NA-ALGINATE AND K-ALGINATE - EFFECT ON CA2-GELATION()

The effect of two different monovalent alginate counterions has been s tudied in Ca2+-mediated sol/gel transitions and in Ca2+-gels at appare nt equilibrium for alginates with different chemical composition and s equence. K-alginates were generally found to undergo faster sol/gel tr ansitions compared to the Na-alginate. At apparent equilibrium and at low Ca2+ concentration, Na-alginate gels showed reduced elastic moduli compared to the K-alginates. The relative differences both in sol/gel transition kinetics acid modulus at apparent equilibrium increased wi th increased content of guluronic acid residues in the alginate sample . Increasing the amount of internally released Ca2+ from 15 to 30 mM r esulted in equal elastic properties at apparent equilibrium, suggestin g that dissimilarities in ion exchange reactions between Ca2+/Na+ and Ca2+/K+ is the main driving force. The specific effect of one of the c ounterion could be reversed by adding increasing amounts of the other. Selectivity coefficient determinations for alginates revealed a sligh t enhanced binding of Na+ compared to K+, most probably due to the gul uronate residues. (C) 1998 Elsevier Science Limited. All rights reserv ed.