The combination of Na^＋ with alanine dipeptide (AD) in gas phase has been studied using den-sity functional theory at the level of B3LYP/6-311＋＋G**, and six Na^＋-AD complexes were obtained, including two bidentate and four monodentate ones. Their total energies and chemical hardnesses have been computed, revealing the relative stabilities of these complexes. The influences of the inclusion of Na^＋ on Ramachandran angles (f and Ψ) and the H-bonds in AD molecules have been discussed in the work.

Key words: B3LYP, alanine dipeptide, Na^＋, structure, ion-complex