Vibrational Spectroscopy of Picolinamide and Water: From Dimers to Condensed Phase

Because of the presence of polar groups in picolinamide, its aqueous solvation is characterized by formation of multiple hydrogen bonds, which are responsible for differences in vibrational spectra of picolinamide in the gas phase and its aqueous solution. In this contribution, we try to identify dominant interactions between the solute and the solvent molecules that are the origin of the observed spectral changes. For this purpose, we analyzed the vibrational properties of picolinamide (a single molecule and also embedded in the environment described with an implicit solvent model) and picolinamide-water dimers: by comparing their vibrational frequencies with experimentally observed values of picolinamides' aqueous solution and by analyzing the computed anharmonic force constants, it is possible to recognize whether and in which way the solvent causes changes in the vibrational properties of the title compound. Calculations performed on the picolinamide three-hydrate confirm conclusions obtained by analyzing monohydrates.