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。     

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-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.     

X-H (X = C, N, O, Si, P, S) 键离解能计算的密度泛函方法研究

使用了不同密度泛函方法计算X-H (X = C, N, O, Si, P, S) 键离解能，并分析不同密度泛函方法的计算精度。研究发现大多数密度泛函方法包括B3LYP, B3P86, B3PW91, G96LYP, PBE1PBE，和BH&HLYP都明显低估键离解能13-25 kJ/mol。该现象与是否使用无限基组无关，因为即使使用无限基组键离解能仍然被低估。因此密度泛函方法不适合用于键离解能的估算。其中B3P86方法的偏差最小。进一步分析表明，使用限制性开壳层计算并无任何优势，在大多数情况下非限制性开壳层计算实际上比限制性开壳层计算要好。最后，我们发现了密度泛函方法对键离解能的低估是系统的，因此建议利用校准后的UDFT/6-311++G(d, p)方法计算化学键离解能。     

6α和6β-羟基雄酮的电子光谱和核磁共振谱的理论研究

在B3LYP/6-31G(d)水平下,优化6α和6β-羟基雄酮的几何构型.用TD-B3LYP/6-31G(d)方法,计算它们的电子吸收光谱;采用规范不变原子轨道GIAO法,计算它们的1H-NMR和13C-NMR化学位移值.结果表明,6β-羟基雄酮比6α-羟基雄酮稳定;6α-羟基雄酮的最长吸收波长比6β-羟基雄酮的要长;6α和6β-羟基雄酮的部分原子的NMR值具有明显差别.     

丙氨酸晶体太赫兹振动光谱的实验和理论研究

利用太赫兹时域光谱和低频拉曼光谱仪研究了丙氨酸晶体在0.2-2.6 THz 范围内的太赫兹吸收和拉曼散射光谱. 研究表明: 在该低频范围有四个振动模式, 其中两个只具有拉曼活性, 其余两个同时具有红外和拉曼活性. 基于B3LYP杂化密度泛函的自洽场晶体轨道法对丙氨酸周期性结构进行了理论研究和光谱计算. 通过比较实验和理论结果, 指认了实验光谱特征峰所属的不可约表示. 通过理论计算得到的图形, 得出在此低频范围的振动模式主要包含分子间氢键的扭转和摇摆运动.     

有机晶体材料DAST和DSTMS的电子结构与光学性质

采用基于赝势平面波基组的密度泛函理论(DFT)方法,研究了有机晶体材料4-(4-二甲氨基苯乙烯基)甲基吡啶对甲苯磺酸盐(DAST)和4-(4-二甲氨基苯乙烯基)甲基吡啶2,4,6-三甲基苯磺酸盐(DSTMS)的电子结构和光学性质.结果表明,两种化合物具有相似的能带结构,其中价带顶和导带底分别含有较多二甲氨基和甲基吡啶中N原子的2p轨道成分.在线性光学性质方面,两种化合物具有较高的双折射率(Δn>0.5),在中远红外区均具有较好的透过性能.在二阶非线性光学性质方面,该类晶体具有较强的二阶倍频(SHG)效应,静态倍频系数d11约为150 pm V-1.由能带结构分析结果可知,体系的SHG效应与推拉电子基团之间的电荷转移密切相关,同时乙烯桥键在该电子转移过程中也起着重要作用.     

固态电解质锂离子输运机制研究进展

全球环境问题推动了可充电锂电池技术的飞速发展.与液态电解液相比,固态电解质不易燃,构筑所得固态电池的安全性能得以提升.如果能够理解固态电解质中的离子输运行为,就能精准调控固态电池锂的动力学稳定性和倍率性能.随着计算机技术的快速发展,原子尺度模拟技术成为理解材料离子输运的重要手段.针对以上问题,本综合评述首先汇总了固体材料中的常见扩散机制;然后介绍了固态电解质中的锂离子输运机制,着重讨论了影响固态电解质锂离子输运的重要因素(晶体结构、电子结构、外部因素及晶界);最后对固态电解质锂离子输运机制研究进行了总结与展望.     

发光共价有机骨架LCOF-NDT1荧光识别甲醛的理论研究

基于密度泛函理论(DFT)和含时密度泛函理论(TD-DFT),探究了发光共价有机骨架LCOF-NDT1与甲醛之间的分叉氢键作用.发现LCOF-NDT1与甲醛氢键作用后发光机理发生改变.氢键复合物的电子激发能减小,激发态下的氢键键长变短,氢键质子供体的~1H-NMR移向高场,氢键质子供体和受体的振动频率发生红移,均表明电子激发态下的氢键增强.氢键复合物的荧光速率系数减小,内转换速率系数增大,阐明电子激发态下氢键的增强有利于非辐射跃迁,不利于辐射跃迁,从而导致LCOF-NDT1荧光减弱或猝灭.计算结果表明LCOF-NDT1在荧光识别甲醛方面有潜在的应用前景.     

单嘧磺隆除草剂的晶体构象-活性构象转换的密度泛函理论研究

应用密度泛函理论在B3LYP/6-31G(d)水平上对新型除草剂单嘧磺隆绕脲桥部分两个C—N键的内旋转势能面进行计算, 然后对势能面上的驻点进行构型优化和过渡态搜索, 得到单嘧磺隆4种稳定构象和构象转换过程所涉及的8个过渡态结构. 研究结果表明, 单嘧磺隆晶体构象-活性构象转换过程中涉及4种稳定构象和8条转换途径, 脲桥部分NH基团与嘧啶环上N原子所形成的分子内氢键对于构象的稳定性及转换过程起着十分重要的作用. 应用极化连续介质溶剂模型(PCM)在B3LYP/6-31＋＋G(d, p)水平下进行溶剂化效应计算, 结果表明单嘧磺隆从晶体构象转换成活性构象主要是在水相中进行的.     

儿茶素-胞嘧啶分子间相互作用的密度泛函研究

采用密度泛函理论的B3LYP方法,在6-31+G*基组水平上研究了儿茶素-胞嘧啶分子间相互作用机制,得到稳定的儿茶素-胞嘧啶复合物11个.计算结果表明氢键对于复合物的稳定性起着重要的作用,并且当复合物形成2个或更多的氢键时,氢键的类型及强度共同决定着复合物的稳定性.我们还应用了分子中的原子(AIM)理论和自然键轨道(NBO)理论对这11种复合物中氢键的性质和特征进行了分析.通过研究发现,所有的氢键复合物进行基组重叠误差(BSSE)校正后的相互作用能为-17.35～-43.27kJ/mol,相互作用能主要由氢键所贡献.振动分析显示,氢键的形成使相对应键的对称伸缩振动频率减小,说明这些复合物中形成的氢键都是正常的红移型氢键,与实验结果相一致.     

Towards Accurate Predictions of Proton NMR Spectroscopic Parameters in Molecular Solids

The factors contributing to the accuracy of quantum-chemical calculations for the prediction of proton NMR chemical shifts in molecular solids are systematically investigated. Proton chemical shifts of six solid amino acids with hydrogen atoms in various bonding environments (CH, CH₂, CH₃, OH, SH and NH₃) were determined experimentally using ultra-fast magic-angle spinning and proton-detected 2D NMR experiments. The standard DFT method commonly used for the calculations of NMR parameters of solids is shown to provide chemical shifts that deviate from experiment by up to 1.5 ppm. The effects of the computational level (hybrid DFT functional, coupled-cluster calculation, inclusion of relativistic spin-orbit coupling) are thoroughly discussed. The effect of molecular dynamics and nuclear quantum effects are investigated using path-integral molecular dynamics (PIMD) simulations. It is demonstrated that the accuracy of the calculated proton chemical shifts is significantly better when these effects are included in the calculations.     

乙烯-乙烯醇共聚物的固体核磁共振研究

乙烯 (Ｅ) /乙烯醇 (Ｖ)共聚物 (ＥＶＯＨ)为结晶性高聚物 ,作为膜材料有着广泛的用途 .在该体系中 ,不仅存在复杂的化学和物理结构 ,如序列分布、立构规整性和共晶结构 ,还存在复杂的氢键相互作用 ,是研究化学结构、聚集态结构和氢键相互作用之间关系的代表性体系 .通过ＤＳＣ[1 ] 、Ｘ 射线衍射[2 ] 、固体高分辨核磁共振碳谱 (1 3Ｃ ＣＰ/ＭＡＳ ＮＭＲ) [3～ 7] 等不同的研究方法 ,前人对ＥＶＯＨ体系及与之直接相关的乙烯醇均聚物(ＰＶＡ)的熔融温度、结晶度以及结晶结构等问题进行了大量研究 .1 984年Ｔｅｒａｏ等[6] 首先报道了在固…     

The coupling constant polarizability and hyperpolarizabilty of 1J(NH) in N-methylacetamide, and its application for the multipole spin-spin coupling constant polarizability/reaction field approach to solvation

We present a benchmark study of a combined multipole spin-spin coupling constant (SSCC) polarizability/reaction field (MJP/RF) approach to the calculation of both specific and bulk solvation effects on SSCCs of solvated molecules. The MJP/RF scheme is defined by an expansion of the SSCCs of the solvated molecule in terms of coupling constant dipole and quadrupole polarizabilities and hyperpolarizabilities derived from single molecule ab initio calculations. The solvent electric field and electric field gradient are calculated based on data derived from molecular dynamics (MD) simulations thereby accounting for solute-solvent dynamical effects. The MJP/RF method is benchmarked against polarizable QM/MM calculations for the one-bond N-H coupling constant in N-methylacetamide. The best agreement between the MJP/RF and QM/MM approaches is found by truncating the electric field expansion in the MJP/RF approach at the linear electric field level. In addition, we investigate the sensitivity of the results due to the choice of one-electron basis set in the ab initio calculations of the coupling constant (hyper-)polarizabilities and find that they are affected by the basis set in a way similar to the coupling constants themselves.     

Influence of fluorine substituents on the NMR properties of phenylboronic acids

The paper presents results of a systematic NMR studies on fluorinated phenylboronic acids. All possible derivatives were studied. The experimental ¹H, ¹³C, ¹⁹F, ¹¹B, and ¹⁷O spectral data were compared with the results of theoretical calculations. The relation between the calculated natural bond orbital parameters and spectral data (chemical shifts and coupling constants) is discussed. The first examples of ¹⁰B/¹¹B isotopic effect on the ¹⁹F spectra and ⁴J_FO scalar coupling in organic compounds are reported. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrogen bonding networks in gabapentin protic pharmaceutical salts: NMR and in silico studies

Hydrogen bonds (HBs) play a key role in the supramolecular arrangement of crystalline solids and, although they have been extensively studied, the influence of their strength and geometry on crystal packing remains poorly understood. Here we describe the crystal structures of two novel protic gabapentin (GBP) pharmaceutical salts prepared with the coformers methanesulfonic acid (GBP:METHA) and ethanesulfonic acid (GBP:ETHA). This study encompasses experimental and computational electronic structure analyses of ¹H NMR chemical shifts (CSs), upon in silico HB cleavage. GBP:METHA and GBP:ETHA crystal packing comprise two main structural domains: an ionic layer (characterized by the presence of charge-assisted ⁺NH_GBP⋯ O⁻_METHA/ETHA HB interactions) and a neutral layer generated in a different way for each salt, mainly due to the presence of bifurcated HB interactions. A comprehensive study of HB networks is presented for GBP:METHA, by isolating molecular fragments involved in distinct HB types (NH⋯ O, OH⋯ O, and CH⋯ O) obtained from in silico disassembling of an optimized three-dimensional packing structure. Formation of HB leads to calculated ¹H NMR CS changes from 0.4 to ~5.8 ppm. This study further attempts to assess how ¹H NMR CS of protons engaged in certain HB are affected when other nearby HB, involving bifurcated or geminal/vicinal hydrogen atoms, are removed.     

固体NMR研究PAA/PEO共混物中氢键相互作用与结构演化

分子间相互作用是决定材料结构和性能的关键因素之一,而如何在分子水上实现对复杂相互作用分子的检测仍然是一个挑战性课题。本工作首先在不同p H值条下以聚丙烯酸/聚环氧乙烷(PAA/PEO)的混合水溶液制备了系列的固体薄膜,然后采用多种基于连续相调制多脉冲技术的一维和二维~1H多脉冲去耦(CRAMPS)固体NMR新技术,并结合高分辨~(13)C交叉极化魔角旋转(CPMAS)、~(23)Na多量子(MQ)等多核固体NMR实验,对PAA/PEO聚合物共混物的微观结构和动力学进行了原位和系统的研究。通过不同类型的~1H高分辨CRAMPS实验检测到共混物中包含多种不同类型质子:通过氢键相互作用形成二聚体的COOH基团、自由COOH基团、与水结合的COOH基团和主链基团。随着p H值的升高,除主链质子外,大部分其它区域的信号都明显降低,这是由于PAA与PEO以及水的氢键作用减弱所致。这些CRAMPS NMR技术也被用来阐明不同p H值制备的样品中不同基团的分子运动性。此外,二维~1H-~1H自旋交换NMR实验提供了关于聚合物PAA与PEO大分子链间、以及水与聚合物的相互作用。~1H自旋扩散实验表明,在这些共混物中明显存在相微观相分离的结构,并且测定的分散相区尺寸约为17 nm。~(23)Na MQMAS实验揭示了在共混物中存在两种类型~(23)Na位,一种是自由的钠离子,另一种是与大分子相互作用的Na离子。特别是通过~1H-检测的~(23)Na-~1H CPMAS实验揭示了Na~+离子的位置远离PEO而与PAA临近。上述这些SSNMR实验结果在分子水平上提供了氢键相互作用对PAA/PEO共混物微观结构和动力学影响的详细信息,可以获得不同p H值对PAA与PEO的氢键作用、相容性、微观结构、水-聚合物相互作用和不同组分分子运动性的影响。在上述核磁共振研究的基础上,我们提出了一种新的PAA/PEO共混物的结构模型,该模型首次成功地揭示了不同的p H值对PAA/PEO共混物中微观结构和动力学的影响。本工作清楚地表明,固态核磁共振是在分子水平上研究具有复杂相互作用的多相聚合物材料的有力工具。本文的研究工作对于探索检测聚合物弱相互作用的新方法和发展基于氢键相互作用的聚合物新材料的开发具有重要意义。     

Modeling of the Response of Hydrogen Bond Properties on an External Electric Field: Geometry,NMR Chemical Shift,Spin-Spin Scalar Coupling

The response of the geometric and NMR properties of molecular systems to an external electric field has been studied theoretically in a wide field range. It has been shown that this adduct under field approach can be used to model the geometric and spectral changes experienced by molecular systems in polar media if the system in question has one and only one bond, the polarizability of which significantly exceeds the polarizability of other bonds. If this requirement is met, then it becomes possible to model even extreme cases, for example, proton dissociation in hydrogen halides. This requirement is fulfilled for many complexes with one hydrogen bond. For such complexes, this approach can be used to facilitate a detailed analysis of spectral changes associated with geometric changes in the hydrogen bond. For example, in hydrogen-bonded complexes of isocyanide C≡¹⁵N-¹H⋯X, ¹J(¹⁵N¹H) depends exclusively on the N-H distance, while δ(¹⁵N) is also slightly influenced by the nature of X.     

Two new lignan-iridoid glucoside diesters from the leaves of Vaccinium bracteatum and their relative and absolute configuration determination by DFT NMR and TDDFT-ECD calculation

Two new lignan-iridoid glucoside diesters (2 and 3), together with their putative biosynthetic precursor 10-O-trans-caffeoyl-6α-hydroxyl-dihydromonotropein (1), were characterized from the leaves of Vaccinium bracteatum. Their planar structures and relative configuration were elucidated by spectroscopic measurements and DFT C NMR calculations, and their absolute configurations were determined by time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The plausible biosynthetic pathways of new compounds were also proposed.     

13C NMR spectroscopic studies of the behaviors of carbonyl compounds in various solutions

¹³C NMR spectroscopic studies were performed for carbonyl compounds having a hydroxyl group, a carboalkoxy group, an acetoxy group, or a carboxyl group in various solvents with different polarities for observation of their behaviors of ¹³C NMR chemical shifts of carbonyl carbons in solutions. It was found that the chemical shifts of the carbonyl carbons in ¹³C NMR have good correlation with the empirical parameter for solvent polarities, E_T^N, depending on the structures. Inter- or intramolecular hydrogen bonding and dipolar-dipolar interactions appear to play a key role in this observation.     

Analyzing Discrepancies in Chemical-Shift Predictions of Solid Pyridinium Fumarates

Highly accurate chemical-shift predictions in molecular solids are behind the success and rapid development of NMR crystallography. However, unusually large errors of predicted hydrogen and carbon chemical shifts are sometimes reported. An understanding of these deviations is crucial for the reliability of NMR crystallography. Here, recently reported large deviations of predicted hydrogen and carbon chemical shifts of a series of solid pyridinium fumarates are thoroughly analyzed. The influence of the geometry optimization protocol and of the computational level of NMR calculations on the accuracy of predicted chemical shifts is investigated. Periodic calculations with GGA, meta-GGA and hybrid functionals are employed. Furthermore, molecular corrections at the coupled-cluster singles-and-doubles (CCSD) level are calculated. The effect of nuclear delocalization on the structure and NMR shielding is also investigated. The geometry optimization with a computationally demanding hybrid functional leads to a substantial improvement in proton chemical-shift predictions.