Semiempirical INDO/S study on the absorption spectrum of violacein

Violacein is the major pigment produced by Chemobacterium violaceum. We now report the results of semiempirical calculations on the electronic spectrum of violacein. We have used the AMI and Intermediate Neglect of Differential Overlap (INDO) model Hamiltonians. Solvent effects have been included with the SCRF model for spectroscopy as proposed by Zerner and Karelson. Our results suggest that in the gas phase violacein is almost planar while in ethanolic solution the H-bond interactions force an internal rotation due to sterical factors. The calculated UV-visible spectrum with the inclusion of specific solvent interactions in the Hamiltonian is on good agreement with the experimental spectrum. (C) 2002 Elsevier Science B.V. All rights reserved.