State Nuclear Magnetic Resonance Experiments Research Articles

Molecular-level insights into structure and dynamics in ionic liquids and polymer gel electrolytes

Designing new electrolytes requires a better understanding of the correlation between their transport properties and their molecular structure. In this work, we present a detailed study of ionic liquids and polymer gel electrolytes probing their structure and dynamics by nuclear magnetic resonance (NMR) spectroscopy. In particular, ammonium- and phosphonium-based ionic liquids (ILs) are combined with different LiTFSI concentrations, and then with different ratios of poly(methylmethacrylate) polymer. The temperature dependence of self-diffusion coefficients of mobile species, DLi+, DTFSI- and DP4441+ or DN4441+, measured by pulsed field gradient (PFG) NMR spectroscopy obeys the Arrhenius equation. Diffusivity of [P4441][TFSI] ILs is found to be greater than those of the [N4441][TFSI] ILs in both liquid and gel electrolytes. Solid state NMR experiments including 13C and 19F MAS, 13C{19F},13C{1H} CPMAS probe the local structure and molecular-level interactions between ions and polymer in gel electrolytes, particularly for samples with higher PMMA content (≥25 wt%). Finally, the fast field cycling relaxometry has been used to unveil the rotational and translational dynamics of P4441+ or N4441+ and TFSI− by measuring 1H and 19F R1 relaxation rate profiles at different temperatures. A comprehensive NMR analysis including relaxation studies at low magnetic field provides decisive new insights regarding the formation of ionic clusters and the interaction of ions with the polymer chain in the case of the gel electrolytes.

Structural Investigations of Li1.5Al0.5Ge1.5(PO4)3 glass-ceramics by Solid State NMR

NASICON-type conductors based on LiGe2(PO4)3 are very promising lithium-conducting electrolytes for all-solid-state lithium-ion and lithium batteries. Al-doped LiGe2(PO4)3 solid electrolytes possessed higher conductivity (∼10-4 S/cm at room temperature) and stability versus metallic Li. In this paper, we present the structure study of Li1.5Al0.5Ge1.5(PO4)3 compound. Fast lithium-ion conductor Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte have been obtained through glass crystallization at 820 °C during 8 h. Structural positions occupied by atoms have been examined by solid state nuclear magnetic resonance experiments. 6Li, 7Li, 27Al и 31P NMR measurements have been performed at room temperature.

A quasi-optical and corrugated waveguide microwave transmission system for simultaneous dynamic nuclear polarization NMR on two separate 14.1 T spectrometers

Nuclear magnetic resonance (NMR) is an intrinsically insensitive technique, with Boltzmann distributions of nuclear spin states on the order of parts per million in conventional magnetic fields. To overcome this limitation, dynamic nuclear polarization (DNP) can be used to gain up to three orders of magnitude in signal enhancement, which can decrease experimental time by up to six orders of magnitude. In DNP experiments, nuclear spin polarization is enhanced by transferring the relatively larger electron polarization to NMR active nuclei via microwave irradiation. Here, we describe the design and performance of a quasi-optical system enabling the use of a single 395 GHz gyrotron microwave source to simultaneously perform DNP experiments on two different 14.1 T (1H 600 MHz) NMR spectrometers: one configured for magic angle spinning (MAS) solid state NMR; the other configured for solution state NMR experiments. In particular, we describe how the high power microwave beam is split, transmitted, and manipulated between the two spectrometers. A 13C enhancement of 128 is achieved via the cross effect for alanine, using the nitroxide biradical AMUPol, under MAS-DNP conditions at 110 K, while a 31P enhancement of 160 is achieved via the Overhauser effect for triphenylphosphine using the monoradical BDPA under solution NMR conditions at room temperature. The latter result is the first demonstration of Overhauser DNP in the solution state at a field of 14.1 T (1H 600 MHz). Moreover these results have been produced with large sample volumes (∼100 µL, i.e. 3 mm diameter NMR tubes).

Solid-State NMR Characterization of S31N M2 Transmembrane Domain Bound to Novel Adamantanes with Persistent In Vitro Efficacy

The M2 proton channel from Influenza A virus is essential for the viral lifecycle and is an important drug target. Amino acid mutations in the residues lining the pore of the channel have abrogated clinical efficacy of the previously FDA-approved antiviral agents, amantadine and rimantadine. More than 95% of the circulating strains isolated from human clinical cases bear S31N mutation and a subsequent resistance to the licensed small molecule inhibitors. Efforts in rational drug design targeting S31N M2 channel have been impeded by the limited number of experimental techniques with capabilities for structural characterization of the protein-ligand interaction in native-like membrane mimetic environments. Solution and Solid State Nuclear Magnetic Resonance (NMR) investigations of the recently introduced adamantane analogues suggest multiple orientations of the inhibitor molecules bound in the pore. Position of the substituent moiety in the channel varies for different compounds, unlike the fixed orientation in the wild type channel. Here we report a Solid State NMR investigation of the transmembrane domain of S31N M2 (TMD) proton channel bound to the novel inhibitor molecules, while also incorporated into a lipid bilayer environment. Oriented sample solid state NMR experiments of S31N M2 TMD indicate that the channel is sampling two states with helical tilts of 28° and 33° relative to the bilayer normal. The kink in the monomer between two helical fragments, observed in the wild type M2 TMD bound with amantadine, is absent for the S31N M2 TMD bound to all inhibitor molecules tested to date. Stabilizing interactions are further investigated with Rotational Echo Double Resonance Magic Angle Spinning (REDOR MAS) experiments for measuring distances from the inhibitor to the protein.

High-resolution solid state NMR experiments for the characterization of calcium phosphate biomaterials and biominerals

Abstract

ChemInform Abstract: Detection and Use of Small J Couplings in Solid State NMR Experiments

AbstractReview: 103 refs.

Detection and use of small J couplings in solid state NMR experiments

Over the years, solid-state nuclear magnetic resonance (NMR) spectroscopy has become an important tool for materials science, with its local point of view that is highly complementary to the structural information provided by diffraction techniques, electron microscopy, and molecular modeling, for example. As compared to other interactions that determine the spectral expression of the local structure of the observed nuclei in solid-state NMR experiments, the J coupling, characteristic of the chemical bonds, has received far less attention because of its being generally so small that it is masked in the line-widths. Nevertheless, the scalar or isotropic part of J couplings, which is not averaged by magic angle spinning (MAS), can be evidenced in many systems, and exploited to unequivocally characterize the extended coordination sphere. In a first step we describe the different experiments that permit the observation and the measurement of J couplings, even when dealing with quadrupolar nuclei. We then present new and recently-published results that illustrate the state of the art of NMR methodologies based on or intended for measuring J couplings in solids and the novel perspectives that they open towards better understanding of ordered and disordered materials at the subnanometric scale, a length scale that is otherwise difficult to access.

Solid State NMR of Membrane Proteins: Towards Complex Structural and Functional Information for Bacterial ABC Class Importers

Despite the wealth of protein structural data available today, membrane protein structural characterization continues to pose a significant challenge in structural biology. Choosing the membrane mimetic is a challenge and often detergent micelles are employed. However, detergents are prone to induce distortions in the protein structure. An emerging technique, solid state nuclear magnetic resonance (NMR), provides a path to structural characterization using an environment similar to the native one, liquid crystalline lipid bilayers.Static solid state NMR experiments on proteins determine the orientation of the peptide planes with respect to the magnetic field. All 15N-1H dipolar couplings and anisotropic 15N chemical shifts observed in two dimensional separated local field experiments (PISEMA) lie within a butterfly shape in the spectrum. Special patterns called PISA wheels arise for uniformly aligned protein samples which directly reflect the orientation of protein secondary structure. Using these wheels the tilt angle of each helical axis from the magnetic field and membrane normal can be determined without complete structure determination. Consequently, a single data set allows for characterization of secondary structure in the membrane mimetic as well as providing a set of high resolution peptide plane orientations that can be used directly in structural refinement.Uniform alignment has been achieved for multiple proteins in our laboratory. Still, studies on larger membrane proteins are required to make solid state NMR a generally applicable technique for membrane protein structure characterization. One excellent example is SugAB, the transmembrane domain of an ABC importer from Mycobacterium tuberculosis. These transport proteins contain at least 10 transmembrane helices. This makes SugAB an excellent target for determining the utility of solid state NMR to structurally characterize large membrane proteins.

Effects of jump dynamics on solid state nuclear magnetic resonance line shapes and spin relaxation times

This paper describes EXPRESS ( EXchange Program for RElaxing Spin Systems), a computer program that simulates the effects of Markovian jump dynamics for a wide variety of solid state nuclear magnetic resonance experiments. A graphical interface is described that facilitates the definition of rotational jumps around non-commuting axes that may occur at arbitrary, different rates. Solid state deuteron NMR is widely used to investigate such processes, and EXPRESS allows simulations of deuteron quadrupole echo and magic angle spinning line (MAS) shapes, as well as partially relaxed line shapes for measurements of anisotropic relaxation of Zeeman and quadrupolar order. Facilities are included for chemical shift tensors (at user-defined orientations relative to the quadrupole coupling tensors), so that EXPRESS is potentially useful for studies of paramagnetic systems where these interactions are of comparable magnitude. Many of the same techniques used for deuterons can be extended to half-integer quadrupolar nuclei. The same interface that specifies rotational “sites” for deuteron NMR studies is usable in EXPRESS to simulate static line shapes, MAS line shapes, and multiple pulse Carr–Purcell–Meiboom–Gill (CPMG) line shapes for the central transition of high spin quadrupoles with second order quadrupole coupling and chemical shift anisotropy. Representative simulations are displayed that show effects of slow libration on deuteron quadrupole echo line shapes and relaxation time anisotropies. EXPRESS is also used to investigate fundamental differences in the mechanism of echo formation in deuteron MAS and quadrupole CPMG experiments, and to illustrate significant differences between these techniques in the context of high spin quadrupolar nuclei. The program is modular and platform-independent, with facilities for users to add routines for experiments not yet envisioned.

Dynamics of Cross Polarization in Solid State Nuclear Magnetic Resonance Experiments of Amorphous and Heterogeneous Natural Organic Substances

Nuclear magnetic resonance (NMR) experiments on carbon-13 in the solid state were done with cross polarization (CP) and magic angle spinning (MAS) in order to overcome the low NMR sensitivity of (13)C and the chemical shift anisotropy, respectively. In the present research, CPMAS (13)C-NMR spectra were collected by modulating the contact time needed for cross polarization (variable contact times experiments, VCT) on two different humic acids (a soil-HA and a coal-HA). VCT data were fitted by a model containing either a monotonic or a non-monotonic cross polarization term. The non-monotonic model, which fitted the experimental results better than the monotonic one, provided two cross-polarization rates, thereby suggesting that two different mechanisms for the energy transfer from protons to carbons arise in amorphous and heterogeneous humic substances. The first mechanism was a fast proton-to-carbon energy transfer due to protons directly bound to carbons. The second mechanism was related to a slow transfer mediated by local segmental motions. Different domains in the humic acids were identified. Soil-HA was made of rigid domains, containing mainly aromatic and carboxylic moieties, and fast moving domains, containing alkyl, C-O and C-O groups. Coal-HA showed a rigid aromatic domain that was differentiated from a very mobile domain made of alkyl and COOH groups.

Using liquid and solid state NMR and photoluminescence to study the synthesis and solubility properties of amine capped silicon nanoparticles

Water soluble silicon nanoparticles were prepared by the reaction of bromine terminated silicon nanoparticles with 3-(dimethylamino)propyl lithium and characterized with liquid and solid state nuclear magnetic resonance (NMR) and photoluminescence (PL) spectroscopies. The surface site dependent 29Si chemical shifts and the nuclear spin relaxation rates from an assortment of 1H– 29Si heteronuclear solid state NMR experiments for the amine coated reaction product are consistent with both the 1H and 13C liquid state NMR results and routine transmission electron microscopy, ultra-violet/visible, and Fourier transform infrared measurements. PL was used to demonstrate the pH dependent solubility properties of the amine passivated silicon nanoparticles.

Description of depolarization effects in double-quantum solid state nuclear magnetic resonance experiments using multipole-multimode Floquet theory

Using an analytical model based on multipole-multimode Floquet theory (MMFT), we describe the polarization loss (or depolarization) observed in double-quantum (DQ) dipolar recoupling magic angle spinning (MAS) experiments. Specifically, the factors responsible for depolarization are analyzed in terms of higher order corrections to the spin Hamiltonian in addition to the usual phenomenological decay rate constant. From the MMFT model and the effective Hamiltonians, we elucidate the rationale behind the inclusion of a phenomenological damping term in DQ recoupling experiments. As a test of this theoretical approach, the recoupling efficiency of one class of (13)C-(13)C and (13)C-(15)N resonance width dipolar recoupling experiments are investigated at different magnetic field strengths and compared with the more exact numerical simulations. In contrast to existing analytical treatments, the role of higher order corrections is clearly explained in the context of the MMFT approach leading to a better understanding of the underlying spin physics. Furthermore, the analytical model presented herein provides a general framework for describing coherent and incoherent effects in homonuclear and heteronuclear DQ MAS recoupling experiments.

NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups

Solid-state 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopic experiments have been performed on isolated meteoritic Insoluble Organic Matter (IOM) spanning four different carbonaceous chondrite meteorite groups; a CR2 (EET92042), a CI1 (Orgueil), a CM2 (Murchison), and the unique C2 meteorite, Tagish Lake. These solid state NMR experiments reveal considerable variation in bulk organic composition across the different meteorite group’s IOM. The fraction of aromatic carbon increases as CR2 < CI1 < CM2 < Tagish Lake. The increases in aromatic carbon are offset by reductions in aliphatic (sp 3) carbon moieties, e.g., “CH x,” and “CH x(O,N).” Oxidized sp 2 bonded carbon, e.g., carboxyls and ketones grouped as “CO,” are largely conservative across these meteorite groups. Single pulse (SP) 13C magic angle spinning (MAS) NMR experiments reveal the presence of nanodiamonds with an apparent concentration ranking in the IOM of CR2 < CI1 < CM2 < Tagish Lake. A pair of independent NMR experiments reveals that, on average, the aromatic moieties in the IOM of all four meteoritic IOM fractions are highly substituted. Fast spinning SP 1H MAS NMR spectral data combined with other NMR experimental data reveal that the average hydrogen content of sp 3 bonded carbon functional groups is low, requiring a high degree of aliphatic chain branching in each IOM fraction. The variation in chemistry across the meteorite groups is consistent with alteration by low temperature chemical oxidation. It is concluded that such chemistry principally affected the aliphatic moieties whereas the aromatic moieties and nanodiamonds may have been largely unaffected.

Advances in Characterisation Methods for Sol-Gel Derived Materials: High Resolution Solid State Nuclear Magnetic Resonance

The objective of this paper is to discuss the recent advances in high resolution solid state Nuclear Magnetic Resonance (NMR) to characterise sol-gel derived materials. The first part will be focused on methods to describe M i --O--M j connectivities in sol-gel networks. After a brief review on techniques based on scalar J-coupling, we will focus on the use of 17O solid state NMR experiments. Then in a second part, techniques to probe through-space interactions in hybrid networks will be described, with a particular emphasis on the use of high resolution 1H solid state NMR sequences and related two-dimensional homonuclear or heteronuclear correlations.

NMR studies of peptide T, an inhibitor of HIV infectivity, in an aqueous environment

The synthetic octapeptide peptide T (ASTTTNYT) has been shown to interfere with binding of the HIV-1 envelope glycoprotein gp120 to the chemokine receptor R5, thus preventing viral infection. This study investigated the degree of conformational order of two analogs of peptide T, one biologically active (D-Ala peptide T amide) and one inactive (D-Ala, D-Tyr peptide T amide) using nuclear magnetic resonance (NMR) spectroscopy in an aqueous environment, both in solution and in the frozen solid state. Standard solution NMR techniques such as DQFCOSY, HMQC, ROESY and inversion recovery measurements have been utilized to characterize these peptides. Solid state NMR experiments were likewise employed to study the peptides in a frozen glycerol:water mixture. The NMR results indicate that the monomeric form of both peptide T analogs have considerable conformational heterogeneity. Solid state NMR studies indicate aggregation of D-Ala peptide T, possibly into a beta-sheet structure, at concentrations higher than 10 mM.

NMR quantum information processing and entanglement

In this essay we discuss the issue of quantum information and recent nuclear magnetic resonance (NMR) experiments. We explain why these experiments should be regarded as quantum information processing (QIP) despite the fact that, in present liquid state NMR experiments, no entanglement is found. We comment on how these experiments contribute to the future of QIP and include a brief discussion on the origin of the power of quantum computers.

MULTIDIMENSIONAL SOLUTION STATE NMR OF HUMIC SUBSTANCES: A PRACTICAL GUIDE AND REVIEW

Multidimensional nuclear magnetic resonance (NMR) is a powerful and diverse tool for the elucidation of organic compounds and mixtures. This communication presents a discussion of the basic multidimensional liquid state NMR experiments that can be applied to humic substances. A range of experiments

High frequency (140 GHz) dynamic nuclear polarization: Polarization transfer to a solute in frozen aqueous solution

Dynamic nuclear polarization (DNP) transfers the large polarization of unpaired electrons to nuclei and thus significantly enhances the signal strength in nuclear magnetic resonance (NMR) spectroscopy. High frequency/field (140 GHz/5 T) DNP has been implemented in solid state NMR experiments using a nitroxide radical as the paramagnetic polarizing agent in a water:glycerol frozen solution. The 1H and 13C NMR signal strengths of both the solvent and an amino acid solute have been enhanced by a factor of 185, which represents a reduction of ≳102 in sample size requirements or ≳104 in signal acquisition time.

Relaxation processes and molecular motion in a new semicrystalline polyimide

AbstractA new polymide was synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane (DMDA), and abbreviated to be BTDA‐DMDA. This polymer possesses three relaxation processes which have been observed through dynamic mechanical and dielectric analyses above–150°C. The α relaxation process has been assigned to be the glass transition and occurs at about 250°C with an apparent activation energy of 420kJ/mol. Two subglass relaxation processes are a β relaxation process at around 100–170°C in a frequency range from 0,1 Hz to 100 kHz with an activation energy of 182 kJ/mol and a γ relaxation process occurs at around −80°C with an activation energy of 44 kJ/mol. Carbon‐13 solid state nuclear magnetic resonance experiments were carried out for the study of molecular dynamics at different temperatures. The results indicate that the γ relaxation is responsible for an oscillation and π flipping motion of the two phenoxy rings in the DMDA portion. The β relaxation was shown to pertain to the kHz‐motion of the aromatic imide rings in the BTDA portion. The molecular motion of the DMDA and BTDA protions are largely decoupled from each other in the frequency region studied.

Concentration fluctuations and dynamic heterogeneity in PIP/PVE blends

Usually the shape of the glass transition dispersion in the mechanical or dielectric spectra of pure polymers is skewed toward higher frequencies. In miscible polymer blends not only is this peak broader than in pure polymers, the broadening is often asymmetric towards lower frequencies. Concentration fluctuations are an obvious source of the broadening; however, a simple distribution of relaxation times, corresponding to a distribution in local compositions, would not account for the reversal in the asymmetry of the dispersion. Intrinsic differences in component mobilities, as directly seen in solid state nuclear magnetic resonance experiments, also exert an influence on segmental relaxation in blends. The differences in the components' segmental relaxation behaviours are also manifested in the thermorheological complexity of miscible blends. An approach to blend dynamics based on the coupling model of relaxation can successfully describe the most prominent features.