Spectroscopic and stability characteristics of Ga-tetraphenyl porphyrin- and Ge- and Sn-tetra (p-methyl-phenyl) porphyrin chlorides

The electronic absorption, emission and excitation spectra of the titled porphyrin complexes have been studied both in cyclohexane and in microemulsion media. The spectral data indicate minimal aggregation of the complexes in microemulsions. The fluorescence quantum yield (φ_f) values are generally higher in microemulsion media compared with cyclohexane. Solutions of the complexes are generally unstable upon prolonged photoirradiation giving open macrorings. A photochemical electron transfer from benzidine to the porphyrin complexes is induced by photoirradiation (λ_ex. = 420 nm) giving the characteristic blue benzidine monoradical cation. This represents a simple photochromic reaction based on inter-molecular photoelectron transfer. The porphyrin complexes undergo fluorescence quenching by benzidine. The fluorescence quenching of the porphyrin complexes using benzidine as a quencher does not give linear Stern-Volmer plots indicating a static-type quenching mechanism. The porphyrin complexes show instability with respect to organic oxidants. The oxidative decomposition of the Ga-porphyrin complex induced by o-chlorodibenzoyl peroxide follows a second-order kinetic law with an activation energy E_a = 64.6 kJ mol⁻¹.     

PHOTOPHYSICS STUDIES OF ORGANIC COMPOUNDS——NANOSECOND LASER PHOTOLYSIS AND TRANSIENT ABSORPTION SPECTRA STUDIES OF PYRENE-AROMATIC AMINES

Nanosecond time-resolved transient absorption spectra of pyrene-triphenylamine, pyrenediphenylamine, pyrene-N, N-dibenzylaniline systems in various solvents have been investigated. In nonpolar solvent, pyrene-triphenylamine exciplex and pyrene-N, N-dibenzylaniline exciplex were observed directly. In acetonitrile, the pyrene anion radical, triphenylamine and diphenylamine cation radicals were detected. On the basis of the present experimental facts, the mechanism of fluorescence quenching processes of pyrene in polar and nonpolar solvents has been established.     

A Spectroscopic Study of the Effects of Various Solvents and Sol-Gel Hosts on the Chemical and Photochemical Properties of Thionin and Nile Blue A

Tetraethyl orthosilicate (TEOS)-based gels were doped with two optically active organic indicators, thionin and nile blue A. Before trapping in a sol-gel host, thionin and nile blue A were both evaluated for solvent and protonation effects on their spectral properties. Only extreme pH values provided by HCl, NaOH, and NH₄OH produced new absorption and/or fluorescence bands. Introduction of nile blue A into alkaline environments (0.1N NaOH, NH₄OH) results in the appearance of a broad absorption band centered near 520 nm whereas highly acidic environments (1N HCl) show a reduction of the 635 nm absorption peak accompanied by an absorption band located near 460 nm. A marked decrease is observed in the optical density of thionin in 1N HCl solution which results in a reduction in the fluorescence intensity. The absorption and fluorescence spectra also reveal a decrease in a pH 11 solution of NH₄OH as compared to neutral conditions. Both dyes formed dimers when the sol-gel host, initially synthesized with TEOS, was organically modified with methyltrimethoxysilane (MTMS). However, thionin dimers were present in all silica-based sol-gel compositions, as evidenced by the absorption and fluorescence spectra. Substitution of MTMS for some of the TEOS in the gel matrix resulted in blue shifts in the absorption and fluorescence spectra of nile blue A. The absorption peak shifted 50 nm to 596 nm whereas the fluorescence shifted around 40 nm to 635 nm. These blue shifts resulted from the reduced polarity of the silica-based xerogel. Thionin also exhibited shifts in its absorption and fluorescence spectra with organic modification by MTMS. The absorption shifted approximately 3 nm to 595 nm while the fluorescence maximum decreased 7 nm to 630 nm. The blue shifts in the spectra of thionin with additions of MTMS were attributed to surface sites that altered the molecular structure of the adsorbed thionin molecules.     

Synthesis and photophysical processes of 9-bromo-10-naphthalen-2-yl-anthracene

A novel luminescent compound, 9-bromo-10-naphthalen-2-yl-anthracene (BNA) is synthesized by Suzuki Cross-coupling reaction of 9-bromo-anthracene and naphthalene-2-boronic acid. The structure is characterized by (1)H NMR, IR and UV-vis spectroscopy. The photophysical processes of 9-bromo-10-naphthalen-2-yl-anthracene have been carefully investigated by UV-vis absorption and fluorescence spectra. The results show that the compound emits blue and blue-violet light. The emission spectra exhibit obvious solvent effect. With the difference in polarity of solvents, The emission spectra is not only slightly blue shift with the increase of the solvent polarity but also change on the intensity of fluorescence at room temperature .The light emitting can be quenched by electron donor, N,N-dimethylaniline (DMA). On adding gradually DMA into the solution of BNA, the emission intensities of fluorescence are gradually decreased. The quenching effect follows the Stern-Volmer equation.     

Investigation of the interaction between chlorophenols and lysozyme in solution

The binding interactions of lysozyme with 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were investigated by UV-vis absorption, CD, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. The binding constants, quenching mechanism, and the number of binding sites were determined by the quenching of lysozyme fluorescence in presence of chlorophenols. H-bonds and hydrophobic interactions played major roles in stabilizing the chlorophenols-lysozyme complex. The distances r between chlorophenols and lysozyme were calculated to be 1.94nm, 2.75nm, 3.54nm, and 3.76nm for 2-CP, 2,4-DCP, 2,4,6-TCP, and PCP, respectively. The effects of chlorophenols on the conformation of lysozyme were analyzed using CD, synchronous fluorescence and three-dimensional fluorescence spectra.     

Dual fluorescence of syringaldazine

The absorption and fluorescence spectra of syringaldazine (SYAZ) has been recorded in solvents of different polarity, pH and beta-cyclodextrin (beta-CD) and compared with syringaldehyde (SYAL). The inclusion complex of SYAZ with beta-CD is investigated by UV-vis, fluorimetry, AM 1, FT-IR, (1)H NMR and scanning electron microscope (SEM). DeltaG value suggests the inclusion process is an exothermic and spontaneous. In all solvents a dual fluorescence is observed for SYAZ, whereas, SYAL shows a dual luminescence only in polar solvents. The excitation spectra for the 410 nm is different from 340 nm indicate two different species present in this molecule. In pH solutions: (i) a large red shifted maxima is observed in the dianion and is due to large interactions between the aromatic ring and (ii) the large blue shift at pH approximately 4.5, is due to dissociation of azine group and formation of aldehyde. beta-CD studies reveal that, SYAZ forms a 1:2 complex from 1:1 complex with beta-CD.     

Spectroscopic studies of a near-infrared absorbing pH sensitive aminodienone-carbocyanine dye system

Synthetic red and near-infrared absorbing dyes may be used as probe molecules in a large number of applications. Dyes exhibiting spectral changes with hydrogen ion concentration are useful as pH probes. Those dyes which have their absorption and fluorescence maxima in the long wavelength region of the visible spectral region are specially valuable because of decreased interference and semiconductor laser applications. In this paper we have evaluated an aminodienone dyes 1 which demostrates pH dependent absorption and fluorescence spectra as well as solvent polarity dependence. In organic solvents the long wavelength absorption band of the dye is in the reduced interference region. The absorption maximum is at 535 nm in neutral or alkaline solutions in methanol. The absorption spectra undergo a strong bathochromic shift in the presence of acids (lambda(max) = 709 nm) with a concomitant change in the fluorescence spectra. This pH sensitive dye was found to be specially especially useful for organic solvents. The analytical utility of this and similar near-infrared absorbing dyes is discussed.     

光谱法研究Cu2+与肌红蛋白的相互作用

用紫外吸收光谱、荧光光谱、同步荧光光谱及圆二色(CD)谱研究了Cu2+与肌红蛋白(Mb)的相互作用. 结果发现, Cu2+使Mb的紫外吸收增强, 峰位蓝移, 说明Cu2+与Mb发生了较强的相互作用; Mb的特征荧光峰猝灭, 且随着温度升高猝灭常数Ksv降低, 表明Cu2+对Mb的荧光猝灭机制属于静态猝灭; 计算了不同温度下的结合常数和结合位点数; 由van′t Hoff方程计算出ΔH和ΔS分别为-11.60 kJ/mol和33.77 J·(mol·K)-1, 得出二者之间的作用力主要为静电力; 并依据Förster非辐射能量转移理论确定了给体-受体间的结合距离r=2.56 nm. 同步荧光光谱表明, Cu2+对Mb的构象产生影响, 使色氨酸残基的疏水性下降. CD光谱测得加入Cu2+后, 二级结构发生改变, 使α-螺旋含量降低.     

Absorption studies of neutral retinal Schiff base chromophores

The neutral retinal Schiff base is connected to opsin in UV sensing pigments and in the blue-shifted meta-II signaling state of the rhodopsin photocycle. We have designed and synthesized two model systems for this neutral chromophore and have measured their gas-phase absorption spectra in the electrostatic storage ring ELISA with a photofragmentation technique. By comparison to the absorption spectrum of the protonated retinal Schiff base in vacuo, we found that the blue shift caused by deprotonation of the Schiff base is more than 200 nm. The absorption properties of the UV absorbing proteins are thus largely determined by the intrinsic properties of the chromophore. The effect of approaching a positive charge to the Schiff base was also studied, as well as the susceptibility of the protonated and unprotonated chromophores to experience spectral shifts in different solvents.     

Electronic spectra of 2-aminopurine and 2,6-diaminopurine: phototautomerism and fluorescence reabsorption

Ultraviolet absorption, fluorescence and excitation spectra of 2-aminopurine (2AP) and 2,6-diaminopurine (2,6DAP) have been studied using aqueous solutions at different pH values. The molecules are found to fluoresce most efficiently near the neutral pH. It is also found that the fluorescence caused by the solutions of these compounds is partly reabsorbed. Molecular orbital calculations on 2AP, its tautomers, anion and cation, and excited state life-time measurements corresponding to the emissions of 2AP and 2,6DAP near 370 and 342 nm, respectively, have been carried out, and have been found to be useful in the interpretation of the experimental observations.     

丙三醇对水溶液中血红蛋白构象的影响——荧光猝灭和动态光散射研究

利用荧光猝灭法和动态光散射法测定丙三醇-水混合溶剂中血红蛋白(Hb)与联苯胺的结合距离和Hb的流体动力学半径, 并通过分析Hb荧光光谱和吸收光谱的变化, 探讨丙三醇与蛋白质分子在水溶液中相互作用的机理及其对蛋白质构象的影响. 结果表明, 丙三醇-水混合溶剂中Hb通过优先水化作用形成更紧密的构象, 溶剂体系的氢键形成能力下降对稳定蛋白质的构象有重要的影响, 丙三醇浓度较高的混合溶剂中氢键网络发生崩塌, 导致蛋白质构象产生进一步的折叠. 实验显示, 尽管Hb在丙三醇-水混合溶剂中保持较完整的血红素疏水空穴结构, 但是血红素疏水空穴以外肽段的构象发生显著变化, 并对血红蛋白的聚集状态造成一定的影响.     

A novel fluorophore with dual fluorescence: local excited state and photoinduced electron-transfer-promoted charge-transfer state.

Absorption and emission spectra of 9-N,N-dimethylaniline decahydroacridinedione (DMAADD) have been studied in different solvents. The fluorescence spectra of DMAADD are found to exhibit dual emission in aprotic solvents and single emission in protic solvents. The effect of solvent polarity and viscosity on the absorption and emission spectra has also been studied. The fluorescence excitation spectra of DMAADD monitored at both the emission bands are different. The presence of two different conformation of the same molecule in the ground state has lead to two close lying excited states, local excited (LE) and charge transfer (CT), and thereby results in the dual fluorescence of the dye. A CTstate involving the N,N-dimethylaniline group and the decahy droacridinedione chromophore as donor and acceptor, respectively, has been identified as the source of the long wavelength anomalous fluorescence. The experimental studies were supported by ab initio time dependent-density functional theory (TDDFT) calculations performed at the B3LYP/6-31G* level. The molecule possesses photoinduced electron transfer (PET) quenching in the LE state, which is confirmed by the fluorescence lifetime and fluorescent intensity enhancement in the presence of transition metal ions.     

Photoinduced Electron Transfer in Dry Gelatin Containing Bound Methylene Blue

Excited states of methylene blue bound to dry gelatin undergo electron-transfer quenching reactions with neighboring amino acid residues to give reduced, methylene blue-free radicals. At the low loadings of methylene blue bound to gelatin used in this work, the absorption spectra indicated that the methylene blue existed principally in its monomeric form. The rates of methylene blue fluorescence quenching depended on the temperature at which the gelatin was dried. There was no detectable fluorescence characteristic of the localized excited singlet state of methylene blue when the dye is bound to gelatin dried at 15°C, where a significant proportion of the protein exists in its a -helical form. Instead, weak emission with a maximum at 645 nm is observed. It is inferred from this that the rate of quenching of any localized excited singlet states of the dye bound to a -helical gelatin is very fast thereby competing efficiently with radiative relaxation. The weak emission at 645 nm is ascribed to a fluorescent exciplex formed between bound methylene blue and a neighboring electron/proton donor residue of the gelatin. While fluorescence characteristic of the localized methylene blue singlet state was observed from dyed gelatin dried at 50°C, i.e. in its random coil form, the triplet state is subject to rapid quenching by electron/proton transfer with protein moieties.     

光谱法研究氨基己酸与牛血清白蛋白的相互作用

利用荧光光谱、紫外-可见吸收光谱及圆二色（CD）光谱研究了模拟生理条件下的氨基己酸(ACA)与牛血清白蛋白(BSA)的相互作用。 实验结果分析表明,氨基己酸对BSA的内源性荧光具有猝灭作用,属于动态猝灭过程。 计算了2种温度下ACA-BSA体系的结合常数、结合位点数及反应的热力学参数ΔG、ΔH和ΔS分别约为-21.00 kJ/mol、-0.64 kJ/mol和-72.00 kJ/(mol·K),由此推出了二者主要通过氢键和范德华力形成摩尔比为1∶1的复合物。 依据Forster非辐射能量转移理论求得二者之间的结合距离为2.3 nm。 位点取代实验指出氨基己酸主要结合在位点Site I。 CD光谱表明,氨基己酸诱导了BSA分子二级结构微变。     

氯硝柳胺及其衍生物与钥孔戚血蓝蛋白的相互作用

以氯硝柳胺为原料合成了聚乙二醇200基氯硝柳胺. 采用荧光光谱、同步荧光光谱、紫外吸收光谱和圆二色谱研究了氯硝柳胺及其衍生物与钥孔戚血蓝蛋白(KLH)的相互作用. 结果表明, 两种药物分子对KLH的荧光猝灭机制属于静态猝灭; 由Lineweaver-Burk方程计算出不同温度下结合常数K, 但是聚乙二醇200基氯硝柳胺与KLH的作用相对较弱; 由Van′t Hoff方程计算出ΔH和ΔS平均值, 结合力主要为静电作用力; 热力学函数计算结果表明, 氯硝柳胺及其衍生物与KLH的作用过程是一个熵增加、Gibbs自由能降低的自发分子间作用过程; 根据Förster非辐射能量转移机制求得给体与受体间的结合距离r均小于7 nm; 同步荧光光谱表明, 氯硝柳胺及其衍生物能够被血蓝蛋白存储和转运, 但结合时对蛋白构象有一定影响; 圆二色谱测得加入两种药物后, KLH的α-螺旋含量均降低, 二级结构发生改变. 通过比较氯硝柳胺及其衍生物与KLH的相互作用, 初步探讨了分子结构与其结合能力之间的联系.     

2,4-二硝基苯胺与牛血清白蛋白相互作用的研究

通过荧光和紫外光谱法研究了2,4-二硝基苯胺同牛血清白蛋白(BSA)的相互作用. 2,4-二硝基苯胺对牛血清白蛋白的内源荧光具有强烈的猝灭作用. 二者之间形成不发荧光的复合物是导致荧光猝灭的主要原因. 计算了其结合常数和结合位点数. 紫外光谱法进一步证明了其猝灭机理为静态猝灭. 根据能量转移理论计算了作用距离(3.13 nm). 同步荧光的结果表明2,4-二硝基苯胺的存在改变了牛血清白蛋白的分子构象.     

Primary electron-transfer dynamics in 2-phenylindole-9-cyanoanthracene system. A comparative study with 2-methylindole

Electrochemical measurements by cyclic voltammetry predict the possibility of occurrence of photoinduced electron-transfer (PET) reactions between the ground state of 2-phenylindole (2PI) (electron donor) and the excited singlet of 9-cyanoanthracene (9CNA) molecule acting as an electron acceptor. However, 2PI should be expected to behave as a relatively weaker electron donating agent than the structurally related donor 2-methylindole (2MI) as it possesses higher oxidation potential value. Both steady-state and time-resolved spectroscopic measurements in the polar acetonitrile (ACN) and ethanol (EtOH) solvents show that the fluorescence quenching phenomenon of 9CNA in presence of 2PI is primarily due to the involvement of dynamic process which in high probability should be PET. Nevertheless, in less polar tetrahydrofuran (THF) medium, the quenching of 9CNA results from the combined effect of dynamic and static modes. The transient absorption spectra, measured by using nanosecond laser flash photolysis, of 9CNA in presence of 2PI exhibit the signature of the bands of the anionic species of 9CNA, cation of the donor 2PI and the contact neutral radical. Observations of the transient absorption at the different delays infer that ion-recombination mechanism is responsible for production of the monomeric triplets of both 9CNA and 2PI. From the transient absorption decays in ACN medium, it has been demonstrated that the diffusional separation of ions from geminate ion-pair is facilitated in the case of 2MI-9CNA pair whereas for 2PI-9CNA system the energy wasting charge recombination dominates over the process of charge dissociation. From the above observations, the possibility of developing much potential photosynthetic model compounds with the donor 2MI, rather than with the other donor 2PI molecule has been hinted.     

比较研究山姜素和豆蔻明与人-γ球蛋白的相互作用

将互为同分异构体的两种植物药活性组分山姜素和豆蔻明作为研究对象,应用荧光光谱法、紫外光谱法以及红外光谱法并结合分子对接技术首次对这两种黄酮类化合物与人-γ球蛋白(Human gammagobulin,HG)的相互作用进行了详细研究.荧光光谱法的研究结果表明,这两种药物均与HG有较强的相互作用(结合常数均在104～105之间);山姜素对HG表现为静态猝灭机理,而豆蔻明对HG表现出非常少见的动态猝灭机理.比较不同温度(298,308和318K)下两种药物与蛋白相互作用的结合参数都有所差别,维持药物-HG体系的作用力也不同.山姜素和豆蔻明分子与HG色氨酸残基间的结合距离r值(分别为3.88和4.52nm)都小于7nm,说明发生了能量转移.同步荧光与红外光谱法定性及定量地研究了药物对HG二级结构的不同影响程度.两种分子对接结果表明了这两种药物与HG的结合区域.     

Study on the fluorescence properties of a new intramolecular charge transfer compound 1,5-diphenyl-3-(N-ethylcarbazole-3-yl)-2-pyrazoline

The fluorescence properties of a newly synthesized compound, 1,5-diphenyl-3-(N-ethylcarbazole-3-yl)-2-pyrazoline (DEP) have been studied. On excitation at 352 nm, the fluorescence spectrum exhibits a large red shift with an increase in the polarity of solvents. The intensity of the band is different in different solvents as well. The change in the dipole moment in various solvents at room temperature has been characterized by the absorption and steady state fluorescence techniques and calculated based on the Lippert-Mataga equation. DEP has an increase of dipole moment of 2.83 D units on excitation to the lowest singlet state. It is concluded that photo-induced charge transfer from N (1) to C (3) actually exists in the excited state of the pyrazoline moiety. Its fluorescence property is relative to viscosity and temperature of solvents. The phi(f) of DEP in neutral medium or basic medium is higher than acidic medium. In addition, when the concentration of DEP is higher than 10(-3) M, its fluorescence is quenched by the collision of each molecule. The red shift of the maximum emission of DEP attributes to the formation of aggregates and the conjugate system is strengthened.     

Fluorescence quenching by charge transfer interaction. Exciplexes of fluorene and hetero-analogues with electron donors and acceptors

The fluorescence quenching of fluorene, dibenzofuran and dibenzothiophen by aliphatic amines (electron donors) and aromatic nitriles (electron acceptors) has been studied in different solvents. Emission spectra, solvent effects and the observed relationship between the quenching rate constants and ionization potentials of the donors or reduction potentials of the acceptors support an electron-transfer mechanism with exciplex formation. Carbazole does not enter in this scheme and is probably quenched via a different mechanism.