This research article published by Open Access Library Journal, 2015The interaction of dimers of glucosamine and acetylglucosamine molecules with sodium ion has been studied using the DFT/B3LYP approach. The optimization of geometrical parameters and vibrational spectra calculations were done under 6-31G(d) basis set, and energies of the reactions were obtained using 6-311++G(d, p) basis set. The enthalpies of the association reactions of the dimers of glucosamine and acetylglucosamine with Na+ have been determined. The internal hydrogen bonds OH…O and NH…O have been shown to play an important role in conformational behavior of a particular molecule.