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A New Fluorescent Probe for Zinc(II): An 8‐Hydroxy‐5‐ N , N ‐dimethylaminosulfonylquinoline‐Pendant 1,4,7,10‐Tetraazacyclododecane
Author(s) -
Aoki Shin,
Sakurama Kazusa,
Matsuo Nanako,
Yamada Yasuyuki,
Takasawa Ryoko,
Tanuma Seiichi,
Shiro Motoo,
Takeda Kei,
Kimura Eiichi
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600379
Subject(s) - cyclen , deprotonation , chemistry , moiety , potentiometric titration , quinoline , aqueous solution , titration , fluorescence , zinc , medicinal chemistry , proton nmr , nuclear chemistry , stereochemistry , crystallography , inorganic chemistry , organic chemistry , ion , physics , quantum mechanics
A new fluorescent probe for Zn 2+ , namely, 8‐hydroxy‐5‐ N , N ‐dimethylaminosulfonylquinolin‐2‐ylmethyl‐pendant cyclen (L 8 ), was designed and synthesized (cyclen=1,4,7,10‐tetraazacyclododecane). By potentiometric pH, 1 H NMR, and UV spectroscopic titrations, the deprotonation constants p K a1 –p K a6 of L 8 ⋅4 HCl were determined to be <2, <2, <2 (for amino groups of the cyclen and quinoline moieties), 7.19±0.05 (for 8‐OH of the quinoline moiety), 10.10±0.05, and 11.49±0.05, respectively, at 25 °C with I =0.1 (NaNO 3 ). The results of 1 H NMR, potentiometric pH, and UV titrations, as well as single‐crystal X‐ray diffraction analysis, showed that L 8 and Zn 2+ form a 1:1 complex [Zn(H −1 L 8 )], in which the 8‐OH group of the quinoline ring of L 8 is deprotonated and coordinates to Zn 2+ , in aqueous solution at neutral pH. On addition of one equivalent of Zn 2+ and Cd 2+ , the fluorescence emission of L 8 (5 μ M ) at 512 nm in aqueous solution at pH 7.4 [10 m M HEPES with I =0.1 (NaNO 3 )] and 25 °C increased by factors of 17 and 43, respectively. We found that the cyclen moiety has the unique property of quenching the fluorescence emission of the quinolinol moiety when not complexed with metal cations, but enhancing emission when complexed with Zn 2+ or Cd 2+ . In addition, the Zn 2+ –L 8 complex [Zn(H −1 L 8 )] is much more thermodynamically and kinetically stable ( K d {Zn(H −1 L 8 )}=[Zn 2+ ] free [L 8 ] free /[Zn(H −1 L 8 )]=8 f M at pH 7.4) than the Zn 2+ complexes of our previous Zn 2+ fluorophores ([Zn(H −1 L 2 )] and [Zn(L 3 )]). Furthermore, formation of [Zn(H −1 L 8 )] is much faster than those of [Zn(H −1 L 2 )] and [Zn(L 3 )]. The staining of early‐stage apoptotic cells with L 8 is also described.