1H, 13C NMR, FT-IR, ESI MS and PM5 studies of a new 3,6,9-trioxadecylamide of monensin A and its complexes with Li+, Na+ and K+ cations

A new 3,6,9-trioxadecylamide of monensin A (M-AM4) has been synthesised and its ability to form complexes with Li+, Na+ and K+ cations has been studied by ESI mass spectrometry, 1H and 13C NMR, FT-IR spectroscopy and PM5 semiempirical method. The ESI MS data indicate that M-AM4 forms complexes with Li+, Na+ and K+ of exclusively 1:1 stoichiometry which are stable up to cv = 70 V. The formation of the M-AM4–Na+ is strongly favoured. Above cv = 70 the fragmentation process is observed. The spectroscopic studies show that the structures of the M-AM4 and its complexes with the cations of 1:1 stoichiometry are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. The CO amide group is engaged in the complexation process of each cation. The M-AM4–K+ complex can also assume a structure in which the CO amide group does not participate in the complexation but the complexes of such structure do not dominate.