用固体^1H MSA NMR研究水在不同吸附质中的状态

应用固体^1H MSA NMR实验技术，根据核磁共振峰线宽的不同，表征了水在不同吸附质中的微观状态。在含水的壳聚糖和明胶中，以氢键形式存在的水的共振峰线宽为2000Hz左右。在含水分子筛和含水硅胶中存在的吸附水的共振峰线宽在1000Hz左右。而自由水的核磁共振峰线宽小于3Hz。     

柑桔溃疡菌的共振散射光谱

研究了柑桔溃疡菌的共振散射光谱,在330、425、465和695 nm产生四个共振散射峰.当激发波长为330 nm （9.09×1014 Hz）时,溃疡菌溶液在330 nm（9.09×1014 Hz）、660 nm（1/2×9.09×1014 Hz）和990 nm（1/3×9.09×1014 Hz）分别产生一共振散射峰和1/2、1/3两个分频散射峰;当激发波长为465 nm（6.45×1014 Hz）时,在456 nm(6.45×1014 Hz)和930 nm(1/2×6.45×1014 Hz)分别产生一个共振散射峰和一个1/2分频射峰; 当激发波长为930 nm(3.23×1014 Hz)时,在930 nm (3.23×1014 Hz)、620 nm(3/2×3.23×1014 Hz)、465 nm(2×3.23×1014 Hz) 和310 nm (3×3.23×1014 Hz)分别产生一个共振散射峰,一个3/2分频共振散射峰,一个2倍频共振散射峰和一个3倍频共振散射峰.柑桔溃疡菌是一种非线性散射光学介质.分频散射和倍频散射峰与共振散射峰具有相似的散射行为.     

核磁共振溶剂的纯化

作为核磁共振溶剂,除有好的溶解性外,必须要求溶剂中不含有质子的杂质,并且杂质不干扰核磁共振光谱的测定。但目前市售溶剂,即使是一级试剂,也不能满足核磁共振测试的要求,需要进一步纯化。氯仿中含有少量的稳定剂乙醇,在核磁共振光谱高场区有三重峰和四重峰,常常干扰测定;丙酮、二甲基亚砜、二甲基甲酰胺、苯,往往含有一定量的水杂质(其氘化溶剂丙酮-d_6、二甲基亚砜-d_6、二甲基甲酞胺-d_7、苯-d_6也含有DHO、D_2O)。不只水杂质共振峰可能掩盖样品共振峰,而且对OH、NH、SH、等基团上的质子进行化学交换,妨碍测定。一些     

大肠杆菌的共振散射光谱研究

研究了大肠杆菌的共振散射光谱.它在470nm、510nm和730nm产生三个瑞利散射峰.当激发波长为470nm(6.38×1014Hz)时,大肠杆菌溶液在470nm(6.38×1014Hz)和940nm(1/2×6.38×1014Hz)分别产生一个瑞利散射峰和一个1/2分频散射峰;当激发波长为510nm(5.88×1014Hz)时,在510nm产生一个共振散射峰;当激发波长为730nm(4.11×1014Hz)时在365nm(2×4.11×1014Hz)和730nm(4.11×1014Hz)分别产生一个2倍频散射峰和一个共振散射峰.分频散射和倍频散峰与共振散射峰具有相似的散射行为.大肠杆菌的浓度在0.074～38×108个/mL范围内与共振光散射强度I470nm、I510nm、I730nm成良好线性关系.     

混合物中稀土元素的NMR法测定

核磁共振检测混合物中的共存金属是新近发展起来的无机分析方法。Fedorov以EDTA和NTA为配体,通过观察络合物Ln(EDTA)和Ln(NTA)_2配体的~1H NMR谱线,率先开展了水溶液中共存稀土元素的同时间接测定研究,这种方法比分别直接检测各稀土核磁核共振信号的方法实用可靠,且方便易行。但采用~1H NMR谱检测水溶液中顺磁稀土离子时,强的溶剂水峰易掩蔽近邻的稀土配合物谱线;某些重稀土配合物的~1H谱线宽,相互重叠,难以用作分     

高聚合度聚磷酸铵中特征磷的31P核磁共振分析

采用一维³¹P核磁共振(³¹P NMR)、 二维J分解谱(J-resolved)和扩散核磁(³¹P DOSY)等方法, 研究了高聚合度聚磷酸铵(APP)和多聚磷酸盐的特征磷及其偶合常数. 研究表明, 多聚磷酸盐及其中所含的二聚磷酸盐端基磷分别呈双峰和单峰特征, 多聚磷酸盐自旋偶合裂分的端基磷共振峰的偶合常数为19.4 Hz. APP中含有小分子二聚磷酸铵和正磷酸铵, 用³¹P NMR定量表征APP聚合度时需排除二聚体端基磷峰的面积. 在100 ℃水中溶解APP制备的APP水溶液中, 部分高聚合度APP发生断链, 中间磷共振峰处出现短链APP的磷共振峰.     

核磁共振定量法测定利培酮含量

采用氢核磁共振定量法和氟核磁共振定量法测定利培酮含量。氢核磁共振定量法以利培酮δ7.29~7.35处质子峰为定量峰,马来酸δ6.02处为内标峰,在恒温300 K,采样时间4.0 s,弛豫延迟时间15 s,扫描次数为32次条件下采集氢谱。氟核磁共振定量法以4-溴-2-氟-乙酰苯胺为内标,在恒温300 K,谱宽12 500.0 Hz,中心频率-43 662.7 Hz下采集氟谱。测试结果显示,利培酮氢核磁共振定量法和氟核磁共振定量法的含量测定结果基本与质量平衡法的结果一致。因此,核磁共振法可用于利培酮绝对含量的测定,具有快速、简单、准确的优势。     

核磁共振法分析甾体化合物

甾体化合物质子核磁共振谱的特征是在δ1—2.5间存在一个连续的峰包,这是甾体骨架上为数众多的次甲基与亚甲基质子共振信号相互重叠造成的结果。在此峰包上,介于δ0.6—1.5处常可见到二个尖峰,它们是C-18及C-19的质子共振峰。尽管甾体的     

溶剂中微量水对取代酞菁锌吸收光谱的影响

测定了6种烷氧基取代酞菁锌在不同溶剂中的电子吸收光谱. 在一些溶剂(如甲苯、氯仿和二氯甲烷)中, 除了存在典型的Q带吸收峰外, 在其长波长一侧还可观测到一个新的吸收峰, 结合对其荧光、核磁共振谱、添加强碱性溶剂(吡啶)以及对溶剂除水后的光谱的研究, 证实了新产生的吸收峰与溶剂中的微量水有关, 探讨了该吸收峰产生的原因.     

模板分子TMEDA在CF-3及ZSM-39沸石笼中的位置及其与骨架的相互作用

用XRD、FTIR、IG-DTA、~(13)C魔角固体核磁共振表征了用四甲基乙基二胺(TMEDA)为结构异向剂合成的高硅沸石CF-3及ZSM-39.TMEDA不同基团的~(13)C化学位移,共振峰相对强度在交叉极化(CP)及高功率去偶(HPDEC)核磁共振谱中的变化,揭示出模板分子在尺寸不同的沸石笼中的位置、运动状态及其与骨架的相互作用.在ZSM-39沸石中的TMEDA分子,它的-C_2H_4-基团~(13)C共振峰明显窄化,向高场的异常位移以及它与-CH_3基团~(13)C共振峰相对强度在CP及HPDEC谱中的明显变化,说明为2个相邻的[5~(12)6~4]笼所共有的TMEDA分子,其-C_2H_4-基团与这2个笼所共用的六氧元环的氧原子有强烈的相互作用.     

WISE NMR characterization of nanoscale heterogeneity and mobility in supercontracted Nephila clavipes spider dragline silk

The addition of water to spider dragline silk results in fiber contraction to 50% its initial length and significant changes to the mechanical properties of the silk. This event has been termed supercontraction. A decrease in strength and increase in elasticity have been reported when the silk is in contact with water. Two-dimensional wide-line separation (WISE) nuclear magnetic resonance (NMR) is implemented to correlate (13)C chemical shifts with mobility by observing the corresponding (1)H line widths and line shapes in water-saturated spider dragline silk. The WISE NMR spectrum of the native silk exhibits (1)H line widths that are approximately 40 kHz for all carbon environments characteristic of a rigid organic system. In contrast, the water-saturated case displays a component of the (1)H line that is narrowed to approximately 5 kHz for the glycine C(alpha) and a newly resolved alanine helical environment while the alanine C(beta) corresponding to the beta-sheet conformation remains broad. These results indicate that water permeates the amorphous, glycine-rich matrix and not the crystalline, polyalanine beta-sheets. A delay time is added to the WISE NMR pulse sequence to monitor spin diffusion between the amorphous, mobile region and the crystalline domains. The time required for spin diffusion to reach spatial equilibrium is related to the length scale of the polyalanine crystallites. This technique is employed to measure crystalline domain sizes on the nanometer length scale in water-solvated spider dragline silk. These results provide further insight into the structure of spider silk and mechanism of supercontraction.     

Molecular dynamics in paramagnetic materials as studied by magic-angle spinning 2H NMR spectra

A magic-angle spinning (MAS) 2H NMR experiment was applied to study the molecular motion in paramagnetic compounds. The temperature dependences of 2H MAS NMR spectra were measured for paramagnetic [M(H2O)6][SiF6] (M=Ni2+, Mn2+, Co2+) and diamagnetic [Zn(H2O)6][SiF6]. The paramagnetic compounds exhibited an asymmetric line shape in 2H MAS NMR spectra because of the electron-nuclear dipolar coupling. The drastic changes in the shape of spinning sideband patterns and in the line width of spinning sidebands due to the 180 degrees flip of water molecules and the reorientation of [M(H2O)6]2+ about its C3 axis were observed. In the paramagnetic compounds, paramagnetic spin-spin relaxation and anisotropic g-factor result in additional linebroadening of each of the spinning sidebands. The spectral simulation of MAS 2H NMR, including the effects of paramagnetic shift and anisotropic spin-spin relaxation due to electron-nuclear dipolar coupling and anisotropic g-factor, was performed for several molecular motions. Information about molecular motions in the dynamic range of 10(2) s(-1)相似文献   

Homonuclear Decoupling in 1H NMR of Solids by Remote Correlation

The typical linewidths of ¹H NMR spectra of powdered organic solids at 111 kHz magic-angle spinning (MAS) are of the order of a few hundred Hz. While this is remarkable in comparison to the tens of kHz observed in spectra of static samples, it is still the key limit to the use of ¹H in solid-state NMR, especially for complex systems. Here, we demonstrate a novel strategy to further improve the spectral resolution. We show that the anti-z-COSY experiment can be used to reduce the residual line broadening of ¹H NMR spectra of powdered organic solids. Results obtained with the anti-z-COSY sequence at 100 kHz MAS on thymol, β-AspAla, and strychnine show an improvement in resolution of up to a factor of two compared to conventional spectra acquired at the same spinning rate.     

Homonuclear Decoupling in 1H NMR of Solids by Remote Correlation

The typical linewidths of ¹H NMR spectra of powdered organic solids at 111 kHz magic‐angle spinning (MAS) are of the order of a few hundred Hz. While this is remarkable in comparison to the tens of kHz observed in spectra of static samples, it is still the key limit to the use of ¹H in solid‐state NMR, especially for complex systems. Here, we demonstrate a novel strategy to further improve the spectral resolution. We show that the anti‐z‐COSY experiment can be used to reduce the residual line broadening of ¹H NMR spectra of powdered organic solids. Results obtained with the anti‐z‐COSY sequence at 100 kHz MAS on thymol, β‐AspAla, and strychnine show an improvement in resolution of up to a factor of two compared to conventional spectra acquired at the same spinning rate.     

Characterization of H2-Splitting Products of Frustrated Lewis Pairs: Benefit of Fast Magic-Angle Spinning

Proton spectroscopy in solid-state NMR on catalytic materials offers new opportunities in structural characterization, in particular of reaction products of catalytic reactions such as hydrogenation reactions. Unfortunately, the ¹H NMR line widths in magic-angle spinning solid-state spectra are often broadened by an incomplete averaging of ¹H-¹H dipolar couplings. We herein discuss two model compounds, namely the H₂-splitting products of two phosphane-borane Frustrated Lewis Pairs (FLPs), to study potentials and limitations of proton solid-state NMR experiments employing magic-angle spinning frequencies larger than 100 kHz at a static magnetic field strength of 20.0 T. The ¹H lines are homogeneously broadened as illustrated by spin-echo decay experiments. We study two structurally similar materials which however show significant differences in ¹H line widths which we explain by differences in their ¹H-¹H dipolar networks. We discuss the benefit of fast MAS experiments up to 110 kHz to detect the resonances of the H⁺/H⁻ pair in the hydrogenation products of FLPs.     

Enhanced sensitivity and resolution in (1)H solid-state NMR spectroscopy of paramagnetic complexes under very fast magic angle spinning

High-resolution NMR spectroscopy for paramagnetic complexes in solids has been rarely performed because of its limited sensitivity and resolution due to large paramagnetic shifts and associated technical difficulties. The present study demonstrates that magic angle spinning (MAS) at speeds exceeding 20 kHz provides unusually high sensitivity and excellent resolution in 1H solid-state NMR (SSNMR) for paramagnetic systems. Spinning-speed dependence of 1H MAS spectra showed that very fast MAS (VFMAS) at 24-28 kHz enhanced sensitivity by a factor of 12-18, compared with the sensitivity of 1H SSNMR spectra under moderate MAS at 10 kHz, for Cu(dl-alanine)2.H2O and Mn(acac)3, for which the spectral ranges due to 1H paramagnetic shifts reach 200 and 1000 ppm, respectively. It was theoretically and experimentally confirmed that the absolute sensitivity of 1H VFMAS for small paramagnetic complexes such as Cu(dl-alanine)2 can be an order of magnitude higher than that of equimolar diamagnetic ligands because of short 1H T1 ( approximately 1 ms) of the paramagnetic systems and improved sensitivity under VFMAS. On the basis of this demonstrated high sensitivity, 1H SSNMR micro analysis of paramagnetic systems in a nanomole scale is proposed. Applications were performed on two polymorphs of Cu(II)(8-quinolinol)2, which is a suppressor of human cancer cells. It was demonstrated that 1H VFMAS SSNMR spectra accumulated for 20 nmol of the polycrystalline samples in 10 min enabled one to distinguish alpha- and beta-forms of Cu(II)(8-quinolinol)2 on the basis of shift positions and line widths.     

Thermal transitions in associating aqueous block copolymers: light scattering,rheology and spectroscopy

Solutions containing a polyoxy-ethylene/polyoxy-propylene/polyoxy-ethylene (PEO–PPO–PEO) block copolymer, indicated as F68, in water were investigated as a function of composition and temperature. Hydrogen nuclear magnetic resonance (¹H NMR) line width, chemical shift, self-diffusion, spin-lattice relaxation times, laser light scattering and rheological methods were used. The monomer–micelle equilibrium and the micelle–liquid crystalline phase transitions depend on the F68 content in the mixture and temperature. Significant changes in light scattering intensity and apparent hydrodynamic radius are associated to micelle formation above the critical micellar temperature (CMT). According to a Contin analysis, this behaviour is reflected in the presence of two populations in the intensity–intensity autocorrelation functions. The contributions due to molecules and micelles can be evaluated separately. No such effects are observed below the CMT. Micelle onset is also associated to variations in ¹H NMR spectra, affecting the chemical shift, line width and spin-lattice relaxation time of the PPO methyl protons and self-diffusion, as well. Spin-lattice relaxation times of PEO chains, conversely, change significantly at temperatures close to the micelle–liquid crystalline thermal transition. Similar results were obtained from the line width of ²H NMR spectra as a function of T. Significant changes in both viscous and elastic modulus were also observed and ascribed to PPO dehydration, at the CMT, as well as to squeezing and dehydration of PEO units in liquid crystal formation, respectively.     

1H detection in MAS solid-state NMR spectroscopy of biomacromolecules employing pulsed field gradients for residual solvent suppression

In this communication, we demonstrate the feasibility of 1H detection in MAS solid-state NMR for a microcrystalline, uniformly 2H,15N-labeled sample of a SH3 domain of chicken alpha-spectrin, using pulsed field gradients for suppression of water magnetization. Today, B0 gradients are employed routinely in solution-state NMR for coherence order selection and solvent suppression. We suggest to use gradients to purge water magnetization which cannot be suppressed using conventional water suppression schemes. The achievable gain in sensitivity for 1H detection is in the order of 5 compared to the 15N detected version of the experiment (at a MAS rotation frequency of 13.5 kHz). We expect that this labeling concept which achieves high sensitivity due to 1H detection, in combination with the possibility to measure long range 1H-1H distances as we have shown previously, to be a useful tool for the determination of protein structures in the solid state.     

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

We investigate ion and polymer dynamics in polymer electrolytes PPO-LiClO4 performing 2H and 7Li NMR line-shape analysis. Comparison of temperature dependent 7Li and 2H NMR spectra gives evidence for a coupling of ion and polymer dynamics. 2H NMR spectra for various salt concentrations reveal a strong slowdown of the polymer segmental motion when the salt content is increased. The 2H NMR line shape further indicates that the segmental motion is governed by dynamical heterogeneities. While the width of the distribution of correlation times G(log tau) is moderate for low and high salt content, an extremely broad distribution exists for an intermediate salt concentration of 15:1 PPO-LiClO4. For the latter composition, a weighted superposition of two spectral components, reflecting the fast and the slow polymer segments of the distribution, describes the 2H NMR line shape over a broad temperature range. Analysis of the temperature dependent relative intensity of both spectral components indicates the existence of a continuous rather than a discontinuous distribution G(log tau). Such continuous distribution is consistent with gradual fluctuations of the local salt concentration and, hence, of the local environments of the polymer segments, whereas it is at variance with the existence of large salt-depleted and salt-rich domains featuring fast and slow polymer dynamics, respectively. Finally, for all studied PPO-LiClO4 mixtures, the 2H NMR line shape strongly depends on the echo delay in the applied echo-pulse sequence, indicating that the structural relaxation of the polymer segments involves successive rotational jumps about small angles gamma < 20 degrees .     

Distribution and dynamics of hydrogen in the low-temperature phase of Mg(2)NiH(4) studied by solid-state NMR

Distribution and dynamics of hydrogen atoms in the low-temperature phase of Mg(2)NiH(4) have been studied by means of (2)H and (1)H NMR for Mg(2)NiD(4) and Mg(2)NiH(4), respectively. (2)H NMR spectra have been measured in the temperature range between 200 and 340 K, and the line shapes were simulated. The temperature dependence of (2)H NMR spectra was quite well simulated assuming a distorted tetrahedral configuration and a pseudoisotropic rotation of the NiD(4) unit. The estimated jump frequency obeyed Arrhenius relation with a frequency factor of (0.8 +/- 0.6) x 10(13) Hz and an activation energy of 50.1 +/- 1.4 kJ/mol. (1)H NMR spectra were acquired from 240 to 360 K. The observed (1)H second moments were 202 kHz(2) in the rigid lattice (240 K) and 46.6 kHz(2) in a motional state (360 K). The value in the rigid lattice supported the tetrahedron model, and the value in a motional state indicated the isotropic rotation of the NiH(4) unit. Conclusively, the NiH(4) unit has the distorted tetrahedral configuration and undergoes the pseudoisotropic rotation.