Probes for microenvironments

Law KY (1980) Fluorescence probe for microenvironments Anomalous viscosity dependence of the fluorescence quantum yield of p-N, N-dialkylaminobenzylidenmalononitrile in 1-alkanols. Chem Phys Lett 75(3) 545-549... 

Another example of fluorescence intensity modulation in cou-marins is the 3-azido substitution that quenches the fluorescence completely. These compounds are used as starting material for the synthesis of fluorescent triazolocoumarins by click chemistry [31], Interestingly, the fluorescence of some coumarins depends strongly on the solvent. This is the case for 7-alkoxycoumarins that have been used as probes for microenvironments [32], 7-hydroxycoumarin that is pH sensitive, and 7-NR2 substituted coumarins such as coumarin 120 whose quantum yield is reduced in nonpolar solvents due to a change in the 3D structure [33],... 

A merocyanine dye, l-ethyl-4-(2-(4-hydroxyphenyl)ethenyl)pyridinium bromide (M-Mc, 2), exhibits a large spectral change according to the acid-base equilibrium [40, 41]. The equilibrium is affected by the local electrostatic potential and the polarity of the microenvironment around the dye. Hence, this dye is useful as a sensitive optical probe for the interfacial potential and polarity when it is covalently attached to the polyelectrolyte backbone. 

Solvatochromic probes have been used for a variety of applications like the study polarity of pure and mixed solvents [99], and the retention behavior in reverse-phase liquid chromatography [100] among other applications. Frechet et al. used 4-(N-methylamino)-l-nitrobenzene (p-MANB), as the chromophore, to probe the microenvironment of polyaromatic ether based dendrimers [101]. 

Cser A, Nagy K, Biczok L (2002) Fluorescence lifetime of Nile red as a probe for the hydrogen bonding strength with its microenvironment. Chem Phys Lett 360(5-6) 473-478... 

The increasing interest of researchers for fluorescent probes can be explained by the great improvement of the sensitivity and the spatial or temporal resolution of instruments, and by the development of a wide choice of commercially available probes for particular applications (Molecular Probes, Inc., United States Lambda Fluoreszenztechnologie Ges.m.b.H., Austria). However, there is still a need for probes with improved specific response and minimum perturbation of the microenvironment, in particular in the field of ion recognition which is the object of this chapter. 

Pyrene shown a number of photophysical features that made it an attractive fluorophore to probe the microenvironment in micellar aggregates [19]. For the peaks of pyrene PL, two important peaks at about 373 nm and 390 nm among the five dominant peaks of pyrene fluorescence were numbered as 1 and III, respectively [20]. It has been known that intensity ratio of peak 111 to I (III/I) increased as the polarity at the solubilization site of pyrene decreases. Figure 6 shows fluorescence spectra (A.ex = 310 nm) of pyrene in precursor gel containing TPA and I-IV samples denoted as (a), (b), (c), (d) and (e), respectively. The value of 111/1 of pyrene does not change under silicalite-1 gel due to no formation of micelle. However, in the Fig. 6d (sample II), III/I ratio is rapidly increased, while sample III and IV are decreased slightly again. Previously, Park et al. have reported that 111/1 ratio of pyrene for... 

Sometimes a very fluorescent molecule (fluoroprobe) is used to measure its microenvironment [fluorescence quenching, fluorescence polarization (developed by Weber60), and fluorescence probe for hydrophobic or hydrophilic regions in biological systems]. A very recent and "hot" label is the green fluorescent protein (238 amino acids, 26.9 kDa) first isolated from the jellyfish... 

Pyrene is a useful probe for studying the polarity of the medium because its fluorescence vibronic structure is very sensitive to the microenvironment [92,93]. In particular, the ratio of the intensities of the first (373 nm) to the third (384 nm) fluorescence vibronic maxima (R = I/III) strongly decreases with the decreasing polarity of the medium. The interaction of pyrene (13) with the three CDs has been thoroughly investigated by photophysical methods. There are considerable discrepancies among the results of the various reports, which are probably related to the very low solubility of 13 in H2O (<5 X 10 M). The low solubility imposes the need for special precautions when preparing the samples [94]. 

While photosensitizers for PDT have been mostly studied in model membrane systems to understand how a membrane interface affects localization, photophysics, and reaction rates with oxygen, they also turn out to be useful as probes for the microenvironment of the model membrane systems. The properties of micelles, reverse micelles, and liposomes are of special interest in understanding biological membrane systems and in the... 

Miyagi, M., Wan, Q., Ahmad, M.F., et al. (2011) Histidine hydrogen-deuterium exchange mass spectrometry for probing the microenvironment of histidine residues in dihydrofolate reductase. PLOS One, 6 (2), el7055. 

In order to obtain independent evidence for the involvement of the cyclodextrin cavity, fluorescence measurements were carried out for copper(II) ternary complexes with L- or D-tryptophan. In fact, the fluorescence spectrum of tryptophan has already been shown to be sensitive to the polarity of the microenvironment in which it is located and has been used in many studies as a probe for the conformation of proteins and peptides [53]. As for many fluorophores, the indole fluorescence of Trp is quenched by the copper(II) ion this effect has been used as a measure of the stability constants of copper(II) complexes [54, 55]. In a recent work, it has been shown that the fluorescence of dansyl derivatives of amino acids undergo enantioselective fluorescence quenching by chiral copper(n) complexes and that fluorescence measurements can be used for the study of enatioselectivity in the formation of ternary complexes in solution [56]. Bearing this in mind, we performed the same type of experiments by adding increasing amounts of the [Cu(CDhm)] + complex to a solution of D- or L-tryptophan [36]. The fluorescence titration curve shows that the artificial receptor inhibits the indole... 

Other applications of photochemistry include the development of sensitive fluorescent chemosensors for analysis of dilute solutions of inorganic cations and anions and the study of the diffusion of individual molecules in solution at room temperature. Fluorescent compoimds have been used as replacements for radioisotopes in the analysis of biological compoimds and the study of biologically active compounds and living systems. Photochemical reactions also offer alternative probes for the characterization of the microenvironments in diverse solid and liquid media, including crystals, zeolites, alumina, silica and clay surfaces, semiconductor surfaces, liquid crystals and host-guest inclusion complexes, polymer films, monolayers and supported multilayers of surfactant molecules, mi-celles, and dendrimers. ... 

The microscopic environment for the substrate-binding site was evaluated from the fluorescence maximum of a selected probe. For guests such as PNA and ANS, whose molecular shapes are similar to each other, capped-APC provides a microenvironment nearly identical in polarity with those provided by THF and the octopus azaparacyclophane [APC(C2Lys2Ci4)4l Et(30) = 37 (see Figure 2). However, capped-APC provides a microenvironment with higher polarity for more slender molecules such as TNS E p(30)... 

Y. Zhao, T. Ji, H. Wang, S. Li, Y. Zhao, and G. Nie, Self-assembled peptide nanoparticles as tumor microenvironment activatable probes for tumor targeting and imaging, / Control Release, 177,11-9, 2014. 

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