Excited states of the bacteriochlorophyll b dimer of rhodopseudomonas viridis. A QM/MM study of the photosynthetic reaction center that includes MM polarization

Journal Article · Thu Apr 27 00:00:00 EDT 1995 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/j100017a017· OSTI ID:50500

Thompson, M A; Schenter, G K ^[1]

---

1. Pacific Northwest Lab., Richland, WA (United States)

We present a hybrid quantum mechanical/molecular mechanical (QM/MM) model for microscopic solvation effects that includes polarizability in the MM region (QM/MMpol). QM/MMpol treatment of both ground and excited states is presented in the formalism. We present QM/MMpol analysis of the ground and electronic excited states of the bacteriochlorophyll b dimer (P) of the photosynthetic reaction center (RC) of Rhodopseudomonas viridis using the INDO/S method. The static-charge potential from the MM model of the RC alone causes Q{sub y1} to have significantly better agreement with the Stark effect results than isolated P. However, consideration of the protein polarization potential is further required to obtain more complete agreement with Stark effect experiments. Thus, we calculate a Q{sub y1} transition energy at 10826 cm{sup -1} with a ground to excited state change in dipole moment of 4.8 D; an absorption Stark effect angle of 43{degree}; a net shift of 0.15 electrons from the L subunit to the M subunit of P; and a linear dichroism angle (between the transition moment of Q{sub y1} and the pseudo-C{sub 2} axis of the RC) of 81{degree}. These results are in good agreement with experiment. Interestingly, we find that net CT increase is greater for Q{sub y1} than for the second excited state of P (Q{sub y2}), a result that we anticipated in an early model dimer study. 77 refs., 3 figs., 2 tabs.

• Sponsoring Organization: USDOE
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 50500
• Journal Information: Journal of Physical Chemistry, Vol. 99, Issue 17; Other Information: PBD: 27 Apr 1995
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
55 BIOLOGY AND MEDICINE
BASIC STUDIES
99 MATHEMATICS
COMPUTERS
INFORMATION SCIENCE
MANAGEMENT
LAW
MISCELLANEOUS
CHLOROPHYLL
EXCITED STATES
CHARGE TRANSPORT
PHOTOSYNTHETIC REACTION CENTERS
DIMERS
BACTERIA
SOLAR ENERGY CONVERSION
QUANTUM MECHANICS
MOLECULAR MODELS
GROUND STATES
MATHEMATICAL MODELS
MOLECULAR ORBITAL METHOD
STARK EFFECT
ELECTRON TRANSFER
CALCULATION METHODS
SPECTRAL SHIFT
HAMILTONIANS
POLARIZATION