NMR Spin-lattice Relaxation Times Research Articles

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 (T1) 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 T1 on the high-temperature side of the T1 minimum. A model is proposed based on the BPP theory to explain the observation.

NMR Study of Cation Motions in Ferroic [C(NH2)3]3Bi2Br9

The proton NMR second moment and spin-lattice relaxation time of polycrystalline [C(NH2)3]3Bi2Br9 were studied in a wide-temperature range. Dynamical inequivalence of two crystallographically different guanidinium cations has been revealed . The C3 reorientation of the two types of cations was found to be hindered by different potential barriers (25.1 kJ/mol and 34.7 kJ/mol). At higher temperatures an overall reorientation of the cations was revealed. The existence and order-disorder character of the phase transitions at 333, 350, 415, and 425 K have been confirmed.

1H Spin-Lattice Relaxation Times of Water, Methanol, and Ethanol under Sub- and Supercritical Conditions

Abstract 1H NMR spin-lattice relaxation times (T1) of water, methanol, and ethanol (abbreviated as W.M.E) were measured in the range of 25 to 400 °C at 30, 20, and 20 Mpa, respectively by using high-pressure NMR. It was found that the T1 values for each group of W.M.E increase with an increase in temperature up to around 220, 160, and 170 °C, and that above these temperatures, the T1 values decrease and approach a constant value at 300, 200, and 220 °C, respectively. It is explained that the spin-lattice relaxation (SLR) processes are dominated by the dipole-dipole (DD) mechanism at lower temperature and by the spin-rotation (SR) mechanism at higher temperatures. The reasons that the T1 values are nearly constant are supposed.

H NMR Study of Ionic Motions in High Temperature Solid Phases of (CH3NH3)2ZnCl4

Abstract The reorientation of the tetrahedral complex anion ZnCl4 2- and the self-diffusion of the cation in (CH3NH3)2ZnCl4 were studied by 1H NMR spin-lattice relaxation time (1H T1) experiments. In the second highest-temperature phase, the temperature dependence of 1H T1 observed at 8.5 MHz could be explained by a magnetic dipolar-electric quadrupolar cross relaxation between 1H and chlorine nuclei, and the activation energy of the anion motion was determined to be 105 kJ mol -1 . In the highest-temperature phase, the activation energy of the self-diffusion of the cation was determined to be 58 kJ mol -1 from the temperature and frequency dependence of 1H T1

Molecular motion and phase transition in perovskite-type (CH 3) nNH 4− nSnCl 3 ( n=1–4) studied by proton NMR spin–lattice relaxation

Powder X-ray diffraction, 119Sn NMR spectra, and 1H NMR spin–lattice relaxation times, T 1, were measured for (CH 3) n NH 4− n SnCl 3 ( n=1–4). From the Rietveld analysis, it is shown that all four compounds crystallize into deformed perovskite-type structures at room temperature. The temperature dependence of 1H T 1 was analyzed in terms of the CH 3 reorientation and other motions of the whole cation. Except for the phase transition in CH 3NH 3SnCl 3, which is from monoclinic to rhombohedral at 331 K, 1H T 1 was continuously changed at other phase transitions in this compound as well as in the n=2–4 compounds, suggesting that the transitions are not caused by the change of the motional state of the cation but by an instability of the [SnCl 3] n n− perovskite lattice.

Cationic Motions and Order-Disorder Phase Transitions in Layer Crystals with a Rotator Phase, (n-C5H11NH3)2ZnCl4 and (n-C12H25NH3)2ZnCl4

Abstract 1H NMR spin-lattice relaxation times T1 and T1ρ as well as the electrical conductivity were measured as a function of temperature in (n-C5H11NH3)2ZnCl4 and (n-C12H25NH3)2ZnCl4. The highest-temperature solid phase in both compounds was found to be the rotator phase, where rod-like cations perform uniaxial reorientations about the molecular long axes accompanied by conformational disordering and translational self-diffusion of the cations within the layer perpendicular to c-axis. In the rotator phase, the cations are considered to have a non-intercalated double layer structure. These rotator phases were shown to be quite analogous to those reported in n-alkylammonium chlorides. (n-C5H11NH3)2ZnCl4 undergoes four structural phase transitions, while (n-C12H25NH3)2ZnCl4 exhibits a single transition above ca. 120 K. All of these transitions were shown to be of order-disorder type.

A133Cs NMR Spin-Lattice Relaxation Study in Incommensurate Cs2CdI4

133Cs NMR spin-lattice relaxation times(T1) in crystalline Cs2CdI4 were measured at 225 - 373 K. The critical exponent ( of T\ observed near the normal-incommensurate transition in the normal phase was determined to be 0.62 ± 0.03, in good agreement with the predicted value for three-dimensional XK-model. The frequency dependent T1 in the incommensurate phase could be explained by the fluctuation of amplitudon and small gap phason.

NMR in magnetite below and around the Verwey transition

NMR on ${}^{57}\mathrm{Fe}$ nuclei was measured in two single crystals of magnetite between 4.2 and 135 K (temperature of the Verwey transition ${T}_{V}=121.5$ and 123.9 K). We were able to register all lines detected at 4.2 K also at higher temperatures up to ${T}_{V}.$ The spectra are compatible with the space group $Cc,$ which predicts 8 and 16 lines for iron on tetrahedral (A) and octahedral (B) sites, respectively. One of the $\mathrm{Fe}(A)$ lines is doubly degenerate for all $T<{T}_{V},$ which restricts the possible models of the ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ ordering on the B sites. Above ${T}_{V}$ no remnant of the low-temperature spectrum was detected. At 4.2 K the NMR spin-spin and spin-lattice relaxation times were determined.

13C solid-state MAS NMR studies of the low temperature phase transition in fullerene C60

At the phase transition near 262 K, the 13C NMR spin–lattice relaxation time, T1, in static samples of pure C60 decreases from 31 to 0.8 s as the temperature decreases by less than 8 K, while X-ray diffraction patterns change little. Under magic-angle spinning T1 decreases from 46 to 0.8 s over only 2 K, while the onset of the phase transition is lowered to 255 K. NMR lineshapes of static samples are unchanged in the 280–235 K range, but the isotropic 13C chemical shift changes linearly by 1.88×10−3 ppm K−1. Uniaxial cage motion cannot average the chemical shift anisotropy to the value observed in static samples, and nutation must be present. Our tentative explanation of the results is based on differences in the nature of C60 cage motions at different temperatures.

Paramagnetic Effects of Iron(III) Species on Nuclear Magnetic Relaxation of Fluid Protons in Porous Media

The 1H NMR spin–lattice relaxation time, T1, of saturated sands depended on the chemistry of the pore fluid, pore size distribution, and relaxivity of the surface. In the absence of paramagnetic impurities, surface relaxivities of quartz sand and silica gel samples of known porosity and surface area at any pH were lower than any previously reported values. Relaxation rate of the bulk pore fluid increased linearly with increasing Fe(III) concentration and varied with speciation of the ion. With only 0.01% of the silica surface sites occupied by sorbed Fe(III) ions, surface relaxivity increased by an order of magnitude. In addition, low concentrations of Fe(III)-bearing solid phases present as surface coatings or as separate mineral grains increased surface relaxation as much as two orders of magnitude. We believe that observations of relatively constant surface relaxivity in rocks by previous researchers were the result of consistently high surface concentrations of paramagnetic materials.

Branching effects on the segmental dynamics of polyethylene melts

13C NMR spin–lattice relaxation time and nuclear Overhauser effect measurements are reported for linear polyethylene, polyethylene with long branches, and linear polyethylene with infrequent short branches at 75 MHz over the temperature range of 400–535 K. A quantitative description of the segmental dynamics of the main-chain methylene units and the branch points is obtained for linear polyethylene with ethyl branches. At 400 K, the correlation time is 29 ps for the segmental dynamics of the branch point but 5 ps for the segmental dynamics of the main-chain methylene units. The activation energy for the segmental dynamics of the main-chain methylene units (4 kcal/mol) is significantly less than the flow activation energy (Eη = 7.2 kcal/mol). In contrast, the activation energy for the segmental dynamics at the branch point (6.4 kcal /mol) is much closer to Eη. This result supports our earlier hypothesis that the lack of side groups in polyethylene allows conformational transitions to happen without substantial intermolecular cooperation. Thus, in contrast to many other polymers, conformational transitions are not the fundamental motion for flow in polyethylene. Branches as small as a methyl group introduce intermolecular cooperation into conformational transitions at the branch point, so conformational transitions at the branch points have a stronger temperature dependence. No difference in local dynamics was found for methylene units in linear polyethylene and polyethylene with long branches. Therefore, local dynamics are not relevant for understanding the factor-of-two difference in the flow activation energies of these two polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2634–2643, 2000

NMR interaction studies of aromatic guanyl hydrazones with micelles: model for mechanism of action of cationic antibiotics.

Interaction studies using hydrogen NMR spin-lattice relaxation time measurements of a series of five antiparasitic guanyl hydrazones with SDS and cetyl trimethylammonium bromide micelles are used as a simple model for the interaction of these compounds with the cell membrane of Trypanosoma cruzi. The results show that the activity of the compounds is related to their capacity to selectively interact with anionic micelles, which reinforces the hypothesis that the mechanism of action of these compounds is related to their selective interaction with the negatively charged parasite membrane.

Study of the Interaction Between Trypanocide 3-Nitrobenzaldehyde Guanyl Hydrazone and Bovine Serum Albumin by Equilibrium Dialysis and Nmr

Equilibrium dialysis and NMR spin-lattice relaxation time (T1) studies of the interaction of the trypanocidal drug 3-nitrobenzaldehyde guanyl hydrazone (3NBGH) with bovine serum albumin (BSA) were used to show that this interaction is weak and nonspecific, making 3NBGH a potential agent for the prophylaxis of Trypanosoma cruzi infected blood.

Molecular Motion in Tetraphenyltin Studied by NMR

NMR second moment and spin-lattice relaxation times in the laboratory (60 and 25 MHz) and in the rotating frame (B1 = 2.1 mT) were studied for polycrystalline tetraphenyltin Sn(C6H5)4 in a wide temperature range. Two kinds of motions were detected: isotropic rotation of whole molecules and reorientations/ oscillations of phenyl rings. A dependence of the potential energy of the molecule in the crystal on the angle of the phenyl ring rotation about the Sn-C bond was obtained on the basis of atom-atom calculations. The amplitude of the ring-oscillations at 133 K was estimated as ± 7°. Below room temperature the magnetisation recovery is significantly non-exponential, which may be interpreted as due to the correlated motion of phenyl rings.

Ionic Dynamics in LiNO2 Studied by 7Li and 15N Solid NMR

The temperature dependences of 7Li and 15N NMR spin-lattice relaxation times and spectra in LiNO2 were measured in the range 120 K -473 K (m.p.). The 180°-flip motion of NO2-- ions along or perpendicular to the molecular C2 -axis and the self-diffusion of Li+ ions (activation energies of 42 -44 and 100 kJ mol-1 , respectively) were observed in this range. From the comparison of the observed activation parameters with those reported for plastic phases of alkali metal nitrites, a new characteristic of the plastic crystal was obtained.

A Dual Role for Intracellular Trehalose in the Resistance of Yeast Cells to Water Stress

It is well known that yeast cells survive environmental stresses such as desiccation and freezing and there is evidence that these phenomena may be related to the presence of trehalose in the cells. However, the molecular mechanism by which trehalose might exert an influence on cell functions remains unknown. In this report, thermogravimetry and differential thermal analysis were used to estimate the amount of bound water in yeast cells. It is shown that when the trehalose content is greater than 2–3% of the cell dry weight, the amount of bound water is drastically decreased and the viability of the dried cells is increased. This implies that a major portion of the bound water is replaced by trehalose. In addition, measurements of the NMR spin-lattice relaxation time of the intracellular water protons show that trehalose acts as a water-structuring agent in hydrated yeast cells. This dual role is essential for high resistance to water stress in yeast cells.

NMR Studies on Dynamics of Water Intercalated in Clay Minerals

Abstract The dynamics of water molecules intercalated in D2O saturated synthetic and natural smectites, and a synthetic Na-fluormica were studied by measurements of solid state 2H NMR spectra and spin-lattice relaxation times at 150 - 370 K. The obtained results could be explained by the 2-site flip, the C2 rotation and the isotropic rotation of the D2O molecules in smectites. In fluormica, the isotropic motion was undetectable, but the axial rotation of the hydration sphere as a whole was observed. The activation energies and correlation times of the C2 rotation were almost independent of the interlayer cations but depended on the character of clay-layers.

133Cs NMR Spin-Lattice Relaxation Studies in Incommensurate Cs2MBr4(M=Cd, Hg)

The 133 Cs NMR spin-lattice relaxation times ( T 1 ) in Cs 2 MBr 4 (M=Cd and Hg) crystals were measured in a range of 207–369 K and 197–369 K, respectively. Critical exponents ζ at the normal-incom...

Electron spin carriers in halogen-bridged 1-d complexes with nondegenerate cdw ground state

We measured temperature dependences of ESR spectra and 1 H NMR spin-lattice relaxation time T 1 on recently prepared mixedvalence hetero-metal complexes [Pd(en) 2 ][PtX 2 (en) 2 ](ClO 2 ) 4 (en: ethylenediamine; X: Cl, Br) which consist of a 1-D structure of-X-Pd II -X-Pt IV -X-Pd II -X-Pt IV -X-chain giving a non-degenerated electronic ground state. The observed low-concentration of paramagnetic M III sites and also long 1 H NMR T 1 compared with those in homo-metal complexes [M II (en) 2 ][M IV X 2 (en) 2 ](ClO 4 ) 4 (M: Pt, Pd; X: Cl, Br) having the degenerated ground state, can be explained well by the hindrance of the formation of domainwall type spin solitons in the hetero-metal complexes. This result supports our previous conclusion of the neutral soliton formation in the homo-metal halogen-bridged complexes.

A study of electron spin dynamics and phase transition in [Co(H2O)6][SiF6] by single crystal 19F NMR spin–lattice relaxation time measurements

The temperature dependence of the 19F NMR spin–lattice relaxation time, T1, was measured for a [Co(H2O)6][SiF6] single crystal in the temperature range 170–320 K. A large hysteresis for the transition was observed: Tc≈265 K with increasing temperature, Tc≈245 K with decreasing temperature. The spin–lattice relaxation time of the unpaired electron spin in the Co2+ ion (T1e) was estimated from 19F NMR T1, which is dominated by a dipole interaction between the 19F nuclei and the electron spins of the Co2+ ions. The energy differences between the electronic ground and excited states in the Co2+ ion involving the Orbach process were estimated from the temperature dependence of T1e as Iµ=180 and 330 cm-1 above and below Tc, respectively. The investigations of the angular variations of 19F NMR T1 were performed at 291 and 193 K. Although T1 for the rotation about the c axis was invariant, the variation of T1 was observed in a plane containing the c axis at both temperatures. An anisotropy of T1e was not seen at either temperature.