April–May 2018 Editorial Board Publication date: April–May 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 90
April–May 2018 Host-guest interaction of styrene and ethylbenzene in MIL-53 studied by solid-state NMR Publication date: April–May 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 90 Author(s): Shenhui Li, Jing Li, Jing Tang, Feng Deng Solid-state NMR was utilized to explore the host-guest interaction between adsorbate and adsorbent at atomic level to understand the separation mechanism of styrene (St) and ethylbenzene (EB) in MIL-53(Al). 13C-27Al double-resonance NMR experiments revealed that the host-guest interaction between St and MIL-53 was much stronger than that of EB adsorption. In addition, 13C DIPSHIFT experiments suggested that the adsorbed St was less mobile than EB confined inside the MIL-53 pore. Furthermore, the host-guest interaction model between St, EB and MIL-53 was established on the basis of the spatial proximities information extracted from 2D 1H-1H homo-nuclear correlation NMR experiments. According to the experimental observation from solid-state NMR, it was found that the presence of
April–May 2018 Simultaneous homonuclear and heteronuclear spin decoupling in magic-angle spinning solid-state NMR Publication date: April–May 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 90 Author(s): Kaustubh R. Mote, Perunthiruthy K. Madhu We show here an effective way of implementing simultaneously homonuclear and heteronuclear dipolar decoupling in magic-angle spinning (MAS) solid-state NMR. Whilst the homonuclear spin decoupling is applied on the 1H channel, heteronuclear spin decoupling is applied on the 13C channel. The 1H spins are observed in a windowed fashion in this case. The resultant 1H spectrum has higher resolution due to the attenuation of broadening arising from both homonuclear 1H-1H and heteronuclear 1H-13C interactions, with the latter normally leading to additional line broadening in 13C labelled samples. The experiments are performed at MAS frequencies of ca. 60
Available online 3 February 2018 Direct detection and characterization of bioinorganic peroxo moieties in a vanadium complex by 17O solid-state NMR and density functional theory Publication date: Available online 19 February 2018 Source:Solid State Nuclear Magnetic Resonance Author(s): Rupal Gupta, John Stringer, Jochem Struppe, Dieter Rehder, Tatyana Polenova Electronic and structural properties of short-lived metal-peroxido complexes, which are key intermediates in many enzymatic reactions, are not fully understood. While detected in various enzymes, their catalytic properties remain elusive because of their transient nature, making them difficult to study spectroscopically. We integrated 17O solid-state NMR and density functional theory (DFT) to directly detect and characterize the peroxido ligand in a bioinorganic V(V) complex mimicking intermediates non-heme vanadium haloperoxidases. 17O chemical shift and quadrupolar tensors, measured by solid-state NMR spectroscopy, probe the electronic structure of the peroxido ligand and its interaction with the metal. DFT analysis reveals the unusually large chemical shift anisotropy arising from the metal orbitals contributing towards the magnetic shielding of the ligand. The results illustrate the power of an integrated approach for studies of oxygen centers in enzyme reaction intermediates.
February 2018 Description of an rf field-strength controller for solid-state NMR experiments Publication date: Available online 3 February 2018 Source:Solid State Nuclear Magnetic Resonance Author(s): Gregory Lusk, Terry Gullion Some MAS NMR experiments are sensitive to fluctuations or drifts in rf field strengths. We examine the simple 1H-13C CPMAS experiment and show that the 13C signal intensities vary over time due to drifts in rf field strengths. The causes of the drifts in rf field strengths are studied. Stabilization of the rf field strengths are obtained by using an rf field-strength controller. The controller is a stand-alone unit, which can be easily incorporated in any spectrometer system. Details of the controller, including circuit design, are provided.
February 2018 Editorial Board Publication date: February 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 89
February 2018 Molecular dynamics of palmitic acid and lead palmitate in cross-linked linseed oil films: Implications from deuterium magnetic resonance for lead soap formation in traditional oil paintings Publication date: February 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 89 Author(s): Jaclyn Catalano, Anna Murphy, Yao Yao, Nicholas Zumbulyadis, Silvia A. Centeno, Cecil Dybowski Many oil paintings, dating from the 15th century to the present, are affected by the formation of heavy-metal carboxylates (soaps) that alter the structural integrity and appearance of the works. Through transport phenomena not yet understood, free fatty acids formed from oils used as binders migrate through the paint film and react with heavy-metal ions that are constituents of pigments and/or driers, forming metal carboxylates. The local molecular dynamics of fatty acids and metal carboxylates are factors influencing material transport in these systems. We report temperature-dependent 2H NMR spectra of palmitic acid and lead palmitate as pure materials, in cross-linked linseed oil films, and in a lead white linseed oil paint film as part of our broader research into metal soap formation. Local dynamics at the
February 2018 Efficient low-power TOBSY sequences for fast MAS Publication date: February 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 89 Author(s): Kong Ooi Tan, Vipin Agarwal, Nils-Alexander Lakomek, Susanne Penzel, Beat H. Meier, Matthias Ernst Through-bond J-coupling based experiments in solid-state NMR spectroscopy are challenging because the J couplings are typically much smaller than the dipolar couplings. This often leads to a lower transfer efficiency compared to dipolar-coupling based sequences. One of the reasons for the low transfer efficiency are the second-order cross terms involving the strong heteronuclear dipolar couplings leading to fast magnetization decay. Here, we show that by employing a symmetry-based C9 sequence, which was carefully selected to suppress second-order terms, efficient polarization transfers of up to 80% can be achieved without decoupling on fully protonated two-spin model systems at a MAS frequency of 55.5 kHz with rf-field amplitudes of about 25 kHz. In addition, we analyse the effects of rf inhomogeneity and crystallites selection due to the polarization preparation method on the TOBSY transfer efficiency. We demonstrate on small model substances as well as on deuterated and 100% back-exchanged ubiquitin that and are efficient and practical TOBSY sequences at experimental conditions ranging from proton Larmor frequencies of 400–850 MHz, and MAS frequencies ranging from 55.5 to 111.1 kHz.
February 2018 Protein dynamics in the solid-state from 2H NMR lineshape analysis. III. MOMD in the presence of Magic Angle Spinning Publication date: February 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 89 Author(s): Eva Meirovitch, Zhichun Liang, Jack H. Freed We report on a new approach to the analysis of dynamic NMR lineshapes from polycrystalline (i.e., macroscopically disordered) samples in the presence of Magic Angle Spinning (MAS). This is an application of the Stochastic Liouville Equation developed by Freed and co-workers for treating restricted (i.e., microscopically ordered) motions. The 2H nucleus in an internally-mobile C–CD3 moiety serves as a prototype probe. The acronym is 2H/MOMD/MAS, where MOMD stands for “microscopic-order-macroscopic-disorder.” The key elements describing internal motions – their type, the local spatial restrictions, and related features of local geometry – are treated in MOMD generally, within their rigorous three-dimensional tensorial requirements. Based on this representation a single physically well-defined model of local motion has the capability of reproducing experimental spectra. There exist other methods for analyzing dynamic 2H/MAS spectra which advocate simple motional modes. Yet, to reproduce satisfactorily the experimental lineshapes, one has either to use unusual parameter values, or combine several simple motional modes. The multi-simple-mode reasoning assumes independence of the constituent modes, features ambiguity as different simple modes may be used, renders inter-system comparison difficult as the overall models differ, and makes possible model-improvement only by adding yet another simple mode, i.e., changing the overall model. 2H/MOMD/MAS is free of such limitations and inherently provides a clear physical interpretation. These features are illustrated. The advantage of 2H/MOMD/MAS in dealing with sensitive but hardly investigated slow-motional lineshapes is demonstrated by applying it to actual experimental data. The results differ from those obtained previously with a two-site exchange scheme that yielded unusual parameters.
November 2017 Selective observation of charge storing ions in supercapacitor electrode materials Publication date: February 2018 Source:Solid State Nuclear Magnetic Resonance, Volume 89 Author(s): Alexander C. Forse, John M. Griffin, Clare P. Grey Nuclear magnetic resonance (NMR) spectroscopy has emerged as a useful technique for probing the structure and dynamics of the electrode-electrolyte interface in supercapacitors, as ions inside the pores of the carbon electrodes can be studied separately from bulk electrolyte. However, in some cases spectral resolution can limit the information that can be obtained. In this study we address this issue by showing how cross polarisation (CP) NMR experiments can be used to selectively observe the in-pore ions in supercapacitor electrode materials. We do this by transferring magnetisation from 13C nuclei in porous carbons to nearby nuclei in the cations (1H) or anions (19F) of an ionic liquid. Two-dimensional NMR experiments and CP kinetics measurements confirm that in-pore ions are located within
November 2017 Editorial Board Publication date: November 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 88
November 2017 Insights into protein misfolding and aggregation enabled by solid-state NMR spectroscopy Publication date: November 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 88 Author(s): Patrick C.A. van der Wel The aggregation of proteins and peptides into a variety of insoluble, and often non-native, aggregated states plays a central role in many devastating diseases. Analogous processes undermine the efficacy of polypeptide-based biological pharmaceuticals, but are also being leveraged in the design of biologically inspired self-assembling materials. This Trends article surveys the essential contributions made by recent solid-state NMR (ssNMR) studies to our understanding of the structural features of polypeptide aggregates, and how such findings are informing our thinking about the molecular mechanisms of misfolding and aggregation. A central focus is on disease-related amyloid fibrils and oligomers involved in neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's disease. SSNMR-enabled structural and dynamics-based findings are surveyed, along with a number of resulting emerging themes that appear common to different amyloidogenic proteins, such as their compact alternating short-
November 2017 Spin diffusion and 1H spin-lattice relaxation in Cs2(HSO4)(H2PO4) containing a small amount of ammonium ions Publication date: November 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 88 Author(s): Shigenobu Hayashi, Keiko Jimura Inorganic solid acid salts with hydrogen bond networks frequently show very long spin-lattice relaxation times even for 1H because the hydrogen bonds suppress motions. In the present work, the 1H spin-lattice relaxation in Cs2(HSO4)(H2PO4) containing a small amount of ammonium ions were studied in detail by use of the effect of magic angle spinning (MAS) on the relaxation. The 1H spin-lattice relaxation times of the acid protons decrease with increase in the content of ammonium ions. Reorientation of the NH4 group fluctuates the dipole-dipole interaction and relaxes the ammonium protons as well as the acid protons. The 1H relaxation times of the acid protons are a little bit longer than those of the ammonium protons at the MAS rate of 8 kHz. The spinning at 50 kHz makes the relaxation times of the acid protons longer and those of the ammonium protons shorter. Spin diffusion between the acid and the ammonium protons averages partially the 1H relaxation of the acid and the ammonium protons at the MAS rate of 8 kHz. The spin diffusion is suppressed completely at the MAS rate of 50 kHz. Spin diffusion between the acid protons is not suppressed at the MAS rate of 50 kHz. The acid protons always show the same relaxation times. The intrinsic relaxation times not affected by spin diffusion are evaluated quantitatively for both the acid and the ammonium protons. Those values are independent of the ammonium content. Contribution of the spin diffusion between the acid and the ammonium protons to the relaxation is estimated quantitatively. Using those parameters, the effect of ammonium ions on the 1H spin-lattice relaxation can be predicted. The 1H spin-lattice relaxation is a sensitive tool to study the distribution of ammonium ions in solids.
November 2017 Comparing the efficacy of solid and magic-echo refocusing sequences: Applications to 1H NMR echo spectroscopy of shale rock Publication date: November 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 88 Author(s): Gregory S. Boutis, Ravinath Kausik Quantitative evaluation of the solid and viscous components of unconventional shale rock, namely kerogen and bitumen, is important for understanding reservoir quality. Short transverse coherence times, due to strong 1H-1H dipolar interactions, motivates the application of solid state refocusing pulse sequences that allow for investigating components of the free-induction decay that are otherwise obscured by instrumental effects such as probe ringdown. This work reports on static, wide-line 1H spectroscopy of shale rock and their extracted components, which include kerogen and bitumen, by the application of solid echo and magic echo pulse sequences. We characterize the efficiency of these cycles as a function of the radio frequency power and inter-pulse spacing. Magic echos are shown to provide superior refocusing in comparison to solid echo based experiments, as can be understood from the truncation of the Magnus expansion and ability to also refocus any Hamiltonians (e.g. static field inhomogeneity). We characterize the optimal echo spacing and RF power for two shale samples of different maturity, motivating routine core and cuttings analysis and applications.
October 2017 TOC Publication date: November 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 88
October 2017 Editorial Board Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87
October 2017 Identification of double four-ring units in germanosilicate ITQ-13 zeolite by solid-state NMR spectroscopy Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87 Author(s): Xiaolong Liu, Yueying Chu, Qiang Wang, Weiyu Wang, Chao Wang, Jun Xu, Feng Deng Well-crystallized Ge-free and Ge-ITQ-13 were successfully obtained by solid state synthesis method. The Ge/Si ratio and the water content that are the two important factors in the synthesis of germanosilicate zeolites were explored for the formation of ITQ-13. The effect of the mineralizing agents (NH4F and NH4Cl) on the ITQ-13 synthesis was investigated as well. The obtained pure silica ITQ-13 and Ge-ITQ-13 were characterized by one- and two-dimensional solid- state NMR techniques. One-dimensional (1D) 19F MAS, 1H
October 2017 Energy efficiency increase of NQR spectrometer transmitter at pulse resonance excitation with noise signals Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87 Author(s): A. Samila, V. Khandozhko, L. Politansky The specific feature of NQR is expansion of spectral lines which is caused not only by dipole-dipole interaction of nuclei, but also by local field nonuniformity caused by the defects and deformation in crystal matrix. Considerable line expansion, which is typical of crystals, requires in pulsed NQR method the optimization of pulse shape and the reserve of transmitter power output. Parametric computer identification was used to study a dependence of parameters of the energy spectra of the output signal of pulsed NQR spectrometer transmitter on the duration of excitation pulses with sine and noise occupation. The energy efficiency of a linear amplifier was calculated and experimental investigations of its temperature conditions were carried out. The energy-efficient broadband transmitter was proposed that can be used in portable setups for the pursuance of research in the field of pulsed NQR spectroscopy, for instance when studying isotopes with quadrupole moments 14N, 35Cl, 63Cu, 69Ga, 71Ga, 113In, 115In and others.
October 2017 Detailed mechanisms of 1H spin-lattice relaxation in ammonium dihydrogen phosphate confirmed by magic angle spinning Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87 Author(s): Shigenobu Hayashi, Keiko Jimura Mechanisms of the 1H spin-lattice relaxation in NH4H2PO4 were studied in detail by use of the effect of magic angle spinning on the relaxation. The acid and the ammonium protons have different relaxation times at the spinning rates higher than 10 kHz due to suppression of spin diffusion between the two kinds of protons. The intrinsic relaxation times not affected by the spin diffusion and the spin-diffusion assisted relaxation times were evaluated separately, taking into consideration temperature dependence. Both mechanisms contribute to the 1H relaxation of the acid protons comparatively. The spin-diffusion assisted relaxation mechanism was suppressed to the level lower than the experimental errors at the spinning rate of 30 kHz.
October 2017 Solid-state NMR spectroscopic trends for supramolecular assemblies and protein aggregates Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87 Author(s): Rasmus Linser Solid-state NMR is able to generate structural data on sample preparations that are explicitly non-crystalline. In particular, for amyloid fibril samples, which can comprise significant degrees of sample disorder, solid-state NMR has been used very successfully. But also solid-state NMR studies of other supramolecular assemblies that have resisted assessment by more standard methods are being performed with increasing ease and biological impact, many of which are briefly reviewed here. New technical trends with respect to structure calculation, protein dynamics and smaller sample amounts have reshaped the field of solid-state NMR recently. In particular, proton-detected approaches based on fast Magic-Angle Spinning (MAS) were demonstrated for crystalline systems initially. Currently, such approaches are being expanded to the above-mentioned non-crystalline targets, the characterization of which can now be pursued with sample amounts on the order of a milligram. In this Trends article, I am giving a brief overview about achievements of the last years as well as the directions that the field has been heading into and delineate some satisfactory perspectives for solid-state NMR's future striving.
October 2017 Resolution enhancement in proton double quantum magic-angle spinning spectra by constant-time acquisition Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87 Author(s): Henri Colaux, Yusuke Nishiyama Although very fast MAS rate (>60 kHz) paves a way to obtain a sufficient resolution in the 1H double-quantum magic-angle spinning (DQMAS) experiments to probe 1H proximities, the 1H resolution still limits wider applications below its potential use. Here, the combination of the DQMAS experiment with the constant-time (CT) acquisition approach is demonstrated, giving an increased peak-separation power in the DQ dimension. The advantages and disadvantages in terms of sensitivity and resolution of the conventional and CT approaches are discussed.
October 2017 Expanding the horizons for structural analysis of fully protonated protein assemblies by NMR spectroscopy at MAS frequencies above 100 kHz Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87 Author(s): Jochem Struppe, Caitlin M. Quinn, Manman Lu, Mingzhang Wang, Guangjin Hou, Xingyu Lu, Jodi Kraus, Loren B. Andreas, Jan Stanek, Daniela Lalli, Anne Lesage, Guido Pintacuda, Werner Maas, Angela M. Gronenborn, Tatyana Polenova The recent breakthroughs in NMR probe technologies resulted in the development of MAS NMR probes with rotation frequencies exceeding 100 kHz. Herein, we explore dramatic increases in sensitivity and resolution observed at MAS frequencies of 110–111 kHz in a novel 0.7 mm HCND probe that enable structural analysis of fully protonated biological systems. Proton- detected 2D and 3D correlation spectroscopy under such conditions requires only 0.1–0.5 mg of sample and a fraction of time compared to conventional 13C-detected experiments. We discuss the performance of several proton- and heteronuclear- (13C-,15N-) based correlation experiments in terms of sensitivity and resolution, using a model microcrystalline fMLF tripeptide. We demonstrate the applications of ultrafast MAS to a large, fully protonated protein assembly of the 231-residue HIV-1 CA capsid protein. Resonance assignments of protons and heteronuclei, as well as 1H-15N dipolar and 1HN CSA tensors are readily obtained from the high sensitivity and resolution proton-detected 3D experiments. The approach demonstrated here is expected to enable the determination of atomic-resolution structures of large protein assemblies, inaccessible by current methodologies.
October 2017 Is protein deuteration beneficial for proton detected solid-state NMR at and above 100 kHz magic-angle spinning? Publication date: October 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 87 Author(s): Diane Cala-De Paepe, Jan Stanek, Kristaps Jaudzems, Kaspars Tars, Loren B. Andreas, Guido Pintacuda 1H-detection in solid-state NMR of proteins has been traditionally combined with deuteration for both resolution and sensitivity reasons, with the optimal level of proton dilution being dependent on MAS rate. Here we present 1H-detected 15N and 13C CP-HSQC spectra on two microcrystalline samples acquired at 60 and 111 kHz MAS and at ultra-high field. We critically compare the benefits of three labeling schemes yielding different levels of proton content in terms of resolution, coherence lifetimes and feasibility of scalar-based 2D correlations under these experimental conditions. We observe unexpectedly high resolution and sensitivity of aromatic resonances in 2D 13C-1H correlation spectra of protonated samples. Ultrafast MAS reduces or even removes the necessity of 1H dilution for high-resolution 1H-detection in biomolecular solid-state NMR. It yields 15N,1H and 13C,1H fingerprint spectra of exceptional resolution for fully protonated samples, with notably superior 1H and 13C lineshapes for side-chain resonances.
September 2017 Community based barriers to the wider acceptance of Solid State NMR Publication date: September 2017 Source:Solid State Nuclear Magnetic Resonance, Volumes 85–86 Author(s): Paul Jonsen During August 2015, the author surveyed 76 solid state NMR scientists from materials science to biology, academic to industrial, based in North America, Europe, India, China, Japan and Australia. The subject concerned barriers to the wider acceptance of solid state NMR and included the various barriers based on experimental, funding, vendor based and community aspects. This survey was confidential. However, many of the survey participants requested that at least the results of the part of the survey relevant to our community be made public. This was agreed by the commissioner of the survey and these findings were presented at the ‘Developments and Applications of Solid State NMR’, Varna, Bulgaria during May 2016. Following the resultant discussion, members of the conference requested that the author publish these findings. These findings are a collection of the opinions of the survey participants and include additional anecdotes from the author, with the intention of stimulating a community debate to ensure that a subject we all have close to our hearts; solid state NMR continues to thrive moving forwards.
September 2017 Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation Publication date: September 2017 Source:Solid State Nuclear Magnetic Resonance, Volumes 85–86 Author(s): Peter A. Beckmann, Joseph M. Bohen, Jamie Ford, William P. Malachowski, Clelia W. Mallory, Frank B. Mallory, Andrew R. McGhie, Arnold L. Rheingold, Gilbert J. Sloan, Steven T. Szewczyk, Xianlong Wang, Kraig A. Wheeler We report a variety of experiments and calculations and their interpretations regarding methyl group (CH3) rotation in samples of pure 3-methylglutaric anhydride (1), pure 3-methylglutaric acid (2), and samples where the anhydride is slowly absorbing water from the air and converting to the acid [C6H8O3(1) + H2O
September 2017 Repetitive experiments of one or two-pulse sequences in NQR of spins I=3/2: Liouville space, steady-state, Ernst angle and optimum signal Publication date: September 2017 Source:Solid State Nuclear Magnetic Resonance, Volumes 85–86 Author(s): Christophe Odin In NMR, the repetition of pulse sequences with a recycle time that does not allow the spin system to completely relax back to equilibrium is a well known and often used method to increase the signal to noise ratio at given total measuring time. For isolated spins I=1/2, the steady-state of a train of strictly identical pulse sequences separated by free evolution periods of same duration is described by the well known Ernst-Anderson model, and the optimum pulse angle is given by the Ernst angle. We showed recently that equivalent formula, but with super-operators in the Liouville space, can be obtained for general spins I. In this article, this formalism is generalized to pure NQR of spins I=3/2, and applied to calculate the signal resulting from single and solid-echo sequences, in the limit when the recycle time , where T2q is the transverse (coherence) quadrupolar relaxation time. In particular, we show that powder samples have a behaviour that is very close to NMR of spins I=1/2. For instance, the generalized Ernst angle
September 2017 Determination of polymer crystallinity by the multivariable curve resolution method in 13C solid NMR spectrum Publication date: September 2017 Source:Solid State Nuclear Magnetic Resonance, Volumes 85–86 Author(s): Xiaoyue Zhou, Kaipin Xu, Pei Ni, Qun Chen, Shanmin Zhang Most of the polymers are composed of a crystal part, an amorphous part, and a transitional interfacial part. These components present disparate physical and chemical characteristics. However, it always suffers from peak overlapping in solid NMR spectrum in order to acquire polymer's crystallinity. The polyethylene oxide (PEO) sample was tested using the Torchia pulse sequence combined with the Multivariate Curve Resolution (MCR) method. A two dimensional CP/MAS spectrum containing spin-lattice relaxation time (T1) information was acquired. After the correction based on the reciprocity relation, the overlapped peaks were resolved and quantified together with their T1's. Crystallinity is therefore observed naturally according to components’ content ratios associated with their T1 values.
July–August 2017 C4: TOC Publication date: September 2017 Source:Solid State Nuclear Magnetic Resonance, Volumes 85–86
Spin-locking of half-integer quadrupolar nuclei in NMR of solids: The far off-resonance case Publication date: July–August 2017 Source:Solid State Nuclear Magnetic Resonance, Volume 84 Author(s): Smita Odedra, Stephen Wimperis Spin-locking of spin and nuclei in the presence of large resonance offsets has been studied using both approximate and exact theoretical approaches and, in the case of , experimentally. We show the variety of coherences and population states produced in a far off-resonance spin-locking NMR experiment (one consisting solely of a spin-locking pulse) and how these vary with the radiofrequency field strength and offset frequency. Under magic angle spinning (MAS) conditions and in the “adiabatic limit”, these spin-locked states acquire a time dependence. We discuss the rotor-driven interconversion of the spin-locked states, using an exact density matrix approach to confirm the results of the approximate model. Using conventional and multiple-quantum filtered spin-locking 23Na () NMR experiments under both static and MAS conditions, we confirm the results of the theoretical calculations, demonstrating the applicability of the approximate theoretical model to the far off-resonance case. This simplified model includes only the effects of the initial rapid dephasing of coherences that occurs at the start of the spin-locking period and its success in reproducing both experimental and exact simulation data indicates that it is this dephasing that is the dominant phenomenon in NMR spin-locking of quadrupolar nuclei, as we have previously found for the on-resonance and near-resonance cases. Potentially, far off-resonance spin-locking of quadrupolar nuclei could be of interest in experiments such as cross polarisation as a consequence of the spin-locking pulse being applied to a better defined initial state (the thermal equilibrium bulk magnetisation aligned along the z-axis) than can be created in a powdered solid with a selective radiofrequency pulse, where the effect of the pulse depends on the orientation of the individual crystallites.