Fluorescent Chromophores

Sensitivity levels more typical of kinetic studies are of the order of lO molecules cm . A schematic diagram of an apparatus for kinetic LIF measurements is shown in figure C3.I.8. A limitation of this approach is that only relative concentrations are easily measured, in contrast to absorjDtion measurements, which yield absolute concentrations. Another important limitation is that not all molecules have measurable fluorescence, as radiationless transitions can be the dominant decay route for electronic excitation in polyatomic molecules. However, the latter situation can also be an advantage in complex molecules, such as proteins, where a lack of background fluorescence allow s the selective introduction of fluorescent chromophores as probes for kinetic studies. (Tryptophan is the only strongly fluorescent amino acid naturally present in proteins, for instance.)... 

Polymers can also be labeled with fluorescent chromophores (66) or radioactive monomers. Other methods have been reviewed (65). 

Gepshtein R, Huppert D, Agmon N (2006) Deactivation mechanism of the green fluorescent chromophore. J Phys Chem B 110 4434-4442... 

Many of the linear conjugated tricyclic systems have interesting fluorescence or other electrophysical properties. Bis-pyrazolepyridines such as compound 30 have been incorporated into polymers as fluorescent chromophores <1999JMC339>, and used in doped polymer matrices <1997JMC2323>. They are electroluminescent at 425 nm and photoluminescent at 427 and 430 nm in a poly(vinylcarbazole) matrix with a quantum efficiency of 0.8. 

Once the alcohol or at least the cluster contains a soft ionization or fluorescence chromophore, a wide range of experimental tools opens up. Experimental methods for hydrogen-bonded aromatic clusters have been reviewed before [3, 19, 175]. Fluorescence can sometimes behave erratically with cluster size [176], and short lifetimes may require ultrafast detection techniques [177]. However, the techniques are very powerful and versatile in the study of alcohol clusters. Aromatic homologs of ethanol and propanol have been studied in this way [35, 120, 121, 178, 179]. By comparison to the corresponding nonaromatic systems [69], the O—H - n interaction can be unraveled and contrasted to that of O—H F contacts [30]. Attachment of nonfunctional aromatic molecules to nonaromatic alcohols and their clusters can induce characteristic switches in hydrogen bond topology [180], like aromatic side chains [36]. Nevertheless, it is a powerful tool for the size-selected study of alcohol clusters. 

N. Shaklai, J. Yguerabide, and H. M. Ranney, Interaction ofhemoglobin with red blood cell membranes as shown by a fluorescent chromophore, Biochemistry 16, 5585-5592 (1977). 

Fluorescence is one of the most sensitive detection methods in HPLC analyses. However, as ginsenosides do not contain a suitable fluorescence chromophore they have to be derivatized before detection. Shangguan... 

Pongor S, Ulrich PC, Bencsath FA and Cerami A (1984) Aging of proteins isolation and identification of a fluorescent chromophore from the reaction of polypeptides with glucose. Proc Natl Acad Sci USA 81, 2684-2688. 

Pyoverdins and Azotobactin are known examples of natural fluorescent siderophores that have been isolated from Pseudomonas aeruginosa and Azotobacter vinelandii, res-pectively ° ° . Pyoverdin Pa (171) ° and pyoverdin Pa Til (172) " are members of the pyoverdin family, which are peptide based hexadentate mixed siderophores that consist of a fluorescent chromophore dihydroxyquinoline, which provides a catecholate ligand for Fe(III) coordination in addition to two bidentate hydroxamate ligating groups. 

The sensory mechanism of AFP is not unlike that employed by conventional fluorescent chromophores. Typically, individual chromophores fluoresce upon excitation by a light source. However, if the chromophore binds with a target analyte, then excitation is not possible and the chromophore does not emit photons. This is illustrated in the top panel of Figure 9.3. 

Figure 9.3 Comparison of conventional fluorescent chromophore sensors versus the molecular wire response of the AFP.

Instead of the phenyl ring, a fluorescent chromophore has been attached to N(4) (85) and this compound has then been used for detecting Vitamin D metabolites and retinoic acid <94TL1917>. 

A vast range of organic chromophoric ring systems exhibit fluorescence, with the notable exception of the ubiquitous azo chromophore. However, in many cases the observed fluorescence is too weak to be of any commercial or technological value. In this section the structures and synthesis of only the main classes of fluorescent chromophores are discussed. More detailed accounts are available in recent reviews of the field. ... 

Perylene, a parent pentacyclic aromatic compound, which exhibits a strong fluorescence has found application in laser dyes and organic light emitting diodes (see section 3.8.5.1). The esters of di-, tri- and tetra-carboxylic acids of perylene are lightfast, yellow to red fluorescent chromophores, exemplified by the diisobutyl ester of the... 

The fluorescent properties of the coumarin ring system have already been described in the section on fluorescent chromophores 3.5.1.1 and not surprisingly colourless... 

Another well-known fluorescent chromophore that has found application in FBAs is naphthalimide. Product (3.63) is widely used in synthetic fibres, especially polyester and cellulose acetates and also in plastic applications. 

A suitable fiuorescent probe is an organic molecule, which must change its characteristic parameters with changes in its microenvironment and the parameter must be measurable when the probe is added to the system [54]. The fluorescent probes are categorized as either extrinsic, intrinsic, or covalently bound probes. The intrinsic probes allow a system to be observed without any chemical perturbation. This occurs when the system to be characterized has an in-built fluorescent chromophore unit like tryptophan, tyrosine and phenyl alanine in protein. In some cases the fluorophore is covalently... 

Morawetz et al. [105,106] were the first to use non-radiative energy transfer (NRET) fluorospectroscopy for exploring polymer-polymer miscibility. The basic principle is as follows. In a system containing two kinds of fluorescence chromophore, if the emission spectrum of one (donor D) overlaps the absorption spectrum of the other (acceptor A), a non-radiative energy transfer from the former to the latter may occur when the system is excited by irradiation that the former selectively absorbs. The efflciency of energy transfer (E) inversely proportional to Icj/Ia> where Id and la denote the emission intensities of D and A, respectively, depends on the average distance r between D and A according to the relationship ... 

FIGURE 2 Green fluorescent protein (GFP), with the fluorescent chromophore shown in ball-and-stick form (derived from PDB ID 1GFL). 

A chromophore 4P that efficiently absorbs radiant energy is attached to the recognition element adjacent to the recognition site. The fluorescent chromophore is attached to... 

Carbohydrates are very difficult compounds to analyze using CE because of their inherent structural complexity, frequent lack of a charge and lack of a UV or fluorescent chromophore. They thus require derivatization to facilitate ion formation and detection. 

Wiesler, U.-M., Berresheim, A.J., Morgenroth, F., Lieser, G. and Miillen, K. (2001) Divergent synthesis of polyphenylene dendrimers the role of core and branching reagents upon size and shape. Macromolecules, 34,187-99. Weil, T., Wiesler, U.M., Herrmann, A., Bauer, R., Hofkens,)., De Schryver, F.C. and Mullen, K. (2001) Polyphenylene dendrimers with different fluorescent chromophores asymmetrically distributed at the periphery. Journal of the American Chemical Society, 123, 8101-8. 

Although the anthracene units are coplanar, there is no electronic interaction between the chromophores in the crystal. Although such an arrangement makes this class of anthracene derivatives unusable for use in applications requiring efficient charge transport (organic transistors or solar cells), the insulation of the fluorescent chromophore induced by this method may make these materials useful as emitters in OLEDs. 

FDCD measurements, and a basic theoretical formalism for this technique, were first reported by Turner, Tinoco and Maestre in 1974 [5]. In this experiment one uses the selectivity and sensitivity of luminescence measurements to probe the local chiral environment of fluorescent chromophores. The ultimate goal in many applications of FDCD is to relate the observed differential fluorescence signal to the conventional CD measurement. In certain multi-component absorbing systems this procedure may be difficult. This technique is sometimes applied to systems for which CD measurements are impossible or very difficult. FDCD, like CPL and other polarization sensitive techniques, is not immune to troublesome background and noise problems, and these will be discussed in Section 3. The only detailed discussion of the applicability of FDCD measurements, and other characteristics of the technique has been presented by Turner in 1978 [6]. In this chapter we will also list some of the more recent applications of FDCD. 

Strashnikova, N.V., Medvedeva, N., and Likhtenshtein, G.I. (2001) Depth of immersio of fluorescence chromophore in biomembranes studied by quenching with nitrioxideradicals, /. Biochem. Biophys. Meth. 48,43-60. 

Figure 2 Structures of representative catecholate and mixed-ligand siderophores (a) enterobactin (b) parabactin (c) mycobacins (R = various alkyl chains, = R = R = MeorH.R = alkyl chains or H ) (d) fluorescent chromophore of pseudobactins and pyoverdins...

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