Structures, stabilization energies, and binding energies of quinoxaline···(H2O)(n), quinoxaline dimer, and...

Quinoxaline is a parent structure for a broad class of N-heteroaromatic compounds, many of which exhibit various biological activities. The interaction of quinoxaline with explicit water molecules or metal ions and the formation of quinoxaline dimer play an important role in many of the biological activities of quinoxaline. This study investigates the structures, stabilization, and binding energies of quinoxaline complexes with water, transition metal ions, and quinoxaline dimer to provide information on the preferred geometries, interaction energies, and type of noncovalent interactions accounting for the stability of the complexes. The investigations are performed in vacuo and in water solution using MP2 and DFT methods. The results of the study on the quinoxaline···(H(2)O)(n) show that the preferred adducts in vacuo involve one, two, or three water molecules hydrogen bonded to the N atom and the neighboring H atom of the C(sp2)-H group. The results in water solution show a preference for water-water clustering. The dimers of quinoxaline are stabilized by either π-π stacking or weak C-H···N intermolecular hydrogen bonds. The relative stability of the quinoxaline···Cu complexes depends on the site on which the Cu ion binds and the binding strength depends on both the nature of the cation and the binding site.