Anion emission, absence

We suggest the following possible reasons for the absence of anion emission in these experiments First, it is possible for water and methanol to form adducts with CO2 which might inhibit their ability to solvate the proton. This possibility was checked using water as a cosolvent in supercritical ethylene, which will not interact with water data do not indicate formation of an anion therefore solvent/cosolvent adducts are not a plausible explanation. Second, perhaps the anion is being formed but is quenched very efficiently. The anion species would be more susceptible to quenching than the neutral molecule. This possibility could be investigated in principle with fluorescence lifetime studies, but this has not been done. It is entirely possible that the anion emission is so weak as to be hidden underneath the tail of the neutral emission. 

The heparin and poly-L-glutamate titrations show a markedly different behavior than do the DNA titrations. As polyanion is added, the fluorescence of the an-thrylpolyamine solution decreases until a well-defined minimum is reached. A new emission at 510 nm, which we assign to the anthracene excimer of 14, increases and decreases coincidently with the titrated fluorescence minimum. Likewise, the UV spectrum of 10 fiM 14 with added heparin shows hypochromism that occurs and disappears coincidently with the fluorescence minimum and a 2-nm red shift. We have proposed template-directed excimer formation as the physical basis for these observations. In the absence of heparin, fluorescence of the unassociated probe is observed. As heparin is added, the fluorescence decreases as a result of heparin-directed interaction between probe molecules. Additional heparin permits the fluorophore population to diffuse over the length of the poly anion, thus avoiding excimer formation and yielding a net CHEF. 

An additional piece of information can be obtained by studying a synthetic compound derived from the GFP chromophore (1-28) fluorescing at room temperature. In Fig. 3a we show the chemical structure of the compound that we studied in dioxan solution by pump-probe spectroscopy. If we look at the differential transmission spectra displayed in Fig. 3b, we observed two important features a stimulated emission centered at 508 nm and a huge and broad induced absorption band (580-700 nm). Both contributions appear within our temporal resolution and display a linear behavior as a function of the pump intensity in the low fluences limit (<1 mJ/cm2). We note that the stimulated emission red shifts with two characteristic time-scales (500 fs and 10 ps) as expected in the case of solvation dynamics. We conclude that in the absence of ESPT this chromophore has the same qualitative dynamical behavior that we attribute to the relaxed anionic form. 

Fig. 7 a Schematic representation for the monolayers of the anion-sensing library, b Relative fluorescence intensity of surfaces modified with different fluorophores and chemical functionalities in the presence of 1CT4 M solutions of HS04", NC>3", TbPCTf and AcCT as tetrabutylammonium salts in acetonitrile. The data have been normalized in the absence of anions the fluorescence emission at 585 and 575 nm for layers LO, L5-L8 and T0-T4, respectively, is set to 0... 

Hybrid amide-thiourea hosts based on p-f-butylcalix[4]arene have been prepared with coloured p-nitrophenyl (11.37a) or fluorescent 1-napthyl substituents (11.37b). In DMSO the host binds strongly to dicarboxylates, particularly adipate (log/T= 2X10" M" ), accompanied by a colour change from yellow to red in the case of the nitrophenyl derivative. The colour change is reversible on addition of protic solvents such as methanol but is not observed for acetate or other basic, monovalent anions. While large chemical shift changes for the thiourea NH protons are observed for 11.37b (A5 up to ca. 3.5 ppm), the thiourea NH resonances for the more acidic 11.37a disappear due to deprotonation. The fluorescence of the napthyl substituent in 11.37b is significantly quenched in the absence of anions due to a PET process. Addition of dicarboxylates results in an increase of fluorescence emission intensity in a broad band from 410 - 600 nm. Addition of anion reduces the efficiency of the PET process. 

A label-free detection of saccharides was proposed by Chung et A boronic acid-containing copolymer was prepared from APBA and acrylamide. The polymer was mixed with a cationic platinum complex 49 in aqueous solution buffered at pH 9.0, and the fluorescence spectra were recorded by excitation at 448 nm. In the absence of saccharides, an emission band at 577 nm is observed. With increasing glucose concentration, this band decreases while a new emission band at 800 nm grows. These spectral changes are caused by the saccharide-induced aggregation of cationic 49 onto the anionic boronate polymer. 

The concept of displacement assays for anions was further developed on the back of the aforementioned results, where the secondary amine within the cyclen structure was functionalised with a long alkyl-thiol chain for attachment to 5nm gold nanoparticles (AuNPs). Since the Eu° complex (Scheme 6.15a) lacks any antenna, the AuNP-complex conjugate was found to be non-luminescent in the absence of the p-diketonate. However, in the presence of the antenna the AuNP conjugate became highly luminescent, with characteristic Eu emission observed in buffered solution at pH 7.4 [74]. This system was then used to detect various anions, such as the phosphate flavin mononucleotide, which... 

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