木犀草素与胞嘧啶相互作用的理论研究

采用密度泛函理论中的B3LYP方法,在6-31＋G＊基组水平上对木犀草素、胞嘧啶、木犀草素-胞嘧啶复合物进行结构优化和振动频率分析,得到了12种稳定复合物.并应用分子中的原子理论（AIM）分析、自然键轨道（NBO）理论分析得到复合物氢键性质和特征.通过基组重叠误差（BSSE）校正后的相互作用能、成键临界点电荷密度、二阶...     

On the Correlation between the Blue Shift of Hydrogen Bonding and the Proton Donor-Proton Acceptor Distance

It is demonstrated that in all types of hydrogen bonds (X—H…Y) there is a balance between the long-range attractive orbital interactions and short-range Pauli/nucleus repulsions. When the proton acceptor approaches the proton donor from distance, the hydrogen bonding energy becomes more negative at relatively large distance, goes through a minimum, and then starts to become less negative when the short-range repulsive forces come into effect.Meanwhile, the X--H bond length increases at relatively large distances, goes through a maximum and starts to shorten when the short-range repulsive forces come into effect. Whether the hydrogen bond is red or blue shifted is dictated by the energy minimum position. If at the energy minimum position the X—H bond length is shorter than that for the free monomer, the hydrogen bond is blue shifted and vice versa. Further studies demonstrate that the recent report about the correlation of C—H bond lengths with proton donor-acceptor distance in F3C—H…OH2 and F3C—H…Cl^- is not fully correct because the authors conducted an inappropriate comparison. Furthermore, it is shown for the first time that the Pauli/nucleus repulsion theory is applicable to the blue-shifted hydrogen bonds in the X—H…π complexes and the blue-shifted lithium bonds in the X—Li…Y complexes.     

A DFT Study on Intramolecular Hydrogen Bond in Substituted Catechols and Their Radicals

Density functional theory(DFT)at B3LYP/6-31G(d,p) level was employed to calculate intramolecular hydrogen bond enthalpies (H1HB),O-H charge differencces,O-H bond lengths and bond orders for various substituted catechols and their radicals generated after H-abstraction.It was found that although the charge difference between hydrogen-bonded H and O played a role in determining H1HB,H1HB was mainly governed by the hydrogen bond length.As the oxygen-centedred radiocal has great tendency to form a chemical bond with the H atom,hydrogen bond lengths in catechloic radicals are systematically shorter than those in catechlos,hence,the H1HB for the former are higher than those for the latter.     

Halogen Bonding versus Hydrogen Bonding: A Molecular Orbital Perspective

We have carried out extensive computational analyses of the structure and bonding mechanism in trihalides DX⋅⋅⋅A⁻ and the analogous hydrogen-bonded complexes DH⋅⋅⋅A⁻ (D, X, A=F, Cl, Br, I) using relativistic density functional theory (DFT) at zeroth-order regular approximation ZORA-BP86/TZ2P. One purpose was to obtain a set of consistent data from which reliable trends in structure and stability can be inferred over a large range of systems. The main objective was to achieve a detailed understanding of the nature of halogen bonds, how they resemble, and also how they differ from, the better understood hydrogen bonds. Thus, we present an accurate physical model of the halogen bond based on quantitative Kohn–Sham molecular orbital (MO) theory, energy decomposition analyses (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. It appears that the halogen bond in DX⋅⋅⋅A⁻ arises not only from classical electrostatic attraction but also receives substantial stabilization from HOMO–LUMO interactions between the lone pair of A⁻ and the σ* orbital of D–X.     

Phenylacetylene: A Hydrogen Bonding Chameleon

Molecules with multiple hydrogen bonding sites offer the opportunity to investigate competitive hydrogen bonding. Such an investigation can become quite interesting, particularly when the molecule of interest has neither lone‐pair electrons nor strongly acidic/basic groups. Phenylacetylene is one such molecule with three hydrogen bonding sites that cannot be ranked into any known hierarchical pattern. Herein we review the structures of several binary complexes of phenylacetylene investigated using infrared optical double‐resonance spectroscopy in combination with high‐level ab initio methods. The diversity of intermolecular structures formed by phenylacetylene with various reagents is remarkable. The nature of intermolecular interaction with various reagents is the result of a subtle balance between various configurations and competition between the electrostatic and dispersion energy terms, while trying to maximize the total interaction strength.     

Quantum Study on the Hydrogen Bonding Interaction of Luteolin-（CH_3OH）_n

The optimized geometries and vibration frequencies of luteolin,methanol and luteolin-(CH3OH)n complexes have been investigated by density functional theory using B3LYP method.Four stable luteolin-CH3OH complexes,six stable luteolin-(CH3OH)2 complexes and four stable luteolin-(CH3OH)3 complexes have been obtained.The theories of atoms in molecules(AIM) and natural bond orbital(NBO) have been used to analyze the hydrogen bonds of these compounds,and their interaction energies corrected by basis set superposition error are between-8.046 and-76.124 kJ/mol.The calculation results indicate strong hydrogen bonding interactions in the luteolin-(CH3OH)n complexes.Then the nuclear magnetic resonance(NMR) and electronic absorption spectrum of luteolin have been calculated,and the results are in agreement with the experimental data.     

A Comparative Study of Hydrogen Bonding Using Density Functional Theory

The hydrogen‐bond energies of water dimer and water‐formaldehyde complexes have been studied using density functional theory (DFT). Basis sets up to aug‐cc‐pVXZ (X=D, T, Q) were used. It was found that counterpoise corrected binding energies using the aug‐cc‐pVDZ basis set are very close to those predicted with the aug‐cc‐pVQZ set. Comparative studies using various DFT functionals on these two systems show that results from B3LYP, mPW1PW91 and PW91PW91 functionals are in better agreements with those predicted using high‐level ab initio methods. These functionals were applied to the study of hydrogen bonding between guanine (G) and cytosine (C), and between adenine (A) and thy mine (T) base pairs. With the aug‐cc‐pVDZ basis set, the predicted binding energies of base pairs are in good agreement with the most elaborate ab initio results.     

On the Mechanism of Hydrogen Activation by Frustrated Lewis Pairs

We report herein a comprehensive theoretical study of the thermodynamics and kinetics of molecular hydrogen activation by frustrated Lewis pairs (FLPs). A series of intermolecularly combined boranes (Lewis acids) and phosphines (Lewis bases), with experimentally established different reactivities towards H₂, have been subjected to DFT and (SCS‐)MP2 calculations, and analyzed in terms of their structural properties, the energetics of association of the FLPs, and the kinetics of their interactions with H₂ and hydrogenation to the ion‐pair products. The analysis included the following steps: 1) assessment of the ability/inability of the Lewis species to preorganize into FLPs with an optimum arrangement of the acid and base sites for preconditioning the reaction with H₂, 2) comprehension of the different thermodynamics of hydrogenation of the selected FLPs by comparing the Gibbs energies of the overall reactions, and 3) estimation of the mechanism of the activation of H₂ by identifying the reaction steps and the associated kinetic barriers. The results of our studies correlate well with experimental findings and have clarified the reasons for the observed different reactivities of the investigated systems, ranging from reversible or nonreversible activation to no reaction with H₂. The derived predictions could assist the future design of Lewis acid–base systems with desired properties and applicability as metal‐free hydrogenation catalysts.     

Theoretical Study on the Structures and Properties of Hydrogen Bonding Complexes between Diazines and Water

Density functional theory B3LYP method and second-order Moller-Plesset perturbation theory MP2 method were employed to obtain the optimized geometries of the ground state and interaction energy for diazines and water complexes. The results show that the ground state complexes have strong hydrogen bonding interaction with -20.99, -16.73 and -15.31 kJ/mol after basis set superposition error and zero-point vibration energy correction for pyridazine-water, pyrimidine-water and pyrazine-water, respectively, and large red-shift for the symmetric H-O stretching vibration frequencies due to the formation of N…H-O hydrogen bond in the diazine-water complexes. The NBO analysis indicates that intermolecular charge transfer are 0.0316, 0.0255 and 0.0265 e respectively. In addition, the first singlet （n,n＊） vertical excitation energy of the monomer and the hydrogen bonding complexes between diazines and water was investigated by time-dependent density functional theory.     

Hydrogen Bonding in Phosphine Oxide/Phosphate–Phenol Complexes

To develop a new solvent‐impregnated resin (SIR) system for the removal of phenols and thiophenols from water, complex formation by hydrogen bonding of phosphine oxides and phosphates is studied using isothermal titration calorimetry (ITC) and quantum chemical modeling. Six different computational methods are used: B3LYP, M06‐2X, MP2, spin component‐scaled (SCS) MP2 [all four with 6‐311+G(d,p) basis set], a complete basis set extrapolation at the MP2 level (MP2/CBS), and the composite CBS‐Q model. This reveals a range of binding enthalpies (ΔH) for phenol–phosphine oxide and phenol–phosphate complexes and their thio analogues. Both structural (bond lengths/angles) and electronic elements (charges, bond orders) are studied. Furthermore, solvent effects are investigated theoretically by the PCM solvent model and experimentally via ITC. From our calculations, a trialkylphosphine oxide is found to be the most promising extractant for phenol in SIRs, yielding ΔH=?14.5 and ?9.8 kcal mol^?1 with phenol and thiophenol, respectively (MP2/CBS), without dimer formation that would hamper the phenol complexation. In ITC measurements, the ΔH of this complex was most negative in the noncoordinating solvent cyclohexane, and slightly less so in π–π interacting solvents such as benzene. The strongest binding is found for the dimethyl phosphate–phenol complex [?15.1 kcal mol^?1 (MP2/CBS)], due to the formation of two H‐bonds (P?O???H‐O‐ and P‐O‐H???O‐H); however, dimer formation of these phosphates competes with complexation of phenol, and would thus hamper their use in industrial extractions. CBS‐Q calculations display erroneous trends for sulfur compounds, and are found to be unsuitable. Computationally relatively cheap SCS‐MP2 and M06‐2X calculations did accurately agree with the much more elaborate MP2/CBS method, with an average deviation of less than 1 kcal mol^?1.     

Rapid Prediction of the Hydrogen Bond Cooperativity in N‐methylacetamide Chains

A method is proposed to rapidly predict the hydrogen bond cooperativity in N‐methylacetamide chains. The parameters needed are obtained from the fittings to the hydrogen bonding energies in the formamide chains containing 2 to 8 monomeric units. The scheme is then used to calculate the individual hydrogen bonding energies in N‐methylacetamide chains containing 2 to 7 monomeric units. The cooperativity predicted is in good agreement with those obtained from MP2/6‐31+G** calculations by including the BSSE correction. Our scheme is further employed to predict the individual hydrogen bonding energies in larger N‐methylacetamide chains containing up to 200 monomeric N‐methylacetamide units, to which the MP2 method cannot be applied. Based on our scheme, a cooperative effect of over 170 % of the dimer hydrogen bonding energy in long N‐methylacetamide chains is predicted. The method is also applied to heterogeneous chains containing formamide, acetamide, N‐methylformamide, and N‐methylacetamide. The individual hydrogen bonding energies in these heterogeneous chains are also in good agreement with those obtained from MP2 calculations with the BSSE correction, further demonstrating that our method is reasonable.     

1,2,4-三氮杂苯-(H2O)n复合物氢键相互作用的密度泛函理论研究

用密度泛函理论方法在B3LYP／6—31 G**水平上对1，2，4-三氮杂苯-(H2O)n(n=1，2，3)氢键复合物的基态进行了结构优化和能量计算，结果表明复合物之间存在较强的氢键作用，所有稳定复合物结构中形成一个N…H--O氢键并终止于弱O…H—C氢键的氢键水链的构型最稳定．同时，用含时密度泛函理论方法(TD—DPT)在TD—B3LYP／6—31 G**水平上计算了1,2，4-三氮杂苯单体及其氢键复合物的单重态第-1(n，π*)垂直激发能．     

Diastereoselective Coupling of Chiral Acetonide Trisubstituted Radicals with Alkenes

The stereochemical outcome of reactions of chiral nucleophilic trisubstituted acetonide radicals with electron‐deficient alkenes is dictated by a delicate balance between destabilizing non‐bonding interactions and stabilizing hydrogen‐bonding between substituents on the α and β carbons.     

Theoretical Characterisation of Phosphinyl Radicals and Their Magnetic Properties: g Matrix

The g matrices (g tensors) of various phosphinyl radicals (R₂P^.) were calculated using the DFT and multireference configuration interaction (MRCI) methods. The g matrices were distinctly dependent on the molecular structure of the radical. To thoroughly examine this dependence, the contributions from individual atoms and excited states were calculated. The former revealed the gain from the phosphorus atom to be preeminent unless P?O or P?S bonds are present in the radical molecule. The contributions owing to excited states arising from electronic transitions between doubly occupied molecular orbitals and the SOMO were clearly positive, as in the case of semiquinone and niroxide radicals. The transitions from the phosphorus lone pair were of paramount importance. Surprisingly, unlike for semiquinones and nitroxides, a significant negative contribution was observed from excitations from the SOMO to unoccupied molecular orbitals. For radicals with P?O bonds, this contribution to the g₂ component was dominant.