The Molal Osmotic Coefficients and Counterion Activity Coefficients of Arabate with Various Counterions

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The interaction of arabic acid with counterions was studied by measuring the molal osmotic coefficients and counterion activity coefficients. The molal osmotic coefficients, φ, of various salt solutions were measured with a vapor pressure osmometer. In the monovalent salts, the φ value slightly decreased with decreasing hydration radii of counterions, but in divalent salts, the φ value was similar to each other and was about a half of those of monovalent salts. The counterion activity coefficients, γ_+, for Na and/or Ca arabate with or without added salts were determined by measuring electromotive force with cation-selective electrodes. In the absence of added salts, γ_+ was slightly larger than φ. In the presence of added salts, the additivity rule held very well for Na and Ca arabate solutions. In such a system with two kinds of counterions, Na and Ca, coexisting in arabate solution, Ca ion was preferentially adsorbed onto the polyions and consequently Na ion was less subject to the influence of the polyion. These results suggest that the interaction of arabic acid with counterions is due to the electrostatic free force alone, and not by any other specific force, and further suggest that Manning's theory for cylindrical polyelectrolytes seems to be applicable to the case of a branched polysaccharide, arabate, if the intercharge distance, "b, "can be assumed to be a parameter reflecting a spatial intercharge distance.
公益社団法人日本薬学会の論文
1984-10-25

The Molal Osmotic Coefficients and Counterion Activity Coefficients of Arabate with Various Counterions

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