Nuclear Magnetic Resonance Linewidth Research Articles

The natural line width of low field nuclear magnetic resonance spectra

The authors suggest a procedure for the determination of the natural nuclear magnetic resonance line width Δ ν of liquids using an air coil system at flux densities from 25 μT to 150 μT. Even if the line broadening caused by instrumental field inhomogeneity is much higher than Δ ν, Δ ν can be found by extrapolating the measured line width’s field dependency. For pure water this procedure yielded Δ ν = 0.125 Hz ± 0.005 Hz. This is shown to be consistent with the smallest line width found for this sample below 25 μT using a superconducting quantum interference device-based spectrometer.

Prospects for sub-micron solid state nuclear magnetic resonance imaging with low-temperature dynamic nuclear polarization.

We evaluate the feasibility of (1)H nuclear magnetic resonance (NMR) imaging with sub-micron voxel dimensions using a combination of low temperatures and dynamic nuclear polarization (DNP). Experiments are performed on nitroxide-doped glycerol-water at 9.4 T and temperatures below 40 K, using a 30 mW tunable microwave source for DNP. With DNP at 7 K, a 0.5 microL sample yields a (1)H NMR signal-to-noise ratio of 770 in two scans with pulsed spin-lock detection and after 80 db signal attenuation. With reasonable extrapolations, we infer that (1)H NMR signals from 1 microm(3) voxel volumes should be readily detectable, and voxels as small as 0.03 microm(3) may eventually be detectable. Through homonuclear decoupling with a frequency-switched Lee-Goldburg spin echo technique, we obtain 830 Hz (1)H NMR linewidths at low temperatures, implying that pulsed field gradients equal to 0.4 G/d or less would be required during spatial encoding dimensions of an imaging sequence, where d is the resolution in each dimension.

Modeling the morphology and mechanical behavior of shape memory polyurethanes based on solid-state NMR and synchrotron SAXS/WAXD

A combination of solid-state proton Wide-line Nuclear Magnetic Resonance (NMR) relaxometry and synchrotron Small-angle (SAXS) and Wide-angle (WAXD) X-ray scattering was used to elucidate the microphase morphology of shape memory thermoplastic multi-block polyurethanes based on poly(e-caprolactone), as switching segment and polyurethane based permanent or hard segments (HS). The polyurethanes are produced from the condensation of 1,4-butanediol (BDO) with hexamethylenediisocyanate (HDI). The morphology – induced by the hard-segment crystallization – converts from dispersed randomly placed hard-segment domains into progressively more periodic, but interconnected HS nanophases with increasing HS content. Irrespective of the actual morphology, the SAXS data could be described satisfactorily by using a clipped Gaussian random field (GRF) model. The NMR data demonstrate that the HS domain fraction corresponds to the chemical feed, pointing at a complete phase separation. The material mechanical behavior during repeated deformation cycles can be explained on morphological grounds and involves a spatially heterogeneous plastic deformation of the hard domains.

Dissolution and Gelation of Cellulose in TBAF/DMSO Solutions: The Roles of Fluoride Ions and Water

Solutions of cellulose in a mixture of tetrabutylammonium fluoride and dimethyl sulfoxide (TBAF/DMSO) containing small and varying amounts of water were studied by nuclear magnetic resonance (NMR). By measuring the composition dependences of (19)F NMR and (1)H NMR chemical shifts and line widths, details on the dissolution and gelation mechanisms for cellulose in TBAF/DMSO were elucidated. Our results suggest that the strongly electronegative fluoride ions act as hydrogen bond acceptors to cellulose hydroxyl groups, thus dissolving the polymer by breaking the cellulose-cellulose hydrogen bonds and by rendering the chains an effective negative charge. It was found that the fluoride ions also interact strongly with water. Small amounts of water remove the fluoride ions from the cellulose chains and allow reformation of the cellulose-cellulose hydrogen bonds, which leads to formation of highly viscous solutions or gels even at low cellulose concentrations.

NMR study of the quasi-one-dimensional compound BaCo 2V 2O 8

We report the results of a 51V nuclear magnetic resonance (NMR) study on the single crystal BaCo 2V 2O 8 at temperatures between 3 and 300 K. The NMR features for fields both parallel and perpendicular to the c-axis have been identified. We found no substantial changes in the NMR shift and line width at low temperatures as a constant field of 7.06 T was applied along the c-axis. The NMR observations thus indicate the absence of magnetic long-range ordering under this field, consistent with the specific heat result which showed the disappearance of the magnetic transition beyond an external field of 4 T in BaCo 2V 2O 8.

Removal of phase transfer agent leads to restricted dynamics of alkyl chains in monolayer protected clusters

The effect of phase transfer agent in the dynamics of monolayer protected gold nanoparticles has been investigated by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies. The experiments were performed with octadecane thiol and dodecane thiol protected gold nanoparticles. The materials prepared were characterized by UV-Visible spectroscopy, transmission electron microscopy and IR spectroscopy. Repeated purification of the monolayer protected gold clusters made the alkyl chains defect- free. Such effects are reflected in the infrared spectra. Interdigitation of the monolayers that followed the purification leads to alkyl chains with limited mobility. This was reflected in 13C and 1H NMR linewidths. The NMR measurements indicate that the removal of phase transfer agent affects the dynamics of isolated clusters and those with interdigitated monolayers in different ways.

Nuclear magnetic resonance linewidth and spin diffusion inS29iisotopically controlled silicon

A nuclear magnetic resonance (NMR) study was performed with $n$-type silicon single crystals containing $^{29}\text{S}\text{i}$ isotope abundance $f$ ranges from 1.2% to 99.2%. The nuclear spin diffusion coefficient $D$ has been determined from the linewidth of significantly enhanced $^{29}\text{S}\text{i}$ NMR signals utilizing a developed dynamic nuclear polarization (DNP) method. The $^{29}\text{S}\text{i}$ NMR linewidth depends linearly on $f$, at least when $fl10%$, and approaches $\ensuremath{\propto}{f}^{1/2}$ dependence when $fg50%$. The estimated $^{29}\text{S}\text{i}$ nuclear spin diffusion time ${T}_{\text{sd}}$ between phosphorus atoms used for DNP is more than ten times shorter than the nuclear polarization time ${T}_{1}^{p}$ of $^{29}\text{S}\text{i}$ nuclei around phosphorus. Therefore, the regime of ``rapid spin diffusion'' is realized in the DNP experiments.

Magnetization and Cu nuclear magnetic resonance study ofSr0.9La0.1Cu1−xNixO2

We report the results from a Cu nuclear magnetic resonance (NMR) and magnetization study of the electron-doped high-temperature superconducting cuprate (HTSC) ${\text{Sr}}_{0.9}{\text{La}}_{0.1}{\text{Cu}}_{1\ensuremath{-}x}{\text{Ni}}_{x}{\text{O}}_{2}$. This compound shows a large suppression of superconductivity by Ni $[\ensuremath{\Delta}{T}_{c}/\ensuremath{\Delta}x=18\text{ }\text{K}/%(\text{Ni})]$ that is comparable to that observed in underdoped and hole-doped HTSCs. We find small effective moments of $0.06{\ensuremath{\mu}}_{B}/\text{Cu}$ for the pure sample and $0.76{\ensuremath{\mu}}_{B}/\text{Ni}$ for the 1% Ni sample in the paramagnetic regime. The partial substitution of Ni for Cu causes the Cu NMR linewidth to increase and there is a further reduction in the Cu NMR intensity with decreasing temperature over and above that observed in the pure compound. This can be interpreted in terms of Ni inducing additional spin disorder and wipeout of the Cu NMR intensity for Cu sites near the Ni impurities.

Zero-field remote detection of NMR with a microfabricated atomic magnetometer.

We demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip sensor consisting of a microfluidic channel and a microfabricated vapor cell (the heart of an atomic magnetometer). Detection occurs at zero magnetic field, which allows operation of the magnetometer in the spin-exchange relaxation-free (SERF) regime and increases the proximity of sensor and sample by eliminating the need for a solenoid to create a leading field. We achieve pulsed NMR linewidths of 26 Hz, limited, we believe, by the residence time and flow dispersion in the encoding region. In a fully optimized system, we estimate that for 1 s of integration, 7 x 10(13) protons in a volume of 1 mm(3), prepolarized in a 10-kG field, can be detected with a signal-to-noise ratio of approximately 3. This level of sensitivity is competitive with that demonstrated by microcoils in 100-kG magnetic fields, without requiring superconducting magnets.

Preparation and Characterization of a New Lipid Nano-Emulsion Containing Two Cosurfactants, Sodium Palmitate for Droplet Size Reduction and Sucrose Palmitate for Stability Enhancement

A new lipid nano-emulsion (LNE) was prepared from soybean oil and phosphatidylcholine (PC) employing two cosurfactants, sodium palmitate (PA) for reduced droplet size and sucrose palmitate (SP) for stability enhancement. The mean droplet size of LNEs prepared at a PA/PC (w/w) ratio of larger than 1/10 was found to be ca. 50 nm by dynamic light scattering and atomic force microscopy. However, during the 12-month storage, the PA/PC (1/10)-LNE showed an increase in mean droplet size and broadening of the droplet size distribution due to coalescence of the LNE particles. In a saline solution, the coalescence proceeded very rapidly, i.e., the mean droplet size increased to more than 150 nm within 0.5 h. To suppress the coalescence of LNE particles, four sucrose fatty acid esters of different chain lengths were examined as candidate cosurfactants. The results showed that PA/SP/PC (1/4/10)-LNE could maintain a mean droplet size around 50 nm for 12 months. In a saline solution, the mean droplet size could be maintained within 100 nm even after 24 h. Slight formation of flocculation in the LNEs depending on the storage period was suggested by measurement of the 31P nuclear magnetic resonance line width of the LNEs.

Order-disorder mixed phase inTlH2PO4

An intermediate phase of partial order, associated with antiferroelectricity, is elucidated in hydrogen-bonded $\mathrm{Tl}{\mathrm{H}}_{2}\mathrm{P}{\mathrm{O}}_{4}$ undergoing separated antiferroelectric and ferroelastic phase transitions. Our $^{1}\mathrm{H}$ and $^{31}\mathrm{P}$ nuclear magnetic resonance linewidth measurements revealed marked changes at an intermediate phase boundary, involving an intermediate phase of mixed order of coexistence of paraelectricity and antiferroelectricity, which was identified by means of impedance spectroscopy. A coupling of the proton and the $\mathrm{P}{\mathrm{O}}_{4}$ tetrahedral motions to the proton ordering in the hydrogen bonds is also manifested.

Quadrupolar nuclear magnetic resonance spectroscopy in solids using frequency-swept echoing pulses

The acquisition of ideal powder line shapes remains a recurring challenge in solid-state wideline nuclear magnetic resonance (NMR). Certain species, particularly quadrupolar spins in sites associated with large electric field gradients, are difficult to excite uniformly and with good efficiencies. This paper discusses some of the opportunities that arise upon departing from standard spin-echo excitation approaches and switching to echo sequences that use low-power, frequency-swept radio frequency (rf) pulses instead. The reduced powers demanded by such swept rf fields allow one to excite spins in different crystallites efficiently and with orientation-independent pulse angles, while the large bandwidths of interest that are needed by the measurement can be covered, thanks to the use of broadband frequency sweeps. The fact that the spins' evolution and ensuing dephasing starts at the beginning of such rf manipulation calls for the use of spin-echo sequences; a number of alternatives capable of providing the desired line shapes both in the frequency and in the time domains are introduced and experimentally demonstrated. Sensitivity- and lineshape-wise these experiments are competitive vis-a-vis current implementations of wideline quadrupolar NMR based on hard rf pulses; additional opportunities that may derive from these ideas are also briefly discussed.

Characterization of β-Sheet Structure in Ure2p1-89 Yeast Prion Fibrils by Solid-State Nuclear Magnetic Resonance

Residues 1-89 constitute the Asn- and Gln-rich segment of the Ure2p protein and produce the [URE3] prion of Saccharomyces cerevisiae by forming the core of intracellular Ure2p amyloid. We report the results of solid-state nuclear magnetic resonance (NMR) measurements that probe the molecular structure of amyloid fibrils formed by Ure2p1-89 in vitro. Data include measurements of intermolecular magnetic dipole-dipole couplings in samples that are 13C-labeled at specific sites and two-dimensional 15N-13C and 13C-13C NMR spectra of samples that are uniformly 15N- and 13C-labeled. Intermolecular dipole-dipole couplings indicate that the beta-sheets in Ure2p1-89 fibrils have an in-register parallel structure. An in-register parallel beta-sheet structure permits polar zipper interactions among side chains of Gln and Asn residues and explains the tolerance of [URE3] to scrambling of the sequence in residues 1-89. Two-dimensional NMR spectra of uniformly labeled Ure2p1-89 fibrils, even when fully hydrated, show NMR linewidths that exceed those in solid-state NMR spectra of fibrils formed by residues 218-289 of the HET-s prion protein of Podospora anserina [as originally reported in Siemer, A. B., Ritter, C., Ernst, M., Riek, R., and Meier, B. H. (2005) Angew. Chem., Int. Ed. 44, 2441-2444 and confirmed by measurements reported here] by factors of three or more, indicating a lower degree of structural order at the molecular level in Ure2p1-89 fibrils. The very high degree of structural order in HET-s fibrils indicated by solid-state NMR data is therefore not a universal characteristic of prion proteins, and is likely to be a consequence of the evolved biological function of HET-s in heterokaryon incompatibility. Analysis of cross peak intensities in two-dimensional NMR spectra of uniformly labeled Ure2p1-89 fibrils suggests that certain portions of the amino acid sequence may not participate in a rigid beta-sheet structure, possibly including portions of the Asn-rich segment between residues 44 and 76.

Redistribution of Charge in the Proximity of the Spin-Peierls Transition: 13C NMR Investigation of (TMTTF)2PF6

13 C nuclear magnetic resonance (NMR) investigations were carried out for a one-dimensional organic conductor, (TMTTF) 2 PF 6 , to determine the charge dynamics and configuration in the proximity of the spin-Peierls phase-transition temperature, T sP . Although no obvious NMR line splitting associated with the charge-ordering transitions in the intermediate paramagnetic states was observed, the charge separation amplitude was estimated to be ρ CO ∼0.14 using the 13 C NMR spin–lattice relaxation rates for the distinct lines. The abrupt decrease in the NMR linewidth below 25 K and the small anisotropy of the NMR linewidth in the spin-Peierls phase indicate the possible redistribution of the charge separation in the proximity of T sP . The low-temperature electronic states of (TMTTF) 2 PF 6 are discussed from a microscopic point of view.

Antiferromagnetic correlations and impurity broadening of NMR linewidths in cuprate superconductors

We study a model of a d-wave superconductor with strong potential scatterers in the presence of antiferromagnetic correlations and apply it to experimental nuclear magnetic resonance (NMR) results on Zn impurities in the superconducting state of YBCO. We then focus on the contribution of impurity-induced paramagnetic moments, with Hubbard correlations in the host system accounted for in Hartree approximation. We show that local magnetism around individual impurities broadens the line, but quasiparticle interference between impurity states plays an important role in smearing out impurity satellite peaks. The model, together with estimates of vortex lattice effects, provides a semi-quantitative description of the impurity concentration dependence of the NMR line shape in the superconducting state, and gives a qualitative description of the temperature dependence of the line asymmetry. We argue that impurity-induced paramagnetism and resonant local density of states effects are both necessary to explain existing experiments.

Thermal transitions in associating aqueous block copolymers: light scattering, rheology and spectroscopy

Solutions containing a polyoxy-ethylene/polyoxy-propylene/polyoxy-ethylene (PEO–PPO–PEO) block copolymer, indicated as F68, in water were investigated as a function of composition and temperature. Hydrogen nuclear magnetic resonance (1H NMR) line width, chemical shift, self-diffusion, spin-lattice relaxation times, laser light scattering and rheological methods were used. The monomer–micelle equilibrium and the micelle–liquid crystalline phase transitions depend on the F68 content in the mixture and temperature. Significant changes in light scattering intensity and apparent hydrodynamic radius are associated to micelle formation above the critical micellar temperature (CMT). According to a Contin analysis, this behaviour is reflected in the presence of two populations in the intensity–intensity autocorrelation functions. The contributions due to molecules and micelles can be evaluated separately. No such effects are observed below the CMT. Micelle onset is also associated to variations in 1H NMR spectra, affecting the chemical shift, line width and spin-lattice relaxation time of the PPO methyl protons and self-diffusion, as well. Spin-lattice relaxation times of PEO chains, conversely, change significantly at temperatures close to the micelle–liquid crystalline thermal transition. Similar results were obtained from the line width of 2H NMR spectra as a function of T. Significant changes in both viscous and elastic modulus were also observed and ascribed to PPO dehydration, at the CMT, as well as to squeezing and dehydration of PEO units in liquid crystal formation, respectively.

27Al NMR study of [formula omitted

We have performed 27Al and 55Mn nuclear magnetic resonance (NMR) measurements on a single crystal of YMn 4Al 3 at 8 T. 27Al NMR spectrum shows two sets of satellites from two different Al sites. Based on the difference in NMR shift, linewidth and relaxation rates, two sets of NMR resonance peaks were assigned to the respective Al sites. NMR shift and spin–lattice and transverse relaxation rates, 1 / T 1 and 1 / T 2 , were measured down to 4 K at 8 T. Shift and linewidth for 27Al and 55Mn NMR follow temperature dependence of the susceptibility, confirming that the hyperfine field from Mn 3d spins dominates local electronic structures at both Al and Mn sites.

Formula omitted] NMR study of [formula omitted

We have performed 11 B nuclear magnetic resonance (NMR) measurements on the single crystals of GdB 4 to investigate local electronic structure and 4f spin dynamics. 11 B NMR spectrum, Knight shift, spin–lattice and spin–spin relaxation rates, 1 / T 1 and 1 / T 2 , were measured down to 4 K at 8 T . 11 B NMR shift and linewidth are huge and strongly temperature-dependent due to the 4f moments. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Gd. Below T N , the single broad resonance peak of 11 B NMR splits into several peaks reflecting the local magnetic fields due to antiferromagnetic spin arrangements. The spin–lattice relaxation rate, independent of temperature above T N , decreases significantly below T N confirming huge suppression of spin fluctuation.

11B NMR study of [formula omitted

We have performed 11B nuclear magnetic resonance (NMR) measurements on a single crystal of TbB 4 to investigate local electronic structure and 4f spin dynamics. 11B NMR spectrum, Knight shift, spin–lattice and spin–spin relaxation rates, 1 / T 1 and 1 / T 2 , were measured down to 5 K at 8 T. 11B NMR shift and linewidth are huge and strongly temperature-dependent due to the 4f moments. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Tb. Below T N , the single broad resonance peak of 11B NMR splits into several peaks reflecting the local magnetic fields due to antiferromagnetic spin arrangements. The spin–lattice relaxation rate, independent of temperature above T N , decreases significantly below T N confirming huge suppression of spin dynamics.

Absence of Mobile Carbohydrate Domains in Dry Humic Substances Proven by NMR, and Implications for Organic-Contaminant Sorption Models

The mobility and domain structure of various standard humic substances have been investigated by 1H and 1H-13C solid-state nuclear magnetic resonance (NMR) experiments. In four dry humic acids, a fulvic acid, a natural organic matter sample, and a whole peat sample, segments that undergo fast, large-amplitude motions account for <9% of the sample. This disproves a previous suggestion, based on 1H NMR data, that flexible domains, presumably carbohydrates, make up >40% of various humic acids; these putative mobile domains were also linked to dual-mode sorption. In particular, neither the polar alkyl (carbohydrate) nor the aromatic components show any fast, large-amplitude mobility. A small fraction of mobile nonpolar alkyl segments identified by us before is the only component undergoing large-amplitude motions, apart from absorbed water that we observe in humic acids exposed to ambient air. 1H-13C wide-line separation NMR shows that, contrary to previous suggestions, the dipolar couplings in the aromatic regions are smaller than in the polar alkyl segments, most likely due to differences in local 1H densities. Series of 1H-13C heteronuclear correlation experiments with 1H spin diffusion reveal close proximity of aromatic and polar alkyl segments in several humic acids, precluding carbohydrate domains on a scale of > 1-nm diameter. In the standard peat humic acid, nonpolar aromatic segments also do not form sorption domains of significant size, while nonpolar aliphatic domains, which we had previously shown to correlate with sorption capacity, have been confirmed.