Reactivity Sites in Dopamine Depend on its Intramolecular Hydrogen Bond

In this work, three conformers of dopamine were theoretically analyzed, two of them forming an intramolecular hydrogen bond between OH groups in the catechol moiety, the third one without this interaction. The used theoretical method was based on the Kohn-Sham method within the hybrid exchange-correlation functionals without empirical parameters, PBE0. The molecular geometry obtained by this method was contrasted with that obtained from the second-order many-body perturbation theory (MP2) method and the 6-31+G(d), 6-311+G(d) and 6-311++G(d,p) basis sets. Global reactivity descriptors were predicted by using only the PBE0/6-311++G(d,p) method. This method revealed that dopamine is not a good acceptor of electrons. Thus, in one charge transfer process, this compound prefers donating electrons, as observed experimentally. All global chemical predictors do not show important changes regardless of the presence of an intramolecular hydrogen bond. However, in the case of local reactivity predictors, oxygen atoms of the catechol moiety exhibit changes when this contact is present. This conclusion was confirmed when 8 catechol derivatives were analyzed with the same procedure applied over the dopamine. Additionally, the carbon atoms opposite to the carbon atoms linked to oxygen atoms, in the catechol moiety, present the biggest changes when these systems donate one electron. Consequently, the electron involved during the charge transfer process of these systems will be detached from the region defined between these two carbon atoms.