Hydrogen-bonding properties of galanthamine: an investigation through crystallographic database observations and computational chemistry

The hydrogen-bonding properties of galanthamine have been investigated experimentally from a thorough analysis of crystallographic data retrieved from the Protein Data Bank and Cambridge Structural Database databases and theoretically through ab initio [MP2/6-311++G(2d,p)] and density functional theory [MPWB1K/6-31++G(d,p)] calculations. The main hydrogen-bond acceptor (HBA) interaction sites of the molecule are the O atoms and their spatial proximity allows multi-centered hydrogen-bond (HB) motifs. The hydrogen-bond donor (HBD) sites of the molecule are the NH⁺ and OH groups as well as several CH donors. Among them, the preferred ones are those directly linked to the ammonium nitrogen, followed by aromatic CH and finally the methyl group of the methoxy substituent. All these observations are in fairly good agreement with the computed positions of the molecular electrostatic potential (MEP) minima and maxima of various galanthamine species. The galanthamine HBD and HBA properties, investigated through the MEP analysis, appear sensitive to the degree of neutralization of the ammonium NH⁺ positive charge.