Effect of Na+ on solvent extraction of alkaline earth metal cations by proton-ionizable calix[4]arenes

Galina G Talanova,Vladimir S Talanov,Richard A Bartsch,Kazimierz Surowiec,Eric Scriven

doi:10.3998/ark.5550190.0011.712

Galina G Talanova, Vladimir S Talanov + Show 3 more

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https://doi.org/10.3998/ark.5550190.0011.712

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Abstract

Metal ion recognition by proton-ionizable calixarenes is often affected by interference from the Na present in many aqueous solutions. To assess the Na-effect on calixarene selectivity towards alkaline earth metal cations (AEMC), competitive solvent extraction of Mg, Ca, Sr, and Ba from aqueous solutions into chloroform by di-ionizable calix[4]arene N(trifluoromethylsulfonyl)carboxamides and corresponding carboxylic acids, conformationally mobile and restricted to cone, partial cone and 1,3-alternate conformations, was investigated in the absence and in the presence of aqueous-phase Na. The extraction selectivities were found to be altered due to contrasting Na-induced changes in the AEMC uptake. Observed increases in loadings of smaller AEMC are rationalized by their co-extraction with Na.

Highlights

Functionalized calixarenes find numerous applications in selective metal ion recognition and separations.1 For such purposes, calix[4]arenes containing pendent proton-ionizable groups2 are of special interest since these ligands generally provide stronger binding of cationic species than their neutral analogs
Di-ionizable calix[4]arene N-(X-sulfonyl)carboxamides and their parent carboxylic acids in competitive solvent extraction of alkali metal cations exhibit strong preference for Na+, with loading of this ion exceeding 100% due to formation of complexes with 2:1 Na+-to-ligand stoichiometry.2c,2d Na+, which is abundant in the environment, including water sources, often interferes with the recognition of other metal ions by calix[4]arenes
Results from competitive solvent extractions of four alkaline earth metal cations (AEMC) (Mg2+, Ca2+, Sr2+, and Ba2+) from basic aqueous solutions into CHCl3 by 1.00 mM calixarenes 1-8 showed that selectivity of the ionophores varies with the type of the proton-ionizable group, as well as the calixarene conformation.2d Figure 2 presents the percent AEMC loading for the four calix[4]arene N-(trifluoromethylsulfonyl)carboxamide ligands

Summary

Introduction

Functionalized calixarenes find numerous applications in selective metal ion recognition and separations.1 For such purposes, calix[4]arenes containing pendent proton-ionizable groups2 are of special interest since these ligands generally provide stronger binding of cationic species than their neutral analogs. We present our results for the effect of Na+ on selectivity in solvent extraction of alkaline earth metal cations (AEMC) by a series of lipophilic, di-ionizable calix[4]arenes 1-8 (Figure 1).

Results

Conclusion