Fractionation of complex mixtures of naphthenic acids, their characterization and biological activity

Naphthenic acids (NAs) are complex mixtures of cycloaliphatic and alkyl-substituted acyclic carboxylic acids whose overall characteristics are determined by the composition of the mixture. A complex mixture of NAs from a commercial fraction of atmospheric oil of the Vojvodina naphthenic crude "Velebit" (Serbia) was separated into narrower fractions on the basis of their acidity. Electrospray ionization mass spectrometry analysis of the fractions showed the occurrence of structural differentiation of acids. By extraction at pH 3-5, about 50% of the total mass of acids was separated, consisting predominantly of tricyclic and bicyclic structures. Acids of lower acidity, (about 22%), separated at pH 9 and 10, and their dominant constituents were acids with three, four and five rings. A correlation was found between the dominant structure and the biological activity of NAs of the fractions. The fraction extracted at pH 8, also with dominant bicyclic and tricyclic structures, showed the highest auxin and gibberellin activities