title: Anomalous small angle x-ray scattering determination of ion distribution around a polyelectrolyte biopolymer in salt solution.
abstract: The distribution of counterions in solutions of high molecular mass hyaluronic acid, in near-physiological conditions where mono- and divalent ions are simultaneously present, is studied by small angle neutron scattering and anomalous small angle x-ray scattering. The solutions contain either sodium or rubidium chloride together with varying concentrations of calcium or strontium chloride. The effects of monovalent-divalent ion exchange dominate the amplitude and the form of the counterion cloud. In the absence of divalent ions, the shape of the anomalous scattering signal from the monovalent ions is consistent with the distribution calculated from the Poisson-Boltzmann equation, as found by other workers. In mixtures of monovalent and divalent ions, however, as the divalent ion concentration increases, both the diameter and the amplitude of the monovalent ion cloud decrease. The divalent counterions always occupy the immediate neighborhood of the charged polyanion. Above a given concentration their anomalous scattering signal saturates. Even in a large excess of divalent ions, ion exchange is incomplete.
authors.affiliation: Section on Tissue Biophysics and Biomimetics, Laboratory of Integrative and Medical Biophysics, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Horkay
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Hecht
authors.forename: Cyrille
authors.initials: C
authors.lastname: Rochas
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Basser
authors.forename: Erik
authors.initials: E
authors.lastname: Geissler
mesh_terms: D002627:Chemistry, Physical / Q000379:methods*; D002712:Chlorides / Q000737:chemistry; D004247:DNA / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry*; D007477:Ions; D015233:Models, Statistical; D009502:Neutrons; D016012:Poisson Distribution; D011108:Polymers / Q000737:chemistry*; D012413:Rubidium / Q000737:chemistry; D012492:Salts / Q000737:chemistry*; D012542:Scattering, Radiation; D012965:Sodium Chloride / Q000737:chemistry; D014965:X-Rays
chemical_list: D002712:Chlorides; D004573:Electrolytes; D007477:Ions; D011108:Polymers; D012492:Salts; D012965:Sodium Chloride; D004247:DNA; D012413:Rubidium; C032710:rubidium chloride