NMR Spin-lattice Relaxation Times Research Articles

Phase Transition Mechanism Studied by1H and87Rb Spin-Lattice Relaxation Time in a RbHSO4Single Crystal

The 1 H and 87 Rb NMR spin-lattice relaxation times for a RbHSO 4 single crystal were measured in the temperature range of 300–170 K for study of the paraelectric (I) to ferroelectric (II) phase transition near T c =264 K. Proton spin-lattice relaxation time on the RbHSO 4 yielded a minimum, attributed to the effect of molecular motion. The activation energy for the reorientational motion in phase I was determined to be 16.54 kJ/mol, whereas, for the molecular motion in the phase II it was 25.53 kJ/mol. The change of the 87 Rb spin-lattice relaxation rate near 264 K corresponds to a phase transition in the crystal. The temperature dependences of the relaxation rate for 87 Rb in this crystal were in accordance with the single phonon process dominated by the phonon mechanism. The activation energies in phases I and II were obtained to be 2.66 kJ/mol and 17.25 kJ/mol, respectively. From 1 H and 87 Rb NMR investigations, the phase transition does play an important role by Rb nucleus, although the activation e...

Solid 63Cu and 127I NMR studies of dynamical structure in the γ-phase of Ag xCu 1− xI ( x=0.05–0.40)

The transport property of the ions and the defect dynamics in the γ-phase of Ag x Cu 1− x I ( x=0.05–0.40) were studied by the 63Cu and 127I NMR spin–lattice relaxation time T 1 and the 63Cu NMR spin–lattice relaxation time in a rotating flame T 1ρ. At low temperatures, T 1 and T 1ρ were dominated by the lattice vibration. The temperature dependence of T 1ρ in the range of 420–280 K can be explained in terms of the distribution of the correlation times which arises from the distribution of the activation energies for the ionic diffusion. The mean of the distribution for the activation energies increased gradually with increasing Cu concentration. The rapid decreases of T 1 and T 1ρ observed at high temperatures can be attributed to the motion of the thermally generated defects. The enthalpy of formation of the Frenkel defect was obtained by 63Cu NMR T 1 and T 1ρ. The defect concentration obtained by analyzing 63Cu NMR T 1 and T 1ρ suggests that the Cu ion possesses disorder structure on the high-temperature side in the γ-phase.

Diffusion of Methylaluminoxane (MAO) in Toluene Probed by1H NMR Spin-Lattice Relaxation Time

A critical evaluation of model-fitted and observed 1H NMR spin-lattice relaxation time data (T1) of methylaluminoxane (MAO) dissolved in toluene suggests that the relaxation time of MAO is predominantly controlled by rotational motions. Within the Al concentration (CAl) range (10–3M T > 20°C) studied, the diffusion of MAO contributes with less than 20% (at the maximum concentration investigated) to the overall relaxation rate. For concentrations smaller than 0.5 M, the diffusion has no significant impact on the spin-lattice relaxation time (< 5%). Nevertheless, the diffusion coefficient of MAO can be estimated from the rotational correlation time, as derived from a spin-lattice relaxation time model discussed thoroughly in this work. This model gives information on the molecular dimension of MAO ((19.4 ± 0.4) A), the activation energy of the diffusion process ((11.2 ± 0.7) kJ/mol), and the temperature/concentration dependence of the viscosity of the MAO solution.

Motions of Ethylammonium Ions in Solid Ethylammonium Chloranilate Studied by 1H Nuclear Magnetic Resonance

Abstract The motions of the ethylammonium ion in solid ethylammonium chloranilate, C2H5NH+ 3 • C6HO4CI- 2, are studied by 1H NMR second moment (M2) and spin-lattice relaxation time {T1) measurements. Re­ orientations of the CH3 group about the C-C bond axis and the NH+ 3 group about C -N bond axis were observed and their motional parameters were evaluated. The internal rotational barriers of the CH3 and NH+ 3 groups of an isolated C2H5NH+ 3 ion were estimated from ab initio molecular orbital calculations.

13C NMR Spin−Lattice Relaxation and Conformational Dynamics in a 1,4-Polybutadiene Melt

We have performed molecular dynamics (MD) simulations of a melt of 1,4-polybutadiene (PBD, 1622 Da) over the temperature range 400-273 K. 13 C NMR spin-lattice relaxation times (T 1 ) and nuclear Overhauser enhancement (NOE) values have been measured from 357 to 272 K for 12 different resonances. The T 1 and NOE values obtained from simulation C-H vector P 2 (t) orientational autocorrelation functions were in good agreement with experiment over the entire temperature range. Analysis of conformational dynamics from MD simulations revealed that T 1 depends much less strongly on the local chain microstructure than does the mean conformational transition time. Spin-lattice relaxation for a given nucleus could not be associated with the dynamics of any particular dihedral; instead, spin-lattice relaxation occurs as the result of multiple conformational events. However, a much closer correspondence was found between torsional autocorrelation times and the C-H vector P 2 (t) autocorrelation times upon which T 1 depends. Both processes exhibited stronger than exponential slowing with decreasing temperature. The non-Arrhenius temperature dependences of these relaxation times as well as the stretched-exponential character of the autocorrelation functions themselves were found to be consistent with increasing dynamic heterogeneity in conformational transition rates with decreasing temperature.

Ionic Conductivity and NMR Self-Diffusion in Poly(macromonomer)s of Vinylbenzyl Poly(ethylene oxide)s

Abstract Ionic conductivity and NMR self-diffusion in the complex of poly(macromonomer)s of VB–PEO doped with the lithium salt Li(CF3SO2)2N were investigated. Ionic conductivity was enhanced by the multibranched structure of the poly(macromonomer). The NMR spin–lattice relaxation times showed that the hopping motion of the Li ions were correlated with PEO chain motion. NMR self-diffusion data showed evidence of the multi-site diffusion of anions in the complex at near room temperature.

Anomalous Larmour Frequency Dependence of Proton Spin-Lattice Relaxation Time (T1) in the Ferroelectric Glycine Phosphite

We report here the results of our $^{1}H$ NMR spin lattice relaxation time $(T_1)$ studies in glycine phosphite which is ferroelectric below 224 K. The experiments have been carried out in the temperature range from 200 to 419 K and at two Larmour frequencies of 11.40 and 23.56 MHz. We have noticed a Larmour frequency dependence of $T_1$ on the high-temperature side of the $T_1$ minimum. A model is proposed based on the BPP theory to explain the observation.

Solvent Effect on Rotational Relaxation Time of Ammonium Ion

The rotational relaxation times of ammonium ion, τ2r, in 11 solvents were determined by the measurements of the 15N NMR spin-lattice relaxation times and the nuclear Overhauser enhancement (NOE) factors under the condition of negligible ion−ion interaction. The observed solvent dependence of the rotational relaxation times showed a poor correlation with those for predicted from a hydrodynamic (Stokes−Einstein−Debye) model or an electro hydrodynamic (Hubbard−Onsager−Felderhof) model, whereas a much better linear relation was found for the plot of the logarithms of the observed rotational relaxation times versus Gutmann's solvent donor numbers. The results of these solvent dependence trends were compared with those perchlorate rotation, and the difference in the validity of the continuum models between the rotational motions of these two ions was discussed. A comparison was also made between the solvent dependences of the rotational and the translational diffusion of the ammonium ion.

35 Cl NQR and 2 H NMR analysis of the critical dynamics by approaching from above the normal-incommensurate phase transition of Bis-(4-chlorophenyl)-sulfone (BCPS)

The inverse of the NQR or NMR spin lattice relaxation time of BCPS exhibits a Landau like critical behaviour on approaching the Normal/Incommensurate phase transition from above. This critical behaviour is interpreted as the contribution from the central peak observed in neutron experiments within the framework of the model of a coupling of the soft mode to pure relaxation modes. This result would be consistent with a central peak of dynamical nature.

Study on the Adsorption Behavior of Dispersants onto Pigment Using 1H NMR Spin-Lattice Relaxation Time.

In order to obtain information concerning the function of the polar group of polymeric dispersants generally used for pigment particles in a non-aqueous medium, alkylamine, alkylammonium salt, amide, and carboxylic acid were selected as the model dispersants and their adsorption behavior onto the phthalocyanine blue (PhB) pigment was studied by means of 1H NMR spin-lattice relaxation time using a high-resolution magic angle spinning 1H NMR probe. The amino group, particularly the primary amino group, was found to be the most effective as the adsorption site for the pigment among the functional groups examined in this study. The results obtained in this work suggest that the coordination of a lone electron pair on the nitrogen atom of an amino group to the Cu(II) of PhB is the driving force for the adsorption.

Adsorption Mechanism of Poly(Ammonium Carboxylate) onto Phthalocyanine Blue Pigment Deduced by 1H NMR Spin-Lattice Relaxation Time.

1H NMR spin-lattice relaxation time of ethylenediammonium dioctanoate (EDADO), a model dispersant (MD) for phthalocyanine blue (PhB) pigment, was examined with a high-resolution magic angle spinning (MAS) 1H NMR probe (1H Nano·nmrTM Probe). The adsorption mechanism of EDADO onto PhB was discussed on the basis of the spin-lattice relaxation time obtained by changing the polarity of the solvent and the temperature in the 1H NMR measurement. In addition to the deduction shown in our previous report that the adsorption of the MD molecule onto the pigment is induced by the coordination of a lone electron pair of a nitrogen atom of the amino group onto Cu(II) of PhB, it became clear that equilibrium among a diammonium salt, a half-salt, and diamine (ethylenediamine, EDA) is an important factor in the adsorption behavior. A comparison of measurements in chloroform-d and in methanol-d4 suggests that the complex of PhB and a half-salt composed of EDA and octanoic acid still has interaction with a carboxylic acid molecule through proton-transfer from the carboxylic acid to PhB (PhB of the complex and/or free PhB) and successive hydrogen bonding which may effect the dispersion of pigment in a nonpolar medium. The results obtained in this model system may afford a basis for explaining the good dispersing ability of poly(ammonium carboxylate), that is, polymeric dispersants in practical use.

1H NMR study of the hydration kinetics of coal fly ash and spent oil shale

Hydrogen NMR spin–lattice relaxation times were measured as a function of time to determine the kinetics of hydration for the Dave Johnston and Laramie River coal fly ashes and for the Lurgi spent oil shale. The kinetic data were compared to the hydration of Portland cement. It was found that the hydration kinetic data for the spent shale were similar to Portland cement with the exception that the dormant period was about 10 times longer. The dormant periods for the coal fly ashes differed from each other and from Portland cement. The Laramie River coal fly ash had almost no dormant period. The extent of hydration for the materials after 119 h can be ranked accordingly: Portland cement>Lurgi spent shale≃Laramie River coal fly ash>Dave Johnston coal fly ash. Data from this study show that an NMR spin–lattice relaxation time measurement may be a good predictor of the compressive strength of hydrated Portland cement and fly ash.

Dynamical structure of AgxCu1-xI (x=0.99–0.80) in ionic and superionic phases studied by solid 63Cu and 127I NMR spin–lattice relaxation time measurements

The temperature dependences of the 63Cu and 127I NMR spin–lattice relaxation time T1 and the 63Cu NMR spin–lattice relaxation time in a rotating frame T1ρ were measured for AgxCu1−xI (x = 0.99–0.80). In the γ phase, T1 and T1ρ were dominated by the lattice vibration at low temperatures. The minimum of T1ρ caused by the diffusion of the Cu ion was observed at ca. 360 K. The temperature dependence of T1ρ in the range 420–300 K can be explained in terms of a distribution of correlation times which arises from a distribution of activation energies for the ionic diffusion. The mean and the width of the distribution for the activation energies increased with increasing Cu concentration. The rapid T1 decrease observed above ca. 400 K can be attributed to the motion of the thermally generated defects. The enthalpy for the formation of the defect was estimated as 120 ± 10 kJ mol−1 from 63Cu NMR T1 and T1ρ values. In the α phase, the relaxation of the 63Cu nucleus was in the fast motion region and the activation energy of the ionic diffusion was determined as 7 ± 1 kJ mol−1 from the temperature dependence of 63Cu NMR T1.

Deconvolving pore shielding effects in mercury porosimetry data using NMR techniques

A new method for removing the so-called “shielding” effect inherent in a pore-size distribution of a porous medium obtained from the mercury porosimetry intrusion curve is presented. The methodology employs data from complementary pore structural characterisation methods, such as nitrogen adsorption BET, gravimetric analysis and NMR relaxometry, which are insensitive to the shielding effect, to correct the pore-size distribution for bidisperse materials obtained from mercury porosimetry. The characterisation of the macropore network of an alumina tablet obtained using the new methodology has been compared with the results of a study of a similar sample using microscopy carried out by earlier workers. NMR imaging studies have placed constraints on the volume of the sample which is necessary to study using microscopy in order to obtain statistically representative results. In conjunction with NMR spin density and spin-lattice relaxation time images the proposed deshielding method may be used to provide a spatially resolved pore-size distribution not possible with conventional methods.

Time scale of short range order fluctuation in the isotropic phase of butylcyano-phenylcyclohexane liquid crystal

The NMR spin-lattice relaxation time at three Larmor frequencies – ν L =28 MHz , 1.235 MHz and 48 kHz – in the isotropic phase of butylcyano-phenylcyclohexane has been measured in the temperature range close to the isotropic–nematic phase transition. Spin-lattice relaxation mechanisms provided by both individual reorientational fluctuations and fluctuations of the local director can be distinguished at the different Larmor frequency scales. We conclude that the Landau–De Gennes theory for the weak first order nematic–isotropic phase transition, together the low frequency approximation can be applied if the experiment is carried out at Larmor frequencies in the kHz range.

Hydrogen Transfer in a Hydrogen-Bonded 1:2 Complex of Chloranilic Acid with 1,2-Diazine Studied by 35Cl NQR

Abstract 35Cl NQR frequencies and spin–lattice relaxation time, and 1H NMR spin–lattice relaxation time were measured on (chloranilic acid)-(1,2-diazine) 1:2 molecular complex to detect H-transfer motions in the H-bonded three molecular system. Only a single H-jump mode was observed by 1H NMR, whereas three kinds of H-transfer modes were obtained in 35Cl NQR in good agreement with the prediction.

Correlating the NMR self-diffusion and relaxation measurements with ionic conductivity in polymer electrolytes composed of cross-linked poly(ethylene oxide-propylene oxide) doped with LiN(SO2CF3)2

A solvent-free solid-polymer electrolyte based on a cross-linked poly(ethylene oxide-propylene oxide) random copolymer doped with LiN(SO2CF3)2, was studied using multinuclear NMR and ionic conductivity. The NMR spin-lattice relaxation times, T1, of the bulk polymer (1H), the lithium ion (7Li) and the anion (19F) were analyzed using single exponential analysis above the glass transition temperatures. Since the temperature dependent H1 and Li7 NMR T1 values had minima, the reorientational correlation times were obtained for the segmental motion of the CH2CH2O/CH2CH(CH3)O moiety of the bulk polymer and the hopping motion of the lithium ions correlated with the segmental motion. The spin–spin relaxation of the anion signals appeared single exponential with respect to time, whereas that of the polymer and the lithium echo signals were at least bi-exponential. Since both the spin-lattice and spin–spin relaxation of the anion indicated a single component, the self-diffusion coefficients, D, were measured using F19 pulsed-gradient spin-echo (PGSE) NMR measurements. Although the PGSE attenuation data appeared single exponential at each value of the separation between the gradient pulses, Δ, the measured D values had a Δ-dependence. Phenomenologically, the anion diffuses quicker in a shorter range and the activation energy of the shorter-time diffusion is smaller than that of the longer-time diffusion. The apparent self-diffusion coefficients became smaller for longer Δ and approached a constant when Δ was longer than 0.05 s. The mean square displacements of the anion were inconsistent with standard diffusion models including “anomalous diffusion” as found for a neutral particle diffusing in a fractal network [i.e., 〈r2(Δ)〉∝Δκ with κ&amp;lt;1(κ≡2/dw where dw is the random walk fractal dimension)]. The apparent diffusion coefficients of the lithium ions at Δ=0.02 s are almost independent of temperature and smaller than the corresponding diffusion coefficients of the anion. Since the activation energy of the anion determined for Δ longer than 0.05 s correlates well with those obtained from the ionic conductivity, the ion conduction in the solid-polymer medium is driven mainly by fast transfer of the anions.

The First Study on the Mobility of Surface-Adsorbed Molecules Using 1H NMR Spin–Lattice Relaxation Time

Abstract The function of alkanoic acid amine salt adsorbed onto the pigment surface was examined by means of 1H NMR spin–lattice relaxation time using a high-resolution magic angle spinning (MAS) 1H NMR probe called 1H Nano·nmrTM Probe. The adsorption mechanism of the salt to the pigment was discussed on the bases of the results.

Molecular Motion and Crystal Structure of Solid Tetrapentylammonium Iodide

Abstract The proton NMR spectra and spin-lattice relaxation times of tetrapentylammonium iodide have been measured between 100 K and the melting point. The room temperature crystal structure has been determined by X-ray diffraction as orthorhombic, space group Ccca, Z = 4 with a = 10.811(2), b = 22.771(5) and c = 9.500(2) Å with fully ordered tetrapentylammonium cations. The existence of a solid-solid phase transition at 400 K has been confirmed by DTA. The onset of C 3 methyl group reorientations characterized by Arrhenius activation parameters has been evidenced. The intracation conformational motions in the pentyl chains start to manifest themselves already at lower temperatures. The appearence of an ionic plastic phase with coexisting liquid-like and solid-like cations has been discovered.

Diffusive Dynamics in a Detailed Potential: Application to Biological Macromolecules

The local dynamics of macromolecules is obtained to second-order in the mode-coupling expansion of the Smoluchowski diffusion theory. The NMR spin-lattice relaxation times of different 13C or 15N nuclei along the chains are calculated and compared to experimental data from the literature. The macromolecules are considered as fluctuating 3D structures undergoing rotational diffusion. The fluctuations can be evaluated with any technique for sampling the configurational space. In the presented test cases Molecular Dynamics simulations have been applied to a DNA fragment and to the NK-2 homeodomain. In the case of the double-stranded DNA fragment d(TpCpGpCpG)2, second and even first order theories are found to be in close agreement with experimental results. The major advantage of the diffusion technique is that only a good statistics is important as input while the solvent dynamic effects enter through hydrodynamic theory. Application based on Hybrid Monte Carlo schemes coupled with J-walking, are now in progress.