Identification and quantitative analysis of the intermediate phase in a linear high-density polyethylene

The observation of chain conformation and mobility in polyethylene by solid-state ¹³C magic angle spinning (MAS) nuclear magnetic resonance (NMR) permits unambiguous identification and quantitative analysis of an intermediate phase. The carbon-carbon bonds in the intermediate phase adopt, on the average, an all-trans conformation and are more mobile than in the crystalline state (room temperature rate of reorientation ≈ 10⁷ Hz). Comparisons of crystallinities by differential scanning calorimetry, wide-angle x-ray diffraction, and NMR support the high orientation of the intermediate phase and suggest a lower heat of fusion than for the crystals. Results from ¹³C spin-lattice relaxation and ¹H spin diffusion show that the mass fractions are ≈ 20% and the domain sizes ≈ 36 Å. Both change with crystallization and annealing conditions. © 1994 John Wiley & Sons, Inc.     

Quantitative determination of aliphatic hydrocarbon compounds by 2D NMR

Quantitative analysis of complex mixtures by NMR is often hampered by heavily overlapping signals in 1D ¹H or ¹³C spectra. To resolve the overlap problem, we have been looking at the possibilities of using heteronuclear correlated 2D NMR methods for quantification. In this work, we applied 2D INEPT to analyze mixtures of tetradecane and squalane, which represent typical substructures of lube oil fractions. The factors affecting correlation peak volumes, namely the polarization transfer delays within pulse sequence, multiplicity of CH_n group and the magnitude of ¹J_{(C, H)} couplings were taken into account by product operator formalism calculations. The results indicate that if absolute precision in quantification is not essential, the current approach can be used for the quantitative analysis of the molecular composition of complex mixtures when conventional 1D NMR methods fail. Copyright © 2002 John Wiley & Sons, Ltd.     

The morphology of gel-spun polyethylene fibers,investigated by solid-state 13C NMR

Gel-spun polyethylene fibers were analyzed at room temperature with ¹³C NMR, using both, CP-MAS and BILEV (Bloch-decay with two-level decoupling). The analysis shows the existence of three different components in the fiber sample—a crystal component, an amorphous component and a third component, named the oriented, mobile component. This latter component has a ¹³ C chemical shift that is similar to the crystalline chemical shift, but with a mobility, expressed by T₁, that is closer to the amorphous component. The chemical shift and T₁ are as follows: 34.06 ppm and 28.1 s for the crystalline part; 31.70 ppm and 0.3 s for the amorphous part; and 34.06 ppm and 1.8 s for the oriented mobile component. The percentages are 63.2% crystalline; 34.0% oriented mobile, 2.8% amorphous component. Using proton spin-diffusion measurements, it was possible to estimate the domain size of the crystalline and oriented mobile components to be 62.8 and 13.2 nm, respectively, in agreement with the results of a full-pattern x-ray study on the same sample. After melting of the fiber at 450 K and recrystallinzation on cooling, the oriented, mobile component is dramatically reduced. © 1994 John Wiley & Sons, Inc.     

环肽配糖体的二维核磁共振谱研究

用600MHz超导核磁共振仪测定了两个具有抗癌活性环肽配糖体RY-2和RY-3的TOCSY, HMQC, HMBC和ROESY谱图, 并正确地对分子RY-2和RY-3的氢谱和碳谱进行了归属。同时订正分子RY-3中糖的连接位置。     

Water and oil signal assignment in low-moisture mozzarella as determined by time-domain NMR T2 relaxometry

A time-domain ¹H nuclear magnetic resonance relaxometry method was elaborated for the rapid microstructural characterization of mozzarella cheese. For this purpose, there is a strong need to know how the experimentally determined T₂ relaxation time distribution can be related to specific constituents in mozzarella. In this study, a detailed investigation is offered for fresh and aged low-moisture mozzarella cheese, often applied as a pizza cheese, by application of both a conventional Carr–Purcell–Meiboom–Gill (CPMG) sequence and a free-induction decay CPMG (FID-CPMG) sequence. The relaxation behavior was further elucidated by addition of deuterium oxide and by mild heat treatment of samples. The relaxation times of water protons in mozzarella were found to range from a few microseconds to some tens of milliseconds (in aged mozzarella) or to about hundred milliseconds (in fresh mozzarella). The upper limit of the T₂ distribution can even be extended to the seconds range upon releasing water protons from the mozzarella matrix using a mild heat treatment or upon addition of deuterated water. Both stimuli also provided evidence for the absorption of water into the cheese matrix. The potential release and uptake of water demonstrated that mozzarella acts as a very dynamic system during production and storage. The detected differences in the behavior of the water fraction between fresh and aged low-moisture mozzarella might be utilized to study the influence of either production and/or storage conditions on the cheese ripening process.     

油菜花粉十二肽的二维核磁共振研究

用核磁共振方法对油菜花粉十二肽溶液构象进行了研究。利用２Ｄ ＣＯＳＹ和ＮＯＥＳＹ归属了＾１Ｈ ＮＭＲ谱的全部共振峰。用Ｋａｒｐｌｕｓ方程从肽键Ｎ－Ｈ质子与α－Ｈ质子的偶合常数计算出了所有肽键的二面角θ及Φ，并对其进行不同温度及不同溶剂条件下的观测。结果表明，在水溶液中该肽链为无规卷曲结构，个别肽段存在γ－ｔｕｒｎ构象。     

西贝素β-氮氧化物及其二维核磁共振谱

本文报告应用化学和光谱法(^1H, ^1^3C NMR, ^1^3C,^1H COLOC, noeds和NOESY) , 对分自川产家种华西贝母(F. siechuanica S. C. Che)藓茎中的碱N确证为西贝素β-氮氧化物(imperialine β-N-oxide )3以及3的二维核磁共振谱的研究. 同时, 对文献[4]报告的3中某些^1^3C信号化学位移的归属也进行了纠正.     

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.     

2D NMR对Sarcophine所有^1H NMR和^1^3C NMR归属的指定

从中国南海软珊瑚Sarcophyton molle中分离得到大环二萜内酯Sarcophine(1)。本文利用^1H-^1H COSY，HMQC，HMBC等二维谱手段首次对Sarcophine所有^1H NMR、^1^3C NMR的信号归属进行了完全的指定。并第一次报道了其^1^3C NMR数据。     

2D NMR Spectroscopic Studies of the Toxic Alkaloid from Oxytropis Glabra D C.

The Oxytropis, legume genus, is native in the northwest of China, and some of its members have been reported to be toxic to grazing livestock. In the course of studying toxic reason of this legume, a toxic alkaloid was isolated from Oxytropis glabra D C. grown in the Inner Mongolian Autonomous Region. The LD+(50) of (—)-thermopsine(Ⅰ) was shown to be 89.98 mg/kg(in mice). This paper reports an approach to the structure elucidation of(-)-thermopsine by combining 2D NMR[~1H-~1H and ~1H-~(13)C (one-bond and long-range) COSY] and other physicochemical methods. The stereochemistry of compound Ⅰ is also discussed.     

矢车菊素结构的2D NMR确定

从菊科药用植物蕴苞麻花头（Serratula stranglata lljin)中分离得到一含氯的愈创木内酯型的倍半萜——矢车菊素（centaurepensin),利用^1H-^1H COSY、HMQC、HMBC及^1H-^1H NOESY等二维波谱技术鉴定了该化合物的结构,并对其^1H和^13C NMR的信号进行了全归属,最终确定了其绝对构型。     

Structure elucidation of a novel group of dithiocarbamate derivatives using 1D and 2D NMR spectroscopy

Compounds 1-7 form a novel group of dithiocarbamates, first synthesized from the reaction of a series of primary amines with carbon disulfide and 3-bromo ethyl pyruvate in the presence of anhydrous potassium phosphate. Structure elucidation of this group of compounds was accomplished using extensive 1D and 2D NMR spectroscopic studies, including (1)H, (13)C, COSY, NOESY, HSQC, and gHMBC experiments. The distinction between the linear structures I, II and the cyclic structure III was made mainly on the basis of the analysis of the cross peak between H-2 and H-4a in the COSY spectra, in combination with the long-range correlation between H-2 and C-4, 6 in the gHMBC spectra.     

Automated Protein Structure Elucidation From 2D NMR

A general method for automated de novo deduction of protein structure from 2D NMR has been developed. The algorithms which extract simple spin coupling topologies from MQF-COSY, construct more complicated spin coupling topologies based upon MQ spectrum including all possible pathways, and extract spin coupling topological fragments for amino acids of a protein, have been implemented in C~(++) language and run on a SUN 4/280 work station. Compared with the manual assignments for melittin, the total identity of the automated de novo method is 86.3%.     

用2D NMR确定金色酰胺醇酯的结构

从中国南海红藻鹧鸪菜（Caloglossa leprieurii）中首次分离得到二肽金色酰胺醇酯(aurantiamide acetate)。利用^1H－^1H COSY、^13C－^1H COSY、HMBC等二维谱手段鉴定了该化合物的结构,对其^1H和^13C NMR的信号进行了归属,并且确定了其绝对构型。     

Structure determination of Aervins A‐D,new coumaronochromone analogues from Aerva persica,by 1D and 2D NMR spectroscopy

Aervins A‐D (1‐4), four new coumaronochromone analogues have been isolated from the CHCl₃‐soluble fraction of the MeOH extract of the whole plant of Aerva persica. Their structures were assigned based on ¹H NMR, ¹³C NMR spectra, DEPT, and by 2DNMR experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

胃泌素有关肽溶液构象的2D-NMR研究

用2D NMR深入研究了五肽、四肽胃泌素在 DMSO 中的构象。利用 COSY 谱、Relayed-COSY 谱、DQF-J 分解谱和 NOESY 谱归属了全部共振峰。计算了肽键平面的Φ角、旋转异构体分布和旋转异构体之间自由能差。根据 NOESY 谱得到了距离约束条件。结合Φ角及旋转异构体分布, 推导出五肽胃泌素分子的构象膜型。结果表明, 五肽、四肽胃泌素在 DMSO 中以半角构象存在, 在其主要的旋转异构体中 Trp 的吲哚环和 Met 的 S 原子具有类似5,1-benzothiazocine 三维结构, 可能是具有生物活性的原因。     

Quantitative estimation of the degree of derivatization: an alternative methodology using 1-D and 2-D NMR experiments

The precise estimation of the degree of derivatization of functional groups in polymers is important for determining their macroscopic properties. In this work, the quantitative estimation of the extent of esterification of novolac copolymers with di-tert-butyl dicarbonate was studied. Although the extent of esterification has been calculated previously by quantifying the signals from FT-IR and UV-Vis spectroscopy, these were restricted to monitoring the progress of the derivatization process. The 13C NMR signal intensities from the inverse-gated 1H-decoupled NMR spectrum have been used recently for the quantitative estimation of the degree of esterification of polymers. An alternative methodology has been suggested by us based on the fully relaxed 1H chemical shift intensities. However, since the proton signals of novolac resins are generally broad and overlapping, the proton decoupled 13C NMR spectrum was used to identify the 1H NMR signals using the 2-D HSQC technique. A TOCSY experiment was also performed to confirm further the 1H NMR signal assignments and, finally, the deconvoluted 1H NMR spectrum was used for the calculation of the extent of derivatization.     

Contribution to Structural Elucidation： Behaviours of Substructures Partially Defined from 2D NMR

Structural elucidation (automatic determination of the structure of a molecule from its spectra) is frequently hampered by com-binatorial explosion when trying to assemble the identified sub-structures. We devised a new method which can avoid this pit-fall by a systematic examination of allowed t3C chemical shifts ranges for all substructures chemically possible and combined with a progressive pruning thanks to neighbouring relationships appearing from 2D NMR. This method is explained by a de-tailed example.     

Structural elucidation of four new furostanol saponins from Tupistra chinensis by 1D and 2D NMR spectroscopy

Four new furostanol saponins (1–4), two pairs of diastereoisomers, were isolated from methanolic extracts of Tupistra chinensis rhizomes and their structures were assigned from ¹H and ¹³C NMR spectra, DEPT, and by 2D COSY, NOESY, HMQC, and HMBC experiments. Copyright © 2008 John Wiley & Sons, Ltd.