Proton Spin-lattice Relaxation Rate Research Articles

Proton $T_1$ and $T_2$ Relaxivities for $CH_2$ and $CH_3$ Peaks in Crude Oil Measured by 400 MHz NMR

Petroleum fluid has been extensively studied at low magnetic fields by Nuclear Magnetic Resonance (NMR) Spectroscopy, but high field NMR studies are rarely found in this area. The aim of this study is to determine the proton spin-lattice relaxation rate (1/T1), T1 relaxivity (R1), proton spin-spin relaxation rate (1/T2) and T2 relaxivity (R2) of paraffinic CH2 and gamma CH3 peaks. For this purpose, crude oil samples were taken from 3 separate wells in the Batman region. Using these samples, 3 different sets were prepared from a mixture of deuterated chloroform (CDCl3) and crude oil. The total volume of each prepared mixture was 1 mL. The crude oil content in each set was changed from 0.05 mL to 0.20 mL in 0.05 mL steps.. Special care has been taken to ensure the best shimming of the NMR spectrometer operating at 400 MHz. T1 measurements were performed using an inversion recovery (IR) pulse sequence. 1/T2 values were determined from the half-height line widths of CH2 and CH3 peaks. 1/T1 and 1/T2 rates and all relaxivities were found to vary from well to well. This change is due to the fluid composition of the wells. The 1/T2 rates and R2 relaxivities were found to be considerably greater than the 1/T1 rates and R1 relaxivities. R2 relaxivities for CH3 were also 2-5 times greater than for CH2.The higher 1/T2 and R2 relaxivities compared with 1/T1 and R1 were attributed to the additional CDCl3-mediated relaxation mechanisms. In conclusion, available data show that high 1/T2 rates and R2 relaxivities measured in the high field NMR laboratory can be applied to separate crude oil from other fluids in the oil field.

NMR Relaxometry: The Canonical Case Glycerol.

We present a quantitative description of the proton spin-lattice relaxation rate R1(T,ω) of glycerol including temperatures from 191 to 360 K and a frequency range 10 kHz < ω/2π < 20 MHz covered by the field-cycling technique. The analysis encompasses the data compiled by Noack and co-workers in 1971, so far, the most complete data set (10 kHz > ω/2π < 117 MHz). Applying frequency-temperature superposition, master curves are constructed extending over 15 decades in frequency/time. They are described by contributions reflecting translational and rotational dynamics mediated by inter- and intramolecular relaxation pathways. The rotational part of the spectral density/susceptibility shows high similarity with those reported by dielectric spectroscopy or photon correlation spectroscopy (PCS). In addition to a Cole-Davidson-like peak, a high-frequency "excess wing" has to be accounted for. Quantitative agreement with the PCS susceptibility is found which probes the same order of the rotational correlation function. The translational contribution is reproduced by applying the force-free hard sphere model, describing diffusion of dipolarly coupled spin systems. Rotational and translational time constants are compared to those from other techniques. Our approach is paradigmatic for the analysis of spin relaxation in glass-forming liquids. It also solves long-standing deficiencies regarding the analyses of deuteron relaxation. Moreover, the case of glycerol is special as its large separation of translation and rotation dynamics, probably because of its hydrogen bond network, is not found in nonassociated liquids.

Metal-Ligand Recognition Index Determination by NMR Proton Relaxation Study.

In this study, we developed and validated a new proposed parameter quantifying the interaction strength between natural and/or synthetic molecules with paramagnetic metal ions. The Metal ion Recognition Index, Miri, is a quantitative parameter to describe the proton environment and to define their involvement in the inner and/or outer sphere of the paramagnetic metal ion. The method is based on the analysis of NMR proton spin-lattice relaxation rates of a specific ligand in both the diamagnetic and paramagnetic conditions. The proposed procedure is also useful to calculate the ligand proton spin-lattice relaxation rate in the paramagnetic bound conditions, which is typically very difficult to determine experimentally. Miri was used to compare the ligand proton involvement toward different paramagnetic species, in particular the Copper(II)-Piroxicam system. Copper(II)-Piroxicam complex is one of the most active anti-inflammatory and anti-arthritic species. Miri provides an opportunity to improve our knowledge of metal-ligand complexes that play a fundamental role in bioinorganic interactions.

A proton T1-nuclear magnetic resonance dispersion study of water motion in snowflakes and hexagonal ice

ABSTRACTSnowflakes and ordinary hexagonal ice were studied measuring water proton spin–lattice relaxation rate -nuclear magnetic resonance dispersion (NMRD) profiles at proton Larmor frequencies ranging from 1 to 30 MHz and at different temperatures ranging from C to C. The spin–spin relaxation rate 1/ was determined at a single Larmor frequency of MHz. The high-field wing of the proton -NMRD profile was characterised by two parameters: a correlation time which described the dipole–dipole spectral density, and the relaxation rate at low fields which was determined from . The correlation time depended on the dynamic model used. A rotation diffusion model yield approximatively s at C to about s at C, whereas for a more realistic six-site discrete exchange model, the correlation times decreased slightly to about 80% for the same temperature interval. Proton dipole–dipole interactions were divided into intramolecular and intermolecular contributions where the intermolecular contribution was about 0.4–0.8 × the intramolecular contribution. It was not possible to discriminate between the dynamic models or to detect ice/water interface effects by comparing the NMRD data from snowflakes with ordinary hexagonal ice data.

Influence of underlying local organisations in typical nematic phase of 6CHBT and induced nematic phase of bicomponent liquid crystalline systems 4DBT–12CB – a Fast Field Cycling NMR investigation

ABSTRACTVariable-temperature proton magnetic relaxation dispersion (PMRD) profiles are collected in the induced nematic phases of the binary liquid crystalline mixtures composed of smectic mesogens: 5-butyl-2-(4-isothiocyanatophenyl)-1,3-dioxane (4DBT) and 4′-dodecyl-4-cyanobiphenyl (12CB) and the low viscous nematogen 4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT), with a view to assess the influence of local organisations on the power spectrum of director fluctuation modes. Two distinct compositions of the binary mixture i.e. 50 mol% of 12CB (without a smectic phase) and 70 mol% of 12CB (with a smectic phase) are used. Fast Field Cycling nuclear magnetic resonance relaxometry is employed to measure proton spin-lattice relaxation rates (R1) as a function of Larmor frequency (10 kHz–30 MHz). PMRD data analysis with the choice of a suitable model indicated nematic clusters of moderate size (~200 Å) found in the broad nematic region of 50 mol% 12CB, whose size is almost invariant with temperature. On the other hand, cybotactic clusters, i.e. local smectic organisations of relatively larger size (~2000–3000 Å), are observed near the nematic–smectic transition (T > TAN) of 70 mol% 12CB. Interestingly, the shape geometry of such local organisations accessed from PMRD analysis is weakly anisotropic near TAN, while being isotropic near TNI for 70 mol% 12CB.

ChemInform Abstract: Review of NMR Studies of Nanoscale Molecular Magnets Composed of Geometrically Frustrated Antiferromagnetic Triangles

AbstractReview: 68 refs.

Intrinsic Proton NMR Studies of Mg(OH)2 and Ca(OH)2

We studied the short proton free induction decay signals and the broad ^1H NMR spectra of Mg(OH)2 and Ca(OH)2 powders at 77-355 K and 42 MHz using pulsed NMR techniques. Using a Gaussian-type back extrapolation procedure for the obscured data of the proton free induction decay signals, we obtained more precise values of the second moments of the Fourier-transformed broad NMR spectra than those in a previous report [Y. Itoh and M. Isobe, J. Phys. Soc. Jpn. Vol. 84, 113601 (2015)] and compared with the theoretical second moments. The decrease in the second moment could not account for the large decrease in the magnitude of the intrinsic proton spin-lattice relaxation rate 1/T_1 from Mg(OH)2 to Ca(OH)2. The analysis of 1/T_1 $propto$ exp(-E_g/k_BT) with E_g~0.01 eV points to a local hopping mechanism, and that of 1/T_1 $propto$ T^n with n~0.5 points to an anharmonic rattling mechanism.

(1)H NMR Relaxation Study of a Magnetic Ionic Liquid as a Potential Contrast Agent.

A proton nuclear magnetic relaxation dispersion (1)H NMRD study of the molecular dynamics in mixtures of magnetic ionic liquid [P66614][FeCl4] with [P66614][Cl] ionic liquid and mixtures of [P66614][FeCl4] with dimethyl sulfoxide (DMSO) is presented. The proton spin-lattice relaxation rate, R1, was measured in the frequency range of 8 kHz-300 MHz. The viscosity of the binary mixtures was measured as a function of an applied magnetic field, B, in the range of 0-2 T. In the case of DMSO/[P66614][FeCl4] the viscosity was found to be independent from the magnetic field, while in the case of the [P66614][Cl]/[P66614][FeCl4] system viscosity decreased with the increase of the magnetic field strength. The spin-lattice relaxation results were analyzed for all systems taking into account the relaxation mechanisms associated with the molecular motions with correlation times in a range between 10(-11) and 10(-7)s, usually observed by NMRD, and the paramagnetic relaxation contributions associated with the presence of the magnetic ions in the systems. In the case of the DMSO/[P66614][FeCl4] system the R1 dispersion shows the relaxation enhancement due to the presence of the magnetic ions, similar to that reported for contrast agents. For the [P66614][Cl]/[P66614][FeCl4] system, the R1 dispersion presents a much larger paramagnetic relaxation contribution, in comparison with that observed for the DMSO/[P66614][FeCl4] mixtures but different from that reported for other magnetic ionic liquid system. In the [P66614][Cl]/[P66614][FeCl4] system the relaxation enhancement associated with the paramagnetic ions is clearly not proportional to the concentration of magnetic ions, in contrast with what is observed for the DMSO/[P66614][FeCl4] system.

Nuclear Magnetic Resonance Study of Atomic Motion in the Mixed Borohydride–Amide Na2(BH4)(NH2)

To study the reorientational motion of the anions and the translational diffusion of Na+ cations in the mixed borohydride–amide Na2(BH4)(NH2) showing fast-ion conduction, we have measured the 1H, 11B, and 23Na NMR spectra and spin–lattice relaxation rates in this compound over broad ranges of temperature (6–480 K) and the resonance frequency (14–132.3 MHz). At low temperatures (T < 190 K), the proton spin–lattice relaxation rate is governed by fast reorientations of BH4 groups. This reorientational process can be satisfactorily described in terms of a Gaussian distribution of the activation energies with the average Ea value of 74 ± 7 meV. Above 250 K, the measured proton spin–lattice relaxation rate originates from two other (slower) reorientational jump processes characterized by the average activation energies of 340 ± 9 meV and 559 ± 7 meV. The 23Na spin–lattice relaxation data in the high-temperature region are governed by translational diffusion of Na+ ions, which is consistent with high Na-ion cond...

Nuclear Magnetic Resonance Studies of BH4 Reorientations and Li Diffusion in LiLa(BH4)3Cl

To study the reorientational motion of BH4 groups and the translational diffusion of Li+ ions in the novel bimetallic borohydride chloride LiLa(BH4)3Cl, we have measured the 1H, 11B, and 7Li NMR spectra and spin–lattice relaxation rates in this compound over the temperature range of 23–418 K. At low temperatures (T < 110 K), the proton spin–lattice relaxation rates are governed by fast reorientations of BH4 groups. This reorientational process can be satisfactorily described in terms of a two-peak distribution of the activation energies with the peak Ea values of 41 and 50 meV. Above 200 K, the NMR data are governed by a combined effect of two types of motion occurring at the same frequency scale: Li ion diffusion and another (slower) reorientational motion of BH4 groups. These results suggest that the Li ion jumps and the slower reorientational jumps of BH4 groups in LiLa(BH4)3Cl may be correlated. The estimate of the tracer Li ion diffusion coefficient at room temperature (5.2 × 10–8 cm2/s) following fr...

Direct interaction of ONO-5046 with human neutrophil elastase through 1H NMR and molecular docking

Human neutrophil elastase (HNE) has been implicated as a major contributor in the pathogenesis of diseases, such as pulmonary emphysema, acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and other inflammatory diseases. Therefore, searching for appropriate and potential human neutrophil elastase inhibitors (HNEI) that would restore the balance between the free enzyme and the endogenous inhibitors would be of therapeutic interest. ONO-5046 is the first specific HNEI to improve respiratory function and protect lung tissues against various lung injuries. However, the mechanism of ONO-5046 to HNE is still unclear. In this study, the binding properties of ONO-5046 were investigated through 1H NMR, molecular docking, and bioassay methods to understand the effect of ONO-5046 to HNE. The proton spin–lattice relaxation rate and molecular rotational correlation time results indicated that ONO-5046 has higher affinity with HNE. The molecular docking study showed that ONO-5046 is perfectly matched for the primary enzyme specificity pocket (S1 pocket), and is tightly bound to this pocket of HNE through hydrophobic and hydrogen bonding interactions. The results of both methods were validated through analysis of the HNE inhibitory activity bioassay of ONO-5046 with an IC50 value of 87.05nM. Our data suggested that ONO-5046 could bind to HNE through direct interaction, and that molecular docking and NMR methods are valid approaches to survey new HNEI.

Slow molecular processes in a nematic liquid crystal confined to random porous network formed by aerosil particles

Frequency dispersion measurements of proton spin–lattice relaxation rates (R 1) of liquid crystal 4-propyl-4′-pentylazoxybenzene in bulk and confined samples (in random porous network of aerosil nano-particles) are reported in isotropic and nematic phases. Significant low-frequency increase in R 1 in confined samples indicates slow molecular reorientations mediated by translational displacements near the adsorbing porous surface. The resulting dispersion behavior of R 1 (∼ω − p ) reflects the nature of the random surface (p = 0.5 for equi-partition of the diffusive modes). The observed temperature-independent exponent in the isotropic phase (p = 0.34) indicates the abundance of low-wavelength surface modes. Its temperature-dependent higher values in the nematic phase (from 0.59 to 0.65 on cooling), and increased spin–lattice coupling via this mechanism, show progressive onset of longer wavelength modes. A detailed analysis shows the effect of confinement on the order director fluctuations, molecular reorientations, and translational diffusion of the molecules.

Effect of confinement on molecular processes in the liquid crystal 8OCB: application of NMR relaxometry

Dispersions of proton spin–lattice relaxation rates (R1) in the nematic and smectic phases of the liquid crystal 4′-octyloxy-4-cyanobiphenyl (8OCB), embedded in a nano-porous medium formed by an aerosil matrix, are investigated over a wide frequency (ν) range (104 Hz to 5 × 107 Hz) at two average pore sizes. In the low frequency (sub-MHz) region we observe a significant increase of R1 in the confined samples, mediated by slow translational displacements (RMTD), arising from the formation of adsorption layers near the porous surface. Dispersion in this region is well accounted for by a power law behaviour (R1 ∼ ω−p), bracketed by low and high cutoff frequencies reflecting the limiting length scales of such displacements in these layers. The exponent p increases from 0.45 to 0.6 with a decrease of the temperature within the nematic phase, due to the progressive onset of longer wavelength diffusive modes within these layers. This signifies the onset of order director fluctuation (ODF) modes within the adsorption layers. Confinement is also seen to place restrictions on the long wavelength ODF modes of the bulk-like region of the liquid crystal, thus weakening considerably their dispersive effects in the low frequency region, relative to the bulk samples. In the smectic phase, p decreases appreciably signalling a depletion of such long range cooperative modes on layer formation. Analysis of the R1 data also shows that individual dynamic processes like translational diffusion and reorientations of the molecules within the voids are largely unaffected due to confinement.

Slow Molecular Processes in a Liquid Crystal Embedded in Aerosil Matrix: Nuclear Magnetic Relaxometric Study

Frequency dispersion studies on proton spin-lattice relaxation rates of a liquid crysal (4′-octyloxy-4-cyanobiphenyl) embedded in Aerosil matrix show significant increase at low frequencies (sub-MHz regime) relative to the bulk sample, and are interpreted as primarily due to slow reorientations near the surface ordered layers mediated by translation displacements. The computed exponent in the power law behavior of the dispersion profiles at different temperatures in the isotropic phase indicates an enhanced role of the low-wavelength diffusion modes during this process. The data also show critical contribution near the isotropic-nematic transition to the length scales relevant to adsorption kinetics.

Proton NMR Relaxometry Study of Nafion Membranes Modified with Ionic Liquid Cations

Proton nuclear magnetic resonance (NMR) relaxometry was used to study the ionic mobility and levels of confinement within Nafion membranes modified by incorporation of selected ionic liquid (IL) cations. These studies were performed aiming at understanding the effect of using different types of ionic liquid cations, and their degree of incorporation, in the values of the spin-lattice relaxation times (T(1)) obtained at different values of frequency and thus detect the influence of confinement level on the ions mobility. The frequency dependence of the proton spin-lattice relaxation rate, R(1) = 1/T(1), for the modified Nafion/IL cation membranes was compared with that obtained for an unmodified Nafion membrane, allowing for distinguishing different contributions of the motions of the molecules depending on the frequency tested. The experimental R(1) results were analyzed in terms of models that consider the sum of the most effective relaxation contributions, to estimate the translational self-diffusion coefficient of the moving molecular species in the modified membranes. The stability of these membranes with temperature in terms of the spin-lattice relaxation was compared with results obtained by thermogravimetric analysis.

A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state

We have measured the solid state nuclear magnetic resonance (NMR) 1H spin-lattice relaxation rate from 93 to 340 K at NMR frequencies of 8.5 and 53 MHz in 5- t-butyl-4-hydroxy-2-methylphenyl sulfide. We have also determined the molecular and crystal structures from X-ray diffraction experiments. The relaxation is caused by methyl and t-butyl group rotation modulating the spin–spin interactions and we relate the NMR dynamical parameters to the structure. A successful fit of the data requires that the 2-methyl groups are rotating fast (on the NMR time scale) even at the lowest temperatures employed. The rotational barrier for the two out-of-plane methyl groups in the t-butyl groups is 14.3±2.7 kJ mol −1 and the rotational barrier for the t-butyl groups and their in-plane methyl groups is 24.0±4.6 kJ mol −1. The uncertainties account for the uncertainties associated with the relationship between the observed NMR activation energy and a model-independent barrier, as well as the experimental uncertainties.

Nuclear Magnetic Resonance Study of Hydrated Bentonite

Impedance spectroscopy and nuclear magnetic resonance (NMR) were used to investigate the mobility of water molecules located in the interlayer space of H+ – exchanged bentonite clay. The conductivity obtained by ac measurements was 1.25 × 10−4 S/cm at 298 K. Proton (1H) lineshapes and spin-lattice relaxation times were measured as a function of temperature over the temperature range 130–320 K. The NMR experiments exhibit the qualitative features associated with the proton motion, namely the presence of a 1H NMR line narrowing and a well-defined spin-lattice relaxation rate maximum. The temperature dependence of the proton spin-lattice relaxation rates was analyzed with the spectral density function appropriate for proton dynamics in a two-dimensional system. The self-diffusion coefficient estimated from our NMR data, D ∼ 2 × 10−7 cm2/s at 300 K, is consistent with those reported for exchanged montmorillonite clay hydrates studied by NMR and quasi-elastic neutron scattering (QNS).

The Dispersion of Water Proton Spin-Lattice Relaxation Rates in Aqueous Human Protein HC (&amp;#945; 1-Microglobulin) Solutions

The (1)H NMR Fast Field Cycling relaxometry was applied to study the molecular dynamics of the human protein HC (alpha (1)-microglobulin), its hydration and aggregation in solution state. The (1)H NMRD data have revealed the complex nature of the water/protein HC system resulting from the co-existence of monomer and dimer forms of the protein in solution as well as the presence of oligosaccharides linked to the polypeptide chain. A comparison of the average correlation time values <tau (c)> obtained from the model-free fits with the values predicted on the basis of hydrodynamic tau (r) theory, suggests that the dynamics in solution state is governed mainly by the dimer form of the protein HC (the dominant contribution to the water proton-spin lattice relaxation comes from exchanging protons from the surface of the dimer). The existence of small number of oligomeric forms of the protein HC in solutions is postulated because of the two-step shape of water proton spin-lattice relaxation rate dispersion profiles.

Nuclear magnetic resonance study of hydrogen mobility in LaY 2Ni 9H x and CeY 2Ni 9H x

In order to investigate the mobility of hydrogen in the ternary compounds LaY 2Ni 9 and CeY 2Ni 9, we have measured the proton nuclear magnetic resonance (NMR) spectra and the proton spin–lattice relaxation rates R 1 for LaY 2Ni 9H x ( x=0.78 and 10.3) and CeY 2Ni 9H x ( x=0.79 and 7.2). The measurements have been performed at the resonance frequencies of 14, 23.8 and 90 MHz over the temperature range of 11–404 K. For LaY 2Ni 9H x , the behavior of R 1 is consistent with the presence of a considerable contribution due to motionally modulated dipole–dipole interaction between nuclear spins. This contribution can be satisfactorily described in terms of the Bloembergen–Purcell–Pound model with a Gaussian distribution of activation energies for hydrogen diffusion; the value of the average activation energy resulting from such a description for LaY 2Ni 9H 10.3 is approximately 0.36 eV. For CeY 2Ni 9H x compounds, the measured proton spin–lattice relaxation rates are dominated by the contribution due to the interaction between proton spins and paramagnetic centers over the entire temperature range studied. Only qualitative information on H mobility in these compounds has been obtained from the narrowing of NMR spectra. Possible paths of H diffusion in LaY 2Ni 9H x and CeY 2Ni 9H x are discussed in terms of the distances between the interstitial sites occupied by hydrogen.

Estimation of free copper ion concentrations in blood serum using T1 relaxation rates

The water proton relaxation rate constant R 1 = 1/ T 1 (at 60 MHz) of blood serum is substantially increased by the presence of free Cu 2+ ions at concentrations above normal physiological levels. Addition of chelating agents to serum containing paramagnetic Cu 2+ nulls this effect. This was demonstrated by looking at the effect of adding a chelating agent—D-penicillamine (D-PEN) to CuSO 4 and CuCl 2 aqueous solutions as well as to rabbit blood serum. We propose that the measurement of water proton spin–lattice relaxation rate constants before and after chelation may be used as an alternative approach for monitoring the presence of free copper ions in blood serum. This method may be used in the diagnosis of some diseases (leukaemia, liver diseases and particularly Wilson’s disease) because, in contrast to conventional methods like spectrophotometry which records the total number of both bound and free ions, the proton relaxation technique is sensitive solely to free paramagnetic ions dissolved in blood serum. The change in R 1 upon chelation was found to be less than 0.06 s −1 for serum from healthy subjects but greater than 0.06 s −1 for serum from untreated Wilson’s patients.