Extraction and complexation of alkali and alkaline earth metal cations by lower-rim calix[4]arene diethylene glycol amide derivatives

Abstract

The novel calix [4]arene derivatives, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(N-(2-(2-metoxyetoxy)ethyl)carbamoyl methoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra(N,N-bis(2-(2-metoxyetoxy)ethyl)carbamoyl methoxy)calix[4]arene (2), were prepared by introducing diethylene glycol subunits at a lower calixarene rim. Complexation affinities of these compounds towards alkali and alkaline earth metal cations were studied at 25 °C in acetonitrile and methanol by means of spectrophotometric, conductometric, and potentiometric titrations. The stability constants of the corresponding complexes with 1:1 (cation:ligand) stoichiometry were determined (in some cases only estimated), and their values obtained by different methods were in good agreement. Much lower stabilities of the complexes with secondary-amide derivative (1) compared to those with tertiary-amide one (2) were observed. That was presumably mostly caused by the presence of intramolecular NH•••O=C hydrogen bonds in the former case. It was found that solvent significantly affected the stability of the complexes, whereby the prepared calixarenes showed considerably higher affinities for cations in acetonitrile than in methanol. Generally, the ligands studied showed better binding abilities for alkaline earth than for alkali metal cations. The extraction of metal picrates from water to dichloromethane by complexation of metal ions with ligands 1 and 2 was also investigated. In accordance with the complex stabilities, all cations were extracted fairly well (in some cases even excelently) with tertiary-amide derivative, whereas that was not the case in the extraction experiments with the other ligand studied.

Complexation of Alkali Metal Cations by a Tertiary Amide Calix[4]Arene Derivative in Strongly Cation Solvating Solvents

“…This can be explained by assuming that the interactions of receptor with Na + cation are the strongest, due to its size complementarity with the binding site of L. As already stated, similar behaviour has been detected for many other lower-rim calix [4]arene derivatives. [4,5,8,[15][16][17] All herein studied complexation processes were accompanied by negative entropy change, which can be, at least partly, explained by the loss in translational entropy of the reactants upon complexation. The much lower affinity of compound L for lithium cation compared to Na + in NMF is primarily a result of far less pronounced enthalpic contribution to complexation Gibbs energy.…”

“…ester, ketone, and amide derivatives) have been affirmed as highly effective receptors due to a well-defined binding site with numerous donor atoms directed towards the guest. [4,5,8,15,16,17] Among these derivatives, the compounds comprising tertiary-amide groups proved to be the most efficient, exhibiting remarkably high affinities towards alkali metal cations. [4,5,17,18] The selectivity of the calixarenebased receptors is in great part a result of size complementarity of host cavity and the cation.…”

“…[4,5,8,15,16,17] Among these derivatives, the compounds comprising tertiary-amide groups proved to be the most efficient, exhibiting remarkably high affinities towards alkali metal cations. [4,5,17,18] The selectivity of the calixarenebased receptors is in great part a result of size complementarity of host cavity and the cation. Therefore, calix [4]arenes usually bind sodium cation most effectively, whereas calix [6]arene analogues bind better larger cations, like Rb + and Cs + .…”

“…[1] These macrocyclic ligands can be relatively easily functionalized at both upper and lower calixarene rim, which allows preparation of efficient receptors for charged and neutral species. [2][3][4] As a result, this class of compounds has been exploited for different tasks, such as catalysis, ion extraction, [5] purification, [6] electrochemical and fluorimetric sensing, [7,8] etc. In recent advancements the potentials of calixarene based compounds as biomimetics, drugdelivery systems, [9] ion chanells, [10,11] nanomaterial components [12,13] etc.…”

“…However, most of the reported studies of alkali metal calixarene complexes were focused on a rather limited series of solvents. The most often used solvents are methanol and acetonitrile, [4,5,15,19,20] whereas the strongly cation-solvating media (e.g. N,N-dimethylformamide and dimethyl sulfoxide) were rarely investigated.…”