An enhanced sampling QM/AMOEBA approach: The case of the excited state intramolecular proton transfer in solvated 3-hydroxyflavone

We present an extension of the polarizable quantum mechanical (QM)/AMOEBA approach to enhanced sampling techniques. This is achieved by connecting the enhanced sampling PLUMED library to the machinery based on the interface of Gaussian and Tinker to perform QM/AMOEBA molecular dynamics. As an application, we study the excited state intramolecular proton transfer of 3-hydroxyflavone in two solvents: methanol and methylcyclohexane. By using a combination of molecular dynamics and umbrella sampling, we find an ultrafast component of the transfer, which is common to the two solvents, and a much slower component, which is active in the protic solvent only. The mechanisms of the two components are explained in terms of intramolecular vibrational redistribution and intermolecular hydrogen-bonding, respectively. Ground and excited state free energies along an effective reaction coordinate are finally obtained allowing for a detailed analysis of the solvent mediated mechanism.

Automated summary

The polarizable quantum mechanical (QM)/AMOEBA approach has been extended to enhanced sampling techniques for studying excited state intramolecular proton transfer. By combining molecular dynamics and umbrella sampling, the fast and slow components of the transfer in two solvents are revealed, with mechanisms involving intramolecular vibrational redistribution and intermolecular hydrogen-bonding. Ground and excited state free energies along an effective reaction coordinate provide detailed analysis of the solvent mediated mechanism.