莽草酸途径中26种代谢物的NMR谱归属

莽草酸代谢途径广泛存在于植物、微生物与某些寄生虫中,是芳香氨基酸、植物激素与多种重要活性次生代谢物的主要合成通路.这些代谢物的系统核磁共振（NMR）研究尚不完备,且5-羟基吲哚乙酸与吲哚乳酸等代谢物的NMR数据归属尚不完整.本文对莽草酸代谢途径介导的26种代谢物（包括2种非芳香羧酸、2种植物激素、3种芳香类氨基酸、19种植物次生代谢物）结构进行了较为系统的NMR分析,对这些代谢物的¹H和¹³C NMR信号进行了归属,为植物化学及代谢组学研究提供了基础数据.     

几种含氮化合物的核磁共振测试

结合曲氨南（Aztreonam）、奥美拉唑（Omeprazole）与一种席夫碱对含氮化合物在核磁共振（NMR）测试中的某些特性进行了研究. 结果表明,¹⁴N四偶极矩、分子间氢键以及分子间质子转移导致的异构,是影响含氮化合物核磁特性的主要因素. 这些因素虽然在NMR的实验设计与谱图分析方面是无法避免的,但却能为结构解析以及其他化学研究方面提供一定的有趣的信息.     

6-(4-氯苯氧基)四唑并[5,1-a]酞嗪的核磁共振谱峰归属

为确保具有独立知识产权的国家级一类抗癫痫创新候选药物的药品安全,采用500 MHz核磁共振（NMR）技术,结合规范不变原子轨道-核磁共振（GIAO-NMR）量子化学计算方法,对进入临床阶段的抗癫痫药6-（4-氯苯氧基）四唑并[5,1-a]酞嗪的¹H NMR、¹³C NMR和¹⁵N NMR信号进行了归属,从而为安全用药提供了精确结构信息．线性回归对比表明,标度法计算的NMR化学位移与实验值吻合较好．     

基于自主研发的500 MHz NMR谱仪的紫杉醇结构解析

中国科学院武汉物理与数学研究所（WIPM）于2010年成功研制了500 MHz（WIPM-I 500）高分辨超导核磁共振（NMR）谱仪,并将其投入实际应用中.然而,关于其二维核磁共振（2D NMR）谱图的准确性及在此基础上对复杂物质的结构解析尚无系统完整的数据报道.该文利用WIPM-I 500型NMR谱仪,对紫杉醇样品进行了1D NMR及2D NMR（包括¹H-¹H COSY、¹H-¹H TOCSY、J-Res、¹H-¹³C HMQC和¹H-¹³C HMBC）实验,将谱图分析结果与进口仪器进行了对比.结果表明：利用WIPM-I 500型NMR谱仪能够采集准确的2D NMR谱图,为紫杉醇的正确归属提供了实验基础;而且该文也纠正了文献中对紫杉醇的错误归属.     

哌啶醇的NMR研究

测定了2，2，6，6-四甲基4-哌啶醇（以下简称化合物1）、1，2，2，6，6-五甲基4-哌啶醇（以下简称化合物2）的NMR谱，并对其¹H，¹³C谱峰进行了全归属，利用2D NMR技术研究了该化合物的立体结构.     

用NMR方法研究三尖杉酯碱诱导HL-60细胞的凋亡

运用核磁共振波谱（NMR）研究三尖杉酯碱（HT）诱导人早幼粒白血病细胞（HL-60）凋亡中三磷酸腺苷（ATP）、磷酸单脂（PME）及脂类的代谢变化. 经HT作用2 h后，从³¹P NMR中发现HL-60细胞中ATP、PME含量减少；而在¹H NMR中甲基 峰有明显的增强，胆碱峰稍微减弱. 这些现象的研究将有利于增进对细胞凋亡发生机制的认识.     

盐酸四环素中可交换氢和氢键的核磁共振波谱研究

四环素类抗生素是一类广谱抗生素,对革兰氏阳性菌、革兰氏阴性菌、支原体、衣原体和立克次体感染均具有抗菌活性.本文运用一维（1D）和二维（2D）核磁共振（NMR）技术对盐酸四环素中可交换氢和氢键进行研究,并将研究结果与RNA和蛋白质结合的四环素以及游离药物的晶体结构进行比较,进一步讨论了药物中的氢键构架与药物活性的相关性.最后对盐酸四环素及其同系物的¹H和¹³C NMR信号进行了全归属和分析,并对文献归属结果进行了细微校正.这些结果有助于进一步探索该类药物在更复杂的生物或环境系统中的构效关系.     

拉呋替丁的波谱学数据和结构确证

对拉呋替丁的氢谱（¹H NMR）、碳谱（¹³C NMR,DEPT）、异核多键相关谱（HMBC）予以解析并进行了报道,对其所有的¹H NMR和¹³C NMR谱信号进行了归属;讨论了红外特征吸收,热差和热重分析;质谱的裂解途径和离子特征也与拉呋替丁的分子结构相符.      

代谢组学方法分析鸡胚胎发育过程中脑代谢物

本文应用高分辨魔角旋转核磁共振（HR-MAS NMR）方法对发育过程中（孵化12天至出壳后1天）鸡胚胎大脑、小脑和视叶3种脑组织中的代谢物含量进行了测定,并利用模式识别方法对整体代谢特征进行了归类分析. 结果表明：胚胎发育过程中不同脑区的代谢物组成存在差异,可能与这些脑区的功能及发育特征等的不同有关. 在NMR方法检测到的多种小分子代谢物中,γ-氨基丁酸、N-乙酰天冬氨酸、牛磺酸、肌醇以及胆碱等在鸡胚胎脑组织中的分布有区域性差异,这些差异也是区分大脑、小脑和视叶组织的特征性代谢物.     

PEO接枝多壁碳纳米管的固体NMR研究

合成了一种聚氧乙烯（PEO）接枝多壁碳纳米管（MWNT）,利用固体NMR研究了接枝在MWNT表面的PEO链的聚集态结构. 实验观察到了MWNT的NMR信号, 并发现PEO的聚集态结构为非晶,这些现象说明PEO的醚氧原子中的n电子与MWNT上π体系中的电子之间存在着一种n-π相互作用,正是这种作用使得PEO不能结晶.     

Further conventions for NMR shielding and chemical shifts IUPAC recommendations 2008

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the ¹H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS).

This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating ¹³C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice.     

Chemical shift referencing in MAS solid state NMR

Solid state 13C magic angle spinning (MAS) NMR spectra are typically referenced externally using a probe which does not incorporate a field frequency lock. Solution NMR shifts on the other hand are more often determined with respect to an internal reference and using a deuterium based field frequency lock. Further differences arise in solution NMR of proteins and nucleic acids where both 13C and 1H shifts are referenced by recording the frequency of the 1H resonance of DSS (sodium salt of 2,2-dimethyl-2-silapentane-5-sulphonic acid) instead of TMS (tetramethylsilane). In this note we investigate the difficulties in relating shifts measured relative to TMS and DSS by these various approaches in solution and solids NMR, and calibrate adamantane as an external 13C standard for solids NMR. We find that external chemical shift referencing of magic angle spinning spectra is typically quite reproducible and accurate, with better than +/-0.03 ppm accuracy being straight forward to achieve. Solid state and liquid phase NMR shifts obtained by magic angle spinning with external referencing agree with those measured using typical solution NMR hardware with the sample tube aligned with the applied field as long as magnetic susceptibility corrections and solvent shifts are taken into account. The DSS and TMS reference scales for 13C and 1H are related accurately using MAS NMR. Large solvent shifts for the 13C resonance in TMS in either deuterochloroform or methanol are observed, being +0.71 ppm and -0.74 ppm from external TMS, respectively. The ratio of the 13C resonance frequencies for the two carbons in solid adamantane to the 1H resonance of TMS is reported.     

NMR Nomenclature: Nuclear Spin Properties and Conventions for Chemical Shifts. IUPAC Recommendations 2001

A unified scale is recommended for reporting the NMR chemical shifts of all nuclei relative to the ¹H resonance of tetramethylsilane. The unified scale is designed to provide a precise ratio, Ξ, of the resonance frequency of a given nuclide to that of the primary reference, the ¹H resonance of tetramethylsilane (TMS) in dilute solution (volume fraction, <1%) in chloroform. Referencing procedures are discussed, including matters of practical application of the unified scale. Special attention is paid to recommended reference samples, and values of Ξ for secondary references on the unified scale are listed, many of which are the results of new measurements. Some earlier recommendations relating to the reporting of chemical shifts are endorsed. The chemical shift, δ, is redefined to avoid previous ambiguities but to leave practical usage unchanged. Relations between the unified scale and recently published recommendations for referencing in aqueous solutions (for specific use in biochemical work) are discussed, as well as the special effects of working in the solid state with magic-angle spinning. In all, nine new recommendations relating to chemical shifts are made. Standardised nuclear spin data are also presented in tabular form for the stable (and some unstable) isotopes of all elements with non-zero quantum numbers. The information given includes quantum numbers, isotopic abundances, magnetic moments, magnetogyric ratios, and receptivities, together with quadrupole moments and line-width factors (where appropriate).     

Controversy about the reference compound for correct chemical shift determination of 195Pt nuclei

Several groups exploring the ¹⁹⁵Pt NMR in solids, including metallic and magnetic materials, use different standards for chemical shift (Knight shift) determination. Commonly applied H₂PtCl₆ and Na₂PtCl₆ (IUPAC δ scale) lead to considerable underestimation of the shifts since H₂PtCl₆ has considerable own ¹⁹⁵Pt NMR shift due to its Van Vleck paramagnetism. In this Letter new results on ¹⁹⁵Pt NMR in heavy fermion system CeInPt₄ are presented and rationalized scale for the Knight shift determination is discussed.     

Susceptibility corrections in solid-state NMR experiments with oriented membrane samples. Part I: applications

Chemical shift referencing of solid-state NMR experiments on oriented membranes has to compensate for bulk magnetic susceptibility effects that are associated with the non-spherical sample shape, as described in the accompanying paper [J. Magn. Reson. 164 (2003) 115-127]. The resulting frequency deviations can be on the order of 10 ppm, which is serious for nuclei with a narrow chemical shift anisotropy such as 1H or 13C, and in some cases even 19F. Two referencing schemes are proposed here to compensate for these effects: A flat (0.4 mm) glass container with an isotropic reference molecule dissolved in a thin film of liquid is stacked on top of the oriented membrane sample. Alternatively, the intrinsic proton signal of the hydrated lipid can be used for chemical shift referencing. Further aspects related to magnetic susceptibility are discussed, such as air gaps in susceptibility-matched probeheads, the benefits of shimming, and limitations in the accuracy of orientational constraints. A biological application is illustrated by a series of experiments on the antimicrobial peptide PGLa, aimed at understanding its concentration-dependent membranolytic effect. To address a wide range of molar peptide/lipid ratios between 1:3000 and 1:8, multilayers of hydrated DMPC containing a 19F-labeled peptide were oriented between stacked glass plates. Maintaining an approximately constant amount of peptide gives rise to thick samples (18 plates) at low, and thin samples (3 plates) at high peptide/lipid ratio. Accurate referencing was critical to reveal a small but significant change over 5 ppm in the anisotropic chemical shift of the 19F label on the peptide, indicative of a change in the orientation and/or dynamics of PGLa in the membrane.     

Stable isotope terminology

In order to achieve better mutual understanding, a uniform and unambiguous language concerning certain terms, symbols, units, and nomenclature in stable isotope - especially in (15)N tracer technique has been recommended. In particular, some definitions of fundamental terms, some nomenclature rules for stable isotopically labelled compounds and some symbols and units in the formula language of isotope stoichiometry are given. Recent fundamental recommendations of the IUPAC have been accepted as a basis, to which, if necessary, specialities of stable isotope chemistry, especially (15)N application are added or adapted.     

Generalized surface thermodynamics with application to nucleation

Gibbs formulated a complete and general thermodynamics for surfaces in multicomponent fluid systems. When considering solid–fluid surfaces, he restricted attention to single-component solids in contact with fluids that could contain multiple components. Attempts that have been offered to generalize Gibbs’ results for surfaces between multicomponent solids and fluid are problematic owing to the difficulty that the surface chemical potentials for components that also reside on substitutional lattice sites in the solids are not well defined. Therefore any expressions involving these surface chemical potentials, such as the conventional definition of the surface energy, will also not be well defined. In order to formulate a general thermodynamics of equilibrium that takes into account capillary effects in systems containing surfaces between a multicomponent solids and fluids, it is shown that the concept of thermodynamic availability (exergy) can be employed that, when applied to surfaces, depends on the extensive but not the intensive variables (such as the chemical potentials) of the surfaces. Using this approach, Gibbs–Thomson–Freundlich effects for finite-size solids, an adsorption equation for solid–fluid surfaces and the thermodynamics of nucleation during solidification can be treated in a straightforward manner without referring to the ill-defined surface chemical potentials. A derivation is given that appears to be the first one that properly generalizes Gibbs’ analysis for the reversible work to form a critical nucleus to the case of solidification.     

Thermal and fluctuation-induced deformations of chemical bonds in surface and boundary layers of polymers

The deformation of chemical bonds in polymer molecules of surface layers of samples, boundary layers between supramolecular aggregates, and boundary layers between polymers and solids in polymer composites is investigated using IR and Raman spectroscopy. It is found that the chemical bonds are elongated on a free surface and in boundary layers between supramolecular aggregates. By contrast, the chemical bonds are contracted in boundary layers between polymers and solids. The concentration and the strain of excited chemical bonds (strained to approximately a theoretical ultimate elongation) are increased on the free surface and in the boundary layers between supramolecular aggregates, whereas the concentration and the strain of excited chemical bonds in the boundary layers between polymers and solids are decreased. These effects are explained by the changes in the atomic vibrations in the surface and boundary layers.     

Stable isotope terminology

In order to achieve better mutual understanding, a uniform and unambiguous language concerning certain terms, symbols, units, and nomenclature in stable isotope – especially in ¹⁵N tracer technique has been recommended. In particular, some definitions of fundamental terms, some nomenclature rules for stable isotopically labelled compounds and some symbols and units in the formula language of isotope stoichiometry are given. Recent fundamental recommendations of the IUPAC have been accepted as a basis, to which, if necessary, specialities of stable isotope chemistry, especially ¹⁵N application are added or adapted.     

同步荧光光谱法测定尿液中依诺沙星含量

文章研究了金属离子对依诺沙星荧光光谱的影响。实验结果表明在pH 6.3的NaH₂PO₄-Na₂B₄O₇缓冲溶液介质中铝离子对依诺沙星荧光具有增敏作用,在此基础上用同步荧光技术建立了测定人体尿液中依诺沙星含量的同步荧光光谱法,方法简便快捷,线性范围为0.04～1.0 mg·L-1。相关系数为0.999 2。检出限为0.018 μg·mL-1。在实际样品的测定当中, 回收率在95%～105%之间。