A transferable electrostatic map for solvation effects on amide I vibrations and its application to linear and...

Area of Science:

• Computational Chemistry
• Spectroscopy
• Physical Chemistry

Background:

• Infrared (IR) spectroscopy is sensitive to molecular environments.
• Solvent effects significantly influence vibrational frequencies and spectral linewidths.
• Accurate modeling of solvent-solute interactions is crucial for interpreting IR spectra.

Purpose of the Study:

• To develop and validate a method for modeling infrared solvent shifts based on electrostatic interactions.
• To parametrize molecular vibrational properties (frequency, anharmonicity, transition dipoles) using electrostatic fields.
• To assess the transferability and accuracy of the developed model for N-methyl acetamide in various solvents.

Main Methods:

• Ab initio calculations were employed to derive parameters for vibrational properties.
• A computational map was generated incorporating electric field and its gradients at specific molecular positions.
• The model was tested against experimental Fourier transform infrared (FTIR) and two-dimensional infrared (2DIR) data.

Main Results:

• The method achieved excellent agreement with experimental FTIR data for solvent shifts (within 7 cm⁻¹) and linewidths (within 4 cm⁻¹) in polar solvents.
• Electrostatic contributions were found to dominate solvation effects in polar solvents, indicating model transferability.
• Simulated 2DIR spectra using the constructed map closely matched experimental results, with negligible impact from anharmonicity fluctuations.

Conclusions:

• The developed electrostatic model effectively captures infrared solvent shifts and linewidths for N-methyl acetamide.
• Electrostatic interactions are the primary drivers of solvation effects in polar solvents for this system.
• The model shows promise for predicting spectral properties in similar solvent environments and for advanced spectroscopic techniques like 2DIR.