ON THE SPECTRAL PROPERTIES OF TRYPTAMINE DERIVATIVES

We report quantum chemical semiempirical calculations of the electroni c structure of serotonin (5-hydroxytryptamine, 5-HT) and 5,7-dihydroxy tryptamine (5,7-DHT). Those substances are important in the context of Alzheimer's disease. Moreover, the tautomerism of 5,7-DHT, which is n ot present in serotonin, is also examined. We have found that the phen ol form of 5,7-DHT is more stable than is the 4-keto form in the gas p hase. However, the large dipole moment of the keto form suggests that a large stabilization of this form can occur in a polar environment, w hich is confirmed by further supermolecule calculations. We have also calculated the absorption spectra of both 5,7-DHT and serotonin (5-HT) using the INDO/S method at the calculated AM1 geometries, with good a greement with experimental data. Our results give strong support to th e hypothesis of the phenol-keto tautomerism of 5,7-DHT being responsib le for the UV-visible spectroscopic features. (C) 1993 John Wiley & So ns, Inc.