Theoretical Studies on the Interaction between 2-Aminobenzothiazole and Water

ABT-(H₂O)_n (n = 1–6) has been studied systematically at the ωB97XD/def2-TZVPP level. Hydrogen bonds in ABT-(H₂O)_n were investigated using quantum theory of atoms in molecules (AIM), interaction region indicator (IRI) and independent gradient model (IGMH) based on Hirshfeld partition. The results show that the strength of hydrogen bond increases with the increasing of the number of water molecules. H₂O can be used as proton-donors to form hydrogen bonds with ABT (O–H^W⋅⋅⋅N1, O–H^W⋅⋅⋅N2, O‒H^W⋅⋅⋅S, O–H^W⋅⋅⋅C, and O–H^W⋅⋅⋅π). Three types of hydrogen bonds (N2–H1⋅⋅⋅O, N2–H2⋅⋅⋅O, and C‒H^ABT⋅⋅⋅O) are formed when H₂O act as proton-acceptors. Both O–H^W⋅⋅⋅N1 and N2–H1⋅⋅⋅O hydrogen bonds exist in the most stable structure, indicating that these bonds are relatively strong. The binding energy of hydrogen bond involving carbon atom is less than 2.5 kcal mol^–1, which belongs to the very weak hydrogen bond. The eight-membered ring structure formed by hydrogen bond between ABT molecule and water molecule is relatively stable structure.