TAUTOMERISM OF HISTAMINE REVISITED

The tautomerism of the histamine molecule was explored based on quantu m chemical calculations both in the gaseous state and in aqueous mediu m. Structural optimizations were performed at the ab initio Hartree-Fo ck (HF) and the second order Moller-Plesset (MP2) perturbation level. The most stable tautomer in aqueous medium appeared to be the N(3)-H m onocation; with strong intramolecular hydrogen bonding. Results from c alculations prove that the previous hypothesis on interaction with the hypothetical H-2 receptor remains valid, even though this hypothesis involved a slightly different assumption regarding the structure of th e most stable form. The most stable neutral form in aqueous medium tur ned out to be the opened N(3)-H gauche structure.