Impact of Doxorubicin on Self-Organization of Congo Red: Quantum Chemical Calculations and Molecular Dynamics Simulations.

Quantum-chemical calculations and molecular dynamics simulation were applied to a model self-organization process of Congo red (CR) molecules in aqueous solution and the impact of doxorubicin (DOX) molecules on such a process. It was demonstrated that both pure CR/CR and mixed CR/DOX dimers were stable. Van der Waals interactions between aromatic units were responsible for a stacked dimer formation. An important source of stabilization in the CR/CR dimer was the polarization energy. In the CR/DOX mixed dimer long range, electrostatic interactions were the main driving force leading to complexation. An implicit solvent model showed that the formation of the CR/CR dimer was favored over the CR/DOX one. Molecular dynamics simulations demonstrated rapid complexation. In the pure CR system, short sequences of ribbon-like structures were formed. Such structures might be glued by hydrogen bonds to form bigger complexes. It was shown that the aromatic part of the DOX molecule enters CR ribbons with the sugar part covering the CR ribbons. These findings demonstrated that CR may find applications as a carrier in delivering DOX molecules; however, further more extensive investigations are required.