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HRMAS NMR for Studying Solvent-Induced Mobility of Polymer Chains and Metallocene Migration Into Low-Density Polyethylene (LDPE). HRMAS NMR 用于研究溶剂诱导的聚合物链流动性以及茂金属向低密度聚乙烯 (LDPE) 的迁移。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-11-06 DOI: 10.1002/mrc.5484
John C Hoefler, Maxwell R Kimball, Janet Blümel

HRMAS (high-resolution magic angle spinning) nuclear magnetic resonance (NMR) spectroscopy of low-density polyethylene (LDPE) affords 1H and 13C NMR spectra with superior resolution. For acquiring HRMAS NMR spectra, the polymer is first swollen with representative organic solvents. Then, the samples are measured with a conventional solid-state NMR spectrometer in the wideline mode or at the low spinning speed of 2 kHz. Anisotropic interactions like CSA (chemical shift anisotropy) and dipolar interactions are reduced due to the additional mobility of the polymer chains in the presence of the solvent within the polymer network. The combined effect of this mobility and MAS leads to signals with substantially reduced halfwidths as compared to classic MAS of the dry polymer. With HRMAS, all signals of the polymer become visible, and the spectra can be used for a quick and easy assessment of the polymer swelling behavior in diverse solvents. Being able to characterize polymers on the molecular level, and identifying the solvents that penetrate the polymer network best, enables the study of post-synthesis modifications of the polymers. It is demonstrated by paramagnetic HRMAS that the metallocene nickelocene (Cp2Ni) penetrates the LDPE network along with the solvent and is homogeneously dispersed in the polymer. SEM images prove that the structure of the polymer is not altered by the presence of a solvent and Cp2Ni. The impact of the paramagnetic Cp2Ni on the 1H signal halfwidth and T1 time of LDPE is studied. HRMAS allows a quick assessment of metal complexes regarding their ability to penetrate the LDPE network and therefore supports future studies of catalytic polymer degradation.

低密度聚乙烯(LDPE)的 HRMAS(高分辨率魔角旋转)核磁共振(NMR)光谱可提供分辨率极高的 1H 和 13C NMR 光谱。要获取 HRMAS NMR 光谱,首先要用有代表性的有机溶剂溶胀聚合物。然后,使用传统固态 NMR 光谱仪以宽线模式或 2 kHz 的低旋转速度测量样品。由于聚合物网络中存在溶剂,聚合物链具有额外的流动性,因此 CSA(化学位移各向异性)和偶极性等各向异性相互作用会减弱。与干聚合物的传统 MAS 相比,这种流动性和 MAS 的共同作用导致信号的半宽度大大减小。有了 HRMAS,聚合物的所有信号都变得清晰可见,光谱可用于快速、轻松地评估聚合物在不同溶剂中的溶胀行为。能够在分子水平上描述聚合物的特性,并确定最能穿透聚合物网络的溶剂,有助于研究聚合物的合成后改性。顺磁 HRMAS 证明,茂金属二茂镍 (Cp2Ni) 与溶剂一起渗透到 LDPE 网络中,并均匀地分散在聚合物中。扫描电子显微镜图像证明,聚合物的结构不会因溶剂和 Cp2Ni 的存在而改变。研究了顺磁 Cp2Ni 对 LDPE 的 1H 信号半宽和 T1 时间的影响。HRMAS 可以快速评估金属复合物穿透 LDPE 网络的能力,因此有助于今后对催化聚合物降解的研究。
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引用次数: 0
Structural Elucidation and Complete NMR Spectral Assignments of Monascus Monacolin Analogs. Monascus Monacolin 类似物的结构阐释和完整 NMR 光谱分配。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-11-05 DOI: 10.1002/mrc.5489
Jiachen Liu, Qingjiang Xu, Xin Wang, Ronghua Pan, Lizhong Zheng, Yonghong Zhang, Xiaoya Shang, Nan Wang

One new monacolin analog, monacolin V (1), together with two new monacolin-like natural products, 6-hydroxyl monacolin P (2) and 3-keto monacolin S (3), were isolated from the ethyl acetate portion of red yeast rice ethanol extract. Their structures were identified by HRESIMS and NMR experiments, and the complete assignments of 1H and 13C NMR data for three compounds were obtained by the aid of HSQC, HMBC, 1H-1H COSY, and NOESY data. This is the first time that the NMR data of compounds 2 and 3 have been fully assigned.

从红曲米乙醇提取物的乙酸乙酯部分中分离出了一种新的独活素类似物--独活素 V(1),以及两种新的独活素类天然产物--6-羟基独活素 P(2)和 3-酮独活素 S(3)。借助 HSQC、HMBC、1H-1H COSY 和 NOESY 数据,对三种化合物的 1H 和 13C NMR 数据进行了完整的分配。这是首次对化合物 2 和 3 的核磁共振数据进行完整的赋值。
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引用次数: 0
Reversibly Compressible Cross-Linked Polystyrene Gels, Compatible With Toluene-d8 and Pyridine-d5, for Measurement of Residual Dipolar Couplings and Residual Chemical Shift Anisotropies. 与甲苯-d8 和吡啶-d5 兼容的可逆压缩交联聚苯乙烯凝胶,用于测量残余双极耦合和残余化学位移各向异性。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-11-04 DOI: 10.1002/mrc.5494
Franciane G Dos Santos, Daiane S Carvalho, Fernando Hallwass, Armando Navarro-Vázquez

A chemically cross-linked version of polystyrene is presented here that allows the preparation of reversibly mechanically compressible gels as NMR weakly aligning media. The gels can be successfully swollen in aromatic solvents such as toluene-d8 and pyridine-d5, as well as in CDCl3, and provided accurate measurements of 1DCH RDCs and 13C-RCSAs.

本文介绍了一种化学交联型聚苯乙烯,它可以制备可逆机械压缩凝胶,作为 NMR 弱对准介质。这种凝胶可以在甲苯-d8 和吡啶-d5 等芳香溶剂以及 CDCl3 中成功溶胀,并提供了 1DCH RDC 和 13C-RCSA 的精确测量。
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引用次数: 0
A New qNMR Compliant Savitzky-Golay Apodization Function for Resolution Enhancement. 用于提高分辨率的新型 qNMR 兼容型 Savitzky-Golay 光晕函数
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-11-03 DOI: 10.1002/mrc.5492
Carlos Cobas, José Antonio García-Pulido, Paula Mora, Giovanni Selva, Stan Sykora

In this work, we introduce a novel NMR apodization function designed to enhance spectral resolution while maintaining compatibility with qNMR standards. This function is based on a modified Savitzky-Golay filter, adapted for time-domain application. It effectively suppresses the negative components typically associated with derivative spectra, while also ensuring the preservation of quantitative integrity in NMR analyses.

在这项工作中,我们介绍了一种新型 NMR 光栅化函数,旨在提高光谱分辨率,同时保持与 qNMR 标准的兼容性。该功能基于改进的 Savitzky-Golay 滤波器,适用于时域应用。它能有效抑制通常与导数光谱相关的负成分,同时还能确保在 NMR 分析中保持定量完整性。
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引用次数: 0
NMR Relaxometry to Monitor In Situ the Loading of Amberlite IR120 and Dowex Marathon MSC Resins With Ni2+ and Cu2+ During a Column Experiment. 核磁共振弛豫测定法用于监测 Amberlite IR120 和 Dowex Marathon MSC 树脂在色谱柱实验中对 Ni2+ 和 Cu2+ 的原位加载。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-10-30 DOI: 10.1002/mrc.5490
Marie Bernardi, Rodrigo de Oliveira Silva, Quoc Lam Vuong, Dimitrios Sakellariou, Yves Gossuin

The removal of heavy metal ions from wastewater often necessitates the use of ion exchange resins. Current methods for assessing ion exchange efficiency are indirect and destructive. Some heavy metal ions, such as Cu2+ and Ni2+, are paramagnetic and influence the NMR relaxation times of water protons. NMR relaxometry can therefore be utilized to track the removal of these ions by ion exchange resins. In this study, we use relaxometry to monitor in situ the loading with Ni2+ and Cu2+ of Amberlite IR120 and Dowex Marathon MSC resins, with the resin column inserted into a low-field NMR device. The multiexponential transverse relaxation curves were fitted using a biexponential model. Before and during the loading of the resin, the water with the slowest relaxation corresponds to treated water (free of Ni2+ or Cu2+) flowing between the resin beads. After saturation, the slowest fraction corresponds to the untreated solution (containing Ni2+ or Cu2+) flowing between the resin beads saturated with paramagnetic ions. The evolution with time of the transverse relaxation rate and the amplitude of the slowly relaxing water fraction shows a clear transition, occurring later at the bottom of the resin bed compared with the middle and top. This is interpreted as an indication of the saturation of the studied zone with paramagnetic ions, confirmed by the quantification of Ni2+ or Cu2+ in the effluent using AES spectroscopy. This proof-of-concept study demonstrates that NMR relaxometry can be used in situ to monitor the loading of a resin bed with paramagnetic ions.

去除废水中的重金属离子通常需要使用离子交换树脂。目前评估离子交换效率的方法既间接又具有破坏性。某些重金属离子(如 Cu2+ 和 Ni2+)具有顺磁性,会影响水质子的核磁共振弛豫时间。因此,核磁共振弛豫测定法可用于跟踪离子交换树脂去除这些离子的情况。在本研究中,我们将树脂柱插入低场 NMR 设备中,使用弛豫测定法原位监测 Amberlite IR120 和 Dowex Marathon MSC 树脂的 Ni2+ 和 Cu2+ 负载情况。使用双指数模型拟合了多指数横向弛豫曲线。在加载树脂之前和期间,弛豫速度最慢的水是在树脂珠之间流动的经过处理的水(不含 Ni2+ 或 Cu2+)。在饱和之后,最慢的部分对应于在树脂珠之间流动的未处理溶液(含有 Ni2+ 或 Cu2+),该溶液已被顺磁离子饱和。随着时间的推移,横向弛豫速率和缓慢弛豫水部分的振幅发生了明显的变化,树脂床底部发生的时间晚于中部和顶部。这可以解释为所研究区域内顺磁性离子达到饱和的迹象,并通过使用 AES 光谱定量检测流出物中的 Ni2+ 或 Cu2+ 得到证实。这项概念验证研究表明,核磁共振弛豫测量法可用于现场监测顺磁离子对树脂床的负载情况。
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引用次数: 0
To Gibbs or Not to Gibbs Effect of Entropic Contribution in the NMR Calculations of Flexible and Polar Molecules-Updating the DP4+App. 柔性和极性分子核磁共振计算中熵贡献的吉布斯效应(To Gibbs or Not to Gibbs Effect of Entropic Contribution in the NMR Calculations of Flexible and Polar Molecules)-更新 DP4+App.
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-10-30 DOI: 10.1002/mrc.5491
Milagros Amichetti, Bruno A Franco, María Marta Zanardi, Ariel M Sarotti

The application of quantum-based NMR methods for the structural elucidation of natural and unnatural products has grown significantly. However, accurately calculating the conformational landscape of flexible molecules with intricate intramolecular hydrogen bonding (IHB) networks continues to be a major challenge. In this work, we thoroughly studied the effect of entropic contributions (trough Gibbs free energies calculations) in the DP4+ performance. Our results show that to solve biased systems with strong IHB interactions requires computing the Boltzmann contributions using Gibbs free energies computed with at least triple-ξ basis set and SMD solvation model. In response to this finding, we have updated our DP4+App, a user-friendly Python applet that automates the entire process of calculating DP4+ probabilities. In the new version, the program allows for calculating of conformational contributions at any selected theory level, using either SCF or Gibbs free energies.

基于量子的核磁共振方法在天然和非天然产物的结构阐释方面的应用已大幅增长。然而,精确计算具有复杂分子内氢键(IHB)网络的柔性分子的构象格局仍然是一项重大挑战。在这项工作中,我们深入研究了熵贡献(通过吉布斯自由能计算)对 DP4+ 性能的影响。结果表明,要求解具有强 IHB 相互作用的偏态系统,需要使用至少三ξ基集和 SMD 溶解模型计算的吉布斯自由能来计算玻尔兹曼贡献。针对这一发现,我们更新了 DP4+App 程序,这是一个用户友好的 Python 小程序,可以自动完成 DP4+ 概率的整个计算过程。在新版本中,该程序允许使用 SCF 或吉布斯自由能计算任何选定理论水平的构象贡献。
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引用次数: 0
Deciphering the Conformations of Glutathione Oxidized Peptide: A Comparative NMR Study in Solution and Solid-State Environments. 解密谷胱甘肽氧化肽的构象:溶液和固态环境下的核磁共振对比研究。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-10-16 DOI: 10.1002/mrc.5486
Dillip K Senapati, Jayasubba Reddy Yarava, K V Ramanathan, S Raghothama

Glutathione (GSH) and its oxidized dimer (GSSG) play an important role in living systems as an antioxidant, balancing the presence of reactive oxygen species (ROS). The central thiol (-S-S-) bond in GSSG can undergo free rotation, providing multiple conformations with respect to the S-S bridge. The six titratable sites of GSSG, which are influenced by pH variations, affect these conformations in solution, whereas in solids, additionally crystal packing effects come into play. In view of differing reports about the structure of GSSG in literature, we have here conducted an extensive reexamination of its conformations using NMR, and contrasting results have been obtained for solution and solid state. In solution, the existence of more than one antiparallel orientation of the monomer unit with different hydrogen bonding schemes has been indicated by NOE and amide temperature coefficient results. On the other hand, in the solid-state, a 1H-1H double-quantum (DQ) to 13C single-quantum (SQ) correlation study has confirmed a parallel orientation, consistent with the reported X-ray crystal structure. Experimentally assigned solid-state NMR resonances have been validated using GIPAW calculations incorporated in the Quantum ESPRESSO package.

谷胱甘肽(GSH)及其氧化二聚体(GSSG)作为一种抗氧化剂,在生命系统中发挥着平衡活性氧(ROS)的重要作用。GSSG 中的中心硫醇(-S-S-)键可以自由旋转,提供了与 S-S 桥有关的多种构象。GSSG 的六个滴定位点会受 pH 值变化的影响,从而影响其在溶液中的构象,而在固体中,晶体的堆积效应也会发挥作用。鉴于文献中对 GSSG 结构的不同报道,我们在此利用核磁共振技术对其构象进行了广泛的重新研究,并在溶液和固体状态下得到了截然不同的结果。NOE 和酰胺温度系数结果表明,在溶液中,单体单元存在不止一种反平行取向,且氢键方案各不相同。另一方面,在固态中,1H-1H 双量子(DQ)到 13C 单量子(SQ)相关性研究证实了平行取向,与所报告的 X 射线晶体结构一致。利用量子 ESPRESSO 软件包中的 GIPAW 计算验证了实验分配的固态核磁共振共振。
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引用次数: 0
Understanding the Interactions of Nanoparticles and Dissolved Organic Matter at the Molecular Level by 1H 2D Multi-Exponential Transverse Relaxation NMR Spectroscopy. 通过 1H 2D 多指数横向弛豫 NMR 光谱了解纳米粒子与溶解有机物在分子水平上的相互作用。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-10-16 DOI: 10.1002/mrc.5487
Malak Dia, Jonathan Farjon, Clotilde Raveleau, André Simpson, Pierre-Emmanuel Peyneau, Béatrice Béchet, Denis Courtier-Murias

The interaction between humic acid (HA) and engineered nanoparticles (NPs) is critical in environmental sciences, especially for understanding the behavior of NPs in natural waters. This study employs 1H 2D Multi-Exponential Transverse Relaxation (METR) NMR spectroscopy to examine the molecular-level interactions between Pahokee Peat humic acid (HA) and carboxyl-functionalized iron oxide nanoparticles (NPCOs). First, 1H 2D METR NMR spectroscopy allowed not only the identification of HA in terms of its chemical composition but also the separation of molecules with the same chemical shift values but different rates of molecular tumbling. Then, using solutions with varying NPCO concentrations (0, 10, 40, and 100 μM), we observed significant changes in the T2 relaxation times of HA components, indicating interactions between HA and NPCO. Analysis showed the biggest effect on two chemical shift regions, corresponding to lipids and carbohydrates, revealing that smaller molecules within these regions exhibit the most significant changes in T2 values upon the addition of NPCO. This suggests that these molecules are the initial sites of interaction, with the entire HA system being affected at higher NPCO concentrations. These findings highlight the utility of METR NMR spectroscopy in studying complex environmental mixtures and provide insights into the behavior of HA and NPs, essential for understanding the fate of NPs in the environment.

腐植酸(HA)与工程纳米粒子(NPs)之间的相互作用在环境科学中至关重要,特别是对于了解天然水体中 NPs 的行为。本研究采用 1H 2D 多指数横向弛豫(METR)核磁共振波谱来研究帕霍基泥炭腐植酸(HA)与羧基功能化氧化铁纳米粒子(NPCOs)之间的分子级相互作用。首先,通过 1H 2D METR NMR 光谱不仅可以识别 HA 的化学成分,还可以分离出化学位移值相同但分子翻滚速率不同的分子。然后,使用不同浓度的 NPCO 溶液(0、10、40 和 100 μM),我们观察到 HA 成分的 T2 弛豫时间发生了显著变化,这表明 HA 与 NPCO 之间存在相互作用。分析表明,与脂质和碳水化合物相对应的两个化学位移区域受到的影响最大,这表明在添加 NPCO 后,这些区域中的小分子在 T2 值上表现出最显著的变化。这表明这些分子是相互作用的初始位点,当 NPCO 浓度较高时,整个 HA 系统都会受到影响。这些发现凸显了 METR NMR 光谱在研究复杂环境混合物方面的实用性,并提供了有关 HA 和 NPs 行为的见解,这对了解 NPs 在环境中的归宿至关重要。
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引用次数: 0
Determination of the pKa Value of a Brønsted Acid by 19F NMR Spectroscopy. 通过 19F NMR 光谱测定布氏酸的 pKa 值。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-10-16 DOI: 10.1002/mrc.5485
Emily F Griffiths, Jay A Dixon, Andrew J M Caffyn, Stuart K Langley, Beatriz Maciá, Vittorio Caprio, Ryan E Mewis

Brønsted acids, such as phosphoric acids derived from chiral 1,1'-bi-2-naphthol (BINOL), are important catalysts in the formation of carbon-carbon and carbon-heteroatom bonds, for example. The catalytic activity of these Brønsted acids is strongly linked to their acidity, and as such, the evaluation of compounds to determine pKa values provides insight into their catalytic activity. Herein, a 19F{1H} NMR methodology is detailed to determine the pKa of a fluorinated binaphthyl-derived phosphinic acid, rac-1, in acetonitrile and in the presence of a fluorinated sulfonamide reference compound (2-4). The approach was tested initially using 2 and 3, with the ΔpKa (0.08) in strong agreement with previously reported values (6.6 for 2 and 6.68/6.73 for 3). Sigmoidal curves of normalised chemical shift change (Δδ) against equivalents of the base phosphazene P1-tBu added overlapped for 2 and 3, but in the case of rac-1 and either 2, 3 or 4, there was significant separation. A variety of different approaches for determining the ΔpKa were compared. Values of pKa determined when the normalised Δδ was 90% were optimal for 2 and 3, whereas a normalised Δδ of 75% was optimal for 4, resulting in the pKa of rac-1 being determined to be 8.47-8.71.

布氏酸(如从手性 1,1'-联-2-萘酚(BINOL)中提取的磷酸)是形成碳-碳键和碳-异原子键等的重要催化剂。这些布氏酸的催化活性与它们的酸性密切相关,因此,通过评估化合物以确定 pKa 值可以深入了解它们的催化活性。本文详细介绍了一种 19F{1H}NMR 方法来确定含氟二萘衍生膦酸 rac-1 在乙腈和含氟磺酰胺参比化合物 (2-4) 存在下的 pKa。最初使用 2 和 3 对该方法进行了测试,其 ΔpKa(0.08)与之前报告的数值(2 为 6.6,3 为 6.68/6.73)非常一致。2 和 3 的归一化化学位移变化(Δδ)与加入的等量膦基 P1-tBu 的西格玛曲线重叠,但 rac-1 与 2、3 或 4 的化学位移变化明显不同。对确定 ΔpKa 的各种不同方法进行了比较。当归一化 Δδ 为 90% 时,2 和 3 的 pKa 值最佳,而归一化 Δδ 为 75% 时,4 的 pKa 值最佳,因此 rac-1 的 pKa 值被确定为 8.47-8.71。
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引用次数: 0
NMR Coupling Constants, Karplus Equations, and Adjusted MD Statistics: Detecting Diagnostic Torsion Angles for the Solution Geometry of 6-[α-d-Mannopyranosyl]-d-Mannopyranose (Mannobiose). NMR 耦合常数、Karplus 方程和调整 MD 统计量:检测 6-[α-d-吡喃甘露糖基]-d-吡喃甘露糖(甘露糖)溶液几何的诊断性扭转角。
IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Pub Date : 2024-10-16 DOI: 10.1002/mrc.5483
Andreas H Franz, Kendall S Bromley, Ei T Aung, Stephen Q L Do, Hana M Rosenblatt, Amelia J Watson

The quantitative solution conformations of 2-(hydroxymethyl)-tetrahydropyran, α-methyl-d-mannopyranoside, and 6-[α-d-mannopyranosyl]-d-mannopyranose (mannobiose) are described. Parametrized Karplus equations for redundant spin pairs across the terminal ω-torsion and the glycosidic ω-torsion for mannobiose are developed, including ω/θ-hypersurfaces for the terminal hydroxymethylene group. Experimental NMR data, algorithmic spectral simulation (clustered Hamiltonian method), molecular dynamics (MD) simulations (GLYCAM06), energy minimizations by DFT, and adjusted torsion angle populations weighted over the Karplus-type equations are used. We demonstrate that spectral simulation is a powerful tool in the refinement of initial J values obtained from static GAIO DFT calculations. We also show that only as few as one of multiple redundant torsions can be diagnostic for conformational analysis of the disaccharide.

描述了 2-(羟甲基)-四氢吡喃、α-甲基-d-吡喃甘露糖苷和 6-[α-d-吡喃甘露糖基]-d-吡喃甘露糖(甘露寡糖)的定量溶液构象。建立了甘露寡糖末端ω-扭转和糖苷ω-扭转上冗余自旋对的参数化卡普拉斯方程,包括末端羟基亚甲基的ω/θ-超表面。我们使用了核磁共振实验数据、算法光谱模拟(聚类哈密顿法)、分子动力学(MD)模拟(GLYCAM06)、DFT 能量最小化以及根据卡普拉斯方程加权的调整扭转角群。我们证明了光谱模拟是完善从静态 GAIO DFT 计算中获得的初始 J 值的有力工具。我们还表明,在对二糖进行构象分析时,多个冗余扭转中只有一个扭转可以进行诊断。
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引用次数: 0
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Magnetic Resonance in Chemistry
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