to evaluate the core polarization constant ? for Cr3+ ion in both crystals

2006-10-01

14

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

Science.gov (United States)

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

Yang, Mei; Wen-Chen, Zheng; Hong-Gang, Liu

2013-12-01

15

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

16

Investigation of the optical spectra and spin-Hamiltonian parameters for the rhombic Cu2+ center in ?-Ca3(PO4)2  

Science.gov (United States)

The four optical band positions and six spin-Hamiltonian parameters (the g factors gi and the hyperfine structure constants Ai, i=x, y, z) for the rhombic Cu2+ center in ?-Ca3(PO4)2 are calculated by two theoretical methods: the complete diagonalization (of energy matrix) method and the perturbation theory method (PTM). Both methods are based on the cluster approach, in which the covalence due to admixture of ligands to the central metal ion is considered. The calculated results of the two methods are close to each other and agree with the experimental values. This suggests that both methods are effective in explaining the optical and electron paramagnetic resonance data for d9 ions in crystals. The calculations also show that although the admixture of |dz2rang to the ground state wave function is small, it should not be neglected in calculations of spin-Hamiltonian parameters. So, in PTM, the high-order perturbation formulae of spin-Hamiltonian parameters based on the cluster approach for d9 ion in rhombic symmetry should be derived by taking into account the admixture of the |dz2rang state to the |dx2-y2rang ground state.

Zheng, Wen-Chen; Zhang, Dong-Ting; He, Lv; Su, Ping

2011-08-01

17

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-11-15

18

Theoretical calculations of the optical band positions and spin-Hamiltonian parameters for Cr3+ ions in Y2Ti2O7 crystal  

Science.gov (United States)

The optical band positions and spin-Hamiltonian parameters (g factors g?g? and zero-field splitting D) for the trigonal Cr3+ centers in Y2Ti2O7 crystal are calculated from the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model. In the calculations, the contributions to spectral data from both the spin-orbit parameter of central dn ion and that of ligand ion are considered and the crystal field parameters used are estimated from the superposition model. The calculated results are in reasonable agreement with the experimental values. The defect structures of Cr3+ center is suggested.

Yang, Mei; Yu-Guang, Yang; Wen-Chen, Zheng

2012-09-01

19

Theoretical investigations of the spin-Hamiltonian parameters and local structural distortion of Fe(3+): ZnAl2O4 crystals.  

Science.gov (United States)

The relations between the spin-Hamiltonian (SH) parameters and the structural parameters of the Fe(3+) ions in Fe(3+): 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 Fe(3+) ions in Fe(3+): 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 Fe(3+) ions in Fe(3+): 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 Fe(3+) ion in Fe(3+): ZnAl2O4 crystals yield a good agreement with experiment findings by taking into account the lattice distortions: ?R=0.0191nm and ??=0.076°. In conclusion, our research shows that there is a slight local structure distortion for Fe(3+) ions in Fe(3+): ZnAl2O4 crystals, but the site of Fe(3+) still retains D3d symmetry. On the other hand, it is found for Fe(3+) ions in Fe(3+): 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. PMID:24835727

Yang, Zi-Yuan

2014-10-15

20

Theoretical studies on the spin Hamiltonian parameters for monovalent chromium in ZnX (X=S, Se, Te) and CdTe  

Science.gov (United States)

The spin Hamiltonian parameters (g factor and hyperfine structure constants) of Cr+ in ZnX (X = S, Se, Te) and CdTe are theoretically investigated, using the perturbation formulas of these parameters for a tetrahedral 3d5 cluster. Both the contributions from the crystal-field (CF) and charge transfer (CT) mechanisms are considered from the cluster approach. The calculated results show good agreement with the experimental data. The CT contribution to g-shift ?g (=g - g s, where g s =2.0023 is the spin only value) is opposite (positive) in sign related to the CF one, and its importance (characterized by the relative ratio (|?g CT/?g CF|) is 11%, 66% and 104% (71%) for ZnS, ZnSe and ZnTe (CdTe), respectively. ACT from the CT contribution to hyperfine structure constant is the same (positive) in sign and about 50-53% in magnitude as compared with ACF from the CF one.

Hu, Xian-Fen; Wu, Shao-Yi; Kuang, Min-Quan; Li, Guo-Liang

2014-03-01

 
 
 
 
21

Studies of the spin Hamiltonian parameters and the local structure of tetragonal Zr{sup 3+} centers in orthophosphate MPO{sub 4} (M=Sc,Lu,Y) crystals  

Energy Technology Data Exchange (ETDEWEB)

The spin Hamiltonian parameters (g factors g {sub parallel}, g {sub perpendicular} {sub to} and hyperfine structure constants A {sub parallel},A {sub perpendicular} {sub to}) of Zr{sup 3+} on the tetragonal M{sup 3+} (M=Sc,Lu,Y) sites of zircon-type orthophosphate MPO{sub 4} crystals are calculated by high-order perturbation formulas of d{sup 1} ions in tetragonal symmetry. The crystal-field parameters are estimated by the superposition model and reasonable local structural data of impurity centers. The results show good agreement with the experimental values. It appears that in the case of size mismatch, the explanation of the spin Hamiltonian parameters of a paramagnetic impurity in crystals should take the impurity-induced local lattice relaxation into account. (orig.)

Qu Gui-Qiang; Fang Wang [Dept. of Material Science, Sichuan Univ., Chengdu (China); Zheng Wen-Chen [Dept. of Material Science, Sichuan Univ., Chengdu (China); International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang (China)

2006-12-15

22

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

International Nuclear Information System (INIS)

ion and p orbitals of ligand ion via covalence effect are taken into account. From the calculations, the spin-Hamiltonian parameters of these tetragonal md9 centers in AgCl are explained reasonably and the tetragonal distortions (characterized by the tetragonal elongation ?R = R|| - Rperpendicular, where R|| and Rperpendicular denote the metal-ligand distances parallel with and perpendicular to the tetragonal axis) of these centers due to Jahn-Teller effect are obtained. The results are discussed.

2010-10-08

23

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

Science.gov (United States)

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

Dong, Hui-Ning; Dong, Meng-Ran; Li, Jin-Jin; Liu, Jun

2013-10-01

24

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

2006-04-17

25

Studies of the optical spectrum band positions and spin-Hamiltonian parameters for Pa{sup 4+} ion in ThX{sub 4} (X=Cl, Br) crystals  

Energy Technology Data Exchange (ETDEWEB)

The optical spectrum band positions and spin-Hamiltonian (SH) parameters (g factors g{sub ||} and g{sub perpendicular} and hyperfine structure constants A{sub ||} and A{sub perpendicular}) for 5f{sup 1} ion Pa{sup 4+} at the tetragonal Th{sup 4+} site of ThX{sub 4} (X=Cl, Br) crystals are calculated from a complete diagonalization (of energy matrix) method (CDM). In the CDM, the magnetic (or Zeeman) interaction and hyperfine interaction terms are added to the Hamiltonian in the conventional CDM and so the optical and EPR spectra data can be studied in a unified way. The calculated results are in reasonable agreement with experimental values. The possible misprints or small errors in the experimental g factors for Pa{sup 4+} in ThX{sub 4} crystals are pointed out. The results are discussed.

Zheng Wenchen, E-mail: zhengwc1@163.co [Department of Material Science, Sichuan University, Chengdu 610064 (China) and International Center for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China); Liu Honggang [Department of Material Science, Sichuan University, Chengdu 610064 (China); Yang Weiqing [Department of Material Science, Sichuan University, Chengdu 610064 (China); Department of Optics and Electronics, Chengdu University of Information Technology, Chengdu 610225 (China); Qu Guiqiang [Department of Material Science, Sichuan University, Chengdu 610064 (China)

2010-11-15

26

Nuclear spin Hamiltonian in magnets involving Cu2+ ions  

International Nuclear Information System (INIS)

Generally, in the hyperfine magnetic field which affects the nuclei of magnetic ions, there are three fields of the Fermi contact field generated by the interaction between d-electrons and the s-electrons in the inner shell, the dipole field due to the interaction of dipoles by unpaired d-electrons, and the orbital field generated by unannihilated orbital angular momentum. It is important to determine accurately and experimentally the scale of hyperfine magnetic field and quadrupole interaction in case of Cu2+ ions. This paper is described on the theories concerning the measurement of NMR (nuclear magnetic resonance) frequency change in Cu nuclei by changing the direction of moment of Cu2+ ions using an external magnetic field, the establishment of the parameters of nuclear spin Hamiltonian, and the separation of the three hyperfine magnetic fields. The wave function for the ground state of Cu2+ ions is near d(x2-y2), where x and y are coordinates. The Fermi contact field, dipole field and orbital field were determined through the measurement of hyperfine interactions in the directions of x, y and z. These were considerably different from the theoretical values for free ions. The main cause of this discrepancy is the electron movement from the ambient Cl- ions. In Fermi contact field, -240 kOe should be considered as reasonable, which is about double as large as the value that has been believed so far. (Wakatsuki, Y.)

1979-01-01

27

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

28

Modeling local structure using crystal field and spin Hamiltonian parameters: the tetragonal Fe{sub K}{sup 3+}-O{sub I}{sup 2-} defect center in KTaO{sub 3} crystal  

Energy Technology Data Exchange (ETDEWEB)

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{sub ||} and g{sub perpendicular}, are theoretically investigated for the Fe{sub K}{sup 3+}-O{sub I}{sup 2-} center in KTaO{sub 3} 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 Fe{sub K}{sup 3+}-O{sub I}{sup 2-} defect center in KTaO{sub 3}. This modeling reveals that the off-center displacement of the Fe{sup 3+} ions, DELTA{sub 1}(Fe{sup 3+}), combined with an inward relaxation of the nearest oxygen ligands, DELTA{sub 2}(O{sup 2-}), and the existence of the interstitial oxygen O{sub I}{sup 2-} give rise to a strong tetragonal crystal field. This finding may explain the large ZFS experimentally observed for the Fe{sub K}{sup 3+}-O{sub I}{sup 2-} center in KTaO{sub 3}. Matching 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 DELTA{sub 1}(Fe{sup 3+}) and DELTA{sub 2}(O{sup 2-}) as well as the possible location of O{sub I}{sup 2-} ligands around Fe{sup 3+} ions in KTaO{sub 3}. The defect structure model obtained using the SPM-CFA/MSH approach reproduces very well the ranges of the experimental SH parameters D, g{sub ||} and g{sub perpendicular} 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.

Gnutek, P; Rudowicz, C [Institute of Physics, West Pomeranian University of Technology, Aleja Piastow 17, 70-310 Szczecin (Poland); Yang, Z Y, E-mail: crudowicz@zut.edu.p [Department of Physics, Baoji University of Arts and Science, Baoji 721007 (China)

2009-11-11

29

When and why do spin-Hamiltonians work  

International Nuclear Information System (INIS)

The use of spin-Hamiltonians is very common in magnetism, and it is natural to assume they may be of value in describing the magnetic properties of the actinides. It is therefore of interest to examine some of the areas where they are known to work well, and ask why this is so. The purpose of this talk will be to suggest that their success has little to do with the validity of crystal field theory, but is much more to do with whether or not it is possible to transform the Hamiltonian into an effective Hamiltonian in which the numbers of electrons at each site and in the conduction band are conserved. For substances which show fluctuating valence such an effective Hamiltonian is unlikely to be found. (author)

1976-09-16

30

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 that of the solid 3He. (author)

1978-01-01

31

Understanding visual map formation through vortex dynamics of spin Hamiltonian models  

CERN Multimedia

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

32

Effective spin Hamiltonian for the CuO planes in La2CuO4 and metamagnetism  

International Nuclear Information System (INIS)

We show that the effective spin Hamiltonian used previously to describe the CuO planes of La2CuO4 does not lead to a net ferromagnetic moment for CuO planes and hence does not describe the metamagnetic behavior seen experimentally. We construct for the first time a Hamiltonian from the symmetries of the crystal structure which does lead to metamagnetism. The linear spin-wave spectrum is also calculated. This work points to the necessity of constructing effective spin Hamiltonians for metamagnetic systems which have the same symmetries as the system they are to describe

1990-10-01

33

The Model of the Theory of the Quantum Brain Dynamics can be cast on the Heisenberg Spin Hamiltonian  

CERN Multimedia

In this note, we show that the model of the quantum brain dynamics can be cast on a kind of the Heisenberg spin Hamiltonian. Therefore, we would like to emphasize that the quantum dynamics of brain should be understood by the physics of quantum spin systems.

Ohsaku, T

2003-01-01

34

Modeling 21Ne NMR parameters for carbon nanosystems.  

Science.gov (United States)

The potential of nuclear magnetic resonance (NMR) technique in probing the structure of porous systems including carbon nanostructures filled with inert gases is analysed theoretically using accurate calculations of neon ((21) Ne) nuclear magnetic shieldings. The CBS estimates of (21) Ne NMR parameters were performed for single atom, its dimer and neon interacting with acetylene, ethylene and 1,3-cyclopentadiene. Several levels of theory including restricted Hartree-Fock (RHF), Møller-Plesset perturbation theory to the second order (MP2), density functional theory (DFT) with van Voorhis and Scuseria's t-dependent gradient-corrected correlation functional (VSXC), coupled cluster with single and doubles excitations (CCSD), with single, doubles and triples included in a perturbative way (CCSD(T)) and single, doubles and tripes excitations (CCSDT) combined with polarization-consistent aug-pcS-n series of basis sets were employed. The impact of neon confinement inside selected fullerene cages used as an NMR probe was studied at the RHF/pcS-2 level of theory. A sensitivity of neon probe to the proximity of multiple CC bonds in C2 H2 , C2 H4 , C5 H6 and inside C28 , C30 , C32 , C34 and C60 fullerenes was predicted from (21) Ne NMR parameters' changes. Copyright © 2013 John Wiley & Sons, Ltd. PMID:23970499

Kupka, Teobald; Nieradka, Marzena; Kaminský, Jakub; Stobi?ski, Leszek

2013-10-01

35

Low-symmetry spin hamiltonian and crystal field tensors analysis: Fe(3+) in natrolite.  

Science.gov (United States)

Electron paramagnetic resonance study of a natural single crystal of natrolite was carried out at the frequency nu=36.772 GHz at room temperature. The angular dependence of the four symmetry-related spectra of Fe(3+) in the three crystallographic planes was fitted to a spin Hamiltonian (S=5/2) of symmetry C(i). The rank 4 crystal field tensors at tetrahedral sites were calculated using the point-charge model to determine the principal axes orientations of their cubic and trigonal components. The analysis of zero-field splitting tensors and comparison with crystal field ones suggests that Fe(3+) substitutes for Al(3+) with no significant distortion of the coordination tetrahedron in natrolite. Comparison of data for several natural and synthetic crystals reveals that the 4-rank zero-field splitting tensor invariants for Fe(3+) at the tetrahedral oxygen-coordinated sites are distinguishably smaller than those for Fe(3+) at octahedral sites. Such comparative analysis may help to determine the substitutional sites in other crystals. PMID:11945033

Vinokurov, V M; Gaite, J M; Bulka, G R; Khasanova, N M; Nizamutdinov, N M; Galeev, A A; Rudowicz, C

2002-03-01

36

Calculating NMR parameters in aluminophosphates: evaluation of dispersion correction schemes.  

Science.gov (United States)

Periodic density functional theory (DFT) calculations have recently emerged as a popular tool for assigning solid-state nuclear magnetic resonance (NMR) spectra. However, in order for the calculations to yield accurate results, accurate structural models are also required. In many cases the structural model (often derived from crystallographic diffraction) must be optimised (i.e., to an energy minimum) using DFT prior to the calculation of NMR parameters. However, DFT does not reproduce weak long-range "dispersion" interactions well, and optimisation using some functionals can expand the crystallographic unit cell, particularly when dispersion interactions are important in defining the structure. Recently, dispersion-corrected DFT (DFT-D) has been extended to periodic calculations, to compensate for these missing interactions. Here, we investigate whether dispersion corrections are important for aluminophosphate zeolites (AlPOs) by comparing the structures optimised by DFT and DFT-D (using the PBE functional). For as-made AlPOs (containing cationic structure-directing agents (SDAs) and framework-bound anions) dispersion interactions appear to be important, with significant changes between the DFT and DFT-D unit cells. However, for calcined AlPOs, where the SDA-anion pairs are removed, dispersion interactions appear much less important, and the DFT and DFT-D unit cells are similar. We show that, while the different optimisation strategies yield similar calculated NMR parameters (providing that the atomic positions are optimised), the DFT-D optimisations provide structures in better agreement with the experimental diffraction measurements. Therefore, it appears that DFT-D calculations can, and should, be used for the optimisation of calcined and as-made AlPOs, in order to provide the closest agreement with all experimental measurements. PMID:24382479

Sneddon, Scott; Dawson, Daniel M; Pickard, Chris J; Ashbrook, Sharon E

2014-02-14

37

Visualization of cerebral and vascular abnormalities by NMR imaging. The effects of imaging parameters on contrast  

International Nuclear Information System (INIS)

The relationship between data acquisition parameters and contrast in nuclear magnetic resonance (NMR) images was studied. NMR imaging by the pulse echo technique selectively enhanced intracranial abnormalities; imaging by the inversion recovery technique heightened the difference between cerebral gray and white matter. Using a blood flow model, the authors also showed that NMR imaging of flow in major vessels is possible

1982-01-01

38

Temperature dependence of the NMR generalized order parameter.  

Science.gov (United States)

The study of protein conformational dynamics is motivated in large part by a desire to understand the forces present at different sites throughout the molecular structure. The generalized order parameter determined by NMR spectroscopy has played a central role in the study of protein dynamics on the picosecond-nanosecond time scale. A modeling procedure is presented for analysis of the temperature dependence of the generalized order parameter that extends a previous analysis (Massi and Palmer, J Am Chem Soc 2003;125:11158-11159). As part of this procedure, the potential of mean force is characterized for the N-H bond vectors of the protein backbone. This procedure accounts for the observed temperature dependence of the generalized order parameter in a representative data set from the B1 domain of Streptococcal protein G (Seewald, Pichumani, Stowell, Tibbals, Regan, and Stone, Protein Sci 2000;9:1177-1193). The results indicate a general trend, in which the force constants associated with the potential of mean force decrease with increasing temperature. The analysis also provides evidence for variations in the potential of mean force for different secondary structural elements. PMID:17173286

Johnson, Eric; Palmer, Arthur G; Rance, Mark

2007-03-01

39

Indicatrix topology and maximum invariant components of tensor spin Hamiltonian of Fe3+ and Gd3+ ions in YAlO3 crystals  

International Nuclear Information System (INIS)

The connection of spin Hamiltonian (SH) invariants relative to the unitary group and its energy invariants is considered. Sign topology of the tensor indicative surface of the L=4SH class of Oh and D?h symmetry is determined and studied. SH parameters of Fe3+ and Gd3+ ions are calculated in YAlO3 crystals from ESR spectrum at 300 K. It is found that (B4M)SH tensor of Fe3+ ions has the predominant maximum invariant component (MJC) of Oh symmetry, while Gd3+ ionsw - D?h symmetry. The topology of the indicative surface and the main (MJC) axes of tensor of the L = 4 [B4M]SH rank of Fe3+, Gd3+ ions and tensor of [4414] model of point charges of Al3+, Y3+ ion environment is compared. It is established that additional Fe3+ and Gd3+ ions substitute Al3+ and Y3+ ions, respectively, causing no considerable changes in coordination polyhedron

1989-01-01

40

Signal Intensities Derived from Different NMR Probes and Parameters Contribute to Variations in Quantification of Metabolites  

Science.gov (United States)

We discovered that serious issues could arise that may complicate interpretation of metabolomic data when identical samples are analyzed at more than one NMR facility, or using slightly different NMR parameters on the same instrument. This is important because cross-center validation metabolomics studies are essential for the reliable application of metabolomics to clinical biomarker discovery. To test the reproducibility of quantified metabolite data at multiple sites, technical replicates of urine samples were assayed by 1D-1H-NMR at the University of Alberta and the University of Michigan. Urine samples were obtained from healthy controls under a standard operating procedure for collection and processing. Subsequent analysis using standard statistical techniques revealed that quantitative data across sites can be achieved, but also that previously unrecognized NMR parameter differences can dramatically and widely perturb results. We present here a confirmed validation of NMR analysis at two sites, and report the range and magnitude that common NMR parameters involved in solvent suppression can have on quantitated metabolomics data. Specifically, saturation power levels greatly influenced peak height intensities in a frequency-dependent manner for a number of metabolites, which markedly impacted the quantification of metabolites. We also investigated other NMR parameters to determine their effects on further quantitative accuracy and precision. Collectively, these findings highlight the importance of and need for consistent use of NMR parameter settings within and across centers in order to generate reliable, reproducible quantified NMR metabolomics data.

Finkel, Michael; Karnovsky, Alla; Woehler, Scott; Lewis, Michael J.; Chang, David; Stringer, Kathleen A.

2014-01-01

 
 
 
 
41

The effect of the probe parameters on the precision of NMR magnetometers  

International Nuclear Information System (INIS)

The effect in the dispersion term content in the NMR signal on the accuracy of automatic magnetometer is discussed. The dependence of the dispersion term content on probe parameters is analysed. The dispersion term content in the NMR signal for typical probe is calculated. (author)

1980-01-01

42

Quantum registers based on single NV + n 13C centers in diamond: I. The spin Hamiltonian method  

Science.gov (United States)

Details of the application of the spin Hamiltonian method for studying spin characteristics of a quantum register that includes an electron spin S = 1 of a single NV center in the ground electronic state and nuclear spins I = 1/2 of several isotopic atoms 13C located at different lattice sites near the vacancy of the NV center. Two methods of finding the hyperfine interaction tensors for these NV + n 13C spin systems are considered, one of which is based on the conventional electron spin resonance (ESR) method, while the other involves methods of quantum chemistry. The results of the latter method are compared with ESR data and with spectra of optically detected magnetic resonance (ODMR) and with the character of the modulation of the ODMR echo decay observed in single NV + n 13C systems. This comparison shows that the ab initio modeling of the spin characteristics of diamond nanoclusters containing NV centers makes it possible to obtain quantitative spin characteristics of the quantum registers under study.

Nizovtsev, A. P.; Kilin, S. Ya.; Pushkarchuk, V. A.; Pushkarchuk, A. L.; Kuten', S. A.

2010-02-01

43

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

Science.gov (United States)

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

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

2012-01-01

44

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

45

Puzzles in Silicon NMR: Sensitivity to Experimental Parameters  

Science.gov (United States)

Recent observations of anomalously long-lived spin echoes in Silicon are still not understood [A.E. Dementyev, D. Li, K. MacLean, S.E. Barrett, Phys. Rev. B 68, 153302 (2003).]. Echo trains exist well beyond the calculated dipolar dephasing time and exhibit unusual even-odd echo asymmetry. This talk will discuss the effects and implications of changing many experimental parameters including magnetic field strength, temperature, pulse width, pulse angle, and repetition rate. Understanding what limits coherent evolution in clean dipolar solids is relevant for all physical qubits.

Li, Dale; Dementyev, Anatoly; Maclean, Kenneth; Dong, Yanqun; Ramos, Rona; Barrett, Sean

2004-03-01

46

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-03-15

47

Observation of slow order parameter fluctuations in superconducting films using beta-detected NMR  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report beta-NMR investigations of polarized 8Li implanted in thin Pb and Ag/Nb films. At the critical superconducting temperature, we observe a singular peak in the spin relaxation rate in small longitudinal magnetic fields, which is attributed to fluctuations in the superconducting order parameter. However, the peak is more than an order of magnitude larger than the prediction based on the enhancement of the dynamic electron spin susceptibility by superconducting fluctua...

Morenzoni, E.; Saadaoui, H.; Wang, D.; Horisberger, M.; Kirk, E.; Macfarlane, W. A.; Morris, G. D.; Chow, K. H.; Hossain, M. D.; Levy, C. P.; Parolin, T. J.; Pearson, M. R.; Song, Q.; Kiefl, R. F.

2011-01-01

48

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

Science.gov (United States)

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

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

2011-08-01

49

On the inversion of diffusion NMR data: Tikhonov regularization and optimal choice of the regularization parameter.  

Science.gov (United States)

The analysis of diffusion NMR data in terms of distributions of diffusion coefficients is hampered by the ill-posed nature of the required inverse Laplace transformation. Naïve approaches such as multiexponential fitting or standard least-squares algorithms are numerically unstable and often fail. This paper updates the CONTIN approach of the application of Tikhonov regularization to stabilise this numerical inversion problem and demonstrates two methods for automatically choosing the optimal value of the regularization parameter. These approaches are computationally efficient and easy to implement using standard matrix algebra techniques. Example analyses are presenting using both synthetic data and experimental results of diffusion NMR studies on the azo-dye sunset yellow and some polymer molecular weight reference standards. PMID:21683632

Day, Iain J

2011-08-01

50

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

Scientific Electronic Library Online (English)

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

Alexandre T., Castro.

51

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

52

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

International Nuclear Information System (INIS)

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

2011-06-05

53

AM1 Parameters for the Prediction of 1H and 13C NMR Chemical Shifts in Proteins  

Science.gov (United States)

The semiempirical quantum mechanical description of NMR chemical shifts has been implemented at the AM1 level with NMR-specific parameters to reproduce experimental 1H and 13C NMR chemical shifts. The methodology adopted here is formally the same as that of the previously published finite perturbation theory GIAO-MNDO-NMR approach [ Wang, B. ; et al. J. Chem. Phys. 2004, 120, 24 . ]. The primary impetus for this parametrization was the accurate capture of chemical environments of atoms in biological systems. Protein-specific parameters were developed on a training set that comprised five globular protein systems with varied secondary structure and a range in size from 46-61 amino acid residues. A separate set of parameters was developed using a training set of small organic compounds with an emphasis on functional groups that are relevant to biological studies. Our approach can be employed using semiempirical (AM1) geometries and can be executed at a fraction of the cost of ab initio and DFT methods, thus providing an attractive option for the computational NMR studies of much larger protein systems. Analysis carried out on 3340 1H and 2233 13C chemical shifts for protein systems shows significant improvement over the standard AM1 parameters. Using 1H and 13C specific parameters, the rms errors are from 1.05 and 21.28 ppm to 0.62 and 4.83 ppm for hydrogen and carbon, respectively.

Williams, Duane E.; Peters, Martin B.; Wang, Bing; Roitberg, Adrian E.; Merz, Kenneth M.

2009-10-01

54

Influence of depyritization on NMR relaxation parameters of Aleksinac oil shale kerogen  

Energy Technology Data Exchange (ETDEWEB)

Parallel proton and cross-polarization/magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) relaxation measurements are reported on Aleksinac oil shale kerogen concentrate and pyrite-free kerogen concentrate. Possible relaxation mechanisms considered include proton-proton and {sup 13}C-proton interactions. The influence of depyritization on relaxation parameters is estimated. Depyritization prolongs the T{sub 1H} relaxation time constant by about five times. However, depyritization has no significant influence on relaxation in the rotating frame ({lt} 5%). The probable explanation is that there is a certain motion of structural units with spectral density in the kHz region, which averages dipolar interactions between protons and pyrite. The repetition delay is found to be 150 ms for kerogen concentrate and 1-2 s for depyritized kerogen concentrate. The favourable value of contact time is identical for both samples, i.e. 1 ms. At the same time there are no significant changes observed in the CP/MAS spectra of Aleksinac oil shale kerogen due to depyritization treatment, except for a small band ({approx} 60 ppm) assigned to alcoholic groups which appeared as a result of the partial reduction of carbonyl groups. Use of the pyrite-containing B{sub 6} sample in solid-state NMR investigations is found to be more favourable because of its shorter T{sub 1H} relaxation time, and consequently, shorter (by a factor of about five) experimental time. 15 refs., 1 fig., 1 tab.

Zujovic, Z.; Srejic, R.; Vucelic, D.; Jovancicevic, B.; Vitorovic, D. [Institute of General and Physical Chemistry, Belgrade (Yugoslavia)

1998-09-01

55

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

56

Essential parameters for structural analysis and dereplication by (1)h NMR spectroscopy.  

Science.gov (United States)

The present study demonstrates the importance of adequate precision when reporting the ? and J parameters of frequency domain (1)H NMR (HNMR) data. Using a variety of structural classes (terpenoids, phenolics, alkaloids) from different taxa (plants, cyanobacteria), this study develops rationales that explain the importance of enhanced precision in NMR spectroscopic analysis and rationalizes the need for reporting ?? and ?J values at the 0.1-1 ppb and 10 mHz level, respectively. Spectral simulations paired with iteration are shown to be essential tools for complete spectral interpretation, adequate precision, and unambiguous HNMR-driven dereplication and metabolomic analysis. The broader applicability of the recommendation relates to the physicochemical properties of hydrogen ((1)H) and its ubiquity in organic molecules, making HNMR spectra an integral component of structure elucidation and verification. Regardless of origin or molecular weight, the HNMR spectrum of a compound can be very complex and encode a wealth of structural information that is often obscured by limited spectral dispersion and the occurrence of higher order effects. This altogether limits spectral interpretation, confines decoding of the underlying spin parameters, and explains the major challenge associated with the translation of HNMR spectra into tabulated information. On the other hand, the reproducibility of the spectral data set of any (new) chemical entity is essential for its structure elucidation and subsequent dereplication. Handling and documenting HNMR data with adequate precision is critical for establishing unequivocal links between chemical structure, analytical data, metabolomes, and biological activity. Using the full potential of HNMR spectra will facilitate the general reproducibility for future studies of bioactive chemicals, especially of compounds obtained from the diversity of terrestrial and marine organisms. PMID:24895010

Pauli, Guido F; Chen, Shao-Nong; Lankin, David C; Bisson, Jonathan; Case, Ryan J; Chadwick, Lucas R; Gödecke, Tanja; Inui, Taichi; Krunic, Aleksej; Jaki, Birgit U; McAlpine, James B; Mo, Shunyan; Napolitano, José G; Orjala, Jimmy; Lehtivarjo, Juuso; Korhonen, Samuli-Petrus; Niemitz, Matthias

2014-06-27

57

Calculation of NMR parameters in ionic solids by an improved self-consistent embedded cluster method.  

Science.gov (United States)

A new embedded cluster method (extended embedded ion method = EEIM) for the calculation of NMR properties in non-conducting crystals is presented. It is similar to the Embedded Ion Method (EIM) (ref. 1) in the way of embedding the quantum chemically treated part in an exact, self-consistent Madelung potential, but requires no empirical parameters. The method is put in relation to already existing cluster models which are classified in a brief review. The influence of the cluster boundary and the cluster charge is investigated, which leads to a better understanding of deficiencies in EIM. A recipe for an improved semi-automated cluster setup is proposed which allows the treatment of crystals composed of highly charged ions and covalent networks. EIM and EEIM results for (19)F and (31)P shielding tensors in NaF and in four different magnesium phosphates are compared with experimental values from solid state MAS NMR, some of which are measured here for the first time. The quantum part of the clusters is treated at hybrid DFT level (mPW1PW) with atomic basis sets up to 6-311G(3df,3pd). The improved agreement of EEIM allows new signal assignments for the different P-sites in Mg(2)P(4)O(12), alpha-Mg(2)P(2)O(7) and MgP(4)O(11). Conversion equations of the type sigma = A + Bdelta between calculated absolute magnetic shieldings sigma and the corresponding experimental chemical shifts delta are obtained independently from linear regressions of plots of isotropically averaged sigma versus delta values on 19 (31)P signals of small molecules. PMID:20066345

Weber, Johannes; Schmedt Auf der Günne, Jörn

2010-01-21

58

NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations.  

Science.gov (United States)

(19)F isotropic chemical shifts for alkali, alkaline earth and rare earth of column 3 basic fluorides are measured and the corresponding isotropic chemical shieldings are calculated using the GIPAW method. When using the PBE exchange-correlation functional for the treatment of the cationic localized empty orbitals of Ca(2+), Sc(3+) (3d) and La(3+) (4f), a correction is needed to accurately calculate (19)F chemical shieldings. We show that the correlation between experimental isotropic chemical shifts and calculated isotropic chemical shieldings established for the studied compounds allows us to predict (19)F NMR spectra of crystalline compounds with a relatively good accuracy. In addition, we experimentally determine the quadrupolar parameters of (25)Mg in MgF(2) and calculate the electric field gradients of (25)Mg in MgF(2) and (139)La in LaF(3) using both PAW and LAPW methods. The orientation of the EFG components in the crystallographic frame, provided by DFT calculations, is analysed in terms of electron densities. It is shown that consideration of the quadrupolar charge deformation is essential for the analysis of slightly distorted environments or highly irregular polyhedra. PMID:21947333

Sadoc, Aymeric; Body, Monique; Legein, Christophe; Biswal, Mamata; Fayon, Franck; Rocquefelte, Xavier; Boucher, Florent

2011-11-01

59

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.

2010-03-21

60

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

 
 
 
 
61

High-Nuclearity Magnetic Clusters: Generalized Spin Hamiltonian and Its Use for the Calculation of the Energy Levels, Bulk Magnetic Properties, and Inelastic Neutron Scattering Spectra.  

Science.gov (United States)

A general solution of the exchange problem in the high-nuclearity spin clusters (HNSC) containing arbitrary number of exchange-coupled centers and topology is developed. All constituent magnetic centers are supposed to possess well-isolated orbitally non-degenerate ground states so that the isotropic Heisenberg-Dirac-Van Vleck (HDVV) term is the leading part of the exchange spin Hamiltonian. Along with the HDVV term, we consider higher-order isotropic exchange terms (biquadratic exchange), as well as the anisotropic terms (anisotropic and antisymmetric exchange interactions and local single-ion anisotropies). All these terms are expressed as irreducible tensor operators (ITO). This allows us to take full advantage of the spin symmetry of the system. At the same time, we have also benefitted by taking into account the point group symmetry of the cluster, which allows us to work with symmetrized spin functions. This results in an additional reduction of the matrices to diagonalize. The approach developed here is accompanied by an efficient computational procedure that allows us to calculate the bulk magnetic properties (magnetic susceptibility, magnetization, and magnetic specific heat) as well as the spectroscopic properties of HNSC. Special attention is paid to calculate the magnetic excitations observed by inelastic neutron scattering (INS), their intensities, and their Q and temperature dependencies. This spectroscopic technique provides direct access to the energies and wave functions of the different spin states of the cluster; thus, it can be applied to spin clusters in order to obtain deep and detailed information on the nature of the magnetic exchange phenomenon. The general expression for the INS cross-section of spin clusters interacting by all kinds of exchange interactions, including also the single-ion zero-field splitting term, is derived for the first time. A closed-form expression is also derived for the particular case in which only the isotropic exchange interactions are involved. Finally this approach has been used to model the magnetic properties as well as the INS spectra of the polyoxometalate anion [Ni(9)(OH)(3)(H(2)O)(6)(HPO(4))(2)(PW(9)O(34))(3)](16)(-), which contains a central magnetic cluster formed by nine exchange-coupled Ni(II) ions surrounded by diamagnetic phosphotungstate ligands (PW(9)O(34))(9)(-). PMID:11671316

Borrás-Almenar, J. J.; Clemente-Juan, J. M.; Coronado, E.; Tsukerblat, B. S.

1999-12-27

62

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

63

Bromine NMR study of cupric compounds (C sub(n)H sub(2n+1)NH sub(3))2CUBr4 (n = 1, 2)  

International Nuclear Information System (INIS)

The spin structure of (C sub(n)H sub(2n+1)NH3)2CuBr4 (n = 1, 2) is studied by Br NMR at 1.7 K. In (C2H5NH3)2CuBr4, the magnetic space group is Pb'c'a type and the moment direction inclines at an angle of 49.50 with the c-axis. A weak ferromagnetic moment appears along to the c-axis. The anisotropic exchange field is estimated to be 2.5 kOe. The inter-layer exchange field and the out-of-layer anisotropy field are much smaller than previously reported values. The parameters of Br nuclear spin Hamiltonian are also obtained. In (CH3NH3)2CuBr4, the moment direction inclines at 270 with the c-axis. It is difficult to interpret the NMR results by the two-sublattice model. A model of the four-sublattice antiferromagnet is developped. (author)

1981-01-01

64

Parameter Estimation with Prior Knowledge of Known Signal Poles for the Quantification of NMR Spectroscopy Data in the Time Domain  

Science.gov (United States)

Many parameter-estimation algorithms have been developed for the accurate quantification of NMR data modeled as a sum of Kexponentially damped sinusoids. Some well-known time-domain techniques based on subspace estimation and the singular value decomposition are Kumaresan and Tuft's linear prediction method and Kung et al.'s method based on state-space modeling, etc. All these methods do not use prior knowledge, except the formulation of the data model and the model order estimate K. The best accuracy is obtained with a variant of Kung's method, called HTLS, using the total least-squares principle. In this paper, the HTLS method is extended to the HTLS-PK method, which has the capability to accommodate prior knowledge of some known signal poles. Simulated and real-world NMR signals are processed using the HTLS and HTLS-PK methods to demonstrate the advantage of the new method.

Chen, Hua; Van Huffel, Sabine; van Ormondt, Dirk; de Beer, Ron

65

[Magnetic resonance imaging of experimental cerebral ischemia: correlations between NMR parameters and water content].  

Science.gov (United States)

Recent studies on proton NMR imaging revealed its remarkable sensitivity for detecting cerebral ischemia. Since proton NMR reflects the distribution and state of water in the brain, an NMR imager becomes a sensitive in vivo detector of brain edema developing soon after the energy state is compromized by ischemia. To further clarify the usefulness of NMR imaging to characterize the ischemia-induced changes, correlations between T1 and T2 relaxation times and water content of the normal and ischemic rat and gerbil brain were studied by means of both spectroscopic and in vivo imaging methods. In the spectroscopic experiment on excised rat brain (cortex, white matter, hippocampus and thalamus for normal and ischemia-laden brain), T1 and T2 relaxation times and water content were determined. The ischemic insult was induced for 60 min by the method of Pulsinelli followed by 60 min of reperfusion. All of the T1, T2 and water content significantly increased in the ischemic tissue. Gray-white difference was evident in T1 and T1 was linearly correlated with the water content of the tissue. T2 was by far prolonged in the ischemic tissue compared with the increase in the water content, showing greater sensitivity of T2 for detection of ischemia. In the imaging experiment, coronal NMR imaging at 0.5 tesla was performed employing proton density-weighted saturation recovery (TR = 1.6 s, TE = 14 ms), T1-weighted inversion recovery (TR = 1.6 s, TI = 300 ms, TE = 14 ms) and T2-weighted spin echo (TR = 1.6 s, TE = 106 ms) pulse sequences.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3707779

Kato, H; Kogure, K; Ohtomo, H; Izumiyama, M; Tobita, M; Matsui, S; Yamamoto, E; Kohno, H; Ikebe, Y; Watanabe, T

1986-03-01

66

Molecular NMR T2 Values Can Predict Cartilage Stress-Relaxation Parameters  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Articular cartilage lines synovial joints and functions as a low-friction deformable tissue to enable smooth and stable joint articulation. The objective of this study was to determine the relationships between cartilage stress-relaxation properties and the collagen and GAG NMR transverse relaxation times (T2) toward understanding mechanisms of cartilage viscoelasticity. Stress-relaxation tests were performed on both cultured and enzymatically-digested bovine cartilage, followed by measuremen...

June, Ronald K.; Fyhrie, David P.

2008-01-01

67

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

Energy Technology Data Exchange (ETDEWEB)

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 ({sup -1/6} or {sup 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 {beta}-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.

Peter, Christine; Daura, Xavier; Gunsteren, Wilfred F. van [ETH-Zentrum, Laboratory of Physical Chemistry, Swiss Federal Institute of Technology Zuerich (Switzerland)

2001-08-15

68

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

Science.gov (United States)

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 ([r(-6)](-1/6) or [r(-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 beta-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. PMID:11563554

Peter, C; Daura, X; van Gunsteren, W F

2001-08-01

69

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

2001-08-01

70

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

International Nuclear Information System (INIS)

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

2013-05-15

71

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

International Nuclear Information System (INIS)

It is proposed to obtain effective Lipari-Szabo order parameters and local correlation times for relaxation vectors of protein 13CO nuclei by carrying out a 13CO-R1 auto relaxation experiment, a transverse 13CO CSA/13CO-13C CSA/dipolar cross correlation and a transverse 13CO CSA/13CO-15N CSA/dipolar cross correlation experiment. Given the global rotational correlation time from 15N relaxation experiments, a new program COMFORD (CO-Modelfree Fitting Of Relaxation Data) is presented to fit the 13CO data to an effective order parameter SCO2, an effective local correlation time and the orientation of the CSA tensor with respect to the molecular frame. It is shown that the effective SCO2 is least sensitive to rotational fluctuations about an imaginary C?-C? axis and most sensitive to rotational fluctuations about an imaginary axis parallel to the NH bond direction. As such, the SCO2 information is fully complementary to the 15N relaxation order parameter, which is least sensitive to fluctuations about the NH axis and most sensitive to fluctuations about the C?-C? axis. The new paradigm is applied on data of Ca2+ saturated Calmodulin, and on available literature data for Ubiquitin. Our data indicate that the SCO2 order parameters rapport on slower, and sometimes different, motions than the 15N relaxation order parameters. The CO local correlation times correlate well with the calmodulin's secondary structure

2006-10-01

72

Spin-spin cross relaxation and spin-Hamiltonian spectroscopy by optical pumping of Pr/sup 3+/:LaF/sub 3/  

Energy Technology Data Exchange (ETDEWEB)

We report the observation of an anticrossing in solid-state laser spectroscopy produced by cross relaxation. Spin-spin cross relaxation between the /sup 141/Pr- and /sup 19/F-spin reservoirs in Pr/sup 3+/:LaF/sub 3/ and its influence on the /sup 141/Pr NMR spectrum is detected by means of optical pumping. The technique employed combines optical pumping and hole burning with either external magnetic field sweep or rf resonance saturation in order to produce slow transient changes in resonant laser transmission. At a certain value of the external Zeeman field, where the energy-level splittings of Pr and F spins match, a level repulsion and discontinuity of the Pr/sup 3+/ NMR lines is observed. This effect is interpreted as the ''anticrossing'' of the combined Pr-F spin-spin reservoir energy states. The Zeeman-quadrupole-Hamiltonian spectrum of the hyperfine optical ground states of Pr/sup 3+/:LaF/sub 3/ is mapped out over a wide range of Zeeman magnetic fields. A new scheme is proposed for dynamic polarization of nuclei by means of optical pumping, based on resonant cross relaxation between rare spins and spin reservoirs.

Lukac, M.; Otto, F.W.; Hahn, E.L.

1989-02-01

73

NMR imaging  

International Nuclear Information System (INIS)

Since hydrogen is the most abundant element in all living organisms, proton NMR lends itself well as a method of investigation in biology and medicine. NMR imaging has some special advantages as a diagnostic tool: no ionizing radiation is used, it is noninvasive; it provides a safer means of imaging than the use of x-rays, gamma rays, positrons, or heavy ions. In contrast with ultrasound, the radiation penetrates the bony structures without attenuation. In additional to morphological information, NMR imaging provides additional diagnostic insights through relaxation parameters, which are not available from other imaging methods. In the decade since the first primitive NMR images were obtained, the quality of images now obtained approaches those from CT x-ray scanners. Prototype instruments are being constructed for clinical evaluation and the first whole-body scanners are beginning to appear on the market at costs comparable to CT scanners. Primary differences in equipment for conventional NMR and NMR imaging are the much larger aperture magnets that are required for the examination of human subjects and the addition of coils to generate field gradients and facilities for manipulating the gradients. Early results from clinical trials in many parts of the world are encouraging, and in a few years, the usefuleness of this modality of medical imaging to the medical profession in diagnosis and treatment of disease will be defined. 10 figures

1983-01-01

74

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

Science.gov (United States)

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

Taka?, Milena Jadrijevi?-Mladar

2010-09-01

75

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

76

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.

2014-01-01

77

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

78

NMR contour maps as a new parameter of carboxyl's OH groups in amino acids recognition: A reason of tRNA–amino acid conjugation  

Science.gov (United States)

In this work, we have applied a statistical method by computing statistical nucleus-independent chemical shifts (SNICS) in point of probes motions within a spatial shielding and de-shielding spaces around the OH groups of some amino acids. NMR contour maps as a new parameter have been created for amino-acyl-tRNA conjugation, by using a computational method to identify this model theoretically, it is critical to understand the reasons for tRNA–amino acid conjugation. DFT, NMR, 3D Gaussian distribution and Monte Carlo methods have been applied for Methionine, Serine, Histidine, Glycine and Glutamine to investigate the structural stability in the active parts of the amino acid–tRNA linkage by chemical shielding effects.

Monajjemi, Majid; Wayne, Robert; Boggs, James E.

2014-03-01

79

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

International Nuclear Information System (INIS)

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

1982-01-01

80

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  

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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

 
 
 
 
81

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

82

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

International Nuclear Information System (INIS)

Finding the dynamics of an entire macromolecule is a complex problem as the model-free parameter values are intricately linked to the Brownian rotational diffusion of the molecule, mathematically through the autocorrelation function of the motion and statistically through model selection. The solution to this problem was formulated using set theory as an element of the universal set U-the union of all model-free spaces (d'Auvergne EJ and Gooley PR (2007) Mol BioSyst 3(7), 483-494). The current procedure commonly used to find the universal solution is to initially estimate the diffusion tensor parameters, to optimise the model-free parameters of numerous models, and then to choose the best model via model selection. The global model is then optimised and the procedure repeated until convergence. In this paper a new methodology is presented which takes a different approach to this diffusion seeded model-free paradigm. Rather than starting with the diffusion tensor this iterative protocol begins by optimising the model-free parameters in the absence of any global model parameters, selecting between all the model-free models, and finally optimising the diffusion tensor. The new model-free optimisation protocol will be validated using synthetic data from Schurr JM et al. (1994) J Magn Reson B 105(3), 211-224 and the relaxation data of the bacteriorhodopsin (1-36)BR fragment from Orekhov VY (1999) J Biomol NMR 14(4), 345-356. To demonstrate the importance of this new procedure the NMR relaxation data of the Olfactory Marker Protein (OMP) of Gitti R et al. (2005) Biochem 44(28), 9673-9679 is reanalysed. The result is that the dynamics for certain secondary structural elements is very different from those originally reported

2008-02-01

83

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

CERN Document Server

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

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

2010-01-01

84

Correlation of tryptophan fluorescence intensity decay parameters with 1H NMR-determined rotamer conformations: [tryptophan2]oxytocin.  

Science.gov (United States)

While the fluorescence decay kinetics of tyrosine model compounds [Laws, W. R., Ross, J. B. A., Wyssbrod, H. R., Beechem, J. M., Brand, L., & Sutherland, J. C. (1986) Biochemistry 25, 599-607] and the tyrosine residue in oxytocin [Ross, J. B. A., Laws, W. R., Buku, A., Sutherland, J. C., & Wyssbrod, H. R. (1986) Biochemistry 25, 607-612] can be explained in terms of heterogeneity derived from the three ground-state chi 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 2 rotations. In this paper, the time-resolved and steady-state fluorescence properties of [tryptophan2]oxytocin at pH 3 are presented and compared with 1H NMR results. According to the unrestricted analyses of individual fluorescence decay curves taken as a function of emission wavelength and a global analysis of these decay curves for common 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 1H NMR-determined chi 1 rotamer populations of the indole side chain. 15N was used in heteronuclear coupling experiments to confirm the rotamer assignments. Inclusion of a linked function restricting the decay amplitudes to the chi 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 2 populations. Depending upon the degree of correlation between chi 2 and chi 1, there may be from three to six side-chain conformations for the tryptophan residue. The combined fluorescence and NMR results are consistent with a rotamer model in which either (i) the chi 2 rotations are fast compared to the fluorescence intensity decay of the tryptophan residue, (ii) environmental factors affecting fluorescence intensity decay properties are dominated by chi 1 interactions, or (iii) the chi 2 and chi 1 rotations are highly correlated. PMID:1737015

Ross, J B; Wyssbrod, H R; Porter, R A; Schwartz, G P; Michaels, C A; Laws, W R

1992-02-18

85

31P-NMR spectroscopy in measurements of physiological parameters and response to therapy of human melanoma xenografts  

International Nuclear Information System (INIS)

The aim of the study was to investigate whether ''31P-NMR spectroscopy can be utilized in prediction and monitoring of response to therapy or tumours. The specific aims were: 1) To investigate possible correlations between on the one hand bio energetics status, phospholipids resonance ratios, intracellular pH and phosphorus T1s and on the other hand tumour blood supply and oxygenation, tumour proliferation and necrotic fraction across tumour lines. 2) Reveal possible correlations between changes in tumour bio energetics status and phosphorus T1s and the changes in tumour blood flow, tumour oxygenation and necrotic fraction. 3) To investigate whether irradiation and hyperthermia treatment of tumours affect bio energetics status and phosphorus T1s. 4) To identify the tumour physiological factors that is effected by the treatment and influence the bio energetics status and phosphorus T1s. The results are presented in 8 papers with titles: 1)''31P-nuclear magnetic resonance spectroscopy in vivo of six human melanoma zeno graft lines: Tumour bio energetic status and blood supply. 2) ''31P NMR spectroscopy studies of phospholipid metabolism in human melanoma xenograft lines differing in rate of tumour cell proliferation. 3) ''31P-nuclear magnetic resonance spectroscopy in vivo of four human melanoma xenograft lines: Spin-lattice relaxation times. 4) Effect of melanin on phosphorus T1s in human melanoma xenografts studied by ''31P MRS 5) Spin-lattice relaxation time of inorganic phosphate in human tumour xenografts measured in vivo by ''31P-magnetic resonance spectroscopy influence of oxygen tension. 6) Effects of hyperthermia on bio energetic status and phosphorus T1s in human melanoma xenografts monitored by ''31P-MRS. 7) Monitoring of tumour reoxygenation following irradiation by ''31P magnetic resonance spectroscopy an experimental study of human melanoma xenografts. 8) Radiation-induced changes in phosphorus T1 values in human melanoma xenografts studied by ''31P-MRS. Conclusions of the study are in brief: 1) There was neither a correlation between phospholipids resonance ratios and tumour proliferation, nor between bio energetic status, intracellular pH and tumour blood supply across tumour lines. Phosphorus T1s were closely associated to the fraction of necrotic tumour tissue across tumour lines. Even though phosphorus T1s were correlated to necrosis, ''31P-NMR spectroscopy is not likely to be utilized in treatment response prediction since tumour necrosis is ambiguously related to treatment response. 2) There were close correlations between changes in bio energetic status and intracellular pH and changes in tumour blood supply within tumour lines during unperturbed tumour growth. 3) There were dose-dependent changes in tumour bio energetic status and phosphorus T1s after irradiation. The change in bio energetic status was attributed to tumour reoxygenation, whereas altered phosphorus T1s were mainly attributed to increased tumour water content. 4) Following hyperthermia there were treatment-induced changes in bio energetic status and phosphorus T1s that were dependent on the thermal dose. Changes in bio energetic status reflected mainly the altered tumour blood flow induced by the treatment, whereas phosphorus T1s probably were influenced by both necrosis and oedema caused by the hyperthermia treatment. ''31P NMR spectroscopy can probably develop into a useful tool in monitoring of tumour response to irradiation and hyperthermia treatment, since blood flow and oxygenation are closely related to tumour response

1999-01-01

86

NMR of live systems  

International Nuclear Information System (INIS)

Continuous non-destructive in vivo biochemical measurements have been a desired but seemingly unattainable goal for many years. Now, however, the use of nuclear magentic resonance (NMR) seems to be close to reaching that end. This review can be divided into two sections. The first introduces and discusses relevant NMR parameters such as chemical shift and relaxation times from the view of their application to biologic systems. The second part highlights recent achievements by showing the variety of chores NMR can perform. In particular, the topics of pH measurement, quantitation and identification of phosphorus and carbon metabolites, and enzyme kinetics are all discussed. Also mentioned are limitations of NMR such as low sensitivity. Finally, there is a discussion of the new NMR technologies such as whole body proton imaging and topical NMR

1982-12-20

87

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

International Nuclear Information System (INIS)

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

2012-02-20

88

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

89

Rapid parameter optimization of low signal-to-noise samples in NMR spectroscopy using rapid CPMG pulsing during acquisition: application to recycle delays.  

Science.gov (United States)

A method is presented that combines Carr-Purcell-Meiboom-Gill (CPMG) during acquisition with either selective or nonselective excitation to produce a considerable intensity enhancement and a simultaneous loss in chemical shift information. A range of parameters can theoretically be optimized very rapidly on the basis of the signal from the entire sample (hard excitation) or spectral subregion (soft excitation) and should prove useful for biological, environmental, and polymer samples that often exhibit highly dispersed and broad spectral profiles. To demonstrate the concept, we focus on the application of our method to T(1) determination, specifically for the slowest relaxing components in a sample, which ultimately determines the optimal recycle delay in quantitative NMR. The traditional inversion recovery (IR) pulse program is combined with a CPMG sequence during acquisition. The slowest relaxing components are selected with a shaped pulse, and then, low-power CPMG echoes are applied during acquisition with intervals shorter than chemical shift evolution (RCPMG) thus producing a single peak with an SNR commensurate with the sum of the signal integrals in the selected region. A traditional (13)C IR experiment is compared with the selective (13)C IR-RCPMG sequence and yields the same T(1) values for samples of lysozyme and riverine dissolved organic matter within error. For lysozyme, the RCPMG approach is ~70 times faster, and in the case of dissolved organic matter is over 600 times faster. This approach can be adapted for the optimization of a host of parameters where chemical shift information is not necessary, such as cross-polarization/mixing times and pulse lengths. PMID:23322645

Farooq, Hashim; Courtier-Murias, Denis; Soong, Ronald; Masoom, Hussain; Maas, Werner; Fey, Michael; Kumar, Rajeev; Monette, Martine; Stronks, Henry; Simpson, Myrna J; Simpson, André J

2013-03-01

90

Benford distributions in NMR  

CERN Document Server

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

Bhole, Gaurav; Mahesh, T S

2014-01-01

91

NMR Spectroscopy  

Science.gov (United States)

This site contains web-based programs that allow the user to predict chemical shifts, spin-spin coupling patterns and NMR line shapes affected by dynamic chemical exchange. This site will be most useful for students with a good background in the fundamentals of NMR theory.

Shattuck, Thomas W.

2011-07-01

92

Quantitative NMR  

Science.gov (United States)

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

Korir, Albert K.; Larive, Cynthia K.

2011-07-18

93

NMR of 11B in glasses with combined techniques of field-swept NMR and high-resolution NMR  

International Nuclear Information System (INIS)

NMR experiments of 11B are reported to probe electric field gradients at B sites in B-Si-O glasses. The central transition of I = 3/2 perturbed by the second order quadrupole effect is usually observed by high-resolution NMR apparatus. However, combined techniques with field-swept NMR are shown to be efficient to get reliable information on electric field gradients and asymmetry parameters at B sites especially when distributions of quadrupole parameters are appreciable. (author)

1996-08-08

94

Nitroaniline diamine.poly(dA-dT) complexes: 1H and 19F NMR parameters for full intercalation of aromatic rings into DNA.  

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High-resolution proton, fluorine, and phosphorus NMR studies have been undertaken on complexes of methyl- and trifluoromethyl-substituted nitroaniline diamines with the synthetic DNA poly(dA-dT) in 10 mM buffer solution. We demonstrate full intercalation of the nitroaniline group of these reporter molecules between base pairs, based on large upfield proton shifts (1.3-1.7 ppm) at all four aromatic proton markers on complex formation. The temperature and pH dependences of the thymidine H-3 Wat...

Patel, D. J.; Gabbay, E. J.

1981-01-01

95

Group theory and NMR dynamics  

International Nuclear Information System (INIS)

NMR spectra in the presence of molecular or macroscopic reorientations reflect the symmetry of the dynamics. These effects can be described within the framework of group theory, which makes it convenient to analyze the effects of the motional symmetry on NMR interaction tensors of various ranks. For molecular motions, this provides information on the motional parameters that can be extracted from NMR spectra. Macroscopic averaging by sample reorientations, such as averaging under icosahedral symmetry and dynamic-angle spinning, can also be analyzed by group theory. (authors). 23 refs., 15 figs

1994-01-01

96

?????????GSC?NMR???????  

Full Text Available ???GSC?NMR???? ??? RIKEN,GSC,Prot. Res. Grp.,NMR Technology Team 7705 ???GSC???? ??????????????NMR???? ???????? Show ???GSC?NMR???? ??? S tandard_Name ???GSC?NMR???? ??? Standard_Name_E RIKEN,GSC,Prot. Res. Grp.,NMR

97

?????????GSC?NMR???????  

Full Text Available ???GSC?NMR???? ??? RIKEN,GSC,Prot. Res. Grp.,NMR Spectroscopy Team 7705 ???GSC??? ???????????????NMR???? ???????? Show ???GSC?NMR???? ??? S tandard_Name ???GSC?NMR???? ??? Standard_Name_E RIKEN,GSC,Prot. Res. Grp.,NMR

98

NMR GHZ  

CERN Document Server

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

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

1998-01-01

99

On domain wall boundary conditions for the XXZ spin Hamiltonian  

CERN Multimedia

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; Reshetikhin, Nicolai

2009-01-01

100

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

 
 
 
 
101

NMR Studies of Peroxidases.  

Science.gov (United States)

Available from UMI in association with The British Library. Requires signed TDF. Peroxidases are a haem-containing group of enzymes with a wide diversity of function within biological systems. While a common characteristic is the ability to catalyse the conversion of hydrogen peroxide to water, it is the accompanying processes of hormone synthesis and degradation which have generated such a high level of interest. However, information at the molecular level is limited to a single well-resolved crystal structure, that of yeast cytochrome c peroxidase. This thesis presents a strategy for the investigation of peroxidase structure and function based on proton nuclear magnetic resonance spectroscopy, a technique which has the ability to address aspects of both protein structure and protein dynamics in solution. The application of one- and two-dimensional NMR techniques has been developed in the context of plant peroxidases, notably the isoenzyme HRP-C derived from the horseradish root. Characterisation of the proton NMR spectra of HRP -C in resting and ligated states provided new information enabling the structure of the binding site for aromatic donor molecules, such as indole-3-propionic, ferulic and benzhydroxamic acids, to be resolved. In order to overcome difficulties encountered with a protein of the complexity of peroxidase, additional information was obtained from chemical shift parameters and the use of peroxidase variants produced by site-directed mutagenesis. A comparative study using NMR spectroscopy was undertaken for wild-type recombinant HRP-C expressed in Escherichia coli, and two protein variants with substitutions made to residues located on the distal side of the haem pocket, Phe41 to Val and Arg38 to Lys. NMR analyses of a plant peroxidase from barley grains and the fungal peroxidase from Coprinus cinereus were also successful using methods conceived with HRP-C. Examination of three specifically constructed recombinant protein variants of C. cinereus peroxidase was essential in confirming the identity of residues participating in the aromatic donor molecule binding site of peroxidases.

Veitch, Nigel Charles

102

NMR imaging of the eye, orbita, and optic nerve  

International Nuclear Information System (INIS)

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

1990-01-01

103

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

104

NMR characteristics of low-grade glioma  

International Nuclear Information System (INIS)

Sixteen low-grade gliomas were evaluated both with nuclear magnetic resonance (NMR) imaging and with computed tomography (CT). In 13 cases (81 %), the NMR images were much better in tissue contrast than the contrast-enhanced CT images. The tumors were shown as well-circumscribed oval lesions in the NMR, though they appeared as ill-defined, irregular, low-attenuation areas in the CT. The extent of the lesion, which was supposed to represent the active tumor tissue, was greater in the NMR than in the CT, because NMR tissue parameters (T1, T2) are more sensitive to pathological changes in brain tissue than is the X-ray attenuation coefficient. Though, in an optic glioma and a brain-stem astrocytoma, the CT with contrast enhancement displayed the contour of the mass as well as did NMR, it was inferior to the NMR in showing the cephalocaudal extension of the tumors. Calcification does not give a proton NMR signal under the present measuring conditions; thus the calcified cystic wall of a hypothalamic astrocytoma was displayed only in the CT images. In conclusion, the NMR imaging was apparently superior to contrast-enhanced CT in demonstrating the lesions due to low-grade glioma. (author)

1985-01-01

105

Fundamentals of NMR  

Science.gov (United States)

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

James, Thomas L.

2011-03-30

106

NMR TECHNIQUES APPLIED TO MARTENSITIC TRANSFORMATION  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The NMR parameters which should be measured in order to obtain microscopic information about Martensitic Phase Transformations are briefly discussed. Recent results of 27Al and 63 CU NMR are presented for both ternary alloy Cu-Zn-Al and binary alloys Cu-Zn and Ni-Al. It is shown that the NMR spectrum allows the study of the coexistence of martensite and austenite in the thermoelastic equilibrium range between MS and MF and that the nuclear spin lattice relaxation rate can detect charge densit...

Dimitropoulos, C.; Borsa, F.; Rubini, S.; Gotthardt, R.

1991-01-01

107

NMR Quantum Information Processing  

CERN Document Server

Nuclear Magnetic Resonance (NMR) has provided a valuable experimental testbed for quantum information processing (QIP). Here, we briefly review the use of nuclear spins as qubits, and discuss the current status of NMR-QIP. Advances in the techniques available for control are described along with the various implementations of quantum algorithms and quantum simulations that have been performed using NMR. The recent application of NMR control techniques to other quantum computing systems are reviewed before concluding with a description of the efforts currently underway to transition to solid state NMR systems that hold promise for scalable architectures.

Ramanathan, C; Chen, Z; Cory, D G; Chuang, I; Steffen, M; Ramanathan, Chandrasekhar; Boulant, Nicolas; Chen, Zhiying; Cory, David G.; Chuang, Isaac; Steffen, Matthias

2004-01-01

108

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nuclear magnetic resonance spectroscopy (NMR) provides robust readouts of many metabolic parameters in one experiment. However, identification of clinically relevant markers in 1H NMR spectra is a major challenge. Association of NMR-derived quantities with genetic variants can uncover biologically relevant metabolic traits. Using NMR data of plasma samples from 1,757 individuals from the KORA study together with 655,658 genetic variants, we show that ratios between NMR intensities at two chem...

Raffler, Johannes; Ro?misch-margl, Werner; Petersen, Ann-kristin; Pagel, Philipp; Blo?chl, Florian; Hengstenberg, Christian; Illig, Thomas; Meisinger, Christa; Stark, Klaus; Wichmann, H-erich; Adamski, Jerzy; Gieger, Christian; Kastenmu?ller, Gabi; Suhre, Karsten

2013-01-01

109

Understanding NMR Spectroscopy  

Science.gov (United States)

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

Keeler, James

2011-04-15

110

Nuclear magnetic resonance (NMR)  

International Nuclear Information System (INIS)

Recently nuclear magnetic resonance (NMR) imaging and topical magnetic resonance (TMR) have been practically introduced into the medical science. 1H-NMR imaging (NMR.CT) would offer us not only tomographic images of human body but also pathophysiological findings at molecular level. On the other hand we can noninvasively observe in situ tissue metabolism with 31P-TMR. In this article we are going to review shortly the probability of NMR technique from view point of the neurological surgeons and to present some of our experience. (author)

1982-01-01

111

NMR imaging and pharmaceutical sciences  

International Nuclear Information System (INIS)

Described is the technique of NMR-imaging in diagnostic medicine. Proton and phosphorus NMR in diagnosis of abnormal tissue pathology. Discussed is the value of NMR to the pharmaceutical sciences. NMR may play an important role in monitoring the response of tissues to drugs, determining the localization of drugs, performing real time pharmacokinetics and testing the use of NMR contrast pharmaceuticals

1986-09-01

112

NMR imaging system software  

International Nuclear Information System (INIS)

FTI program used for NMR imaging i.e. for obtaining, recording and decoding of two-dimensional object image is described. The NMR apparatus connected on line with MERA 400 microcomputer is presented. The exemplary image is give. 3 refs., 3 figs. (A.S.)

1986-12-02

113

Dynamic Range and NMR.  

Czech Academy of Sciences Publication Activity Database

. Brno : The Spectroscopic Society of Johannes Marcus Marci, Central European NMR Discussion Group, 1998. s. 24.[NMR Valtice /13./. 27.04.1998-29.04.1998, Valtice]Grant CEP: GA ?R GA102/96/1509Kód oboru RIV: JA - Elektronika a optoelektronika, elektrotechnika

Halámek, Josef; Kasal, Miroslav; Jurák, Pavel; Villa, M.; Cofrancesco, P.

114

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

115

Optimization and practical implementation of ultrafast 2D NMR experiments  

Directory of Open Access Journals (Sweden)

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

Luiz H. K. Queiroz Júnior

2013-01-01

116

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

117

Rapid prediction of multi-dimensional NMR data sets  

International Nuclear Information System (INIS)

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).

2012-12-01

118

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

119

?-NMR sample optimization  

CERN Document Server

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

Zakoucka, Eva

2013-01-01

120

Lorentz-to-Gauss multiplication (LGM) in FT NMR  

International Nuclear Information System (INIS)

High resolution proton and carbon NMR spectra of macromolecules and biomolecules are often overcrowded and with many partly overlapped signals. Several data processing methods to resolve partly overlapped NMR peaks have been reported. Among the Lorentz-to-Gauss and CDRE (Convulsion Difference Resolution Enhancement) methods are wide used. In this work calculation of the best set of parameters were carried out from a raw spectral data (initial FID and the corresponding untreated spectrum) and a method of prediction of optimal Lorentz-to-Gauss method parameters are suggested. The feasibility of this approach to improve the quality of NMR spectra from various resonating nuclei was shown too

1993-12-01

 
 
 
 
121

Theoretical and experimental insights into applicability of solid-state 93Nb NMR in catalysis.  

Science.gov (United States)

Ab initio DFT calculations of (93)Nb NMR parameters using the NMR-CASTEP code were performed for a series of over fifty individual niobates, and a good agreement has been found with experimental NMR parameters. New experimental and calculated (93)Nb NMR data were obtained for several compounds, AlNbO4, VNb9O25, K8Nb6O19 and Cs3NbO8, which are of particular interest for catalysis. Several interesting trends have been identified between (93)Nb NMR parameters and the specifics of niobium site environments in niobates. These trends may serve as useful guidelines in interpreting (93)Nb NMR spectra of complex niobium oxide systems, including amorphous samples and niobium-based multicomponent heterogeneous catalysts. Potential applications of (93)Nb NMR to study solid polyoxoniobates are discussed. PMID:23450163

Papulovskiy, Evgeniy; Shubin, Alexandre A; Terskikh, Victor V; Pickard, Chris J; Lapina, Olga B

2013-04-14

122

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

123

Charge and Orbital Ordering in the Triangular-Lattice t_{2g}-Orbital System in One Dimension A Possible Ground State of Bi_xV_8O_{16}  

CERN Document Server

We consider the possible charge and orbital ordering in a Hollandite compound Bi_xV_8O_{16}, which is a new one-dimensional triangular-lattice t_{2g}-orbital system. Using the strong-coupling perturbation theory, we derive the effective spin-orbit Hamiltonian in the approximation neglecting the small off-diagonal hopping parameters or orbital fluctuation, whereby we obtain the spin Hamiltonians in the partial space of each orbital-ordering pattern. We then apply an exact-diagonalization technique on small clusters to these spin Hamiltonians and calculate the ground-state phase diagram. We find that a variety of orbital-ordering patterns appear in the parameter space, which include the state characterized by the partial singlet formation consistent with recent NMR experiment.

Shibata, Y

2002-01-01

124

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)

1985-04-19

125

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

126

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.)

1980-10-03

127

THz Dynamic Nuclear Polarization NMR  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 Alessandro; Barnes, Alexander; Griffin, Robert Guy; Temkin, Richard J.

2011-01-01

128

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

129

Boolean logic gate design principles in unconventional computers: an NMR case study  

CERN Multimedia

We present a general method for analysing novel computational substrates to determine which of their parameters can be manipulated to exhibit the complete set of 2-input boolean logical operations. We demonstrate this approach with an NMR-based case study, showing which NMR parameters can be used to perform boolean logic.

Bechmann, Matthias; Stepney, Susan

2011-01-01

130

The current situation and perspectives of NMR tomography  

International Nuclear Information System (INIS)

The work accomplished by research teams in the USA and Great Britain in the first ten years following the discovery of NMR as a diagnostic tool has developed this technique to a method offering a high standard of image quality, with a high signal-to-noise ratio and good spatial resolution. Achievements in terms of biochemical information and accuracy of parameter measurement, however, still called for further research, so that in the last few years work has been devoted to enhancing the specificity and quantification of the NMR imaging method, and to rapid NMR tomography. (orig./TRV)

1987-01-01

131

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.)

1983-03-01

132

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

133

Proton NMR imaging in experimental ischemic infarction  

International Nuclear Information System (INIS)

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

1983-01-01

134

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.)

1985-01-01

135

?-nmr of Palladium foil  

International Nuclear Information System (INIS)

Beta-detected NMR (?-nmr) of low-energy implanted 8Li+ was studied in metallic palladium. The resonance was found to have a large negative shift with respect to the reference signal in the cubic insulator MgO. This shift exhibited significant temperature dependence on cooling below room temperature, approximately proportionate to the temperature-dependent spin susceptibility of pure Pd. Thus it is tentatively attributed to a Knight shift (K) caused by a large negative hyperfine coupling; a phenomenon common in transition metal ions, but not in alkalis. However, the spin-lattice relaxation of 8Li is much slower than expected from the Korringa law for such a large K. We compare results from samples of very different thicknesses: 12.5?m foil and a 100nm thin film

2006-03-31

136

A Detailed Study of the Magnetism of Chiral {Cr7M} 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

137

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

International Nuclear Information System (INIS)

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

2013-04-01

138

Automatic maximum entropy spectral reconstruction in NMR  

International Nuclear Information System (INIS)

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

2007-10-01

139

NMR imaging of the spine  

Energy Technology Data Exchange (ETDEWEB)

The usefulness of nuclear magnetic resonance (NMR) images in the evaluation of spinal disorders below the craniocervical junction was studied. Six normal subjects and 41 patients with various spinal abnormalities were examined. NMR proved capable of demonstrating important normal and pathologic anatomic structures; it was useful in the evaluation of syringohydromyelia and cystic spinal cord tumors, and the bright signal intensity of lipoma was quite impressive. In the evaluation of herniated disk, NMR images offered a new perspective by visualizing abnormal degradation of the signal intensity of the nucleus pulposus itself. NMR images were least valuable in the evaluation of spondylosis and spinal stenosis. Although NMR imaging of the spine is still in a very early developmental stage, the absence of both ionizing radiation and risks associated with contrast material makes it especially attractive as a new diagnostic method. This limited experience with currently available equipment suggests that, with technical refinement, the efficacy of NMR of the spine will increase.

Han, J.S. (Case Western Reserve Univ. School of Medicine, Cleveland, OH); Kaufman, B.; El Yousef, S.J.; Benson, J.E.; Bonstelle, C.T.; Alfidi, R.J.; Haaga, J.R.; Yeung, H.; Huss, R.G.

1983-12-01

140

NMR imaging of the spine  

International Nuclear Information System (INIS)

The usefulness of nuclear magnetic resonance (NMR) images in the evaluation of spinal disorders below the craniocervical junction was studied. Six normal subjects and 41 patients with various spinal abnormalities were examined. NMR proved capable of demonstrating important normal and pathologic anatomic structures; it was useful in the evaluation of syringohydromyelia and cystic spinal cord tumors, and the bright signal intensity of lipoma was quite impressive. In the evaluation of herniated disk, NMR images offered a new perspective by visualizing abnormal degradation of the signal intensity of the nucleus pulposus itself. NMR images were least valuable in the evaluation of spondylosis and spinal stenosis. Although NMR imaging of the spine is still in a very early developmental stage, the absence of both ionizing radiation and risks associated with contrast material makes it especially attractive as a new diagnostic method. This limited experience with currently available equipment suggests that, with technical refinement, the efficacy of NMR of the spine will increase

1983-01-01

 
 
 
 
141

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.)

1984-01-01

142

Protein structure determination from NMR chemical shifts.  

Science.gov (United States)

NMR spectroscopy plays a major role in the determination of the structures and dynamics of proteins and other biological macromolecules. Chemical shifts are the most readily and accurately measurable NMR parameters, and they reflect with great specificity the conformations of native and nonnative states of proteins. We show, using 11 examples of proteins representative of the major structural classes and containing up to 123 residues, that it is possible to use chemical shifts as structural restraints in combination with a conventional molecular mechanics force field to determine the conformations of proteins at a resolution of 2 angstroms or better. This strategy should be widely applicable and, subject to further development, will enable quantitative structural analysis to be carried out to address a range of complex biological problems not accessible to current structural techniques. PMID:17535901

Cavalli, Andrea; Salvatella, Xavier; Dobson, Christopher M; Vendruscolo, Michele

2007-06-01

143

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

Science.gov (United States)

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

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

2014-01-01

144

A two-element tuning circuit of the NMR magnetometer and the analysis of its properties  

International Nuclear Information System (INIS)

The paper presents a new tuning circuit of the marginal oscillator in the NMR magnetometers. This circuit contains two regulating elements and allows to obtain a broader tuning range and a greater NMR signal than those obtained by means of traditional one-element circuits. The results of calculations of parameters for such a circuit are given. (author)

1979-01-01

145

Fundamentals of Protein NMR Spectroscopy  

CERN Multimedia

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

146

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

International Nuclear Information System (INIS)

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

1991-01-01

147

Carbon-13 NMR spectroscopy  

International Nuclear Information System (INIS)

Features in this edition are references (over 1,000), profuse illustration, a discussion of modern pulse techniques for spectral analysis, and extensive and thorough cataloguing of chemical shift data (over 200 pages) in readily accessible form. An attractive feature is the use of structural formulae with shifts inscribed in the structure. This new edition has been completely revised to take into account new techniques and the increased use of computers. The new methods described include those for multiplicity analysis and two-dimensional homo- or hetero-nuclear shift correlations. New sections about coupling constants, organophosphorus and organometalic compounds as well as synthetic polymers have been added. As in the second edition, the authors survey the large number of /sup 13/C NMR applications to organic molecule and natural products in a representative and systematic rather than an exhaustive way

1987-01-01

148

NMR-tomography of the heart  

Energy Technology Data Exchange (ETDEWEB)

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

Weikl, A.; Bachmann, K.

1987-04-03

149

DFT- NMR Study of 4-Phenoxychlorophenylglioxime  

International Nuclear Information System (INIS)

We present the results of density functional theory (DFT) calculations of chemical shifts and shielding constants in suggested anti-, amphi-, and syn-, geometrical isomers of 4 -phenoxychlorophenylglioxime. In this study, our main scope is to determine anti-, amphi-, and syn- isomer structure of 4- phenoxychlorophenylglioxime computationally using DFT NMR parameter( chemical shift and shielding constant) calculation. In order to achieve this goal, chemical shifts and shielding constants calculations of 4- phenoxychlorophenylglioxime's geometrical isomers are performed using different DFT functionals in combination with Gaussian basis sets. Theoretically calculated values are compared with the experimentally observed values

2008-08-25

150

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

151

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

Science.gov (United States)

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

2013-01-01

152

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

Science.gov (United States)

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

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

2013-01-01

153

NMR Study of Strontium Binding by a Micaceous Mineral  

International Nuclear Information System (INIS)

The nature of strontium binding by soil minerals directly affects the transport and sequestration/remediation of radioactive strontium species released from leaking high-level nuclear waste storage tanks. However, the molecular-level structure of strontium binding sites has seldom been explored in phyllosilicate minerals by direct spectroscopic means and is not well-understood. In this work, we use solid-state NMR to analyze strontium directly and indirectly in a fully strontium-exchanged synthetic mica of nominal composition Na4Mg6Al4Si4O20F4. Thermogravimetric analysis, X-ray diffraction analysis, and NMR evidence supports that heat treatment at 500 C for 4 h fully dehydrates the mica, creating a hydrogen-free interlayer. Analysis of the strontium NMR spectrum of the heat-treated mica shows a single strontium environment with a quadrupolar coupling constant of 9.02 MHz and a quadrupolar asymmetry parameter of 1.0. These quadrupolar parameters are consistent with a highly distorted and asymmetric coordination environment that would be produced by strontium cations without water in the coordination sphere bound deep within the ditrigonal holes. Evidence for at least one additional strontium environment, where proton-strontium couplings may occur, was found via a 1H-87Sr transfer of populations by double resonance NMR experiment. We conclude that the strontium cations in the proton-free interlayer are observable by 87Sr NMR and bound through electrostatic interactions as nine coordinate inner-sphere complexes sitting in the ditrigonal holes. Partially hydrated strontium cations invisible to direct 87Sr NMR are also present and located on the external mica surfaces, which are known to hydrate upon exposure to atmospheric moisture. These results demonstrate that modern pulsed NMR techniques and high fields can be used effectively to provide structural details of strontium binding by phyllosilicate minerals

2006-04-13

154

APSY-NMR with proteins: practical aspects and backbone assignment  

International Nuclear Information System (INIS)

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

2008-11-01

155

APSY-NMR with proteins: practical aspects and backbone assignment  

Energy Technology Data Exchange (ETDEWEB)

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

Hiller, Sebastian [Harvard Medical School, Department of Biological Chemistry and Molecular Pharmacology (United States)], E-mail: hiller.sebastian@gmail.com; Wider, Gerhard; Wuethrich, Kurt [ETH Zuerich, Institute of Molecular Biology and Biophysics (Switzerland)], E-mail: wuthrich@mol.biol.ethz.ch

2008-11-15

156

Rekonstruktion von Proteinstrukturen aus unvollständigen NMR-Daten  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Gegenstand dieser Arbeit ist die Anwendung der Bayes'schen Wahrscheinlichkeitstheorie auf das Problem der makromolekularen Strukturbestimmung aus NMR-Daten. Ausgehend vom Prinzip der Inferentiellen Strukturbestimmung (ISD), habe ich wahrscheinlichkeitstheoretische Modelle für Messungen skalarer und dipolarer Kopplungen entwickelt. Es zeigt sich, daß die Regeln der Wahrscheinlichkeitstheorie zusätzliche Parameter wie die Fehler der

2004-01-01

157

An electron paramagnetic resonance (EPR) study of a molybdenum-phthalocyanine powder  

International Nuclear Information System (INIS)

EPR measurements of the spin-Hamiltonian parameters of a molybdenum-phthalocyanine powder sample and its solution in sulphuric acid are reported. The EPR spectra are analyzed in terms of an axial spin-Hamiltonian (S = 1/2) and computer spectra simulation using these parameters are presented, together with suggestions on the structure of this compound. (author)

1986-01-01

158

Towards an Effective Spin Hamiltonian of the Pyrochlore Spin Liquid Tb2Ti2O7  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Tb2Ti2O7 is a pyrochlore antiferromagnet that has dynamical spins and only short-range correlations even at 50 mK; the lowest temperature explored so far, which is much smaller than the scale set by the Curie-Weiss temperature T_{CW}~14 K. The absence of long-range order in this material is not understood. Recently, virtual crystal field excitations (VCFEs) have been shown to be significant in Tb2Ti2O7. While previous work found that VCFEs-induced renormalization of the near...

Molavian, Hamid R.; Mcclarty, Paul A.; Gingras, Michel J. P.

2009-01-01

159

FAST-NMR - Functional Annotation Screening Technology Using NMR Spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An abundance of protein structures emerging from structural genomics and the Protein Structure Initiative (PSI) are not amenable to ready functional assignment because of a lack of sequence and structural homology to proteins of known function. We describe a high-throughput NMR methodology (FAST-NMR) to annotate the biological function of novel proteins through the structural and sequence analysis of protein-ligand interactions. This is based on basic tenets of biochemistry where proteins wit...

Mercier, Kelly A.; Baran, Michael; Ramanathan, Viswanathan; Revesz, Peter; Xiao, Rong; Montelione, Gaetano T.; Powers, Robert

2006-01-01

160

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 Ca"2"+ on flexibility of actin polymer are presented

1994-12-01

 
 
 
 
161

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

162

Polarization transfer NMR imaging  

Science.gov (United States)

A nuclear magnetic resonance (NMR) image is obtained with spatial information modulated by chemical information. The modulation is obtained through polarization transfer from a first element representing the desired chemical, or functional, information, which is covalently bonded and spin-spin coupled with a second element effective to provide the imaging data. First and second rf pulses are provided at first and second frequencies for exciting the imaging and functional elements, with imaging gradients applied therebetween to spatially separate the nuclei response for imaging. The second rf pulse is applied at a time after the first pulse which is the inverse of the spin coupling constant to select the transfer element nuclei which are spin coupled to the functional element nuclei for imaging. In a particular application, compounds such as glucose, lactate, or lactose, can be labeled with .sup.13 C and metabolic processes involving the compounds can be imaged with the sensitivity of .sup.1 H and the selectivity of .sup.13 C.

Sillerud, Laurel O. (Los Alamos, NM); van Hulsteyn, David B. (Santa Fe, NM)

1990-01-01

163

89Y NMR in YIG  

International Nuclear Information System (INIS)

89Y NMR sigrals (I=1/2, ?=208.6 kHz/kE, abundance -100%) are detected for the first time in yttrium ferrite-garnet under helium temperatures. NMR spectrum consists of two lines with 3.69 and 3.83 MHz frequency lines. Values of times of spin-lattice and spin-spin relaxation for two recorded lines. The main contribution into local field on 89Y nuclei is of superfine nature

1993-01-01

164

NMR insights into protein allostery  

Science.gov (United States)

Allosterism is one of nature's principal methods for regulating protein function. Allosterism utilizes ligand binding at one site to regulate the function of the protein by modulating the structure and dynamics of a distant binding site. In this review, we first survey solution NMR techniques and how they may be applied to the study of allostery. Subsequently, we describe several examples of application of NMR to protein allostery and highlight the unique insight provided by this experimental technique.

Manley, Gregory; Loria, J. Patrick

2014-01-01

165

Optical pumping and xenon NMR  

International Nuclear Information System (INIS)

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

1991-01-01

166

NMR spectroscopy in bioinorganic chemistry  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Multinuclear and multidimensional nuclear magnetic resonance (NMR) spectroscopy is applied in our groups to gain insights into the role of metal ions for the function and structure of large biomolecules. Specifically, NMR is used i) to investigate how metal ions bind to nucleic acids and thereby control the folding and structure of RNAs, ii) to characterize how metal ions are able to stabilize modified nucleic acids to be used as potential nanowires, and iii) to characterize the formation, st...

Donghi, Daniela; Johannsen, Silke; Sigel, Roland K. O.; Freisinger, Eva

2012-01-01

167

Practical applications of NMR in civil engineering  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2003-01-01

168

Investigation of structure, vibrational and NMR spectra of oxycodone and naltrexone: A combined experimental and theoretical study  

Science.gov (United States)

In this work, two important opioid antagonists, naltrexone and oxycodone, were prepared from thebaine and were characterized by IR, 1H NMR and 13C NMR spectroscopy. Moreover, computational NMR and IR parameters were obtained using density functional theory (DFT) at B3LYP/6-311++G** level of theory. Complete NMR and vibrational assignment were carried out using the observed and calculated spectra. The IR frequencies and NMR chemical shifts, determined experimentally, were compared with those obtained theoretically from DFT calculations, showed good agreements. The RMS errors observed between experimental and calculated data for the IR absorptions are 85 and 105 cm -1, for the 1H NMR peaks are 0.87 and 0.17 ppm and for those of 13C NMR are 5.6 and 5.3 ppm, respectively for naltrexone and oxycodone.

Tavakol, Hossein; Esfandyari, Maryam; Taheri, Salman; Heydari, Akbar

2011-08-01

169

Variable-temperature NMR and conformational analysis of Oenothein B  

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-02-15

170

High-dimensional NMR spectra for structural studies of biomolecules.  

Science.gov (United States)

Recent developments in the acquisition and processing of NMR data sets facilitate the recording of ultra-high-resolution NMR spectra in a reasonable time. The new experiments allow easy resonance assignment for folded and unfolded proteins, as well as the precise determination of spectral parameters, for example, chemical shifts, NOE contacts, coupling constants or cross-correlated relaxation rates. Owing to exceptional resolution of 4D-6D spectroscopy, detailed studies of biomolecules of unprecedented complexity are now possible. Herein, the principles of acquisition and processing methods are presented. The main applications of high-dimensional NMR experiments, including backbone and side-chain resonance assignment in proteins, as well as heteronuclear edited NOE techniques are reviewed. PMID:23794393

Kazimierczuk, Krzysztof; Stanek, Jan; Zawadzka-Kazimierczuk, Anna; Ko?mi?ski, Wiktor

2013-09-16

171

AUREMOL: Automatic protein structure determination from NMR data  

Energy Technology Data Exchange (ETDEWEB)

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

Donaubauer, Harald; Harsch, Tobias; Malloni, Willhelm; Sanctis, Silvia de; Kieninger, Baerbel; Danilova, Nina; Brunner, Konrad; Gronwald, Wolfram; Trenner, Jochen; Kalbitzer, Hans Robert [University of Regensburg (Germany); Neidig, Klaus-Peter [Bruker BioSpin (Germany)

2010-07-01

172

AUREMOL: Automatic protein structure determination from NMR data  

International Nuclear Information System (INIS)

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

2010-03-21

173

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

International Nuclear Information System (INIS)

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

1983-03-12

174

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

1984-06-05

175

Application of Solution NMR Spectroscopy to Study Protein Dynamics  

Directory of Open Access Journals (Sweden)

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

Christoph Göbl

2012-03-01

176

Effective rotational correlation times of proteins from NMR relaxation interference  

Science.gov (United States)

Knowledge of the effective rotational correlation times, ?c, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of ?c enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [ 15N, 1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine ?c for 15N- 1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [ 15N, 1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.

Lee, Donghan; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt

2006-01-01

177

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

1981-01-01

178

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-12-07

179

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

International Nuclear Information System (INIS)

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

2010-12-07

180

A web-based database for EPR centers in semiconductors  

International Nuclear Information System (INIS)

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

2006-04-01

 
 
 
 
181

Microscale simulations of NMR relaxation in porous media  

Science.gov (United States)

In petrophysical applications of nuclear magnetic resonance (NMR), the measured relaxation signals originate from the fluid filled pore space. Hence, in rocks or sediments the water content directly corresponds to the initial amplitude of the recorded NMR relaxation signals. The relaxation rate (longitudinal/transversal decay time T1, T2) is sensitive to pore sizes and physiochemical properties of rock-fluid interfaces (surface relaxivity), as well as the concentration of paramagnetic ions in the fluid phases (bulk relaxivity). In the subproject A2 of the TR32 we aim at improving the basic understanding of these processes at the pore scale and thereby advancing the interpretation of NMR data by reducing the application of restrictive approximated interpretation schemes, e.g. for deriving pore size distributions, connectivity or permeability. In this respect we numerically simulate NMR relaxation data at the micro sale to study the impact of physical and hydrological parameters such as internal field gradients or pore connectivities on NMR signals. Joint numerical simulations of the NMR relaxation behavior (Bloch equations) in the presence of internal gradients (Ampere's law) and fluid flow (Navier-Stokes) on a pore scale dimension have been implemented in a finite element (FE) model using Comsol Multiphysics. Processes governing the time and spatial behavior of the nuclear magnetization density in a porous medium are diffusion and surface interactions at the rock-fluid interface. Based on Fick's law of diffusive motion Brownstein and Tarr (1979) introduced differential equations that describe the relaxation behavior of the Spin magnetization in single isolated pores and derived analytical solutions for simple geometries, i.e. spherical, cylindrical and planar. However, by numerically solving these equations in a general way using a FE algorithm this approach can be applied to study and simulate coupled complex pore systems, e.g. derived from computer tomography (CT). In this respect substantial coupling effects in typical porous rocks can be observed at pore sizes about Ampere's law. Contrary to common assumptions of a constant ratio between T1 and T2 in petrophysical NMR the CPMG simulations in the presence of internal gradients show a significant increase of T1/T2 ratios with decreasing pore sizes. This implies a shift of derived signal contributions to smaller pore sizes, e.g. air-oil, to study basic correlations between NMR and hydrological parameters of partially saturated rocks. This study was conducted within the framework of the Transregional Collaborative Research Centre 32, funded by the German Research Foundation (DFG).

Mohnke, Oliver; Klitzsch, Norbert

2010-05-01

182

?-NMR of a thin Pt film  

International Nuclear Information System (INIS)

We report beta-detected NMR (?-NMR) measurements on a 50 nm thick platinum (Pt) film grown on a magnesium oxide (MgO) substrate. The frequency of the ?-NMR resonance in Pt was compared to the MgO reference frequency to estimate the Knight shift at various temperatures (100-300 K). The Knight shift was found to be negative and strongly temperature dependent. The implications are discussed and compared to other transition metals that have been studied via ?-NMR previously.

2009-04-15

183

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

184

Computer system architecture for NMR imaging  

International Nuclear Information System (INIS)

NMR imaging makes extensive use of computers in data acquisition, image reconstruction, processing and display. Furthermore, in order to fully utilise the capability of the method, flexible control must be exercised over the radiofrequency and gradient pulse sequence. The requirements of operational flexibility and speed favour a distributed architecture with dedicated programmable devices taking on separate tasks under the overall control of a host computer. A fast, versatile pulse programmer is required to provide real-time control of a number of rapidly varying, experimental parameters. A state-memory-based, pulse programmer, having the architecture of a computer control unit, affords the optimum design for imaging applications. In image processing, array processors have a considerable speed advantage and will find increasing use in clinical imaging systems

1987-01-01

185

Analysis of deuteron NMR signals  

International Nuclear Information System (INIS)

A method of extracting the Q-curve from deuteron NMR signals has been developed in order to treat signals which are highly distorted because of Q-curve instabilities. The extracted Q-curve can then be used to calculate the subtracted signals, thus leading to the determination of the polarization. ((orig.))

1995-03-01

186

Deuterium Exchange Kinetics by NMR.  

Science.gov (United States)

Describes a physical chemistry experiment which allows such concepts as kinetics, catalysis, isotope shifts, coupling constants, and the use of nuclear magnetic resonance (NMR) for quantitative work to be covered in the same exercise. Background information, experimental procedures used, and typical results obtained are included. (JN)

Roper, G. C.

1985-01-01

187

Magic-angle-spinning NMR  

International Nuclear Information System (INIS)

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

1985-06-01

188

Complete NMR assignments of tubulosine.  

Science.gov (United States)

This article reports the structural elucidation of the Alangium alkaloid, tubulosine (1) on the basis of systematic 2D-NMR analyses (DEPT, COSY, TOCSY, NOESY, ROESY, HMQC and HMBC). The data obtained allowed the unambiguous assignment of all proton and carbon signals in 1 for the first time. PMID:22428233

Kantamreddia, Venkata Siva Satyanarayana; Wright, Colin W

2012-01-01

189

QUANTITATIVE 15N NMR SPECTROSCOPY  

Science.gov (United States)

Line intensities in 15N NMR spectra are strongly influenced by spin-lattice and spin-spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 1...

190

Ultrahigh-resolution NMR spectroscopy.  

Science.gov (United States)

All psyched up: A flexible and general pure shift experiment (PSYCHE) has been developed that offers superior sensitivity, spectral purity, and tolerance of strong coupling over existing methods for broadband homonuclear decoupling. The partial spectra of estradiol in [D6 ]DMSO obtained by normal (1) H?NMR spectroscopy and PSYCHE are shown for comparison. PMID:24861024

Foroozandeh, Mohammadali; Adams, Ralph W; Meharry, Nicola J; Jeannerat, Damien; Nilsson, Mathias; Morris, Gareth A

2014-07-01

191

Development of NMR investigations of magnetic materials  

International Nuclear Information System (INIS)

The application of NMR to investigations of magnetically ordered materials is reviewed. The characteristics of the NMR spin-echo technique are analysed with respect to recently developed broad band solutions. The recent achievements of NMR spectrometry in magnetics are briefly discussed. (author). 34 refs.; 9 figs

1988-09-03

192

Indirect use of deuterium in solution NMR studies of protein structure and hydrogen bonding.  

Science.gov (United States)

A description of the utility of deuteration in protein NMR is provided with an emphasis on quantitative evaluation of the effects of deuteration on a number of NMR parameters of proteins: (1) chemical shifts, (2) scalar coupling constants, (3) relaxation properties (R1 and R2 rates) of nuclei directly attached to one or more deuterons as well as protons of methyl groups in a highly deuterated environment, (4) scalar relaxation of 15N and 13C nuclei in 15N-D and 13C-D spin systems as a measure of hydrogen bonding strength, and (5) NOE-based applications of deuteration in NMR studies of protein structure. The discussion is restricted to the 'indirect' use of deuterium in the sense that the description of NMR parameters and properties of the nuclei affected by nearby deuterons (15N, 13C, 1H) is provided rather than those of deuterium itself. PMID:24411830

Tugarinov, Vitali

2014-02-01

193

Interactions between cations and peat organic matter monitored with NMR wideline, static and FFC NMR relaxometry  

Science.gov (United States)

The molecular size of humic substances is still under debate and is believed to range up to several hundred thousands Dalton, although a number of recent studies suggest much lower molecular weights. Nowadays an increasing number of authors suggest a model of molecular aggregates. One explanation why results on the molecular mass of humic materials are contradictory, may be that individual OM molecules are linked via intermolecular interactions, by bridges of water molecules or by cations bridging cation exchange sites (Schaumann, 2006a, b). Properties of such cross-linked systems can be similar to macromolecular systems revealing covalent cross-links. In this context, multivalent cations play an important ecological role, serving as reversible cross-linking agent. Formation and disruption of such cation bridges may close or open sorption sites in soil organic matter. Although cross-linking by multivalent cations has been proposed in many studies, the cross-linking effect has not yet been demonstrated on the molecular scale. The objective of this study was to investigate the interactions between cations and peat organic matter using NMR wideline techniques as well as static and fast field cycling (FFC) NMR relaxometry. Peat treated with solutions containing either Na+, Ca2+ or Al3+ was investigated in air-dried state for longitudinal relaxation times (T1) and NMR wideline characteristics. T1 distributions were separated into two Gaussian functions which were interpreted to represent two proton populations belonging to two environments of differing mobility. The relaxation rates (R1 = T1-1) in the cation treated samples spread over a range of 87-123 s-1 (R1a: fast component) and 32-42 s-1 (R1b: slow component). The rates in all treatments are significantly different from each other. and decrease in the order conditioned sample > desalinated sample > Na-treated sample. The treatment with multivalent cations affects R1a and R1b in different ways and needs more detailed explanation. Wideline proton NMR spectra can be used to quantify proton containing material, mainly water, based on their mobility. Spectra were decomposed into a Gaussian and Lorentzian line and changes to mobility after heat treatment indicate the water binding strength. In this study, differences in the various NMR parameters on the cation treatments will be presented and discussed with respect to the crosslinking hypothesis.

Schaumann, Gabriele E.; Conte, Pellegrino; Jäger, Alexander; Alonzo, Giuseppe; Bertmer, Marko

2010-05-01

194

Solid-state NMR monitoring of a double bond isomerization in propene on ZnO  

Science.gov (United States)

Monitoring of the 13C-label scrambling from the position 3 to the position 1 in the 13C-labeled propene adsorbed on zinc oxide has been performed with 1H and 13C solid state NMR in situ. This allowed us to characterize the dynamics of a double bond shift reaction in adsorbed propene, and derive the kinetic parameters of this reaction, which were not earlier available without using solid state NMR and 13C-labeling of the olefin.

Gabrienko, Anton A.; Stepanov, Alexander G.

2014-06-01

195

NMR in ferro- and antiferromagnets in conditions of magnon ''bottleneck''. Derivation of equations of motion  

International Nuclear Information System (INIS)

The equations are derived describing the NMR under magnon ''battleneck'' conditions for an arbitrary relationship between the NMR line width and the width magnon line. The expression is obtained for the ''bottleneck'' parameter. The calculation is made for uniaxial ferromagnetics (both one-domain and multidomain) and antiferromagnetics of the ''light plane'' type. The equations obtained are compared with the corresponding equations of the phonon ''bottleneck'' theory

1976-11-01

196

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

1984-01-01

197

Ultraslow Electron Spin Dynamics in GaAs Quantum Wells Probed by Optically Pumped NMR  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state nu=1/3. Below 0.5K, the spectra provide evidence that spin-reversed charged excitations of the nu=1/3 ground state are localized over the NMR time scale of ~40 microseconds. Furthermore, by varying NMR pulse parameters, the electron spin temperature (as measured by the Knight shift) ...

Kuzma, N. N.; Khandelwal, P.; Barrett, S. E.; Pfeiffer, L. N.; West, K. W.

1999-01-01

198

Two dimensional NMR and NMR relaxation studies of coal structure  

Energy Technology Data Exchange (ETDEWEB)

This report covers the progress made on the title project for the project period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups that determine the reactivity of coals. Special attention is being paid to methods that are compatible with the very high magic angle sample spinning rates needed for operation at the high magnetic field strengths available today. Polarization inversion methods utilizing the difference in heat capacities of small groups of spins are particularly promising. Methods combining proton-proton spin diffusion with {sup 13}C CPMAS readout are being developed to determine the connectivity of functional groups in coals in a high sensitivity relay type of experiment. Additional work is aimed a delineating the role of methyl group rotation in the proton NMR relaxation behavior of coals.

Zilm, K.W.

1992-05-27

199

Refinement of the protein backbone angle ? in NMR structure calculations  

International Nuclear Information System (INIS)

Cross-correlated relaxation rates involving the C?-H? dipolar interaction and the carbonyl (C') chemical shift anisotropy (CSA) have been measured using two complementary 3D experiments. We show that the protein backbone angle ? can be directly refined against such cross-correlated relaxation rates (?H?C?,C') and the three-bond H/D isotope effect on the C? chemical shifts (3?C?(ND)). By simultaneously using both experimental parameters as restraints during NMR structure calculations, a unique value for the backbone angle ? is defined. We have applied the new refinement method to the ?-Spectrin SH3 domain (a ?-sheet protein) and to the Sgs1p HRDC domain (an ?-helical protein) and show that the quality of the NMR structures is substantially improved, judging from the atomic coordinate precision and the Ramachandran map. In addition, the ?-refined NMR structures of the SH3 domain deviate less from the 1.8 A crystal structure, suggesting an improved accuracy. The proposed refinement method can be used to significantly improve the quality of NMR structures and will be applicable to larger proteins

2000-01-01

200

Noise figure characterization of preamplifiers at NMR frequencies  

Science.gov (United States)

A method for characterizing the noise figure of preamplifiers at NMR frequencies is presented. The noise figure of preamplifiers as used for NMR and MRI detection varies with source impedance and with the operating frequency. Therefore, to characterize a preamplifier's noise behavior, it is necessary to perform noise measurements at the targeted frequency while varying the source impedance with high accuracy. At high radiofrequencies, such impedance variation is typically achieved with transmission-line tuners, which however are not available for the relatively low range of typical NMR frequencies. To solve this issue, this work describes an alternative approach that relies on lumped-element circuits for impedance manipulation. It is shown that, using a fixed-impedance noise source and suitable ENR correction, this approach permits noise figure characterization for NMR and MRI purposes. The method is demonstrated for two preamplifiers, a generic BF998 MOSFET module and an MRI-dedicated, integrated preamplifier, which were both studied at 128 MHz, i.e., at the Larmor frequency of protons at 3 Tesla. Variations in noise figure of 0.01 dB or less over repeated measurements reflect high precision even for small noise figures in the order of 0.4 dB. For validation, large sets of measured noise figure values are shown to be consistent with the general noise-parameter model of linear two-ports. Finally, the measured noise characteristics of the superior preamplifier are illustrated by SNR measurements in MRI data.

Nordmeyer-Massner, J. A.; De Zanche, N.; Pruessmann, K. P.

2011-05-01

 
 
 
 
201

New methodological approaches in solid-state NMR  

International Nuclear Information System (INIS)

Full text: Spectacular advances in solid-state NMR methodology, instrumentation and sample preparation have made possible studies of structure and dynamics on increasingly complex molecular systems, such as proteins that cannot be investigated by X-ray, or solution-state NMR (amyloid fibrils, membrane proteins embedded in native environments, protein aggregates), other large biomolecular systems (DNA, RNA, carbohydrates), functionalized polymeric materials, selfassembled and inclusion molecular complexes, molecular nano-devices, etc. Many of these applications rely on the development of solid-state NMR techniques tailored to specifically address characteristic structural and dynamical features of larger and larger molecules, where often the dynamics of abundant spins, for instance, 1H, or 13C(15N) in uniformly labeled samples, represents a major challenge. To account for a broad range of multi-spin processes in such systems that may influence the efficiency of the proposed experimental scheme, or the reliability of the extracted parameters from the measured data, adequate theoretical tools are also highly desirable. In this context, here, we present some of our recent developments that address exactly these issues, namely: (i) elaboration of viable approaches for symbolic algebra computation of dynamics in extended spin networks, within a framework called SD-CAS (Spin Dynamics by Computer Algebra System), and (ii) development of new solid-state NMR methods for structural investigation of complex molecular systems. (author)

2007-09-20

202

Multinuclear NMR studies of gaseous and liquid sevoflurane  

Science.gov (United States)

For the first time, a small amount of sevoflurane ((CF 3) 2CHOCH 2F) in carbon dioxide and xenon as the gaseous solvents has been studied using 19F and 1H NMR spectra. Density-dependent 19F and 1H nuclear magnetic shielding was observed when the pressure of each solvent was increased. After extrapolation of the results to the zero-density limit it was possible to determine the appropriate shielding constants free from intermolecular interactions, ?0(F) and ?0(H). Similar procedure has also been applied for the investigation of fluorine-proton spin-spin couplings and the 2J 0(FH) and 3J 0(FH) constants of an isolated (CF 3) 2CHOCH 2F molecule were also obtained. Additionally, high-resolution 1H, 13C, 17O and 19F NMR spectra of pure liquid sevoflurane were also recorded and all the 1H- 13C, 1H- 19F and 19F- 13C spin-spin coupling constants and NMR chemical shifts were measured. It is shown that the experimental NMR parameters are suitable for comparison with the results of recent quantum-chemical calculations.

Maci?ga, E.; Makulski, W.; Jackowski, K.; Blicharska, B.

2006-03-01

203

Orientation of Amphipathic Helical Peptides in Membrane Bilayers Determined by Solid-State NMR Spectroscopy. (Reannouncement with New Availability Information).  

Science.gov (United States)

Solid-state NMR spectroscopy was used to determine the orientations of two amphipathic helical peptides associated with lipid bilayers. A single spectral parameter provides sufficient orientational information for these peptides, which are known, from oth...

B. Bechinger Y. Kim L. E. Chirlian J. Gesell J. M. Neumann

1991-01-01

204

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 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)

2005-12-01

205

REDOR NMR for drug discovery.  

Science.gov (United States)

Rotational-echo double-resonance (REDOR) NMR is a powerful and versatile solid-state NMR measurement that has been recruited to elucidate drug modes of action and to drive the design of new therapeutics. REDOR has been implemented to examine composition, structure, and dynamics in diverse macromolecular and whole-cell systems, including taxol-bound microtubules, enzyme-cofactor-inhibitor ternary complexes, and antibiotic-whole-cell complexes. The REDOR approach involves the integrated design of specific isotopic labeling strategies and the selection of appropriate REDOR experiments. By way of example, this digest illustrates the versatility of the REDOR approach, with an emphasis on the practical considerations of experimental design and data interpretation. PMID:24035486

Cegelski, Lynette

2013-11-01

206

NMR spectra of transient radicals  

International Nuclear Information System (INIS)

A time-resolved method for the study of structure and spin dynamics of transient radicals in liquids is described. Pulsed electron beam or pulsed laser irradiation is used to create transient radicals in solution. Irradiation is carried out in the field of a variable electromagnet, and the diamagnetic products are transferred rapidly using a fast flow system to an NMR probe. During the radical reaction, a 0.5 to 10 ?s rf pulse is applied to the reacting sample at an appropriate frequency, corresponding to a nuclear energy level spacing of the given radical. Nuclear spin level population changes in the radical are transferred to its reaction product and detected as intensity changes in their NMR spectra. The method is illustrated using radiolyzed sodium malonate

1984-09-04

207

Resonance phenomena in the region of NMR and EMR overlapping  

International Nuclear Information System (INIS)

The review is devoted to theoretical and experimental investigations in the new field of the magnetic resonance -under conditions of nuclear and electron resonance frequencies overlapping in magnetic substances. A typical for magnets situation when the electron relaxation parameter greatly exceeds the parameter of the electron-nuclear interaction is analysed in detail. Both stationary and transient processes are considered; new phenomena which were discovered in the last years in the region of resonance overlapping are discussed in detail. The possibility of detection the NMR signal by a simple ferro- and antiferromagnetic resonance methods is demonstrated

1981-01-01

208

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

Science.gov (United States)

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

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

2012-08-01

209

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

210

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

Scientific Electronic Library Online (English)

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

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

211

Transverse NMR relaxation as a probe of mesoscopic structure  

CERN Multimedia

We show that transverse NMR signal relaxation averaged over a macroscopic volume is extremely sensitive to structure of mesoscopic paramagnetic inhomogeneities. Such a sensitivity is proposed as a novel kind of contrast in the NMR measurements. We model the medium by a suspension of arbitrary shaped mesoscopic paramagnetic objects, and find transverse relaxation without adjustable parameters in the case when the dephasing effect of an individual object is small. Results indicate a strong relaxation rate dependence on the shape of the objects. As a major application we consider transverse spin relaxation in the whole blood, for which our theory agrees well with experiments and Monte-Carlo simulations. Applications to a wide range of problems in complex systems (porous media, biological systems, diffusion limited reaction rates) are discussed.

Kiselev, V G; Kiselev, Valerij G.; Novikov, Dmitry S.

2002-01-01

212

Saliva metabolomics by NMR for the evaluation of sport performance.  

Science.gov (United States)

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

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

2014-01-01

213

Advanced NMR Methodologies in Cultural Heritage  

Digital Repository Infrastructure Vision for European Research (DRIVER)

NMR methodologies were applied and optimized to characterize and monitor Cultural Heritage. The various cases reported, clearly evidence how NMR is not confined to a few specific applications, but its use can be successfully extended to a wide number of different issues regarding Cultural Heritage. In fact NMR is a very powerful tool in the chemical characterization of materials allowing to shed light in the techniques used by artists, and in the knowledge of materials constituting the artif...

2013-01-01

214

Applications of NMR in Dairy Research  

Directory of Open Access Journals (Sweden)

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

Anthony D. Maher

2014-03-01

215

NMR studies of host-pathogen interactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis describes the use of Nuclear Magnetic Resonance (NMR) for characterizing two host-pathogen interactions: The behavior of a regulatory RNA of the Hepatitis B virus (HBV) and the attachment of Helicobacter pylori (H. pylori) to the gastric mucosa. NMR is a powerful tool in biomedicine, because molecules ranging from small ligands to biomacromolecules can be studied with atomic resolution. Different NMR experiments are designed to determine structures, or to monitor interactions, fol...

Petzold, Katja

2009-01-01

216

Time domain NMR applied to food products  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Time-domain NMR is being used throughout all areas of food science and technology. A wide range of one- and two-dimensional relaxometric and diffusometric applications have been implemented on cost-effective, robust and easy-to-use benchtop NMR equipment. Time-domain NMR applications do not only cover research and development but also quality and process control in the food supply chain. Here the opportunity to further downsize and tailor equipment has allowed for “mobile” sensor applicat...

Duynhoven, J.; Voda, A.; Witek, M. M.; As, H.

2010-01-01

217

A microscale protein NMR sample screening pipeline  

Digital Repository Infrastructure Vision for European Research (DRIVER)

As part of efforts to develop improved methods for NMR protein sample preparation and structure determination, the Northeast Structural Genomics Consortium (NESG) has implemented an NMR screening pipeline for protein target selection, construct optimization, and buffer optimization, incorporating efficient microscale NMR screening of proteins using a micro-cryoprobe. The process is feasible because the newest generation probe requires only small amounts of protein, typically 30–200 ?g in ...

Rossi, Paolo; Swapna, G. V. T.; Huang, Yuanpeng J.; Aramini, James M.; Anklin, Clemens; Conover, Kenith; Hamilton, Keith; Xiao, Rong; Acton, Thomas B.; Ertekin, Asli; Everett, John K.; Montelione, Gaetano T.

2010-01-01

218

Operator and algebraic methods for NMR spectroscopy. I. Generation of NMR spin species  

International Nuclear Information System (INIS)

Algebraic methods are developed for generating NMR spin species and irreducible representations spanned by spin functions. These methods use generalized character cycle indices (S function when NMR groups are symmetric groups). A correspondence between the unitary group approach and the permutation group method for NMR is established by generating NMR Gel'fand states using Schur functions. The generalized character cycle indices of molecules whose NMR groups are expressible as generalized wreath products are shown to be generalized NMR plethysms of Schur functions. These techniques enable generation of spin species without the knowledge of the character tables of NMR groups. We illustrate the methods developed here with several examples. The use of these techniques in generating symmetry-adapted NMR spin functions can be found in the accompanying paper

1983-06-01

219

NMR studies of isotopically labeled RNA  

International Nuclear Information System (INIS)

In summary, the ability to generate NMR quantities of 15N and 13C-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

1994-12-01

220

Solution NMR structure determination of proteins revisited  

International Nuclear Information System (INIS)

This 'Perspective' bears on the present state of protein structure determination by NMR in solution. The focus is on a comparison of the infrastructure available for NMR structure determination when compared to protein crystal structure determination by X-ray diffraction. The main conclusion emerges that the unique potential of NMR to generate high resolution data also on dynamics, interactions and conformational equilibria has contributed to a lack of standard procedures for structure determination which would be readily amenable to improved efficiency by automation. To spark renewed discussion on the topic of NMR structure determination of proteins, procedural steps with high potential for improvement are identified

2008-11-01

 
 
 
 
221

Solution NMR structure determination of proteins revisited  

Energy Technology Data Exchange (ETDEWEB)

This 'Perspective' bears on the present state of protein structure determination by NMR in solution. The focus is on a comparison of the infrastructure available for NMR structure determination when compared to protein crystal structure determination by X-ray diffraction. The main conclusion emerges that the unique potential of NMR to generate high resolution data also on dynamics, interactions and conformational equilibria has contributed to a lack of standard procedures for structure determination which would be readily amenable to improved efficiency by automation. To spark renewed discussion on the topic of NMR structure determination of proteins, procedural steps with high potential for improvement are identified.

Billeter, Martin [University of Gothenburg, Department of Chemistry (Sweden)], E-mail: martin.billeter@chem.gu.se; Wagner, Gerhard [Harvard Medical School, Department of Biological Chemistry and Molecular Pharmacology (United States); Wuethrich, Kurt [The Scripps Research Institute, Department of Molecular Biology and The Skaggs Institute for Chemical Biology (United States)

2008-11-15

222

NMR Methods for Strongly Inhomogeneous Magnetic Fields : Application on Elastomers using the NMR-MOUSE  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Die vorliegende Arbeit beschreibt neue Ergebnisse und NMR-Methoden für stark inhomogene Magnetfelder, insbesondere für die NMR-MOUSE und deren Anwendungen. Die Ergebnisse kann man wie folgt summarisch darstellen: 1. Die Möglichkeit der Aufnahme von NMR-Spektren von Elastomeren mit der NMR-MOUSE wurde untersucht. 2. Dipolar kodierte longitudinale Magnetisierung, Doppelquanten (DQ) Kohärenzen und dipolare Ordnung wurden erstmalig in stark inhomogenen Magnetfeldern zur Charakterisierung von ...

Wiesmath, Anette

2001-01-01

223

NMR characterization of pituitary tumors  

International Nuclear Information System (INIS)

Twelve patients (5 male, 7 female, mean age 37.9 +- 20) with pituitary tumors were extensively evaluated with NMR imaging using a 1.5K gauss resistive magnet. Saturation recovery (SR), inversion recovery (IR) and spin echo (SE) pulse sequences were used for qualitative characterization of the lesions. T/sub 1/ calculations were also performed for brain and pituitary. Tumor histology and endocrine status were correlated with NMR data. All tumors were large with suprasellar extension (6 with prolactin secretion, 6 without). Pituitary T/sub 1/'s ranged from .2 to .64, the mean T/sub 1/ being longer than that of brain (Brain = .4 +- .04; Pit = .48 +- .14). 3 patients with histological evidence of homogeneous adenomas had long T/sub 1/'s (0.58 +- .05). 3 patients with evidence of recent or old hemorhage into the pituitary had much shorter T/sub 1/'s (0.29 +- .12). There was no relationship between prolactin secretion and T/sub 1/. Qualitative T/sub 1/ and T/sub 2/ information can be obtained by using a combination of SR, IR, and SE images. Using this method in the patients, homogeneous adenomas had similar T/sub 1/'s and longer T/sub 2/'s compared to the brain, while patients with bleeds had shorter T/sub 1/'s and T/sub 2/'s. Image T/sub 1/ characteristics correlated well with the calculated T/sub 1/ values. The range of T/sub 1/ (and potentially T/sub 2/) values which occur in apparently similar lesions are most likely due to anatomical and pathophysiological variations in these lesions. It may be ultimately possible to separate different types of pathological processes based on NMR image T/sub 1/ and T/sub 2/ characteristics after careful comparative studies of NMR and histological data are completed. The combination of calculated T/sub 1/ and T/sub 2/ with image T/sub 1/ and T/sub 2/ information may also be useful in further characterization of lesions

1984-06-05

224

NMR properties of 3He-A in biaxially anisotropic aerogel  

Science.gov (United States)

Theoretical model of G.E. Volovik for A-like phase of 3He in aerogel suggests formation of Larkin-Imry-Ma state of Anderson-Brinkmann-Morel order parameter. Most of results of NMR studies of A-like phase are in a good agreement with this model in assumption of uniaxial anisotropy, except for some of experiments in weakly anisotropic aerogel samples. We demonstrate that these results can be described in frames of the same model in assumption of biaxial anisotropy. Parameters of anisotropy in these experiments can be determined from the NMR data.

Dmitriev, V. V.; Krasnikhin, D. A.; Senin, A. A.; Yudin, A. N.

2012-12-01

225

NMR quantum computation with indirectly coupled gates  

CERN Multimedia

An NMR realization of a two-qubit quantum gate which processes quantum information indirectly via couplings to a spectator qubit is presented in the context of the Deutsch-Jozsa algorithm. This enables a successful comprehensive NMR implementation of the Deutsch-Jozsa algorithm for functions with three argument bits and demonstrates a technique essential for multi-qubit quantum computation.

Collins, D; Holton, W C; Sierzputowska-Gracz, H; Stejskal, E O; Collins, David

1999-01-01

226

An Inversion Recovery NMR Kinetics Experiment  

Science.gov (United States)

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…

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

2011-01-01

227

Using Cloud Storage for NMR Data Distribution  

Science.gov (United States)

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

Soulsby, David

2012-01-01

228

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

1989-01-01

229

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

1998-04-15

230

93Nb NMR chemical shift scale for niobia systems.  

Science.gov (United States)

93Nb solid-state NMR spectra of a series of inorganic niobates with Nb in different oxygen coordination environments were measured. For all studied compounds the chemical shielding and quadrupole tensor parameters were determined using conventional and ultrahigh field NMR facilities, ultrahigh speed MAS, DQ STMAS, solid-echo and computer modeling. It has been demonstrated that the 93Nb isotropic chemical shift is sensitive to the coordination number of Nb sites. For the first time the 93Nb NMR chemical shift scale for NbOx polyhedra in solid materials has been proposed: for four-coordinated Nb sites, the isotropic shifts occur from -650 to -950 ppm; five-coordinated Nb sites have the isotropic shifts in the range of -900 to -980 ppm; for six-coordinated Nb sites the isotropic shifts vary from -900 to -1360 ppm; the shifts from -1200 to -1600 ppm are typical for seven-coordinated Nb sites; for eight-coordinated Nb sites the shifts are higher than -1400 ppm. The possible correlation between the value of the isotropic chemical shift and the ionic character of the NbOx-MOy polyhedra association has been suggested. The magnitude of the 93Nb quadrupole coupling constant depends on the local symmetry of Nb sites and may vary from hundreds of kHz to hundreds of MHz. PMID:16216475

Lapina, Olga B; Khabibulin, Dzhalil F; Romanenko, Konstantin V; Gan, Zhehong; Zuev, Mikhail G; Krasil'nikov, Vladimir N; Fedorov, Vladimir E

2005-09-01

231

NMR of small solutes in liquid crystals and molecular sieves  

Science.gov (United States)

The present thesis deals with the nuclear magnetic resonance (NMR) spectroscopy of small solutes applied to the studies of liquid crystals and molecular sieves. In this method, changes induced by the investigated environment to the static spectral parameters (i.e. nuclear shielding, indirect and direct spin-spin coupling and quadrupole coupling) of the solute are measured. The nuclear shielding of dissolved noble gases is utilized for the studies of thermotropic liquid crystals. The relation between the symmetry properties of mesophases and the nuclear shielding is described. The different interaction mechanisms perturbing the observed noble gas nuclear shielding are discussed, particularly, the role of long-range attractive van der Waals interactions is brought out. The suitability of the noble gas NMR spectroscopy to the studies of Iyotropic liquid crystals is investigated in terms of nuclear shielding and quadrupole coupling interactions. In molecular sieve systems, the effect of inter- and intracrystalline motions of solutes on their NMR spectra is discussed. A novel method for the measurement of the intracrystalline motions is developed. The distinctions in the 13C shielding of methane adsorbed in AlPO4-11 and SAPO-11, two structurally similar molecular sieves differing in composition, are indicated.

Ylihautala, Mika Petri

232

NMR studies of molecules in liquid crystals and graphite  

Energy Technology Data Exchange (ETDEWEB)

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

Rosen, M.E.

1992-06-01

233

Solution NMR of polypeptides hyperpolarized by dynamic nuclear polarization.  

Science.gov (United States)

Hyperpolarization of nuclear spins through techniques such as dynamic nuclear polarization (DNP) can greatly increase the signal-to-noise ratio in NMR measurements, thus eliminating the need for signal averaging. This enables the study of many dynamic processes which would otherwise not be amenable to study by NMR spectroscopy. A report of solid- to liquid-state DNP of a short peptide, bacitracin A, as well as of a full-length protein, L23, is presented here. The polypeptides are hyperpolarized at low temperature and dissolved for NMR signal acquisition in the liquid state in mixtures of organic solvent and water. Signal enhancements of 300-2000 are obtained in partially deuterated polypeptide when hyperpolarized on (13)C and of 30-180 when hyperpolarized on (1)H. A simulated spectrum is used to identify different resonances in the hyperpolarized (13)C spectra, and the relation between observed signal enhancement for various groups in the protein and relaxation parameters measured from the hyperpolarized samples is discussed. Thus far, solid- to liquid-state DNP has been used in conjunction with small molecules. The results presented here, however, demonstrate the feasibility of hyperpolarizing larger proteins, with potential applications toward the study of protein folding or macromolecular interactions. PMID:21651293

Ragavan, Mukundan; Chen, Hsueh-Ying; Sekar, Giridhar; Hilty, Christian

2011-08-01

234

1H NMR spectroscopic identification of a glue sniffing biomarker.  

Science.gov (United States)

Organic solvent abuse typically involves sniffing organic solvents to experience the mind-altering conditions they induce. In Republic of Korea, organic solvent abuse is a serious social problem, especially among teenagers. Several studies have addressed the effects of organic solvent abuse on mind and body, but there are no simple methods by which such abuse can be positively identified. In this report, we describe a method for analyzing toluene metabolites (toluene is the main ingredient of glue) in glue-sniffers' urine using (1)H NMR spectroscopy. Toluene is a commonly used solvent in the rubber, paint, plastics, leather, printing, and chemical industries. Inhaled toluene is metabolized to hippuric acid in the liver and excreted in the urine. Hippuric acid is known as a good biomarker for biological monitoring of toluene exposure. We have scanned hippuric acid and other toluene metabolites by NMR spectroscopy and performed statistical multivariate analysis of the data. Based on this analysis, we sought to determine parameters by which glue-sniffing (toluene inhalation) behavior may be verified. We also demonstrate the use of a pattern recognition method for accurate and efficient analysis of NMR data. In comparison to conventional methods, such as mass spectroscopy coupled with liquid chromatography or gas chromatography, nuclear magnetic resonance spectroscopy has several advantages, including simple sample preparation, non-destructive sampling, accuracy, short acquisition time, and reproducibility in the determination of urinary hippuric acid. PMID:21316881

Kwon, Bobae; Kim, Siwon; Kim, Sosun; Lee, Dong-Kye; Park, Yu-Jin; Kim, Myung-Duck; Lee, Jae-Shin; Kim, Suhkmann

2011-06-15

235

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

International Nuclear Information System (INIS)

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

2012-01-01

236

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

Science.gov (United States)

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

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

2013-11-01

237

High temperature approximation in NMR  

International Nuclear Information System (INIS)

Recently, Warren S Warren has challenged one of the basic assumptions on nuclear magnetic resonance (NMR) at ambient temperatures, known as High Temperature Approximation (HTA), presenting convincing evidence for the need to include the second, and the higher order terms in the density matrix expansion (?). In this paper, new experiments designed to test for the existence or otherwise of higher order terms in the expansion of ? are presented and discussed. Using the UNSW 600 MHz spectrometer we found, to our astonishment, strong multiple quantum signals in excess of ?m ±2, in accord with Warren. However, by partially de-tuning the tank circuit, all of the ?m > ±2 peaks could be made to disappear. This points to 'radiation damping' as the source of the high-order peaks, but at this stage other mechanisms cannot be ruled out

1996-02-02

238

Synthesis, IR and NMR spectral correlations in some symmetrical diimines  

Directory of Open Access Journals (Sweden)

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

G. Thirunarayanan

2014-01-01

239

Advanced NMR-based techniques for pore structure analysis of coal  

Energy Technology Data Exchange (ETDEWEB)

One of the main problems in coal utilization is the inability to properly characterize its complex pore structure. Coals typically have micro/ultra-micro pores but they also exhibit meso and macroporosity. We believe that measurement of the NMR parameters of various gas phase and adsorbed phase NMR active probes can provide the resolution to this problem. We will investigate the dependence of the common NMR parameters such as chemical shifts and relaxation times of several different nuclei and compounds on the pore structure of model microporous solids, carbons, and coals. In particular, we will study the interaction between several small molecules ({sup 129}Xe, {sup 3}He, {sup 2}H{sub 2}, {sup 14}N{sub 2}, {sup 14}NH{sub 3}, {sup 15}N{sub 2}, {sup 13}CH{sub 4}, {sup 13}CO{sub 2}) and the pore surfaces in coals. These molecules have been selected for their chemical and physical properties. A special NMR probe will be constructed which will allow the concurrent measurement of NMR properties and adsorption uptake at a variety of temperatures. All samples will be subjected to a suite of conventional'' pore structure analyses. These include nitrogen adsorption at 77 K with BET analysis, C0{sub 2} and CH{sub 4} adsorption at 273 K with D-R (Dubinin-Radushkevich) analysis, helium pycnometry, and small angle X-ray scattering as well as gas diffusion measurements. The project combines expertise at the UNM (pore structure, NMR), Los Alamos National Laboratory (NMR), and Air Products (porous materials).

Smith, D.M.

1992-01-01

240

Application of /sup 1/H and /sup 13/C NMR spectroscopy in structural investigations of Vinca indole alkaloids  

Energy Technology Data Exchange (ETDEWEB)

This paper considers the laws connecting the parameters of the H 1 and C 13 NMR spectra with the structure of the substances and the use of these laws for solving structural and stereochemical problems of the Vinca indole alkaloids and other compounds of closely related structure. For each type of alkaloid, characteristic features of the PMR and C 13 NMR spectra are given that permit the structures of similar bases to be established and their stereochemical identification to be performed.

Yagudaev, M.R.

1986-07-01

 
 
 
 
241

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

242

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

International Nuclear Information System (INIS)

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

2010-01-01

243

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

Science.gov (United States)

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

Atkinson, D.; Chechik, V.

2004-01-01

244

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.)

1986-01-01

245

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

246

NMR study of LaPb2  

International Nuclear Information System (INIS)

La and Pb NMR signals were observed in LaPb2 with a superconducting transition temperature of about 7 K. The width of the Pb NMR spectrum with an asymmetric line shape was rather narrower than those of Er-, Gd- and Ho-Pb2. The spin-lattice relaxation time of Pb nuclei was twice longer than that of Pb metal. La NMR spectrum had satellites due to the electric quadrupole interaction. These results show that each local environment at La or Pb site in LaPb2 compound is uniquely determined, compared with those in randomly substituted alloys. ((orig.))

1995-02-09

247

On electrophoretic NMR. Exploring high conductivity samples  

Science.gov (United States)

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

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

2014-06-01

248

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

249

NMR-spektroskopische Untersuchungen an Fettsäurebindungsproteinen  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ziel dieser Arbeit war es, mit der Methode der NMR-Spektroskopie strukturelle und funktionelle Eigenschaften von Fettsäurebindungsproteinen zu untersuchen. NMR-Spektren von Proteinen mit hohem -Faltblattanteil, wie H-FABP, zeigen häufig eine große Dispersion mit einer typischen Verteilung tief- und hochfeldverschobener Signale. Es wurden 1D/2D 1H-NMR Spektren für den Wildtyp und mehrere Mutanten (F4E, F4S, F4S/W8E, W8E, F16E, F16S, K21I, F64S, L66G und E72S) des humanen H-FABP aufgenommen...

2003-01-01

250

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)

1999-01-01

251

NMR mechanisms in gel dosimetry  

Energy Technology Data Exchange (ETDEWEB)

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 [Departments of Oncology and Physics, Queen' s University (United Kingdom), and Cancer of Centre Southeastern Ontario at KGH, Kingston, Canada, K7L 5P9 (Canada)], E-mail: john.schreiner@krcc.on.ca

2009-05-01

252

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)

2008-01-01

253

Ultrafast NMR T-1 Relaxation Measurements: Probing Molecular Properties in Real Time  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The longitudinal relaxation properties of NMR active nuclei carry useful information about the site-specific chemical environments and about the mobility of molecular fragments. Molecular mobility is in turn a key parameter reporting both on stable properties, such as size, as well as on dynamic ones, such as transient interactions and irreversible aggregation. In order to fully investigate the latter, a fast sampling of the relaxation parameters of transiently formed molecular species may be...

2013-01-01

254

Substituent Effects in the 13C-NMR Spectra of Six-Membered Nitrogen Heteroaromatic Compounds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract: It is shown that the 13C-NMR chemical shifts of carbon atoms in substituted sixmembered heteroaromatic compounds correlate with the correponding "additivity parameters" for substituted benzene derivatives. Thus, for precalculation of chemical shifts in such compounds, just one set of parameters can be used. The differences between experimental chemical shifts and those calculated from correlation with the common set may provide insights into intramolecular interactions not reported ...

Janusz Oszczapowicz

2005-01-01

255

NMR in the SPINE Structural Proteomics project.  

Science.gov (United States)

This paper describes the developments, role and contributions of the NMR spectroscopy groups in the Structural Proteomics In Europe (SPINE) consortium. Focusing on the development of high-throughput (HTP) pipelines for NMR structure determinations of proteins, all aspects from sample preparation, data acquisition, data processing, data analysis to structure determination have been improved with respect to sensitivity, automation, speed, robustness and validation. Specific highlights are protonless (13)C-direct detection methods and inferential structure determinations (ISD). In addition to technological improvements, these methods have been applied to deliver over 60 NMR structures of proteins, among which are five that failed to crystallize. The inclusion of NMR spectroscopy in structural proteomics pipelines improves the success rate for protein structure determinations. PMID:17001092

Ab, E; Atkinson, A R; Banci, L; Bertini, I; Ciofi-Baffoni, S; Brunner, K; Diercks, T; Dötsch, V; Engelke, F; Folkers, G E; Griesinger, C; Gronwald, W; Günther, U; Habeck, M; de Jong, R N; Kalbitzer, H R; Kieffer, B; Leeflang, B R; Loss, S; Luchinat, C; Marquardsen, T; Moskau, D; Neidig, K P; Nilges, M; Piccioli, M; Pierattelli, R; Rieping, W; Schippmann, T; Schwalbe, H; Travé, G; Trenner, J; Wöhnert, J; Zweckstetter, M; Kaptein, R

2006-10-01

256

NMR studies of cerebral metabolism in vivo  

International Nuclear Information System (INIS)

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

1986-01-01

257

NMR of 5-methylene-barbiturates  

International Nuclear Information System (INIS)

This work presents the use of heterocyclic compounds in the chemical preparation of a new family of pyridines. NMR was used to elucidate the reaction characteristics. Results are presented and discussed

1993-05-11

258

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

Science.gov (United States)

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

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

2006-08-14

259

Deuterium NMR study of mobility and fluctuations in nematic and isotropic elastomers.  

Science.gov (United States)

Orientational ordering in polydomain nematic and isotropic elastomers with identical polysiloxane backbone and different deuterium-labeled side groups is studied by D-NMR. In the nematic elastomer the orientational order parameter grows in a critical fashion on crossing the I-N transition implying a continuous phase transition driven by critical fluctuations of local director. The orientational (nematic) ordering occurs on the background of the polymer dynamics exhibited by the backbone, which is similar in the nematic and the analogous isotropic elastomers. The temperature dependence of NMR linewidths is compatible with a Vogel-Fulcher glassy dynamics. PMID:19708759

Feio, G; Figueirinhas, J L; Tajbakhsh, A R; Terentjev, E M

2009-08-21

260

SedNMR: a web tool for optimizing sedimentation of macromolecular solutes for SSNMR.  

Science.gov (United States)

We have proposed solid state NMR (SSNMR) of sedimented solutes as a novel approach to sample preparation for biomolecular SSNMR without crystallization or other sample manipulations. The biomolecules are confined by high gravity--obtained by centrifugal forces either directly in a SSNMR rotor or in a ultracentrifugal device--into a hydrated non-crystalline solid suitable for SSNMR investigations. When gravity is removed, the sample reverts to solution and can be treated as any solution NMR sample. We here describe a simple web tool to calculate the relevant parameters for the success of the experiment. PMID:24243317

Ferella, Lucio; Luchinat, Claudio; Ravera, Enrico; Rosato, Antonio

2013-12-01

 
 
 
 
261

Microscopic evidence of the FFLO state in CeCoIn5 probed by NMR study  

International Nuclear Information System (INIS)

An anomalous temperature dependence of 115In-NMR spectrum is observed in the newly-discovered high field and low temperature superconducting phase of CeCoIn5. The anomalies near the upper limit of H C 2 are attributed to spatially-distributed local density of states of quasiparticles. From a simulation with the phenomenological model for the sinusoidally-modulated superconducting order parameter, the present NMR study provides a microscopic evidence that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is realized at the high field phase in CeCoIn5. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2006-09-01

262

Theoretical NMR correlations based Structure Discussion  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Junker Jochen

2011-01-01

263

NMR spectroscopy of bone and bone substitutes  

Energy Technology Data Exchange (ETDEWEB)

High resolution solid state NMR spectroscopy appears as a powerful method for a better understanding of bone structure and bone implant. In particular it is efficient to estimate osteoformation via bioceramics bone colonization. In this work {sup 31}P, {sup 1}H NMR are used to the analysis of different type of bioceramics, to follow the transformation of calcium phosphate ceramics versus implantation time, to examine the influence of a protein. (orig.)

Legrand, A.P.; Bresson, B. [ESA, Paris (France). Lab. de Physique Quantique; Bouler, J.M. [INSERM, Nantes (France). Lab. de Recherche sur les Materiaux d' Interet Biologique

2001-07-01

264

NMR method of assay for gentamicin  

International Nuclear Information System (INIS)

Nuclear Magnetic Resonance (NMR) has been used successfully to assay gentamicin dosage forms. The method gives 100.5% accuracy with a variation of 2.3% for pure samples. It is a fast method of analysis. An assay which normally takes 14 or 18 hours by microbiological or ion exchange chromatographic methods respectively can now be performed in 30 minutes by the use of NMR. (author). 8 refs.; 3 tabs.; 1 fig

1990-06-01

265

NMR based metabolic profiling of liver cancer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

1H and 31P magic angle spinning (MAS) NMR spectroscopy in conjunction with multivariate statistical analysis and 1H and 31P heterostatistical total correlation NMR spectroscopy (1H-31P HET-STOCSY) were used to investigate changes in the hepatic metabolome correlated with the development of human hepatocellular carcinoma (HCC) from tumor, tumor adjacent, and liver tissue from patients without HCC (control). HCC tumor tissue showed lower levels of lipids, glucose, phosphodiesters (PDE), and ele...

2011-01-01

266

A microscale protein NMR sample screening pipeline  

Energy Technology Data Exchange (ETDEWEB)

As part of efforts to develop improved methods for NMR protein sample preparation and structure determination, the Northeast Structural Genomics Consortium (NESG) has implemented an NMR screening pipeline for protein target selection, construct optimization, and buffer optimization, incorporating efficient microscale NMR screening of proteins using a micro-cryoprobe. The process is feasible because the newest generation probe requires only small amounts of protein, typically 30-200 {mu}g in 8-35 {mu}l volume. Extensive automation has been made possible by the combination of database tools, mechanization of key process steps, and the use of a micro-cryoprobe that gives excellent data while requiring little optimization and manual setup. In this perspective, we describe the overall process used by the NESG for screening NMR samples as part of a sample optimization process, assessing optimal construct design and solution conditions, as well as for determining protein rotational correlation times in order to assess protein oligomerization states. Database infrastructure has been developed to allow for flexible implementation of new screening protocols and harvesting of the resulting output. The NESG micro NMR screening pipeline has also been used for detergent screening of membrane proteins. Descriptions of the individual steps in the NESG NMR sample design, production, and screening pipeline are presented in the format of a standard operating procedure.

Rossi, Paolo; Swapna, G. V. T.; Huang, Yuanpeng J.; Aramini, James M. [State University of New Jersey, Center for Advanced Biotechnology and Medicine, Department of Molecular Biology and Biochemistry, Rutgers (United States); Anklin, Clemens [Bruker Biospin Corporation (United States); Conover, Kenith; Hamilton, Keith; Xiao, Rong; Acton, Thomas B.; Ertekin, Asli; Everett, John K.; Montelione, Gaetano T., E-mail: guy@cabm.rutgers.ed [State University of New Jersey, Center for Advanced Biotechnology and Medicine, Department of Molecular Biology and Biochemistry, Rutgers (United States)

2010-01-15

267

Physics parameters  

International Nuclear Information System (INIS)

This report describes the work of the Parameters Group active during the Stanford Linear Collider Workshop. The purpose of the physicists in this group was to investigate experimental aspects of the electron-positron annihilation mediated by the weak neutral gauge boson. Since their goal was to establish the experimental requirements to be met by detectors, rather than solve the technical problems they raise, a conscious effort was made to avoid technological issues. The interests of the participants are reflected in the three chapters of this report: Z"0 ? HADRONS, Z"0 ? CHARGED LEPTONS, and OTHER PROCESSES. The sections on hadrons review general characteristics of the multi-hadron final states and investigate the parameters of detectors capable of studying the jets of produced particles, with special emphasis on the solid angle, segmentation, and energy and momentum resolution issues. The studies of the charged lepton channels deals with these topics too, but in addition consider the statistical accuracy of the data, the magnitude of the weak effects, and the accuracy of determination of weak parameters in the framework of the SU(2) x U(1) model. Finally, the studies of lower rate processes, such as Higgs particle production and radiative Z"0 production, expand the discussion to include the magnitude of background processes and specific detector requirements

1982-03-01

268

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.)

269

Basics of spectroscopic instruments. Hardware of NMR spectrometer  

International Nuclear Information System (INIS)

NMR is a powerful tool for structure analysis of small molecules, natural products, biological macromolecules, synthesized polymers, samples from material science and so on. Magnetic Resonance Imaging (MRI) is applicable to plants and animals Because most of NMR experiments can be done by an automation mode, one can forget hardware of NMR spectrometers. It would be good to understand features and performance of NMR spectrometers. Here I present hardware of a modern NMR spectrometer which is fully equipped with digital technology. (author)

2009-08-01

270

Carbon-13 NMR characterization of actinyl(VI) carbonate complexes in aqueous solution  

International Nuclear Information System (INIS)

The uranyl(VI) carbonate system has been re-examined using 13C NMR of 99.9% 13C-enriched UVIO2 (13CO3)34- in millimolar concentrations. By careful control of carbonate ion concentration, we have confirmed the existence of the trimer, and observed dynamic equilibrium between the monomer and the timer. In addition, the ligand exchange reaction between free and coordinated carbonate on PuVIO2(13CO3)34- and AmVIO2(13CO3)34- systems has been examined by variable temperature 13C NMR line-broadening techniques 13C NMR line-broadening techniques. A modified Carr-Purcell-Meiboom-Gill NMR pulse sequence was written to allow for experimental determination of ligand exchange parameters for paramagnetic actinide complexes. Preliminary Eyring analysis has provided activation parameters of ?Gdouble-dagger295 = 56 kJ/M, ?Hdouble-dagger = 38 kJ/M, and ?Sdouble-dagger = -60 J/M-K for the plutonyl triscarbonate system, suggesting an associative transition state for the plutonyl (VI) carbonate complex self-exchange reaction. Experiments for determination of the activation parameters for the americium (VI) carbonate system are in progress

1992-06-01

271

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

272

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

273

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

274

Contact-metamorphic effect on parameters for kerogen maturation  

Energy Technology Data Exchange (ETDEWEB)

This study examines the effect of contact metamorphism by an igneous dyke on parameters for kerogen maturation, such as elemental composition (H/C, O/C, N/C), /sup 1/H-NMR T/sub 1/, vitrinite reflectance and infrared spectra. Although elemental composition and /sup 1/H-NMR T/sub 1/ of the kerogen changed only within 1.5 and 5.0 m from the dyke respectively, vitrinite reflectance of the kerogen was thermally affected beyond 10.0 m from the intrusion. It is concluded that vitrinite reflectance is the most sensitive of the parameters evaluated to assess thermal stress of kerogens.

Ujiie, Y.

1986-01-01

275

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)

2009-01-01

276

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

Directory of Open Access Journals (Sweden)

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

Karl-Heinz Böhm

2014-04-01

277

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

CERN Document Server

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

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

2010-01-01

278

Residual broadening in high-resolution NMR of quadrupolar nuclei in solids  

CERN Multimedia

amorphous materials. The spectra of these compounds show significant additional broadening due to the presence of distributions of chemical shift and quadrupolar parameters. A lineshape-fitting routine is proposed, tested and applied to obtain quantitative estimates of these distributions in the sup 2 sup 7 AI MQMAS NMR spectra of a series of amorphous aluminosilicate compounds. Solid-state NMR spectra of quadrupolar nuclei are often poorly resolved due to the presence of anisotropic second-order quadrupolar broadening, even under conventional magic angle spinning (MAS) conditions. The two-dimensional multiple-quantum MAS (MQMAS) experiment is one of several techniques which have been designed to remove this broadening and provide high-resolution NMR spectra of half-integer quadrupolar nuclei. This thesis demonstrates that, in the absence of this pure quadrupolar broadening, it is possible to observe a weak quadrupolar-dipolar interaction which also survives conventional MAS and is the result of dipolar coupl...

McManus, J

2001-01-01

279

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)

2008-03-01

280

Spectroscopic and magnetic properties of a gadolinium macrobicyclic complex  

International Nuclear Information System (INIS)

As a result of Schiff base condensation, gadolinium cryptate has been synthesized and investigated by infrared (IR) spectroscopy and electron paramagnetic resonance (EPR) technique. Comparison of IR bands in a ligand and the gadolinium complex confirmed the formation of the gadolinium cryptate complex. IR and thermogravimetry-differential thermal analysis (TG-DTA) analyses indicate the presence of two water molecules in the inner sphere of the complex. Mass spectroscopy investigations confirmed a monometallic substitution of the Gd3+ ion into the macrobicycle ligand. EPR spectra of the complex have been registered in the 3-300 K temperature range. Each spectrum has been simulated using the EPR-NMR computer program and the values of the spin Hamiltonian parameters at each temperature have been calculated. The thermal dependence of the spin Hamiltonian parameters has been investigated. The temperature dependence of the integrated intensity of the EPR spectrum revealed the magnetic interactions in the spin system of this compound. No long-range magnetic order has been detected in the 3-300 K range, but a strong antiferromagnetic interaction in the high-temperature range, above 160 K, has been observed

2006-11-01

 
 
 
 
281

NMR at low and ultralow temperatures.  

Science.gov (United States)

Solid state nuclear magnetic resonance (NMR) measurements at low temperatures have been common in physical sciences for many years and are becoming increasingly important in studies of biomolecular systems. This Account reviews a diverse set of projects from my laboratory, dating back to the early 1990s, that illustrate the motivations for low-temperature solid state NMR, the types of information that are available from the measurements, and likely directions for future research. These projects include NMR studies of both physical and biological systems, performed at low (cooled with nitrogen, down to 77 K) and ultralow (cooled with helium, below 77 K) temperatures, and performed with and without magic-angle spinning (MAS). NMR studies of physical systems often focus on phenomena that occur only at low temperatures. Two examples from my laboratory are studies of molecular rotation and orientational ordering in solid C60 at low temperatures and studies of unusual electronic states, called skyrmions, in two-dimensionally confined electron systems within semiconductor quantum wells. To study quantum wells, we used optical pumping of nuclear spin polarizations to enhance their NMR signals. The optical pumping phenomenon exists only at ultralow temperatures. In studies of biomolecular systems, low-temperature NMR has several motivations. In some cases, low temperatures suppress molecular tumbling, thereby permitting solid state NMR measurements on soluble proteins. Studies of AIDS-related peptide/antibody complexes illustrate this effect. In other cases, low temperatures suppress conformational exchange, thereby permitting quantitation of conformational distributions. Studies of chemically denatured states of the model protein HP35 illustrate this effect. Low temperatures and rapid freeze-quenching can also be used to trap transient intermediate states in a non-equilibrium kinetic process, as shown in studies of a transient intermediate in the rapid folding pathway of HP35. NMR sensitivity generally increases with decreasing sample temperature. Therefore, it can be useful to carry out experiments at the lowest possible temperatures, particularly in studies of biomolecular systems in frozen solutions. However, solid state NMR studies of biomolecular systems generally require rapid MAS. A novel MAS NMR probe design that uses nitrogen gas for sample spinning and cold helium only for sample cooling allows a wide variety of solid state NMR measurements to be performed on biomolecular systems at 20-25 K, where signals are enhanced by factors of 12-15 relative to measurements at room temperature. MAS NMR at ultralow temperatures also facilitates dynamic nuclear polarization (DNP), allowing sizeable additional signal enhancements and large absolute NMR signal amplitudes with relatively low microwave powers. Current research in my laboratory seeks to develop and exploit DNP-enhanced MAS NMR at ultralow temperatures, for example, in studies of transient intermediates in protein folding and aggregation processes and studies of peptide/protein complexes that can be prepared only at low concentrations. PMID:23470028

Tycko, Robert

2013-09-17

282

Investigation of ferroelectric nanostructured systems by ESR and NMR methods  

International Nuclear Information System (INIS)

Full text: The theoretical and experimental investigation of ferroelectric nanopowders is performed. Since the most prominent size effect in ferroelectric nanomaterials was known to be size driven ferroelectric-paraelectric phase transition at some critical particle size R = Rcr the study of this effect manifestation in radiospectroscopy spectra was the main goal of the paper. In the theoretical part, the size effect of the parameters of the central transition +1/2 -1/2 lines which are known to be the most intensive for powder sample both in ESR and NMR are considered for the materials with ferroelectric tetragonal phase at room temperature and cubic paraelectric phase in the bulk. Therefore the transformation of axial symmetry spectra into cubic symmetry ones can be expected at R ? Rcr. For this transformation description the spontaneous polarization inhomogeneity inside a particle and distribution of particle sizes calculated previously were taken into account. Both these factors lead to inhomogeneous broadening of the lines. In ESR spectra the transformation of the spectra from axial symmetry to cubic symmetry lines was obtained with decreasing of nanoparticle sizes with practically complete disappearance of axial spectra at R ? Rcr. The method of Rcr value extraction from the ratio of the different symmetry spectra intensities was proposed. Size effect in NMR spectra for nuclei with quadrupole moments was considered, i.e. +1/2 -1/2 transition perturbed by second order quadrupole interaction of the nuclei with electric field gradient was calculated. Allowing for the absence of cubic symmetry in the vicinity of surface even in paraelectric phase, namely at R ? Rcr (P = 0), we described this size effect in core and shell model. Measurements of Fe3+ ESR spectra and 137Ba NMR spectra in nanopowder of BaTiO3 were carried out. The samples were prepared by rate-controlled method. Laser granulometry method analysis had shown that the particles sizes are distributed around two maxima with R bar ? 160 nm and R bar ? 40 nm. The decrease of intensity of axial symmetry ESR lines of Fe3+ and appearance of cubic symmetry line was observed with the average sizes decrease with complete disappearance of axial spectra at R bar ? 40 nm. NMR spectra practically did not change in all the samples although the essential narrowing of the line was expected at R ? Rcr. The comparison of the theory with experiment was carried out. The theory fits experimental data pretty good. The value of critical size Rcr ? 40 nm was extracted from ESR data. The asymmetry and broadening of right hand side shoulder of ESR cubic symmetry line was shown to be related to contribution of paramagnetic centers in the vicinity of the particles surface with lower than cubic symmetry. Such type of contribution to NMR line can be the main reason of absence of the pronounced size effect, namely the narrowing of the line, in NMR spectra of nuclei with quadrupole mechanism that defined the spectra main characteristics. The nuclei with chemical shift mechanism can be more sensitive for size effect investigations by NMR method. (author)

2005-09-22

283

NMR-CT of craniocerebral trauma  

International Nuclear Information System (INIS)

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

1984-01-01

284

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

Science.gov (United States)

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

Minch, Michael J.

1998-02-01

285

A case study of NMR interpretation in complex reservoirs using variable T 2 cutoff  

Energy Technology Data Exchange (ETDEWEB)

A complete formation evaluation requires determination of irreducible fluids, movable fluids, and formation permeability. Analysis of NMR measurements to determine these parameters is strongly dependent on formation lithology and mineralogy, especially in complex and heterogeneous reservoirs. Therefore, NMR measurements must be combined with measurements from conventional logs for comprehensive formation evaluation. In this paper an interpretation method that combines these data is discussed and is applied to complex formations. An important advantage of the method presented in this paper is its capacity to generate a variable T2 cutoff for NMR interpretation that depends on the volumetrics of the calculated formation lithology. In NMR analysis, the T2 cutoff is required to divide effective porosity into irreducible and movable porosity. In traditional T2 interpretation, the T2 cutoff is usually a constant value throughout a formation; however, the methodology proposed in this paper uses a variable T2 cutoffs and their effect on formation evaluation are included, and recommendations are discussed. An error minimization technique is used to solve a system of equations derived from the log data. In this system of equations, the NMR effective porosity is used as the formation effective porosity. To evaluate the goodness of the fit between the original logs and the reconstructed logs, the chi-square of the difference between logs is calculated. In this methodology, weighting factors can be applied to the log data, and geological and petrophysical constraints can be imposed. (author)

Oraby, M. [Halliburton Energy Services, Houston, TX (United States); Chafai, N. [Sonatrach Oil Company, XX (Algeria)

1997-07-01

286

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

Energy Technology Data Exchange (ETDEWEB)

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

287

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

Energy Technology Data Exchange (ETDEWEB)

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

Jackson, J.A.

1981-01-01

288

Operator and algebraic methods for NMR spectroscopy. II. NMR projection operators and spin functions  

International Nuclear Information System (INIS)

We outline double coset and restricted character cycle index methods which generate the equivalence classes of NMR spin functions and the irreducible representations in the representation spanned by spin functions in any equivalence class. Elegant operator methods are developed by which the projection operators of NMR groups can be obtained in terms of the projection operators of composing groups. Thus, the projection operators of NMR groups of many molecules can be obtained without the knowledge of their character tables. Projection operators thus obtained are applied on the set of spin functions in an equivalence class of NMR spin functions (rather than the whole set of spin functions) which are generated by double coset methods to obtain symmetry-adapted NMR spin functions in the composite particle representation. Methods are illustrated with several examples of molecules containing as many as 230 NMR spin functions. The methods developed here are quite general so that they can be applied to NMR of nuclei with multispin states and they do not require the character tables of NMR groups. The techniques outlined here are illustrated with 2, 2, 3, 3-tetramethyl butane for which the symmetry-adapted NMR spin couplings are obtained in the composite particle representation. The NMR Hamiltonian matrix of this molecule which is of order 218 x 218 is factored into 26 x 26 matrix by the composite particle treatment. This is further factored into 8 1 x 1 matrices and 6 4 x 4, 4 2 x 2, and 3 8 x 8 matrices in the symmetry-adapted basis

1983-06-01

289

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.

290

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

291

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

292

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

293

NMR spectra simulation for quantum computing  

Energy Technology Data Exchange (ETDEWEB)

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)

Diaz Bulnes, J.; Sarthour, R.S.; Guimaraes, A.P.; Oliveira, I.S. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Freitas, J.C.C. [Universidade Federal do Espirito Santo (UFES), Vitoria, ES (Brazil). Dept. de Fisica

2002-07-01

294

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)

2002-05-07

295

Nuclear magnetic resonance (NMR): principles and applications  

International Nuclear Information System (INIS)

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

1979-12-06

296

Chemical applications of 99Tc NMR spectroscopy: preparation of novel Tc(VII) species and their characterization by multinuclear NMR spectroscopy  

International Nuclear Information System (INIS)

The 99Tc NMR parameters of a number of Tc(VII) and one Tc(V) species have been determined. The anion TcO4- (? = 22.508 311 MHz in H2O) was chosen as the standard for 99Tc NMR spectroscopy. A 99Tc-17O coupling constant of 131.4 Hz was obtained from a 17O- and 18O-enriched sample of TcO4- whose 99Tc spectrum also showed an isotopic shift of 0.22 ppm/mass number arising from a statistical distribution of 16O/17O/18O isotopic isomers. Technetium-99 and proton NMR provided definitive proof for the existence of the stereochemically nonrigid TcH92- anion. Both TcO3F and the novel TcO3+ cation were synthesized and characterized by 99Tc, 17O, and 19F NMR spectroscopy. Preliminary results on two new technetium(VII) oxyfluorides tentatively identified as F2O2TcOTcO2F2 and TcO2F3 are also reported. The diagmagnetic d2 anion, TcO2(CN)43-, represents the most deshielded 99Tc environment encountered in the present study

1982-10-06

297

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)

1984-01-01

298

Characterization by NMR of ozonized methyl linoleate  

International Nuclear Information System (INIS)

In the present study ozonized methyl linoleate with peroxide index of 1,800 mmol-equiv kg-1 was chemically characterized. Ozonation of methyl linoleate produced hydroperoxides, ozonides and aldehydes which were identified by 1H and 13C NMR two-dimensional. The standard methyl linoleate and ozonized methyl linoleate shown very similar 1H NMR spectra except for the signals at ? 9.7 and ? 9.6 that correspond to aldehydic hydrogen, ? 5.7 and ? 5.5 (olefinic signals from hydroperoxides) and ? 5.2 ppm (multiplet from ozonides methynic hydrogen). Other resonance assignments are based on the connectivities provided by the hydrogen scalar coupling constants. These results indicate that NMR spectroscopy can provide valuable information about the amount of formed oxygenated compounds in the ozonized methyl linoleate in order to use it to follow up ozone therapy and chemistry of ozonized vegetable oil. (author)

2007-01-01

299

Characterization by NMR of ozonized methyl linoleate  

Energy Technology Data Exchange (ETDEWEB)

In the present study ozonized methyl linoleate with peroxide index of 1,800 mmol-equiv kg{sup -1} was chemically characterized. Ozonation of methyl linoleate produced hydroperoxides, ozonides and aldehydes which were identified by {sup 1}H and {sup 13}C NMR two-dimensional. The standard methyl linoleate and ozonized methyl linoleate shown very similar {sup 1}H NMR spectra except for the signals at {delta} 9.7 and {delta} 9.6 that correspond to aldehydic hydrogen, {delta} 5.7 and {delta} 5.5 (olefinic signals from hydroperoxides) and {delta} 5.2 ppm (multiplet from ozonides methynic hydrogen). Other resonance assignments are based on the connectivities provided by the hydrogen scalar coupling constants. These results indicate that NMR spectroscopy can provide valuable information about the amount of formed oxygenated compounds in the ozonized methyl linoleate in order to use it to follow up ozone therapy and chemistry of ozonized vegetable oil. (author)

Diaz, Maritza F. [National Center for Scientific Research, Havana (Cuba). Ozone Research Center. Dept. of Ozonized Substances]. E-mail: maritza.diaz@cnic.edu.cu; Gavin, Jose A. [University of the Laguna, Tenerife (Spain)

2007-07-01

300

O17 NMR spectra of diphosphatopolyoxomolybdates  

International Nuclear Information System (INIS)

Aqueous solutions of the salts Na6P2Mo18O62x52H2O(1), Na4H2P2Mo5O23x10H2O(2) and Na6P2Mo5O23x14H2O(3) with concentration 0.2(1), and 0.4(2)(3) mol/l have been studied using NMR method on the 17O and 31P nuclei. Chemical shifts of 17O and 31P NMR of heteropolyanions P2Mo5O236- and P2Mo18O626- are measured. It is shown that chemical shift of 17O NMR in polyoxomolybdate correlates with the distance to the nearest molybdenum atom

1980-03-01

 
 
 
 
301

Remote Tuning of NMR Probe Circuits  

Science.gov (United States)

There are many circumstances in which the probe tuning adjustments cannot be located near the rf NMR coil. These may occur in high-temperature NMR, low-temperature NMR, and in the use of magnets with small diameter access bores. We address here circuitry for connecting a fixed-tuned probe circuit by a transmission line to a remotely located tuning network. In particular, the bandwidth over which the probe may be remotely tuned while keeping the losses in the transmission line acceptably low is considered. The results show that for all resonant circuit geometries (series, parallel, series-parallel), overcoupling of the line to the tuned circuit is key to obtaining a large tuning bandwidth. At equivalent extents of overcoupling, all resonant circuit geometries have nearly equal remote tuning bandwidths. Particularly for the case of low-loss transmission line, the tuning bandwidth can be many times the tuned circuit's bandwidth, f o/Q.

Kodibagkar, Vikram D.; Conradi, Mark S.

2000-05-01

302

Wide-line NMR and protein hydration.  

Science.gov (United States)

In this chapter, the reader is introduced to the basics of wide-line NMR, with particular focus on the following: (1) basic theoretical and experimental NMR elements, necessary before switching the spectrometer and designing the experiment, (2) models/theories for the interpretation of measured data, (3) definition of wide-line NMR spectrometry, the description of the measurement and evaluation variants, useful hints for the novice, (4) advice on selecting the solvent, which is not a trivial task, (5) a note of warning that not all data are acceptable in spite of the statistical confidence. Finally, we wrap up the chapter with the results on two proteins (a globular and an intrinsically disordered). PMID:22760320

Tompa, K; Bokor, M; Tompa, P

2012-01-01

303

Gas NMR Characterization of Oil Shale  

Science.gov (United States)

Accurate descriptions and simulations of oil reservoirs such as carbonate-rich sedimentary rock are important for the efficient development and conversion of recoverable energy reserves. These descriptions depend on reliable measures of the properties of the formation rock such as absolute and effective porosity, mineralogical composition, permeability, and tortuosity. NMR signal relaxation time (T1 and T2) and measurements of restricted diffusion of gases in porous media can be used to probe multi-pore media, yielding valuable petrophysical information and allowing the characterization of internal topology and pore size distribution. We employ NMR techniques on imbibed fluorinated and hyperpolarized noble gases - gases with the unique properties of being chemically inert and minimally invasive while exhibiting favorable NMR properties - at various pressure and temperatures to characterize the shale heterogeneity. We show current results of our characterizations and explore ideas for future work.

Sorte, Eric; Laicher, Gernot; Saam, Brian

2007-10-01

304

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.)

2005-10-01

305

Fast multidimensional NMR spectroscopy for sparse spectra.  

Science.gov (United States)

Multidimensional NMR spectroscopy is widely used for studies of molecular and biomolecular structure. A major disadvantage of multidimensional NMR is the long acquisition time which, regardless of sensitivity considerations, may be needed to obtain the final multidimensional frequency domain coefficients. In this article, a method for under-sampling multidimensional NMR acquisition of sparse spectra is presented. The approach is presented in the case of two-dimensional NMR acquisitions. It relies on prior knowledge about the support in the two-dimensional frequency domain to recover an over-determined system from the under-determined system induced in the linear acquisition model when under-sampled acquisitions are performed. This over-determined system can then be solved with linear least squares. The prior knowledge is obtained efficiently at a low cost from the one-dimensional NMR acquisition, which is generally acquired as a first step in multidimensional NMR. If this one-dimensional acquisition is intrinsically sparse, it is possible to reconstruct the corresponding two-dimensional acquisition from far fewer observations than those imposed by the Nyquist criterion, and subsequently to reduce the acquisition time. Further improvements are obtained by optimizing the sampling procedure for the least-squares reconstruction using the sequential backward selection algorithm. Theoretical and experimental results are given in the case of a traditional acquisition scheme, which demonstrate reliable and fast reconstructions with acceleration factors in the range 3-6. The proposed method outperforms the CS methods (OMP, L1) in terms of the reconstruction performance, implementation and computation time. The approach can be easily extended to higher dimensions and spectroscopic imaging. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24664959

Merhej, Dany; Ratiney, Hélène; Diab, Chaouki; Khalil, Mohamad; Sdika, Michaël; Prost, Rémy

2014-06-01

306

Protein Motions and Folding Investigated by NMR Spectroscopy  

Science.gov (United States)

NMR spin relaxation spectroscopy is a powerful experimental approach for globally characterizing conformational dynamics of proteins in solution. Laboratory frame relaxation measurements are sensitive to overall rotational diffusion and internal motions on picosecond-nanosecond time scales, while rotating frame relaxation measurements are sensitive to chemical exchange processes on microsecond-millisecond time scales. The former approach is illustrated by ^15N laboratory-frame relaxation experiments as a function of temperature for the helical subdomain HP36 of the F-actin-binding headpiece domain of chicken villin. The data are analyzed using the model-free formalism to characterize order parameters and effective correlation times for intramolecular motions of individual ^15N sites. The latter approach is illustrated by ^13C Carr-Purcell-Meiboom-Gill relaxation measurements for the de novo designed ?_2D protein and by ^15N rotating-frame relaxation measurements for the peripheral subunit-binding domain (PSBD) from the dihydrolopoamide acetyltransferase component of the pyruvate dehydrogenase multienzyme complex from Bacillus stearothermophilus. These experiments are used to determine the folding and unfolding kinetic rate constants for the two proteins. The results for HP36, ?_2D, and PSBD illustrate the capability of current NMR methods for characterizing dynamic processes on multiple time scales in proteins.

Palmer, Arthur

2002-03-01

307

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

308

NMR evidence of hydrogen bonds in cellulose solutions  

Energy Technology Data Exchange (ETDEWEB)

The nature of cellulose dissolution in the complex solvent system, N,N-dimethylacetamide (DMA) containing lithium chloride, has been studied. The aprotic character of this complex solvent allows us to investigate the dissolution mechanism, using the behavior of the methyl-..beta delta..-cellubioside hydroxyl /sup 1/H NMR signals. It is shown that each hydroxyl group of this cellulose model compound is linked with one lithium chloride molecule in solution. Determination of the hydroxyl proton NMR parameters (chemical shift, coupling constant, temperature increment) in this complex solvent and in DMSO allows us to point out the peculiar behavior of the OH-3 hydroxyl group. It is explained by the existence of an intramolecular hydrogen bond involving this hydroxyl group and the heterocyclic oxygen atom of the neighboring D-glucopyranosyl unit. Similar observations are made for cellulose oligomers of DP = 10 in the complex solvent DMA/LiCl and in DMSO solution and for cellulose in the complex solvent. 25 references, 10 figures, 2 tables.

Gagnaire, D.; Saint-Germain, J.; Vincendon, M.

1983-01-01

309

Fixed point theory of iterative excitation schemes in NMR  

International Nuclear Information System (INIS)

Iterative schemes for NMR have been developed by several groups. A theoretical framework based on mathematical dynamics is described for such iterative schemes in nonlinear NMR excitation. This is applicable to any system subjected to coherent radiation or other experimentally controllable external forces. The effect of the excitation, usually a pulse sequence, can be summarized by a propagator or superpropagator (U). The iterative scheme (F) is regarded as a map of propagator space into itself, U/sub n/+1 = FU/sub n/. One designs maps for which a particular propagator U-bar or set of propagators ]U-bar] is a fixed point or invariant set. The stability of the fixed points along various directions is characterized by linearizing F around the fixed point, in analogy to the evaluation of an average Hamiltonian. Stable directions of fixed points typically give rise to broadband behavior (in parameters such as frequency, rf amplitude, or coupling constants) and unstable directions to narrowband behavior. The dynamics of the maps are illustrated by ''basin images'' which depict the convergence of points in propagator space to the stable fixed points. The basin images facilitate the optimal selection of initial pulse sequences to ensure convergence to a desired excitation. Extensions to iterative schemes with several fixed points are discussed. Maps are shown for the propagator space SO(3) appropriate to iterative schemes for isolated spins or two-level systems. Some maps exhibit smooth, continuous dynamics whereas others have basin images with complex and fractal structures

1985-09-15

310

Capillary HPLC-NMR Coupling:? High-Resolution (1)H NMR Spectroscopy in the Nanoliter Scale.  

Science.gov (United States)

Coupling HPLC and NMR is one of the most powerful techniques for simultaneous separation and structural elucidation of unknown compounds in mixtures. To date, however, minimizing the detection volume, as is required when coupling NMR with miniaturized separation techniques, has been accompanied by a dramatic loss in resolution of the NMR spectra. Here, we report on the coupling of gradient capillary HPLC with on-column, high-resolution NMR detection. On-line stopped-flow and static (1)H NMR spectra were acquired with capillary columns of 75-315 ?m i.d. With detection over a length of 1.2 cm, cell volumes cover a range of 50-900 nL. An on-line-detected NMR separation of dansylated amino acids was carried out in a 315 ?m i.d. fused silica capillary packed to a length of 12 cm with C(18) stationary phase. The low solvent consumption makes the use of fully deuterated solvents economically feasible. NMR spectra with resolution on the order of 3 Hz were obtained using a 50 nL detection cell to measure 1.1 nmol of dansylated ?-aminobutyric acid under static conditions in a 75 ?m i.d. capillary. PMID:21619141

Behnke, B; Schlotterbeck, G; Tallarek, U; Strohschein, S; Tseng, L H; Keller, T; Albert, K; Bayer, E

1996-04-01

311

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

312

Tritiation methods and tritium NMR spectroscopy  

International Nuclear Information System (INIS)

We have used a simple process for the production of highly tritiated water and characterized the product species by "1H and "3H NMR spectroscopy. The water is readily manipulated and used in subsequent reactions either as T_2O, CH_3COOT or CF_3COOT. Development of tritiated diimide has progressed to the point where cis-hydrogenated products at 1-20 Ci/mmole S.A. are possible. Tri-n-butyl tin tritide has been produced at >95% tritium content and well characterized by multinuclear NMR techniques. 27 refs., 3 figs

1991-09-03

313

NMR studies of single crystal chromium diboride  

International Nuclear Information System (INIS)

We report 11B NMR studies of a single crystal CrB2. From the temperature dependence of the Fourier-transformed NMR spectra in the paramagnetic state, the hyperfine coupling constants are estimated to be ACr-B = -0.64,-0.74 and -0.71kOe/?B for H parallel c, H parallel a and H parallel [210], respectively. In the magnetically ordered state, the spectra in H parallel a and H parallel [210] consist of superposition of a broad hump and five peaks, which correspond to the incommensurate and commensurate spin structures

2007-03-01

314

NMR studies of single crystal chromium diboride  

Energy Technology Data Exchange (ETDEWEB)

We report {sup 11}B NMR studies of a single crystal CrB{sub 2}. From the temperature dependence of the Fourier-transformed NMR spectra in the paramagnetic state, the hyperfine coupling constants are estimated to be A{sub Cr-B} = -0.64,-0.74 and -0.71kOe/{mu}{sub B} for H parallel c, H parallel a and H parallel [210], respectively. In the magnetically ordered state, the spectra in H parallel a and H parallel [210] consist of superposition of a broad hump and five peaks, which correspond to the incommensurate and commensurate spin structures.

Michioka, C. [Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)]. E-mail: michioka@kuchem.kyoto-u.ac.jp; Itoh, Y. [Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan); Yoshimura, K. [Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan); Watabe, Y. [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa 229-8558 (Japan); Kousaka, Y. [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa 229-8558 (Japan); Ichikawa, H. [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa 229-8558 (Japan); Akimitsu, J. [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa 229-8558 (Japan)

2007-03-15

315

NMR studies of single crystal chromium diboride  

Science.gov (United States)

We report 11B NMR studies of a single crystal CrB2. From the temperature dependence of the Fourier-transformed NMR spectra in the paramagnetic state, the hyperfine coupling constants are estimated to be A = -0.64,-0.74 and -0.71 kOe/?B for H||c, H||a and H|| [2 1 0], respectively. In the magnetically ordered state, the spectra in H||a and H|| [2 1 0] consist of superposition of a broad hump and five peaks, which correspond to the incommensurate and commensurate spin structures.

Michioka, C.; Itoh, Y.; Yoshimura, K.; Watabe, Y.; Kousaka, Y.; Ichikawa, H.; Akimitsu, J.

316

The Quiet Renaissance of Protein NMR  

Science.gov (United States)

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 fitted and kept in order, the air may tingle and thrill with the message, but it will not reach my spirit and consciousness.” Mary Slessor, Calabar, circa 1910

Barrett, Paul J.; Chen, Jiang; Cho, Min-Kyu; Kim, Ji-Hun; Lu, Zhenwei; Mathew, Sijo; Peng, Dungeng; Song, Yuanli; Van Horn, Wade D.; Zhuang, Tiandi; Sonnichsen, Frank D.; Sanders, Charles R.

2013-01-01

317

NMR linewidth and skyrmion localization in quantum hall ferromagnets  

International Nuclear Information System (INIS)

Full text: The ground state of the two-dimensional electron gas (2DEG) at filling factor one (V = 1) is a spin-polarized state in which all electrons completely fill the lowest Landau level with spin up polarization (quantum Hall ferromagnet). The low lying charged excitation of the 2DEG is called skyrmion, or charged spin texture, and carries an unusual spin distribution. Pictorially, this distribution can be viewed as a conguration in which the spin field points down at a given position and smoothly rotates as one moves radially outwards from that point, until all the spins are polarized as in the ground state. The existence of this many body electronic state was confirmed performing optically pumped nuclear magnetic resonance (OPNMR) measurements of the 71Ga nuclei located in an n-doped GaAs multiple quantum well. As the nuclei of the quantum wells are coupled to the the spins of the 2DEG via the isotropic Fermi contact interaction, the Knight shift (Ks) from the NMR signal gives information about the spin polarization of the 2DEG. It was reported that Ks symmetrically drops around v = 1, showing that the charged excitation of the quantum Hall ferromagnet involves a large number of spin-ips. However, recently new OPNMR measurements in multiple quantum wells were performed at very low temperatures (T = 0:3 K) showing that the Knight shift data around v = 1 consist of a tilted plateau, in contrast to the symmetrical fall at higher temperatures. As NMR is a local probe, it was argued that the existence of the tilted plateau is related to the localization of the skyrmions. In addition, the full width at half maximum (FWHM) of the OPNMR signal has a non-monotonic temperature dependence at v = 1, increasing when the temperature is lowered up to a critical value and then, falling down. It is well known that the linewidth of the NMR measurements is aected by the dynamics of the nuclei (motional narrowing effect). However, as the 71Ga nuclei are spatially fixed in the GaAs quantum wells, any observed dynamical effect must be related to the dynamics of 2DEG. In particular, if v = 1, those effects should be related to the skyrmion dynamics. Therefore, the present work will be devoted to show that the interplay between skyrmion dynamics and localization effects are enough to explain the NMR profile in the whole range of the experimentally available parameters. (author)

2004-11-08

318

NMR2: a powerful software system for processing multi-dimensional NMR data  

International Nuclear Information System (INIS)

The modular FORTRAN 77 program NMR2 was developed to meet the data reduction requirements of multi-dimensional NMR data processing. The problems inherent in the treatment and presentation of such data are introduced, and the program features that meet these problems are discussed. Details of the program co-ordination with the most virtual memory management are also discussed. Actual and projected program performance times on a variety of computer systems are reported, and future extensions for NMR spectroscopy and magnetic resonance imaging are discussed. (author)

1986-01-01

319

The Gradient Coils for NMR Spectro-Tomographic System.  

Czech Academy of Sciences Publication Activity Database

. Brno : The Spectroscopic Society of Johannes Marcus Marci, Central European NMR Discussion Group, 1998. s. 23.[NMR Valtice /13./. 27.04.1998-29.04.1998, Valtice]Kód oboru RIV: BM - Fyzika pevných látek a magnetismus

Konzbul, Pavel; Švéda, Karel

320

Study of Cultured Fibroblasts in Vivo Using NMR.  

Science.gov (United States)

The goal was to study the compartmentation of phosphorylated glycolytic intermediates in intact Chicken Embryo Fibroblasts (CEFs) using sup 31 P NMR at 109 MHz. A technique for maintaining functional cells at high densities in an NMR magnet is described. ...

G. S. Karczmar

1984-01-01

 
 
 
 
321

Comparative study of models for predicting permeability from nuclear magnetic resonance (NMR) logs in two Chinese tight sandstone reservoirs  

Science.gov (United States)

Based on the analysis of mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) experimental data for core plugs, which were drilled from two Chinese tight sandstone reservoirs, permeability prediction models, such as the classical SDR, Timur-Coates, the Swanson parameter, the Capillary Parachor, the R10 and R35 models, are calibrated to estimating permeabilities from field NMR logs, and the applicabilities of these permeability prediction models are compared. The processing results of several field examples show that the SDR model is unavailable in tight sandstone reservoirs. The Timur-Coates model is effective once the optimal T 2cutoff can be acquired to accurately calculate FFI and BVI from field NMR logs. The Swanson parameter model and the Capillary Parachor model are not always available in tight sandstone reservoirs. The R35 based model cannot effectively work in tight sandstone reservoirs, while the R10 based model is optimal in permeability prediction.

Xiao, Liang; Liu, Xiao-Peng; Zou, Chang-Chun; Hu, Xiao-Xin; Mao, Zhi-Qiang; Shi, Yu-Jiang; Guo, Hao-Peng; Li, Gao-Ren

2014-02-01

322

SPE-NMR metabolite sub-profiling of urine  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

323

Novel fast imaging techniques for diagnostic NMR imaging  

International Nuclear Information System (INIS)

The dissertation deals with a methodological enhancement of a fast MR imaging technique, the snapshot-FLASH (fast low-angle shot) technique. The first and primary goal was to optimize the snapshot-FLASH technique with a view to its application for diagnostic imaging of the heart. This optimization was to achieve a further reduction of measuring time per single shot and an increase in information gained per time unit. Another very important goal was to improve the method towards more exact, faster and as efficient as possible measurement of n.m.r. parameters. With these goals in mind, new two- or three-dimensional versions and a multilayered version of the snapshot-FLASH imaging sequence were developed. The results obtained in practice are explained and discussed. (orig./DG)

1993-01-01

324

Sodium-23 NMR of intact bovine lens and vitreous humor  

Science.gov (United States)

Sodium-23 nuclear magnetic resonance was used to investigate the chemical functionality of sodium ion in the intact, crystalline bovine lens and vitreous humor, as compared to physiologic saline. The NMR parameters of chemical shift and T1 and T2 relaxation are consistent with the interpretation that the chemical functionality of sodium ion in bovine vitreous humor is identical with that of sodium ion in physiologic salt solution. Identical studies on intact bovine lens demonstrated that some fraction of the sodium ion in the lens is relatively immobilized. The calculated sodium ion interaction lifetime in the crystalline bovine lens is 3 × 10 -9 s, which is qualitatively similar to interactions described between sodium ion and the proteins troponin C and calmodulin.

Pettegrew, Jay W.; Glonek, Thomas; Minshew, Nancy J.; Woessner, Donald E.

325

Genetic algorithms and solid state NMR pulse sequences  

CERN Multimedia

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

326

NMR study of ion motion in cesium hydrogen selenate  

International Nuclear Information System (INIS)

1H, 77Se and 133Cs NMR spectra and times of spin-lattice and spin-spin relaxation of 1H nuclei are measured in mono- and plycrystalline samples of cesium hydrogen selenate in a wide temperature range including phase transition into superion state. Based on the data obtained H+ and Cs+ cation diffusional motion parameters are determined. It is ascertained for the first time that phase transition into a superion phase is accompanied by the occurrance of a slow (with the frequency of the order of 104 Hz) cesium ion diffusion with the contribution to its observed conductivity being negligeably low in the whole temperature area of CsHSeO4 existence. Two different types of proton diffusion are detected in the low-temperature phase. It is shown that high conductivity in cesium hydrogen selenate in both phases is conditioned by fast proton diffusion

1988-01-01

327

Experimental aspects in acquisition of wide bandwidth solid-state MAS NMR spectra of low-? nuclei with different opportunities on two commercial NMR spectrometers  

Science.gov (United States)

The acquisition and different appearances observed for wide bandwidth solid-state MAS NMR spectra of low-? nuclei, using 14N as an illustrative nucleus and employing two different commercial spectrometers (Varian, 14.1 T and Bruker, 19.6 T), have been compared/evaluated and optimized from an experimental NMR and an electronic engineering point of view, to account for the huge differences in these spectra. The large differences in their spectral appearances, employing the recommended/standard experimental set-up for the two different spectrometers, are shown to be associated with quite large differences in the electronic design of the two types of preamplifiers, which are connected to their respective probes through a 50 ? cable, and are here completely accounted for. This has led to different opportunities for optimum performances in the acquisition of nearly ideal wide bandwidth spectra for low-? nuclei on the two spectrometers by careful evaluation of the length for the 50 ? probe-to-preamp cable for the Varian system and appropriate changes to the bandwidth ( Q) of the NMR probe used on the Bruker spectrometer. Earlier, we reported quite distorted spectra obtained with Varian Unity INOVA spectrometers (at 11.4 and 14.1 T) in several exploratory wide bandwidth 14N MAS NMR studies of inorganic nitrates and amino acids. These spectra have now been compared/evaluated with fully analyzed 14N MAS spectra correspondingly acquired at 19.6 T on a Bruker spectrometer. It is shown that our upgraded version of the STARS simulation/iterative-fitting software is capable of providing identical sets for the molecular spectral parameters and corresponding fits to the experimental spectra, which fully agree with the electronic measurements, despite the highly different appearances for the MAS NMR spectra acquired on the Varian and Bruker spectrometers.

Jakobsen, Hans J.; Bildsøe, Henrik; Gan, Zhehong; Brey, William W.

2011-08-01

328

Crack Parameters  

Energy Technology Data Exchange (ETDEWEB)

One of the important variables in the design of the end cap calorimeter is the number of angular divisions that should be made in the face of the calorimeter array. While it would be ideal to have no such divisions, they are unavoidable because the maximum size for uranium sheets is less than the diameter of the array. These divisions create regions which are either partially or totally devoid of absorber and readout. It is the purpose of this note to analyze the effects of different parameters on the size of these cracks. This analysis assumes wedge shaped structures of significant depth (i.e. > 20% of the total depth). For such modules there are five variables which affect the size of a crack. They are: (1) The clearance between modules. The extent to which the module wall and the array extend into this region depends on the tolerances on the manufacture of the module. All of the module construction techniques currently under consideration have very tight tolerances (e.g. 2 mils). Therefore, this region is assumed to be void of solid material. In the C.C this region is thought to be .090 inches wide. (2) The thickness of the module walls. The wall thickness depends on which module is discussed. Design thicknesses range from .078 inches in the C.C. modules to .150 inches in the E.C leakage modules. Because tight tolerances are assumed on the construction of the modules the skin is assumed to be perfectly flat. (3) The dimension tolerance on the uranium width. The effect of the dimension tolerance varies depending on the location of the module. Modules near the a o'clock and 9 o'clock position will see a gray zone equal to the dimension tolerance at the top of each module. There will be a solid black zone at the bottom of each module. This results from gravity pulling the uranium plates down to touch the lower wall of the module. Modules near the 6 o'clock and 12 o'clock region will see a gray zone equal to the dimension tolerance at both edges of a module since there are no plans for a mechanism to insure their alignment along one wall. (4) The straightness tolerance on the plate edges. The straightness tolerance creates a gray zone equal to its width along each side of a module. (5) The region of reduced signal pickup. The extent of this region is not yet well understood. The current design requires an area along the edge of the module which does not have resistive coat. The width of this region has not been determined. Some portion of this region should still collect all of the signal. The size of this region is not known, either. As an example we can use the tolerances currently achieved for the Harvard plates at Rocky Flats. The width tolerance requested was +0.000, -0.020 inches. Rocky Flats is delivering plates with a width tolerance of +0.000, -0.040 inch. There is no tolerance on the straightness of the datum edge. If we assume that .010 inch of the .040 inch tolerance is do to straightness variation then we can determine the crack sizes for a C.C. E.M. module.

Pitas, A.; /Fermilab

1985-10-31

329

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

1986-01-01

330

The NMR experiment based on Labview  

International Nuclear Information System (INIS)

In this paper, the essential principles of the virtual instrument are introduced, and two kinds of the virtual instrument which are used in the NMR experiment are designed. One is used in real experiment, and the other is used in emulation experiment, both can be operated through IE browser. (authors)

2007-07-01

331

NMR in the elucidation of complex structures  

International Nuclear Information System (INIS)

The author is interested in developing ideas and procedures whereby the process of structural elucidation by means of NMR spectroscopy are considered. In this paper he demonstrates how it is possible to construct a structural elucidation argument for a reasonable complex molecule without having to invent 'candidate structures' or refer to a 'working structure'. (A.S.). 36 refs.; 6 figs

1991-01-01

332

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

333

MAGNETISM AND SUPERCONDUCTIVITY BY NMR STUDY  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Results of NMR measurement on high Tc oxide superconductor are reviewed together with heavy electron superconductor. In high Tc compounds, superconductivity and antiferromagnetism compete with each other, while in heavy electron system both coexist or compete. The property of Cooper pair is discussed in high Tc superconductor together with the heavy electron superconductor.

Asayama, K.; Kitaoka, Y.; Kohori, Y.

1988-01-01

334

NMR analysis of a fluorocarbon copolymer  

Energy Technology Data Exchange (ETDEWEB)

Vinylidene fluoride (VF/sub 2/) 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 VF/sub 2/ 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 VF/sub 2/, the emulsifier (perfluorodecanoate) concentration, and the randomness of copolymerization can be determined. A trifluorotoluene internal standard is added to a d/sub 6/-acetone solution of the fluoropolymer. Proton NMR is used to determine the amount of VF/sub 2/. 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.

Smith, R.E.; Smith, C.H.

1987-10-01

335

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

1988-04-18

336

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

1994-12-01

337

Method of producing images by NMR techniques  

International Nuclear Information System (INIS)

The patent relates to methods of producing images of samples by NMR techniques. The method involves free induction signals, which are generated by gyro-magnetically excited nuclei in a sample. Fourier transformation of the signals yields the image. (U.K.)

1983-08-01

338

Molecular Structure and Dynamics by NMR Spectroscopy  

Science.gov (United States)

This site provides PowerPoint slides for a lecture for a graduate-level course in NMR spectroscopy. The slides include useful animations which help to demonstrate the concepts described. While the casual student may find it hard to follow everything on the slides without an accompanying lecture, the files should be very useful for advanced students or educators putting together similar courses.

Edison, Arthur S.; Long, Joanna

2011-07-04

339

NMR imaging: its potential clinical impact  

Energy Technology Data Exchange (ETDEWEB)

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.

Oldendorf, W.H.

1982-09-01

340

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

1982-01-01

 
 
 
 
341

NMR spectra line asymmetry in the Lee-Goldburg experiment  

International Nuclear Information System (INIS)

A method is proposed for calculation of satellites and the degree of symmetry of spectral lines in the Lee-Goldburg experiment is investigated. The results obtained are compared with analogous results for NMR with sample rotation under the magic angle. The conclusion is made that the NMR central line and satellites in NMR with sample rotation under magic angle are symmetric

1994-04-01

342

Applications of special NMR experiments to the characterization of disaccharides  

International Nuclear Information System (INIS)

Special NMR experiments were applied to the unequivocal characterization of two disaccharides. The main experiments relied on the inverse carbon detection and selective excitation, beside others common two dimensional NMR procedures. Various combinations of the 2 D contours plots containing projections of 1 D selective NMR spectra are shown

1999-05-01

343

Solid-state NMR studies of globular and membrane proteins  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Spektroskopie erlaubt die Eigenschaften und Struktur der Materie durch Einsatz elektromagnetischer Strahlung auf molekularer Ebene zu untersuchen. Die Kernspinresonanz (NMR) ist ein spezielles Gebiet der Spektroskopie, die die magnetischen Eigenschaften der Atomkerne auswertet. Ein kurzer Überblick über die historischen Weiterentwicklungen im Bereich der NMR ergibt sich aus einer Betrachtung der Nobelpreise, die bisher im Zusammenhang der NMR vergeben wurden: 1952 empfingen Felix Bloch und ...

Luca, Sorin

2003-01-01

344

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

2003-05-01

345

Optically pumped NMR in semiconductor InP  

Energy Technology Data Exchange (ETDEWEB)

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 {sup 31}P NMR signal strongly depends on the temperature and the helicity of the laser light.

Hashi, Kenjiro; Goto, Atsushi; Miyabe, Ryo; Shimizu, Tadashi; Kido, Giyuu; Ohki, Shinobu; Machida, Susumu

2003-05-01

346

NMR Data Analysis: A Time-Domain Parametric Approach Using Adaptive Subband Decomposition  

International Nuclear Information System (INIS)

This paper presents a fast time-domain data analysis method for one- and two-dimensional Nuclear Magnetic Resonance (NMR) spectroscopy, assuming Lorentzian lineshapes, based on an adaptive spectral decomposition. The latter is achieved through successive filtering and decimation steps ending up in a decomposition tree. At each node of the tree, the parameters of the corresponding subband signal are estimated using some high-resolution method. The resulting estimation error is then processed through a stopping criterion which allows one to decide whether the decimation should be carried on or not. Thus the method leads to an automated selection of the decimation level and consequently to a signal-adaptive decomposition. Moreover, it enables one to reduce the processing time and makes the choice of usual free parameters easier, comparatively to the case where the whole signal is processed at once. The efficiency of the method is demonstrated using 1-D and 2-D 13C NMR signals. (authors)

2014-01-01

347

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

348

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 and interproton distances have been compared to those inferred from the NMR measurements. The obtained results are in fair agreement with the experimental data

1997-07-01

349

NMR-Experiments on metallic single crystal surfaces; NMR-Experimente auf metallischen Einkristalloberflaechen  

Energy Technology Data Exchange (ETDEWEB)

For the first time we present NMR-Experiments with Xenon, adsorbed on metallic single crystal surfaces (Ir(111) and Cu(111)). The inherently low sensitivity of NMR could be raised by five orders of magnitude through optical pumping with Rubidium. Large chemical shifts have been obtained, far above the shift range commonly attributed to physisorption. The Knight-Shift (Fermi contact interaction) could clearly be identified as the main reason for the measured shifts. (Orig.)

Koch, M.

2006-07-01

350

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

Energy Technology Data Exchange (ETDEWEB)

The new methods for the correction of {sup 31}P NMR spectra in vivo NMR spectroscopy have been performed. A method for the baseline correction of the spectra which represents a combination of time-domain and frequency-domain has been discussed.The method is very fast and efficient for minimization of base line artifacts of biological tissues impact. 7 refs, 1 fig.

Starcuk, Z.; Bartusek, K.; Starcuk, Z. jr. [Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, Brno (Czech Republic)

1994-12-31

351

Simultaneous multinuclear NMR studies of brain metabolism  

International Nuclear Information System (INIS)

The brain is a complex metabolic system with intricate interactions between the various metabolic pathways to provide the tight regulation necessary to maintain homeostasis. A major problem faced by investigators studying metabolic regulation in vivo, is the inability to noninvasively follow the evolution of changes in metabolite concentrations during imposed metabolic stress. The work described in this thesis develops in vivo NMR spectroscopy into a technique to simultaneously monitor levels of high energy phosphate metabolites, intracellular pH, lactate concentrations and ionic equilibria in a time resolved fashion, and applies this technique to study metabolic regulation in the brain. The basic technique involves frequency interleaved NMR data acquisition, allowing spectra from several nuclei to be acquired in the same time it would take to acquire a spectrum from a single nucleus. In order to permit such frequency time shared use of the NMR spectrometer, it is necessary to develop multiple tuned NMR probes, capable of operating at several different frequencies with high sensitivity. Probes using multiple-pole tuning networks and coupled tank circuits individually or in combination are described. Applications of double (31P, 1H) and triple 23Na, 1H, 31P) nuclear NMR to study metabolic regulation in cat brain models of hypoxic ischemia and global seizure are described. The results are consistent with regulation of oxidative metabolism in the brain in vivo by the phosphorylation ratio, a potent regulator of in vitro mitochondrial function. Measurements of the brain buffering capacity and post isochemic lactate efflux are presented. A close correlation between the transmembrane Na+ gradient and the energy state is established

1986-01-01

352

Analysis of Structural Variability in Pharmaceutical Excipients Using Solid-State NMR Spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Polysaccharide-based excipients comprise the majority of most solid dosage forms and can vary dramatically in terms of structural and functionally related properties. Analytical methods for characterizing these important formulation components are crucial. Solid-state NMR spectroscopy (SSNMR) can provide a wealth of information on these materials while offering the advantages of non-destructive sample preparation and selectivity. The overall objective of this work is to identify SSNMR paramet...

Sperger, Diana M.; Munson, Eric Jon

2011-01-01

353

High-Resolution 2D NMR Spectroscopy of Bicelles to Measure the Membrane Interaction of Ligands  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetically aligned bicelles are increasingly being used as model membranes in solutionand solid-state NMR studies of the structure, dynamics, topology, and interaction of membraneassociated peptides and proteins. These studies commonly utilize the PISEMA pulse sequence to measure dipolar coupling and chemical shift, the two key parameters used in subsequent structural analysis. In the present study, we demonstrate that the PISEMA and other rotating-frame pulse sequences are not suitable for...

2007-01-01

354

Structural Characterization of MAO and Related Aluminum Complexes. 1. Solid-State 27 Al NMR with Comparison to EFG Tensors from ab Initio Molecular Orbital Calculations  

Energy Technology Data Exchange (ETDEWEB)

Aminato and propanolato aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three 27Al NMR techniques optimized for large 27Al Quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. The 27Al quadrupole coupling constants and asymmetry parameters of molecular species, both experimental and derived from ab initio molecular orbital calculations, are correlated with structure.

Bryant, Pamela L.; Harwell, Chris; Mrse, Anthony A.; Emery, Earl F.; Gan, Zhedong; Caldwell, Tod; Reyes, Arneil P.; Kuhns, Philip; Hoyt, David W.; Simeral, Larry S.; Hall, Randall W.; Butler, Leslie G.

2001-11-07

355

Exploring the anion-cation interaction in m-terphenyltetrafluorosilicates by using multinuclear NMR spectroscopy, X-ray diffraction, and ICR-FT-MS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The synthesis of a series of m-terphenyl-substituted tetrafluorosilicates withdifferent cations (Na+, K+, Rb+, Cs+, Ag+, Tl+) is described and the interactions between the anion and cation are investigated in the solid, solution, and gas states by using multinuclear NMR spectroscopy, X-ray diffraction, and ion cyclotron resonance Fourier- transform mass spectrometry (ICRFT- MS). In solution, heteronuclear NMR spectroscopy parameters show only limited sensitivity to the nature of the cation, w...

Spirk, Stefan; Belaj, Ferdinand; Nieger, Martin; Ko?feler, Harald; Rechberger, Gerald N.; Pietschnig, Rudolf

2012-01-01

356

Structural Dynamics and Conformational Equilibria of SERCA Regulatory Proteins in Membranes by Solid-State NMR Restrained Simulations.  

Science.gov (United States)

Solid-state NMR spectroscopy is emerging as a powerful approach to determine structure, topology, and conformational dynamics of membrane proteins at the atomic level. Conformational dynamics are often inferred and quantified from the motional averaging of the NMR parameters. However, the nature of these motions is difficult to envision based only on spectroscopic data. Here, we utilized restrained molecular dynamics simulations to probe the structural dynamics, topology and conformational transitions of regulatory membrane proteins of the calcium ATPase SERCA, namely sarcolipin and phospholamban, in explicit lipid bilayers. Specifically, we employed oriented solid-state NMR data, such as dipolar couplings and chemical shift anisotropy measured in lipid bicelles, to refine the conformational ensemble of these proteins in lipid membranes. The samplings accurately reproduced the orientations of transmembrane helices and showed a significant degree of convergence with all of the NMR parameters. Unlike the unrestrained simulations, the resulting sarcolipin structures are in agreement with distances and angles for hydrogen bonds in ideal helices. In the case of phospholamban, the restrained ensemble sampled the conformational interconversion between T (helical) and R (unfolded) states for the cytoplasmic region that could not be observed using standard structural refinements with the same experimental data set. This study underscores the importance of implementing NMR data in molecular dynamics protocols to better describe the conformational landscapes of membrane proteins embedded in realistic lipid membranes. PMID:24940774

De Simone, Alfonso; Mote, Kaustubh R; Veglia, Gianluigi

2014-06-17

357

Measuring the contrast-enhancement in the skin and subcutaneous fatty tissue with the NMR-Mouse {sup registered}: a feasibility study; Messung der Kontrastmittelanreicherung in der Haut und im subkutanen Fettgewebe mit der NMR-Mouse {sup registered} - eine Machbarkeitsstudie  

Energy Technology Data Exchange (ETDEWEB)

Purpose: the NMR-Mouse {sup 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 {sup 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 {sup 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.)

Heller, F. [Frauenklinik Diakoniekrankenhaus, Schwaebisch Hall (Germany); Schwaiger, A.; Eymael, R.; Bluemich, B. [Inst. fuer Technische Chemie und Makromolekulare Chemie, RWTH, Aachen (Germany); Schulz-Wendtland, R. [Inst. fuer Diagnostische Radiologie, Univ. Erlangen-Nuernberg, Erlangen (Germany)

2005-10-01

358

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

359

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

360

13C NMR tracers in neurochemistry implications for molecular imaging  

International Nuclear Information System (INIS)

An overview of 13C nuclear magnetic resonance (NMR) spectroscopy methods and their applications in the study of the metabolism of brain cells in vitro and in the in vivo brain is presented as well as their implications for modern molecular imaging techniques. Various topics will be discussed, such as general properties of the 13C NMR spectrum, 13C NMR spectroscopy acquisition protocols, determination of fractional 13C enrichment, 13C(2H) NMR methodologies, and the use of 13C hyper polarized substrates for NMR spectroscopy and imaging. Some illustrative applications are described, both in vitro and in vivo.

2009-12-01

 
 
 
 
361

Refinement of the protein backbone angle {psi} in NMR structure calculations  

Energy Technology Data Exchange (ETDEWEB)

Cross-correlated relaxation rates involving the C{sup {alpha}}-H{sup {alpha}} dipolar interaction and the carbonyl (C') chemical shift anisotropy (CSA) have been measured using two complementary 3D experiments. We show that the protein backbone angle {psi} can be directly refined against such cross-correlated relaxation rates ({gamma}{sup H{alpha}}{sup C{alpha}}{sup ,C'}) and the three-bond H/D isotope effect on the C{sup {alpha}} chemical shifts ({sup 3}{delta}C{sup {alpha}}{sub (ND)}). By simultaneously using both experimental parameters as restraints during NMR structure calculations, a unique value for the backbone angle {psi} is defined. We have applied the new refinement method to the {alpha}-Spectrin SH3 domain (a {beta}-sheet protein) and to the Sgs1p HRDC domain (an {alpha}-helical protein) and show that the quality of the NMR structures is substantially improved, judging from the atomic coordinate precision and the Ramachandran map. In addition, the {psi}-refined NMR structures of the SH3 domain deviate less from the 1.8 A crystal structure, suggesting an improved accuracy. The proposed refinement method can be used to significantly improve the quality of NMR structures and will be applicable to larger proteins.

Sprangers, R.; Bottomley, M.J.; Linge, J.P.; Schultz, J.; Nilges, M.; Sattler, M. [European Molecular Biology Laboratory (Germany)

2000-01-15

362

The Evaluation of Polyethylene/Clay Composite from Solid State NMR  

Directory of Open Access Journals (Sweden)

Full Text Available Polymeric nanocomposites based on polyethylene (PE and Brazilian natural montmorillonite clay (MN were obtained by melt processing, using a twin-screw extruder. The main objective of this work is focusing on the characterization of composites materials by solid-state nuclear magnetic resonance (NMR. The solid-state NMR measurements were used to observe both polymer matrix (through carbon-13 and hydrogen nuclei and the clay (silicon-29 and aluminum-27. The polymer matrix analyses were carried out applying solid state techniques, such as: cross-polarization magic angle spinning (CPMAS, variable contact time (VCT and by the proton spin-lattice relaxation time in the rotating frame parameter (T1?H, detected from the resolved carbon-13 decay of the VCT experiment and through the determination of spin-lattice relaxation time, T1H (using low field NMR. The clay was analyzed by 29Si and 27Al, employing MAS NMR technique. From those techniques we can have principally response on clay dispersion in the polyethylene matrix, as well as the interactions between both components in the nanostructured material. The T1H response was an important result which showed, that the materials formed, presented different molecular domains (according to the domain size that varied from 25 to 50 nm, measured by relaxation, considering the clay dispersion mode in terms of intercalation and/or exfoliation in the polymer matrix.

Antônio G. Ferreira

2011-05-01

363

Biaxial nematic order and phase behavior studies in an organosiloxane tetrapode using complementary deuterium NMR experiments.  

Science.gov (United States)

The biaxial nematic phase was recently observed in different thermotropic liquid crystals, namely bent-core compounds, side-chain polymers, bent-core dimers, and organosiloxane tetrapodes. In this work, a series of experiments with a nematic organosiloxane tetrapode where nuclear magnetic resonance (NMR) spectra are collected while the sample is continuously rotating around an axis perpendicular to the magnetic field, are discussed in conjunction with the analysis of a deuterium NMR experiment on the same system reported earlier. The sample used is a mixture of a deuterated probe with the tetrapode. The mixture exhibits a nematic range between -40 degrees C and 37 degrees C. The results of the two independent, but complementary deuterium NMR experiments confirm the existence of a biaxial nematic phase for temperatures below 0 degrees C with high values of the asymmetry parameter at low temperatures. The presence of slow movements of the tetrapode mesogenic units in the low-temperature regime could also be detected through the analysis of the NMR spectra. Simulations indicate that these movements are mainly slow molecular reorientations of the mesogenic units associated with the presence of collective modes in the nematic phases of this compound. In the case of tetrapodes, recent investigations attribute the origin of biaxiality to the hindering of reorientations of the laterally attached mesogenic units which constitute the tetrapode. This study relates the molecular movements with the nematic biaxial ordering of the system. PMID:19113138

Cruz, C; Figueirinhas, J L; Filip, D; Feio, G; Ribeiro, A C; Frère, Y; Meyer, T; Mehl, G H

2008-11-01

364

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

2014-06-01

365

From NMR chemical shifts to amino acid types: Investigation of the predictive power carried by nuclei  

International Nuclear Information System (INIS)

An approach to automatic prediction of the amino acid type from NMR chemical shift values of its nuclei is presented here, in the frame of a model to calculate the probability of an amino acid type given the set of chemical shifts. The method relies on systematic use of all chemical shift values contained in the BioMagResBank (BMRB). Two programs were designed, one (BMRB stats) for extracting statistical chemical shift parameters from the BMRB and another one (RESCUE2) for computing the probabilities of each amino acid type, given a set of chemical shifts. The Bayesian prediction scheme presented here is compared to other methods already proposed: PROTYP (Grzesiek and Bax, J. Biomol. NMR, 3, 185-204, 1993) RESCUE (Pons and Delsuc, J. Biomol. NMR, 15, 15-26, 1999) and PLATON (Labudde et al., J. Biomol. NMR, 25, 41-53, 2003) and is found to be more sensitive and more specific. Using this scheme, we tested various sets of nuclei. The two nuclei carrying the most information are C? and H?, in agreement with observations made in Grzesiek and Bax, 1993. Based on four nuclei: H?, C?, C? and C', it is possible to increase correct predictions to a rate of more than 75%. Taking into account the correlations between the nuclei chemical shifts has only a slight impact on the percentage of correct predictions: indeed, the largest correlation coefficients display similar features on all amino acids

2004-09-01

366

Comparative study of inversion methods of three-dimensional NMR and sensitivity to fluids  

Science.gov (United States)

Three-dimensional nuclear magnetic resonance (3D NMR) logging can simultaneously measure transverse relaxation time (T2), longitudinal relaxation time (T1), and diffusion coefficient (D). These parameters can be used to distinguish fluids in the porous reservoirs. For 3D NMR logging, the relaxation mechanism and mathematical model, Fredholm equation, are introduced, and the inversion methods including Singular Value Decomposition (SVD), Butler–Reeds–Dawson (BRD), and Global Inversion (GI) methods are studied in detail, respectively. During one simulation test, multi-echo CPMG sequence activation is designed firstly, echo trains of the ideal fluid models are synthesized, then an inversion algorithm is carried on these synthetic echo trains, and finally T2–T1–D map is built. Futhermore, SVD, BRD, and GI methods are respectively applied into a same fluid model, and the computing speed and inversion accuracy are compared and analyzed. When the optimal inversion method and matrix dimention are applied, the inversion results are in good aggreement with the supposed fluid model, which indicates that the inversion method of 3D NMR is applieable for fluid typing of oil and gas reservoirs. Additionally, the forward modeling and inversion tests are made in oil–water and gas–water models, respectively, the sensitivity to the fluids in different magnetic field gradients is also examined in detail. The effect of magnetic gradient on fluid typing in 3D NMR logging is stuied and the optimal manetic gradient is choosen.

Tan, Maojin; Wang, Peng; Mao, Keyu

2014-04-01

367

A carbon-13 nuclear magnetic resonance spectroscopic study of inter-proton pair order parameters: a new approach to study order and dynamics in phospholipid membrane systems.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a simple new nuclear magnetic resonance (NMR) spectroscopic method to investigate order and dynamics in phospholipids in which inter-proton pair order parameters are derived by using high resolution 13C cross-polarization/magic angle spinning (CP/MAS) NMR combined with 1H dipolar echo preparation. The resulting two-dimensional NMR spectra permit determination of the motionally averaged interpair second moment for protons attached to each resolved 13C site, from which the correspondi...

Urbina, J. A.; Moreno, B.; Arnold, W.; Taron, C. H.; Orlean, P.; Oldfield, E.

1998-01-01

368

NMR Quantum Calculations of the Jones Polynomial  

CERN Multimedia

The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for a small-scale approximate evaluation of the Jones Polynomial by nuclear-magnetic resonance (NMR), in addition we show how to escape from the limitations of NMR approaches that employ pseudo pure states. Specifically, we use two spin 1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the Trefoil Knot, the Figure Eight Knot and the Borromean Rings. After measuring the state of the molecule in each case, we are able to estimate the value of the Jones Polynomial for each of the knots.

Marx, Raimund; Kauffman, Louis; Lomonaco, Samuel; Spörl, Andreas; Pomplun, Nikolas; Myers, John; Glaser, Steffen J

2009-01-01

369

An NMR study on shale wettability  

Energy Technology Data Exchange (ETDEWEB)

In recent years, the importance of shales as unconventional gas resources has grown significantly. It is therefore important to reach a better understanding of their petrophysical properties. One of the important rock properties that is directly linked to successful hydrocarbon recovery is wettability. This paper presents a study on shale wettability using nuclear magnetic resonance (NMR) to monitor sequential imbibition of brine and oil. Due to the presence of mineralogical variations, low permeability and viscosity, and complex pore structure, the interpretation of wettability using conventional approaches becomes complex. Samples that included 21 core plugs from the Eagle Ford shale, 12 from the Barnett, 11 from the Floyd, and 10 from the Woodford shale were analyzed. The NMR study confirmed the water-wet behavior of Berea sandstone. From the study, it was seen that the Woodford shale showed more affinity for dodecane than did the other shales.

Odusina, Elijah; Sondergeld, Carl; Rai, Chandra [University of Oklahoma (United States)

2011-07-01

370

{beta}-nmr of Palladium foil  

Energy Technology Data Exchange (ETDEWEB)

Beta-detected NMR ({beta}-nmr) of low-energy implanted {sup 8}Li{sup +} was studied in metallic palladium. The resonance was found to have a large negative shift with respect to the reference signal in the cubic insulator MgO. This shift exhibited significant temperature dependence on cooling below room temperature, approximately proportionate to the temperature-dependent spin susceptibility of pure Pd. Thus it is tentatively attributed to a Knight shift (K) caused by a large negative hyperfine coupling; a phenomenon common in transition metal ions, but not in alkalis. However, the spin-lattice relaxation of {sup 8}Li is much slower than expected from the Korringa law for such a large K. We compare results from samples of very different thicknesses: 12.5{mu}m foil and a 100nm thin film.

Parolin, T.J. [Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Salman, Z. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Chakhalian, J. [Max-Plank Institute for Solid State Research, D-70569 Stuttgart (Germany); Wang, D. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Keeler, T.A. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Hossain, Md. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Kiefl, R.F. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Canadian Institute for Advanced Research (Canada); Chow, K.H. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2J1 (Canada); Morris, G.D. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Miller, R.I. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); MacFarlane, W.A. [Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada)]. E-mail: wam@chem.ubc.ca

2006-03-31

371

NMR imaging of the honeybee brain  

Directory of Open Access Journals (Sweden)

Full Text Available NMR microscopy provides non-invasively distinct soft-tissue contrast in small biological samples. We were able to visualize the three-dimensional structure of the honeybee brain in its natural shape in the intact head capsule. Thus, in addition to acquiring detailed information about the shapes and volumes of the different brain compartments, we were able to show their relative orientations toward each other within the head capsule. Since the brain was lightly fixed but not dehydrated, and stayed attached to the head capsule and its internal structures, the NMR experiments exhibited larger volumes and a more natural stereo geometry of the various brain structures compared to confocal laser microscopy experiments on dissected, dehydrated and cleared brains.

D. Haddad

2004-03-01

372

NMR-Based Diffusion Lattice Imaging  

CERN Document Server

Nuclear magnetic resonance (NMR) diffusion experiments are widely employed as they yield information about structures hindering the diffusion process, e.g. about cell membranes. While it has been shown in recent articles, that these experiments can be used to determine the exact shape of closed pores averaged over a volume of interest, it is still an open question how much information can be gained in open systems. In this theoretical work, we show that the full structure information of periodic open systems is accessible. To this end, the so-called 'SEquential Rephasing by Pulsed field-gradient Encoding N Time-intervals' (SERPENT) sequence is used, which employs several diffusion weighting gradient pulses with different amplitudes. The structural information is obtained by an iterative technique relying on a Gaussian envelope model of the diffusion propagator. Two solid matrices that are surrounded by an NMR-visible medium are considered: a hexagonal lattice of cylinders and a cubic lattice of triangles.

Laun, Frederik Bernd

2013-01-01

373

Coherence Transfer in Spatially Resolved NMR  

Directory of Open Access Journals (Sweden)

Full Text Available We present an overview of some applications of coherence transfer experiments in spatially resolved NMR, with examples from imaging and volume localized spectroscopy. While the major preoccupation of spatially resolved NMR experiments is normally with the dominant component (e.g. water of heterogeneous multi-component systems, the interest in minor components (e.g. metabolites of such systems is a strong motivation to develop and apply special techniques. Unlike water, these components typically involve scalar coupled spin systems. They lend themselves therefore to investigations based on the correlated evolution of coupled spins. Specifically, we briefly describe in this contribution the spatially resolved version of multiple quantum experiments, indirect detection experiments and spin correlation experiments.

Narayanan Chandrakumar

2008-01-01

374

NMR and the local structure of relaxors  

Directory of Open Access Journals (Sweden)

Full Text Available The relaxor transition in cubic perovskite relaxors (PMN, PSN and PST and tungsten bronze relaxor (SBN has been studied by NMR. The observed spectra are composed of a narrow -1/2 « 1/2 central transition superimposed on a broad background due to satellite transitions. The chemical heterogeneity, responsible for relaxor properties, is reflected here in the structure of the central transition part. The latter is composed of two components, one due to ordered and the other due to disordered regions. Despite of the fact that the macroscopic symmetry does not change when relaxor transition occurs, a non-zero quadruple coupling constant determined from NMR clearly demonstrates the broken local symmetry.

Blinc R.

2002-01-01

375

Exploring the limits to spatially resolved NMR  

Energy Technology Data Exchange (ETDEWEB)

Recent advances in MRI have demonstrated resolutions down to 1 {mu}m. Magnetic resonance force microscopy has the potential to reach sensitivity for single nuclear spins. Given these numbers, in vivo imaging of single cells or even biomacromolecules may seem possible. However, for in vivo applications, there are fundamental differences in the contrast mechanisms compared to MRI at macroscopic scales as the length scale of of molecular self-diffusion exceeds that of the spatial resolution on the NMR time scale. Those effects - which are fundamentally different from the echo attenuation in field gradient NMR - even may lead to general limitations on the spatial resolution achievable in aqueous systems with high water content. In our contribution, we explore those effects on a model system in a high-resolution stray-field imaging setup. In addition to experimental results, simulations based on the Bloch-Torrey equation are presented.

Gaedke, Achim; Nestle, Nikolaus [TU Darmstadt, Institute of Condensed Matter Physics (Germany)

2010-07-01

376

NMR study of some organophosphorus compounds  

International Nuclear Information System (INIS)

Some organophosphorus compounds are studied in the present work. Spectra of these compounds were discussed. 1H, 13C and 31P NMR methods were used. Some of these organophosphorus compounds were analysed using 17O technique. It was observed that TBP, TEP and TMP practically present the same 13C chemical shift range and in some trialkylphosphates, Karplus effect was notified. The present work allowed to withdraw other important conclusions which can have effective practical applications

1988-01-01

377

Quantum Pattern Recognition With Liquid State NMR  

CERN Multimedia

A novel quantum pattern recognition scheme is presented, which combines the idea of a classic Hopfield neural network with quantum adiabatic computation. Both the input and the memorized patterns are represented by means of the problem Hamiltonian. In contrast to classic neural networks, the algorithm can simultaneously return multiple recognized patterns. The approach also promises extension of classic memory capacity. A proof of principle for the algorithm for two qubits is provided using a liquid state NMR quantum computer.

Neigovzen, Rodion; Sollacher, Rudolf; Glaser, Steffen J

2008-01-01

378

Video: Proton Nuclear Magnetic Resonance (NMR)  

Science.gov (United States)

This video, distributed on YouTube by the Royal Society of Chemistry, describes the basic principles of Nuclear Magnetic Resonance. This video is a good primer and would be very useful to supplement introductory lectures on NMR. The video covers the basic theory behind a 1H spectrum and goes through actually acquiring a spectrum. The top-off look of the instrument is useful and how the superconducting magnet is mounted. Running time for the video is 8:43.

2011-06-03

379

3D Reconstruction of NMR Images  

Directory of Open Access Journals (Sweden)

Full Text Available This paper introduces experiment of 3D reconstruction NMR images scanned from magnetic resonance device. There are described methods which can be used for 3D reconstruction magnetic resonance images in biomedical application. The main idea is based on marching cubes algorithm. For this task was chosen sophistication method by program Vision Assistant, which is a part of program LabVIEW.

Peter Izak

2007-01-01

380

NMR and Mushrooms : imaging post harvest senescence  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The objective of the study described in this thesis was to explore the potentials of NMR for the study of water relations in harvested mushrooms ( Agaricus bisporus ). Since harvested mushrooms tend to continue their growth after harvest, their morphogenesis is heavily influenced by the external climatic conditions. Their respirative resources as well as their internal water can not be replenished after harvest and has therefore to be present in the mushroom before harvest.The main metabolic ...

Donker, H. C. W.

1999-01-01

 
 
 
 
381

NMR characteristics of rat mammary tumors  

International Nuclear Information System (INIS)

12 rats were injected intradermally with 13762A rat mammary adenocarcinoma (1 x 10/sup 6/ cells). 3 rats died before completion of the study and 2 rat had tumor regression; the first 3 were excluded from data analysis. NMR imaging with a 1.5K gauss resistive magnet at 2, 3, 4, and 5 weeks after injection demonstrated increasing tumor mass. Saturation recovery (SR), inversion recovery (IR), and spin echo (SE) pulse sequence images and T/sub 1/ calculation were done for tumor characterization. (Tumor size was too small to identify at 2 weeks.) 3 rats were sacrificed after the last 3 imaging periods for histological studies, done to distinguish solid tumor mass from necrosis. Planimetry of tumor areas showed that as tumors grew in size, the ratio of necrotic area to area of solid tumor increased (week 3 = .3 +- .11; week 4 = .45 +- .07; week 5 = .51 +- 05); simultaneous calculated T/sub 1/ values also increased (week 3 = .35 +- .15; week 4 = .45 +- .06; week 5 = .42 +- 03). Qualitative NMR image T/sub 1/ values also increased as evidenced by progression of SR and IR tumor image intensity from very bright compared to the rest of the body at week 3 to less intense than other structures at week 5. These findings indicate that change in T/sub 1/ may be secondary to the pathophysiological change in the tumor (the increasing in necrosis, associated with increased free water). Thus, the range of T/sub 1/ values obtained in tumors in this study (and in previous studies) may be due to change in tumor physiology and anatomy. Careful correlation of histological with NMR data may allow ultimate use of NMR relaxation characteristics for determination of the physiological state of tumors

1984-06-05

382

High Pressure NMR Study of Ammonium Thiocyanate  

Science.gov (United States)

Wide-line proton NMR spectra of ammonium thiocyanate have been recorded at 77 K as a function of external hydrostatic pressure. Contrary to expectations the line-width and the second moment decrease with the increase of pressure. This, however, is in accordance with the anomalous behaviour observed in other magnetic resonance studies of this compound and can be understood in terms of the change of electron density around the nitrogen atom of the SCN- group.

Ramanathan, K. V.

1993-06-01

383

Milk identification of different species: 13C-NMR spectroscopy of triacylglycerols from cows and buffaloes' milks.  

Science.gov (United States)

Triacylglycerols from cows and buffaloes' milk fat were investigated by 13C nuclear magnetic resonance (NMR) spectroscopy. By the addition of pure triacylglycerols standards, we identified the resonances of both milk fats, and the peaks were used for qualitative and quantitative analysis of acyl groups. Multivariate analysis treatment of triacylglycerols distribution and composition parameters enabled us to identify milk. This study shows that NMR can safely be used to quantitate milk fatty acid content, providing unique information for milk identification of different animal species. PMID:11104260

Andreotti, G; Trivellone, E; Lamanna, R; Di Luccia, A; Motta, A

2000-11-01

384

Improved processing of selective NMR spectra of biopolymers by separation of noise and signal subspaces through singular-value decomposition.  

Science.gov (United States)

A novel sensitivity-enhancement procedure is introduced for 2D NMR data matrices. It is based on the separation of the signal-and-noise subspaces by means of singular-value decomposition of the experimental 2D array. Although no theoretical limitation exists for a general application of the method, the reliability of the results increases considerably with reduced data sets such as those of selective measurements. Advantageous applications can be envisaged for the quantitation of NMR parameters in biopolymers whose linewidths are often large enough to undermine severely the sensitivity of selective experiments. PMID:8948139

Fedrigo, M; Fogolari, F; Viglino, P; Esposito, G

1996-11-01

385

Thermal maturity of type II kerogen from the New Albany Shale assessed by 13C CP/MAS NMR.  

Science.gov (United States)

Thermal maturity of oil and gas source rocks is typically quantified in terms of vitrinite reflectance, which is based on optical properties of terrestrial woody remains. This study evaluates 13C CP/MAS NMR parameters in kerogen (i.e., the insoluble fraction of organic matter in sediments and sedimentary rocks) as proxies for thermal maturity in marine-derived source rocks where terrestrially derived vitrinite is often absent or sparse. In a suite of samples from the New Albany Shale (Middle Devonian to the Early Mississippian, Illinois Basin) the abundance of aromatic carbon in kerogen determined by 13C CP/MAS NMR correlates linearly well with vitrinite reflectance. PMID:15589735

Werner-Zwanziger, Ulrike; Lis, Grzegorz; Mastalerz, Maria; Schimmelmann, Arndt

2005-01-01

386

Structural characterization of Heusler compounds using NMR  

International Nuclear Information System (INIS)

The L21 ordered Heusler alloys Co2Mn1-xFexSi with 0?x?1 attracted much scientific interest, as they are predicted to show high spin polarisation at the Fermi-energy. Therefore Co2Mn1-xFexSi samples were investigated using spin echo nuclear magnetic resonance (NMR) measurements. This method provides a tool to measure the hyperfine fields. The hyperfine fields represent a very sensitive local probe to order-disorder phenomena. The NMR measurements of polycrystalline Co2FeSi samples exhibit a two-peak spectrum with an additional shoulder. This additional signals are attributed to second-order quadrupole splitting, a so called asymmetric line broadening and might be caused by tension within the structure (strain). This effect occurs even in highly ordered systems. Thus previous structural results are corroborated, demonstrating even locally a very high degree of order in Co2FeSi. The NMR spectra of the series Co2Mn1-xFexSi (0.1?x?0.9) exhibit multiplet structures. These might be explained by quadrupole splitting and statistical distribution of Mn and Fe atoms on the Mn site. In summary, the high degree of order in Co2Mn1-xFexSi is shown

2007-03-26

387

Cutoff-Free Traveling Wave NMR  

CERN Document Server

Recently, the concept of traveling-wave NMR/MRI was introduced by Brunner et al. (Nature 457, 994-992 (2009)), who demonstrated MR images acquired using radio frequency (RF) waves propagating down the bore of an MR scanner. One of the significant limitations of this approach is that each bore has a specific cutoff frequency, which can be higher than most Larmor frequencies of at the magnetic field strengths commonly in use for MR imaging and spectroscopy today. We overcome this limitation by using a central conductor in the waveguide and thereby converting it to a transmission line (TL), which has no cutoff frequency. Broadband propagation of waves through the sample thus becomes possible. NMR spectra and images with such an arrangement are presented and genuine traveling wave behavior is demonstrated. In addition to facilitating NMR spectroscopy and imaging in smaller bores via traveling waves, this approach also allows one to perform multinuclear traveling wave experiments (an example of which is shown), an...

Tang, Joel A; Sodickson, Daniel K; Jerschow, Alexej

2011-01-01

388

Origin of NMR shielding in fluorides  

Science.gov (United States)

In this work, we analyze in detail the relation between electronic structure and fluorine nuclear magnetic resonance (NMR) shielding in a series of solid state alkali fluorides (LiF, NaF, KF, RbF, and CsF). For that purpose, we use solid-state NMR calculations implemented in the density functional theory full potential wien2k code (APW+lo). Both measurements and calculations show that the NMR shielding varies across the series by approximately 200 ppm. We focus our discussion on an explanation of the origin of the observed trend, and we show that the variation is mainly determined by contributions from “semicore” metal-p and valence F-p bands. More specifically, the trend in fluorine shielding can be related to the small but significant change in the hybridization of these states. A second important ingredient determining the value of the shielding is the presence and position of metal-d states in the unoccupied part of the Kohn-Sham bands. Although the present analysis has been demonstrated for the 19F nucleus in alkali fluorides, the main results are more general and can explain similar trends observed in other solids and for other nuclei.

Laskowski, Robert; Blaha, Peter

2012-06-01

389

Sol-gel kinetics by NMR  

Energy Technology Data Exchange (ETDEWEB)

The chemical synthesis of advanced ceramic and glass materials by the sol-gel process has become an area of increasing activity in the field of material science. The sol-gel process provides a means to prepare homogeneous, high purity materials with tailored chemical and physical properties. This paper surveyed the nuclear magnetic resonance (NMR) studies of silicon-based sol-gel kinetics. A review of the various models which have been used to analyze the chemical kinetics of various sol-gel systems was presented. The utility of NMR spectroscopy was demonstrated in investigating the influence that various reaction conditions have on the reaction pathways by which sol-gel derived materials are synthesized. By observing in a direct fashion the chemical pathway of the sol-gel, it is often possible to relate the final properties of the material to the formulation and reaction conditions of the sol-gel. The study of reaction kinetics by NMR is expected to play an increasingly important role in understanding sol-gel processing and material properties. 15 refs. (DP)

Assink, R.A.; Kay, B.D.

1991-01-01

390

NMR methodologies for studying mitochondrial bioenergetics.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) spectroscopy is a technique with an increasing importance in the study of metabolic diseases. Its initial important role in the determination of chemical structures (1, 2) has been considerably overcome by its potential for the in vivo study of metabolism (3-5). The main characteristic that makes this technique so attractive is its noninvasiveness. Only nuclei capable of transitioning between energy states, in the presence of an intense and constant magnetic field, are studied. This includes abundant nuclei such as proton ((1)H) and phosphorous ((31)P), as well as stable isotopes such as deuterium ((2)H) and carbon 13 ((13)C). This allows a wide range of applications that vary from the determination of water distribution in tissues (as obtained in a magnetic resonance imaging scan) to the calculation of metabolic fluxes under ex vivo and in vivo conditions without the need to use radioactive tracers or tissue biopsies (as in a magnetic resonance spectroscopy (MRS) scan). In this chapter, some technical aspects of the methodology of an NMR/MRS experiment as well as how it can be used to study mitochondrial bioenergetics are overviewed. Advantages and disadvantages of in vivo MRS versus high-resolution NMR using proton high rotation magic angle spinning (HRMAS) of tissue biopsies and tissue extracts are also discussed. PMID:22057574

Alves, Tiago C; Jarak, Ivana; Carvalho, Rui A

2012-01-01

391

NMR Studies of Cartilage Dynamics, Diffusion, Degradation  

Science.gov (United States)

An increasing number of people is suffering from rheumatic diseases, and, therefore, methods of early diagnosis of joint degeneration are urgently required. For their establishment, however, an improved knowledge about the molecular organisation of cartilage would be helpful. Cartilage consists of three main components: Water, collagen and chondroitin sulfate (CS) that is (together with further polysaccharides and proteins) a major constituent of the proteoglycans of cartilage. 1H and 13C MAS (magic-angle spinning) NMR (nuclear magnetic resonance) opened new perspectives for the study of the macromolecular components in cartilage. We have primarily studied the mobilities of CS and collagen in bovine nasal and pig articular cartilage (that differ significantly in their collagen/polysaccharide content) by measuring 13C NMR relaxation times as well as the corresponding 13C CP (cross polarisation) MAS NMR spectra. These data clearly indicate that the mobility of cartilage macromolecules is broadly distributed from almost completely rigid (collagen) to highly mobile (polysaccharides), which lends cartilage its mechanical strength and shock-absorbing properties.

Huster, Daniel; Schiller, Jürgen; Naji, Lama; et al.

392

Phosphorus NMR of isolated perfused morris hepatomas  

International Nuclear Information System (INIS)

The authors are developing techniques for the study of perfused solid tumors by NMR. Tissue-isolated solid hepatomas were grown to 1-2 cm diameter as described previously. The arterial supply was isolated and the tumors perfused (0.5 - 1.0 ml/min) in vitro at 25 C with a 15% suspension of red blood cells in Krebs-Henseliet solution. "3"1P-NMR spectra were acquired at 162 MHz in a specially-designed NMR probe using a solenoidal coil. Intracellular pH (monitored from the chemical shift of inorganic phosphate) and ATP levels were stable for up to 6 hrs during perfusion. During 30 min of global ischemia, ATP decreased by 75% and pH fell from 7.0 to 6.7. These changes were reversed by 1 hr reperfusion. In addition to ATP and phosphate, the spectra included a large resonance due to phosphomonoesters, as well as peaks consistent with glycerylphosphocholine, glyceryl-phosphoethanolamine, phosphocreatine, NAD, and UDPG. However, the most novel feature of the spectra was the presence of an unidentified peak in the phosphonate region (+ 16.9 ppm). The peak was not present in spectra of muscle, liver, brain, kidney, or fat tissues excised from the same animals. They are presently attempting to identify the compound that gives rise to this peak and to establish its metabolic origin

1986-03-05

393

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

International Nuclear Information System (INIS)

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, to enable NMR measurements to be taken from selected regions inside an object, particularly 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 electric field interactions. The coil may be combined with a like orthogonal coil and suitably driven to provide a circularly polarised field; or it may be used in conjunction with a concentrically nested smaller semitoroidal coil to move the maximum field further from the coil assembly. (author)

1983-03-28

394

Fused state 13C-NMR study on molecular orientation in a carbonaceous mesophase  

International Nuclear Information System (INIS)

The molecular behaviour of coronene, pyrene, and hexamethylbenzene blended in a carbonaceous mesophase was investigated by fused state 13C-NMR (nuclear magnetic resonance). Sharp signals attributed to aromatic carbons of these compounds in the fused mesophase pitch were observed at markedly lower fields compared with those in solution, indicating that their aromatic planes were oriented parallel to the mesophase lamellae aligning along the magnetic field. Order parameters of these compounds, as well as the mesophase constituents, were calculated from the observed chemical shifts, a correlation between their order parameter and molecular weight being observed. This correlation suggested that probe molecules in the fused mesophase behave like mesogens. (Author)

1992-01-01

395

NMR studies of actinide carbide and nitride electronic properties  

International Nuclear Information System (INIS)

N.M.R. studies applied to "1"3C and "1"5N in the solid solutions ThCsub(1-x)Nsub(x), UCsub(1-x)Nsub(x) and in the compounds ThCsub(1-x) and U_2C_3, were undertaken to study carbon and nitrogen contribution to chemical bonds and magnetism. For THORIUM MONOCARBIDE AND CARBONITRIDE: ThCsub(1-x) and ThCsub(1-x)Nsub(x), the very strong orbital contribution to the frequency shift reveals an important covalent character of the valence band 6d metal and 2p metalloid states. The ThCsub(1-x) band structure stoichiometry variation is due to 6d? metal states appearing at the Fermi level and is in-opposition to a rigid band model. A non-saturated bond mechanism is suggested. For URANIUM CARBONITRIDE: UCsub(1-x)Nsub(x), in the concentration range in which no magnetic order appears at low temperature (x<0.90), the results are in opposition to a localized 5f"2 configuration model, and show that the uranium fundamental state is non-magnetic. Nevertheless two qualitatively different behaviors exist: nitrogen concentration lower than 40%: and nitrogen concentration higher than 40%. A model is proposed to account for those domains: it relies on the 5f-2p hybridization parameter which is maximum on 2p band edge (UC) and almost nul for UN. For URANIUM SESQUICARBIDE: U_2C_3: the N.M.R. line observation at 4.2 K indicates a non-magnetic fundamental state although the magnetic susceptibility presents a maximum at 60 K. Spin fluctuations in 5f bands are proposed to describe the electronic properties of this compound

1976-01-01

396

Pulsed NMR study of the curing process of epoxy resin.  

Science.gov (United States)

To analyze a curing process of epoxy resin in terms of molecular motion, we adapted a pulsed NMR method. Three kinds of (1)H spin-spin relaxation times (T(2L) (long), T(2S) (short) and T(2M) (intermediate)) were estimated from observed solid echo train signals as the curing process proceeded. A short T(2S) value below 20 micros suggests the existence of a motion-restricted chain, that is, cured elements of resin, and its fraction, P(S), sigmoidally increased with the curing time. On the other hand, the fraction of T(2L), P(L), decreased with the reaction time reciprocally against P(S), suggesting the disappearance of highly mobile molecules raised from pre-cured resin. The spin-lattice relaxation time, T(1), was also measured to check another aspect of molecular motion in the process. T(1) of the mixed epoxy resin and curing agent gradually increased just after mixing both of them. This corresponds to an increment of a less-mobile fraction, of which the correction time is more than 10(-6) s, and also means that the occurrence of a network structure whose mobility is strongly restricted by chemically bonded bridges between the epoxy resin and curing agent. The time courses of these parameters coincided with those of IR peaks pertinent to the curing reaction. Therefore, pulsed NMR is a useful tool to monitor the hardening process of epoxy resin in real time non-distractively in terms of the molecular motion of protons. PMID:18614836

Kimoto, Hiroki; Tanaka, Chikako; Yaginuma, Michiko; Shinohara, Emi; Asano, Atsushi; Kurotsu, Takuzo

2008-07-01

397

Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations.  

Science.gov (United States)

Complexation of tetrakis(?2-N,N'-diphenylformamidinato-N,N')-di-rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using (1)H, (13)C and (15)N NMR, (13)C and (15)N cross polarisation-magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1 , and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan-1-amine), pentanenitrile, and (1-isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan-2-amine and 1-azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of ?? parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of (1)H NMR, ?? values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively ?? parameters. PMID:24327228

Cmoch, Piotr; G?aszczka, Rafa?; Ja?wi?ski, Jaros?aw; Kamie?ski, Bohdan; Senkara, El?bieta

2014-03-01

398

Portable NMR systems for non destructive testing  

International Nuclear Information System (INIS)

Nuclear Magnetic Resonance (NMR) is one of the more recent sensing technologies and has become very popular for its ability to non-invasively probe down to the molecular level the properties of many materials and living organisms. Its greatest impact has been in the areas of chemistry and medical radiology, but now it is being applied to biochemistry, structural biology, and materials science research. In the past ten years, NMR has made significant contributions to horticulture, biotechnology, chemical engineering, petroleum science and food technology and now stands on the threshold of making an impact on environmental monitoring, building technology, and security technology. Traditionally NMR/MRI is performed using laboratory or clinic based superconducting magnets, but now it is moving out into industry in the form of portable permanent magnet based systems. NMR development is being driven by advancements in electronics, computing and magnet technology and so continues to advance in capability and application. In the building industry, it is often necessary to determine the moisture content of concrete so that it can be optimally cured for strength or to know when floor coverings can be applied. Presently the only way to accurately gauge the true moisture content is to use destructive techniques. This is the method that Parrot used to generate the graph shown in figure 1. Typically the industry yardstick of a 'month per inch' is used for estimating the time required before the concrete surface can be covered, but from this data it is clear that even after a year there can still remain a significant amount of moisture. Concrete is inherently porous and so is greatly affected by the environment and the laying process methods. This makes it very difficult to make predictions based on calibrated standards. What is required is a portable instrument that can be taken to a site to non-destructively obtain the moisture content. NMR technology is now being developed for this specific application in the form of a permanent magnet based probe and an associated backpack containing the necessary signal processing, control electronics and batteries

2005-01-01

399

Fractional order analysis of Sephadex gel structures: NMR measurements reflecting anomalous diffusion  

Science.gov (United States)

We report the appearance of anomalous water diffusion in hydrophilic Sephadex gels observed using pulse field gradient (PFG) nuclear magnetic resonance (NMR). The NMR diffusion data was collected using a Varian 14.1 Tesla imaging system with a home-built RF saddle coil. A fractional order analysis of the data was used to characterize heterogeneity in the gels for the dynamics of water diffusion in this restricted environment. Several recent studies of anomalous diffusion have used the stretched exponential function to model the decay of the NMR signal, i.e., exp[-( bD) ?], where D is the apparent diffusion constant, b is determined the experimental conditions (gradient pulse separation, durations and strength), and ? is a measure of structural complexity. In this work, we consider a different case where the spatial Laplacian in the Bloch-Torrey equation is generalized to a fractional order model of diffusivity via a complexity parameter, ?, a space constant, ?, and a diffusion coefficient, D. This treatment reverts to the classical result for the integer order case. The fractional order decay model was fit to the diffusion-weighted signal attenuation for a range of b-values (0 < b < 4000 s mm -2). Throughout this range of b values, the parameters ?, ? and D, were found to correlate with the porosity and tortuosity of the gel structure.

Magin, Richard L.; Akpa, Belinda S.; Neuberger, Thomas; Webb, Andrew G.

2011-12-01

400

13C-NMR determination of the molecular dynamics of cholesterol in dimyristoylphosphatidylcholine vesicles.  

Science.gov (United States)

Using 13C-NMR measurements of T1, T2 and the nuclear Overhauser enhancement factor at 50.32, 90.56 and 150.87 MHz, we have measured the dynamics of cholesterol in dimyristoylphosphatidylcholine (DMPC) vesicles from 28 to 50 degrees C. Using the model-free approach of Lipari and Szabo, we have found that at 37 degrees C the motion of the rigid steroid ring can be described by an equal contribution from two effective motions with correlation times of 63 and 0.85 ns. The C26 and C27 carbon atoms of cholesterol were found to have an effective correlation time of 8 +/- 2 ps and a value for the square of the generalised order parameter of 0.03 +/- 0.01. The corresponding values for the C25 carbon atom were 17 +/- 4 ps and 0.09 +/- 0.02, showing slower motion and greater order for this carbon atom, which is nearer to the rigid steroid ring. Apart from the effect of vesicle size on T2, no concentration dependence of the dynamics of cholesterol was detected over the cholesterol concentration range 2-30 mol%. The order parameters and correlation times from the present 13C-NMR experiments are shown to be compatible with those from 2H-NMR experiments. This establishes the validity of the present approach, which we are currently extending to low concentrations of cholesteryl oleate in DMPC vesicles. PMID:8118912

Higinbotham, J; Beswick, P H; Malcolmson, R J; Reed, D; Parkinson, J A; Sadler, I H

1993-11-01

 
 
 
 
401

Ensemble-Based Interpretations of NMR Structural Data to Describe Protein Internal Dynamics  

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Full Text Available NMR spectroscopy is the leading technique to characterize protein internal dynamics at the atomic level and on multiple time scales. However, the structural interpretation of the observables obtained by various measurements is not always straightforward and in many cases dynamics-related parameters are only used to “decorate” static structural models without offering explicit description of conformational heterogeneity. To overcome such limitations, several computational techniques have been developed to generate ensemble-based representations of protein structure and dynamics with the use of NMR-derived data. An important common aspect of the methods is that NMR observables and derived parameters are interpreted as properties of the ensemble instead of individual conformers. The resulting ensembles reflect the experimentally determined internal mobility of proteins at a given time scale and can be used to understand the role of internal motions in biological processes at atomic detail. In this review we provide an overview of the calculation methods currently available and examples of biological insights obtained by the ensemble-based models of the proteins investigated.

Annamária F. Ángyán

2013-08-01

402

NMR-D study of the local spin dynamics and magnetic anisotropy in different nearly monodispersed ferrite nanoparticles.  

Science.gov (United States)

We present a systematic experimental comparison of the superparamagnetic relaxation time constants obtained by means of dynamic magnetic measurements and (1)H-NMR relaxometry, on ferrite-based nanosystems with different composition, various core sizes and dispersed in different solvents. The application of a heuristic model for the relaxivity allowed a comparison between the reversal time of magnetization as seen by NMR and the results from the AC susceptibility experiments, and an estimation of fundamental microscopic properties. A good agreement between the NMR and AC results was found when fitting the AC data to a Vogel-Fulcher law. Key parameters obtained from the model have been exploited to evaluate the impact of the contribution from magnetic anisotropy to the relaxivity curves and estimate the minimum approach distance of the bulk solvent. PMID:23315450

Bordonali, L; Kalaivani, T; Sabareesh, K P V; Innocenti, C; Fantechi, E; Sangregorio, C; Casula, M F; Lartigue, L; Larionova, J; Guari, Y; Corti, M; Arosio, P; Lascialfari, A

2013-02-13

403

NMR-D study of the local spin dynamics and magnetic anisotropy in different nearly monodispersed ferrite nanoparticles  

International Nuclear Information System (INIS)

We present a systematic experimental comparison of the superparamagnetic relaxation time constants obtained by means of dynamic magnetic measurements and 1H-NMR relaxometry, on ferrite-based nanosystems with different composition, various core sizes and dispersed in different solvents. The application of a heuristic model for the relaxivity allowed a comparison between the reversal time of magnetization as seen by NMR and the results from the AC susceptibility experiments, and an estimation of fundamental microscopic properties. A good agreement between the NMR and AC results was found when fitting the AC data to a Vogel-Fulcher law. Key parameters obtained from the model have been exploited to evaluate the impact of the contribution from magnetic anisotropy to the relaxivity curves and estimate the minimum approach distance of the bulk solvent.

2013-02-13

404

The NMR and X-ray study of L-arginine derived Schiff bases and its cadmium complexes  

Science.gov (United States)

The structure study of five Schiff bases derived from L-arginine (L-Arg) and 2-hydroxy carbonyl compounds were performed in both solution and solid state using NMR and X-ray methods. Both analytical methods applied to the solid state sample of two Schiff bases showed a significant difference in molecular structures of unsubstituted and 7-CH3 substituted compounds. This effect was explained as a steric interaction of methyl group. Additionally the structure of two Cd2+ complexes with some Schiff bases were determined by NMR methods in DMSO solution and in the solid state. On the base of heteronuclear NMR measurement (13C, 15N and 113Cd) it was possible to define the complexation site on nitrogen atom. The large set of spectral parameters: chemical shifts, homo- and heteronuclear coupling constants, were used in structure study.

Ko?odziej, B.; Grech, E.; Schilf, W.; Kamie?ski, B.; Pazio, A.; Wo?niak, K.

2014-04-01

405

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

Science.gov (United States)

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 of 1H, 13C, and 15N signals to specific atoms in the covalent structure of the protein. Data collection and assignment calculations continue until the addition of new data no longer improves the assignment score. ADAPT-NMR was first implemented on Varian (Agilent) spectrometers [A. Bahrami, M. Tonelli, S.C. Sahu, K.K. Singarapu, H.R. Eghbalnia, J.L. Markley, PLoS One 7 (2012) e33173]. Because of broader interest in the approach, we present here a version of ADAPT-NMR for Bruker spectrometers. We have developed two AU console programs (ADAPT_ORTHO_run and ADAPT_NMR_run) that run under TOPSPIN Versions 3.0 and higher. To illustrate the performance of the algorithm on a Bruker spectrometer, we tested one protein, chlorella ubiquitin (76 amino acid residues), that had been used with the Varian version: the Bruker and Varian versions achieved the same level of assignment completeness (98% in 20 h). As a more rigorous evaluation of the Bruker version, we tested a larger protein, BRPF1 bromodomain (114 amino acid residues), which yielded an automated assignment completeness of 86% in 55 h. Both experiments were carried out on a 500 MHz Bruker AVANCE III spectrometer equipped with a z-gradient 5 mm TCI probe. ADAPT-NMR is available at http://pine.nmrfam.wisc.edu/ADAPT-NMR in the form of pulse programs, the two AU programs, and instructions for installation and use.

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

2013-11-01

406

Quasicritical behaviour of the NMR and ?SR relaxation in YMn2Dx  

International Nuclear Information System (INIS)

The magnetic and structural properties of YMn2 are strongly influenced by introduction of hydrogen (deuterium) in the structure, however, it only slightly modifies the noncollinear antiferromagnetic structure of the compound. The temperature dependences of the NMR relaxation times T+1 and T2 of deuterium and the zero-field relaxation of muons in YMn2Dx were measured at temperatures above the magnetic ordering temperature TN. The corresponding relaxation rates are described by the empirical expression (T/TN - 1)-?, where the exponent ? increases linearly with deuterium concentration x. To explain this behaviour, the Moriya theory of spin fluctuations was used. The expressions for NMR and ?SR relaxation rates have been calculated. The resultant formulae agree well with tbe experiment, giving reasonable values of fitting parameters. The results obtained are discussed in terms of spin fluctuation excitation spectrum. (author)

1999-06-21

407

Monitoring of crystallization processes during synthesis of zeolite A by in situ 27Al NMR spectroscopy  

International Nuclear Information System (INIS)

In situ 27Al NMR spectroscopy has been used for monitoring of crystallization processes during synthesis of zeolite A. Changes of relative intensity and width at half-width of NMR lines originated from solid and liquid phase during crystallization were observed. The line at 79 ppm originated from liquid phase was selected for monitoring of crystallization processes. Kinetic analysis is performed using modified Sharp and Hancock equation. Depending on batch composition, obtained values of parameter n of 1.06 and 1.08 indicate contribution of both diffusion and phase boundary controlled mechanisms, while the synthesis with values of n ranged from 1.89 to 3.09 obey the Avrami-Erofe'ev nucleation and crystal growth model. Exceptions from usual monotonic decay of signal intensity originated from liquid phase observed in some synthesis could be explained by terms of autocatalytic nucleation model

2007-08-15

408

NMR chemical shift and asymmetric dipolar tensors of water protons in sodium nitroprusside (SNP)  

Science.gov (United States)

NMR spectra of the protons in single crystals of Na 2Fe(CN) 5NO·2H 2O (SNP) were measured by FT NMR techniques between 200 and 350 K. The dipolar coupling tensors of the water protons in SNP, their asymmetry parameters and the orientations of the dipole—dipole (DD) tensors relative to the crystal axes were obtained at 200, 290, 305, 315 and 340 K. The proton—proton distance rHH and the angle HOH of the water molecules in SNP were found to be 1.53 Å and 106.5°, respectively. All 1H DD tensors are not axially symmetric. These results are interpreted in terms of librational motions of the H 2O molecules in SNP in addition to the well-established flips. At 290 K the proton shielding tensor of the water molecules in SNP has been extracted directly from wide line spectra.

Tritt-Goc, J.; Pi?lewski, N.; Haeberlen, U.

1986-02-01

409

Solid-state 13C NMR studies of the morphology and orientational order of polymer fibers  

International Nuclear Information System (INIS)

The author conducted detailed studies of the morphology of as-spun PET (poly(ethylene terephthalate)) and gel-spun PE (poly(ethylene)) fibers by 13C CP/MAS (Cross Polarization/Magic Angle Spinning) NMR technique. The presence of multiple-component resonance line-shapes allows one to calculate the true population of various morphological components, after correcting for pin relaxation effects. From these NMR measurements, two different models for PET and PE polymer systems are proposed. The advanced two-dimensional rotor synchronized MAS (2D ROSMAS) technique was also used to study the orientational order of various morphological components. A wide range of orientational order is clearly displayed on 2D spectra for samples under different fabrication conditions. A regression simulation program was used to deduce the order parameter used in computing the orientational distribution function (ODF) for each component

1991-01-01

410

H NMR probes for inter-segmental hydrogen bonds in myoglobins.  

Science.gov (United States)

NMR signals arising from the HisB5 N delta H and HisEF5 N epsilon H protons in sperm whale skeletal and horse heart myoglobins have been located for the first time in the downfield shifted portion of the spectra. The shifts and hydrogen exchange rates indicate that these His imidazole ring NH protons are involved in the inter-segmental hydrogen bonds of the protein in solution, as demonstrated by a crystallographic study [Takano, T. (1977) J. Mol. Biol. 220, 381-399]. The assigned His imidazole ring NH proton resonances can serve as new sensitive structural probes in the study of the local conformation of myoglobin. The applicability of the NMR spectral parameters in the study of the tertiary structure of apomyoglobin, the denaturation of the protein, and the protein stability of sperm whale and horse myoglobins is presented in some detail. PMID:8864854

Yamamoto, Y

1996-07-01

411

NMR imaging of human atherosclerosis; Role de l`IRM dans le diagnostic d`atherosclerose  

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Diagnosis and prognosis of atherosclerosis can no longer be evaluated with morphological parameters only. A description of atherosclerotic plaque composition is necessary to study the mechanisms of plaque rupture, which depends on collagenous cap and lipid core thicknesses. NMR, as a biochemical imaging technique, allows visualization of these components using T1 contrast (mobile lipids), T2 contrast (cap vs. core), spin density (calcifications), diffusion imaging, 1H and 13C spectroscopy. Today, these imaging sequences allow to study in vitro the effects of interventional techniques such as angioplasty or atherectomy. Clinical investigations begin, which will attempt to develop in