Localized NMR Spectroscopy Research Articles

Direct observation of sodium dendrites to decipher the complicated behavior of electrolyte systems

The compatibility of the electrolyte system with the metal anode, which is often overlooked, is pivotal in realizing the development of a long-life battery. In the present contribution, the compatibility of the diglyme-based electrolyte systems with the sodium metal anode is examined and found that the solvation structure of the electrolyte plays a central role in controlling the sodium deposition morphology. The localized Raman and 1H NMR spectroscopy reveals that the solvation structure for ClO4—, PF6—, and CF3SO3— is distinct and differs from each other. While a loose solvation structure is observed for ClO4—, CF3SO3— based electrolytes exhibit a compact solvation structure. In-situ optical microscopy provides real-time information about the sodium deposition morphology, varying from needle-, tree- and moose-like morphology in ClO4—, PF6—, and CF3SO3— based electrolytes, respectively. The Coulombic efficiency (Na//Cu) and stripping/plating overpotential of sodium (Na//Na) are also sensitive to the structure of the solvation shell. In addition, the post-cycle XPS analysis suggests that the CF3SO3— based electrolytes lead to the formation of an inorganic-rich SEI. This comprehensive study underscores the importance of electrolyte composition in achieving stable sodium metal anodes, providing valuable insights for the development of high-performance sodium metal batteries.

Multinuclear magnetic resonance imaging and local NMR spectroscopy

Principles of magnetic resonance imaging and local NMR spectroscopy with adjustment of the Larmor frequencies for nuclei different from protons (nuclei of deuterium, fluorine, carbon, phosphorus, sodium, boron, and chlorine) are considered.

Magnetic resonance imaging and local NMR spectroscopy with fluorine-19 nuclei

Methods of magnetic resonance imaging and local NMR spectroscopy with fluorine nuclei, which are needed to identify fluorine-containing medications in human and animal organisms, are developed.

Hadamard-encoded localized high-resolution NMR spectroscopy via intermolecular double-quantum coherences

A scheme based on Hadamard encoding and intermolecular double-quantum coherences is designed to obtain localized one-dimensional high-resolution NMR spectra in inhomogeneous fields. Brief theoretical derivation was performed to illuminate its principle. Experiments were carried out on phantom solution and biological tissues to verify its effectiveness in yielding useful spectral information and efficiency in suppressing solvent signal even when the field inhomogeneity is sufficiently severe to erase almost all spectral information. This sequence may provide a promising way for analyzing heterogeneous biological tissues and chemical systems.

Conformational Dynamics of Surfactant in a Mesolamellar Composite Studied by Local Field NMR Spectroscopy

Ordered mesostructured materials possess unique surface, structural, and bulk properties that lead to important practical applications. Mesostructured organic–inorganic composites are also of broad interest for fundamental studies of confinement effects and surface interaction on structural and dynamic properties of organic molecules. In the present study, solid state dipolar 13C–1H NMR spectroscopy is applied to quantitatively characterize the conformational dynamics of a surfactant in a mesolamellar composite. By applying dipolar recoupling and separated local field spectroscopy techniques, the motion of surfactant molecules was studied in a wide range of mobilities from an essentially immobilized rigid state to a highly flexible and anistropically tumbling state. From the analysis of the measured heteronuclear dipolar couplings, the orientational order parameters of C–H bonds along the surfactant chain were determined. The study shows that in surfactant bilayers in AlPO layered structure at room temper...

Diffusion of small molecules in a chitosan/water gel determined by proton localized NMR spectroscopy

Proton localized NMR spectroscopy (MRS) has been applied to study the diffusion of three small molecules, caffeine, theophylline and caprolactam, in chitosan gels with different concentration of water. This technique allows the non-destructive monitorization of diffusant concentration as a function of time and location. Concentration profiles were compared with theoretical curves based on solutions of Fick’s diffusion equation for the best fitting, with the appropriate boundary conditions. The measured concentration profiles show a good agreement with the Fickian law. Values of the diffusion coefficients D ranging from 6.1×10−6 to 3.4×10−6cm2s−1 depending on chitosan concentration and type of diffusant molecule were determined. In addition, measurements of diffusion coefficients at equilibrium conditions with proton pulsed field gradient NMR methods supported the observed Fickian behavior and showed values of D in excellent agreement with those determined by proton MRS. All these facts demonstrate that proton MRS is an appropriate method for investigating diffusion process in complex systems, such as polymer gels.

Determination of Oxidative Glucose Metabolism In Vivo in the Young Rat Brain Using Localized Direct-Detected 13C NMR Spectroscopy

Determination of oxidative metabolism in the brain using in vivo ¹³C NMR spectroscopy (¹³C MRS) typically requires repeated blood sampling throughout the study to measure blood glucose concentration and fractional enrichment (input function). However, drawing blood from small animals, such as young rats, placed deep inside the magnet is technically difficult due to their small total blood volume. In the present study, a custom-built animal holder enabled temporary removal of the animal from the magnet for blood collection, followed by accurate repositioning in the exact presampling position without degradation of B₀ shimming. ¹³C label incorporation into glutamate C4 and C3 positions during a 120 min [1,6-¹³C₂] glucose infusion was determined in 28-day-old rats (n = 4) under α-chloralose sedation using localized, direct-detected in vivo ¹³C MRS at 9.4T. The tricarboxylic acid cycle activity rate (V(TCA)) determined using a one-compartment metabolic modeling was 0.67 ± 0.13 μmol/g/min, a value comparable to previous ex vivo studies. This methodology opens the avenue for in vivo measurements of brain metabolic rates using ¹³C MRS in small animals.

Bio-Composite Membrane Electrolytes for Direct Methanol Fuel Cells

A new class of bio-composite polymer electrolyte membranes comprising chitosan (CS) and certain biomolecules in particular, plant hormones such as 3-indole acetic acid (IAA), 4-chlorophenoxy acetic acid (CAA) and 1-naphthalene acetic acid (NAA) are explored to realize proton-conducting bio-composite membranes for application in direct methanol fuel cells (DMFCs). The sorption capability, proton conductivity and ion-exchange capacity of the membranes are characterized in conjunction with their thermal and mechanical behaviour. A novel approach to measure the permeability of the membranes to both water and methanol is also reported, employing NMR imaging and volume localized NMR spectroscopy, using a two compartment permeability cell. A DMFC using CS-IAA composite membrane, operating with 2M aqueous methanol and air at 70°C delivers a peak power density of 25 mW/cm2 at a load current density of 150 mA/cm2. The study opens up the use of bio-compatible membranes in polymer-electrolyte-membrane fuel cells.

High-resolution 2D NMR spectra in inhomogeneous fields based on intermolecular multiple-quantum coherences with efficient acquisition schemes

High-resolution 2D NMR spectra in inhomogeneous fields can be achieved by the use of intermolecular multiple-quantum coherences and shearing reconstruction of 3D data. However, the long acquisition time of 3D spectral data is generally unbearable for invivo applications. To overcome this problem, two pulse sequences dubbed as iDH-COSY and iDH-JRES were proposed in this paper. Although 3D acquisition is still required for the new sequences, the high-resolution 2D spectra can be obtained with a relatively short scanning time utilizing the manipulation of indirect evolution period and sparse sampling. The intermolecular multiple-quantum coherence treatment combined with the raising and lowering operators was applied to derive analytical signal expressions for the new sequences. And the experimental observations agree with the theoretical predictions. Our results show that the new sequences possess bright perspective in the applications on invivo localized NMR spectroscopy.

NMR Separation of Intra- and Extracellular Compounds Based on Intermolecular Coherences

NMR spectroscopy is a powerful tool for detection and characterization of chemical compounds in biological systems. Its application in pharmaceutical studies in cell cultures, however, has been hampered by the enormous technical challenges in separating intra- from extracellular amounts of one substance. We introduce a novel approach to separate intra- from extracellular NMR signal based on the detection of intermolecular zero-quantum coherences in presence of a chemical shift agent. In a sample of large cells in culture, the investigation of cellular uptake of pharmacological substances becomes feasible. The addition of 10 mM Tm-DOTP to a suspension of 100 Xenopus laevis oocytes resulted in sufficient separation of resonance frequencies between intra- and extracellular water. Upon selective excitation of either intra- or extracellular water signal, only intra- or extracellular components were observed, respectively. The presented localization technique provides intrinsic averaging over a large number of cells, resulting in a significant signal gain. The method works on standard NMR spectrometers, which are available at most scientific research institutions today. On a high-resolution NMR system with a cryoprobe, a 20-fold sensitivity gain was observed as compared to conventionally localized NMR spectroscopy of a single X. laevis oocyte on dedicated NMR microscopes.

Fast multidimensional localized parallel NMR spectroscopy for the analysis of samples

A parallel localized spectroscopy (PALSY) method is presented to speed up the acquisition of multidimensional NMR (nD) spectra. The sample is virtually divided into a discrete number of nonoverlapping slices that relax independently during consecutive scans of the experiment, affording a substantial reduction in the interscan relaxation delay and the total experiment time. PALSY was tested for the acquisition of three experiments 2D COSY, 2D DQF-COSY and 2D TQF-COSY in parallel, affording a time-saving factor of 3-4. Some unique advantages are that the achievable resolution in any dimension is not compromised in any way: it uses conventional NMR data processing, it is not prone to generate spectral artifacts, and once calibrated, it can be used routinely with these and other combinations of NMR spectra.

Separated Local Field 13C NMR Spectroscopy Reveals Lipid Order Fluctuations

Solid-state NMR and small angle X-ray scattering (SAXS) are currently among the most widely used experimental methods for investigating structural and dynamic properties of phospholipid bilayers [1]. However, SAXS measurements provide information about membrane dynamics only at very high-resolution, whereas 2H NMR has a prerequisite of isotopic enrichment of the phospholipid. An alternative is magic-angle spinning (MAS) solid-state 13C NMR spectroscopy, where direct magnetic-dipolar couplings and nuclear spin-lattice relaxation times are measured at natural isotopic abundance [2]. This method provides structure and dynamics for the headgroup, glycerol backbone, and acyl chains in one experiment. As proof of principle, we measured the magnetic-dipolar couplings and nuclear spin-lattice relaxation rates in the liquid-crystalline state for the homologous series of phosphatidylcholine lipids (DLPC, DMPC, DPPC). The quasi-static dipolar lineshapes exhibit segmental order parameters that can be compared with previously measured 2H couplings. In terms of dynamics, correlation of the effective segmental order parameters with the nuclear spin-lattice relaxation rates shows that the square-law scaling for the 13C and 2H systems is universal. Moreover, 13C measurements provide valuable information about the highly dynamic headgroup region that is not commonly observed in 2H NMR experiments. Combination of solid-state 2H and 13C NMR methodologies provides greater insight into the structure and dynamics of membranes than would be determined from either technique alone [3]. This study establishes further precedent for the use of solid-state 13C NMR for research into complex biological membranes and biomaterials at natural isotopic abundance. [1] H.I. Petrache and M.F. Brown (2007) Methods in Membrane Lipids, Humana Press, 339-351. [2] J.D. Gross et al. (1997) JACS119, 796-802. [3] M.F. Brown and S.I. Chan, Encyclopedia of Nuclear Magnetic Resonance, Wiley, New York 1996, 871-885.

Target Immobilization and NMR Screening of Fragments in Early Drug Discovery

Using localized NMR spectroscopy on immobilized targets provides us with a method to simultaneously assess binding of small molecules to two different samples. This Target Immobilized NMR Screening (TINS) has a number of advantages, not least is the requirement for minimal quantities of non-isotopically labeled protein and the applicability to insoluble or unstable targets. The technique is sensitive to binding with K(D) values in the range of 100 nM to 20 mM, while careful selection of the reference protein reduces the number of false positive hits. This combination ensures a maximal number of valid hits from which to select starting points for hit elaboration projects. Hits can be prioritized using biological assays when appropriate, as well as an array of biophysical techniques. So far a variety of soluble proteins, including kinases, GTPases, viral targets and proteases, as well as a membrane protein, have been successfully screened against our fragment library. Here we illustrate our experiences with a number of examples which emphasize the usefulness of the method in selecting and prioritizing fragment hits for elaboration towards leads.

Chain Structure of Substituted Stilbene−Maleic Anhydride Alternating Copolymer Probed by Solid-State NMR

Double-quantum heteronuclear local field solid-state NMR spectroscopy (2Q-HLF solid-state NMR) has been employed to investigate the chain structure of N,N,N',N -tetraethyl-4, 4'-diaminostilbene (TDAS) and 13 C labeled maleic anhydride (MA) alternating copolymer. The torsional angle of the H- 13 C- 13 C-H part of the anhydride ring was found to be 0°, indicating an all cis configuration of the H- 13 C- 13 C-H moiety of the anhydride ring. After hydrolysis of the anhydride groups and protonation of the amino groups, the torsional angle of the H- 13 C- 13 C-H moiety of the hydrolyzed anhydride groups appears to be 60°, indicating significant rotation of the polymer backbone. Because of the predominately cis configuration of the H- 13 C- 13 C-H part of the anhydride ring, the diethylamino phenyl groups are concentrated on the two sides of the backbone plane and the anhydride groups are in the backbone plane.

Limit of detection of cerebral metabolites by localized NMR spectroscopy using microcoils

NMR has the ability to investigate biological systems non-destructively; however, its low sensitivity has primarily hampered their investigation compared to other techniques. Therefore, optimizing radiofrequency coils to improve sensitivity do offer benefits in NMR spectroscopy. Sensitivity may be improved for mass and volume limited samples if the size of the detection RF coils matches the sample size. In this paper, the mass and concentration limits of detection (LODm, LODc) for a microcoil will be estimated by MRS measurements and then compared with analytical values. For the Choline case, the LODc is close to 4.4 mM. These preliminary results enable us to open largely the biomedical applications based on cerebral metabolism investigation by experiments in small animals.

Carnosine as molecular probe for sensitive detection of Cu(II) ions using localized 1H NMR spectroscopy

Complex formation of carnosine (Csn) with Cu(II) is suspected to be of significant biochemical importance and can be detected by NMR via ion-induced paramagnetic relaxation of Csn signals. Here, we present quantification of the sensitivity achieved with localized 1H NMR spectroscopy at physiological pH and high ligand-to-metal ratios. While characterizing the highly effective relaxation transfer onto a huge Csn pool due to fast ligand exchange, it is demonstrated that a metal-to-ligand ratio of ∼100 ppm suffices to reduce Csn signals by ∼50% in vitro, thus making the dipeptide a sensitive probe for such ions. Variation of the donor accessibility reveals that the paramagnetic effect is transferred onto a ∼1370-fold donor abundance for a given ion concentration. A method is presented to characterize such effective ligand exchange relaxation transfer. These studies focus on the monomer formation since comparison with 1H NMR data of human calf muscle demonstrates that the dimer complex is insignificant in vivo. Observed line broadening in living tissue yields an upper limit of ca. 195 ppm for the Csn-related copper concentration in human skeletal muscle.

Separated local field NMR spectroscopy by windowless isotropic mixing

A new separated local field NMR experiment, designed for accurate measurements of heteronuclear dipolar couplings, is described. The pulse sequence is based on a homonuclear decoupling windowless heteronuclear isotropic mixing approach to achieve the coherent polarization exchange between the z-components of the magnetizations in heteronuclear spin system. This technique suppresses chemical shifts and frequency offset variations irrespective of the dipolar coupling value. The experiment is demonstrated on a columnar liquid crystal.

Investigating brain metabolism at high fields using localized 13C NMR spectroscopy without 1H decoupling

Most in vivo 13C NMR spectroscopy studies in the brain have been performed using 1H decoupling during acquisition. Decoupling imposes significant constraints on the experimental setup (particularly for human studies at high magnetic field) in order to stay within safety limits for power deposition. We show here that incorporation of the 13C label from 13C-labeled glucose into brain amino acids can be monitored accurately using localized 13C NMR spectroscopy without the application of 1H decoupling. Using LCModel quantification with prior knowledge of one-bond and multiple-bond J(CH) coupling constants, the uncertainty on metabolites concentrations was only 35% to 91% higher (depending on the carbon resonance of interest) in undecoupled spectra compared to decoupled spectra in the rat brain at 9.4 Tesla. Although less sensitive, 13C NMR without decoupling dramatically reduces experimental constraints on coil setup and pulse sequence design required to keep power deposition within safety guidelines. This opens the prospect of safely measuring 13C NMR spectra in humans at varied brain locations (not only the occipital lobe) and at very high magnetic fields above 4 Tesla.

Detection of intracellular lactate with localized diffusion { 1H– 13C}-spectroscopy in rat glioma in vivo

The aim of this study was to compare the diffusion characteristic of lactate and alanine in a brain tumor model to that of normal brain metabolites known to be mainly intracellular such as N-acetylaspartate or creatine. The diffusion of 13C-labeled metabolites was measured in vivo with localized NMR spectroscopy at 9.4 T (400 MHz) using a previously described localization and editing pulse sequence known as ACED-STEAM (‘adiabatic carbon editing and decoupling’). 13C-labeled glucose was administered and the apparent diffusion coefficients of the glycolytic products, { 1H– 13C}-lactate and { 1H– 13C}-alanine, were determined in rat intracerebral 9L glioma. To obtain insights into { 1H– 13C}-lactate compartmentation (intra- versus extracellular), the pulse sequence used very large diffusion weighting (50 ms/μm 2). Multi-exponential diffusion attenuation of the lactate metabolite signals was observed. The persistence of a lactate signal at very large diffusion weighting provided direct experimental evidence of significant intracellular lactate concentration. To investigate the spatial distribution of lactate and other metabolites, 1H spectroscopic images were also acquired. Lactate and choline-containing compounds were consistently elevated in tumor tissue, but not in necrotic regions and surrounding normal-appearing brain. Overall, these findings suggest that lactate is mainly associated with tumor tissue and that within the time-frame of these experiments at least some of the glycolytic product ([ 13C] lactate) originates from an intracellular compartment.

Biomedical applications of10B and11B NMR

This review focuses mainly on the detection and investigation of molecules used for boron neutron capture therapy (BNCT) by 10B and 11B NMR. In this binary radiation treatment, boron-containing molecules (also called 'BNCT agents') enriched in the 10B isotope, are targeted to the tumor, and irradiated with thermal or epithermal neutrons. Capture of these neutrons by 10B nuclei generates cell-damaging radiation, confined to single cell dimensions. NMR research efforts have primarily been applied in two directions: first, to investigate the metabolism and pharmaco-kinetics of BNCT agents in-vivo, and second, to use localized NMR spectroscopy and/or MRI for non-invasive mapping of the administered molecules in treated animals or patients. While the first goal can be pursued using 11B NMR for natural-abundance samples (80% 11B / 20% 10B), molecules used in the actual treatment are > 95% enriched in 10B, and must therefore be detected by 10B NMR. Both 10B (spin 3) and 11B (spin 3/2) are quadrupolar nuclei, and their typical relaxation times, in common BNCT agents in biological environments, are rather short. This poses some technical challenges, particularly for MRI, which will be reviewed, along with possible solutions. The first attempts at 11B NMR and MRI detection of BNCT agents in biological tissue were conducted over a decade ago. Since then, results from 11B MRI in laboratory animals and in humans have been reported, and 11B NMR spectroscopy provided interesting and unique information about the metabolism of some BNCT agents in cultured cells. 10B NMR was applied either 'indirectly' (in double-resonance experiments involving coupled protons), but also by direct 10B MRI in mice. However, no results involving the NMR detection of 10B-enriched compounds in treated patients have been reported yet.