Measurement of spin-lattice relaxation times of C in organic solids

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 T₁^C < T₁^H and those obeying T₁^C < T₁^H is clearly indicated. The methyl group resonances in solid-state -valine are examined, and the experimental results agree well with the theoretical results.     

Cl nuclear quadrupole resonance studies of molecular motions of ClO3 and water diffusion in Ca(ClO3)2·2H2O

A ³⁵Cl nuclear quadrupole resonance (³⁵Cl-NQR) investigation of polycrystalline Ca(ClO₃)₂·2H₂O is described. The ³⁵Cl-NQR frequencies (ν_Q) for two resonance lines (ν_Q1 and ν_Q2), the spin lattice relaxation time (T_1Q) for ν_Q2 only and the line width δν_Q2 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 T_1Q 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 δν_Q2 confirmed the conclusions drawn from the analysis of T_1Q(T).     

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.     

Spin-lattice relaxation times and nuclear overhauser enhancement effect for P metabolites in model solutions at two frequencies: Implications for in vivo spectroscopy

The relaxation time T₁ values and nuclear Overhauser enhancement factor for ³¹P signal were determined in model solutions of metabolites ATP, PCr and Pi, and AMP at two frequencies and in H₂O and ²H₂O solutions. The data were analyzed to resolve the contribution of different relaxation mechanisms. A knowledge of NOE is important in the light of recent applications of double resonance methods to enhance the sensitivity of in vivo ³¹P spectroscopy. The results show that chemical shift anisotropy is the dominant mechanism for ³¹P in ATP at the high field, whereas the dipolar interaction mechanism is the main feature for the ³¹P relaxation of PCr and Pi. The dipolar mechanism responsible for NOE originates from interactions of solvent water with ³¹P moiety. Implications for in vivo spectroscopy are indicated.     

PVP在水/丙酮混合溶剂中分子运动行为的研究

通过对粘度、自旋-自旋弛豫时间以及1H NMR谱的测定,研究了PVP在不同体积配比的水/丙酮溶液中的特性粘数变化和分子运动规律,并讨论了引起这些变化的原因.结果表明:随着丙酮的不断加入,PVP的特性粘数[η]先增加后减小,而T2H先减小后增大.[η]出现最大值也是T2H出现最小值的时候,丙酮的体积百分数为40%.丙酮的加入破坏了水分子间自身氢键相互作用形成的网状结构,解离出来的水分子被PVP优先吸附到大分子链上,部分与羰基形成氢键,另一部分以自由水的形式被包裹在大分子线团内.水分子的不断进入以及与水形成新的氢键使PVP链逐渐伸展,引起特性粘数的增大,分子运动受阻.当丙酮含量增加到一定程度时,水的含量不足以使大分子链继续膨胀,故链呈卷缩状态,使大分子运动逐渐恢复自由.1H NMR谱中各质子的化学位移变化也证实了此过程中的氢键变化规律.     

邻啡啰啉─吡啶2,6二甲酸铕二、三元配合物的NMR研究

报道了稀上铕(Eu³⁺)与吡啶-2,6-二甲酸(H₂DPC)及邻啡啉(Phen)形成的二元和三元固体配合物的制备.对它们进行了元素分析,确定该配合物的组成为二元Na₃[Eu(DPC)₃]·2H₂O和三元NaEu(DPC)₂·4H₂O,对上述配合物的结构作了核磁共振氢谱(¹H NMR)、碳谱(¹³CNMR)和氮谱(¹⁴N NMR)及红外光谱(IR)的研究.吡啶-2,6-二甲酸中的羧基以单齿配位(整个分子为三齿配位),二、三元配合物中铕的配位数分别为9和8.     

几种易溶性有机溶剂水溶液的1H、13C、17O和31P NMR研究

本文用络合平衡及快交换的方法定量描述了磷酸三乙酯(TEP)、四氢呋喃(THF)、二氧六环(DO)和乙腈(AN)水溶液中化学位移随浓度变化的曲线。发现体系中未配位水的¹H化学位移与其浓度的关系为:H₂O δ₀=1.07+3.71e^{k(0.018-1)/[H₂O]}。K值与溶剂的供电性和分子量有关。溶剂破坏水结构的能力取决于它的供电性。     

Measurement of the slope parameter for the neutral pion spectrum in KL → πππ decay

The π⁰ spectrum in the K_L⁰ → 3π decay was measured using a wire chambers magnetic spectrometer. In the usual approximation, the matrix element can be expressed as: M² ≈ 1 + 2a₀(M_K/M_π²)(2T_π⁰−T_π⁰max) + a₁(M_K²/M_π⁴)(2T_π⁰−T_π⁰max)². We obtained a₀ = −0.282 ± 0.011 and a₁ consistent with zero.     

1-(2-羧基苯基甲酰基)氨基硫脲及其Cu+配合物的NMR研究

利用¹H-¹H COSY,¹H-¹³C HMQC,HMBC等2D NMR技术对一种新的配体1-(2-羧基苯基甲酰基)氨基硫脲(H₃L)进行¹H、¹³C NMR谱数据分析与归属,对于它与Cu⁺离子配位的化合物[Cu₂(H₃L)₂Cl₂](H₂O)₃也作了¹H、¹³C NMR的测定,简单讨论了它的配位行为,粗略确定了它的结构.     

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.     

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.     

{Cu3}单分子磁体在磁场中的热纠缠

本文研究单分子磁体Na₉[Cu₃Na₃(H₂O)₉ (α-AsW₉O₃₃)₂]·26H₂O中三角自旋 环在磁场作用下的热纠缠性质, 利用数值计算求出任意两个Cu²⁺离子量子比特之间的配对纠缠度, 分别记为C₁₂, C₂₃和C₁₃. 研究结果表明, 磁场的方向和大小以及温度对配对纠缠度具有重要影响, 而且参数的变化对C₁₂, C₂₃和C₁₃的影响也是各不相同. 给出外加三个不同方向的磁场时, 配对纠缠度C₁₂, C₂₃和C₁₃各自对应的临界温度T_c随磁场强度的变化图, 由此可以得到单分子磁体三角自旋环中存在纠缠态的参数范围. 通过选择适当的磁场方向和大小以及温度等实验参数, 可以有效地调节和提高单分子磁体中的配对纠缠度. 关键词： 配对纠缠 单分子磁体 三角自旋环     

Measurement of Hartmann-Hahn cross-polarization dynamics with quenching of proton T1ρ relaxation dependence

A simple modification of the standard cross-polarization method designed for quenching the proton T_1ρ 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_1ρ(¹H) effect, can be observed in dipolar-coupled spin systems.     

Characterization of polyalkylvinyl ether phases by solid-state and suspended-state nuclear magnetic resonance investigations

Pure organic polyalkylvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C₄VE) and n-octadecylvinyl ether (C₁₈VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and ¹H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of ¹H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the ¹H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin–lattice relaxation times (T₁) as well as accumulation of a 2D wide line separation NMR spectrum.     

Proton transference number of PFSA ionomer membranes

The cation transference number of the novel XUS (Dow Chemical) ionomer membrane was measured by the employment of protonic conducting solution electrodes. The limiting values of the equivalent conductivity of H⁺ and OH^- at various solution concentrations were obtained by extrapolation to yield the membrane proton transference number. The result of 81% was compared to that of NAFION^R and aqueous solution to show an inverse relationship between the transference number and the size of the environment accommodating the water molecules, which constitutes some understanding of the ionic conducting mechanism.     

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.     

[Co(H2O)4(NCS)2](18-C-6)配合物的NMR研究

该文测定了最近合成的[Co(H₂O)₄(NCS)₂](18-C-6)的¹H、¹³C、¹⁴N核磁共振谱,验证了其配合物的结构,并用红外光谱(IR)作了进一步的确定.     

Proton dynamics in letovicite, (NH4)3H(SO4)2: a 1H and 14N NMR spectroscopic study

The improper ferroelastic phase letovicite (NH₄)₃H(SO₄)₂ has been studied by ¹H MAS NMR as well as by static ¹⁴N NMR experiments in the temperature range of 296–425 K. The ¹H MAS NMR resonance from ammonium protons can be well distinguished from that of acidic protons. A third resonance appears just below the phase transition temperature which is due to the acidic protons in the paraelastic phase. The lowering of the second moment M₂ for the ammonium protons takes place in the same temperature range as the formation of domain boundaries, while the signals of the acidic protons suffer a line narrowing in the area of T_c. The static ¹⁴N NMR spectra confirm the temperature of the motional changes of the ammonium tetrahedra. Two-dimensional ¹H NOESY spectra indicate a chemical exchange between ammonium protons and the acidic protons of the paraphase.     

Radiation-induced changes in phosphorus T1values in human melanoma xenografts studied by P-MRS

³¹P-magnetic resonance spectroscopy (MRS) has been shown to be a promising method for monitoring tumor response to radiation therapy. The purpose of the work reported here was to investigate whether the usefulness of ³¹P-MRS might be enhanced by measurement of spin-lattice relaxation times (T₁s) in addition to resonance ratios. The work was based on the hypothesis that tumors having a high probability of being controlled locally would show shortened T₁s during the treatment course due to reoxygenation and development of necrosis. BEX-t human melanoma xenografts, which show efficient reoxygenation and development of necrosis following single dose irradiation, were used as tumor models. Tumors were treated with single doses of 5.0 or 15.0 Gy and the T₁s of the inorganic phosphate and nucleoside triphosphate β resonances were measured as a function of time after irradiation by using the superfast inversion recovery method. Fractional tumor water content was determined by drying excised tumors at 50°C until a constant weight was reached. The T₁s in irradiated tumors were either longer than or not significantly different from those in unirradiated control tumors. The increase in the T₁s following irradiation coincided in time with a radiation-induced increase in tumor water content, suggesting a causal relationship. The effects of reoxygenation and development of necrosis on T₁s were probably overshadowed by the effects of tumor water content. Consequently, the usefulness of ³¹P-MRS in monitoring tumor response to radiation therapy might not be significantly enhanced by measurement of T₁s.