Fluorescence studies on R-phycoerythrin and C-phycoerythrin

Biliproteins are photosynthetic light-harvesting proteins, which transfer excitons with high efficiencies over relatively long distances until they arrive at a photosynthetic reaction center. Purified R-phycoerythrin (isolated from a red alga) and C-phycoerythrin (isolated from a cyanobacterium), each of which contains several chromophores, were studied by a combination of fluorescence emission, fluorescence excitation polarization, and absorption methods. The polarization spectra of both these biliproteins showed that there was a minimum of two spectrally distinct sensitizing chromophores, which, after absorbing photons, transfer excitons to the lowest-energy (fluorescing) chromophores. Some of these spectroscopic data were used to deconvolute the absorption spectra into the spectra of the two sensitizing and one fluorescing chromophores. It was shown that the higher-energy sensitizing chromophore could readily transfer its excitation energy to the fluorescing chromophore using the lower-energy sensitizing chromophore as an intermediary. However, there was sufficient spectral overlap between the higher-energy sensitizing chromophore and the fluorescing chromophore so that direct transfer between them could not be ruled out.     

A linac-pumped excimer laser: Fluorescence and scaling studies

This work was an experimental investigation of a potential large-scale excimer laser system, in which a high-pressure KrF gas mix was pumped by the 4-MeV electron beam from an available linear accelerator. As a function of the mix and the pressure, fluorescence from KrF^* and/or Kr₂F^* were produced with good efficiency. Comparing measured data with a kinetic model, it was found that the kinetics followed the “normal” patterns seen in low-energy electron pumping. The data fitting process also resulted in a new value for the three-body quenching rate constant for reactions involving Ar. A critical factor in the development of this laser will be an improvement in beam control over that afforded by a simple solenoidal magnet. The conditions necessary for lasing are predicted; no inherent limitations on scaling of the device were found.     

Fluorescence studies and semiempirical calculations on alkali ion indicators

Two newly synthesized cryptands act as sensitive Na⁺- and K⁺-selective indicators for cation concentrations above 20 M. The fluorescence properties change markedly upon cation binding. In addition, the free ligands exhibit a pronounced sensitivity to pH, which is considerably lower for the cation complexes. Time resolved fluorescence is characterized by a decay time of about 5 ns that is attributed to the diprotonated protolytic state of the uncomplexed ligands. Semiempirical calculations show the systematic influence of the nitrogen lone pairs or the N–H bond on the stability of the system. The cause of the strong fluorescence intensity increase observed upon protonation of the fluorescent cryptands may be attributed to an increase in the S₁–T _x energy gap as a consequence of bridgehead nitrogen protonation.This is a peer-reviewed conference proceeding article from the Third Conference on Methods and Applications of Fluorescence Spectroscopy, Prague, Czech Republic, October 18–21, 1993.     

Fluorescence studies of electron-beam pumped POPOP dye vapor

Fluorescence studies on electron-beam excited mixtures of POPOP dye vapor and various buffer gases are reported. Xenon has been found to be a promising candidate as a buffer gas for efficient energy deposition of the electron-beam and energy transfer to the POPOP dye vapor. These experiments may be an important step towards realization of an electrically excited dye vapor laser. Work supported in part by the National Aeronautics and Space Administration and the Energy Research and Development Administration.     

Fluorescence studies of some protonated cinchona alkaloids in polymers

In the present paper we report spectral and photophysical properties of two probes viz. cinchonidine and quinidine in two different polymers viz. polyvinyl alcohol (PVA) and polymethylmethacrylate (PMMA). The emission spectra exhibit edge excitation red shift (EERS) for both the probes and multiexponential decays are observed. Presence of various conformers and geometries is suggested to explain the observed results. The photophysical properties and excited state behavior of Cd++ are more sensitive towards the microenvironment of the polymer.     

Fluorescence anisotropy and light-scattering studies of the interaction of insulin with liposomes

The interaction between zinc-stabilized insulin and lecithin liposomal membranes was studied using DPH fluorescence anisotropy and light-scattering techniques. To ascertain a possible influence of a charge on the insulin molecule, experiments were performed at pH 4.5 (insulin possesses a positive charge) and at pH 7.4 (the charge of insulin is negative). Measurements at pH 4.5 revealed significant changes in scattered light intensity induced by the addition of insulin to lecithin liposomes. With increasing time of storage of liposomes the insulin effect became faster and more pronounced. At pH 7.4, significant changes in scattered light were registered only in the case of liposomes stored for 5 days. In these liposomes a peroxidation process of lecithin was revealed. No significant changes induced by insulin were observed in DPH fluorescence anisotropy either at pH 4.5 or at pH 7.4, which suggested the absence of an interaction of insulin with the hycrophobic core of liposomes. Thus, the observed changes in scattered light could be interpreted in terms of the insulin association to the liposomal surface in the case of phospholipid peroxidation and/or acidic pH.     

Fluorescence and ESR studies on membrane oxidative damage by gamma radiation

Oxidative damage to cellular membranes critically controls the manifestation of cellular response to ionizing radiation. To gain further insight into the damaging mechanisms, we have investigated the effects of γ-radiation-generated free-radical-mediated peroxidative damage in egg yolk lecithin unilamellar liposomal membranes by employing 1,6-diphenyl-1,3,5-hexatriene (DPH). Alterations in lipid bilayer fluidity and malondialdehyde (MDA) formation were measured in irradiated liposomal membranes as a function of radiation dose (0.1-1 kGy). A relationship seems to exist between the degree of radiation-induced peroxidative damage and the magnitude of DPH fluorescence decay in irradiated membranes. Radiation-induced membrane rigidization and MDA formation were significantly reduced when α-tocopherol, a natural membrane antioxidant, was present in the liposomes suggesting an involvement of lipid free radicals in the mechanism of the damage process. The results of the present study have been compared with those obtained by the electron spin resonance (ESR) technique on human erythrocyte ghost membranes with spin-labeled phospholipids having the unique capability to sensitively report on the dynamic state of the lipid environment inside the bilayer membrane. Iodoacetamide and N-ethylmaleimide spin labels were used to investigate alterations in membrane proteins. These results have contributed to our understanding of mechanisms involved in radiation membrane oxidative damage in terms of lipid peroxidation, fluidity changes and involvement of -SH groups of membrane proteins. Combined use of fluorescence and ESR spin-label techniques is of potential interest in probing the deeper molecular mechanisms of radiation injury in cellular membranes for developing strategies to modify the radiation damage to cells.     

Fluorescence excitation studies of anthracene employing vacuum uv synchrotron radiation

Reported here are preliminary results of our investigation of the excitation and fluorescence spectra of crystalline anthracene at 200°K using synchrotron radiation in the range 300 to 2400 Å.     

Magnetic resonance studies of the properties of water in cellulose acetate membranes

The properties of water in various cellulose acetate (CA) membranes have been investigated by magnetic resonance techniques. It has been observed that the longitudinal (T₁) relaxation time of ¹⁷O in CA membranes containing H₂ ¹⁷O is considerably shorter (by a factor of 5 to 6) than the corresponding value in pure water. The T₁ values of ²³Na ions contained in these membranes were, however, shorter than the corresponding values observed in measurements of the aqueous mother solution by a factor smaller than 2. The EPR spectra of Mn²⁺ and of Cr³⁺ contained in CA membranes were practically identical to the spectra of the pure aqueous solution.

The data suggest the existence, in the CA membrane, of two “types” of water; a small fraction of highly immobilized “bound” water and the remaining large fraction of “free” water displaying properties almost identical to those of pure bulk water. This model is supported by measurements of the longitudinal relaxation rates of H₂ ¹⁷O in CA membranes which were gradually dehydrated from their water.     

Fluorescence characterization and gain studies on a dye-doped graded index polymer optical-fiber preform

Preparation of an appropriate optical-fiber preform is vital for the fabrication of graded-index polymer optical fibers (GIPOF), which are considered to be a good choice for providing inexpensive high bandwidth data links, for local area networks and telecommunication applications. Recent development of the interfacial gel polymerization technique has caused a dramatic reduction in the total attenuation in GIPOF, and this is one of the potential methods to prepare fiber preforms for the fabrication of dye-doped polymer-fiber amplifiers. In this paper, the preparation of a dye-doped graded-index poly(methyl methacrylate) (PMMA) rod by the interfacial gel polymerization method using a PMMA tube is reported. An organic compound of high-refractive index, viz., diphenyl phthalate (DPP), was used to obtain a graded-index distribution, and Rhodamine B (Rh B), was used to dope the PMMA rod. The refractive index profile of the rod was measured using an interferometric technique and the index exponent was estimated. The single pass gain of the rod was measured at a pump wavelength of 532 nm. The extent of doping of the Rh B in the preform was studied by axially exciting a thin slice of the rod with white light and measuring the spatial variation of the fluorescence intensity across the sample.     

Electron paramagnetic resonance and FT-IR spectroscopic studies of DL-2-aminoadipic acid and ammonium acetate powders

Exposure of powder forms of DL-2-aminoadipic acid and ammonium acetate to gamma radiation results in the formation of free radicals detected by the electron paramagnetic resonance spectroscopy at room temperature. In these compounds, the observed paramagnetic species were attributed to the HOOCCH₂CH₂CH₂CHCOOH and CH₂COONH₄ radicals, respectively. The g values and the hyperfine coupling constants of the unpaired electron with the environmental protons were determined for these two radicals. In work, the observed paramagnetic species were found to be stable at room temperature for more than two months. Also, these compounds were characterised by FT-IR and UV–VIS. Their thermal stabilities were determined by TGA and DTA measurements. Thermal analyses were shown to be unstable of the HOOCCH₂CH₂CH₂CH(NH₂)COOH and CH₃COONH₄ against thermo-oxidative decomposition.     

A Fluorescence and Fluorescence Probe Study of Benzonaphthyridines

A series of benzo[b][1,8]naphthyridines has been synthesized by Friedl?nder condensation of 2-aminoquinoline-3-carbaldehyde 1 (o-aminoaldehyde) with alicyclic ketones in basic medium. Benzonaphthyridines branched with various side-chains and substituents are prepared with the aim of being investigated as a good fluorescent material. Electronic absorption and fluorescence properties of some representative benzonaphthyridines in organic solvents, water-dioxane, and SDS, CTAB and Triton-X-100 micelles have been examined. The linear correlation between solvent polarity and fluorescence properties is observed. This study may provide new directions for the development of fluorescence probes as reporters of microenvironments of organized assemblies.     

邻苯二甲酸铕—铽络合体系的荧光性能和红外光谱研究

本文对在３６５ｎｍ波长紫外光激发下均可发出特征荧光的铕、铽邻苯二甲酸固体络合物以机械混合和化学作用两种混合方式，研究了这两系列混合络合物的荧光光谱和红外光谱。结果表明，无论其荧光发射波长还是其发射强度，铕、铽之间均存在相互影响；其中荧光发射峰位的变化较小，而荧光强度变化较大，铕、铽的荧光性能之间即存在相互敏化作用，又存在相互猝灭作用。红外光谱结果表明机械混合和化学作用都使络合物的结构发生了变化。     

Density, viscosity and ultrasonic velocity studies of aqueous solutions of sodium acetate at different temperatures

The densities and viscosities of aqueous solutions of sodium acetate have been measured at 298.15, 303.15, 308.15 and 313.15 K and at atmospheric pressure. The molality range has been studied between 6.09 × 10^− 2 to 7.314 × 10^− 1 mol kg^− 1. The experimental values of density have been used to calculate apparent molar volume, partial molar volume, solute–solute interaction parameter, and Hepler's constant. The viscosity data have been analyzed with Jone–Dole equation. Furthermore, ultrasonic velocity measurements of aqueous solutions of sodium acetate have been made at 298.15 and 308.15 K and at atmospheric pressure. From experimental values of ultrasonic velocity, apparent molar isentropic compressibility and limiting apparent molar isentropic compressibility have been calculated. All the parameters calculated from density, viscosity, and ultrasonic velocity indicate that the sodium acetate is water structure maker.     

Fluorescence studies on the conformation of litorin in solution and in the presence of model membranes

The conformation of the nonapeptide hormone litorin has been studied in buffer and in the presence of lipids, using static and dynamic fluorescence. The results obtained show that, in buffer, the hormone probably exists in a collection of flexible conformers, slowly interconverting between them. The marked changes observed in fluorescence spectra and lifetimes upon addition of dimyristoylphosphatidylserine vesicles clearly show that the peptide interacts with lipids assuming lipid specific conformations. Interestingly, no significative spectroscopic changes are produced by exposure to dimirystoylphosphatidylcholine vesicles both in the gel and liquid-christalline phases, suggesting a requirement for negatively charged lipids during the process of hormone-membrane interaction.     

磺基水杨酸的荧光光谱与荧光量子产率

报道了磺基水杨酸 (SSA)的荧光光谱和荧光量子产率。在 pH <2时 ,SSA无荧光 ,随pH升高 ,SSA荧光增强 ,在 pH 5～ 10 5之间 ,SSA有稳定的强荧光 ,最大发射波长为 4 0 2nm ,激发波长为 2 12 ,2 38和2 97nm。在 pH >13的强碱性条件下 ,SSA转变为另一种荧光型体 ,最大激发波长 2 6 1nm ,最大发射波长390nm。SSA浓度较高时 ,荧光激发光谱发生变化 ,但发射光谱不变。在近中性条件下 ,SSA稀溶液的荧光强度与浓度之间存在良好的线性关系 ,线性范围为 5～ 2 5 0ng·mL- 1 ,检测下限为 5ng·mL- 1 。以硫酸奎宁为参比 ,测量了SSA在不同波长下的荧光量子产率 ,在最大激发波长 2 97nm处的荧光量子产率为 0 5 4。