品红甲亚胺染料影像光稳定性的研究 Ⅱ.抗氧化剂猝灭单重态氧的反应速率常数测定

本文利用高效液相色谱法测定了色满类,双螺色满类,对一甲氧基苯酚类和双螺茚类抗氧化剂与单重态氧反应的物理猝灭速率常数和化学猝灭速率常数。实验结果表明,抗氧化剂猝灭单重态氧的过程以物理猝灭为主,物理猝灭速率常数和总猝灭速率常数愈大,品红甲亚胺染料的防褪色效果愈好,但存在一极限褪色率。     

5%Al-Zn-0.1%RE合金非晶带的研究

用急冷法制取５％Ａｌ－Ｚｎ－０．１％ＲＥ合金薄带,通过Ｘ射线衍射,差式量热扫描和高分辨透射电子显微镜观察表明,这种合金薄带为纳米晶粒弥散的非晶合金。对不同冷却速度得到的合金薄带进行观察比较,发现冷却速度越快得到的合金晶粒越差,在低冷却速度下反而容易获得室温下稳定的纳米晶粒弥散的非晶合金,而且晶粒细化。     

单重态氧化学VII. 迷迭香中主要抗氧化成分对单重态氧的猝灭作用

本文研究了迷迭香酚和鼠尾草酚对单重态氧的猝灭作用。实验证明迷迭香酚和鼠尾草酚在甲醇中猝灭单重态氧的总速率常数K~A分别为2.51×10^7和7.19×10^6mol^1.dm^-3.s^-1, 其中化学猝灭的速率常数k~r分别为1.27×10^7和9.82×10^5mol.dm^-3.s^-1, 相应的半猝灭浓度β值为4.6×10^-3和1.6×10^-2mol.dm^-3。这是一类有实用价值的高效抗氧化剂。     

The fluorescence quenching rate constant for the distance-dependent quenching processes in the presence of diffusion

It is shown that the fluorescence quenching constant is given by the Laplace transform of the time-dependent bimolecular rate constant k(t). The dependence of the quenching rate constant on the transformation parameter can be obtained from measurements of the fluorescence decay functions and a Stern-Volmer-type analysis in the Laplace domain. The advantages of this type of investigation of the quenching rate function are demonstrated by a numerical calculation for the distance-dependentquenching process in     

Fluorescence quenching of CdS quantum dots by 4-azetidinyl-7-nitrobenz-2-oxa-1,3-diazole: a mechanistic study

Fluorescence quenching of CdS quantum dots (QDs) by 4‐azetidinyl‐7‐nitrobenz‐2‐oxa‐1,3‐diazole (NBD), where the two quenching partners satisfy the spectral overlap criterion necessary for Förster resonance energy transfer (FRET), is studied by steady‐state and time‐resolved fluorescence techniques. The fluorescence quenching of the QDs is accompanied by an enhancement of the acceptor fluorescence and a reduction of the average fluorescence lifetime of the donor. Even though these observations are suggestive of a dynamic energy transfer process, it is shown that the quenching actually proceeds through a static interaction between the quenching partners and is probably mediated by charge‐transfer interactions. The bimolecular quenching rate constant estimated from the Stern–Volmer plot of the fluorescence intensities, is found to be exceptionally high and unrealistic for the dynamic quenching process. Hence, a kinetic model is employed for the estimation of actual quencher/QD ratio dependent exciton quenching rate constants of the fluorescence quenching of CdS by NBD. The present results point to the need for a deeper analysis of the experimental quenching data to avoid erroneous conclusions.     

烷烃和胺类分子对电子激发态CH(A~2Δ和B~2Σ~-)自由基猝灭

用266nm激光光解CHBr_3分子产生CH(A,B)态自由基,通过测量CH(A,B→X)自发辐射的时间分辨信号测定室温下(CH_3)_2NH、(C_2H_5)_2NH、(C_2H_5)_3N、n-C_5H_(12)、n-C_6H_(14)和n-C_7H_(16)对CH(A,B,v'=0)的猝灭速率常数.发现猝灭速率常数与猝灭剂烷烃分子中的C-H键数近似成线性关系,但对大的烷烃分子,这种增加逐渐趋缓.用碰撞络合物模型计算胺类分子及烷烃分子与CH形成碰撞络合物时的生成截面,结果表明,在电子激发态CH自由基的猝灭过程中,碰撞对子间的多极相互吸引势和色散力作用势可能起重要作用.     

Time-resolved kinetic studies on quenching of HCF(A1A'') by alkane and alcohol molecules

HCF(X1A') radicals were produced by laser photolysis of CHFBr2 at 213 nm and were electronically excited from the ground state to A1A'(030) at 492.7 nm with a dye laser pumped by a Nd:YAG laser. With the analysis of the lifetime of the time-resolved total fluorescence signals collected in the reaction cell where the total pressure was fixed to be 14.0 Torr, the quenching data of HCF(A1A') by alkane and alcohol molecules at room temperature were derived from variation of pseudo-first-order rate constant with different quencher pressures. It is found that the quenching rate constants are close to the collision rate constants (10(-10) cm3 molecule(-1) s(-1)), indicating the long-range attractive forces between the collision partners play an important role in the entrance channel of quenching process. Several kinetic models were applied to analyze the mechanism of the quenching process. The complex formation cross sections are calculated with the collision complex model. Correlations of the quenching rate constant for the removal of the HCF(A1A') state with ionization potential of the quenching partners show that the insertion reactive mechanism is probably the dominant reaction channel, which is analogous to the behaviors of other three-atom carbenes in corresponding electronic states.     

蒈烯芳氰敏化光氧化反应的研究——Ⅰ.蒈烯对9,10-二腈基蒽荧光的猝灭特性

本文通过研究在不同溶剂中蒈烯对9,10-二腈基蒽(DCA)荧光猝灭的光物理特性及溶剂极性对猝灭速度的影响,温度效应的测定及其在乙腈中双分子猝灭速率常数k_q值与计算所得自由能的变化(△G)之间的关系符合 RehmWeller关系,证明了菇烯对DCA荧光的猝灭是一个电子转移的动态猝灭过程。     

Fluorescence quenching of pyrene monomer and excimer by CH3I

The fluorescence quenching rate constants of pyrene monomer and excimer by CH₃I were obtained at several temperatures in methylcyclohexane. Both quenching processes are kinetically controlled, allowing insight on the mechanism of quenching. The rate constants have both temperature-independent and temperature-dependent components. The temperature-independent component for both monomer and excimer fluorescence is consistent with quenching due to enhanced intersystem crossing to a lower energy triplet state. The monomer temperature-dependent component comes from the enhancement of the intersystem crossing to a higher energy triplet state. The thermally activated excimer quenching is associated with the excimer dissociation step to give a pyrene in a second triplet state plus a ground state pyrene molecule.     

The electronic quenching rates of NO(AΣ, v=0–2)

The electronic quenching rates of NO(A²Σ⁺, v^′=0–2) are measured for the gases He, Ar, Xe, N₂, O₂, CO₂, N₂O, and SF₆. The variations of the fluorescence intensity were measured for the (0,0), (1,0), and (2,0) bands of the γ band system when the quencher gases were added. The quenching rates were determined by using the Stern–Volmer plots with the known radiative lifetimes of the excited states. The electronic quenching rate constants are fast for the group of gases of O₂, CO₂, N₂O, and SF₆, whose quenching rate constants are in the order of 10⁻¹⁰ cm³/s. The quenching rate constants are slow for the group of gases including He, Ar, Xe, and N₂ whose rate constants are in the order of 10⁻¹⁴ cm³/s. For the slow group, the quenching rate constants increase rapidly for v^′=2 compared with those of v^′=0 and 1.

The charge transfer model and collision complex model are used to understand the quenching mechanism. For the fast group which mainly consists of gases with positive electron affinities, the charge transfer model adequately describes the mechanism. For the slow quenching group, a theoretical background is provided by consider the coupling of initial and final states in the complex potential surfaces.     

降冰片二烯衍生物的染料敏化电子转移光异构化反应的研究

降冰片二烯及其衍生物的光异构化反应已有广泛的研究, 反应生成的四环烷衍生物是储能的重要化合物, 为了更好地利用太阳能, 并进一步提高光敏化异构化反应的量子效率, 本文选用了具有强荧光的吖啶染料为敏化剂, 利用它们的单重态电子转移来引发反应, 在这类染料的光敏作用下异构化成为四环烷储能化合物。     

AN EVALUATION OF CHARGE EFFECTS ON THE QUENCHING OF TRYPTOPHAN FLUORESCENCE IN SMALL PEPTIDES BY IODIDE ION

Abstract— Charge effects on the quenching of tryptophan fluorescence in small peptides by iodide ion have been analyzed by the conventional "static" quenching model and by a recently proposed competitive quenching model. The former involves a fit of the quenching data using two quenching parameters—one for dynamic and one for static quenching contributions. The latter model involves a single parameter fit in which the fitting parameter is the characteristic rate constant for quenching of the fluorescent state. Both models indicate a clear charge effect on the efficiency of quenching by iodide ion. However, the static model results are obscured by the interdependence of the two fitting parameters and the fact that the true physical meaning of the static parameter is uncertain. Rate constants derived from the competitive model can be converted into relative quenching efficiencies. These efficiencies, which vary by more than a factor of two for the molecules studied, are greatest when the positive charge is on the tryptophan and least when this residue contains a negative charge.     

Characterization of endoperoxide and hydroperoxide intermediates in the reaction of pyridoxine with singlet oxygen

The photosensitized oxidation of vitamin B6, pyridoxine, is investigated by product and kinetic analysis. Singlet oxygen quenching rates, measured by time-resolved laser flash generation of singlet oxygen followed by monitoring singlet oxygen phosphorescence decay, confirm previous observations that pyridoxine is a moderate quencher. The quenching rate for 3-methoxypyridine is 100 times slower than that for 3-hydroxypyridine, indicating the hydroxy moiety is required for efficient quenching. The chemical quenching rate constant, kr, was estimated by comparison with a known singlet oxygen reaction. Results indicate that the chemical quenching rate of pyridoxine dominates the total quenching. The major reaction product in methanol was isolated and characterized by NMR and MS. The data are consistent with a solvent adduct of the substituted 2,5-pyridinedione. At low temperature, two semistable intermediates were characterized by NMR. The data are consistent with a hydroperoxide and endoperoxide. These intermediates suggest initial attack of singlet oxygen para to the hydroxy group followed by either proton transfer to form the hydroperoxide or addition of the peroxide to the imine to form the endoperoxide. In the presence of protic solvents, the solvent adducts to the imine and elimination of water yield the observed 2,5-pyridinedione product.     

Fluorescence quenching induced by conformational fluctuations in unsolvated polypeptides

Time-resolved measurements were conducted to relate the fluorescence lifetimes of dye-derivatized polypeptides to local conformational dynamics in trapped, unsolvated peptide ions. This research was performed to better understand the intramolecular interactions leading to the observed increase of fluorescence quenching with temperature and, in particular, how this quenching is related to conformational fluctuations. Dye-derivatized polyproline ions, Dye-[Pro] n -Arg (+)-Trp, are formed by electrospray ionization and trapped in a variable-temperature quadrupole ion trap where they are exposed to a pulsed laser which excites fluorescence. Lifetime data exhibit fluorescence quenching as a result of an interaction between the dye and tryptophan (Trp) side chain. This result is consistent with solution measurements performed for comparison. The lifetime temperature dependence is closely fit over the range 150-463 K by an Arrhenius model of the ensemble averaged quenching rate, k q. Model fits of the measured lifetimes yield a frequency prefactor of approximately 10 (11) s (-1) for k q characteristic of collective motions of the side chains identified in molecular dynamics (MD) simulations. The data fits also yield activation barriers of approximately 0.3 eV, which are comparable to intramolecular electrostatic interactions calculated between the unshielded charge on the Arg residue and the dye. As a result, the quenching rate appears to be determined by the rate of conformational fluctuations and not by the rate of a specific quenching mechanism. The peptide sequence of Dye-Trp-[Pro] n -Arg (+) was also studied and identified a dependence of the quenching rate on the electrostatic field in the vicinity of the dye, Trp pair. Molecular dynamics simulations were performed over the range of experimental measurements to study trajectories relevant to the quenching interaction. The MD simulations indicate that as the temperature is increased, conformational fluctuations in the presence of strong electrostatic fields of the charged Arg (+) residue can result in both (a) an increased number of dye and Trp separations <8 A and (b) increased exothermicity for electron transfer reactions between the dye and Trp. Consequently, the MD simulations are consistent with increased fluorescence quenching with temperature resulting from the occurrence of conformers having specific positions of the dye, Trp, and Arg (+). As a result, the fluorescence lifetime provides a local probe of conformational fluctuations averaged over the ion ensemble.     

Comparison of the Kinetics of Electron Transfer in the Diffusion Limit for the Singlet and Triplet Quenching of Eosin Y by Quinones

Electron transfer (ET) rate constants were determined by means of lifetime measurements for the fluorescence quenching and by laser flash photolysis for the triplet quenching of the dye eosin Y by benzoquinones in acetonitrile. The results represent a new aspect of the dependence of the rate constants with the driving force in the diffusion limit region. That is, the rate constants for singlet quenching in the highly negative region of ΔG_et do not decrease as predicted by Marcus theory, but rather show a small positive dependence on the driving force. However, it is found that, in the same free energy range, the triplet rate constants are lower than those for the singlet process. They also increase with the exergonicity of the reaction, but the dependence with ΔG_et is less marked than that found for the singlet reaction. Even at a Gibbs energy change of ?1.0 eV the triplet quenching rate constants do not reach the theoretical diffusion limit. The results are analyzed using the current theories for diffusion‐mediated ET reactions.     

Fluorescence quenching of anthracene by indole derivatives in phospholipid bilayers

The quenching of anthracene fluorescence by indole, 1,2-dimethylindole (DMI), tryptophan (Trp) and indole 3-acetic acid (IAA) in palmitoyloleoylphosphatidylcholine (POPC) lipid bilayers was investigated. A very efficient quenching of the anthracene fluorescence in the lipid membrane is observed. Stern-Volmer plots are linear for DMI but present a downward curvature for the other quenchers. This was interpreted as an indication of the presence of an inaccessible fraction of anthracene molecules. By a modified Stern-Volmer analysis the fraction accessible to the quenchers and the quenching constant were determined. The changes in the fluorescence emission spectrum of indole and DMI have been used to calculate the partition constants of these probes into the membranes, and bimolecular quenching rate constants were determined in terms of the local concentration of quencher in the lipid bilayer. The rate constants are lower than those in homogeneous solvents, which may be ascribed to a higher viscosity of the bilayer. No changes in the emission spectra of Trp and IAA are observed in the presence of vesicles, indicating that these probes locate preferentially in the aqueous phase, or in close proximity to the vesicular external interface in a medium resembling pure water. In these cases quenching rate constants were determined in terms of the analytical concentration. In the quenching by DMI a new, red shifted, emission band appears; it is similar to that observed in non-polar solvents and it is ascribable to an exciplex emission. The exciplex band is absent in the quenching by IAA and Trp and only very weakly present when the quencher is indole. From the position of the maximum of the exciplex emission, a relatively high local polarity could be estimated for the region of the bilayer where the quenching reaction takes place.     

Photo-acoustic detection on electronic quenching rate constants of NO excited states

The electronic quenching rate constants of NO A(2)Σ (υ'=0, 1), E(2)Σ (υ'=2, 3, 4) and F(2)Δ (υ'=1, 2, 3) states by gas air are reported. The experiments were carried out by measuring the total fluorescence intensity of A(2)Σ (υ'=0, 1)→X(2)Π (υ″) transition at various air pressures. It gives the Stern-Volmer plots. The quenching rate constants of A(2)Σ (υ'=0, 1) states are obtained from the slope of Stern-Volmer plots and the known radiative lifetime. Based on the primary results of the work, we have measured the quenching rate constants of high excited E(2)Σ (υ'=2, 3, 4), F(2)Δ (υ'=1, 2, 3) states for the first time with the technique of photo-acoustic (PA) spectroscopy. It is shown that the electronic quenching rate constants of NO E (υ') and F (υ') states are in the order of 10(-10)cm(3)/molecules. They are much larger than those of A(2)Σ (υ') state, whose rate constants are in the order of 10(-13)cm(3)/molecules. For E (υ') and F (υ') states, it is also found that the quenching rate constants increase with the vibrational energy levels. Similar result has been reported also for A(2)Σ (υ'≥2) states in existing literatures. The agreement indicates the potential use of PA spectroscopy for measuring the electronic quenching rate.     

一些氮氧自由基和受阻胺化合物对单重态氧的猝灭能力及其与光稳定作用的关系

本工作测定了一系列稳定氟氧自由基( )化合物及一些受阻胺光稳定剂对单重态氧(¹O₂)的猝灭速率常数(k_q^1O₂),发现不同结构的 对¹O₂的猝灭能力很接近,但它们对聚丙烯(PP)膜的光稳定作用却相差很大。四甲基哌啶醇(TMP)及其衍生物对¹O₂的猝灭能力远不如相应的五甲基哌啶醇(PMP)及其衍生物,但前者对PP的光稳定能力却胜于后者。这说明在对聚合物的光稳定作用中, 和受阻胺光稳定剂对¹O₂的粹灭作用不占重要地位,也说明¹O₂在PP的光氧化过程中很可能不是主要因素。     

(CX~3)~2CO,CF~3COX和CXCl~3(X=H或D)对CH(A,B)自由基的猝灭

本文报道室温下用266nm激光光解-荧光猝灭方法测定CH~3COCH~3,CD~3COCD~3,CF~3CO~2H,CF~3CO~2D,CHCl~3和CDCl~3分子猝灭电子激发态CH(A,B) 自由基的速率常数,考察了含不同同位素原子的猝灭剂分子对CH(A,B)猝灭的同位素效应. 实验发现,含D的分子比相应含H的分子对CH(A,B)的猝灭具有更大的速率常数     

Quenching of Na resonance radiation; collisions of excited sodium with atoms,molecules and electrons in the ICP

Spatial distributions of Na resonance level lifetimes in the inductively coupled plasma (ICP) are measured by time-resolved laser-excited fluorimetry. In order to elucidate the quenching mechanism, the lifetimes obtained are compared to theoretical values estimated from the quenching rate coefficients and number densities of colliding species. As a result, it is shown that resonance level Na atoms are mainly deactivated by electrons at lower heights in the plasma, while collisions with nitrogen molecules entrained from the surrounding atmosphere dominated the quenching reaction in the tail flame region.