Complex investigation of H-bond in Water-N-methylacetamide system: Volumetric properties, DFT, IR, MD analysis

Abstract

• Behavior of the volumetric properties of the binary water-NMA mixture was studied over wide pressure ranges. • Hydrogen bonds in NMA–water mixtures were analyzed using computer chemistry and vibrational spectroscopy. • The analysis of the strength of the hydrogen bond between amides and surrounding water molecules is carried out. • The hydrogen atoms of water and amide compete as hydrogen bond donors. A combined approach of computational chemistry, vibrational spectroscopy experiments, and density measurements was used to study the structural properties of water-N-methylacetamide mixtures over the entire concentration range. The structure of N-methylacetamide dimers and hydrogen-bonded complexes of N-methylacetamide with water molecules was investigated by the quantum chemical method on the basis of the density functional theory. The vibrational spectra of aqueous solutions of N-methylacetamide were recorded. Based on quantum chemical calculations, the bands of the vibrational spectrum were identified, which made it possible to trace the change in hydrogen bonding in the system. At increased N-methylacetamide concentration, the hydrogen bond network rearranges. The number of hydrogen bonds between water molecules decreases, water molecules bind to N-methylacetamide molecules, changing the nature of its environment. Aqueous mixture containing N-methylacetamide shows strong deviations of volumetric properties from ideality. For the further analysis of the data obtained, molecular dynamics simulation of this system was conducted at various temperatures and pressures. It was shown that the resulting hydrogen bonds are of medium strength, but their strength depends on the water molecule environment, which is proved by NBO and QTAIM data. A network of hydrogen bonds is formed in N-methylacetamide aqueous solution, which is noticeably destroyed with an increase in temperature and slightly changes with an increase in pressure.