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 - Mueller, Holger A1 - Ast, Sandra A1 - Steinbrück, Dorte A1 - Eidner, Sascha A1 - Geißler, Felix A1 - Kumke, Michael Uwe A1 - Holdt, Hans-Jürgen T1 - Fluorescence lifetime-based sensing of sodium by an optode JF - Chemical communications N2 - We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1-10 mM by measuring reversible fluorescence decay time changes. Y1 - 2014 U6 - https://doi.org/10.1039/c4cc06112h SN - 1359-7345 SN - 1364-548X VL - 50 IS - 91 SP - 14167 EP - 14170 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Mueller, Holger A1 - Junginger, Matthias A1 - Kelling, Alexandra A1 - Schilde, Uwe A1 - Strehmel, Veronika A1 - Holdt, Hans-Jürgen T1 - Imidazolium 2-substituted 4,5-dicyanoimidazolate ionic liquids: synthesis, crystal structures and structure-thermal property relationships JF - Chemistry - a European journal N2 - Thirty six novel ionic liquids (ILs) with 1-butyl-3-methylimidazolium and 3-methyl-1-octylimidazolium cations paired with 2-substitited 4,5-dicyanoimidazolate anions (substituent at C2=chloro, bromo, methoxy, vinyl, amino, methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and phenyl) have been synthesized and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and single-crystal X-ray crystallography. The effects of cation and anion type and structure on the thermal properties of the resulting ionic liquids, including several room temperature ionic liquids (RTILs) are examined and discussed. ILs exhibited large liquid and crystallization ranges and formed glasses on cooling with glass transition temperatures in the range of -22 to -68 degrees C. The effects of alkyl substituents of the imidazolate anion reflected the crystallization, melting points and thermal decomposition of the ILs. The Coulombic packing force, van der Waals forces and size of the anions can be considered for altering the thermal transitions. Three crystal structures of the ILs were determined and the effects of changes to the cations and anions on the packing of the structure were investigated. KW - crystal structures KW - imidazole KW - ion exchange KW - ionic liquids KW - pi-pi stacking Y1 - 2014 U6 - https://doi.org/10.1002/chem.201304934 SN - 0947-6539 SN - 1521-3765 VL - 20 IS - 26 SP - 8170 EP - 8181 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schwarze, Thomas A1 - Mueller, Holger A1 - Dosche, Carsten A1 - Klamroth, Tillmann A1 - Mickler, Wulfhard A1 - Kelling, Alexandra T1 - Luminescence detection of open-shell transition-metal ions by photoinduced electron transfer controlled by internal charge transfer of a receptor Y1 - 2007 UR - http://onlinelibrary.wiley.com/doi/10.1002/ange.200603992/pdf U6 - https://doi.org/10.1002/anie.200603992 ER -