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Experimental results on the nuclear spin-lattice and nuclear spin-spin relaxation times in the ferromagnetic EuB6 at temperatures below 4·2 K are presented using the external magnetic field,H
ext, in the range of 0 ⩽H
ext ⩽ 10 kG. Nuclear spin-spin relaxation time computed on the basis of the Suhl-Nakamura process turns out to be 3·2μs, which compares well with the experimental value 11·1μs obtained with the 10 kG magnetic field at 1·7 K. It is found that in the ferromagnetic EuB6,T
1 is approximately 5 × 103 times larger thanT
2 at 1·7 K with the 10 kG magnetic field. Thus the effect ofT
1 onT
2 can be neglected. From the experimental value ofT
2, the value of the homogeneous line broadening is found to be 14 kHz. The corresponding value obtained from the cw method
is 175 kHz. This evidently shows the presence of the inhomogeneous line broadening in the cw NMR. 相似文献
3.
Wojciech Medycki 《Solid state nuclear magnetic resonance》1999,13(4):213-218
Spin-lattice relaxation times T1 and T1ρ are determined for protons in three polycrystals (CH3NH3)5Bi2Cl11, (CD3NH3)5Bi2Cl11 and (CH3ND3)5Bi2Cl11. The temperature dependencies of the relaxation times obtained for (CH3NH3)5Bi2Cl11 and (CD3NH3)5Bi2Cl11 are interpreted as a result of correlated motions of the three-proton groups of the monomethylammonium cation. The minimum of the T1ρ relaxation time is explained as a result of the oscillations of the symmetry axis of the whole cation. 相似文献
4.
自旋回波的简易观测方法及共振弛豫分析 总被引:7,自引:2,他引:5
在脉冲核磁共振实验中,通常采用自旋回波法测量共振弛豫时间,但模拟示波器观测难以获得准确的实验数据.通过对计算机标准配置资源声卡的性能检测及标定,使其达到物理实验测量数据定量分析的教学要求,同时利用免费的简易程序实现多通道数字信号采集功能并用于观测记录脉冲核磁共振信号.配合实验操作技术改进,既准确地测量了横向弛豫时间,又展现了符合物理实验教学的计算机应用方法. 相似文献
5.
Ferrini V Forte C Geppi M Pizzanelli S Veracini CA 《Solid state nuclear magnetic resonance》2005,27(4):215-222
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
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Equilibrium dialysis and NMR spin-lattice relaxation time (T1) studies of the interaction of the trypanocidal drug 3-nitrobenzaldehyde guanyl hydrazone (3NBGH) with bovine serum albumin (BSA) were used to show that this interaction is weak and nonspecific, making 3NBGH a potential agent for the prophylaxis of Trypanosoma cruzi infected blood. 相似文献
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We address the problem of correlating the observed FID and T1ρ components in wideline 1H relaxation measurements of motionally heterogeneous polymers, and show that different methods of data treatment can highlight different aspects of the correlations present. For a sample of polypropylene we find that the T1ρ relaxation behaviour is driven by relaxation associated with the intermediate FID component, which strongly suggests a motionally inhomogeneous amorphous region in the sample. 相似文献
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Gary D. Fullerton Ph.D. Janet L. Potter M.D. N.Carol Dornbluth M.D. 《Magnetic resonance imaging》1982,1(4):209-226
Nuclear magnetic resonance (NMR) longitudinal (T1) and transverse (T2) relaxation parameters have been evaluated for protein solutions, cellular suspensions and tissues using both data from our laboratory and the extensive literature. It is found that this data can be generalized and explained in terms of three water phases: free water, hydration water, and crystalline water. The proposed model which we refer to as the FPD model differs from similar models in that it assumes that free and hydration water are two phases with distinct relaxation times but that T1 = T2 in each phase. In addition there is a single correlation time for each rather than a distribution as assumed in most other models. Longitudinal decay is predicted to be single exponent in character resulting from a fast exchange between the free and hydration compartments. Transverse decay is predicted to be multiphasic with crystalline (T2 10 μsec), hydration (T2 10 sec) and free (T2 100 sec) water normally visible. The observed or effective transverse relaxation times for both the hydration and free water phases are greatly affected by the crystalline phase and are much shorter than the inherent relaxation times. 相似文献
9.
T. Ida M. MizunoK. Endo M. SuharaK. Nishidate K. Nishikawa 《Journal of Physics and Chemistry of Solids》2002,63(2):249-256
Solid 63Cu NMR and Molecular Dynamics (MD) methods have been used to investigate the dynamical structure of Ag0.99Cu0.01I crystal, through the viewpoint of the chemical shift and the spin-lattice relaxation. In the superionic phase (α-phase), we obtained the temperature variation of the chemical shift as −0.2 ppm/K, and the activation energy of the Cu+ ion diffusion as 11 kJ/mol. The temperature dependence of the chemical shift was explained by the calculated chemical shielding surface based on ab initio MO calculation, and by the probability density of Cu+ ion estimated by MD simulation. The spin-lattice relaxation was also analyzed by using the MD method in which we assumed two jumping models as the diffusion process of the mobile cations. It is concluded that the temperature dependence of the chemical shift is dominated by the shielding in the vicinity of the 24(h) site, and the observed activation energy is due to the diffusion process of the mobile cations jumping from the 6(b) intrasub-lattice to the nearest-neighbor 6(b) sub-lattice. 相似文献
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Sarkar R Concistrè M Johannessen OG Beckett P Denning M Carravetta M Al-Mosawi M Beduz C Yang Y Levitt MH 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,212(2):460-463
The accurate temperature measurement of solid samples under magic-angle spinning (MAS) is difficult in the cryogenic regime. It has been demonstrated by Thurber et al. (J. Magn. Reson., 196 (2009) 84-87) [10] that the temperature dependent spin-lattice relaxation time constant of 79Br in KBr powder can be useful for measuring sample temperature under MAS over a wide temperature range (20–296 K). However the value of T1 exceeds 3 min at temperatures below 20 K, which is inconveniently long. In this communication, we show that the spin-lattice relaxation time constant of 127I in CsI powder can be used to accurately measure sample temperature under MAS within a reasonable experimental time down to 10 K. 相似文献
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Yan J Kline AD Mo H Shapiro MJ Zartler ER 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,163(2):270-276
The effect of longitudinal relaxation of ligand protons on saturation transfer difference (STD) was investigated by using a known binding system, dihydrofolate reductase and trimethoprim. The results indicate that T1 relaxation of ligand protons has a severe interference on the epitope map derived from a STD measurement. When the T1s of individual ligand protons are distinctly different, STD experiments may not give an accurate epitope map for the ligand-target interactions. Measuring the relaxation times prior to mapping is strongly advised. A saturation time shorter than T1s is suggested for improving the potential epitope map. Reduction in temperature was seen to enhance the saturation efficiency in small to medium size targets. 相似文献
13.
实验基于核磁共振技术(Nuclear Magnetic Resonance,NMR)检测的无损性,利用低场NMR技术测定热处理前后花旗松的纤维饱和点(Fiber Saturation Point,FSP).在-3℃和25℃条件下,对CPMG(Carr-Purcell-Meiboom-Gill)脉冲测得的信号进行横向弛豫时间(T2)分析,对比试样冷冻前后信号反演峰面积,确定试样吸着水饱和含量,得到不同热处理条件下花旗松的纤维饱和点依次为38.76%(对照材)、32.82%(180℃热处理)、29.40%(200℃热处理)、24.90%(220℃热处理).实验结果表明,热处理温度越高,纤维饱和点越低.该结果测试结果与木材学理论相符,表明NMR技术可应用于快速确定木材纤维饱和点. 相似文献
14.
Wen-Yi Tseng Yu-Huei Chen Ilias I. Khairullin Soofin Cheng Lian-Pin Hwang 《Solid state nuclear magnetic resonance》1997,8(4):219-229
A solid complex of C60 with γ-cyclodextrin (γ-CyD) was examined with NMR spectroscopic methods in order to understand the dynamics of C60, and the interaction between C60 and γ-CyD. A 13C solid-state cross-polarization magic angle spinning (CP/MAS) NMR spectra shows C60 resonance at 142.6 ppm. This provides the evidence of interaction between 13C spins in C60 and 1H spins in the γ-CyD host. Ambient temperature experiments on the 13C CP/MAS NMR, with varying contact time, shows that the water associated with γ-CyDs plays an important role in the nuclear relaxation processes. The dynamics of C60 in γ-CyD was investigated using temperature and field-dependent 13C spin-lattice relaxation time measurements. The influence of water on the dynamics of C60 was less significant below 250 K. 相似文献
15.
Dielectric relaxation measurements of methyl cellulose with substituted phenols p-cresol, m-cresol and o-cresol mixture in different non-polar solvents CCl4, benzene and 1,4-dioxan for different concentrations over the frequency range of 10 MHz–20 GHz at 303 K have been carried out using Time Domain Reflectometry (TDR). Dielectric parameters such as static permittivity (ε0) and relaxation time (τ) were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The dielectric constant and relaxation time were found to be high for methyl cellulose with p-cresol in CCl4 compared with the other mixtures. 相似文献
16.
Asja Kozak 《Molecular physics》2013,111(20):2345-2356
It has been shown that if reorientational jumps of molecules or their parts take place through inequivalent potential barriers, it is possible to draw information on the multiplicity of the axis of reorientation from the spin-lattice T 1 time measurements in the NMR experiment. For the model of n potential wells of which one is deeper than the others, for n = 2, 3, 4, 6 the analytical formulae have been derived for the T 1 relaxation time as a function of the correlation time and n. The recurrent form of the formulae for the conditional probability of the well population has been obtained, which permits calculation of the relaxation time for any n. 相似文献
17.
To help understand which tissue parameters best account for the water proton NMR relaxation times, the longitudinal relaxation time (T2), the transverse relaxation time (T2), and the water content of 16 tissues from normal adult rats were measured at 10.7 MHz and 29°C. Regression analyses between the above and other tissue parameters were performed. These other tissue parameters included: the amounts of various organic and inorganic components, protein synthetic rate, oxygen consumption rate, and morphological composition. In addition, the differences in T1, T2, and water content values between normal liver and malignant tumor (Morris #7777 a transplantable hepatoma) were studied to help understand how a disease state can be detected and characterized by NMR spectroscopy. The results of this study and information from the literature allow the following generalizations to be made about tissue T1 and T2 values: (1) Each normal tissue has rather consistent and characteristic T1 and T2 relaxation times which are always shorter than the T1 and T2 of bulk water; (2) tissues with higher water content tend to have longer T1 relaxation times; (3) tissue T2 values are not, however, as well correlated with water content as T1 values; (4) tissues with shorter T1 values have higher calculated hydration fractions, greater amounts of rough endoplasmic reticulum, and a greater rate of protein synthetic activity; (5) tissues with higher lipid content, associated with intracellular non-membrane bounded lipid droplets, tend to have longer T2 values; (6) tissues with greater overall surface area, whether in the form of cellular membranes or intracellular or extracellular fibrillar macromolecules, tend to have shorter T2 values; (7) the differences between T1 and T2 values between tumor and normal tissues correlated with differences in the volume fraction (amounts) of extracellular fluid volumes and in the amounts of membrane and fibrillar surface area in the cells. The above generalizations should be useful in predicting T1 and T2 changes associated with specific tissue pathologies. 相似文献
18.
Paramagnetic relaxation enhancement (PRE) solid-state NMR (ssNMR) was used to monitor the valence state alternation of copper species doped in HY zeolite during catalytic reaction processes. The combination of PRE ssNMR and in-situ NMR spectroscopy facilitates the detection of copper species as well as the monitoring of evolution from reactants, intermediates to products in heterogeneously catalyzed processes, which is of great importance for elucidating the detailed catalytic reaction mechanism. 相似文献
19.
Blicharska B Peemoeller H Witek M 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2010,207(2):287-293
Assuming dipole-dipole interaction as the dominant relaxation mechanism of protons of water molecules adsorbed onto macromolecule (biopolymer) surfaces we have been able to model the dependences of relaxation rates on temperature and frequency. For adsorbed water molecules the correlation times are of the order of 10(-5)s, for which the dispersion region of spin-lattice relaxation rates in the rotating frame R(1)(ρ)=1/T(1)(ρ) appears over a range of easily accessible B(1) values. Measurements of T(1)(ρ) at constant temperature and different B(1) values then give the "dispersion profiles" for biopolymers. Fitting a theoretical relaxation model to these profiles allows for the estimation of correlation times. This way of obtaining the correlation time is easier and faster than approaches involving measurements of the temperature dependence of R(1)=1/T(1). The T(1)(ρ) dispersion approach, as a tool for molecular dynamics study, has been demonstrated for several hydrated biopolymer systems including crystalline cellulose, starch of different origins (potato, corn, oat, wheat), paper (modern, old) and lyophilized proteins (albumin, lysozyme). 相似文献
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Solid polymer electrolytes (SPEs) contain amorphous and crystalline regions, each of which have unique contributions to the 13C NMR spectrum. Understanding and assigning the 13C NMR signals are vital to interpreting the NMR data collected for each phase. The 13C CPMAS solid-state NMR spectrum of poly(ethylene oxide), a common polymer electrolyte host material, has superimposed broad and narrow components. Previously, the narrow component has been assigned to the amorphous region and the broad component to the crystalline PEO fraction. These assignments for pure PEO have been applied to various PEO:salt systems. Using lithium triflate salt dissolved in PEO, we revisit the spectral assignments and discover that the narrow component is due to crystalline PEO:LiTf component, which is reversed from the previous pure PEO assignment. This paradigm shift is based on data collected from a 100% crystalline PEO:LiTf with a 3:1 oxygen:lithium ratio sample, which exhibited only the narrow peak. For dilute electrolytes, such as 20:1 PEO:LiTf, the 13C CPMAS spectra contain the narrow peak superimposed on a broad peak as seen with pure PEO. As dilute electrolytes are heterogeneous with crystalline and amorphous regions of both pure PEO and PEO:LiTf complex, peak assignments for pure PEO and PEO:LiTf are important. Thus, we reexamine the previous assignment for pure PEO using samples of pure powdered PEO, thermally treated pure powdered PEO, and a thin film PEO cast from an acetonitrile solution. With these different samples, we observed the growth of the narrow peak under conditions that favor crystallization. Therefore, for pure PEO, we have reassigned the narrow peak to the crystalline region and the broad peak to the amorphous region. In light of our observations, previous NMR studies of pure PEO and PEO SPEs should be reinvestigated. We also use rotational echo double resonance (REDOR) to study the 20:1 PEO:LiTf created from 2 and 100 kDa PEO. We find that the lithium environment is similar in the respective microcrystalline domains. However, the 100 kDa samples have a larger fraction of pure crystalline PEO. 相似文献