Dual photoisomerization mechanism of azobenzene embedded in a lipid membrane

TL;DR

This study uses computational methods to elucidate the distinct photoisomerization mechanisms of azobenzene embedded in a lipid membrane, revealing different dynamics for trans-to-cis and cis-to-trans conversions.

Contribution

It provides a detailed computational analysis of azobenzene photoisomerization in a biological membrane environment, highlighting the different mechanisms and timescales involved.

Findings

Trans-to-cis isomerization is slow and torsion-driven.

Cis-to-trans isomerization occurs rapidly via a pedal-like mechanism.

Environmental interactions influence the isomerization pathways.

Abstract

The photoisomerization of chromophores embedded in biological environments is of high importance for biomedical applications, but it is still challenging to define the photoisomerization mechanism both experimentally and computationally. We present here a computational study of the azobenzene molecule embedded in a DPPC lipid membrane, and assess the photoisomerization mechanism by means of the quantum mechanics/molecular mechanics surface hopping (QM/MM-SH) method. We observe that while the trans-to-cis isomerization is a slow process governed by a torsional mechanism due to the strong interaction with the environment, the cis-to-trans mechanism is completed in sub-ps time scale and is governed by a pedal-like mechanism in which both weaker interactions with the environment and a different geometry of the potential energy surface play a key role.