Behavior of anchor functionalized ZnPc molecules on a graphene nanoflake near membrane cell

We present a theoretical study of two different zinc phthalocyanine molecules, the 2-aminoethoxy-ZnPc (ZnPc-NH) and ZnPc-Lys molecules, covalently anchored on a graphene nanoflake to increase the stability of the system. By means of density functional theory calculations, we determine the atomic structure of the molecule/graphene nanoflake systems. Then, time-dependent density functional theory calculations show that the optical properties of the two molecules are preserved in water plus salt conditions, which is crucial for photodynamic therapy applications. In the case of the ZnPc-NH molecule, molecular dynamics (MD) simulations show that, whatever the chosen conformation, the adsorbed molecule lies on the substrate, which seems to be more favorable at the approach of the cell membrane. On the contrary, the three long arms of the ZnPc-Lys molecule allow to enhance the solubility and avoid molecule aggregation, but make the membrane approach harder. Finally, a balance between the diffusion of the ZnPc/graphene nanoflake system toward the membrane cell and the solubility, both related to the ligand length, should be found to optimize the PDT efficiency.