Protein-water interactions in solution: The water-gelatin-electrolyte system

Abstract

The interactions between water and gelatin have been studied by means of infrared and polarized Raman spectroscopy. The variations in band position and band intensity of the infrared vibrational band indicated that in the gelled state water molecules were tightly bound and probably bridged between carbonyl and amide groups. This tight bonding was broken in the ungelled state. The relaxation parameters of the nitrate ion were used to probe the influence of the electrolytes NaNO₃ and (Me₄N)NO₃. For both electrolytes there was a considerable increase in the reorientational relaxation time with increase in gelatin concentration. This confirmed the strong binding of water to the protein. The vibrational relaxation time in the presence of sodium ions showed little dependence on gelatin concentration; however, in the presence of the tetramethylammonium ion the vibrational relaxation time decreased sharply as the concentration of gelatin increased. This indicated that the nitrate ion was closely associated with the water bound to the protein.