Photosynthetic reaction centre and chlorosomal pigments, a computational study

M. Kutý¹, P. Palenčár and J. Pšenčík³

¹Institute of Physical Biology, University of South Bohemia, Zámek 136, 37333 Nové Hrady, Czech Republic

²Institute of Systems Biology and Ecology, Academy of Sciences of the Czech Republic,

Zámek 136, 37333 Nové Hrady, Czech Republic

³Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague, Czech Republic

Photosynthetic pigments are subject of wide variety of studies, in particular electronic structures of the ground and excited state. Molecular modelling method such as molecular dynamics coupled with quantum chemistry is a powerful tool for understanding and interpreting optical spectra experiments [1]. Quantum chemical calculations have been applied to elucidate absorption and CD spectra of chlorophyll a, phehophytine a and bacteriochlorophyll c monomers and multimers and their excitonic interaction. In this study we examine excited states by: a) semiempirical ZINDO/S calculations, b) configuration interaction (CI) and time dependent method at ab initio HF and density functional approximation with Pople basis set 6-31G (including diffussion and polarization functions) and c) empirical point-dipol calculations (diagonalization of Frenkel Hamiltonian). All mentioned calculations were performed on actual X-ray molecular structures of algae photosystem II reaction centre and on a theoretical model of chlorosomal bacteriochlorophyll “c”. The spectral effects of the functional groups and pigments orientation were interpreted.

1. Vácha, F., Durchan, M., Šiffel, P.: Excitonic interactions in the reaction centre of photosystem II studied by using circular dichroism. – Biochim. biophys. Acta. 1554: 147-152, 2002.

This research was supported by the Ministry of Education, Youth and Sports of the Czech Republic (MSM6007665808, GACR206/02/D177) and by the Academy of Sciences of the Czech Republic (Institutional research concept AVOZ60870520 and AV0Z50510513).