Isomeric Effect on H/D Exchange of Resveratrol Studied by NMR Spectroscopy

Resveratrol (3,5,4′‐trihydroxylstilbene), a phytoalexin in response to injury or fungal attack, is found in grapes and other food products. It has been well documented that the compound has beneficial effects as hypolipidemic, anticancer, antiviral, neuroprotective, antiaging, and anti‐inflammatory natural active principle. It was observed that both trans‐ and cis‐resveratrols undergo hydrogen‐deuterium (H/D) exchange at H‐2,6 and H‐4 positions of the A‐ring. The exchange rates were determined by ¹H NMR spectroscopy. The results reveal that the exchange rates are configuration and pH dependent. Derivative of 2‐O‐β‐D‐glucoside can significantly speed up the H/D exchange reactions for both isomers. The trans‐resveratrol experiences faster H/D exchanging than the cis‐resveratrol. Such isomeric effect is possibly due to the factor that the trans‐resveratrol is in favor of forming larger/super conjugative system and has less spatial interference. Theoretical calculation shows that electronegativity at these positions is in the order of H‐2,6>H‐4, which is in consistent with the exchange rates observed by NMR. The results may be of help in understanding the properties of resveratrol, and in analysis of resveratrol in natural products or body fluids using mass spectroscopy that occasionally requires stable deuterium isotope labeling.     

环丙烷衍生物在CD3OD离子体系中的H/D交换反应

研究了环丙烷衍物生物在CD3OD离子体系中的H/D交换反应产物离子[M 1]^*,[M 2]^ 和[M 3]^*的碰撞诱民碎裂(CID)反应特征,实验结果表明这些产物离子是由反应物与试剂离子之间生H/D交换反应生成的,获得了环丙烷衍生物结构中活泼氢位置及其数量的信息.     

In ESI‐source H/D exchange under atmospheric pressure for peptides and proteins of different molecular weights from 1 to 66 kDa: the role of the temperature of the desolvating capillary on H/D exchange

Transition of proteins from the solution to the gas phase during electrospray ionization remains a challenging problem despite the large amount of attention it has received during the past few decades. One of the major questions relates to the extent to which proteins in the gas phase retain their condensed phase structures. We have used in‐electrospray source hydrogen/deuterium exchange to determine the number of deuterium incorporations as a function of protein mass, charge state and temperature of the desolvating capillary where the reaction occurs. All experiments were performed on a Thermo LTQ FT Ultra equipped with a 7‐T superconducting magnet. Ions were generated by an IonMax Electrospray ion source operated in the positive ESI mode. Deuterium exchange was performed by introducing a droplet of D₂O beneath the ESI capillary. We systematically investigated gas phase hydrogen/deuterium (H/D) exchange under atmospheric pressure for peptides and proteins of different molecular weights from 1 to 66 kDa. We observed that almost all proteins demonstrate similar exchange rates for all charge states and that these rates increase exponentially with the temperature of the desolvating capillary. We did not observe any clear correlation of the number of H/D exchanges with the value of the cross section for a corresponding charge state. We have demonstrated the possibility of performing in‐ESI source H/D exchange of large proteins under atmospheric pressure. The simplicity of the experimental setup makes it a useful experimental technique that can be applied for the investigation of gas phase conformations of proteins. Copyright © 2015 John Wiley & Sons, Ltd.     

High-resolution H/D exchange studies on the HET-s218-295 prion protein

In a search for improved resolution of hydrogen/deuterium (H/D) exchange experiments analyzed by mass spectrometry (HXMS), we evaluated two methodologies for a detailed structural study of solvent accessibility in the case of the HET-s(218-295) prion protein. For the first approach, after incubation in the deuterated solvent, aggregated HET-s(218-295) was digested with pepsin and the generated peptides were analyzed by nanospray mass spectrometry in an ion trap, with and without collision-induced dissociation (CID). We compared deuterium incorporation in peptides as determined on peptide pseudomolecular ions and on b and y fragments produced by longer peptides under CID conditions. For both b and y fragment ions, an extensive H/D scrambling phenomenon was observed, in contrast with previous studies comparing CID-MS experiments and (1)H NMR data. Thus, the spatial resolution of HXMS experiments could not be improved by means of MS/MS data generated by an ion trap mass spectrometer. In a second approach, the incorporation of deuterium was analyzed by MS for 76 peptides of the HET-s(218-289) peptide mass fingerprint, and the use of shared boundaries among peptic peptides allowed us to determine deuteration levels of small regions ranging from one to four amino acids. This methodology led to evidence of highly protected regions along the HET-s(218-295) sequence.     

氘代DMSO试剂中残留~1H的检测

本文提出一种利用尿素作为内标物质,通过加入不同量的尿素测量它与氘代DMSO中溶剂残留信号峰面积比变化的方法。结果表明,尿素和DMSO溶剂峰的1H共振峰面积比与它们之间摩尔比之间有很强的线性关系,进而可以计算DMSO溶剂的氘代率。该方法简单、快速,所需试剂较少,低毒,可在实验室准确测试DMSO试剂的氘代率,也可以将此方法推广到其他氘代试剂的检测。     

Epitope mapping of 7S cashew antigen in complex with antibody by solution‐phase H/D exchange monitored by FT‐ICR mass spectrometry

The potential epitope of a recombinant food allergen protein, cashew Ana o 1, reactive to monoclonal antibody, mAb 2G4, has been mapped by solution‐phase amide backbone H/D exchange (HDX) monitored by Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). Purified mAb 2G4 was incubated with recombinant Ana o 1 (rAna o 1) to form antigen:monoclonal antibody (Ag:mAb) complexes. Complexed and uncomplexed (free) rAna o 1 were then subjected to HDX‐MS analysis. Five regions protected from H/D exchange upon mAb binding are identified as potential conformational epitope‐contributing segments. Copyright © 2015 John Wiley & Sons, Ltd.     

Recovering Invisible Signals by Two‐Field NMR Spectroscopy

Nuclear magnetic resonance (NMR) studies have benefited tremendously from the steady increase in the strength of magnetic fields. Spectacular improvements in both sensitivity and resolution have enabled the investigation of molecular systems of rising complexity. At very high fields, this progress may be jeopardized by line broadening, which is due to chemical exchange or relaxation by chemical shift anisotropy. In this work, we introduce a two‐field NMR spectrometer designed for both excitation and observation of nuclear spins in two distinct magnetic fields in a single experiment. NMR spectra of several small molecules as well as a protein were obtained, with two dimensions acquired at vastly different magnetic fields. Resonances of exchanging groups that are broadened beyond recognition at high field can be sharpened to narrow peaks in the low‐field dimension. Two‐field NMR spectroscopy enables the measurement of chemical shifts at optimal fields and the study of molecular systems that suffer from internal dynamics, and opens new avenues for NMR spectroscopy at very high magnetic fields.     

核磁共振技术(NMR)在组合化学中的应用

对科学产生最大影响的分析方法是核磁共振技术(NMR),它被广泛用于许多领域.本文结合作者的研究结果评述了NMR在组合化学中的应用,着重于NMR在固相合成的应用、液态NMR和NMR在高通量筛选中的应用.     

The First Application of 1H NMR Spectroscopy for the Assessment of the Authenticity of Perfumes

The manufacture of counterfeit goods is one of the world’s largest underground businesses and is rapidly growing. Counterfeits can lead not only to the loss of profit for honest producers but also have a negative impact on consumers who pay excessive prices for poor quality goods that may result in health or safety problems. The perfume industry is constantly vulnerable to counterfeits, particularly in the fast developing market of “smell-alike” designer-inspired perfumes because these prompt the identification of the methods that classify their quality. In this paper, the application of proton nuclear magnetic resonance (¹H NMR) spectroscopy is employed for the first time to authenticate perfumery products. The molecular composition of several types of authentic brand fragrances for women was compared with cheap inspired equivalents and fakes. Our approach offers the prospect of a fast and simple method for detecting counterfeit perfumes using ¹H NMR spectroscopy.     

DFT和热力学研究氢键协同效应及对关联1H NMR的影响

用DFT方法在B3LYP／6—311 G(d,p)水平下研究了甲醇线性和环状分子簇．对于不同大小的分子簇之间定义了协同因子,计算得到的协同因子可以验证氢键的强协同效应,环状分子簇之间的协同效应远远大于线性分子簇,做为理论验证和比较,热力学模型分别采用含氢键缔合的格子流体状态方程(LFHB),以及含氢键协同效应的LFHB,关联醇一惰性体系的^1H核磁共振化学位移．考虑协同效应的关联结果优于原始的LFHB,比较量子化学计算的和热力学模型中采用的协同因子,认为甲醇和乙醇在溶液中更可能大部分以线性缔合形式存在。     

活泼氢的核磁共振氢谱

核磁共振氢谱是有机化合物结构表征中最常使用的波谱方法之一,提供了有机化合物质子的化学位移、积分面积和耦合裂分等信息。常见的活泼氢是与氧、氮和硫共价相连的氢原子,存在着快速交换机制,与碳上的氢有显著的差异。在不同条件下活泼氢化学位移不固定、峰形多变并且耦合裂分情况复杂。本文探讨了如何通过核磁共振氢谱解析活泼氢,培养学生对谱图进行观察、分析以及结构推导的能力。     

超极化129Xe核磁共振技术及其在多孔催化材料研究中的应用

 激光抽运和自旋交换的超极化 129Xe 核磁共振是近几年发展起来的一种新方法,它比普通 129Xe 核磁共振的检测灵敏度提高约104 ～105倍,是研究材料孔结构和孔内粒子分布的强有力工具. 本文介绍了超极化 129Xe 核磁共振技术并综述了其在多孔催化材料研究中的应用,特别是对催化反应中广泛使用的无机微孔和介孔材料中的应用进行了详细的讨论. 最后展望了此技术的应用前景.     

Progress in Hyperpolarized Ultrafast 2D NMR Spectroscopy

An important development in the field of NMR spectroscopy has been the advent of hyperpolarization approaches, capable of yielding nuclear spin states whose value exceeds by orders‐of‐magnitude what even the highest‐field spectrometers can afford under Boltzmann equilibrium. Included among these methods is an ex situ dynamic nuclear polarization (DNP) approach, which yields liquid‐phase samples possessing spin polarizations of up to 50 %. Although capable of providing an NMR sensitivity equivalent to the averaging of about 1 000 000 scans, this methodology is constrained to extract its “superspectrum” within a single—or at most a few—transients. This makes it a poor starting point for conventional 2D NMR acquisition experiments, which require a large number of scans that are identical to one another except for the increment of a certain t₁ delay. It has been recently suggested that by merging this ex situ DNP approach with spatially encoded “ultrafast” methods, a suitable starting point could arise for the acquisition of 2D spectra on hyperpolarized liquids. Herein, we describe the experimental principles, potential features, and current limitations of such integration between the two methodologies. For a variety of small molecules, these new hyperpolarized ultrafast experiments can, for equivalent overall durations, provide heteronuclear correlation spectra at significantly lower concentrations than those currently achievable by conventional 2D NMR acquisitions. A variety of challenges still remain to be solved before bringing the full potential of this new integrated 2D NMR approach to fruition; these outstanding issues are discussed.     

自制固体液体两用核磁共振谱仪

描述了研制的固体液体两用２００ＭＨｚ高分辨率核磁共振仪的基本结构,功能和一些重要的技术指标。实验结果表明,作为经济型的仪器,该仪器性能优良,功能较全,达到了预期的设计要求。     

Assessment of the Extent of Starch Dissolution in Dimethyl Sulfoxide by 1H NMR Spectroscopy

Complete dissolution is needed for the separation, characterization, or homogeneous labeling of whole starch molecules. A method is presented to quantify the extent of starch dissolution in DMSO for the first time; it is validated on a commercial rice starch. It is used directly on starch dispersions containing possible undissolved or co‐dissolved species. High‐amylose maize starches, known to be digested slowly in vivo, only quantitatively dissolve in the presence of high concentrations of an H‐bond disrupter, LiBr, although they form clear dispersions at low LiBr concentrations. Starch quantitatively dissolves from waxy rice flours; non‐starch components partially co‐dissolve but do not interfere with the dissolution quantification.

     

二维NMR确定吡喃酮衍生物C_9H_（12）O_4的结构

利用Ｈ－ＨＣＯＳＹ和Ｃ－ＨＣＯＳＹ谱实现对~１Ｈ和~（１３）Ｃ谱的指认和归属；利用ＨＭ－ＢＣ谱确定分子的骨架；根据~１Ｈ－~１Ｈ标量偶合常数的大小推出相邻碳原子上质子的相对位置；并结合其它谱学数据，确定了从天然产物分离得到的吡喃酮衍生物Ｃ_９Ｈ_（１２）－Ｏ_４的化学结构并命名为２－（１’，２’－环氧丙烷基）－４－羟基－５－甲基－２－戊烯－５－酸内酯。