Neutron scattering studies of hydration of molecules of biological importance

Abstract

The isotopic difference method of neutron diffraction has been used to study aqueous solutions of 2 molal urea, formamide and acetamide, to obtain information on the hydration structure around the polar amide group. In each case the difference between the coherent differential cross-sections for solutions containing natural abundance nitrogen and nitrogen-15 has been determined and Fourier transformed to give the atomic distribution function with reference to nitrogen. Although the difference measurements obained from formamide and acetamide are of less good quality than that from urea, the results in the intramolecular distance range are in agreement with the known molecular structures. The intermolecular structures, assumed to be due to solute-water correlations at this concentration, give water-coordination numbers consistent with the results of computer simulation studies.