基于密度泛函方法的梓醇红外光谱的预测

梓醇是一种具有特殊药理活性的环烯醚萜苷类化合物。采用密度泛函(DFT)B3LYP/6-311G**方法对梓醇分子的几何构型进行全优化,得到其几何构型参数,进一步计算得到梓醇的红外振动光谱,振动频率校正因子为0.96。对计算得到的振动频率进行归属和解析并与实验测定得到的梓醇IR光谱特征峰比较,发现理论计算出的IR光谱与实验测定IR特征峰位具有很好的一致性,说明所采用的DFT方法能够用于梓醇分子几何构型的优化,预测难以得到标准对照品的环烯醚萜苷类化合物的IR光谱数据。     

Analysis of structure and vibrational spectra of 2,5‐dihydroxybenzoicacid based on density functional theory calculations

The spectra of 2,5‐dihydroxybenzoic acid (DHBA) have been recorded using Fourier transform‐infrared spectroscopy (FT‐IR) and FT‐Raman measurements. The total energy calculations of DHBA were evaluated for various possible conformers. The spectra were interpreted with the help of normal coordinate analysis based on density functional theory (DFT) using standard B3LYP/6–31G* method for the most optimized geometry. The effect of intramolecular hydrogen bonding was discussed. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors, yielding fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined. Copyright © 2009 John Wiley & Sons, Ltd.     

一种对羟基苯甲醛希夫碱的红外光谱及核磁共振理论研究

采用Gaussian03软件,用密度泛函理论的B3LYP方法在6-31G基组水平上优化了对羟基苯甲醛缩2,4-二硝基苯胺希夫碱,得到其最稳定构型及其能量。在优化结构基础上用Hartree-Fock(HF)/6-31G方法计算了该分子的红外光谱振动频率并绘制了红外光谱图,对图中各峰位进行了分析探讨。用同样的方法计算了该化合物分子的核磁共振氢谱。     

Theoretical and FT-IR, FT-Raman studies of nipecotamide and its tautomers, isomers

The structure, conformers, energies and vibrational spectra of the important nipecotamide molecule have been characterized by FT-IR (mid-IR, far-IR), FT-Raman spectroscopy and by DFT calculations. The structure is optimized by B3LYP/6-311++G(d,p) calculations. All vibrational frequencies assigned in detail with the help of total energy distribution (TED). The calculated vibrational wavenumbers were compared with IR and Ra experimental data. In the most stable tautomer (NT-1), the piperidine ring adopts the chair conformation and the amide group is in the axial orientation and is stabilized by an intramolecular N-H…O hydrogen bond of 4.37 Å.     

2-吡啶甲醇红外光谱的密度泛函理论研究

利用密度泛函理论(density functional theory,DFT) 在B3LYP/6-311G(d,p)水平上对2-吡啶甲醇分子进行了结构优化和频率计算,得到了该分子的稳定构型和全部振动模式。通过与吡啶分子的结构参数以及相关文献数据的对比,发现理论值与实验值相吻合。理论计算和实验测得的红外光谱数据的比较分析表明,理论计算与实验测量结果符合得较好, 并对2-吡啶甲醇分子的振动模式进行了归属。     

Scaled DFT Force Constants and Vibrational Spectrum of Cyclopropylamine

Abstract

The molecular structure and harmonic vibrational frequencies of cyclopropylamine have been calculated using the B3LYP density functional method with the 6‐31G(2d,2p) basis set. The scaled DFT force field gives very good reproduction of the experimental vibrational frequencies. Several of the vibrational fundamental modes assigned previously are reassigned on the basis of the B3LYP/6‐31G(2d,2p) method and the scaled force field calculations. The optimized scaling factors were used to scale the B3LYP/6‐31G(2d,2p) force field of cyclopropane and cyclopropylamine (–ND₂) molecules.     

Molecular structure,NMR and vibrational spectral analysis of 2,4‐difluorophenol by ab initio HF and density functional theory

Quantum chemical calculations of energies, geometries and vibrational wavenumbers of 2,4‐difluorophenol (2,4‐DFP) were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6‐311G(d,p) as basis set. The optimized geometrical parameters obtained by HF and DFT calculations are in good agreement with related molecules. The best level of theory in order to reproduce the experimental wavenumbers is the B3LYP method with the 6‐311G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of 2,4‐DFP is also reported. The entropy of the title compound was also performed at HF/6‐311G(d,p) and B3LYP/6‐311G(d,p) levels of theory. The isotropic chemical shift computed by ¹H, ¹³C NMR analyses also shows good agreement with experimental observations. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule have been constructed. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and DFT calculations of di‐amino acid peptides: α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu in the solid state

Experimental vibrational spectroscopic studies and density functional theory (DFT) calculations of the di‐amino acid peptide derivatives α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu have been undertaken. Raman and infrared spectra have been recorded for samples in the solid state. DFT simulations were conducted using the B3‐LYP correlation functional and the cc‐pVDZ basis set to determine energy minimized/geometry optimized structures (based on a single isolated molecule in the gaseous state). Normal coordinate calculations have provided vibrational assignments for fundamental modes, including their potential energy distributions. Significant differences are observed between α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu both in the computed structures and in the vibrational spectra. The combination of experimental and calculated spectra provide an insight into the structural and vibrational spectroscopic properties of di‐amino acid peptide derivatives. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,experimental and theoretical analysis,and antiproliferative activity of 2-(4-methoxyphenylamino)-2-oxoethyl methacrylate

In this study 2-(4-methoxyphenylamino)-2-oxoethyl methacrylate (MPAEMA) has been synthesized and characterized experimentally (FTIR, NMR). Theoretically, physical, electronic and vibrational properties of MPAEMA molecule have been investigated using density functional theory (DFT) calculations at B3LYP/6-311++G(d,p) basis set. Bond distance, FTIR spectrum, NMR spectra and vibrational frequencies have been carried out. The calculated FTIR and NMR spectra of the headline molecule from the DFT have been compared with the measured ones, and good results have been obtained. UV spectrum characteristics and the electronic properties, like frontier orbitals, and band gap energy of MPAEMA have also been recorded by time-dependent (TD-DFT) method based on optimized structure with different solvent. The experimental results have been compared with theoretical values. Both experimental and theoretical methods have shown that the compound has successfully been synthesized. Cytotoxicity of MPAEMA has been investigated by XTT cell proliferation assay. IC50 values of MPAEMA have been identified as 1.8 mM on HeLa cell line.     

胞嘧啶分子拉曼光谱研究

本文通过实验测量了胞嘧啶的常规拉曼光谱,有四个弱拉曼峰在以前胞嘧啶的常规拉曼光谱中未检测到。采用密度泛函(Density Function Theory)B3LYP/6-31+G(d,p)计算了胞嘧啶分子的拉曼光谱。结合理论计算结果对实验拉曼光谱振动模式进行了指认,并对其中几个拉曼峰非常弱的原因进行了分析。     

Analysis of vibrational spectra of 2‐fluoro‐6‐nitrotoluene based on density functional theory calculations

The conformational behavior and structural stability of 2‐fluoro‐6‐nitrotoluene (FNT) were investigated by utilizing density functional theory (DFT) with the standard B3LYP/6‐311 + G** method and basis set combinations. The vibrational wavenumbers of FNT were computed at DFT levels and complete vibrational assignments were made on the basis of normal coordinate calculations. Normal coordinate analysis (NCA) has been carried out to support the vibrational analysis. The results were compared with the experimental values. The observed Fourier transform infrared (FTIR) and Fourier transform (FT) Raman vibrational wavenumbers were analyzed and compared with the theoretically predicted vibrational spectra. The results of vibrational spectra of FNT were also compared with the vibrational spectra of some toluene derivatives. The assignments of bands to various normal modes of the molecules were also carried out. Copyright © 2008 John Wiley & Sons, Ltd.     

Density functional theory calculations for ethylene carbonate-based binary electrolyte mixtures in lithium ion batteries

The density functional theory (DFT) calculations have been performed to investigate the interaction of Li⁺ with various organic solvents widely used as Li ion rechargeable battery electrolytes such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC); and their EC-based binary mixtures at the level of B3LYP/6-31G (d). The interaction of Li⁺ with these solvents has been calculated in terms of electronic structures of clusters of the mixtures of organic solvents including a lithium ion. The main objective of our investigation is to help in understanding a stable and enhancing ionic transfer at graphite/electrolyte interface assisted by the mixtures of the solvents. The calculated results favor the stability of EC-based binary mixtures and high EC-content binary mixture systems. In infrared (IR) vibrational spectra, the IR active modes of the solvent show significant changes due to the cation-solvent interaction.     

氧化槐果碱结构的测定及其振动圆二色谱研究

采用傅里叶红外光谱仪(FTIR)和振动圆二色谱仪(VCD)测量氧化槐果碱固体的红外光谱和振动圆二色谱。采用密度泛函方法(DFT)分别在B3LYP/cc-PVTZ和B3LYP/6-311+G(d, p)水平下,对气相中氧化槐果碱分子结构进行了优化,然后在相同水平下计算了氧化槐果碱的红外光谱(IR)以及振动圆二色谱(VCD)。将实验谱图与理论计算谱图进行对照,以确定氧化槐果碱的实际构象以及构象分布。由对比结果可知：采用B3LYP/6-311+G(d,p)水平下,以吉布斯自由能进行玻尔兹曼加权平均后的理论IR和VCD谱图与实际光谱图最为接近,说明在常温下氧化槐果碱具有A/B-trans C/D-trans和A/B-trans C/D-cis两种优势构象,且玻尔兹曼分布显示两种构象均以一定比例共存,且通过对氧化槐果碱的两种优势构象分析,发现A/B环的立体结构为：椅式-椅式,C/D环的立体结构为：椅式-沙发式。     

Theoretical and spectroscopic studies of 5‐aminoorotic acid and its new lanthanide(III) complexes

The complexes of cerium(III) and neodymium(III) were synthesized by reaction of the respective inorganic salts with 5‐aminoorotic acid (H₄L) in amounts equal to the metal:ligand molar ratio of 1:3. The structures of the final complexes were determined by means of spectral (IR, Raman, ¹H NMR and ¹³C NMR) and elemental analysis. Significant differences in the IR spectra of the complexes were observed as compared to the spectrum of the ligand. A comparative analysis of the Raman spectra of the complexes with that of the free H₄L allowed a straightforward assignment of the vibrations of the ligand groups involved in coordination. The geometry of H₄L was computed and optimized for the first time with the Gaussian03 program using the B3PW91/6‐311++G**, B3PW91/LANL2DZ, B3LYP/6‐311++G** and B3LYP/LANL2DZ methods. The experimental IR and Raman bands of the ligand were assigned to normal modes on the basis of DFT calculations. The vibrational analysis performed for the studied species, H₄L and its complexes, helped to explain the vibrational behavior of the ligand vibrational modes sensitive to interaction with the lanthanides. The vibrational study gave evidence for the coordination mode of the ligand to lanthanide ions and was in agreement with the other theoretical prediction. Copyright © 2006 John Wiley & Sons, Ltd.     

磷基的几何结构与光电子能谱

基于ab initio/DFT理论,对磷基分子以其阴离子态进行了几何结构优化和谐振频率计算。在B3LYP/6-311+G(2d,p)理论水平下,通过Franck-Condon因子计算模拟了磷基的光电子能谱[K. M. Ervin and W. C. Lineberger, J. Chem. Phys. 122 (2005) 194303],计算得到的理论谱与实验谱完全一致。另外,通过迭代Franck-Condon分析,得到优于ab initio/DFT理论计算的离子的几何结构参数。     

磷基的几何结构与光电子能谱

基于ab initio/DFT理论,对磷基PH2分子X~2B1态和PH-2阴离子X~1A1态进行了几何结构优化和谐振频率计算.在B3LYP/6-311+G(2d,p)理论水平下,通过Franck-Condon因子计算模拟了PH-2实验的光电子能谱,计算得到的理论谱与实验谱完全一致,确认属于PH2(X~2B1)-PH-2(X~1A1)光脱附过程.另外,通过迭代Franck-Condon分析,得到优于ab initio/DFT理论计算的PH-2离子的几何结构参数R(PH)=0.1438±0.0002 nm和∠(HPH)=92.2±0.2°.     

Structural and vibrational analyses of 2‐(2‐benzofuranyl)‐2‐imidazoline

We have studied 2‐(2‐benzofuranyl)‐2‐imidazoline (BFI) and characterized it by using infrared and Raman spectroscopies. The density functional theory (DFT) method together with Pople's basis set shows that two conformers exist for the title molecule as have been theoretically determined in the gas phase and that, probably, an average of both conformations is present in the solid phase. The harmonic vibrational wavenumbers for the optimized geometry of the latter conformer were calculated at the B3LYP/6‐31G* level in the proximity of the isolated molecule. For a complete assignment of the IR and Raman spectra in the compound in the solid phase, DFT calculations were combined with Pulay's scaled quantum mechanics force field (SQMFF) methodology in order to fit the theoretical wavenumbers to the experimental ones. Copyright © 2010 John Wiley & Sons, Ltd.     

Quantum-chemical calculation on 5-phenyl-2-(4-pyridyl)pyrimidine

The molecular geometry and vibrational frequencies of 5-phenyl-2-(4-pyridyl)pyrimidine in the ground state have been calculated by the density functional theory with B3LYP/6-311G(d) as the basis set. The observed frequencies of 5-phenyl-2-(4-pyridyl)pyrimidine and those calculated are nearly the same. The form of the modes for all fundamentals is based on potential energy distribution calculations.     

β-D-吡喃半乳糖的太赫兹光谱研究

为深入了解β-D-吡喃半乳糖在太赫兹波段的光谱特性, 利用太赫兹时域光谱技术测量了室温下β-D-吡喃半乳糖晶体在0.3～3.0 THz范围内的吸收谱及折射率谱, 同时利用傅里叶变换红外光谱技术获得了半乳糖在1.5～19.5 THz之间的吸收谱。实验研究的同时, 运用密度泛函理论和6-311+G**基组计算了气态孤立β-D-吡喃半乳糖分子的结构及其在太赫兹波段的振动频率, 并据此对实验光谱吸收峰进行了指认。研究结果表明, 除了因为分子间效应而导致的少许偏移外, 理论计算结果与实验数据吻合得很好; 实验光谱在6 THz以上频段的共振吸收峰来源于明确的分子内振动模式, 而6 THz以下低频段的共振吸收峰则主要来源于分子间氢键或晶体的声子模式。实验和理论研究的对比表明物质的远红外吸收特征对于分子的结构和空间排列非常敏感。