Evaluation of polarizable continuum model for the prediction of vibrational frequencies of biomimetic molecules in solution

The prediction accuracy of density functional theory (DFT) has been investigated for the calculation of harmonic vibrational frequencies of natural, protected amino acids and dipeptides in solution within two implementations of polarizable conductor continuum model (CPCM). A training set of 20 amino acids and dipeptides has been used to establish mode-specific local scaling factors for the carboxylate stretches, the amide I and symmetric bending mode of ammonium group. With the new implementation of the PCM cavity based on a continuous apparent surface charge formalism, it has been found that these modes can be simulated with typical prediction errors of ca. 10 cm−1. This approach should thus be able to provide conformer assignments of biomimetic molecules from their infrared spectra in solution.