时间分辨偏振红外光谱及其应用

时间分辨偏振红外光谱已被广泛应用于研究光化学过程中的分子结构动力学. 通过测定瞬态物质跃迁偶极矩之间的角度等结构信息,可以提供光化学过程中伴随的电荷分布、分子结构和构象变化等动态信息. 包括简要介绍时间分辨偏振红外光谱技术的原理和应用：(i) 时间分辨偏振红外光谱概述;(ii) 时间分辨偏振红外光谱的原理及其优势;(iii) 利用时间分辨偏振红外光谱探测多种化学动力学过程,例如蛋白质构象动力学、激发态的电子局域化和光致异构化等;(iv) 时间分辨偏振红外光谱的局限和发展前景.     

安息香笼化合物光化学反应的时间分辨红外光谱

采用时间分辨红外吸收光谱方法,研究了邻甲基苯甲酸安息香酯在266 nm激光作用下发生的光化学反应,并考察了溶剂对反应过程的影响. 从瞬态红外光谱上观察到了邻甲基苯甲酸和苯甲酰自由基及苯偶酰,提供了直接的光谱证据证明了脱保护反应及C-C=O处均裂反应的发生. 通过对比溶剂中不同水含量下均裂反应中间体及邻甲基苯甲酸的产率,发现水含量在溶剂中的增加能促进脱保护反应的发生.     

Measurement and characterization of singlet oxygen production in copper ion-catalyzed aerobic oxidation of ascorbic acid

Production of singlet molecular oxygen (¹O₂) in the aerobic oxidation of ascorbic acid catalyzed by copper ion was measured and characterized using [4′-(9-anthryl)-2,2′:6′,2″-terpyridine-6,6″-diyl]bis(methylenenitrilo)tetrakis(acetate)-Eu³⁺ (ATTA-Eu³⁺) as a highly sensitive and selective time-resolved luminescence probe for ¹O₂. The ¹O₂ produced in the reaction was further characterized and confirmed by (i) chemical trapping of ¹O₂ with 9,10-diphenylanthracene (DPA), the corresponding endoperoxide was detected by HPLC and (ii) spin trapping of ¹O₂ with 2,2,6,6-tetramethyl-4-piperidinol (TMP-OH), the corresponding free radical of TMP-OH oxide (TMPO) was detected by electron spin resonance (ESR) spectroscopy. The effects of deuterium oxide, sodium azide and histidine on the ¹O₂ signal were investigated. The mechanism investigation of ¹O₂ production implied that the ascorbic acid-Cu(I) complex formed in the reaction could be an important intermediate for the ¹O₂ production. The reaction of ascorbic acid with copper ion monitored by ¹H NMR and absorption spectroscopy demonstrated the formation of a copper ion-ascorbic acid complex. Except for Cu²⁺ and Cu⁺-ascorbic acid systems, no detectable ¹O₂ was produced in other transition metal cation-ascorbic acid systems in the studied range.     

Europium(III)-chelates embedded in nanoparticles are protected from interfering compounds present in assay media

Lanthanide chelates are excellent labels in ligand binding assays due to their long lifetime fluorescence, which enables efficient background reduction using time-resolved measurement. In separation-free homogeneous assays, however, some compounds in the sample may cause quenching of the lanthanide fluorescence and extra steps are required before these samples can be measured. In this study we have evaluated whether europium chelates packed inside a polystyrene nanoparticle are better protected from the environment than individual Eu(III)-chelates, and do these particles have higher tolerance against known interfering compounds (bivalent metal ions and variation of pH). We also tested whether metal ions had any effect on a fluorescence resonance energy transfer (FRET) based detection of a bioaffinity binding reaction. The presence of metal ions or variation of pH did not affect the fluorescence of the Eu(III)-chelate dyed nanoparticles, while significant decrease of the fluorescence was detected with a 9-dentate Eu(III)-chelate. Metal ions also decreased the fluorescence lifetime of the 9-dentate Eu(III)-chelate from 0.960 to 0.050 ms. Coloured metal ions caused a minor decrease in sensitised emission generated by FRET when Eu(III)-chelate dyed nanoparticles were used as donor labels. The decreased signal was due to the absorption of the sensitised emission by the coloured metal ions, since the metal ions had no effect on the lifetime of the sensitised emission. Thus the Eu(III)-chelate dyed nanoparticles are preferred labels in homogeneous bioaffinity assays, when interfering compounds are known to be present.     

Polaritonic coupling and spin dynamics in GaAs microcavities

We have used time-resolved photoluminescence spectroscopy to study the light emission dynamics in a semiconductor microcavity as a function of excitation density and exciton-cavity detuning. We paid special attention to polariton spin relaxation by using circularly polarized excitation. We have found a striking behavior of the photoluminescence degree of polarization, which reaches its maximum value at a finite time. As the excitation density is increased and the system enters the stimulated emission regime, this maximum is followed by a negative dip, whose depth strongly depends on exciton-cavity detuning.     

A Fluorescence Quenching Method for the Determination of Nitrite with Indole

A new fluorescence quenching method has been developed to determine nitrite in water and food samples. The method is based on the reaction between nitrite and the fluorescent indole to form a compound which has no fluorescence in acidic medium. The fluorescence intensity was measured in 1 cm quartz cell with excitation and emission wavelengths of 285 and 350 nm, respectively. The relationship was obtained between the fluorescence intensity and nitrite concentration in the range 0.01–0.6 μg ml⁻¹. The detection limit was 2.5 ng ml⁻¹. The proposed method was applied to determine nitrite in water and food samples. The mechanism involved in the reaction was studied.     

反相胶束增稳室温荧光法测定中药痕量有效成分氯原酸的研究

研究了双－「２－乙基己基」－磺酸基琥珀酸（气溶胶ＯＴ或ＡＯＴ）／环己烷／水反相胶束介质吕草药有效成分氯原酸的荧光性质,发现氯原酸在上述反相胶束体系中,不仅荧光有增强现象,而且分子激发和发射光谱发生红移。首次建立了反相胶束增稳室温荧光法测定氯原酸的新方法。该法测定的线性范围为：６×１０＾－７－－４×１０＾－６（ｇ／ｍＬ）,检出限为：１．２×１０＾－７ｇ／ｍＬ）,相地标准偏差为：１．３（％）。     

反相胶束增稳荧光法测定兔血浆中痕量盐酸小檗碱的研究

本文研究了气溶胶（ＡＯＴ）／环己烷／水反相胶束介质中中草药有效成分盐酸小檗碱的荧光性质,并将该法应用于兔血浆中痕量盐酸小檗碱的测定。该法的线性范围为１．０×１０－ ７～３×１０－ ５（ｇ／ｍ Ｌ）,检出限为８．３×１０－ ８（ｇ／ｍ Ｌ）,相对标准偏差为１．１％ 。     

Fluorescence quenching, time-resolved fluorescence and chemical modification studies on the tryptophan residues of snake gourd (Trichosanthes anguina) seed lectin

Fluorescence quenching and time-resolved fluorescence studies have been performed on the galactose-specific lectin purified from snake gourd (Trichosanthes anguina) seeds, in order to investigate the tryptophan accessibility and environment in the native protein and in the presence of bound ligand. Estimation of the tryptophan content by N-bromosuccinimide modification in the presence of 8 M urea yields four residues per dimeric molecule. The emission spectrum of native lectin in the absence as well as in the presence of 50 mM methyl--d-galatopyranoside (MeGal) shows a maximum around 331 nm, which shifts to 361.8 nm upon reduction of the disulfide bonds and denaturation with 8 M urea, indicating that all four tryptophan residues in the native state of this protein are in a hydrophobic environment. The extent of quenching that is observed is highest with acrylamide, intermediate with succinimide, and low with Cs⁺ and I⁻, further supporting the idea that the tryptophan residues are predominantly buried in the hydrophobic core of the protein. The presence of MeGal (50 mM) affects the quenching only marginally. Time-resolved fluorescence measurements yield bi-exponential decay curves with lifetimes of 1.45 and 4.99 ns in the absence of sugar, and 1.36 and 4.8 ns in its presence. These results suggest that the tryptophan residues are not directly involved in the saccharide binding activity of the T. anguina lectin. Of the four quenchers employed in this study, the cationic quencher, Cs⁺, is found to be a very sensitive probe for the tryptophan environment of this lectin and may be useful in investigating the environment of partially buried tryptophan residues and unfolding processes in other proteins as well.     

The characterisation and application of a pulsed neodymium YAG laser DGV system to a time-varying high-speed flow

Doppler Global Velocimetry (DGV) is a whole-field measurement technique which has attracted significant interest from the fluid-flow research community since its introduction in 1991. Practical implementations of the methodology have focused on two principal laser light sources: the argon ion laser, applied to steady state or slowly varying flows; and the pulsed neodymium YAG laser for the measurement of instantaneous velocity fields. However, the emphasis in the published literature has been very much on research using the argon laser. This paper reports the application of a Q-switched, injection-seeded neodymium YAG laser to the proven Oxford DGV system, and the use of this combination in a short duration unsteady high-speed flow. The pertinent characteristics of the apparatus are described, and the impact of these on the integrity of the resulting velocity measurements is presented. Adaptations to the commercial laser system that make it suitable for application to the measurement of transient high-speed flows are described. Finally, the application of this system to a short duration unsteady flow is described. This application is based on the flow found in a new type of transdermal drug delivery device, where particles of the drug material are projected at high speed through the skin. Whole-field velocities are recorded, and values as high as 800 m/s are evident.