Light‐scattering properties of sodium and magnesium alginate

Abstract

The weight-average molecular weight of a fraction of magnesium alginate was found by light-scattering to be identical within experimental error to that of the corresponding fraction of sodium alginate. The difference in the charge density of sodium and magnes: ium alginate had no detectable effect on their measured radii of gyration at ionic strength 0.1, but had a great effect on the second virial coefficient of the solutions. The Orfino-Flory theory was used to calculate expansion factors, a, from the second virial coefficients, assuming that these were composed of two terms, one due to polymersolvent interaction and one due to electrostatic interactions. .A comparison with a-values obtained from viscosity data at different ionic strengths suggested that alginate is soluble in water because of electrostatic stabilisation and not because of a favourable polymerwater interaction.

Revisiting Cation Complexation and Hydrogen Bonding of Single-Chain Polyguluronate Alginate

“…The present work used an explicit water model, which allowed the interaction between water and alginate to be carefully examined. Previous studies mainly attribute the solubility of alginate to the mutual repulsion of negatively charged chains (i.e., electrostatic stabilization). , When the charge on the chain is neutralized, such as through protonation, the dispersion is destabilized and chain association may occur, which explains why decreasing pH can trigger an association between alginate molecules . Similarly, Ca 2+ forms ionic bonds with carboxyl oxygens (shown in Figure ) and therefore neutralizes the charge on the chain, whereas Na + binds to alginate much less frequently, maintaining the electrostatic stabilization between alginate chains.…”

Experimental Evidence of Counterion Affinity in Alginates: The Case of Nongelling Ion Mg2+

“…Although a limited amount of experimental data on Mg 2+ -alginate are available, the lack of strong polymer-ion interactions and chain-chain associations have been unquestionably demonstrated. 18 Therefore, despite the less appealing industrial and biotechnological application of such system, Mg 2+ ion can represent the best candidate to test the applicability of the counterion condensation (CC) theory, as originally developed by Manning. 19 The latter approach, although derived in the limit of zero salt concentration, has proved to describe fairly well the experimental behavior of biopolyelectrolytes [20][21][22][23] and in particular of ionic polysaccharides.…”

“…With respect to the great amount of work performed on Ca 2+ (and to a lower extent on Ba 2+ ), relatively little attention has been devoted to the behavior of this polysaccharide in the presence of Mg 2+ . Although a limited amount of experimental data on Mg 2+ −alginate are available, the lack of strong polymer−ion interactions and chain−chain associations have been unquestionably demonstrated . Therefore, despite the less appealing industrial and biotechnological application of such system, Mg 2+ ion can represent the best candidate to test the applicability of the counterion condensation (CC) theory, as originally developed by Manning .…”

Dynamic and static light scattering on aqueous solutions of sodium alginate

“…For the ionic strength the lower limit (4.4 mM) was set by the concentration of EDTA and the upper limit (95 mM) was chosen to be close to the value used in earlier static light scattering studies. 3,10 The alginate concentration was determined by use of the phenol-sulfuric acid color reaction. 2,10 For each of the solutions the pH was 6.3 ± 0.1.…”