Fluorescent molecules property

Molecular fluorescence and, to a lesser extent, phosphorescence have been used for the direct or indirect quantitative analysis of analytes in a variety of matrices. A direct quantitative analysis is feasible when the analyte s quantum yield for fluorescence or phosphorescence is favorable. When the analyte is not fluorescent or phosphorescent or when the quantum yield for fluorescence or phosphorescence is unfavorable, an indirect analysis may be feasible. One approach to an indirect analysis is to react the analyte with a reagent, forming a product with fluorescent properties. Another approach is to measure a decrease in fluorescence when the analyte is added to a solution containing a fluorescent molecule. A decrease in fluorescence is observed when the reaction between the analyte and the fluorescent species enhances radiationless deactivation, or produces a nonfluorescent product. The application of fluorescence and phosphorescence to inorganic and organic analytes is considered in this section. 

To perform structural research on a food stuff into which a colorant is incorporated, special properties of fluorescing molecules are exploited fluorescence efficiency, fluorescence lifetime, fluorescence quenching, radiationless energy (Foerster) transfer, stationary or time-dependent fluorescence polarization and depolarization." Generally, if food colorants fluoresce, they allow very sensitive investigations which in most cases cannot be surpassed by other methods. 

Homogeneous Time Resolved Fluorescence (HTRF) (Cisbio International) is an assay based on the proximity of a lanthanide cryptate donor and a fluorescent acceptor molecule whose excitation wavelength overlaps that of the cryptate s emission. The utility of this technique is based on the time resolved fluorescence properties of lanthanides. Lanthanides are unique in the increased lifetime of their fluorescence decay relative to other atoms, so a delay in collection of the emission intensity removes the background from other fluorescent molecules. An example of the HTRF assay is a generic protein-protein interaction assay shown in Fig. 2. 

Fluorescence correlation spectroscopy (FCS) measures rates of diffusion, chemical reaction, and other dynamic processes of fluorescent molecules. These rates are deduced from measurements of fluorescence fluctuations that arise as molecules with specific fluorescence properties enter or leave an open sample volume by diffusion, by undergoing a chemical reaction, or by other transport or reaction processes. Studies of unfolded proteins benefit from the fact that FCS can provide information about rates of protein conformational change both by a direct readout from conformation-dependent fluorescence changes and by changes in diffusion coefficient. 

Fluorescent molecules can participate in different intermolecular reactions starting from Si state with rate klnl as a result, their properties, such as the quantum yield, , and the fluorescence lifetime, x, can change. The proper equations for x and , as illustrated in Jablonski diagram (Fig. 1), may be written as [1, 2] ... 

The lifetime of the excited state of fluorophores may be altered by physical and biochemical properties of its environment. Fluorescence lifetime imaging microscopy (FLIM) is thus a powerful analytical tool for the quantitative mapping of fluorescent molecules that reports, for instance, on local ion concentration, pH, and viscosity, the fluorescence lifetime of a donor fluorophore, Forster resonance energy transfer can be also imaged by FLIM. This provides a robust method for mapping protein-protein interactions and for probing the complexity of molecular interaction networks. 

Fluorophores are relative small molecules that, with some exceptions, are not naturally occurring and have to be synthesized chemically. There has been a large development in the synthesis of fluorescent molecules and nowadays there is a vast range of alternatives including dyes with improved photochemical properties, solubility or modified reactivity that allow for conjugation to other molecules of interest and the synthesis and application of fluorescent sensors [10, 13], Although a lot is known about the physics of fluorescence and a lot of information is available about the properties of dyes, their prediction from the chemical structures cannot be accurately done. For this reason, there has been a... 

Another important property of fluorescing molecules is the lifetime of the lowest excited singlet state (X/). If the mean rate of fluorescence is the number of fluorescence events per unit of time, the mean lifetime of the excited state is the reciprocal rate, or the mean time per fluorescence event. The quantum yield of fluorescence and the lifetime of the excited state are related by... 

Module 1, Determination of Chemical and Structural Information on the Sample. The task of Module 1 is to provide non-chromato-graphic data for analytes prior to specification of the chromatographic method. Data bases have been developed for pK values of organic molecules, isoelectric points of proteins, and fluorescence spectral properties of organic molecules. 

Several vibrational modes in the excited singlet states of DPA have been identified from picosecond CARS measurements. The central C—C bond of DPA retains much of its triple-bond-like character in the S2 state however, the central C—C bond has double-bond-like character in the state. By analogy with the trans-bent form of S acetylene, it was proposed that S DPA has a trans-or cis-form bent structure that is consistent a previously proposed strucmre. It has been cautioned that, because of the conjugation between the phenyl groups and the central C—C bond, the S state may assume a structure different from the bent form. The interpretation of recent picosecond IR absorption measurements provide support for the trans-bent planar structure for S of DPA. The diphenylace-tylenic fluorophore has recently been incorporated into several chemosensor structures whose fluorescent signaling properties are controlled by the relative flexibilities of the molecules. ... 

In summary, an adiabatic model for the first excited state of BA is able to account well for the equilibrium absorption and emission properties of BA. It seems reasonable to assume that many of the dual fluorescent molecules would be well described by an adiabatic model of this type. In the following section we show the dynamic properties of BA are also well described by an adiabatic model. Indeed, the results are revealing from the standpoint of understanding small barrier charge transfer reactions in general. 

Pliquett, U.F., and J.C. Weaver. 1996. Electroporation of human skin Simultaneous measurement of changes in the transport of two fluorescent molecules and in the passive electrical properties. Bioelectrochem Bioenerg 39 1. 

The absorption spectra and the fluorescence spectra are mirror-images of each other. The duration of the fluorescence is of the order of 10-8 seconds. The fluorescence spectra are insensitive to small impurities and small changes in the preparation methods. The conclusion is that the color and the fluorescence are properties of the molecule and not of the lattice272 so the color must originate from the peculiar type of bonds in the system. 

Fluorescent dyes such as calcein-AM and rhodamine derivatives have been demonstrated to be P-gp substrates (400-407). These compounds can be used in any competition assay in which the test compound is added with these dyes. Any reduction in the dye efflux would be indicative of the inhibitory properties of the test compounds toward P-gp. Both rhodamine 123 and calcein-AM have been used in high-throughput assays, including the NCI assay, to screen large numbers of compounds as inhibitors of P-gp in several cell types. Calcein-AM itself is a weakly fluorescent molecule. When the acetoxymethyl ester group is cleaved by... 

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