Behavior of Drug Excited States within Macromolecules: Binding of Colchicine and Derivatives to Albumin

The aqueous solutions of colchicine (COL) and analogues such as colchiceine (CEI), and N-deacetylcolchiceine (DCEI) have been studied by laser flash photolysis (LFP) with and without the presence of human serum albumin (HSA) to determine the possible interactions between the drugs and the albumin. When irradiation of these drugs was performed in aqueous media, transient absorption species were not detected. However, triplet excited states of CEI and DCEI were detected when the experiments were carried out in the presence of albumin. Contrary to expectations, in the case of COL, no transient absorption species was observed. A deep study of COL triplet excited-state properties has revelaed that intersystem crossing quantum yield (phi(ISC)) decreases from organic media such as dichloromethane to water with phi(ISC) values ca. 0.035 and