Thursday, January 28, 2010

J. Phys. Chem. A, 2010, 114 (1), pp 324–335

High-Field Solid-State 67Zn NMR Spectroscopy of Several Zinc−Amino Acid Complexes
Kamal H. Mrou and William P. Power*

We report the results of our solid-state 67Zn NMR study of the various zinc sites in four zinc−amino acid coordination complexes: bis(glycinato)zinc(II) monohydrate; bis(l-alaninato)zinc(II); bis(l-histidinato)zinc(II) dihydrate; and sodium bis(l-cysteinato)zincate(II) hexahydrate; as well as a related complex, bis(imidazole)zinc(II) chloride. We demonstrate the advantages of using high (21.1 T) applied magnetic fields for detecting 67Zn directly at ambient temperatures using the quadrupolar Carr−Purcell Meiboom−Gill (QCPMG) pulse sequence. The stepped-frequency technique was employed in cases where the central-transition (CT) 67Zn NMR spectra were too broad to be uniformly excited. The parameters of the anisotropic zinc tensors were extracted by iterative simulations of the experimental spectra. In all cases, the quadrupolar interaction is found to dominate the central-transition 67Zn NMR spectra; no convincing effects from chemical shift anisotropy (CSA) on the NMR spectra of the five complexes could be reliably detected at this field strength. Analyses of the experimental NMR spectra reveal that the 67Zn quadrupolar coupling constants (CQ) range from 7.05 to 26.4 MHz, the isotropic chemical shifts (δiso) range from 140 to 265 ppm, and the quadrupolar asymmetry parameters (ηQ) range from 0.20 to 0.95. The first report of the NMR spectral features of pentacoordinated zinc sites is included for two complexes. Quantum chemical calculations of the electric field gradient (EFG) and magnetic shielding tensors reproduced the experimental results to a reasonable extent. Moreover, the computationally determined orientations of both tensors permit correlations between NMR tensor properties and zinc local environments to be understood.

J. Phys. Chem. A, 2010, 114 (1), pp 309–316

High Field 33S Solid State NMR and First-Principles Calculations in Potassium Sulfates
Igor Moudrakovski*, Stephen Lang, Serguei Patchkovskii and John Ripmeester

A set of potassium sulfates presenting a variety of sulfur environments (K2SO4, KHSO4, K2S2O7, and K2S2O8) has been studied by 33S solid state NMR at 21 T. Low natural abundance (0.75%) and small gyromagnetic ratio of 33S presented a serious challenge even at such a high magnetic field. Nevertheless, using the QCPMG technique we were able to obtain good signals from the sites with CQ values approaching 16 MHz. Assignment of the sites and the relative orientations of the EFG tensors were assisted by quantum mechanical calculations using the Gaussian 98 and CASTEP packages. The Gaussian 98 calculations were performed using the density functional method and gauge independent atomic orbitals on molecular clusters of about 100−120 atoms. The CASTEP calculations utilized periodic boundary conditions and a gauge-including projector augmented-wave pseudopotential approach. Although only semiquantitative agreement is observed between the experimental and calculated parameters, the calculations are a very useful aid in the interpretation of experimental data.

J. Am. Chem. Soc., 2010, 132 (1), pp 303–308

Intermediate Rate Atomic Trajectories of RNA by Solid-State NMR Spectroscopy
Greg L. Olsen†, Michael F. Bardaro, Jr.†, Dorothy C. Echodu†, Gary P. Drobny*† and Gabriele Varani*‡

Many RNAs undergo large conformational changes in response to the binding of proteins and small molecules. However, when RNA functional dynamics occur in the nanosecond−microsecond time scale, they become invisible to traditional solution NMR relaxation methods. Residual dipolar coupling methods have revealed the presence of extensive nanosecond−microsecond domain motions in HIV-1 TAR RNA, but this technique lacks information on the rates of motions. We have used solid-state deuterium NMR to quantitatively describe trajectories of key residues in TAR by exploiting the sensitivity of this technique to motions that occur in the nanosecond−microsecond regime. Deuterium line shape and relaxation data were used to model motions of residues within the TAR binding interface. The resulting motional models indicate two functionally essential bases within the single-stranded bulge sample both the free and Tat-bound conformations on the microsecond time scale in the complete absence of the protein. Thus, our results strongly support a conformational capture mechanism for recognition: the protein does not induce a new RNA structure, but instead captures an already-populated conformation.

J. Am. Chem. Soc., 2010, 132 (1), pp 223–233

Probing Molecular Motion by Double-Quantum (13C,13C) Solid-State NMR Spectroscopy: Application to Ubiquitin
Robert Schneider†, Karsten Seidel†§, Manuel Etzkorn†, Adam Lange†, Stefan Becker† and Marc Baldus*‡

We demonstrate the use of two-dimensional (13C,13C) double-quantum spectroscopy to detect molecular dynamics by solid-state NMR. Data collected on tyrosine-ethylester (TEE) are in line with previously determined (1H,13C) order parameters. Application of these experiments to microcrystalline ubiquitin reveals the presence of dynamics on millisecond or faster time scales and differences in local mobility depending on microcrystal preparation. In addition, solid-state NMR-based structure calculation indicates conformational variability of loop regions between different solid-phase ubiquitin preparations. Our data relate preparation-dependent changes observed in NMR spectral parameters such as chemical shifts and through-space correlations to differences in ubiquitin dynamics and conformation and suggest a prominent role of molecular mobility in microcrystalline ubiquitin.

J. Am. Chem. Soc., 2010, 132 (1), pp 24–25

Detection of a Transient Intermediate in a Rapid Protein Folding Process by Solid-State Nuclear Magnetic Resonance
Kan-Nian Hu, Wai-Ming Yau and Robert Tycko*

We describe the use of solid-state NMR spectroscopy to characterize a partially folded state of the 35-residue helical protein HP35 created by rapid freeze-quenching from a thermally unfolded state on the 10−20 μs time scale. Two-dimensional solid-state 13C NMR spectra of 13C-labeled HP35 in frozen glycerol/water solution exhibit two sets of signals, one corresponding to strongly unfolded protein molecules and the other to an ensemble of molecules having native helical secondary structure but incomplete tertiary structure. The NMR data indicate that secondary structure forms within the freeze-quenching time scale but that full folding involves a slower phase of structural annealing. The 5 μs folding time observed in earlier studies of HP35 by time-resolved optical techniques may not represent the time scale for full folding.

Monday, January 25, 2010

The complete iodine and nitrogen nuclear electric quadrupole coupling tensors for fluoroiodoacetonitrile determined by chirped pulse Fourier transform microwave spectroscopy

G. S. Grubbs, II, G. Kadiwar, W. C. Bailey, and S. A. Cooke

Molecular pulsed jet, chirped-pulse Fourier transform microwave spectroscopy has been used to record 499 transitions for the title molecule. Measurements have been made in the 8–16 GHz regions. Vibrational and electronic ground state rotational constants A, B, and C have been obtained, together with centrifugal distortion terms. The complete iodine and nitrogen nuclear quadrupole coupling tensors have been determined for the first time. Quantum chemical calculations have been performed to aid with analyses and, in particular, to aid in determining the signs of the off-diagonal components of the nuclear quadrupole coupling tensors. An experimentally determined relative electronegativity scale for several polyhalomethyl groups is proposed.

An NMR study of macromolecular aggregation in a model polymer-surfactant solution

Suliman Barhoum and Anand Yethiraj

A model complex-forming nonionic polymer–anionic surfactant system in aqueous solution has been studied at different surfactant concentrations. Using pulsed-field-gradient diffusion NMR spectroscopy, we obtain the self-diffusion coefficients of poly(ethylene glycol) (PEO) and sodium dodecyl sulfate (SDS) simultaneously and as a function of SDS concentration. In addition, we obtain NMR relaxation rates and chemical shifts as a function of SDS concentration. Within the context of a simple model, our experimental results yield the onset of aggregation of SDS on PEO chains (CAC=3.5 mM), a crossover concentration (C2=60 mM) which signals a sharp change in relaxation behavior, as well as an increase in free surfactant concentration and a critical concentration (Cm=145 mM) which signals a distinct change in diffusion behavior and a crossover to a solution containing free micelles. Cm also marks the concentration above which obstruction effects are definitely important. In addition, we obtain the concentration of SDS in monomeric form and in the form of free micelles, as well as the average number of SDS molecules in a PEO-SDS aggregate (NAggr). Taken together, our results suggests continuous changes in the aggregation phenomenon over much of the concentration but with three distinct concentrations that signal changes in the nature of the aggregates.

Communications: Nanomagnetic shielding: High-resolution NMR in carbon allotropes

Y. Kim,1 E. Abou-Hamad,2 A. Rubio,3 T. Wågberg,4 A. V. Talyzin,4 D. Boesch,5 S. Aloni,5 A. Zettl,5 D. E. Luzzi,1,6 and C. Goze-Bac2

The understanding and control of the magnetic properties of carbon-based materials is of fundamental relevance in applications in nano- and biosciences. Ring currents do play a basic role in those systems. In particular the inner cavities of nanotubes offer an ideal environment to investigate the magnetism of synthetic materials at the nanoscale. Here, by means of 13C high resolution NMR of encapsulated molecules in peapod hybrid materials, we report the largest diamagnetic shifts (down to −68.3 ppm) ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon doping. This diamagnetic shift can be externally controlled by in situ modifications such as doping or electrostatic charging. Moreover, defects such as C-vacancies, pentagons, and chemical functionalization of the outer nanotube quench this diamagnetic effect and restore NMR signatures to slightly paramagnetic shifts compared to nonencapsulated molecules. The magnetic interactions reported here are robust phenomena independent of temperature and proportional to the applied magnetic field. The magnitude, tunability, and stability of the magnetic effects make the peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronics and nanobiomedical engineering.

Detecting diffusion-diffraction patterns in size distribution phantoms using double-pulsed field gradient NMR: Theory and experiments

Noam Shemesh, Evren Ozarslan, Peter J. Basser, and Yoram Cohen

NMR observable nuclei undergoing restricted diffusion within confining pores are important reporters for microstructural features of porous media including, inter-alia, biological tissues, emulsions and rocks. Diffusion NMR, and especially the single-pulsed field gradient (s-PFG) methodology, is one of the most important noninvasive tools for studying such opaque samples, enabling extraction of important microstructural information from diffusion-diffraction phenomena. However, when the pores are not monodisperse and are characterized by a size distribution, the diffusion-diffraction patterns disappear from the signal decay, and the relevant microstructural information is mostly lost. A recent theoretical study predicted that the diffusion-diffraction patterns in double-PFG (d-PFG) experiments have unique characteristics, such as zero-crossings, that make them more robust with respect to size distributions. In this study, we theoretically compared the signal decay arising from diffusion in isolated cylindrical pores characterized by lognormal size distributions in both s-PFG and d-PFG methodologies using a recently presented general framework for treating diffusion in NMR experiments. We showed the gradual loss of diffusion-diffraction patterns in broadening size distributions in s-PFG and the robustness of the zero-crossings in d-PFG even for very large standard deviations of the size distribution. We then performed s-PFG and d-PFG experiments on well-controlled size distribution phantoms in which the ground-truth is well-known a priori. We showed that the microstructural information, as manifested in the diffusion-diffraction patterns, is lost in the s-PFG experiments, whereas in d-PFG experiments the zero-crossings of the signal persist from which relevant microstructural information can be extracted. This study provides a proof of concept that d-PFG may be useful in obtaining important microstructural features in samples characterized by size distributions.

Determination of outer-sphere dipolar time correlation functions from high-field NMR measurements. Example of a Gd complex in a viscous solvent

Pascal H. Fries, Daniel Imbert, and Andrea Melchior

We consider a diamagnetic species carrying a nuclear spin and having a purely outer-sphere dynamics with respect to a Gd3+ complex. The maximal structural and dynamic information attainable from the paramagnetic relaxation (rate) enhancement (PRE) of this nuclear spin due to the Gd3+ electronic spin is the outer-sphere dipolar time correlation function (OS-DTCF) of the relative position of these spins. We show how to determine this OS-DTCF by a model-free analysis of high-field PRE measurements, which accounts for the relative diffusion coefficient of the spin carrying species derived from pulsed-gradient spin-echo experiments. The method rests on the spectral characterization of the OS-DTCF through a PRE property, the “star” relaxivity, which can be measured over an unexpectedly large frequency range by combining multiple field and temperature NMR experiments. It is illustrated in the case of the 1H spins on the three diamagnetic probes tert-butanol CHD2(CD3)2COD and glycerol (CD2OD)2CHOD and CHDOD–CDOD–CD2OD interacting with Gddtpa2− (dtpa5−=diethylen triamin pentaacetate) in a viscous glycerol-d8/D2O solvent. The general usefulness of the OS-DTCF for the description of the liquid state and electronic spin relaxation is discussed.

^{75} As NMR study of single crystals of the heavily overdoped pnictide superconductors Ba_{1−x} K_{x} Fe_{2} As_{2} ( x=0.7 and 1)

from Recent Articles in Phys. Rev. B We performed 75As NMR studies on two overdoped high-quality Ba1−xKxFe2As2 (x=0.7 and 1.0) single crystals. In the normal states, we found a dramatic increase in the spin-lattice relaxation (1/75T1) from the x=0.7 to the x=1.0 samples. In KFe2As2, the ratio of 1/75T1TKn2, where 75Kn is the Knight shift, increases as temperature drops. These results indicate the existence of another type of spin fluctuations in KFe2As2 which is accustomed to being treated as a simple Fermi liquid. In the superconducting state, the temperature scalings of 1/75T1 below Tc in the overdoped samples are significantly different from those in the under or optimally doped ones. A power-law scaling behavior 1/75T1TT0.5 is observed, which indicates universal strong low-energy excitations in the overdoped hole-type superconductors.

Quantum interface between light and nuclear spins in quantum dots

from Recent Articles in Phys. Rev. B The coherent coupling of flying photonic qubits to stationary matter-based qubits is an essential building block for quantum-communication networks. We show how such a quantum interface can be realized between a traveling-wave optical field and the polarized nuclear spins in a singly charged quantum dot strongly coupled to a high-finesse optical cavity. By adiabatically eliminating the electron a direct effective coupling is achieved. Depending on the laser field applied, interactions that enable either write-in or read-out are obtained.

nhomogeneous nuclear spin flips: Feedback mechanism between electronic states in a double quantum dot and the underlying nuclear spin bath

Phys. Rev. Lett.

NMR Implementation of a Molecular Hydrogen Quantum Simulation with Adiabatic State Preparation

from Recent Articles in Phys. Rev. Lett. It is difficult to simulate quantum systems on classical computers, while quantum computers have been proved to be able to efficiently perform such kinds of simulations. We report an NMR implementation simulating the hydrogen molecule (H2) in a minimal basis to obtain its ground-state energy. Using an iterative NMR interferometer to measure the phase shift, we achieve a 45-bit estimation of the energy value. The efficiency of the adiabatic state preparation is also experimentally tested with various configurations of the same molecule.

Contrasting Spin Dynamics between Underdoped and Overdoped Ba(Fe_{1-x} Co_{x} )_{2} As_{2}

Author(s): F. L. Ning, K. Ahilan, T. Imai, A. S. Sefat, M. A. McGuire, B. C. Sales, D. Mandrus, P. Cheng, B. Shen, and H.-H Wen

We report the first NMR investigation of spin dynamics in the overdoped nonsuperconducting regime of Ba(Fe1-xCox)2As2 up to x=0.26. We demonstrate that the absence of interband transitions with large momentum transfer QAF∼(π/a,0) between the hole and electron Fermi surfaces results in complete suppression of antiferromagnetic spin fluctuations for x≳0.15. Our experimental results provide direct evidence for a correlation between Tc and the strength of QAF antiferromagnetic spin fluctuations.

Journal of Magnetic Resonance

New high dielectric constant materials for tailoring the B1+ distribution at high magnetic fields

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 11 January 2010

K., Haines , N.B., Smith , A.G., Webb
The spatial distribution of electromagnetic fields within the human body can be tailored using external dielectric materials. Here, we introduce a new material with high dielectric constant, and also low background MRI signal. The material is based upon metal titanates, which can be made into a geometrically-formable suspension in deionized water. The material properties of the suspension are characterized from 100-400 MHz. Results obtained at 7 Tesla show a significant increase in image intensity in areas such as the temporal lobe and base of the brain with the new material placed around the head, and improved performance compared to purely water-based gels.

Solid–State NMR Calculations for Metal Oxides and Gallates: Shielding and Quadrupolar Parameters for Perovskites and Related Phases

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 13 January 2010
Derek S., Middlemiss , Frédéric, Blanc , Chris J., Pickard , Clare P., Grey

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 (a– and b–Ga2O3, LiGaO2, NaGaO2, GaPO4, 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 analysed. 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 ηQ–values. The high quality of the computed results suggests that this approach can be extended to study more complex and disordered phases.

1H-Detected 1H−1H Correlation Spectroscopy of a Stereo-Array Isotope Labeled Amino Acid under Fast Magic-Angle Spinning

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 15 January 2010
Hiroki, Takahashi , Masatsune, Kainosho , Hideo, Akutsu , Toshimichi, Fujiwara

The combined use of selective deuteration, stereo-array isotope labeling (SAIL), and fast magic-angle spinning effectively suppresses the 1H−1H dipolar couplings in organic solids. This method provided the high-field 1H-NMR linewidths comparable to those achieved by combined rotation and multiple-pulse spectroscopy. This technique was applied to two-dimensional 1H-detected 1H−1H polarization transfer CHH experiments of valine. The signal sensitivity for the 1H-detected CHH experiments was greater than that for the 13C-detected 1H−1H polarization transfer experiments by a factor of 2-4. We obtained the 1H−1H distances in SAIL valine by CHH experiments with an accuracy of about 0.2 Å by using a theory developed for 1H−1H polarization transfer in 13C-labeled organic compounds.

Operation of a 500 MHz high temperature superconducting NMR: Towards an NMR spectrometer operating beyond 1 GHz

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 18 January 2010
Y. Yanagisawaa, b, H. Nakagomeb, K. Tennmeic, M. Hamadad, M. Yoshikawae, A. Otsukae, M. Hosonof, T. Kiyoshig, M. Takahashia, c, T. Yamazakia and H. Maedaa, c,

We have begun a project to develop an NMR spectrometer that operates at frequencies beyond 1 GHz (magnetic field strength in excess of 23.5T) using a high temperature superconductor (HTS) innermost coil. As the first step, we developed a 500 MHz NMR with a Bi-2223 HTS innermost coil, which was operated in external current mode. The temporal magnetic field change of the NMR magnet after the coil charge was dominated by (i) the field fluctuation due to a DC power supply and (ii) relaxation in the screening current in the HTS tape conductor; effect (i) was stabilized by the 2H field-frequency lock system, while effect (ii) decreased with time due to relaxation of the screening current induced in the HTS coil and reached 10-8(0.01ppm)/h on the 20th day after the coil charge, which was as small as the persistent current mode of the NMR magnet. The 1D 1H NMR spectra obtained by the 500 MHz LTS/HTS magnet were nearly equivalent to those obtained by the LTS NMR magnet. The 2D-NOESY, 3D-HNCO and 3D-HNCACB spectra were achieved for ubiquitin by the 500 MHz LTS/HTS magnet; their quality was closely equivalent to that achieved by a conventional LTS NMR. Based on the results of numerical simulation, the effects of screening current-induced magnetic field changes are predicted to be harmless for the 1.03GHz NMR magnet system.

Pulse sequence editing by symbolic calculation

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 22 January 2010
Michael P., Barnett , Istvàn, Pelczer

Our apseq software package interprets commands to alter, combine and draw NMR pulse sequences that are expressed in a simple mnemonic style. The package is coded in mathematica. It can be extended to meet specialized needs.

Solid State Nuclear Magnetic Resonance

1H, 13C and 31P MAS NMR studies of lyophilized brain tumors

Publication year: 2010
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 11 January 2010
R., Marszałek , M., Pisklak , D., Horsztyński , I., Wawer

H, 13C and 31P magic angle spinning magnetic resonance spectra (MAS NMR) of lyophilized brain tissue specimens were recorded. Among the 35 cases of brain tumors there were 24 glioblastomas, 7 meningiomas and a few other types. 1H NMR measurements were performed with a MAS speed of 33 kHz. The intense CH3, CH2 and CH=peaks in the 1H spectrum result from fatty acid residues of phospholipids, which are „mobile enough” besides the anhydrous environment. 13C CPMAS spectra revealed the resonances of creatine and guanidine carbons; the high intensity signals arise from carbonyl groups and methylene carbons of lipids. In particular we found a fraction of mobile lipids, characterized by narrow resonances and long TH. Overlapped resonances of phospholipids head groups contributed to the peak at 4-7 ppm in the 31P MAS NMR spectra. Our results indicate that 1H and 13C MAS NMR are able to characterize tumor types: differentiate glioblastomas from meningiomas and shed light on tumor biochemical characteristics. However, water soluble metabolites are not observed and macromolecules yield broad overlapped resonances. Generally, lyophilization significantly decreases discriminative potential of NMR analysis.

Three-pulse spin echo signals from quadrupolar nuclei in magnetic materials

Publication year: 2010
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 22 January 2010
S.N., Polulyakh , N.A., Sergeev , A.I., Gorbovanov , V.N., Berzhansky

The time evolutions of the three-pulse spin echo signals from quadrupolar nuclei 63Cu and 53Cr in ferromagnetic CuCr2S4:Sb have been investigated at the temperature T=77 K. The experimental results were well explained by the developed theory of the time evolutions of the three-pulse echoes. The main assumption of this theory is the assumption that the temporal fluctuations in the electron magnetization lead to the fluctuations in the hyperfine and quadrupole interaction Hamiltonians.

Friday, January 15, 2010

J. Phys. Chem. A, 2009, 113 (52), pp 14936–14942

NMR Chemical Shielding and Spin−Spin Coupling Constants of Liquid NH3: A Systematic Investigation using the Sequential QM/MM Method†
Rodrigo M. Gester‡, Herbert C. Georg‡§, Sylvio Canuto‡, M. Cristina Caputo* and Patricio F. Provasi

The NMR spin coupling parameters, 1J(N,H) and 2J(H,H), and the chemical shielding, σ(15N), of liquid ammonia are studied from a combined and sequential QM/MM methodology. Monte Carlo simulations are performed to generate statistically uncorrelated configurations that are submitted to density functional theory calculations. Two different Lennard−Jones potentials are used in the liquid simulations. Electronic polarization is included in these two potentials via an iterative procedure with and without geometry relaxation, and the influence on the calculated properties are analyzed. B3LYP/aug-cc-pVTZ-J calculations were used to compute the 1J(N,H) constants in the interval of −67.8 to −63.9 Hz, depending on the theoretical model used. These can be compared with the experimental results of −61.6 Hz. For the 2J(H,H) coupling the theoretical results vary between −10.6 to −13.01 Hz. The indirect experimental result derived from partially deuterated liquid is −11.1 Hz. Inclusion of explicit hydrogen bonded molecules gives a small but important contribution. The vapor-to-liquid shifts are also considered. This shift is calculated to be negligible for 1J(N,H) in agreement with experiment. This is rationalized as a cancellation of the geometry relaxation and pure solvent effects. For the chemical shielding, σ(15N) calculations at the B3LYP/aug-pcS-3 show that the vapor-to-liquid chemical shift requires the explicit use of solvent molecules. Considering only one ammonia molecule in an electrostatic embedding gives a wrong sign for the chemical shift that is corrected only with the use of explicit additional molecules. The best result calculated for the vapor to liquid chemical shift Δσ(15N) is −25.2 ppm, in good agreement with the experimental value of −22.6 ppm.

J. Phys. Chem. A, 2010, 114 (2), pp 715–720

Nuclear Magnetic Resonance Parameters of Water Hexamers
G. Bilalbegovi†

Nuclear magnetic resonance 1H, 16O, and 17O chemical shifts, as well as 17O 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 16O and 17O 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.

Monday, January 11, 2010

Phys. Rev. B and Phys. Rev. Lett.

Spin Susceptibility of Noncentrosymmetric Heavy-Fermion Superconductor CeIrSi_{3} under Pressure: ^{29} Si Knight-Shift Study on Single Crystal

from Recent Articles in Phys. Rev. Lett. We report 29Si NMR study on a single crystal of the heavy-fermion superconductor CeIrSi3 without an inversion symmetry along the c axis. The 29Si Knight-shift measurements under pressure have revealed that the spin susceptibility for the ab plane decreases slightly below Tc, whereas along the c axis it does not change at all. The result can be accounted for by the spin susceptibility in the superconducting state being dominated by the strong antisymmetric (Rashba-type) spin-orbit interaction that originates from the absence of an inversion center along the c axis and it being much larger than superconducting condensation energy. This is the first observation which exhibits an anisotropy of the spin susceptibility below Tc in the noncentrosymmetric superconductor dominated by strong Rashba-type spin-orbit interaction.

^{31} P and ^{75} As NMR evidence for a residual density of states at zero energy in superconducting BaFe_{2} (As_{0.67} P_{0.33} )_{2}

from Recent Articles in Phys. Rev. B 31P and 75As NMR measurements were performed in superconducting BaFe2(As0.67P0.33)2 with Tc=30 K. The nuclear-spin-lattice relaxation rate T 1−1 and the Knight shift in the normal state indicate the development of antiferromagnetic fluctuations, and T 1−1 in the superconducting (SC) state decreases without a coherence peak just below Tc, as observed in (Ba1−xKx)Fe2As2. In contrast to other iron arsenide superconductors, the T 1−1T behavior is observed below 4 K, indicating the presence of a residual density of states at zero energy. Our results suggest that strikingly different SC gaps appear in BaFe2(As1−xPx)2 despite a comparable Tc value, an analogous phase diagram, and similar Fermi surfaces to (Ba1−xKx)Fe2As2.

Spin-singlet state formation in the cluster Mott insulator GaNb_{4} S_{8} studied by μSR and NMR spectroscopy

from Recent Articles in Phys. Rev. B Muon spin relaxation (μSR) and nuclear magnetic resonance experiments revealed that the spin-singlet state with an excitation gap of ∼200 K is realized from S=1/2 Nb4 tetrahedral clusters in a cluster Mott insulator GaNb4S8. The intercluster cooperative phenomenon to the singlet state at TS=32 k is triggered by intracluster Jahn-Teller type structural instability developed from ∼3TS. Referring to the lattice symmetry, the formation of Nb8 octamer (Nb4-Nb4 bond) is suggested.

Wednesday, January 06, 2010

First 1 GHz NMR spectrometer is now online!

The first 1000 MHz high-resolution NMR spectrometer is now online at the RALF-NMR (European Large Scale NMR Facility) in Lyon, France (director of the facility is Lyndon Emsley).

For more on this item, check out the full article at Stan's NMR blog:

Tuesday, January 05, 2010

Phys. Rev. B

Identification of individual ^{13} C isotopes of nitrogen-vacancy center in diamond by combining the polarization studies of nuclear spins and first-principles calculations

from Recent Articles in Phys. Rev. B We determine the charge- and spin-density distributions of nitrogen-vacancy center in diamond for both the ground and excited states by ab initio supercell calculations yielding very good agreement with the experiment. We correctly determine the polarization of 15N nuclear spin in the level anticrossing (LAC) mechanism. We show that LAC together with the accurate ab initio data can be used to identify the individual 13C nuclei around the defect that can also reveal the dominant component of the precession vector responsible for the decoherence of the addressed nuclear-spin qubit.

Nutation versus angular-dependent NQR spectroscopy and impact of underdoping on charge inhomogeneities in YBa_{2} Cu_{3} O_{y}

Author(s): Rinat Ofer and Amit Keren
We describe two different nuclear quadrupole resonance (NQR) based techniques, designed to measure the local asymmetry of the internal electric field gradient η and the tilt angle α of the main NQR principal axis ẑ from the crystallographic axis ĉ. These techniques use the dependence of the NQR signal on the duration of the radio frequency (rf) pulse and on the direction of the rf field H1 with respect to the crystal axis. The techniques are applied to oriented powder of YBa2Cu3Oy fully enriched with 63Cu. Measurements were performed at different frequencies, corresponding to different in-plane copper sites with respect to the dopant. Combining the results from both techniques, we conclude that oxygen deficiency in the chain layer lead to a rotation of the NQR main principal axis at the nearby Cu on the CuO2 planes by α≃20°±5°. This occurs with no change to η. The axis rotation associated with oxygen deficiency means that there must be electric field inhomogeneities in the CuO2 planes only in the vicinity of the missing oxygen.

Nuclear quadrupole resonance and x-ray investigation of the structure of Na_{2/3} CoO_{2}

from Recent Articles in Phys. Rev. B We have synthesized various samples of the x=2/3 phase of sodium cobaltate NaxCoO2 and performed x-ray powder diffractions spectra to compare the diffraction with the structure proposed previously from NMR and nuclear quadrupole resonance (NQR) experiments [H. Alloul, I. R. Mukhamedshin, T. A. Platova, and A. V. Dooglav, EPL 85, 47006 (2009)]. Rietveld analyses of the data are found in perfect agreement with those and confirm the concentration x=2/3 obtained in the synthesis procedure. They even give indications on the atomic displacements of Na inside the unit cell. The detailed NQR data allow us to identify the NQR transitions and electric field gradient parameters for four cobalt sites and three Na sites. The spin-lattice and spin-spin relaxation rates are found much smaller for the nonmagnetic Co3+ sites than for the magnetic sites on which the holes are delocalized. The atomic ordering of the Na layers is therefore at the source of this ordered distribution of cobalt charges. The method used here to resolve the Na ordering and the subsequent Co charge order can be used valuably for similar structural determinations for various phases with x>0.45 for which Na ordering has been established.

Journal of Chemical Physics

An integrated approach to NMR spin relaxation in flexible biomolecules: Application to beta-D-glucopyranosyl-(1-->6)-alpha-D-mannopyranosyl-OMe

Mirco Zerbetto,1 Antonino Polimeno,1 Dmytro Kotsyubynskyy,2 Leila Ghalebani,2 Jozef Kowalewski,2 Eva Meirovitch,3 Ulrika Olsson,4 and Göran Widmalm4

J. Chem. Phys. 131, 234501 (2009); doi:10.1063/1.3268766

The description of the reorientational dynamics of flexible molecules is a challenging task, in particular when the rates of internal and global motions are comparable. The commonly used simple mode-decoupling models are based on the assumption of statistical independence between these motions. This assumption is not valid when the time scale separation between their rates is small, a situation that was found to arise in oligosaccharides in the context of certain internal motions. To make possible the interpretation of NMR spin relaxation data from such molecules, we developed a comprehensive approach generally applicable to flexible rotators with one internal degree of freedom. This approach integrates a stochastic description of coupled global tumbling and internal torsional motion, quantum chemical calculations of the local potential and the local geometry at the site of the restricted torsion, and hydrodynamics-based calculations of the diffusive properties. The method is applied to the disaccharide beta-D-Glcp-(1" align="bottom" border="0">6)-alpha-D-[6-13C]-Manp-OMe dissolved in a DMSO-d6/D2O cryosolvent. The experimental NMR relaxation parameters, associated with the 13CH2 probe residing at the glycosidic linkage, include 13C T1 and T2 and 13C-{1H} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253–293 K. These data are predicted successfully by the new theory with only the H–C–H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed

Derivatives of spin dynamics simulations

Ilya Kuprov and Christopher T. Rodgers

We report analytical equations for the derivatives of spin dynamics simulations with respect to pulse sequence and spin system parameters. The methods described are significantly faster, more accurate, and more reliable than the finite difference approximations typically employed. The resulting derivatives may be used in fitting, optimization, performance evaluation, and stability analysis of spin dynamics simulations and experiments.

A new experimental absolute nuclear magnetic shielding scale for oxygen based on the rotational hyperfine structure of HO

Cristina Puzzarini, Gabriele Cazzoli, Michael E. Harding, Juana Vazquez, and Jurgen Gauss

The hyperfine structure in the rotational spectrum of water containing 17O has been investigated experimentally and by means of quantum-chemical calculations. The Lamb-dip technique has been used to resolve the hyperfine structure due to spin-rotation as well as spin-spin interactions and allowed the determination of the corresponding hyperfine parameters with high accuracy. The experimental investigation and, in particular, the analysis of the spectra have been supported by quantum-chemical computations at the coupled-cluster level. The experimental 17O isotropic spin-rotation constant of H217" align="middle" border="0">O has been used in a further step for the determination of the paramagnetic part of the corresponding nuclear magnetic shielding constant, whereas the diamagnetic contribution as well as vibrational and temperature corrections have been obtained from quantum-chemical calculations. This joint procedure leads to a value of 325.3(3) ppm for the oxygen shielding in H217" align="middle" border="0">O at 300 K, in good agreement with pure theoretical predictions, and in this way provides the basis for a new absolute oxygen shielding scale.

Shimmed matching pulses: Simultaneous control of rf and static gradients for inhomogeneity correction

John M. Franck, Vasiliki Demas, Rachel W. Martin, Louis-S. Bouchard, and Alexander Pines
Portable NMR systems generally suffer from poor field homogeneity and are therefore used more commonly for imaging and relaxation measurements rather than for spectroscopy. In recent years, various approaches have been proposed to increase the sample volume that is usable for spectroscopy. These include approaches based on manual shimming and those based on clever combinations of modulated radio frequency and gradient fields. However, this volume remains small and, therefore, of limited utility. We present improved pulses designed to correct for inhomogeneous dispersion across wide ranges of frequency offsets without eliminating chemical shift or spatial encoding. This method, based on the adiabatic double passage, combines the relatively larger corrections available from spatially matched rf gradients [C. Meriles et al., J. Magn. Reson. 164, 177 (2003)]. with the adjustable corrections available from time-modulated static field gradients [D. Topgaard et al., Proc. Natl. Acad. Sci. U.S.A. 101, 17576 (2004)]. We explain the origins of these corrections with a theoretical model that simplifies and expedites the design of the pulse waveforms. We also present a generalized method for evaluating and comparing pulses designed for inhomogeneity correction. Experiments validate this method and support simulations that offer new possibilities for significantly enhanced performance in portable environments.

Theory of damped quantum rotation in nuclear magnetic resonance spectra. III. Nuclear permutation symmetry of the line shape equation

S. Szymanski
The damped quantum rotation (DQR) theory describes manifestations in nuclear magnetic resonance spectra of the coherent and stochastic dynamics of N-fold molecular rotors composed of indistinguishable particles. The standard jump model is only a limiting case of the DQR approach; outside this limit, the stochastic motions of such rotors have no kinematic description. In this paper, completing the previous two of this series, consequences of nuclear permutation symmetry for the properties of the DQR line shape equation are considered. The systems addressed are planar rotors, such as aromatic hydrocarbons' rings, occurring inside of molecular crystals oriented in the magnetic field. Under such conditions, oddfold rotors can have nontrivial permutation symmetries only for peculiar orientations while evenfold ones always retain their intrinsic symmetry element, which is rotation by 180° about the N-fold axis; in specific orientations the latter can gain two additional symmetry elements. It is shown that the symmetry selection rules applicable to the classical rate processes in fluids, once recognized as having two diverse aspects, macroscopic and microscopic, are also rigorously valid for the DQR processes in the solid state. However, formal justification of these rules is different because the DQR equation is based on the Pauli principle, which is ignored in the jump model. For objects like the benzene ring, exploitation of these rules in simulations of spectra using the DQR equation can be of critical significance for the feasibility of the calculations. Examples of such calculations for the proton system of the benzene ring in a general orientation are provided. It is also shown that, because of the intrinsic symmetries of the evenfold rotors, many of the DQR processes, which such rotors can undergo, are unobservable in NMR spectra.

Four-component relativistic theory for nuclear magnetic shielding: Magnetically balanced gauge-including atomic orbitals

Lan Cheng, Yunlong Xiao, and Wenjian Liu

It is recognized only recently that the incorporation of the magnetic balance condition is absolutely essential for four-component relativistic theories of magnetic properties. Another important issue to be handled is the so-called gauge problem in calculations of, e.g., molecular magnetic shielding tensors with finite bases. It is shown here that the magnetic balance can be adapted to distributed gauge origins, leading to, e.g., magnetically balanced gauge-including atomic orbitals (MB-GIAOs) in which each magnetically balanced atomic orbital has its own local gauge origin placed on its center. Such a MB-GIAO scheme can be combined with any level of theory for electron correlation. The first implementation is done here at the coupled-perturbed Dirac–Kohn–Sham level. The calculated molecular magnetic shielding tensors are not only independent of the choice of gauge origin but also converge rapidly to the basis set limit. Close inspections reveal that (zeroth order) negative energy states are only important for the expansion of first order electronic core orbitals. Their contributions to the paramagnetism are therefore transferable from atoms to molecule and are essentially canceled out for chemical shifts. This allows for simplifications of the coupled-perturbed equations.

Journal of Magnetic Resonance

Designing Gradient Coils With Reduced Hot Spot Temperatures

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 9 December 2009
Peter T., While , Larry K., Forbes , Stuart, Crozier

Gradient coil temperature is an important concern in the design and construction of MRI scanners. Closely spaced gradient coil windings cause temperature hot spots within the system as a result of Ohmic heating associated with large current being driven through resistive material, and can strongly affect the performance of the coils. In this paper, a model is presented for predicting the spatial temperature distribution of a gradient coil, including the location and extent of temperature hot spots. Subsequently, a method is described for designing gradient coils with improved temperature distributions and reduced hot spot temperatures. Maximum temperature represents a non-linear constraint and a relaxed fixed point iteration routine is proposed to adjust coil windings iteratively to minimise this coil feature. Several examples are considered that assume different thermal material properties and cooling mechanisms for the gradient system. Coil winding solutions are obtained for all cases considered that display a considerable drop in hot spot temperature (>20%) when compared to standard minimum power gradient coils with equivalent gradient homogeneity, efficiency and inductance. The method is semi-analytical in nature and can be adapted easily to consider other non-linear constraints in the design of gradient coils or similar systems.

Homonuclear dipolar recoupling under ultra-fast magic-angle spinning: probing 19F19F proximities by solid-state NMR

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 16 December 2009
Qiang, Wang , Bingwen, Hu , Olivier, Lafon , Julien, Trébosc , Feng, Deng , and Jean-Paul Amoureux

We describe dipolar recoupling methods that accomplish, at high magic-angle spinning (MAS) frequencies, the excitation of double-quantum (DQ) coherences between spin-1/2 nuclei. We employ rotor-synchronized symmetry-based pulse sequences which are either γ-encoded or non-γ-encoded. The sensitivity and the robustness to both chemical-shift anisotropy and offset are examined. We also compare different techniques to avoid signal folding in the indirect dimension of two-dimensional double-quantum ↔ single-quantum (DQ−SQ) spectra. This comprehensive analysis results in the identification of satisfactory conditions for dipolar 19F−19F recoupling at high magnetic fields and high MAS frequencies. The utility of these recoupling methods is demonstrated with high-resolution DQ−SQ NMR spectra, which allow probing 19F−19F proximities in powered fluoroaluminates.

Intermolecular single-quantum coherence sequences for high-resolution NMR spectra in inhomogeneous fields

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 16 December 2009
Yuqing, Huang , Shuhui, Cai , Xi, Chen , Zhong, Chen

A new pulse sequence based on intermolecular single-quantum coherences (iSQCs) is proposed to obtain high-resolution NMR spectroscopy in inhomogeneous magnetic fields via fast 2D acquisition. Taking the intrinsic properties of iSQCs, the sequence is time-efficient with a narrow spectral width in the indirect dimension. It can recover useful information of chemical shifts, relative peak areas, J coupling constants, and multiplet patterns even when the field inhomogeneity is severe enough to erase almost all spectroscopic information. Moreover, good solvent suppression efficiency can be achieved by this sequence even with imperfect radio-frequency pulse flip angles. Spatially localized iSQC spectroscopy was performed on a sample packed with pig brain tissue and cucumber to show the feasibility of the sequence in in vivo magnetic resonance spectroscopy (MRS). This sequence may provide a promising way for the applications on in vivo and in situ high-resolution NMR spectroscopy.

Echo-time independent signal modulations for Strongly Coupled Systems in Triple Echo Localization schemes: An extension of S-PRESS editing

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 17 December 2009
Nils, Kickler , Giulio, Gambarota , Ralf, Mekle , Rolf, Gruetter , Robert, Mulkern

The double spin-echo point resolved spectroscopy sequence (PRESS) is a widely used method and standard in clinical MR spectroscopy. Existence of important J-modulations at constant echo times, depending on the temporal delays between the rf-pulses, have been demonstrated recently for strongly coupled spin systems and were exploited for difference editing, removing singlets from the spectrum (strong-coupling PRESS, S-PRESS). A drawback of this method for in vivo applications is that large signal modulations needed for difference editing occur only at relatively long echo times. In this work we demonstrate that, by simply adding a third refocusing pulse (3S-PRESS), difference editing becomes possible at substantially shorter echo times while, as applied to citrate, more favorable lineshapes can be obtained. For the example of an AB system an analytical description of the MR signal, obtained with this triple refocusing sequence (3S-PRESS), is provided.

On the applications of μr=-1 metamaterial lenses for magnetic resonance imaging

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 17 December 2009
Manuel J., Freire , Lukas, Jelinek , Ricardo, Marques , Mikhail, Lapine

In this work some possible applications of negative permeability magnetic metamaterial lenses for magnetic resonance imaging (MRI) are analyzed. It is shown that using magnetic metamaterials lenses it is possible to manipulate the spatial distribution of the radio-frequency (RF) field used in MR systems and, under some circumstances, improve the sensitivity of surface coils. Furthermore a collimation of the RF field, phenomenon that may find application in parallel imaging, is presented. MR images of real tissues are shown in order to prove the suitability of the theoretical analysis for practical applications.

L-Band Overhauser Dynamic Nuclear Polarization

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 21 December 2009
Sandra, Garcia , Jeffrey H., Walton , Brandon, Armstrong , Songi, Han , Michael J., McCarthy

We present the development of an Overhauser dynamic nuclear polarization (DNP) instrument at 0.04 T using 1.1 GHz (L-band) electron spin resonance frequencies (ESR) and 1.7 MHz 1H nuclear magnetic resonance frequencies. Using this home-built DNP system, the electron–nucleus coupling factor of 4-oxo-TEMPO dissolved in water was determined as 0.39 ± 0.06 at 0.04 T. The higher coupling factor obtained at this field compared to higher magnetic fields, such as 0.35 T, directly translates to higher enhancement of the NMR signal and opens up a wider time scale window for observing water dynamics interacting with macromolecular systems, including proteins, polymers or lipid vesicles. The higher enhancements obtained will facilitate the observation of water dynamics at correlation times up to 10 ns, that corresponds to more than one order of magnitude slower dynamics than accessible at 0.35 T using X-band ESR frequencies.

Efficient Heteronuclear Dipolar Decoupling in Solid-State Nuclear Magnetic Resonance at Rotary Resonance Conditions

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 21 December 2009
Subhradip, Paul , Venus Singh, Mithu , Narayanan D., Kurur , P.K., Madhu

We introduce here a heteronuclear dipolar decoupling scheme in solid-state nuclear magnetic resonance that performs efficiently at the rotary-resonance conditions, where otherwise dipolar couplings are re-introduced. Results are shown proving the efficiency of this scheme at two magnetic fields under magic-angle spinning frequencies of 30 kHz and 20 kHz.

Homonuclear dipolar decoupling under fast MAS: Resolution patterns and simple optimization strategy

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 22 December 2009
Kanmi, Mao , Marek, Pruski

A simple method is shown for optimization of 1H homonuclear dipolar decoupling at MAS rates exceeding 10 kHz. By monitoring the intensity of a spin-echo under the decoupling conditions, it is possible to optimize the amplitude of the RF magnetic field, the cycle time of the decoupling sequence and the resonance offset within minutes. As a result, the decoupling efficiency can be quickly and reliably fine-tuned without using a reference sample. The utility of this method has been confirmed by studying the resolution patterns for the supercycled PMLG scheme, which were found to be in excellent agreement with earlier theoretical predictions and verified in high-resolution 2D 1H-1H experiments.

Optimized Excitation Pulses for the Acquisition of Static NMR Powder Patterns from Half-Integer Quadrupolar Nuclei

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 23 December 2009
Luke A., O’Dell , Kristopher J., Harris , Robert W., Schurko

Various amplitude- and phase-modulated excitation pulses for the observation of static NMR powder patterns from half-integer quadrupolar nuclei have been generated using the optimal control routines implemented in SIMPSON 2.0. Such pulses are capable of both excitation of the central transition and signal enhancement by population transfer from the satellites. Enhancements in excess of 100% have been achieved for the central transition of the spin-3/2 87Rb nucleus compared with a selective π/2 pulse. These pulses are shown to be relatively insensitive to changes in RF power and transmitter offsets, and can achieve a more uniform signal enhancement than double frequency sweeps (DFS), resulting in more accurate spectral lineshapes. We also investigate the possibility of “calibration-free” optimized pulses for general use on half-integer quadrupoles with unknown interaction parameters. Such pulses could prove extremely useful for studying low abundance or insensitive nuclei for which experimental optimization of the DFS scheme may be difficult. We demonstrate that a pulse optimized for an arbitrary spin-3/2 system can function well on multiple samples, and can also excite the central transition of higher spin numbers, albeit with a smaller enhancement. The mechanism by which these optimized pulses achieve the signal enhancement is highly complex and, unlike DFS, involves a non-linear excitation of the satellite transition manifold, as well as the generation and manipulation of significant multiple-quantum coherences.

Benchmarking NMR experiments: a relational database of protein pulse sequences

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 23 December 2009
Russell R.P., Senthamarai , Ilya, Kuprov , Konstantin, Pervushin

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 (, 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 αXβ2 Integrin and 440 amino acids NS3 helicase.

Estimating Quadrupole Couplings of Amide Deuterons in Proteins from Direct Measurements of 2H Spin Relaxation Rates

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 24 December 2009
Devon, Sheppard , Vitali, Tugarinov

The measurements of longitudinal and transverse 2H spin relaxation rates of backbone amide deuterons (DN) in the [U-13C,15N]-labeled protein ubiquitin show that the utility of amide deuterons as probes of backbone order in proteins is compromised by substantial variability of DN quadrupolar coupling constants (QCC) from one amide site to another. However, using the dynamics parameters of 15N-2H bond vectors evaluated from 15N relaxation data, site-specific QCC values can be estimated directly from DN R1 and R2 rates providing useful information on hydrogen bonding in proteins. In agreement with previous indirect scalar relaxation-based measurements, the DN QCC values estimated directly from R1 and R2 2H relaxation rates correlate with the inverse cube of the x-ray structure-derived hydrogen bond distances in ubiquitin: QCC = (232±2.3) + (118±17) Σi(cosα)ri-3 where r is the inter-nuclear hydrogen bond distance in ångströms, and α is the ND····Oi angle.

Nuclear acoustic resonance in fluids using piezoelectric nanoparticles

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 24 December 2009
J., Mende , N., Elmiladi , C., Höhl , K., Maier

The influence of acoustic radiation in the form of ultrasound (US) on the nuclear magnetic resonance (NMR) signal of liquids in the presence of piezo- and ferroelectric nanoparticles was investigated. The NMR resonances of 1H and 23Na were influenced by US with a frequency of ωUS = 18.26 MHz. For hydrogen, US with a frequency ωUS = ω0 was used where ω0 is the Larmor frequency of 18.26 MHz. For sodium, US with a frequency ωUS = 2ω0, Na was used with ω0, Na = 9.13 MHz. A detailed description of nanoparticle properties and sample preparation is given. The influence of US on the spin-lattice relaxation time T1 was determined with an inversion recovery sequence for different concentrations of PZT. An elongation of T1 of 1H by 1.7% at a PZT concentration of 0.05% and an elongation of T1 of 23Na by 3% at a PZT concentration of 0.04% was observed. The elongation scales with the concentration of the PZT. An possible explanation of the effect of elongation is discussed.

A Practical Implementation of Cross-spectrum in Protein Backbone Resonance Assignment

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 24 December 2009
Kang, Chen , Frank, Delaglio , Nico, Tjandra

The concept of cross-spectrum is applied in protein NMR spectroscopy to assist in the backbone sequential resonance assignment. Cross-spectrum analysis is used routinely to reveal correlations in frequency domains as a means to reveal common features contained in multiple time series. Here the cross-spectrum between related NMR spectra, for example HNCO and HN(CA)CO, can be calculated with point-by-point multiplications along their common C’ carbon axis. In the resulting higher order cross-spectrum, an enhanced correlation signal occurs at every common i-1 carbon frequency allowing the amide proton HN (and nitrogen N) resonances from residues i and i-1 to be identified. The cross-spectrum approach is demonstrated using 2D spectra H(N)CO, H(NCA)CO, H(NCO)CACB, and H(N)CACB measured on a 15N/13C double-labeled Ubiquitin sample. These 2D spectra are used to calculate two pseudo-3D cross-spectra, Hi-Hi-1-C’i-1 and Hi-Hi-1-CAi-1CBi-1. We show using this approach, backbone resonances of H, C’, CA, and CB can be fully assigned without ambiguity. The cross-spectrum principle is expected to offer an easy, practical, and more quantitative approach for heteronuclear backbone resonance assignment.

Inter-residue carbonyl-carbonyl polarization transfer experiments in uniformly 13C,15N-labeled peptides and proteins

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 24 December 2009
Rafal, Janik , Emily, Ritz , Andrew, Gravelle , Lichi, Shi , Xiaohu, Peng , and Vladimir Ladizhansky

In this work, we demonstrate that Homonuclear Rotary Resonance Recoupling (HORROR) can be used to reintroduce carbonyl-carbonyl interresidue dipolar interactions and to achieve efficient polarization transfer between carbonyl atoms in uniformly 13C,15N-labeled peptides and proteins. We show that the HORROR condition is anisotropically broadened and overall shifted to higher radio frequency intensities because of the CSA effects. These effects are analyzed theoretically using Average Hamiltonian Theory. At spinning frequencies used in this study, 22 kHz, this broadening is experimentally found to be on the order of a kilohertz at a proton field of 600 MHz. To match HORROR condition over all powder orientations, variable amplitude RF fields are required, and efficient direct transfers on the order of 20-30% can be straightforwardly established. Two- and three-dimensional chemical shift correlation experiments establishing interresidue long-range interresidue connectivities (e.g., (N[i]-CO[i-2])) are demonstrated on the model peptide N-Acetyl-Valine-Leucine, and on the third immunoglobulin binding domain of protein G. Possible future developments are discussed.

Spectral Estimation of Irregularly Sampled Exponentially Decaying Signals with Applications to RF Spectroscopy

Publication year: 2009
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 24 December 2009 Erik Gudmundsona, , Petre Stoicaa, Jian Lib, Andreas Jakobssonc, Michael D. Rowed, John A. S. Smithd and Jun Lingb

The problem of estimating the spectral content of exponentially decaying signals from a set of irregularly sampled data is of considerable interest in several applications, for example in various forms of radio frequency spectroscopy. In this paper, we propose a new nonparametric iterative adaptive approach that provides a solution to this estimation problem. As opposed to commonly used methods in the field, the damping coefficient, or linewidth, is explicitly modelled, which allows for an improved estimation performance. Numerical examples using both simulated data and data from NQR experiments illustrate the benefits of the proposed estimator as compared to currently available nonparametric methods.

Measurement of dipolar structure of 17O nuclear quadrupole resonance lines by three-frequency irradiation

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 4 January 2010
J., Seliger , V., Žagar

A modification of nuclear quadrupole double resonance with coupled multiplet is proposed which can be used for the measurement of the dipolar structure of the 17O nuclear quadrupole resonance lines in case of a strong 1H-17O dipolar interaction. The technique is based on magnetic field cycling between a high magnetic field and zero magnetic field and on the simultaneous application of three rf magnetic fields with the frequencies that are close to the three 17O NQR frequencies ν5/2-1/2 > ν5/2-3/2 greater-or-equal, slanted ν3/2-1/2 during the time spent in zero static magnetic field. When the sum of the two lower irradiation frequencies ν12 is not equal to the highest irradiation frequencyν, the three-frequency irradiation increases the proton relaxation rate in zero magnetic field and consequently decreases the proton NMR signal at the end of the magnetic field cycle. The new technique is theoretically analyzed and compared to the single-frequency and two-frequency irradiation techniques. It is shown that the sensitivity of the new technique exceeds the sensitivity of the two-frequency irradiation technique. As a test of the new technique we measured the shape of the highest-frequency 17O NQR line in paraelectric KH2PO4.

Improving sensitivity and resolution of MQMAS spectra: a 45Sc-NMR case study of scandium sulphate pentahydrate

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 4 January 2010
C. Vinod Chandrana, Jérôme Cunyb, Régis Gautierb, Laurent Le Pollèsb, Chris J. Pickardc and Thomas Bräunigera,

To efficiently obtain multiple-quantum magic-angle spinning (MQMAS) spectra of the nuclide 45Sc (I=7/2), we have combined several previously suggested techniques to enhance the signal-to-noise ratio and to improve spectral resolution for the test sample, scandium sulphate pentahydrate (ScSPH). Whereas the 45Sc-3QMAS spectrum of ScSPH does not offer sufficient resolution to clearly distinguish between the 3 scandium sites present in the crystal structure, these sites are well-resolved in the 5QMAS spectrum. The loss of sensitivity incurred by using MQMAS with 5Q coherence order is partly compensated for by using fast-amplitude modulated (FAM) sequences to improve the efficiency of both 5Q coherence excitation and conversion. Also, heteronuclear decoupling is employed to minimise dephasing of the 45Sc signal during the 5Q evolution period due to dipolar couplings with the water protons in the ScSPH sample. Application of multi-pulse decoupling schemes such as TPPM and SPINAL results in improved sensitivity and resolution in the F1 (isotropic) dimension of the 5QMAS spectrum, the best results being achieved with the recently suggested SWf-TPPM sequence. By numerical fitting of the 45Sc-NMR spectra of ScSPH from 3QMAS, 5QMAS and single-quantum MAS at magnetic fields B0=9.4 T and 17.6 T, the isotropic chemical shift δiso, the quadrupolar coupling constant χ, and the asymmetry parameter η were obtained. Averaging over all experiments, the NMR parameters determined for the 3 scandium sites, designated (a), (b) and (c) are: δiso(a)=-15.5±0.5 ppm, χ(a)=5.60± 0.10 MHz, η(a)=0.06±0.05; δiso(b)=-12.9±0.5 ppm, χ(b)=4.50± 0.10 MHz, η(b)=1.00± 0.00; and δiso(c)=-4.7± 0.2 ppm, χ(c)=4.55± 0.05 MHz, η(c)=0.50±0.02. The NMR scandium species were assigned to the independent crystallographic sites by evaluating their experimental response to proton decoupling, and by density functional theory (DFT) calculations using the PAW and GIPAW approaches, in the following way: Sc(1) to (c), Sc(2) to (a), and Sc(3) to (b). The need to compute NMR parameters using an energy-optimised crystal structure is once again demonstrated.