BODIPY‐Equipped Benzo‐Crown‐Ethers as Fluorescent Sensors for pH Independent Detection of Sodium and Potassium Ions

Abstract

Herein, we report on fluorescent probes which enable the selective quantification of Na+ and K+ in water by fluorescence enhancement (FE) independent of the pH value. These fluorescent probes, so called fluoroionophores, consist of benzo‐crown‐ether derivatives as ionophores, a benzo‐15‐crown‐5 (cf. 5) or a benzo‐18‐crown‐6 (cf. 6), respectively, to selectively bind either Na+ or K+ and a 4,4‐difluoro‐1,3,5,7‐tetramethyl‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) fluorophore. The fluoroionophore 5 shows a FE factor of 7.3 in the presence of 1000 mM Na+ and 6 of 4.7 upon addition of 250 mM K+ in an acidic environment. The dissociation constants (Kd) for 5+Na+ is 276 mM and for 6+K+ is 18 mM enabling the fluorometric determination of biological relevant Na+ or K+ levels. The fluorescence intensities of 5 and 6 were not impacted over a broad range of proton concentrations (pH stable from 3.5 to 9.5) and by the presence of other biologically relevant cations.

Selective and pH‐Independent Detection of Ba2+ in Water by a Benzo‐21‐crown‐7‐Functionalized BODIPY

“…Figure 4c) interact stronger with Ba 2+ than O1 and O7 in 1 (Figure 4a). Further, although surprisingly K + should also fit excellently into the benzo‐18‐crown‐6 it only shows a minor fluorescence enhancement ( 2 +10 mM K + , FEF =2.3 [17] ) presumably due to the lower charge density of K + compared to Ba 2+ [29] . The ion‐dipole interaction of Ba 2+ with the two benzo oxygen donors in 2 is higher than for 2 +K + and even lower for 1 +K + .…”

“…This was also observed for probe 2. [17] Further, the fluorescent probe 1 shows almost constant FEFs in the pH range from 3.5 to 9.5 in the presence of 60 mM Ba 2 + (cf. Figure S9a).…”

“…[11f] In a recent study, which aimed on the selective recognition of alkali ions in water, we reported on Na + and K + sensitive BODIPY benzo-crown-ether fluoroionophores. [17] For K + detection, a benzo-18-crown-6 equipped fluorescent probe 2 (cf. Scheme 1) was synthesized, which showed high affinity to K + , but also a cross-sensitivity to Ba 2 + .…”

“…In a recent study, which aimed on the selective recognition of alkali ions in water, we reported on Na + and K + sensitive BODIPY benzo‐crown‐ether fluoroionophores [17] . For K + detection, a benzo‐18‐crown‐6 equipped fluorescent probe 2 (cf.…”

Ternary recognition fluorescent probe for lysosome acidification counter-ion studies via Cl−, K+, and pH

“…18 Fortunately, a K + probe that does not rely on organic amines was recently developed, but without lysosome targeting capability. 19 Dextran is a protonation-independent lysosomal targeting agent, which is delivered to lysosomes through the endocytic pathway. [20][21][22] Therefore, it is promising to prepare fluorescent probes for lysosomal Cl À , K + , and pH by rational design of ionsensitive fluorophores and assembling them with dextran.…”