• dynamics
• excitation
• light
• residues
• hydrogen bonds
• canthaxanthin
• dihedral
• non-adiabatic
• excited states
• orange carotenoid protein
• carotenoid

In the present thesis the photoactivation of Orange Carotenoid Protein (OCP) is investigated by means of non-adiabatic molecular dynamics. OCP is a water soluble protein found in some photosynthetic organisms, such as cyanobacteria, that has the role photoprotective agent of those organisms. When exposed to high-light intensity, the photosynthetic apparatus, called phycobilisome (PBS), can be overloaded with excitation energy, which can indeed bring harm to the cells. The mechanisms that regulates the photoprotection is still far from being completely understood, but the chromophore that is found within the protein's domains, a carotenoid called canthaxanthin (CAN), should initiate the activation mechanism through the light absorption and subsequent evolution of its excited states, and then take part to a process named non-photochemical quenching (NPQ), in which the excess energy harvested in the PBS is dissipated as harmless heat. The purpose of this work is to provide an insight on the photochemical trigger that initiates the series of conformational changes that bring OCP from the inactive form to the active one.