NMR Spin-lattice Relaxation Times Research Articles

Quenched molecular reorientation and angular momentum for liquids confined to nanopores of silica glasses

The results of a theoretical and experimental study of the confinement effects on molecular dynamics of nonpolar liquids in porous silica glasses prepared by the sol-gel process are discussed. The natural abundance 13C and 33S NMR spin-lattice relaxation times of liquid CS2 are reported as a function of pore radius in the range from 15 Å to 102 Å over the temperature range of 168 K to 293 K. Since spin-rotation interactions dominate the 13C relaxation at higher temperatures these experiments allowed us for the first time to follow the confinement effects on angular momentum correlation times. The low-temperature 13C T1 data and the 33S T1 data provide information about reorientational motions. In order to interpret the experimental NMR relaxation data, a theoretical model for anisotropic molecular reorientation and angular velocity, which accounts for the motional behavior of nonpolar liquids confined to nanopores, is proposed. This model predicts an increase of the reorientational and angular momentum correlation times when the pore size is decreased. Application of this theoretical model to the interpretation of the CS2 NMR relaxation data and to earlier relaxation results obtained for confined nonpolar cyclohexane-d12 liquid proved successful.

Measurement of Aperture and Multiphase Flow in Fractures With NMR Imaging

Summary Nuclear magnetic resonance imaging (NMRI) techniques were used for the measurement of the spatial distribution of apertures and two-phase fluid distributions in rock fractures. Rock models of known apertures were used to validate the NMRI technique. NMRI aperture values were in good agreement with nominal and hydraulic aperture values. The fracture signal in porous rock was isolated by NMR spin-spin relaxation times. Areal distributions of oil and water in an immiscible fracture flow were resolved on the basis of their NMR spin-lattice relaxation times.

A 1H NMR study of molecular motions in chloropentamethylbenzene

The temperature dependence of the 1H NMR spin-lattice relaxation time T 1 has been measured for solid chloropentamethylbenzene in the range 90–380 K. A single T 1 minimum of 36.5 ms was observed around 278 K at the Larmor frequency of 18 MHz and has been assigned to in-plane molecular reorientation about the pseudohexad C′ 6 axis over the nonequivalent potential wells. With the aid of the reported X-ray analyses, the results have been analyzed by employing the method developed by Anderson. The activation energy has been evaluated as 27 kJ mol −1 which amounts to nearly the same value as hexamethylbenzene. A gradual decrease of T 1 below 150 K was attributed to the methyl groups rotation about their C 3 axes over the barriers of 3.0 kJ mol −1.

Molecular dynamics of methoxy polyoxyethylene macromonomer micelles in the absence and presence of SDS micelles using 1H NMR spin-lattice relaxation time measurements

Molecular dynamics studies performed by 1H NMR spin-lattice relaxation time measurements suggest the occurrence of a mutual interaction between aqueous micelles of a macromonomer (acrylic ester of ω-methoxypolyethyleneglycol, Mol. wt. 460) and sodium dodecylsulfate (SDS). The α-CH 2 of SDS and ω-OCH 3 of the macromonomer seem to contribute to the maximum electrostatic interaction. The counterion association for SDS micelles is also hindered in the presence of larger macromonomer micelles as observed by conductivity measurements.

Indications for change of dynamical regime in pure liquids

13C NMR spin-lattice relaxation times T 1 of quinoline (1) of some of its methyl derivatives (quinaldine (3), lepidine (4), 6-methylquinoline (5), 7-methylquinoline (6)) of isoquinoline (2), and of two quinoline related compounds having two nitrogen atoms in one fused sixmembered ring skeleton (quinazoline (7), quinoxaline (8)) have been measured in pure liquid form as a function of temperature. The temperature range is not the same for all the compounds. It is at least 46 K for (7) and it reaches 93 K for (4). ln T 1 is plotted as a function of the inverse of the absolute temperature T −1. For (2), (6), (7) and (8) the data can be accounted for by only one activation energy, for (1), (3), (4) and (5) by two activation energies one above temperature T t, one below. For all these compounds the high temperature relaxation corresponds to an energy barrier which is less than 20·5 kJ mol−1, and the low temperature process (when a two energy barrier regime exists) corresponds to an energy barrier close to 30 kJ mol−1. For quinoline and isoquinoline, the saturated specific heat C s plotted as a function of T exhibits behaviour similar to that of ln T 1 studied as a function of T −1. The results reported here suggest the existence of a dynamical transition in the liquid state at a given temperature, a process somewhat similar to that proposed for some super-cooled liquids.

13C NMR spin–lattice relaxation times as a probe of local polymer dynamics in plasticized polyethers

Download options Please wait... Article information DOI https://doi.org/10.1039/A604781E Article type Paper Download Citation J. Mater. Chem., 1997,7, 193-201 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions 13 C NMR spin–lattice relaxation times as a probe of local polymer dynamics in plasticized polyethers M. Forsyth, P. Meakin and D. R. MacFarlane, J. Mater. Chem., 1997, 7, 193 DOI: 10.1039/A604781E To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author M. Forsyth P. Meakin D. R. MacFarlane

Nuclear magnetic resonance and electron spins: Some history, ancient and in the making

Abstract Scaling relationships for Nmr spin-lattice relaxation time T 1 and Gaussian transverse relaxation tme T 2G c reviewed and applied to analyse experiments in the normal state of YBa2Cu4O8. Studies of T 2G in the superconducting state are analysed using the theory of Pines and Wrobel to show a preference for d-state orbital pairing over anisotropic s-state. Data on 13C Nmr in the normal and superconducting state of the two dimensional organic conductor (ET)2Cu[N(CN)2]Br are presented and shown to have great similarity to that of the cuprates.

1H and 19 F NMR Study of Cation and Anion Motions in Guanidinium Hexafluorozirconate

Abstract Proton and fluorine NMR second moments and spin-lattice relaxation times of polycrystalline guanidinium hexafluorozirconate and its deuterated analogue were studied in laboratory (60 MHz) and rotating (H1 = 20 G) frames over a wide range of temperature. An analysis of the experimental results enabled us to reveal a dynamical inequivalence of two crystallographically independent cations and an unexpected high mobility of nonspherical anion dimers. A comparison of the ions dynamics in 2:1 complex studied with the guanidinium 1:1 and 3:1 complexes has shown a significant contribution of the hydrogen bonds to the potential barriers hindering the anion reorientations. At low temperatures a proton motion in the hydrogen bond and at 400 K a solid-solid phase transition have been discerned.

Dynamics of β-Cyclodextrin hydrate: solid state 2H NMR studies

The 2H NMR spectra and spin-lattice relaxation times of powder samples of C-deuterated β-cyclodextrin (CD) hydrate β-CD-2,3,6,6- d 28 · 11H 2O) 1 and O-deuterated β-CD hydrate (β-CD d 21 · 11H 2O- d 22 ) 2 were measured in the temperature ange from 160 to 295 K at 46 MHz. Information about the degree and time scales of dynamic disorder processes was obtained by comparing the powder patterns with computer simulations and analyzing the multi-exponential recovery curves. The data on 1 provide evidence for small-angle reorientations of the C-D groups with a correlation times τ c ∼- 10 −7 s at 295 K and suggest that the β-CD macrocycles do not move as a rigid entity. The NMR responses of 2 at 295 K show two components and are consistent with the hydroxyl O-D groups undergoing 2-fold reorientational jumps with τ c ∼- 10 −8 s and with the water molecules exchanging between all sites and a significant fraction performing reorientational jumps with τ c ∼- 10 −8 s. Below 235 K, at least three components are evident: two were associated with slow reorientations ( τ c ∼- 10 −4 s at 60 K) of hydroxyl and water O-D groups, and the third with a small number of water molecules for which rapid eorientations ( τ c < 10 −7 s) persist at 160 K. These dynamic features are considered in terms of the known structure and the indings of other techniques. These results suggest that the reorientation jumps of the hydroxyls and water molecules are lower than previously thought.

Water permeability in wheat root protoplasts determined from nuclear magnetic resonance relaxation times

Diffusional water permeability coefficients (P d) of wheat root protoplasts were determined by measuring NMR spin-lattice (T 1) and spin-spin (T 2) relaxation times in the absence and presence of added Mn 2+ at various concentrations. These measurements enabled the determination of exchange times ( λ a) for water molecules between cells and their surrounding medium. It was found that λ a determined from T 1 measurement was much larger than λ a determined from T 2 measurement: ca. 135 ms versus 9.4 ms. Whilst λ a determined by the two methods do not agree, they are each similar to individual values of λ a from the literature using T 1 and T 2 measurements. The P d value of 3.0 × 10 −5 m s −1 determined from T 1 measurements is lower than the osmotic water permeability (P f) of wheat root cells (P f = 8.6 × 10 −5 m s −1) obtained from pressure probe measurements and can be accounted for by the presence of the water selective channels. The T 2 measurements, on the other hand, give rise to P d value of at least four times greater than the P f value determined from pressure probe measurements. Furthermore, T 2 relaxation of protoplasts in the absence of added Mn 2+ showed multi-exponential decay. These differences between the T 1 and T 2 measurements might be attributed to the presence of endogenous paramagnetic ions in the cells and their binding to cell membranes. In the absence of the detailed knowledge of the distribution of paramagnetic ions in plant cells, it is proposed that NMR T 1 rather than T 2 measurements be used to obtain meaningful values of λ a.

NQR and NMR Studies of Phase Transitions in R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4)

Abstract 39K, 87, 85Rb, 133Cs, 205T1, and 1, 2H NMR spin-lattice relaxation times T1 and 14N NQR spin-lattice relaxation times T1Q were determined for R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4). T1 of 39K and 87Rb showed very short values in the incommensurate phase as compared with those in the other phases. When the commensurate-incommensurate phase transition point is approached from below, 14N T1Q of the R = K, Rb, Tl, and NH4 compounds showed rapid decrease. On the other hand, that of the R = Cs compound began to decrease first after passing beyond the corresponding transition point. The difference of the T1Q behavior may be ascribed to the difference of the condensed phonon mode in the incommensurate phase.

15N and 133Cs Solid NMR Studies on Ionic Dynamics in Plastic CsNO2

The temperature dependence of the 15N and 133Cs NMR spin-lattice relaxation times, the 15N spin-spin relaxation time, and the 15N and 133Cs spectra of CsNO2 was observed in the plastic phase (209.2 &lt; T &lt; 673 K (m. p.)) and the low-temperature phase (Phase II). In Phase II we found the NO- 2 180°-flip, which could be attributed to the anomalous increase of the heat capacity curve, and determined the activation energy of this motion to be 8.7-11.7 kJ mol-1. The 15N and 133Cs spectra in this phase are inconsistent with the reported crystal structure R3̅m and can be explained by lower crystal symmetry. In the plastic phase we detected a new anionic motion with 11 kJ mol-1 , an isotropic NO- 2 reorientation with 8.5-9 kJ mol-1, and ionic self-diffusion with 47 kJ mol-1. The presence of ionic self-diffusion was confirmed by measuring the electrical conductivity.

Motion of Water Molecules and Hydrogen Bonds in Zinc Hexachlorostannate (IV) Hexahydrate as Studied by 1H NMR and 35Cl NQR

Abstract The 1H NMR spin-lattice relaxation time T1, 35Cl NQR frequency νQ, and 35Cl NQR spin-lattice relaxation time T1Q of [Zn(H2O)6] [SnCl6] (zinc hexachlorostannate(IV) hexahydrate) have been measured at temperatures between 77 and 350 K. The NQR spin echo signal with νQ = 15.689 MHz at 77 K showed a positive temperature coefficient attributable to O-H-Cl type H-bonds in the crystal. νQ at 77 K is strongly correlated with the electronegativity χM of the metal M in the series of stannates [M(H2O)6] [SnCl6] (M = Mg, Ca, Mn, Co, Ni, Zn). A T1 minimum observed for the Zn salt is ascribed to 180° flips of water molecules with an activation energy of 20 kJ mol-1. The motion is influenced by repulsive forces among the water molecules within a cation rather than by attractive forces between the H-bonded H and CI atoms. T1Q proved to be mainly governed by lattice vibrations, weakly modulated by the fluctuating electric field gradient caused by the 180° flip motions.

Attractive Potential Effect on the Rotational Correlation Times for Benzene-d6 in Organic Solvents

Abstract 2H NMR spin-lattice relaxation times have been measured to obtain the rotational correlation times τ2R for benzene C6D6 (50 mol m−3) in various organic solvents, such as benzene (C6H6), hexane, decane, carbon tetrachloride, chloroform, dichloromethane, methanol, ethanol, 1-propanol, 1-butanol, and acetonitrile over the widest possible range of temperature. Plots of the determined values of τ2R against solvent viscosity η divided by temperature T are linear in the apolar and polar aprotic solvents, as predicted by the Stokes–Einstein–Debye (SED) law. However, the plots of τ2R vs. η/T in the alcohols are concave upward, the slope in the high temperature region being ca. 2 times as large as that in the low temperature region. The nonlinearity and the decrease in the slope reflect the influence of the hydrogen-bonded solvent structure. For the benzene rotation in solutions, fairly good positive linear correlations are found between the slopes and the negative dissolution enthalpies at infinite dilution at room temperature. These results indicate an important role played by attractive solute–solvent interactions in controlling the molecular rotation in solution.

Ionic conduction and mixed cation effect in silicate glasses and liquids: 23Na and 7Li NMR spin-lattice relaxation and a multiple-barrier model of percolation

Abstract The mixed cation effect in glasses affects transport properties such as diffusion and ionic conductivity. The temperature dependence of 7Li and 23Na NMR spin-lattice relaxation times, T1, have been measured in a series of trisilicate (Na2Si3O7, NaRbSi3O7, NaCsSi3O7 and NaCa0.5Si3O7) and disilicate (Li2Si2O5, LiKSi2O5 and LiBa0.5Si2O5) glasses in order to understand the atomic scale mechanism of this effect. Diffusion-induced NMR spin-lattice relaxation of alkali cations is shown to be affected by a mixed cation effect which tends to shift the T1 minimum to a higher temperature and increases the slope of the T1 vs. 1000 T curve on the low temperature side of the minimum. These changes are consistent with an effective reduction in the number of hopping sites available to the alkali cation in a mixed cation glass. As a result the high energy cutoff for percolation in a disordered barrier height landscape increases significantly on going from a single alkali to a mixed alkali (or, alkali-alkaline earth) glass. The dc conductivities calculated on the basis of a random walk model with different percolation thresholds for single and mixed alkali glasses are in reasonably good agreement with the experimental results. This interpretation of the NMR spin-lattice relaxation results, thus, successfully combines the two recent models — that of Svare et al. on the general relationship between ionic transport and spin-lattice relaxation and of Maass et al. on mixed alkali effect resulting from strong energetic preference for hopping associated with percolation transition. In addition, the mixed alkali effect can be generalized to mixed alkali-alkaline earth systems.

13C NMR studies of the molecular dynamics of chlorpromazine in solution

The optimum structure, which is expected to lead to biological activity, of chlorpromazine hydrochloride salt (compound ( I)) in solution was determined on the basis of NMR data and molecular orbital calculations; compound ( I) favours a bent structure in which the side-chain tilts toward the chlorinated benzene ring. The molecular mobility of compound ( I) in CDCl 3 and D 2O was also examined on the basis of 13C NMR spin-lattice relaxation time ( T 1). T 1 depends on the magnetic field strength and the solvent. The dependence indicates that the molecular mobility of compound ( I) is larger in D 2O than in CDCl 3

13C NMR studies of the molecular dynamics of chlorpromazine in solution

The optimum structure, which is expected to lead to biological activity, of chlorpromazine hydrochloride salt (compound ( I)) in solution was determined on the basis of NMR data and molecular orbital calculations; compound ( I) favours a bent structure in which the side-chain tilts toward the chlorinated benzene ring. The molecular mobility of compound ( I) in CDCl 3 and D 2O was also examined on the basis of 13C NMR spin-lattice relaxation time ( T 1). T 1 depends on the magnetic field strength and the solvent. The dependence indicates that the molecular mobility of compound ( I) is larger in D 2O than in CDCl 3

Structural and dynamic properties of the 1,10-dibromodecane/urea inclusion compound, investigated by variable-temperature powder X-ray diffraction, solid-state2H NMR lineshape analysis and solid-state2H NMR spin–lattice relaxation time measurements

Powder X-ray diffraction and solid-state 2H NMR lineshape analysis and spin–lattice relaxation time measurements have been used to investigate structural and dynamic properties of the 1,10-dibromodecane/urea inclusion compound. This solid has the characteristic urea ‘host’ tunnel structure of conventional urea inclusion compounds and the 1,10-dibromodecane ‘guest’ molecules are located within these tunnels.Variable-temperarture powder X-ray diffraction studies have demonstrated that a phase transition (at ca. 140–146 K) in 1,10-dibromodecane is associated with a change in the (average) symmetry of the urea tunnel structure from hexagonal (high-temperature phase) to orthorhombic (low-temperature phase) and is associated with only a minor structural distortion. From 2H NMR spectroscopy of [2H20]1,10-dibromodecane/urea, the dynamic properties of the guest molecules are best described as rotational diffusion in a six-fold cosine potential, and there is no significant discontinuity in this dynamic process at the phase-transition temperature. The results suggest that the dynamic properties of all CD2 groups in the guest molecule are indistinguishable (on the timescale of the 2H NMR technique). 2H NMR spectroscopy of 1,10-dibromodecane/[2H4]urea indicates that, at sufficiently high temperature, the urea molecules undergo 180° jumps about their CO bonds. Activation parameters have been determined for the reorientational motions of the 1,10-dibromodecane and urea molecules.The structural and dynamic properties of the 1,10-dibromodecane/urea inclusion compound, determined in this work, are compared in detail with the corresponding properties determined previously for alkane/urea inclusion compounds.

H and 13C NMR Relaxation Studies of Molecular Dynamics of the Thyroid Hormones Thyroxine, 3,5,3‘-Triiodothyronine, and 3,5-Diiodothyronine

1H and 13C NMR spin-lattice relaxation times and 13C{1H} nuclear Overhauser enhancement factors have been measured for the thyroid hormones thyroxine, 3,5,3'-triiodothyronine, and 3,5-diiodothyronine, with the aim of determining the internal molecular dynamics in these molecules. Spin-lattice relaxation times of protons on the two aromatic rings of these hormones show remarkable differences, with values for the hydroxyl-bearing ring being a factor of 4-12 times larger than those for the alanyl-bearing ring. This difference is not mirrored in the 13C relaxation times, which are identical within experimental error for the two rings. The 13C data show that the mobility of the two rings is similar, and therefore the difference in proton spin-lattice relaxation times arises because the protons of the alanyl-bearing ring are efficiently relaxed by interactions with neighboring protons on the side chain. Quantitative analysis of the 13C relaxation data shows that there must be a significant degree of internal flexibility in the thyroid hormone molecules. The NMR data suggest that in methanol the molecules tumble with an overall correlation time of approximately 0.35 ns, but that rapid internal motion (in the form of jumps between two stable conformations) occurs on a 30-fold faster time scale. When combined with previous variable temperature NMR studies that show interconversion between proximal and distal forms of the outer ring on the microsecond time scale, the results provide a complete description of the conformations and both fast and slow internal motions in the thyroid hormones. The findings suggest that modeling studies of thyroid hormone interactions with receptor proteins should take into account the possibility that these internal motions are present. In effect, the thyroid hormones may likely populate a larger range of conformations in the bound state than might be inferred from just the lowest energy forms seen in the crystal and solution states.

Charge transport and water molecular motion in variable molecular weight nafion membranes: High pressure electrical conductivity and NMR

Measurements of the electrical conductivity and deuteron NMR spin-lattice relaxation times ( T 1) in three different molecular weights of acid form NAFION conditioned at various levels of relative humidity have been carried out. Complex impedance studies were made along the plane of the film at frequencies from 10-10 8 Hz at room temperature and pressures up to 0.3 GPa. The high pressure electrical data were only obtained for water contents less than 8 wt%. The NMR measurements were also made at room temperature and pressures up to 0.25 GPa. The NMR data are primarily for water contents greater than 6 wt%. The calculated activation volume exhibits a large decrease (from 16 to 3 cm 3/mol) as the water content is increased from 2.4–8 wt%. In addition, the activation volumes are larger and the electrical conductivity is smaller for the higher molecular weight material. These results represent further evidence that the transport mechanism in low water content materials is dominated by segmental motions of the polymer chain and that proton transport and water molecular rotation are correlated. The activation volumes extracted from the NMR data show only a small further decrease as the water content is increased from 6–22 wt%. Possible explanations for the high water content NMR pressure results are given.