基质辅助 NMR 中色谱技术的研究进展

被誉为“ NMR 中色谱技术”的二维扩散排序 NMR 谱(DOSY)技术是检测混合物溶液中不同分子组分的一种有效手段．但是当面对自扩散系数差别较小的不同分子时, DOSY技术便无法对上述混合物进行基线分离． 在 NMR 魔角旋转转子或 NMR 样品管中添加一些色谱填料或高分子等基质（或称为虚拟“色谱固定相”）是一种行之有效的手段．这些虚拟“色谱固定相”与混合物组分发生相互作用并改变其自扩散系数,从而对混合物实现基线分离．该文综述了近年来基质辅助 NMR中色谱技术的研究进展．
     

两种短链醇与叔丁醇的互扩散系数

叔丁醇作为一种优良的助溶剂,被广泛应用于生物柴油的生产过程中。本文利用数字全息干涉法测量了乙醇、正丙醇与叔丁醇的互扩散系数,实验测量的质量分数范围为0.1到0.9(间隔0.1),温度范围为303.15K到323.15K。实验结果显示:对于本文所研究的体系,混合物的互扩散系数随着温度的升高而增大;在相同的温度条件下,混合物的互扩散系数与溶液的浓度近似呈正比例关系;在相同的温度和浓度条件下,乙醇与叔丁醇的互扩散系数大于正丙醇和叔丁醇的互扩散系数。本文还提出了一个可以精确回归实验数据的关联式。     

柚皮素7-O-葡萄糖苷非对映异构体的NMR波谱分析

二氢黄酮糖苷化后产生的R与S构型非对映异构体在¹H NMR谱上会呈现一些差别,但文献对其差别描述非常有限.为便于利用¹H NMR谱图判断二氢黄酮糖苷的R与S构型非对映异构体,本文首先在植物药皂荚提取物中分离得到一种二氢黄酮苷-柚皮素7-O-葡萄糖苷R与S构型混合物,分析其氘代二甲亚砜（DMSO-d₆）溶液的¹H NMR、¹³C NMR、¹H-¹H COSY、¹H-¹³C HSQC和¹H-¹³C HMBC谱,对其¹H和¹³C NMR谱峰进行了归属;然后,采用手性色谱柱对该混合物进行分离,结合圆二色光谱（CD）技术确定构型;最后,为鉴别R与S构型柚皮素7-O-葡萄糖苷在¹H NMR谱中特征差别谱峰,避免葡萄糖残基质子对二氢黄酮苷元质子化学位移的影响,采集了R与S构型柚皮素7-O-葡萄糖苷及其混合物氘代乙腈（CD₃CN）溶液的NMR谱,结果显示葡萄糖残基端基质子H-1″化学位移差别最为明显,为9.4 Hz;5-位酚羟基质子化学位移差别为5.8 Hz,C环上3个质子化学位移差也较明显．     

聚对苯撑乙炔咔唑薄膜对TNT挥发物的检测

以3, 6-二溴-9-辛基咔唑和2, 5-二戊烷氧基-1, 4-二乙炔基苯为单体,通过Pd催化的Sonogashira偶联反应合成了聚对苯撑乙炔咔唑衍生物PPECz。PPECz的溶液和固体薄膜都具有较好的发光性能,并且均对2, 4, 6-三硝基甲苯(TNT)有明显的响应。在常温常压条件下,微量(40 μg)的TNT挥发物在60 s内就能使聚合物PPECz薄膜的荧光强度被猝灭56%,可作为一种潜在的硝基苯类爆炸物的荧光检测材料。     

有机双过氧钒化合物的合成及其与小分子相互作用研究

在过去的20年里,双过氧钒化合物的合成及其与小分子相互作用一直是化学和生物学研究的热点之一．本文在合成并表征数种双过氧钒化合物的基础上,利用多核（¹H、¹³C、¹⁴N、¹⁵N和⁵¹V）、多维（¹H-¹H COSY、¹³C-¹H COSY和DOSY）和变温NMR等谱学手段,结合ESI-MS技术和理论计算,系统研究了相互作用前后体系中各物种的溶液结构,对一些实验现象进行了解释,探讨了相互作用的模式和规律．主要结果总结如下：  1. 在合成草酸双过氧钒的基础上,利用多种NMR谱学手段研究了双过氧钒和组氨酸类化合物的相互作用,在溶液中观察到His和Carns等有机配体主要以其咪唑环上的ε-N与中心金属钒配位,这和从海洋生物 Curvularia inaequalis 分离出来的氯过氧化物酶(Chloroperoxidase)的活性中心His496有着相同的配位方式．理论计算表明溶剂效应对该配位方式起着关键的作用．此外,利用ESI-MS技术结合理论计算,通过比较体系在溶液和气相中行为的异同,对气相中物种[OV(O₂)₂(L)₂]-（L为配体）可能的结构给予了解释,认为中心金属钒与溶液中一样还是6配位而不是Conte等人认为的7配位,第二个配体分子通过氢键与物种[OV(O₂)₂(L)₂]-结合在一起． 2. 在合成数种双过氧钒化合物的基础上,利用多种NMR技术结合ESI-MS等谱学方法系统研究了双过氧钒化合物和咪唑、吡啶、取代吡啶、精氨酸、皮考啉酯以及皮考啉酰胺等有机配体的相互作用,建立了一套适合研究过氧钒化合物与有机小分子相互作用的谱学方法．利用核磁共振中扩散排序（DOSY）技术,实现了混合物中各组分在样品管中的“虚”分离,并利用谱图编辑技术得到混合物中各组分的化学位移即结构信息．由于DOSY的使用避免了繁琐的分离,因此它是一种非常有应用前景的研究混合物的谱学方法． 3. 在相互作用体系NH₄VO₃/H₂O₂/2-(2′-Py)Imi中合成了一种新的双过氧钒化合物．经NMR、IR、X-ray衍射和元素分析等谱学方法或分析手段确定其组成[NH₄{OV(O₂)₂{2-(2′-Py)-Imi}·4H₂O}]和结构,其⁵¹V的化学位移在单核双过氧钒化合物中是最大的．目前已报道双过氧钒化合物的晶体结构约为10个,本文所合成的为第一个具有不对称双氮双齿配体的双过氧钒化合物．     

基于19F化学标记磷酸化泛素的温度传感器开发

泛素是一种真核细胞信号分子,主要参与蛋白质降解和DNA修复等生命活动.泛素Ser65位被磷酸化之后,在溶液中呈现两个稳定的溶液构象,这两种构象的比例能够被pH调控,本研究利用NMR进一步发现它还受到温度影响.基于该发现,对磷酸化泛素进行了¹⁹F化学标记,利用¹⁹F NMR方法表征了不同温度下磷酸化泛素两种构象的比例,发现两者比例变化与温度之间的关系可以通过线性方程来描述,利用该方程可以通过构象比例计算样品内部温度,因此可以作为一种基于NMR检测的温度传感器.本文所开发的基于¹⁹F化学标记磷酸化泛素的温度传感器不仅能够作为体外样品温度检测的有力工具,还有望用于检测细胞内部的温度.从而有助于揭示生物学特性和功能.     

高效液相色谱-核磁共振联用技术在蛇葡萄根提取混合物中的应用研究

建立了用高效液相-核磁共振联用技术（LC-NMR）检测微量级蛇葡萄(Ampelopsis sinica)根提取物中混合组分结构的方法. 用停止流动的方法,对混合物的各个组分进行分离,并获得¹H NMR及COSY谱,通过与此类化合物所建立的氢谱数据库进行比较,分析,确定了微克级的天然产物混合物中的主要组分的化学结构及立体结构.     

标准芳烃及其混合溶液的同步荧光光谱分析

为了提供区分标准芳烃的实验依据,并为环境中芳烃污染检测提供参考.对10个标准芳烃样品(萘、芴、蒽、菲、荧蒽、苊、芘、1,2-苯并[A]蒽、苯并[k]荧蒽、苯并菲)及其混合溶液(蒽、萘、芴混合溶液,苊、荧蒽、菲混合溶液和芘、1,2-苯并[A]蒽、苯并[k]荧蒽、苯并菲混合溶液)的同步荧光特性进行了分析,获得10种标准芳烃标志峰最好时对应的Δλ值及其标志峰位.在此基础上,通过同步荧光光谱分析区分了三种标准芳烃混合溶液的组分,实验发现对蒽、萘、芴混合溶液,Δλ=3 nm时最易区分三种组分|对苊、荧蒽、菲混合溶液,Δλ=3 nm或Δλ=10 nm均可区分三种组分,相对而言,Δλ=10 nm更简便些|对芘、1,2-苯并[A]蒽、苯并[k]荧蒽、苯并菲混合溶液,Δλ=5 nm时是最好的,但也仅能区分芘、1,2-苯并[A]蒽、苯并[k]荧蒽三种组分,苯并菲不确定.     

混合物物态方程的计算

 在采用体积相加原理计算混合物物态方程的基础上,建立了一种物理模型确定混合物温度。根据混合物中各组分温度和压强平衡条件,采用压强-密度迭代方法计算给出混合物物态方程,编制了两种组分的混合物物态方程计算程序。为检验建立的温度模型的合理性及程序的有效性,分析了不同密度、温度状态的氢（H2）和钨（W）组成的混合物状态参量,计算了以下情形及其组合情形的混合物物态方程：H₂和W以不同质量比混合;质量比固定,单组分状态不同;温度区间和密度区间不同。研究表明:实际应用中在建立的混合物温度模型基础上确定的混合物物态方程是合理的。     

甲基丙烯酸甲酯-萘乙烯共聚物的NMR研究Ⅱ.甲基丙烯酸甲酯-萘乙烯共聚物的核弛豫研究

用核弛豫研究了溶液中甲基丙烯酸甲酯-萘乙烯共聚物体系中高分子链间的凝聚态结构.通过对溶液中甲基丙烯酸甲酯-萘乙烯共聚物的变温¹³C NMR自旋-晶格弛豫的研究,发现此体系具有类似小分子在溶液中的弛豫特性.变温¹H NMR自旋-自旅弛豫呈现出双指数特性,弛豫快的部分随温度升高而减少对应于聚合物链间凝聚缠结的解缠,当温度继续升高时,主链的这种组分又开始增加,说明主链中形成新的缠结.研究结果还表明,在这种共聚物中,例基萘环的叠加较少.     

A new type of sample tube for reducing convection effects in PGSE-NMR measurements of self-diffusion coefficients of liquid samples

Pulsed gradient spin-echo (PGSE) NMR measurements of the self-diffusion coefficients of low viscosity liquids are greatly hampered by the effects of convection especially away from ambient temperature. Here we report on a new NMR tube designed to minimize the deleterious effects of convection. In this tube, which derives from a Shigemi symmetrical NMR tube, the sample is contained in an annulus formed from a concentric cylinder of susceptibility matched glass. The performance of this tube was demonstrated by conducting measurements on the electrochemically important LiN(SO3CF3)2 (LiTFSI)-diglyme (DG) system. Calibrations were first made using DG at column heights of 2, 3, and 4-mm in the temperature range between -40 and 100 degrees C. Measurements of the diffusion coefficients of the lithium, anion, and DG were then performed to probe the solvent-ion and ion-ion interactions in the DG doped with LiTFSI. Changes in the 1H, 7Li, and 19F PGSE-NMR attenuation curves at -40 degrees C provided clear evidence of interactions between the DG and lithium ion.     

Collective dynamics and self-diffusion in a diblock copolymer melt in the body-centered cubic phase

The structure and dynamics of a strongly asymmetric poly(ethylene propylene)-poly(dimethylsiloxane) (PEP-PDMS) diblock copolymer in the melt have been studied over a wide temperature range. Small-angle neutron scattering reveals that the sample exhibits two stable phases in this temperature range: Above the order-to-disorder transition temperature, it is disordered, whereas the domain structure is body-centered cubic (bcc) below, being stable down to the lowest temperatures measured. In the disordered state, dynamic light scattering (DLS) in the polarized geometry reveals the heterogeneity mode and the cluster mode. In the bcc phase, the PEP and the PDMS blocks form the micellar cores and the matrix, respectively. Here, two modes are observed in DLS, and the diffusion coefficients measured using pulsed field gradient (PFG) NMR are broadly distributed with the most probable diffusion coefficient coinciding with the slow DLS mode. We attribute the fast process in the bcc state to concentration fluctuations of the micellar cores (PEP), relaxing by mutual diffusion of the micelles with copolymers dissolved in the PDMS matrix. The slower process in the bcc state is ascribed to activated long-range self-diffusion of single copolymers from micelle to micelle through the PDMS matrix. This assignment is corroborated by the good coincidence of the reduced diffusivities with the ones from the literature. However, this mode may also be assigned to the rearrangement of entire micelles.This paper is dedicated to the memory of G. Fleischer     

The bulk dynamics of a compositionally asymmetric diblock copolymer studied using dynamic light scattering

We have studied the bulk dynamics of a compositionally asymmetric poly(ethylene propylene)-poly(dimethylsiloxane) (PEP-PDMS) diblock copolymer in a large temperature range both in the ordered and in the disordered state. The volume fraction of the PEP block is 0.22. Apart from the disordered state, the sample shows three ordered morphologies. Using dynamic light scattering, we have investigated the dynamics in all four phases and combined these results with those obtained using pulsed field gradient NMR. In the disordered state, we find--apart from the slow cluster mode--the heterogeneity mode related to the self-diffusion of single chains. The relaxation time of this mode, reduced by temperature and the zero-shear viscosity , , increases with temperature. In the cubic phase right below the ODT temperature, we observe two diffusive processes, and we attribute the faster one to the mutual diffusion of micelles and block copolymers not bound to micelles (“free chains”) through the PDMS matrix. The slower mode may either be due to the mutual diffusion of free chains and chains bound to PEP micelles or to the cooperative diffusion of micellar aggregates. In the non-cubic ordered state at intermediate temperatures, an additional weak diffusive mode is observed. The low-temperature ordered state is body-centered cubic, and here, only the mutual diffusion of micelles and free chains lies in our experimental time window. Received 19 March 1999 and Received in final form 25 August 1999     

Pulsed field gradient magic angle spinning NMR self-diffusion measurements in liquids

Several investigations have recently reported the combined use of pulsed field gradient (PFG) with magic angle spinning (MAS) for the analysis of molecular mobility in heterogeneous materials. In contrast, little attention has been devoted so far to delimiting the role of the extra force field induced by sample rotation on the significance and reliability of self-diffusivity measurements. The main purpose of this work is to examine this phenomenon by focusing on pure liquids for which its impact is expected to be largest. Specifically, we show that self-diffusion coefficients can be accurately determined by PFG MAS NMR diffusion measurements in liquids, provided that specific experimental conditions are met. First, the methodology to estimate the gradient uniformity and to properly calibrate its absolute strength is briefly reviewed and applied on a MAS probe equipped with a gradient coil aligned along the rotor spinning axis, the so-called 'magic angle gradient' coil. Second, the influence of MAS on the outcome of PFG MAS diffusion measurements in liquids is investigated for two distinct typical rotors of different active volumes, 12 and 50 microL. While the latter rotor led to totally unreliable results, especially for low viscosity compounds, the former allowed for the determination of accurate self-diffusion coefficients both for fast and slowly diffusing species. Potential implications of this work are the possibility to measure accurate self-diffusion coefficients of sample-limited mixtures or to avoid radiation damping interferences in NMR diffusion measurements. Overall, the outlined methodology should be of interest to anyone who strives to improve the reliability of MAS diffusion studies, both in homogeneous and heterogeneous media.     

Novel Rotating Hairy Black Hole in (2+1)-Dimensions and Shear Viscosity to Entropy Ratio

The novel rotating hairy black hole metric in (2 + 1) dimensions, which is an exact solution to the field equations of the Einstein-scalar AdS theory with a non-minimal coupling, considered in this paper and some hydrodynamics quantities such as diffusion constant and shear viscosity investigated. By using thermodynamics quantities such as temperature and entropy we can use diffusion constant to obtain shear viscosity and then calculate shear viscosity to entropy ratio.     

The Influence of a Nonconstant Magnetic-Field Gradient on PFG NMR Diffusion Experiments. A Brownian-Dynamics Computer Simulation Study

The influence of a nonconstant magnetic-field gradient on the performance of pulsed-field-gradient NMR diffusion experiments was investigated by performing Brownian-dynamics simulations for two different coil designs using two different active sample volumes for each coil. The active sample volumes were chosen in order to represent different degrees of deviation from a perfectly constant magnetic-field gradient. The results show that one can actually tolerate a rather large deviation from a perfectly constant magnetic-field gradient and still obtain accurate values of the self-diffusion coefficients. The dependence of Δ (the observation time) and the dependence ofD(the self-diffusion coefficient) while keepingDand Δ constant, respectively, were also investigated for three of the active sample volumes. The simulations show that the effects due to a nonconstant field gradient depend only slightly on the values of Δ andD. In conclusion, the Brownian-dynamics computer simulations procedure is a quantitative way of investigating the performance characteristics of a gradient coil of a certain design before it is built.     

Fluctuation effects in spin diffusion measurements in liquid He

We have measured spin diffusion coefficients of liquid ³He at a frequency of 920 kHz by pulsed NMR. By analyzing our data in the framework of the Leggett–Rice theory we got a spin diffusion coefficient and a Leggett–Rice parameter =λωτ simultaneously at each temperature. On approaching the superfluid transition the spin diffusion coefficients showed a deviation from predictions of the Fermi liquid theory. The deviation at low pressure was larger than that at high pressure. This anomaly may be due to the effects of fluctuations of superfluidity which were recently observed in the viscosity measurement of liquid ³He.     

Experimental verification of the Stokes-Einstein relation in liquid Fe—FeS at 5 GPa

Experiments have been performed at 5 GPa on liquid Fe-FeS in order to determine Fe and S self-diffusivity as a function of temperature. The viscosity of the sample was then obtained using the Stokes-Einstein relation. The results are in excellent agreement with previous experiments where the viscosity of a material of the same composition under similar conditions was measured directly. These results support high, near-metallic, values of diffusivity and low viscosity in liquid Fe-S up to a few hundred K above the eutectic temperature, in contrast with some previous studies. Moreover, these results fully confirm the validity of the Stokes-Einstein relation between viscosity and diffusion coefficients for Fe_0.61S_0.39.     

Dynamic properties of aqueous electrolyte solutions from non-polarisable,polarisable, and scaled-charge models

We investigated the dynamic properties of alkali halide solutions (NaCl, NaF, NaBr, NaI, LiCl, and KCl) using molecular dynamics simulations and several non-polarisable, polarisable, and scaled-charge models. The concentration dependence of shear viscosity was obtained with low statistical uncertainties to allow for calculation of the viscosity Jones-Dole B-coefficients. No prior values are available for the B-coefficients from molecular simulations of fully atomistic models for electrolyte solutions. In addition, we obtained diffusion coefficients with rigorous finite-size corrections to access ion mobilities; these provide insights on single ion hydration behaviour. We find that all models studied, even polarisable and scaled-charge models, quantitatively over-predict water structuring but qualitatively follow the experimentally determined Hofmeister series. All ion models considered are kosmotropes based on their calculated B-coefficient and diffusion coefficients, even for ions experimentally found to be chaotropes. These observations indicate that the water-ion interactions in these models are not adequately represented; additional interactions such as charge transfer must be incorporated in future models in order to better represent electrolyte solution properties.     

PDMAEMA多重环境响应行为的NMR研究

利用原子转移自由基聚合（Atom Transfer Radical Polymerization, ATRP）合成了分子量分布较窄的聚甲基丙烯酸N, N-二甲氨基乙酯{Poly\[2 (diethylamino)ethylmethacry-late], PDMAEMA}并通过对液体核磁共振氢谱（¹H NMR）化学位移以及弛豫时间（T₁、T₂）的测量,研究了聚合物PDMAEMA的温度敏感、pH敏感以及离子敏感3种环境敏感行为. 发现聚合物链段的运动性,以及温度和离子强度诱导的相变行为,都与体系的pH值具有强依赖关系. 室温下,聚合物链段的运动性随pH值的增大而降低. 酸性条件下,聚合物表现出离子敏感性,而不表现出温度敏感性. 碱性条件下,聚合物表现出温度敏感性,不表现出离子敏感性.