title: A Highly K(+) -Selective Fluorescent Probe - Tuning the K(+) -Complex Stability and the K(+) /Na(+) Selectivity by Varying the Lariat-Alkoxy Unit of a Phenylaza[18]crown-6 Ionophore.
abstract: A desirable goal is to synthesize easily accessible and highly K(+) /Na(+) -selective fluoroionophores to monitor physiological K(+) levels in vitro and in vivo. Therefore, highly K(+) /Na(+) -selective ionophores have to be developed. Herein, we obtained in a sequence of only four synthetic steps a set of K(+) -responsive fluorescent probes 4, 5 and 6. In a systematic study, we investigated the influence of the alkoxy substitution in ortho position of the aniline moiety in π-conjugated aniline-1,2,3-triazole-coumarin-fluoroionophores 4, 5 and 6 [R=MeO (4), EtO (5) and iPrO (6)] towards the K(+) -complex stability and K(+) /Na(+) selectivity. The highest K(+) -complex stability showed fluoroionophore 4 with a dissociation constant Kd of 19 mm, but the Kd value increases to 31 mm in combined K(+) /Na(+) solutions, indicating a poor K(+) /Na(+) selectivity. By contrast, 6 showed even in the presence of competitive Na(+) ions equal Kd values (Kd (K+) =45 mm and Kd (K+/Na+) =45 mm) and equal K(+) -induced fluorescence enhancement factors (FEFs=2.3). Thus, the fluorescent probe 6 showed an outstanding K(+) /Na(+) selectivity and is a suitable fluorescent tool to measure physiological K(+) levels in the range of 10-80 mm in vitro. Further, the isopropoxy-substituted N-phenylaza[18]crown-6 ionophore in 6 is a highly K(+) -selective building block with a feasible synthetic route.
authors.affiliation: Institut für Chemie, Anorganische Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schwarze
authors.affiliation: Institut für Chemie, Anorganische Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany.
authors.forename: Radu
authors.initials: R
authors.lastname: Schneider
authors.affiliation: Institut für Chemie, Anorganische Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany.
authors.forename: Janine
authors.initials: J
authors.lastname: Riemer
authors.affiliation: Institut für Chemie, Anorganische Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany. holdt@uni-potsdam.de.
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Holdt
keywords: crown compounds; fluorescence; fluorescent probes; potassium; sodium