Study of activation parameters and NMR spin-lattice relaxation time in some substituted amines

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 (ΔE_A) obtained using dielectric relaxation time, have been correlated with calculated values of ΔE_A 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).     

Nuclear magnetic resonance relaxometry of the normal heart: Relationship between collagen content and relaxation times of the four chambers

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.     

Local and global dynamics in the glass-forming di-isobutyl phthalate as studied by H NMR

Spin-lattice relaxation times T₁ and T_1ρ as well as ¹H NMR spectra have been employed to study the dynamics of the glass-forming di-isobutyl phthalate in the temperature range extending from 100 K, through the glass transition temperature T_g, up to 340 K. Below T_g NMR relaxation is governed by local dynamics and may be attributed to rotation of methyl groups at low temperatures and to motion of isobutyl groups in the intermediate temperature interval. Above T_g the main relaxation mechanism is provided by overall molecular motion. The observed relaxation behavior is explained by motional models assuming asymmetrical distributions of correlation times. The motional parameters obtained from Davidson-Cole distribution, which yields the best fit of the data at all temperatures are given.     

Two separate Li ionic motions observed by Li and B NMR in xLi2S + (1 − x)B2S3 glassy fast ionic conductors

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’.     

Molecular dynamics in solid riboflavin as studied by 1H NMR

Spin–lattice relaxation times T₁ and T_1d as well as NMR second moment were employed to study the molecular dynamics of riboflavin (vitamin B₂) in the temperature range 55–350 K. The broad and flat T₁ minimum observed at low temperatures is attributed to the motion of two nonequivalent methyl groups. The motion of the methyl groups is interpreted in terms of Haupt's theory, which takes into account the tunneling assisted relaxation. An additional mechanism of relaxation in the high temperature region is provided by the motion of a proton in one of the hydroxyl groups. The Davidson–Cole distribution of correlation times for this motion is assumed.     

NMR relaxation of protons in tissues and other macromolecular water solutions

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.     

基于T2截止值的幂函数构建毛管压力曲线

岩心核磁共振（NMR）T₂谱和毛管压力曲线都在一定程度上反映了岩石孔隙结构，理论分析表明可利用T₂谱构建毛管压力曲线，由此快速获取储层孔隙结构的信息．本文对18块岩样T₂分布和毛管压力曲线进行了分析，提出将T₂截止值作为幂函数的分段点，采用分段幂函数方法构建岩样的NMR毛管压力曲线，并与采用不分段幂函数方法获得的毛管压力曲线进行了对比．研究结果表明，与不分段幂函数方法相比，分段幂函数方法得到的结果和压汞实验测定的毛管压力曲线吻合度更高，平均拟合度（R²）达到0.943 1，并且论证了T₂截止值作为分段点进行分段幂函数法构建NMR毛管压力曲线的合理性和可靠性．T₂截止值的引入提高了幂函数法构建NMR毛管压力曲线的精度，是利用NMR T₂谱构建岩样毛管压力曲线的有价值探索．     

回波间隔对核磁共振表观孔隙度的影响及矫正方法

本文对具有特定横向弛豫时间（T₂）的硫酸铜溶液进行了多回波间隔（T_E）的核磁共振（NMR）实验,并利用数值模拟对32组具有不同弛豫分量的模型进行了变T_E模拟实验,定量研究了T_E对致密油气、页岩气等低孔低渗储层NMR孔隙度的影响规律.实验结果表明,随着T_E的增大,各T₂弛豫组分NMR孔隙度先维持在100%左右,然后迅速衰减,当T_E增加到一定数值时,趋近于0;不同T₂弛豫组分NMR孔隙度开始迅速衰减及最后变为0的T_E值存在显著差异.根据不同T₂弛豫组分NMR孔隙度与T_E的关系,将整个NMR测量分为无损测量区、快速衰减区、无效参数区和仪器盲区4个区域.对特定弛豫组分而言,在快速衰减区弛豫组分损失量与T_E呈对数关系,本文还给出了该区域NMR孔隙度的校正公式及方法.     

In vivo NMR T2 relaxation of experimental brain tumors in the cat: a multiparameter tissue characterization.

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 T_2(normal) < T_2(tumor) < T_2(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.     

川西气田白云岩储层二维核磁共振测井气水识别方法

川西气田雷口坡组四段白云岩储层具有良好的天然气勘探开发前景,但是储层分布具有较强的非均质性,利用常规测井和一维核磁共振测井方法判断储层流体性质存在多解性．通过分析川西雷四段白云岩储层地质特征与测井响应特征,开展岩心二维核磁共振实验,明确了实验室分析与测井过程中环境、参数等影响因素,建立了岩心分析结果的校正方法,明确了钻井液、束缚流体、可动水与天然气信号在二维核磁共振测井中谱分布区间,建立了基于T₂-T₁、T₁/T₂（R）的白云岩储层二维核磁共振测井气水识别图版．利用图版对川西雷四段储层流体性质开展评价,二维核磁共振测井解释结论得到了实钻测试结果的验证,该气水识别方法填补了常规测井、一维核磁共振测井在评价储层气水关系中的缺陷,可有效解决白云岩储层流体性质判别难题．     

Myocardial proton spin-lattice relaxation times in vitro: Effect of elapsed time after excision

An assumption made in using excised tissue for in vitro nuclear magnetic resonance (NMR) studies is that variables of interest, such as spin-lattice (T₁) relaxation times, remain stable for periods of time after excision sufficient to perform NMR spectroscopy. In this study, we evaluated the changes in T₁ of rat myocardium, measured at two NMR field strengths, at serial time intervals up to 72 hours postmortem. Left ventricular myocardium from six male Sprague-Dawley rats was excised and stored at room temperature in sealed NMR sample tubes. Spin-lattice relaxation times were determined with a modified inversion-recovery pulse sequence immediately postmortem and at intervals up to 72 hours post-excision; NMR studies were performed using 90 MHz and 360 MHz spectrometers. A gradual decrease in T₁ was noted with increasing time post-excision; T₁ was not significantly shorter than baseline until 72 hours postmortem at either field strength. The rate of change of T₁ was similar at the two field strengths. At any given time post-excision, T₁ was significantly higher (p < 0.001) at 360 MHz than at 90 MHz. We conclude that, with proper tissue handling and storage techniques, rat myocardial T₁ is stable postmortem sufficiently long to permit meaningful NMR studies of excised tissue.     

基于二维核磁共振弛豫谱的雷四段孔隙度计算方法

基于常规测井资料的体积模型和一维核磁共振（NMR）测井资料的固定截止值法,可以计算地层孔隙度,但是扩径段孔隙度计算结果偏大.本文通过川西海相雷四段岩心样品NMR实验和实测二维NMR测井资料,开展扩径段的T₂、T₁孔隙度计算方法研究.首先总结不同孔径流体在T₂谱和T₁谱上的响应特征,分析钻井液流体峰截止值的分布范围和影响因素,建立钻井液流体弛豫时间截止值的计算模型;然后根据未扩径段和扩径段的粘土束缚水弛豫时间截止值确定原则,确立变粘土束缚水弛豫时间截止值的有效孔隙度计算方法.多口井的应用效果表明,基于T₁谱的孔隙度计算结果精度更高、定量分析误差小,能有效解决扩径段孔隙度计算结果偏大的问题,满足储层评价的要求.     

固体核磁共振研究半晶聚-3-羟基丁酸酯和聚羟基丁酸戊酸酯的分子动力学

本文在150~370 K温度范围内,采用固体核磁共振（NMR）测定了半晶聚-3-羟基丁酸酯（PHB）,以及3-羟基戊酸酯单体质量分数分别为5%（PHBV5）和12%（PHBV12）的聚羟基丁酸戊酸酯共聚物在实验室坐标系和旋转坐标系条件下质子的自旋-晶格弛豫时间T₁和T_1ρ.通过弛豫时间随温度变化的理论拟合,分别获得上述半晶聚合物晶区和结晶区的分子动力学参数（包括E_a和τ₀）.这些结果从分子水平上阐述了PHB结构修饰和增强的原因.     

Selection of pulse sequences producing maximum tissue contrast in magnetic resonance imaging

The importance of spin density [N(H)] and spin-lattice (T₁) and spin-spin (T₂) relaxation in the characterization of tissue by nuclear magnetic resonance (NMR) is clearly recognized. This work considers which optimized pulse sequences provide the best tissue discrimination between a given pair of tissues. The effects of tissue spin density and machine-imposed minimum rephasing echo times (TE_MIN) for achieving maximum signal tissue contrast are discussed. A long TE_MIN sacrifices T₁-dependent contrast in saturation recovery (SR) and inversion recovery (IR) pulse sequences so that spin-echo (SE) becomes the optimum sequence to provide tissue contrast, due to T₂ relaxation. Pulse sequences providing superior performance may be selected based on spin density and T₁ and T₂ ratios for a given pair of tissues. Selection of the preferred pulse sequence and interpulse delay times to produce maximum tissue contrast is strongly dependent on knowledge of tissue spin densities as well as T₁ and T₂ characteristics. As the spin density ratio increases, IR replaces SR as the preferred sequence and SE replaces IR and SR as the pulse sequence providing superior contrast. To select the optimal pulse sequence and interpulse delay times, an accurate knowledge of tissue spin density, T₁ and T₂ must be known for each tissue.     

Cu NMR study of the superconducting thiospinel Cu1.5Rh1.5S4

The ⁶³Cu NMR Knight shift K and spin-lattice relaxation rate 1/T₁ have been measured to study the thiospinel superconductor Cu_1.5Rh_1.5S₄ from a microscopic viewpoint. K is negative and has a weak dependence on temperature, and the hyperfine coupling constant H_hf^d is estimated to be −52.4 kOe/μ_B. 1/T₁ is proportional to the temperature in the normal state. In the superconducting state, 1/T₁ takes a coherence peak just below T_c, and decreases exponentially well below T_c, from whose temperature dependence the superconducting energy gap has been proved to be close to 2Δ = 3.52k_BT_c given by the BCS theory.     

MRI of hepatic lymphoma

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.     

Molecular dynamics of polycrystalline cellobiose studied by solid-state NMR

Molecular motions of polycrystalline cellobiose have been investigated by measuring proton spin–lattice relaxation times, T₁ and T_1ρ, 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_1ρ relaxation is driven by the motions of the same groups between 120 and 300 K. T_1ρ 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.     

Correlation between 1H FID and T1rho components in heterogeneous polymer systems: an application to SBS

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 (T_1ρ) 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 T_1ρ data, to be revealed. In the case examined, the correlation found could be confirmed by high-resolution ¹H T_1ρ-selective ¹³C Cross Polarization experiments.     

The effect of Magic Angle Spinning on proton spin–lattice relaxation times in some organic solids

Proton spectra of solids are usually broadened by strong proton homonuclear dipolar interactions. However, substantial line narrowing may be achieved by Magic Angle Spinning (MAS) in systems of low proton density or in systems in which rapid molecular motions occur. In such conditions, T₁(H) measurements are often used to characterise the dynamics of each resolved proton site. We show that T₁(H) values measured for solid organic compounds with high proton abundance, such as adamantane and glycine, may be strongly dependent on the spinning rate employed, so that care is required when values are compared. The effects of molecular motion and proton density on T₁(H) and its dependence on spinning rate were investigated. We found that an increase in molecular motion leads to an increase of T₁(H) at higher spinning rates. The opposite is found for systems with low proton densities which show relatively lower T₁(H), at higher spinning rates. A possible interpretation is suggested in terms of the reduced spin diffusion efficiency at higher spinning rates.     

C CPMAS studies of plant cell wall materials and model systems using proton relaxation-induced spectral editing techniques

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_1ρ, 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.