Effect of halogenated compounds on the photophysics of C70 and a monoadduct of C70: Some implications on optical limiting behaviour

The fluorescence spectra, quantum yields and lifetimes of C₇₀ and a pseudo-dihydro derivative (C₇₀R) have been measured in a wide range of solvents at room temperature. This information is important for the development of reverse saturable absorbers. Phosphorescence spectra and phosphorescence lifetimes were also measured at low temperature. The fluorescence is subject to quenching by halogenated compounds. The efficiency of quenching follows the order I>Br≫Cl. The nature of the quenching is shown to vary, with chlorinated compounds exhibiting static quenching of fullerene fluorescence, owing to nonfluorescent complex formation, whilst those compounds containing bromine and iodine exhibit dynamic quenching due to the external heavy-atom effect, that increases the intersystem crossing rate constant in the fluorophore–perturber complex. This constant is evaluated by an original method from the bimolecular quenching rate constants. The phosphorescence quantum yield of both fullerenes at 77 K slightly increases in the presence of iodobenzene, in spite of a strong decrease in phosphorescence lifetime. The marked increase of the intersystem crossing rate constant in concentrated solutions owing to the external heavy-atom effect is of interest for the application of fullerenes as fast-responding optical limiters (reverse saturable absorbers) of intense laser pulses, even in cases where the triplet quantum yield is of the order of unity.     

Fluorescence studies on binding of pyrene and its derivatives to humic acid

Binding of pyrene (PyH) and its derivatives to humic acid (HA) has been studied by fluorescence spectroscopy. The nature of the interaction between HA and pyrene derivatives are extensively investigated by employing three derivatives ranging from anionic to cationic compounds: 1-pyrenebutylic acid (PyA), 1-pyrenemethanol (PyM), and 1-pyrenebutyltrimethylammonium bromide (PyB). Binding constants between HA and PyX (X=H, A, M, B) are obtained by steady-state fluorescence quenching techniques, and it is found that PyB has a markedly large binding constant among the pyrene family. This is attributed to a strong electrostatic interaction between cationic PyB and anionic HA. The result suggests that an electrostatic interaction plays a dominant role in binding of pyrenes to humic acid. The importance of electrostatic interaction was also confirmed by a salt effect on the binding constant. Influence of collisional quenching on the binding constant, which causes overestimation of the binding constant, was examined by time-resolved fluorescence spectroscopy as well as temperature effect in steady-state fluorescence measurements. It is elucidated that collisional quenching does not much bring overestimation into the binding constants.     

Effects of Hydrogen-bonding Interaction and Polarity on Emission Spectrum of Naphthalene-Triethylamine in Mixed Solvent

The effects of the protic and aprotic polar solvents on the emission spectrum of the naphthalene-triethyl-amine system in THF were studied under conditions of steady-state illumination. The fluorescence spectrum of the naphthalene-triethylamine system consists of two emission bands, the fluorescence band of naphthalene (band A, 329 nm) and the emission band of the exciplex(band B, 468 nm). The intensities of both the emission bands decrease with increasing the solvent polarity. The intensity of band B also decreases due to the hy-drogen-bonding interaction between triethylamine and protic solvent, while that of band A increases. It is thus suggested that the quenching of naphthalene fluorescence by triethylamine in THF occurs through the charge transfer and electron transfer reactions. The spectral changes upon the increase of solvent polarity can be explained by the dependences of the equilibrium constant between exciplex and ion-pair and the rate constant for the electron transfer reaction from triethyl.amine to the excited naphthalene on the rel.ative permittivity of solvent. It is shown that the formation of intermolecular hydrogen-bonding between triethylamine and protic solvent suppresses the quenching reaction by the decrease in free amine. Acetonitrile has only a polar effect and trichloroacetic acid only a hydrogen-bonding(or protonation) effect, while alcohols have both the effects. The effects of alcohols could be separated into the effects of solvent polarity and intermolecular hy-drogen-bonding interaction quantitatively.     

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.     

Mechanism of interaction of vincristine sulphate and rifampicin with bovine serum albumin: A spectroscopic study

The mechanism of interaction of vincristine sulphate (VS) and rifampicin (RF) with bovine serum albumin (BSA) has been studied by quenching of BSA fluorescence by RF/VS. The Stern-Volmer plot indicates the presence of a static component in the quenching mechanism. Results also show that both the tryptophan residues of BSA are accessible to VS and RF. The high magnitude of rate constant of quenching indicates that the process of energy transfer occurs by intermolecular interaction and VS/RF-binding site is in close proximity to the tryptophan residues of BSA. Binding studies in the presence of a hydrophobic probe, 8-anilino-1-naphthalene-sulphonic acid sodium salt (ANS) indicate that the VS and RF compete with ANS for hydrophobic sites on the surface of BSA. Small decreases in critical micellar concentrations (CMC) of anionic surfactants in presence of VS/ RF show that the ionic character of VS/RF also contributes to binding. The temperature dependence of the association constant is used to estimate the values of the thermodynamic parameters involved in the interaction of VS/RF with BSA and the results indicate that hydrophobic forces play a significant role in the binding. Circular dichroism studies reveal that the change in helicity of BSA are due to binding of VS/RF to BSA.     

Study on the Interaction between Gatifloxacin Mesylate and Salmon Sperm DNA by Fluorescence Method

The interaction between gatifloxacin mesylate (GM) and salmon sperm DNA was studied by fluorescence spectrometry and ultra‐violet (UV) spectrometry. Additions of salmon sperm DNA to GM solution resulted in its strong fluorescence quenching and UV absorbance decrease due to the strong interaction between GM and salmon sperm DNA. Both the maximum fluorescence emission wavelength and the maximum UV absorbance wavelength of GM did not change with the increasing concentration of salmon sperm DNA, indicating no intercalative binding existed between them. The Stern‐Volmer plot indicated that the fluorescence‐quenching constant at different temperatures or different salmon sperm DNA concentration ranges was different. Effects of ionic strength and I^? on the fluorescence quenching of GM by salmon sperm DNA indicated that electrostatic interaction and groove binding coexisted between them.     

利用荧光能量转移设计高灵敏苦味酸光极膜

利用荧光能量转移设计高灵敏苦味酸光极膜王柯敏，曾恚恚，俞汝勤（湖南大学化学化工系，长沙，４１００８２）关键词荧光能量转移，光极，苦味酸基于稠环芳烃荧光熄灭的苦味酸光极膜［１ａ，２］在选择性方面优于传统苦味酸根离子电极，较适于实际应用，但在检测低浓度苦...     

Photochemistry of iminium salts : Electron transfer mechanisms for singlet quenching and photoaddition of n-electron donating alcohols and ethers

Several aspects of past and current studies in the area of iminium salt photochemistry are discussed. Investigations of olefin-iminium salt photoaddition and photocyclization reactions are reviewed and conclusions about electron-transfer pathways for fluorescence quenching and reaction are discussed. The results of recent studies of alcohol and ether photoaddition to 2-phenyl-1-pyrrolinium salts are presented. These C-C bond forming processes occur in moderate yields to produce β-amino alcohol or ether products. In addition, alcohols and ethers serve as efficient quenchers of pyrrolinium salt fluorescence. Rate constants for quenching appear to be dependent upon both the oxidation potential of the alcohols and ethers and the availability of C-H bond α to oxygen. This data along with deuterium isotope effects on quenching combine to suggest a common mechanism for both fluorescence quenching and photoaddition. The nature of this mechanism is tested using the comparative quenching effeciencies of the tertiary alcohols t-butyl alcohol and 1,2,2-trimethyl-1-cyclopropanol. The latter alcohol having a weak C-C bond adjacent to the hydroxyl function quenches the fluorescence of 2-phenyl-1-pyrrolium salts at a rate two orders of magnitude greater than for t-butyl alcohol. The observations made are interpreted in terms of a sequential electron-proton transfer mechanism for quenching and photoaddition. Lastly, the relationship of iminium salt photochemical studies to other investigations of electron-transfer photochemistry is discussed.     

Studies of Adriamycin Binding to Histone H1 by Resonant Mirror Biosensor and Fluorescence Spectroscopy

Abstract

Adriamycin is a clinically used antitumor anthracycline antibiotic. Histone H1 is a target for the activity of anthracycline drug at the chromatin level. A new optical biosensor technique based on the resonant mirror was used to characterize interaction of adriamycin with H1, and the binding constant was obtained. By the analysis of fluorescence spectrum and fluorescence intensity, it was shown that adriamycin can quench the intrinsic fluorescence of tyrosine in H1 through a static quenching procedure. The binding constants of adriamycin with H1 were determined at different temperatures based on the fluorescence quenching results. The binding sites were obtained, and the binding forces were suggested to be mainly hydrophobic. The interaction of adriamycin and H1 in the presence of denaturant or salt was studied. The effect of Fe³⁺ on the binding constant was also investigated by optical biosensor and fluorescence spectroscopy. Furthermore, the steady‐state Stern–Volmer collisional quenching study of Tyr72 with acrylamide indicated that the association between adriamycin and H1 did not change molecular conformation of H1.     

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     

利用荧光探针技术研究氧鎓盐光引发丁基乙烯基醚的阳离子聚合

本工作合成了一组带不同取代基的氧鎓盐化合物,并对它们的荧光寿命、荧光量子产率以及用丁基乙烯基醚(BVE)进行猝灭的荧光猝灭常数进行了测定,发现带拉电子基的氧鎓盐化合物和BVE间存在着较强的相互作用,相反,推电子基的引入则减弱了这种影响,表明反应具有电子转移性质.由于在BVE的聚合过程中,被猝灭的氧鎓盐荧光会因BVE聚合、双键减少而使氧鎓盐荧光逐步恢复.因此利用这一现象作为荧光探针,考察了氧鎓盐光引发BVE的阳离子聚合过程.文中还对氧鎓盐光引发BVE聚合的机理进行了初步讨论.     

Fluorescence quenching of BPBD by aniline in benzene–acetonitrile mixtures

The quenching of fluorescence of 2-(4′-t-butylphenyl)-5-(4′′-biphenylyl)-1,3,4-oxadiazole (BPBD) has been studied by aniline in different solvent mixtures of benzene and acetonitrile at room temperature. The quenching is found to be appreciable and a positive deviation from linearity was observed in the Stern–Volmer plot in all the solvent mixtures. Various rate parameters for the quenching process have been determined by sphere of action static quenching model and finite sink approximation model. The magnitudes of these rate parameters indicate that positive deviation in the Stern–Volmer plot is due to both static and dynamic processes. The dependence of Stern–Volmer constant on dielectric constant of the solvent mixture indicates the possibility of different solvent molecule composition around the fluorescent from that of the bulk.     

Synthesis, characterization and theoretical analysis on a oxygen-sensing phosphorescent copper(I) complex

The fluorescence quenching of 9-aminoacridine by certain substituted uracils in water was studied using absorption, steady state and time resolved measurements. The bimolecular quenching rate constants (k_q), binding constant K and number of binding sites (n) were calculated based on the fluorescence quenching data. The free energy change (ΔG_et) for electron transfer process was calculated by Rehm–Weller equation. From lifetime measurement we observed that the quenching was mainly due to static mechanism involving ground state complex formation.     

单宁酸与牛血红蛋白相互作用的光谱研究

利用荧光光谱技术研究了单宁酸与牛血红蛋白分子的相互作用。实验结果表明:单宁酸分子与BHb发生反应生成基态复合物,导致BHb内源荧光的猝灭,该猝灭属于静态猝灭。测定了不同温度下该反应的表观结合常数、结合位点数及结合热力学参数,热力学参数的变化表明上述作用过程是一个熵增加、自由能降低的自发分子间作用过程,单宁酸与BHb之间以疏水和氢键作用力为主;根据Frster能量转移理论,测得供体与受体间结合距离r和能量转移效率E;并用同步荧光光谱法探讨了单宁酸对BHb构象的影响。     

Inclusion as a driving force for the intramolecular charge transfer (ICT) fluorescence of p-(N,N-diphenylamino)benzoic acid methyl ester (DPABME) in α-cyclodextrin (α-CD) aqueous solution

A 1:1 inclusion complex between p-(N,N-diphenylamino)benzoic acid methyl ester (DPABME) molecule and α-cyclodextrin (α-CD) in aqueous solution is formed with a stabilization constant of ca. 45.65 ± 3.59 M^?1 at 25 °C. The formation of the complex is accompanied by enhancement of the long wavelength fluorescence at 510 nm (attributed to intramolecular charge transfer (ICT) due to twisting) relative to the normal fluorescence at 420 nm. In water, the long-wavelength fluorescence is hidden under the red tail of the normal fluorescence band due to quenching by non-radiative transition. Inclusion by CD reduces quenching and thus constitutes a driving force for DPABME to emit at longer wavelength via ICT process.     

岩白菜素与牛血清蛋白相互作用的荧光光谱研究

应用荧光光谱研究了岩白菜素与牛血清白蛋白(BSA)分子间的相互作用.结果表明,岩白菜素对BSA内源荧光的猝灭机制属于形成化合物所引起的静态猝灭,猝灭常数Ksv为1.905×104L.mol-1;岩白菜素与BSA反应的结合常数为2.083×104,结合位点数为1.由热力学参数确定了岩白菜素与牛血清白蛋白的结合作用主要为静电作用.实验还发现随着岩白菜素的加入,BSA的猝灭值与岩白菜素浓度在1.5×10-5~1.5×10-4mol.L-1的范围内呈良好的线性关系,检出限2.0×10-6mol.L-1,可用于岩白菜素的测定.     

Study of the interaction between bovine serum albumin and ZnS quantum dots with spectroscopic techniques

The interaction between bovine serum albumin (BSA) and ZnS quantum dots (QDs) was studied by fluorescence, UV-vis spectroscopic techniques. The results showed that the fluorescence of BSA was strongly quenched by ZnS QDs and the quenching mechanism was discussed to be a static quenching procedure, which was proved by quenching rate constant K(q.) The recorded UV-vis data and the fluorescence data quenching by the QDs demonstrated that the interaction between them leads to the formation of QDs-BSA complex. Furthermore, the temperature effects on the structural and spectroscopic properties of individual QDs and protein and their bioconjugates (QDs-BSA) were also researched. It was found that, compared to the monotonically decrease of the individual QDs fluorescence intensity, the temperature dependence of the QDs-BSA emission had a much more complex behavior, highly sensitive to the conformational changes of the protein.     

TEMPERATURE AND VISCOSITY DEPENDENCE OF FLUORESCENCE QUENCHING BY OXYGEN IN MODEL SYSTEMS

Abstract— The bimolecular rate constant, k _q, for the quenching of the fluorescence of pyrenebutyric acid and naphthaleneacetic acid by molecular oxygen has been studied as a function of temperature and viscosity, η. Fluorescence lifetime measurements were used to monitor the degree of quenching. Glycerol-water and sucrose-water mixtures were used to increase the bulk viscosity. Plots of log k _q vs log η show deviations from Stokes-Einstein behavior, but the data are consistent with the patterns that have been observed for other diffusion limited reactions. This work provides background information, regarding the viscosity dependence of oxygen quenching reactions, which is essential for the correct interpretation of oxygen quenching/viscosity dependence studies with more complex systems (i.e. quenching of tryptophan residues in proteins).     

以共价键相连的卟啉-酞菁化合物分子内能量传递及光诱导电子转移

合成了叶啉与酞菁以共价键连接起来的双发色团分子。测定了它们的吸收光谱,荧光光谱,荧光寿命等。计算了分子内能量传递过程的效率(φ_EnT)及速率常数(κ_EnT)。结果表明:在稀溶液中,卟啉与酞菁等克分子混合时,观察不到分子间能量传递过程现象的发生;而双发色团分子的分子内能量传递过程则明显发生了,其效率(φ_EnT=13～70%)与速率常数(κ_EnT=1.2×10⁷～2.0×10⁸s^-1)取决于分子的结构类型。电子转移与能量传递过程与介质性质有关。在极性溶剂中有利于电子转移过程的进行,而不利于能量传递过程;在非极性溶剂中,则有利于能量传递过程的进行,而不利于电子转移。 选择性激发酞菁发色团,观测到了只有电子转移发生的过程,其电子转移效率达到38%。     

Electronic excited state energy transfer,trapping by dimers and fluorescence quenching in concentrated dye solutions: Picosecond transient grating exp

Picosecond transient grating experiments are used to examine electronic excited state dynamics in concentrated dye solutions. A model based on radiationless excited state transport and trapping by dimers describes the phenomena responsible for fluorescence quenching. The trapping rate constant is found to have a cubic concentration dependence. Rhodamine 6G dimer lifetimes in glycerol and ethanol are 830 ps and <50 ps respectively. The difference arises due to the viscosity dependence of the dimer radiationless relaxation rate.