scispace - formally typeset
Search or ask a question

Showing papers on "Relaxation (NMR) published in 1982"



Book
Ad Bax1
01 Jan 1982

425 citations


Journal ArticleDOI
TL;DR: The solid-state cross polarization and magic-angle spinning analog of an earlier 2D FT experiment on liquids is introduced in this article, which permits the observation of spin exchange processes.

400 citations


Journal ArticleDOI
TL;DR: In this paper, a theory for the effects of repulsive and spatially slowly varying attractive forces on the vibrational frequency and dephasing of polyatomic molecular liquids is developed.
Abstract: A theory for the effects of repulsive and spatially slowly varying attractive forces on the vibrational frequency and dephasing of polyatomic molecular liquids is developed. Thermodynamic state dependence of these features is of particular interest because of the competition between the two types of forces. Solvent shifts of vibrational lines are computed. Proper separation of the rapidly and slowly varying branches of the intermolecular potentials leads to a separation of time scales that allows the dephasing relaxation to be computed using a combination of binary collision and mean field ideas. The question of homogeneous vs inhomogeneous broadening of the isotropic Raman line is addressed. The theory is applied to several polyatomic fluids with special emphasis on the isothermal density dependence of the spectral features. Agreement with experiment is good. The slowly varying attractive forces are found to play a significant role in determining the Raman linewidth for all the systems studied. Comparison with previous theories is made.

367 citations


Journal ArticleDOI
TL;DR: In this article, a novel class of NMR expts, based on the systematic variation of 3 time variables, permits both the identification of exchange networks and the direct measurement of the corresponding rate consts.
Abstract: A novel class of NMR expts., based on the systematic variation of 3 time variables, permits both the identification of exchange networks and the direct measurement of the corresponding rate consts. in soln. Linear combinations of cross sections taken from 2 dimensional spectra allow a straightforward anal. of nonexponential recovery behavior by identifying normal modes. The line widths of the resulting Lorentzian line shapes provide a direct measure of the rate consts. of various dynamic processes, such as chem. exchange, transient Overhauser effects, and spin-lattice relaxation. [on SciFinder (R)]

274 citations


Journal ArticleDOI
TL;DR: The proposed model which the authors refer to as the FPD model differs from similar models in that it assumes that free and hydration water are two phases with distinct relaxation times but that T1 = T2 in each phase.

219 citations


Journal ArticleDOI
TL;DR: In this article, the influence of polar solvent dynamics in solution reactions is investigated for a simple model, where a charge is subject to a chemical free energy barrier, the successful crossing of which constitutes reaction.
Abstract: The influence of polar solvent dynamics in solution reactions is investigated for a simple model. In this model, a charge is subject to a chemical free energy barrier, the successful crossing of which constitutes reaction. The retarding influence of the time dependent solvent polarization is described at the continuum Debye relaxation level. The reaction rate constant k is determined as a function of the barrier curvature, the charge‐solvent interaction strength, and the solvent polarization relaxation time. The reduction of k with increasingly slower solvent relaxation is found to depend sensitively on the magnitude of charge‐solvent interactions. When the latter are weak, the behavior of k differs qualitatively from a standard Kramers prediction. The analogous reaction problem for a dipole is discussed briefly. Directions for a more realistic treatment of polar solvent effects on reaction rates are described.

212 citations


Journal ArticleDOI
TL;DR: In this article, nuclear magnetic relaxation in the pore fluid within a detrital sedimentary rock was studied and the results showed that local uniformity within a pore is set up rapidly.
Abstract: In this paper we study nuclear magnetic relaxation in the pore fluid within a detrital sedimentary rock. Bloch equations are introduced for the magnetization and solved for the case of uniform magnetization, yielding a single relaxation rate linearly related to the surface to volume ratio of the pore space. The surface magnetization is then eliminated and a closed set of equations for the bulk magnetization is developed. These equations are solved in detail in a spherical pore. The results show that local uniformity within a pore is set up rapidly. We show how to partition the pore space into individual pores separated by throats and obtain a set of coupled relaxation equations for the magnetization within each pore. The equations have the form encountered in the theory of disordered materials. When the throat size is sufficiently small, the relaxation function yields directly the probability distribution of the surface to volume ratios of individual pores. Otherwise, geometric information about pores and throats is enfolded in the relaxation function.

190 citations


Journal ArticleDOI
TL;DR: Brown et al. as mentioned in this paper derived the quadrupolar spin-lattice (T1) relaxation rates of 2H and 14N in lipid bilayers, as a function of temperature and frequency, and extended the analysis to include relatively slow fluctuations of the local director with respect to the macroscopic bilayer normal.
Abstract: Based on a previous, more approximate treatment [M. F. Brown, J. Magn. Reson. 35, 203 (1979)], expressions are derived for the quadrupolar spin‐lattice (T1) relaxation rates of 2H and 14N in lipid bilayers. Results are presented for the most general, anisotropic rotational diffusion model describing the segmental or molecular reorientation in lipid bilayers, and the analysis is extended to include relatively slow fluctuations of the local director with respect to the macroscopic bilayer normal. Numerically computed values of T1 for the diffusion model suggest that, even for extremes of ordering and motional anisotropy, such a model cannot by itself quantitatively account for the observed 2H T1 values of multilamellar dispersions of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine (DPPC), in the liquid crystalline state, as a function of temperature and frequency. The contribution from relatively low frequency motions is modeled in terms either (i) a simple noncollective model in which the slow motions are described in terms of a single effective correlation time, or (ii) a collective model in which the relatively slow reorientation is described by a distribution of correlation times, corresponding to collective fluctuations of the instantaneous director. The experimentally observed dependence of the 2H T1 relaxation rates on the acyl chain segmental order parameter SCD and the resonance frequency ω0 are most consistent with a collective model for slow molecular reorientations in lipid bilayers. The 2H T1 data for the saturated DPPC bilayer, in the liquid crystalline state, can be quantitatively described by a relaxation law of the form T−11 = Aτf+BS2CD ω−1/20 as observed for simpler nematic and smectic liquid crystals. The first (A) term is suggested to correspond to trans–gauche isomerizations of the lipid acyl chains, while the (B) term describes collective bilayer modes which predominantly influence the frequency dependence of the relaxation. In contrast to earlier conclusions [M. F. Brown et al., J. Chem. Phys. 70, 5045 (1979)], the dominant contribution to the 2H T1 relaxation rates of the saturated DPPC bilayer may arise from collective order fluctuations rather than fast local motions. The value of τf∼10−11 s obtained by extrapolating T−11 to infinite frequency or zero ordering is consistent with the correlation times calculated from 2H or 13C T1 data for n‐alkanes of equivalent chain lengths, suggesting that the microviscosity of the bilayer hydrocarbon region is not appreciably different from that of paraffinic liquids.

171 citations


Journal ArticleDOI
TL;DR: In this article, a deuterated liquid-crystal-like spin probe was used for line shape analysis of a benzilidene derivative (40,6) and in cyanobiphenyl derivative (S2 and 5CB) liquid crystals.
Abstract: We report on careful line shape studies of slow motional and orientation dependent ESR spectra of a deuterated liquid‐crystal‐like spin probe dissolved in a benzilidene‐derivative (40,6) and in cyanobiphenyl derivative (S2 and 5CB) liquid crystals. The simulation of the ESR spectra is based on the Lanczos algorithm recently applied by Moro and Freed in a general and efficient formulation of slow motional and ordering effects on ESR line shapes. With 40,6 which exhibits monolayer smectic phases, we find that the main change in the spin relaxation upon passing from the nematic to the smectic A phase consists of changes occuring in ordering attributable to packing forces on functional groups. Such ordering effects appear to be further enhanced in the SB phase with consequent alterations in dynamics. With S2, which exhibits an interpenetrating bilayer smectic A phase, we find unusual ESR spectra in that phase which may be simulated on the basis of a model of cooperative distortions static on the ESR time scale, and superimposed on individual molecular reorientation. This mode is interpreted as a collective chain distortion which affects the orientational distribution of the piperidine ring of the spin probe. A similar phenomenon is observed in the supercooled nematic phase of 5CB, which is aligned by an electric field, and evidence is also found that the reorientational dynamics of this ring are affected by interaction with local cooperative modes in the liquid crystal (i.e., a SRLS mechanism previously proposed by Freed and co‐workers). Some microscopic characteristics of liquid crystals revealed by this and previous ESR spin probe studies are discussed.

136 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported the vibration energy relaxation (T1) of the CN− ion in saturated H2O/D2O and dilute H 2O solutions at room temperature.
Abstract: Vibrational energy relaxation (T1) of the CN− ion is reported for NaCN in saturated H2O/D2O and dilute H2O solutions at room temperature. Time domain measurements of the v = 1, 2080 cm−1 vibration shown T1 is on the order of a few picoseconds. The relaxation time increases with dilution and is apparently sensitive to cation (Na+,K+) and local solution structure.

Journal ArticleDOI
TL;DR: Phase and modulation measurements can distinguish between time-dependent processes and spectral heterogeneity by observation of any feature described above and under favorable conditions, a two-state excited-state process can be distinguished from a continuous multiple- state process.

Journal ArticleDOI
01 Nov 1982-Nature
TL;DR: In this paper, the authors compare molecular dynamics simulations of proteins with nuclear magnetic resonance (NMR) relaxation measurements, based on the recently developed model-free approach to the interpretation of NMR data.
Abstract: Comparisons between molecular dynamics simulations of proteins and experiment have been based on temperature factors1–5 derived from X-ray spectra and on the stability of hydrogen bonds6. Here we present a novel method of testing molecular dynamics simulations against nuclear magnetic resonance (NMR) relaxation measurements, based on the recently developed model-free approach7 to the interpretation of NMR data. As NMR relaxation in proteins is determined by dynamics on the picosecond–nanosecond time scale, a comparison of NMR experiments and molecular dynamics simulations that last for less than ∼100ps is more meaningful than previous ones3–6 involving much longer time scales. We make contact between a molecular dynamics simulation8 and a 13C-NMR relaxation study9 of pancreatic trypsin inhibitor (PTI) by comparing generalized order parameters (which are measures of the extent of angular motion of the bonds) extracted from the relaxation data9 with those calculated10 from a 96-ps trajectory8. We show that the theoretical order parameters indicate less motion than their experimental counterparts. The relative flexibility of the residues studied, however, is reasonably well described by the simulation.

Journal ArticleDOI
TL;DR: Electron spin relaxation data from five ferric proteins are analyzed in terms of the fractal model of protein structures to determine the temperature dependence of the Raman electron spin relaxation rate, which varies as T3 + 2d.

Journal ArticleDOI
TL;DR: The results of this work strongly support the significant dye fluorescence spectral shifts on protein binding, being determined not only by polarity changes in their environment, but also by relaxation properties of protein groups in this environment.

Patent
05 Apr 1982
TL;DR: In this paper, a planar slab of excited nuclear spins in a nuclear magnetic resonance (NMR) imaging sample is selected such that the excited spins are contained well within the optimum sensitive region defined by the radio frequency (RF) transmitter and receiver coils.
Abstract: Selective excitation is used to define a thick planar slab of excited nuclear spins in a nuclear magnetic resonance (NMR) imaging sample. The thick slab is selected such that the excited spins are contained well within the optimum sensitive region defined by the radio frequency (RF) transmitter and receiver coils. Three-dimensional spatial information of an NMR imaging parameter, such as nuclear spin density or nuclear spin relaxation time, is collected simultaneously from the excited slab and can be used to construct a series of several tomographic section images of the slab. The spatial information is encoded in the NMR signal by application of pulsed gradient magnetic fields subsequent to excitation. Image picture information is obtained from the NMR signals via three-dimensional Fourier transformation.

Journal ArticleDOI
TL;DR: Fluorescence phase shift and demodulation methods were used in the analysis of excited-state reactions and to investigate solvent relaxation around fluorophores in viscous solvents to test the theoretical predictions and illustrate the characteristic features of phase-modulation data expected from samples which display time-dependent spectral shifts.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the nuclear magnetic relaxation for dipole nuclei (I = 1/2) coupled to quadrupole (S = 1) by dipolar interaction.
Abstract: Nuclear magnetic relaxation has been investigated for dipole nuclei (I = 1/2) coupled to quadrupole nuclei (S = 1) by dipolar interaction. Quadrupole dips in the frequency dependence of the longitudinal relaxation time of the I-spins are predicted under certain conditions. Relaxation dispersion experiments have been performed with Bovine Serum Albumin, which contains 14N1H-groups as representatives of the envisaged class of two-spin systems. In the dry and hydrated protein, quadrupole dips have been observed. The conclusion is that near room temperature and up to frequencies of the order of at least 107 Hz the 14H1H-groups are the dominant relaxation centres. The relevance for investigations of other biological systems is briefly discussed.

Journal ArticleDOI
TL;DR: In this paper, the origins of the two NMR lines seen in almost all samples of $a$-Si: H are discussed and solid-echo measurements are presented which indicate that these two components are due to spatially isolated groups of protons.
Abstract: Results of pulsed NMR studies of hydrogen in $a$-Si: H prepared at several laboratories by glow discharge of silane are presented. The origins of the two $^{1}\mathrm{H}$ NMR lines seen in almost all samples of $a$-Si: H are discussed. Solid-echo measurements are presented which indicate that these two components are due to spatially isolated groups of protons. We attribute the narrow line to protons slightly clustered in the bulk of the material and the broad line to protons distributed on internal surfaces. The spin-lattice relaxation time shows a minimum at $T\ensuremath{\approx}30$ K which is interpreted as due to relaxation via spin diffusion to a small number of ${\mathrm{H}}_{2}$ molecules acting as relaxation centers. Annealing results suggest that all the hydrogen molecules are trapped in very similar sites.

Journal ArticleDOI
01 Dec 1982-Fuel
TL;DR: In this article, a model of pericondensed aromatic rings was used to estimate the average number of condensed polynuclear rings in an average molecule in anthracite coal.

Journal ArticleDOI
TL;DR: In this paper, a simple relaxation model of the expansion process yields rotational collision numbers of 10±4 And 14±4 for N2 and O2 but these values may be high because of condensation heating.
Abstract: CARS spectra are reported for N2, O2, H2, D2, C2H4, and various mixtures cooled by supersonic jet expansion. Analysis of the Q branch structure of the diatomic molecules permits direct measurement of rotational populations, temperatures, and densities as a function of position in the free jet zone. Good agreement is obtained with temperature results for N2 from electron beam fluorescence studies and with densities calculated from the customary isentropic expansion equations. The detection sensitivity was sufficient that, for the first time, broadband CARS spectra were obtained for a molecular beam (D2). A simple relaxation model of the expansion process yields rotational collision numbers of 10±4 And 14±4 for N2 and O2 but these values may be high because of condensation heating. The model was not successful in treating the rotational relaxation of D2 and H2 but temperature measurements show qualitatively that D2 ⋅⋅⋅ X transfer efficiency increases in the order X = D2

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of microcrystals are discussed on the basis of results obtained by use of M?ssbauer spectroscopy, and the anisotropy energy constants of micro-crystals of Fe, Co, Ni and Fe3O4 are found to change upon chemisorption.
Abstract: The magnetic properties of microcrystals are discussed on the basis of results obtained by use of M?ssbauer spectroscopy. Spectra of microcrystals with dimensions smaller than about 100 A are influenced by magnetic fluctuation effects such as superparamagnetic relaxation and collective magnetic excitations, and these effects allow a determination of the product of the particle size and the magnetic anisotropy energy constant. Measurements on ferromagnetic and ferrimagnetic particles as a function of applied magnetic fields allow a determination of the particle volume. The anisotropy energy constants of microcrystals of Fe, Co, Ni and Fe3O4 are found to change upon chemisorption. Spectra of small particles at low temperatures also give information on the magnetic properties of the atoms in the surface layer. These studies as well as thin film studies show that no magnetically dead layers are present at the surface of the samples. In the case of metallic iron an enhanced magnetic hyperfine field is found, in agreement with theoretical results.

Journal ArticleDOI
TL;DR: The transient nonlinear-optical phenomena associated with the extremely fast relaxation processes in condensed matter are investigated from a microscopic viewpoint, taking into account the non-Markovian nature of the system as discussed by the authors.
Abstract: The transient nonlinear-optical phenomena associated with the extremely fast relaxation processes in condensed matter are investigated from a microscopic viewpoint, taking into account the non-Markovian nature of the system. It is found that, in the ultrashort time region comparable to the thermal-reservoir correlation time, the transient nonlinear-optical response exhibits the characteristic time variation inherent in the non-Markovian nature of the matter system. This result cannot be explained by the conventional phenomenological theory based on the relaxation time description. The general formula obtained is applied, as an example, to the transient four-photon parametric coupling generated by the two-pulse excitation of the localized-electron-phonon system. It is found that not only the time variation of the signal intensity, but also the dependence of the time-integrated intensity of the pulse interval exhibits the characteristic feature which reflects the dynamics of the relaxation of the phonon system. It is emphasized that this result provides us the most practical tool to observe the extremely fast relaxation processes in condensed matter.

Journal ArticleDOI
TL;DR: In this paper, the effects of thermal aging on specific volume V and specific enthalpy H of polystyrene below the glass transition temperature were investigated, and it was shown that the dependence of V and H on the order parameters specifying the glassy state are similar but not exactly the same.
Abstract: A study was carried out on the effects of thermal aging on specific volume V and specific enthalpy H of polystyrene below the glass transition temperature. The dependence of V and H on annealing time was similar. No significant effect of the distribution of molecular weight on the relaxation behavior was found. The behavior of V and H reaching a maximum after a double-step temperature-jump was also investigated. The time for the maximum V and H varied in proportion to the period of pre-annealing. The time for the maximum volume was slightly longer than that for the maximum enthalpy. These facts indicate that the dependence of V and H on the order parameters specifying the glassy state are similar but not exactly the same. From the enthalpy and volume relaxation curves, the enthalpy required for creating free volumes in polystyrene was calculated to be 2.0 kJ cm−3. The behavior of the volume relaxation was discussed by assuming a wide distribution of relaxation time.

Journal ArticleDOI
TL;DR: The P(1) member of the rotational manifold of the 6a10 transition in the 1B3u(nπ) state of pyrazine shows intermediate level structure and quantum beats in its decay as discussed by the authors.
Abstract: The P(1) member of the rotational manifold of the 6a10 transition in the 1B3u (nπ) state of pyrazine shows intermediate level structure and quantum beats in its decay. The P(2) member already shows a fast component. The effect of nuclear spin on the relative magnitude of the fast component is shown by partial deuterium substitution.

Journal ArticleDOI
TL;DR: In this paper, the authors used Brillouin spectroscopy to provide information about the hypersonic velocity and absorption of thermal waves in a glass-forming 60% KNO3-40% Ca(NO3)2 mixture (mol %) in a temperature range of 90-380°C for gigahertzian frequencies.
Abstract: Brillouin spectroscopy has been used to provide information about the hypersonic velocity and absorption of thermal waves in a glass‐forming 60% KNO3–40% Ca(NO3)2 mixture (mol %) in a temperature range of 90–380°C for gigahertzian frequencies. A relaxation process was revealed in both the longitudinal velocity and attenuation. The data are consistent with ultrasonic results for the limiting low‐frequency velocity. The limiting high‐frequency velocity is considerably larger than that reported from ultrasonic studies and the position of the maximum of the amplitude absorption coefficient is shifted to higher temperatures. The variation of the relaxation time with temperature was found to be Arrhenius with a temperature‐independent activation energy in excellent accordance with the model proposed by Weiler, Bose, and Macedo. At low temperatures, a transverse mode due to shear waves was observed close to the Rayleigh line.

Journal ArticleDOI
11 Jun 1982-Science
TL;DR: The principles of this technique are presented; its usefulness is illustrated by several specific examples of studies of molecular liquids, water, and supercritical dense fluids; and the promising future of high-resolution nuclear magnetic resonance spectroscopy at high pressure is indicated.
Abstract: Nuclear magnetic resonance relaxation measurements at high pressure provide unique information about the microscopic behavior of liquids. This article presents the principles of this technique; illustrates its usefulness by several specific examples of studies of molecular liquids, water, and supercritical dense fluids; and indicates the promising future of high-resolution nuclear magnetic resonance spectroscopy at high pressure with examples of studies of chemical exchange and homogeneous catalytic processes.

Journal ArticleDOI
TL;DR: The 400 MHz 1H-nuclear magnetic resonance spectrum of sodium cholate in dilute aqueous solution has been successfully resolved using a combination of decoupling, partial relaxation, and decoupled partial relaxation techniques.

Journal ArticleDOI
R. Kimmich1, R. Bachus1
TL;DR: In this article, the nuclear magnetic relaxation times and the self-diffusion coefficient of polyethylene and polystyrene have been investigated over several orders of magnitude and the relation to viscous behaviour is established.
Abstract: Molecular weight and frequency dependences, respectively, of the nuclear magnetic relaxation times and the self-diffusion coefficient of polyethylene and polystyrene have been investigated over several orders of magnitude. The relation to viscous behaviour is established. A closed concept is developed. Conclusions are:

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrated that well-resolved 14 N- 195 Pt couplings can be observed in the NMR spectra of Pt(II) and Pt(IV) amine complexes, including anti-tumour agents, at elevated temperature.