NMR, Calorimetry, and Computational Studies of Aqueous Solutions of N-Methyl-2-pyrrolidone

N-Methyl-2-pyrrolidone (NMP) is a solvent with applications in different industrial fields. Although largely employed in aqueous mixtures, little is known on the structural and dynamic properties of this system. In order to improve the knowledge on NMP aqueous solutions, useful to the development of their applications, NMR spectroscopy, calorimetric titration, and puckering analysis of molecular dynamics (MD) simulations were employed in this work. Our calorimetric study evidenced the presence of strong interactions between NMP and water and revealed that, under comparable conditions, the solvation of NMP by water results in an interaction stronger than the solvation of water by NMP. Overall, the changes of 1H and 13C chemical shifts and 2D ROESY spectra upon dilution suggested a preferential location of water nearby the carbonyl group of NMP and the formation of hydrogen bonding between these two molecules. In parallel, observation of correlation times by 13C NMR spectroscopy evidenced a different dynamic behavior moving from the NMP-rich region to the water-rich region, characterized by a maximum value at about 0.7 water mole fraction. MD simulations showed that the NMP conformation remains the same over the whole concentration range. Our results were discussed in terms of changes in the NMP assembling upon dilution.