Recently it has been shown that
Chlorin e6 (Ce6) when complexed with
Pluronics (hydrophilic
ethylene and
propylene oxide block copolymers) and poly(
N-vinylpyrrolidone) (PVP) exhibits considerably higher
phototoxicity towards
tumor cells than free Ce6. The present work aimed to model Ce6 interactions with hydrophilic
Pluronic F127 and PVP and find out the nature of intermolecular forces stabilizing these complexes. Modeling included 3 steps: (i) application of molecular dynamics to study
polymer folding using
AMBER 8 program, (ii) evaluation of partial charges in the Ce6 molecule using different quantum mechanical, semi-empirical and topological approaches and (iii) docking analysis of Ce6 interactions with
polymer coils using AUTODOCK 4.2. It was found that the folding in regular
polymers does not occur stochastically, but involves the formation of "primary" helical structures, which further combined to form hairpin-like "secondary" structures. The latter in turn associated to form coils with minimal
solvent accessible hydrophobic area. The Ce6 ring lies flat on the surface of the
polymer coil at the interface between hydrophobic and hydrophilic regions. Calculations showed higher affinity of Ce6 for PVP in comparison to
Pluronic and revealed marginal contribution of Coulomb forces to the stabilization of both complexes, which are mainly stabilized by van der Waals and
hydrogen interactions.