Ionic gel formation of a (pseudo)alginate characterised by an alternating MG sequence produced by epimerising mannuronan with AlgE4

The scope of this paper is the characterization, in terms of viscoelastic and mechanical properties, of ionic gels obtained from solutions of pseudoalginates characterized by a strictly alternating MG sequence (ALG(47%, 0%GG)) in the presence of calcium ions. ALG(47%, 0%GG) was obtained using a recombinantly produced mannuronan C-5 epimerase, named AlgE4 which catalyses the conversion of mannuronic residues into guluronic mannuronic (GM) blocks. It was established that the kinetics of gelation as well as the mechanical properties and degree of syneresis of the ensuing gels are markedly dependent on both polymer concentration and Ca2+ content. The molecular dynamic investigation was carried out on a comparative basis between poly(MG) vs. poly(G) and demonstrated that in the case of poly(MG) the structural unit composed by two calcium paired MG oligomer enjoy a higher degree of flexibility in comparison to the equivalent structure based on GG sequence. Furthermore, the electrostatic interaction between Ca2+ ions and carboxylate groups of M and G units is the main driving force to gel formation. (c) 2006 Elsevier Ltd. All rights reserved.