Clarifying and illustrating the electronic energy transfer pathways in trimeric and hexameric aggregation state of cyanobacteria allophycocyanin within the framework of Förster theory

• Published in: Journal of computational chemistry 2015-01, Vol.36 (3), p.137-145
• Main Authors: Ren, Yanliang, Melhem, Osama, Li, Yongjian, Chi, Bo, Han, Xinya, Zhu, Hao, Feng, Lingling, Wan, Jian, Xu, Xin
• Format: Article
• Language: English
• Subjects: allophycocyanin; Approximation; Bioenergetics; Biopolymers - chemistry; Cyanobacteria - chemistry; electronic energy transfer rates; Electrons; Fluorescence Resonance Energy Transfer; Förster theory; Gram-negative bacteria; Mathematical models; Models, Molecular; Phycocyanin - chemistry; Physical chemistry; Proteins; Quantum physics; TDDFT
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.23770

Within the framework of the Förster theory, the electronic excitation energy transfer pathways in the cyanobacteria allophycocyanin (APC) trimer and hexamer were studied. The associated physical quantities (i.e., excitation energy, oscillator strength, and transition dipole moments) of the phycocyanobilins (PCBs) located in APC were calculated at time‐dependent density functional theory (TDDFT) level of theory. To estimate the influence of protein environment on the preceding calculated physical quantities, the long‐range interactions were approximately considered with the polarizable continuum model at the TDDFT level of theory, and the short‐range interaction caused by surrounding aspartate residue of PCBs were taken into account as well. The shortest energy transfer time calculated in the framework of the Förster model at TDDFT/B3LYP/6–31+G* level of theory are about 0.10 ps in the APC trimer and about 170 ps in the APC monomer, which are in qualitative agreement with the experimental finding that a very fast lifetime of 0.43–0.44 ps in APC trimers, whereas its monomers lacked any corresponding lifetime. These results suggest that the lifetime of 0.43–0.44 ps in the APC trimers determined by Sharkov et al. was most likely attributed to the energy transfer of α1‐84 ↔ β3‐84 (0.23 ps), β1‐84 ↔ α2‐84 (0.11 ps) or β2‐84 ↔ α3‐84 (0.10 ps). So far, no experimental or theoretical energy transfer rates between two APC trimmers were reported, our calculations predict that the predominate energy transfer pathway between APC trimers is likely to occur from α3‐84 in one trimer to α5‐84 in an adjacent trimer with a rate of 32.51 ps. © 2014 Wiley Periodicals, Inc. The electronic energy transfer is a fundamental step in the development of synthetic light‐harvesting devices. Insight into the EET pathways in APC trimer and hexamer was gained by the first principle calculations within the framework of Förster theory.