UV-Vis and ESI MS/MS Study of Calix[4]arene Derivatives and Their Lanthanide Complexes

Abstract

Coordination properties of calix [4]arenes bearing substituents on the lower rim: tetraethyl ester (1), tetraethylamide (2), and newly synthesized tetraethylmethylamide derivative (3), towards selected lanthanide cations (La 3+ , Eu 3+ , Yb 3+ ) were studied by spectrophotometric titrations. No complexation was observed with ester derivative, while amide derivatives formed 1:1 complexes and bound lanthanide cations very efficiently (lgKLa2 = 5.1; lgKEu2 ≥ 6; lgKYb2 ≥ 6; lgKLa3 ≥ 6; lgKEu3 ≥ 6; lgKYb3 ≥ 6). The ligands and complexes were also analysed by ESI MS and MS/MS spectrometry. Both inductive cleavage and proton rearrangement fragmentation reactions were observed. Corresponding fragmentation pathways were proposed. The results obtained by MS analysis were in accordance with those obtained by spectrophotometric titrations.