An ab initio conformational study on 2,3-dihydrobilin-1,19(21H,24H)-dione, a model compound for open-chain tetrapyrroles

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

“…The usually narrow absorption bands of bilins in PBPs compared to those in solution indicate a quite rigid structure of the binding sites and a limited number of occurring conformations. [427] According to semiempirical and ab initio calculations on phycocyanobilin [432] and a reduced model for phycobilins, [433] respectively, the preferred configuration of the central methine bridge is syn-cis. These structures are stabilized by minimal steric strain and hydrogen bonds.…”

“…The authors stress that these factors may differ in a protein environment. [433] For bilins embedded in the b unit of the PC in the thermophilic cyanobacterium Mastigocladus laminosus, extended conformations are predicted by quantum chemical calculations to be favored and mainly stabilized by a salt bridge to a nearby aspartate residue. [434] The restriction to the extended conformation is essential for the light-harvesting ability of bilins, since it leads to an increased absorption intensity and excited-state lifetime.…”

Developing a Structure–Function Model for the Cryptophyte Phycoerythrin 545 Using Ultrahigh Resolution Crystallography and Ultrafast Laser Spectroscopy

“…The electronic states of the bilins in Cphycocyanin have been calculated previously by quantum mechanical methods. 64,65 The interactions of the bilins with the protein environment, the conformations of the side-chains and non-negligible chromophore-chromophore interactions were found to be very important parameters in reproducing absorption energies and intensities. Although the computational studies here are for the pigments in the gas phase, neglecting any influence of the protein environment, there is still plenty of information to be gained from these results.…”

A full conformational space analysis of bilirubin

“…This ridge-tile conformation occurs in solution too, although the bilirubin molecule can flip between two enantiomeric conformers (P or M) both of which maintain the internal hydrogen bond network [4]. Between these conformations, various intermediate structures exist due to the conformational flexibility of the tetrapyrrole backbone [5] and propionic acid side chains.…”