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

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 K_d of 19 mm , but the K_d 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 K_d values (K_d^K+=45 mm and K_d^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.     

ACE applied to the quantitative characterization of benzo‐18‐crown‐6‐ether binding with alkali metal ions in a methanol–water solvent system

ACE was applied to the quantitative evaluation of noncovalent binding interactions between benzo‐18‐crown‐6‐ether (B18C6) and several alkali metal ions, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in a mixed binary solvent system, methanol–water (50/50 v/v). The apparent binding (stability) constants (K_b) of B18C6–alkali metal ion complexes in the hydro‐organic medium above were determined from the dependence of the effective electrophoretic mobility of B18C6 on the concentration of alkali metal ions in the BGE using a nonlinear regression analysis. Before regression analysis, the mobilities measured by ACE at ambient temperature and variable ionic strength of the BGE were corrected by a new procedure to the reference temperature, 25°C, and the constant ionic strength, 10 mM . In the 50% v/v methanol–water solvent system, like in pure methanol, B18C6 formed the strongest complex with potassium ion (log K_b=2.89±0.17), the weakest complex with cesium ion (log K_b=2.04±0.20), and no complexation was observed between B18C6 and the lithium ion. In the mixed methanol–water solvent system, the binding constants of the complexes above were found to be about two orders lower than in methanol and about one order higher than in water.     

Two‐Photon Probes for Zn2+ Ions with Various Dissociation Constants. Detection of Zn2+ Ions in Live Cells and Tissues by Two‐Photon Microscopy

A series of Zn²⁺‐selective two‐photon fluorescent probes (AZnM1−AZnN) that had a wide range of dissociation constants (K_d^TP=8 nm‐ 12 μM ) were synthesized. These probes showed appreciable water solubility (>3 μM ), cell permeability, high photostability, pH insensitivity at pH>7, significant two‐photon action cross‐sections (86–110 GM) upon complexation with Zn²⁺, and can detect the Zn²⁺ ions in HeLa cells and in living tissue slices of rat hippocampal at a depth of >80 μm without mistargeting and photobleaching problems. These probes can potentially find application in the detection of various amounts of Zn²⁺ ions in live cells and intact tissues.     

A Highly K+‐Selective Phenylaza‐[18]crown‐6‐Lariat‐Ether‐Based Fluoroionophore and Its Application in the Sensing of K+ Ions with an Optical Sensor Film and in Cells

Herein, we report the synthesis of two phenylaza‐[18]crown‐6 lariat ethers with a coumarin fluorophore ( 1 and 2 ) and we reveal that compound 1 is an excellent probe for K⁺ ions under simulated physiological conditions. The presence of a 2‐methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat‐free phenylaza‐[18]crown‐6 ether analogues. Probe 1 shows a high K⁺/Na⁺ selectivity and a 2.5‐fold fluorescence enhancement was observed in the presence of 100 mM K⁺ ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8 % per 1 mM K⁺ within the range 1–10 mM K⁺. The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K⁺ ions on both the extracellular and intracellular levels.     

Kinetic isotope effects and rate constants for the gas‐phase reactions of three deuterated toluenes with OH from 298 to 353 K

The rate constants for the gas‐phase reactions of three deuterated toluenes with hydroxyl radicals were measured using the relative rate technique over the temperature range 298–353 K at about 1 atm total pressure. The OH radicals were generated by photolysis of H₂O₂, and helium was used as the diluent gas. The disappearance of reactants was followed by online mass spectrometry, which resulted in high time resolution, allowing for a large amount of data to be collected and used in the determination of the Arrhenius parameters. The following Arrhenius expressions have been determined for these reactions (in units of cm³ molecule^?1 s^?1): k=(6.42_?0.99^+1.17)×10^?13exp [(661±54)/T] for toluene‐d₃, k=(2.11_?0.69^+1.03)×10^?12exp [(287±128)/T]for toluene‐d₅, and k=(1.40^+0.44_?0.33)×10^?12exp [(404±88)/T]for toluene‐d₈. The kinetic isotope effects (KIEs, k_H/k_D) of these reactions were 1.003 ± 0.042 for all three compounds at 298 K. The KIE for toluene‐d₃ was temperature dependent; at 350 K, its KIE was 1.122^+0.048_?0.046. The KIE of toluene‐d₅ and toluene‐d₈ did not vary significantly with temperature. These KIE results suggest that methyl H‐atom abstraction is more important than aromatic OH addition at higher temperatures. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 821–827, 2012     

Na+ Selective Fluorescent Tools Based on Fluorescence Intensity Enhancements,Lifetime Changes,and on a Ratiometric Response

Over the years, we developed highly selective fluorescent probes for K⁺ in water, which show K⁺-induced fluorescence intensity enhancements, lifetime changes, or a ratiometric behavior at two emission wavelengths (cf. Scheme 1, K1 – K4 ). In this paper, we introduce selective fluorescent probes for Na⁺ in water, which also show Na⁺ induced signal changes, which are analyzed by diverse fluorescence techniques. Initially, we synthesized the fluorescent probes 2 , 4 , 5 , 6 and 10 for a fluorescence analysis by intensity enhancements at one wavelength by varying the Na⁺ responsive ionophore unit and the fluorophore moiety to adjust different K_d values for an intra- or extracellular Na⁺ analysis. Thus, we found that 2 , 4 and 5 are Na⁺ selective fluorescent tools, which are able to measure physiologically important Na⁺ levels at wavelengths higher than 500 nm. Secondly, we developed the fluorescent probes 7 and 8 to analyze precise Na⁺ levels by fluorescence lifetime changes. Herein, only 8 (K_d=106 mm ) is a capable fluorescent tool to measure Na⁺ levels in blood samples by lifetime changes. Finally, the fluorescent probe 9 was designed to show a Na⁺ induced ratiometric fluorescence behavior at two emission wavelengths. As desired, 9 (K_d=78 mm ) showed a ratiometric fluorescence response towards Na⁺ ions and is a suitable tool to measure physiologically relevant Na⁺ levels by the intensity change of two emission wavelengths at 404 nm and 492 nm.     

Non‐Resonant z‐Scan Characterization of the Third‐Order Nonlinear Optical Properties of Conjugated Poly(thiophene azines)

The nonlinear optical properties of a functionalized poly(thiophene azine), namely, poly(3,4‐didodecylthiophene azine), PAZ, at the optical telecommunication wavelength of 1550 nm are investigated by means of the closed‐aperture z‐scan technique in both thin films and solutions. Values of χ⁽³⁾=(2.4±0.4)×10^?13 esu, n₂=(4.0±0.7)×10^?15 cm² W^?1, and γ=(4.5±0.7)×10^?34 esu are estimated for the third‐order (Kerr) susceptibility, the intensity‐dependent refractive index, and the molecular second hyperpolarizability of solution samples, respectively. A very small dependence on the polymer chain length is found. Markedly higher values of (4.4±1.1)×10^?11 esu, (6.6±1.0)×10^?13 cm² W^?1, and (5.0±0.8)×10^?33 esu are measured for the corresponding quantities in thick (up to 20 μm) polymer films cast on quartz plates. The enhancement of the NLO responses on going from solution to solid samples is attributed to a partially ordered structure and to the presence of interchain interactions leading to greater π‐electron delocalization in the cast polymer films. The results are compared with those previously obtained by using third‐harmonic generation (THG), taking into account that those data were measured under conditions of three‐photon resonance, whereas our z‐scan measurements are fully off‐resonance.     

β,β‐(1,4‐Dithiino)subporphyrin Dimers Capturing Fullerenes with Large Association Constants

β,β‐(1,4‐Dithiino)subporphyrin dimers 7‐syn and 7‐anti were synthesized by the nucleophilic aromatic substitution reaction of 2‐bromo‐3‐(4‐methoxyphenylsulfonyl)subporphyrin 4 with 2,3‐dimercaptosubporphyrin 5 under basic conditions followed by axial arylation. Additions of C₆₀ or C₇₀ to a dilute solution of 7‐anti (ca. 10^?6 m ) in toluene did not cause appreciable UV/Vis spectral changes, while similar additions to a concentrated solution (ca. 10^?3 m ) resulted in precipitation of complexes. In contrast, dimer 7‐syn captured C₆₀ and C₇₀ in different complexation stoichiometries in toluene; a 1:1 manner and a 2:1 manner, respectively, with large association constants; K_a=(1.9±0.2)×10⁶ m ^?1 for C₆₀@ 7‐syn , and K₁=(1.6±0.5)×10⁶ and K₂=(1.8±0.9)×10⁵ m ^?1 for C₇₀@( 7‐syn )₂. These association constants are the largest for fullerenes‐capture by bowl‐shaped molecules reported so far. The structures of C₆₀@ 7‐anti , C₇₀@ 7‐anti , C₆₀@ 7‐syn , and C₇₀@ 7‐syn have been determined by single‐crystal X‐ray diffraction analysis.     

Pressure effects on cation migration in 2,5‐di‐tert‐butyl‐1,4‐benzoquinone radical anion

Pressure effects on the two‐site jumping of sodium and potassium cations in a 2,5‐di‐tert‐butyl‐1,4‐benzoquinone ion pair have been studied using a high‐pressure EPR technique. The rate constants of the intramolecular and intermolecular migrations for Na⁺ and K⁺ were determined from an EPR spectral simulation. The migration rates were found to be accelerated by increasing the external pressure. Using the pressure dependence of the migration rates, we estimated the activation volumes of the intramolecular (ΔV₁^?) and intermolecular (ΔV₂^?) processes for the Na⁺ and K⁺ migrations: ΔV₁^? = ?5.3 cm³ mol^?1 and ΔV₂^? = ?29 cm³ mol^?1 for Na⁺, and ΔV₁^? = ?8.3 cm³ mol^?1 and ΔV₂^? = ?0.85 cm³ mol^?1 for K⁺. Based on the results, the mechanisms for the two‐site jumping of Na⁺ and K⁺ are discussed in terms of volume. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 397–401, 2001     

Ions Can Move a Proton‐Coupled Electron‐Transfer Reaction into Tunneling Regime

The effects of charged species on proton‐coupled electron‐transfer (PCET) reaction should be of significance for understanding/application of important chemical and biological PCET systems. Such species can be found in proximity of activated complex in a PCET reaction, although they are not involved in the charge transfer process. Reported here is the first study of the above‐mentioned effects. Here, the effects of Na⁺, K⁺, Li⁺, Ca²⁺, Mg²⁺, and Me₄N⁺ observed in PCET reaction of ascorbate monoanions with hexacyanoferrate(III) ions in H₂O reveal that, in presence of ions, this over‐the‐barrier reaction entered into tunneling regime. The observations are: a) dependence of the rate constant on the cation concentration, where the rate constant is 71 (at I = 0.0023), and 821 (at 0.5M K⁺), 847 (at 1.0M Na⁺), and 438 M ^?1 s^?1 (at 0.011M Ca²⁺); b) changes of kinetic isotope effect (KIE) in the presence of ions, where k_H/k_D=4.6 (at I = 0.0023), and 3.4 (in the presence of 0.5M K⁺), 3.3 (at 1.0M Na⁺), 3.9 (at 0.001M Ca²⁺), and 3.9 (at 0.001M Mg²⁺), respectively; c) the isotope effects on Arrhenius pre‐factor where A_H/A_D=0.97 (0.15) in absence of ions, and 2.29 (0.60) (at 0.5M Na⁺), 1.77 (0.29) (at 1.0M Na⁺), 1.61 (0.25) (at 0.5M K⁺), 0.42 (0.16) (at 0.001M Ca²⁺) and 0.16 (0.19) (at 0.001M Mg²⁺); d) isotope differences in the enthalpies of activation in H₂O and in D₂O, where ΔΔH^?(D,H)=3.9 (0.4) kJ mol^?1 in the absence of cations, 1.3 (0.6) at 0.5M Na⁺, 1.8 (0.4) at 0.5M K⁺, 1.5 (0.4) at 1.0M Na⁺, 5.5 (0.9) (at 0.001M Ca²⁺), and 7.9 (2.8) (at 0.001M Mg²⁺) kJ mol^?1; e) nonlinear proton inventory in reaction. In the H₂O/dioxane 1 : 1, the observed KIE is 7.8 and 4.4 in the absence and in the presence of 0.1M K⁺, respectively, and A_H/A_D=0.14 (0.03). The changes when cations are present in the reaction are explained in terms of termolecular encounter complex consisting of redox partners, and the cation where the cation can be found in a near proximity of the reaction‐activated complex thus influencing the proton/electron double tunneling event in the PCET process. A molecule of H₂O is involved in the transition state. The resulting ‘configuration’ is more ‘rigid’ and more appropriate for efficient tunneling with Na⁺ or K⁺ (extensive tunneling observed), i.e., there is more precise organized H transfer coordinate than in the case of Ca²⁺ and Mg²⁺ (moderate tunneling observed) in the reaction.     

A Macrocycle Based on a Heptagon‐Containing Hexa‐peri‐hexabenzocoronene

A cyclophane is reported incorporating two units of a heptagon‐containing extended polycyclic aromatic hydrocarbon (PAH) analogue of the hexa‐peri‐hexabenzocoronene (HBC) moiety (hept‐HBC). This cyclophane represents a new class of macrocyclic structures that incorporate for the first time seven‐membered rings within extended PAH frameworks. The saddle curvature of the hept‐HBC macrocycle units induced by the presence of the nonhexagonal ring along with the flexible alkyl linkers generate a cavity with shape complementarity and appropriate size to enable π interactions with fullerenes. Therefore, the cyclophane forms host–guest complexes with C₆₀ and C₇₀ with estimated binding constants of K_a=420±2 m ^?1 and K_a=(6.49±0.23)×10³ m ^?1, respectively. As a result, the macrocycle can selectively bind C₇₀ in the presence of an excess of a mixture of C₆₀ and C₇₀.     

Synthesis and optical properties of cis‐dibenzothiazolyldibenzo‐24‐crown‐8

New crown ether carrying two fluorionophores of cis‐dibenzothiazolyldibenzo‐24‐crown‐8 was synthesized from cis‐diformyldibenzo‐24‐crown‐8 and 2‐aminobenzenethiol. The binding behavior and the optical properties of the crown ether were examined through UV‐visible spectroscopy and fluorescence spectroscopy. When complexed with Na⁺, K⁺, Rb⁺, and Cs⁺ ions, it led to intramolecular charge transfer and caused the changes of the fluorescence spectra. The protonation of the crown ether was also studied. With protonation using CF₃COOH, the absorption bands and the fluorescence spectroscopy changed, the maximal fluorescence wavelengths red shifted and the fluorescence intensity with the maximum at 433 nm enhanced strongly. J. Heterocyclic Chem., (2011).     

Glu 87 of Channelrhodopsin‐1 Causes pH‐dependent Color Tuning and Fast Photocurrent Inactivation†

Channelrhodopsins (ChR1 and ChR2) are directly light‐gated ion channels acting as sensory photoreceptors in the green alga Chlamydomonas reinhardtii. These channels open rapidly after light absorption and both become permeable for cations such as H⁺, Li⁺, Na⁺, K⁺ and Ca²⁺. K_m for Ca²⁺ is 16.6 mm in ChR1 and 18.3 mm in ChR2 whereas the K_m values for Na⁺ are higher than 100 mm for both ChRs. Action spectra of ChR1 peak between 470 and 500 nm depending on the pH conditions, whereas ChR2 peaks at 470 nm regardless of the pH value. Now we created two chimeric ChRs possessing helix 1–5 of ChR1 and 6, 7 of ChR2 (ChR1/2_5/2), or 1, 2 from ChR1 and 3–7 from ChR2 (ChR1/2_2/5). Both ChR‐chimera still showed pH‐dependent action spectra shifts. Finally, a mutant ChR1E87Q was generated that inactivated only slowly in the light and showed no spectral shift upon pH change. The results indicate that protonation/deprotonation of E87 in helix 1 alters the chromophore polarity, which shifts the absorption and modifies channel inactivation accordingly. We propose a trimodal counter ion complex for ChR1 but only a bimodal complex for ChR2.     

Sodium 2‐oxo‐3‐semicarbazono‐2,3‐dihydro‐1H‐indole‐5‐sulfonate dihydrate

The title compound, Na⁺·C₉H₇N₄O₅S⁻·2H₂O, presents a Z configuration around the imine C=N bond and an E configuration around the C(O)NH₂ group, stabilized by two intra­molecular hydrogen bonds. The packing is governed by ionic inter­actions between the Na⁺ cation and the surrounding O atoms. The ionic unit, Na⁺ and 2‐oxo‐3‐semicarbazono‐2,3‐dihydro‐1H‐indole‐5‐sulfonate, forms layers extending in the bc plane. The layers are connected by hydrogen bonds involving the water mol­ecules.     

Study of small chlorine‐doped potassium clusters by thermal ionization mass spectrometry

The theoretical calculations have predicted that nonmetal‐doped potassium clusters can be used in the synthesis of a new class of charge‐transfer salts which can be considered as potential building blocks for the assembly of novel nanostructured material. In this work, K_nCl (n = 2–6) and K_nCl_n?1 (n = 3 and 4) clusters were produced by vaporization of a solid potassium chloride salt in a thermal ionization mass spectrometry. The ionization energies (IEs) were measured, and found to be 3.64 ± 0.20 eV for K₂Cl, 3.67 ± 0.20 eV for K₃Cl, 3.62 ± 0.20 eV for K₄Cl, 3.57 ± 0.20 eV for K₅Cl, 3.69 ± 0.20 eV for K₆Cl, 3.71 ± 0.20 eV for K₃Cl₂ and 3.72 ± 0.20 eV for K₄Cl₃. The K_nCl⁺ (n = 3–6) clusters were detected for the first time in a cluster beam generated by the thermal ionization source of modified design. Also, this work is the first to report experimentally obtained values of IEs for K_nCl⁺ (n = 3–6) and K_nCl_n?1⁺ (n = 3 and 4) clusters. The ionization energies for K_nCl⁺ and K_nCl_n?1⁺ clusters are much lower than the 4.34 eV of the potassium atom; hence, these clusters should be classified as ‘superalkali’ species. Copyright © 2012 John Wiley & Sons, Ltd.     

Capillary affinity electrophoresis and ab initio calculation studies of valinomycin complexation with Na+ ion

In a combined experimental and theoretical approach, the interactions of valinomycin (Val), macrocyclic depsipeptide antibiotic ionophore, with sodium cation Na⁺ have been investigated. The strength of the Val–Na⁺ complex was evaluated experimentally by means of capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the sodium ion concentration in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, 0–40 mM NaCl), the apparent binding (stability) constant (K_b) of the Val–Na⁺ complex in methanol was evaluated as log K_b = 1.71 ± 0.16. Besides, using quantum mechanical density functional theory (DFT) calculations, the most probable structures of the nonhydrated Val–Na⁺ as well as hydrated Val–Na⁺·H₂O complex species were proposed. Compared to Val–Na⁺, the optimized structure of Val–Na⁺·H₂O complex appears to be more realistic as follows from the substantially higher binding energy (118.4 kcal/mol) of the hydrated complex than that of the nonhydrated complex (102.8 kcal/mol). In the hydrated complex, the central Na⁺ cation is bound by strong bonds to one oxygen atom of the respective water molecule and to four oxygens of the corresponding C=O groups of the parent valinomycin ligand.     

ESI‐MS studies of the non‐covalent interactions between biologically important metal ions and N‐sulfonylcytosine derivatives

The aim of this report is to present the electrospray ionization mass spectrometry results of the non‐covalent interaction of two biologically active ligands, N‐1 ‐ (p‐toluenesulfonyl)cytosine, 1‐TsC, 1 and N‐1 ‐ methanesulfonylcytosine, 1‐MsC, 2 and their Cu(II) complexes Cu(1‐TsC‐N3)₂Cl₂, 3 and Cu(1‐MsC‐N3)₂Cl₂ and 4 with biologically important cations: Na⁺, K⁺, Ca²⁺, Mg²⁺ and Zn²⁺. The formation of various complex metal ions was observed. The alkali metals Na⁺ and K⁺ formed clusters because of electrostatic interactions. Ca²⁺ and Mg²⁺ salts produced the tris ligand and mixed ligand complexes. The interaction of Zn²⁺ with 1–4 produced monometal and dimetal Zn²⁺ complexes as a result of the affinity of Zn²⁺ ions toward both O and N atoms. Copyright © 2016 John Wiley & Sons, Ltd.     

Rate constants for the reactions of OH radicals and Cl atoms with Di‐n‐Propyl ether and Di‐n‐Butyl ether and their deuterated analogs

Using relative rate methods, rate constants for the gas‐phase reactions of OH radicals and Cl atoms with di‐n‐propyl ether, di‐n‐propyl ether‐d₁₄, di‐n‐butyl ether and di‐n‐butyl ether‐d₁₈ have been measured at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in cm³ molecule⁻¹ s⁻¹ units) were: OH radical reactions, di‐n‐propyl ether, (2.18 ± 0.17) × 10⁻¹¹; di‐n‐propyl ether‐d₁₄, (1.13 ± 0.06) × 10⁻¹¹; di‐n‐butyl ether, (3.30 ± 0.25) × 10⁻¹¹; and di‐n‐butyl ether‐d₁₈, (1.49 ± 0.12) × 10⁻¹¹; Cl atom reactions, di‐n‐propyl ether, (3.83 ± 0.05) × 10⁻¹⁰; di‐n‐propyl ether‐d₁₄, (2.84 ± 0.31) × 10⁻¹⁰; di‐n‐butyl ether, (5.15 ± 0.05) × 10⁻¹⁰; and di‐n‐butyl ether‐d₁₈, (4.03 ± 0.06) × 10⁻¹⁰. The rate constants for the di‐n‐propyl ether and di‐n‐butyl ether reactions are in agreement with literature data, and the deuterium isotope effects are consistent with H‐atom abstraction being the rate‐determining steps for both the OH radical and Cl atom reactions. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 425–431, 1999     

Facilitated Ion‐Transfer of Sodium Cation by (Anthraquinone‐1‐yloxy) methane‐15‐crown‐5 Across the Water/1,2‐Dichloroethane Microinterface

The transfer of sodium cation facilitated by (anthraquinone‐1‐yloxy) methane‐15‐crown‐5 (L) has been investigated at the water/1,2‐dichloroethane microinterface supported at the tip of a micropipette. The diffusion coefficient of (anthraquinone‐1‐yloxy) methane‐15‐crown‐5 obtained was (3.42±0.20)×10^?6 cm² s^?1. The steady‐state voltammograms were observed for forward and backward scans due to sodium ion transfer facilitated by L with 1 : 1 stoichiometry. The mechanism corresponded to an interfacial complexation (TIC) and interfacial dissociation (TID) process. The association constant was calculated to be log β_o=11.08±0.03 in the DCE phase. The association constant of other alkali metals (Li⁺, K⁺, Rb⁺) were also obtained.     

Metal‐Cation Recognition in Water by a Tetrapyrazinoporphyrazine‐Based Tweezer Receptor

A series of zinc azaphthalocyanines with two azacrowns in a rigid tweezer arrangement were prepared and the fluorescence sensing properties were investigated. The size‐driven recognition of alkali and alkaline earth metal cations was significantly enhanced by the close cooperation of the two azacrown units, in which both donor nitrogen atoms need to be involved in analyte binding to switch the sensor on. The mono‐ or biphasic character of the binding isotherms, together with the binding stoichiometry and magnitude of association constants (K_A), indicated specific complexation of particular analytes. Water solvation was shown to play an important role and resulted in a strong quenching of sensor fluorescence in the ON state. The lead compound was embedded into silica nanoparticles and advantageous sensing properties towards K⁺ were demonstrated in water (λ_F=671 nm, apparent K_A=82 m ^?1, increase of 17×), even in the presence of (supra)physiological concentrations of Na⁺ and Ca²⁺.