Explicit versus implicit solvent modeling of Raman optical activity spectra.

Area of Science:

• Spectroscopy
• Computational Chemistry
• Biophysics

Background:

• Raman and Raman optical activity (ROA) spectra reveal molecular structure, dynamics, and solvent interactions.
• Interpreting spectra of polar molecules in water is challenging due to complex band assignments.

Purpose of the Study:

• To compare implicit dielectric and explicit solvent models for their effect on spectral shape.
• To assess the accuracy of different molecular dynamics simulations in reproducing experimental spectra.

Main Methods:

• Experimental measurement of Raman and ROA spectra for lactamide and 2-aminopropanol enantiomers.
• Quantum-mechanical calculations and molecular dynamics (MD) simulations (classical and Car-Parrinello) to derive geometries of explicitly solvated clusters.
• Comparison of spectral features obtained from implicit and explicit solvent models.

Main Results:

• Explicit solvent models, particularly Car-Parrinello molecular dynamics (CPMD) clusters, yield more faithful spectral intensity profiles and inhomogeneous band broadening than implicit models.
• The first hydration shell's hydrogen-bonded water molecules significantly impact spectral intensities.
• Sufficient simulation time is crucial for CPMD to fully sample conformational space and accurately reproduce spectral features.

Conclusions:

• Explicit solvent modeling is essential for accurately reproducing Raman and ROA spectra of polar molecules in aqueous environments.
• Advanced computational techniques enable accurate explicit solvent modeling, improving spectral interpretation.