In photosynthetic organisms, carotenoids function as light harvesting accessory pigments that absorb energy for use in photosynthesis, protect against photooxidative damage, and serve as a structural component in some photosynthetic pigment-protein complexes.  Over 750 structurally distinct carotenoids have been described.  An incredible structural variety exists due the symmetric and asymmetric introduction of numerous functional groups to produce derivatives of a- and �-carotenes.  When examining these pigments in algal species, it has been shown that this rich diversity of carotenoids is due to the diversity of the carotenogenic enzymes and pathways.  Certain carotenoids such as fucoxanthin, siphonaxanthin, and derivatives of a-carotene can be used as chemotaxonomic markers in phylogenetic analysis.  A search of the protein data bank for known structures of these unique pigments in their native environments has been initiated.  3D molecular modeling studies have also been employed to further examine the conformational arrangements of some of these chromophores.  Molecular models were constructed with the modeling program Sybyl-X and were subjected to dynamics simulation.  Representative structures from the trajectories were minimized utilizing different protocols within the program.  Electronic structure calculations employing semi-empirical molecular orbital methods (AMPAC/MOPAC) were used to predict spectral properties by calculating the energy differences between the occupied molecular orbitals and the unoccupied molecular orbitals.  Comparisons between experimental spectral properties and calculated results are presented for several carotenoids.

Molecular modeling studies of phylogenetically significant carotenoids of oxygenic phototrophs

247th National Meeting (2014)

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