NMR, FT-IR, ESI MS and PM5 semiempirical study of new lasalocid 5-hydroxy-3-oxapentyl ester and its complexes with monovalent cations

A new ester of lasalocid with di(ethylene glycol) (Las6) was synthesised and its ability to complex formation with monovalent cations was studied by the ESI mass spectrometry, 1H, 13C NMR and FT-IR spectroscopic methods. The ESI MS spectra indicated that Las6 formed stable 1:1 complexes with all cations, except for the Li+ cation, irrespective of the stoichiometry and cone voltage values used. With increasing cone voltages, the complexes degraded with formation of fragmentary metal cation complexes. The NMR and FT-IR spectra of Las6 in chloroform indicated formation of the keto form, whereas in acetonitrile an equilibrium between the keto and enol forms was detected, whereby the keto form was predominant. Comparable conclusions could be drawn from the spectra of all complexes. The PM5 semiempirical calculations data are in agreement with the spectroscopic data and allow visualisation of the Las6 structure, its complexes with monovalent cations and the fragmentary complexes.