Proton Nuclear Spin Research Articles

Dynamical Behavior of Carbohydrates As Studied by Carbon-13 and Proton Nuclear Spin Relaxation

Variable-field carbon-13 and proton relaxation data are reported for two saccharides: a monosaccharide, 1,6-anhydro-β-d-galactopyranoside; and a disaccharide, methyl 3-O-α-d-mannopyranosyl-β-d-glucopyranoside. Carbon-13 measurements were perfomed at two fields, 4.7 and 9.4 T, and at 268, 288, and 303 K for the monosaccharide and at 268, 288, 303, and 323 K for the disaccharide. Proton cross-relaxation measurements were performed at three magnetic field strengths, 7.05, 9.4, and 11.75 T, and at several temperatures, 268, 288, and 303 K for the monosaccharide and 268, 282, 288, and 323 K for the disaccharide. The carbon-13 results were analyzed with the Lipari−Szabo “model-free” approach to obtain estimates of the global correlation times and order parameters. The monosaccharide was found to be very rigid, with S2 = 0.91, while the disaccharide showed some internal motions reflected in a lower order parameter, S2 around 0.8. The intra-ring proton cross-relaxation could be explained by the motional paramete...

A Bulk and Spatially Resolved NMR Relaxation Study of Sandstone Rock Plugs

A detailed study of the proton nuclear magnetic-resonance spin–lattice and spin–spin relaxation time of water in a series of 10 well-characterized sandstone rock plugs has been made as a function of saturation. The saturation levels range from 0.06%, equivalent to monolayer coverage of the surface of the pore space, to 100%. Both bulk and spatially resolved measurements have been made. The results have been used to test fast-diffusion relaxation theory in rock over the full saturation range for the first time. Evidence has been obtained for the effect of pore throats on the relaxation rates for each plug and estimates have been made of pore-throat sizes which correlate well with water-vapor percolation thresholds.

Optical detection of magnetic resonance in a single molecule

MAGNETIC resonance spectroscopy1 is a powerful tool for molecular characterization and structure determination. The sensitivity of conventional approaches is limited to about 1010 electron spins or 1016 nuclear spins; this sensitivity can be improved to about 105 spins by polarizing the spins via optical pumping and detecting optical rather than microwave photons2. Recently, fluorescence from single molecules was detected by tuning a single-frequency laser in the inhomogeneously broadened fluorescence excitation band of a dilute dispersion of pentacene in a host crystal of p-terphenyl3,4. Here we report that, by combining single-molecule fluorescence spectroscopy with optically detected magnetic resonance for the pentacene-doped p-terphenyl system, we can detect magnetic resonance in a single pentacene molecule. We observe two of the three possible transitions between sublevels of the metastable triplet state. The spectral lineshapes indicate that the proton nuclear spin states change during the measurement, leading to spectral diffusion within the magnetic resonance line.

Observation of the pure rotational spectra of the ArOH and ArOD complexes by a Fourier-transform microwave spectrometer

Pure rotational spectra of open-shell van der Waals complexes, ArOH and ArOD, have been observed for the first time by a pulsed-nozzle Fourier-transform microwave spectrometer. The complexes were produced in a pulsed electronic discharge in a water/Ar mixture, with subsequent expansion of the discharge products into a supersonic jet. The observed J =5/2–3/2 transitions for both the species showed P-type doublings, as well as magnetic hyperfine splittings due to the proton or deuterium nuclear spin. The hyperfine coupling constants of the complexes are much smaller than those of free OH or OD, showing that the complex is undergoing a large amplitude motion in the ground vibronic state with an average amplitude exceeding 50°.

Cross relaxation between proton and quadrupolar nuclear spins in metal-hydrogen systems.

Enhanced proton-NMR spin-lattice-relaxation rates ${\mathit{R}}_{1}$ measured over a range of frequencies and temperatures in the Nb-H, Nb-V-H, and Ta-H metal-hydrogen systems are attributed to dipolar cross relaxation between the Zeeman energy levels of the proton spin and the combined Zeeman-quadrupole levels of the metal nuclear spin. This cross-relaxation mechanism can dominate the total ${\mathit{R}}_{1}$ at low temperatures even in static (nonrotating) polycrystalline samples, resulting in relaxation rates up to 400 times greater than those expected from electronic relaxation alone. At low temperatures, the relaxation rates decreased roughly linearly with temperature, in some cases extrapolating to zero at 0 K, and in other cases having a finite intercept at 0 K. We calculate the cross-relaxation rate for the cases of Nb-H and Ta-H and compare the results with experimental data. A crucial feature of our interpretation is that, even in the ordered hydrides, there is substantial structural disorder. Although experiments were limited to proton relaxation in metal-hydrogen systems, our conclusions about the effects of cross relaxation on the total spin-lattice-relaxation rate should apply equally well to other heteronuclear spin systems in solids having some degree of structural disorder.

Determination of the protein activity of corn zeins in alkaline solutions from proton nuclear spin relaxation data as a function of concentration and heat treatments

Determination of the protein activity of corn zeins in alkaline solutions from proton nuclear spin relaxation data as a function of concentration and heat treatments

The microwave spectrum and structure of the H2O–SO2 complex

The microwave spectrum of H2O–SO2 has been observed with a pulsed beam, Fabry–Perot cavity, Fourier-transform microwave spectrometer. In addition to the normal isotopic form, we have observed the spectra of H2O–34SO2, HDO–SO2, and D2O–SO2. For the normal and dideuterated forms we observe two states with a- and c-type spectra which are split by internal rotation of the water unit, while for the 34 S and HDO species two states are observed but only the a-type spectrum was assigned. Rotational analysis of each spectrum for H2O–SO2 provides the constants A=8763.071(3) MHz, B=3819.655(2) MHz, and C=2900.899(2) MHz for the I=0 state and A=8734.268(4) MHz, B=3821.281(2) MHz, and C=2900.837(2) MHz for the I=l state, where I is the resultant proton nuclear spin. Stark effect measurements give electric dipole components μa =1.984(2) D and μc =0.488(4) D for H2O–SO2. The geometry obtained from fitting the derived moments of inertia has the planes of the two monomer units tilted approximately 45° from the parallel orientation with the oxygen atom of the water closest to the S atom of SO2, giving an S–O distance of 2.824(16) Å and a center-of-mass distance Rc.m. =2.962(5) Å. The (SO2)2 species was also produced with the same nozzle expansion conditions as used for H2O–SO2. New measurements on (SO2)2 are reported and fitted with the measurements from Nelson, Fraser and Klemperer [J. Chem. Phys. 83, 945 (1985)], providing improved rotational and centrifugal distortion constants.

4719098 Enteral contrast medium useful for nuclear magnetic resonance imaging and its preparation

An enteral contrast medium useful for proton nuclear spin tomography contains at least one physiologically compatible paramagnetic compound in combination with a physiologically compatible, osmotically active substance, as well as a physiologically compatible base/buffer or buffer mixture with a pH value of 3 to 8, and, optionally, also a viscosity-raising material, all dissolved or suspended in water. It is excellently suitable for enhancing contrast in imaging, e.g., of the gastrointestinal tract by nuclear spin tomography.

The lineshape of quadrupolar satellites in level anticrossing (LAC) optical nuclear polarization (ONP) spectra

Satellite lines appear in the optical nuclear polarization (ONP) spectra of doped molecular single crystals when the guest or host contains bromine. The satellites, which are separated by the Br quadrupolar splitting, are observed in the level anticrossing (LAC) region of systems in the lowest excited triplet state. In the present paper we derive the satellite LAC ONP lineshape for a model system comprised of a triplet S = 1 coupled to a Br and a proton nuclear spin. We find that the satellite lineshape has the unusual form, L(B) ▪, where L is a Lorentzian function that depends only on the magnetic field strength, B, and bromine hyperfine (hf) coupling parameters. Surprisingly the proton hf coupling affects only the overall amplitude, not the form, of the lineshape function.

The effect of hydration on the mobility of phospholipids in the gel state. A proton nuclear magnetic resonance spin echo study

Proton nuclear magnetic resonance (NMR) dipolar echo studies are presented for the gel state of dipalmitoylglycerophosphocholine (dipalmitoyl-GPC) — heavy water dispersions. The mobility and the mean order of the chains and the head group of dipalmitoyl-GPC were determined for different water concentrations and temperatures. For smaller than 5 mol D 2O per mol dipalmitoyl-GPC the molecule undergoes temperature- and hydration-dependent restricted rotational oscillations about the long axis of the molecule. For hydration numbers equal or larger than 5 mol D 2O per mol dipalmitoyl-GPC the molecules rotate effectively about their long axes and intermolecular dipolar interactions between proton groups of neighbour molecules are averaged. The onset of the lateral diffusion of dipalmitoyl-GPC is observed which averages out all intermolecular dipolar interactions. Deviations of the individual segments of the chains from the all- trans state have to be considered. The widely accepted model that the dipalmitoyl-GPC molecules rotate about their long axes with stiff all- trans chains should be modified. The polar head groups of dipalmitoyl-GPC effectively rotate about the bilayer-normal and restricted rotations about single bonds in the head group are allowed. An order parameter of about 0.6 for the head group was obtained for fully hydrated dipalmitoyl-GPC molecules at ambient temperature.

Proton-nuclear spin relaxation and molecular dynamics in the lysozyme-water system

Proton-nuclear spin relaxation and molecular dynamics in the lysozyme-water system

Proton and boron-11 nuclear spin relaxation and the molecular tumbling of nido-decaborane in perdeuterotoluene solution. An interesting transition in solute–solvent interaction behaviour

The variations with temperature of the 1H and 11B longitudinal relaxation times, T1, for B10H14 in CD3C6D5 solution show that there is a transition from anisotropic motion at lower temperatures to essentially isotropic tumbling at higher temperatures. The dominant relaxation mechanisms are (11B–1H) and (1H–1H) dipolar for the 1H nuclei and quadrupolar for the 11B nuclei. The activation energy EA for the high-temperature isotropic tumbling is 9.9(5) kJ mol–1, and analysis of the 1H relaxation at lower temperatures shows activation energies ExA≅ 20, EyA≅ 18 and EzA≅ 15 kJ mol–1 about molecular cartesian axes x, y and z, z being the C2 axis of the molecule. Proton nuclear-shielding behaviour permits description of the modes of solute–solvent interaction and shows that ΔH and ΔS for the motional transition are +25 ± 3 kJ mol–1 and +110 ± 20 J mol–1 K–1, respectively. Some of the observations have important wider implications.

Electron spin echo modulation of triplet methylenes by nitrogen photochemical by-product

Electron spin echo modulations in two triplet arylmethylenes have been observed with rf fields which are too weak to induce coherent branching transitions among proton nuclear spin states. Modulation by the 14N nuclei of N 2 released in the photolysis of the diazomethane precursor is consistent with the frequencies and angular dependences of the modulations.

Double group considerations, Jahn-Teller induced rovibronic effects, and the nuclear spin-electron spin hyperfine Hamiltonian for a molecule of symmetry C3 v in an electronic 2E state

Two different double groups of the point group C 3 v are compared. These double groups arise for molecules in a 2 E state, and are associated with the half-integral electron spin, and with a half-integral vibronic quantum number, respectively. For many aspects of molecular energy level calculations, the use of these double groups can be avoided if desired. Contributions to the effective rotational Hamiltonian for a C 3 v molecule in a 2 E electronic state are derived. These contributions correspond to large “ l-type doubling” and “(2, −1) resonance” terms, and arise because of the Jahn-Teller distortion tendencies of the molecule. Similar contributions to the effective rotational Hamiltonian, which arise from interactions with other electronic states, are also briefly considered. A hyperfine Hamiltonian is derived, which describes the interaction of the three proton nuclear spins in a C 3 v molecule of the type CH 3O with the odd electron spin in a 2 E electronic state. A prescription for determining hyperfine matrix elements in a Hund's case ( a β ) basis set is given.

Solid state phase transitions and molecular reorientation in o r t h o- and p a r a-carborane: An isomer effect

The proton nuclear spin–lattice relaxation times at 30 MHz have been measured for ortho- and para-carborane between 170 and 310 K and between 210 and 320 K, respectively. Para-carborane undergoes solid–solid transitions at about 300 and 238 K while the ortho isomer shows only one transition at about 265 K. The details of the phase transitions are discussed and molecular reorientation in the isomers is compared.

The thermal polymerization of styrene: A proton NMR study

The proton nuclear spin–lattice relaxation has been measured as a function of reaction time during the thermal polymerization of styrene. Initially the proton relaxation in the monomer is exponential and the measured T1 is 21 s, a value typical of oxygen free organic liquids. Within a few hours of the start of the experiment, the relaxation is observed to be the sum of two exponential components. The component with the longer relaxation time is due to the monomer. The second component which has a much shorter relaxation time is assigned to the polymer formed during the reaction. For a polymerization carried out at 86°C the proportion of monomer is observed to decrease initially at rate of 0.93%/h. T1 for the monomer decreases linearly until about 35% of the monomer remains when the polymerization rate becomes less. The results are independent of the NMR frequency and an analysis of the results indicates that the translational diffusion of the monomer decreases substantially during the reaction. T1 for the polymer depends on the NMR frequency. Initially it decreases with reaction time, goes through a minimum, then increases. The value of the T1 at the minimum suggests that the molecular motions involving the hindered rotation about the carbon backbone of the long polymer chain are being observed.

Experimental evidence for the role of cross-relaxation in proton nuclear magnetic resonance spin lattice relaxation time measurements in proteins

Proton nuclear magnetic resonance (NMR) spin lattice relaxation time (T1) and spin-spin relaxation time (T2) measurements are presented for a number of proteins with molecular weights spanning the range of 6,500-150,000 daltons. These measurements provide experimental evidence for the role of cross-relaxation in 1H NMR T1 measurements in proteins. The relationship between these measurements and the theory recently presented by Kalk and Berendsen is discussed. The results indicate that cross-relaxation dominates the T1 measurements for the larger proteins, even at relatively low resonance frequencies such as 100 MHz.

Nuclear Spin Relaxation in Solutions Prepared from Normal and Tumor Hepatic Tissues: Brief Communication 2

Water proton nuclear spin relaxation times were investigated at two frequencies (10.7 and 100 MHz) in solutions prepared from Dunning hepatomas (LC-18) and normal Iivers of F344 rats. The solutions (saps) were prepared by homogenization of the tissue without the addition of water or chemieals, followed by two centrifugations. The water proton spin-lattice and spin-spin relaxation times (T1 and T2, respectively) were longer in the tumor sap than in the Iiver sap. The T1/T2 ratio was higher than that for pure water, and the T1 values were higher at the higher frequency. A rough correlation with significant scatter was found between T1−1 and F/(1−F), where F is grams protein/grams solution. Precipitation of protein with trichloroacetic acid yielded solutions that showed higher T1 values when prepared from tumor sap than from Iiver sap. Glycogen concentrations were much higher in the deproteinated liver saps than in deproteinated hepatoma saps. Dialysis of fresh sap against butter for 4 hours produced no change in T1. Addition of the reducing agent sodium dithionite produced no change in T1. It was concluded that water-protein and water-glycogen interactions are the predominant mechanism for the shortening of sap relaxation times relative to that of distilled water. The higher concentrations of protein and glycogen in liver sap compared to hepatoma sap were the likely cause of the liver sap T1 values being shorter than those of hepatoma sap. No evidence of a significant paramagnetic speeies ettect on sap T1 was found.

Carbon-13 nuclear magnetic resonance studies of proteins.

Nuclear magnetic resonance (NMR) methods, in principle, are capable of resolving resonances of single atoms in protein molecules. In practice, most of the resonances from hydrogen nuclei (lH NMR) in proteins overlap to produce a broad unresolved envelope (1). Carbon-13 NMR (13C NMR) has an intrinsically higher resolving power than proton NMR by a factor of about 20 because of the greater range of electronic configurations experienced by carbon atoms (2). Consequently, initial results on amino acids were interpreted to indicate that I3C NMR would be a potentially valuable tool in studies of proteins in solution (3). Initially, sensitivity problems made this potential unrealizable. The sensitivity of carbon-13 relative to proton NMR at the same magnetic field strength is 1:62.9. If the fact that I3C has a natural abundance of 1.1 % is taken into account (12C has no resonance condition), this leads to a relative sensitivity of 1:5716. This sensitivity problem in l3C NMR, however, has to a large extent been overcome by the introduc­ tion of the pulse Fourier transform method (4). Further losses of signal intensity in BC NMR spectra arise as a result of coupling between 13C and IH nuclear spins. These couplings can be removed by the applica­ tion of a second radiofrequency field at the resonance value for protons. If this frequency has sufficient power and is spread over the entire range of proton absorp­ tions, a process often accomplished by noise modulation, then complete decoupling of the proton nuclear spins from the 13C nuclear spins results. Each carbon atom in the molecule then gives rise to a single resonance, and the resultant proton­ decoupled I3C spectra are relatively simplified. In addition, applying a IH decou­ piing frequency leads to changes in the relative populations of the energy levels for the DC nuclear spins; this phenomenon, known as the nuclear Overhauser effect

Carbon-13, proton spin–spin coupling constants in some 4-substituted isothiazoles and related heterocyclics

Carbon-13, proton nuclear spin–spin coupling constants have been measured for a number of 4-substituted isothiazoles. The observed values are compared with those measured in other heterocyclic systems and those calculated in the parent and related heterocyclics using finite perturbation theory and semi-empirical molecular orbital theory at the CNDO/2 and INDO levels of approximation.