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Zwitterionic N2O2‑Type Protonated Dipyrrin Bearing a Phosphate Anionic Moiety as a pH-Responsive Fluorescence Indicator

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posted on 2015-06-19, 00:00 authored by Masaki Yamamura, Hiroyuki Takizawa, Tatsuya Nabeshima
Zwitterionic protonated-dipyrrin 1 bearing a phosphate unit was synthesized from the N2O2-type tetradentate dipyrrin ligand. Compound 1 is in equilibrium with the deprotonated form 1′ with a pKa value of 5.8. Compound 1 exhibited a pH-responsive fluorescence under physiological conditions; the fluorescence intensity increased in aqueous media as the pH increased. In living cells, 1 also exhibited emission responsive to pH. Thus, 1 should be applicable as a pH probe for detecting tumor cells.