Spectroscopic, spectrometric and PM5 semiempirical investigation of new lasalocid 8-hydroxy-3,6-dioxaoctyl ester and its complexes with monovalent cations

A new ester of lasalocid with tri(ethylene glycol) (Las7) was synthesised and its ability to complex formation with monovalent cations was studied by the ESI mass spectrometry as well as 1H, 13C NMR and FT-IR spectroscopic methods. The ESI MS spectra indicated that Las7 formed stable 1:1 complexes with all cations, except for Li+ and Na+, irrespective of the stoichiometry and cone voltages used. With increasing cone voltage, the complexes degraded with formation of fragmentary metal cation complexes. The NMR and FT-IR spectra of Las7 in chloroform indicated the formation of the keto form, whereas in acetonitrile the existence of keto and enol forms was detected, with the keto form dominant. The existence of both tautomeric forms was also observed in all complexes. Results of the PM5 semiempirical calculations are in agreement with the spectroscopic data and allow visualisation of Las7 structure, its complexes with monovalent cations and the fragmentary complexes. The structures of complexes are discussed in details.