Fluorescence intensity and lifetime-based cyanide sensitive probes for physiological safeguard |
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Authors: | Ramachandram Badugu Chris D. Geddes |
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Affiliation: | a Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, Medical Biotechnology Center, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA b Institute of Fluorescence and Center for Fluorescence Spectroscopy, Medical Biotechnology Center, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201, USA |
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Abstract: | We characterize six new fluorescent probes that show both intensity and lifetime changes in the presence of free uncomplexed aqueous cyanide, allowing for fluorescence based cyanide sensing up to physiological safeguard levels, i.e. <30 μM. One of the probes, m-BMQBA, shows a ≈15-fold reduction in intensity and a ≈10% change in mean lifetime at this level.The response of the new probes is based on their ability to bind the cyanide anion through a boronic acid functional group, changing from the neutral form of the boronic acid group R-B(OH)2 to the anionic R-B−(CN)3 form, a new cyanide binding mechanism which we have recently reported. The presence of an electron deficient quaternary heterocyclic nitrogen nucleus, and the electron rich cyanide bound form, provides for the intensity changes observed. We have determined the disassociation constants of the probes to be in the range ≈15-84 μM3. In addition we have synthesized control compounds which do not contain the boronic acid moiety, allowing for a rationale of the cyanide responses between the probe isomers to be made.The lifetime of the cyanide bound probes are significantly shorter than the free R-B(OH)2 probe forms, providing for the opportunity of lifetime based cyanide sensing up to physiologically lethal levels.Finally, while fluorescent probes containing the boronic acid moiety have earned a well-deserved reputation for monosaccharide sensing, we show that strong bases such as CN− and OH− preferentially bind as compared to glucose, enabling the potential use of these probes for cyanide safeguard and determination in physiological fluids, especially given that physiologies do not experience any notable changes in pH. |
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Keywords: | BA, boronic acid BAF and BAFs, boronic acid containing fluorophore/s o-BAQBA, N-(2-boronobenzyl)-6-aminoquinolinium bromide o, m, p-BMOQBA, N-(2, 3 or 4-boronobenzyl)-6-methoxyquinolinium bromide BMOQ, N-benzyl-6-methoxyquinolinium bromide o, m, p-BMQBA, N-(2,3,4-boronobenzyl)-6-methylquinolinium bromide BMQ, N-benzyl-6-methylquinolinium bromide KSV, Stern-Volmer quenching constant LD, laser diode LD50, lethal dose to 50% of the population LED, light emitting diode PET, photoinduced electron transfer TCSPC, time-correlated single photon counting |
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