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1

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

International Nuclear Information System (INIS)

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

1982-01-01

2

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

Energy Technology Data Exchange (ETDEWEB)

The spin Hamiltonian parameters of Gd/sup 3 +/ in a single crystal of Thorium disulfide (ThS/sub 2/) are analysed by means of the superposition model, in its most general form of a two exponents power law. In fact, the approximated one exponent power law is not suitable for this compound, where the ion-ligand distances show a quite large spread. The results of the analysis are then applied to the case of Gd/sup 3 +/ doped Thorium oxysulfide (ThOS), where the fitting of the experimental data is possible only assuming some distortion of the ligand cage.

Amoretti, G.; Varacca, V.; Fava, C.

1982-06-01

3

Investigation of the spin-Hamiltonian parameters for the trigonal U5+ center in CaF2 crystal.  

Science.gov (United States)

The spin-Hamiltonian parameters (g factor g(//), g(perpendicular) and hyperfine structure constants A(//), A(perpendicular)) of the trigonal U(5+) center in CaF(2) crystal have been calculated from the complete diagonalization (of energy matrix) method (CDM) for 5f(1) ions in trigonal crystal field and under an external magnetic field. In the calculation, the crystal-field parameters are estimated from the superposition model. From the calculations, these spin-Hamiltonian parameters are reasonably explained, and the defect model (i.e., the trigonal U(5+) center is attributed to U(5+) substituting for Ca(2+) in CaF(2) with six F(-) ions replaced by O(2-) and the other two F(-) sites vacant because of charge compensation) given in the previous paper is confirmed. The results are discussed. PMID:20308011

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

2010-03-06

4

Investigation of the spin-Hamiltonian parameters for the trigonal U5+ center in CaF2 crystal.  

UK PubMed Central (United Kingdom)

The spin-Hamiltonian parameters (g factor g(//), g(perpendicular) and hyperfine structure constants A(//), A(perpendicular)) of the trigonal U(5+) center in CaF(2) crystal have been calculated from the complete diagonalization (of energy matrix) method (CDM) for 5f(1) ions in trigonal crystal field and under an external magnetic field. In the calculation, the crystal-field parameters are estimated from the superposition model. From the calculations, these spin-Hamiltonian parameters are reasonably explained, and the defect model (i.e., the trigonal U(5+) center is attributed to U(5+) substituting for Ca(2+) in CaF(2) with six F(-) ions replaced by O(2-) and the other two F(-) sites vacant because of charge compensation) given in the previous paper is confirmed. The results are discussed.

Zheng WC; Liu HG; Yang WQ; Su P

2010-06-01

5

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

6

Spin-Hamiltonian parameters for the tetragonal Gd(M)3+-F(i)- centers in CaF(2) and SrF(2) crystals.  

UK PubMed Central (United Kingdom)

The spin-Hamiltonian parameters (g factors g(//), g(?) and zero-field splittings b(2)(0), b(4)(0), b(4)(4), b(6)(0), b(6)(4)) of the tetragonal Gd(M)(3+)-F(i)(-) centers in CaF(2) and SrF(2) crystals at T?1.8K are calculated from the diagonalization (of energy matrix) method based on the one-electron crystal field mechanism. In the calculations, the crystal field parameters used are estimated from the superposition model with the reported defect structural data obtained from the analyses of superhyperfire interaction constants at the same temperature. The calculated results are in reasonable agreement with the experimental values. It appears that the above defect structural data reported in the previous paper are suitable and the diagonalization (of energy matrix) method is effective to the studies of spin-Hamiltonian parameters for 4f(7) ions in crystals.

Yang WQ; Zhang Y; Lin Y; Zheng WC

2013-02-01

7

Microscopic spin-Hamiltonian parameters and crystal field energy levels for the low C3 symmetry Ni2+ centre in LiNbO3 crystals  

International Nuclear Information System (INIS)

The microscopic spin-Hamiltonian (MSH) parameters and the crystal field (CF) energy levels for Ni2+ ions in LiNbO3 crystals have been investigated using the crystal field analysis/microscopic spin-Hamiltonian package recently developed. The investigations considered for the first time the spin-spin (SS) and spin-other-orbit (SOO) interactions. The low-symmetry effects (LSE) arising from the additional terms (Im(B43)?0) induced at the C3 symmetry sites by the distortion angle ?, which have been omitted in earlier works, have also been dealt with. This study shows that for LiNbO3 : Ni2+ the contributions arising from SS and SOO interactions to the zero-field splitting parameter D are appreciable, whereas those to g|| and gp-erpendicular are quite small. Since the distortion angle ? ( congruent with 0.68 deg. ) for LiNbO3 : Ni2+ is rather small, the contributions to the spin-Hamiltonian (SH) parameters arising from LSE are also small. Feasibility of application of the superposition model is also discussed. A good overall agreement between the theoretical and experimental results for the SH parameters and the CF energy levels has been obtained.

2004-05-01

8

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

9

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

Directory of Open Access Journals (Sweden)

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

H.M. Zhang; S.Y. Wu; Z.H. Zhang

2011-01-01

10

Spin-spin and spin-other-orbit effects of optical spectra and the spin-Hamiltonian parameters for Cr3+ ions in MgO crystals  

International Nuclear Information System (INIS)

An extended complete diagonalization method/microscopic spin-Hamiltonian (CDM/MSH) program has been developed, which is applicable for d3 ions at sites of tetragonal symmetry type I (C4v, D2d, D4, D4h) and trigonal symmetry type I (C3v, D3, D3d). The Hamiltonian includes the spin-spin (SS) and spin-other-orbit (SOO) magnetic interactions besides the spin-orbit (SO) magnetic interaction usually taken into account. Utilizing the extended CDM/MSH program, the optical spectra, the spin-Hamiltonian (SH) parameters of the ground state 4B1, and the splitting ?(2E) of the first excited 2E state for Cr3+ (3d3) ions at C4v symmetry sites in MgO crystals have been successfully investigated. It is found that although the SO magnetic interaction is the most important one, the contributions to the SH parameters and the optical spectra from the SS and SOO magnetic interactions for Cr3+:MgO crystals are appreciable and should not be omitted, especially reaching 27.8% for the zero field splitting parameter D.

2007-01-01

11

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

International Nuclear Information System (INIS)

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

2009-03-20

12

Spin-Hamiltonian parameters for the tetragonal Gd(M)3+-F(i)- centers in CaF(2) and SrF(2) crystals.  

Science.gov (United States)

The spin-Hamiltonian parameters (g factors g(//), g(?) and zero-field splittings b(2)(0), b(4)(0), b(4)(4), b(6)(0), b(6)(4)) of the tetragonal Gd(M)(3+)-F(i)(-) centers in CaF(2) and SrF(2) crystals at T?1.8K are calculated from the diagonalization (of energy matrix) method based on the one-electron crystal field mechanism. In the calculations, the crystal field parameters used are estimated from the superposition model with the reported defect structural data obtained from the analyses of superhyperfire interaction constants at the same temperature. The calculated results are in reasonable agreement with the experimental values. It appears that the above defect structural data reported in the previous paper are suitable and the diagonalization (of energy matrix) method is effective to the studies of spin-Hamiltonian parameters for 4f(7) ions in crystals. PMID:23298858

Yang, Wei-Qing; Zhang, Ying; Lin, Yuan; Zheng, Wen-Chen

2012-12-20

13

Investigations of the spin-Hamiltonian parameters for Ta{sup 4+} ions in LiTaO{sub 3} crystal  

Energy Technology Data Exchange (ETDEWEB)

The spin-Hamiltonian parameters (g factors g{sub ||} , g{sub perpendicular} and hyperfine structure constants A{sub ||} , A{sub perpendicular}) of Ta{sup 4+} ion (which is produced by a self-trapped electron at the Ta{sup 5+} site) in LiTaO{sub 3} 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 {sup 2}T{sub 2} 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 Ta{sup 4+} defect in LiTaO{sub 3} is also obtained from the calculations. The result is coincident with the expectation based on the electrostatic interaction and electron cloud overlap.

He Lv [Department of Material Science, Sichuan University, Chengdu 610064 (China); Department of Physics, Zhejiang Normal University, Jinghua 321004 (China); Zheng Wenchen [Department of Material Science, Sichuan University, Chengdu 610064 (China) and International Centre for Materials Physics, Chinese Academy of Sciences, Senyang 110016 (China)], E-mail: zhengwc1@163.com

2009-05-27

14

Microscopic spin-Hamiltonian parameters and crystal field energy levels for the low C{sub 3} symmetry Ni{sup 2+} centre in LiNbO{sub 3} crystals  

Energy Technology Data Exchange (ETDEWEB)

The microscopic spin-Hamiltonian (MSH) parameters and the crystal field (CF) energy levels for Ni{sup 2+} ions in LiNbO{sub 3} crystals have been investigated using the crystal field analysis/microscopic spin-Hamiltonian package recently developed. The investigations considered for the first time the spin-spin (SS) and spin-other-orbit (SOO) interactions. The low-symmetry effects (LSE) arising from the additional terms (Im(B{sub 43}){ne}0) induced at the C{sub 3} symmetry sites by the distortion angle {phi}, which have been omitted in earlier works, have also been dealt with. This study shows that for LiNbO{sub 3} : Ni{sup 2+} the contributions arising from SS and SOO interactions to the zero-field splitting parameter D are appreciable, whereas those to g{sub ||} and g{sub p}-e{sub rpendicular} are quite small. Since the distortion angle {phi} ( congruent with 0.68 deg. ) for LiNbO{sub 3} : Ni{sup 2+} is rather small, the contributions to the spin-Hamiltonian (SH) parameters arising from LSE are also small. Feasibility of application of the superposition model is also discussed. A good overall agreement between the theoretical and experimental results for the SH parameters and the CF energy levels has been obtained.

Yang Ziyuan; Rudowicz, Czeslaw; Yeung Yauyuen

2004-05-01

15

Defect structure and spin-Hamiltonian parameters for the CuCl(6)(4-) cluster in the tetragonal RbCdCl(3):Cu(2+) crystal.  

UK PubMed Central (United Kingdom)

The tetragonal distortion (characterized by R( parallel)-R( perpendicular) where R( parallel) and R( perpendicular) denote the metal-ligand distances parallel with and perpendicular to the tetragonal axis, respectively) for CuCl(6)(4-) cluster in the tetragonal RbCdCl(3):Cu(2+) crystal is studied by calculating its spin-Hamiltonian (SH) parameters (g factors g( parallel), g( perpendicular) and hyperfine structure constants A( parallel), A( perpendicular)). The calculations are performed by using the complete high-order perturbation formulas for 3d(9) ions in tetragonal symmetry based on a two-mechanism model, in which both the widely-used crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (which is omitted in CF theory) are considered. From the calculations, the SH parameters are reasonably explained and the tetragonal distortion R( parallel)-R( perpendicular) approximately 0.14A is obtained. The distortion is much larger than those caused by the cubic-tetragonal transition phase, but is in the same order as those found in many similar CuCl(6)(4-) Jahn-Teller systems. So, the tetragonal distortion (or defect structure) for the CuCl(6)(4-) cluster in RbCdCl(3):Cu(2+) is due mainly to the Jahn-Teller effect. The relative importance of CT mechanism (characterized by Q(CT)/Q(CF), where Q=Deltag(i) or A(i)((2)), i= || or perpendicular are about 12% and 9% for Q=Deltag(i) and A(i)((2)), respectively. It appears that for the exact calculations of SH parameters of CuCl(6)(4-) clusters in crystals, the contributions due to both CF and CT mechanisms should be taken into account.

Yang M; Wen-Chen Z; Lv H

2009-04-01

16

Defect structure and spin-Hamiltonian parameters for the CuCl(6)(4-) cluster in the tetragonal RbCdCl(3):Cu(2+) crystal.  

Science.gov (United States)

The tetragonal distortion (characterized by R( parallel)-R( perpendicular) where R( parallel) and R( perpendicular) denote the metal-ligand distances parallel with and perpendicular to the tetragonal axis, respectively) for CuCl(6)(4-) cluster in the tetragonal RbCdCl(3):Cu(2+) crystal is studied by calculating its spin-Hamiltonian (SH) parameters (g factors g( parallel), g( perpendicular) and hyperfine structure constants A( parallel), A( perpendicular)). The calculations are performed by using the complete high-order perturbation formulas for 3d(9) ions in tetragonal symmetry based on a two-mechanism model, in which both the widely-used crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (which is omitted in CF theory) are considered. From the calculations, the SH parameters are reasonably explained and the tetragonal distortion R( parallel)-R( perpendicular) approximately 0.14A is obtained. The distortion is much larger than those caused by the cubic-tetragonal transition phase, but is in the same order as those found in many similar CuCl(6)(4-) Jahn-Teller systems. So, the tetragonal distortion (or defect structure) for the CuCl(6)(4-) cluster in RbCdCl(3):Cu(2+) is due mainly to the Jahn-Teller effect. The relative importance of CT mechanism (characterized by Q(CT)/Q(CF), where Q=Deltag(i) or A(i)((2)), i= || or perpendicular are about 12% and 9% for Q=Deltag(i) and A(i)((2)), respectively. It appears that for the exact calculations of SH parameters of CuCl(6)(4-) clusters in crystals, the contributions due to both CF and CT mechanisms should be taken into account. PMID:19062334

Yang, Mei; Wen-Chen, Zheng; Lv, He

2008-10-28

17

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

18

Spin-spin and spin-other-orbit effects of optical spectra and the spin-Hamiltonian parameters for Cr{sup 3+} ions in MgO crystals  

Energy Technology Data Exchange (ETDEWEB)

An extended complete diagonalization method/microscopic spin-Hamiltonian (CDM/MSH) program has been developed, which is applicable for d{sup 3} ions at sites of tetragonal symmetry type I (C{sub 4v}, D{sub 2d}, D{sub 4}, D{sub 4h}) and trigonal symmetry type I (C{sub 3v}, D{sub 3}, D{sub 3d}). The Hamiltonian includes the spin-spin (SS) and spin-other-orbit (SOO) magnetic interactions besides the spin-orbit (SO) magnetic interaction usually taken into account. Utilizing the extended CDM/MSH program, the optical spectra, the spin-Hamiltonian (SH) parameters of the ground state {sup 4}B{sub 1}, and the splitting {delta}({sup 2}E) of the first excited {sup 2}E state for Cr{sup 3+} (3d{sup 3}) ions at C{sub 4v} symmetry sites in MgO crystals have been successfully investigated. It is found that although the SO magnetic interaction is the most important one, the contributions to the SH parameters and the optical spectra from the SS and SOO magnetic interactions for Cr{sup 3+}:MgO crystals are appreciable and should not be omitted, especially reaching 27.8% for the zero field splitting parameter D.

Yang Ziyuan [Department of Physics, Baoji University of Arts and Science, Baoji 721007 (China)]. E-mail: yziyuan@163.com

2007-10-15

19

Theoretical investigations of the local structures and spin Hamiltonian parameters for the trigonal Co{sup 2+} centers in LiNbO{sub 3} and LiTaO{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

The local structures and spin Hamiltonian parameters (g factors g{sub parallel}, g{sub perpendicular} and the hyperfine structure constants) for the trigonal Co{sup 2+} centers in LiNbO{sub 3} and LiTaO{sub 3} are theoretically studied from diagonalization of the 6 x 6 energy matrix within {sup 4}T{sub 1} ground state for a 3d{sup 7} ion under trigonal symmetry. The contributions from the admixtures of various J (=1/2, 3/2, 5/2) states and the ligand orbitals and spin-orbit coupling interactions, which were usually ignored in the previous studies, are taken into account in this work. From the calculations, the impurity Co{sup 2+} is found not to occupy exactly the host Li{sup +} site but to undergo an off-center displacement 0.06 A (or 0.03 A) away from the oxygen octahedron center in LiNbO{sub 3} (or LiTaO{sub 3}). The theoretical spin Hamiltonian parameters based on the above local structures show good agreement with the experimental data. The various contributions to these parameters are also discussed.

Wu Shaoyi [Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054 (China); International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China)], E-mail: wushaoyi@netease.com; Lu Guangduo; Zhang Zhihong; Wei Lihua; Hu Yuexia [Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2009-03-20

20

Studies of the spin-Hamiltonian parameters, d-d transitions and defect structures for two tetragonal Cu2+ centers in Ba2ZnF6:Cu2+ crystal  

International Nuclear Information System (INIS)

Two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM), are applied to calculate the spin-Hamiltonian parameters (g-factors g|| , gperpendicular and hyperfine structure constants A|| , Aperpendicular , obtained from electron paramagnetic resonance (EPR) spectra) and d-d transitions (obtained from optical spectra) for two tetragonal Cu2+ centers in Ba2ZnF6:Cu2+ crystals. The Cu2+(I) ion replaces the Zn2+ ion at tetragonally compressed octahedral coordination and has the ground state 2A1(|dz2>), whereas the Cu2+(II) ion is at an interstitial site with a square-planar F-coordination and has the ground state 2B2(|dx2-y2>). The calculated spin-Hamiltonian parameters and d-d transitions from the PTM and CDM coincide and are in reasonable agreement with the experimental values. This suggests that both methods are effective for the theoretical studies of EPR and optical spectral data for 3d9 ions in tetragonal symmetry with different ground states. The defect structures of the two Cu2+ centers in Ba2ZnF6:Cu2+ are also estimated.

2009-01-01

 
 
 
 
21

Theoretical investigations of the microscopic spin Hamiltonian parameters including the spin-spin and spin-other-orbit interactions for Ni{sup 2+}(3d{sup 8}) ions in trigonal crystal fields  

Energy Technology Data Exchange (ETDEWEB)

The microscopic origin of the spin Hamiltonian (SH) parameters for Ni{sup 2+}(3d{sup 8}) ions in a trigonal type I symmetry (C{sub 3v},D{sub 3d},D{sub 3}) crystal field (CF) is studied. In addition to the spin-orbit (SO) interaction, we consider also the spin-spin (SS) and spin-other-orbit (SOO) interactions. The relative importance of the four (SO, SS, SOO, and combined SO-SS-SOO) contributions to the SH parameters is investigated using the CFA/MSH package and the complete diagonalization method (CDM). The SO mechanism is dominant for all CF parameter (CFP) ranges studied, except where the contributions D{sub SO} to the zero-field splitting (ZFS) parameter D change sign. For the trigonal CFP, v{sub c} {approx} 1200cm{sup -1}D due to the other three mechanisms exceeds D{sub SO}. Although vertical bar D{sub SOO} vertical bar is quite small, the combined vertical bar D{sub SO-SOO} vertical bar is appreciable. The SO-based perturbation theory (PT) works generally well for the g-factors: g{sub parallel} and g{sub perp}, while it fails for D in the vicinity of v{sub c} and for large vertical bar v' vertical bar and v>0. The high percentage discrepancy ratio {delta}{sub D} = 2020% for v{sub c} indicates unreliability of D{sub SO} (in PT). Applications to Ni{sup 2+} ions at trigonal symmetry sites in LiNbO{sub 3}, {alpha}-LiIO{sub 3}, and Al{sub 2}O{sub 3}, are provided. The theoretical SH parameters are in good agreement with the experimental data. The low symmetry (C{sub 3}) effects induced by the angle {psi} are tentatively studied, but appear to be quite small.

Yang Ziyuan [Microelectronics Institute, Xidian University, Xi' an 710071 (China); Hao Yue [Microelectronics Institute, Xidian University, Xi' an 710071 (China); Rudowicz, Czeslaw [Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR (China); Yeung Yauyuen [Department of Science, Hong Kong Institute of Education, 10 Lo Ping Road, Tai Po, New Territories, Hong Kong SAR (China)

2004-05-26

22

Theoretical investigations of the microscopic spin Hamiltonian parameters including the spin-spin and spin-other-orbit interactions for Ni2+(3d8) ions in trigonal crystal fields  

International Nuclear Information System (INIS)

The microscopic origin of the spin Hamiltonian (SH) parameters for Ni2+(3d8) ions in a trigonal type I symmetry (C3v,D3d,D3) crystal field (CF) is studied. In addition to the spin-orbit (SO) interaction, we consider also the spin-spin (SS) and spin-other-orbit (SOO) interactions. The relative importance of the four (SO, SS, SOO, and combined SO-SS-SOO) contributions to the SH parameters is investigated using the CFA/MSH package and the complete diagonalization method (CDM). The SO mechanism is dominant for all CF parameter (CFP) ranges studied, except where the contributions DSO to the zero-field splitting (ZFS) parameter D change sign. For the trigonal CFP, vc ? 1200cm-1D due to the other three mechanisms exceeds DSO. Although vertical bar DSOO vertical bar is quite small, the combined vertical bar DSO-SOO vertical bar is appreciable. The SO-based perturbation theory (PT) works generally well for the g-factors: gparallel and gperp, while it fails for D in the vicinity of vc and for large vertical bar v' vertical bar and v>0. The high percentage discrepancy ratio ?D = 2020% for vc indicates unreliability of DSO (in PT). Applications to Ni2+ ions at trigonal symmetry sites in LiNbO3, ?-LiIO3, and Al2O3, are provided. The theoretical SH parameters are in good agreement with the experimental data. The low symmetry (C3) effects induced by the angle ? are tentatively studied, but appear to be quite small.

2004-05-26

23

Magnetic interactions and microscopic spin Hamiltonian approaches for 3d3 ions at trigonal symmetry sites  

International Nuclear Information System (INIS)

The spin-Hamiltonian (SH) parameters (D, g//, and g-bar ) for 4A2(3d3)-state ions at trigonal symmetry sites, taking into account the spin-spin (SS), the spin-other-orbit (SOO), the orbit-orbit (OO) magnetic interactions besides the well-known spin-orbit (SO) magnetic interaction, are studied in the intermediate-field coupling scheme using the CDM/MSH (Complete Diagonalization Method/ Microscopic Spin Hamiltonian) program recently developed. It is shown that the SH parameters arise from five microscopic mechanisms including SO coupling mechanism, SS coupling mechanism, SOO coupling mechanism, OO coupling mechanism, and SO-SS-SOO-OO combined coupling mechanism. The relative importance of the five (SO, SS, SOO, OO and combined SO-SS-SOO-OO) contributions to the SH parameters is investigated. It is shown that the SO coupling mechanism in these coupling mechanisms is the most important one. The effect of the OO coupling mechanism on the energy levels is appreciable whereas that on the SH parameters is negligible. The contribution from the SS coupling mechanism to the zero-field splitting (ZFS) parameter D is appreciable but is quite small to g-factors: g// and g-bar . In contrast, the contribution from the SOO coupling mechanism to the ZFS parameter D is quite small but is appreciable to g-factors. Two perturbation theory method approaches have been examined using CDM/MSH program. It is found that the analytical expressions developed by Macfarlane for D, g//, and g-bar work well in most of the CF ranges considered whereas those developed by Zdansky for D do not work well in almost all the CF ranges considered. The illustrative evaluation is performed for typical laser material Cr3+: Al2O3. The good agreements between the theoretical values and the experimental finding are obtained. It is found that the percentage difference ?D(=|DTotal(CDM)-DSO(CDM)|/|DTotal(CDM)|x100%) reaches 20.9% for laser material Cr3+: Al2O3. The investigation indicates that the contribution to the ZFS parameter D from the SS and SOO magnetic interactions should not be omitted.

2006-01-01

24

Large transverse field tunnel splittings in the $Fe_{8}$ spin Hamiltonian  

CERN Multimedia

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

Garg, A

1999-01-01

25

On the energy landscape of 3D spin Hamiltonians with topological order  

CERN Document Server

We explore feasibility of a quantum self-correcting memory based on 3D spin Hamiltonians with topological quantum order in which thermal diffusion of topological defects is suppressed by macroscopic energy barriers. To this end we characterize the energy landscape of stabilizer code Hamiltonians with local bounded-strength interactions which have a topologically ordered ground state but do not have string-like logical operators. We prove that any sequence of local errors mapping a ground state of such Hamiltonian to an orthogonal ground state must cross an energy barrier growing at least as a logarithm of the lattice size. Our bound on the energy barrier is shown to be tight up to a constant factor for one particular 3D spin Hamiltonian.

Bravyi, Sergey

2011-01-01

26

Magnetic interactions and microscopic spin Hamiltonian approaches for 3d{sup 3} ions at trigonal symmetry sites  

Energy Technology Data Exchange (ETDEWEB)

The spin-Hamiltonian (SH) parameters (D, g{sub //}, and g{sub -}bar ) for {sup 4}A{sub 2}(3d{sup 3})-state ions at trigonal symmetry sites, taking into account the spin-spin (SS), the spin-other-orbit (SOO), the orbit-orbit (OO) magnetic interactions besides the well-known spin-orbit (SO) magnetic interaction, are studied in the intermediate-field coupling scheme using the CDM/MSH (Complete Diagonalization Method/ Microscopic Spin Hamiltonian) program recently developed. It is shown that the SH parameters arise from five microscopic mechanisms including SO coupling mechanism, SS coupling mechanism, SOO coupling mechanism, OO coupling mechanism, and SO-SS-SOO-OO combined coupling mechanism. The relative importance of the five (SO, SS, SOO, OO and combined SO-SS-SOO-OO) contributions to the SH parameters is investigated. It is shown that the SO coupling mechanism in these coupling mechanisms is the most important one. The effect of the OO coupling mechanism on the energy levels is appreciable whereas that on the SH parameters is negligible. The contribution from the SS coupling mechanism to the zero-field splitting (ZFS) parameter D is appreciable but is quite small to g-factors: g{sub //} and g{sub -}bar . In contrast, the contribution from the SOO coupling mechanism to the ZFS parameter D is quite small but is appreciable to g-factors. Two perturbation theory method approaches have been examined using CDM/MSH program. It is found that the analytical expressions developed by Macfarlane for D, g{sub //}, and g{sub -}bar work well in most of the CF ranges considered whereas those developed by Zdansky for D do not work well in almost all the CF ranges considered. The illustrative evaluation is performed for typical laser material Cr{sup 3+}: Al{sub 2}O{sub 3}. The good agreements between the theoretical values and the experimental finding are obtained. It is found that the percentage difference {delta}{sub D}(=|D{sub Total(CDM)}-D{sub SO(CDM)}|/|D{sub Total(CDM)}|x100= %) reaches 20.9% for laser material Cr{sup 3+}: Al{sub 2}O{sub 3}. The investigation indicates that the contribution to the ZFS parameter D from the SS and SOO magnetic interactions should not be omitted.

Hao Yue [Microelectronics Institute of Xidian University, Xi' an 710071 (China); Yang Ziyuan [Microelectronics Institute of Xidian University, Xi' an 710071 (China) and Department of Physics, Baoji University of Arts and Science, Baoji 721007 (China)]. E-mail: yziyuan@tom.com

2006-04-15

27

Projected BCS states and spin Hamiltonians for the SO(n)_1 WZW model  

CERN Multimedia

We propose a class of projected BCS wave functions and derive their parent spin Hamiltonians. These wave functions can be formulated as infinite Matrix Product States constructed by chiral correlators of Majorana fermions, which are primary fields of the SO(n)_1 Wess-Zumino-Witten model. We numerically compute their spin-spin correlation functions and Renyi entropies for n=5 and 6. Together with the results for n=3 and 4, we conclude that these states are critical and their low-energy effective theory is an SO(n)_1 Wess-Zumino-Witten model.

Tu, Hong-Hao

2012-01-01

28

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

International Nuclear Information System (INIS)

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

2009-06-17

29

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

Science.gov (United States)

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

McGavin, Dennis G.; Tennant, W. Craighead

2009-06-01

30

Modeling 21Ne NMR parameters for carbon nanosystems.  

UK PubMed Central (United Kingdom)

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.

Kupka T; Nieradka M; Kaminský J; Stobi?ski L

2013-10-01

31

Spin Hamiltonian of hyper-kagome Na{sub 4}Ir{sub 3}O{sub 8}.  

Energy Technology Data Exchange (ETDEWEB)

We derive the spin Hamiltonian for the quantum spin liquid Na{sub 4}Ir{sub 3}O{sub 8}, and then estimate the direct and superexchange contributions between near neighbor iridium ions using a tight-binding parametrization of the electronic structure. We find a magnitude of the exchange interaction comparable to experiment for a reasonable value of the on-site Coulomb repulsion. For one of the two tight-binding parametrizations we have studied, the direct exchange term, which is isotropic, dominates the total exchange. This provides support for those theories proposed to describe this quantum spin liquid that assume an isotropic Heisenberg model.

Micklitz, T.; Norman, M. R.; Materials Science Division; Freie Univ.

2010-01-01

32

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

33

Direct measurement of the spin Hamiltonian and observation of condensation of magnons in the 2D frustrated quantum magnet Cs2CuCl4.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose a method for measuring spin Hamiltonians and apply it to the spin- 1/2 Heisenberg antiferromagnet Cs2CuCl4, which shows a 2D fractionalized resonating valence bond state at low fields. By applying strong fields we fully align the spin moment of Cs2CuCl4, transforming it into an effective ...

Coldea, R; Tennant, DA; Habicht, K; Smeibidl, P; Wolters, C

34

NMR spectroscopic parameters of molecular systems with strong hydrogen bonds.  

UK PubMed Central (United Kingdom)

A series of closed H-bonded molecules that have (or not) delocalized bonds were studied. The dependence of both NMR spectroscopic parameters sigma and J-couplings, and also the energy stability of such molecules with H-bond strength, were analyzed. The selected basic geometrical structure was that of malonaldehyde. From its full optimized geometry, the corresponding geometry of 3-OH propanal was obtained, fixing either the d(O-O) distance or a more extended local geometry and then optimizing the other part of the whole structure. Nitromalonaldehyde and nitromalonamide were also studied because they should have stronger H-bonds and their basic structure is also malonaldehyde. The last one also has electronic effects that may be varied by rotating the amino groups. By doing this it is possible to show that the effects on acidity of donors are more important than the equivalent effects on the basicity of acceptors. It is also shown that J-couplings that involve atoms close to the H-bond have important noncontact contributions that must be included in order to reproduce total J values. Noncontact contributions are more important than the Fermi contact (FC) one for J(O-O) in malonaldehyde. In nitromalonamide all three terms, FC, paramagnetic spin-orbital, and spin-dipolar are of the same order of magnitude when both amino groups are rotated. This does not happen for its planar configuration. Nuclear magnetic shielding of the hydrogen belonging to the H-bond is quite sensitive to it. The magnetic behavior of such hydrogen atom is modified when it is part of a closed H-bonded molecule. Then a relationship between the H-bond strength with the paramagnetic contributions of the shieldings of both atoms, C and O of the donor substructure, was obtained. We have found a cubic correlation between sigma(p) (C) of the C-O donor bond with sigma (H) of the H-bonded hydrogen. It is observed that both the noncontact J-coupling contributions and shieldings on atoms belonging to the donor substructure, give a clear evidence about the presence of the resonance phenomenon in the model compounds that have been studied, malonaldehyde, nitromalonaldehyde, and nitromalonamide.

Zarycz N; Aucar GA; Della Védova CO

2010-07-01

35

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

CERN Multimedia

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

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

2006-01-01

36

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

UK PubMed Central (United Kingdom)

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.

Schneider O; Fogh RH; Sternberg U; Klenin K; Kondov I

2012-01-01

37

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

International Nuclear Information System (INIS)

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

2007-02-04

38

Protein dynamics using frequency-dependent order parameters from analysis of NMR relaxation data.  

Science.gov (United States)

A novel approach is described to analyze NMR relaxation data on proteins. This method introduces the frequency-dependent order parameter, S(2)(omega), in order to estimate contributions to the generalized order parameter S(2) from different motional frequencies occurring on the picosecond to nanosecond time scales. S(2)(omega) is defined as the sum of a specified set of weighting coefficients from the Lorentzian expansion of the spectral density function. 15N NMR relaxation data (500, 600, and 800 MHz) on protein GB1 exemplify the method. Using this approach provides information on motional restrictions over specific frequency or time scale ranges and provides a normalized comparison of motional restrictions between proteins having different overall tumbling correlation times. PMID:12660119

Idiyatullin, Djaudat; Daragan, Vladimir A; Mayo, Kevin H

2003-03-01

39

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

2011-05-31

40

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

UK PubMed Central (United Kingdom)

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.

Day IJ

2011-08-01

 
 
 
 
41

?-Stacking effects on the EPR parameters of a prototypical DNA spin label.  

UK PubMed Central (United Kingdom)

The character and value of spin labels for probing environments like double-stranded DNA depend on the degree of change in the spin Hamiltonian parameters of the spin label induced by the environment. Herein we provide a systematic theoretical investigation of this issue, based on a density functional theory method applied to a spin labeled DNA model system, focusing on the dependence of the EPR properties of the spin label on the ? stacking and hydrogen bonding that occur upon incorporating the spin label into the selected base pair inside DNA. It is found that the EPR spin Hamiltonian parameters of the spin label are only negligibly affected by its incorporation into DNA, when compared to its free form. This result gives a theoretical ground for the common empirical assumption regarding the behaviour of spin Hamiltonian parameters made in EPR based measurements of the distance between spin labels incorporated into DNA.

Frecus B; Rinkevicius Z; Ågren H

2013-07-01

42

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

Scientific Electronic Library Online (English)

Full Text Available 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 (more) 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 order to allow the adequate optimization of production processes. In this study, petroleum residues of different refineries were studied by NMR, FTIR and elemental analysis. Optimu (more) m 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.

Castro, Alexandre T.

2006-10-01

43

Sidechain order parameters via 2H NMR in polypeptide liquid crystals  

International Nuclear Information System (INIS)

We have selectively deuterated the sidechain of the synthetic polypeptide poly(-?-benzyl-L-glutamate), PBLG. In magnetically oriented nematic solutions of PBLG, the helical polymer rods are aligned parallel to the field. The Brownian motion of the flexible PBLG sidechain is anisotropic, resulting in quadrupole splittings of the 2H NMR resonances. The order parameters of C-D bond directions in the sidechain can be determined. These studies permit new insights into the nature of organization of sidechains on the periphery of the ?-helix

1978-07-05

44

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)

2011-01-01

45

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

46

Microscopic anisotropy revealed by NMR double pulsed field gradient experiments with arbitrary timing parameters.  

UK PubMed Central (United Kingdom)

We consider a general double pulsed field gradient experiment with arbitrary experimental parameters and calculate an exact expression for the NMR signal attenuation from restricted geometries, which is valid at long wavelengths, i.e., when the product of the gyromagnetic ratio of the spins, the pulsed gradients' duration, and their magnitude is small compared to the reciprocal of the pore size. It is possible to observe microscopic anisotropy within the pore space induced by the boundaries of the pore, which can be used to differentiate restricted from free or multicompartmental diffusion and to estimate a characteristic pore dimension in the former case. Explicit solutions for diffusion taking place between parallel plates as well as in cylindrical and spherical pores are provided. In coherently packed cylindrical pores, it is possible to measure simultaneously the cylinders' orientation and diameter using small gradient strengths. The presence of orientational heterogeneity of cylinders is addressed, and a scheme for differentiating microscopic from ensemble anisotropy is proposed.

Ozarslan E; Basser PJ

2008-04-01

47

Rapid access to 183W NMR parameters of tungsten complexes via reverse 2D, 1H, 183W and 31P, 183W NMR spectroscopy  

International Nuclear Information System (INIS)

The indirect two-dimensional 31P, 183W and 1H, 183W shift correlation spectroscopy is presented for the most efficient access to 183W NMR parameters of tungsten complexes that exhibit a J(W,P) of J(W,H) coupling. For the Cp-bridged binuclear tungsten complex with terminal hydrido groups [W(CO)3H]2[?-[eta5-C5H4)2Si(CH3)2

1987-01-01

48

Solid state NMR characterization of structural and motional parameter distributions in polyamidoammonium dendrimers  

Science.gov (United States)

The characterization of narrow distributions of structural and motional parameters, and their evolution during the broad glass transition, is performed for deuterated PAMAM dendrimer salts using solid state NMR. The broadening of deuteron quadrupole echo (QE) lineshapes is consistent with the presence of narrow hydrogen bond length distribution (?r 5), are distinguished by interior and termini dynamics. In the regime of fast motion QE lineshapes are highly sensitive to the presence of narrow structural and motional parameter distributions, and provide constraints on motional geometry independent of rates. The precise characterization of narrow log-normal rate distributions in the intermediate regime can be done using 2H magic angle spinning (MAS). Deuteron inversion-recovery techniques provide quantitative information on the rates of fast motion. For PAMAM salts, the influence of narrow distributions of structural and motional parameters, and fast planar libration, is negligible for distance determination using Rotational Echo Double Resonance (REDOR). The discrimination between inter- and intra-molecular hydrogen bonding can be done through selective labeling of dendrimer core and termini and dilution in natural abundance samples according to developed strategies. The internuclear distances evaluated on the basis of QE results are 3.4-4.0 Å. These fall within the sensitivity range of 13C-15N REDOR, as exemplified by the measurements on small amino acids according to analytically predicted optimum dephasing scheme.

Malyarenko, Dariya Ivanovna

49

Measurement and Application of Anisotropic NMR Parameters in Stretched Polymer Gels: Structure Determination of Small Molecules Messung und Anwendung anisotroper NMR-Parameter in gestreckten Polymergelen zur Strukturbestimmung kleiner Moleküle  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Different polymer gels have been developed, which are suited to partially align small organic molecules for the measurement of anisotropic NMR parameters. Furthermore, a stretching device based on flexible elastomer tubes, which can be used for the arbitrary and reversible scaling of the alignment s...

Kummerlöwe, Grit

50

Crosslinked Poly(ethylene oxide) as a Versatile Alignment Medium for the Measurement of Residual Anisotropic NMR Parameters.  

UK PubMed Central (United Kingdom)

A universal alignment medium for the measurement of anisotropic NMR parameters that can be used for almost any type of sample would be highly useful for structure analysis in solution. Cross-linked poly(ethylene oxide) with incredible solvent and solute compatibility range provides this medium. The picture shows residual (15) N?chemical shift anisotropies (RCSAs) of (15) N-labeled ubiquitin.

Merle C; Kummerlöwe G; Freudenberger JC; Halbach F; Stöwer W; Gostomski CL; Höpfner J; Beskers T; Wilhelm M; Luy B

2013-09-01

51

Microscopic anisotropy revealed by NMR double pulsed field gradient experiments with arbitrary timing parameters.  

Science.gov (United States)

We consider a general double pulsed field gradient experiment with arbitrary experimental parameters and calculate an exact expression for the NMR signal attenuation from restricted geometries, which is valid at long wavelengths, i.e., when the product of the gyromagnetic ratio of the spins, the pulsed gradients' duration, and their magnitude is small compared to the reciprocal of the pore size. It is possible to observe microscopic anisotropy within the pore space induced by the boundaries of the pore, which can be used to differentiate restricted from free or multicompartmental diffusion and to estimate a characteristic pore dimension in the former case. Explicit solutions for diffusion taking place between parallel plates as well as in cylindrical and spherical pores are provided. In coherently packed cylindrical pores, it is possible to measure simultaneously the cylinders' orientation and diameter using small gradient strengths. The presence of orientational heterogeneity of cylinders is addressed, and a scheme for differentiating microscopic from ensemble anisotropy is proposed. PMID:18433239

Ozarslan, Evren; Basser, Peter J

2008-04-21

52

14N overtone NMR spectra under magic angle spinning: Experiments and numerically exact simulations  

Science.gov (United States)

It was recently shown that high resolution 14N overtone NMR spectra can be obtained directly under magic angle spinning (MAS) conditions [L. A. O'Dell and C. I. Ratcliffe, Chem. Phys. Lett. 514, 168 (2011)]. Preliminary experimental results showed narrowed powder pattern widths, a frequency shift that is dependent on the MAS rate, and an apparent absence of spinning sidebands, observations which appeared to be inconsistent with previous theoretical treatments. Herein, we reproduce these effects using numerically exact simulations that take into account the full nuclear spin Hamiltonian. Under sample spinning, the 14N overtone signal is split into five (0, +/-1, +/-2) overtone sidebands separated by the spinning frequency. For a powder sample spinning at the magic angle, the +2?r sideband is dominant while the others show significantly lower signal intensities. The resultant MAS powder patterns show characteristic quadrupolar lineshapes from which the 14N quadrupolar parameters and isotropic chemical shift can be determined. Spinning the sample at other angles is shown to alter both the shapes and relative intensities of the five overtone sidebands, with MAS providing the benefit of averaging dipolar couplings and shielding anisotropy. To demonstrate the advantages of this experimental approach, we present the 14N overtone MAS spectrum obtained from L-histidine, in which powder patterns from all three nitrogen sites are clearly resolved.

O'Dell, Luke A.; Brinkmann, Andreas

2013-02-01

53

Validation and first application of palaeotemperature models of isomerization and NMR aromatization parameters  

Energy Technology Data Exchange (ETDEWEB)

Palaeotemperature information at locations in the Viking Graben and the Barents Sea has been obtained from distributed activation energy models of sterane isomerization at C20, hopane isomerization at C22 and of a [sup 1]H-NMR parameter that reflects the percentage of aromatic protons in the aromatic fraction of extracts (FAP). Frequency factor, mean activation energy and distribution factor of hopane- and sterane isomerization are 10[sup 8] Hz, 37.0 kcal/mol, 2.9%, and 3.5[center dot]10[sup 7] Hz, 37.5 kcal/mol, 2.9%. FAP is characterized by two distributions at 1.3[center dot]10[sup 13] Hz, 51.3 kcal/mol, 0.8% and 4.5[center dot]10[sup 10] Hz, 43.2 kcal/mol, 12.9%. Application of the indicators to Viking Graben data makes use of the ability of indicator systems to record selectively thermal conditions for different time intervals and with strongly increased sensitivity. Integration of geological and isomerization data at a cross section near the Svalis Dome, Barents Sea, allows differentiation between the effects of two different heating events which affected the isomerization profiles. The onset of the reaction resulting from renewed heating depends on the temperatures and extents of reaction reached during the previous event, which is in accordance with a model of selective consumption of the reactants according to their reaction temperature. Comparison with accepted hydrocarbon generation models suggests that most of the isomerization reaction take place prior to the onset of oil generation. In contrast to previous single activation energy models, strongly different mean activation energies in distributed models do not lead to significantly different maturation pathway at different heating rates. 48 refs., 12 figs., 4 tabs.

Ritter, U.; Myhr, M.B.; Aareskjold, K.; Schou, L.

1992-11-01

54

Recent advances in computational predictions of NMR parameters for the structure elucidation of carbohydrates: methods and limitations.  

UK PubMed Central (United Kingdom)

All living systems are comprised of four fundamental classes of macromolecules - nucleic acids, proteins, lipids, and carbohydrates (glycans). Glycans play a unique role of joining three principal hierarchical levels of the living world: (1) the molecular level (pathogenic agents and vaccine recognition by the immune system, metabolic pathways involving saccharides that provide cells with energy, and energy accumulation via photosynthesis); (2) the nanoscale level (cell membrane mechanics, structural support of biomolecules, and the glycosylation of macromolecules); (3) the microscale and macroscale levels (polymeric materials, such as cellulose, starch, glycogen, and biomass). NMR spectroscopy is the most powerful research approach for getting insight into the solution structure and function of carbohydrates at all hierarchical levels, from monosaccharides to oligo- and polysaccharides. Recent progress in computational procedures has opened up novel opportunities to reveal the structural information available in the NMR spectra of saccharides and to advance our understanding of the corresponding biochemical processes. The ability to predict the molecular geometry and NMR parameters is crucial for the elucidation of carbohydrate structures. In the present paper, we review the major NMR spectrum simulation techniques with regard to chemical shifts, coupling constants, relaxation rates and nuclear Overhauser effect prediction applied to the three levels of glycomics. Outstanding development in the related fields of genomics and proteomics has clearly shown that it is the advancement of research tools (automated spectrum analysis, structure elucidation, synthesis, sequencing and amplification) that drives the large challenges in modern science. Combining NMR spectroscopy and the computational analysis of structural information encoded in the NMR spectra reveals a way to the automated elucidation of the structure of carbohydrates.

Toukach FV; Ananikov VP

2013-07-01

55

In VivoP NMR Spectroscopic Studies of Soybean Bradyrhizobium Symbiosis: I. Optimization of Parameters.  

UK PubMed Central (United Kingdom)

(31)P NMR spectroscopy was used to study in vivo the symbiotic state established between soybean (Glycine max [L.] Merr. cv Williams) and Bradyrhizobium japonicum (USDA 110 and 138). Different experimental conditions were used to maintain perfused, respiring detached or attached nodules in an NMR magnet. The pH of the perfusion medium affected the cytoplasmic pH and the resolution of the spectra. The internal Pi content and distribution were assessed as a function of nodule age and green-house growth conditions and the rate of glucose and 2-deoxyglucose uptake into nodules in split and intact states. The major metabolites (glucose-6-P, fructose-1,6-diP, P-choline, Pi, NTP, UDP-glc, and NAD) were readily identified from (31)P NMR spectra of perchloric acid extracts of nodules with the exception of one unknown phosphorus metabolite. Nodules stressed by glucose deprivation demonstrated movement of Pi between the vacuole and cytoplasmic compartments not previously observed in (31)P NMR studies.

Rolin DB; Boswell RT; Sloger C; Tu SI; Pfeffer PE

1989-04-01

56

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

Science.gov (United States)

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

Krutikov, A. A.; Shtyrlin, V. G.; Spiridonov, A. O.; Serov, N. Yu; Il'yin, A. N.; Bukharov, M. S.; Gilyazetdinov, E. M.

2012-11-01

57

Microscopic spin Hamiltonian approaches for 3d{sup 8} and 3d{sup 2} ions in a trigonal crystal field - perturbation theory methods versus complete diagonalization methods  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we critically review the existing microscopic spin Hamiltonian (MSH) approaches, namely the complete diagonalization method (CDM) and the perturbation theory method (PTM), for 3d{sup 8}(3d{sup 2}) ions in a trigonal (C{sub 3v}, D{sub 3}, D{sub 3d}) symmetry crystal field (CF). A new CDM is presented and a CFA/MSH computer package based on our crystal-field analysis (CFA) package for 3d{sup N} ions is developed for numerical calculations. Our method takes into account the contribution to the SH parameters (D, g{sub parallel} and g{sub perpendicular} to) from all 45 CF states for 3d{sup 8}(3d{sup 2}) ions and is based on the complete diagonalization of the Hamiltonian including the electrostatic interactions, the CF terms (in the intermediate CF scheme) and the spin-orbit coupling. The CFA/MSH package enables us to study not only the CF energy levels and wavefunctions but also the SH parameters as functions of the CF parameters (B{sub 20}, B{sub 40} and B{sub 43} or alternatively Dq, {nu} and {nu}') for 3d{sup 8}(3d{sup 2}) ions in trigonal symmetry. Extensive comparative studies of other MSH approaches are carried out using the CFA/MSH package. First, we check the accuracy of the approximate PTM based on the 'quasi-fourth-order' perturbation formulae developed by Petrosyan and Mirzakhanyan (PM). The present investigations indicate that the PM formulae for the g-factors (g{sub parallel} and g{sub perpendicular} to) indeed work well, especially for the cases of small v and {nu}' and large Dq, whereas the PM formula for the zero-field splitting (ZFS) exhibits serious shortcomings. Earlier criticism of the PM approach by Zhou et al (Zhou K W, Zhao S B, Wu P F and Xie J K 1990 Phys. Status Solidi b 162 193) is then revisited. Second, we carry out an extensive comparison of the results of the present CFA/MSH package and those of other CDMs based on the strong- and weak-CF schemes. The CF energy levels and the SH parameters for 3d{sup 2} and 3d{sup 8} ions at C{sub 3v} symmetry sites in several crystals are calculated and analysed. Our investigations reveal serious inconsistencies in the CDM results of Zhou et al and Li (Li Y 1995 J. Phys.: Condens. Matter 7 4075) based on the strong-CF scheme for Ni{sup 2+} ions in LiNbO{sub 3} crystals. The correctness of our CFA/MSH package is verified by comparing our results with the predictions of Ma et al (Ma D P, Ma N, Ma X D and Zhang H M 1998 J. Phys. Chem. Solids 59 1211, Ma D P, Ma X D, Chen J R and Liu Y Y 1997 Phys. Rev. B 56 1780) and Macfarlane (Macfarlane R M 1964 J. Chem. Phys. 40 373) for {alpha}-Al{sub 2}O{sub 3}:V{sup 3+}(3d{sup 2}) and MgO:Ni{sup 2+}(3d{sup 8}). It appears that the two independent approaches show perfect agreement with our approach, unlike those of Zhou et al and Li, which turn out to be unreliable. Our results reveal that the contributions to the ZFS parameter from the higher excited states cannot be neglected; also, the ZFS parameter is very sensitive to slight changes of the crystal structure. Hence our CFA/MSH package, which takes into account the contributions to the ZFS parameter from the higher excited states, can provide reliable results and proves to be a useful tool for the studies of the effect of the lattice distortions, defects and structural disorder on the spectroscopic properties of 3d{sup 2} and 3d{sup 8} ions at trigonal symmetry sites in crystals. (author)

Rudowicz, Czeslaw; Qin Jian; Yang Ziyuan [Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong (China); Yeung Yauyuen [Department of Science, Hong Kong Institute of Education, Kong Kong (China)]. E-mail: APCESLAW@cityu.edu.hk

2002-06-10

58

Longitudinal NMR parameter measurements of Japanese pear fruit during the growing process using a mobile magnetic resonance imaging system.  

UK PubMed Central (United Kingdom)

Longitudinal nuclear magnetic resonance (NMR) parameter measurements of Japanese pear fruit (Pyrus pyrifolia Nakai, Kosui) were performed using an electrically mobile magnetic resonance imaging (MRI) system with a 0.2 T and 16 cm gap permanent magnet. To measure the relaxation times and apparent diffusion coefficients of the pear fruit in relation to their weight, seven pear fruits were harvested almost every week during the cell enlargement period and measured in a research orchard. To evaluate the in situ relaxation times, six pear fruits were longitudinally measured for about two months during the same period. The measurements for the harvested samples showed good agreement with the in situ measurements. From the measurements of the harvested samples, it is clear that the relaxation rates of the pear fruits linearly change with the inverse of the linear dimension of the fruits, demonstrating that the relaxation mechanism is a surface relaxation. We therefore conclude that the mobile MRI system is a useful device for measuring the NMR parameters of outdoor living plants.

Geya Y; Kimura T; Fujisaki H; Terada Y; Kose K; Haishi T; Gemma H; Sekozawa Y

2013-01-01

59

Cholesterol and POPC segmental order parameters in lipid membranes: solid state 1H-13C NMR and MD simulation studies.  

UK PubMed Central (United Kingdom)

The concentration of cholesterol in cell membranes affects membrane fluidity and thickness, and might regulate different processes such as the formation of lipid rafts. Since interpreting experimental data from biological membranes is rather intricate, investigations on simple models with biological relevance are necessary to understand the natural systems. We study the effect of cholesterol on the molecular structure of multi-lamellar vesicles (MLVs) composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a phospholipid ubiquitous in cell membranes, with compositions in the range 0-60 mol% cholesterol. Order parameters, |S(CH)|, are experimentally determined by using (1)H-(13)C solid-state nuclear magnetic resonance (NMR) spectroscopy with segmental detail for all parts of both the cholesterol and POPC molecules, namely the ring system and alkyl chain of the sterol, as well as the glycerol backbone, choline headgroup and the sn-1 and sn-2 acyl chains of POPC. With increasing cholesterol concentration the acyl chains gradually adopt a more extended conformation while the orientation and dynamics of the polar groups are rather unaffected. Additionally, we perform classical molecular dynamics simulations on virtual bilayers mimicking the POPC-cholesterol MLVs investigated by NMR. Good agreement between experiments and simulations is found for the cholesterol alignment in the bilayer and for the |S(CH)| profiles of acyl chains below 15 mol% cholesterol. Deviations occur for the choline headgroup and glycerol backbone parts of POPC, as well as for the phospholipid and cholesterol alkyl chains at higher cholesterol concentrations. The unprecedented detail of the NMR data enables a more complete comparison between simulations and experiments on POPC-cholesterol bilayers and may aid in developing more realistic model descriptions of biological membranes.

Ferreira TM; Coreta-Gomes F; Ollila OH; Moreno MJ; Vaz WL; Topgaard D

2013-02-01

60

Dual Substituent Parameter Modeling of Theoretical, NMR and IR Spectral Data of 5-Substituted Indole-2,3-diones  

Directory of Open Access Journals (Sweden)

Full Text Available Correlations of AM1 and PM3 theoretical data, 13C-NMR substituent chemical shifts (13C-SCS) and IR carbonyl group wave numbers [ν(C3═O)] were studied using dual substituent parameter (DSP) models for 5-substituted indole-2,3-diones. For the C7 atom a reverse substituent effect attributed to extended π-polarization was observed. On the other hand, the DSP approaches for the C3 atom showed normal substituent effects with some contribution of reverse effect supported strongly by 13C-SCS correlations. In the ν(C3═O) and p(C3═O) DSP correlations the field effect contribution predominates over the resonance effect, which justifies the using of earlier suggested vibrational coupling (V-C) model for 5- and 6-substituted indole-2,3-diones.

Ghazwan F. Fadhil; Hanan A. Radhy; Alexander Perjéssy; Mária Šamalíková; Erkki Kolehmainen; Walter M.F. Fabian; Katri Laihia; Zora Šusteková

2002-01-01

 
 
 
 
61

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

International Nuclear Information System (INIS)

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

2011-01-01

62

Multinuclear high-resolution NMR study of compounds from the ternary system NaF-CaF2-AlF3: from determination to modeling of NMR parameters.  

UK PubMed Central (United Kingdom)

27Al and 23Na NMR satellite transition spectroscopy and 3Q magic-angle-spinning spectra are recorded for three compounds from the ternary NaF-CaF2-AlF3 system. The quadrupolar frequency nuQ, asymmetry parameter etaQ, and isotropic chemical shift deltaiso are extracted from the spectrum reconstructions for five aluminum and four sodium sites. The quadrupolar parameters are calculated using the LAPW-based ab initio code WIEN2k. It is necessary to perform a structure optimization of all compounds to ensure a fine agreement between experimental and calculated parameters. By a comparison of experimental and calculated values, an attribution of all of the 27Al and 23Na NMR lines to the crystallographic sites is achieved. High-speed 19F NMR MAS spectra are recorded and reconstructed for the same compounds, leading to the determination of 18 isotropic chemical shifts. The superposition model developed by Bureau et al. is used, allowing a bijective assignment of the 19F NMR lines to the crystallographic sites.

Martineau C; Body M; Legein C; Silly G; Buzaré JY; Fayon F

2006-12-01

63

Multinuclear high-resolution NMR study of compounds from the ternary system NaF-CaF2-AlF3: from determination to modeling of NMR parameters.  

Science.gov (United States)

27Al and 23Na NMR satellite transition spectroscopy and 3Q magic-angle-spinning spectra are recorded for three compounds from the ternary NaF-CaF2-AlF3 system. The quadrupolar frequency nuQ, asymmetry parameter etaQ, and isotropic chemical shift deltaiso are extracted from the spectrum reconstructions for five aluminum and four sodium sites. The quadrupolar parameters are calculated using the LAPW-based ab initio code WIEN2k. It is necessary to perform a structure optimization of all compounds to ensure a fine agreement between experimental and calculated parameters. By a comparison of experimental and calculated values, an attribution of all of the 27Al and 23Na NMR lines to the crystallographic sites is achieved. High-speed 19F NMR MAS spectra are recorded and reconstructed for the same compounds, leading to the determination of 18 isotropic chemical shifts. The superposition model developed by Bureau et al. is used, allowing a bijective assignment of the 19F NMR lines to the crystallographic sites. PMID:17140229

Martineau, C; Body, M; Legein, C; Silly, G; Buzaré, J-Y; Fayon, F

2006-12-11

64

Solid-state NMR calculations for metal oxides and gallates: Shielding and quadrupolar parameters for perovskites and related phases  

Science.gov (United States)

The NMR parameters obtained from solid-state DFT calculations within the GIPAW approach for 17O- and 69/71Ga-sites in a range of predominantly oxide-based (group II monoxides, SrTiO3, BaZrO3, BaSnO3, BaTiO3, LaAlO3, LaGaO3, SrZrO3, MgSiO3 and Ba2In2O5), and gallate (?- and ?-Ga2O3, LiGaO2, NaGaO2, GaPO4 and LaGaO3) materials are compared with experimental values, with a view to the future application of a similar approach to doped phases of interest as candidate intermediate temperature solid oxide fuel cell (ITSOFC) electrolytes. Isotropic and anisotropic chemical shift parameters, quadrupolar coupling constants, and associated asymmetries are presented and analyzed. The unusual GaO5 site occurring in LaGaGe2O7 is also fully characterised. In general, it is found that the theoretical results closely track the experimental trends, though some deviations are identified and discussed, particularly in regard to quadrupolar ?Q-values. The high quality of the computed results suggests that this approach can be extended to study more complex and disordered phases.

Middlemiss, Derek S.; Blanc, Frédéric; Pickard, Chris J.; Grey, Clare P.

2010-05-01

65

Study of correlations in molecular motion by multiple quantum NMR  

International Nuclear Information System (INIS)

Nuclear magnetic resonance is a very useful tool for characterizing molecular configurations through the measurement of transition frequencies and dipolar couplings. The measurement of spectral lineshapes, spin-lattice relaxation times, and transverse relaxation times also provide us with valuable information about correlations in molecular motion. The new technique of multiple quantum nuclear magnetic resonance has numerous advantages over the conventional single quantum NMR techniques in obtaining information about static and dynamic interactions of coupled spin systems. In the first two chapters, the theoretical background of spin Hamiltonians and the density matrix formalism of multiple quantum NMR is discussed. The creation and detection of multiple quantum coherence by multiple pulse sequence are discussed. Prototype multiple quantum spectra of oriented benzene are presented. Redfield relaxation theory and the application of multiple quantum NMR to the study of correlations in fluctuations are presented. A specific example of an oriented methyl group relaxed by paramagnetic impurities is studied in detail. The study of possible correlated motion between two coupled methyl groups by multiple quantum NMR is presented. For a six spin system it is shown that the four-quantum spectrum is sensitive to two-body correlations, and serves a ready test of correlated motion. The study of the spin-lattice dynamics of orienting or tunneling methyl groups (CH3 and CD3) at low temperatures is presented. The anisotropic spin-lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules, is investigated, and the NMR spectrometers and other experimental details are discussed

1981-01-01

66

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

67

NMR imaging  

Energy Technology Data Exchange (ETDEWEB)

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.

Andrew, E.R.

1983-04-01

68

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1987-07-01

69

Correlations between (51)V solid-state NMR parameters and chemical structure of vanadium (V) complexes as models for related metalloproteins and catalysts.  

Science.gov (United States)

The parameters describing the quadrupolar and CSA interactions of 51V solid-state MAS NMR investigations of model complexes mimicking vanadoenzymes as well as vanadium containing catalysts and enzyme complexes are interpreted with respect to the chemical structure. The interpretation is based on the data of 15 vanadium complexes including two new complexes with previously unpublished data and 13 complexes with data previously published by us. Correlations between the chemical structure and the 51V solid-state NMR data of this class of compounds have been established. Especially for the isotropic chemical shift delta(iso) and the chemical shift anisotropy delta(sigma), correlations with specific structural features like the coordination number of the vanadium atom, the number of coordinating nitrogens, the number of oxygen atoms and the chemical surrounding of the complex could be established for these compounds. Moreover, quantitative correlations between the solid-state NMR parameters and specific bond angles and bond lengths have been obtained. Our results can be of particular interest for future investigations concerning the structure and the mode of action of related vanadoenzymes and vanadate protein assemblies, including the use of vanadate adducts as transition state analogs for phosphate metabolizing systems. PMID:20045295

Fenn, Annika; Wächtler, Maria; Gutmann, Torsten; Breitzke, Hergen; Buchholz, Axel; Lippold, Ines; Plass, Winfried; Buntkowsky, Gerd

2009-12-04

70

Correlations between (51)V solid-state NMR parameters and chemical structure of vanadium (V) complexes as models for related metalloproteins and catalysts.  

UK PubMed Central (United Kingdom)

The parameters describing the quadrupolar and CSA interactions of 51V solid-state MAS NMR investigations of model complexes mimicking vanadoenzymes as well as vanadium containing catalysts and enzyme complexes are interpreted with respect to the chemical structure. The interpretation is based on the data of 15 vanadium complexes including two new complexes with previously unpublished data and 13 complexes with data previously published by us. Correlations between the chemical structure and the 51V solid-state NMR data of this class of compounds have been established. Especially for the isotropic chemical shift delta(iso) and the chemical shift anisotropy delta(sigma), correlations with specific structural features like the coordination number of the vanadium atom, the number of coordinating nitrogens, the number of oxygen atoms and the chemical surrounding of the complex could be established for these compounds. Moreover, quantitative correlations between the solid-state NMR parameters and specific bond angles and bond lengths have been obtained. Our results can be of particular interest for future investigations concerning the structure and the mode of action of related vanadoenzymes and vanadate protein assemblies, including the use of vanadate adducts as transition state analogs for phosphate metabolizing systems.

Fenn A; Wächtler M; Gutmann T; Breitzke H; Buchholz A; Lippold I; Plass W; Buntkowsky G

2009-12-01

71

The Influence of Porosity, Saturation Degree, Clay Content and Pore Water Conductivity on NMR and SIP Parameters  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The general objective of this thesis is to estimate the petrophysical properties of sand and clay artificial samples such as clay content (CC), porosity (phi), saturation degree (S), permeability (k) and pore water conductivity (sigma_{w}) by use of nuclear magnetic resonance (NMR) and spectral indu...

Alali, Firas

72

Spectral assignments and NMR parameter-structure relationships in borates using high-resolution 11B NMR and density functional theory.  

UK PubMed Central (United Kingdom)

High-resolution, solid-state (11)B NMR spectra have been obtained at high magnetic fields for a range of polycrystalline borates using double-rotation (DOR), multiple-quantum magic angle spinning and isotopic dilution. DOR linewidths can be less than 0.2 ppm in isotopically diluted samples, allowing highly accurate values for the isotropic chemical shift, ?iso, and electric field gradient to be obtained. The experimental values are used as a test of density functional calculations using both projector augmented wave based CASTEP and WIEN2k. The CASTEP calculations of ?iso are generally in very good agreement with experiment, having r.m.s. deviation 0.40 ppm. WIEN2k calculations of electric field gradient magnitude, CQ, and asymmetry, ?, are also in excellent agreement with experiment, with r.m.s. deviations 0.038 MHz and 0.042 respectively. However, whilst CASTEP gives a similar deviation for ? (0.043) it overestimates CQ by ?15%. After scaling of the calculated electric field gradient by 0.842 the deviation in CQ is practically identical to that of the WIEN2k calculations. The spectral assignments that follow from the experimental and computational results allow identification of correlations between ?iso and (a) the average B-O-B bond angle, ?[combining overline], for both three and four coordinated boron, giving ?iso(B(III)) = (185.1 -?[combining overline])/3.42 ppm and ?iso(B(IV)) = (130.2 -?[combining overline])/5.31 ppm; and (b) the ring-site T(3) unit trigonal planar angular deviation, Stri, giving ?iso(T(3)(ring)) = (1.642 × 10(-2)-Stri)/(8.339 × 10(-4)) ppm.

Alderman OL; Iuga D; Howes AP; Pike KJ; Holland D; Dupree R

2013-06-01

73

Spectral assignments and NMR parameter-structure relationships in borates using high-resolution 11B NMR and density functional theory.  

Science.gov (United States)

High-resolution, solid-state (11)B NMR spectra have been obtained at high magnetic fields for a range of polycrystalline borates using double-rotation (DOR), multiple-quantum magic angle spinning and isotopic dilution. DOR linewidths can be less than 0.2 ppm in isotopically diluted samples, allowing highly accurate values for the isotropic chemical shift, ?iso, and electric field gradient to be obtained. The experimental values are used as a test of density functional calculations using both projector augmented wave based CASTEP and WIEN2k. The CASTEP calculations of ?iso are generally in very good agreement with experiment, having r.m.s. deviation 0.40 ppm. WIEN2k calculations of electric field gradient magnitude, CQ, and asymmetry, ?, are also in excellent agreement with experiment, with r.m.s. deviations 0.038 MHz and 0.042 respectively. However, whilst CASTEP gives a similar deviation for ? (0.043) it overestimates CQ by ?15%. After scaling of the calculated electric field gradient by 0.842 the deviation in CQ is practically identical to that of the WIEN2k calculations. The spectral assignments that follow from the experimental and computational results allow identification of correlations between ?iso and (a) the average B-O-B bond angle, ?[combining overline], for both three and four coordinated boron, giving ?iso(B(III)) = (185.1 -?[combining overline])/3.42 ppm and ?iso(B(IV)) = (130.2 -?[combining overline])/5.31 ppm; and (b) the ring-site T(3) unit trigonal planar angular deviation, Stri, giving ?iso(T(3)(ring)) = (1.642 × 10(-2)-Stri)/(8.339 × 10(-4)) ppm. PMID:23608768

Alderman, Oliver L G; Iuga, Dinu; Howes, Andrew P; Pike, Kevin J; Holland, Diane; Dupree, Ray

2013-04-23

74

Bohr-Sommerfeld quantization of spin Hamiltonians  

CERN Multimedia

The Bohr-Sommerfeld rule for a spin system is obtained, including the first quantum corrections. The rule applies to both integer and half-integer spin, and respects Kramers degeneracy for time-reversal invariant systems. It is tested for various models, in particular the Lipkin-Meshkov-Glick model, and found to agree very well with exact results.

Garg, A; Garg, Anupam; Stone, Michael

2003-01-01

75

Determination of average molecular parameters of vacuum residues and asphalt by elementary analysis and 1 H NMR and comparison with 13 C NMR results  

International Nuclear Information System (INIS)

This work proposes a new approach for determining average molecular parameters in petroleum fractions, from some approximation based on consideration about average composition of petroleum heavy fractions. A comparative evaluation between the proposed method and the traditional one has been carried out, showing 60 hours saving in time spent at analysis. The results were present and discussed

1995-01-01

76

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

International Nuclear Information System (INIS)

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

1987-01-01

77

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

Energy Technology Data Exchange (ETDEWEB)

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.

D' Auvergne, Edward J. [Max Planck Institute for Biophysical Chemistry, Department of NMR-based Structural Biology (Germany)], E-mail: edward@nmr-relax.com; Gooley, Paul R. [University of Melbourne, Department of Biochemistry and Molecular Biology, Bio21 Institute of Biotechnology and Molecular Science (Australia)

2008-02-15

78

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

UK PubMed Central (United Kingdom)

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 [formula: see text]-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.

d'Auvergne EJ; Gooley PR

2008-02-01

79

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

2008-01-01

80

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

Science.gov (United States)

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 [formula: see text]-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. PMID:18085411

d'Auvergne, Edward J; Gooley, Paul R

2007-12-18

 
 
 
 
81

Alkali metals in ethylenediamine: a computational study of the optical absorption spectra and NMR parameters of [M(en)3(?+)·M(?-)] ion pairs.  

UK PubMed Central (United Kingdom)

The optical absorption spectra of alkali metals in ethylenediamine have provided evidence for a third oxidation state, -1, of all of the alkali metals heavier than lithium. Experimentally determined NMR parameters have supported this interpretation, further indicating that whereas Na(-) is a genuine metal anion, the interaction of the alkali anion with the medium becomes progressively stronger for the larger metals. Herein, first-principles computations based upon density functional theory are carried out on various species which may be present in solutions composed of alkali metals and ethylenediamine. The energies of a number of hypothetical reactions computed with a continuum solvation model indicate that neither free metal anions, M(-), nor solvated electrons are the most stable species. Instead, [Li(en)(3)](2) and [M(en)(3)(?+)·M(?-)] (M = Na, K, Rb, Cs) are predicted to have enhanced stability. The M(en)(3) complexes can be viewed as superalkalis or expanded alkalis, ones in which the valence electron density is pulled out to a greater extent than in the alkali metals alone. The computed optical absorption spectra and NMR parameters of the [Li(en)(3)](2) superalkali dimer and the [M(en)(3)(?+)·M(?-)] superalkali-alkali mixed dimers are in good agreement with the aforementioned experimental results, providing further evidence that these may be the dominant species in solution. The latter can also be thought of as an ion pair formed from an alkali metal anion (M(-)) and solvated cation (M(en)(3)(+)).

Zurek E

2011-04-01

82

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1992-02-18

83

Texture in the superconducting order parameter of CeCoIn5; FFLO state as evidenced by ultrasound and NMR  

Science.gov (United States)

A myriad of fascinating properties have been proposed for unconventional superconductors in the presence of a strong magnetic field. Among the possible exotic superconducting (SC) phases, a spatially nonuniform SC state originating from the paramagnetism of conduction electrons has become a subject of particular interest after the pioneering work by Fulde and Ferrel and Larkin and Ovchinnikov (FFLO) in the mid-1960's. We present here ultrasound and NMR studies of the quasi-2D heavy-fermion superconductor CeCoIn5 with extremely large Pauli paramagnetic susceptibility, which is believed to host a FFLO state. Ultrasound velocity measurements reveal an unusual structural transformation of the flux line lattice (FLL) in the vicinity of the upper critical field and with a magnetic field applied parallel to the ab plane. The transition field coincides with that at which heat capacity measurements reveal a second order phase transition. The lowering of the sound velocity at the transition is consistent with the collapse of the FLL tilt modulus and a crossover to quasi two-dimensional FLL pinning. In the vicinity of the upper critical field , the ^115In NMR spectrum also exhibits a dramatic change below T^*(H) which well coincides with the position of reported anomalies in specific heat and ultrasound velocity. Below T^*(H) a new resonance line appears at higher frequency, which can be attributed to the normal quasiparticle sheets formed in the SC regime. The NMR spectrum also indicate that the vortex core structure of CeCoIn5 appears to be markedly different from that of ordinary superconductors. On the basis of these results, we were able to establish a clear evidence of the spatially inhomogeneous SC state at high field and low temperatures, precisely as expected in a FFLO state. In collaboration with T.Watanabe, Y.Kasahara, K.Izawa (Univ. of Tokyo), C.J. van der Beek(Ecole Polytechnique),K.Kakuyanagi, K.Kumagai (Hokkaido Univ.), M.Nohara, T.Hanaguri, H.Takagi,(Univ. of Tokyo) H.Shishido, R.Settai, and Y.Onuki(Osaka Univ.)

Matsuda, Yuji

2005-03-01

84

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

85

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

International Nuclear Information System (INIS)

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

1979-03-01

86

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

87

Mixed lipid aggregates containing gangliosides impose different 2H-NMR dynamical parameters on water environment depending on their lipid composition.  

UK PubMed Central (United Kingdom)

Water dynamics in samples of ceramide tetrasaccharide (Gg4Cer) vesicles and GM1 ganglioside micelles at 300:1 water/lipid mole ratio were studied by using deuterium nuclear magnetic resonance (2H-NMR). GM1 imposes a different restriction on water dynamics that is insensitive to temperatures either above or below its phase transition temperature or below the freezing point of water. The calculated correlation times are in the range of 10(-10) s, typical of water molecules near to the polar groups. Pure GM1 micelles have two distinct water microenvironments dynamically characterized. Their dynamic parameters remain constant with temperature ranging from -18 to 32 degrees C, but the amount of strongly associated water is modified. By contrast, a mixture of single soluble carbohydrates corresponding to GM1 polar head group does not preserve the dynamic parameters of water hydration when the temperature is varied. Incorporation of cholesterol or lysophosphatidylcholine into GM1 micelles substantially increases the mobility of water molecules compared with that found in pure GM1 micelles. The overall results indicate that both the supramolecular organization and the local surface quality (lipid-lipid interaction) strongly influence the interfacial water mobility and the extent of hydration layers in glycosphingolipid aggregates.

Arnulphi C; Martin CA; Fidelio GD

2003-10-01

88

MULTIPLE-QUANTUM NMR IN SOLIDS  

Energy Technology Data Exchange (ETDEWEB)

Time domain multiple-quantum (MQ) nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for spectral simplification and for providing new information on molecular dynamics. In this thesis, applications of MQ NMR are presented and show distinctly the advantages of this method over the conventional single-quantum NMR. Chapter 1 introduces the spin Hamiltonians, the density matrix formalism and some basic concepts of MQ NMR spectroscopy. In chapter 2, {sup 14}N double-quantum coherence is observed with high sensitivity in isotropic solution, using only the magnetization of bound protons. Spin echoes are used to obtain the homogeneous double-quantum spectrum and to suppress a large H{sub 2}O solvent signal. Chapter 3 resolves the main difficulty in observing high MQ transitions in solids. Due to the profusion of spin transitions in a solid, individual lines are unresolved. Excitation and detection of high quantum transitions by normal schemes are thus difficult. To ensure that overlapping lines add constructively and thereby to enhance sensitivity, time-reversal pulse sequences are used to generate all lines in phase. Up to 22-quantum {sup 1}H absorption in solid adamantane is observed. A time dependence study shows an increase in spin correlations as the excitation time increased. In chapter 4, a statistical theory of MQ second moments is developed for coupled spins of spin I = 1/2. The model reveals that the ratio of the average dipolar coupling to the rms value largely determines the dependence of second moments on the number of quanta. The results of this model are checked against computer-calculated and experimental second moments, and show good agreement. A simple scheme is proposed in chapter 5 for sensitivity improvement in a MQ experiment. The scheme involves acquiring all of the signal energy available in the detection period by applying pulsed spinlocking and sampling between pulses. Using this technique on polycrystalline adamantane, a large increase in sensitivity is observed. Correlation of motion of two interacting methyl groups is the subject of chapter 6. This system serves as a model for the study of hindered internal motion. Because the spin system is small and the motions are well-defined, the calculations involved are tractable. Group theory appropriate for nonrigid molecules is used to treat the change in the Hamiltonian as the methyl groups transit from correlated to uncorrelated motion. Results show that the four-quantum order alone is sufficient to distinguish between the two motions.

Yen, Y-S.

1982-11-01

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

2013-01-16

90

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

UK PubMed Central (United Kingdom)

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.

Farooq H; Courtier-Murias D; Soong R; Masoom H; Maas W; Fey M; Kumar R; Monette M; Stronks H; Simpson MJ; Simpson AJ

2013-03-01

91

Ab initio calculation of 1H, 17O, 27Al and 29Si NMR parameters, vibrational frequencies and bonding energetics in hydrous silica and Na-aluminosilicate glasses  

Science.gov (United States)

Ab initio, molecular orbital (MO) calculations were performed on model systems of SiO 2, NaAlSi 3O 8 (albite), H 2O-SiO 2 and H 2O-NaAlSi 3O 8 glasses. Model nuclear magnetic resonance (NMR) isotropic chemical shifts (? iso) for 1H, 17O, 27Al and 29Si are consistent with experimental data for the SiO 2, NaAlSi 3O 8, H 2O-SiO 2 systems where structural interpretations of the NMR peak assignments are accepted. For H 2O-NaSi 3AlO 8 glass, controversy has surrounded the interpretation of NMR and infrared (IR) spectra. Calculated ? iso1H, ? iso17O, ? iso27Al and ? iso29Si are consistent with the interpretation of Kohn et al. (1992) that Si-(OH)-Al linkages are responsible for the observed peaks in hydrous Na-aluminosilicate glasses. In addition, a theoretical vibrational frequency associated with the Kohn et al. (1992) model agrees well with the observed shoulder near 900 cm -1 in the IR and Raman spectra of hydrous albite glasses. MO calculations suggest that breaking this Si-(OH)-Al linkage requires ˜+56 to +82 kJ/mol which is comparable to the activation energies for viscous flow in hydrous aluminosilicate melts.

Kubicki, J. D.; Sykes, D. G.

2004-10-01

92

Correlation among the gas-phase, solution, and solid-phase geometrical and NMR parameters of dative bonds in the pentacoordinate silicon compounds. 1-Substituted silatranes.  

UK PubMed Central (United Kingdom)

Silatranes XSi(OCH2CH2)3N exhibit a good linear relationship between their experimental and calculated (IGLO and GIAO) values of the NMR chemical shifts of (15)N, ?N, and the lengths of dative bonds Si?N, dSiN, determined in the gas phase (ED, CCSD), solutions (COSMO PBE0, B3PW91), and crystals (X-ray). An aggregate of the obtained data provides strong evidence that the gas-phase value of dSiN in MeSi(OCH2CH2)3N should be greater by ?0.05 Å than that determined in the electron diffraction (ED) experiment (2.45 Å). Given this condition, a long-standing contradiction between the data of the structural (X-ray, ED) and NMR (15)N experiments for the molecules of 1-methyl- and 1-fluorosilatrane regarding the sensitivity of their coordination contact Si?N to the medium effect is resolved.

Belogolova EF; Sidorkin VF

2013-06-01

93

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

UK PubMed Central (United Kingdom)

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

Godelmann R; Fang F; Humpfer E; Schütz B; Bansbach M; Schäfer H; Spraul M

2013-06-01

94

Group theory and NMR dynamics  

Energy Technology Data Exchange (ETDEWEB)

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.

Emsley, L. [CEA Centre d`Etudes de Grenoble, 38 (France). Dept. de Recherche Fondamentale sur la Matiere Condensee; Schmidt-Rohr, K.; Pines, A. [Lawrence Berkeley Lab., CA (United States)]|[California Univ., Berkeley, CA (United States). Dept. of Chemistry

1994-12-31

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

{sup 3}1P-NMR spectroscopy in measurements of physiological parameters and response to therapy of human melanoma xenografts  

Energy Technology Data Exchange (ETDEWEB)

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 T{sub 1}s 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 T{sub 1}s 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 T{sub 1}s. 4) To identify the tumour physiological factors that is effected by the treatment and influence the bio energetics status and phosphorus T{sub 1}s. 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 T{sub 1}s 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 T{sub 1}s 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 T{sub 1} 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 T{sub 1}s were closely associated to the fraction of necrotic tumour tissue across tumour lines. Even though phosphorus T{sub 1}s 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 T{sub 1}s 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 T{sub 1}s 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 T{sub 1}s 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.

Olsen, Dag Rune

1999-07-01

97

First-principles calculations of finite temperature Sc and O NMR parameters in Pb(Sc2/3W1/3)O3  

Science.gov (United States)

Understanding the dynamics of complex relaxor ferroelectrics is important to characterizing their large electromechanical coupling. Preliminary NMR measurements of Sc electric-field-gradients (EFG) in Pb(Sc2/3W1/3)O3 (PSW) show a strong temperature dependence in the range T = 250 - 330 K. To understand this behavior, we use the first-principles GIPAWootnotetextC. J. Pickard and F. Mauri, Phys. Rev. B 63, 245101 (2001); method within the Quantum Espresso (QE) packageootnotetextP. Giannozzi et al., Journal of Physics: Condensed Matter 21, 395502 (2009) to calculate ^45Sc and ^17O chemical-shifts and EFG tensors. To study finite temperature effects, we incorporate the thermal expansion of the lattice and sample thermal disorder, using the phonon degrees of freedom. As in our previous studies of perovksites,ootnotetextD. L. Pechkis, E. J. Walter, and H. Krakauer. J. Chem. Phys. 135, 114507 (2011); ibid. 131, 184511 (2009) we show that the ^17O chemical shifts in PSW also exhibit a linear correlation with the nearest-neighbor B-O bond length.

Krakauer, Henry; Walter, Eric J.; Ellden, Jeremy; Hoatson, Gina L.; Vold, Robert L.

2012-02-01

98

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

International Nuclear Information System (INIS)

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

2010-03-15

99

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-03-15

100

NMR spectroscopy  

International Nuclear Information System (INIS)

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

1989-01-01

 
 
 
 
101

New methods for NMR spectral analysis  

Directory of Open Access Journals (Sweden)

Full Text Available A set of novel methods for signal enhancement and artifact suppression in multidimensional NMR spectra have been developed. These methods, independent of the experiment type, aim at improvising resonance assignments, accurate measurement of NMR parameters and automated peak picking in spectra acquired with low sensitivity or containing artifacts.

Garima Jaipuria; Adil Hayat; Hanudatta S. Atreya

2011-01-01

102

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

UK PubMed Central (United Kingdom)

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

Haapaniemi E; Mesilaakso M

2012-03-01

103

NMR and dynamics of biopolymers  

International Nuclear Information System (INIS)

Several basic experimental analytical NMR techniques that are frequently used for the qualitative and quantitative analysis of dynamic and exchange processes, focusing on proteins systems, are described: chemical exchange (slow exchange, fast exchange, intermediate exchange), heteronuclear relaxation measurements (relaxation parameters, strategy of relaxation data analysis, experimental results and examples, motional model interpretation of relaxation data, homonuclear relaxation); slow large-scale exchange and hydrogen-deuterium exchange are also studied: mechanisms of hydrogen exchange in a native protein, methods for measuring amide exchange rates by NMR, interpretation of amide exchange rates. 9 fig., 3 tab., 56 ref

1994-01-01

104

NMR and dynamics of biopolymers  

Energy Technology Data Exchange (ETDEWEB)

Several basic experimental analytical NMR techniques that are frequently used for the qualitative and quantitative analysis of dynamic and exchange processes, focusing on proteins systems, are described: chemical exchange (slow exchange, fast exchange, intermediate exchange), heteronuclear relaxation measurements (relaxation parameters, strategy of relaxation data analysis, experimental results and examples, motional model interpretation of relaxation data, homonuclear relaxation); slow large-scale exchange and hydrogen-deuterium exchange are also studied: mechanisms of hydrogen exchange in a native protein, methods for measuring amide exchange rates by NMR, interpretation of amide exchange rates. 9 fig., 3 tab., 56 ref.

Lian, L.Y.; Barsukov, I.L. [Leicester Univ. (United Kingdom)

1994-12-31

105

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.

Tepeš, P.; Novak. P.

2008-01-01

106

NMR studies of metabolism  

International Nuclear Information System (INIS)

In this paper, the authors present applications of NMR to the study of different aspects of metabolism. The authors begin with a brief outline of localization methods that are commonly used to obtain in vivo NMR spectra. The authors then describe in more detail metabolic information recently obtained by NMR of perfused organs, intact animals, and humans. Previous reviews have already covered the applications of NMR to the study of metabolism in microorganisms, isolated or cultivated cells, and tumors. NMR spectroscopy of the brain, and human in vivo NMR spectroscopy have also been reviewed.

1990-01-01

107

NMR and NQR parameters of ethanol crystal  

CERN Multimedia

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

Milinkovic, M

2012-01-01

108

NMR imaging in medicine  

Energy Technology Data Exchange (ETDEWEB)

Medical applications of nuclear magnetic resonance (NMR) are discussed. One of the chief advantages of NMR is its ability to generate images of internal body structures without the use of X-rays. In addition to the medical applications. NMR technique is also briefly detailed, along with its advantages over computerized tomography. (JMT)

Pykett, I.L.

1982-05-01

109

NMR studies of multiphase flows II  

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-12-31

110

NMR Quantum Information Processing  

CERN Multimedia

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

111

11B NMR spectroscopy  

International Nuclear Information System (INIS)

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

1988-01-01

112

Development of Halbach magnet for portable NMR device  

International Nuclear Information System (INIS)

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

2009-03-01

113

Rapid FLASH NMR imaging  

Energy Technology Data Exchange (ETDEWEB)

Nuclear magnetic resonance (NMR) spectroscopy and imaging provide new tools for non-invasive investigations of living systems. Recent developments in rapid NMR imaging now offer considerable improvements for both scientific applications and medical diagnosis. Using fast imaging sequences cross-sectional images may be recorded within seconds and, therefore, become free from motional artifacts due to breathing or peristalsis. New functional imaging experiments include dynamic studies of the application of paramagnetic contrast agents or ECG-synchronized recordings of cardiac NMR movies. Superior anatomical information is achieved by three-dimensional NMR imaging with measuring times of minutes rather than hours.

Frahm, J.

1987-09-01

114

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; Antonio G. Ferreira; Patrick Giraudeau

2013-01-01

115

Rapid prediction of multi-dimensional NMR data sets  

International Nuclear Information System (INIS)

[en] 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).

2012-01-01

116

Artificial intelligence in NMR imaging and image processing  

International Nuclear Information System (INIS)

NMR tomography offers a wealth of information and data acquisition variants. Artificial intelligence is able to efficiently support the selection of measuring parameters and the evaluation of results. (orig.)

1988-01-01

117

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

Energy Technology Data Exchange (ETDEWEB)

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. 8 refs, 1 fig.

Makhiyanov, N. [Production Association ``Nizhnekamskneftekhym``, Nizhnekamsk, Tatarstan (Russian Federation); Kupka, T. [Uniwersytet Slaski, Katowice (Poland)]|[Zaklad Fizyki Ciala Stalego, Polska Akademia Nauk, Zabrze (Poland); Pasterna, G. [Institute of Nuclear Physics, Cracow (Poland); Dziegielewski, J.O. [Uniwersytet Slaski, Katowice (Poland)

1994-12-31

118

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

International Nuclear Information System (INIS)

[en] 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

1994-01-01

119

The use of isotopes in NMR studies of biological systems  

International Nuclear Information System (INIS)

[en] Isotopes have been used extensively in biochemistry for studying the kinetics of individual enzymes and suites of enzymes that make up metabolic pathways. NMR is able to add a new dimension to such studies by introducing parameters such as chemical shift, spin coupling and multiple quantum frequencies. These pure NMR parameters, while of no direct biological relevance, allow new types of experiments which can separate the information from chemically different labeled species and isotopomers of a single chemical species. These features combined with the ability of NMR to examine complex mixtures, crude biological preparations and tissue make it a powerful tool for the biologist. 11 refs

1986-01-01

120

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

 
 
 
 
121

Structural NMR assignment  

International Nuclear Information System (INIS)

Full text: General automated NMR assignment approaches are aimed at full heteronuclear assignment, which is needed for structure determination. Usually, full assignment requires at least as much spectral information as is used for structure generation. For large proteins, obtaining sufficient spectral information may require a number of sample preparations and many spectra, resulting in a significant overhead for the use of NMR in biochemical investigation. For a protein of biochemical interest one may already have an x-ray crystal structure, but spectral assignment is still needed to use NMR as a structural probe for ligand binding studies. In this situation it may be possible to use much less spectral information to make an assignment based purely on the correspondence of structural data to the measurements contained in a few simple spectra. We introduce a framework to accomplish this 'structural assignment', and give some observations on the practical requirements for a structural assignment to succeed

1999-01-01

122

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

Science.gov (United States)

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

Rodriguez, Jorge H.

2013-04-01

123

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

124

Prediction of peak overlap in NMR spectra  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-06-15

125

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

126

Phosphorous NMR in biology  

Energy Technology Data Exchange (ETDEWEB)

This book reviews the technique of phosphorous NMR and its relationship to every existing level of biology and biochemistry. The bulk of the book is broken into three sections: simple biomolecules; macromolecules/macromolecular assemblages; and complex systems necessary to maintain life. Topics include: relaxation time of inorganic phosphate, behavior of ATP with biological molecules and characterization of t-RNA.

Burt, C.T.

1987-01-01

127

Solid-state 73Ge NMR spectroscopy of simple organogermanes.  

UK PubMed Central (United Kingdom)

Germanium-73 is an extremely challenging nucleus to examine by NMR spectroscopy due to its unfavorable NMR properties. Through the use of an ultrahigh (21.1 T) magnetic field, a systematic study of a series of simple organogermanes was carried out. In those cases for which X-ray structural data were available, correlations were drawn between the NMR parameters and structural metrics. These data were combined with DFT calculations to obtain insight into the structures of several compounds with unknown crystal structures.

Hanson MA; Sutrisno A; Terskikh VV; Baines KM; Huang Y

2012-10-01

128

Moessbauer and NMR study of novel Tin(IV)-lactames  

Energy Technology Data Exchange (ETDEWEB)

N-tributylstannylated 2-pyrrolidinone was reacted with tributyltin triflate in different molar ratios and the complex formation monitored using {sup 1}H-NMR, {sup 13}C-NMR and {sup 119}Sn Moessbauer spectroscopy. Comparing the carbon NMR and tin Moessbauer results, a reaction scheme is suggested for the complexation which assumes the formation of a simultaneously O- and N-tributylstannylated pyrrolidinone cation. The formation of the only O-stannylated pyrrolidinone is also assumed to account for the non-constant Moessbauer parameters of the two tin environments in the distannylated pyrrolidinone cation when the ratio of tributyltin triflate is increased in the reaction.

Kuzmann, Erno; Szalay, Roland; Homonnay, Zoltan, E-mail: homonnay@ludens.elte.hu; Nagy, Sandor [Eoetvoes Lorand University, Institute of Chemistry (Hungary)

2012-03-15

129

Mössbauer and NMR study of novel Tin(IV)-lactames  

International Nuclear Information System (INIS)

[en] N-tributylstannylated 2-pyrrolidinone was reacted with tributyltin triflate in different molar ratios and the complex formation monitored using 1H-NMR, 13C-NMR and 119Sn Mössbauer spectroscopy. Comparing the carbon NMR and tin Mössbauer results, a reaction scheme is suggested for the complexation which assumes the formation of a simultaneously O- and N-tributylstannylated pyrrolidinone cation. The formation of the only O-stannylated pyrrolidinone is also assumed to account for the non-constant Mössbauer parameters of the two tin environments in the distannylated pyrrolidinone cation when the ratio of tributyltin triflate is increased in the reaction.

2012-01-01

130

Carbon-13 NMR of some aliphatic ketones  

International Nuclear Information System (INIS)

H-1 and C-13 NMR chemical shifts for some aliphatic ketones are reported. A good linear relationship was observed between the aliphatic carbons chemical shifts experimental and calculated for the global effect empirical method. Additivity of substituent chemical shifts are observed and sets of empirical parameter is re-estimate and proposed for the estimation of alkyl carbons in these compounds. The chemical shifts of the aliphatic carbons are in close agreement with those calculated using substituent chemical shifts. (author)

1993-01-01

131

Carbon-14 NMR of some aliphatic ketones  

International Nuclear Information System (INIS)

H-1 and C-13 NMR chemical shifts for some aliphatic ketones are reported. A good linear relationship was observed between the aliphatic carbons chemical shifts experimental and calculated for the global effect empirical method. Additivity of substituent chemical shifts are observed and sets of empirical parameter is reestimate and proposed for the estimation of alkyl carbons in these compounds. The chemical shifts of the aliphatic carbons are in close agreement with those calculated using substituent chemical shifts. (author)

1993-01-01

132

NMR METHODS IN FOOD CHEMISTRY  

Science.gov (United States)

Nuclear Magnetic Resonance (NMR) spectroscopy has enormously facilitated investigations into structural aspects of simple molecules and complex polymers. NMR has developed far beyond the simple running of a proton or carbon spectrum. Today there are literally thousands of “NMR experiments” and varia...

133

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

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 tomography today  

International Nuclear Information System (INIS)

In NMR tomography, superconducting magnets achieving high homogeneity have come to the fore, all the more as the magnetic stray field, e.g. in a 2 tesla magnet with direct flux feedback could be reduced to the values of a 0.5 tesla magnet without additional magnetic shielding. In addition, consumption of cryogenic agents could be cut back. Examination conditions have been improved by faster switches to stronger gradients and advanced high-frequency systems with antennas adapted to organ conditions (surface coils). This also brought about better imaging quality and higher local resolution values up to less than one mm. Efforts for further improvements will concentrate on the software and measuring methods and are expected to achieve shorter examination times and at the same time better images, as the potentials of NMR tomography are far from being depleted today. It remains to be seen whether and when spectroscopy will become as important in clinical diagnostics as imaging is now. (orig.).

1986-01-01

136

?-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

137

NMR, water and plants  

International Nuclear Information System (INIS)

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

1982-01-01

138

NMR imaging of materials  

Energy Technology Data Exchange (ETDEWEB)

A method for obtaining at least one petrophysical property of a porous material containing therein at least one preselected fluid, is described, comprising: NMR imaging the material to generate signals dependent upon both M(0) and T/sub 1/ and M(0) and T/sub 2/, generating separate M(0), T/sub 1/ and T/sub 2/ images from the signals, and determining at least one petrophysical property from at least one of the images.

Vinegar, H.J.; Rothwell, W.P.

1988-03-01

139

Determination of average molecular parameters of vacuum residues and asphalt by elementary analysis and {sup 1} H NMR and comparison with {sup 13} C NMR results; Determinacao de parametros moleculares medios de residuos de vacuo e asfalto por analise elementar e RMN {sup 1} H e comparacao com resultados obtidos por RMN {sup 13} C  

Energy Technology Data Exchange (ETDEWEB)

This work proposes a new approach for determining average molecular parameters in petroleum fractions, from some approximation based on consideration about average composition of petroleum heavy fractions. A comparative evaluation between the proposed method and the traditional one has been carried out, showing 60 hours saving in time spent at analysis. The results were present and discussed 2 refs.

Teixeira, Marco Antonio; Marques, Rosana Garrido [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas

1995-12-31

140

Benchmarking NMR experiments: a relational database of protein pulse sequences.  

UK PubMed Central (United Kingdom)

Systematic benchmarking of multi-dimensional protein NMR experiments is a critical prerequisite for optimal allocation of NMR resources for structural analysis of challenging proteins, e.g. large proteins with limited solubility or proteins prone to aggregation. We propose a set of benchmarking parameters for essential protein NMR experiments organized into a lightweight (single XML file) relational database (RDB), which includes all the necessary auxiliaries (waveforms, decoupling sequences, calibration tables, setup algorithms and an RDB management system). The database is interfaced to the Spinach library (http://spindynamics.org), which enables accurate simulation and benchmarking of NMR experiments on large spin systems. A key feature is the ability to use a single user-specified spin system to simulate the majority of deposited solution state NMR experiments, thus providing the (hitherto unavailable) unified framework for pulse sequence evaluation. This development enables predicting relative sensitivity of deposited implementations of NMR experiments, thus providing a basis for comparison, optimization and, eventually, automation of NMR analysis. The benchmarking is demonstrated with two proteins, of 170 amino acids I domain of alphaXbeta2 Integrin and 440 amino acids NS3 helicase.

Senthamarai RR; Kuprov I; Pervushin K

2010-03-01

 
 
 
 
141

DNA oligonucleotide conformations: high resolution NMR studies  

International Nuclear Information System (INIS)

[en] 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

NMR in biology and medicine  

Energy Technology Data Exchange (ETDEWEB)

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

Chien, S.; Chien, H.

1986-01-01

143

Summary of Miniature NMR Development  

International Nuclear Information System (INIS)

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

2000-01-01

144

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

International Nuclear Information System (INIS)

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

1994-01-01

145

Quasi-Exactly Solvable N-Body Spin Hamiltonians with Short-Range Interaction Potentials  

CERN Multimedia

We review some recent results on quasi-exactly solvable spin models presenting near-neighbors interactions. These systems can be understood as cyclic generalizations of the usual Calogero-Sutherland models. A nontrivial modification of the exchange operator formalism is used to obtain several infinite families of eigenfunctions of these models in closed form.

Enciso, A; González-López, A; Rodríguez, M A

2006-01-01

146

Quasi-Exactly Solvable N-Body Spin Hamiltonians with Short-Range Interaction Potentials  

Directory of Open Access Journals (Sweden)

Full Text Available We review some recent results on quasi-exactly solvable spin models presenting near-neighbors interactions. These systems can be understood as cyclic generalizations of the usual Calogero-Sutherland models. A nontrivial modification of the exchange operator formalism is used to obtain several infinite families of eigenfunctions of these models in closed form.

A. Enciso; F. Finkel; A. González-López; M.A. Rodríguez

2006-01-01

147

Studies towards rotational dynamics of dimethyl 2-(triphenylphosphoranylidene) succinate by 1H NMR  

Science.gov (United States)

We describe here the dynamic 1H NMR studies of dimethyl 2-(triphenylphosphoranylidene) succinate (1). Phosphorane 1 has a bond presenting slow (in the 1H NMR time scale) rotation which results in spectra of two isomers at the same time. From the spectral data were calculated the rate constant and thermodynamic parameters for the rotational process.

Rodrigues, Shirley M. M.; Palaretti, Vinicius; Nardini, Viviani; Constantino, Mauricio G.; da Silva, Gil Valdo J.

2013-11-01

148

NMR studies of fast-ion conductors  

International Nuclear Information System (INIS)

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

149

NMR imaging of the kidney  

International Nuclear Information System (INIS)

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

1984-01-01

150

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

151

Solid state NMR of sulfa-drugs  

Energy Technology Data Exchange (ETDEWEB)

This work has been a study of systems, mostly of sulfa-drugs, showing polymorphic behaviour. Using different means as solid state NMR, X-ray analysis, * and theoretical calculations, we have seen how it is possible to understand results obtained from the different techniques, proving how the study of polymorphic systems needs cooperative advice from the different techniques that are able to detect polymorphic differences. Within the sulfa-drugs I have been mostly concentrating on sulfanilamide, studying {sup 13}C and {sup 15}N solid state NMR spectra of the different polymorphs. The NMR parameters that have been most interesting to study, have been the relaxation times that have revealed complicated motion of the molecule despite it being a small molecule. In order to obtain detailed information from {sup 15}N spectra it has been necessary to enrich the samples and this has enabled a study of the shielding tensors of the nitrogens in the molecule. {sup 13}C spectra were also recorded of systems studied sulfathiazole solvates, that proved to show some of the same solid state effects in the NMR spectra as sulfanilamide. Shielding calculations have proved to be still limited in order to obtain reliable information on the shielding of both {sup 13}C and {sup 15}N nuclei but considering hydrogen-bonded molecules, as opposed to isolated molecules, seemed to have improved the calculations quite a lot, so that some idea of intermolecular effects could be deducted. Exact positions of the hydrogen has proved to be essential as well in order to improve the calculations. Finally a case study for the REDOR pulse sequence has been carried out. Different attempts to understand the effects influencing this particular experiment have been carried out on 20% and 99% doubly enriched glycine, as well as on a particular sample, doubly enriched BRL55834, but the internuclear distances measured with this technique still displayed some uncertainties that made results not thoroughly reliable. (author)

Portieri, A

2001-07-01

152

Solid state NMR of sulfa-drugs  

International Nuclear Information System (INIS)

This work has been a study of systems, mostly of sulfa-drugs, showing polymorphic behaviour. Using different means as solid state NMR, X-ray analysis, * and theoretical calculations, we have seen how it is possible to understand results obtained from the different techniques, proving how the study of polymorphic systems needs cooperative advice from the different techniques that are able to detect polymorphic differences. Within the sulfa-drugs I have been mostly concentrating on sulfanilamide, studying 13C and 15N solid state NMR spectra of the different polymorphs. The NMR parameters that have been most interesting to study, have been the relaxation times that have revealed complicated motion of the molecule despite it being a small molecule. In order to obtain detailed information from 15N spectra it has been necessary to enrich the samples and this has enabled a study of the shielding tensors of the nitrogens in the molecule. 13C spectra were also recorded of systems studied sulfathiazole solvates, that proved to show some of the same solid state effects in the NMR spectra as sulfanilamide. Shielding calculations have proved to be still limited in order to obtain reliable information on the shielding of both 13C and 15N nuclei but considering hydrogen-bonded molecules, as opposed to isolated molecules, seemed to have improved the calculations quite a lot, so that some idea of intermolecular effects could be deducted. Exact positions of the hydrogen has proved to be essential as well in order to improve the calculations. Finally a case study for the REDOR pulse sequence has been carried out. Different attempts to understand the effects influencing this particular experiment have been carried out on 20% and 99% doubly enriched glycine, as well as on a particular sample, doubly enriched BRL55834, but the internuclear distances measured with this technique still displayed some uncertainties that made results not thoroughly reliable. (author)

2001-01-01

153

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

154

First principles NMR study of fluorapatite under pressure.  

UK PubMed Central (United Kingdom)

NMR is the technique of election to probe the local properties of materials. Herein we present the results of density functional theory (DFT) ab initio calculations of the NMR parameters for fluorapatite (FAp), a calcium orthophosphate mineral belonging to the apatite family, by using the GIPAW method (Pickard and Mauri, 2001). Understanding the local effects of pressure on apatites is particularly relevant because of their important role in many solid state and biomedical applications. Apatites are open structures, which can undergo complex anisotropic deformations, and the response of NMR can elucidate the microscopic changes induced by an applied pressure. The computed NMR parameters proved to be in good agreement with the available experimental data. The structural evaluation of the material behavior under hydrostatic pressure (from -5 to +100 kbar) indicated a shrinkage of the diameter of the apatitic channel, and a strong correlation between NMR shielding and pressure, proving the sensitivity of this technique to even small changes in the chemical environment around the nuclei. This theoretical approach allows the exploration of all the different nuclei composing the material, thus providing a very useful guidance in the interpretation of experimental results, particularly valuable for the more challenging nuclei such as (43)Ca and (17)O.

Pavan B; Ceresoli D; Tecklenburg MM; Fornari M

2012-07-01

155

Two dimensional solid state NMR  

International Nuclear Information System (INIS)

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

1987-01-01

156

Ordering and intramolecular mobility in the nematic phase of PAA investigated by means of NMR lineshape analysis and computer simulations of the lineshape  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have recorded the 1H- and 2H-NMR spectra of PAA, PAA-d6, and PAA-d8. The order parameter S = Szz = 1/2. has been determined from the different types of NMR experiments and shown to be quite sufficient for the interpretation of both proton and deuterium NMR data since the values o...

Limmer, St.; Schmiedel, H.; Hillner, B.; Lösche, A.; Grande, S.

157

(14)N solid-state NMR: a sensitive probe of the local order in zeolites.  

Science.gov (United States)

Local order in as-synthesised zeolites templated by tetraalkylammonium cations is proven from solid-state (14)N NMR and related quadrupolar parameters, opening new perspectives in the study of porous materials. PMID:23877332

Dib, Eddy; Mineva, Tzonka; Gaveau, Philippe; Alonso, Bruno

2013-10-01

158

(14)N solid-state NMR: a sensitive probe of the local order in zeolites.  

UK PubMed Central (United Kingdom)

Local order in as-synthesised zeolites templated by tetraalkylammonium cations is proven from solid-state (14)N NMR and related quadrupolar parameters, opening new perspectives in the study of porous materials.

Dib E; Mineva T; Gaveau P; Alonso B

2013-10-01

159

A comprehensive NMR study of cubic and hexagonal boron nitride.  

UK PubMed Central (United Kingdom)

A variety of techniques and measurements on all NMR accessible nuclei allow one to obtain a complete and precise set of chemical shift and quadrupole coupling parameters for both boron and nitrogen in cubic and hexagonal boron nitride. For hexagonal boron nitride, 11B to 15N cross polarization under magic angle sample spinning conditions is demonstrated at natural isotope abundance. The presented approach for NMR characterization of the crystalline boron nitrides should also be applicable to structurally related composite materials, nanotubes, and amorphous ceramics.

Jeschke G; Hoffbauer W; Jansen M

1998-08-01

160

A comprehensive NMR study of cubic and hexagonal boron nitride.  

Science.gov (United States)

A variety of techniques and measurements on all NMR accessible nuclei allow one to obtain a complete and precise set of chemical shift and quadrupole coupling parameters for both boron and nitrogen in cubic and hexagonal boron nitride. For hexagonal boron nitride, 11B to 15N cross polarization under magic angle sample spinning conditions is demonstrated at natural isotope abundance. The presented approach for NMR characterization of the crystalline boron nitrides should also be applicable to structurally related composite materials, nanotubes, and amorphous ceramics. PMID:9808290

Jeschke, G; Hoffbauer, W; Jansen, M

1998-08-01

 
 
 
 
161

NMR-based structural biology of proteins in supercooled water.  

UK PubMed Central (United Kingdom)

NMR-based structural biology of proteins can be pursued efficiently in supercooled water at temperatures well below the freezing point of water. This enables one to study protein structure, dynamics, hydration and cold denaturation in an unperturbed aqueous solution at very low temperatures. Furthermore, such studies enable one to accurately measure thermodynamic parameters associated with protein cold denaturation. Presently available approaches to acquire NMR data for supercooled aqueous protein solutions are surveyed, new insights obtained from such studies are summarized, and future perspectives are discussed.

Szyperski T; Mills JL

2011-03-01

162

NMR-based structural biology of proteins in supercooled water.  

Science.gov (United States)

NMR-based structural biology of proteins can be pursued efficiently in supercooled water at temperatures well below the freezing point of water. This enables one to study protein structure, dynamics, hydration and cold denaturation in an unperturbed aqueous solution at very low temperatures. Furthermore, such studies enable one to accurately measure thermodynamic parameters associated with protein cold denaturation. Presently available approaches to acquire NMR data for supercooled aqueous protein solutions are surveyed, new insights obtained from such studies are summarized, and future perspectives are discussed. PMID:21533787

Szyperski, Thomas; Mills, Jeffrey L

2011-05-01

163

NMR STUDY OF MOLECULAR REFORIENTATION UNDER FIVEFOLD SYMMETRY SOLID PERMETHYLFERROCENE  

Energy Technology Data Exchange (ETDEWEB)

The ring reorientation in permethylferrocene has been studied using high resolution solid state {sup 13}C NMR. The constraints which symmetry places upon the number and types of motional parameters which may be determined from the NMR spectrum are discussed. From comparison of the experimental lineshapes in the slow reorientation temperatures range with theoretical models for random rotations and symmetry related jumps, it is concluded that the reorientation occurs as jumps between symmetry related orientations with jumps of 2{pi}/5 highly favored over 4{pi}/5. The activation energy derived for the jump process is 13.5 kjoules/mole.

Wemmer, D.E.; Ruben, D.J.; Pines, A.

1980-08-01

164

Development of NMR-CT  

Energy Technology Data Exchange (ETDEWEB)

A human whole body NMR-CT device using constantly conducting vacant coils was completed and is under clinical assessment. The outline and measuring method of the device were described, and human images obtained primarily on healthy volunteers were explained.

Suzuki, Hirokazu; Suzuki, Tohru; Sato, Kozo; Sato, Masataka; Muto, Yasuhiro

1982-12-01

165

Compact orthogonal NMR field sensor  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-02-03

166

NMR spectroscopy of muscle proteins  

International Nuclear Information System (INIS)

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

1995-01-01

167

Polarization transfer NMR imaging  

Energy Technology Data Exchange (ETDEWEB)

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

168

Novel NMR and EPR techniques  

Energy Technology Data Exchange (ETDEWEB)

This book delivers a survey of recent research in the fields of condensed matter physics and chemistry based on novel NMR and ESR techniques. Applications include quantum computing, metal nanoparticles, low dimensional magnets, fullerenes as atomic cages, superconductors, porous media, and laser assisted studies. The book is dedicated to Professor Robert Blinc, on the occasion of his seventieth birthday, in appreciation of his remarkable scientific accomplishments in the NMR of condensed matter. (orig.)

Dolinsek, J.; Zumer, S. (eds.) [Ljubljana Univ. (Slovenia). Dept. of Physics]|[Institut Jozef Stefan, Ljubljana (Slovenia); Vilfan, M. [Institut Jozef Stefan, Ljubljana (Slovenia)

2006-07-01

169

Optical pumping and xenon NMR  

Energy Technology Data Exchange (ETDEWEB)

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

Raftery, M.D.

1991-11-01

170

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

171

Optical pumping and xenon NMR  

Energy Technology Data Exchange (ETDEWEB)

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

Raftery, M.D.

1991-11-01

172

NMR Relaxation and Petrophysical Properties  

Science.gov (United States)

NMR relaxation is routinely used in the field of geosciences to give basic petrophysical properties such as porosity, pore size distribution, saturation etc. In this tutorial, we focus on the pore size distribution deduced from NMR. We recall the basic principle used in the interpretation of the NMR signal and compare the results with other standard petrophysical techniques such as mercury pore size distribution, BET specific surface measurements, thin section visualizations. The NMR pore size distribution is a unique information available on water saturated porous media and can give similar results as MICP in certain situations. The scaling of NMR relaxation time distribution (s) into pore sizes (?m) requires the knowledge of the surface relaxivity (?m/s) and we recommend using specific surface measurements as an independent determination of solid surface areas. With usual surface relaxivities, the NMR technique can explore length-scales starting from nano-meters and ending around 100 ?m. Finally, we will introduce briefly recent techniques sensitive to the pore to pore diffusional exchange, providing new information on the connectivity of the pore network, but showing another possibility of discrepancy in the determination of pore size distribution with standard techniques.

Fleury, Marc

2011-03-01

173

NMR study in sodium-hydrogen-C{sub 60} superconductor  

Energy Technology Data Exchange (ETDEWEB)

{sup 23}Na and {sup 1}H NMR studies have been carried out for a Na{sub x}H{sub y}C{sub 60} superconductor. The peak position of the {sup 23}Na NMR spectrum exhibits discontinuous upfield shift of 30 ppm at about 250 K, indicates a first order phase transition. From the line shape of the {sup 23}Na spectrum obtained at 7 K, the quadrupole coupling constant tensor is evaluated to be {vert_bar}e{sup 2}Qq/h{vert_bar} = 3.7 MHz with the asymmetry parameter {eta} = 0.95. The {sup 1}H NMR spectrum suggests an anionic hydrogen state with weakly delocalized nature.

Ogata, H.; Miyajima, S.; Imaeda, K.; Inokuchi, H. [Inst. for Molecular Science, Myodaiji, Okazaki (Japan)

1998-12-31

174

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

175

NMR characterization of shocked quartz  

Energy Technology Data Exchange (ETDEWEB)

We have characterized experimentally and naturally-shocked quartz (both synthetic and natural samples) by solid state nuclear magnetic resonance (NMR) spectroscopy. Relaxation analysis of experimentally-shocked samples provides a means for quantitative characterization of the amorphous/disordered silica component NMR spectra demonstrate that magnetization in both the amorphous and crystalline components follows power-law behavior as a function of recycle time. This observation is consistent with the relaxation of nuclear spins by paramagnetic impurities. A fractal dimension can be extracted from the power-law exponent associated with each phase, and relative abundances can be extracted from integrated intensities of deconvolved peaks. NMR spectroscopy of naturally-shocked sandstone from Meteor Crater, Arizona (USA) led to the discovery of a new amorphous hydroxylated silica phase. Solid state NMR spectra of both experimentally and naturally shocked quartz were unexpectedly rich in microstructural information, especially when combined with relaxation analysis and cross-polarization studies. We suggest solid state NMR as a potentially useful tool for examining shock-induced microstructural changes in other inorganic compounds, with possible implications for shock processing of structural ceramics.

Boslough, M.B.; Cygan, R.T.; Assink, R.A. [Sandia National Labs., Albuquerque, NM (United States); Kirkpatrick, R.J. [Illinois Univ., Urbana, IL (United States)

1994-03-01

176

Pulsed zero field NMR of solids and liquid crystals  

Energy Technology Data Exchange (ETDEWEB)

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

Thayer, A.M.

1987-02-01

177

Pulsed zero field NMR of solids and liquid crystals  

International Nuclear Information System (INIS)

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

1987-01-01

178

Dynamics of amyloid ? fibrils revealed by solid-state NMR.  

UK PubMed Central (United Kingdom)

We have investigated the site-specific backbone dynamics of mature amyloid ? (A?) fibrils using solid-state NMR spectroscopy. Overall, the known ?-sheet segments and the turn linking these two ?-strands exhibit high order parameters between 0.8 and 0.95, suggesting low conformational flexibility. The first approximately eight N-terminal and the last C-terminal residues exhibit lower order parameters between ?0.4 and 0.8. Interestingly, the order parameters increase again for the first two residues, Asp(1) and Ala(2), suggesting that the N terminus could carry some structural importance.

Scheidt HA; Morgado I; Rothemund S; Huster D

2012-01-01

179

Quantitative chemical analysis by NMR  

International Nuclear Information System (INIS)

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

1991-01-01

180

Solid state NMR of polymers  

Energy Technology Data Exchange (ETDEWEB)

The solid state NMR is used not so much in distinguishing chemical species and analyzing components and chemical structure as in collecting the various kind of informations of solid state of polymer, such as conformation, phase structure, a kind of molecular motion, velocity and compatibility by the measurement of relaxation time and linear analysis. The report introduces the interest papers from 1993 to 1995 applied the solid state NMR to synthetic polymers. On the measurement methods, CP/MAS, pulse NMR, heteronuclear correlation (HETCOR) method, wide-line separation (WISE), 2D exchange method and new rotational echo double resonance (REDOR) method are explained. The examples of application such as chemical component, chemical structure, conformation, crosslinked molecule, polymer gel, solid state structure, molecular motion, copolymer, phase structure of polymer blend and orientation are explained, too. (S.Y.)

Tabata, Sachio [Mitsubishi Chemical Corp., Tokyo (Japan)

1996-07-01

 
 
 
 
181

Solid state NMR of polymers  

International Nuclear Information System (INIS)

The solid state NMR is used not so much in distinguishing chemical species and analyzing components and chemical structure as in collecting the various kind of informations of solid state of polymer, such as conformation, phase structure, a kind of molecular motion, velocity and compatibility by the measurement of relaxation time and linear analysis. The report introduces the interest papers from 1993 to 1995 applied the solid state NMR to synthetic polymers. On the measurement methods, CP/MAS, pulse NMR, heteronuclear correlation (HETCOR) method, wide-line separation (WISE), 2D exchange method and new rotational echo double resonance (REDOR) method are explained. The examples of application such as chemical component, chemical structure, conformation, crosslinked molecule, polymer gel, solid state structure, molecular motion, copolymer, phase structure of polymer blend and orientation are explained, too. (S.Y.).

1996-01-01

182

In situ high temperature NMR  

International Nuclear Information System (INIS)

It is important to analyze structure of slag and mold flux in the steel-making process with complicated multi-component systems from the viewpoint of appropriate management of the process and their effective use. Nuclear magnetic resonance (NMR), a nuclide specific method, is a powerful tool for structural analysis of slag with complicated structure. We have developed in situ high temperature NMR technique for analysis of melt structure and dynamics up to 1500 degrees Celsius and some information have been obtained: (1) an averaged coordination number around Al increases with elevating temperature and (2) atomic-scale motion is closely related to macroscopic viscous flow. (author)

2010-01-01

183

Computer system architecture for NMR imaging  

International Nuclear Information System (INIS)

[en] 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

184

Understanding NMR: self-learning manual  

International Nuclear Information System (INIS)

[en] This initiation to the principles of nuclear magnetic resonance (NMR) imaging allows to understand the essential basic physical principles for the realization and the interpretation of an NMR examination. (J.S.)

2000-01-01

185

Push-through Direction Injectin NMR Automation  

Science.gov (United States)

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

186

Radiofrequency and magnet technology in medical NMR  

International Nuclear Information System (INIS)

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

1984-05-02

187

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 ef...

Rossi, Paolo; Swapna, G. V. T.; Huang, Yuanpeng J.; Aramini, James M.; Anklin, Clemens; Conover, Kenith; Hamilton, Keith

188

?-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

189

Petrophysical applications of NMR imaging  

Energy Technology Data Exchange (ETDEWEB)

A system for obtaining high-resolution NMR images of oil field cores is described. Separate proton density and T/sub 2/ relaxation images are obtained to distinguish spatial variations of fluid-filled porosity and the physical nature of the pores. Results are presented for typical sandstones.

Rothwell, W.P.; Vinegar, H.J.

1985-12-01

190

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

International Nuclear Information System (INIS)

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

1985-01-01

191

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

192

An NMR study of 165 Ho in a Pauli paramagnet  

International Nuclear Information System (INIS)

The NMR of 165 Ho in (Ho0.01 Y0.99) was measured on polycrystalline sample at liquid helium temperatures, in applied magnetic field up to 6.0 Tesla. It is shown that the magnetic dipole hyperfine parameter at is highly field dependent and highly quenched at low fields. There is quite a good agreement between the measured and calculated values of at over the field region considered. (author). 8 refs., 1 fig., 1 tab.

1994-01-01

193

Entanglement Witness for NMR Quantum Information Processing  

CERN Multimedia

We discuss the tricky issue of entanglement in NMR quantum information processing and particularly NMR implementation of superdense coding. The signal intensity is introduced as a critical experimental property and an experimental approach for detection of entanglement is proposed based on the signal intesity measurements in a single NMR experiment.

Rahimi, R; Ozawa, M; Kitagawa, M

2004-01-01

194

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

International Nuclear Information System (INIS)

[en] 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

1976-01-01

195

Parameter Estimation  

DEFF Research Database (Denmark)

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

Sales-Cruz, Mauricio; Heitzig, Martina

2011-01-01

196

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

Energy Technology Data Exchange (ETDEWEB)

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

Sternberg, Ulrich, E-mail: Ulrich.Sternberg@ibg.fzk.de; Witter, Raiker; Ulrich, Anne S. [Forschungszentrum Karlsruhe, Institute of Biological Interfaces (Germany)], E-mail: anne.ulrich@ibg.fzk.de

2007-05-15

197

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

International Nuclear Information System (INIS)

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

2007-01-01

198

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

199

Evidence by proton NMR of the alignment of a thermotropic nematic polymer by a magnetic field of ? 1 tesla  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A thermotropic polymer is studied by proton NMR in the solid and in the nematic phases. It is shown that this polymer macroscopically aligns in a magnetic field of ? I T. The corresponding nematic order parameter is estimated.

Volino, F.; Martins, A.F.; Blumstein, R.B.; Blumstein, A.

200

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

Science.gov (United States)

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

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

2011-02-02

 
 
 
 
201

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

UK PubMed Central (United Kingdom)

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

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

2011-05-01

202

A unified view of coherent and incoherent dihydrogen exchange in transition metal hydrides by nuclear resonance and inelastic neutron scattering  

Energy Technology Data Exchange (ETDEWEB)

In this paper a unified view of coherent and incoherent dihydrogen exchange in transition metal hydrides by nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) is presented. It is shown that both exchange processes coexist i.e. do not transform into each other although they may dominate the spectra in different temperature ranges. This superposition is the consequence of the incorporation of the tunnel frequency J of the coherent process into the nuclear two-spin hamiltonian of hydrogen pairs which allows to treat the problem using the well known density matrix theory of NMR line-shapes developed by Alexander and Binsch. It is shown that this theory can also be used to predict the line-shapes of the rotational tunneling transitions observed in the INS spectra of transition metal dihydrogen complexes and that both NMR and INS spectra depend on similar parameters.

Limbach, H.H.; Ulrich, S.; Buntkowsky, G. [Freie Univ. Berlin (Germany). Inst. fuer Organische Chemie; Sabo-Etienne, S.; Chaudret, B. [Toulouse-3 Univ., 31 (France). Lab. de Chimie de Coordination du C.N.R.S.; Kubas, G.J.; Eckert, J. [Los Alamos National Lab., NM (United States)

1995-08-12

203

REDOR NMR for drug discovery.  

UK PubMed Central (United Kingdom)

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.

Cegelski L

2013-08-01

204

Two-dimensional NMR spectrometry  

Energy Technology Data Exchange (ETDEWEB)

This article is the second in a two-part series. In part one (ANALYTICAL CHEMISTRY, May 15) the authors discussed one-dimensional nuclear magnetic resonance (NMR) spectra and some relatively advanced nuclear spin gymnastics experiments that provide a capability for selective sensitivity enhancements. In this article and overview and some applications of two-dimensional NMR experiments are presented. These powerful experiments are important complements to the one-dimensional experiments. As in the more sophisticated one-dimensional experiments, the two-dimensional experiments involve three distinct time periods: a preparation period, t/sub 0/; an evolution period, t/sub 1/; and a detection period, t/sub 2/.

Farrar, T.C.

1987-06-01

205

NMR in pulsed magnetic fields  

International Nuclear Information System (INIS)

The first observation of NMR in the pulsed high magnetic field at the Hochfeldmagnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf (FZD) is reported. The new spectrometer that operates at up to 3.0 GHz is described, as well as its implementation in the pulsed field facility. Free induction decays and spin echo experiments on 1H and 63,65Cu in various magnets are described and discussed in terms of sensitivity and resolution.

2010-01-01

206

High resolution NMR in zeolites  

International Nuclear Information System (INIS)

In this work 29 Si and 27 Al NMR spectroscopy was used to study various types of zeolites. The corresponding spectra were used to measure the Si/Al ratios, to follow chemical modifications induced by acid and hydrothermal treatments, to determine non-equivalent crystallographic sites in highly dealuminated mordenites, and to detect modifications of faujasites due to the insertion of titanium atoms in the lattice. (author)

1991-01-01

207

Hyperpolarized (131)Xe NMR spectroscopy.  

UK PubMed Central (United Kingdom)

Hyperpolarized (hp) (131)Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T(1) relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent (131)Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in (129)Xe SEOP. (131)Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase (131)Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp (131)Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp (131)Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I ? 1/2 nuclei is presented.

Stupic KF; Cleveland ZI; Pavlovskaya GE; Meersmann T

2011-01-01

208

Hyperpolarized (131)Xe NMR spectroscopy.  

Science.gov (United States)

Hyperpolarized (hp) (131)Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T(1) relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent (131)Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in (129)Xe SEOP. (131)Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase (131)Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp (131)Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp (131)Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I ? 1/2 nuclei is presented. PMID:21051249

Stupic, Karl F; Cleveland, Zackary I; Pavlovskaya, Galina E; Meersmann, Thomas

2010-11-03

209

NMR for process control: imaging and localized NMr in soft matter; NMR in der Prozesskontrolle: Bildgebende und unilaterale NMR in weicher Materie  

Energy Technology Data Exchange (ETDEWEB)

NMR or nuclear magnetic resonance is a spectroscopic method which employs magnetic fields and radio-frequency waves. In chemistry it is a standard method for structural analysis, but it is also known in medicine as magnetic resonance tomography which is a well established diagnostic imaging method. Its success in medical imaging derives from the comparatively high sensitivity of protons and the manifold of contrast mechanisms which can be exploited to visualize structures in heterogeneous objects and cannot be resolved by many other methods. The same possibilities exist in materials science comprising product and process control in particular of soft materials like elastomers, polymer melts, and food. While NMR for analysis of chemical structures requires highly homogeneous magnetic fields and thus expensive technology, many issues in materials science and process control can be tackled by NMR in such inhomogeneous fields as generated by simple permanent magnets. In this way inexpensive sensors can be realized with an open geometry. The main application area of such unilateral NMR concepts is in nondestructive analysis of large objects. In addition to static objects the stream lines in flowing liquids, granular media, and complex mixtures can be followed by NMR (flow NMR). The fields of flow NMR and unilateral NMR are addressed in particular in view of development and applications of the NMR MOUSE {sup trademark} (Mobile Universal Surface Explorer). (orig.) [German] Die Kernmagnetische Resonanz (engl.: Nuclear Magnetic Resonance, NMR) ist ein spektroskopisches Verfahren, das mit Radiofrequenz in magnetischen Feldern arbeitet. Bekannt ist vor allem die NMR-Spektroskopie, die in der Chemie als Standardmethode zur Strukturaufklaerung eingesetzt wird, sowie die bildgebende Kernspintomographie, die heutzutage eine etablierte diagnostische Methode in der Medizin darstellt. Der Erfolg der medizinischen Bildgebung ruehrte von der relativ hohen NMR-Empfindlichkeit des Protons und von der Vielfalt an anwendbaren Kontrastmechanismen her, wodurch in heterogenen Objekten Strukturen sichtbar werden, die mit vielen anderen Methoden nicht aufgeloest werden koennen. Dieselben Moeglichkeiten bieten sich fuer die Materialforschung, was die Produkt- und Prozesskontrolle insbesondere weicher Materialien wie Elastomere, Polymerschmelzen und Nahrungsmittel einschliesst. Waehrend der Einsatsz der NMR zur chemischen Strukturanalyse hochgradig homogene Magnetfelder und damit eine kostspielige und empfindliche Technik erfordert, koennen viele Aspekte aus Materialforschung und Prozesskontrolle auch mit inhomogenenen Magnetfeldern untersucht werden, wie sie durch einfache Permanentmagnete erzeugt werden. Dadurch lassen sich preiswerte Messsonden mit offener Geometrie realisieren. Der Hauptanwendungsbereich solcher unilateraler NMR-Konzepte liegt daher in der zerstoerungsfreien Materialanalyse grosser Objekte. Neben statischen Objekten koennen auch Stroemungsvorgaenge von Fluessigkeiten, granularen Medien oder komplexen Stoffgemischen verfolgt werden (Flow-NMR). Die Bereiche Flow-NMR unilaterale NMR werden speziell im Hinblick auf die Anwendungen und Entwicklungen der NMR-MOUSE {sup trademark} (Mobile Universal Surface Explorer) angesprochen. (orig.)

Eymael, R.; Bluemich, B. [Lehrstuhl fuer Makromolekulare Chemie und Zentrum fuer Magnetische Resonanz MARC, RWTH Aachen, Aachen (Germany)

2002-08-01

210

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

2012-06-16

211

NMR metabolomics for assessment of exercise effects with mouse biofluids.  

UK PubMed Central (United Kingdom)

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.

Le Moyec L; Mille-Hamard L; Triba MN; Breuneval C; Petot H; Billat VL

2012-08-01

212

Automated NMR relaxation dispersion data analysis using NESSY  

Directory of Open Access Journals (Sweden)

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

Bieri Michael; Gooley Paul R

2011-01-01

213

Automated NMR relaxation dispersion data analysis using NESSY.  

UK PubMed Central (United Kingdom)

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

Bieri M; Gooley PR

2011-01-01

214

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

Science.gov (United States)

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

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

2013-01-31

215

Timescales in NMR: nuclear site exchange and dynamic NMR  

Energy Technology Data Exchange (ETDEWEB)

An overview of one fundamental aspect of molecular dynamics, magnetization transfer phenomena induced by molecular rate processes (dynamic NMR) is presented: various DNMR procedures (lineshape analysis, transient methods, inversion and saturation transfer, two-dimensional exchange spectroscopy) are brought together under the unifying themes of transverse and longitudinal magnetization transfer experiments. Determination of exchange rates as correlation times are then displayed, preceded by mechanical considerations relating the magnetic site exchange to chemical rate constants. Typical examples of reactions liable to DNMR measurements are given. 16 fig., 223 ref.

Delpuech, J.J. [Nancy-1 Univ., 54 (France)

1994-12-31

216

13C NMR studies of the molecular flexibility of antidepressants  

International Nuclear Information System (INIS)

[en] The solution dynamics of a series of clinically potent antidepressants have been investigated by measuring 13C NMR relaxation parameters. Correlation times and internal motional rates were calculated from spin-lattice relaxation times and nuclear Overhauser effects for the protonated carbons in mianserin, imipramine-like antidepressants, and amitriptyline-like antidepressants. These data were interpreted in terms of overall molecular tumbling, internal rotations, and inherent flexibility of these structures. Of particular interest was the conformational variability of the tricyclic nucleus of the tricyclic antidepressants, where the data indicated a fivefold difference in mobility of the dimethylene bridge of imipramine-like antidepressants relative to amitriptyline-like compounds. The implications of such a difference in internal motions is discussed in relation to previous NMR studies and to the reported differences in pharmacological activity of these antidepressants

1986-01-01

217

Low-frequency NMR with a non-resonant circuit.  

UK PubMed Central (United Kingdom)

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

Hopper T; Mandal S; Cory D; Hürlimann M; Song YQ

2011-05-01

218

The fluorescence properties and NMR analysis of protopine and allocryptopine  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-07-15

219

The fluorescence properties and NMR analysis of protopine and allocryptopine  

International Nuclear Information System (INIS)

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

2011-01-01

220

23Na NMR studies of doped nasicon systems  

Science.gov (United States)

The positions of sodium ions in two doped nasicon systems were investigated by using 23Na solid state NMR techniques. The 23Na NMR spectra with a characteristic powder pattern of quadrupole interaction in the Na 1- XZr 2- XNb XP 3O 12 system indicated that sodium ions occupy Na(1) sites in the crystal structure. For the Na 1 + 2 XZr 2- XMg XP 3O 12 system, excepting the compound with X = 0.1, Gaussian lineshapes were observed due to the distribution of quadrupole parameters and the occupation of both Na(1) and Na(2) sites in the crystal structure. Two sodium sites can be distinguished by applying an inversion-recovery experiment.

Yue, Yong; Deng, Feng; Hu, Hongbin; Ye, Choahui

1995-03-01

 
 
 
 
221

Baseline Correction for NMR Spectroscopic Metabolomics Data Analysis  

Directory of Open Access Journals (Sweden)

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

Xi Yuanxin; Rocke David M

2008-01-01

222

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

223

NMR techniques in biomedical and pharmaceutical analysis.  

UK PubMed Central (United Kingdom)

This article focuses on the description of some of the NMR techniques used in the field of biomedical and pharmaceutical research. Indeed, the NMR method has special characteristics which make it uniquely suitable for these kinds of studies. It is non-selective so that all the low molecular weight compounds in the sample investigated are detected simultaneously in a single run. NMR also provides rich structural information which is an important asset to characterize complex mixture components. NMR is quantitative, i.e. the area of a NMR signal is directly proportional to the number of corresponding nuclei and thus, at variance with other techniques, the response factor is not dependent on the molecular structure. It is also a non-invasive tool that permits in vivo studies in humans. Compared with other techniques, NMR is significantly insensitive, which represents the main drawback of the technique. The recent technological developments of the technique have nevertheless considerably improved its sensitivity. The first part of this article presents an overview of the advantages and limitations of NMR for in vitro quantitative analysis of complex matrices in liquid or semi-solid phases. The second part deals with the NMR-based metabolomics methodology. The third part describes the in vivo clinical magnetic resonance spectroscopy techniques. The fourth part reports some examples of NMR applications in the biomedical and pharmaceutical research fields.

Malet-Martino M; Holzgrabe U

2011-04-01

224

NMR studies of isotopically labeled RNA  

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-12-01

225

NMR of small platinum particles  

International Nuclear Information System (INIS)

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

1980-11-20

226

NMR, DNP and EPR spectrometers  

International Nuclear Information System (INIS)

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

1993-01-01

227

Microscopic origins of the zero-field splitting parameters for 6S(3d5) state ions at tetragonal symmetry crystal field  

International Nuclear Information System (INIS)

The microscopic origin of the zero-field splitting (ZFS) parameters including D and (a+2F/3), for 6S(3d5) state ion at tetragonal symmetry crystal field (CF), 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, have been investigated using the complete diagonalization method (CDM) and the microscopic spin Hamiltonian theory. Although the SO mechanism is the most important one, the contributions to the ZFS parameters D and (a+2F/3) due to the four additional mechanisms: SS, SOO, OO, and the combined SO?SS?SOO?OO coupling mechanism, are appreciable and shall not be omitted. The individual contributions to the ZFS parameters arising from the spin quartet states and the spin doublet states have been analyzed. It is shown that the ZFS parameters D and (a+2F/3) arise from the spin quartet states as well as the combined effects between the spin doublet states and the spin quartets states, whereas the contributions to D and (a+2F/3) from the spin doublet states are zero. Our investigations show that the rank-2 ZFS parameter D primarily results from the spin quartet states, whereas the rank-4 ZFS parameter (a+2F/3) primarily results from the combined effects between the spin doublet states and the spin quartet states. The contributions to the rank-2 ZFS parameter D from the net spin quartet states exceed 95% and the contributions to the rank-4 ZFS parameter (a+2F/3) from the combined effects between the spin doublet states and the spin quartet states exceed 88.2% for the selected ranges of the crystal field parameters. The dependence of the ZFS parameters D and (a+2F/3) on the CF parameters Dq, B20, and Bl40 for 6S(3d5) state ions at tetragonal symmetry have been studied. It is found that the relations hold: |D(-Dq)|?-|D(Dq)|, (a+2F/3)(-Dq)?(a+2F/3)(-Dq) for |Dq|>800 cm-1. The illustrative evaluation is performed for typical crystal materials: Mn2+: Rb2CdF4, Mn2+: K2MgF4, and Mn2+: K2ZnF4 crystals. The good agreements between the theoretical values and the experimental finding are obtained.

2010-12-01

228

Microscopic origins of the zero-field splitting parameters for {sup 6}S(3d{sup 5}) state ions at tetragonal symmetry crystal field  

Energy Technology Data Exchange (ETDEWEB)

The microscopic origin of the zero-field splitting (ZFS) parameters including D and (a+2F/3), for {sup 6}S(3d{sup 5}) state ion at tetragonal symmetry crystal field (CF), 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, have been investigated using the complete diagonalization method (CDM) and the microscopic spin Hamiltonian theory. Although the SO mechanism is the most important one, the contributions to the ZFS parameters D and (a+2F/3) due to the four additional mechanisms: SS, SOO, OO, and the combined SO{approx}SS{approx}SOO{approx}OO coupling mechanism, are appreciable and shall not be omitted. The individual contributions to the ZFS parameters arising from the spin quartet states and the spin doublet states have been analyzed. It is shown that the ZFS parameters D and (a+2F/3) arise from the spin quartet states as well as the combined effects between the spin doublet states and the spin quartets states, whereas the contributions to D and (a+2F/3) from the spin doublet states are zero. Our investigations show that the rank-2 ZFS parameter D primarily results from the spin quartet states, whereas the rank-4 ZFS parameter (a+2F/3) primarily results from the combined effects between the spin doublet states and the spin quartet states. The contributions to the rank-2 ZFS parameter D from the net spin quartet states exceed 95% and the contributions to the rank-4 ZFS parameter (a+2F/3) from the combined effects between the spin doublet states and the spin quartet states exceed 88.2% for the selected ranges of the crystal field parameters. The dependence of the ZFS parameters D and (a+2F/3) on the CF parameters Dq, B{sub 20}, and B{sup l}{sub 40} for {sup 6}S(3d{sup 5}) state ions at tetragonal symmetry have been studied. It is found that the relations hold: |D(-Dq)|{approx}-|D(Dq)|, (a+2F/3)(-Dq){approx}(a+2F/3)(-Dq) for |Dq|>800 cm{sup -1}. The illustrative evaluation is performed for typical crystal materials: Mn{sup 2+}: Rb{sub 2}CdF{sub 4}, Mn{sup 2+}: K{sub 2}MgF{sub 4}, and Mn{sup 2+}: K{sub 2}ZnF{sub 4} crystals. The good agreements between the theoretical values and the experimental finding are obtained.

Yang Ziyuan, E-mail: yziyuan@tom.co [Department of Physics and Information Technology, Baoji University of Arts and Science, Baoji, 721007 Shaanxi (China)

2010-12-01

229

1H-NMR urinalysis  

International Nuclear Information System (INIS)

[en] In an effort to examine the usefulness of 1H-nuclear magnetic resonance (NMR) urinalysis in the diagnosis of congenital metabolic disorders, 70 kinds of urinary metabolites were analysed in relation to the diagnosis of inborn errors of amino acid and organic acid disorders. Homogated decoupling (HMG) method failed to analyze six metabolites within the undetectable range. When non-decoupling method (NON), in which the materials are dissolved in dimethyl sulfoxide, was used, the identification of signals became possible. The combination of HMG and NON methods was, therefore, considered to identify all of the metabolites. When the urine samples, which were obtained from patients with hyperglycerolemia, hyperornithinemia, glutaric acidemia type II, or glycerol kinase deficiency, were analysed by using both HMG and NON methods, abnormally increased urinary metabolites were detected. 1H-NMR urinalysis, if used in the combination of HMG and NON methods, may allow simultanenous screening of inborn errors of metabolism of amino acid and organic acid disorders. (Namekawa, K.)

1988-01-01

230

NMR-profiles of protein solutions.  

Science.gov (United States)

NMR-Profiles are quantitative one-dimensional (1D) presentations of 2D [(15) N,(1) H]-correlation spectra used to monitor the quality of protein solutions prior to and during NMR structure determinations and functional studies. In our current use in structural genomics projects, an NMR-Profile is recorded at the outset of a structure determination, using a uniformly (15) N-labeled microscale sample of the protein. We thus assess the extent to which polypeptide backbone resonance assignments can be achieved with given NMR techniques, for example, conventional triple resonance experiments or APSY-NMR. With the availability of sequence-specific polypeptide backbone resonance assignments in the course of the structure determination, an "Assigned NMR-Profile" is generated, which visualizes the variation of the (15) N-(1) H correlation cross peak intensities along the sequence and thus maps the sequence locations of polypeptide segments for which the NMR line shapes are affected by conformational exchange or other processes. The Assigned NMR-Profile provides a guiding reference during later stages of the structure determination, and is of special interest for monitoring the protein during functional studies, where dynamic features may be modulated during physiological processes. © 2013 Wiley Periodicals, Inc. Biopolymers 99: 825-831, 2013. PMID:23839514

Pedrini, Bill; Serrano, Pedro; Mohanty, Biswaranjan; Geralt, Michael; Wüthrich, Kurt

2013-11-01

231

NMR studies on irradiated lecithin systems  

International Nuclear Information System (INIS)

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

1989-01-01

232

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.

1998-01-01

233

NMR anatomy of the male pelvis  

Energy Technology Data Exchange (ETDEWEB)

Novel imaging methods like the nuclear magnetic resonance (NMR) imaging have to be measured against their representational capacity of anatomico-morphological structures. That is why we conducted a retrospective study involving the assessment of over 150 NMR examinations of the male pelvis for their imaging sensitivity of anatomical fine structures.

Zilch, H.G.; Baumgartl, F.W.

1987-07-01

234

NMR anatomy of the male pelvis  

International Nuclear Information System (INIS)

[en] Novel imaging methods like the nuclear magnetic resonance (NMR) imaging have to be measured against their representational capacity of anatomico-morphological structures. That is why we conducted a retrospective study involving the assessment of over 150 NMR examinations of the male pelvis for their imaging sensitivity of anatomical fine structures. (orig./MG)

1987-01-01

235

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

236

Early history of NMR at Los Alamos  

International Nuclear Information System (INIS)

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

1985-01-01

237

NMR quantum computation with indirectly coupled gates  

CERN Document Server

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

238

NMR imaging of soft tissue tumors  

Energy Technology Data Exchange (ETDEWEB)

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

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

1986-05-01

239

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

240

A frequency determination method for digitized NMR signals  

CERN Multimedia

We present a high precision frequency determination method for digitized NMR FID signals. The method employs high precision numerical integration rather than simple summation as in many other techniques. With no independent knowledge of the other parameters of a NMR FID signal (phase $\\phi$, amplitude $A$, and transverse relaxation time $T_{2}$) this method can determine the signal frequency $f_{0}$ with a precision of $1/(8\\pi^{2}f_{0}^{2}T_{2}^{2})$ if the observation time $T$ is long enough. The method is especially convenient when the detailed shape of the observed FT NMR spectrum is not well defined. When $T_{2}$ is $+\\infty$ and the signal becomes pure sinusoidal, the precision of the method is $3/(2\\pi^{2}f_{0}^{2}T^{2})$ which is one order more precise than a typical frequency counter. Analysis of this method shows that the integration reduces the noise by bandwidth narrowing as in a lock-in amplifier, and no extra signal filters are needed. For a pure sinusoidal signal we find from numerical simulati...

Yan, H; Khatiwada, R; Smith, E; Snow, W M; Fu, C B; Chu, P -H; Gao, H; Zheng, W

2013-01-01

 
 
 
 
241

NMR imaging of the brain: current status and perspectives  

International Nuclear Information System (INIS)

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

1983-01-01

242

NMR imaging of the brain: current status and perspectives  

Energy Technology Data Exchange (ETDEWEB)

Recent developments in NMR imaging of the brain are summarised and preliminary results from cranial examination of 230 patients and 60 volunteers at Hammersmith Hospital are discussed. An NMR scanner is described and three pulse sequences which produce images with varying dependence on the basic imaging parameters proton density, T/sub 1/ and T/sub 2/ are outlined. The first of these pulse sequences, Repeated Free Induction Decay, produces images which demonstrate changes in proton density although these have limited diagnostic utility. The second sequence, Inversion-recovery, produces images which depend on T/sub 1/. These show a high level of grey white matter contrast giving considerable anatomical detail. In addition pathological changes such as infarction, haemorrhage, demyelination and malignancy produce changes in T/sub 1/ enabling lesions to be localised. The third sequence, Spin-echo, produces images dependent on T/sub 2/. Whilst these display little grey-white matter contrast they frequently highlight pathological changes in the brain. Images of these three basic types can also be produced in transverse coronal and sagittal planes. Although much more work remains to be done, NMR imaging appears likely to play a major role in neurological diagnosis within the foreseeable future.

Bydder, G.M.; Steiner, R.E.; Spencer, D.H.; Soleimanpour, C. (Royal Postgraduate Medical School, London (UK); Hammersmith Hospital, London (UK))

1983-01-01

243

An NMR Approach to Structural Proteomics  

Energy Technology Data Exchange (ETDEWEB)

The influx of genomic sequence information has led to the concept of structural proteomics, the determination of protein structures on a genome-wide scale. Here we describe an approach to structural proteomics of small proteins using NMR spectroscopy. Over 500 small proteins from several from several organisms were cloned, expressed , purified and evaluated by NMR . Although there was variability among proteomes, overall 20% of these proteins were found to be readily amendable to NMR structure determination. NMR sample preparation was centralized in on facility , a distributive approach was used for NMR data collection and analysis. Twelve structures are reported here as part of this approach, which allowed us to infer putative functions for several conserved hypothetical proteins.

Yee, Adelinda; Chang, Xiaoqing; Pineda-Lucena, Antonio; Wu, Bin; Semsesi, Anthony; Le , Brian; Ramelot, Theresa A.; Lee, Gregory M.; Bhattacharyya, Sudeepa; Gutierrez, Pablo; Denisov, Aleksej; Lee, Chang-Hun; Cort, John R.; Kozlov, Guennadi; Liao, Jack; Finak, Grzegorz; Chen, Limin; Wishart, David; Lee, Weontae; Mclntosh, Lawrence P.; Gehring, Kalle; Kennedy, Michael A.; Edwards, Aled M.; Arrowsmith, Cheryl H.

2002-02-19

244

Magnetic resonance spectroscopy. 1. Basics of NMR  

International Nuclear Information System (INIS)

[en] Nuclear Magnetic Resonance (NMR) is one of the key methodology of spectroscopy, which is based on the resonation between nuclear spin and radio frequency electric wave under the strong magnetic field. Although NMR began its history as a phenomena of quantum physics, its modern pulse-FT NMR have been widely applied in the area of analytical chemistry, molecular biology, medicine and quantum computing. In this review, the basic theory of NMR is introduced according to the classical magnetization model rather than the view of quantum mechanics. The meaning of the data available from NMR, such as chemical shift, spin coupling, and coupling constant as well as basics of density matrix and product operator formalism is briefly described. (author)

2006-01-01

245

A classical approximation scheme for the ground-state energy of Ising spin Hamiltonians on planar graphs  

CERN Document Server

We show that there exists a classical PTAS (Polynomial Time Approximation Scheme) for the ground-state energy problem of classical Hamiltonians which consist of interactions between the vertices of a planar graph. The problem of determining the ground-state energy exactly is known to be NP-complete for classical Hamiltonians on a 2D square lattice. We discuss the classical and possible quantum running times of our schemes.

Bansal, Nikhil; Terhal, Barbara M

2007-01-01

246

Nonlinear longitudinal NMR in superfluid /sup 3/He  

Energy Technology Data Exchange (ETDEWEB)

The effect of a strong magnetic field on the relative orientation of the field, average spin, and order parameter vectors is considered for longitudinal NMR in superfluid /sup 3/He. It is shown that the orientation is stabilized by strong static fields. Resonant effects are considered for nonlinear parallel ''ringing'' in which there is a slow broadening or stochastic modulation of the ringing frequency. The angle orientation is shown to be stable for the A phase, but in the B phase the stability depends on the remanent static field after the nonlinear ringing has been excited.

Kesaev, V.I.; Ugulava, A.I.

1985-11-01

247

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

248

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

UK PubMed Central (United Kingdom)

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

Kuhn A; Kunze M; Sreeraj P; Wiemhöfer HD; Thangadurai V; Wilkening M; Heitjans P

2012-04-01

249

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

Energy Technology Data Exchange (ETDEWEB)

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

Haber, Agnes

2012-11-01

250

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.)

251

Topics in NMR polarization measurement  

International Nuclear Information System (INIS)

[en] Using a precise circuit theoretical treatment of the series Q-meter, analytical expressions are derived for the relationship between the experimental NMR signal and the RF susceptibility on one hand, and their integrals and the polarization on the other. These are used for the ab initio calculation of the signal-to-noise ratio for deuteron targets, which yield a realistic ultimate calibration precision of 0.1% at 1 K. The experimental signal distortions and drift are discussed, which lead to proposed optimized tuning and design rules, improved circuits, and new applications. Among these are the measurement of 14N polarization in irradiated NH3 targets, and the improvement of the temperature scale around 1 K by one order of magnitude. ((orig.))

1995-03-01

252

Application of NMR to the determination of structures; Application de la RMN a la determination des structures  

Energy Technology Data Exchange (ETDEWEB)

High resolution NMR is an exceptional tool for the determination of the structure of a natural or synthetic molecule. Thanks to the diversity of the measurable parameters, it allows to approach the overall problems raised by the examination of a molecule in solution. The originality of NMR with respect to other spectroscopic techniques concerns its capability to identify most of the atoms of a molecule, their bonds, the skeleton and functional groups of the molecule with their relative spatial arrangement. This article is essentially devoted to the NMR analysis of medium-size organic and bio-organic molecules: available techniques, general strategy, synthetic molecules, biomolecules. (J.S.)

Platzer, N. [Ecole Nationale Superieure de Chimie, 75 - Paris (France); Lab. de RMN Biologique-ICSN-CNRS, 91 - Gif sur Yvette (France)

2002-09-01

253

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

254

Electronic relaxation of paramagnetic metal ions and NMR relaxivity in solution: Critical analysis of various approaches and application to a Gd(III)-based contrast agent  

Science.gov (United States)

The time correlation functions (TCFs) G??(t)? (?=x,y,z) of the electronic spin components of a complexed paramagnetic metal ion give information about the time fluctuations of its zero-field splitting (ZFS) Hamiltonian due to the random dynamics of the coordination polyhedron. These TCFs reflect the electronic spin relaxation which plays an essential role in the inner- and outer-sphere paramagnetic relaxation enhancements of the various nuclear spins in solution. When a static ZFS Hamiltonian is allowed by symmetry, its modulation by the random rotational motion of the complex has a great influence on the TCFs. We discuss several attempts to describe this mechanism and show that subtle mathematical pitfalls should be avoided in order to obtain a theoretical framework, within which reliable adjustable parameters can be fitted through the interpretation of nuclear-magnetic relaxation dispersion experimental results. We underline the advantage of the numerical simulation of the TCFs, which avoids the above difficulties and allows one to include the effect of the transient ZFS for all the relative magnitudes of the various terms in the electron-spin Hamiltonian and arbitrary correlation times. This method is applied for various values of the magnetic field taken to be along the z direction. At low field, contrary to previous theoretical expectations, if the transient ZFS has negligible influence, the longitudinal TCF G?(t)?Gzz(t) has a monoexponential decay with an electronic relaxation time T1e different from 1/(2Dr), Dr being the rotational diffusion coefficient of the complex. At intermediate and high field, the simulation results show that G?(t) still has a monoexponential decay with a characteristic time T1e, which is surprisingly well approximated by a simple analytical expression derived from the Redfield perturbation approximation of the time-independent Zeeman Hamiltonian, even in the case of a strong ZFS where this approximation is expected to fail. These results are illustrated for spins S=1, 3/2, and 5/2 in axial and rhombic symmetries. Finally, the simulation method is applied to the reinterpretation of the water-proton relaxivity profile due to P760-Gd(III), an efficient blood pool contrast agent for magnetic-resonance imaging.

Fries, Pascal H.; Belorizky, Elie

2005-09-01

255

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

256

Structrural analysis of alkylated coal by /sup 1/H and /sup 13/C NMR spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

A method is presented for derivation of a series of structural parameters describing the 'average molecule' of soluble butylated coal. It is based on /sup 1/H and /sup 13/C NMR spectral data, molecular mass measurement and ultimate analysis. Average structural models of coals can be constructed in this way.

Lazarov, L.; Simeonov, M.F.; Marinov, S.P.

1984-11-01

257

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

International Nuclear Information System (INIS)

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

2011-10-21

258

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

International Nuclear Information System (INIS)

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

1979-01-01

259

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

CERN Multimedia

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

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

2003-01-01

260

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

 
 
 
 
261

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

Science.gov (United States)

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

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

2012-08-23

262

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

UK PubMed Central (United Kingdom)

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

Kong X; O'Dell LA; Terskikh V; Ye E; Wang R; Wu G

2012-09-01

263

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.

Ángyán Annamária F; Szappanos Balázs; Perczel András; Gáspári Zoltán

2010-01-01

264

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

DEFF Research Database (Denmark)

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

Anderson, J. Edgar; Heki, Katsuhiko

1987-01-01

265

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

2010-12-07

266

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

Science.gov (United States)

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 °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 T2 of fat versus Tb.Sp: r = -0.716, p bone structure.

Prantner, Viktória; Isaksson, Hanna; Närväinen, Johanna; Lammentausta, Eveliina; Nissi, Mikko J.; Avela, Janne; Gröhn, Olli H. J.; Jurvelin, Jukka S.

2010-12-01

267

Modern NMR techniques for chemistry research  

Energy Technology Data Exchange (ETDEWEB)

This book presents an introduction to modern NMR methods at a level suited to organic and inorganic chemists engaged in the solution of structural and mechanistic problems. The book assumes familiarity only with the simple use of proton and carbon spectra as sources of structural information and describes the advantages of pulse and Fourier transform spectroscopy which form the basis of all modern NMR experiments. Discussion of key experiments is illustrated by numerous examples of the solutions to real problems. The emphasis throughout is on the practical side of NMR.

Derome, A.E.

1987-01-01

268

Graphical programming for pulse automated NMR experiments  

Energy Technology Data Exchange (ETDEWEB)

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

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

1999-01-01

269

Evaluation of exercise muscle energetics by NMR.  

UK PubMed Central (United Kingdom)

Magnetic resonance imaging (MRI) is superior to ultrasonography and X-CT especially in density resolution in soft tissue. 31P NMR provides information on metabolism, which has not been obtained in vivo by conventional methods, such as phosphocreatine (PCr), inorganic phosphate (Pi), ATP, and intracellular pH. We used MRI and 31P NMR spectroscopy to study skeletal muscle metabolism of human and rat. These NMR results suggested that 1) estimation of muscle fiber composition, 2) evaluation of muscle ATP turnover and 3) imaging of local muscle fatigue are possible.

Kuno S; Akisada M; Katsuta S; Mitsumori F

1990-04-01

270

Evaluation of exercise muscle energetics by NMR.  

Science.gov (United States)

Magnetic resonance imaging (MRI) is superior to ultrasonography and X-CT especially in density resolution in soft tissue. 31P NMR provides information on metabolism, which has not been obtained in vivo by conventional methods, such as phosphocreatine (PCr), inorganic phosphate (Pi), ATP, and intracellular pH. We used MRI and 31P NMR spectroscopy to study skeletal muscle metabolism of human and rat. These NMR results suggested that 1) estimation of muscle fiber composition, 2) evaluation of muscle ATP turnover and 3) imaging of local muscle fatigue are possible. PMID:2400464

Kuno, S; Akisada, M; Katsuta, S; Mitsumori, F

1990-04-01

271

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

272

Introduction to some basic aspects of NMR  

International Nuclear Information System (INIS)

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

1992-01-01

273

Resistive NMR of brain stem gliomas  

International Nuclear Information System (INIS)

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

1985-01-01

274

Resistive NMR of brain stem gliomas  

Energy Technology Data Exchange (ETDEWEB)

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

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

1985-01-01

275

The Local Structure of Bismuth-Borates Characterized by 11B MAS NMR  

Science.gov (United States)

Bismuth-borate glasses and vitroceramics belonging to xBi2O3 . (100 - x) B2O3 system, 0 = 60, by heat treatment at 550°C, in which two types of three-coordinated boron are identified. The mean values of the NMR parameters like chemical shift, asymmetry parameter and quadrupolar coupling constant are less influenced by the bismuth/boron ratio, showing that boron structural units are relatively stable on the entire investigated composition range.

Vasilescu, M.; Simon, S.

276

Applications of 1H-NMR relaxometry in experimental liver studies  

International Nuclear Information System (INIS)

Purpose of this study was to investigate applications of proton nuclear magnetic resonance (1H-NMR) relaxometry in experimental medicine. Relaxometry was performed by measurements of spin-lattice (T1) and spin-spin (T2) relaxation time parameters on liver biopsies up to four hours after biopsy excision. Variations of relaxation times due to species and strain, different sample handling and different liver damage models, ethionine fatty liver and paracetamol liver necrosis, were investigated. Cell integrity effects were studied on homogenized liver samples. Relaxation time parameters, especially 'main' components T1A and T2A of biexponential model fit, were identified to react very sensitive after tissue damages as well as to cell viability. Thus, investigation of stored liver grafts was performed in order to evaluate the possibility of a rapid liver graft viability testing method for human liver transplantation surgery by 1H-NMR relaxometry. Another series of measurements was performed to investigate the applicability of isoflurane anesthesia for in vivo NMR experiments. This study proved the good appropriateness of isoflurane for that purpose provided that physiological monitoring and individual adjustment of anesthesia are performed. In these investigations it could be revealed that mainly T1A and T2A are influenced by tissue condition and that different information is inherent in these two parameters, with T2A reflecting tissue viability and changes of tissue conditions very sensitively but rather unspecifically in respect to the damage applied. Based on these results the following future applications of 1H-NMR relaxometry are suggested : (1) model investigations, (2) investigation of given pathologies, (3) investigation of basic requirements for in vivo NMR and (4) application in a liver graft viability testing protocol, which seems to be the most important future application of 1H-NMR relaxometry in medicine. (author)

1992-01-01

277

NMR lineshape in diamagnetic crystals with a rigid lattice  

Energy Technology Data Exchange (ETDEWEB)

The author have constructed a crystallochemical theory for the NMR lineshape in diamagnetic crystals with a rigid lattice. The author shown that the Abragam trial function, exp(-a/sup 2/t/sup 2//2)/sub bt//sup sin bt/, is a physically validated approximation to the real shape of the response of the spin system to a pulsed field. The author have determined the criteria defining the effectiveness of separating the NMR signal into a Guassian of width a and an envelope of width b (b > a). The parameter a/sup 2/ (the second moment of the Gaussian) is inversely proportional to the product of the specific volume V/sub 1/ per nucleus in the lattice times the volume V/sub 0/ of the cluster containing several (tens of) magnetic nuclei which are nearest neighbors to the nucleus under consideration. The parameter b (with width of the rectangle) is calculated according to van Vleck in terms of the theoretically predicted ratio b/sup 2//a/sup 2/. The quantity b/sup 2/ is proportional to V/sub 0//sup -2/. The author gives an estimate for the errors which result from application of the Abragam formula in several limiting cases.

Fedin, E.I.

1987-03-01

278

NMR lineshape in diamagnetic crystals with a rigid lattice  

International Nuclear Information System (INIS)

The author have constructed a crystallochemical theory for the NMR lineshape in diamagnetic crystals with a rigid lattice. The author shown that the Abragam trial function, exp(-a2t2/2)/sub bt//sup sin bt/, is a physically validated approximation to the real shape of the response of the spin system to a pulsed field. The author have determined the criteria defining the effectiveness of separating the NMR signal into a Guassian of width a and an envelope of width b (b > a). The parameter a2 (the second moment of the Gaussian) is inversely proportional to the product of the specific volume V1 per nucleus in the lattice times the volume V0 of the cluster containing several (tens of) magnetic nuclei which are nearest neighbors to the nucleus under consideration. The parameter b (with width of the rectangle) is calculated according to van Vleck in terms of the theoretically predicted ratio b2/a2. The quantity b2 is proportional to V0-2. The author gives an estimate for the errors which result from application of the Abragam formula in several limiting cases

1987-01-01

279

(13)C CPMAS NMR and DFT calculations of anthocyanidins.  

UK PubMed Central (United Kingdom)

Anthocyanidins, red dyes from flower petals and fruits, are beneficial to human health. They attract considerable attention owing to their strong antioxidant and radical scavenging properties, however they are unstable in solution and available in small amounts only. (13)C CP MAS NMR spectra were recorded to characterize solid-state conformation of nine anthocyanidins: apigenidin, pelargonidin, cyanidin, delphinidin, peonidin, malvidin robinetidin, luteolinidin and diosmetinidin chlorides. For some carbons, the solid-state chemical shifts were different from those obtained for solutions, indicating differences in conformation and intermolecular interactions. The principal elements of the (13)C chemical shift tensor were measured for pelargonidin, cyanidin, delphinidin and malvidin chlorides using PASS-2D NMR technique. DFT GIAO calculations of shielding constants were performed for apigenidin and several geometric isomers of pelargonidin. Comparison of experimental (13)C delta(ii) with the theoretical shielding parameters was helpful in predicting the most reliable geometry in the solid state. The cross-polarization parameters were obtained from variable-contact time experiments; T(CH) are longer and the values of T(1)(rho)(H) are shorter in the order: pelargonidin

Wolniak M; Wawer I

2008-07-01

280

(13)C CPMAS NMR and DFT calculations of anthocyanidins.  

Science.gov (United States)

Anthocyanidins, red dyes from flower petals and fruits, are beneficial to human health. They attract considerable attention owing to their strong antioxidant and radical scavenging properties, however they are unstable in solution and available in small amounts only. (13)C CP MAS NMR spectra were recorded to characterize solid-state conformation of nine anthocyanidins: apigenidin, pelargonidin, cyanidin, delphinidin, peonidin, malvidin robinetidin, luteolinidin and diosmetinidin chlorides. For some carbons, the solid-state chemical shifts were different from those obtained for solutions, indicating differences in conformation and intermolecular interactions. The principal elements of the (13)C chemical shift tensor were measured for pelargonidin, cyanidin, delphinidin and malvidin chlorides using PASS-2D NMR technique. DFT GIAO calculations of shielding constants were performed for apigenidin and several geometric isomers of pelargonidin. Comparison of experimental (13)C delta(ii) with the theoretical shielding parameters was helpful in predicting the most reliable geometry in the solid state. The cross-polarization parameters were obtained from variable-contact time experiments; T(CH) are longer and the values of T(1)(rho)(H) are shorter in the order: pelargonidin

Wolniak, M; Wawer, I

2008-07-04

 
 
 
 
281

19F NMR investigation of uranyl difluoride selfassociation in aqueous medium  

International Nuclear Information System (INIS)

[en] Using the method of 19F NMR uranyl difluoride self-association in aqueous solution at different temperatures is studied, the main thermodynamic parameters of the process are determined. It is shown that UO2F2 self-association is limited by dimer formation. Temperature dependence of dimerization constant is plotted and the corresponding change in the mole enthalpy of the process is calculated (?H -36 +- 4 kJ/mole). The suggested method of dimerization constant calculation by 19F NMR data can be used for other fluorine-containing compounds

1988-01-01

282

Addressing the stereochemistry of complex organic molecules by DFT-NMR: vannusal B in retrospective  

Science.gov (United States)

We have employed DFT protocols to calculate the NMR properties of the vannusals, a class of natural products whose structures have been the subject of recent investigations. The originally assigned structure of vannusal B was revised after a long synthetic journey which generated a series of closely related diastereomers. In this work we show how DFT calculations based on density functionals and basis sets designed for the prediction of NMR spectra (M06/pcS-2 level of theory) can be used to reproduce the observed parameters, thereby offering to the synthetic chemist a useful tool to discard or accept putative structures of unknown organic molecules.

Saielli, Giacomo; Nicolaou, K. C.; Ortiz, Adrian; Zhang, Hongjun; Bagno, Alessandro

2011-01-01

283

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

284

NMR studies on irradiated lecithin systems  

International Nuclear Information System (INIS)

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

1988-01-01

285

NMR study of Albemoschus esculentus characterization  

International Nuclear Information System (INIS)

[en] The investigation of the main compounds presented in the Albemoschus esculentus has been carried out employing nuclear magnetic resonance spectroscopy (NMR), using solution and solid state NMR when it one was necessary. The evaluation of NMR data allowed us to characterize the main type of components presented in this kind of sample. It was necessary to use a total information from solid state NMR and also the solution response. From these information we could get that four main components were presented in this sample. One in the shell, that is cellulose, another one between the shell and seeds that is a polysaccharide and in the seed two components were found one is a starch and the second one is an oil, a triacylglycerol. These components are responsible by its physical chemistry properties. (author)

2001-01-01

286

Design of an electromagnet for NMR tomography  

Energy Technology Data Exchange (ETDEWEB)

Magnetic field homogeneity problems of NMR tomography are discussed. The differences between ideal and actual conditions are analyzed and a new design is presented allowing the optimum position of electromagnet coils to be found by a simple algorithm.

Holec, P. (Vysoke Uceni Technicke, Brno (Czechoslovakia))

1983-01-01

287

9th European experimental NMR conference  

International Nuclear Information System (INIS)

[en] 30 oral contributions and 105 posters are presented by abstracts or short communications. The subject matter are various aspects of the experimental technique and various applications of NMR. (qui)

1988-01-01

288

Phosphorus-31 NMR spectroscopy in stereochemical analysis  

Energy Technology Data Exchange (ETDEWEB)

This book is a summary of modern applications of 31p NMR spectroscopy in organic and coordination chemistry. Actually the work is introductory in nature. Data on compounds associated with new frontiers in phosphorus chemistry are also included.

Verkade, J.G.; Quin, L.D.

1987-01-01

289

NMR imaging of the abdomen: technical considerations  

International Nuclear Information System (INIS)

Evaluation of nuclear magnetic resonance (NMR) imaging of the abdomen was done in 41 patients with focal and diffuse disorders of the liver and retroperitoneal and vascular abnormalities. Spin-echo technique was used in each situation with varying time to echo (TE) and repetition rates (TR). No single pulsing technique was optimal in all situations. Three false-negative NMR studies of 22 patients with focal lesions of the liver were attributed to incomplete coverage of the involved area or inappropriate pulsing technique. When appropriate technique was achieved, NMR was equal to computed tomography (CT) in detecting abdominal disorders, except in fatty infiltration of the liver. NMR was superior to CT in imaging vascular anatomy because of the inherent increased contrast produced by the absence of signal from flowing blood and the flexibility of imaging planes

1983-01-01

290

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

291

Proton NMR spectroscopy of sulfmyoglobin.  

UK PubMed Central (United Kingdom)

The 1H NMR spectra of ferrous sulfmyoglobin, metsulfmyoglobin, and ferric cyanosulfmyoglobin were obtained at 300 MHz. Hyperfine-shifted resonances are observed in the case of metsulfmyoglobin and ferric cyanosulfmyoglobin that have line widths and cover a chemical shift range that are comparable to the corresponding forms of normal myoglobin. Two methyl resonances are observed in the spectrum of ferric cyanosulfmyoglobin at 44.19 and 25.48 ppm (25 degrees C, pH 8.3) that have been assigned to heme methyls at the 8- and 5-positions on the basis of pH titration effects homologous to the corresponding methyl resonances in ferric cyanomyoglobin. Examination of aromatic region resonances and the pH titration profiles of histidine resonances lead to the conclusion that the overall conformation of sulfmyoglobin was highly homologous to that of normal myoglobin and afforded assignments of histidine residues of the former. The most likely position for the addition of a sulfur atom to the heme of sulfmyoglobin is pyrrole ring A, with ring B a possible, but less likely, alternative.

Timkovich R; Vavra MR

1985-09-01

292

Proton NMR spectroscopy of sulfmyoglobin.  

Science.gov (United States)

The 1H NMR spectra of ferrous sulfmyoglobin, metsulfmyoglobin, and ferric cyanosulfmyoglobin were obtained at 300 MHz. Hyperfine-shifted resonances are observed in the case of metsulfmyoglobin and ferric cyanosulfmyoglobin that have line widths and cover a chemical shift range that are comparable to the corresponding forms of normal myoglobin. Two methyl resonances are observed in the spectrum of ferric cyanosulfmyoglobin at 44.19 and 25.48 ppm (25 degrees C, pH 8.3) that have been assigned to heme methyls at the 8- and 5-positions on the basis of pH titration effects homologous to the corresponding methyl resonances in ferric cyanomyoglobin. Examination of aromatic region resonances and the pH titration profiles of histidine resonances lead to the conclusion that the overall conformation of sulfmyoglobin was highly homologous to that of normal myoglobin and afforded assignments of histidine residues of the former. The most likely position for the addition of a sulfur atom to the heme of sulfmyoglobin is pyrrole ring A, with ring B a possible, but less likely, alternative. PMID:4074688

Timkovich, R; Vavra, M R

1985-09-10

293

NMR study of trialuminide intermetallics  

Science.gov (United States)

We present a systematic study of the DO22-structure trialuminide intermetallic alloys using 27Al NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times on Al3Ti, Al3V, Al3Nb, and Al3Ta have been identified. Knight-shift tensors were isolated by observation of quadrupole satellite lines and fitting to the central-transition powder patterns. The results are associated with the local electronic density of states for each crystallographic site. Universally small isotropic Knight shifts and long T1's are consistent with low Fermi-surface densities of states indicating the importance of Fermi-surface features for the phase stability of these alloys. Larger anisotropic Knight shifts occurring at aluminum site I indicate strong hybridization at this site, and the electric-field-gradient tensors confirm the strong ab plane bonding configuration. Local-moment magnetism is found in Al3V, yet electrically this material appears very similar to the other DO22 aluminides.

Lue, Chin-Shan; Chepin, Suchitra; Chepin, James; Ross, Joseph H., Jr.

1998-03-01

294

NMR study of hydride systems  

International Nuclear Information System (INIS)

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

1980-01-01

295

Molecular dynamics of solid cortisol studied by NMR  

Science.gov (United States)

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

Andrew, E. R.

296

NMR imaging of thermally polarized helium-3 gas.  

UK PubMed Central (United Kingdom)

It is shown that thermally polarized 3He gas can be used to measure important physical parameters and to design, test, and tune imaging sequences. The bulk values of T1, T2, and the diffusion coefficient were measured in a glass cell containing a mixture of helium-3 (0.8 bar) and oxygen (0.2 bar). They were found to be T1 = 7 s, T2 = 2.4 s, and D = 1.6 cm2 s(-1). The relaxation times T2* and T1 and the apparent diffusion coefficient of thermally polarized helium-3 gas were measured in the rat lung, and these parameters were used to design a helium-3 optimized multi-spin-echo sequence which was shown to increase the signal-to-noise ratio sufficiently to obtain the first NMR-images of thermally polarized helium-3 in the rat lung.

Kober F; Koenigsberg B; Belle V; Viallon M; Leviel JL; Delon A; Ziegler A; Décorps M

1999-06-01

297

One and two dimensional NMR spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

The book starts from fundamental principles of modern NMR spectroscopy, describing the instrumentation and its optimum use, and extends to the latest developments such as inverse measurements. Emphasis is laid on problem-solving. Basic aspects of the operation of modern NMR spectrometers as shimming, probe tuning, and methods for improvement of resolution and sensitivity are described. At the end of each chapter problems and worked solutions are given. (author). 116 refs.; figs.; tabs.

Atta-ur-Rahman.

1989-01-01

298

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

299

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

1992-01-01

300

A microscale protein NMR sample screening pipeline  

International Nuclear Information System (INIS)

[en] 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 8-35 ?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.

2010-01-01

 
 
 
 
301

A microscale protein NMR sample screening pipeline.  

Science.gov (United States)

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 microg in 8-35 microl 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. PMID:19915800

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

2009-11-14

302

Physiological parameters  

International Nuclear Information System (INIS)

The physiological characteristics of man depend on the intake, metabolism and excretion of stable elements from food, water, and air. The physiological behavior of natural radionuclides and radionuclides from nuclear weapons testing and from the utilization of nuclear energy is believed to follow the pattern of stable elements. Hence information on the normal physiological processes occurring in the human body plays an important role in the assessment of the radiation dose received by man. Two important physiological parameters needed for internal dose determination are the pulmonary function and the water balance. In the Coordinated Research Programme on the characterization of Asian population, five participants submitted data on these physiological characteristics - China, India, Japan, Philippines and Viet Nam. During the CRP, data on other pertinent characteristics such as physical and dietary were simultaneously being collected. Hence, the information on the physiological characteristics alone, coming from the five participants were not complete and are probably not sufficient to establish standard values for the Reference Asian Man. Nonetheless, the data collected is a valuable contribution to this research programme

303

A simple method for analyzing 51V solid-state NMR spectra of complex systems.  

Science.gov (United States)

Five vanadium complexes as models for biological systems were investigated using (51)V-MAS-NMR spectroscopy. All spectra show an uncommon line shape, which can be attributed to a shorter relaxation time of the satellite transition in contrast to the central one. A method for the reliable analysis of such kind of spectra is presented for the first time and the most important NMR parameters of the investigated complexes (quadrupolar coupling constant C(Q), asymmetry of the EFG tensor ?(Q), isotropic chemical shift ?(iso), chemical shift anisotropy ?(?) and asymmetry of the CSA tensor ?(?)) are presented. These results are of particular importance with respect to the analysis of the (51)V-MAS-NMR spectra of vanadium moieties in biological matrices such as vanadium chloroperoxidase, which show hitherto unexplained low intensity of the satellite sideband pattern. PMID:21601435

Fenn, Annika; Wächtler, Maria; Breitzke, Hergen; Buchholz, Axel; Lippold, Ines; Plass, Winfried; Buntkowsky, Gerd

2011-05-14

304

A simple method for analyzing 51V solid-state NMR spectra of complex systems.  

UK PubMed Central (United Kingdom)

Five vanadium complexes as models for biological systems were investigated using (51)V-MAS-NMR spectroscopy. All spectra show an uncommon line shape, which can be attributed to a shorter relaxation time of the satellite transition in contrast to the central one. A method for the reliable analysis of such kind of spectra is presented for the first time and the most important NMR parameters of the investigated complexes (quadrupolar coupling constant C(Q), asymmetry of the EFG tensor ?(Q), isotropic chemical shift ?(iso), chemical shift anisotropy ?(?) and asymmetry of the CSA tensor ?(?)) are presented. These results are of particular importance with respect to the analysis of the (51)V-MAS-NMR spectra of vanadium moieties in biological matrices such as vanadium chloroperoxidase, which show hitherto unexplained low intensity of the satellite sideband pattern.

Fenn A; Wächtler M; Breitzke H; Buchholz A; Lippold I; Plass W; Buntkowsky G

2011-09-01

305

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

International Nuclear Information System (INIS)

[en] 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)

2008-01-01

306

Iron Responsive Element RNA Flexibility Described by NMR and Isotropic Reorientational Eigenmode Dynamics  

International Nuclear Information System (INIS)

The first example of the application of reorientational eigenmode dynamics (RED) to RNA is shown here for the small and floppy Iron Responsive Element (IRE) RNA hairpin. Order parameters calculated for bases and riboses from a 12 ns molecular dynamics trajectory are compared to experimentally determined order parameters from 13C-1H NMR relaxation experiments, and shown to be in qualitative agreement. Given the small size of the IRE hairpin and its very flexible loop, isotropic RED (iRED) was also used to analyze the trajectory in order to describe its dynamic motions. iRED analysis shows that the global and internal dynamics of the IRE are not rigorously separable, which will result in inaccurate experimental order parameters. In addition, the iRED analysis described the many correlated motions that comprise the dynamics of the IRE RNA. The combined use of NMR relaxation, RED, and iRED provide a uniquely detailed description of IRE RNA dynamics

2005-01-01

307

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

UK PubMed Central (United Kingdom)

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

Huang J; MacKerell AD Jr

2013-09-01

308

Resolution-by-proxy: a simple measure for assessing and comparing the overall quality of NMR protein structures  

International Nuclear Information System (INIS)

In protein X-ray crystallography, resolution is often used as a good indicator of structural quality. Diffraction resolution of protein crystals correlates well with the number of X-ray observables that are used in structure generation and, therefore, with protein coordinate errors. In protein NMR, there is no parameter identical to X-ray resolution. Instead, resolution is often used as a synonym of NMR model quality. Resolution of NMR structures is often deduced from ensemble precision, torsion angle normality and number of distance restraints per residue. The lack of common techniques to assess the resolution of X-ray and NMR structures complicates the comparison of structures solved by these two methods. This problem is sometimes approached by calculating “equivalent resolution” from structure quality metrics. However, existing protocols do not offer a comprehensive assessment of protein structure as they calculate equivalent resolution from a relatively small number (

2012-01-01

309

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

Science.gov (United States)

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

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

2009-01-01

310

Research on physical properties using optical pump NMR: NMR of C-60FET and nanotubes  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) is recognized as a very powerful instrument for study of microstructure and electronic states, but the essential weak point is in its poor sensitivity. In order to overcome this weak point and to able to apply NMR to nanometer size region, a light irradiation method was introduced. In light pumping NMR, NMR is measured during irradiation of circularly polarized light being equivalent to transition energies of an electron system. The light pumping NMR instrument was set up, and experiments were tentatively carried out to silicon and GaAs wafers. Remarkable enhancement of signal intensity was observed in the experiment, but the mechanism of the enhancement was not fully resolved. (Y. Kazumata)

2004-01-01

311

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

312

NMR studies of human plasma high density lipoproteins  

Energy Technology Data Exchange (ETDEWEB)

Molecular motions and conformation(s) of lipids in human plasma high density lipoproteins, HDL/sub 2/ (density = 1.063-1.125 g/mL) and HDL/sub 3/ (density = 1.125-1.21 g/mL) have been studied by /sup 2/H- and /sup 31/P NMR. The acyl chain organization of lipids was quantified by the C-/sup 2/H bond order parameter, S/sub CD/, which measures the time-averaged angular excursions of the C-/sup 2/H bond about the axis of motional averaging. Selectively deuterated palmitic acids were incorporated (approx.5 mol%) into the surface monolayer of HDL/sub 2/ and HDL/sub 3/. Cholesteryl palmitate selectively deuterated along the acyl chain was incorporated into the core of reconstituted HDL. The /sup 2/H NMR line widths (430-350 Hz) for the C/sub 2/-C/sub 6/ deuterons are consistent with an average ester conformation wherein the ester acyl chain is extended. Using a radius, R = 4.0 nm, obtained from electron microscopy, a line width y = 2350 Hz for a static all-trans C/sup 2/H/sub 2/ was calculated, indicating the presence of considerable ester chain motions in the HDL core. The lateral diffusion coefficient of phospholipids in HDL/sub 2/ was (2 +/- 1) x 10/sup -8/cm/sup 2/s/sup -1/ at approx.25/sup 0/C. The /sup 31/P residual chemical shift anisotropy (CSA), calculated from the field and viscosity dependence of /sup 31/P NMR line width, was approx.69 ppm and approx.75 ppm, respectively. These values are larger than the CSA approx.45 ppm in phospholipids bilayers, suggesting conformational and/or motional differences of the head group in the two systems.

Parmar, Y.I.

1985-01-01

313

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; M. Müller-Petke

2012-01-01

314

NMR techniques in the study of cardiovascular structure and functions  

Energy Technology Data Exchange (ETDEWEB)

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

Osbakken, M.; Haselgrove, J.

1987-01-01

315

BOOK REVIEW: NMR Imaging of Materials  

Science.gov (United States)

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

Blümich, Bernhard

2003-09-01

316

Magic angle spinning NMR of paramagnetic proteins.  

Science.gov (United States)

Metal ions are ubiquitous in biochemical and cellular processes. Since many metal ions are paramagnetic due to the presence of unpaired electrons, paramagnetic molecules are an important class of targets for research in structural biology and related fields. Today, NMR spectroscopy plays a central role in the investigation of the structure and chemical properties of paramagnetic metalloproteins, linking the observed paramagnetic phenomena directly to electronic and molecular structure. A major step forward in the study of proteins by solid-state NMR came with the advent of ultrafast magic angle spinning (MAS) and the ability to use (1)H detection. Combined, these techniques have allowed investigators to observe nuclei that previously were invisible in highly paramagnetic metalloproteins. In addition, these techniques have enabled quantitative site-specific measurement of a variety of long-range paramagnetic effects. Instead of limiting solid-state NMR studies of biological systems, paramagnetism provides an information-rich phenomenon that can be exploited in these studies. This Account emphasizes state-of-the-art methods and applications of solid-state NMR in paramagnetic systems in biological chemistry. In particular, we discuss the use of ultrafast MAS and (1)H-detection in perdeuterated paramagnetic metalloproteins. Current methodology allows us to determine the structure and dynamics of metalloenzymes, and, as an example, we describe solid-state NMR studies of microcrystalline superoxide dismutase, a 32 kDa dimer. Data were acquired with remarkably short times, and these experiments required only a few milligrams of sample. PMID:23506094

Knight, Michael J; Felli, Isabella C; Pierattelli, Roberta; Emsley, Lyndon; Pintacuda, Guido

2013-03-18

317

Magic angle spinning NMR of paramagnetic proteins.  

UK PubMed Central (United Kingdom)

Metal ions are ubiquitous in biochemical and cellular processes. Since many metal ions are paramagnetic due to the presence of unpaired electrons, paramagnetic molecules are an important class of targets for research in structural biology and related fields. Today, NMR spectroscopy plays a central role in the investigation of the structure and chemical properties of paramagnetic metalloproteins, linking the observed paramagnetic phenomena directly to electronic and molecular structure. A major step forward in the study of proteins by solid-state NMR came with the advent of ultrafast magic angle spinning (MAS) and the ability to use (1)H detection. Combined, these techniques have allowed investigators to observe nuclei that previously were invisible in highly paramagnetic metalloproteins. In addition, these techniques have enabled quantitative site-specific measurement of a variety of long-range paramagnetic effects. Instead of limiting solid-state NMR studies of biological systems, paramagnetism provides an information-rich phenomenon that can be exploited in these studies. This Account emphasizes state-of-the-art methods and applications of solid-state NMR in paramagnetic systems in biological chemistry. In particular, we discuss the use of ultrafast MAS and (1)H-detection in perdeuterated paramagnetic metalloproteins. Current methodology allows us to determine the structure and dynamics of metalloenzymes, and, as an example, we describe solid-state NMR studies of microcrystalline superoxide dismutase, a 32 kDa dimer. Data were acquired with remarkably short times, and these experiments required only a few milligrams of sample.

Knight MJ; Felli IC; Pierattelli R; Emsley L; Pintacuda G

2013-09-01

318

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)

2002-01-01

319

Electric field gradients in fluoride crystalline powders: correlation of NMR measurements with ab initio calculations.  

UK PubMed Central (United Kingdom)

Electric field gradients (EFG) of 23Na and 27Al in three model fluoride crystalline powders AlF3, Na3AlF6 and Na5Al3F14 were computed using the density functional based electronic structure code WIEN97 and compared to values derived from nuclear magnetic resonance (NMR). First, results of measurements of 23Na and 27Al quadrupolar parameters in AlF3, Na3AlF6 and Na5Al3F14 were revisited by using high-resolution solid-state NMR. To determine chemical shifts and quadrupolar parameters with a high precision, the experimental procedure involved magic angle spinning, satellite transition spectroscopy and multi-quanta techniques applied to the quadrupolar nuclei together with a computed reconstruction of the NMR spectra. The large discrepancies which appear between previously published results in some cases, justify the use of ab initio calculations of the corresponding EFG using the WIEN97 code based on the known structural data of the crystalline phases. The agreement obtained between these calculations and the experimental results which is better than 10% in almost all cases supports the reliability of the present NMR investigations and of the crystallographic data.

Silly G; Legein C; Buzaré JY; Calvayrac F

2004-06-01

320

Electric field gradients in fluoride crystalline powders: correlation of NMR measurements with ab initio calculations.  

Science.gov (United States)

Electric field gradients (EFG) of 23Na and 27Al in three model fluoride crystalline powders AlF3, Na3AlF6 and Na5Al3F14 were computed using the density functional based electronic structure code WIEN97 and compared to values derived from nuclear magnetic resonance (NMR). First, results of measurements of 23Na and 27Al quadrupolar parameters in AlF3, Na3AlF6 and Na5Al3F14 were revisited by using high-resolution solid-state NMR. To determine chemical shifts and quadrupolar parameters with a high precision, the experimental procedure involved magic angle spinning, satellite transition spectroscopy and multi-quanta techniques applied to the quadrupolar nuclei together with a computed reconstruction of the NMR spectra. The large discrepancies which appear between previously published results in some cases, justify the use of ab initio calculations of the corresponding EFG using the WIEN97 code based on the known structural data of the crystalline phases. The agreement obtained between these calculations and the experimental results which is better than 10% in almost all cases supports the reliability of the present NMR investigations and of the crystallographic data. PMID:15028274

Silly, G; Legein, C; Buzaré, J Y; Calvayrac, F

2004-06-01

 
 
 
 
321

31Phosphorus NMR studies of renal membrane phospholipids  

International Nuclear Information System (INIS)

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

1988-01-01

322

Determination of dipole coupling constants using heteronuclear multiple quantum NMR  

International Nuclear Information System (INIS)

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

1982-01-01

323

Determination of dipole coupling constants using heteronuclear multiple quantum NMR  

Energy Technology Data Exchange (ETDEWEB)

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

Weitekamp, D.P.; Garbow, J.R.; Pines, A.

1982-09-15

324

25Mg NMR site analysis in metals and intermetallics.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) of the low abundance and low gyromagnetic ratio isotope (25)Mg, I=5/2, 2.606MHz/T, 10% abundant, is shown here to provide an informative probe for phase identification, site symmetry and site multiplicity of the intermetallic compounds which occur as strengthening precipitate phases in lightweight alloys. The intermetallics discussed here, Mg(17)Al(12), MgZn(2), Mg(2)Al(3) and Al(2)CuMg, are the final equilibrium precipitate phases in a number of Mg- and Al-based heat-treatable alloys. The (25)Mg spectra of Mg in Al-10at%Mg alloy show the progressive precipitation of Mg(2)Al(3) from Mg in solid solution as a function of annealing time at 150 degrees C. Also reported are (25)Mg spectra for CuMg(2), Mg(44)Al(15)Zn(41) and Mg(2)Sn, along with the counter atom (67)Zn and (63)Cu NMR spectra for MgZn(2) and CuMg(2). All spectra are simulated to determine nuclear interaction parameters and confirm site occupancy. PMID:19307108

Bastow, T J; Celotto, S

2009-02-26

325

25Mg NMR site analysis in metals and intermetallics.  

UK PubMed Central (United Kingdom)

Nuclear magnetic resonance (NMR) of the low abundance and low gyromagnetic ratio isotope (25)Mg, I=5/2, 2.606MHz/T, 10% abundant, is shown here to provide an informative probe for phase identification, site symmetry and site multiplicity of the intermetallic compounds which occur as strengthening precipitate phases in lightweight alloys. The intermetallics discussed here, Mg(17)Al(12), MgZn(2), Mg(2)Al(3) and Al(2)CuMg, are the final equilibrium precipitate phases in a number of Mg- and Al-based heat-treatable alloys. The (25)Mg spectra of Mg in Al-10at%Mg alloy show the progressive precipitation of Mg(2)Al(3) from Mg in solid solution as a function of annealing time at 150 degrees C. Also reported are (25)Mg spectra for CuMg(2), Mg(44)Al(15)Zn(41) and Mg(2)Sn, along with the counter atom (67)Zn and (63)Cu NMR spectra for MgZn(2) and CuMg(2). All spectra are simulated to determine nuclear interaction parameters and confirm site occupancy.

Bastow TJ; Celotto S

2009-07-01

326

NMR-based metabolomics of mammalian cell and tissue cultures  

Energy Technology Data Exchange (ETDEWEB)

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

Aranibar, Nelly; Borys, Michael; Mackin, Nancy A.; Ly, Van; Abu-Absi, Nicholas; Abu-Absi, Susan [Bristol-Myers Squibb Company (United States); Niemitz, Matthias [PERCH Solutions Ltd. (Finland); Schilling, Bernhard; Li, Zheng Jian; Brock, Barry; Russell, Reb J.; Tymiak, Adrienne; Reily, Michael D., E-mail: michael.reily@bms.com [Bristol-Myers Squibb Company (United States)

2011-04-15

327

NMR-based metabolomics of mammalian cell and tissue cultures  

International Nuclear Information System (INIS)

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

2011-01-01

328

NMR studies of aging effects in palladium tritide  

International Nuclear Information System (INIS)

This paper presents Nuclear Magnetic Resonance (NMR) studies of aging phenomena in palladium tritide. 3He NMR relaxation parameters have been measured as a function of temperature for 6-, 13-, and 22-month-old beta phase palladium tritide. The most significant result of this study is the observation of a solid/fluid phase transition near 250 K of 3He that has accumulated in the PdTx substrate via triton decay. Although the existence of solid helium at relatively high temperatures had been predicted for helium in metals, it had not previously been confirmed in any metal/helium system. The observed melting temperatures, together with the known equation of state for 4He, allow a determination of the helium density as a function of age. The atomic density obtained in this way is approximately 2.0 times that of palladium metal, agreeing with densities inferred from dilatometric measurements of other metal tritides and also with predictions based on the concept of dislocation loop punching by highly overpressurized He bubbles. The 3He signal in the 22-month-old sample was sufficiently strong to allow a detailed study of melting as a function of temperature, and provides information on the distribution of densities over the ensemble of bubbles.

1988-01-01

329

High field NMR in low dimensional quantum antiferromagnets  

Energy Technology Data Exchange (ETDEWEB)

We present high field NMR studies of the field induced magnetic ordering in a few quasi-1D quantum antiferromagnets. Cu{sub 2}(C{sub 5}H{sub 12}N{sub 2}){sub 2}Cl{sub 4} (Cu(Hp)Cl) has for long been considered as the archetype of a strong coupling spin-ladder system. We show that it can be well understood in the framework of a spin-ladder with a staggered Dzyaloshinskii-Moriya (DM) interaction on the rungs. CuBr{sub 4}(C{sub 5}H{sub 12}N){sub 2} (BPCB) is made of regular spin-ladders (without DM interaction) weakly coupled together. Its phase diagram between the two quantum critical field H{sub c1} and H{sub c2} is fully dominated by the H dependence of the Luttinger liquid parameters of the ladders. We also briefly report the NMR evidence for the existence of an unconventional quantum ground state in the 1/3 magnetization plateau in the frustrated diamond chain compound Cu{sub 3}(CO{sub 3}){sub 2}(OH){sub 2} (azurite).

Berthier, Claude; Klanjsek, Martin; Kraemer, Steffen; Horvatic, Mladen [Grenoble High Magnetic Field Laboratory (GHMFL), CNRS, BP (France); Mayaffre, Hadrien [Lab. de Spectrometrie Physique, UJF Grenoble I (France)

2008-07-01

330

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

331

NMR detection with an atomic magnetometer  

CERN Document Server

We demonstrate detection of NMR signals using a non-cryogenic atomic magnetometer and describe several novel applications of this technique. A water free induction decay (FID) signal in a 0.5 $\\mu$T field is detected using a spin-exchange-relaxation-free K magnetometer and the possibility of using a multi-channel magnetometer for 3-D MRI requiring only a single FID signal is described. We also demonstrate detection of less than $10^{13}$ $^{129}$Xe atoms whose NMR signal is enhanced by a factor of 540 due to Fermi-contact interaction with K atoms. This technique allows detection of less than $10^{9}$ $^{129}$Xe spins in a flowing system suitable for remote NMR applications.

Savukov, I M

2004-01-01

332

Wide-line NMR and protein hydration.  

UK PubMed Central (United Kingdom)

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).

Tompa K; Bokor M; Tompa P

2012-01-01

333

Remote tuning of NMR probe circuits.  

UK PubMed Central (United Kingdom)

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 VD; Conradi MS

2000-05-01

334

Deuterium NMR, induced and intrinsic cholesteric lyomesophases  

International Nuclear Information System (INIS)

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

1982-01-01

335

Hyperpolarized xenon for NMR and MRI applications.  

UK PubMed Central (United Kingdom)

Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) suffer from intrinsic low sensitivity because even strong external magnetic fields of ~10 T generate only a small detectable net-magnetization of the sample at room temperature (1). Hence, most NMR and MRI applications rely on the detection of molecules at relative high concentration (e.g., water for imaging of biological tissue) or require excessive acquisition times. This limits our ability to exploit the very useful molecular specificity of NMR signals for many biochemical and medical applications. However, novel approaches have emerged in the past few years: Manipulation of the detected spin species prior to detection inside the NMR/MRI magnet can dramatically increase the magnetization and therefore allows detection of molecules at much lower concentration (2). Here, we present a method for polarization of a xenon gas mixture (2-5% Xe, 10% N2, He balance) in a compact setup with a ca. 16000-fold signal enhancement. Modern line-narrowed diode lasers allow efficient polarization (7) and immediate use of gas mixture even if the noble gas is not separated from the other components. The SEOP apparatus is explained and determination of the achieved spin polarization is demonstrated for performance control of the method. The hyperpolarized gas can be used for void space imaging, including gas flow imaging or diffusion studies at the interfaces with other materials (8,9). Moreover, the Xe NMR signal is extremely sensitive to its molecular environment (6). This enables the option to use it as an NMR/MRI contrast agent when dissolved in aqueous solution with functionalized molecular hosts that temporarily trap the gas (10,11). Direct detection and high-sensitivity indirect detection of such constructs is demonstrated in both spectroscopic and imaging mode.

Witte C; Kunth M; Döpfert J; Rossella F; Schröder L

2012-01-01

336

Hyperpolarized xenon for NMR and MRI applications.  

Science.gov (United States)

Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) suffer from intrinsic low sensitivity because even strong external magnetic fields of ~10 T generate only a small detectable net-magnetization of the sample at room temperature (1). Hence, most NMR and MRI applications rely on the detection of molecules at relative high concentration (e.g., water for imaging of biological tissue) or require excessive acquisition times. This limits our ability to exploit the very useful molecular specificity of NMR signals for many biochemical and medical applications. However, novel approaches have emerged in the past few years: Manipulation of the detected spin species prior to detection inside the NMR/MRI magnet can dramatically increase the magnetization and therefore allows detection of molecules at much lower concentration (2). Here, we present a method for polarization of a xenon gas mixture (2-5% Xe, 10% N2, He balance) in a compact setup with a ca. 16000-fold signal enhancement. Modern line-narrowed diode lasers allow efficient polarization (7) and immediate use of gas mixture even if the noble gas is not separated from the other components. The SEOP apparatus is explained and determination of the achieved spin polarization is demonstrated for performance control of the method. The hyperpolarized gas can be used for void space imaging, including gas flow imaging or diffusion studies at the interfaces with other materials (8,9). Moreover, the Xe NMR signal is extremely sensitive to its molecular environment (6). This enables the option to use it as an NMR/MRI contrast agent when dissolved in aqueous solution with functionalized molecular hosts that temporarily trap the gas (10,11). Direct detection and high-sensitivity indirect detection of such constructs is demonstrated in both spectroscopic and imaging mode. PMID:22986346

Witte, Christopher; Kunth, Martin; Döpfert, Jörg; Rossella, Federica; Schröder, Leif

2012-09-06

337

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)

2004-01-01

338

NMR characterization of high cis polybutadiene  

International Nuclear Information System (INIS)

In this work a laboratory scale process was studied for the production of polybutadiene with high content of cis-1,4 repeating units. A Ziegler-Natta catalytic system constituted of neodymium versatate (Nd), tert-butyl chloride (Cl) and an organo aluminium compound (Al) was used. The influence of the organo aluminium (co catalyst) type, Al/Nd and Cl/Nd molar ratios on the polymer microstructure was verified. The polymers microstructures were characterized by 13C nuclear magnetic resonance (NMR). The maximum content of cis-1,4 repeating units determined by 13C-NMR was 97.37%. (author)

2004-01-01

339

Contrast agents and spectroscopic probes in NMR.  

UK PubMed Central (United Kingdom)

The demand for higher diagnostic specificity has led to the increased use of "foreign" agents to increase tissue contrast and/or spectroscopic sensitivity in NMR studies. The primary agents used to enhance tissue contrast in NMR imaging are paramagnetic. They cause a decrease in the proton T1 of H2O leading to enhanced signal intensity. This effect depends on the large gyromagnetic ratio of the electron, the number of unpaired electrons, the concentration of paramagnetic ions, the number of coordinated water molecules, and the rate of exchange of water. Spectroscopic enhancement has relied primarily on attempt at isotopic enrichment (usually C-13), which causes a direct increase in signal.

Koutcher JA; Burt CT; Lauffer RB; Brady TJ

1984-04-01

340

Using NMR to Measure Fractal Dimensions  

CERN Multimedia

A comment is made on the recent PFG NMR measurements by Stallmach, et al. on water-saturated sands [Phys. Rev. Lett. 88, 105505 (2002)]. It is pointed out that the usual law for the time-dependent diffusion coefficient D(t) used by these authors is not valid for a fractal surface. It is shown that (1-D(t)/D0) \\~ t^[(3-Ds)/2] at short times for a surface of fractal dimension Ds, where D0 is the bulk diffusion coefficient. Preliminary PFG NMR data on water saturated limestone and plastic beads are presented to illustrate this analysis.

Candela, D; Wong, Po-zen

2002-01-01

 
 
 
 
341

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 T2O, CH3COOT or CF3COOT. 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

342

NMR relaxation times of natural rubber latex  

International Nuclear Information System (INIS)

[en] NMR relaxation times T sub 1 and T sub 2 of natural rubber latex have been measured at 25 degree C on a pulsed NMR spectrometer. The work focuses on the variation of the relaxation times with the amount of water content from 0% to 50%. The water content was adjusted by centrifuging and removing a certain amount of water from the sample. The data were analysed using a biexponential fitting procedure which yields simultaneously either T sub 1a and T sub 1b or T sub 2a and T sub 2b. The amount of solid was compared with the known amount of dry rubber content

1994-01-01

343

From crystalline to glassy gallium fluoride materials: an NMR study of 69Ga and 71Ga quadrupolar nuclei.  

UK PubMed Central (United Kingdom)

Owing to the implementation of acquisition techniques specific for nuclei with very large quadrupolar interaction (full shifted echo and variable offset cumulative spectra (VOCS)), NMR spectra of 69Ga and 71Ga are obtained in crystallised (PbGaF5, Pb3Ga2F12, Pb9Ga2F24 and CsZnGaF6) and glassy (PbF2-ZnF2-GaF3) gallium fluorides. Simulations of both static (full echo or VOCS) and 15 kHz MAS spectra allow to obtain consistent determinations of isotropic chemical shifts and very large quadrupolar parameters (nu(Q) up to 14 MHz). In the crystalline compounds whose structures are unknown, the number and the local symmetry of the different gallium sites are tentatively worked out. For the glassy systems, a continuous Czjzek's distribution of the NMR quadrupolar parameters accounts for the particular shape of the NMR spectrum.

Bureau B; Silly G; Buzaré JY; Legein C; Massiot D

1999-09-01

344

From crystalline to glassy gallium fluoride materials: an NMR study of 69Ga and 71Ga quadrupolar nuclei.  

UK PubMed Central (United Kingdom)

Owing to the implementation of acquisition techniques specific for nuclei with very large quadrupolar interaction (full shifted echo and variable offset cumulative spectra (VOCS)), NMR spectra of 69Ga and 71Ga are obtained in crystallised (PbGaF5, Pb3Ga2F12, Pb9Ga2F24 and CsZnGaF6) and glassy (PbF2-ZnF2-GaF3) gallium fluorides. Simulations of both static (full echo or VOCS) and 15 kHz MAS spectra allow to obtain consistent determinations of isotropic chemical shifts and very large quadrupolar parameters (nuQ up to 14 MHz). In the crystalline compounds whose structures are unknown, the number and the local symmetry of the different gallium sites are tentatively worked out. For the glassy systems, a continuous Czjzek's distribution of the NMR quadrupolar parameters accounts for the particular shape of the NMR spectrum.

Bureau B; Silly G; Buzaré JY; Legein C; Massiot D

1999-11-01

345

119Sn, 13C and 1H NMR studies of aryloxy- and arylthio(1-butyl)stannanes  

International Nuclear Information System (INIS)

Two series of compounds were prepared and studied by means of 119 Sn, 13C, and 1H NMR spectroscopy, viz aryloxy-and N-heteroaryloxytris(1-butyl)stannanes and their thio analogues Bu3SnER, and diaryloxy- and di (N-heteroaryloxy)bis(1-butyl)stannanes and their thio analogues Bu2Sn(ER)2, where E means oxygen or sulfur, Bu is 1-butyl, R=phenyl, 1-naphthyl, or 8-quinolyl. Based on a comparison of NMR spectral parameters of both series of organotin compounds, and on a comparison with NMR spectral parameters of analogous, purely organic compounds CH3ER, the consequences are discussed of the presence of tin atoms in the organotin substituents and of nitrogen heteroatoms in the aromatic systems, and the ensuing structure of the organotin compounds is considered. (author). 4 tabs., 31 refs

1989-01-01

346

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

347

Studies of domain morphology in segmented polyurethanes by pulsed NMR.  

Science.gov (United States)

A new technique based on the Goldman-Shen pulse sequence with varying preparation interval is proposed for the study of domain morphology of segmented polyurethanes. The results of numerical calculations of the magnetization recovery in different models of domain morphology show that the method provides new information about the domain morphology which is beyond the reach of the conventional Goldman-Shen experiment. A close agreement of the theoretical predictions with the experimental data on samples of segmented polyurethanes with a fixed molecular mass of the hard blocks and variable molecular mass of the soft blocks reinforces the above statement. The resulting structural parameters obtained by this new NMR technique are compared with the data from the small-angle X-ray scattering (SAXS) method. PMID:8906412

Idiyatullin, D S; Khozina, E V; Smirnov, V S

1996-08-01

348

Hyperfine interaction in USi3: 29Si NMR study  

International Nuclear Information System (INIS)

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

1995-01-01

349

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

350

NMR microscopy of heavy metal absorption in calcium alginate beads  

Energy Technology Data Exchange (ETDEWEB)

In recent years, heavy metal uptake by biopolymer gels, such as Cal-Alginate or chitosan, has been studied by various methods. This is of interest because such materials might be an alternative to synthetical ion-exchange resins in the treatment of industrial waste waters. Most of the work done in this field consisted of studies of equilibrium absorption of different heavy metal ions with dependence on various experimental parameters. In some publications, the kinetics of absorption were studied, too. However, no experiments on the spatial distribution of heavy metals during the absorption process are known to us. Using Cu as an example, it is demonstrated in this article that NMR microscopy is an appropriate tool for such studies. By the method presented here, it is possible to monitor the spatial distribution of heavy metal ions with a time resolution of about 5 min and a spatial resolution of 100 {mu}m or even better. 14 refs., 10 figs.

Nestle, N.; Kimmich, R. [Universitaet Ulm (Germany)

1996-01-01

351

Genetic algorithms and solid state NMR pulse sequences.  

UK PubMed Central (United Kingdom)

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(2)(1) 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(2)(1) pulse sequence. The optimised pulse sequence breaks the synchronicity between r.f. pulses and sample spinning.

Bechmann M; Clark J; Sebald A

2013-03-01

352

Recommendations of the wwPDB NMR Validation Task Force.  

UK PubMed Central (United Kingdom)

As methods for analysis of biomolecular structure and dynamics using nuclear magnetic resonance spectroscopy (NMR) continue to advance, the resulting 3D structures, chemical shifts, and other NMR data are broadly impacting biology, chemistry, and medicine. Structure model assessment is a critical area of NMR methods development, and is an essential component of the process of making these structures accessible and useful to the wider scientific community. For these reasons, the Worldwide Protein Data Bank (wwPDB) has convened an NMR Validation Task Force (NMR-VTF) to work with wwPDB partners in developing metrics and policies for biomolecular NMR data harvesting, structure representation, and structure quality assessment. This paper summarizes the recommendations of the NMR-VTF, and lays the groundwork for future work in developing standards and metrics for biomolecular NMR structure quality assessment.

Montelione GT; Nilges M; Bax A; Güntert P; Herrmann T; Richardson JS; Schwieters CD; Vranken WF; Vuister GW; Wishart DS; Berman HM; Kleywegt GJ; Markley JL

2013-09-01

353

Microscopic insights into the NMR relaxation-based protein conformational entropy meter.  

UK PubMed Central (United Kingdom)

Conformational entropy is a potentially important thermodynamic parameter contributing to protein function. Quantitative measures of conformational entropy are necessary for an understanding of its role but have been difficult to obtain. An empirical method that utilizes changes in conformational dynamics as a proxy for changes in conformational entropy has recently been introduced. Here we probe the microscopic origins of the link between conformational dynamics and conformational entropy using molecular dynamics simulations. Simulation of seven proteins gave an excellent correlation with measures of side-chain motion derived from NMR relaxation. The simulations show that the motion of methyl-bearing side chains are sufficiently coupled to that of other side chains to serve as excellent reporters of the overall side-chain conformational entropy. These results tend to validate the use of experimentally accessible measures of methyl motion-the NMR-derived generalized order parameters-as a proxy from which to derive changes in protein conformational entropy.

Kasinath V; Sharp KA; Wand AJ

2013-10-01

354

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

International Nuclear Information System (INIS)

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

1987-01-01

355

Strange kinetics, porous media, and NMR  

International Nuclear Information System (INIS)

Nuclear magnetic resonance (NMR) techniques cover a broad range of length and time scales on which dynamic properties of fluids confined in porous media can be investigated. This report refers to field-cycling NMR relaxometry, field gradient NMR diffusometry and NMR microscopy. The objective was to examine diffusion, hydrodynamic dispersion, flow, and thermal convection under the influence of geometrical confinements and surface interactions in porous media. The anomalous character of these phenomena will be demonstrated and discussed in comparison with computer simulations and theoretical concepts. The first part of this presentation is devoted to nanoporous samples. It is shown that molecular Levy walks along inner surfaces occur under certain conditions. Mutual 'obstruction' of molecules in molecular sieves and zeolites is another source of diffusion anomaly known as single-file diffusion which can be described by Gaussian propagators with a diffusion coefficient depending on time in a certain limit. In the case of polymers confined in narrow artificial tubes of a porous solid matrix, the characteristics of reptation were experimentally verified. The second part mainly refers to 'trapping' effects as a source of anomalous transport characterised by non-Gaussian propagators. Model objects fabricated on the basis of percolation cluster models were examined with respect to flow, diffusion, thermal convection and hydrodynamic dispersion. The elucidation of transport laws in model systems of well defined and mathematically describable geometries is considered to be a promising way for the exploration of the structure/dynamics relationship in porous media as a long-term objective

2002-11-01

356

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

357

Ensemble quantum computing by NMR spectroscopy  

Science.gov (United States)

A quantum computer (QC) can operate in parallel on all its possible inputs at once, but the amount of information that can be extracted from the result is limited by the phenomenon of wave function collapse. We present a new computational model, which differs from a QC only in that the result of a measurement is the expectation value of the observable, rather than a random eigenvalue thereof. Such an expectation value QC can solve nondeterministic polynomial-time complete problems in polynomial time. This observation is significant precisely because the computational model can be realized, to a certain extent, by NMR spectroscopy on macroscopic ensembles of quantum spins, namely molecules in a test tube. This is made possible by identifying a manifold of statistical spin states, called pseudo-pure states, the mathematical description of which is isomorphic to that of an isolated spin system. The result is a novel NMR computer that can be programmed much like a QC, but in other respects more closely resembles a DNA computer. Most notably, when applied to intractable combinatorial problems, an NMR computer can use an amount of sample, rather than time, which grows exponentially with the size of the problem. Although NMR computers will be limited by current technology to exhaustive searches over only 15 to 20 bits, searches over as much as 50 bits are in principle possible, and more advanced algorithms could greatly extend the range of applicability of such machines.

Cory, David G.; Fahmy, Amr F.; Havel, Timothy F.

1997-01-01

358

Analysis of goyazensolide, in solution, by NMR  

International Nuclear Information System (INIS)

[en] The identification and characterization of goyazensolide, a sesquiterpenic lactone, from Lychnophora passerina, was made based on comparative study of its spectral data. The methods used in this work include 1 H and 13 C NMR besides IR and UV spectroscopies. Data on chemical shifts as well as coupling constants were presented and analysed, furthermore the results were discussed

1995-01-01

359

NMR Study of Aramid Model Compounds.  

Science.gov (United States)

An NMR has been done on benzanilide, terephthalamide, isophthalamide, and their sodium and methylated derivatives. A data base of chemical shift values for aromatic carbons ipso, ortho, meta and para to C6H5CONH- and C6H5NCO-functional groups was generate...

L. J. Mathias M. Yoneyama W. L. Jarrett

1990-01-01

360

NMR analysis of a fluorocarbon copolymer  

International Nuclear Information System (INIS)

[en] 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

1987-01-01

 
 
 
 
361

NMR based geographical characterization of roasted coffee.  

UK PubMed Central (United Kingdom)

The increasing attention for food quality and safety led to develop several analytical techniques suitable to address these demands. Coffee has been already demonstrated to represent a worldwide appreciated beverage and its high economical value could induce frauds or adulteration practices involving both compositional and geographical aspects. In the last years, metabolic profiling revealed to be suitable to face the quality determination of food matrices and NMR confirmed its potentiality in metabolites characterization. The present study reports the capability of NMR spectroscopy to investigate the metabolite content of roasted Coffea arabica samples from the three main production areas, America, Africa and Asia. OPLS-DA models performed on (1)H NMR data led to a clear separation of samples according to their origin: fatty acids, chlorogenic acids and lactate and finally acetate and trigonelline resulted the main compounds characterizing the American, African and Asian samples respectively. The analytical approach here presented confirmed the potentiality of the joined NMR analysis and statistical treatments in quality determination of food matrices.

Consonni R; Cagliani LR; Cogliati C

2012-01-01

362

Dynamic nuclear polarization surface enhanced NMR spectroscopy.  

UK PubMed Central (United Kingdom)

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

Rossini AJ; Zagdoun A; Lelli M; Lesage A; Copéret C; Emsley L

2013-09-01

363

Dynamic nuclear polarization surface enhanced NMR spectroscopy.  

Science.gov (United States)

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

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

2013-03-21

364

NMR spectroscopy and surface tension measurements applied to the study of self-association of casopitant mesylate, a novel NK1 antagonist.  

UK PubMed Central (United Kingdom)

The aggregation behaviour of casopitant mesylate, a new NK1 antagonist drug, was investigated by means of NMR spectroscopy and surface tension measurements. The critical micelle concentration (CMC) in glycine buffer at pH 3.5 was determined by analyzing the (1)H NMR chemical shifts variation and the surface tension in function of the concentration in a series of solutions. The temperature dependence of the CMC was also evaluated by NMR spectroscopy as well as the thermodynamic parameters contributing to the aggregation discussed. Surface tension measurements were conducted as well in the formulation conditions, e.g. in the presence of sodium chloride.

Provera S; Beato S; Cimarosti Z; Turco L; Casazza A; Caivano G; Marchioro C

2011-01-01

365

Application of NMR spectroscopy in characterising the local environments of heavy metals in wastes  

Energy Technology Data Exchange (ETDEWEB)

In order to give a good description of lead sites in waste materials, various crystalline compounds with known crystallographic structure have been characterized by nuclear magnetic resonance spectroscopy. {sup 207}Pb NMR chemical shift has been correlated to structural parameters related to its local environment, in the case of a lead-model-glass, with a composition close to the composition of a vitrified waste

Fayon, F.; Farnan, I.; Bessada, C.; Coutures, J.P. [Centre National de la Recherche Scientifique (CNRS), 45 - Orleans-la-Source (France). Centre de Recherches sur la Physique des Hautes Temperatures; Jalvy, P.; Cote, B. [Centre de Recherches et d`Essais pour l`Environnement et de Dechet, 78 - Limay (France)

1997-12-31

366

NMR Spin-Spin Relaxation as Kinetics in Spin Phase Space  

Energy Technology Data Exchange (ETDEWEB)

A new approach is presented that treats NMR spin-spin relaxation as kinetics in spin phase space. The approach is applied to free induction decay (FID) in solids containing equivalent nuclear spins 1/2 . The description obtained does not involve adjustable parameters. As an example, the calculation is performed for {sup 19}F FID in CaF{sub 2} , and the results are in good agreement with experiment. {copyright} {ital 1997} {ital The American Physical Society}

Fine, B.V. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

1997-12-01

367

NMR Spin-Spin Relaxation as Kinetics in Spin Phase Space  

CERN Multimedia

A new approach is presented that treats NMR spin-spin relaxation as kinetics in spin phase space. The approach is applied to free induction decay (FID) in solids containing equivalent nuclear spins 1/2. The description obtained does not involve adjustable parameters. As an example, the calculation is performed for the fluorine FID in calcium fluoride, and the results are in good agreement with experiment.

Fine, B V

1997-01-01

368

Spatial mapping of translational diffusion coefficients by the NMR imaging technique  

Energy Technology Data Exchange (ETDEWEB)

The authors have developed a method for the spatial mapping of an additional NMR parameter, the molecular translational diffusion coefficient, and have illustrated it by presenting their results using a hen's egg as phantom. The technique will permit the measurement of perfusion and blood flow rates. The technique must by used with care on living subjects as the sequence is sensitive to all types of movement.

Taylor, D.G.; Bushell, M.C. (Surrey Univ., Guildford (UK). Dept. of Physics)

1985-04-01

369

Superoxygenated Water as an Experimental Sample for NMR Relaxometry  

Science.gov (United States)

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

Nestle, Nikolaus; Dakkouri, Marwan; Rauscher, Hubert

2004-01-01

370

A low-field NMR tool for soil moisture  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Due to the increasing need in hydrology for techniques which could measure partial saturation of soils in a non-invasive way, the development of a low-field NMR sensor has been undertaken in this dissertation. Based on prior designs of low-field NMR instruments like the NMR-MOUSE and the well loggi...

Sucre Reyes, Oscar Elías

371

Optimised polyolefin branch quantification by 13 C NMR spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantitative branch determination in polyolefins by solid- and melt-state 13C NMR has been investigated. Both methods were optimised toward sensitivity per unit time. While solid-state NMR was shown to give quick albeit only qualitative results, melt-state NMR allowed highly time efficient accurate ...

Klimke, Katja

372

Nuclear magnetic resonance parameters of water hexamers.  

UK PubMed Central (United Kingdom)

Nuclear magnetic resonance (1)H, (16)O, and (17)O chemical shifts, as well as (17)O quadrupolar parameters in several isomers of water hexamer clusters, are studied using density functional theory calculations and the gauge including projector augmented wave (GIPAW) pseudopotential method. The prism, cage, book, bag, chain, and two cyclic isomers are investigated, and structures with (16)O and (17)O nuclei are examined. It is found that the hydrogen and oxygen chemical shifts show a substantial variation. In six more stable hexamers, all quadrupole coupling constants decrease and asymmetry parameters increase in a comparison with bulk water, whereas a chain isomer shows an opposite behavior. The values of NMR parameters are in reasonable agreement with existing results obtained by more computationally demanding methods.

Bilalbegovi? G

2010-01-01

373

Structural investigations on betacyanin pigments by LC NMR and 2D NMR spectroscopy.  

UK PubMed Central (United Kingdom)

Four betacyanin pigments were analysed by LC NMR and subjected to extensive NMR characterisation after isolation. Previously, low pH values were applied for NMR investigations of betalains resulting in rapid degradation of the purified substances thus preventing extensive NMR studies. Consequently, up to now only one single (13)C NMR spectrum of a betalain pigment, namely that of neobetanin (=14,15-dehydrobetanin), was available. Because of its sufficient stability under highly acidic conditions otherwise detrimental for betacyanins, this pigment remained an exemption. Since betalains are most stable in the pH range of 5-7, a new solvent system has been developed allowing improved data acquisition through improved pigment stability at near neutral pH. Thus, not only (1)H, but for the first time also partial (13)C data of betanin, isobetanin, phyllocactin and hylocerenin isolated from red-purple pitaya [Hylocereus polyrhizus (Weber) Britton & Rose, Cactaceae] could be indirectly obtained by gHSQC- and gHMQC-NMR experiments.

Stintzing FC; Conrad J; Klaiber I; Beifuss U; Carle R

2004-02-01

374

Structural investigations on betacyanin pigments by LC NMR and 2D NMR spectroscopy.  

Science.gov (United States)

Four betacyanin pigments were analysed by LC NMR and subjected to extensive NMR characterisation after isolation. Previously, low pH values were applied for NMR investigations of betalains resulting in rapid degradation of the purified substances thus preventing extensive NMR studies. Consequently, up to now only one single (13)C NMR spectrum of a betalain pigment, namely that of neobetanin (=14,15-dehydrobetanin), was available. Because of its sufficient stability under highly acidic conditions otherwise detrimental for betacyanins, this pigment remained an exemption. Since betalains are most stable in the pH range of 5-7, a new solvent system has been developed allowing improved data acquisition through improved pigment stability at near neutral pH. Thus, not only (1)H, but for the first time also partial (13)C data of betanin, isobetanin, phyllocactin and hylocerenin isolated from red-purple pitaya [Hylocereus polyrhizus (Weber) Britton & Rose, Cactaceae] could be indirectly obtained by gHSQC- and gHMQC-NMR experiments. PMID:14759534

Stintzing, Florian C; Conrad, Jürgen; Klaiber, Iris; Beifuss, Uwe; Carle, Reinhold

2004-02-01

375

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

UK PubMed Central (United Kingdom)

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

Takeda K

2008-06-01

376

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

Science.gov (United States)

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

Takeda, Kazuyuki

2008-02-29

377

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

Science.gov (United States)

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

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

2013-10-01

378

Observation of "hidden" magnesium: first-principles calculations and 25Mg solid-state NMR of enstatite.  

UK PubMed Central (United Kingdom)

(25)Mg NMR parameters have been determined for two polymorphs of enstatite (MgSiO(3)), an important magnesium silicate phase present as a major component of the Earth's upper mantle. The crystal structures of both polymorphs contain two crystallographically distinct magnesium sites; however, only a single resonance is observed in (25)Mg MAS NMR spectra recorded at 14.1 and 20.0 T. First-principles calculations performed on geometry-optimised crystal structures reveal that the quadrupolar interaction for the second site is expected to be very large, resulting in extensive broadening of the spectral resonance, explaining its apparent absence in the NMR spectrum. (25)Mg QCPMG NMR experiments employing variable offset cumulative spectroscopy (VOCS) are used to observe the broadened site and enable measurement of NMR parameters. The large difference in quadrupolar interaction between the two crystallographic magnesium sites is rationalised qualitatively in terms of the distortion of the local coordination environment as well as longer-range effects using a simple point charge model.

Griffin JM; Berry AJ; Ashbrook SE

2011-09-01

379

Observation of "hidden" magnesium: first-principles calculations and 25Mg solid-state NMR of enstatite.  

Science.gov (United States)

(25)Mg NMR parameters have been determined for two polymorphs of enstatite (MgSiO(3)), an important magnesium silicate phase present as a major component of the Earth's upper mantle. The crystal structures of both polymorphs contain two crystallographically distinct magnesium sites; however, only a single resonance is observed in (25)Mg MAS NMR spectra recorded at 14.1 and 20.0 T. First-principles calculations performed on geometry-optimised crystal structures reveal that the quadrupolar interaction for the second site is expected to be very large, resulting in extensive broadening of the spectral resonance, explaining its apparent absence in the NMR spectrum. (25)Mg QCPMG NMR experiments employing variable offset cumulative spectroscopy (VOCS) are used to observe the broadened site and enable measurement of NMR parameters. The large difference in quadrupolar interaction between the two crystallographic magnesium sites is rationalised qualitatively in terms of the distortion of the local coordination environment as well as longer-range effects using a simple point charge model. PMID:21871785

Griffin, John M; Berry, Andrew J; Ashbrook, Sharon E

2011-08-11

380

1H NMR signal broadening in spectra of alkane molecules adsorbed on MFI-type zeolites.  

Science.gov (United States)

The anisotropic behavior of C1-C6 alkane molecules adsorbed in MFI zeolite was studied by 1H nuclear magnetic resonance (NMR) using single-pulse excitation, Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence, Hahn echo (HE) pulse sequence, and magic-angle spinning. The molecular order parameter was obtained by both static 2H NMR spectroscopy and molecular simulations. This yields an order parameter in the range of 0.28-0.42 for linear alkanes in MFI zeolite, whereas the parameter equals zero for FAU zeolite with a cubic symmetry. Thus, in the case of a zeolite with a non-cubic symmetry like MFI, the mobility of the molecules in one crystallite cannot fully average the dipolar interaction. As a consequence, transverse nuclear magnetization as revealed in the echo attenuation notably deviates from a mono-exponential decay. This information is of particular relevance for the performance of pulsed field gradient (PFG) NMR diffusion experiments, since the occurrence of non-exponential magnetization attenuation could be taken as an indication of the existence of different molecules or of molecules in different states of mobility. PMID:18406581

Romanova, Ekaterina E; Krause, Cordula B; Stepanov, Alexander G; Wilczok, Ursula; Schmidt, Wolfgang; van Baten, Jasper M; Krishna, Rajamani; Pampel, André; Kärger, Jörg; Freude, Dieter

2008-03-15

 
 
 
 
381

Computational estimation of tricarboxylic acid cycle fluxes using noisy NMR data from cardiac biopsies.  

UK PubMed Central (United Kingdom)

BACKGROUND: The aerobic energy metabolism of cardiac muscle cells is of major importance for the contractile function of the heart. Because energy metabolism is very heterogeneously distributed in heart tissue, especially during coronary disease, a method to quantify metabolic fluxes in small tissue samples is desirable. Taking tissue biopsies after infusion of substrates labeled with stable carbon isotopes makes this possible in animal experiments. However, the appreciable noise level in NMR spectra of extracted tissue samples makes computational estimation of metabolic fluxes challenging and a good method to define confidence regions was not yet available. RESULTS: Here we present a computational analysis method for nuclear magnetic resonance (NMR) measurements of tricarboxylic acid (TCA) cycle metabolites. The method was validated using measurements on extracts of single tissue biopsies taken from porcine heart in vivo. Isotopic enrichment of glutamate was measured by NMR spectroscopy in tissue samples taken at a single time point after the timed infusion of 13C labeled substrates for the TCA cycle. The NMR intensities for glutamate were analyzed with a computational model describing carbon transitions in the TCA cycle and carbon exchange with amino acids. The model dynamics depended on five flux parameters, which were optimized to fit the NMR measurements. To determine confidence regions for the estimated fluxes, we used the Metropolis-Hastings algorithm for Markov chain Monte Carlo (MCMC) sampling to generate extensive ensembles of feasible flux combinations that describe the data within measurement precision limits. To validate our method, we compared myocardial oxygen consumption calculated from the TCA cycle flux with in vivo blood gas measurements for 38 hearts under several experimental conditions, e.g. during coronary artery narrowing. CONCLUSIONS: Despite the appreciable NMR noise level, the oxygen consumption in the tissue samples, estimated from the NMR spectra, correlates with blood-gas oxygen uptake measurements for the whole heart. The MCMC method provides confidence regions for the estimated metabolic fluxes in single cardiac biopsies, taking the quantified measurement noise level and the nonlinear dependencies between parameters fully into account.

Hettling H; Alders DJ; Heringa J; Binsl TW; Groeneveld AB; van Beek JH

2013-01-01

382

Solid state NMR of biopolymers and synthetic polymers  

International Nuclear Information System (INIS)

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

1995-01-01

383

An Introduction to a Hyphenated Technique: HPLC-SPE-NMR  

Directory of Open Access Journals (Sweden)

Full Text Available Liquid chromatography–solid phase extraction–nuclear magnetic resonance (HPLC-SPE-NMR), noveland highly promising hyphenated technique which is based on post-column analyte trapping by solidphaseextraction. The analytes are subsequently eluted from the SPE cartridges using deuteratedsolvents. This indirect HPLC-NMR hyphenation offers numerous advantages compared to direct HPLCNMRmethods. Multiple trapping leads to a dramatic increase of analyte amounts available for NMR,enabling acquisition of high-quality 2D NMR data within a short time. The well-defined NMR solventconditions make spectra comparisons feasible, which means databases and spectra catalogues.

Patel RC; Dixit PB; Vyas HA; Patel NK; Sharda AM

2013-01-01

384

[Solid-state NMR spectroscopy and its pharmaceutical use].  

UK PubMed Central (United Kingdom)

Liquid-state NMR spectroscopy has become an essential analytical tool in almost all fields of chemical research. However, the scope of NMR spectroscopy is not confined to the analysis of fluids. The progress in the investigation of solid samples is remarkably fast and solid-state NMR has developed to a high performance method. The majority of drug substances and products manufactured in the pharmaceutical industry are formulated in solid state, their analysis gains the increasing potential of solid-state NMR spectroscopy. The aim of this work is to survey the basics of solid-state NMR and to highlight some pharmaceutical applications focusing on polymorphism.

Marosi A; Szalay Z; Demeter A

2010-01-01

385

[Solid-state NMR spectroscopy and its pharmaceutical use].  

Science.gov (United States)

Liquid-state NMR spectroscopy has become an essential analytical tool in almost all fields of chemical research. However, the scope of NMR spectroscopy is not confined to the analysis of fluids. The progress in the investigation of solid samples is remarkably fast and solid-state NMR has developed to a high performance method. The majority of drug substances and products manufactured in the pharmaceutical industry are formulated in solid state, their analysis gains the increasing potential of solid-state NMR spectroscopy. The aim of this work is to survey the basics of solid-state NMR and to highlight some pharmaceutical applications focusing on polymorphism. PMID:20443364

Marosi, Attila; Szalay, Zsófia; Demeter, Adám

2010-01-01

386

Squid detected NMR and MRI at ultralow fields  

Energy Technology Data Exchange (ETDEWEB)

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

Clarke, John (Berkeley, CA); McDermott, Robert (Louisville, CO); Pines, Alexander (Berkeley, CA); Trabesinger, Andreas Heinz (CH-8006 Zurich, CH)

2007-05-15

387

13C NMR tracers in neurochemistry: implications for molecular imaging.  

UK PubMed Central (United Kingdom)

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 hyperpolarized substrates for NMR spectroscopy and imaging. Some illustrative applications are described, both in vitro and in vivo.

Rodrigues TB; Fonseca CP; Castro MM; Cerdán S; Geraldes CF

2009-12-01

388

TELEMETRY THROUGH REMOTE DETECTION OF NMR-ACTIVE PARTICLES  

UK PubMed Central (United Kingdom)

Various methods of telemetry for nuclear magnetic resonance applications are described. NMR-active particles are introduced into a system which is to undergo an NMR measurement. In various embodiments, the NMR-active particles have a resonance peak in a spectral region which is substantially free from any NMR signal originating from material native to the system. In some embodiments, the NMR-active particles are chemically functionalized to target a constituent within the system. In certain applications, changes in the detected resonance peak can be used to quantify certain characteristics about the system, e.g., a concentration of an analyte, whether a targeted constituent is present within the system.

MARCUS CHARLES M; MARMUREK JONATHAN; APTEKAR JACOB W; VON MALTZAHN GEOFFREY

389

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

UK PubMed Central (United Kingdom)

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

Jacob D; Deborde C; Moing A

2013-06-01

390

Connecting discrete stereoclusters by using DFT and NMR spectroscopy: the case of nivariol.  

UK PubMed Central (United Kingdom)

The structural determination of small organic molecules is mainly undertaken by using NMR techniques, although it is increasingly supplemented by using computational methods. NMR parameters, such as chemical shifts and coupling constants, are extremely sensitive indicators of local molecular conformation and are a source of structural evidence. However, their interpretation is fairly challenging in many circumstances, such as the case of the new polyether squalene derivative nivariol, the structure of which was elucidated by means of NMR spectroscopy and DFT calculations. The potential flexibility of this molecule and the high number of quaternary carbon atoms that it contains make its configurational assignment very difficult. Moreover, the relative configuration of four separated stereoclusters was established and subsequently connected by using NOE and J-based analysis, as well as by a comparison of its experimental (13)C?NMR chemical shifts with the corresponding population-weighted values, as calculated by using DFT methods. Limitations of these used approaches became apparent but were overcome by combining the two methods.

Cen-Pacheco F; Rodríguez J; Norte M; Fernández JJ; Hernández Daranas A

2013-06-01

391

Connecting discrete stereoclusters by using DFT and NMR spectroscopy: the case of nivariol.  

Science.gov (United States)

The structural determination of small organic molecules is mainly undertaken by using NMR techniques, although it is increasingly supplemented by using computational methods. NMR parameters, such as chemical shifts and coupling constants, are extremely sensitive indicators of local molecular conformation and are a source of structural evidence. However, their interpretation is fairly challenging in many circumstances, such as the case of the new polyether squalene derivative nivariol, the structure of which was elucidated by means of NMR spectroscopy and DFT calculations. The potential flexibility of this molecule and the high number of quaternary carbon atoms that it contains make its configurational assignment very difficult. Moreover, the relative configuration of four separated stereoclusters was established and subsequently connected by using NOE and J-based analysis, as well as by a comparison of its experimental (13)C?NMR chemical shifts with the corresponding population-weighted values, as calculated by using DFT methods. Limitations of these used approaches became apparent but were overcome by combining the two methods. PMID:23649973

Cen-Pacheco, Francisco; Rodríguez, Jaime; Norte, Manuel; Fernández, José J; Hernández Daranas, Antonio

2013-05-06

392

NMR imaging and spectroscopy of the mammalian central nervous system after heavy ion radiation  

International Nuclear Information System (INIS)

[en] NMR imaging, NMR spectroscopic, and histopathologic techniques were used to study the proton relaxation time and related biochemical changes in the central nervous system after helium beam in vivo irradiation of the rodent brain. The spectroscopic observations reported in this dissertation were made possible by development of methods for measuring the NMR parameters of the rodent brain in vivo and in vitro. The methods include (1) depth selective spectroscopy using an optimization of rf pulse energy based on a priori knowledge of N-acetyl aspartate and lipid spectra of the normal brain, (2) phase-encoded proton spectroscopy of the living rodent using a surface coil, and (3) dual aqueous and organic tissue extraction technique for spectroscopy. Radiation induced increases were observed in lipid and p-choline peaks of the proton spectrum, in vivo. Proton NMR spectroscopy measurements on brain extracts (aqueous and organic solvents) were made to observe chemical changes that could not be seen in vivo. Radiation-induced changes were observed in lactate, GABA, glutamate, and p-choline peak areas of the aqueous fraction spectra. In the organic fraction, decreases were observed in peak area ratios of the terminal-methyl peaks, the N-methyl groups of choline, and at a peak at 2.84 ppM (phosphatidyl ethanolamine and phosphatidyl serine resonances) relative to TMS. With histology and Evans blue injections, blood-brain barrier alternations were seen as early as 4 days after irradiation. 83 references, 53 figures

1984-01-01

393

Determination of the casein content in bovine milk by 31P-NMR.  

Science.gov (United States)

The relative proportion of caseins to total protein is a parameter that can be used to control the protein quality in standardised milk, an increasing tendency in dairy industries. 31P-NMR was used to analyse the casein content of milk, by the quantitation of the area under the resonances belonging to SerP, and using methylenediphosphonic acid as internal standard. This procedure yielded good results, as similar values of caseins were obtained from N Kjeldahl and NMR analysis for slightly heated milk samples. Heating at 95 degrees C for 15 min did not alter the casein content results. Casein content of raw, pasteurised and UHT milks (25.6 +/- 1.4, 26.4 +/- 1.8, 25.5 +/- 1.6 g casein/l milk, respectively), obtained by NMR, were not significantly different, giving an average of 25.8 +/- 1.6 g casein/l for bulk liquid milk. This work concluded that 31P-NMR could be used as an alternative method to determine casein in raw, pasteurised, dry and UHT milks. PMID:12369412

Belloque, Josefina; Ramos, Mercedes

2002-08-01

394

Non-destructive characterization of materials by single-sided NMR  

Energy Technology Data Exchange (ETDEWEB)

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

Goga, Nicolae-Octavian

2007-08-20

395

NMR CHARACTERIZATIONS OF PROPERTIES OF HETEROGENEOUS MEDIA  

Energy Technology Data Exchange (ETDEWEB)

A critical and long-standing need within the petroleum industry is the specification of suitable petrophysical properties for mathematical simulation of fluid flow in petroleum reservoirs (i.e., reservoir characterization). The development of accurate reservoir characterizations is extremely challenging. Property variations may be described on many scales, and the information available from measurements reflect different scales. In fact, experiments on laboratory core samples, well-log data, well-test data, and reservoir-production data all represent information potentially valuable to reservoir characterization, yet they all reflect information about spatial variations of properties at different scales. Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) provide enormous potential for developing new descriptions and understandings of heterogeneous media. NMR has the rare capability to probe permeable media non-invasively, with spatial resolution, and it provides unique information about molecular motions and interactions that are sensitive to morphology. NMR well-logging provides the best opportunity ever to resolve permeability distributions within petroleum reservoirs. We develop MRI methods to determine, for the first time, spatially resolved distributions of porosity and permeability within permeable media samples that approach the intrinsic scale: the finest resolution of these macroscopic properties possible. To our knowledge, this is the first time that the permeability is actually resolved at a scale smaller than the sample. In order to do this, we have developed a robust method to determine of relaxation distributions from NMR experiments and a novel implementation and analysis of MRI experiments to determine the amount of fluid corresponding to imaging regions, which are in turn used to determine porosity and saturation distributions. We have developed a novel MRI experiment to determine velocity distributions within flowing experiments, and developed methodology using that data to determine spatially resolved permeability distributions. We investigate the use of intrinsic properties for developing improved correlations for predicting permeability from NMR well-logging data and for obtaining more accurate estimates of multiphase flow properties--the relative permeability and capillary pressure--from displacement experiments. We demonstrate the use of MRI measurements of saturation and relaxation for prediction wetting-phase relative permeability for unstable experiments. Finally, we developed an improved method for determining surface relaxivity with NMR experiments, which can provide better descriptions of permeable media microstructures and improved correlations for permeability predictions.

C.T. Philip Chang; Changho Choi; Jeromy T. Hollenshead; Rudi Michalak; Jack Phan; Ramon Saavedra; John C. Slattery; Jinsoo Uh; Randi Valestrand; A. Ted Watson; Song Xue

2005-01-01

396

13C-NMR under pressure on [PM?Cu(NO3)2?(H2O)2]n  

International Nuclear Information System (INIS)

We present an investigation of the S=((1)/(2)) antiferromagnetically coupled Heisenberg spin chain [PM?Cu(NO3)2?(H2O)2]n (PM=pyrimidine=C4N2H4) with field-induced gap ? by means of 13C-NMR experiments. From these studies, carried out as function of pressure, we determine the NMR shift and the spin-lattice relaxation rate 1/T1 and extract the magnetic exchange parameter J/kB and the size of the spin gap ?. The observed pressure response is discussed in comparison to related molecular materials.

2003-08-01

397

(129)Xe NMR of Mesoporous Silicas  

Energy Technology Data Exchange (ETDEWEB)

The porosities of three mesoporous silica materials were characterized with {sup 129}Xe NMR spectroscopy. The materials were synthesized by a sol-gel process with r = 0, 25, and 70% methanol by weight in an aqueous cetyltrimethylammonium bromide solution. Temperature dependent chemical shifts and spin lattice relaxation times reveal that xenon does not penetrate the pores of the largely disordered (r= 70%) silica. For both r = 0 and 25%, temperature dependent resonances corresponding to physisorbed xenon were observed. An additional resonance for the r = 25% sample was attributed to xenon between the disordered cylindrical pores. 2D NMR exchange experiments corroborate the spin lattice relaxation data which show that xenon is in rapid exchange between the adsorbed and the gas phase.

Anderson, M.T.; Asink, R.A.; Kneller, J.M.; Pietrass, T.

1999-04-23

398

NMR Quantum Calculations of the Jones Polynomial  

CERN Document Server

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

399

NMR-Based Diffusion Lattice Imaging  

CERN Multimedia

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

400

Exploring the limits to spatially resolved NMR  

International Nuclear Information System (INIS)

Recent advances in MRI have demonstrated resolutions down to 1 ?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.

2010-01-01

 
 
 
 
401

NMR dispersion measurement of dynamic nuclear polarization  

International Nuclear Information System (INIS)

The feasibility of monitoring dynamic nuclear polarization from the NMR dispersive susceptibility is examined. Two prototype instruments are tested in a polarized proton target using organic target material. The more promising employs a tunnel diode oscillator, inside the target cavity, and should provide a precise polarization measurement working at a frequency far enough from the main resonance for the disturbance of the measured polarization to be negligible. Other existing methods for measuring target polarization are briefly reviewed. (author)

1978-01-01

402

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

403

NMR measurements on cerium and uranium compounds  

Energy Technology Data Exchange (ETDEWEB)

Magnetic and superconducting properties of several heavy fermion materials, CeCu{sub 2}Si{sub 2}, (Ce, Th)Cu{sub 2}Si{sub 2}, UCu{sub 5}, CeNiSn, UPd{sub 2}Al{sub 3}, UNi{sub 2}Al{sub 3} and UBe{sub 13} are discussed on the basis of NMR results. (author).

Asayama, Kunisuke; Kitaoka, Yoshio; Nakamura, Hiroyuki; Kyogaku, Masafumi; Hirooka, Shoichi [Osaka Univ., Toyonaka (Japan). Faculty of Engineering Science

1993-01-01

404

NMR in copper-Oxide Metals  

CERN Multimedia

The anomalous part of the NMR relaxation rate of coppernuclei in the normal state of copper-oxide metals is calculated using the orbital magnetic parts of the fluctuations derived in a recent theory to explain the long wavelength transport anomalies. Oxygen and Yttrium reside on lattice sites at which the anomalous contribution is absent at all hole densities. The frequency, momentum dependence, and the form-factor of the fluctuations is predicted,which is verifiable by inelastic neutron scattering experiments.

Varma, C M

1996-01-01

405

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

406

Quantum Pattern Recognition With Liquid State NMR  

CERN Document Server

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

407

NMR study of Corynebacterium melassecola metabolism  

International Nuclear Information System (INIS)

Corynebacterium melassecola is a microorganism producing glutamic acid, an aminate acid used as food additive. Knowledge of its metabolism is essential for improving the phyla. A study is carried out on intracellular extracts with NMR spectrometry in order to determine certain glucose catabolism pathways using a partial isotopic enrichment with (1-13C) or (6-13C) glucose. Results demonstrate the particular metabolism of Corynebacteria. 2 tabs., 3 refs

1994-01-01

408

Protein structure elucidation from NMR proton densities.  

UK PubMed Central (United Kingdom)

The NMR-generated foc proton density affords a template to which the molecule has to be fitted to derive the structure. Here we present a computational protocol that achieves this goal. H(N) atoms are readily recognizable from (1)H/(2)H exchange or (1)H/(15)N heteronuclear single quantum correlation (HSQC) experiments. The primary structure is threaded through the unassigned foc by leapfrogging along peptidyl amide H(N)s and the connected H(alpha)s. Via a Bayesian approach, the probabilities of the sequential connectivity hypotheses are inferred from likelihoods of H(N)/H(N), H(N)/H(alpha), and H(alpha)/H(alpha) interatomic distances as well as (1)H NMR chemical shifts, both derived from public databases. Once the polypeptide sequence is identified, directionality becomes established, and the foc N and C termini are recognized. After a similar procedure, side chain H atoms are found, including discriminated cis/trans proline loci. The folded structure then is derived via a direct molecular dynamics embedding into mirror image-related representations of the foc and selected according to a lowest energy criterion. The method was applied to foc densities calculated for two protein domains, col 2 and kringle 2. The obtained structures are within 1.0-1.5 A (backbone heavy atoms) and 1.5-2.0 A (all heavy atoms) rms deviations from reported x-ray and/or NMR structures.

Grishaev A; Llinas M

2002-05-01

409

Protein structure elucidation from NMR proton densities.  

Science.gov (United States)

The NMR-generated foc proton density affords a template to which the molecule has to be fitted to derive the structure. Here we present a computational protocol that achieves this goal. H(N) atoms are readily recognizable from (1)H/(2)H exchange or (1)H/(15)N heteronuclear single quantum correlation (HSQC) experiments. The primary structure is threaded through the unassigned foc by leapfrogging along peptidyl amide H(N)s and the connected H(alpha)s. Via a Bayesian approach, the probabilities of the sequential connectivity hypotheses are inferred from likelihoods of H(N)/H(N), H(N)/H(alpha), and H(alpha)/H(alpha) interatomic distances as