Interaction of anthracene and its oxidative derivatives with human serum albumin

Binding affinities of ten polycyclic aromatic hydrocarbons to albumin were determined: anthracene, its eight oxy-derivatives: anthraquinone, 9-anthracenemethanol, 9-anthraldehyde, 9-anthracenecarboxylic acid, 1,4-dihydroxyanthraquinone, 1,5-dihydroxyanthraquinone, 1,8-dihydroxyanthraquinone, 2,6-dihydroxyanthraquinone and benzo[a]pyrene. The quenching of albumin fluorescence was used to measure the PAH - protein interaction. The theoretical curve of calculated fluorescence was fitted to experimental data after necessary corrections regarding PAHs fluorescence and inner filter effect. From the numerical fitting the final association constants were calculated. Anthracene and anthraquinone failed to quench the albumin fluorescence. 9-anthracenecarboxylic acid showed the highest, while 9-anthracenemethanol the weakest albumin binding affinity. The affinity constants determined for 9-anthraldehyde and benzo[a]pyrene were of the same magnitude and indicated low-affinity binding to albumin. The constants obtained for the four dihydroxyanthraquinones were higher, but dissimilar, which suggests that the position of the functional group in anthracene molecule influences the binding constant. Moreover, this study suggests that the type of substituent plays a significant role in PAH-albumin complex formation. The carboxylic group increases the binding affinity of the anthracene molecule the most rather than the presence of both carbonyl and hydroxyl groups. The lowest affinity constants were obtained for aldehyde, methyl and carbonyl substituents.