Proton Nuclear Magnetic Resonance Line Research Articles

Bound water freezing in AntarcticUmbilicaria aprinafrom Schirmacher Oasis

AbstractThe effect of low temperature onUmbilicaria aprinacollected from Schirmacher Oasis, East Antarctica, was determined over a wide range of hydration using proton free induction decays, proton nuclear magnetic resonance (NMR) spectra and differential scanning calorimetry methods. The proton NMR line is a superposition of the broad component from the solid matrix of the thallus and a narrower component from the averaged bound water pool. Proton free induction decays may be resolved into three components: a solid component well described by the Abragam function and two exponentially decaying components from water loosely bound and water tightly bound in the thallus. With decreased temperature the loosely bound water pool (freezing water) is transferred to the tightly bound water pool (non-freezing water), and vanishes below -40°C. Bound water freezing and melting temperatures decrease with the decrease of hydration level, suggesting that heterogeneous ice nucleation is responsible for water freezing. The onset of bound water freezing temperature isc.10°C lower than the melting temperature. TheU. aprinathalli do not reveal the ability to stimulated ice nucleation at higher temperature. Freeze-thaw cycles showed that forn> 5 cycles no substantial change occurs in the difference between melting and freezing temperatures.

On the feasibility of neurocurrent imaging by low-field nuclear magnetic resonance

We describe a nuclear magnetic resonance (NMR) spectrometer operating at 20 μT with a frequency resolution of 2 mHz to determine the intrinsic linewidth of the proton resonance in the human brain to be about 3 Hz. Using the same system we measured a biomagnetic field of 0.5 to 1 pT amplitude, which was generated by sustained brain activity evoked during repetitive median nerve stimulation. From these data, the effect of neuronal currents on the proton NMR signal was estimated. We conclude that neuronal currents may cause a measurable shift of the proton NMR line of brain tissue in low-fields.

Proton NMR study of molecular motion in bulk and in highly drawn fiber polyamide-6

The proton motion in bulk and highly drawn fiber polyamide-6 has been studied by field cycling relaxometry and proton line shape measurements. The dips in theT 1 dispersion allowed for the determination of the14N quadrupole coupling tensor. The fact that only one set of14N nuclear quadrupole resonance lines, has been found shows that all N-H groups in nylon-6 are H-bonded. A striking difference in the main line width transition and the low-frequency molecular dynamics has been observed between a slowly cooled “bulk” polyamide-6 sample and a rapidly cooled and highly drawn “fiber” sample by wide line proton nuclear magnetic resonance line shape and spin-lattice relaxation time measurements. This result is consistent with the picture that shearing melt processing procedures, such as spinning, plant stable and long-lived crystallization nuclei into the amorphous phase which impose additional motional constraints on the surroundings and inhibit the self-diffusion process.

Proton NMR study of α-MnH 0.06

Proton nuclear magnetic resonance (NMR) spectra and spin–lattice relaxation rates for the solid solution α-MnH 0.06 have been measured over the temperature range 11–297 K and the resonance frequency range 20–90 MHz. A considerable shift and broadening of the proton NMR line and a sharp peak of the spin–lattice relaxation rate are observed near 130 K. These effects are attributed to the onset of antiferromagnetic ordering below the Néel temperature T N≈130 K. The proton NMR line does not disappear in the antiferromagnetic phase; this suggests a small magnitude of the local magnetic fields at H-sites in α-MnH 0.06. The spin–lattice relaxation rate in the paramagnetic phase is dominated by the effects of spin fluctuations.

NMR Investigation of Molecular Motion in the Neat Solid and Plastic-Crystalline Phases of Cyclohexane1

The molecular dynamics of neat solid and plastic phase cyclohexane are investigated using solid state carbon, deuteron, and proton nuclear magnetic resonance (NMR) techniques. Particular emphasis is placed on deciphering the dynamical origin of a line width/line shape transformation in the static proton NMR spectrum of plastic phase cyclohexane near 199 K, and it is examined in terms of rotational, translational, and conformational contributions. It is shown that translational diffusion within lattice defect sites is the probable dynamical mode associated with the static proton NMR line shape modulation. The rate of conformational isomerism by ring inversion in the plastic phase is measured for the first time at two temperatures, and the time scale of this process suggests a mechanistic correlation with translational diffusion within single crystals in the plastic phase. Finally, the time scale and symmetry associated with rotational diffusion in solid-phase cyclohexane are found (respectively) to be longer and more complex than previously reported.

1H NMR and Calorimetric Measurements on Rabbit Eye Lenses

The dynamic properties of water molecules in the rabbit lens were studied by proton nuclear magnetic resonance line shape analysis, measurements of relaxation times as a function of temperature and calorimetric measurements. The experiments prove, as already suggested by other authors, that there are two types of water in the lens of rabbit eyes, namely bound unfreezable hydration water and bulk freezable water. Line shape analysis and relaxometry showed, that this two types of water exist in two different environments, which may be identified as the nucleus and the cortex of the lens. The line shape analysis showed furthermore that water molecules in the rabbit lens has a common spin lattice relaxation time (T1), but two different transverse relaxation times (T2A and T2B). The tentative model of fast water exchange on the T1 time scale and slow water exchange on the T2 time scale, was used to explain experimental proton relaxation data of the rabbit lens. An estimation for this exchange rate kex by comparing it to the relaxation times is given (T1(-1) << kex << T1(-1)). It has also been shown by a calorimetric measurements, that the lenses can be easily under-cooled to temperatures well below the freezing point of water. The achievable maximum undercooling temperature of the lens is a function of the cooling rate KC, therefore it has to be considered as an experimentally adjustable parameter which is not characteristic for the investigated sample. Thus it must be noted that any previous discussions about the specific value of the temperature of water crystallisation in biological systems need to be carefully reconsidered.

Molecular dynamics simulation of a nematic liquid crystal

The article describes molecular dynamics simulations of 4-n-pentyl-4′-cyanobiphenyl (5CB) in the nematic phase at 300 K using two interaction models. The first model comprises united atoms, while in the second, shorter simulation, the hydrogen atoms are explicitly included. Liquid crystalline order parameters were calculated using various definitions of molecular frames and were found to be in reasonable agreement with experiments. Distributions of dihedral angles and relative populations of various conformations in the alkyl chain have been determined. Translational and rotational diffusion processes were investigated using time correlation functions, and were compared with experimental results. Local order parameters, relevant for deuterium nuclear magnetic resonance (NMR) spectra, were determined for the segments in the alkyl chain. Proton NMR line shapes were calculated from the trajectory using an approximate method for determination of the dipole–dipole Hamiltonian matrix. These line shapes were found to be very sensitive to conformational distributions and therefore to the force field used in the simulation.

Proton nuclear magnetic resonance line narrowing and tetragonal lattice distortion in SmH 2+ ξ (0 ⩽ ξ ⩽ 0.40)

Proton magnetic resonance experiments have been made on samarium hydride samples SmH 2+ξ (0⩽ ξ⩽0.40) to search for proton self-diffusion and hydrogen ordering effects. Data are presented for the linewidths and some line shapes for temperatures from about 78 K to 295 K. For all samples except SmH 2.00, proton line narrowing was observed. However, for ξ=0.30 and ξ=0.40 a system of two lines appeared below about 250 K. One of these lines is broad, and its second and fourth moments exhibit a weak temperature dependence. This indicates a possible hydrogen sublattice ordering below 250 K since this effect may hinder the proton diffusion and thus a broad resonance line results. Our X-ray studies revealed a very small ( c: a≈1.003) tetragonal deformation in SmH 2.30 at low temperatures. The effect was much less distinct in SmH 2.40 and not detected in SmH 2.12.

A structural model of hydrogenated amorphous silicon

Abstract A hand-built continuous random-network structural model of a-Si: H has been constructed. The model contains 800 Si atoms and 84 H atoms in the monohydride form. We have investigated possible ways of incorporating hydrogen. We have found that the amorphous silicon matrix is interwoven by micropores, which are mainly of an open type and their internal surfaces are covered by the H atoms. The model was relaxed with respect to Keating forces. Various structural characteristics, density, radial distribution functions, X-ray and neutron diffraction intensities, and also proton nuclear magnetic resonance line shape have been calculated and compared with accessible experimental data. We have found that the presence of hydrogen lowers the deformation energy per silicon atom in comparison with pure a-Si, as represented by the Polk model.

Spatial system of the Wiser model of coal structure according to the second moment of the nuclear magnetic resonance line

The second moment of the proton nuclear magnetic resonance line was calculated for the Wiser structure of coal according to the Van Vleck theory. The calculations were carried out assuming that the predominant interaction was the dipole interaction between protons. The interaction between protons and paramagnetic centers was estimated as minor, in the range of 0.15–0.27 G2. The result of the calculations both for the rigid structure and for the one with rotating fragments is similar to the experimental spin-spin relaxation time of the Gaussian component of free-induction decay observed for some coals. This result suggests that the Wiser molecule presents the macromolecular part in the molecular-macromolecular model of coal. Its maximal dimensions are X=24.1, Y=29.3, and Z=11.29 Å and the distance between the two remotest protons is 34.5 Å.

Myoglobin diffusion in bovine heart muscle.

The rotational mobility of myoglobin in situ was determined by proton nuclear magnetic resonance line width measurements of a characteristic myoglobin resonance observed in bovine heart muscle spectra. The protein diffuses intracellularly at nearly half the rate observed in dilute solution. This high mobility allows the oxygenated form of myoglobin to contribute significantly to the overall diffusive flux of oxygen in respiring heart muscle.

Anisotropy of the dielectric constant of polyacetylene

AbstractThe dielectric constant ϵ of polyacetylene films oriented by rolling was measured. The variation of ϵ and also that of the proton nuclear magnetic resonance line shape indicate that rolling partially isomerizes cis(CH)x. For oriented trans(CH)x we find ϵ∥ = 5.7 and ϵ⟂ = 4.0 in the plane of the film. A calculation based on bond polarizabilities leads to qualitative agreement with experiment.

Exchange and inversion in 2-methylbutyllithium: proton nuclear magnetic resonance line shapes at 300 MHz

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExchange and inversion in 2-methylbutyllithium: proton nuclear magnetic resonance line shapes at 300 MHzGideon Fraenkel, William E. Beckenbaugh, and Ping Pin YangCite this: J. Am. Chem. Soc. 1976, 98, 22, 6878–6885Publication Date (Print):October 1, 1976Publication History Published online1 May 2002Published inissue 1 October 1976https://doi.org/10.1021/ja00438a019RIGHTS & PERMISSIONSArticle Views147Altmetric-Citations44LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (856 KB) Get e-Alerts Get e-Alerts

Proton NMR Study of the Molecular Reorientation in the Trigonal Phase of Sodium Hydrosulfide

The second moment of the proton nuclear magnetic resonance line and the spin–lattice relaxation time were measured as functions of temperature throughout the trigonal phase of NaSH. Motional narrowing of the resonance line occurs at about 120 K. A T1 minimum was also observed indicating molecular reorientation of the SH− ion. The second moment and the relaxation times were calculated using several models for possible SH− ion motion. The best agreement with experimental results was obtained when the proton was considered to move between two positions either side of the sulfur atom along the trigonal axis.

Proton nuclear magnetic resonance line widths and spin relaxation in paramagnetic metalloporphyrins of chromium(3), manganese(3), and iron(3).

Proton nuclear magnetic resonance line widths and spin relaxation in paramagnetic metalloporphyrins of chromium(3), manganese(3), and iron(3).

Wide line nuclear magnetic resonance studies on transition aluminas—Distribution of protons between surface and bulk phases

Wide line nuclear magnetic resonance (NMR) has been used to study the distribution of protons between the surface and bulk phases in a transition alumina. The width of the proton NMR line in a series of transition aluminas was shown to be a function of the surface area as measured by the nitrogen adsorption method (BET). The NMR method can be used to quantitatively estimate the concentration of total hydroxyl content in a transition alumina. The fraction of hydroxyl groups located on the surface of the sample can be estimated from the width of the proton NMR line. This fraction was shown to be related to the surface area of the sample. Proton line widths were combined with aluminum-27 amplitudes to estimate the concentration of protons in the first two molecular layers of a transition alumina.

NMR Study of Water Metabolism in the Olfactory Nerve of Garfish

The proton nuclear magnetic resonance line for H2O in nerve is broadened when the K+ concentration of the physiological solution is increased 30×. The difference between nerve in normal compared to high K+ solution was maintained during an observation period of 100 h. Changes in linewidth are attributed to alteration in viscosity of the H2O associated with a changing contribution of metabolic H2O to the signal.