In this work, we present our latest results on how QM/MM calculations enabled us to relate the structure of carotenoid-containing photosynthetic proteins with their visible absorption spectrum. We first present results on supramolecular qm/mm simulations on the peridinin–chlorophyll <i>a</i> protein (PCP) complex. We reproduce the distinct peridinin absorptions, identify multi-chromophoric molecular excitations, and elucidate the mechanisms regulating the strongly allowed S0 → S2 absorptions of the bound peridinins. In a second study, we tackle the translocation process of the carotenoid in the Orange Carotenoid Protein (OCP). We mimic the translocation of the carotenoid from the inactive form of OCP and obtain metastable red-shifted states in the photoactivation mechanism, replicating the λmax values of reference experimental spectra.

QM/MM simulations enable structure spectral relationships in photosynthetic proteins

ACS Spring 2022

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