LC－NMR联用的现状与展望

介绍了ＬＣ－ＮＭＲ联用的现状．近年来ＬＣ－ＮＭＲ的快速发展表明这两种分析方法联用时所面临的主要技术障碍已经克服．以尿样中的代谢物为例说明ＬＣ－ＮＭＲ联用在临床检测和鉴定中的应用．     

槲皮素—3—鼠李糖—（6—对羟基反式桂皮酰）葡萄糖甙1—2连接的NMR谱 …

用２Ｄ ＮＭＲ技术研究了从银杏叶提取物中分离的一个黄酮双糖甙［槲皮素－３－鼠李糖－（６－对羟基反式桂皮酰）葡萄糖甙］的结构,对鼠李糖部分的＾１Ｈ ＮＭＲ,＾１３Ｃ ＮＭＲ化学位移进行了归属。＾１３Ｃ化学位移和＾１Ｈ ＮＯＥ相关性都证明鼠李糖为１″－２″连接。     

5—Meng氧基—3,4—二取代丁烯内酯NMR的研究

报道了光学纯５－（１－Ｍｅｎｇ氧基）－３，４－二取代２（５Ｈ）－呋喃酮的＾１Ｈ ＮＭＲ和＾１３Ｃ ＮＭＲ数据，研究了不同取代基对结构以及核磁参数的影响。     

化合物（Et_4N）_2［Pd_2（mp）_2（μ－mpH）_2］的NMR研究

采用１Ｈ－１ＨＣＯＳＹ，ＨＭＱＣ、ＨＭＢＣ等２ＤＮＭＲ技术对化合物（Ｅｔ４Ｎ）２［Ｐｄ２（ｍｐ）２（μ－ｍｐＨ）２］进行１Ｈ、１３ＣＮＭＲ谱数据分析与归属．表明它在ＤＭＳＯ溶液中仍保持原有固体状态的分子结构．     

二氟化膦配位化合物的^19F—NMR光谱化学位移规律

本文通过了实验和已有的报道，综合一批Ｎｉ（０），Ｍｏ（０），Ａｕ，Ｃｕ与二氟化膦形成的配位化合物的＾１９Ｆ－ＮＭＲ光谱数据，讨论了此类配合物的＾１９Ｆ－ＮＭＲ化学位移的特点和受影响的主要因素。     

β－烷氧羰乙撑基三氯化锡与N－芳基－2－羟基乙酰苯叉亚胺配合物的NMR谱与结构

测定了１２个新合成的有机锡－Ｓｃｈｉｆｆ碱配合物的１ＨＮＭＲ谱和１３ＣＮＭＲ谱．详细研究了化合物结构与ＮＭＲ谱的关系．通过比较配体和配合物的ＮＭＲ谱，得出配合物是通过酚羟基氧原子和锡原子的配键生成的．     

四维NMR谱

尽管３ＤＮＭＲ谱的分辨率有所提高，但解释较大的三维异核ＮＭＲ谱时，仍存在含糊性。因此，人们希望通过增加维数进一步提高分辨率，在最近几年中出现了４ＤＮＭＲ谱，４ＤＮＭＲ谱常常是说明２ＤＮＭＲ谱的方法，４ＤＮＭＲ实验可简单地看作是由三个２ＤＮＭＲ实验所组成，新的４ＤＮＭＲ技术仍在不断地发展，已有许多将４ＤＮＭＲ谱应用于蛋白质及核酸研究的报道。     

6─或8─脂代─7─氧香豆素与二氢呋喃香豆素的NMR，MS研究

对从重齿毛当归（ＡｎｇｅｌｉｃａｐｕｂｅｓｃｅｎｓＭａｘｉｍｆ．ｂｉｓｅｒｒａｔａＳｈａｎｅｔＹｕａｎ）根及根茎中分得的１２种６－或８－脂代－７－氧－香豆素和８种二氢呋喃香豆素衍生物进行了１Ｈ和１３ＣＮＭＲ分析研究．结合文献．做出规律性总结．运用２ＤＮＭＲ技术．对文献中当归醇类化合物碳谱中的个别错误归属给予了纠正，并首次探讨了此类化合物的ＭＳ裂解途径．     

合成抗孕酮新药RU-486中间体3,3-乙撑二氧-5α,10α及5β,10β-环氧-Δ~(9(11))-雌烯-17α(1-丙炔基)-17β-羟基的~1H和~(13)C NMR谱线全归属

用１Ｄ及２ＤＮＭＲ技术（ＣＯＳＹ，ＴＯＣＳＹ，ＨＭＱＣ及ＨＭＢＣ）归属了合成抗孕酮新药ＲＵ－４８６中间体３，３乙撑二氧５α，１０α及５β，１０β环氧－Δ９（１１），雌烯１７α（１－丙炔基）１７β羟基的１Ｈ和１３ＣＮＭＲ谱线．     

绿原酸乙酯的NMR研究

从西南忍冬中分离得到了绿原酸乙酯，该化合物系首次从该属植物中获得。我们应用＾１Ｈ ＮＭＲ、＾１３Ｃ－ＮＭＲ、ＨＳＱＣ、ＨＭＢＣ等核磁共振技术明确归属了其碳信号及氢信号，并订正了文献中对部分信号的错误归属。     

Polarizing agents and mechanisms for high-field dynamic nuclear polarization of frozen dielectric solids

This article provides an overview of polarizing mechanisms involved in high-frequency dynamic nuclear polarization (DNP) of frozen biological samples at temperatures maintained using liquid nitrogen, compatible with contemporary magic-angle spinning (MAS) nuclear magnetic resonance (NMR). Typical DNP experiments require unpaired electrons that are usually exogenous in samples via paramagnetic doping with polarizing agents. Thus, the resulting nuclear polarization mechanism depends on the electron and nuclear spin interactions induced by the paramagnetic species. The Overhauser Effect (OE) DNP, which relies on time-dependent spin–spin interactions, is excluded from our discussion due the lack of conducting electrons in frozen aqueous solutions containing biological entities. DNP of particular interest to us relies primarily on time-independent, spin-spin interactions for significant electron–nucleus polarization transfer through mechanisms such as the Solid Effect (SE), the Cross Effect (CE) or Thermal Mixing (TM), involving one, two or multiple electron spins, respectively. Derived from monomeric radicals initially used in high-field DNP experiments, bi- or multiple-radical polarizing agents facilitate CE/TM to generate significant NMR signal enhancements in dielectric solids at low temperatures (<100 K). For example, large DNP enhancements (∼300 times at 5 T) from a biologically compatible biradical, 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL), have enabled high-resolution MAS NMR in sample systems existing in submicron domains or embedded in larger biomolecular complexes. The scope of this review is focused on recently developed DNP polarizing agents for high-field applications and leads up to future developments per the CE DNP mechanism. Because DNP experiments are feasible with a solid-state microwave source when performed at <20 K, nuclear polarization using lower microwave power (<100 mW) is possible by forcing a high proportion of biradicals to fulfill the frequency matching condition of CE (two EPR frequencies separated by the NMR frequency) using the strategies involving hetero-radical moieties and/or molecular alignment. In addition, the combination of an excited triplet and a stable radical might provide alternative DNP mechanisms without the microwave requirement.     

广西大风子中2个新木脂素的NMR研究

从广西大风子的皮中分离得到两个新木脂素1和2,并通过高分辨质谱和核磁共振确定了其结构. 利用多种二维核磁共振技术,包括HSQC, HMBC, DQF-COSY 和NOESY谱,对其碳氢信号进行了全归属. 毛细管电泳分析显示1和2均为外消旋体.     

Theoretical Aspects of Dynamic Nuclear Polarization in the Solid State: The Influence of High Radical Concentrations on the Solid Effect and Cross Effect Mechanisms

Dynamic nuclear polarization (DNP) is used to enhance signals in NMR and MRI experiments. During these experiments microwave (MW) irradiation mediates transfer of spin polarization from unpaired electrons to their neighboring nuclei. Solid state DNP is typically applied to samples containing high concentrations (i.e. 10–40?mM) of stable radicals that are dissolved in glass forming solvents together with molecules of interest. Three DNP mechanisms can be responsible for enhancing the NMR signals: the solid effect (SE), the cross effect (CE), and thermal mixing (TM). Recently, numerical simulations were performed to describe the SE and CE mechanisms in model systems composed of several nuclei and one or two electrons. It was shown that the presence of core nuclei, close to DNP active electrons, can result in a decrease of the nuclear polarization, due to broadening of the double quantum (DQ) and zero quantum (ZQ) spectra. In this publication we consider samples with high radical concentrations, exhibiting broad inhomogeneous EPR line-shapes and slow electron cross-relaxation rates, where the TM mechanism is not the main source for the signal enhancements. In this case most of the electrons in the sample are not affected by the MW field applied at a discrete frequency. Numerical simulations are performed on spin systems composed of several electrons and nuclei in an effort to examine the role of the DNP inactive electrons. Here we show that these electrons also broaden the DQ and ZQ spectra, but that they hardly cause any loss to the DNP enhanced nuclear polarization due to their spin-lattice relaxation mechanism. Their presence can also prevent some of the polarization losses due to the core nuclei.     

Application of capillary electrophoresis in anion binding studies: Complexation and separation of nitrate and nitrite by an azacryptand

Capillary electrophoresis (CE) was employed for studying the complexation of an azacryptand with nitrate and nitrite in aqueous solution. CE separation of a mixture of nitrate and nitrite with 10 mM acetate buffer (pH 3.3) showed two peaks at the retention times of 2.8 and 3.1 min for nitrate and nitrite, respectively. However, when the ligand (2 mM) was added to the running buffer, the peaks emerged in the reverse order and at shorter retention times of 2.7 and 2.5 min for nitrate and nitrite, respectively. The longer retention time for nitrate compared with nitrite indicates a stronger complex formation between the ligand and nitrate, that reduces the migration speed of nitrate as compared with the less strongly bound nitrite. The (1)H NMR titrations of L with these two anions at the pH 3.3, gave the binding constants (log K), 3.75 and 4.23, for nitrite and nitrate, respectively which were in consistence with the results obtained from the CE method.     

地基CE312热红外辐射计定标方法分析与评价

地基CE312热红外辐射计用于星载传感器的定标,其定标精度直接影响热红外传感器的场地定标精度。文章论述CE312-1b带宽辐亮度定标法和分谱辐亮度定标法的定标原理,利用实验室黑体对CE312-1b热红外辐射计进行定标,最后利用2010年8月青海湖的野外实测数据结合MODIS观测值,分析对比两种定标方法所得定标结果的准确性及误差来源。结果表明,带宽辐亮度定标法得到的CE312热红外辐射计定标系数相对分谱辐亮度定标法所得结果在准确性、适用性方面表现更好。     

Evolution of surfaces and mechanisms of contact electrification between metals and polymers

Contact electrification (CE) is a pretty common phenomenon, but still is poorly understood. The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity. In this paper, the CE between metals and polymers is systematically studied, which shows the evolution of surfaces is accompanied by variations of CE outputs. The variations of CE charge quantity are closely related to the creep and deformation of the polymer and metal surfaces. Then the relationship between CE and polymer structures is put forward, which is essentially determined by the electronegativity of elements and the functional groups in the polymers. The effects of load and contact frequency on the CE process and outputs are also investigated, indicating the increase of CE charge quantity with load and frequency. Material transfer from polymer to metal is observed during CE while electrons transfer from metal to polymer, both of which are believed to have an influence on each other. The findings advance our understanding of the mechanism of CE between metal and polymers, and provides insights into the performance of CE-based application in various conditions, which sheds light on the design and optimization of CE-based energy harvest and self-powered sensing devices.     

Conical emission from laser plasma interactions in the filamentation of powerful ultrashort laser pulses in air

We performed detailed experimental and numerical investigations of the conical emission (CE) accompanying the filamentation of powerful ultrashort laser pulses in air. It was found that the CE originates from self-phase modulation in the plasma produced by the pulse during propagation. The experiment and the simulation agree on the essential features of the CE: The CE angle decreases with increasing wavelength and is independent of the position along the filament, and there is no CE at Stokes-shifted wavelengths.     

Cavitation erosion mechanisms in Co-based coatings exposed to seawater

The cavitation erosion (CE) of most materials in seawater is more serious than in fresh water due to the onset of corrosion; however, in a previous study we reported results that contradict this widely accepted trend. In this research our objective is to provide fundamental insight into the mechanisms that may be responsible for these earlier results. To accomplish this objective, two types of Co-based coatings, prepared by high velocity oxygen fuel (HVOF) spraying system, were used to further investigate the underlying corrosion-mitigating CE mechanism in seawater. Accordingly, the influence of spraying parameters on microstructure, composition and mechanical properties of the coatings was analyzed on the basis of SEM, XRD, Raman spectroscopy, Vicker’s hardness and nano-indentation results. Electrochemical corrosion tests were used to evaluate the corrosion behavior of the Co-based coatings. Their CE performances in seawater and deionized water were comparatively studied by a vibratory apparatus. Results demonstrated that a higher flame temperature facilitated the oxides formation with associated improvements in compactness, hardness and toughness of the coatings. The presence of alumina in combination with the oxides formed in-situ facilitated the formation of an oxidation film on surfaces, and effectively enhanced the charge transfer resistance of the coating, thereby significantly improving the corrosion resistance in seawater. Metallic Co was not only more easily oxidized but also more readily corroded than the alloyed Co. Compactness was identified as an important factor affecting CE resistance of coatings in deionized water, because defects facilitate the nucleation and eventual collapse of bubbles. Moreover, bubble collapse produced a transient high temperature spike in excess of 600 °C that also caused Co and Cr elements to oxidize. Because the CE tests were carried out in seawater, additional Co₃O₄ and Cr₂O₃ were generated owing to corrosion that more effectively increased the surface compactness and mechanical properties of the coatings. This behavior was particular notable for coatings with metallic Co and Cr, which should be why seawater corrosion could weaken the CE of Co-based coatings.     

铝电解中SnO2+Sb2O3+CuO惰性阳极的电流效率、腐蚀性及结构变化

系统研究了霍尔赫鲁特铝电解池中SnO₂基惰性阳极 (96%SnO₂+2%Sb₂O₃+2%CuO)的电流效率,腐蚀性以及结构变化. 评价了各种操作参数(温度、电流密度、阴阳两级的距离、冰晶石量比、Al₂O₃ 浓度和电解质组成)对电流效率和腐蚀性的影响.