基于DFT的间羟基苯甲酸分子表面增强拉曼光谱研究

本文研究了间羟基苯甲酸(m-hydroxybenzoic acid,MHBA)的常规拉曼散射(normal Raman scattering,NRS)光谱及其吸附在Ag纳米颗粒上的表面增强拉曼散射(surface-enhanced Raman scattering,SERS)光谱。采用密度泛函理论(density functional theory,DFT),在B3LYP/6-31+G**(C、H、O)/LANL2DZ(Ag)水平上,对MHBA分子进行了几何结构优化,在此基础上计算了MHBA分子的NRS光谱以及其吸附在Ag纳米颗粒上两种不同吸附构型下的SERS光谱,并和实验值进行比较。结果表明,间羟基苯甲酸分子通过羧基与羟基共同吸附构型的计算结果比该分子通过羧基吸附构型的计算结果更符合实验值。最后,利用GaussView可视化软件对其振动模式进行了全面归属。     

黄曲霉素B1及异构体的前线轨道与拉曼光谱研究

采用B3LYP混合泛函和6-311+g(d, p)基组,利用DFT密度泛函理论优化得到了黄曲霉素Aflatoxin B1(cis)(AFB1(cis))及其反式异构体分子AFB1(trans)的稳定结构, 通过单点能计算和几何结构分析,其顺式结构比反式结构更加稳定;计算了两种分子的Raman光谱,并与AFB1(c)粉末的实验Raman光谱进行比较,吻合较好。把最强的三个峰1 582,3 065和1 626 cm-1指认为顺式结构的特征峰,把1 616,3 065和1 659 cm-1指认为反式结构的特征峰;在优化计算的基础上采用Hirshfeld原子划分方法结合Multiwfn软件分析了前线轨道成分,两种分子的亲电能力明显强于其亲核能力,通过计算C1原子在LUMO轨道中的占据权重分别为21.48%和20.62%,预测出C1原子是这两种顺反异构分子夺走DNA中的电子致癌的最主要位点。结果对该类顺反异构分子的检测、转化以及毒性抑制方面具有一定的理论指导意义。     

环草酰胺表面增强拉曼光谱密度泛函理论研究

根据密度泛函理论(DFT),在B3LYP方法下,Ag原子使用LANL2DZ赝式基组,C,H,N,O和Cl原子使用6-31++G(d,p)基组,优化并计算了环草酰胺和环草酰胺银配合物的拉曼光谱,并利用密度泛函理论对环草酰胺分子拉曼光谱及其SERS进行详细归属,为食品和产品中吩噻嗪残留的定性、定量测定提供理论依据。计算结果说明连接Ag原子越多,增强效果越明显。     

噻虫啉的表面增强拉曼光谱密度泛函理论研究

依据DFT理论的B3LYP方法下,在6-31G(d,p)(C,H,N,S,Cl)/Lanl2dz(Ag)基组,计算得到噻虫啉及其银配合物的稳定结构和表面增强拉曼光谱(SERS)。并进一步探究SERS与Ag4银簇吸附的位置,分子分别以单端(吡啶氮/氰基)和双端(吡啶氮和氰基)与Ag4银簇吸附。通过比较,TPD在双端吸附银簇下比单端(吡啶氮/氰基)吸附下的SERS(频率)更符合实验值。     

胸腺嘧啶分子表面增强拉曼光谱的密度泛函理论和从头计算研究

采用量子化学B3LYP(含电子相关效应的杂化密度泛函)方法和HF(Hartree-Fock, 哈特利-福克)方法,在6-31+G**(C,H,N,O)/LANL2DZ(Ag)水平上,对TH(Thymine, 胸腺嘧啶)分子进行了几何结构优化,计算了TH分子的NRS(normal Raman scattering, 常规拉曼散射)光谱和TH与Ag原子以及Ag₂团簇吸附的SERS(surface-enhanced Raman scattering, 表面增强拉曼散射)光谱,并将两种理论方法计算的结果和实验值进行比较。结果表明：对于NRS光谱,采用DFT方法的计算结果比HF方法的计算结果更符合已有实验值;而对于SERS光谱,采用HF方法的计算结果更好。最后,通过GaussView可视化软件,对TH分子的振动频率进行了更为全面地归属。     

糠醛分子表面增强拉曼光谱的密度泛函理论研究

采用密度泛函理论(density functional theory,DFT),在B3LYP/6-31+G**(C,H,O)/LANL2DZ(Ag)水平上,对糠醛(furfural,FUR)分子进行了几何结构优化,并计算了FUR分子的常规拉曼散射(normal Raman scattering,NRS)光谱和FUR与Ag原子以及Ag2和Ag4团簇吸附的表面增强拉曼散射(surface-enhanced Raman scattering,SERS)光谱。结果表明,理论值与已有的实验值符合得较好,采用FUR-Ag4吸附构型的计算结果比FUR-Ag和FUR-Ag2吸附构型的计算结果更符合已有实验值。最后,通过Gauss View可视化软件,对FUR分子的振动频率进行了更为全面地归属。通过FUR分子SERS与NRS的比较,可得出FUR分子与Ag原子发生了相互作用,且被吸附的糠醛分子的杂五环是与银表面垂直的。     

甲萘威的表面增强拉曼光谱密度泛函理论研究

根据密度泛函理论,在B3LYP方法下,Ag原子使用LANL2DZ赝式基组,C,H,N,O原子使用6-31++G(d,p)基组,计算了甲萘威及其银配合物的拉曼光谱,并利用GaussianView对甲萘威分子及SERS进行详细归属,为农产品和环境监测中甲萘威残留的表面增强拉曼光谱测定提供理论依据。     

2,6-二氯苯硫代甲酰胺的表面增强拉曼光谱密度泛函理论研究

根据密度泛函理论,在B3LYP方法下,Ag原子使用LANL2DZ赝式基组,C,H,N,S,Cl原子使用6-31++G(d,p)基组,计算了2,6-二氯苯硫代甲酰胺及其银配合物的拉曼光谱,并利用GaussianView对2,6-二氯苯硫代甲酰胺分子及SERS进行详细归属,为食品和产品中2,6-二氯苯硫代甲酰胺残留的表面增强拉曼光谱测定提供理论依据。     

杀草强分子的拉曼光谱的密度泛函理论研究

本文采用密度泛函理论(density functional theory,DFT),在B3LYP杂化泛函,6-31++g(d,p)(C,H,N)和LanL2DZ(Ag)基组下对杀草强分子及其Ag复合物的结构进行了优化;通过频率计算,获得了杀草强分子及其Ag复合物的拉曼光谱,并利用势能函数分布(PED)对拉曼光谱进行了指认,结合SERS光谱推测了杀草强和增强基底之间的吸附方式;采用含时密度泛函理论(time dependent density functional theory,TDDFT)对杀草强分子和杀草强分子-Ag复合物进行了激发态的分析计算。     

表面增强拉曼光谱研究胞嘧啶在银胶上的吸附行为

为探讨胞嘧啶(Cytosine,Cy)在基底银表面的吸附特性和规律,采用表面增强拉曼散射(SERS)光谱对其吸附行为进行分析,并结合量子化学密度泛函理论(DFT)/B3LYP计算方法对Cy分子的常规拉曼光谱(NRS)及Cy与Ag团簇吸附的SERS光谱进行计算,与测定结果进行比对且对其拉曼峰进行系统指认及归属,理论计算结合实测值探讨了Cy在基底Ag上的增强效应和吸附行为。考察了Cy分子在Ag纳米粒子上的不同吸附时间、浓度、pH等条件对SERS光谱的影响及优化,发现pH影响最大,在中性和强碱性条件下的增强效应明显优于酸性。Cy分子存在2种不同的异构体和3种不同的存在形态,并随酸度变化相互转化而达动态平衡。基于Cy在不同pH时的形态分布和相应的SERS变化规律,结合DFT算得的Cy分子中的电荷分布及在银基底表面的吸附机制,详细探讨了酸碱对Cy分子的SRES光谱影响的内因和吸附机理,指出在中性和弱碱性时,是Cy中的N3和O与Ag形成配位吸附;在pH大于11时,N与Ag形成配位吸附,而O与Ag形成共价吸附。     

质子酸功能化离子液体中银纳米颗粒的制备及其光学性能研究

以质子酸功能化离子液体1-丁基-3-甲基咪唑磷酸二氢盐([Bmim]H₂PO₄)为反应介质和表面活性剂,采用简单的化学还原法制备了具有形状各向异性的块状银纳米颗粒。通过X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见(UV-Vis)吸收光谱等一系列手段对其结构、形貌及光吸收特性进行了表征。结果表明,所制备的银纳米块具有立方结构,其平均横向尺寸约为30 nm,在硅片上自组装形成密堆积结构的多层膜。以1,2-二(4-吡啶基)乙烯(BPE)作为探针分子,研究所制备银纳米颗粒的表面增强拉曼散射(SERS)活性。结果表明所制的银纳米颗粒是较好的SERS基底,具有良好的增强效果,痕检能力及稳定性。对BPE分子的最低检测浓度可低至10-9mol·L-1,而且保存了90天后,其检测灵敏度没有显著的降低。     

Surface‐enhanced Raman scattering study of human serum on PVA?Ag nanofilm prepared by using electrostatic self‐assembly

Polyvinyl alcohol (PVA)‐protected silver nanoarchitecture (PVA Ag nanofilm) on the surface of the glass substrate was prepared by using electrostatic self‐assembly at a proper voltage. The two‐dimensional morphology of the PVA Ag nanofilm has been examined by scanning electron microscopy (SEM). The surface‐enhanced Raman scattering (SERS) spectra of human serum (HS) on PVA Ag nanofilms were recorded. The results show that the Raman scattering of HS can be enhanced efficiently based on these PVA Ag nanofilms. However, it also can be seen that the effect of sodium citrate (SC) acting as anticoagulant on the SERS spectrum of HS is unnegligible, which has not been discussed adequately in the previous reports. To discuss the effect of SC on the SERS spectrum of HS, we have studied the normal Raman spectra of solid SC and the SERS spectra of 1.0 × 10⁻³ mol/l aqueous solution of SC adsorbed on the PVA–Ag nanofilms. Meanwhile, Raman wavenumbers of the SC molecule were calculated by using the method of DFT‐B3LYP/6‐31G*, and the dominant assignations of the calculated wavenumbers were performed. It was found that the density functional theory (DFT) calculation of SC Raman spectrum matches well with the experimental results. With the perfect reproducibility and high SERS activity, this method will be useful in the development of HS detection methods. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface-enhanced Raman spectra of a complex of antimony with phenylfluorone and their interpretation

We present the resonance Raman scattering and surface enhanced Raman scattering (SERS) spectra of a complex of antimony with phenylfluorone (Sb-PF). Using the quantum-mechanical density functional method, we have calculated the geometric structure and frequencies of vibrations of the Sb-PF molecule and proposed for the first time an interpretation of its Raman spectra. Based on analysis of spectral changes that occur upon formation of a complex of phenylfluorone with Sb, we have found lines—markers—that can be used for detection and quantitative determination of the content of antimony by the SERS spectroscopy method.     

Adsorption of aniline on silver mirror studied by surface‐enhanced Raman scattering spectroscopy and density functional theory calculations

The adsorption of aniline on a silver mirror was studied by surface‐enhanced Raman scattering (SERS) spectroscopy and density functional theory (DFT) calculation methods. The normal Raman and SERS spectra of pure aniline liquid and its solutions were recorded by a micro‐Raman spectrometer with excitation at 514.5 nm. Orientation of the aniline molecule adsorbed on the Ag mirror is discussed. The results indicate that pure aniline is adsorbed on the surface of the Ag mirror with a tilted orientation. The conformer with the nitrogen atom interacting with the metal surface would be dominant. DFT calculations further confirm the experimental results that charge transfer (CT) takes place from the highest occupied molecular orbital(HOMO) of aniline to the singly occupied molecular orbital (SOMO) of the silver surface. In this paper, the frontier molecular orbital theory has been successfully used to explore the interaction between the aniline molecule and the silver surface. Copyright © 2011 John Wiley & Sons, Ltd.     

Identification of species formed after pyridine adsorption on iron,cobalt, nickel and silver electrodes by SERS and theoretical calculations

The adsorption of pyridine (py) on Fe, Co, Ni and Ag electrodes was studied using surface‐enhanced Raman scattering (SERS) to gain insight into the nature of the adsorbed species. The wavenumber values and relative intensities of the SERS bands were compared to the normal Raman spectrum of the chemically prepared transition metal complexes. Raman spectra of model clusters M₄(py) (four metal atoms bonded to one py moiety) and M₄(α‐pyridil) where M = Ag, Fe, Co or Ni were calculated by density functional theory (DFT) and used to interpret the experimental SERS results. The similarity of the calculated M₄(py) spectra with the experimental SERS spectra confirm the molecular adsorption of py on the surface of the metallic electrodes. All these results exclude the formation of adsorbed α‐pyridil species, as suggested previously. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental and theoretical studies of Raman spectroscopy on 4‐mercaptopyridine aqueous solution and 4‐mercaptopyridine/Ag complex system

Raman scattering and surface‐enhanced Raman scattering (SERS) have been used to study the behavior of 4‐mercaptopyridine (4‐Mpy) dissolved in water and adsorbed on silver mirrors. In order to gain the actual structure and the theoretical modes of the 4‐Mpy dissolved in water and adsorbed on the surface of silver mirror, ab initio calculation at the Hartree–Fock (HF) level and density functional theory (DFT) at Beck's three‐parameter Lee‐Yang‐Parr (B3LYP) level were performed to calculate the vibrational modes and wavenumbers. 4‐Mpy/2H₂O and 4‐Mpy/Ag complex systems were optimized, and then the corresponding Raman spectra were calculated and analyzed. Compared with the experimental results, the calculated results of 4‐Mpy and 4‐Mpy/2H₂O complex systems obtained from DFT method were more accurate. Among the results calculated with HF method, the one with three Ag atoms was economical, which took less computer time but gave equivalent results to those with more noumber of Ag atoms. Copyright © 2007 John Wiley & Sons, Ltd.     

Adsorption of 1,2,4‐triazole on a silver electrode: surface‐enhanced Raman spectroscopy and density functional theory studies

The pH‐dependent surface‐enhanced Raman scattering (SERS) of 1,2,4‐triazole adsorbed on silver electrode and normal Raman (NR) spectra of this compound in the aqueous solutions were investigated. The observed bands in the NR and SERS spectra were assigned with the help of density functional theory calculations for model molecules in the neutral, anionic, and cationic forms and their complexes with silver. The Raman wavenumbers and intensities were computed at the optimized molecular geometry. Vibrational assignments of the SERS and NR spectra are provided by calculated potential energy distributions. The combination of experimental SERS results and density functional theory calculations provide an insight into the molecular structure of adlayers formed by 1,2,4‐triazole on a silver surface at varying pH values and enable the determination of molecular orientation with respect to the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering of hydroxyproline

Surface‐enhanced Raman scattering (SERS) spectra of hydroxyproline and one deuterated analogue are reported. In this work, we tackled the problem of SERS reproducibility by employing gold colloids instead of the usual silver sols to achieve plasmon enhanced Raman scattering. We slightly modified modified a previously published procedure to obtain to obtain the colloid, and concentrated the gold particles by centrifugation. The SERS spectra show distinctive bands of hydroxyproline, assigned by comparison to normal Raman spectra and density functional theory calculations. Repeated measurements using this procedure showed reproducible SERS spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface-enhanced Raman scattering study of silver deposition on thin Alq3 layers

Surface-enhanced Raman scattering (SERS) spectroscopy is applied to study in situ the interface formation of silver on thin Alq₃ films. The changes in the frequencies of Alq₃ vibrational modes are moderate and their line-shape is preserved upon Ag deposition. Moreover, a good correspondence appears between the SERS and powder spectra and frequencies predicted by density functional calculations for the meridianal isomer. The behaviour of Raman spectra indicates that no chemical interaction occurs between the Ag atoms and Alq₃ molecules.