Spectroscopic and PM5 semiempirical study of new lasalocid 5-hydroxypentyl ester and its complexes with monovalent cations

A new ester of lasalocid with 1,5-pentanediol (Las5) was synthesised. The new ester 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 the new ester formed stable 1:1 complexes with all studied cations independently of the stoichiometry and cone voltage values used. With increasing cone voltages, the degradation of the complexes with formation of fragmentary cation complexes was found. The NMR and FT-IR spectra of Las5 in chloroform indicated the formation of the keto form, whereas in acetonitrile the existence of keto and enol forms was detected, whereby the keto form was dominant. The existence of both tautomeric forms was also observed in the spectra of all complexes. Results of the PM5 semiempirical calculations are in agreement with the spectroscopic data and allow visualisation of Las5 structure, its complexes with monovalent cations and the fragmentary complexes. The structures of complexes are discussed in details. q 2004 Elsevier B.V. All rights reserved.