pH Effects on fluorescence of umbelliferone
About: This article is published in Analytical Chemistry.The article was published on 1970-08-01. It has received 127 citations till now. The article focuses on the topics: Umbelliferone.
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TL;DR: In this paper, the acid-base properties of electronically excited states of organic molecules are discussed and the effects of solvation on 0-0 energies are discussed. And the changes in molecular fluorescence with acidity give information about the protolytic behavior of the excited singlet state of a compound.
Abstract: Publisher Summary This chapter discusses acid–base properties of electronically excited states of organic molecules. Excited state pK-values are most easily accessible through the use of the Forster cycle. To perform this calculation for a particular molecule, it is necessary to know the ground state equilibrium constant for the reaction in question and to have some measure of the energy difference between the lowest vibrational level of the ground and the excited state in both the B and BH + forms. The effects of solvation on 0–0 energies are discussed. The changes in molecular fluorescence with acidity give information about the protolytic behavior of the excited singlet state of a compound. Two techniques, phase and pulse fluorometry, are used for the direct measurement of fluorescence decay rates. The excited state acid-base behavior of molecules has direct implications in the field of analytical fluorimetry and phosphorimetry.
538 citations
TL;DR: A simple, convenient, and inexpensive method to quantitatively determine fluoride anion concentration in acetonitrile as well as in water has shown a high selectivity and a great sensitivity toward fluoride anions through "turn-on" chromogenic and fluorogenic dual modes.
Abstract: A simple, convenient, and inexpensive method has been developed to quantitatively determine fluoride anion concentration in acetonitrile as well as in water. The method exhibited a high selectivity and a great sensitivity toward fluoride anions through “turn-on” chromogenic and fluorogenic dual modes. The fluoride driven silyl deprotection and the subsequent spectral changes of hydroxyl coumarin were the operating foundations for the observed selectivity and sensitivity. 1H NMR spectral titration with F– revealed that complete deprotection of a triisopropylsilyl (TIPS) group needed exactly 1 equiv of TBAF. UV–vis and fluorescence titration studies exhibited the appearance of a new intense absorption band centered at 434 nm and green emission peak at 500 nm, accompanied by bright yellow color development to the naked eye. An easy-to-prepare test paper, obtained by dipping the paper into the solution of TIPS-protected coumarin derivative, was able to detect F– in aqueous media. The method has also shown hig...
187 citations
TL;DR: This work indicates that the substitution of phenylalanine by glycine significantly impacts on the mode of assembly and illustrates the versatility of aromatic peptide amphiphiles in the formation of structurally diverse nanostructures.
Abstract: We have investigated the self-assembly behavior of fluorenyl-9-methoxycarbonyl (Fmoc)-FG, Fmoc-GG, and Fmoc-GF and compared it to that of Fmoc-FF using potentiometry, fluorescence and infrared spectroscopy, transmission electron microscopy, wide-angle X-ray scattering, and oscillatory rheometry. Titration experiments revealed a substantially shifted apparent pK(a) transition for Fmoc-FG, Fmoc-GG, and Fmoc-GF. The apparent plc values observed correlated with the hydrophobicity (log P) of the Fmoc-dipeptide molecules. Fmoc-GG and Fmoc-GF were found to self-assemble only in their protonated form (below their apparent pK(a)), while Fmoc-FG formed self-assembled structures above and below its apparent pK(a). Fmoc-GG and Fmoc-FG were found to form hydrogels below their apparent pK(a) transitions in agreement with the entangled fibers morphologies revealed by TEM. Unlike Fmoc-FF and Fmoc-GG, Fmoc-FG showed unusual gelation behavior as gels were found to form upon heating. Fmoc-GF formed precipitates instead of a hydrogel below its apparent pK(a) in agreement with the formation of micrometer scale sheetlike structures observed by TEM. The fact that all four Fmoc-dipeptides were found to self-assemble suggests that the main driving force behind the self-assembly process is a combination of the hydrophobic and pi-pi interactions of the fluorenyl moieties with a secondary role for hydrogen bonding of the peptidic components. The nature of the peptidic tail was found to have a pronounced effect on the type of self-assembled structure formed. This work indicates that the substitution of phenylalanine by glycine significantly impacts on the mode of assembly and illustrates the versatility of aromatic peptide amphiphiles in the formation of structurally diverse nanostructures.
168 citations
TL;DR: It is concluded that measurements of cell pH by fluorescence techniques are subject to artifacts induced by self-quenching and protein binding, and the fluorescence ratio technique does not correct for changes in fluoroprobe concentration.
166 citations
TL;DR: Using time-dependent density functional theory (TD-DFT) and the polarizable continuum model, a large panel of coumarin dyes in their enol, keto, cationic, and anionic forms are computed and it turns out that for a given electronic transition the experimental shifts resulting from the substitution of the Coumarin core are nicely reproduced.
Abstract: Using time-dependent density functional theory (TD-DFT) and the polarizable continuum model, we have computed the electronic transitions of a large panel of coumarin dyes in their enol, keto, cationic, and anionic forms. Several processes have been studied: absorption, fluorescence, 0-0 phosphorescence, and triplet-triplet excitations. For each process, detailed comparison with experimental data has been carried out. Using the PBE06-31+G(d) scheme, it turns out that for a given electronic transition the experimental shifts resulting from the substitution of the coumarin core are nicely reproduced. Indeed, once a simple statistical correction is applied, the mean absolute errors on the absorption and fluorescence wavelengths are limited to 8 nm (0.09 eV) and 9 nm (0.07 eV), respectively. A valuable correlation between the experimental and theoretical phosphorescence auxochromic displacements has also been unravelled. The differences between the wavelengths of the various electronic processes of a given dye tend to be fairly predicted, especially for the fluorescence-phosphoresence shifts that are strongly overestimated by TD-DFT.
116 citations
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TL;DR: A sensitive and specific chemical method for the estimation of malic acid in biological materials has long been desired and the quantitative precipitation of calcium malate by alcohol as a means of fractionation from biological materials gives it additional specificity.
69 citations