Fluorescence quenching selectivity

The observation of selective fluorescence quenching by G C base pairs is consistent with the energetics of electron transfer (charge separation) from the bases to the singlet excited state Sa, which can be estimated using Weller s equation [26] ... 

Fig. 3 Typical ICT probes (left) and representative spectroscopic responses toward selected metal ions (right). Color code (left) coordinating atoms in blue, bridgehead atom of the fluorophore that takes part in complexation in orange, formal donor fragment in red, formal acceptor fragment in green (right) hypsochromic shifts in red, bathochromic shifts in green, fluorescence enhancement in violet, fluorescence quenching in blue. Symbols in table Aabs, 7em,

Figure 5 shows two typical core-shell structures (a) contains a metal core and a dye doped silica shell [30, 32, 33, 78-85] and (b) has a dye doped silica core and a metal shell [31, 34]. There is a spacer between the core and the shell to maintain the distance between the fluorophores and the metal to avoid fluorescence quenching [30, 32, 33, 78-80, 83]. Usually, the spacer is a silica layer in this type of nanostructures. Various Ag and Au nanomaterials in different shapes have been used for fluorescence enhancement. Occasionally, Pt and Au-Ag alloys are selected as the metal. A few fluorophores have been studied in these two core-shell structures including Cy3 [30], cascade yellow [78], carboxyfluorescein [78], Ru(bpy)32+ [31, 34], R6G [34], fluorescein isothiocyanate [79], Rhodamine 800 [32, 33], Alexa Fluor 647 [32], NIR 797 [82], dansylamide [84], oxazin 725 [85], and Eu3+ complexes [33, 83]. 

Appropriate combinations of boronic acid and fluorophores lead to a remarkable class of fluorescent sensors of saccharides (Shinkai et ah, 1997, 2000, 2001). The concept of PET (photoinduced electron transfer) sensors (see Section 10.2.2.5 and Figure 10.7) has been introduced successfully as follows a boronic acid moiety is combined intramolecularly with an aminomethylfluorophore consequently, PET from the amine to the fluorophore causes fluorescence quenching of the latter. In the presence of a bound saccharide, the interaction between boronic acid and amine is intensified, which inhibits the PET process (Figure 10.42). S-l is an outstanding example of a selective sensor for glucose based on this concept (see Box 10.4). 

J. M. East and A. G. Lee, Lipid selectivity of the calcium and magnesium ion dependent adenosinetriphosphatase, studied with fluorescence quenching by a brominated phospholipid, Biochemistry 21, 4144-4151 (1982). 

Expansion of the data bases in Module 1 to include spectroscopic and electrochemical data to be used by the detector selection rules of Module 3. (This would include UV absorbance spectral properties of organic molecules, fluorescence quenching and activating properties of solvent environments, and electro-... 

Selected entries from Methods in Enzymology [vol, page(s)] Design, 178, 551 immunoassay, 178, 542 production, 178, 531 purification, 178, 543 substrates and enzymatic assay, 178, 544 derivatization with spectroscopic probe, 178, 567 ester cleavage assays, 178, 565 fluorescence quenching binding assay, 178,... 

Fletcher, K.A., Pandey, S., Storey, I.K., Hendricks, A.E., and Pandey, S., Selective fluorescence quenching of polycyclic aromatic hydrocarbons by nitromethane within room temperature ionic liquid l-butyl-3-methylimidazolium hexafluoro-phosphate. Anal. Chim. Acta, 453, 89-96, 2002. 

The predictive power of the luminescent PET sensor principle is again apparent here. Further, the benzocrown ether and the amine receptors would selectively bind Na" and H, respectively. A remarkable feature here is that no molecular wiring is needed to allow the human operation of this two-input molecular device. The device self-selects its own ion inputs into the appropriate signal channels by means of the chemoselective receptor modules. Since the output signal is fluorescence, even a single molecule can interface with detectors in the human domain, including the dark-adapted eye. Tanaka s 45 is another example where fluorescence quenching is achieved only when Ba and SCN are present. This was mentioned in Section 6. Similarly, several sensor systems—1,17, and 21—could be employed... 

The fluorescence properties of two fulvic acids, one derived from the soil and the other from river water, were studied. The maximum emission intensity occurred at 445-450 nm upon excitation at 350 nm, and the intensity varied with pH, reaching a maximum at pH 5.0 and decreasing rapidly as the pH dropped below 4. Neither oxygen nor electrolyte concentration affected the fluorescence of the fulvic acid derived from the soil. Complexes of fulvic acid with copper, lead, cobalt, nickel and manganese were examined and it was found that bound copper II ions quench fulvic acid fluorescence. Ion-selective electrode potentiometry was used to demonstrate the close relationship between fluorescence quenching and fulvic acid complexation of cupric ions. It is suggested that fluorescence and ion-selective electrode analysis may not be measuring the same complexation phenomenon in the cases of nickel and cobalt complexes with fulvic acid. 

Also for the anion library two selectivity experiments for the binding of HS(V, N03- and AcCT were conducted with T3. In both experiments, first 10 M N(>3" was added to a T3 layer, showing no response as expected. Then, two separate experiments were performed reversing subsequent additions of solutions of HS04 and AcCT, ranging from 10-6 M to 10-3 M. In each case, the addition of AcCT caused 70% fluorescence quenching, but only when the HSC>4- was added first did the HSCV result in a fluorescence intensity in-... 

The first fluorescence PET sensors for saccharides were based on fluorophore boronic acids. Czarnik and Yoon showed that 2- and 9-anthryboronic acid [50] 19 and 20 could be used to detect saccharides. However, the fluorescence change was small [/ (in the presence of saccharide)// (in the absence of saccharide) = ca. 0.7], The pA/a of the fluorophore boronic acids are shifted by saccharide present in the medium. The extent of the effect is in line with the inherent selectivity of phenylboronic acid [49], The PET from the boronate anion is believed to be the source of the fluorescence quenching. Although... 

Cabaniss, S. E., and Shuman, M. S. (1986). Combined ion-selective electrode and fluorescence quenching detection for copper-dissolved organic-matter titrations. Anal. Chem. 58(2), 398 101. 

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