Dielectric Relaxation in Aqueous Solutions of Some Dipolar Organic Molecules

The solutes are D‐(+)‐glucose, tris(hydroxymethyl)aminomethane, urea, 4‐hydroxypyridine, and three n‐amino acids. The complex permittivity of the solutions has been measured in dependence of the frequency between 0.3 GHz and 38 GHz at 25°C. By fitting an appropriate relaxation function to the measured frequency dependence of the permittivity, a subdivision into contributions of the water influenced by the solute molecules (“hydration water”), of the non‐influenced water, and of the solute has been performed. Hydration numbers, reorientation times of the hydration molecules and of the solute molecules, and dipole moments of the solute molecules are presented. Characteristic effects of the hydrophobic groups and adjacent hydrophilic (especially hydrogen bond forming) groups of the solute on the hydration water can be seen. The possibility of detecting chemically induced dielectric relaxation in the zwitterion solutions is discussed.