Spectroscopic, mass spectrometry and semiempirical investigation of a new Monensin A allyl ester and its complexes with Li+, Na+ and K+cations

Monensin A allyl ester (MON4) has been synthesized by a new method 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. It is shown that MON4 preferentially forms complexes with Na+ cations. ESI mass spectrometry indicates that up cv = 50 V stable complexes of exclusively 1:1 stoichiometry between MON4 and monovalent cations are formed. With increasing cone voltage value fragmentation of the respective complexes is observed, which is primarily characterized by several dehydration steps. The structures of the MON4 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 MON4 is preferred in complexes with Na+ cations.