Fluorophores fluorescent properties

When compared to fluorescent proteins, fluorophores and quenchers of fluorescence (short quenchers) are small molecules with sizes varying from 1 to 10 A. They are the main building blocks for constructing small molecule FRET probes. As molecular entities, they might influence the performance of the probe to a great extent. Their fluorescent properties will determine the sensitivity and dynamic range of the sensor. The success of the probe for a specific application will depend on the selection of the right fluorophores... 

Fluorescence is a process that occurs after excitation of a molecule with light. It involves transitions of the outermost electrons between different electronic states of the molecule, resulting in emission of a photon of lower energy than the previously absorbed photon. This is represented in the Jablonski diagram (see Fig. 6.1). As every molecule has different energy levels, the fluorescent properties vary from one fluorophore to the other. The main characteristics of a fluorescent dye are absorption and emission wavelengths, extinction... 

Fluorescent properties of some fluorophores commonly used for the construction of fluorescent probes... 

A fluorophore in the proximity of the NP senses the altered EM-field and its fluorescence properties are consequently modified. There are (at least) two enhancement effects an increase in the excitation of the fluorophore and an increase in its quantum efficiency (QE). The increased excitation of the fluorophore is directly proportional to the to the square of the strength of the E-field and is a function of the wavelength and relative position of the NP. The maximum enhancement of this type is achieved if /.res equals the peak absorption wavelength of the dye. 

Aminomethylcoumarin derivatives possess intense fluorescent properties within the blue region of the visible spectrum. Their emission range is sufficiently removed from other common fluorophores that they are excellent choices for double-labeling techniques. In fact, coumarin fluorescent probes are very good donors for excited-state energy transfer to fluoresceins. 

Emission-Excitation Matrix (EEM) fluorescence spectroscopy as a nondestructive and sensitive analytical technique was successfully applied in this study to characterize DOM in landfill leachte. The DOM is composed of complex mixture of organic compounds with different fluorescence properties. In particular, the EEM profiles of DOM show two well-defined peaks at Ex/Em=320-350 /400-420 nm, Ex/Em=320-350 /420-450 nm reasonably due to the presence of two different groups of fluorophores. An additional and less intense band at Ex/Em=280-290 /320-350 nm can be assigned to aromatic amino acids and phenol-like compounds. 

Among several fluorescence properties, fluorescence quantum yield and lifetime are the two most important characteristics of a fluorophore. Studies of the effects of the silica nanomatrixes on these two characteristics reveal the mechanism of enhanced fluorescence intensity of DDSNs. 

Intracellular reduced pyridine nucleotides NAD(P)H are the primary suppliers of reducing power to anabolic and catabolic pathways. They can be measured because of their fluorescent properties.<16) The fluorescence is caused by the presence of the reduced forms of the pyridine nucleotides NADH and NADPH (jointly referred to as NAD(P)H). These fluorophores absorb light in a wide band around 340 nm, and reemit, or fluoresce, light in a wide band around 460 nm. The phosphorylated and nonphos-phorylated nucleotides have essentially equivalent fluorescence properties while the oxidized forms of these nucleotides are nonfluorescent. 

Fluorescence spectroscopy S Conformational change with ligand binding induces change in fluorescence properties of intrinsic or extrinsic fluorophore... 

The same group extended their work recently to the synthesis of a peptide-based device detecting Zn2+ in aqueous solutions. [441 The principle is to add a dansyl fluorophore on a Lys side chain of a synthetic Zn finger peptide. Upon complexation of Zn2+, an important conformational change occurs that brings the fluorophore into a different environment and leads to a change in the fluorescence properties. 

Cyanines are by far the most popular and extensively researched chromo-phore for use in biological and medical imaging applications [70,72], They are used almost exclusively in fluorescence-related protocols. Their popularity may be attributable to factors such as their excellent synthetic flexibility and fluorescence properties, the latter being very high in some instances. Cyanines are the only synthetic near-infrared fluorophores which are commercially available (for... 

FPA results obtained at different salt conditions may not be directly comparable because the fluorescence properties of 6-MI, including the lifetime (t), are salt dependent. The salt dependence of the FPA of a helix in a complex construct should thereby be normalized relative to the FPA of a short control duplex of the same sequence of the targeted helix to account for salt effects on the local environment of the 6-MI fluorophore. The normalization ratio, rnoml, can be calculated as the ratio between the apparent rotational correlation time, 9, of the constructs and the control duplex only, rnomi = construct/ control- is related to the rate of anisotropy decay, with larger 9 associated with higher anisotropy. If the basic Perrin equation for a sphere (Eq. (14.3)) is used to simplify calculation, then... 

The intensity, position of the emission wavelength, and lifetime are some of the observables that will characterize a fluorophore. Each fluorophore has its own fluorescence properties and observables. These properties are intrinsic to the fluorophore and are modified with the environment. A fluorescence spectrum is the plot of the fluorescence intensity as a function of wavelength (Figure 7.3). 

Many of the fully aromatic 6-6-5 tricyclics show good fluorescence properties, and in some instances this has been utilized in biochemical applications. The reader is directed to the literature cited in Section 7.22.12.1 (benzo-separated purines) for examples of how the sensitivity of the fluorescence properties of tricyclic fluorophores to environmental conditions can be utilized to analyze the binding parameters associated with biomacromolecules. Of particular interest in this regard is a method known as fluorescence-polarization titration (83B2347). 

A high degree of sensitivity and selectivity can be obtained with certain biomolecules by the chemical attachment of fluorophores. The most common fluorescent derivatization reagents include fluorescamine, dansyl chloride, pyridoxal, pyridoxal 5-phosphate, dansyl hydrazine, and pyr-idoxamine. Such derivatization procedures can be used to enhance the fluorescence of compounds with low quantum yields as well as impart fluorescent properties to compounds that do not fluoresce naturally. 

Indolizine is an aromatic 1 On-electron system and constitutional isomer of l-H indole and, consequently, has received a considerable theoretical and practical interest [100]. Considering the well-established fluorescence properties of indolizines [101-103] and biindolizines [102], and the steadily increasing importance of fluorophores in biolabeling and environmental trace analysis, we have been seeking for a new, efficient synthesis of fluorescent indolizines. Two general ways of indolizine syntheses have been known so far [100]. The first route is based on the intramolecular formation of the indolizine by cyclocondensation of suitable pyridinium precursors. However, the second approach takes advantage of a [3 + 2]... 

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