Ab initio molecular orbital calculations of electronic couplings in the LH2 bacterial light-harvesting complex of Rps. acidophila

Gregory D. Scholes, Ian R. Gould, Richard J. Cogdell, Graham R. Fleming

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Abstract

The results of ab initio molecular orbital calculations of excited states and electronic couplings (for energy transfer) between the B800 and B850 bacteriochlorophyll a (Bchl) chromophores in the peripheral light-harvesting complex (LH2) of the purple photosynthetic bacterium Rhodopseudomonas acidophila are reported. Electronic couplings are estimated from "supermolecule" calculations of Bchl dimers using the CI-singles methodology and 3-21G* or 6-31G* basis sets. A scheme for dissecting the coupling into contributions from the Coulombic coupling and the short-range coupling (i.e., dependent on interchromophore orbital overlap) is reported. B850 couplings are calculated to be [total (Coulombic + short)]: intrapolypeptide dimer 320 (265 + 55) cm-1 and interpolypeptide dimer 255 (195 + 60) cm-1 at the CIS/6-31G* level. These results differ significantly from those estimated using the point dipole approximation. The effect of including Mg ligands (His residues) and H-bonding residues (Trp and Tyr) is also investigated. The consequences for superradiance and energy transfer dynamics and mechanism are discussed.

Original languageEnglish (US)
Pages (from-to)2543-2553
Number of pages11
JournalJournal of Physical Chemistry B
Volume103
Issue number13
DOIs
StatePublished - Apr 1 1999

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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