A Theoretical Investigation About the Excited State Dynamical Mechanism for Doxorubicin Sensor

Abstract

We theoretically investigate the excited state intramolecular proton transfer (ESIPT) mechanism about a novel doxorubicin (DOX) system based on density functional theory (DFT) and time-dependent DFT methods. We mainly focus on the double proton transfer process regarding the stepwise versus synchronous dual proton transfer mechanism. The changes in our calculated primary bond lengths and bond angles show that the intramolecular hydrogen bonds (O1–H2···O3 and O4–H5···O6) are both strengthened in the S1 state, which provides the possibility of the ESIPT process. Though our computational simulations, the DOX indicates the lowest absorption at around 490 nm. After excitation, we find three emission bands maximized at 656, 663 and 687 nm, which are ascribed to the tautomer. To further elucidate the ESIPT mechanism, we construct the potential energy surfaces (PESs) of both S0 and S1 states. Clearly, three kinds of stable structures could be located on the S1-state PES. We establish a new mechanism of DOX that excludes synchronous double proton transfer, while the stepwise double proton transfer mechanism is confirmed theoretically. We believe that the systematic investigation for photo-physical and photochemical properties of the antineoplastic drug DOX might be significant to obtain fundamental insight into the transport mechanism of DOX inside cultured cells.