Spectroscopic, mass spectrometry and semiempirical investigation of a new 2-methoxyethyl ester of monensin A and its complexes with Li+, Na+ and K+ cations

A new 2-methoxyethyl ester of monensin A (MON5) has been synthesized and its capability of complex formation with Li+, Na+ and K+ cations has been studied by ESI MS, 1H and 13C NMR, FT-IR and PM5 semiempirical methods. ESI mass spectrometry indicates that MON5 forms complexes with Li+, Na+ and K+ of exclusively 1:1 stoichiometry which are stable up cv = 90 V. The formation of complexes between MON5 and Na+ cations is strongly favoured. Starting from cv = 110 V the fragmentation of the respective complexes is observed, primarily characterized by several dehydration steps. The structures of the MON5 complexes with Li+, Na+ and K+ cations are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. The structures are visualized and discussed in detail. It has been proved that the formation of a pseudo crown ring structure formed by MON5 is preferred in complexes with Na+ cations.