Abstract
Silver ion chromatography of unsaturated fatty acid derivatives can be described satisfactorily by the suggestion of Ag(I) complexation with more than a single bonding site of esters of the 18:1, 18:2, etc. series (that is, one, two, etc. methylene-interrupted double bonds in the C18 hydrocarbon chain) and by the formation of chelate-like complexes. Ab initio RHF effective core potential CEP-31G calculations of model C6 to C18 complexes in the gas phase and in solution indicate that the stability of such complexes depends on the position of C=C double bonds in ligand molecules, while a significant part of the complexation energy is contributed by the interaction of Ag(I) and alkoxy- (or aryloxy-)carbonyl groups of fatty acid esters. Factors important to the stability of Ag(I) fatty acid chelates are the ring sizes and strain, particularly manifested in unsaturated acids with the C=C double bond closer to the carboxyl group, i.e. with smaller chelate rings, as well as conformations of larger rings and hydrocarbon chains. Calculated theoretical solvent effects on chelation are more significant for larger Ag(I) containing rings and increase with increasing ring size.