Solvatochromic Studies of Fluorescein Dianion in N,N-Dimethylformamide/Water and Dimethylsulphoxide/Water Mixtures

Abstract

The absorption, excitation and fluorescence spectra of the fluorescein dianion (FL^2?) in N, N-Dimethylformamide (DMF)/water (H₂O) and Dimethylsulphoxide (DMSO)/H₂O solvent mixtures have been investigated. It is found that the absorption λ_max and emission maxima EX, _nax are both hypsochromic shifted when the H₂O content in the solvent mixtures increases. However, the shoulder peaks λ_s remain constant at 483. 5nm within the range of H₂O mole fraction, x= 0 to 0. 518 in a DMF/H₂O solvent mixture and at 484. 4nm within the range, x=0 to 0. 304, in a DMSO/H₂O mixture. Further increases in H₂O content, cause a hypsochromic shift in λ_s. The molar energies for the electronic transition from the ground state (S₀) to S₁, the first excited singlet state, (E_T(1)) and to S₂, the 2nd excited singlet state, (E_T(2)) of FL^2?in the solvent mixtures are also plotted against x. Linear straight lines and intersection points are observed at x=0. 73 for E_T(1) and at x=0. 51 for E_T(2) in the DMF/H₂O mixture and at x=0. 71 for E_T(1) and at x=0. 31 &; 0. 69 for E_T(2) in the DMSO/H₂O mixture. Hydrogen-bonding stabilization effects are used to explain the above observations. The variation in relative fluorescence quantum yields of S₁ and S₂ of FL^2? with x in the aprotic solvent-H₂O mixtures to FL^2? in pure aprotic solvent are determined and discussed.     

Tuning the photophysics of a bio-active molecular probe ‘3-pyrazolyl-2-pyrazoline’ derivative in different solvents: Dual effect of polarity and hydrogen bonding

The solvatochromic behavior of 3-pyrazolyl 2-pyrazoline derivative (PYZ), a newly synthesized molecular probe having pharmaceutical importance, has been studied in various solvents of different polarity. The Kamlet and Taft solvatochromic comparison method was utilized to rationalize the solute-solvent interactions from absorption and emission measurements. Spectroscopic studies reveal that the solvatochromic behavior of the dye depends not only on the polarity of the medium but also on the hydrogen-bonding properties of the solvents. The non-radiative relaxation process is facilitated by an increase in the polarity of the media. The photophysical response of PYZ in different solvents has been explained considering solute-solvent interactions.     

Effect of hydrostatic pressure on the fluorescence of indole derivatives

Effects of hydrostatic pressure on the fluorescence emission of L-tryptophan, N-acetyl-L-trytophanamide and indole were investigated. An increase in pressure ranging from 1 bar to 2.4 kbar results in reversible red-shifts of the emission of the three fluorophores. The pressure-induced redshift amounts to about 170 cm^–1 at 2.4 kbar, and appears related to changes in Stokes shift of the fluorophores caused by pressure effects on the dielectric constant and/or refractive index of the medium. As the pressure range investigated here is the range commonly used in studies of protein subunit association and/or folding, these observations raise the need for caution in interpreting pressure-induced spectral shifts. The significance of these observations to pressure studies of proteins is illustrated by investigation of pressure effects on human Cu,Zn Superoxide dismutase (SOD) and azurin fromPseudomonas aeruginosa. A reversible 170 cm^–1 red-shift of the emission of SOD was observed upon pressurization to 2.4 kbar. This might be interpreted as pressure-induced conformational changes of the protein. However, further studies using SOD that had been fully unfolded by guanidine hydrochloride, and fluorescence anisotropy measurements indicated that the observed red-shift was likely due to a direct effect of pressure on the fluorescence of the single tryptophan residue of SOD. Similar pressure-induced red-shifts were also observed for the buried tryptophan residue of azurin or for azurin that had been previously denatured by guanidine hydrochloride. These observations further suggest that the effective dielectric constant of the protein matrix is affected by pressure similarly to water.     

原子系统中偶极-偶极相互作用对量子存储支撑熵不确定度的调控研究

本文研究了Markovian过程和non-Markovian过程两种情况下,原子系统中偶极-偶极(D-D)相互作用和失谐量对两原子系统量子存储支撑(QMA)熵不确定度的调控作用.与Markovian过程相比,在non-Markovian过程中,由于库环境的记忆效应使得具有D-D相互作用的两原子系统QMA熵不确定度的演化行为呈现出振荡上升现象,且熵不确定度的上升趋势得到减缓,从而抑制了由系统量子噪声引起的退相干效应.此外,D-D相互作用对两原子系统QMA熵不确定度具有显著的调控能力,且D-D相互作用比失谐量的调控能力更强.     

Influence of molecules with chloro group on the associative liquid methanol: A dielectric relaxation approach

The dielectric relaxation parameters, viz., static dielectric constant, ɛ, and relaxation times, τ, have been determined for chlorobenzene-methanol (CB-MET), 1,2 dichloro ethanemethanol (DE-MET) and dimethylene chloride-methanol (DC-MET) mixtures with thirteen different concentrations at three temperatures, viz., 15, 25 and 45°C. The experimental technique used for this work was the time domain reflectometry (TDR) in the frequency range of 10 MHz to 20 GHz using the Hewlett Packard HP 54750 sampling oscilloscope. The information regarding hydrogen bonding structural behavior in MET due to CB, DE and DC are obtained by using the theoretical models based on the excess properties. The data suggest that CB and DE are not influenced by hydrogen bonding in MET whereas DC is influenced by the hydrogen bonding mechanism in MET. It appears that the behavior of DC on MET is different from CB and DE in MET.     

3种多环芳烃化合物荧光光谱的量子化学研究

采用量子化学半经验方法AM1对3种多环芳烃电致发光材料(EL)的性质进行了理论研究。对各化合物优化后的构型作振动分析,均未出现虚频率,在此基础上,采用CIS方法计算电子光谱,并给出了3种化合物电子光谱的波长与CIS组态数之间的关系。所得计算结果与实验值基本吻合。     

Spectroscopic properties and photophysics of the synthesized compound 5-nitro-benzo[b]thiophene-2-carboxylic acid in non-polar/polar media and in the presence of TiO2 nanoparticles

The present work investigates by electrochemical and steady-state and time-resolved spectroscopic methods a synthesized compound 5-nitro-benzo[b]thiophene-2-carboxylic acid (5NBTC), both in normal solvents and in the presence of TiO₂ nanoparticles to reveal the nature of the photophysical processes involved. From the present experimental observations it is inferred that both in the ground state and the excited electronic state S₁, there exists a strong binding between -COOH functionality of 5NBTC and TiO₂ nanoparticles. However, the rupture of this binding in the presence of excess TiO₂, as apparent from the steady-state and time-resolved spectroscopic measurements, is responsible for the increase in radiative transitions. Formations of aggregations of TiO₂ nanoparticles at higher concentrations appear the cause of such rupturing. The redox potential measurements by cyclic voltammetry and theoretical computations by time-dependent density functional theory (TD-DFT) with B3LYP/6-311 G(d, p) basis function implemented in the Gaussian package confirm the electron accepting nature of 5NBTC and hence no electron transfer is possible between the organic compound and TiO₂ nanoparticles. It is most likely that the interaction model between 5NBTC and TiO₂ nanoparticles should be that the -COOH group of 5NBTC molecule coordinates either directly or through a hydrogen bond to the TiO₂ surface.     

Influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives: a time‐resolved resonance Raman and density functional theory study

A nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the photoreduction reactions and ability of several chloro‐substituted benzophenone (Cl‐BP) triplets is described. The TR³ results show that the 3‐chlorobenzophenone (3‐Cl‐BP), 4‐chlorobenzophenone (4‐Cl‐BP) and 4,4′‐dichlorobenzophenone (4,4′‐dichloro‐BP) triplets exhibit similar hydrogen abstraction ability with the parent BP triplet. In 2‐propanol, the 3‐Cl‐, 4‐Cl‐ and 4,4′‐dichloro‐diphenylketyl (DPK) radicals were observed and they appear to react with dimethylketyl radicals at the para‐position to form a light absorption transient species. These transient species were characterized with TR³ spectra, and identified with the help of results from density functional theory calculations. In an acetontitrile/water (MeCN:H₂O) 1:1 mixed solvent, these DPK radicals were also observed but with slower formation rates. However, the 2‐Cl‐DPK radical was observed to form with a lower yield and a significantly slower formation rate than the other chloro‐substituted benzophenones examined here in 2‐propanol under the same experimental conditions. These results reveal that the 2‐chloro substituent reduces the hydrogen abstraction ability of the substituted BP triplet, which was not as expected based on the assumption that the electron‐withdrawing group could increase its photoreduction ability. This unusual ortho effect of the chlorine substitution is briefly discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Water Soluble Metallo-Phthalocyanines: The Role of the Functional Groups on the Spectral and Photophysical Properties

Strategies are reported that produce symmetrical metal-free and metallo-phthalocyanine dyes, Pc and MPc, respectively, containing various numbers of water solubilizing carboxylic acid groups on their periphery that provide a dual role by also serving as functional groups to covalently link primary amine-containing targets to these dyes. In order to induce water compatibility and to minimize the degree of aggregation, the periphery of the macrocycle was decorated with various numbers of water-solubilizing groups and/or altering the identity of the metal center. The influence of the number of solubilizing groups and metal center on the spectral and photophysical properties were evaluated. MPc dyes containing 4, 8, or 16 carboxylic acid groups exhibited similar absorption and emission maxima (677 and 686 nm, respectively) with the molar absorptivity of the Q-band ∼10⁵ M⁻¹ cm⁻¹. Results indicated that the fluorescence lifetimes and quantum yields varied as a function of the metal center; the degree of carboxylation did not significantly alter these properties in DMSO, but did mediate the solubility and aggregation states when placed in aqueous solvents. The water solubilizing groups could also serve as labeling moieties for targets bearing primary amines. Results showed that the conjugate, produced by covalently linking an MPc to streptavidin through one of its carboxylate groups, generated a red-shift in the emission maximum with a fluorescence lifetime shorter than that of the native MPc dye.     

Effect of glycyl dipeptides on the micellar behavior of gemini surfactant: A conductometric and fluorescence spectroscopic study

The effect of glycyl dipeptides (glycylglycine, glycyl-L-valine, and glycyl-L-leucine) on the micellar properties of gemini surfactant pentamethylene-1,5-bis(dodecyldimethylammonium bromide) (12-5-12) has been investigated by means of conductivity and fluorescence spectroscopy. The results obtained from conductivity show that the effect of glycyl dipeptides depends upon their nature and concentration, as well as the temperature. The values of critical micelle concentration (cmc) of 12-5-12 have been estimated in water + glycyl dipeptide media at various concentrations of dipeptide in the 293.15-318.15 K temperature range at 5 K intervals. From cmc values, it is observed that the micellization tendency of the surfactant increases in the presence of glycyl dipeptides. Thermodynamic parameters (ΔG_m^o, ΔH_m^o, and ΔS_m^o) of micellization of 12-5-12 in aqueous glycyl dipeptide solutions have been obtained by applying the mass action model and an enthalpy-entropy compensation effect was observed. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of 12-5-12 with glycyl dipeptides, and the aggregation behavior of 12-5-12.     

A study on the luminescence properties of CaAl2B2O7:Eu phosphor

The blue-emitting CaAl₂B₂O₇:Eu²⁺ phosphor was prepared at 800 °C by a modified solid-state reaction. The results of X-ray powder diffraction (XRD) analysis confirmed the formation of CaAl₂B₂O₇:Eu²⁺. Photoluminescence (PL) spectroscopy showed that the phosphor could be excited efficiently by UV-vis light from 250 to 410 nm, and exhibit blue emission (460 nm). The emission intensity of CaAl₂B₂O₇:Eu²⁺ phosphor varies with the increase of Eu²⁺concentration. The mechanism of resonance-type energy transfer from Eu²⁺ to Eu²⁺ was established to be electric multipole-multipole interaction. TEM images showed that the grain size of CaAl₂B₂O₇:Eu²⁺ is about 45 nm, which is in full agreement with the theoretical calculation data from the XRD patterns.     

Spectrofluorimetric study on the interaction between antimicrobial drug sulfamethazine and bovine serum albumin

The interaction between the antimicrobial drug sulfamethazine (STM) and bovine serum albumin (BSA) has been studied using steady state and synchronous fluorescence spectroscopy. Fluorescence emission data revealed that BSA (2×10⁻⁶ M) fluorescence was statically quenched by STM at various concentrations, which implies that STM-BSA complex has been formed. The fluorescence emission data was analyzed via applying the Stern-Volmer analysis in combination with thermodynamic investigation, where obtained results revealed that quenching is static with quenching constants of 2.371, 1.658, and 0.916×10⁵ M⁻¹ at 298, 304, and 310 K, respectively. Binding constants and number of binding sites at different temperatures were also determined by applying the Scatchard method, which in turn were used to construct the van't Hoff plot in order to estimate the enthalpy (ΔH) and entropy changes (ΔS) for the complexation process. An average of 1.00±0.17 was estimated for the number of sites of BSA, which indicated that STM binds to BSA with stoichiometric ratio of 1:1. The values that were estimated from the van't Hoff plot for ΔH and (ΔS) were −36.8 kJ mol⁻¹ and −14.9 J mol⁻¹ K⁻¹, respectively, which indicate that the STM-BSA complex is stabilized with hydrogen bonds and van der Waals interactions. Synchronous fluorescence data was obtained at Δλ of 15 and 60 nm, where obtained results confirmed that STM binds to BSA at the tryptophan residue (Trp. 213). In addition, the distance between STM and the Trp. 213 was estimated via employing the Förster's non-radiative energy-transfer theory, and was found to be 2.73 nm, which in turn indicated that STM can bind to BSA with high probability.     

Solvent effect on the steady-state fluorescence anisotropy of two-photon absorbing fluorene derivatives

The effect of solvent polarity on the fluorescence properties of several two-photon absorbing fluorene derivatives was investigated. A strong solvatochromic effect was observed for symmetrical fluorene compound, which can be explained by large changes in the quadrupolar moment under excitation. Limiting values of excitation anisotropy of the investigated fluorenes exhibited a dependence on solvent polarity, and the angles between the absorption and emission transition dipole moments decrease in polar solvents by more than a factor of two.     

荧光光谱法研究乙酰水杨酸和牛血清蛋白的相互作用

应用荧光光谱法研究了乙酰水杨酸和牛血清蛋白(BSA)分子间的相互作用。研究表明乙酰水杨酸可猝灭BSA的荧光,同时自身的荧光增强并存在一个等发射点,表明两者之间形成稳定的复合物并发生能量转移。乙酰水杨酸和BSA分子间的结合常数为1.35×103,结合数0.87,静电引力是结合反应的主要的作用力。同时观察了乙酰水杨酸的加入对BSA构象的影响。     

Supramolecular interactions of meso-tetra-2-chlorophenylporphyrin with fullerenes: A luminescence study

Emission spectroscopic studies were performed to follow the intermolecular complexation of [60]- and [70]-fullerene as well as of o- and p-chloranils with meso-tetra-2-chlorophenylporphyrin (clTP) in non-interacting toluene medium. This has revealed different quenching mechanisms to be operational for these two groups of compounds. The ground state association constants of the intermolecular complexes were determined on the basis of the Stern-Volmer (SV) equation of fluorescence quenching. Theoretical justification for complex formation in terms of charge distribution, HOMO-LUMO interactions were provided in terms of DFT and ab initio Hartree-Fock calculations.     

Effect of surfactants on the spectrofluorimetric properties of zearalenone

The chemiluminescent properties of the estrogenic mycotoxin zearalenone in the presence of aqueous micellar media were investigated using steady state fluorescence techniques. Micelles of surfactants sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), and non-ionic Triton X-100 enhanced the fluorescence intensity of zearalenone in aqueous solutions. The binding constants have been determined and indicate zearalenone has the highest affinity for Triton X-100, followed by CTAB, and then by SDS. The encapsulation of zearalenone by the micelles studied is spontaneous and exothermic. The selective microenvironments provided by organized micellar systems offer an attractive medium to modulate fluorescence detection of zearalenone.     

荧光光谱研究两性表面活性剂CHAPS对钝顶螺旋藻藻胆体的解离作用

用蔗糖密度梯度高速离心的方法分离得到钝顶螺旋藻 (Spirulinaplatensis)的藻胆体 ,其室温荧光发射峰位于 6 71nm。以室温荧光光谱为表征研究了离子强度及两性表面活性剂CHAPS对藻胆体稳定性的影响。在 1mol·L-1的磷酸缓冲液中 ,藻胆体的稳定性强 ,7d内藻胆体的室温荧光发射峰位置没有变化。当用水稀释磷酸缓冲液浓度为 0 1mol·L-1,1h后藻胆体溶液的室温荧光发射峰即蓝移至 6 4 8nm ,表明藻胆体已经解离。在低浓度 (<0 6mol·L-1)磷酸缓冲液中 ,藻胆体易解离 ,解离速度随磷酸缓冲液浓度的降低而加快。在磷酸缓冲液浓度为 1mol·L-1的藻胆体的溶液中加入终浓度为 10mmol·L-1的两性表面活性剂CHAPS ,可导致藻胆体的室温荧光发射峰发生蓝移 ,说明CHAPS在高离子强度条件下也可以使藻胆体解离 ,这有利于进一步分离组成藻胆体的各种亚结构     

脂肪醇对槲皮素-环糊精包合物包合作用的研究

采用荧光光谱法研究了 β 环糊精及其衍生物与槲皮素的包合作用 ,测定了包合物的形成常数 ,并用等摩尔连续变化法确定了包合物形成的计量比 ,探讨了有机小分子醇对包合过程的影响。结果表明 :槲皮素 环糊精包合物包合能力强弱顺序为 :HP β CD >M β CD >β CD ,脂肪醇对槲皮素 环糊精包合物包合作用的影响与其所含碳数及体积有关     

氧对钌(Ⅱ)配合物溶胶-凝胶膜荧光响应的影响

利用蓝光LED(λmax =4 6 0nm )构建的氧荧光猝灭检测系统 ,考察了不同Ru配合物以甲基硅氧烷(TMOS)和二甲基二甲氧基硅烷 (DiMe DMOS)为共先驱体 ,制备的有机改性溶胶 凝胶 (sol gel)膜内荧光猝灭行为。DiMe DMOS的加入量会影响敏感膜的极性 ,从而影响敏感膜对氧浓度的响应。利用自行构建的装置对水体中氧进行了检测 ,传感膜对氧饱和水溶液测定的相对标准偏差为 1 12 % (n =6 ) ,响应时间为 30s,对氮饱和水溶液测定相对标准偏差为 0 39% (n =6 ) ,响应时间为 90s,敏感膜使用寿命大于 6个月。