The IR absorption spectrum of hydrated alanine was determined by considering the electric dipole moments of the solute and the solvent molecules within the first solvation shell only, i.e. within a radius of 3.85 Å, in such a way as not to obscure the signal in the relevant spectroscopic region of 1000-2000 cm -1 by that of the water solvent. In crystalline phase, the IR spectrum was computed considering the whole environment.