Bilindionostilbenoparacyclophanes Mimic the Spectroscopic Properties of Photoreceptors for Bacterial Oxygenic Photosynthesis

Abstract

Bilindionostilbenoparacyclophanes are a new type of photodynamic molecules capable of stabilizing, at convenience, helical-shaped or «stretched» conformations of bile pigment chromophores without changing the structure of the latter. – Why do «native» phycobiliproteins intensively fluoresce, but they do not after denaturation? Which is the reason for the enhanced absorption of visible light of biliprotein chromophores when compared with free bile pigment molecules? These and other related questions have to be answered by the study of the spectroscopic properties of bilindionostilbenoparacyclophanes, particularly of their E-isomers, in which the bile pigment chromophore is constrained in «stretched» conformations of adjustable strain, otherwise not accessible in model systems for biliproteins so far investigated. – Our present results prove, for the first time experimentally, the intimate relationship between the conformation of biliprotein chromophores and their light absorption. Until now, however, the origin of the fluorescence of native phycobiliproteins could not be elucidated. Most likely, the bile pigment chromophores are immobilized, in a particular conformation, within the apoprotein framework. In order to verify this hypothesis more sophisticated models are required, whose synthesis is a target of current work on this area.