时间分辨激光荧光光谱分析技术研究——Ⅱ.微秒级时间分辨激光荧光光谱测量

本文主要以进行稀土元素分析为目的,在已建立的激光荧光寿命测量装置的基础上,建立了时间分辨激光荧光光谱测量装置。结合在此装置上取得的初步实验结果,对装置的原理、特点、使用范围、工作条件进行了讨论。为进行稀土元素的时间分辩激光荧光光谱分析建立了必要的手段,也为某些发光材料的发光动力学研究提供了一定的方法。     

Bioluminescence and exogenous compounds: physico-chemical basis for bioluminescent assay

Bioluminescent systems are convenient objects to study mechanisms of influence of exogenous molecules on living organisms. Classification of physical and physico-chemical mechanisms of the effects of luminous bacteria Photobacterium leiognathi on bioluminescent reactions is suggested. Five mechanisms are discussed: (1) change of electron-excited states' population and energy transfer, (2) change of efficiency of S-T conversion in the presence of external heavy atom, (3) change of rates of coupled reactions, (4) interactions with enzymes and variation of enzymatic activity, (5) nonspecific effects of electron acceptors. Effects of various groups of chemical compounds are discussed according to the classification suggested. The compounds are: a series of fluorescent dyes, organic oxidizers, organic and inorganic heavy-atom containing compounds, and metallic salts. Applications of fluorescence time-resolved and steady-state techniques, as well as bioluminescence kinetics study, are discussed. The patterns of exogenous compounds' influence form a physico-chemical basis for bioluminescent ecological assay.     

Time-resolved high-performance liquid chromatography fluorescence detector using a nanosecond pulsed light source for detecting lanthanide-chelated compounds

We have constructed a time-resolved fluorescence detection (TRFD) system for the analysis of amino compounds with high-performance liquid chromatography (HPLC) using lanthanide ion chelates. In order to carry out time-resolved measurements, we have employed a nanosecond pulsed xenon-arc lamp as an excitation light source. Amino compounds derivatized by isothiocyanobenzyl-EDTA (IEDTA) with the lanthanide chelate are mixed with an enhancer solution in a post-column manner and detected by TRFD. Taking advantage of a property of the long fluorescence lifetime of the lanthanide chelates, high selectivity against background fluorescence was achieved. In order to demonstrate the usefulness of TRFD, fundamental performance tests were carried out. Details of the system are also described.     

Time-resolved laser-induced fluorimetry for screening polycylic aromatic hydrocarbons on solid-phase extraction membranes

The potential of solid-phase extraction (SPE) time-resolved laser-induced fluorimetry (TRLIF) is evaluated for screening polycyclic aromatic hydrocarbons (PAHs) in aqueous samples. Octadecyl membranes are used with the dual purpose of extracting the pollutants from the water sample and serving as the solid substrate for fluorescence detection. Excitation of fluorescence is performed with a Nd:YAG pumped tunable dye laser pumped with a pulsed source for time-resolving spectral interference. Wavelength time matrices (WTMs) and real time-resolved fluorescence spectra are recorded with a pulsed delay generator, a spectrograph and an intensified charge-coupled device (ICCD). In comparison to SPE solid-matrix luminescence (SML) with conventional instrumentation, this approach provides better limits of detection (LOD) and selectivity. The improvement in LOD is of one order of magnitude, reaching the parts-per-trillion level with 10 ml of water sample. The improvement in selectivity allows the direct determination of target compounds in complex samples. The direct determination of benzo[a]pyrene from a spiked river water sample of unknown composition is presented.     

Semiempirical formula for the estimation of organic radical ion mobility in liquid n-alkanes

The mobilities of radical ions of a series of organic compounds in n-alkanes with viscosities within the range of 0.2-4 cP were determined by applying the method of time-resolved electric field effect. The obtained data were used to express the correlation between the mobilities and solvent viscosity in the form of the modified Stokes-Einstein relation. The relation was parametrized in such a way that the specific molecular properties of both solvent and solute appear in the expression only as the ratio of the volumes of their molecules. A significant difference between aromatic and aliphatic compounds was found with respect to the dependence of radical ion mobility on this volume ratio, and two different parametrizations were suggested for mobility estimation in these cases.     

Organic analysis by luminescence methods

This review presents the major features of luminescence methods relating to the estimation of organic compounds in solution. A notation for reporting fluorimetric determinations is proposed. The outstanding factors affecting the fluorescence of solutions are briefly reviewed, and determinations of compounds offering a native fluorescence are illustrated by selected examples. Special attention is paid to functional fluorimetry and to the determination of non-fluorescent compounds by means of chemical reactions giving rise to fluorescent species. Some enzymatic reactions are described, as far as they allow the estimation of definite chemicals. Phosphorimetry and chemiluminescence are exemplified. An appendix presents some new functional fluorimetric determinations developed by the authors.     

Estimation of unsaturated hydrocarbon pollutants in air based on selective gas chromatography with ozone

Regular monitoring of toxic organic pollutants in air is a very important issue in environmental pollution control. Among these, unsaturated hydrocarbon pollutants (UHP) such as ethylene and beta-propylene and another 18 olefins are of prime importance. A very fast method for the individual identification of UHPs in air is proposed. This method is based on gas-chromatographic separation with selective detection of unsaturated organic compounds (UOC) and on the chemical reaction of UOC with ozone in the gas phase. In view of the mathematical model derived for this ozonation process, a comparison of FID-chromatogram and ozonogram can be carried out for identification of the contaminants. This identification can be performed without preliminary separation in the presence of the main components. The method provides a high sensitivity (< 0.005 to 0.72 mass %) and selectivity.     

X-ray fluorescence determination of bromine in halogenated organic compounds using quasisolid emitters

A series of quasi-solid emitters is proposed for the X-ray fluorescence determination of bromine in different bromine-containing compounds. It is shown that sucrose-based glasses are the best emitters for analyzing alkali solutions of halogenated organic compounds, saccharose-based glasses and polymer films are best for analyzing powder samples, and organic gels offer most promise for analyzing liquid (at normal conditions) samples. It is noted that the proposed method can expand the possibilities of commercially produced element analyzers, which are currently intended for determining only C, H, O, N, and S in organic compounds and cannot be used for determining halogens.     

Statistical Model for Organic Chromatographic Trace Analysis of Complex Samples. A Case Study: Plant Extracts

Abstract

The use of pooled plant extracts is described in the estimation of matrix interference in HPLC (UV and EC) determinations of organic compounds in plant extracts. An extract from freeze dried leaves of 134 different plant species was used for this purpose. It was split in different subgroups with solid extraction clean-up procedures. UV, EC and chromatographic data of the subgroups were used in the calculation of minimum concentrations of organic compounds which are still accurately determinable in plant samples with HPLC methods. The UV and/or EC characteristics of the compound must be known. The contribution of the solid phase extraction procedures and of the analytical system to the selectivity of the method can be estimated. Information is also supplied which allows rapid comparison of the selectivity of the UV and EC (single, or dual parallel) detectors for the determination of a specified compound.     

Estimation of unsaturated hydrocarbon pollutants in air based on selective gas chromatography with ozone

Regular monitoring of toxic organic pollutants in air is a very important issue in environmental pollution control. Among these, unsaturated hydrocarbon pollutants (UHP) such as ethylene and β-propylene and another ¶18 olefins are of prime importance. A very fast method for the individual identification of UHPs in air is proposed. This method is based on gas-chromatographic separation with selective detection of unsaturated organic compounds (UOC) and on the chemical reaction of UOC with ozone in the gas phase. In view of the mathematical model derived for this ozonation process, a comparison of FID-chromatogram and ozonogram can be carried out for identification of the contaminants. This identification can be performed without preliminary separation in the presence of the main components. The method provides a high sensitivity (< 0.005 to 0.72 mass %) and selectivity.     

Photoinduced intramolecular charge transfer of sodium 4-(N,N-dimethylamino) benzenesulfonate

A new dual fluorescent N,N-dimethylaniline derivative, sodium 4-(N,N-dimethylamino)-benzenesulfonate (SDMAS), is reported. In SDMAS, the electron acceptor is linked to the phenyl ring via a sulfur atom at the para-position of the electron donor. It was found that SDMAS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as formamide, methanol and acetonitrile. In organic solvents only a single-band emission at ca.360 nm was observed in the short wavelength region. The dual fluorescence of SDMAS in water was found at 365 and 475 nm, respectively. Introduction of organic solvent such as ethanol, acetonitrile, and 1,4-dioxane into aqueous solution of SDMAS leads to blue-shift and quenching of the long-wavelength emission. Measurements of steady-state and picosecond time-resolved fluorescence indicate that the long wavelength fluorescence is emitted from a charge transfer (CT) state that is populated from the locally excited (LE) state, with the latter giving off the     

Spectral properties and G-quadruplex DNA binding selectivities of a series of unsymmetrical perylene diimides

A series of new unsymmetrical perylene diimides have been synthesized to investigate their binding selectivities to G-quadruplex DNA structure, a unique four-stranded DNA motif, which is significant to the regulation of telomerase activity. The structures of the perylene diimides have been characterized by IR spectrophotometer, ¹H NMR, ¹³C NMR, MS, TGA and time-resolved instruments. Spectrochemical behaviors have been investigated by visible absorption and fluorescence emission spectra. The spectral characterization of the compounds has been investigated in five common organic solvents of different polarity and in water (in 170 mM phosphate buffer at pH 6). Marked red shifts of absorbance and fluorescence emission bands of the compounds in aqueous solution are compared with the other organic solutions. The fluorescence quantum yields are determined low in more polar solvents and also calculated to be about less than about 0.05 in aqueous solution because of the aggregation effects. Photodegradation rate constants (k_p) of the synthesized compounds have been compared under xenon lamp irradiation in acetonitrile solution.Binding abilities of the synthesized perylene diimides to different form of DNA strands have been investigated by visible absorption and fluorescence spectroscopy in the phosphate buffer solutions. Also, pH-dependent aggregation and G-quadruplex DNA binding selectivity of these ligands have been compared. Among these ligands, N-(2,6-diisopropylphenyl)-N′-(4-pyridyl)-perylene-3,4,9,10-tetracarboxylic diimide (PYPER) has been found to be the most selective interactive ligand for G-quadruplex formed in the G4′-DNA structure. PYPER has shown a significant selectivity to G4′-DNA which is comprised of d(TTAGGG) repeats, known as human telomeres, in the phosphate buffer at pH 6. The absorption maximum of the PYPER/G4′-DNA complex has given bathochromic shift of 7 nm with respect to the absorption maximum of DNA-free solution of PYPER in phosphate buffer at pH 6. Fluorescence quenching experiments between PYPER and G4′-DNA show that PYPER demonstrates about a 9.3-fold selectivity for binding to G4′-DNA versus ds-DNA base pairs with the bimolecular rate constant of 0.95 × 10¹² M⁻¹ s⁻¹.     

Fluorescence analysis in air pollution research

Luminescence phenomena are of value in the analysis of air pollutants. The problems arising in the use of excitation and emission spectra under various conditions are discussed. Phenomena such as solvent, pH, and photochemical effects are shown to play an important role in the fluorimetric analysis of air pollutants. Many of the fluorimetric methods used in the trace analysis of organic airborne particulates involve factors such as direct measurement of the separated pollutant on a chromatogram or pherogram, quenching phenomena, scanning, excimer formation, charge-transfer fluorescence, sensitized fluorescence, and photo-oxidation on adsorbent or in solution. In addition, fluorescence assay methods are discussed in terms of selectivity, sensitivity, speed, simplicity, accuracy, precision, interferences, and the relation between concentration and fluorescence intensity.     

Application of long-lived luminescence for detection in liquid chromatography

Summary Quenched and sensitized lanthanide luminescence as detection in liquid chromatography has been investigated. An important advantage in comparison with phosphorescence is that the long-lived luminescence as applied does not require deoxygenation of the samples. In order to obtain a high luminescence intensity Tb(III) complexes with acetylacetonate have been formed, after which indirect excitation of Tb(III) can be realized via the ligands. The potential of Tb(III) luminescence as a detection method in ion chromatography has been shown for chromate, which is an efficient quencher. Sensitizing of the Tb(III) luminescence has been applied for thiol-containing analytes. These compounds are derivatized with maleimidyl salicylic acid to complexes that sensitize the Tb(III) luminescence. From a comparison of the results obtained with normal fluorescence detection and time-resolved sensitized Tb(III) luminescence detection it has become clear that the last method has a higher sensitivity, but in particular a higher selectivity.     

Ultrafast time-resolved study of photophysical processes involved in the photodeprotection of p-hydroxyphenacyl caged phototrigger compounds

A combined femtosecond Kerr gated time-resolved fluorescence (fs-KTRF) and picosecond Kerr gated time-resolved resonance Raman (ps-KTR(3)) study is reported for two p-hydroxyphenacyl (pHP) caged phototriggers, HPDP and HPA, in neat acetonitrile and water/acetonitrile (1:1 by volume) solvents. Fs-KTRF spectroscopy was employed to characterize the spectral properties and dynamics of the singlet excited states, and the ps-KTR(3) was used to monitor the formation and subsequent reaction of triplet state. These results provide important evidence for elucidation of the initial steps for the pHP deprotection mechanism. An improved fs-KTRF setup was developed to extend its detectable spectral range down to the 270 nm UV region while still covering the visible region up to 600 nm. This combined with the advantage of KTRF in directly monitoring the temporal evolution of the overall fluorescence profile enables the first time-resolved observation of dual fluorescence for pHP phototriggers upon 267 nm excitation. The two emitting components were assigned to originate from the (1)pipi (S(3)) and (1)npi (S(1)) states, respectively. This was based on the lifetime, the spectral location, and how these varied with the type of solvent. By correlating the dynamics of the singlet decay with the triplet formation, a direct (1)npi --> (3)pipi ISC mechanism was found for these compounds with the ISC rate estimated to be approximately 5 x 10(11) s(-)(1) in both solvent systems. These photophysical processes were found to be little affected by the kind of leaving group indicating the common local pHP chromophore is largely responsible for the fluorescence and relevant deactivation processes. The triplet lifetime was found to be approximately 420 and 2130 ps for HPDP and HPA, respectively, in the mixed solvent compared to 150 and 137 ns, respectively, in neat MeCN. The solvent and leaving group dependent quenching of the triplet is believed to be associated with the pHP deprotection photochemistry and indicates that the triplet is the reactive precursor for pHP photorelease reactions for the compounds examined in this study.     

Thermally activated delayed fluorescence molecules and their new applications aside from OLEDs

Thermally activated delayed fluorescence molecules (TADF) molecules have been found to undergo efficient intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes, which benefit their successful applications in organic light emitting diodes (OLEDs). Due to their long-lived delayed fluorescence, TADF molecules can also be applied in time-resolved luminescence imaging. Besides their special singlet properties, their excited triplet characteristics provide their potential applications in triplet-triplet annihilation upconversion (TTA-UC), photodynamic therapy (PDT) and organic photocatalytic synthesis by used as a triplet photosensitizer.     

Thermally activated delayed fluorescence molecules and their new applications aside from OLEDs

Thermally activated delayed fluorescence (TADF) organic molecules feature with long-lived delayed fluorescence, because they can undergo not only efficient intersystem crossing (ISC), but also efficient reverse intersystem crossing (RISC) at room temperature. As a new type of luminescent molecules, they have exhibited successful applications in organic light emitting diodes (OLEDs). Aside from OLEDs, they are also found to have potential applications in time-resolved luminescence imaging based on long-lived fluorescence property. Meanwhile, due to their excited triplet characteristic originated from efficient ISC, they were found to be applied in triplet-triplet annihilation upconversion (TTA-UC), photodynamic therapy (PDT) and organic photocatalytic synthesis. This review briefly summarizes the characteristics and excellent photophysical properties of TADF organic compounds, then covers their applications to date aside from OLEDs based on their highly efficient ISC ability and RISC ability at room temperature.     

Simplified method of the quantum chemical analysis for determination of thermodynamic parameters of 2D cluster formation of amphiphilic compounds at the air/water interface

A simplified method is proposed to estimate the thermodynamic parameters of clusterization at the air/water interface for various classes of amphiphilic compounds with a single alkyl chain. The method is based on the calculation of thermodynamic characteristics only for one of the homologous series of dimers (n=6-16) governing the formation of infinite clusters. The method is used to calculate the thermodynamic parameters of clusterization for alcohols, thioalcohols, carboxylic acids and amines, and the dependencies of the Gibbs energy of clusterization on the alkyl chain length are evaluated. It is shown that the alkyl chain length, at which the spontaneous clusterization begins, as calculated using the proposed simplified method, is in fact the same as that calculated using the additive scheme developed earlier. The simplified method proposed was verified using alkylnitriles as example. In contrast to alcohols, thioalcohols and amines, infinite 'rhombic' clusters are formed rather than 'rectangular' clusters for this class of compounds. Spontaneous clusterization of nitriles is shown to start for alkyl chains containing 18-19 carbon atoms. This value agrees with that obtained from experimental data with 17-18 carbon atoms. The proposed simplified method introduces an exact and suitable tool for the estimation of thermodynamic parameters of the clusterization of amphiphilic compounds.     

Polymer‐coated Boron Doped Diamond Optically Transparent Electrodes for Spectroelectrochemical Sensors

Spectroelectrochemical sensors combine electrochemistry, spectroscopy, and partitioning into a film to provide improved selectivity for the target analyte. The sensor usually consists of an optically transparent electrode (OTE) coated with a charge selective polymer film. The polymer film is chosen to pre‐concentrate analyte at the OTE surface to improve the sensitivity and provide selectivity against like charged interferences. OTEs such as Indium Tin Oxide (ITO) have been used extensively for spectroelectrochemical sensors, but little is known about the applicability of such sensors using other OTE materials, such as Boron Doped Diamond (BDD). One distinct advantage of BDD OTEs over ITO OTEs is their significant increase in sensitivity for organic compounds, such as 4‐aminophenol and hydroquinone. We have developed absorption and fluorescence‐based sensing methods with a BDD OTE coated with a sulfonated ionomer film, Nafion. This is demonstrated with tris(2,2′‐bipyridyl)ruthenium(II) ion [Ru(bpy)₃²⁺] using an attenuated total reflectance (ATR) flow cell setup for both absorption and fluorescence. With a Nafion coated BDD optically transparent thin layer electrode (OTTLE), we developed a fluorescence based sensor for a common polyaromatic hydrocarbon (PAH), 1‐hydroxypyrene (1‐pyOH), achieving a detection limit of 80 nM (17 ppb). This work manifests new sensing applications while broadening the use of spectroelectrochemistry, OTEs, and BDD as an electrode material.     

A close look at fluorescence quenching of organic dyes by tryptophan.

Understanding fluorescence quenching processes of organic dyes by biomolecular compounds is of fundamental importance for in-vitro and in-vivo fluorescence studies. It has been reported that the excited singlet state of some oxazine and rhodamine derivatives is efficiently and almost exclusively quenched by the amino acid tryptophan (Trp) and the DNA base guanine via photoinduced electron transfer (PET). We present a detailed analysis of the quenching interactions between the oxazine dye MR121 and Trp in aqueous buffer. Steady-state and time-resolved fluorescence spectroscopy, together with fluorescence correlation spectroscopy (FCS), reveal three contributing quenching mechanisms: 1) diffusion-limited dynamic quenching with a bimolecular quenching rate constant k(d) of 4.0 x 10(9) s(-1) M(-1), 2) static quenching with a bimolecular association constant K(s) of 61 M(-1), and 3) a sphere-of-action contribution to static quenching described by an exponential factor with a quenching constant lambda of 22 M(-1). The latter two are characterized as nonfluorescent complexes, formed with approximately 30 % efficiency upon encounter, that are stable for tens of nanoseconds. The measured binding energy of 20-30 kJ mol(-1) is consistent with previous estimates from molecular dynamics simulations that proposed stacked complexes due to hydrophobic forces. We further evaluate the influence of glycerol and denaturant (guanidine hydrochloride) on the formation and stability of quenched complexes. Comparative measurements performed with two other dyes, ATTO 655 and Rhodamine 6G show similar results and thus demonstrate the general applicability of utilizing PET between organic dyes and Trp for the study of conformational dynamics of biopolymers on sub-nanometer length and nanosecond time-scales.