晶体学辅助的2-吡啶甲酸固体~(13)C化学位移理论计算归属（英文）

有机分子的互变异构现象在溶液中较为常见.而对于有机固体而言,存在互变异构可能的分子常以单一的能量最稳定的异构体形式存在. 2-吡啶甲酸(PCA)是一个较为罕见的案例,它的晶体结构中同时存在有中性分子和两性离子两种互变异构体.由于超长的质子纵向弛豫时间,PCA的固体~(13)C核磁共振(NMR)实验的化学位移归属存在困难.密度泛函理论(DFT)计算,特别是基于周期性模型的方式是一种可以准确快捷归属其化学位移的方案.然而,由于PCA结构中活泼质子的占位无序,其结构并不能直接或经简单处理后递交计算.本文中,我们通过晶体学手段构建了一个虚拟晶体结构.基于该虚拟结构的~(13)C化学位移计算值可与实验值准确吻合.此外,不同互变异构状态的PCA表现出不同的特征化学位移,这一信息可被用来分析PCA在其晶体复合物中的分子状态.     

固体丁酸类代谢物13C化学位移的结构依赖性

丁酸类代谢物广泛存在于动物、植物和微生物中,且具有多种重要的生理功能,但它们的固体核磁共振参数、分子动力学性质及其结构依赖性并未得到清楚的认识. 该文使用高分辨交叉极化与魔角旋转核磁共振（¹³C CPMAS）实验技术,分析了一系列固体丁酸类代谢物的¹³C化学位移, 发现了这些代谢物的¹³C化学位移与其分子结构的一些相关性规律. 另外还发现,固体丁酸类代谢物与其在溶液中的¹³C化学位移有显著的差异. 这些代谢物中甲基参与的疏水作用以及羟基、氨基和羧基参与的氢键作用均对其化学位移大小有重要的影响. 上述结果为认识代谢物的结构和功能以及功能对结构的依赖性提供了重要信息.     

榄香烯及其衍生物的计算化学研究I β-榄香烯13C NMR化学位移的理论计算

报道了抗癌新药β-榄香烯的¹³C NMR化学位移的量子化学计算.在分子力学MMX和量子化学RHF/6-31G^*或B3LYP/6-31G^*优化结构的基础上进行了两种规范变换方法GIAO和CSGT的Hartree-Fock和B3LYP (6-31G^*基组)的化学位移计算.并对计算结果进行了误差分析和线性相关分析.所有的这些结果中,采用GIAO规范变换方法都好于CSGT,而以GIAO-B3LYP/6-31G^*//B3LYP/6-31G^*计算的结果最好,RMS为4.3ppm,相关系数R²为0.998,SD为2.42 ppm.而GIAO-B3LYP/6-31G^*//MMX是一种能兼顾计算时间和计算精度的方法,其RMS、R²和SD分别为4.9、0.996和3.0 4 ppm.     

榄香烯及其衍生物的计算化学研究I β-榄香烯13C NMR化学位移的理论计算

报道了抗癌新药β-榄香烯的¹³C NMR化学位移的量子化学计算.在分子力学MMX和量子化学RHF/6-31G^*或B3LYP/6-31G^*优化结构的基础上进行了两种规范变换方法GIAO和CSGT的Hartree-Fock和B3LYP (6-31G^*基组)的化学位移计算.并对计算结果进行了误差分析和线性相关分析.所有的这些结果中,采用GIAO规范变换方法都好于CSGT,而以GIAO-B3LYP/6-31G^*//B3LYP/6-31G^*计算的结果最好,RMS为4.3ppm,相关系数R²为0.998,SD为2.42 ppm.而GIAO-B3LYP/6-31G^*//MMX是一种能兼顾计算时间和计算精度的方法,其RMS、R²和SD分别为4.9、0.996和3.0 4 ppm.     

羰基13C NMR化学位移的计算

根据核外电子云球对称效应原理,建立化学位移统一计算公式,计算了醛、酮、酰氯、羧酸和酯中羰基的¹³C NMR化学位移,在一定程度上说明了影响¹³C NMR化学位移的主要结构因素,并对一些反常现象作出了直观合理的解释。     

高分子化学位移的量化计算与固体NMR实验研究

该文以2种不同立构聚丙烯（iPP和sPP）为讨论对象,首先研究了量化计算方法在预测高分子¹³C 各向同性和各向异性化学位移（CSA）中的应用,然后讨论了近年来发展的测定¹³C CSA粉末线形的2种重要固体NMR实验技术（SUPER和RAI）的特点和实验优化问题. 最后,利用可获得接近无扭曲线形的SUPER技术测定了等规立构聚丙烯样品的¹³C CSA粉末线形,并与量化计算理论结果比较. 结果表明：¹³C 各向同性化学位移及CSA粉末线形的理论计算结果均与固体NMR实验结果有很好的符合,预示通过¹³C CSA量化计算结合固体NMR实验是阐明高分子微观结构的有力工具.     

固体核磁共振结合密度泛函理论计算研究SSZ-39分子筛的钠离子落位与铝分布

具有AEI结构的SSZ-39分子筛的骨架外阳离子落位和铝分布对其催化性能影响显著.AEI笼中有三个结晶学不等价位,且铝取代T位具有一定的倾向性.本文结合固体核磁共振（NMR）技术（²⁷Al/²³Na MQ MAS NMR）,以及密度泛函理论（DFT）计算,研究了不同硅铝比Na-SSZ-39分子筛中的Na⁺落位和铝分布.在孤立铝分布的情况下,铝原子优先占据于T3位,Na⁺主要落位于AEI笼中的SIIa0和SIII'a0位点上,其中SIII'a0位点的优先度较高,此外少部分Na⁺还落位于六棱柱内部的SIa0.当铝对存在时,AlSiSiAl分布的铝对占据六元环的对位（T3-T3）,对应的Na⁺分别落位于SIIa1和SⅢ'a1位点.随着分子筛结构的部分破坏,游离的Na⁺可能形成明显的SIII'b位点.本文可加深对SSZ-39分子筛构效关系的理解,为更好地调控催化性能奠定基础.     

多环芳烃^13C—NMR化学位移的理论模拟

本文利用ＣＮＤＯ方法对十个多环芳烃化合物的＾１３Ｃ－ＮＭＲ的化学位移进行了理论上的计算，并提出了一个联系分子电荷密度、键级和键长等参数的半经验公式，同时利用逆磁环电流，顺磁环电流，湾区推斥效庆和迫位效应的影响。又对多环芳烃的化学位移进行了校正，从而使得理论计算与实验值吻合得很好，通过对多环芳烃的＾１３Ｃ－ＮＭＲ化学位移的回是分析表明：回归系数达到０．９５，较好地反映了多环芳烃＾１３Ｃ－ＮＭＲ化学位     

多环化合物中共轭双键13C NMR化学位移计算

介绍多环化合物中共轭双键¹³C NMR化学位移计算.     

氮杂多环芳烃^13C—NMR化学位移的理论探讨

本文主要是对氮原子以ｓｐ＾２杂化，孤氮电子占据ｓｐ＾２杂化轨道，以这种形式成健的氮杂交变多环芳烃中的１１个化合物的＾１３Ｃ－ＮＭＲ的化学位移进行了计算。该计算依据ＣＮＤＯ方法一个联系分析电荷密度，键级和键长等参数的半经验公式。同时利用环电流、空间效应以及针对氮原子物屏蔽效应和去屏蔽效应的影响，通过分子动力学的考虑，得到理论上计算的化学位移，该计算结果与实验值吻得很好，通过对＾１３Ｃ－ＮＭＲ化学位移     

NMR and DFT calculation study on structures of 2‐[2‐nitro‐4‐(trifluoromethyl)benzoyl]cyclohexane‐1,3‐dione (NTBC) and its two metabolites isolated from urine of patients suffering from tyrosinemia type I

2‐[2‐Nitro‐4‐(trifluoromethyl)benzoyl]cyclohexane‐1,3‐dione (NTBC) is an active component of nitisinone, a medicine against tyrosinemia type I. Using ¹H, ¹³C and ¹⁹F NMR spectroscopy it has been found that in the urine of patients treated with nitisinone two compounds possessing CF₃ group are always present. They have been isolated by using TLC technique and identified as 4‐hydroxy‐2‐[2‐nitro‐4‐(trifluoromethyl)benzoyl]cyclohexane‐1,3‐dione and 5‐hydroxy‐2‐[2‐nitro‐4‐(trifluoromethyl)benzoyl]cyclohexane‐1,3‐dione, the latter being previously unknown. The constitution, tautomerism and stereochemistry of these compounds have been thoroughly investigated using ¹H and ¹³C NMR spectroscopy supported by theoretical calculations. Molecular structures have been optimized using density functional theory (DFT) with PBE1PBE functional and 6‐31G* basis set. In NMR parameter calculations, the larger 6‐311++G(2d,p) basis set has been used. At both calculation stages, the polarizable continuum model of the solvent has been employed. Copyright © 2010 John Wiley & Sons, Ltd.     

药物小分子化学位移的量子化学计算研究

核磁共振的谱峰归属对分子结构的确定至关重要,用理论计算方法预测化学位移对谱峰的正确归属是极其有帮助的. 我们用量子化学的方法预测了乙酰水杨酸及其衍生物分子上碳原子的化学位移,并通过比较计算值和实验值得到不同理论计算方法的误差范围. 用HF和DFT理论计算芳环碳的化学位移时,CSGT方法比GIAO方法更为准确. 与其它方法相比,B3PW91//CSGT 在6-311G(d,p)基组下得到的芳环碳的化学位移最接近实验值. 采用B3LYP//GIAO计算时, 使用不同的基组 6-31G(d,p)和6-311++G(3df,3pd)得到的化学位移计算值只有δ 0.01~2.04的差异. MP2方法非常耗时,且对于计算精度的改善并不显著; 并且,由于电子相关性的影响,碳原子周围的电子环境对化学位移计算的准确性影响很大. 与实验值比较,HF方法由于忽略电子相关效应所以表现较差. 另外,碳链的增长对计算准确性也存在一定影响.      

盐酸氯丙嗪1H NMR、 13C NMR谱的归属及结构表征

通过运用¹H-¹H COSY(¹H-¹H COrrelation SpectroscopY)、TOCSY(TOtal Correlation SpectroscopY)、HSQC(Heteronuclear Single Quantum Correlation)、HMBC (Heteronuclear Multiple Bond Correlation)、NOESY(Nuclear Overhauser Enhancement SpectroscopY)等多种二维核磁技术,对盐酸氯丙嗪（Chlorpromazine hydrochloride CPZ· HCl）在CDCl₃、CD₃COCD₃和D₂O三种溶剂中的¹H、¹³C NMR谱进行了准确归属（重点集中于谱峰重叠程度较高的芳香族区域）．实验表明：杂环上N与苯环存在部分共轭;在CDCl₃、CD₃COCD₃中,侧链卷曲至芳环上方处于屏蔽区,且侧链上N为较稳定的四面体构型;比较了CPZ· HCl在不同溶剂与浓度下的¹H NMR谱的变化,对文献中其核磁共振谱（特别是芳香区的谱峰）归属的争议作了解释．量子化学计算结果与实验结果相吻合．     

改性VOx/Al2O3催化剂催化氧化甲醇的固体核磁共振研究

采用固体核磁共振研究了NaOH 和HNO₃改性的VO_x/Al₂O₃上甲醇选择性催化氧化反应. 实验结果表明: 在甲醇的氧化反应中, 酸位对二甲氧基甲烷的生成起了重要作用. 与VO_x/Al₂O₃催化剂相比, 酸改性的VO_x/Al₂O₃上的强的Bronsted酸位对二甲氧基甲烷的选择性较高, 没有Bronsted酸位的碱改性的VO_x/Al₂O₃上生成的不是二甲氧基甲烷而是甲酸盐.     

Growth of β-MnO2 films on TiO2(110) by oxygen plasma assisted molecular beam epitaxy

We have used oxygen plasma assisted MBE to grow epitaxial films of pyrolusite (β-MnO₂) on TiO₂(110) for thicknesses of one to six bilayers (BL). We define a bilayer to be a layer of Mn and lattice O and an adjacent layer of bridging O within the rutile structure. The resulting surfaces have been characterized in situ by reflection high-energy electron diffraction, low-energy electron diffraction, X-ray photoelectron spectroscopy and diffraction, and atomic force microscopy. Well-ordered, pseudomorphic overlayers form for substrate temperatures between 400 and 500°C. Mn–Ti intermixing occurs over the time scale of film growth (1 BL/min) for substrate temperatures in excess of 500°C. Films grown at 400–500°C exhibit island growth, whereas intermixed films grown at temperatures of 500–600°C are more laminar. 1 BL films grown at 450°C are more laminar than multilayer films grown at the same temperature, and form a well-ordered surface cation layer of Mn on the rutile structure with at most 10% indiffusion to the second cation layer.     

Assignment of the 1H and 13C NMR Chemical Shifts of (3,4-Dihydro-2H-pyran-5-yl)-oxo-acetic Acid Methyl Ester Using the Two Dimensional HMBC Technique

The identification of (3, 4-dihydro-2H-pyran-5-yl)-oxo-acetic acid methyl ester has been realized by combination of two dimensional HETCOR and HMBC techniques. ¹³C and ¹H chemical shifts asignements are described.     

Two- and Three-Dimensional H/C PISEMA Experiments and Their Application to Backbone and Side Chain Sites of Amino Acids and Peptides

Two-dimensional ¹H/¹³C polarization inversion spin exchange at the magic angle experiments were applied to single crystal samples of amino acids to demonstrate their potential utility on oriented samples of peptides and proteins. High resolution is achieved and structural information obtained on backbone and side chain sites from these spectra. A triple-resonance experiment that correlates the ¹H–¹³C_α dipolar coupling frequency with the chemical shift frequencies of the α-carbon, as well as the directly bonded amide ¹⁵N site, is also demonstrated. In this experiment the large ¹H–¹³C_α heteronuclear dipolar interaction provides an independent frequency dimension that significantly improves the resolution among overlapping ¹³C resonances of oriented polypeptides, while simultaneously providing measurements of the ¹³C_α chemical shift, ¹H–¹³C dipolar coupling, and ¹⁵N chemical shift frequencies and angular restraints for backbone structure determination.     

Magnitudes and Orientations of the N Chemical Shift Tensor of [1-N]-2′-Deoxyguanosine Determined on a Polycrystalline Sample by Two-Dimensional Solid-State NMR Spectroscopy

The magnitudes and orientations of the ¹⁵N chemical shift tensor of [1-¹⁵N]-2′-deoxyguanosine were determined from a polycrystalline sample using the two-dimensional PISEMA experiment. The magnitudes of the principal values of the ¹⁵N chemical shift tensor of the N1 nitrogen of [1-¹⁵N]-2′-deoxyguanosine were found to be ς₁₁ = 54 ppm, ς₂₂ = 148 ppm, and ς₃₃ = 201 ppm with respect to (¹⁵NH₄)₂SO₄ in aqueous solution. Comparisons of experimental and simulated two-dimensional powder pattern spectra show that ς_33N is approximately collinear with the N–H bond. The tensor orientation of ς_33N for N1 of [1-¹⁵N]-2′-deoxyguanosine is similar to the values obtained for the side chain residues of ¹⁵N_ε1-tryptophan and ¹⁵N_π-histidine even though the magnitudes differ significantly.     

Elastic origin of the O/Cu(1 1 0) self-ordering evidenced by GIXD

We have studied by grazing incidence X-ray diffraction the self-ordering of the Cu-CuO stripe pattern. By comparing the experimental results to molecular dynamics simulations and anisotropic linear elastic calculations, we have been able to determine the atomic relaxations within the Cu substrate. The results show the importance of the crystalline anisotropy in the relaxation field. These relaxations are due to the surface stress difference Δσ between oxygen-covered and bare Cu(1 1 0) regions. For the different oxygen coverages studied, we have always found Δσ=1.0±0.1 N m⁻¹. This surface stress difference is shown to be the origin of the self-ordering.