Lasalocid polyoxaalkyl esters complexes with Liþ, Naþ, Kþ, Rbþ and Csþ cations studied by ESI MS and semiempirical methods

Formation of complexes between the cations (Liþ, Naþ, Kþ, Rbþ and Csþ) and three lasalocid esters was studied by electron spray ionization (ESI) mass spectrometry and the PM5 semiempirical method. The structures of the complexes are discussed. The 1:1 and 1:2 stoichiometry structures of the complexes are favoured. Under ESI conditions, the formation of stable fragment complexes with the involvement of polyoxaalkyl chains was observed, demonstrating the importance of these chains in the complexation process. These results also confirmed that the complexes of lasalocid polyoxaalkyl esters with monovalent cations existed in the keto equilibrium form. q 2003 Elsevier B.V. All rights reserved