20种α-氨基酸的太赫兹光谱及其分子结构的相关性

应用太赫兹时域光谱(THz-TDS)技术, 在室温下对构成蛋白质的20种基本氨基酸的多晶粉末压片样品进行了光谱测试分析. 结果表明, 所有氨基酸对THz波反应非常灵敏, 在0.2-3.0 THz的有效频谱范围内, 表现出各自特征吸收峰, 故而利用THz光谱可以有效地区别不同种类的氨基酸. 我们以新数据验证和补充了前人的研究结果, 建立了以氨基酸分子结构及其THz光谱特征为基础的分类方案, 讨论并揭示了氨基酸分子的结构差异与其THz吸收光谱之间的相关性. 认知这些相关性将有助于鉴定氨基酸分子, 促进THz光谱学的理论研究以及在生物医学领域的推广应用.     

含硫氨基酸的太赫兹光谱

利用太赫兹时域光谱(THz-TDS)技术研究室温条件下多晶含硫氨基酸L-蛋氨酸(Met)和L-半胱氨酸(Cys)的光谱特性, 得到相应的吸收谱和折射率谱, 表明含硫氨基酸在THz波段具有区别于其它氨基酸的显著特征. 在实验测量的有效光谱范围0.2～2.8 THz内, L-蛋氨酸的THz吸收峰分别位于1.06, 1.88和2.70 THz; L-半胱氨酸的吸收峰分别位于1.40, 1.70, 2.33和2.61 THz, 两种氨基酸的平均折射率均为1.44. 利用GAUSSIAN 03软件包中的Hartree-Fock理论计算了蛋氨酸双分子的低频振动谱, 表明了与蛋氨酸各吸收峰对应的分子微观振动模式, 并对实验光谱进行了解析讨论.     

萘醌及其衍生物的太赫兹时域光谱研究

用太赫兹(THz)时域光谱技术研究了室温条件下的萘醌及其衍生物1,2-萘醌、1,2-萘醌-4-磺酸钠、甲萘醌、白花丹素、胡桃醌的光谱特征,得到了各自的吸收谱和折射率。结果表明,萘醌及其衍生物在此波段有不同的吸收特征,利用太赫兹时域光谱能够鉴别分子结构存在微小差别的化合物。在对样品的吸收谱进行比较的基础上,讨论了分子结构和分子间晶格振动与THz光谱特征吸收的关系。     

Angle-dependent terahertz time-domain spectroscopy of amino acid single crystals

The measurement of absorption spectra using angle-dependent terahertz (THz) time-domain spectroscopy for amino acid single crystals of l-cysteine and l-histidine is reported for the first time. Linearly polarized THz radiation enables us to observe angle-dependent far-infrared absorption spectra of amino acid single crystals and determine the direction of the oscillating dipole of the molecules in the 20-100 cm(-1) range. By comparing the THz spectra of a single crystal and powder, we found that there was a clear hydrogen-bond peak in the crystal spectrum as a result of the larger hydrogen-bond network. The low-temperature THz spectra of amino acid microcrystals showed more intermolecular vibrational modes than those measured at room temperature. An ab initio frequency calculation of a single amino acid molecule was used to predict the intramolecular vibrational modes. The validity of the calculation models was confirmed by comparing the results with experimentally obtained data in the Raman spectral region.     

Multi-parameter evaluation of fast sol–gel process by terahertz measurements

We present a feasibility study to apply terahertz (THz) spectroscopy and THz imaging as non-destructive diagnostic tools for sol–gel analysis, manufacturing and quality control. By performing THz spectroscopy on liquid and solid samples we were able to follow several key parameters during the sol–gel formation process and of the final product. Sol–gel transformations were monitored by THz absorption, whereas density changes have been observed through changes in refractive indices. Time domain spectroscopy (TDS), both in transmission and reflection geometries, was used to monitor the properties of fast sol–gel resins. THz imaging of gold coated, thin-film sol–gel enables us to determine inhomogeneities and defects in their internal structure. We demonstrated that THz spectroscopy can be implemented as an online analytical tool for multi-parameter evaluation of the sol–gel process during fabrication, and of the final product.     

Analytical terahertz spectroscopy.

Recent progress in analytical terahertz (THz) spectroscopy is reviewed with illustrative examples showing that it is an effective method for detecting and identifying intermolecular interactions in chemical compounds, such as hydrogen bonds. The unique and characteristic properties of THz waves, their significance to both science and industry, and the bases of one of the successful fields of analytical THz spectroscopy, namely THz time-domain spectroscopy and THz imaging for chemical analysis, are described. Preliminary quantitative studies are presented to show the potential of THz spectroscopy for the detection and identification of intermolecular hydrogen bonds in unknown mixture samples. The selective detection of intramolecular hydrogen bonds and the detection of intramolecular interactions in ice are also introduced. Some brief remarks are provided on future developments, the main issues, and the prospects for analytical THz spectroscopy.     

Compilation of an ESI-MS Library of β-Lactam Antibiotics for Rapid Identification of Drugs

β-Lactam antibiotics are among the most frequently used in clinical therapy. Thirty-three cephalosporin and eleven penicillin antibiotics frequently used in China have been used to create an ESI-MS library. A single-quadrupole mass analyzer was used for rapid identification. The product ions of these 44 β-lactam antibiotics were assigned to establish the fragmentation patterns and a standard ESI-MS library was established. Along with the specificity that product ion spectral information provides, the library provides another means to help identify β-lactam antibiotics. This is an important complement to the retention time from LC separations, and a valuable tool for confirming the identity of counterfeit drugs.     

THz spectroscopic investigation of 2,4-dinitrotoluene

We have investigated the terahertz (THz) spectrum of 2,4-DNT by using Fourier transform infrared spectroscopy in the 0.2–19.5 THz region. We also examined low-frequency intermolecular or phonon modes between 0.2 and 1.8 THz via THz time-domain spectroscopy. The extracted absorption coefficient and refractive index of an intermolecular band at 1.08 THz are 110 cm⁻¹ and 1.67, respectively. Density functional theory (DFT) was applied to obtain structure and vibrational frequencies of 2,4-DNT. The calculated results are in agreement with the experimental data. Observed vibrational frequencies have been interpreted using DFT. Two intermolecular or phonon modes were identified at 1.08 and 2.52 THz.     

Terahertz time-domain spectroscopy of some pentoses

1 Introduction Terahertz time-domain spectroscopy (THz-TDS) is a new spectral technique based on femto-second laser technology developed since the 1980s[1]. Terahertz (THz) waves lie between the infrared and microwave bands in the electromagnetic spectrum covering the frequency range from 100 GHz to 10 THz. Despite great scientific interest, the THz frequency range re- mains one of the least tapped regions of the electro- magnetic spectrum because there are neither conven- ient high-power…     

Terahertz time-domain spectroscopy of imidazolium ionic liquids

We have measured the terahertz (THz) complex dielectric spectra of imidazolium ionic liquids by THz time-domain spectroscopy (THz-TDS) in the frequency range from 5 (0.15 THz) to 140 cm(-1) (4.2 THz). The ionic liquids investigated are 1-ethyl-3-methylimidazolium (EMIm+)/trifluoromethanesulfonate (TfO-), EMIm+/tetrafluoroborate (BF(4)-), 1-butyl-3-methylimidazolium (BMIm+)/TfO-, and BMIm+/BF(4)-. The dielectric values of the ionic liquids in the THz region are similar to those of short-chain alcohols. The THz dielectric values are related to subpicosecond-to-picosecond dynamics. The same trend has been observed in the empirical polarity ET(30) although it is related to the static characteristics of polarity and hydrogen bonding ability. A difference between the two types of liquids is observed in the THz dielectric spectral shapes: the ionic liquids show structured lineshapes but short-chain alcohols show much less structured ones. The structured lineshapes of the ionic liquids reflect the low-frequency motions of interion and/or intramolecular vibrations. When the ionic liquids composed of the different imidazolium cations contain the same anions as counterions, their density-normalized THz dielectric spectra above 20 cm(-1) bear strong resemblance to each other in shape and magnitude. It shows clearly that the THz spectra do not originate from the intramolecular vibrations of the imodazolium cations. All of the intramolecular vibrations of the anions are located above 140 cm(-1) except the CF3-SO3 torsion of TfO-, the band of which alone cannot explain the broad THz dielectric spectra of the ionic liquids. Therefore, we conclude that the interion vibrations rather than the intramolecular vibrations dominantly contribute to the THz dielectric spectra. The results strongly indicate that even in the liquid phase the ionic liquids have local structures similar to their solid-phase structures.     

Ground-state spectral features of molecular clusters RDX excited at THz frequencies

Calculations are presented of ground state resonance structure at THz frequencies for molecular clusters of the high explosive RDX using density functional theory (DFT). The spectral features of this resonance structure are due to coupling of resonance modes for ground state excitation. In particular, the coupling among ground state resonance modes provides a reasonable molecular level interpretation of spectral features associated with THz excitation of molecular clusters. THz excitation is associated with frequencies that are characteristically perturbative to molecular electronic states, in contrast to frequencies that can induce appreciable electronic state transition. Owing to this characteristic of THz excitation, one is able to make a direct association between local oscillations about ground-state minima of molecules, either isolated or comprising a cluster, and THz excitation spectra. The DFT software GAUSSIAN was used for the calculations of ground state resonance structure presented here.     

Excited-State THz Vibrations in Aggregates of PtII Complexes Contribute to the Enhancement of Near-Infrared Emission Efficiencies**

The exploration of deactivation mechanisms for near-infrared(NIR)-emissive organic molecules has been a key issue in chemistry, materials science and molecular biology. In this study, based on transient absorption spectroscopy and transient grating photoluminescence spectroscopy, we demonstrate that the aggregated Pt^II complex 4H (efficient NIR emitter) exhibits collective out-of-plane motions with a frequency of 32 cm⁻¹ (0.96 THz) in the excited states. Importantly, similar THz characteristics were also observed in analogous Pt^II complexes with prominent NIR emission efficiency. The conservation of THz motions enables excited-state deactivation to proceed along low-frequency vibrational coordinates, contributing to the suppression of nonradiative decay and remarkable NIR emission. These novel results highlight the significance of excited-state vibrations in nonradiative processes, which serve as a benchmark for improving device performance.     

Measurement of coherent terahertz radiation for time-domain spectroscopy and imaging

A high-power terahertz (THz) source for THz time-domain spectroscopy (THz-TDS) and THz imaging has been developed based on an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). A THz pulse was generated as coherent synchrotron radiation (CSR) from an ultra-short electron bunch and expected to have peak power of kW-order with frequency range of 0.1–2 THz. The electro-optic (EO) sampling method with a ZnTe crystal for the THz pulse measurement has been prepared for THz-TDS system. The timing measurement between the THz pulse and a probe laser was carried out. A preliminary experiment of THz transmission imaging of an integrated circuit (IC) card has been successfully demonstrated using the THz CSR pulse and a W-band rf detector. The imaging result was experimentally compared with a result of X-ray imaging. It is confirmed that its intensity and stability are enough to perform for the THz applications.     

Terahertz time-domain spectroscopy as a novel tool for crystallographic analysis in cellulose: the potentiality of being a new standard for evaluating crystallinity

Cellulose - Given that terahertz (THz) radiation responds to intermolecular forces such as hydrogen bonds, THz time-domain spectroscopy (THz-TDS) has expanded possibilities in cellulose research....     

Importance of accurate spectral simulations for the analysis of terahertz spectra: citric acid anhydrate and monohydrate

The terahertz (THz) spectra of crystalline solids are typically uniquely sensitive to the molecular packing configurations, allowing for the detection of polymorphs and hydrates by THz spectroscopic techniques. It is possible, however, that coincident absorptions may be observed between related crystal forms, in which case careful assessment of the lattice vibrations of each system must be performed. Presented here is a THz spectroscopic investigation of citric acid in its anhydrous and monohydrate phases. Remarkably similar features were observed in the THz spectra of both systems, requiring the accurate calculation of the low-frequency vibrational modes by solid-state density functional theory to determine the origins of these spectral features. The results of the simulations demonstrate the necessity of reliable and rigorous methods for THz vibrational modes to ensure the proper evaluation of the THz spectra of molecular solids.     

胆酸和脱氧胆酸分子的远红外与THz吸收光谱研究

胆酸和脱氧胆酸是胆汁酸中的主要成分, 是人体中重要的生物表面活性剂. 两种分子只相差一个羟基, 在远红外和太赫兹波段有不同的吸收光谱. 胆酸分子的太赫兹(THz)吸收光谱有1.26 THz(42 cm-1)和2.02 THz(67 cm-1)两个吸收峰, 脱氧胆酸分子的THz吸收光谱有1.13, 1.26, 1.69和2.17 THz(即38, 42, 56, 72 cm-1)等几个吸收峰. 两个分子的THz吸收光谱都包含有1.26 THz(42 cm-1) 峰, 反映出二者结构的相似性. 它们的远红外光谱都有部分频率相近的谱带, 但对比之下可以观察到峰位位移和相对峰强的改变. 指认了两种物质的某些可能与羧基振动有关的特征吸收峰. 为找出THz光谱隐含的信息, 利用Omnic程序采用二阶导数方法来处理THz光谱数据, 观察到多个子峰, 说明分子结构中可能存在更复杂的氢键状态. 实验结果表明, 远红外和THz吸收光谱是研究生物分子及鉴别生物分子结构的很好方法.     

乐果分子的太赫兹时域光谱研究

研究了有机磷农药乐果在0.2~2.5 THz波段的光谱特性。应用密度泛函理论的Becke-3-Lee-Yang-Parr(B3LYP)方法计算了乐果分子在THz波段的振动吸收谱,同时利用THz时域光谱系统(THz-TDS)测得了乐果在此波段的吸收谱和折射率谱。根据理论计算结果,借助于Gaussian View软件对乐果的THz吸收谱进行了指认,并给出了与光谱特征吸收对应的分子振动构象。研究表明:乐果分子在THz波段存在吸收峰,理论计算与实验结果符合较好,且乐果分子在THz波段的吸收是由分子内和分子间振动共同引起。本研究证明了将THz-TDS技术用于乐果分子探测和识别的可行性,为THz时域光谱技术在其它农药分子识别和残留检测中的应用提供了有益的借鉴。     

L-和DL-福多司坦的太赫兹光谱分析

利用太赫兹时域光谱技术(THz-TDS)在室温下对L-福多司坦和DL-福多司坦进行测量,发现L-和DL-福多司坦在THz波段都有特征吸收峰,且两者的吸收谱有明显差异.运用密度泛函理论的B3LYP方法计算了L-和DL-福多司坦在太赫兹波段的吸收谱,并对L-和DL-福多司坦的特征吸收峰进行了指认,理论计算与实验结果基本吻合.此外,还对福多司坦胶囊成品药进行了测量,发现该胶囊的吸收谱与L-福多司坦非常吻合,证明胶囊药的主要成分为L-福多司坦.这项研究对手性物质的检测以及化合物有效成分的鉴别有一定的参考作用.     

Application of THz Vibrational Spectroscopy to Molecular Characterization and the Theoretical Fundamentals: An Illustration Using Saccharide Molecules

This work illustrates several theoretical fundamentals for the application of THz vibrational spectroscopy to molecular characterization in the solid state using two different types of saccharide systems as examples. Four subjects have been specifically addressed: (1) the qualitative differences in the molecular vibrational signatures monitored by THz and mid‐IR vibrational spectroscopy; (2) the selection rules for THz vibrational spectroscopy as applied to crystalline and amorphous systems; (3) a normal mode simulation, using α‐l ‐xylose as an example; and (4) a rigorous mode analysis to quantify the percentage contributions of the intermolecular and intramolecular vibrations to the normal mode of interest.