Multinuclear NMR, FT-IR, ESI MS studies and PM5 semiempirical calculations of new ethylene glycol ester of lasalocid acid and their complexes with Kþ cation

A new lasalocid ester with ethylene glycol (Las4) was synthesised. The new ester and its ability to complex formation with Kþ cations was studied by the electron spray ionization (ESI) mass spectrometry, 1H, 13C NMR and FT-IR spectroscopic methods. The ESI MS spectra indicated that the new ester formed stable 1:1 complex with Kþ cation independent of the stoichiometry and cone voltage values used. With increasing cone voltages, only the degradations of the Las4–Kþ complex with formation of fragmentary cation complexes were found. The NMR and FT-IR spectra of Las4 in chloroform indicated the formation of the keto form, whereas in acetonitrile, the existence of keto and enol forms was detected. For the Las4–Kþ complex, these two tautomeric forms were conserved. The PM5 semiempirical calculations are in agreement with the spectroscopic data and allow visualization of Las4 structure, its complex with Kþ cation and the fragmentary Kþ complexes. q 2004 Elsevier B.V. All rights reserved.