Interaction between Monoaza-, Diaza-, or Polyazacrown Ethers and Alkali Metal Ions in Acetonitrile by Polarography

Abstract

Crown-type compounds are of general relevance as synthetic model substances for studying physiological ion-transport processed in biological membranes, for investigating receptor and enzyme interactions as well as for the salt balance and for metabolic processes of living organisms. 1 The complexation between alkali metal ions and macrocyclic polyethers, polyamines or polyetheramines has been extensively studied by means of various methods in many solvent systems. 2,3 The fitness of the cavity size of a macrocyclic compound is an important factor for determining the stability of an alkali metal complex. 4 Solvent effects in the complexation of cryptand [2.2] (1,10-diaza-18-crown-6) with Li + have indicated that the stability of the complex varies inversely with the donicity of the solvent.5 However, little attention may have been paid to the increase in the basicity of coordinating atoms by substitution of the oxygen atoms with NH groups in crown ethers.In the present study, the formation constants of alkali metal complexes with monoaza-, diaza-, and polyazacrown ethers were obtained by means of mainly d.c. polarography; differential pulse polarography on DME and cyclic voltammetry on HMDE were additionally employed.The mercurydissolution processes of the macrocyclic compounds were clarified during the course of examining alkali metal ion complexation. The variation in the formation constants is discussed from the viewpoint of not only cavity size, but also the interaction between the Lewis acids and bases. The main purpose of the present study was to investigate the effects of the number of substitution of the oxygen atoms with NH groups in the crown ethers on the stabilities of the Li + and Na + complexs of 12-crown-4, 15-crown-5, and 18-crown-6.We have developed a new analytical method in d.c. polarography for obtaining the complex formation constant between cations and an anion which induces the mercurydissolution wave on DME. 6 This method was first successfully applied to the Li + -CH3COO-system in acetonitrile. The formation constants of a "reverse coordinated" species, CH3COO -(M + )2 (M + = Li + or Na + ), 6 and later that of (Li + )2Cl -7were obtained. Since then, we have revealed that the Li + ion operates an unexpectedly strong coordination ability in protophobic aprotic solvents. 8,9 Our method was found to be very useful for examining complex formation between alkali metal ions and macrocyclic polyamines (cyclam, tetramethylcyclam) 10,11 as well as acyclic polyamines (ethylenediamine, trien, tetren). 12The complex formation of cryptand[2.2] and its sulfur derivative (ATCO: 1,10-diaza-4,7,13,16-tetrathiacyclooctadecane) with alkali metal or alkaline earth metal ions in acetonitrile has been examined. 13 In principle, "the mercury-dissolution method" utilizes the The complex formation constants between alkali metal ions and monoaza-or diazacrown ethers (L) in acetonitrile have been obtained by the analytical method of d.c. polarography, in which a positive shift in E1/2 of the mercury-dissolution w...

The role of the size of aza-crown recognition moiety in azaphthalocyanine fluorescence sensors for alkali and alkaline earth metal cations

“…Their stronger binding was demonstrated both in absorption and fluorescence experiments, in which fluorescence increased by up to 100 Â and F F reached values of approximately 0.20. The stronger binding of alkaline earth metal cations is in accordance with published data in which different methods (i.e., absorption spectroscopy of chromoionophores [27], polarography [28], or laser infrared multiple photon dissociation spectroscopy [23]) were applied.…”

Organometallic Elaboration as a Strategy for Tuning the Supramolecular Characteristics of Aza-Crown Ethers

“…Starting from 1-aza-15-crown-5 ether (a15c5), reductive amination provides m -(aza-15-crown-5)­methylphenol ( 1 , Chart S1 in the Supporting Information). , The pincer-crown ether ligand precursor 1 binds Li + and Na + cations tightly in a 1:1 fashion in CD 3 CN at 25 ± 1 °C, as evidenced by the linear response of 1 H NMR spectroscopic titrations up until 1 equiv of the cation relative to the macrocycle. A competitive binding technique (see Section S2 in the Supporting Information) provided association constants ( K a ) for 1 with both LiOTf ( K a (Li + ) = 130000 ± 4000 M –1 ) and NaBAr F 4 ( K a (Na + ) = 79000 ± 4000 M –1 , Ar F = 3,5-bis­(trifluoromethyl)­phenyl) .…”

Host–Guest Complexes of Oligopyridine Cryptands: Prediction of Ion Selectivity by Quantum Chemical Calculations

“…[28,29] This is surprising since different cryptand/cryptate or crown ether-solvent combinations have been investigated, [30][31][32][33][34] especially with respect to their transport properties [35] or ion conductivity and potential applications in batteries and capacitors, [36] while parallel alkali and alkaline-earth ion complexes with phenanthroline and bipyridine moieties have also been studied. [37] In a recent report we demonstrated that ion selectivity can be studied by quantum chemical methods for [2.2.2] and smaller homologues.…”