title: A quasi-elastic neutron-scattering study of the molecular mobility of water associated with a protein both in aqueous solution and adjacent to a charged surfactant interface.
abstract: The quasi-elastic incoherent neutron-scattering method has been used to investigate the mobility of water molecules associated with the protein, alpha-chymotrypsin, both in aqueous solution and adjacent to a charged surfactant interface. The latter was studied by solubilizing the protein as monomer in the aqueous cores of small water-in-oil microemulsion droplets (radius 3.5 nm). The droplets were stabilised by an interfacial shell of a double-chain surfactant (Aerosol-OT). The spectra of the water in both these protein-containing system contained a component corresponding to a 7-fold reduction in mobility as compared with bulk water. The integrated intensity of this 'immobilised' spectra component shows that a maximum of approx. 450 water molecules, corresponding to half complete monolayer coverage, are associated with a single protein molecule. This value of 450 may contain a contribution from exchangeable hydrogens within the protein, but this contribution is estimated to be small. The mobility of the remainder of the water is unaffected. The solvation behaviour of the protein is similar in bulk water and in the microemulsion water droplets.
authors: Chemistry Department, University of Hull, North Humberside, U.K.
authors: P D
authors: PD
authors: Fletcher
authors: B H
authors: BH
authors: Robinson
authors: J
authors: J
authors: Tabony
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002918:Chymotrypsin; D004655:Emulsions; D009502:Neutrons; D011506:Proteins; D012542:Scattering, Radiation; D013057:Spectrum Analysis; D013501:Surface-Active Agents; D014867:Water
chemical_list: D004655:Emulsions; D011506:Proteins; D013501:Surface-Active Agents; D014867:Water; D002918:Chymotrypsin