QM/MM dynamics of a Peridinin model in triplet state in three prototypical solvents

The vibrational properties of the 3PMS dynamics in the three solvents have been analyzed by means of decomposition of the vibrational density of states in effective normal modes. The results show that the solute-solvent interactions can influence some vibrational bands of 3PMS; in particular, they are able to modulate the position of the lactonic CO stretching band. The situation is particularly evident in the case of MeOH, where the dynamics of the MeOH⋯OC hydrogen bond interactions can strongly influence the band position and shape. As vibrational spectroscopy (notably step-scan FTIR difference spectroscopy) has been largely used to investigate 3Per in PCPs, especially using the lactonic carbonyl stretching as a marker band to investigate the different photophysical role of each Per in the protein complex, this study represents an important step to understand the experimental spectra and to identify the Per(s) molecule(s) bearing the triplet in PCPs.