Comparative analysis of interactions of some lariat crown ethers and their unsubstituted analogues with alkali metal salts in the gas phase by MALDI mass spectrometry

Abstract

In this work, interactions of some crown ethers, including lariat ethers bearing a side-arm methoxyphenoxymethyl substituent, with alkali metal salts were studied by matrix assisted laser desorption/ionization mass spectrometry. Peaks of cationized molecules [M + Cat]+, sandwich complexes [2M + Cat]+, [3M + Cat]+ ions, and cluster ions [2M + 2Cat + An]+ and [2M + 3Cat + 2An]+ were observed in the mass spectra; herein M is a crown ether molecule, Cat is an alkali metal cation, and An is a monobasic acid anion. The results were compared with previously obtained data for 15-crown-5, [ortho]- and [para]-methoxyphenoxymethyl-15-crown-5 ether mixtures with sodium salts. The conclusions made before, that an increase in the shielding degree of the cation in complexes with lariat ethers led to a significant decrease in the peak intensity of cluster ions [2M + 2Cat + An]+, were confirmed. For potential lariat ethers the absence or only trace amounts of such cluster ions along with the presence of an intense cluster ion peak in the mass spectrum for an unsubstituted analogue can serve a test for the involvement of the lateral fragment of the crown ether in complex formation, i.e., the lariat effect.