FLUORESCENCE QUENCHING OF ALLOPHYCOCYANIN AND PHYTOCHROME BY ESTRIOL*

Abstract— At 293 K the long-wavelength absorption and emission band of 1.4 μM allophycocyanin is decreased by estriol (Δ¹-³-⁵⁽¹⁰⁾-estratriene-3,16α, 17β-trio!) in the range 0.8-6.6 μM in the presence of 11% alcohol (vol/vol). The binding of estriol is shown to be of high affinity, 1:1 with allophycocyanin. The free energy of this binding process (ΔG^°) is -33.6 kJ mol' and single binding site dissociation constant (K_D) 1.0 ×10–6M. Estriol at 21 μM effectively quenches the fluorescence of 1.4 M large molecular weight phytochrome in its red absorbing form at 77 K while having little or no effect on the phototransformation difference spectrum at 293 K.     

QUENCHING OF CHLOROPHYLL FLUORESCENCE BY NITROBENZENE

Abstract—Nitrobenzene quenching of chlorophyll fluorescence in ethanol has been investigated. Steady state relative quantum yields have been measured and fluorescence decay rates were determined using both nanosecond photon counting and picosecond pulses from a mode-locked Nd³⁺ glass laser.
The fluorescence decay is described by
1( t )= I ₀ exp (- t/τ−At^1/2 )
the form predicted for decay governed by the kinetics of the continuum model of diffusion controlled reactions. From the parameters of the fluorescence decay, the encounter distance is 5–7 A° the mutual diffusion coefficient is 0.62 × 10^--⁵ cm2s^-1± 12%.
Some of the fluorescence quenching is also attributed to static quenching by a nitrobenzene-chlorophyll, ground-state complex. The equilibrium constant for formation of this ground-state complex was determined to be 4.1 M ^-1. The combined dynamic and static quenching model allows calculation of quantum yields of fluorescence in good agreement with the experimentally determined quantum yields.     

FLUORESCENCE QUENCHING OF INDOLE BY DIMETHYLFORMAMIDE

Abstract— The effect of dimethylformamide on the lifetime (T) and quantum yield ( F ) of indole has been determined. Negative Stern-Volmer deviations prevail for T and F , but F ⁰/ F T⁰/T at all DMF concentrations. The deviation between F ⁰/ F and T⁰/T is ascribed to changes in F ⁰ and T⁰ induced by the change in solvent composition at the higher quencher concentrations.     

DISTANCE-DEPENDENT FLUORESCENCE QUENCHING OF TRYPTOPHAN BY ACRYLAMIDE

Abstract We used GHz frequency-domain fluorometry to investigate the time-dependent intensity decays of N -acetyl -L-trytophanamide (NATA) when collisionally quenched by acrylamide in propylene glycol at 20°C. The intensity decays of NATA became increasingly heterogeneous in the presence of acrylamide. The NATA intensity decays were not consistent with the Collins-Kimball radiation boundary condition (RBC) model for quenching. The steady-state Stern-Volmer plots show significant upward curvature. At low temperature in vitrified propylene glycol (-60%), where translational diffusion cannot occur during the lifetime of the excited state, quenching of NATA by acrylamide was observed. The Smoluchowski and RBC quenching models do not predict any quenching in the absence of translational diffusion. Hence, these frequency-domain and steady-state data indicate a through-space quenching interaction between NATA and acrylamide. The rate for quenching of NAT A by acrylamide appears to depend exponentially on the fluorophore-quencher separation distance. Comparison of the time-resolved and steady-state data provides a sensitive method to determine the distance dependence of the fluorophore-quencher interaction. The distance-dependent rate of quenching also explains the upward curvature of the Stern-Volmer plot, which is often observed for quenching by acrylamide. These results suggest that the distance-dependent quenching rates need to be considered in the interpretation of quenching data of proteins by acrylamide.     

FREE ENERGY DEPENDENCE OF THE QUENCHING OF CHLOROPHYLL a FLUORESCENCE BY SUBSTITUTED QUINONES*

The quenching of chlorophyll a (Chl a) fluorescence hy a series of substituted benzoquinones. naphthoquinones and anthraquinones has been examined employing ethanol and acetonitrile as solvents. All quinones are good quenchers of fluorescence. There is an excellent linear relation between the Stern-Volmer quenching constants, K, and the polarographic half wave potentials (E₁₂) of the quinones, with more oxidizing quinones being better quenchers. The quenching data are consistent with the excited state half wave potential of ?1.31 eV predicted theoretically, demonstrating that the kinetically estimated value of the Chl a excited state reduction potential agrees with that expected on spectroscopic grounds. The results of quenching are not in agreement with the conventional Marcus theory of electron-transfer reactions, as there is no evidence of quenching constant. K_q. decrease vsΔG⁰ even for free energy changes nearly twice that expected for the onset of the Marcus inverted region. However, the kinetically estimated K_q values are in good agreement with the ones calculated by using the Rehm and Weller equation for fluorescence quenching by electron transfer. Our experimental results support the electron transfer mechanism of quenching proposed by Seely.     

FLUORESCENCE QUENCHING OF INDOLES BY N,N-DIMETHYLFORMAMIDE

Abstract. The quenching of the excited state of indoles by small polar molecules is believed to occur via the formation of excited state complexes. The rate of excited state complex formation of indoles with dimethylformamide is shown to be a function of the group appended to the indole ring at the 3- or 5-position. Substituents which can strengthen the charge transfer character of the exciplex are observed to enhance the rate of fluorescence quenching. In contrast to other amides, dimethylformamide appears to be a moderately good quencher of indole fluorescence, and may be a useful probe for proteins.     

FLUORESCENCE QUENCHING OF 10-METHYLACRJDINIUM CHLORIDE BY NUCLEOTIDES

Abstract— All nucleotides examined (AMP, GMP, TMP and CMP) quench the fluorescence or 10–methylacridinium chloride (10–MEAC). The fluorescence spectrum of 10–MEAC-nucleotide system is identical with that of 10–MEAC itself, and the fluorescence decay kinetics follow a single-exponential decay law. The dependence of fluorescence quantum yields and fluorescence lifetimes upon the concentration of nucleotides indicates that the fluorescence of 10–MEAC is greatly quenched in both dynamic and static processes by nucleotides. The quenching constants increase in the order: AMP ≳ GMP > TMP ≳ CMP. The results of 10–MEAC are compared with those of other acridine dyes (proflavine, 9–aminoacridine and acridine orange).     

QUENCHING OF INTRAMOLECULAR AMINE-HYDROCARBON EXCIPLEX FLUORESCENCE BY WATER

Abstract— The quenching of intramolecular exciplex fluorescence in 2,6-bis(methylamino)naphtha]ene, (II), 2,6-bis(/V-methyl, methylamino)naphthalene, (III) and 2,6-bis(N-dimethy], methylamino)naphthalene, (IV) by water was investigated. Exciplex fluorescence intensity decreased continuously with increase in water concentration; while monomer fluorescence intensity remained constant up to 25% of water, followed by a rapid increase in intensity.
Absorption spectra showed that specific interaction occurred between water and ground state amine molecules at high concentrations (25% by volume) of water. These observations were interpreted in terms of a static quenching involving the interaction of water with the ground-state amine and a dynamic quenching involving the interactions of water with the exciplex. Our observations explain the greater efficiency of exciplex-fluorescence quenching by protic polar solvents.     

QUENCHING OF THE FLUORESCENCE OF 8-METHOXYPSORALEN BY PROTONS

Abstract— The quenching of 8-methoxypsoralen (8-MOP) fluorescence by protons was observed to occur at the diffusion controlled rates in aqueous solutions at room temperature. Enhanced basicity of 8-MOP in the excited state compared to the ground state is expected on theoretical grounds. The fluorescence yield. which we determined as 6.3 × 10^--⁴ at pH 1 is surprisingly low and indicative of extremely fast radiationless decay pathways. The fluorescence lifetime of 8-MOP in neutral aqueous solution is on the order of 1–2 ns.     

磺化竹红菌素对蛋白质荧光猝灭机理的研究

本文详细研究了磺化竹红菌素对多种蛋白质在溶液状态下的荧光猝灭过程。结果表明,磺化竹红菌素对多种蛋白质荧光猝灭服从Stern-Volmer曲线,实验观察了温度、粘度、pH值和盐酸胍对荧光猝灭过程的影响。由于磺化竹红菌素是一两性分子,对于不同蛋白具有不同猝灭过程;磺化竹红菌素对蛋白质的荧光猝灭常数K_q在10¹³mol/L·s^-1左右,这说明,磺化竹红菌素是一种比其它蛋白质荧光猝灭剂更加有效的荧光猝灭剂。     

QUENCHING OF PYRENE FLUORESCENCE BY TRYPTOPHAN IN MICELLAR SOLUTIONS

Deactivation of excited pyrene incorporated to cationic (cetyltrimethylammonium chloride), anionic (sodium dodecyl sulfate) and neutral (Triton X-100) micelles by tryptophan has been investigated over a wide pH range. Data obtained allow an estimation of the tryptophan association to the micelles, of the tryptophan apparent p K in the micellar solutions, and of the dynamics of tryptophan incorporation to the micellar pseudophase. In particular, the data obtained at pH 7 allow an estimation of the effect of the micellar charge upon the binding capacity of the tryptophan zwitterion.     

咔唑荧光的猝灭

我们已报道咔唑和对苯二甲酸二甲酯(DMTP)不能生成激基复合物^[1],DMTP仅能猝灭咔唑的荧光。这一现象可用激发态的咔唑与猝灭剂之间形成氢键^[2]加以解释,也可以用激发态的咔唑中-NH基与猝灭剂的吸电性较强的侧基之间的相互作用解释^[3]。因此我们开展了下面的研究,实验结果表明,本文采用的体系,猝灭剂中侧基的吸电性对荧光猝灭有很大的影响.     

卤素离子对联有吖啶基三元共聚物薄膜的荧光猝灭

在合成了几种带不同组成比吖啶基三元共聚物的基础上,对其溶液和薄膜的吸收与荧光发光光谱进行了表征.研究了上述薄膜在含有卤素阴离子溶液中的荧光猝灭问题,发现含有不同吖啶组成比的薄膜对不同卤素离子具有不同的选择性,过多或过少吖啶含量的薄膜均对选择性的识别卤素阴离子不利,只有在某种特定组成条件下方能得到最佳、具有特征识别阴离子能力的薄膜器件.对所得结果进行了详细的讨论.     

烷基苄基铵对芘的荧光猝灭行为研究

广义的荧光猝灭系指所有能使荧光强度降低的物理和化学过程,但通常涉及的主要有动态猝灭和静态猝灭,二者均遵从Stern-Volmer方程,但由于猝灭作用本质不同,它们在荧光寿命变化、温度效应及吸收光谱等方面表现出差异可资区别.本文通过稳态荧光强度变化和荧光衰减速率的比较研究了具有不同烷基链长的十四烷基苄基二甲基氯化铵(Zeph)和苄基三甲基溴化铵(TMBA)对芘的荧光猝灭,并基于电导实验结果以及猝灭剂全反式构象从理论上计算了Zeph和TMBA的猝灭速率常数,讨论了荧光猝灭的性质和长链分子的构型。     

二溴苯基萤光酮-阳离子表面活性剂荧光熄灭法测定微量铌

本文研究了铌—二溴苯基萤光酮—阳离子表面活性剂三元体系的荧光特性,提出了以二溴苯基萤光酮-溴化十六烷基三甲铵荧光熄灭法测定铌的新方法。该方法的选择性和重现性好,采用适当的掩蔽剂,测定了铁矿中的微量铌,获得满意的结果。     

INTRAMICELLAR QUENCHING OF 2,3-DIMETHYLNAPHTHALENE FLUORESCENCE BY PEROXIDES and HYDROPEROXIDES

Hydrogen peroxide, t -butyl hydroperoxide, di- t -butyl peroxide and dibenzoyl peroxide efficiently quench the fluorescence of 2,3-dimethylnaphthalene incorporated into sodium dodecyl sulfate and cetyltrimethylammonium chloride micelles. Potassium persulfate only is effective when the probe is incorporated into a cationic micelle. The binding constant of the peroxides and the intramiccllar quenching rate constants have been evaluated for all the systems considered and the data are compared to that obtained in homogeneous solution. It is concluded that, even for processes which are not diffusion controlled, the quenching process is slower in the micelles.     

FLUORESCENCE QUENCHING OF PYRENE DERIVATIVES BY NITROXIDES IN MICROHETEROGENEOUS SYSTEMS

Abstract Fluorescence quenching of pyrene derivatives by 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidinyl-1-oxy and 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy has been measured in homogeneous solvents and microheterogeneous systems: cetyltrimethylammonium chloride micelles, large unilamellar vesicles of dioctadecyldimethylammonium chloride and dipalmitoylphosphatidylcholine (DPPC) and rat liver microsomes. The extent of intraaggregate quenching is mostly determined by the quencher incorporation to the micro-phases. In particular, it is observed that quenching by TEMPO in vesicles is considerably faster when the bilayer is in the liquid crystalline state. This significant increase in quenching rate with the melting of the bilayer is not observed for the other TEMPO derivatives, indicating that the effect of the lipid organization upon the solubility is related to the hydrophobicity of the solute. The data obtained in rat liver microsomes at 37°C show a pattern very similar to that observed in DPPC vesicles in the liquid crystalline state.     

硝酮化合物对9-氰蒽荧光猝灭作用的研究

本工作对硝酮化合物猝灭9-氰蒽荧光的机制进行了研究,发现不同的9-氰蒽/硝酮体系可能经历包括电子转移、能量转移及竞争吸收等不同的猝灭过程。其中α,N-二苯基硝酮对荧光猝灭遵循电子转移机制,分别形成猝灭剂和敏化剂的离子自由基,但硝酮正离子自由基不能导致环化反应发生,结果还表明：硝酮化合物的四π电子1,3偶极结构在猝灭过程中起主要作用,因此当光环化反应破环1,3偶极结构生成氧氮丙啶时,即失去其原有的猝灭能力,导致已被猝灭的荧光重新回复。