利用时间分辨相干反斯托克斯拉曼散射技术研究光催化产氢反应动力学

基于飞秒再生放大器及飞秒光学参量放大器输出的激光脉冲, 搭建了宽带时间分辨相干反斯托克斯拉曼散射(CARS)测试装置, 并利用该装置研究了氢气与空气混合气体中氢气的相对含量, 探测相对延时与CARS光谱之间的关系. 通过调整延时, 获得了无非共振背景干扰的氢气CARS信号. 实验中测得的CARS信号强度与氢气浓度(分压)的平方呈良好的线性关系, 符合CARS理论预测. 同时测得的实验数据的信噪比表明: 在当前的实验条件下, 在氢气与空气混合气的总压为0.1 MPa时, 该装置可以对氢气的浓度进行测量, 且其检测极限可低至0.2%. 本文还利用该装置对三联吡啶苯乙炔Pt 配合物-Co 配合物-三乙醇胺(TEOA)的三元化学催化体系的产氢动力学行为进行了研究, 通过改变pH值讨论了该催化体系的产氢动力学机制. 结果表明过高的质子浓度会降低体系的产氢效率, 这可能是因为在酸性条件下, 作为质子和电子供体的三乙醇胺分解被抑制, 电子供应中断, 导致产氢反应的停止.     

激光功率和积分时间对表面增强拉曼光谱的影响EI北大核心CSCD

表面增强拉曼光谱(SERS)技术能够有效增强低浓度样品的拉曼光谱强度,然而由于SERS的结构、材质等工艺原因,SERS实际应用中往往由于未能正确选择激光功率与积分时间而导致测量效果显著下降。本文以浓度为2,0.08μg/mL的三聚氰胺溶液样品、Au@Ag NPs纳米柱结构固态SERS基底为例,使用自主搭建的便携式拉曼光谱仪,采集不同激光功率和积分时间下的SERS光谱,使用算法平滑光谱、计算光谱基线,得到样品SERS光谱强度和SERS光谱基线强度变化趋势。实验表明,激发光源功率和积分时间改变时,SERS光谱基线强度在不同光谱区域变化幅度不同,部分光谱区域基线强度的变化幅度远大于样品光谱强度,导致使用拉曼光谱仪进行光谱测量时极易造成光谱强度饱和,影响低浓度样品的测量。临时更换样品试剂或SERS基底又会增加成本,且操作繁琐。研究发现,通过控制激光功率和积分时间这2个简单可控的变量,可以在一定程度上抑制SERS光谱基线、提高样品光谱强度,从而避免因光谱强度易饱和而无法测得低浓度样品光谱信号的问题。     

时间分辨拉曼光谱研究一氧化氮与肌红蛋白的结合过程

纳秒瞬态拉曼光谱技术是研究分子结构变化超快动态过程的重要实验手段之一.而肌红蛋白(Mb)与小分子配体的结合过程一直是人们研究的焦点.本文旨在利用纳秒瞬态拉曼光谱技术研究小分子配体NO与肌红蛋白结合的动力学过程.通过考察MbNO光解后产物脱氧肌红蛋白(DeoxyMb)与反应物MbNO的ν4特征振动峰的强度比值随激光激发功率的变化,阐述了利用纳秒瞬态拉曼光谱技术研究MbNO体系中NO与DeoxyMb结合过程的可行性.利用纳秒瞬态拉曼光谱技术,获得了与皮秒时间分辨拉曼和皮秒时间分辨吸收相一致的结合动力学实验结果.为研究其它复杂体系的超快结合动力学过程提供了一种新的思路.     

利用红外光谱和拉曼光谱研究离子液体结构与相互作用的进展

热力学实验、理论计算以及计算机模拟是离子液体微观结构与相互作用研究中常用的三种手段,但是目前采用这些手段对离子液体结构的认识尚处于初步探索阶段,还没有完全找到离子液体性质随结构变化的规律,尚未完全能够对离子液体进行"设计",这也使得对离子液体的进一步开发和应用受到极大的限制.近年来,谱学方法成为研究溶液结构的重要手段.其中,红外光谱(IR)和拉曼光谱(Raman)等谱学手段在离子液体的结构与相互作用研究中发挥着越来越重要的作用.本文着重概述了红外光谱和拉曼光谱在纯离子液体及离子液体混合溶液结构与相互作用方面的研究进展、挑战以及发展方向.     

反丁烯二酰基桥连的带不同取代基的卟啉二联体的合成与性质

合成了反丁烯二酰基桥连的3种带不同取代基的卟啉二联体, 通过红外光谱, 紫外-可见光谱, 核磁共振波谱和质谱对化合物的结构进行了确认, 并研究了二联体的表面光电压谱, 荧光光谱和激光拉曼光谱的变化. 结果表明, 取代基的类型对卟啉二联体分子的荧光量子产率有显著影响, 带供电子基团的甲氧基增强了荧光量子产率, 而带吸电子基团的氯则降低了荧光量子产率, 并且吸电子基团的氯比供电子基团的甲氧基对荧光的影响更大. 取代基的电子效应对卟啉二联体的荧光性和激光拉曼光谱有较大影响.     

钕（Ⅲ）与对－氨基苯甲酸、邻菲咯啉混配配合物的晶体结构和激光拉曼光谱

报道了钕与对－氨基苯甲酸、邻菲咯啉的配合物［（Ｎｄ（ｐ－ＡＢＡ）４·２Ｐｈｅｎ］Ｈ３Ｏ·２Ｐｈｅｎ的合成。测定了它的结构和激光拉曼光谱。配合物属单斜晶系，空间群为Ｃ２／ｃ，ａ＝１９０６７（５）ｎｍ，６ｂ＝１，９１９２（３）ｎｍ，ｃ＝２．０１９０（４）ｎｍ，Ｂ＝２１１７．２５（２）℃，Ｖ＝６．５６８（５）ｎｍ３Ｍ＝１４２８．６３，ｚ＝４，Ｄｘ＝１．４５ｇ·ｃｍ－３。钕离子的配位数为１０，钕原子周围的配位原子形成畸变的四帽三角棱柱体。     

表面增强拉曼光谱研究自组装单分子层在化学接触和纳米隔绝下的分子振动活性变化(英文)

为确定表面增强拉曼光谱中某些有争议的弱振动模式是来自高阶的影响还是分子基团对称性变化的影响,本文以1,4-苯二硫醇作为探针分子提供了一种实验验证的框架方法.光谱实验显示,观测到的有争议的弱振动模式并不是来自高阶的影响,而是分子基团对称性变化所致.我们的实验框架方法很容易拓展开来,如用于研究其它波长激光激发的类似体系或有机分子搭接的分子结.     

食品中苏丹红Ⅰ和辣椒红的表面增强拉曼散射(SERS)光谱与激发-发射矩阵荧光光谱鉴别

利用表面增强拉曼散射(SERS)光谱及激发-发射矩阵(EEM)荧光光谱对食品中非法添加剂苏丹红Ⅰ和合法食品添加剂辣椒红进行了定性分析和检测. SERS光谱结果表明, 苏丹红Ⅰ在低波数区域分子的扭转振动信号增强比较明显; 而辣椒红在1521和1158 cm^-1处拉曼信号增强效果比较明显; EEM荧光光谱结果表明, 苏丹红Ⅰ的乙醇溶液在P₁(λ_ex=285 nm, λ_em=345 nm)和P₂(λ_ex= 335 nm, λ_em=548 nm)处有2个明显的荧光特征峰; 而辣椒红的乙醇溶液有3个特征荧光峰, 分别为P₁(λ_ex=545 nm, λ_em=580 nm), P₂(λ_ex=560 nm, λ_em=665 nm)和P₃(λ_ex=608 nm, λ_em=672 nm).     

应用停流时间分辨光谱研究氧合血红蛋白与过氧化氢反应中间体的动力学和机理

研究血红蛋白与H2O2的相互作用过程及其反应机理具有重要的意义,关于H2O2与血红蛋白相互作用的研究已有报道,但观点不尽相同,结论各异,快速混合停流光谱是研究快速反应动力学的主要手段,在解释化学和生化反应机理方面发挥了重要的作用,本文利用停流时间分辨光谱研究了氧     

烷烃客体分子(C_nH_m,n≤6,m≤14)在5~(12)6~2和5~(12)6~4水笼中的稳定性与拉曼光谱的密度泛函理论计算

可燃冰矿藏中气体成分非常复杂,通过谱学分析对水合物样品成分进行指认具有重要意义.基于B97-D/6-311++G(2d,2p)的密度泛函理论(DFT)计算,我们系统地探索了构成水合物的两种标准水笼(51262和51264)包络十八种不同烷烃客体分子的稳定性.从计算结果可以看出,除了3-甲基戊烷和2,3-二甲基丁烷两个烷烃客体分子,其它16个烷烃客体分子都可以被容纳在51262笼中;但是与51262笼不同,十八种烷烃客体分子都可以被容纳在尺寸较大的51264笼中.同时,我们也模拟了五种直链烷烃和四种环状烷烃在51262和51264笼中相应的谱学特征,从拉曼谱图上可以看出,随着碳原子数量的增多,直链烷烃客体分子C―H键伸缩振动区的多数拉曼谱带向高波数移动,而环状烷烃客体分子C―H键伸缩振动区的拉曼谱带则向低波数移动.这些结果为实验上通过拉曼谱测量指认水合物矿藏的成分提供理论参考.     

Symmetry and selection rules in the Raman spectra of carbon nanotubes

The symmetry of achiral single-walled (n,0) and (n,n) carbon nanotubes (CNTs) was examined and the frequencies and types of vibrations allowed in the Raman spectra were calculated. The vibrational spectrum was evaluated as the eigenvalues of the dynamical matrix at the -point of the Brillouin zone. The selection rules for the Raman active vibrations were estimated by the values of the matrix elements responsible for the intensities of corresponding vibrational transitions. The (n,n)-CNTs with even and odd n values are characterized by five and six allowed Raman active vibrations, respectively. The number of Raman active vibrations for (n,0)-CNTs is five if n is even and eight if n is odd. Detailed analysis of the results obtained is presented for the (10,10)-CNT as an example.     

RMSD and Symmetry

A common approach for comparing the structures of biomolecules or solid bodies is to translate and rotate one structure with respect to the other to minimize the pointwise root-mean-square deviation (RMSD). We present a new, robust numerical algorithm that computes the RMSD between two molecules or all the mutual RMSDs of a list of molecules and, if desired, the corresponding rotation matrix in a minimal number of operations as compared to previous algorithms. The RMSD gradient can also be computed. We address the problem of symmetry, both in alignment (possible alternative alignments due to indistinguishable atoms) as well as geometry. In the latter case, it is possible to have degenerate superposition. A necessary condition is optimal superimposability to one's mirror image. Double (respectively, triple) degeneracy results in a one- (respectively, two)-parameter family of rotations leaving the superposition invariant. The software, frmsd , is freely available at http://www.ams.stonybrook.edu/~coutsias/codes/frmsd.tgz . © 2019 Wiley Periodicals, Inc.     

Symmetry calculation for molecules and transition states

The symmetry of molecules and transition states of elementary reactions is an essential property with important implications for computational chemistry. The automated identification of symmetry by computers is a very useful tool for many applications, but often relies on the availability of three‐dimensional coordinates of the atoms in the molecule and hence becomes less useful when these coordinates are a priori unavailable. This article presents a new algorithm that identifies symmetry of molecules and transition states based on an augmented graph representation of the corresponding structures, in which both topology and the presence of stereocenters are accounted for. The automorphism group order of the graph associated with the molecule or transition state is used as a starting point. A novel concept of label‐stereoisomers, that is, stereoisomers that arise after labeling homomorph substituents in the original molecule so that they become distinguishable, is introduced and used to obtain the symmetry number. The algorithm is characterized by its generic nature and avoids the use of heuristic rules that would limit the applicability. The calculated symmetry numbers are in agreement with expected values for a large and diverse set of structures, ranging from asymmetric, small molecules such as fluorochlorobromomethane to highly symmetric structures found in drug discovery assays. The new algorithm opens up new possibilities for the fast screening of the degree of symmetry of large sets of molecules. © 2014 Wiley Periodicals, Inc.     

Vibrational Relaxation in beta-Carotene Probed by Picosecond Stokes and Anti-Stokes Resonance Raman Spectroscopy

Picosecond time-resolved Stokes and anti-Stokes resonance Raman spectra of all-trans-beta-carotene are obtained and analyzed to reveal the dynamics of excited-state (S(1)) population and decay, as well as ground-state vibrational relaxation. Time-resolved Stokes spectra show that the ground state recovers with a 12.6 ps time constant, in agreement with the observed decay of the unique S(1) Stokes bands. The anti-Stokes spectra exhibit no peaks attributable to the S(1) (2A(g) (-)) state, indicating that vibrational relaxation in S(1) must be nearly complete within 2 ps. After photoexcitation there is a large increase in anti-Stokes scattering from ground-state modes that are vibrationally excited through internal conversion. The anti-Stokes data are fit to a kinetic scheme in which the C=C mode relaxes in 0.7 ps, the C-C mode relaxes in 5.4 ps and the C-CH(3) mode relaxes in 12.1 ps. These results are consistent with a model for S(1)-S(0) internal conversion in which the C=C mode is the primary acceptor, the C-C mode is a minor acceptor, and the C-CH(3) mode is excited via intramolecular vibrational energy redistribution.     

Label‐Free Molecular Imaging of Biological Cells and Tissues by Linear and Nonlinear Raman Spectroscopic Approaches

Raman spectroscopy is an emerging technique in bioanalysis and imaging of biomaterials owing to its unique capability of generating spectroscopic fingerprints. Imaging cells and tissues by Raman microspectroscopy represents a nondestructive and label‐free approach. All components of cells or tissues contribute to the Raman signals, giving rise to complex spectral signatures. Resonance Raman scattering and surface‐enhanced Raman scattering can be used to enhance the signals and reduce the spectral complexity. Raman‐active labels can be introduced to increase specificity and multimodality. In addition, nonlinear coherent Raman scattering methods offer higher sensitivities, which enable the rapid imaging of larger sampling areas. Finally, fiber‐based imaging techniques pave the way towards in vivo applications of Raman spectroscopy. This Review summarizes the basic principles behind medical Raman imaging and its progress since 2012.     

Hepatic Vitamin A Content Investigation Using Coherent Anti‐Stokes Raman Scattering Microscopy

Standard techniques for examining the distribution of vitamin A in liver either require staining or lead to rapid photobleaching of the molecule. A potentially better alternative approach is to use coherent anti‐Stokes Raman scattering (CARS) microscopy; a fast, label‐free, non‐disruptive imaging method that provides contrast based on molecular vibrations. This contribution evaluates the viability of CARS microscopy for imaging vitamin A within thick hepatic tissue under physiological conditions by tuning into its characteristic vibrational band in the fingerprint region. Additional information about the morphology and architecture of the tissue was acquired using second harmonic generation (SHG) and multi‐photon excited fluorescence (MPEF) to help mapping the intra‐lobular positions of the vitamin A droplets. We demonstrate the capability of our multimodal imaging framework to selectively image lipid‐soluble vitamin A droplets deep in bulk liver tissue with a high contrast while co‐registering a complementary morphological background that clearly visualizes hepatic lobules. The results obtained envisage the good prospect of the technique for in vivo studies assessing vitamin A distribution heterogeneity and how it is affected by the progression of hepatic diseases.     

乐果涂膜表面增强拉曼光谱研究

通过蒸发乐果饱和水溶液在磁控溅射银膜上形成乐果涂膜,利用表面增强拉曼光谱(SERS)技术研究了乐果涂膜的分子振动特性,并与乐果固体拉曼谱进行比较。研究结果表明,乐果晶体结构长程有序性的破坏造成涂膜SERS体系中υ(P—S)和υ(PS)振动峰的展宽和蓝移,水解引起乐果δ(SPOC)和δs(COPOC)振动模式强度降低,OC—N键中的O原子和N原子以及水解质子化的O在银表面吸附造成υ(OC—N)、υ(OC)、δ(N—H)、υ(CN)、δ(C—N—C)、δ(OPO)和υ(P—O)等振动模式显著增强。这为利用SERS技术研究乐果溶液以及乐果在植物体、食品中的残留提供了实验和理论依据。     

Overview of Popular Techniques of Raman Spectroscopy and Their Potential in the Study of Plant Tissues

Raman spectroscopy is one of the main analytical techniques used in optical metrology. It is a vibration, marker-free technique that provides insight into the structure and composition of tissues and cells at the molecular level. Raman spectroscopy is an outstanding material identification technique. It provides spatial information of vibrations from complex biological samples which renders it a very accurate tool for the analysis of highly complex plant tissues. Raman spectra can be used as a fingerprint tool for a very wide range of compounds. Raman spectroscopy enables all the polymers that build the cell walls of plants to be tracked simultaneously; it facilitates the analysis of both the molecular composition and the molecular structure of cell walls. Due to its high sensitivity to even minute structural changes, this method is used for comparative tests. The introduction of new and improved Raman techniques by scientists as well as the constant technological development of the apparatus has resulted in an increased importance of Raman spectroscopy in the discovery and defining of tissues and the processes taking place in them.