Thermodynamics and kinetics of aggregation processes in aqueous media of ellipticine derivatives: the alkyl-oxazolopyridocarbazole series

Abstract

Spectroscopic, thermodynamic, and kinetic results have allowed the characterization of two aggregation modes in the alkyl-substituted oxazolopyridocarbazole (OPC) series. Short-chain substituted derivatives (H-, methyl-, ethyl-, and propyl-OPCs) self-associated by stacking according to a simple monomer-dimer model involving mainly London dispersion interactions between the chromophores. Long-chain substituted derivatives (butyl- and pentyl-OPCs) self-associate according to a micellization process involving chain-chain hydrophobic interactions. The binding mechanisms of these derivatives to DNAs and membranes also depend on the side-chain length with a clear-cut difference on going from ethyl- to butyl-OPC. From these data it was concluded that, in the OPC series, the interaction mechanisms involved in either aggregation processes or in binding to DNAs and membranes strongly depend on the side-chain length; beyond four methylene units these mechanisms are mainly monitored by the hydrophobic character of the chain. 27 refs., 12 figs., 4 tabs.