Spectroscopic and PM5 semiempirical study of a new lasalocid ester with 2-allyloxyethanol and its complexes with monovalent cations

A new ester of lasalocid with 2-allyloxyethanol (Las9) has been synthesised and its ability to form complexes with Li+, Na+, K+, Rb+ and Cs+ cations has been studied by ESI mass spectrometry as well as 1H, 13C NMR and FT-IR spectroscopic methods. The ESI-MS spectra indicate that Las9 forms stable 1:1 complexes with all cations studied. The FT-IR spectra of Las9 in acetonitrile solution have evidenced the existence of an equilibrium between keto and enol forms, with the predominance of the keto form. No effect of the kind of cations on this keto–enol equilibrium has been found. The results of the PM5 semiempirical calculations show that the keto form of Las9 is more favourable than the enol form. In the Las9 molecule two parts can be distinguished, stabilised by hydrogen bonds. In the structure of the complexes these two parts are no longer observed.