SEMIEMPIRICAL MOLECULAR-ORBITAL CALCULATIONS OF BILIVERDIN - STABILITY STUDY OF VARIOUS ISOMERS AND CONFORMATION ANALYSIS

Semiempirical molecular orbital methods were applied to the computatio n of the three isomeric forms, diketo, keto-enol, and dienol of bilive rdin. The fully optimized structures so obtained were compared and the most stable isomer (diketo form) agreed well with the structure deter mined from X-ray crystallographic studies. Results of the calculations based on the three hamiltonians, AM1, MNDO and PM3 were compared with the experimental parameters. AM1 hamiltonian results were determined to be closest to the experimental results. Conformational studies on t he diketo isomer were carried out using the AM1 hamiltonian while rota ting the central dihedral angle N10-C13-C15-C16. No evidence of any su dden changes in pyrrole ring planarity was observed as expected. (C) 1 998 Elsevier Science B.V. All rights reserved.