New insight into the dynamics of rhodopsin photoisomerization from one-dimensional quantum-classical modeling

TL;DR

This paper presents a minimal one-dimensional quantum-classical model that accurately describes the primary photoisomerization events in rhodopsin, aligning well with experimental data without complex multiparametric computations.

Contribution

The study introduces the first successful application of a minimal one-dimensional model to explain rhodopsin photoisomerization, simplifying the understanding of this fundamental photoreaction.

Findings

Model agrees with experimental quantum yield and reaction times

Reveals energy redistribution among vibrational modes

Demonstrates the fundamental nature of the photoreaction

Abstract

Characterization of the primary events involved in the $cis-trans$ photoisomerization of the rhodopsin retinal chromophore was approximated by a minimum one-dimensional quantum-classical model. The developed mathematical model is identical to that obtained using conventional quantum-classical approaches, and multiparametric quantum-chemical or molecular dynamics (MD) computations were not required. The quantum subsystem of the model includes three electronic states for rhodopsin: (i) the ground state, (ii) the excited state, and (iii) the primary photoproduct in the ground state. The resultant model is in perfect agreement with experimental data in terms of the quantum yield, the time required to reach the conical intersection and to complete the quantum evolution, the range of the characteristic low frequencies active within the primary events of the $11-cis$ retinal isomerization, and the coherent character of the photoreaction. An effective redistribution of excess energy between the vibration modes of rhodopsin was revealed by analysis of the dissipation process. The results confirm the validity of the minimal model, despite its one-dimensional character. The fundamental nature of the photoreaction was therefore demonstrated using a minimum mathematical model for the first time.