Limiting-laws of polyelectrolyte solutions. Ionic distribution in mixed-valency counterions systems. II. A comparison of conductometric data and theoretical predictions

The competitive binding of monovalent and divalent counterions (M + and M 2+ , respectively) has been studied by a conductometric procedure as described by De Jong et al. (Biophysical Chemistry 27 (1987) 173) for aqueous solutions of alkali metal polymethacrylates in the presence of Ca (NO 3) 2 or M...

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Published in:Biophysical chemistry 1992-04, Vol.42 (3), p.297-303
Main Authors: C. Benegas, Julio, Paoletti, Sergio, Cesàro, Attilio, van den Hoop, Marc A.G.T., van Leeuwen, Herman P.
Format: Article
Language:English
Subjects:
Analytical, structural and metabolic biochemistry
Biological and medical sciences
Conductometry
Fundamental and applied biological sciences. Psychology
Inorganic compounds
Mixed-valency counterions system
Other biological molecules
Polyelectrolyte theory
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Summary:The competitive binding of monovalent and divalent counterions (M + and M 2+ , respectively) has been studied by a conductometric procedure as described by De Jong et al. (Biophysical Chemistry 27 (1987) 173) for aqueous solutions of alkali metal polymethacrylates in the presence of Ca (NO 3) 2 or Mg(NO 3) 2. The experimentally obtained fractions of conductometrically free counterions are compared with theoretical values computed according to a new thermodynamic model recently developed by Paoletti et al. (Biophysical Chemistry, 41 (1991) 73). For the systems studied, the fractions of free monovalent and divalent counterions can be fairly well described by the theory. In fact, the results support the assumption that under the present conditions the conductometrically obtained distribution parameters ⨍ l and ⨍ 2 approximate the equilibrium fractions of free monovalent and divalent counterions. For a degree of neutralization of 0.8 and a molar concentration ratio of divalent counterions and charged groups on the polyion up to 0.25, the mean M +/M 2+, exchange ratio ν has been found to be 1.39 ± 0.03 and 1.33 ± 0.03 for the alkali metal/Ca/PMA and alkali metal/Mg/PMA systems, respectively. These values agree well with the theoretical value, which for this particular case is 1.38.
ISSN:0301-4622
1873-4200
DOI:10.1016/0301-4622(92)80022-W