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1.
Wideline 1H FID and relaxation measurements of a relatively simple motionally heterogeneous system, the triblock copolymer styrene–butadiene–styrene, have been performed in a temperature range between the polystyrene and polybutadiene glass transition temperatures. The two FID and the two spin lattice relaxation time in the rotating frame (T1ρ) components found at each temperature have been correlated by means of a two-dimensional approach. It is shown that this approach allows dynamic information, not accessible simply by interpreting proton T1 and T1ρ data, to be revealed. In the case examined, the correlation found could be confirmed by high-resolution 1H T1ρ-selective 13C Cross Polarization experiments.  相似文献   

2.
A transient nuclear Overhauser effect (NOE) makes measurements of the 13C spin-lattice relaxation times in organic solids complicated. Extended Solomon equations are applied in order to describe 13C spin-lattice relaxation with 1H r.f. field irradiation. Spin-lattice relaxation under r.f. irradiation is shown to be generally a triple-exponential process, but it can be reduced to be single-exponential under stronger r.f. field irradiation as well as in the absence of 1H initial magnetizations. Based on numerical calculations, the difference between spin-lattice relaxation curves obeying T1C < T1H and those obeying T1C < T1H is clearly indicated. The methyl group resonances in solid-state -valine are examined, and the experimental results agree well with the theoretical results.  相似文献   

3.
The solid state 13C CPMAS NMR spectra of plant cell walls are often complex owing to superposition of resonances from different polysaccharides and the heterogeneity of the cell wall assembly. In this paper, we describe the application of a set of proton relaxation-induced spectral editing (PRISE) experiments which combine 1H relaxation properties (T1, T, T2) with 13C high resolution spectroscopy (CPMAS) to relate the dynamics of the plant cell walls and model systems to their domain structural details. With PRISE it has been found that in plant cell wall materials, cellulose is always associated with the long components of spin–lattice relaxation in both the laboratory and rotating frames whereas non-cellulose polysaccharides (pectin and hemicellulose) are associated with the short ones. For the proton T2 relaxation, cellulose is only associated with the short component (below 20 μs), pectin contributes to both the short component and the long one.  相似文献   

4.
Molecular dynamics of polycrystalline cellobiose studied by solid-state NMR   总被引:1,自引:0,他引:1  
Molecular motions of polycrystalline cellobiose have been investigated by measuring proton spin–lattice relaxation times, T1 and T, and the second moment, M2, in both protonated and D2O exchanged forms over the temperature range 120–380 K. T1 relaxation is dominated by the motions of hydroxyl groups between 150 and 380 K, characterised by an activation energy of about 8.74 kJ/mol, whereas T relaxation is driven by the motions of the same groups between 120 and 300 K. T results suggest that hydroxyl groups have a distribution of dynamics. Motion of methylene groups was detected in the second-moment experiments at about 350 K, characterised by activation energy of about 40 kJ/mol. Consideration of the calculated and observed rigid-lattice second moments suggests that the reported X-ray data are incorrect for the inter-proton distance on C6′. 13C CPMAS spectra of both protonated and deuterated cellobiose have also been measured. Spectra of the deuterated material showed the existence of a second crystalline form in addition to the normal form.  相似文献   

5.
Studies of ion dynamics in the highly conductive glassy fast ionic conductor (FIC) xLi2S + (1 − x)B2S3 (x = 0.65 and 0.70) were made with NMR nuclear spin lattice relaxation (NSLR) R1(ω, T) of both mobile 7Li and immobile 11B ions, and 7Li NMR line narrowing δν(T). The possible dependence of ion dynamics on the short range order structures (SRO) and the distribution of activation energies (DAE) in this highly conductive FIC was investigated. Two Gaussian DAE were employed to fit 7Li NSLR data, where each Gaussian DAE was correlated to a separate 11B NSLR in a BS3 and in a BS4 group. The long range diffusion of Li ions among BS3 groups and a seemingly localized ionic hopping motion around BS4 group is suggested as a microscopic model for the ion dynamics in thioborate glasses, namely a ‘two channel relaxation’.  相似文献   

6.
The interaction of a soluble Melanin Free Acid (MFA) from Sepia melanin with Mn2+ ions is investigated by measuring the proton water relaxation rates. The similarity between MFA and the parent melanin is assessed by means of their high resolution 13C cross polarization magic angle spinning NMR spectra. The observed marked increase in longitudinal proton relaxation rates and the characteristic 1/T1 NMRD profile are associated to the formation of a macromolecular metal complex. The presence of similar paramagnetic species is expected to cause the high contrast shown by melanotic tissues in MRI.  相似文献   

7.
139La-NQR measurements have been carried out in the ternary carbide superconductor LaNiC2. The nuclear quadrupole frequency and the asymmetry parameter of 139La in LaNiC2 were estimated to be about 1.9 MHz and 0, respectively. In the normal state, the nuclear spin relaxation rate (1/T1) in the 139La NQR signal was proportional to temperature (T) in zero external field above the superconducting transition temperature (Tc) or in an external field larger than the superconducting critical field, which means the system is in the Fermi-liquid state. In the superconducting state, on the other hand, 1/T1 decreases no more linearly with T, but decreases rapidly exponentially as exp (−Δ/kBT) at low T with an appreciable enhancement just below Tc. The value of the superconducting energy gap, 2Δ, was estimated to be 3.34kBTc, compared with 3.52kBTc of the BCS-value. This result strongly suggests that the superconductivity in LaNiC2 is of a conventional BCS type.  相似文献   

8.
The 63Cu NMR Knight shift K and spin-lattice relaxation rate 1/T1 have been measured to study the thiospinel superconductor Cu1.5Rh1.5S4 from a microscopic viewpoint. K is negative and has a weak dependence on temperature, and the hyperfine coupling constant Hhfd is estimated to be −52.4 kOe/μB. 1/T1 is proportional to the temperature in the normal state. In the superconducting state, 1/T1 takes a coherence peak just below Tc, and decreases exponentially well below Tc, from whose temperature dependence the superconducting energy gap has been proved to be close to 2Δ = 3.52kBTc given by the BCS theory.  相似文献   

9.
The use of nuclear magnetic resonance (NMR) relaxation time measurements for characterization of abnormal cardiac tissue depends upon knowledge of variations of relaxation times of normal myocardium and determinants of these variations. We calculated in vitro NMR T1 and T2 relaxation times of canine myocardium from the four cardiac chambers, and determined hydroxyproline concentration (as a measure of collagen) and percent water content of the samples. We found both water content and T1 relaxation time of the right ventricle to be significantly greater than the left atrium (p < 0.05). T2 relaxation time of the left ventricle was found to be shorter than each of the other three chambers (p < 0.05). There were significant correlations between the spin-lattice relaxation time and both percent water content (r = 0.58) and hydroxyproline concentration (r = 0.45). A significant correlation was also found between T2 relaxation time and hydroxyproline concentration (r = 0.49). When T1 and T2 were adjusted for water and hydroxyproline content, there was no longer any evidence for significant interchamber differences for either T1 or T2. These data suggest that differences in NMR relaxation times exist among the four chambers of the normal canine heart. Furthermore, a major determinant of myocardial spin-lattice relaxation time is tissue water content while both collagen content and percent water content significantly contribute to variability in cardiac chamber T2 relaxation times.  相似文献   

10.
A 35Cl nuclear quadrupole resonance (35Cl-NQR) investigation of polycrystalline Ca(ClO3)2·2H2O is described. The 35Cl-NQR frequencies (νQ) for two resonance lines (νQ1 and νQ2), the spin lattice relaxation time (T1Q) for νQ2 only and the line width δνQ2 were measured in the temperature range 292–345 K, except for the frequency measured up to 455 K. The observed decrease in the resonance frequencies with increasing temperature permitted the determination of the frequencies of librations of the ClO3 ion about two axes perpendicular to the three-fold axis of the ion mainly responsible for this effect. The temperature dependence of the relaxation time T1Q proved the occurrence of water diffusion and hindered rotation of ClO3 ions. The activation energies of these two molecular motions were determined, and their effect on the electric field gradient at the site of a chlorine nucleus was discussed. Temperature measurements of the line width δνQ2 confirmed the conclusions drawn from the analysis of T1Q(T).  相似文献   

11.
13C及29Si核磁共振研究了苯乙烯(S)及二甲基硅氧烷(Si)嵌段共聚物中硅氧烷软段的固体及溶液谱的自旋-晶格弛豫时间T1。固态嵌段共聚物主链29Si及侧甲基13C的T1都与均聚物的T1相近,但在CdCl3溶液中各种嵌段共聚物的T1与均聚硅氧烷相差颇大。用偶极-偶极相互作用来解释高聚物的自旋-晶格弛豫。苯乙烯-二甲基硅氧烷嵌段共聚物具两相结构,所以嵌段共聚物中软段及硬段微区中链段的运动与在均聚物分子中链段的运动模式基本相同。而CdCl3对聚苯乙烯或聚硅氧烷都是良溶剂,软段硬段之间有相互影响。所以其链段运动与均聚物不同,从而导致链段运动的相关时间τc变短和T1的增长。  相似文献   

12.
The present communication reports the experimental values of NMR spin-lattice relaxation time (T1) and dielectric relaxation time (τ) of piperidine, pyrrole, pyridine, diethylamine, triethylamine and pyrrolidine. The values of activation energy (ΔEA) obtained using dielectric relaxation time, have been correlated with calculated values of ΔEA obtained using Arrhenius equation of NMR relaxation time (T1) for pyridine, diethylamine and pyrrole. Authors have also established a correlation between the experimental values of NMR spin-relaxation time (T1) with its calculated values obtained using different equations of dielectric relaxation time (τ).  相似文献   

13.
Polarization parameters have been determined for deuteron elastic scattering from 27Al, Si and 60Ni at energies between 7 and 11 MeV and laboratory scattering angles from 30° to 135°. The vector polarization, iT11, and two tensor parameters T20 and T22, were measured by scattering polarized and unpolarized deuterons which were obtained from a tandem accelerator. The largest polarization was |iT11| ≈ 0.3 and |T20| ≈ 0.2 for 27Al at 11 MeV. For 60Ni, the observed polarizations were substantially smaller. Angular distributions of the unpolarized cross section were also measured for 27Al and Si. An optical-model analysis of the polarization and cross-section data was performed. The vector polarization was reproduced reasonably well by a vector spin-orbit coupling of similar strength as found for nucleon scattering. A tensor interaction appears to be needed to account for the observed tensor polarizations.  相似文献   

14.
Poly(vinyl alcohol) (PVA) with 55% and 61% syndiotacticity, and their related dry and hydrated gels obtained by two different freeze–thawing cycles have been investigated using the solid-state 13C CP-MAS NMR technique. From a comparative analysis of the spectra, evidence was obtained that the gelation process largely disrupts the intramolecular hydrogen-bonded network of the PVA. The addition of water to the dry gels favours their swelling, destroying intra-chain hydrogen bonds between hydroxyl groups as a function of the degree of tacticity and the gelation procedure, and promotes the formation of new networks of interchain hydrogen bonds. Information on the dynamics of the polymeric domains in the kilohertz range has been obtained from the analysis of the spin relaxation times T1ρ(1H) and T1ρ(13C), indicating that homogeneous arrangements of the amorphous or swollen polymeric chains exist, independent of the preparation method or the tacticity of the PVA chains.  相似文献   

15.
Thirteen patients with biopsy proven hepatic lymphoma (2 Hodgkin, 11 Non-Hodgkin) and a control group of 15 patients with hepatic metastases were analyzed quantitatively and qualitatively by MRI. Focal hepatic lymphoma was most reliably detected (eight of eight patients) and appeared hypointense relative to liver on T1 weighted (CNR − 7.4 ± 2.3) and hyperintense on T2 weighted (CNR + 8.4 ± 2.9) images. The mean T1 and T2 relaxation times of focal hepatic lymphoma (T1 = 832 ± 234 msec, T2 = 84 ± 16 ms) differed significantly from adjacent non-tumorous liver (T1 = 420 ± 121 ms, T2 = 51 ± 9 ms; p < 0.05), however CNR values and relaxation times were similar to those of hepatic metastases. Diffuse hepatic lymphoma (microscopic periportal infiltration) was undetectable by MRI in three patients by either morphologic features or quantitative criteria. A mixed pattern of hepatic lymphoma (focal lesions and diffuse infiltration) showed focal areas of slightly decreased signal intensity on T1 weighted images (CNR = −1.7 ± 0.4) while T2 weighted images revealed multiple regions of focal hyperintensity (CNR = +13.3 ± 8.4) superimposed on a diffusely hyperintense liver. Our experience demonstrates that either T1 or T2 weighted techniques are useful in detecting focal and that T2 weighted techniques are useful in detecting mixed hepatic lymphoma. Conventional image derived relaxation time measurements and quantitative parameters were of no additional diagnostic value.  相似文献   

16.
A simple modification of the standard cross-polarization method designed for quenching the proton T dependence when studying polarization transfer is presented. It is demonstrated that by using this simple procedure, new and subtle details of cross-polarization dynamics, previously hidden by the T(1H) effect, can be observed in dipolar-coupled spin systems.  相似文献   

17.
Experimental gliomas (F98) were inoculated in cat brain for the systematic study of their in vivo T2 relaxation time behavior. With a CPMG multi-echo imaging sequence, a train of 16 echoes was evaluated to obtain the transverse relaxation time and the magnetization M(0) at time T = 0. The magnetization decay curves were analyzed for biexponentiality. All tissues showed monoexponential T2, only that of the ventricular fluid and part of the vital tumor tissue were biexponential. Based on these NMR relaxation parameters the tissues were characterized, their correct assignment being assured by comparison with histological slices. T2 of normal grey and white matter was 74 ± 6 and 72 ± 6 msec, respectively. These two tissue types were distinguished through M(0) which for white matter was only 0.88 of the intensity of grey matter in full agreement with water content, determined from tissue specimens. At the time of maximal tumor growth and edema spread a tissue differentiation was possible in NMR relaxation parameter images. Separation of the three tissue groups of normal tissue, tumor and edema was based on T2 with T2(normal) < T2(tumor) < T2(edema). Using M(0) as a second parameter the differentiation was supported, in particular between white matter and tumor or edema. Animals were studied at 1–4 wk after tumor implantation to study tumor development. The magnetization M(0) of both tumor and peritumoral edema went through a maximum between the second and third week of tumor growth. T2 of edema was maximal at the same time with 133 ± 4 msec, while the relaxation time of tumor continued to increase during the whole growth period, reaching values of 114 ± 12 msec at the fourth week. Thus, a complete characterization of pathological tissues with NMR relaxometry must include a detailed study of the developmental changes of these tissues to assure correct experimental conditions for the goal of optimal contrast between normal and pathological regions in the NMR images.  相似文献   

18.
A new synthesis procedure is reported for the preparation of mixed Al,Ga-offretites over the entire solid solution range 0 ≤ Ga/(Ga + Al) ≤ 1. The resulting materials are characterized by X-ray powder diffraction, adsorption microcalorimetry and multinuclear solid state NMR. The 29Si MAS-NMR data are consistent with statistical occupancy of the T1 and T2 sites by aluminum and gallium, and also show no positive evidence for preferential siting effects between both framework metals. Isotropic chemical shifts and nuclear electric quadrupolar coupling constants for 27Al and 71Ga have been obtained from a field-dependent analysis of the center of gravity in the MAS-NMR spectra. H-Al, Ga-offretites produced by ammonium exchange and subsequent calcination reveal evidence of partial demetallation of the framework with formation of extra-lattice metal species.  相似文献   

19.
Crystalline 2,3-dicyano-5,7-dimethyl-6H-1,4-diazepine (A) was investigated by solid-state NMR spectroscopy, X-ray diffraction, and spectral simulations. The solid-state 13C NMR spectra of A display peculiar splittings for the methyl and cyano resonances. The crystal structure of A indicates that the methyl doublet is a consequence of two crystallographically inequivalent environments. The methyl motions associated with each site was examined via spin-lattice relaxation time (T1) measurements, and the carbon relaxation times (T1C) were used to calculate energy barriers to methyl rotation. The energy barriers to rotation were then used to correlate each methyl 13C shift with a particular crystallographic environment. The complex cyano splittings, however, are a result of both crystallographic inequivalence and residual 13C–14N dipolar coupling. The multiplet patterns of the isotropic shifts (centerbands) are dependent upon the magic-angle spinning (MAS) rate. Spectral simulations, using the perturbation method, of the centerbands and first-order sidebands were used to demonstrate, and elucidate, the observed MAS rate-dependent multiplet patterns of the cyano signals.  相似文献   

20.
The spin-lattice relaxation times T1 of 1H and 29Si spins in talc have been measured at room temperature with and without magic-angle spinning (MAS) of the sample. Paramagnetic impurities work as relaxation centers. 1H T1 depends on the spinning rate, whereas 29Si T1 is independent of the spinning rate. These facts demonstrate that spin diffusion plays an important role in 1H relaxation but not in 29Si relaxation. 29Si spins relax through dipole-dipole interactions with electron spins directly, which mechanism is not affected by spinning. The relaxation rates have been analyzed theoretically.  相似文献   

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