Using molecular dynamics and quantum mechanics calculations to model fluorescence observables

Area of Science:

• Computational Chemistry
• Biophysics
• Spectroscopy

Background:

• Accurately modeling fluorescence observables from molecular dynamics (MD) simulations requires robust methods for calculating electronic coupling trajectories.
• Existing methods often rely on approximations that may not fully capture the dynamics of energy transfer.

Purpose of the Study:

• To critically examine two distinct methods for generating electronic coupling trajectories from MD simulations.
• To evaluate three different sampling techniques for these coupling trajectories.
• To enable direct modeling of experimental observables, such as Förster Resonance Energy Transfer (FRET), from MD simulations.

Main Methods:

• Generated electronic coupling trajectories using two methods: 1) single quantum-mechanical (QM) calculation with ideal dipole approximation (IDA) and 2) QM calculation on each MD snapshot.
• Sampled coupling trajectories using three methods: independent snapshot, and Markov chain treatment.
• Calculated energy transfer rates and compared simulated observables with experimental data.

Main Results:

• The IDA method significantly overestimates energy transfer rates (by 2.6x) when probes are in close proximity.
• The Markov chain sampling method yields more realistic observables across a range of FRET efficiencies compared to other sampling methods.
• Differences in sampling methods highlight varying mechanisms for averaging structural dynamics.

Conclusions:

• The choice of electronic coupling calculation and trajectory sampling significantly impacts the accuracy of simulated fluorescence observables.
• The Markov chain approach offers a more reliable method for connecting MD structural dynamics to FRET experimental observables.
• These combined methods provide a powerful framework for directly linking molecular simulations to experimental fluorescence data.