Hydration of amines, diamines, polyamines and amides studied by NMR
Abstract
The spin–lattice relaxation times, T1, of natural abundance H217O have been measured for aqueous solutions of nine amines, five diamines, two polyamines and five amides, as a function of the concentration at 25 °C. The water-accessible surface areas of the solute molecules were calculated. The coordination number, nh, and the rotational correlation times, τhc, of water molecules around the solute molecules were estimated and compared with that of pure water τ0c. The value of τhc/τ0c= 2.02 for tert-butylamine is the largest and that of τhc/τ0c= 0.97 for urea the smallest obtained. The value of nh(τhc/τ0c– 1) was defined as the dynamic hydration number (DHN).
The partial molar volumes and the partial molar heat capacities for these homologues at infinite dilution are linearly dependent on their DHN.