NMR studies of hydrogen diffusion in hydrogen uranyl phosphate tetrahydrate (HUP)

¹H NMR spin-lattice relaxation times, T₁ (Zeeman) and T_1ϱ (rotating frame) and spin-spin relaxation times, T₂, and ³¹P NMR solid-echoes are reported for phase I and II of hydrogen uranyl phosphate tetrahydrate (HUP) at temperatures in the range 200–323 K. The spectral density functions extracted from the measured relaxation times for phases I and II are consistent with a 2D diffusion mechanism for hydrogen motion. ³¹P second moments determined from the solid-echoes show that all the hydrogens diffuse rapidly in phase I, and that the hydrogen-bond site nearest to the phosphate oxygen is not occupied in phase II. The mechanism for diffusion in phase II is discussed.     

Magic-angle-spinning NMR on solid biological systems. Analysis Of the origin of the spectral linewidths

Magic-angle-spinning (MAS) high-power ¹H-decoupled ¹³C and ³¹P NMR has been applied to solid biological materials to obtain information about the mechanisms that determine the spectral linewidths. The line broadening in MAS ³¹P NMR spectra of solid tobacco mosaic virus (TMV) has been investigated by selective saturation and T₂ measurements. About 90 Hz stems from homogeneous effects, whereas the inhomogeneous contribution is approximately 100 Hz. The inhomogeneous line broadening is assigned to macroscopic inhomogeneities in the sample and not to variations in the nucleotide bases along the RNA strand in TMV. It is concluded that sample preparation is of vital importance for obtaining well-resolved spectra. Under optimal preparation techniques the isotropic values of the chemical shift of the different ³¹P sites have been determined to obtain information about the secondary structure of the viral RNA. The chemical shift anisotropy has been determined from the relative intensities of the spinning side bands in the spectra. The chemical shift information is used to make a tentative assignment of the resonance in terms of the three structurally distinguishable phosphate groups in TMV. The origin of the linewidths in MAS NMR has been examined further by ¹³C NMR of approximately 10% ¹³C-enriched coat protein of cowpea chlorotic mottle virus, using selective excitation and saturation techniques, as well as measurements of the relaxation times T_1γ and T₂. The CO resonance in the spectrum is composed of an inhomogeneous and homogeneous part with a total linewidth of 700 Hz. The homogeneous linewidth, contributing with 200 Hz, is found to arise from slow molecular motions in the solid on a millisecond timescale.     

NMR study of YP and YPO4 as 2-qubits quantum computers

The ³¹P-NMR experiments in YP and YPO₄ as 2-qubits quantum computers were performed at room temperature under magnetic fields of 6.3 and 11.75 T with a coherent type pulsed FT-NMR spectrometer. The full width at half of the maximum intensity of NMR spectrum for ³¹P is compared with the second moment caused by the dipolar field. The obtained spin–lattice relaxation times T₁ of 1.2 and 320 s for the P nuclei in YP and YPO₄, respectively, suggest both compounds have the advantage of increasing the numbers of quantum computing operations.     

Study on ethyl groups with two different orientations in [N(C2H5)4]2CuBr4

The crystal structure and phase transition temperature of [N(C₂H₅)₄]₂CuBr₄ are studied using X-ray diffraction and differential scanning calorimetry (DSC); measurements revealed a tetragonal structure and the two phase transition temperatures T_C of 204 K and 255.5 K. The structural geometry near T_C is discussed in terms of the chemical shifts for ¹H magic angle spinning (MAS) nuclear magnetic resonance (NMR) and ¹³C cross-polarization (CP)/MAS NMR. The two inequivalent ethyl groups are distinguishable by the ¹³C NMR spectrum. The molecular motions are discussed in terms of the spin–lattice relaxation times T_1ρ in the rotating frame for ¹H MAS NMR and ¹³C CP/MAS NMR. The T_1ρ results reveal that the ethyl groups undergo tumbling motion, and furthermore that the ethyl groups are highly mobile.     

In vivo relaxation time measurements on a murine tumor model—Prolongation of T1 after photodynamic therapy

RIF tumors implanted on mice feet were investigated for changes in relaxation times (T₁ and T₂) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed using the untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T₁s of water protons were observed after PDT treatment. In all experiments, ³¹P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T₁s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T₂ values after PDT treatment.     

Quantitative characterization of the Mn2+ complexes of ADP and ATPγS by W-band ENDOR

W-band (95 GHz) pulsed electron nuclear double resonance (ENDOR) measurements were carried out to determine quantitatively the first coordination shell of Mn²⁺ with ADP and ATPγS. The intensity of the ENDOR effect was used for counting the number of equivalent phosphate oxygens and water ligands. Titration curves for determining the binding constant of Mn²⁺. ADP were obtained using the intensity of the X-band EPR spectrum and the³¹P ENDOR effect. Both curves gave the same binding constant showing that phosphate ligand counting is plausible, provided that an appropriate reference is available. The comparison of the³¹P ENDOR effect of the 1:1 ADP and ATPγS complexes shows that two phosphates are coordinated in both; while in ADP they are equivalent, in ATPγS they are slightly different. The reference system for water ligand counting was Mn(H₂O) ₆ ²⁺ in a H₂O-D₂O mixture. The results show a smaller error for the²H ENDOR effect, compared to the¹H ENDOR effect. Unlike the³¹P ENDOR effect, the¹H ENDOR effect dependence on [ADP] in the titration experiments showed that it is sensitive to variations in the zero-field splitting, which in turn alters the contributions of transitions other than the ‖?1/2>?‖1/2>. This results in a larger error in the determination of the number of water ligands.     

MR imaging of teeth using a silent single point imaging technique

Magnetic resonance imaging (MRI) of teeth is an emerging application area which is still in development. Previous investigations did not fully focus on potential in vivo applications. Using ¹H and ³¹P MRI, we obtained ex vivo microimages of teeth with a silent single point imaging (SPI) technique. ¹H Images with an in-plane resolution of 310×310 μm² were obtained. Utilizing sine-shaped gradient ramps significantly reduced the sound pressure level of the experiment to that of background noise. ¹H magnetic resonance spectroscopy (MRS) was used to characterize the major components in the observed resonance. The spin–spin (T₂) relaxation times of water in enamel and dentin differed by at least one order of magnitude. Three-dimensional surface reconstruction of the data allowed for complete visualization of the tooth’s surface while volume reconstruction displayed the internal geometry. PACS 82.56.Na; 83.85.Fg; 87.61.-c; 87.19.-j; 43.50.Cb     

Influence of magnetic impurities on proton spin relaxation of water in clay

The¹H nuclear magnetic spin relaxation of water in slurry of kaolin clay was investigated in the presence of magnetite (black iron oxide, Fe₃O₄) at 0.2 T and room temperature. The water spectra at high magnetite contents showed two different resonances, presumably from surface-associated water and free interstitial water. The difference in observed resonance frequencies increased as much as 200 ppm with increasing magnetite content. The apparent nuclear magnetic resonance intensity decreased biexponentially as a function of magnetite added. The observedT ₂^* values at low magnetite contents were in accordance with the predicted values from the resonance intensities and the estimated magnetic susceptibilities. TheT ₁ relaxation was multiexponential in character, so a uniform penalty program was used for the analysis of distribution. At 0.2 T for¹H, kaolin slurry containing less than 5.5 ppm magnetite did not differ significantly from magnetite-free clay in the longitudinal relaxation rates of water. However, higher concentrations of magnetite produced features in theT ₁ distribution significantly different from those of magnetite-free clay. TheT ₂ could be approximated by monoexponential relaxation, probably because the fast-decaying components relaxed before they could be recorded. The apparent transverse relaxation ratesR ₂ increased linearly as a function of magnetite content. On the basis of the comparison of spin-echo and Carr-Purcell-Meiboom-Gill data, an empirical relation was derived to describe the signal loss due to diffusion. It can be expressed by a power function of magnetite amount, which is multiplied by the sum of volume-dependent and volume-independent terms.     

H and K spin-lattice relaxation, ionic motion and Raman processes in the proton conducting KHSeO4 single crystal

The spin-lattice relaxation rates of ¹H and ³⁹K nuclei in KHSeO₄ crystals were studied in the temperature range 160-400 K. The spin-lattice relaxation recovery of ¹H nucleus in this crystal can be represented with a single exponential function, and the relaxation T₁⁻¹ curve of ¹H can be represented with the Bloembergen-Purcell-Pound (BPP) function. The relaxation process of ³⁹K with dominant quadrupole relaxation can be described by a linear combination of two exponential functions. T₁⁻¹ for the ³⁹K nucleus was found to have a very strong temperature dependence, T₁⁻¹=βT⁷. Rapid variations in relaxation rates are associated with critical fluctuations in the electronic spin system. The T⁷ temperature dependence of the Raman relaxation rate is shown here to be due to phonon-magnon coupling.     

NMR study of the magnetic properties and electronic structure of amorphous Ni−B−P alloys

The¹¹B and³¹P NMR Knight shift (K) and Korringa spin-lattice relaxation rate (1/T ₁ T) have been measured for amorphous Ni_81.5B_18.5−x P _x alloys with 0≤x≤18.5. In accordance with previous bulk measurements, the³¹P NMR parameters vary markedly with composition whereas the¹¹B NMR parameters remain almost constant except for small P-contents. It is suggested that the d-band contribution toK(³¹P) is positive and that toK(¹¹B) is negative. The data further support our previous conclusion that amorphous Ni_81.5B_18.5 is a Pauli paramagnet rather than a weak itinerant ferromagnet.     

Deuterium Nuclear Spin–Lattice Relaxation Times and Quadrupolar Coupling Constants in Isotopically Labeled Saccharides

¹³C and ²H spin–lattice relaxation times have been determined by inversion recovery in a range of site-specific ¹³C- and ²H-labeled saccharides under identical solution conditions, and the data were used to calculate deuterium nuclear quadrupolar coupling constants (²H NQCC) at specific sites within cyclic and acyclic forms in solution. ¹³C T₁ values ranged from 0.6 to 8.2 s, and ²H T₁ values ranged from 79 to 450 ms, depending on molecular structure (0.4 M sugar in 5 mM EDTA (disodium salt) in ²H₂O-depleted H₂O, pH 4.8, 30°C). In addition to providing new information on ¹³C and ²H relaxation behavior of saccharides in solution, the resulting ²H1 NQCC values reveal a dependency on anomeric configuration within aldopyranose rings, whereas ²H NQCC values at other ring sites appear less sensitive to configuration at C1. In contrast, ²H NQCC values at both anomeric and nonanomeric sites within aldofuranose rings appear to be influenced by anomeric configuration. These experimental observations were confirmed by density functional theory (DFT) calculations of ²H NQCC values in model aldopyranosyl and aldofuranosyl rings.     

Toward an Optimal Paramagnetic Relaxation Agent for 31P NMR Spectroscopy

The dynamics of the use of relaxation agents for ³¹P NMR spectroscopy were investigated. It was found that non-lability of the associated ligand is essential, in order for line broadening to be prevented. Thus, chelates were found to be most suitable. In addition, evidence was accumulated that indicates an outer sphere coordination is significant for effective reduction of spin-lattice relaxation times (T₁'s). Finally, the magnitude of the magnetic moment, as pertains to Gd⁺³ and Fe⁺³, was examined and related to effective reduction of T₁'s.     

Deoxidation Rate of Oil-Covered Water as the Oil Quality Indicator Oxygen Concentration in Water,NMR Relaxation Time T2, Lubricating Oils

The results of the investigations of deoxidation rate of oil-covered water obtained by measuring the ¹ ₁H NMR spin-spin relaxation time T₂ have been reported. This characteristics are related with oils quality and wear.     

Water-filled MCM-41 characterized by double-quantum-filtered2H NMR spectral analysis

The dynamics of water molecules confined in adsorbed layers of siliceous MCM-41 with a pore diameter of 2.8 nm is investigated at 230 K by deuteron nuclear magnetic resonance (NMR) relaxation studies including line shapes of theT ₁ process and double quantum filtered (DQF) spectral analyses.²H DQF NMR is a particularly sensitive tool for the determination of the adsorbate dynamics resulting from residual quadrupolar interaction due to the local order. The amount of monolayer water is determined. The monolayer water is composed of two different water components characterized by water, with isotropic reorientational motions, exchanging with water displaying a solid-like spectrum with 4 kHz edge splitting. One may expect that the latter water is situated on surface sites in MCM-41. The restricted wobbling motion of the D-O bond is used to describe its dynamics which is one order of magnitude slower than the isotropic reorientational motion. The order parameter, the motional correlation time, and the exchange rate thus determined provide useful information on the structure and the adsorptive properties of the mesoporous system.     

7Li NMR analysis on perovskite structured Li0.15La0.28TaO3

The nanocrystalline perovskite material Li_0.15La_0.28TaO₃ has been synthesized by alkoxide-free Pechini type sol gel method. ⁷Li NMR measurements were carried out using a Bruker Avance 300 spectrometer at 116 MHz over the temperature range 150 to 400 K. Longitudinal spin-lattice relaxation times (T₁) measured by saturation recovery and longitudinal relaxation times in the rotating frame (T_1ρ) measured using the pulse sequence (π/2–spin lock τ acquisition) with lock radio-frequency field υ = 62.5 kHz and the T₂ relaxation time measured by Hahn echo are presented. The static Hahn-echo spectra show two different lithium sites in this perovskite oxide. Further, the relaxation measurements T₁ and T_1ρ show two different types of lithium cations with fast and slow dynamics.     

Slow relaxation experiments in disordered charge and spin density waves: collective dynamics of randomly distributed solitons

We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon. The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain an estimate of the glass cross-over temperature (typically T _g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T _g/T). The glass cross-over temperature T_g related to correlations among solitons is equal to the average energy barrier and scales like T _g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap. Received 12 December 2001     

Simultaneous measurement of total water content and myelin water fraction in brain at 3 T using a T2 relaxation based method

PurposeThis work demonstrates the in vivo application of a T₂ relaxation based total water content (TWC) measurement technique at 3 T in healthy human brain, and evaluates accuracy using simulations that model brain tissue. The benefit of using T₂ relaxation is that it provides simultaneous measurements of myelin water fraction, which correlates to myelin content.MethodsT₂ relaxation data was collected from 10 healthy human subjects with a gradient and spin echo (GRASE) sequence, along with inversion recovery for T₁ mapping. Voxel-wise T₂ distributions were calculated by fitting the T₂ relaxation data with a non-negative least squares algorithm incorporating B₁⁺ inhomogeneity corrections. TWC was the sum of the signals in the T₂ distribution, corrected for T₁ relaxation and receiver coil inhomogeneity, relative to either an external water standard or cerebrospinal fluid (CSF). Simulations were performed to determine theoretical errors in TWC.ResultsTWC values measured in healthy human brain relative to both external and CSF standards agreed with literature values. Simulations demonstrated that TWC could be measured to within 3–4% accuracy.ConclusionIn vivo TWC measurement using T₂ relaxation at 3 T works well and provides a valuable tool for studying neurological diseases with both myelin and water changes.     

A study of molecular motion and Raman processes in K3H(SO4)2 and KHSO4 single crystals by observation of H and K spin-lattice relaxation

The spin-lattice relaxation rates for ¹H and ³⁹K nuclei in K₃H(SO₄)₂ and KHSO₄ single crystals, which are potential candidate materials for use in fuel cells, were determined as a function of temperature. The spin-lattice relaxation recovery of ¹H can be represented for both crystals with a single exponential function, but cannot be represented by the Bloembergen-Purcell-Pound (BPP) function, so is not related to HSO₄ motion. The recovery traces of ³⁹K, which predominantly undergoes quadrupole relaxation, can be represented by a linear combination of two exponential functions. The temperature dependences of the relaxation rates for ³⁹K can be described with a simple power law T₁⁻¹=αT². The spin-lattice relaxation rates for the ³⁹K nucleus in K₃H(SO₄)₂ and KHSO₄ crystals are in accordance with a Raman process dominated by a phonon mechanism.     

Molecular Diffusion in NMR Microscopy

The signal-to-noise ratio and the T₂ contrast in ¹H NMR microscopy are strongly affected by self-diffusion effects. Here, we investigate the free diffusion of water within imaging gradients. As a result we obtain an apparent relaxation time T₂ which in NMR microscopy is at least one order of magnitude smaller than the true T₂ value of water in the object. This apparent T₂ relaxation is considerably reduced by improving spatial resolution. We conclude that quantitative true T₂ values cannot be calculated from series of images with increasing echo time. Furthermore, from the knowledge of the apparent T₂, an optimum short echo time can be found in order to maximize signal-to-noise ratio. Our theoretical findings are confirmed by phantom experiments at 11.75 T field strength.     

2H nuclear magnetic resonance study of deuterated water dynamics in perfluorosulfonic acid ionomer Nafion

We have employed deuteron nuclear magnetic resonance (NMR) spectroscopy in order to study the dynamics of the deuterated water (D₂O) molecules introduced into a perfluorosulfonic acid ionomer Nafion (NR-211) film. According to the ²H NMR spectral analysis, the deuterated water molecules at low temperatures occupied either relatively rigid or mobile sites up to the temperature T_M=240 K where all the deuterated water molecules became mobile. The temperature-dependent NMR linewidths sensitively reflected the motional narrowing of the rigid and mobile sites, and the NMR chemical shift reflected significant changes in the hydrogen bonds of the deuterated water. While a slow- to fast-limit motional transition was manifested at T_M in the laboratory-frame NMR spin–lattice relaxation, the rotating-frame spin–lattice relaxation indicated no bulk liquid water state down to 200 K.