Water structure around dipeptides in aqueous solutions.

The bulk water structure around small peptide fragments--glycyl-L-alanine, glycyl-L-proline and L:-alanyl-L-proline-has been determined by a combination of neutron diffraction with isotopic substitution and empirical potential structural refinement techniques. The addition of each of the dipeptides to water gives rise to decreased water-water coordination in the surrounding water solvent. Additionally, both the Ow-Ow radial distribution functions and the water-water spatial density functions in all of the solutions indicate an electrostrictive effect in the second water coordination shell of the bulk water network. This effect is not observed in similar experiments on the amino acid L: -proline alone in solution, which is one component of two of the peptides measured here.