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THEORETICAL STUDIES OF BILIPROTEIN CHROMOPHORES AND RELATED BILE PIGMENTS BY MOLECULAR ORBITAL AND RAMACHANDRAN TYPE CALCULATIONS
Author(s) -
Scheer H.,
Formanek H.,
Schneider S.
Publication year - 1982
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1982.tb04374.x
Subject(s) - chromophore , chemistry , ramachandran plot , molecular orbital , bile pigments , ring (chemistry) , steric effects , crystallography , molecule , phycocyanin , photochemistry , computational chemistry , pigment , stereochemistry , organic chemistry , protein structure , cyanobacteria , biochemistry , biology , bacteria , genetics
Ramachandran calculations have been used to gain insight into steric hindrance in bile pigments related to biliprotein chromophores. The high optical activity of denatured phycocyanin, as compared to phycoerythrin, has been related to the asymmetric substitution at ring A, which shifts the equilibrium towards the P‐helical form of the chromophore. Geometric effects on the electronic structures and transitions have then been studied by molecular orbital calculations for several conjugation systems including the chromophores of phycocyanin, phytochrome P r , cations, cation radicals and tautomeric forms. For these different chromophores some general trends can be deduced. For instance, for a given change in the gross shape (e.g. either unfolding of the molecule from a cyclic‐helical to a fully extended geometry, or upon out‐of‐plane twists of the pyrrole ring A) of the molecules under study, the predicted absorption spectra all change in a similar way. Nonetheless, there are characteristic distinctions between the different n ‐systems, both in the transition energies and the charge distribution, which can be related to their known differences in spectroscopic properties and their reactivity.