NMR Spin-lattice Relaxation Times Research Articles

31P Spin‐Lattice Relaxation Times and Resonance Linewidths of Rat Tissue in Vivo: Dependence upon the Static Magnetic Field Strength

Phosphorus-31 NMR spin-lattice relaxation times and resonance linewidths of rat leg muscle, brain, and liver metabolites in vivo have been examined at 1.9-, 4.7-, and 8.5-T static magnetic field strengths. The resonance linewidths expressed in ppm that have been measured are independent of field strength. The spin-lattice relaxation times of muscle and brain phosphorus metabolites decrease linearly with increasing field strength while those of liver are constant over the range of static fields examined.

Cd-113 and Al-27 NMR relaxation study of aquoeus solutions adsorbed on silica gels and zeolite NaY

Cd-113 and Al-27 NMR parameters were used to investigate the Cd 2+ and Al 3+ hexaaquo metal ions adsorbed on some silica gels and zeolite NaY. No significant variations of the chemical shifts of cadmium and aluminum signals were observed for the aquated ions onto the pores with respect to those of the bulk solutions, thus indicating the absence of oservable specific interactions with the surface. On the contrary an increasing broadness of the signals as the pore size decreased as well as dramatic shortenings of Cd-113 and Al-27 NMR spin-lattice relaxation times were obtained. These variations were mainly ascribed to a reduced mobility of the aquo ions inside the pores. From the comparative analysis of Cd-113 and Al-27 relaxation data the correlation times of Cd(H 2O) 6 2+ and Al(H 2O) 6 3+ adsorbed species were estimated together with the quadrupolar coupling constants for Al(H 2O) 6 3+.

Solid-state silicon-29 spin-lattice relaxation in several 2:1 phyllosilicate minerals

Si NMR spin-lattice relaxation times have been measured for the two 2:1 layered phyllosilicates, sepiolite and rectorite. In sepiolite, it is shown that water contained within the structural channel provides a Si-H dipolar contribution to Si spin-lattice relaxation. In rectorite, hydrated interlayer paramagnetic cations provide very efficient relaxation either via spin diffusion or, more likely, via direct electron-nuclear relaxation facilitated by relatively high cation mobility. Of the two types of tetrahedral sheet in rectorite, the one further removed from the paramagnetic ions exhibits a relaxation time approximately 15 times longer than that for the closer sheet. Removal of the paramagnetic cations by exchange causes a significant increase in spin-lattice relaxation times for both types of silicate sheets. However, a smaller relaxation time difference still exists through a Si-H dipolar contribution to one type of sheet from the interlayer water. This contribution disappears when the interlayer water is removed by heating. The presence of considerable contributions from these mechanisms to Si spin-lattice relaxations in solid silicates will clearly be beneficial where the use of Si-H cross-polarization is either impossible or undesirable and where long relaxation times, typical of rigid solids, would otherwise be expected.

Driven-equilibrium single-pulse observation of T1 relaxation. A reevaluation of a rapid “new” method for determining NMR spin-lattice relaxation times

The little-used variable nutation angle method that permits the very rapid measurement of NMR spin-lattice relaxation times is reevaluated. The selection of the appropriate experimental conditions is discussed and the sensitivity of the deduced T 1′s to these conditions is explored. To facilitate the more widespread use of this time-saving, yet accurate, method the experimental conditions and procedures are reported in some detail. The basic method is extended to provide an extremely rapid method for measuring T 1. It is concluded that the driven-equilibrium single-pulse methods of measuring T 1, yield values for T 1 that are consistent with those obtained from the classical (180-τ-90) pulse sequence and have the advantage of being at least 100 times faster than the classical method.

Search for magnetic coupling between adsorbed 3He and small copper particles.

We have measured the NMR linewidth, line shift, and spin-lattice relaxation time ${T}_{1}$ of $^{3}\mathrm{He}$ adsorbed on small copper particles with an average diameter of 500 A\r{} in the temperature range 0.1--1 K. The linewidth and line shift depend upon the oxygen content of the copper particles. ${T}_{1}$ is also sensitive to the oxygen content. We discuss the connection between our results and the Kapitza resistances of metal-particle--liquid${\mathrm{\ensuremath{-}}}^{3}$He boundaries.

The stability, structure and reactivity of the outer sphere complex formed between the hexakis (d 4-methanol) cobalt(II) ion and pyridine in d 4-methanol

Proton NMR spinlattice ( Tι) relaxation times and chemical shifts were used to characterize the outer sphere complex formed between the hexakis (d 4-methanol) cobalt(II) ion and pyridine in d 4-methanol. Analysis of the bulk α-hydrogen Tι data of pyridine resulted in an outer sphere complex stability constant ( K os) which varied from 0.51 ± 0.16 M −1 at −60.0 °C to 0.62 ± 0.17 M −1 at −40.0 °C. The extrapolated K os value at 25.0 °C (1.0 M −1) is almost an order of magnitude larger than predicted larger predicted by theory. The combination of Tι and shift data suggested a preferred orientation of pyridine in the outer sphere of the [Co(CD 3OD) 6] 2+ ion. Further quantitative structural information was obtained by the application of the Solomon-Bloembergen relationship to the system studied. Pyridine dissociation rate constant data were combined with solvent exchange and equilibrium data to obtain values for the interchange probability or statistical factor (f) which ranged from (7.0 ± 3.7) × 10 −3 at −60.0 °C to (9.5 ± 4.7) × 1- −3 at −40.0 °C. These values are more than two orders of magnitude smaller than normally assumed and represent the first direct measurement of an ion-neutral outer sphere complex's reactivity. Implications regarding the relationship between outer sphere complex stability and reactivity are discussed.

1H NMR and Differential Scanning Calorimetry Studies of Molecular Motion and Phase Transition in Butylammonium Iodide

The temperature variations of 1H NMR spin-lattice relaxation times and 1H NMR second moments in n-C4H9NH3I and its N-deuterated analog were studied in a wide range of temperatures above 77 K. DTA experiments revealed a solid-solid phase transition between room and low temperature phases taking place at 268 K for the former salt and at 267 K for the latter. For rapidly cooled ( ≳ 2 Kmin-1 ) samples, another phase transition possibly between substable low temperature phases was found at ca. 210 K for the former and ca. 205 K for the latter. The transition entropy observed at 268 K was 33 J K-1 mol-1. This is much larger than the melting entropy (16 J K-1 mol-1), suggesting that butylammonium ions obtain their motional freedom mostly at the phase transition. In the low temperature phase of n-C4H9NH3I, the CH3 and NH3 + groups perform C3 reorientation about their respective symmetry axes with the activation energies 10.4 and 26.8kJmol-1, respectively. The rapidly cooled sample showed two T1 components attributable to the stable and substable low temperature phases indicating the coexistence of both phases. In the room temperature phase, the cations rotate rapidly about their long axes and partly conformational disorder of the alkyl chains takes place. The mechanism of the phase transitions is discussed.

Rotational transitions in monolayer molecular solids.

We have measured the NMR spin-lattice relaxation time and second moment for ethylene and methane monolayers adsorbed on a graphite substrate. Coverages were in the low-density-solid region. Substantial rotational mobility (apparently isotropic) is found for both systems at temperatures below the freezing transition. Some or all of this mobility is lost in a second, rotational transition for ethylene at about 35 K and for methane at about 17 K.

1H, 13C, and 31P nuclear magnetic resonance studies of cowpea mosaic virus: detection and exchange of polyamines and dynamics of the RNA.

1H and 13C NMR studies on cowpea mosaic virus (CpMV) revealed that polyamines are present in the middle (M) and upper bottom (BU) components obtained by CsCl density gradient centrifugation but not in the top (T) component; the lower bottom (BL) component contains trace amounts of polyamine. Dialysis of the BL component against spermidine led to incorporation of spermidine which gave rise to NMR peaks very similar to those observed with the natural M and BU components. NMR results conclusively demonstrate that polyamines in the M and BU components of CpMV are exchangeable with cesium ions and the exchange process is pH dependent. They also provide experimental support for the hypothesis that the BU to BL conversion results from the displacement of polyamines and possibly other natural counter ions of the RNA by cesium ions [G. Bruening, (1977), In "Comprehensive Virology" (H. Fraenkel-Conrat and R. R. Wagner, eds.), Vol. 11, pp. 55-141. Plenum, New York]. No sharp peaks, attributable to mobile amino acid side chains, were seen in spectra of an intact CpMV particle or its empty protein shell (T component). 31P NMR spin-lattice relaxation time and nuclear Overhauser effect parameters, which are sensitive to high-frequency motions, suggest that the RNA and, when present, the bound polyamine undergo internal motions with correlation times in the nanosecond range.

7Li NMR STUDIES ON IONIC CONDUCTOR IN THE SOLID SOLUTIONS Li3VO4-Li4TO4 (T = Ge, Si)

The 7Li NMR spectra of the solid solutions between Li3VO4 and Li4TO4 (T=Ge, Si) with different composition were investigated in the range 150-573 K. It was found that the values of 7Li NMR linewidth and spin-lattice relaxation time T1 in γII phase solid solutions are about an order of magnitude less than that of Li4GeO4, Li4SiO4, and Li3VO4 at room temperature. The temperature dependence of the number and the intensity ratio of 7Li NMR quadrupole satellite lines, and the composition dependence of the former were observed. It is suggested that the Li+ ions in samples of γII structural compositions move probably about one order of magnitude faster than that of the three pure compounds. The number of inequivalent sites occupied by the Li+ ions changes with the composition. The occupancy of the Li+ ions in the inequivalent sites changes with the temperature.

Association of alkali metal salts with polyene macrolides in methanol solution

23Na NMR spin-lattice relaxation times and 1H NMR chemical shift changes demonstrate weak association between alkali metal ions and polyene macrolides in methanol solution.

Molecular reorientations in the ordered phases of KCN and NaCN studied by NMR

We have measured $^{13}\mathrm{C}$ and $^{23}\mathrm{Na}$ NMR spin-lattice relaxation times as a function of temperature in KCN and NaCN in order to study the head-to-tail reorientations of the ${\mathrm{CN}}^{\ensuremath{-}}$ molecules in the two low-temperature ordered phases. We have combined our data with those of dielectric-response and ionic-thermal-conductivity measurements and have determined the correlation time ${\ensuremath{\tau}}_{c}$ of the reorientations over more than five decades. We found ${\ensuremath{\tau}}_{c}$ to be continuous through the electric-ordering phase transition with the same activation energy in both phases. In the elastically ordered phase of KCN, we detected small-angle ${\mathrm{CN}}^{\ensuremath{-}}$ reorientations about directions nearly parallel to the orthorhombic $b$ axis, leading to a small disorder in the ${\mathrm{CN}}^{\ensuremath{-}}$ orientation along that axis. We found the rms average of the angle between the C-N and $b$ axes to be 3.9\ifmmode^\circ\else\textdegree\fi{}. Our experiments resulted in the first direct observations of NMR relaxation arising from chemical-shift anisotropy in a solid.

1H NMR and Differential Scanning Calorimetry Studies on Molecular Motions and Phase Transitions in Butylammonium Bromide

Abstract The temperature dependences of the 1H NMR spin-lattice relaxation time and of the second moment of 1H NMR absorptions in the temperature ranges of 90–400 K and 77–456 K, respectively, were studied for butylammonium bromide and its N-deuterated analog. There are three known crystalline phases in butylammonium bromide as a result of two phase transitions which are confirmed by the present differential thermal analysis (DTA) experiments. The transition temperatures determined in this study are 200 and 249 K for butylammonium bromide. In the low temperature phase of this salt, CH3 groups perform the C3 reorientation with a relatively low activation energy of 11.0 kJ mol−1. The asymmetric T1 curves observed suggest the existence of some kind of disorder in the crystal structure of this phase. In the intermediate phase, the C3 reorientation of NH3+ groups and the 180 ° flip motion of butylammonium chains are activated with the activation energies of 23 and 14 kJ mol−1, respectively. The present NMR results for the high temperature phase indicate the occurrence of the conformational melting of the cation chains. The mechanism of the phase transitions is discussed.

Thickness dependence of the properties of plasma-deposited a-Si:H films — NMR studies

Both the NMR spectrum and spin-lattice relaxation time, T 1, have been measured on plasma-deposited a-Si:H films of different thickness, t, varying from 0.1 μm to 10 μm, prepared on heated substrates under similar conditions. The NMR spectrum shows the standard two-component line in all samples with substantial differences in H content with thickness: ≈ 10 atomic % for films with t ⩾ 1 μm, the normal result, but ≈ 30% for t = 0.1 μm. This indicates that the thin sample is similar to films that have been prepared on room temperature substrates and have poor electronic properties. The NMR T 1 versus temperature exhibits the standard u-shaped curve with a minimum near 50K for all samples, due to the presence of a small amount of molecular H 2 trapped in voids. The thin sample (t = 0.1 μm) shows an additional relaxation mechanism, not present in the samples with t ⩾ 1 μm, that causes T 1 to drop exponentially as the temperature is raised from 200K to 300K. This is most likely due to an electronic relaxation mechanism present in the thin samples but not in the thicker materials.

Spin-lattice relaxation time and chemical shift for structural determination in crude oil and petroleum products by carbon-13 nuclear magnetic resonance spectrometry

/sup 13/C NMR spin-lattice relaxation times of dominant resonances observed in the spectra of the oil samples were determined for solutions without and with a paramagnetic relaxation reagent, Cr(acac)/sub 3/, added. The average carbon chain length of the straight chain alkanes which are present in the petroleum samples can be estimated from the relaxation data, and it agrees with that determined from the NMR intensity measurements. In the aliphatic region of the /sup 13/C spectra, electron-nuclear spin-lattice relaxa

Dynamics of non-rigid molecules. - I. — 13C T 1 NMR study of the reorientational and ring-puckering motions of cyclopentene in the liquid state

The 13 C NMR spin-lattice relaxation time T 1 and Nuclear Overhauser Effect (NOE) of the three distinct carbons of cyclopentene have been measured between 220 and 300 K in order to obtain some information about the ring-puckering motion in the liquid state. The data are first analysed under the hypothesis that the rotational diffusion of cyclopentene resembles that of a rigid asymmetric top. The slower rotation is then calculated to occur around the pseudo-C 5 axis and large differences are found between the three rotational diffusion constants D xx , D yy , D zz . These results seem to have little physical meaning. Furthermore they do not agree with those obtained by infrared, Raman and quasielastic neutron scattering. Therefore the ring-puckering motion has to be considered as an efficient 13 C relaxation mechanism. Although parameters needed to describe both external and internal motions cannot all be determined from the information available one can qualitatively show that at 300 K the molecule executes about (5±4), 10 12 jumps s −1 between its two equivalent bent conformations characterized by a puckering angle of 25 to 30°. The activation energy associated with this process seems to be low since the jump rate is still about (1±0.5).10 12 s −1 at 220 K. On the other hand, the whole molecule rotation is found to be nearly isotropic in agreement with the conclusions of the optical and neutron spectroscopies D r =(0.22±0.02)•10 12 s −1 at 300 K with an activation energy of 5.1 kJ.mole −1 Mesure du temps de relaxation spin reseau et de l'effet nucleaire Overhauser afin d'etudier la dynamique d'inversion du cyclopentene en phase liquide. Le mouvement d'inversion du cycle est considere comme un mecanisme efficace de relaxation de 13 C. La molecule execute environ (S±4).10 12 sauts par seconde a 300 K entre ses deux conformations equivalentes, pliees selon un angle de 25 a 30°

1H NMR study of the α phase of Mg 2NiH x system

Hydrogen behavior in the α phase of Mg 2NiH x system was studied by 1H NMR. 1H NMR spectra and spin-lattice relaxation times, T 1 and T 1ρ, of Mg 2NiH 0.22 were measured in the temperature range between 100 and 480 K. The drastic change in the linewidth is observed between 170 and 340 K, and 1H rigid lattice is observed below 170 K, from which it is deduced that the hydrogen atoms are randomly distributed in α-Mg 2NiH x . The relaxation mechanism for t 1 is the paramagnetic one, while the T 1ρ value is determined partially by hydrogen diffusion. The hydrogen diffusion rate has been determined from the linewidth and the T 1ρ value. The paramagnetic relaxations observed in T 1 and T 1ρ have been discussed relating to the hydrogen diffusion.

35Cl NQR and 1H NMR studies of [C(NH 2) 3]AuCl 4, [C(NH 2) 3] 2PtCl 4, and [C(NH 2) 3] 2PdCl 4

The temperature dependence measurements of 35Cl NQR frequencies and 1H NMR spin-lattice relaxation time T 1 were carried out for guanidinium tetrachloro-aurate(III), -platinate(II), and -palladate(II). The gold(III) complex showed four NQR lines at various temperatures between 77 and 344 K, while the platinum-(II) and palladium(II) complexes gave two NQR lines in the temperature ranges 77–169 K and 77–220 K, respectively. An unusual phase transition was located at 363 K for the gold(III) complex. The high-temperature phase was easily supercooled. All the complexes studied yielded a T 1 minimum attributable to the reorientation of the planar cation about its C 3 axis. The motional parameters were evaluated. The Zeeman-quadrupole cross relaxation between protons and chlorine nuclei was observed for the platinum(II) and palladium(II) complexes at various temperatures below room temperature, while it was also detected for the high-temperature phase of the gold(III) complex.

C-13 NMR Spectra and Spin-Lattice Relaxation Times of Poly(alkyl vinyl ether)s

13C NMR spectra of isotactic-rich poly(alkyl vinyl ether)s were measured in toluene-d8 at 110°C, with some improvements on peak separation. The 13C spin-lattice relaxation times (T1’s) for syndiotactic sequences were consistently longer than those for isotactic ones, in contrast to the case of polypropylene and polymethacrylates, in which the T1’s for isotactic sequences are longer than those for syndiotactic sequences. The nuclear Overhauser enhancement factors for the polymers of methyl and t-butyl vinyl ethers were close to the theoretical maximum. These results indicate higher flexibility of the syndiotactic sequences in poly(alkyl vinyl ether)s.

Effect of electron correlation on the magnetic properties of expanded liquid sodium

The magnetic susceptibility, NMR Knight shift and spin-lattice relaxation time of sodium have been measured up to 1000 degrees C. Strong deviations from simple interacting electron-gas behaviour are found above 400 degrees C. The paramagnetism is still further enhanced and the NMR data show that changes in the wavevector dependence of the susceptibility consistent with fluctuations towards a spin density wave occur. Such behaviour is expected for an itinerant antiferromagnet above its ordering temperature as predicted by some recent theories of the metal-nonmetal transition in an expanded fluid metal.