Argentivorous Molecules with Oxyethylene Chains in Side-Arms: Silver Ion-Induced Selectivity Changes toward Alkali Metal Ions.

Argentivorous molecules with mono, di, tri, tetra, and penta-oxyethylene chains in aromatic side-arms were prepared (-). Titration experiments using proton nuclear magnetic resonance and cold electrospray ionization (cold-spray ionization, CSI) mass spectrometry showed that silver ions were trapped in the cyclen moiety and the arranged oxyethylene chains of the side-arms when two equivalents of silver ions were added. The silver complexes formed by adding one equivalent of silver ion to - bind alkali metal ions using the oxyethylene chains; alkali metal ion-induced CSI mass spectral changes of - were measured in the absence and presence of silver ions to compare the binding properties of the ligand for Li, Na, and K ions. As a result, the intensity ratios of [ + H + M]/[ + H] in - were almost zero or very low. and , which have tetra(oxyethylene) and penta(oxyethylene) chains, respectively, bind a larger size of alkali metal ions. On the other hand, in the presence of silver ions, the ratio for [ + Ag + M]/[ + H] (M = Li, Na, K) in - was increased. The highest [ + Ag + M]/[ + H] ratios for K were observed in and , while selectivity for Na was observed in the case of and . These results indicate that the increased binding ability and selectivity by - are due to the arrangement of oxyethylene chains by the conformational change of the aromatic side-arms. The Ag-induced carbon-13 nuclear magnetic resonance spectral changes suggested that the second and third oxyethylene units, close to the benzene, are involved in the coordination of the second metal ion.