Static and dynamic quenching of Ru(II) polypyridyl excited states by iodide

The metal-to-ligand charge-transfer (MLCT) excited states of Ru(bpy)(2)(deeb)(PF(6))(2), where bpy is 2,2-bipyridine and deeb is 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-bipyridine, in dichloromethane were found to be efficiently quenched by iodide at room temperature. The ionic strength dependence of the UV-visible absorption spectra gave evidence for ion pairing. Iodide was found to quench the excited states by static and dynamic mechanisms. Stern-Volmer and Benesi-Hildebrand analysis of the spectral data provided a self-consistent estimate of the iodide-Ru(bpy)(2)(deeb)(2+) adduct in dichloromethane, K = 59 700 M(-1). Transient absorption studies clearly demonstrated an electron-transfer quenching mechanism with transient formation of I(2)(*)(-) in high yield, phi = 0.25 for 355 or 532 nm excitation. For Ru(bpy)(2)(deeb)(PF(6))(2) in acetonitrile, similar behavior could be observed at higher iodide concentrations than that required in dichloromethane. The parent Ru(bpy)(3)(2+) compound also ion pairs with iodide in CH(2)Cl(2), and light excitation gave a higher I(2)(*)(-) yield, phi = 0.50. X-ray crystallographic, IR, and Raman data gave evidence for interactions between iodide and the coordinated deeb ligand in the solid state.     

Pyrene fluorescence in the presence of nonquenching and dynamic quenching salting-out agents

A new, simple, and rapid method to determine Setschenow (i.e., salting-out) constants for luminescent organic compounds in aqueous solutions has been developed using steady-state and time-resolved fluorescence measurements. Application of the new method was demonstrated using pyrene in the presence of nonquenching (K⁺) and dynamically quenching (Cs⁺) akali metal chloride salt solutions at room temperature. For these two model systems, Setschenow constants for pyrene salting-out by KCl and CsCl were determined to be 0.211 and 0.355 M⁻¹, respectively. We expect that the methodology reported in this paper can be applied equally well to interactions between a variety of salting-out agents and fluorescent biological and/or environmental molecules in aqueous solutions.     

Pyrene fluorescence quenching by aromatic azides

Pyrene fluorescence quenching by phenylazide derivatives with donor and acceptor substituents has been studied by fluorescence spectroscopy and flash photolysis. The rate constants of quenching (k _q) in acetonitrile ((0.2–1.2) × 10¹⁰ l mol^?1 s^?1) are found to be close to a diffusion limit; the rate constants were somewhat higher for perfluoro-substituted arylazides. It is found that k _q does not depend on solvent polarity; the formation of the pyrene cation in the course of pyrene fluorescence quenching by tolylazide was not detected. Pyrene fluorescence quenching occurred by an energy-transfer mechanism; this is supported by the coincidence of the quantum yields of the direct and sensitized photodecomposition of tolylazide. As estimated, energy transfer in rigid media occurs at characteristic distances of about 10 Å.     

Static luminescence quenching by oxygen and nitric oxide for phenanthrene in glassy matrices

Steady-state and pulsed methods have been applied to static phosphorescence and fluorescence quenching for phenanthrene caused by oxygen and nitric oxide. The characteristic fluorescence quenching distances have been determined for oxygen (8.7±0.5 Å) and nitric oxide (8.9±0,5 Å); the phosphorescence quenching involves an exchange mechanism, and measurements have been made on the characteristic quenching distances R₀ and exchange-interaction attenuation parameters L. Estimates have been made on the rate constants for dynamic quenching of the triplet excited states of phenanthrene in low-viscosity liquids, which agree well with the measured values for hexane.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 667–672, November–December, 1988.     

荧光猝灭法测定次黄嘌呤及机理研究

研究了次黄嘌呤猝灭伊文思蓝的荧光猝灭机理并根据次黄嘌呤对伊文思蓝荧光的猝灭作用建立了测定次黄嘌呤的新方法.线性回归方程为:ρ=6.292×103F-1-26.49,相关系数为0.9990,线性范围为0.20～20.0 μg/mL,检出限为0.14 μg/mL,相对标准偏差(RSD)为2.5%.求算了伊文思蓝与次黄嘌呤的形成常数K=2.63×102L/moL,实验了pH、放置时间、干扰离子等对测定的影响.     

Discovery and characterization of catalysts for azide-alkyne cycloaddition by fluorescence quenching

Copper-based catalysts for the 1,3-dipolar cycloaddition of azides and alkynes were screened in parallel fashion using a fluorescence quenching assay. The method was designed to identify systems able to accelerate the coupling of reactants at micromolar concentrations in aqueous mixtures and to obtain quantitative comparisons of their activities. In addition to the tris(triazolylamines) previously reported, two types of compounds (bipy/phen and 2-pyridyl Schiff bases) were found to exhibit significant ligand-accelerated catalysis, with one complex showing especially dramatic rate enhancements. Preliminary explorations of the dependence of reaction rate on pH, ligand:Cu ratio, and Cu concentration are described.     

Long-range perylene fluorescence quenching by electron acceptors

Diffusion-controlled fluorescence quenching for perylene by dinitrobenzene has been examined; Smoluchowski's equation does not apply. The reaction radius R in relatively viscous solvents (isopropanol and benzonitrile) exceed the contact radius by more than a factor two. R decreases as the mutual diffusion coefficient D increases. The in D dependence for R has been used to determine the electron-tunneling parameters. The Frank-Condon factors increase with the electron-acceptor strength. Electron-tunneling barrier heights from excited perylene to the oxidizing agent have been calculated. It is concluded that virtual solvent states are involved.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 672–677, November–December, 1988.We are indebted to G. P. Gurinovich, Corresponding Member, Belorussian Academy of Sciences, for support in this work and for providing facilities for the measurements, and to Professor A. I. Burshtein for discussion.     

Dynamic and static quenching of fluorescence by 1-4 nm diameter gold monolayer-protected clusters

How the efficiency of molecular quenching by Au nanoparticles depends on nanoparticle size is reported for (a) dynamic (collisional) quenching of four different fluorophores by three Au nanoparticles having similar protective layers but differing core diameters (1.1, 1.6, and 2.0 nm) and (b) static quenching in the electrostatic association between [Ru(bpy)3]2+ and five tiopronin-protected Au nanoparticles having core diameters from 1.3 to 3.9 nm. The quenching constants systematically increase with core size. In (a), the dynamic constants scale with the molar absorbance coefficients of the nanoparticles, showing the essentially of the absorbance/emission spectral overlap, and the associated nanoparticle core density of electronic states, in energy-transfer quenching. In (b), the fluorescence of the Au nanoparticle itself was enhanced by energy transfer from the [Ru(bpy)3]2+ fluorophore.     

基于荧光猝灭原理的光纤化学传感器定量分析模 型的建立与应用

根据光纤化学传感器的结构与信号传输特征,推导并建立了适合于定量描述基于荧光猝灭原理的光纤化学传感器对待测物响应的非线性数学模型。以此为基础,为更加简捷、直观地反映响应信号与待测物浓度的函数关系,建立可线性化的回归方程,准确预报待测物的浓度,提出了多模型回归技术建立此类光纤化学传感器定量分析模型的方法。为难定量分析模型的适用性,将该法应用于芘丁酸光纤化学传感器对甲硝唑、呋喃妥因和氧氟沙星等待测物响应的最佳数学模型的选择之中。结果表明,所选的数学模型对各待测物在一定范围内的浓度都能进行准确的预报。     

四溴荧光素荧光猝灭法测定司帕沙星

基于司帕沙星能够猝灭四溴荧光素的荧光且荧光猝灭程度与司帕沙星的量成正比,建立了一种测定微量司帕沙星的方法。在pH3．5的Clark—Lubs缓冲溶液中,四溴荧光素激发波长λex=485nm、发射波长λem=545nm,司帕沙星的质量浓度在0～2．0mg／L范围内符合比耳定律,方法检出限为42．7μg/L。已用于片剂及胶囊中司帕沙星的测定。6次平行测定回收率为93．8％～104．3％,相对标准偏差为1．1％～2．8％。     

Stimulated fluorescence and fluorescence quenching in chlorophyll a and bacteriochlorophyll a

This communication deals with the photophysical processes that take place in chlorophyll solutions under intense nitrogen laser irradiation. The effect of the pump photon density on the fluorescence yield depends strongly on the geometry of the irradiation and the sampling set-up. If the fluorescence cell and sampling probe are placed close to the transverse arrangement used for obtaining laser output, line narrowing and gain, which are processes associated with high population inversions and stimulated fluorescence, are observed. A normal fluorescence spectrum and a decrease in fluorescence quantum yield with increasing pump power are observed in the fluorescence cells in oriented at an angle of 20–40° with respect to the transverse axis of the exciting beam. The decrease in quantum yield appears to result from absorption of the pump photons by the excited singlet of the chlorophylls, and it is suggested that an analogous mechanism may be responsible for the anomalous fluorescence quantum yield reported for in in vivo Chlorella vulgaris algae.     

The mechanism of riboflavin fluorescence quenching by nucleophiles

It is shown that the quenching of riboflavin (RF) fluorescence by nucleophiles, i.e., sulfite-, nitrite-, thiocyanate-, iodide-, and bromide ions, occurs by both a dynamic and static mechanism. The constants of quenching excited RF by anions and the constants of equilibrium of RF in the ground state and anions are determined. The formation of RF radicals in the presence of low concentrations of nucleophiles is revealed using flash photolysis.     

Flow injection determination of nitrite by fluorescence quenching

A simple, sensitive and selective fluorimetric method for the determination of nitrite ion in waters using a merging zones flow injection system is described. The fluorimetric determination is based on the measurement of the quenching effect produced by nitrite on proflavine (3,6-diaminoacridine) fluorescence (λ_ex/λ_em=290/519 nm).

The optimum experimental conditions were investigated by merging 0.5 ml of the sample and 0.5 ml of a solution of 5 mg l⁻¹ of proflavine (in 0.1 M HCl) in a flow injection system, on-line connected to a flow-cell placed in the conventional sample compartment of a spectrofluorimeter. The selected carrier solution and final flow rate were 0.1 M HCl and 0.5 ml min⁻¹, respectively. A reaction coil of 2 ml was used. As a result of the simplicity of this system, a sample throughput of about 50 samples h⁻¹ can be achieved with the proposed methodology.

The detection limit was 1.1 ng ml⁻¹ (3σ criterion) of nitrite. The repeatability for five sample injections containing 100 ng ml⁻¹ of nitrite was ±0.3% and the observed linear range extended up to 400 ng ml⁻¹. Also, the effect of interferences from various metals and anions commonly present in waters was also studied.

The method was successfully applied to the determination of low levels of nitrite in different water samples (river, fountain, tap and commercial drinking waters).     

High-efficiency fluorescence quenching of conjugated polymers by proteins

The fluorescence of the water-soluble anionic conjugated polymer, poly[lithium 5-methoxy-2-(4-sulfobutoxy)-1,4-phenylenevinylene] (MBL-PPV), is quenched in dilute aqueous solution by cytochrome c, a small, naturally occurring electron-transfer protein. The large value obtained for the Stern-Volmer constant (K(sv) = 3.2 x 10(8) at pH 7.4, and approximately 10(9) in acidic solutions) is attributed to a combination of two factors: (1) facile ET between the luminescent semiconducting polymer and the protein and (2) the Columb attraction between the oppositely charged polyelectrolytes. This system shows significant potential for biosensor applications.     

Orientation effects in fluorescence quenching for adsorbed aromatic hydrocarbons

Fluorescence quenching by a potential electron donor or acceptor has been examined for an aromatic hydrocarbon adsorbed on aerosil, for which unusual temperature effects have been observed, where the process is dependent on the nature of the quencher. These phenomena are examined in terms of reaction stereospecificity. By this is meant the resultant displacement from a series of jumps between localization positions. Surface Chemistry Institute, Ukrainian National Academy of Sciences, Prospekt Nauki 31, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 12–16, January–February, 1997.     

荧光淬灭法测定食品中的硼砂残留量

基于硼砂对姜黄素的荧光强度有显著的淬灭作用,建立了一种简单、快速、灵敏的测定食品中硼砂的新方法,选择了最佳实验条件,并将此方法用于面条、茶叶和腐竹中硼砂的测定,平均回收率为99.2%,相对标准偏差为1%。     

Stereoselective fluorescence quenching by photoinduced electron transfer in naphthalene-amine dyads

Intramolecular chiral recognition in electron-transfer-induced fluorescence quenching has been observed for diastereomeric dyads composed of a naphthalene chromophore and an amine.     

Probing the interaction between fluorophores and DNA nucleotides by fluorescence correlation spectroscopy and fluorescence quenching

We have investigated the association interactions between the fluorescent dyes TAMRA, Cy3B and Alexa-546 and the DNA deoxynucleoside monophosphates by means of fluorescence quenching and fluorescence correlation spectroscopy (FCS). The interactions of Cy3B and TAMRA with the nucleotides produce a decrease in the apparent diffusion coefficient of the dyes, which result in a shift toward longer times in the FCS autocorrelation decays. Our results with Cy3B demonstrate the existence of Cy3B-nucleotide interactions that do not affect the fluorescence intensity or lifetime of the dye significantly. The same is true for TAMRA in the presence of dAMP, dCMP and dTMP. In contrast, the diffusion coefficient of Alexa 546 remains practically unchanged even at high concentrations of nucleotide. These results demonstrate that interactions between this dye and the four dNMPs are not significant. The presence of the negatively charged sulfonates and the bulky chlorine atoms in the phenyl group of Alexa 546 possibly prevent strong interactions that are otherwise possible for TAMRA. The characterization of dye-DNA interactions is important in biophysical research because they play an important role in the interpretation of energy transfer experiments, and because they can potentially affect the structure and dynamics of the DNA.     

A sensitive method for the detection of proteins by high-efficiency fluorescence quenching

A successful method for the detection of electron transfer proteins such as cytochrome c, hemoglobin and myoglobin has been developed based on the fluorescence quenching of semiconductor nanocrystals. High sensitivity and a good linear relationship are obtained.