Nuclear Magnetic Spin-lattice Relaxation Times Research Articles

New Surface Relaxation Mechanism for LiquidH3einH4e

Measurements of the nuclear magnetic spin-lattice relaxation time T{sub 1} of liquid {sup 3}He containing 0.5{percent} {sup 4}He and of {sup 3}He{minus} {sup 4}He mixtures as a function of magnetic field up to 22T and at temperatures down to 40mK show a new surface relaxation mechanism for liquid {sup 3}He , which is proportional to the square of the magnetic field and can be described by classical relaxation theory. The intrinsic relaxation time of liquid {sup 3}He , obtained from T{sub 1} measurements by eliminating the surface relaxation contribution, is in good agreement with existing Fermi liquid theory. {copyright} {ital 1997} {ital The American Physical Society}

Fermi Level Density of States in AgAu Alloys. Nuclear Magnetic Spin‐Lattice Relaxation Rate and Low‐Temperature Specific Heat

AbstractThe electronic structure of AgAu alloys is studied using LMTO self‐consistent band structure calculations. Both, the total and partial density of states as function of Au‐content at the Fermi level are presented. Some results of band structure calculations are analysed using a simple cluster model, which reveals that the behaviour of the partial density of states at the Fermi level can be explained by the s–d hybridisation strength and the position of the top of the d‐band. The results obtained for specific heat and spin–lattice relaxation are in general agreement with experimental observations. Furthermore, the calculations predict that the nuclear magnetic spin–lattice relaxation time of Au would decrease with increasing Ag‐content.

Metabolism and structure of triacylglycerols in rat epididymal fat pad adipocytes determined by 13C nuclear magnetic resonance.

Carbon-13 nuclear magnetic resonance (NMR) methods have been applied to a study of the structure and metabolism of the triacylglycerols from rat epididymal fat pad adipocytes. Complete NMR signal assignments are provided for adipocytes, the extracted triacylglycerols, and methyl esters of the derived fatty acids. 13C NMR yielded rapid, nondestructive, quantitative analysis of the amounts of unsaturation of the fatty acyl chains; in cells from rats given ad libitum access to a standard laboratory diet the predominant fatty acids were found to be palmitate (29.9%), oleate (27.9%), and linoleate (34.1%). These results agreed with gas chromatographic separation of the derived methyl esters of the extracted lipids. Lipid dynamics were examined in situ and showed a substantial restriction of motion of glyceride-glycerol as compared with free glycerol; the nuclear magnetic spin-lattice relaxation times for free glycerol of 2.52 +/- 0.12 (C1,3) and 4.37 +/- 0.21 (C2) s decreased to 0.15 +/- 0.009 and 0.21 +/- 0.013 s, respectively, upon esterification. Segmental motion of the chains, monitored by relaxation time measurements, increased progressively from the alpha-carbon (nT1 = 0.70 s) to the methyl ends of the chains (nT1 = 9.63). The incorporation of C-13-labeled substrates ([1-13C]glucose and [3-13C]lactate) into the glycerol moiety of triacylglycerols was monitored in real time, in the presence of insulin. Lactate (10 mM) inhibited the incorporation of glucose (5.5 mM) into glyceride-glycerol. Lipolysis at the natural abundance level of 13C was measured in the presence of 10 microM isoproterenol. Simultaneous lipogenesis and lipolysis were found to occur in situ and were measured with the aid of [1-13C]glucose and isoproterenol; the labeling pattern of medium glycerol versus extracted triacylglycerols was significantly different from that found using natural abundance glucose. Our results indicate that 13C NMR is a useful new method for the real-time monitoring of lipid structure and metabolism in vivo.

The melting line for ethylene on graphite

Using the minimum in the nuclear magnetic spin-lattice relaxation time versus temperature as an indicator of melting we have mapped out the solid-fluid phase boundary for ethylene adsorbed on graphite. At low coverages the ethylene forms a self-bound monolayer solid with a melting temperature of about 68 K. The molecules in the solid retain orientational mobility down to 55 K, the lowest temperatures explored.

The melting line for ethylene on graphite

Using the minimum in the nuclear magnetic spin-lattice relaxation time versus temperature as an indicator of melting we have mapped out the solid-fluid phase boundary for ethylene adsorbed on graphite. At low coverages the ethylene forms a self-bound monolayer solid with a melting temperature of about 68 K. The molecules in the solid retain orientational mobility down to 55 K, the lowest temperatures explored.

Etude du systeme vitreux Li 2Si 2O 5, xLi 2SO 4 par RMN du 7Li

The 7Li nuclear magnetic spin-lattice relaxation times T 1 were measured over a wide temperature range for vitreous electrolytes belonging to the Li 2Si 2O 5 · xLi 2SO 4 ( x = 0, 0.1, 0.2, 0.3) system. The temperature and frequency dependence of T 1 compared with the variation of the conductivity has shown the existence of two relaxation mechanisms, one due to the long-range 7Li ionic motions and the other due to the short-range motions. This can be explained by a distribution of correlation times in the glasses which does not exclude only one diffusion mechanism.

A 13C NMR spin-lattice relaxation study of the interaction of myelin proteins with lipid vesicles

Natural abundance 13C nuclear magnetic spin-lattice relaxation times have been measured for bovine brain phosphatidylserine vesicles with and without bound proteins. The relaxation times were lower than published values for the corresponding nuclei in egg phosphatidylcholine, but showed the same trend, with relaxation times increasing along the acyl chains away from the polar headgroup. These times were inversely related to the degree of saturation of the lipid. Cytochrome c caused insignificant changes in the lipid acyl chain relaxation rates but reduced the resonance intensities, in agreement with Brown and Wuthrich (Biochem. Biophys. Acta 468 (1977) 389). In contrast, the basic protein from bovine myelin did not affect the intensities but reduced the relaxation times for 13C nuclei near the bilayer centre, and for nuclei near carbon-carbon double bonds. These proteins also dramatically broadened the serine headgroup carboxyl resonance. It appears, in accord with other recent evidence, that the basic protein does penetrate the hydrophobic region of the bilayer (possibly to the centre), producing quantitatively similar changes in the relaxation rates to proteolipid protein, an integral membrane protein.

Spin-lattice relaxation of some less common weakly quadrupolar nuclei

Nuclear magnetic spin-lattice relaxation times have been measured for the weakly quadrupolar nuclei 6Li, 9Be, and 133Cs in some simple inorganic and organometallic compounds in isotropic liquid phase. In an attempt to separate the various mechanistic contributions to the total relaxation rate, temperature-dependent T 1 and NOE experiments were performed. For aqueous solutions of the lithium ion extraordinarily long relaxation times were found (up to 1000 sec), with negligible quadrupolar relaxation and with the bulk of the relaxation rate arising from dipolar interactions involving hydrate protons. In systems of lower symmetry, quadrupolar and 6Li 1H dipolar relaxations account for up to 50% of the relaxation rate and the observed relaxation times are typically of the order of tens of seconds. In the hydrated beryllium ion 9Be relaxation is predominantly quadrupolar and dipolar at low temperatures, while spin-rotation prevails at elevated temperatures. In systems of lower beryllium valence electron symmetry the quadrupolar mechanism dominates. In spite of relaxation times of up to 30 sec, 133Cs relaxation in the solvated ionic state appears to be entirely quadrupole dominated.

Conformational studies on angiotensin-II. Least-squares fit of carbon-13 nuclear magnetic resonance relaxation times to extended and folded conformations

We have fitted the carbon-13 nuclear magnetic spin-lattice relaxation time ( T 1) data of the proton-bearing carbons in angiotensin-II to T 1 values obtained from a plausible model for reorientational relaxation. In the absence of X-ray data, we used conformations that were deduced from energy calculations. In particular, we assessed the conformational sensitivity of the calculated (best fit) relaxation parameters by comparing results for a low energy folded structure with the fully extended one. Furthermore, we estimated the relative importance and physical relevance of interpreting the observed relaxation behaviour of angiotensin-II in aqueous solution either in terms of rigid overall isotropic molecular tumbling only or with the additional assumption of internal motion in the side chains. A non-linear least-squares procedure was used to fit the theoretical T 1 values to the measured ones. For a given conformation the T 1 values were calculated from stochastic rotational diffusion models for both overall (isotropic and anisotropic) and internal molecular motion. The computational results are consistent with nearly isotropic overall tumbling of angiotensin-II. Furthermore, it seems essential to invoke internal motion for some of the linear side chains and all methyl groups in order to arrive at a physically meaningful description of the molecular dynamics. Without the premise of internal motion, an anisotropic rigid body model of the overall tumbling cannot explain the experimental relaxation results. The distinction between isotropic and anisotropic overall motion is not crucial, provided internal motion is also considered. The calculated effective correlation times for internal motion about side-chain CC bonds are rather insensitive to overall conformation, particularly beyond the C gaC β bond. This observation leads to the important conclusion that side chain-side chain interactions and their influence on the flexibility of adjacent residues in peptides and peptide hormones can be profitably studied via 13C relaxation without precise knowledge of the overall conformation.

Spin-lattice relaxation times of 13C satellites in proton nuclear magnetic resonance spectra and their use in determining molecular rotational diffusion constants

The nuclear magnetic spin-lattice relaxation times of the naturally abundant 13C satellites in the proton n.m.r. spectra of CH2Cl2, CH3I, CH3CN, CH3CCl3, (CH3)3CCl, (CH3)4Si and mesitylene have been measured and compared with the relaxation times of the predominant 12C-containing molecules. Although each satellite forms a coupled relaxation system with the other satellite and the 13C spin, it is shown that the relaxation is closely exponential with an effective relaxation time T*1 which depends on the 13C relaxation probabilities as well as on the proton relaxation mechanisms. T*1 also depends on the method of measurement. Computer calculation of the coupled relaxation system has been used to determine intermolecular, spin-rotation, and intramolecular contributions to the proton relaxation. The intramolecular part has been used to evaluate molecular rotational diffusion constants. There is generally good agreement with those parameters that have been determined by other methods.

Measurement of nuclear magnetic spin-lattice relaxation times by the use of repetitive sweep techniques

A simple analysis of the behaviour of a spin system under the influence of a series of sweeps through resonance with moderately high r.f. field strengths show that nuclear magnetic spin-lattice relaxation times may be determined from the “progressive saturation” of the magnetisation, initially at thermal equilibrium, as it approaches a partially saturated constant value. The method shows advantages in sensitivity and resolution over other sweep methods, and is applied to the measurement of the relaxation time of natural abundance 13C satellite lines in methylene dichloride.

Nuclear magnetic spin-lattice relaxation times of phosphorus-31 in some organic and inorganic compounds

Nuclear magnetic spin-lattice relaxation times of phosphorus-31 in some organic and inorganic compounds

Nuclear magnetic relaxation in two ferromagnetic Heusler alloys

The nuclear magnetic spin-lattice relaxation times of the 63Cu and 55Mn nuclear spins in the ferromagnetic domains of Cu2MnAl and Cu2MnIn are found to be inversely proportional to the absolute temperature, and related to the magnitude of the hyperfine field. In Cu2MnAl ( gamma 2T1T)-1 is 8.4+or-0.2 and 4.7+or-0.1 s Oe2 deg-1 for the 55Mn and 63Cu nuclei respectively, and for Cu2MnIn the same parameters have the values 9.1+or-0.2 and 3.6+or-0.1 s Oe2 deg-1. The transverse relaxation rates and the longitudinal rates associated with the centres of the domain walls are also temperature dependent. The hyperfine fields at the Al and In nuclei are found to be 68.2+or-0.5 and 89.7+or-0.5 kOe respectively.

Nuclear Magnetic Relaxation in Solid Para-Deuterium

In this note we point out the difference of the nuclear relaxation mechanism between solid ortho-H2 and para-D2 below T,. It has been investigated theoretically by a number of authors1> that the low-lying rotational excited states of solid ortho-H2 or para-D2 can be described in terms of a quasi-particle of librational excitation; this quasi-particle may be called a libron. The present author estimated the nuclear magnetic spin-lattice relaxation time T 1 of solid ortho-H2 below TA on the basis of the inelastic scattering of librons by nuclear spins.2> The relaxation mechanism assumed is the intramolecular magnetic dipole coupling and 1-J coupling modulated by the intermolecular electric quadrupole interaction which gives rise to librons. However, for para-D1 another relaxation mechanism has to be taken into account in addition to the mechanism assumed for ortho-H2 • This mechanism arises from the coupling between the electric quadrupole moment of deuteron and the field gradient at its position; The perturbation Hamiltonian lf' responsible for the nuclear relaxation for a homonuclear 1 I diatomic molecule in the subspace J=1 can be written as8> (c-1.5d)l·J+3d(l·J)2, (1)

Phase transitions in ammonium and deutero-ammonium halides

Abstract Recent results obtained by dilatometric, calorimetric, X-ray, and NMR methods for the phase transitions in ammonium and deutero-ammonium halides are reported. The dilatometric observations on the kinetics of the transitions I-II of NH4Cl and NH4Br, and the effects of deuteration on the I-II transformation temperature and volume change, and on the thermal expansion coefficients of the modifications I and II of NH4Br are described. Lattice parameter data, obtained by X-ray diffraction for NH4Cl between 167° and 250°. for NH4Br and ND4Br between -192° and 196 °C, and for NH4I between -116° and +22 °C are presented. From these data, the molar volume changes for the I-II transition of NH4Cl, for the I-II, II-III, and III-IV transitions of NH4Br and ND4Br, and for the I-II and II-III transitions of NH4I are reported. The effect of deuteration on the thermal expansion of modifications I, II, and III of NH4Br, and the structural nature of the III-IV transition of NH4Br are examined. The energies of the transitions I-II of NH4Cl, NH4Br, and NH4I, and of the Λ-transition of NH4Cl, determined by a direct differential calorimetric method with an accuracy of about 3 per cent, are presented. The activation energies of the reorientational motions of ND4+ and NH4+ ions in polycrystalline NH4Cl, ND4Cl, NH4Br, and ND4Br, and NH4I and ND4I, obtained by measuring nuclear magnetic spin-lattice relaxation times of deuteron and proton as functions of temperature, are discussed.

Nuclear Magnetic Relaxation and Dielectric Relaxation in Isoamyl Bromide

Nuclear magnetic spin—lattice relaxation times have been measured for supercooled isoamyl bromide at 20 and 60 Mc/sec over the temperature range 113° to 300°K. A distributed correlation function is introduced in order to explain the data. An expression for T1 which fits the data within the experimental error is obtained by using the Cole—Davidson distribution function to distribute the Kubo and Tomita expression for T1. Both the cutoff correlation time of the distribution function and the width parameter are allowed to vary with temperature. These parameters are compared with those reported in the literature from an analysis of the dielectric relaxation of supercooled isoamyl bromide using the Cole—Davidson distribution function. Similarities in the distribution function cutoff times and differences in the width parameters are observed. The distribution function parameters are related to molecular and liquid structure. Measurements of spin—spin relaxation times at 20 Mc/sec are discussed briefly.