聚酰胺66溶液弛豫行为的NMR研究

用1D和2D NMR技术归属了聚酰胺66的1H和13C的NMR共振信号,并通过聚酰胺66溶液温度和浓度改变对氢核弛豫时间的影响,得到了其分子运动信息.结果表明随着温度的升高,聚酰胺66链间氢键逐渐解离,大分子链间相互作用逐渐减弱.而解离出来的链段又与溶剂小分子可以形成新的氢键,使聚酰胺66链卷曲并包含着部分溶剂分子一起运动.随着溶液浓度的增大,由于分子链间距变小,使得分子间作用力增强,链缠结程度加大,使链运动受限.     

NMR Relaxation Study of Cholesterol Binding with Plant Metabolites

Nuclear magnetic resonance relaxation technique has been applied to study the interaction of cholesterol and its oxidation products with plant metabolite, glycyrrhizic acid. In all cases, the decay kinetics of echo signal shows bi-exponential behavior. It was demonstrated that the fast component of the decay kinetics belongs to the complex with stoichiometry of 1:2. The stability constants and thermodynamic parameters of these complexes have been measured. We propose that the complexation with glycyrrhizic acid could be an effective approach to regulate the cholesterol level inside and outside of cage membranes. In addition, the importance of this approach as a tool for reducing the cytotoxicity of the oxidation products of cholesterol is under discussion.     

岩心孔隙介质中流体的核磁共振弛豫

弛豫时间是核磁共振研究中的一个重要参数,岩心孔隙介质流体的弛豫过程是自由流体弛豫机制、表面弛豫机制和流体的扩散弛豫机制共同作用的结果,它包含了丰富的孔隙和流体本身的信息. 弛豫时间和自扩散系数的测量及对弛豫时间的分析是核磁共振技术应用于岩心分析和石油勘测的重要内容.     

Dipolar Relaxation of Multiple Quantum NMR Coherences as a Model of Decoherence of Many-Qubit Coherent Clusters

Dipolar relaxation of multiple quantum (MQ) nuclear magnetic resonance (NMR) coherence is investigated on the evolution period of the MQ NMR experiment in chains of ¹⁹F nuclei in a single crystal of calcium fluorapatite. The dependence of the relaxation time of the MQ coherence of the second order on the size of the coherent spin cluster formed on the preparation period is obtained. The dipolar relaxation of MQ NMR coherences is considered as a model for the investigation of decoherence of quantum states of many-qubit spin clusters.     

1H NMR Study of Some Thiosalicylic Acid Complexes

Five thiosalicylic acid (TSA) complexes were prepared. The ¹H NMR of these complexes were recorded and analysed. It was found that molybdenum, arsenic, selenium, silver and tellurium metals coordinates through the sulfur atom. The ¹H NMR chemical shift of ring protons of As, Se and Te shift to low field upon complexation, while it shifts to high field when TSA complex with Ag and Mo     

核磁共振弛豫时间与溶液浓度关系的实验研究

利用小型核磁共振成像仪可以测量样品弛豫时间的功能，设计方案，实验测定了硫酸铜水溶液中氢原子核的核磁共振弛豫时间T1、T2随硫酸铜浓度的变化关系，得到T1与T2随溶质浓度的增大而减小的实验结果．在误差允许的范围内，验证了T1与溶液浓度成反比的规律，并进行了分析和理论解释．     

Local NMR Relaxation of Dendrimers in the Presence of Hydrodynamic Interactions

We study the role of hydrodynamic interactions for the relaxation of segments’ orientations in dendrimers. The dynamics is considered in the Zimm framework. It is shown that inclusion of correlations between segments’ orientations plays a major role for the segments’ mobility, which reveals itself in the nuclear magnetic resonance relaxation functions. The enhancement of the reorientation dynamics of segments due to the hydrodynamic interactions is more significant for the inner segments. This effect is clearly pronounced in the reduced spectral density \(\omega J(\omega )\), maximum of which shifts to higher frequencies when the hydrodynamic interactions are taken into account.     

Numerical Determination of the Relaxation Parameters of NMR in Complex Heterogeneous Systems

The methods of mathematical processing of the envelopes of spin-echo signals have been considered within the framework of the multiphase relaxation theory. A mathematical model for separation of multiexponential relaxation curves into individual exponential components of spin-spin relaxation times T _2i and amplitudes I _i is described. The multiphase nature of the relaxation of protons in complex heterogeneous systems has been revealed, and the relaxation characteristics of individual components — spin-spin relaxation times and amplitudes — have been determined.     

NMR Solvent Spin‐Lattice Relaxation Rate in Colostrum

Abstract

In this study, by using a FT‐NMR spectrometer operating at 60 MHz for proton, the solvent spin‐lattice relaxation times (T ₁) in colostrum were measured versus the days of lactation, whereas the T ₁ values in dehydrated colostrum were determined versus concentration of its hydrating solid. Data show that the spin‐lattice relaxation rate (1/T ₁ or R ₁) in colostrum is linearly dependent upon the inverse of time (1/days), and the R ₁ in dehydrated colostrum increases linearly with increasing concentration of its hydrating solid content (C). From data, the total paramagnetic contribution of ions in colostrum to the R ₁ was found to be negligible. The dehydrated colostrum data indicates that the R ₁ in colostrum is linearly dependent upon its hydrating solid content. Therefore, the R ₁ changes in colostrum were analyzed in terms of the relaxivities (increase in relaxation rate per unit concentration of solid) and the concentrations of milk constituents. Such an analysis provides a relation similar to that of the R ₁ in dehydrated colostrum. The current data imply that the relaxation changes in colostrum by days may be explained through changes in the concentrations of milk constituents. Also, the data suggest that the relaxation mechanism in colostrum can be explained in terms of fast chemical exchange of protons between free water and water bound to milk constituents.     

A New Approach of Two-Dimensional the NMR Relaxation Measurement in Flowing Fluid

Driven-equilibrium fast saturation recovery (DEFSR), as a new method for two-dimensional (2-D) nuclear magnetic resonance (NMR) relaxation measurement based on pulse sequence in flowing fluid, is proposed. The two-dimensional functional relationship between the ratio of transverse relaxation time to longitudinal relaxation time of fluid (T ₁/T ₂) and T ₁ distribution is obtained by means of DEFSR with only two one-dimensional measurements. The rapid measurement of relaxation characteristics for flowing fluid is achieved. A set of the down-hole NMR fluid analysis system is independently designed and developed for the fluid measurement. The accuracy and practicability of DEFSR are demonstrated.     

Modeling of Self-Diffusion and Relaxation Time NMR in Multi-Compartment Systems

The theory of pulsed field gradient (pfg) NMR applied to molecules in cellular systems which contain different subcellular compartments separated by permeable membranes, acting as diffusion barriers, has been extended. A numerical model of restricted diffusion and magnetization relaxation behavior in pfg-CPMG NMR experiments, based on the Fick's second law of diffusion, is presented. This model is applicable to a wide range of systems and allows the exploration of temporal and spatial behavior of the magnetization with and without the influence of gradient pulses. Results of the numerical experiments show their correspondence to the previously observed ones and demonstrate the importance of the inclusion of the time domain data in analyzing diffusion measurements.     

Nuclear Spin Relaxation in Some Non-viscous Media Using the 181Hf Probe

Perturbed angular correlation (PAC) studies have been performed in liquid mercury, HCl media of different acid strengths, H₂O and H₃PO₄ using a ¹⁸¹Hf probe. It is found that, in case of H₂O, interaction between the nucleus and its excited atom following the β⁻ decay of ¹⁸¹Hf is a possible mechanism for the nuclear spin relaxation in this environment. In the liquid mercury and different acid media, however, the perturbations are found to arise due to molecular fluctuations.     

Unusual Increase of Apparent Transverse Relaxation Times in NMR Profiling of a Drying Polymer Solution

In this contribution, we present results from a nuclear magnetic resonance (NMR) profiling study of drying polymer solutions using polyvinylpyrrolidone (PVP) as a model system. The careful evaluation of the experimental data reveals a surprising increase in the apparent transverse relaxation time of the water phase of the drying solution over the first few hours of drying (where usually a decrease would be expected). By using additional information obtained from diffusion-weighted profiles, we can explain this finding as the result of a strong reduction of the diffusion effect on the apparent relaxation time during this time interval. Understanding this effect provides a better basis for making optimal use of profiling NMR in drying studies and avoids possible misinterpretation on the data.     

羟基磷灰石-碳酸钙-BSA水溶性复合物中蛋白质微观结构的研究

利用傅里叶变换红外光谱，结合二阶导数谱、退卷、积和曲线拟合等计算机解析方法，对牛血清白蛋白（BSA）－羟基磷灰灰石－碳酸钙水溶性复合物中BSA的二级结构进行了研究。结果表明，BSA的α－螺旋结构的含量增加，蛋白质结构趋于有序化；紫外光谱和紫外二阶导数谱的研究发现，BSA的芳香族氨基酸残基的微环境受到扰动，在生物体内，正是蛋白质结构的这些变化导致生物矿化过程的发生和进行。     

NMR 63.65Cu in a Local Field and Relaxation of Nuclear Spins in a CuFeS2 Magnetic Semiconductor

Applied Magnetic Resonance - The results of the study of the spectral and relaxation parameters of 63.65Cu nuclear magnetic resonance (NMR) in a local field in natural samples of the semiconductor...     

DNA Duplex Dynamics: NMR Relaxation Studies of a Decamer with UniformlyC-Labeled Purine Nucleotides

Dynamics in a DNA decamer duplex,d(CATTTGCATC) ·d(GATGCAAATG), were investigated via a detailed¹³C NMR relaxation study. Every 2′-deoxyadenosine and 2′-deoxyguanidine was chemically enriched with 15%¹³C and 98%¹⁵N isotopes. Six nuclear relaxation parameters [R(¹³C_z),R(¹H_z),R(2¹H_z¹³C_z),R(¹³C_x),R(2¹H_z¹³C_x) and steady-state¹³C{¹H} NOE] were measured at 600 MHz and three were measured at 500 MHz (¹H frequency) for the CH spin systems of sugar 1′, 3′, and 4′ as well as base 8 and 2 positions. A dependence of relaxation parameter values on chemical position was clearly observed; however, no sequence-specific variation was readily evident within our experimental error of ∼5–10%, except for 3′ and 5′ termini. It was demonstrated that the random 15%¹³C enrichment effectively suppressed both scalar and dipolar contributions of the neighboring carbons and protons on the relaxation parameters. To analyze dynamics via all observed relaxation parameters, full spectral density mapping (1992, J. W. Peng and G. Wagner,J. Magn. Reson.98, 308) and the “model-free” approach (1982, Lipari and Szabo,J. Am. Chem. Soc.104, 4546) were applied complementarily. A linear correlation between three spectral density values,J(ω_C),J(ω_H− ω_C), andJ(ω_H+ ω_C) was observed in plots containing all measured values, but not for the other spectral density terms includingJ(0). These linear correlations reflect the effect of overall motion and similar internal motions for each CH vector in the decamer. The correlations yielded two correlation times, 3–4 ns and 10–200 ps. One value, 3–4 ns, corresponds to the value of 3.3 ns obtained for the overall isotropic tumbling correlation time determined from analysis of¹³C T1/T2 ratios. The possibility of overall anisotropic tumbling was examined, but statistical analysis showed no advantage over the assumption of simple isotropic tumbling. Lack of correlations entailingJ(0) implies that a relatively slow chemical exchange contributes to yielding of effectiveJ_eff(0) values. Based on spectral density mapping and the T1/T2 ratio analysis, three basic assumptions were initially employed (and subsequently justified) for the model-free calculation: isotropic overall tumbling, one internal motion, and the presence of chemical exchange terms. Except for terminal residues, the order parameterS²and the corresponding fast internal motion correlation time were determined to be about 0.8 ± 0.1 and 20 ± 20 ps, respectively, for the various CH vectors. Only a few differences were observed between or within sugars and bases. The internal motion is very fast (ps–ns time scale) and its amplitude restricted; e.g., assuming a simple wobble-in-a-cone model, the internal motion is restricted to an angular amplitude of ±22.5° for each of the 1′, 3′, 4′, 2, and 8 positions in the purine nucleotides in the entire duplex.