Journal of magnetic resonance

On the choice of heteronuclear dipolar decoupling scheme in solid-state NMR

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 9 September 2010
Subhradip, Paul , N.D., Kurur , P.K., Madhu

We present here a comparison of different heteronuclear dipolar decoupling sequences at the moderate magic-angle spinning (MAS) frequency (ν_r) of 30 kHz. The radio-frequency (RF) amplitude (ν₁) ranges from the low power (ν₁ < ν_r) to the high power regime (ν₁ > 2ν_r) and includes the rotary resonance conditions (ν₁ = nν_r) wheren = 1, 2. For decoupling at the rotary resonance condition, we recently introduced a modification of TPPM, namely high-phase TPPM, whose properties will be discussed here. Finally, based on earlier published and current experimental results we suggest the optimal sequence for heteronuclear dipolar decoupling at any RF amplitude and MAS frequencies up to 35 kHz.

Z-spectroscopy with Alternating Phase Irradiation

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 15 September 2010
Johanna, Närväinen , Penny L., Hubbard , Risto A., Kauppinen , Gareth A., Morris

Magnetization transfer (MT) MRI and Z-spectroscopy are tools to study both water–macromolecule interactions and pH-sensitive exchange dynamics between water and the protons of mobile chemical groups within these macromolecules. Both rely on saturation of frequencies offset from water and observation of the on-resonance water signal. In this work, an RF saturation method called Z-spectroscopy with Alternating-Phase Irradiation (ZAPI) is introduced. Based on the T₂-selectivity of the irradiation pulse, ZAPI can be used to separate the different contributions to a Z-spectrum, as well as to study the T₂ distribution of the macromolecules contributing to the MT signal. ZAPI can be run at resonance for water and with low power, thus minimizing problems with specific absorption rate (SAR) limits in clinical applications. In this paper, physical and practical aspects of ZAPI are discussed and the sequence is applied in vitro to sample systems and in vivo to rat head to demonstrate the method.

Application of Optimal Control to CPMG Refocusing Pulse Design

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 15 September 2010
Troy W., Borneman , Martin D., Hürlimann , David G., Cory

We apply optimal control theory (OCT) to the design of refocusing pulses suitable for the CPMG sequence that are robust over a wide range of B₀ and B₁ offsets. We also introduce a model, based on recent progress in the analysis of unitary dynamics in the field of quantum information processing (QIP), that describes the multiple refocusing dynamics of the CPMG sequence as a dephasing Pauli channel. This model provides a compact characterization of the consequences and severity of residual pulse errors. We illustrate the methods by considering a specific example of designing and analyzing broadband OCT refocusing pulses of length 10 t₁₈₀that are constrained by the maximum instantaneous pulse power. We show that with this refocusing pulse, the CPMG sequence can refocus over 98% of magnetization for resonance offsets up to 3.2 times the maximum RF amplitude, even in the presence of ±10% RF inhomogeneity.

A simple one-dimensional method of chemical shift anisotropy determination under MAS conditions

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 18 September 2010
Piotr, Bernatowicz

A method of determination of chemical shift anisotropy (CSA) tensor principal components under MAS condition is presented. It is a simple, one-dimensional, and robust alternative to the commonly exploited, but more complicated 2D-PASS. The required CSA components are delivered by simultaneous numerical analysis of a few regular MAS spectra acquired under different spinning rates.

On the measurement of 15N-{1H} nuclear Overhauser effects. 2. Effects of the saturation scheme and water signal suppression

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 24 September 2010
Fabien, Ferrage , Amy, Reichel , Shibani, Battacharya , David, Cowburn , Ranajeet, Ghose

Measurement of steady-state ¹⁵N-{¹H} nuclear Overhauser effects forms a cornerstone of most methods to determine protein backbone dynamics from spin-relaxation data, since it is the most reliable probe of very fast motions on the ps-ns timescale. We have, in two previous publications (J. Magn. Reson. 192 (2008), 302-313; J. Am. Chem. Soc. 131 (2009), 6048-6049) reevaluated spin-dynamics during steady-state (or “saturated”) and reference experiments, both of which are required to determine the NOE ratio. Here we assess the performance of several windowed and windowless sequences to achieve effective saturation of protons in steady-state experiments. We also evaluate the influence of the residual water signal due to radiation damping on the NOE ratio. We suggest a recipe that allows one to determine steady-state ¹⁵N-{¹H} NOE’s without artifacts and with the highest possible accuracy.

Hydration Water Dynamics in Biopolymers from NMR Relaxation in the Rotating Frame

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 24 September 2010
Barbara, Blicharska , Hartwig, Peemoeller , Magdalena, Witek

Assuming dipole-dipole interaction as the dominant relaxation mechanism of protons of water molecules adsorbed onto macromolecule (biopolymer) surfaces we have been able to model the dependences of relaxation rates on temperature and frequency. For adsorbed water molecules the correlation times are of the order of 10^-5 s, for which the dispersion region of spin-lattice relaxation rates in the rotating frame R₁ρ = 1/T₁ρ appears over a range of easily accessible B₁ values. Measurements of T₁ρ at constant temperature and different B₁ values then give the “dispersion profiles” for biopolymers. Fitting a theoretical relaxation model to these profiles allows for the estimation of correlation times. This way of obtaining the correlation time is easier and faster than approaches involving measurements of the temperature dependence of R₁ = 1/T₁. The T₁ρ dispersion approach, as a tool for molecular dynamics study, has been demonstrated for several hydrated biopolymer systems including crystalline cellulose, starch of different origins (potato, corn, oat, wheat), paper (modern, old) and lyophilized proteins (albumin, lysozyme).

IPAP- HSQMBC: Measurement of Long-Range Heteronuclear Coupling Constants from Spin-State Selective Multiplets

Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 29 September 2010
Sergi, Gil , Juan Félix, Espinosa , Teodor, Parella

A new NMR approach is proposed for the measurement of long-range heteronuclear coupling constants (ⁿJ_XH, n>1) in natural abundance molecules. Two complementary in-phase (IP) and anti-phase (AP) data are separately recorded from a modified HSQMBC experiment and then added/subtracted to provide spin-state-selective α/β-HSQMBC spectra. The magnitude of ⁿJ_XHcan be directly determined by simple analysis of the relative displacement between α- and β-cross-peaks. The robustness of this IPAP-HSQMBC experiment is evaluated experimentally and by simulation using a variety of different conditions. Important aspects such as signal intensity dependence and presence of unwanted cross-talk effects are discussed and examples on the measurement of small proton-carbon (ⁿJ_CH) and proton-nitrogen (ⁿJ_NH) coupling constants are provided.

Characterization of a 3D MEMS fabricated micro solenoid at 9.4T

M. Mohmmadzadeh^a,, N. Baxan^a, V. Badilita^b, K. Kratt^b, H. Weber^a, J.G. Korvink^{c, d}, U. Wallrabe^{b, d}, J. Hennig^a and D. von Elverfeldt^a

We present for the first time a complete characterization of a micro-solenoid for high resolution MR imaging of mass- and volume-limited samples based on three-dimensional B₀, B₁ per unit current (B_1unit) and SNR maps. The micro-solenoids are fabricated using a fully micro-electromechanical systems (MEMS) compatible process in conjunction with an automatic wire-bonder. We present 15 μm isotropic resolution 3D B₀ maps performed using the phase difference method. The resulting B₀ variation in the range of [-0.07 ppm-0.157 ppm] around the coil center, compares favorably with the 0.5 ppm limit accepted for MR microscopy. 3D B_1unit maps of 40 μm isotropic voxel size were acquired according to the extended multi flip angle (ExMFA) method. The results demonstrate that the characterized microcoil provides a high and uniform sensitivity distribution around its center (B_1unit = 3.4 mT/A ± 3.86%) which is in agreement with the corresponding 1D theoretical data computed along the coil axis. The 3D SNR maps reveal a rather uniform signal distribution around the coil center with a mean value of 53.69 ± 19%, in good agreement with the analytical 1D data along coil axis in the axial slice. Finally, we prove the microcoil capabilities for MR microscopy by imaging Eremosphaera Viridis cells with 18 μm isotropic resolution.