Geometric and spectroscopic study of some molecules related to eumelanins. 1. Monomers

We have carried out ab initio and semiempirical PM3 (parametric method 3) and ZINDO (Zerner's intermediate neglect of differential overlap) calculations on neutral and charged 5,6-indolequinone and its reduced forms semiquinone and hydroquinone. These molecules are believed to compose the major part of the active material of eumelanin, a biological pigment present in illuminated and nonilluminated areas in living organisms. Our results show that these molecules can behave as electron accepters and that their electronic behavior is consistent with that of the semiconductor models proposed for melanins. The relationship between electronic behavior and biological functions is also addressed.103152993300