A new computational methodology for the characterization of complex molecular environments using IR spectroscopy:...

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Infrared (IR) and 2D IR spectroscopy measure molecular interactions and dynamics in liquid solutions.
• Frequency Fluctuation Correlation Function (FFCF) quantifies vibrational dynamics, while center frequency reveals the chemical environment (solvatochromism).
• Assigning molecular interactions in complex solutions using IR spectroscopy is challenging due to heterogeneity.

Purpose of the Study:

• To introduce a novel, parameter-free method, Instantaneous Frequencies of Molecules (IFM), for analyzing molecular behavior in solutions.
• To enable unambiguous assignment of molecular interactions and dynamics in complex liquid environments.
• To enhance the interpretation of IR and 2D IR spectroscopic data.

Main Methods:

• Coupling the IFM method with classical molecular simulations.
• Testing the IFM method using N-methylacetamide (NMA) in seven diverse chemical environments.
• Comparing IFM results with experimental data and conventional frequency mapping techniques.

Main Results:

• IFM accurately predicts the FFCF dynamics, including fluctuation times and amplitudes, for NMA in various solutions.
• The method shows good agreement with experimental data regarding NMA solvatochromism.
• IFM provides results comparable or superior to traditional frequency mapping methods.

Conclusions:

• The IFM method, when combined with molecular dynamics simulations, effectively predicts molecular vibrational dynamics and solvatochromism.
• IFM unlocks the potential of IR spectroscopy to generate detailed molecular maps of complex systems.
• This approach facilitates a deeper understanding of the interaction landscape in heterogeneous molecular solutions.