Peridinin (Per) is a carbonyl-containing carotenoid playing a key role in light harvesting and photoprotection in dinoflagellates. This carotenoid plays its photoprotective role by quenching the potentially dangerous 3Chl-a triplet state through the formation of the non-reactive 3Per triplet state through Dexter energy transfer mechanism. We have investigated by means of Quantum Mechanics/Molecular Mechanics dynamics simulations at room temperature the structural and dynamical properties of a Peridinin model system (PMS) in triplet state in three different solvents: cyclohexane, apolar/aprotic; acetonitrile, polar/aprotic; and methanol (MeOH), polar/protic. Our results of 3PMS in MeOH show that the lactonic carbonyl has a stronger tendency to accept hydrogen bonds compared to the corresponding singlet ground state (1PMS). This effect may play some so far overlooked role in Per-containing proteins (notably the water soluble Peridinin-Chlorophyll-Proteins – PCPs). 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 C[dbnd]O stretching band. The situation is particularly evident in the case of MeOH, where the dynamics of the MeOH⋯O[dbnd]C 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.
|Titolo:||QM/MM dynamics of a Peridinin model in triplet state in three prototypical solvents|
|Data di pubblicazione:||2016|
|Appare nelle tipologie:||1.1 Articolo in rivista|