Investigation of complex structures of a new 2-hydroxyethyl ester of Monensin A with Mg2+, Ca2+, Sr2+, Ba2+ cations using electrospray ionization mass spectrometry and semiempirical PM5 methods

A new 2-hydroxyethyl ester of Monensin A (MON2) was synthesized and its ability to complex formation with divalent cations was studied by the ESI mass spectrometry and PM5 semiempirical calculations. The ESI-MS spectra indicated that MON2 forms stable 1:1 complexes with the divalent cations studied. Additionally also complexes of MON2 with divalent cations and perchlorate anions were also detected. With increasing cone voltage values the fragmentation process of the complexes with the formation of respective fragmentary cations occurred. The structures of the complexes are discussed in detail on the basis of conformational analysis together with the PM5 semiempirical calculations.