State NMR Research Articles

Probing membrane topology of the antimicrobial peptide distinctin by solid-state NMR spectroscopy in zwitterionic and charged lipid bilayers

Distinctin is a 47-residue antimicrobial peptide, which interacts with negatively charged membranes and is active against Gram-positive and Gram-negative bacteria. Its primary sequence comprises two linear chains of 22 (chain 1) and 25 (chain 2) residues, linked by a disulfide bridge between Cys19 of chain 1 and Cys23 of chain 2. Unlike other antimicrobial peptides, distinctin in the absence of the lipid membrane has a well-defined three-dimensional structure, which protects it from protease degradation. Here, we used static solid-state NMR spectroscopy in mechanically aligned lipid bilayers (charged or zwitterionic) to study the topology of distinctin in lipid bilayers. We found that this heterodimeric peptide adopts an ordered conformation absorbed on the surface of the membrane, with the long helix (chain 2), approximately parallel to the lipid bilayer (~5° from the membrane plane) and the short helix (chain 1) forming a ~24° angle with respect to the bilayer plane. Since the peptide does not disrupt the macroscopic alignment of charged or zwitterionic lipid bilayers at lipid-to-protein molar ratio of 50:1, it is possible that higher peptide concentrations might be needed for pore formation, or alternatively, distinctin elicits its cell disruption action by another mechanism.

Synthesis, structure characterization and ionic conductivity of star-branched organic–inorganic hybrid electrolytes based on cyanuric chloride, diamine-capped poly(oxyalkylene) and alkoxysilane

A synthesis route for preparing highly conductive solid organic–inorganic hybrid electrolytes has been developed by using cyanuric chloride as the coupling core to react with diamino-terminated poly(oxyalkylene) triblock copolymers, followed by cross-linking with an epoxy alkoxysilane 3-glycidyloxypropyl trimethoxysilane via a sol-gel process. The present hybrid electrolyte with a [O]/[Li] ratio of 32 was found to be the most conductive, reaching a maximum lithium ion conductivity of 6.8 × 10−5 Scm−1 at 30 °C. The Li-ion mobility was determined from 7Li static NMR line width measurements and correlated with their ionic conductivities. The onset of 7Li line narrowing was closely related to the Tg of the hybrid electrolytes as measured by DSC experiments. Thus, the motions of the lithium cations are strongly coupled with the segmental motion of the polymer chains, which is in line with the Vogel-Tamman-Fulcher behavior as observed in ionic conductivity.

Investigating the impact of cholesterol on magnetically aligned sphingomyelin/cholesterol multilamellar vesicles using static 31P NMR

The effect of cholesterol (5-40mol%) on the magnetic induced orientation of sphingomyelin/cholesterol multilamellar vesicles (MLVs) was examined using static solid state (31)P NMR spectroscopy. The orientation was modeled assuming an ellipsoidal deformation of the vesicles and was monitored as a function of cholesterol concentration and temperature. In addition, the static (31)P chemical shift anisotropy (CSA) was used to assess the motional and dynamical changes occurring in the bilayer are reported. An exploration of the factors determining the magnetic orientation in sphingomyelin/cholesterol bilayers from the gel (s(o)) to liquid crystalline (or liquid-ordered, l(o)) phases is presented and discussed.

A 93Nb Solid‐State NMR and Density Functional Theory Study of Four‐ and Six‐Coordinate Niobate Systems

A variable B(0) field static (broadline) NMR study of a large suite of niobate materials has enabled the elucidation of high-precision measurement of (93)Nb NMR interaction parameters such as the isotropic chemical shift (delta(iso)), quadrupole coupling constant and asymmetry parameter (C(Q) and eta(Q)), chemical shift span/anisotropy and skew/asymmetry (Omega/Deltadelta and kappa/eta(delta)) and Euler angles (alpha, beta, gamma) describing the relative orientation of the quadrupolar and chemical shift tensorial frames. These measurements have been augmented with ab initio DFT calculations by using WIEN2k and NMR-CASTEP codes, which corroborate these reported values. Unlike previous assertions made about the inability to detect CSA (chemical shift anisotropy) contributions from Nb(V) in most oxo environments, this study emphasises that a thorough variable B(0) approach coupled with the VOCS (variable offset cumulative spectroscopy) technique for the acquisition of undistorted broad (-1/2<-->+1/2) central transition resonances facilitates the unambiguous observation of both quadrupolar and CSA contributions within these (93)Nb broadline data. These measurements reveal that the (93)Nb electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the Nb(V) positions, with C(Q) values in the 0 to >80 MHz range being measured; similarly, the delta(iso) (covering an approximately 250 ppm range) and Omega values (covering a 0 to approximately 800 ppm range) characteristic of these niobate systems are also sensitive to structural disposition. However, their systematic rationalisation in terms of the Nb-O bond angles and distances defining the immediate Nb(V) oxo environment is complicated by longer-range influences that usually involve other heavy elements comprising the structure. It has also been established in this study that the best computational method(s) of analysis for the (93)Nb NMR interaction parameters generated here are the all-electron WIEN2k and the gauge included projector augmented wave (GIPAW) NMR-CASTEP DFT approaches, which account for the short- and long-range symmetries, periodicities and interaction-potential characteristics for all elements (and particularly the heavy elements) in comparison with Gaussian 03 methods, which focus on terminated portions of the total structure.

An extension of the Czjzek model for the distributions of electric fieldgradients in disordered solids and an application to NMR spectra of 71Ga in chalcogenide glasses

First, the basis and the characteristics of the Czjzek model for the distribution of electricfield gradient (EFG) tensor in disordered solids, some of which are still unnoticed, aredepicted. That model results from the statistical invariance by rotation of the structure ofthe considered disordered solid and from the applicability of a central limit theorem to theEFG tensor. These two conditions, which are physically realistic for a wealth of disorderedsolids, simplify tremendously the derivation of the EFG distribution but at the cost of acomplete loss of structural information about the investigated solid. Next, we describe asimple extension of it which is intended to mimic a well-defined local environment,with given values of the asymmetry parameter and of the principal componentVzz of the EFG tensor, perturbed by the disorder of more remote atoms. The effect of disorderis rendered by a Gaussian (Czjzek) noise with an adjustable weight relative toVzz. The number of free parameters is limited to three, as compared to a sole scale factor forthe Czjzek model. Its characteristics are described as a function of the given asymmetryparameter and of the strength of the noise. The aim is to lead to a practical tool which mayhelp to retrieve, as far as possible, the information about the local environment perturbedby disorder from hyperfine measurements and notably from NMR spectra of quadrupolarnuclei. As an example, that extension is applied to some static NMR spectra of 71Ga in covalent glasses.Calculated static 71Ga NMR lineshapes are shown as a function of the parameters of the extended model.

Dynamics on the microsecond timescale in hydrous silicates studied by solid-state 2H NMR spectroscopy

Solid-state (2)H NMR spectroscopy has been used to probe the dynamic disorder of hydroxyl deuterons in a synthetic sample of deuterated hydroxyl-clinohumite (4Mg(2)SiO(4).Mg(OD)(2)), a proposed model for the incorporation of water within the Earth's mantle. Both static and magic angle spinning (MAS) NMR methods were used. Static (2)H NMR appears to reveal little evidence of the dynamic process, yielding results similar to those obtained from deuterated brucite (Mg(OD)(2)), where no dynamics on the relevant timescale are expected to be present. However, in (2)H MAS NMR spectra, considerable line broadening is observed for hydroxyl-clinohumite and a (2)H double-quantum (DQ) MAS NMR spectrum confirms that this is due to motion on the microsecond timescale. Using a model for dynamic exchange of the hydroxyl deuterons between two sites identified in previous diffraction studies, first-principles density functional theory (DFT) calculations of (2)H (spin I = 1) quadrupolar NMR parameters, and a simple analytical model for dynamic line broadening in MAS NMR experiments, we were able to reproduce the observed motional line broadening and use this to estimate a rate constant for the dynamic process. From analysis of the observed (2)H linewidths in variable-temperature MAS experiments, an activation energy for the exchange process was also determined. A simulated static (2)H NMR lineshape based on our dynamic model is consistent with the observed experimental static NMR spectrum, confirming that the motion present in this system is not easily detectable using a static NMR approach. Finally, a (2)H DQMAS NMR spectrum of fluorine-substituted (2)H-enriched hydroxyl-clinohumite shows how the dynamic exchange process is inhibited by O-DF(-) hydrogen-bonding interactions.

Solid-State NMR Structural Studies of Alzheimer's Disease Aβ(1-42) And Aβ(1-40) In Phospholipid Bilayers

Amyloid-β peptides, Aβ(1-42) and Aβ(1-40) are believed to cause loss of nerve cell function in individuals suffering from Alzheimer's disease, where evidence suggests that interaction with the cell membrane correlates strongly with cytotoxicity. Previous studies report a range of different but plausible structures, which depend on the molecular environment of the peptide. This sensitivity to sample preparation suggests that the structure relevant to disease is found in lipid bilayer membranes. While model membrane vesicles are too large to be studied by conventional solution NMR, solid-state NMR is one of the few technologies available to study such systems. We present recent magic angle spinning NMR measurements which suggest a novel peptide structure in a lipid bilayer environment: (i) rotational-echo double-resonance (REDOR) distance measurements between selectively enriched 13C-carbonyl and 15N-amide positions constrain dihedral angles of intervening residues and suggest that at least part of the Aβ(1-42) peptide folds into a β-sheet like conformation, in contrast to the helical and coiled structures in previous reports; and (ii) double quantum filtered DRAWS measurements indicate that the extended strand does not assemble into an in-register parallel sheet as reported for amyloid fibrils. Additional static NMR experiments (sensitivity enhance PISEMA) of 15N labelled Aβ(1-40) in mechanically aligned phospholipid bilayers and magnetically oriented bicelles indicate that the peptide has multiple conformations in model membranes.

Temperature Dependence of the Interaction of Antimicrobial Peptides With Mixed Lipid Bilayers

The interactions of two α-helical antimicrobial peptides, aurein 1.2 (13 residues) and maculatin 1.1 (21 residues), with model membranes have been examined using solid-state NMR and surface plasmon resonance techniques. P-31 NMR of multilamellar (MLV) dimyristoylphosphatidycholine (DMPC) vesicles with aurein 1.2 revealed minor disruptions in the bilayer above the gel-liquid phase transition. However, below the phase transition temperature an isotropic signal was observed, indicating that the peptide disrupted the bilayer and formed small, rapidly tumbling aggregates ∼ 22 nm in diameter as determined by light scattering measurements. However, the isotropic signal was not seen with the longer peptide. Additional experiments conducted using different lipid compositions revealed that both fluidity and temperature influence the peptide interaction. Gel phase lipid bilayers were more strongly affected by the peptide although similar effects were observed at lower temperatures in unsaturated chain lipid bilayers in the liquid crystalline state.A preliminary study on membranes mimicking the lipid composition of S. aureus has demonstrated a disruptive effect on the bilayer organization by addition of maculatin 1.1, a potent antibacterial peptide. As revealed in P-31 static NMR spectra of MLV composed of dimyristoylphosphatidylglycerol (DMPG) and tetramyristoylcardiolipin (TMCL), the peptide promoted formation of a dominant isotropic phase at 15°C, well below the liquid-crystalline transition temperature; while the lamellar organization was mainly restored above 50°C and an intermediate state was observed at 30°C. Interestingly, relaxation experiments on MLV without peptide indicated coexistence of two populations in the temperature range 30-50°C, most likely composed of fluid DMPG and rigid TMCL. The antimicrobial peptide may insert preferentially at domain boundaries, using defects in membrane packing to lower energy costs. Further experiments are ongoing to determine the nature of the isotropic phase and its relevance to antimicrobial activity.

Optimized excitation pulses for the acquisition of static NMR powder patterns from half-integer quadrupolar nuclei

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

The Effect of Incorporation of Gramicidin on the Translational Lipid Diffusion in Bicontinuous Cubic Monoolein/Water Mesophases

Abstract The influence of incorporating the polypeptide gramicidin on the lateral mobility of the monoacylglyceride monoolein (MO) in its bicontinuous cubic lipid mesophases is studied applying static field gradient NMR. The effects of gramicidin on the topology, structure and phase behaviour of the system are characterized by small-angle x-ray scattering (SAXS) experiments. On the structural level the experiments show significant shifts in the boundaries of the various mesophases. Measurements of the translational dynamics are restricted to cubic mesophases, where the diffusion coefficients of lipid and additive are determined both by geometrical obstruction and by lipid-protein interaction effects.

Combined 135/137Ba Solid-State NMR at an Ultrahigh Magnetic Field and Computational Study of β-Barium Borate

β-Barium Borate (β-BBO or β-BaB2O4) is an important nonlinear optical material with many practical applications. In this work, we have directly probed the local Ba environment in β-BBO by acquiring static 135Ba and 137Ba solid-state NMR spectra at an ultrahigh magnetic field of 21.1 T. The observed spectra are completely dominated by the second-order quadrupolar interaction. The measured quadrupolar coupling constants are 14.9 and 22.8 MHz for 135Ba and 137Ba, respectively. A computational study of the electric field gradient tensor at Ba2+ was also performed using both plane-wave pseudopotentials (CASTEP) and ab initio (Gaussian 03) methods. Combining the experimental and theoretical results allows one to shed some light on the controversy regarding the true space group of β-BBO. We conclude that the space group R3c represents the true structure of β-BBO rather than does the space group R3. This work demonstrates that a combination of 135/137Ba NMR and theoretical calculations is a useful tool for charac...

Implementation of High Resolution 43Ca Solid State NMR Spectroscopy: Toward the Elucidation of Calcium Sites in Biological Materials

Calcium is one of the most abundant cations in living organisms. It is found in the mineral phase of bone and in proteins like calmodulin. However, its exact environment beyond the first coordination sphere is often unknown, thus hampering the understanding of many biological processes. Here, calcium benzoate trihydrate (Ca(C(6)H(5)COO)(2) x 3 H(2)O) was used as a model for the NMR analysis of calcium sites in biological materials, because of the similarity of its calcium coordination, to water and carboxylate ligands, to that in several calcium-proteins. First, calcium-43 magic angle spinning (MAS) and static NMR spectra of a (43)Ca enriched sample were recorded at different magnetic fields, to investigate the electronic environment of calcium. Complex static lineshapes were obtained because of the presence of anisotropic NMR interactions of similar magnitude (chemical shift anisotropy and quadrupolar interaction), and the full interpretation of the spectra required simulations and gauge-including projector augmented wave (GIPAW) DFT calculations. An NMR investigation of the coordination environment of Ca(2+) was carried out, using high resolution (13)C-(43)Ca MAS NMR experiments such as TRAPDOR (transfer of population double resonance) and heteronuclear J-spin-echoes. It was shown that despite the weakness of (13)C-(43)Ca interactions, it is possible to discriminate carbon atoms according to their calcium environment. Long-range calcium-carbon correlations were even evidenced by TRAPDOR, reaching distances >5.6 A. This work demonstrates that by combining solid state NMR experiments, DFT calculations, and simulations, it will be possible to elucidate the electronic and coordination environment of calcium in many important and complex materials.

Synthesis, Electronic and Crystal Structures, and Physical Studies of the Superconductor Cs∼1Mo12S14, Final Step of the Condensation of the Mo6L8iL6a Unit

The ternary reduced molybdenum sulphide Cs(~1)Mo12S14 has been synthesized by solid-state reaction at 1400 degrees C for 96 h in sealed molybdenum crucibles. The compound crystallizes in the trigonal space group P31c with the following lattice parameters: a = 9.9793 (2) A, c = 6.3730 (2) A, Z = 1. Its crystal structure was determined from single crystal X-ray diffraction data and consists of interconnected Mo6S8(i)S6(a) units forming an original three-dimensional framework in which large tunnels are occupied randomly by the Cs+ ions. 133Cs static NMR studies are in favor of a static cesium disorder. Unlike Ba4Mo12S18 where some Mo6S8(i)S6(a) units are also connected through S(i-i) ligands, this connection mode does not lead to significant interactions in the title compound. Single-crystal resistivity measurements show that Cs(~1)Mo12S14 presents a metallic behavior with a superconducting transition at 7.7 K as confirmed by magnetic measurements.

A highly conductive organic–inorganic hybrid electrolyte based on co-condensation of di-ureasil and ethylene glycol-containing alkoxysilane

Organic–inorganic hybrid electrolytes based on di-ureasil backbone structures by reacting poly(propylene glycol)- block-poly(ethylene glycol)- block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2000) with 3-(triethoxysilyl)propyl isocyanate (ICPTES), followed by co-condensation with methoxy(polyethylenoxy)propyl trimethoxysilane (MPEOP) in the presence of LiClO 4 were prepared and characterized by a variety of techniques. The hybrid electrolytes showed good resistance to crystallization and excellent conductivity for use in lithium-ion batteries, as determined by differential scanning calorimetry (DSC) and impedance measurements, respectively. The temperature dependence of the ionic conductivity exhibited a VTF (Vogel–Tamman–Fulcher)-like behavior for all the compositions studied and a maximum ionic conductivity value of 6.9 × 10 −5 S cm −1, a relatively high value for solid polymer electrolytes, was achieved at 30 °C for the hybrid electrolyte with a [O]/[Li] ratio of 16. A microscopic view of the dynamic behavior of the polymer chains ( 13C) and the ionic species ( 7Li) was provided by the 1H and 7Li line widths measured from 2D 1H– 13C WISE (Wideline Separation) and variable temperature 7Li static NMR, respectively, to elucidate the influence of the mobility of the polymer chains and the charge carriers on the observed ionic conductivity. The present salt-free hybrid electrolyte after plasticization with 1 M LiClO 4 in EC/PC solution exhibited a swelling ratio of 275% and reached an ionic conductivity value up to 8.3 × 10 −3 S cm −1 at 30 °C, which make it a good candidate for the further development of advanced rechargeable lithium-ion batteries.

Forsterite, hydrous and anhydrous wadsleyite and ringwoodite (Mg2SiO4): 29Si NMR results for chemical shift anisotropy, spin-lattice relaxation, and mechanism of hydration

We present a detailed 29 Si NMR spectroscopic study of isotopically enriched samples of forsterite and of anhydrous and hydrous wadsleyite and ringwoodite (α, β, and γ phases of Mg 2 SiO 4 ), which complement previous extensive studies of these minerals by XRD and vibrational spectroscopy. VI Si is not detected in any of the phases at levels of about 0.1 to 0.5%. When coupled with recent theoretical calculations on ringwoodite, this suggests the possibility of re-ordering of high-temperature octahedral-tetrahedral disorder during cooling. Cross-polarization ( 29 Si{ 1 H} CPMAS) NMR supports the protonation of O1 oxygen atoms in hydrous wadsleyite without formation of significant amounts of Si-OH groups. In contrast, new NMR peaks appear in hydrous ringwoodite that cross-polarize very rapidly, indicating very short Si-H distances and the presence of Si-OH, as expected from models in which much of the H + substitutes into Mg 2+ vacancies. Static NMR spectra provide new constraints on chemical shift anisotropies in wadsleyite and are fully consistent with the cubic structure of ringwoodite. Spin-lattice relaxation in all phases is much better fitted by a stretched exponential function than with a more conventional “T 1 ” exponential, as expected when relaxation is dominated by paramagnetic impurities. However, the effects of paramagnetic impurity on ion contents on relaxation, and on the formation of newly observed minor peaks that may result from “pseudo-contact shifts,” appear to depend on mineral structure, and will require considerable future study to understand in detail.

Proton dynamics in CsHSO 4 confined in mesoporous silica FSM-16 as studied by 1H solid-state NMR

Cesium hydrogen sulfate CsHSO 4 was introduced in a nanospace of mesoporous silica FSM-16, and we have investigated proton dynamics of CsHSO 4 confined in the mesopores by means of 1H solid-state NMR. X-ray powder diffraction patterns demonstrate accommodation of CsHSO 4 in the mesopores and suggest that confined CsHSO 4 is amorphous. Thermal analyses indicate that the confinement suppresses the transition from phases II to I and the melting. The motional narrowing in the 1H static NMR spectra takes place in the temperature range lower than that for bulk CsHSO 4, and the spectral line shape indicates that the proton motional rate has a distribution. The proton mean residence times are estimated from the spectrum simulation assuming the distribution of the motional rate. The obtained central values are smaller by one order of magnitude than those for bulk CsHSO 4 although the central values of the activation energies are comparable.

A 47/49Ti Solid-State NMR Study of Layered Titanium Phosphates at Ultrahigh Magnetic Field

Layered titanium phosphates (TiPs) have many potentially important applications in ion exchange, catalysis, intercalation, and sorption. Characterization of metal local environments by solid-state 47/49Ti NMR has been difficult due to many unfavorable 47/49Ti NMR properties. In this work, we have directly characterized the local structures around Ti in several representative layered TiPs, including α-, β-, and γ-TiP, by examining the 47/49Ti static NMR spectra of these materials at an ultrahigh magnetic field of 21.1 T. The 47/49Ti chemical shielding and electric field gradient (EFG) tensors have been extracted from spectral analysis. The observed 47/49Ti spectra are mainly determined by the second-order quadrupolar interactions. The quadrupole coupling constants (CQ) are sensitive to the distortion of the TiO6 octahedron in this series of layered TiPs. Quantum mechanical calculations have been performed on several model clusters as well as periodic systems. The results indicate that, in addition to the o...

Preparation and structural characterization of rare-earth doped lead lanthanum zirconate titanate ceramics

A new preparation route towards rare-earth (RE) doped polycrystalline lead lanthanum zirconate titanate (PLZT) ceramics (RE = Y 3+, Nd 3+, Yb 3+), based on the use of doped lanthanum oxide or zirconia, is reported. Structural characterization by X-ray powder diffraction reveals that secondary phase formation can be substantially diminished in comparison to conventional preparation methods. The distribution of the rare-earth dopants was investigated as a function of concentration by static 207Pb spin echo NMR spectra, using Fourier Transformation of Carr–Purcell–Meiboom–Gill spin echo trains. For the Nd- and Yb-doped materials, the interaction of the 207Pb nuclei with the unpaired electron spin density results in significant broadening and shifting of the NMR signal, whereas these effects are absent in the diamagnetic Y 3+ doped materials. Based on different concentration dependences of the NMR lineshape parameters, we conclude that the structural role of the Nd 3+ dopants differs significantly from that of Yb 3+. While the Nd 3+ ions appear to be statistically distributed in the PLZT lattice, incorporation of Yb 3+ into PLZT appears to be limited by the appearance of doped cubic zirconia as a secondary phase.

Metal-Induced Folding of Diels−Alderase Ribozymes Studied by Static and Time-Resolved NMR Spectroscopy

The metal ion-induced folding of the Diels-Alder ribozyme into a catalytically active form with a complex RNA pseudoknot has been characterized by static and time-resolved NMR spectroscopy. The conformations of two sequences from the Diels-Alder ribozyme family, A27 WT and G27 MUT, were studied in the absence and presence of metal ions and of ligand. The single nucleotide mutant G27 MUT in the absence of metal ions displayed conformational heterogeneity which greatly influences its folding trajectory. Time-resolved NMR experiments were applied using a sample-mixing technique to rapidly add Ca(2+) ions to induce folding in situ. The folding rates observed for the G27 MUT ribozyme differed by 3 orders of magnitude from the A27 WT folding rates determined previously by FRET experiments. A model based on the characterization of the free and metal-bound forms of the ribozymes is proposed to account for the difference in the folding rates of the two ribozymes. Evidence is provided that the reactivity is modulated due to local dynamics around the catalytic pocket for the G27 MUT ribozyme.

Sensitivity enhancement in static solid-state NMR experiments via single- and multiple-quantum dipolar coherences.

We present a new method for enhancing the sensitivity in static solid-state NMR experiments for a gain in signal-to-noise ratio of up to 40%. This sensitivity enhancement is different from the corresponding solution NMR sensitivity enhancement schemes and is achieved by combining single- and multiple-quantum dipolar coherences. While this new approach is demonstrated for the polarization inversion spin exchange at magic angle (PISEMA) experiment, it can be generalized to the other separated local field experiments for solid-state NMR spectroscopy. This method will have a direct impact on solid-state NMR spectroscopy of liquid crystals as well as of membrane proteins aligned in lipid membranes.