New hypothesis on the role of alternating sequences in calcium-alginate gels
| Autor: | Massimiliano Borgogna, Ivan Donati, Yrr A. Mørch, Synnøve Holtan, Mariella Dentini, Gudmund Skjåk-Bræk |
|---|---|
| Přispěvatelé: | Donati, Ivan, Holtan, S, MØRCH Y., A, Borgogna, MASSIMILIANO ANTONIO, Dentini, M, SKJÅK BRÆK, G. |
| Rok vydání: | 2005 |
| Předmět: |
Circular dichroism
Calcium alginate Polymers and Plastics calcium hydrogel Alginates chemistry.chemical_element Mineralogy Bioengineering syneresi Calcium Viscoelasticity Biomaterials chemistry.chemical_compound Glucuronic Acid Materials Chemistry alginate binding propertie Cagels chemistry.chemical_classification Syneresis Chemistry Circular Dichroism Hexuronic Acids Alginate MG polymers Hydrogels Polymer Models Theoretical binding properties syneresis alternating sequences NMR Polyelectrolyte epimerases Chemical engineering Carbohydrate Sequence circular dichroism hydrogels rheology Self-healing hydrogels |
| Zdroj: | Biomacromolecules. 6(2) |
| ISSN: | 1525-7797 |
| Popis: | The availability of mannuronan and mannuronan C-5 epimerases allows the production of a strictly alternating mannuronate−guluronate (MG) polymer and the MG-enrichment of natural alginates, providing a powerful tool for the analysis of the role of such sequences in the calcium−alginate gel network. In view of the calcium binding properties of long alternating sequences revealed by circular dichroism studies which leads eventually to the formation of stable hydrogels, their direct involvement in the gel network is here suggested. In particular, 1H NMR results obtained from a mixed alginate sample containing three polymeric species, G blocks, M blocks, and MG blocks, without chemical linkages between the block structures, indicate for the first time the formation of mixed junctions between G and MG blocks. This is supported by the analysis of the Young's modulus of hydrogels from natural and epimerized samples obtained at low calcium concentrations. Furthermore, the “zipping” of long alternating sequences in secondary MG/MG junctions is suggested to account for the shrinking (syneresis) of alginate gels in view of its dependence on the length of the MG blocks. As a consequence, a partial network collapse, macroscopically revealed by a decrease in the Young's modulus, occurred as the calcium concentration in the gel was increased. The effect of such “secondary” junctions on the viscoelastic properties of alginate gels was evaluated measuring their creep compliance under uniaxial compression. The experimental curves, fitted by a model composed of a Maxwell and a Voigt element in series, revealed an increase in the frictional forces between network chains with increasing length of the alternating sequences. This suggests the presence of an ion mediated mechanism preventing the shear of the gel. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|