Carotenoid interactions in peridinin chlorophyll a proteins from dinoflagellates. Evidence for optical excitions and triplet migration

Abstract

Optical and magnetic resonance spectroscopy has been used to investigate two peridinin–chlorophyll a–protein (PCP) complexes constituting the peripheral antenna of the photosystem of two dinoflagellate species. One protein contains a cluster of four peridinins and one chlorophyll molecule, the other contains two such clusters in a ‘quasi’ dimer of the former. Evidence of intra-cluster excitonic interactions between peridinins is provided by low-temperature absorption and circular dichroism spectra. Peridinin triplets are detected in zero-field magnetic resonance spectroscopy by both optical emission and absorption. Interaction among peridinin molecules causes a fast intra-cluster and a slow inter-cluster triplet migration. The origin of the interactions is discussed by correlating optical and magnetic spectroscopic data.