Theoretical Calculations of Photosynthetic Pigments

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

“…If this is true, such interactions are considerable in at least either the ground state or the excited state and the pigment-protein complex may even be regarded as a rather strongly coupled hexamer in which the different absorption bands carry oscillator strength from, in principle, all pigments. Comparison of calculated and measured steadystate spectra have indicated that the six pigments in reaction centers of purple bacteria interact (3)(4)(5)(6), and admixture of oscillator strength near 795 nm with P has been proposed on the basis of a photon echo excitation spectrum (25), but no consensus has been reached on the extent of these interactions and on the role of charge transfer states in these interactions. Our dynamic experiment suggests that interpigment interactions are observable; however, no calculations of the excited state spectrum are available for direct comparison with our data.…”

“…The individual Qy bands are usually named after the chromophores that are thought to provide the major contribution-i.e., B (BL and BM), for Rhodobacter sphaeroides around 800 nm, and H (HL and HM) around 750 nm, and the exciton bands of P (P-around 890 nm at cryogenic temperatures; P+ around 810 nm). In addition to interchromophore interactions, the spectrum presumably is influenced by charge transfer transitions (3,4) and by electrostatic interactions with the protein solvent (5)(6)(7). Various calculations of exciton interactions have been published, but the degree of excitonic coupling, the environmental influences, and the possible contribution of charge transfer transitions to the spectrum are still subject to debate (5)(6)(7).…”

“…In addition to interchromophore interactions, the spectrum presumably is influenced by charge transfer transitions (3,4) and by electrostatic interactions with the protein solvent (5)(6)(7). Various calculations of exciton interactions have been published, but the degree of excitonic coupling, the environmental influences, and the possible contribution of charge transfer transitions to the spectrum are still subject to debate (5)(6)(7). An alteration of the electronic state is bound to perturb any interaction and, viewing the reaction center as an interacting hexamer, modify all bands.…”

Theory of the optical spectra of the bacteriochlorophyll a antenna protein trimer from Prosthecochloris aestuarii

“…It is puzzling because an enormous amount is known, both experimentally and theoretically, regarding this protein. This knowledge includes the three-dimensional structure of the protein at near-atomic resolution (Fenna and Matthews 1975, Matthews et al 1979, Tronrud et al 1986), exceptionally well-resolved low-temperature optical spectra (Philipson andSauer 1972, Whitten et al 1978a), almost unambiguous theoretical description of the BChl molecular Q-orbitals (Weiss 1972, Hanson 1988, and the straightforward physics of the (exciton) interactions of transition dipoles (Pearlstein 1991). It is frustrating because of initial high hopes that the protein might serve as a 'Rosetta stone' for the interpretation of antenna protein spectra.…”

The Role of the Electronic Structure of the Porphyrin as Viewed by EPR/ENDOR Methods in the Efficiency of Biomimetic Model Compounds for Photosynthesis

“…Saturating the β-positions of one or two pyrrole rings to form a chlorin or a bacteriochlorin derivative also results in the a 1u orbital being the HOMO (see also Table 1). [33,34] The LUMOs in porphyrins have received comparatively less attention than the HOMOs. Spectroscopic properties of P-1 and P-2 anion radicals investigated by Seth and Bocian [31] reveal that the degeneracy of the LUMOs dominate the EPR spectra.…”