Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The values of activity coefficients γ_Ca²⁺, determined earlier in solutions of calcium oligoguluronates and oligogalacturonates of various polymerization degree n, were interpreted. Values γ_Ca²⁺ corresponding to an intramolecular Ca²⁺ bond to a polymeric chain of L-guluronan and D-galacturonan were obtained by extrapolation of functions γ_Ca²⁺ = f(1/n) and γ_Ca²⁺ = f((n-2)/n) to lim n → ##h. The γ_Ca²⁺ values were compared with those determined in solutions of calcium salts of O-acetyl derivatives of pectic acid and D-mannuronan. In molecular disperse solutions the Ca²⁺ ions are bound to L-guluronan and D-galacturonan by an electrostatic bond. The course of the above-mentioned functions leads to the conclusion that both terminal uronic acid units in polyuronates under study bind Ca²⁺ ions less firmly than do the inner units in the macromolecule chain. The linear course of the function γ_Ca²⁺ = f((n-2)/n) for L-guluronan proves the additivity of contribution of the terminal and inner uronic acid units to the total activity of Ca²⁺ counterions bound to L-guluronan.