Spin-lattice Relaxation Time T1 Research Articles

The spectral density in simple organic glass formers: Comparison of dielectric and spin-lattice relaxation

The spin-lattice relaxation time T1 of simple organic glass formers is analyzed by introducing a spectral density obtained from broadband dielectric susceptibility data χ″(ω). For this purpose χ″(ω) was measured for several glass formers, that do not exhibit a Johari-type secondary relaxation process, covering a frequency range between 10−2 Hz and 109 Hz at temperatures above and below the glass transition temperature Tg. We introduce an analytical function to fit the shape of the main relaxation (α-process) above Tg, in particular taking into account high-frequency contributions in χ″(ω) commonly known as high-frequency wing. Below Tg the latter feature appears as a power law susceptibility χ″(ω)∝ω−γ, with γ<0.1 and a characteristic temperature dependence χ″(T)∝exp(T/const.), yielding almost 1/ω behavior in the spectral density. On the base of this complete description of χ″(ω), a quantitative comparison of dielectric and NMR spectroscopy is possible, which is carried out in full detail for glycerol-d3 (2H-NMR), yielding almost identical spectral densities at the Larmor frequency in both cases. In particular the temperature dependence of the high-frequency wing reappears in that of the spin lattice relaxation rate. In addition a semiquantitative analysis is given for trinaphthyl benzene (1H-NMR) and tricresyl phosphate (31P-NMR).

Magnetic resonance angiography with hyperpolarized 129Xe dissolved in a lipid emulsion.

Hyperpolarized (HP) 129Xe can be dissolved in biologically compatible lipid emulsions while maintaining sufficient polarization for in vivo vascular imaging. For xenon in Intralipid 30%, in vitro spectroscopy at 2 T yielded a chemical shift of 197 +/- 1 ppm with reference to xenon gas, a spin-lattice relaxation time T1 = 25.3 +/- 2.1 sec, and a T2* time constant of 37 +/- 5 msec. Angiograms of the abdominal and pelvic veins in the rat obtained with 129Xe MRI after intravenous injection of HP 129Xe/Intralipid 30% into the tail demonstrated signal-to-noise ratios between 8 and 29. An analysis of the inflow effect on time-of-flight images of two segments of the inferior vena cava yielded additional information. The mean blood flow velocity was 34.7 +/- 1.0 mm/sec between the junction of the caudal veins and the kidneys and 13.3 +/- 0.8 mm/sec at the position of the diaphragm. The mean volume flow rates in these segments were 7.2 +/- 3.4 ml/min and 11.0 +/- 2.8 ml/min, respectively. Intravenous delivery of HP 129Xe dissolved in a carrier may lead to novel biomedical applications of laser-polarized gases.

Magnetic resonance angiography with hyperpolarized 129Xe dissolved in a lipid emulsion

Hyperpolarized (HP) 129Xe can be dissolved in biologically compatible lipid emulsions while maintaining sufficient polarization for in vivo vascular imaging. For xenon in Intralipid 30%, in vitro spectroscopy at 2 T yielded a chemical shift of 197 ± 1 ppm with reference to xenon gas, a spin-lattice relaxation time T1 = 25.3 ± 2.1 sec, and a T2* time constant of 37 ± 5 msec. Angiograms of the abdominal and pelvic veins in the rat obtained with 129Xe MRI after intravenous injection of HP 129Xe/Intralipid 30% into the tail demonstrated signal-to-noise ratios between 8 and 29. An analysis of the inflow effect on time-of-flight images of two segments of the inferior vena cava yielded additional information. The mean blood flow velocity was 34.7 ± 1.0 mm/sec between the junction of the caudal veins and the kidneys and 13.3 ± 0.8 mm/sec at the position of the diaphragm. The mean volume flow rates in these segments were 7.2 ± 3.4 ml/min and 11.0 ± 2.8 ml/min, respectively. Intravenous delivery of HP 129Xe dissolved in a carrier may lead to novel biomedical applications of laser-polarized gases. Magn Reson Med 41:1058–1064, 1999. © 1999 Wiley-Liss, Inc.

NMR and ESR study of the local dynamics in some polyisoprene solutions

The spin–lattice relaxation time T1 of the protons attached to the polymeric chain was measured in some polyisoprene–C7D8, polyisoprene–CCl4 and polyisoprene–CDCl3 solutions, over a wide range of the temperature above the glass transition temperature. The correlation time τc of the local motion of the polymeric segments, corresponding to the maximum spin–lattice relaxation rate, is about 10−9s. The experimental curves T1(T,Φ) obtained for the polyisoprene–C7D8, polyisoprene–CCl4 and polyisoprene–CDCl3 solutions obey the superposition property. The ESR spectra were recorded from nitroxide labelled molecules (2,2,6,6, tetramethyl piperidin-1-yloxyl) dissolved in the polyisoprene–CCl4 solutions. The analysis of the ESR spectra indicates only a weak interaction between the nitroxide molecules and the polymeric segments. The correlation time τc of the rotational motion of the nitroxide molecules motion is about 10−11s at room temperature.

Smoluchowski dynamics of the vnd/NK‐2 homeodomain from Drosophila melanogaster: First‐order mode‐coupling approximation

This work is the first in a series devoted to applying mode coupling diffusion theory to the derivation of local dynamics properties of proteins in solution. The first-order mode-coupling approximation, or optimized Rouse–Zimm local dynamics (ORZLD), is applied here to derive the rotational dynamics of the bonds and compare the calculated with the experimental nmr 15N spin–lattice relaxation time behavior of the vnd/NK-2 homeodomain from Drosophila melanogaster. The starting point for the calculations is the experimental three-dimensional structure of the homeodomain determined by multidimensional nmr spectroscopy. The results of the computations are compared with experimentally measured 15N spin–lattice relaxation times T1, at 34.5 and 60.8 MHz, to check the first-order approximation. To estimate the relative importance of internal and overall rotation, both rigid and fluctuating dynamic models are examined, with fluctuations evaluated using molecular dynamics (MD) simulations. The correlation times for the fundamental bond vector time correlation function and for the second-order bond orientational TCF are obtained as a function of the residue number for vnd/NK-2. The stability of the corresponding local dynamics pattern for the fluctuating structure as a function of the length of the MD trajectory is presented. Diffusive dynamics, which is essentially free of model parameters even at first order in the mode-coupling diffusion approach, confirm that local dynamics of proteins can be described in terms of rotational diffusion of a fluctuating quasi-rigid structure. The comparison with the nmr data shows that the first-order mode coupling diffusion approximation accounts for the correct order of magnitude of the results and of important qualitative aspects of the data sensitive to conformational changes. Indications are obtained from this study to efficiently extend the theory to higher order in the mode-coupling expansion. These results demonstrate the promise of the mode-coupling approach, where the local dynamics of proteins is described in terms of rotational diffusion of a fluctuating quasi-rigid structure, to analyze nmr spin–lattice relaxation behavior. © 1999 John Wiley & Sons, Inc. Biopoly 49: 235–254, 1999

Smoluchowski dynamics of the vnd/NK-2 homeodomain from Drosophila melanogaster: first-order mode-coupling approximation.

This work is the first in a series devoted to applying mode coupling diffusion theory to the derivation of local dynamics properties of proteins in solution. The first-order mode-coupling approximation, or optimized Rouse-Zimm local dynamics (ORZLD), is applied here to derive the rotational dynamics of the bonds and compare the calculated with the experimental nmr 15N spin-lattice relaxation time behavior of the vnd/NK-2 homeodomain from Drosophila melanogaster. The starting point for the calculations is the experimental three-dimensional structure of the homeodomain determined by multidimensional nmr spectroscopy. The results of the computations are compared with experimentally measured 15N spin-lattice relaxation times T1, at 34.5 and 60.8 MHz, to check the first-order approximation. To estimate the relative importance of internal and overall rotation, both rigid and fluctuating dynamic models are examined, with fluctuations evaluated using molecular dynamics (MD) simulations. The correlation times for the fundamental bond vector time correlation function and for the second-order bond orientational TCF are obtained as a function of the residue number for vnd/NK-2. The stability of the corresponding local dynamics pattern for the fluctuating structure as a function of the length of the MD trajectory is presented. Diffusive dynamics, which is essentially free of model parameters even at first order in the mode-coupling diffusion approach, confirm that local dynamics of proteins can be described in terms of rotational diffusion of a fluctuating quasi-rigid structure. The comparison with the nmr data shows that the first-order mode coupling diffusion approximation accounts for the correct order of magnitude of the results and of important qualitative aspects of the data sensitive to conformational changes. Indications are obtained from this study to efficiently extend the theory to higher order in the mode-coupling expansion. These results demonstrate the promise of the mode-coupling approach, where the local dynamics of proteins is described in terms of rotational diffusion of a fluctuating quasi-rigid structure, to analyze nmr spin-lattice relaxation behavior.

High-field multinuclear magnetic resonance studies of molecular motions in the liquid and solid phases of 3-chloropivalic acid

The phase behaviour and the translational and rotational dynamics of the different phases of 3-chloropivalic acid (CPA) were studied using high-field multinuclear magnetic resonance. Two components of CPA with very different line widths were observed within a large part of the investigated temperature region between the melting point (316.7K) and 160K. The coexisting narrow line and broad line components are ascribed to the disordered and ordered solids I and II, respectively. The relatively narrow NMR signals of solid I allowed observation of the individual resonances from the methyl, chloromethyl and carboxyl groups.The diffusion in the liquid and solid I phases of CPA appears to involve the migration of the strongly hydrogen-bonded dimers with activation energies of 18 and 84kJ mol−1, respectively. The temperature variation of the spin-lattice relaxation time T1 of the carboxyl deuteron reflects the overall tumbling motion with activation energies of 33 and 53kJ mol−1 for the liquid and solid I phases, respectively. 1H T1 of solid II was also measured over a large temperature region from 163 to 299K. The broad and shallow T1 minimum indicates that the rotations of the alkyl groups are correlated in this phase.

T1 imaging using phase acquisition of composite echoes.

A new magnetic resonance method for T1 imaging is presented. It is based on the simultaneous acquisition of a spin echo and a phase-shifted, stimulated echo. The phase of this composite echo image is modulated heavily by the spin-lattice relaxation time T1, whereas spin density and T2 do not influence the phase information. This phase information can be assigned easily to corresponding T1 values. Although this method is sensitive to radiofrequency inhomogenities, phantom studies showed that high precision and reasonable accuracy of T1 determination can be achieved. Moreover, this method was found to be very robust, because no fitting is required. T1 imaging of the human brain was performed to confirm the in vivo utility of this method.

Knight shifts for short-lived beta emitters in Pt

The Knight shifts K for short-lived β emitters 12N and 27Si implanted in Pt have been measured by means of β-NMR technique. The results were K(12N in Pt)= +(5.8 ± 2.1)× 10-4 and K(27Si in Pt)= +(1.4 ± 0.8)× 10-3. The spin–lattice relaxation time T1 was measured for 12N in Pt. The result was T1(12N in Pt, T=300 K)= 66 ± 8 ms, thus, T1T= 20 ± 2 Ks. The present Knight shifts are in good agreement with the KKR band structure calculation with local lattice relaxation determined theoretically.

Nuclearmagnetic relaxation study of carbon-13 in di-pentyl phthalate

Spin-lattice relaxation times T1 and nuclear Overhauser enhancement factors of chemically non-equivalent carbons in di-pentyl phthalate (DPP), a simple glass-forming liquid, are measured as functions of temperature. The analysis shows that the correlation function describing the overall molecular dynamics in DPP can be well described in terms of an asymmetric distribution of correlation times predicted by the Davidson-Cole model. The distribution parameters of the successive chain carbons are derived and analysed in terms of internal motions occurring in DPP.

Molecular Rotation in an Antiferroelectric Liquid Crystal Studied by 13C-Nuclear Magnetic Resonance Spin-Lattice Relaxation Time Measurement

Temperature dependence of the spin-lattice relaxation time T1 was measured in an antiferroelectric liquid crystal, 4-(1-methylheptyloxycarbonyl) phenyl-4′-octyloxybiphenyl-4-carboxylate (MHPOBC) by means of 13C-nuclear magnetic resonance (NMR). The activation energies determined by the temperature dependence of T1 are the same for most of the carbon nuclei in the SmA and SmCA* phases, whereas they are different for carbon nuclei at the chiral center and at the carbonyl carbons. The rotational correlation time changes continuously through the phase change from SmA to SmCA*. Critical slowing down of the molecular rotatioin was not observed.

Structural Changes and Hydrogen Motion in A-SI:H Observed by Proton Nmr

AbstractProton nuclear magnetic resonance (NMR) is applied to investigate hydrogen dynamics and microstructures in a-Si:H. In addition to the generic broad and narrow lines observed in all aSi:H, an additional narrow line (about 1 kHz wide) is observed as the temperature is raised above RT. This narrow line is shifted to the up-field by about 4 ppm with respect to the generic narrow line of a few kHz in width. Below 150°C, the change of the proton spectrum with temperature is reversible; the hydrogen associated with this additional narrow line is shown to originate from hydrogen originally associated with the broad line. The spin-lattice relaxation time T1 of this up-field shifted narrow line is about 0.4 s. This short T1, along with its small linewidth, suggests that this line is associated with molecular hydrogen, possibly trapped in sites of atomic dimensions.

Hyperfine interactions of short-lived β-emitter 8 Li in ferromagnetic Ni

Hyperfine interactions of 8Li impurity nucleus imbedded in ferromagnetic Ni metal were studied using the β-NMR technique. Two kinds of hyperfine fields B82 were found, corresponding to two different final sites of Li atoms in the Ni lattice. The nuclear spin-lattice relaxation times T1 of 8Li in Ni were also determined for each field. Temperature dependencies of B82 and T1 were observed to deduce these values at T=0 K that can be compared with those calculated recently by Akai et al.

A field-cycling NMR study of nematic 4-pentyl-4′-cyanobiphenyl confined in porous glasses

The proton spin-lattice relaxation time T1, in the nematic liquid crystal 4-pentyl-4′-cyanobiphenyl confined in a glassy porous matrix has been measured in a wide Larmor frequency range of 1 · 102−2 · 107 Hz employing the fast field-cycling NMR technique. A strong influence of the restricted geometry on the character of the T1 dispersion was found. Our investigation clearly demonstrates the importance of the translationally induced molecular reorientations in inhomogeneous director field for the relaxation in the samples with 200 and 80 nm mean pore size. The experimental results are in a good agreement with the theoretical predictions. In the sample with 7 nm pore size the main contribution to the relaxation is ascribed to the slowing down of the molecular motion in the near-surface layer. Zero-field 1H NMR spectra of a microconfined liquid crystal are reported for the first time.

Analysis of13C−NMRspectra inC60superconductors: Hyperfine coupling constants, electronic correlation effect, and magnetic penetration depth

A C-NMR anisotropic hyperfine coupling tensor was determined as 2p(21.68, 21.68, 3.37) 310 rad/sec for C60 32 in A3C60 superconductors, where A is an alkali metal, by analyzing C-NMR spectra below 85 K. Combined with an isotropic coupling constant of (2p30.69)310 rad/sec, the 2s and 2p characters of the electronic wave functions at the Fermi level were deduced. The results were compatible with local-density-approximation band calculations. From a simulation of C-NMR spectra at superconducting state, the traceless chemical ~orbital! shift tensor and isotropic chemical shift were determined as ~67, 34, 2101! ppm and ;150 ppm, respectively. An estimated magnetic penetration depth is larger than 570 nm in K3C60. Furthermore, the modified Korringa relation, T1TK ;bS ~with Knight shift K, spin-lattice relaxation time T1 , and Korringa constant S!, clearly showed the existence of weak but substantial antiferromagnetic spin fluctuation in A3C60; b50.40– 0.58 with an error of 620%. The Stoner enhancement factor was also determined as 1–1.5 from a comparison between spin susceptibility obtained from NMR and band-calculation results. @S0163-1829~98!00542-6#

Non-invasive temperature imaging of muscles with magnetic resonance imaging using spin-echo sequences.

The application of spin-echo magnetic resonance imaging sequences on non-invasive temperature imaging for temperature mapping of human limbs is investigated. In an in vitro experiment performed on a meat sample, the equilibrium magnetisation P and the spin-lattice relaxation time T1 are calculated from the values for the repetition time TR and the signal intensities obtained by a spin-echo sequence at different tissue temperatures as measured by a fibre-optic probe. T1 is linearly correlated to the tissue temperature, and P is linearly correlated to the reciprocal value of the absolute temperature. Both effects, taken together, lead to a non-linear dependency of the signal intensity on temperature. Therefore a TR leading to maximum temperature dependency of the signal intensity is calculated and used in the further experiments. In the in vivo experiments, the lower legs of two volunteers are cooled from outside. Images are acquired with a spin-echo sequence (1.5 T, TR = 1200 ms, TE = 10 ms). A rise in signal intensity in the muscle with falling skin temperature is observed, particularly in more peripheral muscle layers. This study shows that spin-echo sequences can be used to monitor temperature changes and temperature differences in living muscle tissue.

Examination of miscibility at molecular level of poly(hydroxyether of bisphenol A)/poly(N-vinyl pyrrolidone) blends by cross-polarization/magic angle spinning13C nuclear magnetic resonance spectroscopy

The miscibility of poly(hydroxyether of bisphenol A) (phenoxy) and poly(N-vinyl pyrrolidone) (PVP) was investigated by differential scanning calorimetry (DSC) and high-resolution solid-state nuclear magnetic resonance (NMR) techniques. The DSC studies showed that the phenoxy/PVP blends have a single, composition-dependent glass transition temperature (Tg). The S-shaped Tg-composition curve of the phenoxy/PVP blends was reported, which is indicative of the strong intermolecular hydrogen-bonding interactions. To examine the miscibility of the system at molecular level, high-resolution solid-state 13C nuclear magnetic resonance (NMR) technique was employed. Upon adding phenoxy to system, the chemical shift of carbonyl carbon resonance of PVP was observed to shift downfield by 1.6 ppm in the 13C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) spectra when the concentration of phenoxy is 90 wt %. The observation was responsible for the formation of intermolecular hydrogen bonding. The proton spin-lattice relaxation time T1(H) and the proton spin-lattice relaxation time in the rotating frame T1ρ(H) were measured as a function of the blend composition. The T1(H) result was in good agreement with the thermal analysis, i.e., the blends are completely homogeneous on the scale of 20 ∼ 30 nm. The six results of T1ρ(H) further indicated that the blends were homogeneous on the scale of 40 ∼ 50Å. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2291–2300, 1998

NMR and dynamic mechanical studies of drawn polypropylene fibers

The influence of drawing on the relaxation processes connected with the glass transition in polypropylene fibers have been studied in terms of the spin—lattice relaxation times T1 and the storage and loss components of the dynamic modulus measured at different temperatures. The measurements were carried out at the frequencies f0 = 30 MHz and fE = 110 Hz, respectively. The experimental results were interpreted using the Williams—Landel—Ferry (WLF) theory. Glass transition tempera-tures Tg and correlation times τg corresponding to this temperature were calculated using conditions for the minimum and maximum of the temperature dependences of the relaxation times T1 and loss modulus E′′. Two sets of the polypropylene fibers drawn within the range of draw ratios 1—5 were investigated. One of them was prepared from polypropylene containing 8 wt% of the polymer modifier, which gives rise to the plastification of polymer, and the other was made from unmodified polypropylene. Under drawing, the former set of fibers was found to give a shift of the Tg towards the lower temperatures whereas the opposite effect appeared in the measurements of the latter set. The values of an isothermal apparent activation energy Ea estimated on the basis of WLF theory lead to the same conclusions as the activation energy values obtained from the Arrhenius relation. Parameters a and b of the modified Fuoss—Kirkwood distribution were computed from the temperature dependences of the spin—lattice relaxation times T1 and loss modulus E′′ using a fitting procedure.

2H and 195 Pt NMR Studies of Molecular and Electron Spin Dynamics in Paramagnetic [Cu(H2O)6][PtCl 6

Abstract The temperature dependences of 2H and 195Pt NMR spectra and the spin-lattice relaxation time T1 were measured for [Cu(H2O)6][PtCl6]. From the simulation of 2H NMR spectra, the jump rate of 180° flips of the water molecules (k), the nuclear quadrupole interaction parameters (e2Qq/h, ƞ) and the electron-nucleon dipolar interaction parameter (vD) were obtained. By measuring 2H T1, k was estimated in the temperature range where the spectrum is insensitive to the motion of the water molecules. Above the phase transition temperature, the pre-exponential factor k0 = 8 x1011 s-1 and the activation energy Ea = 15 kJmol-1 for 180° flips of the water molecules were obtained from the spectral simulation and T1. 195Pt NMR spectra showed an axially symmetric and unsymmetric powder pattern of the chemical shift anisotropy at the high and low temperature phase, respectively. For the deuterated compound, the correlation times of the electron spin in Cu2+ were estimated from 195Pt T1 and the activation energy for jumping between the different configurations of Jahn-Teller distortion Δ = 200 K was obtained.

New Li+ ion-conducting ormolytes

The preparation and characterization of two new families of lithium-conducting solid-state electrolytes is reported. Both systems are silica (SiO2) – polyethyleneglycol (PEGn) hybrid materials with (type I) or without (type II) covalent organic-inorganic chemical bonds. Their electrical conductivity has been studied by complex impedance spectroscopy between 20°C and 100°C in the frequency range 1Hz to 10MHz as a function of the polymer chain length (200<n<1900), polymer concentration and lithium concentration (4<[O]/[Li]<80). The highest room-temperature ionic conductivity (σ≅6×10−2Scm−1) has been found for type II material for ratios [O]/[Li]=15 and PEG300/TEOS=1.0. The effect of the chain length on the polymer mobility has been studied by nuclear magnetic resonance by measuring the Li+ line widths and the spin-lattice relaxation time T1 between -100°C and +100°C. The bonded chain mobility increases with the chain length (type II) while the opposite occurs with unbonded chain material (type I). Both types of materials present high ionic conductivity at room temperature and are adequate as Li+-conducting electrolyte in all solid-state electrochemical devices.