TY  - JOUR
A1  - Schwarze, Thomas
A1  - Mueller, Holger
A1  - Schmidt, Darya
A1  - Riemer, Janine
A1  - Holdt, Hans-Jürgen
T1  - Design of Na+-Selective Fluorescent Probes: A Systematic Study of the Na+-Complex Stability and the Na+/K+ Selectivity in Acetonitrile and Water
JF  - Chemistry - a European journal
N2  - There is a tremendous demand for highly Na+-selective fluoroionophores to monitor the top analyte Na+ in life science. Here, we report a systematic route to develop highly Na+/K+ selective fluorescent probes. Thus, we synthesized a set of fluoroionophores 1, 3, 4, 5, 8 and 9 (see Scheme 1) to investigate the Na+/K+ selectivity and Na(+-)complex stability in CH3CN and H2O. These Na+-probes bear different 15-crown-5 moieties to bind Na+ stronger than K+. In the set of the diethylaminocoumarin-substituted fluoroionophores 1-5, the following trend of fluorescence quenching 1 > 3 > 2 > 4 > 5 in CH3CN was observed. Therefore, the flexibility of the aza-15-crown-5 moieties in 1-4 determines the conjugation of the nitrogen lone pair with the aromatic ring. As a consequence, 1 showed in CH3CN the highest Na+-induced fluorescence enhancement (FE) by a factor of 46.5 and a weaker K+ induced FE of 3.7. The Na+-complex stability of 1-4 in CH3CN is enhanced in the following order of 2 > 4 > 3 > 1, assuming that the O-atom of the methoxy group in the ortho-position, as shown in 2, strengthened the Na+-complex formation. Furthermore, we found for the N( o-methoxyphenyl) aza-15-crown-5 substituted fluoroionophores 2, 8 and 9 in H2O, an enhanced Na+-complex stability in the following order 8 > 2 > 9 and an increased Na+/K+ selectivity in the reverse order 9 > 2 > 8. Notably, the Na+-induced FE of 8 (FEF = 10.9), 2 (FEF = 5.0) and 9 (FEF = 2.0) showed a similar trend associated with a decreased K+-induced FE [8 (FEF = 2.7) > 2 (FEF = 1.5) > 9 (FEF = 1.1)]. Here, the Na+-complex stability and Na+/K+ selectivity is also influenced by the fluorophore moiety. Thus, fluorescent probe 8 (K-d = 48 mm) allows high-contrast, sensitive, and selective Na+ measurements over extracellular K+ levels. A higher Na+/K+ selectivity showed fluorescent probe 9, but also a higher Kd value of 223 mm. Therefore, 9 is a suitable tool to measure Na+ concentrations up to 300 mm at a fluorescence emission of 614 nm.
KW  - crown compounds
KW  - fluorescence
KW  - fluorescent probes
KW  - potassium
KW  - sodium
Y1  - 2017
U6  - https://doi.org/10.1002/chem.201605986
SN  - 0947-6539
SN  - 1521-3765
VL  - 23
SP  - 7255
EP  - 7263
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Schwarze, Thomas
A1  - Mertens, Monique
A1  - Mueller, Peter
A1  - Riemer, Janine
A1  - Wessig, Pablo
A1  - Holdt, Hans-Jürgen
T1  - Highly K+-Selective Fluorescent Probes for Lifetime Sensing of K+ in Living Cells
JF  - Chemistry - a European journal
N2  - The new K+-selective fluorescent probes 1 and 2 were obtained by Cu-I-catalyzed 1,3-dipolar azide alkyne cycloaddition (CuAAC) reactions of an alkyne-substituted [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD) ester fluorophore with azido-functionalized N-phenylaza-18-crown-6 ether and N-(o-isopropoxy) phenylaza-18-crown-6 ether, respectively. Probes 1 and 2 allow the detection of K+ in the presence of Na+ in water by fluorescence enhancement (2.2 for 1 at 2000mm K+ and 2.5 for 2 at 160mm K+). Fluorescence lifetime measurements in the absence and presence of K+ revealed bi-exponential decay kinetics with similar lifetimes, however with different proportions changing the averaged fluorescence decay times ((f(av))). For 1 a decrease of (f(av)) from 12.4 to 9.3ns and for 2 an increase from 17.8 to 21.8ns was observed. Variation of the substituent in ortho position of the aniline unit of the N-phenylaza-18-crown-6 host permits the modulation of the K-d value for a certain K+ concentration. For example, substitution of H in 1 by the isopropoxy group (2) decreased the K-d value from >300mm to 10mm. 2 was chosen for studying the efflux of K+ from human red blood cells (RBC). Upon addition of the Ca2+ ionophor ionomycin to a RBC suspension in a buffer containing Ca2+, the fluorescence of 2 slightly rose within 10min, however, after 120min a significant increase was observed.
KW  - electron transfer
KW  - fluorescence lifetime
KW  - fluorescent probes
KW  - living cells
KW  - potassium
Y1  - 2017
U6  - https://doi.org/10.1002/chem.201704368
SN  - 0947-6539
SN  - 1521-3765
VL  - 23
SP  - 17186
EP  - 17190
PB  - Wiley-VCH
CY  - Weinheim
ER  -