Absorption spectra of the purple nonsulfur bacteria light-harvesting complex: A DFT study of the B800 part

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 450; p. 115454
• Main Authors: Begunovich, L.V., Kovaleva, E.A., Korshunov, M.M., Shabanov, V.F.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2024
• Subjects: Bacteriochlorophyll; DFT; DFTB; LH2; Light harvesting; Optical spectra; Photosynthesis; Rhodoblastus acidophilus; Bacteriochlorophyll; DFT; Light harvesting; LH2; Photosynthesis; Optical spectra; Rhodoblastus acidophilus; DFTB
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2023.115454

[Display omitted] •B800 part of Rdb. acidophilus LH2 complex was modeled by DFT and DFTB methods.•Minimal reliable model to describe B800 structural features was determined.•Crucial role of HF exchange for optical spectra description was established.•Computationally effective ways to simulate B800 structure and optics were proposed. We’ve studied the B800 part of Rhodoblastus acidophilus light-harvesting complex (LH2) by several quantum chemical techniques based on the density functional theory (DFT) and determined the specific method and a minimal reliable model suitable for further studies of the LH2. In addition to bacteriochlorophyll a molecules, the minimal model includes two α and one β chain amino acids. Within the model, we are able to reproduce the contribution of the B800 ring of nine bacteriochlorophyll a molecules to the near infrared Qy absorption band. We also discuss the use of hybrid DFT calculations for precise energy and optical estimations and DFT-based tight binding (DFTB) method for the large-scale calculations. Crucial importance of Hartree-Fock exchange interaction for the correct description of B800 peak position was shown.