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Fish diseases have a "stress-related" nature, whereas fish exposure to stressors will increase their susceptibility to infections. It was also noted that fish exposure to biotic and abiotic stressors would exaggerate the disease signs, elicit high mortalities, and cause severe economic losses. Motile aeromonad septicemia (MAS) is a major bacterial disease affecting a variety of finfish species throughout the globe and is caused by Aeromonas hydrophila. Herein, we have evaluated the impacts of ammonia-N stress and/or Nile tilapia challenge with pathogenic A. hydrophila on the clinical picture of MAS disease. Clinical signs, postmortem lesions, histoarchitectural changes, and gene transcription analysis were studied. Fish experimentally infected with A. hydrophila were exophthalmic and showed darkened skin. Moreover, opercular hyperemia, petechial hemorrhages, and gill congestion alongside dermal ulcerations were noticed in ammonia-exposed fish. On the other side, fish exposed to both stressors exhibited exophthalmia, corneal opacity, severe dropsy, and hemorrhagic dermal ulcerations. At the tissue levels, the histopathological lesions were exaggerated in the fish group exposed to ammonia stress and challenged with A. hydrophila than fish group exposed to each one alone. At the molecular levels, the mRNA expression analysis reveals significant upregulation of inflammatory cytokines such as interleukin-1 beta, CXC chemokine , and tumor necrosis factor-alpha in the kidney tissues of Nile tilapia exposed to ammonia and/or challenged with A. hydrophila. In a similar trend, the mRNA expression values of heat shock protein 70 (HSP70), oxidative stress related genes (SOD and CAT) and apoptosis-related genes (caspase 3 , BAX , and cytochrome P450) were also increased in the hepatic tissues of fish exposed to singular or dual stressors. Interestingly, the highest expression levels of the above-mentioned genes were found in the fish group exposed to both stressors. Taken together, these findings indicate the occurrence of severe inflammatory and apoptotic changes in fish exposed to ammonia and infected with A. hydrophila more than each one alone. In contrast, there was a significant decrease in the expression values of the antioxidant enzyme glutathione-S-transferase (GST) in stressed fish, suggesting the occurrence of oxidative stress. This study will be helpful to draw mechanistic insights into the exposure of fish to ammonia stress and infection with A. hydrophila. • Dual ammonia-N and Aeromonas hydrophila challenge exaggerate signs and PM lesions in Nile tilapia. • Histopathological scores are increased in Nile tilapia exposed to dual stressors than each alone. • Upregulation of HSP70 , inflammatory cytokines, and apoptosis genes in fish challenged by ammonia and/or A. hydrophila. • Increase expression of SOD and CAT genes in fish challenged by ammonia and/or A. hydrophila. • This study draws mechanistic insights in Nile tilapia exposed to ammonia-N and A. hydrophila at molecular and tissue levels. [ABSTRACT FROM AUTHOR]

Improving the spectral sensitivity and resolution of biological solids is one of the long-standing problems in nuclear magnetic resonance (NMR) spectroscopy. In this report, we introduce low-power supercycled variants of two-pulse phase-modulated (TPPM) sequence for heteronuclear decoupling. The utility of the sequence is shown by improvements in the transverse relaxation time of observed nuclei (with 1H decoupling) with its application to different samples (uniformly 13C, 15N, 2H-labeled GB1 back-exchanged with 25% H 2 O and 75% D 2 O, uniformly 13C, 15N, 2H-labeled human derived Asyn fibril back-exchanged with 100% H 2 O and uniformly 13C, 15N -labeled human derived Asyn fibril) at fast MAS using low radiofrequency (RF) fields. To understand the effect of spinning speed, the transverse relaxation time is monitored under different spinning frequencies. In comparison to existing heteronuclear decoupling sequences, the supercycled TPPM (sTPPM) sequence significantly improves the spectral sensitivity and resolution and is robust towards B 1 inhomogeneity and decoupler offset. [Display omitted] • Low power supercycled TPPM sequence for heteronuclear decoupling in solid-state NMR. • Improved robustness towards B 1 inhomogeneity and chemical shift offset. • Robust performance over a large range of parameters. • Improved protocol for 1H detection in solid-state NMR. [ABSTRACT FROM AUTHOR]

• A (S + 1/2) loss in many correlation and polarization-transfer experiments of quadrupole nuclei S. • Level-crossings of satellite transition and rf frequency under MAS complicate the spin dynamics of quadrupole nuclei. • NMR method development, high magnetic fields, efficient and high-power probes are important to quadrupole nuclei. High magnetic field can dramatically increase the spectral resolution and sensitivity of quadrupole nuclei S > 1/2 by the reduction of the second-order quadrupole broadening. A brief overview and outlook on spectral acquisition, the importance of high magnetic field, inter-nuclei distance measurement, various 2D separation and correlation methods of quadrupole nuclei are presented. The complications and consequences of spin dynamics under rf irradiation for the (2S + 1) level system and level-crossing with the satellite transition frequencies under magic-angle spinning are discussed. There is a scaling down of (S + 1/2) to the efficiency of many experiments in comparison with a spin-1/2 due to the fact that only two central transition spin states out of the (2S + 1) levels contribute to polarization transfer and spin correlation. [ABSTRACT FROM AUTHOR]

We characterize a new generation of MAS probes, designed for 1H detection in solid and viscous structures. High top speed (currently 170 kHz), existence of a wide speed range and quick acceleration enable numerous new experiment categories. Most notably, massive biomolecular structures become amenable to a detailed structural and dynamics studies. [ABSTRACT FROM AUTHOR]

Cross Effect (CE) Dynamic Nuclear Polarization (DNP) relies on the dipolar (D) and exchange (J) coupling interaction between two electron spins. Until recently only the electron spin D coupling was explicitly included in quantifying the DNP mechanism. Recent literature discusses the potential role of J coupling in DNP, but does not provide an account of the distribution and source of electron spin J coupling of commonly used biradicals in DNP. In this study, we quantified the distribution of electron spin J coupling in AMUPol and TOTAPol biradicals using a combination of continuous wave (CW) X-band electron paramagnetic resonance (EPR) lineshape analysis in a series of solvents and at variable temperatures in solution – a state to be vitrified for DNP. We found that both radicals show a temperature dependent distribution of J couplings, and the source of this distribution to be conformational dynamics. To qualify this conformational dependence of J coupling in both molecules we carry out Broken Symmetry DFT calculations which show that the biradical rotamer distribution can account for a large distribution of J couplings, with the magnitude of J coupling directly depending on the relative orientation of the electron spin pair. We demonstrate that the electron spin J couplings in both AMUPol and TOTAPol span a much wider distribution than suggested in the literature. We affirm the importance of electron spin J coupling for DNP with density matrix simulations of DNP in Liouville space and under magic angle spinning, showcasing that a rotamer with high J coupling and optimum relative g-tensor orientation can significantly boost the DNP performance compared to random orientations of the electron spin pair. We conclude that moderate electron spin J coupling above a threshold value can facilitate DNP enhancements. Image 1 • Biradicals demonstrate temperature dependent J coupling. • J coupling exists as a distribution in solution state. • J coupling is dependent on biradical rotamer state. • DNP performance is tuned by J coupling. [ABSTRACT FROM AUTHOR]

Abstract Significant progress has been made in obtaining structural insight into the assembly of the β-barrel assembly machinery complex (BAM). These crystallography and electron microscopy studies used detergent as a membrane mimetic and revealed structural variations in the central domain, BamA, as well as in the lipoprotein BamC. We have used cellular solid-state NMR spectroscopy to examine the entire BamABCDE complex in native outer membranes and obtained data on the BamCDE subcomplex in outer membranes, in addition to synthetic bilayers. To reduce spectral crowding, we utilized proton-detected experiments and employed amino-acid specific isotope-labelling in (13C, 13C) correlation experiments. Taken together, the results provide insight into the overall fold and assembly of the BAM complex in native membranes, in particular regarding the structural flexibility of BamC in the absence of the core unit BamA. [ABSTRACT FROM AUTHOR]

[Display omitted] • Instrumental development to achieve sustainable, cost-effective cryogenic Helium sample spinning. • Solid-state NMR and DNP at ultra-low temperature. • Closed-loop helium system composed of a powerful heat exchanger, a cryocooler and a single Helium compressor. • 30 K at the sample with a single cryocooler. • Cryogenic sample exchange system. We report here instrumental developments to achieve sustainable, cost-effective cryogenic Helium sample spinning in order to conduct dynamic nuclear polarisation (DNP) and solid-state NMR (ssNMR) at ultra-low temperatures (<30 K). More specifically, we describe an efficient closed-loop helium system composed of a powerful heat exchanger (95% efficient), a single cryocooler, and a single helium compressor to power the sample spinning and cooling. The system is integrated with a newly designed triple-channel NMR probe that minimizes thermal losses without compromising the radio frequency (RF) performance and spinning stability (±0.05%). The probe is equipped with an innovative cryogenic sample exchange system that allows swapping samples in minutes without introducing impurities in the closeloop system. We report that significant gain in sensitivity can be obtained at 30–40 K on large micro-crystalline molecules with unfavorable relaxation timescales, making them difficult or impossible to polarize at 100 K. We also report rotor-synchronized 2D experiments to demonstrate the stability of the system. [ABSTRACT FROM AUTHOR]

Abstract Several alleles at the pvr2 locus are known to control recessive resistance to Potato virus Y (PVY) in pepper. In this study, PVY resistant F 2 pepper lines were developed from local germplasm carrying recessive genes (pvr2 1 and pvr2 2 ) using marker-assisted selection (MAS). The F 1 and F 2 generations were assessed for the presence of resistant/susceptible alleles (pvr2 + / pvr2 1 / pvr2 2 ) at the pvr2 - elF4E locus using the tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) procedure. Our results show that ARMS-PCR can be used to successfully screen pepper genotypes for alleles that confer PVY resistance thereby contributing to the improvement of pepper production. Highlights • Recessive alleles at the pvr2 locus resistance to Potato virus Y (PVY) in pepper. • PVY resistant F 2 pepper lines were developed using marker-assisted selection (MAS). • F 1 and F 2 generations were assessed for PVY resistant alleles at the pvr2 - elF4E locus. • Tetra-primer ARMS-PCR was used to identify PVY resistant/susceptible alleles (pvr2 + / pvr2 1 / pvr2 2 ) at the pvr2 - elF4E locus. [ABSTRACT FROM AUTHOR]

Previously our lab has created a mouse ovarian xenograft model of copy number variation (CNV)-mediated G protein-coupled receptor (GPCR) MAS-driven tumorigenesis, and RNA profiling identified a putative chemokine tumor-induced factor ( Tif ). Sequence analysis and chemotactic study suggested that Tif was likely to be a hamster homolog of human GROγ ( CXCL3 ) [IJC 125 (2009): 1316–1327]. In the present study, we report the molecular and functional characterization of the Tif gene. Genomic study of CHO-K1 cells indicated that Tif gene consisted of 4 exons, characterized with an antisense B1 element which is embedded in the fourth exon. Two Tif transcripts were identified which shared identical sequences except that a string of 71-nt derived from the antisense B1 element was deficient in the shorter transcript. Of interests, B1- like RNA ladder was detected in xenografts. Functional studies showed that TIF induced chemotaxis and neovessel formation. Pharmacological studies suggested that TIF activated Gi-coupled CXCR2 and induced both calcium mobilization and ERK1/2 phosphorylation, and suppressed forskolin-stimulated cAMP accumulation. In addition, secreted matured TIF functioned as an autocrine factor and promoted anchorage-independent growth. Unexpectedly, TIF delayed the onset of tumor formation, possibly via suppressing proliferation of stromal fibroblasts. However, TIF did not exert any inhibitory effect on tumor growth. Potentially, TIF could be used for preventing cancer relapse. [ABSTRACT FROM AUTHOR]

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 2 H nucleus in an internally-mobile C–CD 3 moiety serves as a prototype probe. The acronym is 2 H/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 2 H/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. 2 H/MOMD/MAS is free of such limitations and inherently provides a clear physical interpretation. These features are illustrated. The advantage of 2 H/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. [ABSTRACT FROM AUTHOR]

An improved implementation of single-crystal magic-angle-spinning (MAS) NMR is presented which gives access to chemical shift tensors both in orientation (relative to the crystal axis system) and principal axis values. For mounting arbitrary crystals inside ordinary MAS rotors, a mounting tool is described which allows to relate the crystal orientation determined by diffraction techniques to the rotor coordinate system. The crystal is finally mounted into a MAS rotor equipped with a special insert which allows a defined reorientation of the single-crystal by 90°. The approach is based on the idea that the dispersive spectra, which are obtained when applying read-pulses at specific rotor-phases, not only yield the size of the eigenvalues but also encode the orientation of the different chemical shift (rank-2) tensors. For this purpose two 2D-data sets with orthogonal crystal orientation are fitted simultaneously. The presented analysis for chemical shift tensors is supported by an analytical formula which allows fast calculation of phase and amplitude of individual spinning side-bands and by a protocol which solves the problem of finding the correct reference phase of the spectrum. Different rotor-synchronized pulse-sequences are introduced for the same reason. Experiments are performed on L -alanine and O-phosphorylethanolamine and the observed errors are analyzed in detail. The experimental data are opposed to DFT-computed chemical shift tensors which have been obtained by the extended embedded ion method. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various recoupling techniques for probing 14N-1H interactions are compared. • Similarity of phase-inverted rotary-resonance recoupling and the symmetry based SR4 1 2 method is explored. • Offset dependence of TRAPDOR for application to nitrogen sites with different quadrupolar coupling constants. 1H-detected 14N heteronuclear multiple-quantum coherence (HMQC) magic-angle-spinning (MAS) NMR experiments performed at fast magic-angle spinning (≥50 kHz) are finding increasing application, e.g., to pharmaceuticals. Of importance to the efficacy of these techniques is the recoupling technique applied to reintroduce the 1H-14N dipolar coupling. In this paper, we compare, by experiment and 2-spin density matrix simulations, two classes of recoupling scheme: first, those based on n = 2 rotary resonance, namely R3 and spin-polarisation inversion SPI-R3, and the symmetry based SR4 1 2 method and, second, the TRAPDOR method. Both classes require optimisation depending on the magnitude of the quadrupolar interaction, and thus there is a compromise choice for samples with more than one nitrogen site, as is the case for the studied dipeptide β-AspAla that contains two nitrogen sites with a small and large quadrupolar coupling constant. Considering this, we observe better sensitivity for the TRAPDOR method, though noting the marked sensitivity of TRAPDOR to the 14N transmitter offset, with both SPI-R3 and SR4 1 2 giving similar recoupling performance. [ABSTRACT FROM AUTHOR]

The paper describes a family of novel recoupling pulse sequences in magic angle spinning (MAS) solid state NMR, called four pulse recoupling. These pulse sequences can be employed for both homonuclear and heteronuclear recoupling experiments and are robust to dispersion in chemical shifts and rf-inhomogeneity. The homonuclear pulse sequence consists of a building block π 2 0 ° 3 π 2 ϕ ° π 2 180 ° + ϕ ° 3 π 2 180 ° where ϕ = π n ϕ ° = 180 ° n , and n is number of blocks in a two rotor period. The heteronuclear recoupling pulse sequence consists of a building block π 2 0 ° 3 π 2 ϕ 1 ° π 2 180 ° + ϕ 1 ° 3 π 2 180 ° and π 2 0 ° 3 π 2 ϕ 2 ° π 2 180 ° + ϕ 2 ° 3 π 2 180 ° on channel I and S , where ϕ 1 = 3 π 2 n , ϕ 2 = π 2 n and n is number of blocks in a two rotor period. The recoupling pulse sequences mix the y magnetization. We show that four pulse recoupling is more broadband compared to three pulse recoupling [1] . Experimental quantification of this method is shown for 13 C α - 13 CO, homonuclear recoupling in a sample of Glycine and 15 N- 13 C α , heteronuclear recoupling in Alanine. Application of this method is demonstrated on a sample of tripeptide N-formyl-[U- 13 C, 15 N]-Met-Leu-Phe-OH (MLF). [ABSTRACT FROM AUTHOR]

The paper describes a family of novel recoupling pulse sequences, called three pulse recoupling. These pulse sequences can be employed for both homonuclear and heteronuclear recoupling experiments and are robust to dispersion in chemical shifts and rf-inhomogeneity. These recoupling pulse sequences can be used in design of two-dimensional solid state NMR experiments that use powdered dephased antiphase coherence ( γ preparation) to encode chemical shifts in the indirect dimension. Both components of this chemical shift encoded gamma-prepared states can be refocused into inphase coherence by a recoupling element. This helps to achieve sensitivity enhancement in 2D NMR experiments by quadrature detection. [ABSTRACT FROM AUTHOR]

Proton NMR spin-diffusion experiments are often combined with magic-angle spinning (MAS) to achieve higher spectral resolution of solid samples. Here we show that local proton spin diffusion can indeed become faster at low (<10 kHz) spinning rates as compared to static conditions. Spin diffusion under static conditions can thus be slower than the often referred value of 0.8 nm 2 /ms, which was determined using slow MAS (Clauss et al., 1993). The enhancement of spin diffusion by slow MAS relies on the modulation of the orientation-dependent dipolar couplings during sample rotation and goes along with transient level crossings in combination with dipolar truncation. The experimental finding and its explanation is supported by density matrix simulations, and also emphasizes the sensitivity of spin diffusion to the local coupling topology. The amplification of spin diffusion by slow MAS cannot be explained by any model based on independent spin pairs; at least three spins have to be considered. [ABSTRACT FROM AUTHOR]

Extended chemical shift anisotropy amplification (xCSA) is applied for measuring 13 C/ 15 N chemical shift anisotropy (CSA) of uniformly labeled proteins under magic-angle spinning (MAS). The amplification sequence consists of a sequence of π-pulses that repetitively interrupt MAS averaging of the CSA interaction. The timing of the pulses is designed to generate amplified spinning sideband manifolds which can be fitted to extract CSA parameters. The 13 C/ 13 C homonuclear dipolar interactions are not affected by the π-pulses due to the bilinear nature of the spin operators and are averaged by MAS in the xCSA experiment. These features make the constant evolution-time experiment suitable for measuring CSA of uniformly labeled samples. The incorporation of xCSA with multi-dimensional 13 C/ 15 N correlation is demonstrated with a GB1 protein sample as a model system for measuring 13 C/ 15 N CSA of all backbone 15 NH, 13 CA and 13 CO sites. [ABSTRACT FROM AUTHOR]

A new method for precise setting of the spinning angle to the magic angle by using a saddle coil is described. The coil, which is referred to as an X 0 shim coil, is wound to produce a uniform static magnetic field B x perpendicular to the main magnetic field B 0 . The magnetic field felt by a sample is a vector sum of the main field B 0 and the transverse field B x produced by the X 0 shim coil. Hence the angle between the spinner axis and the effective magnetic field can be controlled by current I supplied to the X 0 shim coil, leading to precise angle adjustment without backlash accompanied with a mechanical system conventionally used. It is shown that the angle range achieved is ± 0.05 ° for I = ± 5 A at B 0 = 7 T. [ABSTRACT FROM AUTHOR]

Magic-angle spinning (MAS) is a technique that is a prerequisite for high-resolution solid-state NMR spectroscopy of proteins and other biomolecules. Recently, the 100 kHz limit for the rotation frequency has been broken, arguably making MAS rotors the man-made objects with the highest rotation frequency. This development is expected to have a significant impact on biomolecular NMR as it facilitates proton detection, which allows to partially compensate the loss in overall sensitivity associated with the small sample amounts that fit into MAS rotors with less than 1 mm outer diameter. Under these conditions, the mass-normalized sensitivity of a small rotor becomes much higher than that of larger-volume rotor. [ABSTRACT FROM AUTHOR]

The negative global impact of the AIDS pandemic is well known. In this perspective article, the utility of magic angle spinning (MAS) NMR spectroscopy to answer pressing questions related to the structure and dynamics of HIV-1 protein assemblies is examined. In recent years, MAS NMR has undergone major technological developments enabling studies of large viral assemblies. We discuss some of these evolving methods and technologies and provide a perspective on the current state of MAS NMR as applied to the investigations into structure and dynamics of HIV-1 assemblies of CA capsid protein and of Gag maturation intermediates. [ABSTRACT FROM AUTHOR]

Understanding the structure of membrane-active peptides faces many challenges associated with the development of appropriate model membrane systems as the peptide structure depends strongly on the lipid environment. This perspective provides a brief overview of the approach taken to study antimicrobial and amyloid peptides in phospholipid bilayers using oriented bilayers and magic angle spinning techniques. In particular, Boltzmann statistics REDOR and maximum entropy analysis of spinning side bands are used to analyse systems where multiple states of peptide or lipid molecules may co-exist. We propose that in future, rather than model membranes, structural studies in whole cells are feasible. [ABSTRACT FROM AUTHOR]

We report on 13 C nuclear spin-lattice relaxation time ( T 1 ) dependence on the magic-angle-spinning (MAS) rate in powder nanodiamond samples. We confirm that the relaxation is caused by interaction of nuclear spins with fluctuating electron spins of localized paramagnetic defects. It was found that T 1 is practically not affected by MAS for small particles, while for larger particles with lower defect density T 1 is different in static and MAS regimes and reveals elongation with increasing MAS rate. This effect is attributed to suppression of nuclear spin diffusion by MAS. We propose an approach that describes T 1 dependence on the MAS rate and allows quantitative analysis of this effect. [ABSTRACT FROM AUTHOR]

Two 3D experiments, capable of producing enhanced resolution two-spin double-quantum (DQ) homonuclear correlations for half-integer quadrupolar nuclei, are described. The first uses a split-t 1 MQMAS sequence followed by a sandwiched oR 3 symmetry-based dipolar recoupling sequence to directly excite DQ coherences. In this case an isotropic single-quantum (SQ) coherence starts the homonuclear DQ excitation. In the second experiment a single strong pulse is used to create triple quantum (TQ) coherence followed by a further single pulse conversion to zero-order before a non-sandwiched oR 3 DQ sequence. The first experiment is demonstrated using 87 Rb in RbNO 3 , with three Rb sites in a ∼5 ppm range, and the second to 11 B in caesium triborate, CsB 3 O 5 , with two three-coordinated sites separated by ∼2 ppm and one four-coordinated boron site. In both cases, all sites are clearly resolved and their connections observed. The second experiment has higher sensitivity and a good signal to noise is obtained in a reasonable time despite the long T 1 relaxation time of 11 B in this material. [ABSTRACT FROM AUTHOR]

Highlights: [•] Correct angular restraints are obtained for rotationally aligned Vpu TM. [•] Pulse sequences for a dipolar assisted assignment protocol are described. [•] Pulse sequences that measure chemical shifts and dipolar frequencies are described. [•] Chemical shift and dipolar frequency correlation provides high resolution. [Copyright &y& Elsevier]

Abstract: Elimination of Artifacts in NMR SpectroscopY (EASY) is a simple but very effective tool to remove simultaneously any real NMR probe background signal, any spectral distortions due to deadtime ringdown effects and -specifically- severe acoustic ringing artifacts in NMR spectra of low-gamma nuclei. EASY enables and maintains quantitative NMR (qNMR) as only a single pulse (preferably 90°) is used for data acquisition. After the acquisition of the first scan (it contains the wanted NMR signal and the background/deadtime/ringing artifacts) the same experiment is repeated immediately afterwards before the T1 waiting delay. This second scan contains only the background/deadtime/ringing parts. Hence, the simple difference of both yields clean NMR line shapes free of artefacts. In this Part I various examples for complete 1H, 11B, 13C, 19F probe background removal due to construction parts of the NMR probes are presented. Furthermore, 25Mg EASY of Mg(OH)2 is presented and this example shows how extremely strong acoustic ringing can be suppressed (more than a factor of 200) such that phase and baseline correction for spectra acquired with a single pulse is no longer a problem. EASY is also a step towards deadtime-free data acquisition as these effects are also canceled completely. EASY can be combined with any other NMR experiment, including 2D NMR, if baseline distortions are a big problem. [Copyright &y& Elsevier]

Highlights: [•] REDOR with CPMG speeds up distance measurement in solids by one order of magnitude. [•] CPMG with XY-8 phase cycling maintains long lasting echo while compensating imperfect refocusing pulses. [•] Full echo acquisition has a √2 gain in S/N over half-echo signal. [ABSTRACT FROM AUTHOR]

Highlights: [•] DANTE 1D excitation in solids works better under ultra-fast MAS. [•] Paramagnetic samples can be excited with weak rf-field. [•] Integer-spin quadrupolar nuclei, such as 14N, can be manipulated with DANTE. [•] Overtone DANTE can be used for 90° excitation, not for 180° inversion. [•] Overtone DANTE works well for excitation of large quadrupole interaction. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fokker–Planck equations can be solved directly for powder-average NMR spectra. [•] Hamiltonian is time-independent and spherical quadrature grids are avoided completely. [•] The proposed formalism contains Floquet theory as a special case. [•] Large matrices are handled with state space restriction and tensor train techniques. [•] Low correlation order basis sets appear to produce accurate answers for powders. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate here that the principle of frequency-selective spin-echoes can be extended to the measurements of long-range homonuclear scalar J-couplings in the solid-state. Singly or doubly frequency-selective pulses were used to generate either a J-modulated experiment (S) or a reference experiment (S 0). The combination of these two distinct experiments provides experimental data that, in favorable cases, are insensitive to incoherent relaxation effects, and which can be used to estimate long-range homonuclear J-couplings in multiple spin-systems. The concept is illustrated in the case of a uniformly 13C and 15N labeled sample of l-histidine, where the absolute value of homonuclear J-couplings between two spins separated by one, two or three covalent bonds are measured. Moreover, we show that a 2 J(15N–C–15N) coupling as small as 0.9Hz can be precisely measured with the method presented here. [Copyright &y& Elsevier]

Abstract: High pressure magic angle spinning (MAS) nuclear magnetic resonance (NMR) with a sample spinning rate exceeding 2.1kHz and pressure greater than 165bar has never been realized. In this work, a new sample cell design is reported, suitable for constructing cells of different sizes. Using a 7.5mm high pressure MAS rotor as an example, internal pressure as high as 200bar at a sample spinning rate of 6kHz is achieved. The new high pressure MAS rotor is re-usable and compatible with most commercial NMR set-ups, exhibiting low 1H and 13C NMR background and offering maximal NMR sensitivity. As an example of its many possible applications, this new capability is applied to determine reaction products associated with the carbonation reaction of a natural mineral, antigorite ((Mg,Fe2+)3Si2O5(OH)4), in contact with liquid water in water-saturated supercritical CO2 (scCO2) at 150bar and 50°C. This mineral is relevant to the deep geologic disposal of CO2, but its iron content results in too many sample spinning sidebands at low spinning rate. Hence, this chemical system is a good case study to demonstrate the utility of the higher sample spinning rates that can be achieved by our new rotor design. We expect this new capability will be useful for exploring solid-state, including interfacial, chemistry at new levels of high-pressure in a wide variety of fields. [Copyright &y& Elsevier]

Abstract: Deuterium magic angle spinning (MAS) NMR spectroscopy and quantum chemical calculations are used to investigate organic solids in which inequivalent hydrogen bonds are present. The use of 2H MAS allows one to measure the chemical shift, δ, quadrupolar coupling constant, C Q , and asymmetry in the quadrupolar interaction, η Q , for each type of hydrogen bond present in the system. Quantum chemical calculations of the magnetic shielding (σ, which can be related to δ) and the electric field gradient (EFG, which can be related to C Q ) are compared to the experimental results and are discussed with respect to the relative strengths of the hydrogen bonds within each system. [Copyright &y& Elsevier]

Abstract: A sensitivity enhancement scheme aiming at selective adiabatic inversion of a single set of satellite transition sidebands under magic angle spinning has been employed on samples of albite containing a single moderately distorted 27Al site and zoisite containing two highly distorted octahedral 27Al sites. Overall enhancements of ∼2.5 for albite and ∼3 for the two AlO6 sites of zoisite are reported by applying this scheme at different spinning speeds reflecting the versatility of this enhancement scheme which achieves significant signal-to-noise enhancements for the systems with moderately high quadrupolar coupling and high quadrupolar coupling. Repeating the sensitivity enhancement scheme and signal readout several times without allowing for spin-lattice relaxation leads to sensitivity enhancements of factors of ∼4 for albite and ∼5 for zoisite which substantially increases the detectability of the quadrupolar sites. The effectiveness of this scheme at high magnetic field under very fast magic angle spinning has been demonstrated. Finally, the possibility of performing spectral editing by selective enhancement of one of the quadrupolar sites in zoisite whilst keeping the other site unaffected has been explored. [Copyright &y& Elsevier]

Abstract: The use of susceptibility matching to minimize spectral distortion of biphasic samples layered in a standard 5mm NMR tube is described. The approach uses magic angle spinning (MAS) to first extract chemical shift differences by suppressing bulk magnetization. Then, using biphasic coaxial samples, magnetic susceptibilities are matched by titration with a paramagnetic salt. The matched phases are then layered in a standard NMR tube where they can be shimmed and examined. Linewidths of two distinct spectral lines, selected to characterize homogeneity in each phase, are simultaneously optimized. Two-dimensional distortion-free, slice-resolved spectra of an octanol/water system illustrate the method. These data are obtained using a 2D stepped-gradient pulse sequence devised for this application. Advantages of this sequence over slice-selective methods are that acquisition efficiency is increased and processing requires only conventional software. [Copyright &y& Elsevier]

Abstract: We present a time-shared Third Spin Assisted Recoupling (TSTSAR) experiment that allows for simultaneous acquisition of homonuclear (13C–13C) and heteronuclear (15N–13C) long-distance contacts in biomolecular solids under magic angle spinning. TSTSAR leads to substantial time savings and increases the information content of 2D correlation spectra. [Copyright &y& Elsevier]

Abstract: Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often contain liquid-, gel- and solid-like phases and it is the synergism between these phases that determine their environmental and biological properties. Studying each phase separately can perturb the sample, removing important structural information such as chemical interactions at the gel-solid interface, kinetics across boundaries and conformation in the natural state. In order to overcome these limitations a Comprehensive Multiphase-Nuclear Magnetic Resonance (CMP-NMR) probe has been developed, and is introduced here, that permits all bonds in all phases to be studied and differentiated in whole unaltered natural samples. The CMP-NMR probe is built with high power circuitry, Magic Angle Spinning (MAS), is fitted with a lock channel, pulse field gradients, and is fully susceptibility matched. Consequently, this novel NMR probe has to cover all HR-MAS aspects without compromising power handling to permit the full range of solution-, gel- and solid-state experiments available today. Using this technology, both structures and interactions can be studied independently in each phase as well as transfer/interactions between phases within a heterogeneous sample. This paper outlines some basic experimental approaches using a model heterogeneous multiphase sample containing liquid-, gel- and solid-like components in water, yielding separate 1H and 13C spectra for the different phases. In addition, 19F performance is also addressed. To illustrate the capability of 19F NMR soil samples, containing two different contaminants, are used, demonstrating a preliminary, but real-world application of this technology. This novel NMR approach possesses a great potential for the in situ study of natural samples in their native state. [Copyright &y& Elsevier]

Abstract: A simple method to automatically shim NMR samples spinning at the magic angle is introduced based on the gradient shimming approach. The field inhomogeneity along the spinning axis is measured and automatically corrected. The combination of a normal magic angle spinning (MAS) probe, a conventional homospoil gradient, and a set of properly chosen standard room-temperature shims are used to perform the gradient shimming of samples spinning at the magic angle. The resulting 13C NMR adamantane linewidth is less than 1Hz (0.0078ppm at 11.7T). [Copyright &y& Elsevier]

Abstract: This article reviews the large increase in applications of high-resolution 1H magic-angle spinning (MAS) solid-state NMR, in particular two-dimensional heteronuclear and homonuclear (double-quantum and spin-diffusion NOESY-like exchange) experiments, in the last five years. These applications benefit from faster MAS frequencies (up to 80kHz), higher magnetic fields (up to 1GHz) and pulse sequence developments (e.g., homonuclear decoupling sequences applicable under moderate and fast MAS). 1H solid-state NMR techniques are shown to provide unique structural insight for a diverse range of systems including pharmaceuticals, self-assembled supramolecular structures and silica-based inorganic–organic materials, such as microporous and mesoporous materials and heterogeneous organometallic catalysts, for which single-crystal diffraction structures cannot be obtained. The power of NMR crystallography approaches that combine experiment with first-principles calculations of NMR parameters (notably using the GIPAW approach) are demonstrated, e.g., to yield quantitative insight into hydrogen-bonding and aromatic CH–π interactions, as well as to generate trial three-dimensional packing arrangements. It is shown how temperature-dependent changes in the 1H chemical shift, linewidth and DQ-filtered signal intensity can be analysed to determine the thermodynamics and kinetics of molecular level processes, such as the making and breaking of hydrogen bonds, with particular application to proton-conducting materials. Other applications to polymers and biopolymers, inorganic compounds and bioinorganic systems, paramagnetic compounds and proteins are presented. The potential of new technological advances such as DNP methods and new microcoil designs is described. [Copyright &y& Elsevier]

Abstract: We have developed a novel variant of REDOR which is applicable to multiple-spin systems without proton decoupling. The pulse sequence is constructed based on a systematic time displacement of the pi pulses of the conventional REDOR sequence. This so-called time displacement REDOR (td-REDOR) is insensitive to the effect of homonuclear dipole–dipole interaction when the higher order effects are negligible. The validity of td-REDOR has been verified experimentally by the P-31{C-13} measurements on glyphosate at a spinning frequency of 25kHz. The experimental dephasing curve is in favorable agreement with the simulation data without considering the homonuclear dipole–dipole interactions. [Copyright &y& Elsevier]

Abstract: A two-dimensional experiment for measuring chemical shift anisotropy (CSA) under fast magic-angle spinning (MAS) is presented. The chemical shift anisotropy evolution is amplified by a sequence of π-pulses that repetitively interrupt MAS averaging. The amplification generates spinning sideband manifolds in the indirect dimension separated by the isotropic shift along the direct dimension. The basic unit of the pulse sequence is designed based on the magic-angle turning experiment and can be concatenated for larger amplification factors. [Copyright &y& Elsevier]

Abstract: An experimental and simulation investigation regarding the effect of various CRAMPS parameters (delays interleaved with the decoupling shape, z-rotation symmetry and offset frequency) on the DUMBO decoupling performance is presented using two model compounds, glycine and tyrosine·HCl. Although the conclusions of this work may be extended to the other homonuclear-decoupling schemes, this work focuses essentially on the effect of adding interleaved delays to DUMBO decoupling during the indirect dimension using different 2D pulse-scheme architectures. While the simulations revealed an increasing loss of the spectral resolution with longer delays (from 0 to 6μs), the experimental 2D 1H DUMBO NMR correlation spectra revealed that the inclusion of delays, during the indirect dimension, improves the 1H resolution whether the z-rotation symmetry was used or not. The best experimental spectra are obtained when z-rotation symmetry and windows are combined. [Copyright &y& Elsevier]

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

Abstract: 1H and 13C solid- and solution-state NMR have been used to characterise waxes produced in the Fischer–Tropsch reaction, using Co-based catalysts either unpromoted or promoted with approximately 1wt% of either cerium or rhenium. The aim was to measure average structural information at the submolecular level of the hydrocarbon waxes produced, along with identification of the minor products, such as oxygenates and olefins, which are typically observed in these waxes. A parameter of key interest is the average number of carbon atoms within the hydrocarbon chain (N C ). A wax prepared using an unpromoted Co/Al2O3 catalyst had N C ∼20, whilst waxes made using rhenium- or cerium-promoted Co/Al2O3 catalysts were found to have N C ∼21. All three samples contained small amounts of oxygenates and alkenes. The subtle differences found in the waxes, in particular the minor species produced, demonstrate that the different promoters have different effects during the reaction, with the Re-promoted catalyst producing the fewest by-products. It is shown in 13C solid-state NMR spectra that for that for longer chain (compared to the lengths of chain in previous studies) waxes that the lack of resolution and the complexities added by the differential cross-polarisation (CP) dynamics mean that it is difficult to accurately determine N C from this approach. However the N C determined by 13C CP magic angle spinning NMR is broadly consistent with the more accurate solution approaches used and suggest that the wax characteristics do not change in solution. On this basis an alternative approach for determining N C is suggested based on 1H solution state NMR that provides a higher degree of accuracy of the chain length as well as information on the minor constituents. [Copyright &y& Elsevier]

Abstract: We present a Floquet theory approach for the analysis of homonuclear recoupling assisted by radio frequency (RF) irradiation of surrounding heteronuclear spins. This description covers a broad range of systems from fully protonated to deuterated proteins, focusing in detail on recoupling via protons and deuterons separately as well as simultaneously by the double nucleus enhanced recoupling (DONER) scheme. The theoretical description, supported by numerical simulations and compared to experimental results from a partially deuterated model compound, indicates that in perdeuterated systems setting the RF amplitude equal to the magic angle spinning (MAS) frequency is not necessarily optimal for recoupling via 1H and/or 2H nuclei and modified recoupling conditions are identified. [Copyright &y& Elsevier]

Abstract: Para-hydrogen induced polarization (PHIP) NMR in solution, combined with solid-state NMR, can be efficiently employed for the highly sensitive in-situ detection of the leaching properties of immobilized catalysts. The knowledge of this property is important for possible applications of PHIP experiments in medicine, biology or industry, where leached catalysts poison the solution of hyperpolarized products. As experimental example Wilkinson''s catalyst RhCl(PPh3)3 (1) immobilized on mesoporous silica is chosen. As model reaction the hydrogenation of styrene in solvents with different polarities (methanol-d4, acetone-d6 and benzene-d6) is used. A 31P solid-state MAS-NMR study reveals that there are two different species of catalysts on the silica, namely coordinatively bound catalysts and physisorbed catalyst. Only the second species exhibits substantial leaching, which is visible in a strong PHIP enhancement of the reaction product. [Copyright &y& Elsevier]

Abstract: We show that rotational echo double resonance (REDOR) experiments can be carried out without proton decoupling under the conditions of fast spinning and strong rf field. Numerical simulations on a five-spin systems show that no significant attenuation of the reference signal (S 0) is observed at a spin rate of 25kHz, provided that the rf power is larger than 100kHz. This approach has been validated by 31P{13C} REDOR measurements on isotopically labeled glyphosate. The obtained van Vleck’s second moment is in favorable agreement with the value calculated based on the crystal structure. [ABSTRACT FROM AUTHOR]

Abstract: The underlying relation between the magic-angle turning (MAT) and phase-adjusted spinning sidebands (PASS) experiments is examined. The MAT experiment satisfies the PASS conditions for separating spinning sidebands with a non-constant total evolution time and only requires linear increments of up to one rotor period. The time-domain data of the two experiments are related by a shearing transformation. A combination of the linear evolution-time increments of MAT and simple data processing of PASS are particularly attractive for the implementation of MAT for measuring chemical shift anisotropy. [Copyright &y& Elsevier]

Abstract: In this article, we show the potential for utilizing proton-detected heteronuclear single quantum correlation (HSQC) NMR in rigid solids under ultra-fast magic angle spinning (MAS) conditions. The indirect detection of carbon-13 from coupled neighboring hydrogen nuclei provides a sensitivity enhancement of 3- to 4-fold in crystalline amino acids over direct-detected versions. Furthermore, the sensitivity enhancement is shown to be significantly larger for disordered solids that display inhomogeneously broadened carbon-13 spectra. Latrodectus hesperus (Black Widow) dragline silk is given as an example where the sample is mass-limited and the sensitivity enhancement for the proton-detected experiment is 8- to 13-fold. The ultra-fast MAS proton-detected HSQC solid-state NMR technique has the added advantage that no proton homonuclear decoupling is applied during the experiment. Further, well-resolved, indirectly observed carbon-13 spectra can be obtained in some cases without heteronuclear proton decoupling. [Copyright &y& Elsevier]

Abstract: In solid-state NMR magic angle spinning is often used to remove line broadening associated with anisotropic interactions, such as chemical shift anisotropy and dipolar couplings. Dipolar recoupling refers to sequences of pulses designed to reintroduce dipolar interactions that are otherwise averaged by magic angle spinning. One of the key applications of homonuclear (and heteronuclear) dipolar recoupling is for the purpose of protein structure determination. Recoupling experiments, originally designed for applications in spin-pair labeled samples, have been revised in recent years for applications in samples with extensive or uniform incorporation of isotopic labels. In these samples multiple internuclear distances can in principle be probed simultaneously, but the dipolar truncation effects (i.e. attenuation of the effects of weak couplings by strong ones) circumvent such measurements. In this article we review some of the recent developments in homonuclear recoupling methods that allow overcoming this problem. [Copyright &y& Elsevier]

Abstract: Accurate determination of 1H NMR signal intensities is useful for quantitative analysis of the hydrogen content and also to determine the relative peak intensity ratios in different application scenarios. To this end we have investigated the reliability and sources of intensity errors in 1H solid-state MAS NMR. If sufficient resolution can be achieved by very high spinning speeds and high magnetic fields, quantification is straight forward. However, for poorly resolved spectra we show that small phase errors add a considerable amount of uncertainty. An analytical expression for the phase induced intensity-errors allowed us to suggest a robust and reliable recipe which is based on a combination of the spin-echo experiment, an extrapolation technique and a deconvolution algorithm which includes fitting of the signal phase. It significantly reduces errors caused by phase distortions, homonuclear dipolar dephasing, the receiver dead time delay and baseline rolling. The method was validated experimentally on samples with strong homonuclear dipolar interactions. [Copyright &y& Elsevier]

Abstract: A protocol is presented for correcting the effect of non-specific cross-polarization in CHHC solid-state MAS NMR experiments, thus allowing the recovery of the 1H–1H magnetization exchange functions from the mixing-time dependent buildup of experimental CHHC peak intensity. The presented protocol also incorporates a scaling procedure to take into account the effect of multiplicity of a CH2 or CH3 moiety. Experimental CHHC buildup curves are presented for l-tyrosine·HCl samples where either all or only one in 10 molecules are U–13C labeled. Good agreement between experiment and 11-spin SPINEVOLUTION simulation (including only isotropic 1H chemical shifts) is demonstrated for the initial buildup (t mix <100μs) of CHHC peak intensity corresponding to an intramolecular close (2.5Å) H–H proximity. Differences in the initial CHHC buildup are observed between the one in 10 dilute and 100% samples for cases where there is a close intermolecular H–H proximity in addition to a close intramolecular H–H proximity. For the dilute sample, CHHC cross-peak intensities tended to significantly lower values for long mixing times (500μs) as compared to the 100% sample. This difference is explained as being due to the dependence of the limiting total magnetization on the ratio N obs/N tot between the number of protons that are directly attached to a 13C nucleus and hence contribute significantly to the observed 13C CHHC NMR signal, and the total number of 1H spins into the system. 1H–1H magnetization exchange curves extracted from CHHC spectra for the 100% l-tyrosine·HCl sample exhibit a clear sensitivity to the root sum squared dipolar coupling, with fast buildup being observed for the shortest intramolecular distances (2.5Å) and slower, yet observable buildup for the longer intermolecular distances (up to 5Å). [Copyright &y& Elsevier]

Abstract: An isotropic–anisotropic shift 2D correlation spectroscopy is introduced that combines the advantages of both magic angle turning (MAT) and magic angle hopping (MAH) technologies. In this new approach, denoted DMAT for “discrete magic angle turning”, the sample rotates clockwise followed by an anticlockwise rotation of exactly the same amount with each rotation less or equal than 360° but greater than 240°, with the rotation speed being constant only for times related to the evolution dimension. This back and forth rotation is repeated and synchronized with a special radio frequency (RF) pulse sequence to produce an isotropic–anisotropic shift 2D correlation spectrum. For any spin-interaction of rank-2 such as chemical shift anisotropy, isotropic magnetic susceptibility interaction, and residual homo-nuclear dipolar interaction in biological fluid samples, the projection along the isotropic dimension is a high resolution spectrum. Since a less than 360° sample rotation is involved, the design potentially allows for in situ control over physical parameters such as pressure, flow conditions, feed compositions, and temperature so that true in situ NMR investigations can be carried out. [Copyright &y& Elsevier]