Search results for "Fluorescence"
showing 10 items of 2463 documents
Miscibility of cyanine dyes in two-dimensional aggregates
1995
Mixed aggregates of cyanine dyes at a charged lipid monolayer surface are studied by absorption spectroscopy, fluorescence microscopy and electron diffraction. We show that slight variations of the molecular structure can convert a system from being fully miscible to being immiscible, and also that the concentrations of dyes in the solution and in the crystal may deviate considerably. The different concentration in the solution and crystal was observed for a molecule where force field calculations indicated the existence of two isomers in solution and where probably only one fits into the lattice.
OH-related Infrared Absorption Bands in Oxide Glasses
2005
We report the infrared activity, in the spectral region of the OH stretching modes, of different composite silicate glasses whose chemical composition is established by X-ray fluorescence measurements. The analysis of the absorption line profiles is made in terms of different spectral contributions, Gaussian in shape. The comparison with analogous spectra obtained in vitreous silica samples with impurity concentrations < 100 part per million moles is evidence of the effects of the different oxides on the vibrational properties of the OH groups. In particular, for oxide glasses a red shift of the composite band at about 3670 cm(-1), assigned to the OH stretching modes of free Si-OH groups an…
On the Low-Lying Excited States ofsym-Triazine-Based Herbicides
2005
We report a joint computational and luminescence study on the low-lying excited states of sym-triazines, namely, 1,3,5-triazine (1) and the ubiquitous herbicides atrazine [6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (2)] and ametryn [6-methylthio-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (3)]. Geometrical structures, energetics, and transition and state properties of I and 2 were computed at the TD-DFT, CASSCF, and CASPT2 levels of theory. The fluorescence and phosphorescence emission spectra, lifetimes, and fluorescence quantum yields were measured for the three compounds, and from these, the energies of the lowest excited states and their corresponding radiative rates…
Polarization-Dependent Disappearance of a Resonance Signal -- Indication for Optical Pumping in a Storage Ring?
2021
We report on laser spectroscopic measurements on Li$^+$ ions in the experimental storage ring ESR at the GSI Helmholtz Centre for Heavy Ion Research. Driving the $2s\,^3\!{S}_1\;(F=\frac{3}{2}) \,\leftrightarrow\,2p\,^3\!P_2\;(F=\frac{5}{2}) \leftrightarrow 2s\,^3\!{S}_1\;(F=\frac{5}{2})$ $\Lambda$-transition in $^7$Li$^+$ with two superimposed laser beams it was found that the use of circularly polarized light leads to a disappearance of the resonance structure in the fluorescence signal. This can be explained by optical pumping into a dark state of polarized ions. We present a detailed theoretical analysis of this process that supports the interpretation of optical pumping and demonstrate…
Metabolic shift of polyphosphate-accumulating organisms with different levels of polyphosphate storage
2012
Previous studies have shown that polyphosphate-accumulating organisms (PAOs) are able to behave as glycogen-accumulating organisms (GAOs) under different conditions. In this study we investigated the behavior of a culture enriched with Accumulibacter at different levels of polyphosphate (poly-P) storage. The results of stoichiometric ratios Gly degraded/HAc uptake, PHB synthesized/HAc uptake, PHV synthesized/HAc uptake and P release/HAc uptake confirmed a metabolic shift from PAO metabolism to GAO metabolism: PAOs with high poly-P content used the poly-P to obtain adenosine tri-phosphate (ATP), and glycogen (Gly) to obtain nicotinamide adenine dinucleotide (NADH) and some ATP. In a test whe…
Fluorimetric determination of amphetamine in urine by flow injection with on-line liquid–liquid extraction
2001
Abstract Determination of amphetamine in urine was performed by batch and flow injection methodologies. The suitable experimental conditions for fluorimetric measurements were established. The liquid–liquid extraction was carried out at pH 13 using diethyl ether as extracting reagent. The measurement conditions were 260 nm and 277 nm for excitation and emission wavelengths, respectively. The method requires standard addition calibration and Youden blank correction. The influence of the main metabolites of amphetamine and metamphetamine were studied. The accuracy and precision of the proposed method was tested and the method is adapted to the flow injection procedure with on-line extraction.
Effectiveness of microwave based digestion procedures for the demineralization of human milk and infant formulas prior to fluorometric determination …
1996
The use of two types of microwave oven, one domestic (A) and the other specially designed for laboratory (B) for microwave-based digestion, to destroy the organic matter in milk and infant formulas prior to fluorometric determination of selenium is studied in order to check their applicability and reliability. In both systems the best results were obtained using the acid mixture HNO3—H2O2, and additional treatment with perchloric acid (60%) in a Thermoblock. The application of two different microwave-based digestion procedures to infant formulas was free of interferences. In the case of human milk, it was necessary to use the standard addition method. Values obtained for detection and quant…
Sample Preparation Improvement in Polycyclic Aromatic Hydrocarbons Determination in Olive Oils by Gel Permeation Chromatography and Liquid Chromatogr…
2005
Abstract The determination of 15 polycyclic aromatic hydrocarbons (PAHs) in olive oil samples has been improved in order to obtain a fast methodology with a low limit of detection through the combination of liquid–liquid extraction with acetonitrile and preparative gel permeation chromatography (GPC) prior to the injection of purified extracts into a C18 column. Acetonitrile–water was used as the mobile phase with a gradient from 50 to 95%, w/w, acetonitrile in 30 min. The oven temperature was maintained at 15°C, and fluorometric detection was made at a fixed excitation wavelength of 264 nm and variable, optimal emission wavelength for each analyte ranging from 352 nm for 11-H-benzo(b)fluor…
Femtosecond up-conversion technique for probing the charge transfer in a P3HT : PCBM blend via photoluminescence quenching
2009
We report on an experimental study of the charge transfer dynamics in a P3HT : PCBM blend by means of a femtosecond fluorescence up-conversion technique. Using two-photon excitation we probe the exciton dynamics in P3HT and a P3HT : PCBM blend with a weight ratio of 1 : 1 at excitation densities of up to 6 × 1018 cm−3. In both samples we find strongly nonexponential decay traces compatible with (i) diffusion-limited exciton–exciton annihilation and (ii) diffusion-limited donor–acceptor charge transfer in the polymer blend. Additionally, our results indicate that in the P3HT : PCBM blend about 50% of the photogenerated excitons undergo a prompt charge transfer process on a time scale of abou…
Synthesis of novel organic-based fluorophores – Implementation to the design of fluorogenic enzyme substrates based on the principle of in situ synth…
2020
Detection and fluorescence imaging of biologic systems requires the implementation of efficient, robust and easy-to-use tools. Conventional fluorogenic probes currently used in microbiology lack efficiency since they are based on the single chemical modification of a fluorophore bearing an optically tunable reactive group, which often leads to incomplete fluorescence quenching. The main goal of my Ph.D thesis was to develop novel fluorogenic enzymatic substrates based on the "covalent assembly" principle. This approach also named "in situ synthesis" is based on the use of domino reactions to form a fluorescent moiety starting from a "caged" non-fluorescent molecule. In our case, the bioanal…