Showing papers on "Relaxation (NMR) published in 1974"
TL;DR: The results of this study are consistent with the notion that the structure and/or motions of all or part of the cellular water are affected by the macromolecular interface and this causes a change in the NMR relaxation rates.
456 citations
TL;DR: In this paper, a relaxation-time model is proposed for the collisions term of the relativistic Boltzmann equation for a single-component gas, and the resultant equation is solved as a power series in the relaxation time and this solution is used to calculate the transport coefficients for the gas.
273 citations
TL;DR: The results show that the principal path for the reversible thermal unfolding of tRNA 1 fMet under these solution conditions is first, transient opening of the dihydrouridine helix, followed by simultaneous melting of the diazepam helix and a “tertiary” interaction, which does not correspond to a cloverleaf helix.
256 citations
TL;DR: In this article, the dipole-dipole interactions between protons in a glucopyranose derivative have been studied by means of the nuclear Overhauser effect and by spin-lattice relaxation experiments.
Abstract: Dipole‐dipole interactions between protons in a glucopyranose derivative have been studied by means of the nuclear Overhauser effect and by spin‐lattice relaxation experiments. The Overhauser enhancement measurements utilize a new pulse technique which permits the saturating field to have any specified spectral density function so that finite frequency bands in the NMR spectrum can be irradiated. By this method, the dipolar interactions between the various pairs of protons are evaluated. In contrast, the dipolar relaxation of a chosen proton by all other protons in the sample has been determined by comparing the inversion‐recovery rates after selective and nonselective 180° pulses. The relaxation measurements indicate that the relaxation in this molecule is purely dipolar in origin. The Overhauser enhancement measurements of one proton are used to determine the contribution to its relaxation from two neighboring protons and, from these results, information about the geometry of the pyranose ring is evaluated.
176 citations
TL;DR: In this article, the viscosity dependence of reorientation times about the individual molecular axes has been measured for benzene, mesitylene, toluene, and nitrobenzene.
Abstract: Measurements of reorientational relaxation times of simple aromatic compounds have been made by both depolarized Rayleigh light scattering and 13C NMR spin‐lattice relaxation. Combination of the reorientation times determined by these techniques makes it possible to extract the reorientation times about the different molecular axes. The viscosity dependence of reorientation times about the individual molecular axes has been measured for benzene, mesitylene, toluene, and nitrobenzene. The viscosity dependence, which is highly anisotropic, is discussed in terms of a ``slip'' model of reorientational motion.
174 citations
TL;DR: In this article, the authors show that resonance Raman scattering and hot luminescence are two distinct physical processes, although they are always simultaneously present and can interfere with each other.
Abstract: Using density-matrix formalism which takes into account relaxation more correctly, we show that resonance Raman scattering and hot luminescence are two distinct physical processes, although they are always simultaneously present and can interfere with each other. The transient response of the two processes are, however, different.
169 citations
168 citations
TL;DR: This identity provides independent evidence that the EPR signal is due to the oxidized primary electron donor which is bacteriochlorophyll, and the decay constant may serve as a probe to investigate the molecular environment of the primary reactants.
145 citations
TL;DR: The theory of dipolar nuclear magnetic relaxation in molecules with multiple internal motions is extended to the case where the motion of the molecule as a whole is anisotropic, with no restriction on the magnitudes of the correlation times involved as discussed by the authors.
Abstract: The theory of dipolar nuclear magnetic relaxation in molecules with multiple internal motions is extended to the case where the motion of the molecule as a whole is anisotropic, with no restriction on the magnitudes of the correlation times involved. Numerical calculations of the 13C relaxation times T1 and T2 for 13C–1H relaxation in a hydrocarbon chain attached to an axially symmetric prolate ellipsoid are presented. Effects of the anisotropic motion of the molecule can be seen as far as five carbons along the chain, even when the motion about the C–C bonds in the chain is a factor of 10 faster than the fastest motion of the molecule as a whole. Two cases have been considered in which the motion about the long axis of the ellipsoid is fast [(ωC + ωH)2 / 6DZ2 ≪ 1] or slow [(ωC + ωH)2 / 6DZ2 > 1] compared to the highest relevant Larmor frequency. The effects on T1 and T2 of changes in the axial ratio of the ellipsoid and in the angle between the first bond in the chain and the long axis of the ellipsoid, which are markedly different in these two cases, can be explained in terms of the effectiveness of the different motions in the system for relaxation. 13C spin‐lattice relaxation times have been determined for all the resolved resonances in n ‐alkanes from C6 to C18 and in n ‐alkyl bromides from C4 to C15. Using the theoretical treatment developed in the first part of the paper, these relaxation times have been used to calculate the diffusion coefficients for the various motions of these molecules (considered as axially symmetric prolate ellipsoids with internal motion). In the shorter‐chain n ‐alkanes (C6 to C10), where the resonances of all the carbons can be resolved, it is possible to calculate the two diffusion coefficients of the molecules as a whole and the diffusion coefficients for motion about each C–C bond in the chain. The diffusion coefficients about all the bonds in the chain (except that to the terminal methyl) are the same, being in the range 0.1−0.2 × 1011 sec−1 (about a factor of 10 slower than the motion of the whole molecule about its long axis). The motion about the terminal bond is a factor of 2–6 faster. In longer chain alkanes (C12–C18), where not all the resonances are resolved, only the diffusion coefficients about the four bonds nearest the terminal methyl can be obtained. Comparison of the present results with those obtained earlier with dipalmitoyl lecithin bilayers indicate that the region of the hydrocarbon chain near the terminal methyl group has essentially identical motional freedom in the bilayer and in the simple n ‐alkanes, while the region near the glycerol moiety in the bilayer is motionally much more restricted.The theory of dipolar nuclear magnetic relaxation in molecules with multiple internal motions is extended to the case where the motion of the molecule as a whole is anisotropic, with no restriction on the magnitudes of the correlation times involved. Numerical calculations of the 13C relaxation times T1 and T2 for 13C–1H relaxation in a hydrocarbon chain attached to an axially symmetric prolate ellipsoid are presented. Effects of the anisotropic motion of the molecule can be seen as far as five carbons along the chain, even when the motion about the C–C bonds in the chain is a factor of 10 faster than the fastest motion of the molecule as a whole. Two cases have been considered in which the motion about the long axis of the ellipsoid is fast [(ωC + ωH)2 / 6DZ2 ≪ 1] or slow [(ωC + ωH)2 / 6DZ2 > 1] compared to the highest relevant Larmor frequency. The effects on T1 and T2 of changes in the axial ratio of the ellipsoid and in the angle between the first bond in the chain and the long axis of the ellipsoid, ...
127 citations
TL;DR: In this paper, the reorientational correlation function for liquid methyl iodide has been measured by analysis of the Raman 526 cm−1 ν3 (a1) band as a function of pressure up to 2.5 kbar within the temperature range 0 to 90°C.
Abstract: The reorientational correlation function for liquid methyl iodide has been measured by analysis of the Raman 526 cm−1 ν3 (a1) band as a function of pressure up to 2.5 kbar within the temperature range 0 to 90°C. These reorientational correlation functions have been obtained from the anisotropic component of the vibrational Raman scattered light using a method of Fourier deconvolution. Density and viscosity of methyl iodide over the same range of temperatures and pressures have also been determined. In order to obtain information about the effects of density and temperature on the internal C3 rotation of the methyl group the NMR deuteron spin‐lattice relaxation times in liquid methyl iodide‐d3 have been measured under the same experimental conditions. In addition the vibrational relaxation rates have been determined from the isotropic Raman band shapes. The Raman experiments enable us to calculate the reorientational correlation function describing the reorientational motion of the CH3I molecules about an ...
126 citations
TL;DR: 2 H NMR spectra have been observed for several selectively deuterated phospholipid and fatty acid probes intercalated in the liquid crystalline phase of egg phosphatidylcholine in aqueous dispersion, and the presence of cholesterol has no effect on the quadrupole splittings and relaxation rates for 2 H in the choline methyl groups.
TL;DR: In this paper, the vibrational relaxation of gaseous H2 in mixtures with He, Ne, Ar, and Kr was studied by the laser Schlieren technique in incidents shock waves at 1350-3000 K.
TL;DR: In this paper, the rotational diffusion coefficient of a liquid is related to the rotation correlation time τ 2 by means of the quasilattice model of liquids, and the results of the large-step random-walk theory of rotations are obtained.
Abstract: Self‐diffusion coefficients and rotational correlation times have been measured in several polar liquids by pulsed nuclear magnetic resonance techniques. Diffusion coefficients were measured for HCCl3, ClC6H5, HF, and HCl and relaxation times for HF. The self‐diffusion coefficient of a liquid is related to the rotational correlation time τ2 by means of the quasilattice model of liquids. The rotational diffusion equation and the Stokes–Einstein expression for the rotational diffusion coefficient are inadequate and are respectively replaced by the results of the large‐step random‐walk theory of rotational diffusion and an expression for τ2 based on the quasilattice model. An expression for τ2, obtained from the dynamical rotational coherence theory, is shown not to apply in the case of the spherical‐top molecule CCl4 which would be anticipated to have a small friction constant. The correspondence between calculated values of τ2 based on the quasilattice model and the observed rotational correlation times is...
TL;DR: In this article, the effect of molecular motion on NMR powder spectra governed by axially symmetric shielding tensors is investigated, and the results show that at low temperatures the powder pattern for a rigid solid is observed, from which we obtain the shielding anisotrophy Δσ = σ − σ⊥ = −405 ± 10 ppm.
TL;DR: In this paper, the dispersion of the proton spin-lattice relaxation time was measured for selected mouse tissue in the laboratory (T1) and rotating frames at 25°C.
TL;DR: In this paper, the phase relaxation of the normal vibrational mode was investigated using single picosecond pulses, and a dephasing time of 75 ± 8 psec was measured in good agreement with spontaneous linewidth data.
TL;DR: In this paper, it was shown that the relative intensities of Tip components, attributed to different regions in the polymer, may be affected appreciably by spin diffusion s. In such cases, the relative information in no way reflect the amounts of material contributing to each component and therefore may not be used as an estimate of either mobile fraction or crystallinity.
TL;DR: It is shown that a small family of closely related conformations fit the nuclear magnetic resonance data and these conformations are very similar to that of the crystal structure of AMP.
TL;DR: In this article, the authors measured the relaxation and frequency shifts for the 0-0 transition of the ground state of Rb-85 at 3.03 GHz in various physical environments.
Abstract: Results are presented on the relaxation and frequency shifts measured for the 0-0 transition of the ground state of Rb-85 at 3.03 GHz in various physical environments. These results include data on spin-exchange, buffer-gas, and wall interactions.
TL;DR: Spin-lattice relaxation times for the water protons in rat gastronemius muscle are reported over the temperature range +37 to −70°C at six resonance frequencies ranging from 4.5 to 60.0 MHz.
TL;DR: The conclusion is reached that the high frequency dispersion and relaxation can be attributed to fluctuations in the distribution of bound counterions along limited parts of the macromolecule.
TL;DR: In this article, the authors used the amplitude of the signal due to unfrozen water at temperatures below the freezing point to estimate the amount of bound water in agarose gels.
Abstract: 1 H spin lattice and spin-spin relaxation together with diffusion rates have been studied in agarose gels as functions of gel concentration and temperature in the ranges 0.9 to 18 % by weight, and from 273 to 323 K. Data have been interpreted in terms of a two phase model where rapid exchange occurs between bulk water molecules and those “bound” to macromolecules. The amount of bound water has been estimated from the amplitude of the signal due to unfrozen water at temperatures below the freezing point. The implications of this method of estimating hydration are discussed, and comparisons made with observations on frozen gels, and on water adsorbed on to agarose. This estimate, 0.59 g of water per g of agarose, is satisfactory for an explanation of spin lattice relaxation, but certain anomalies occur when applied to spin-spin relaxation. Interpretation of diffusion in terms of the Wang theory leads to a hydration value of 0.35. Previous estimates of hydration have been 0.1 and 3.5.
TL;DR: In this paper, the motion of guest THF and host water molecules has been studied to 2°K by proton CW measurements and by propton T1 measurements of the THF-H2O, H2O-d8-H 2O, and THF1320 systems.
TL;DR: The theory of high-field nuclear-spin relaxation due to random-walk diffusion in monoatomic crystals is extended to correlated diffusion mechanisms in this paper, and the effect of the diffusion mechanism on the relaxation times can be observed in three different ways.
Abstract: The theory of high-field nuclear-spin relaxation due to random-walk diffusion in monoatomic crystals is extended to correlated diffusion mechanisms. It is predicted that the effect of the diffusion mechanism on the relaxation times ${T}_{1}$, ${T}_{2}$, and ${T}_{1\ensuremath{\rho}}$ can be observed in three different ways: (i) In single crystals the relaxation times are shown to depend on the crystallographic orientation of the magnetic field. Whereas on the low-temperature side of the ${T}_{1}$ minimum these anisotropies should characterize the diffusion mechanism, they are expected to disappear on the high-temperature side. (ii) Shape and width of the ${T}_{1}$ and ${T}_{1\ensuremath{\rho}}$ minimum as a function of temperature are found to depend on the diffusion mechanism---in both single crystals and polycrystalline samples. (iii) Assuming that in a single crystal the decay of the transverse magnetization can be described by a single relaxation time ${T}_{2}$ (usually true at temperatures above the ${T}_{1}$ minimum), deviations from the exponential decay, which should be characteristic for a given diffusion mechanism, are predicted in polycrystalline samples. The numerical results obtained for diffusion via monovacancies in bcc and fcc crystals are compared with those obtained for the limiting case of random-walk diffusion. It is found that for these two mechanisms the orientation dependences of the relaxation times are similar, but that considerable differences in the shapes of the relaxation rates versus temperature should exist.
TL;DR: In this paper, the interchange of the monomers to and from the micelles is assumed to be an adsorption mechanism governed by the fundamental kinetic principles introduced by Langmuir in his adsoreption theory, and the origin of the chemical relaxation observed in detergent solutions is reconsidered.
Abstract: The kinetics of micelle formation for a range of ionic surfactants in aqueous solution have been investigated using the ultrasonic relaxation technique. In order to understand the concentration dependance of both the relaxation time and the relaxation strength, and other aspects of the relaxation data, it was necessary to modify our previous two state kinetic model describing micellisation. In this new theoretical treatment the interchange of the monomers to and from the micelles is assumed to be an adsorption mechanism governed by the fundamental kinetic principles introduced by Langmuir in his adsorption theory. Finally we have reconsidered the origin of the chemical relaxation observed in detergent solutions resulting from temperature- and pressure-jump experiments.
TL;DR: In this article, the 15N NMR of pyridine was studied in the liquid and solid state, and the spin-lattice relaxation time T1 was studied from −60 to +55°C at 14 and 30 MHz.
TL;DR: Determination of diffusion coefficients and studies on physiologically inert lenses indicate that reduced relaxation times do not provide direct evidence for ordering of the bulk of the cell water.
Abstract: Nuclear magnetic resonance studies of the relaxation times of the water in the crystalline lens show that, as in all interfacial systems, these parameters are markedly reduced from their values in pure water, that T2 is less than T1, and that both depend on water content. Determination of diffusion coefficients and studies on physiologically inert lenses indicate that reduced relaxation times do not provide direct evidence for ordering of the bulk of the cell water.