Aggregation and disaggregation of Aeromonas gum in an aqueous solution under different conditions

Abstract

The aggregation and disaggregation of Aeromonas (A) gum, an acidic heteropolysaccharide, were investigated by viscometry, a fluorescent probe, and gel permeation chromatography combined with laser light scattering techniques in aqueous solutions containing desired NaCl at different temperatures. The A gum had a strong tendency of aggregation and high viscosity in the aqueous solutions. The weight‐average molecular weight, z‐average radius of gyration, weight‐average molar number (wag), and apparent aggregation number (Nap) of the aggregates were investigated and discussed. The results indicated that there were three regions that corresponded to three kinds of aggregates and two transition temperatures at about 35 and 75 °C in the disaggregation course. When the temperature was higher than 75 °C, the wag hardly changed, and there was still a certain amount of aggregates even at 100 °C, indicating that the aggregates were difficult to disrupt completely. Moreover, the aggregation was thermally irreversible. Decreasing polysaccharide concentration reduced the content of the aggregate. However, Nap remained constant around 20, independent of the polysaccharide concentration in a 0.5 M NaCl aqueous solution at 25 °C. At a salt concentration greater than or equal to 0.05 M, the aggregation was almost independent of the salt concentration used here. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2644–2651, 2000

Aggregation behavior of 3,6‐O‐carboxymethylated chitin in aqueous solutions

“…It is likely that, to a large extend 3,6‐O‐CM‐chitin exists in aqueous solution as aggregates and the increasing temperature leads to disruption of the aggregates by destruction of the aggregating interactions. The dissociation process of the aggregates can be ascribed as follows, taking reference to the literature 5. When the system obtained a certain energy above 60°C, the aggregates with relatively low cohesive energy were first dissociated, the aggregates with middle cohesive energy were then dissociated at 80 to 90°C, and a small part of aggregates with high cohesive energy were difficult to be dissociated by heating.…”

“…This result seems to be different from those obtained by Eisenberg and Zhang et al Eisenberg et al1 reported two block polyelectrolyte samples as a function of NaCl concentration, and found that at low salt concentration ( c s < 0.2 M ) aggregation numbers initially increased with c s and then eventually leveled off. Zhang et al5 reported that the aggregation behavior of Aeromonas gum was almost independent of the salt concentration, but reduced dimensions caused by decrease of electrostatic force was likely to have strong effect on [η], thus intrinsic viscosity [η] decreased with salt concentration. To verify the result obtained from viscometry method, 3,6‐O‐CM‐chitin solutions of desired NaCl concentration were injected into the GPC column at 30°C.…”

“…Polymer aggregations have been an extensive research attracting a great deal of attention in recent years because they determine the apparent molecular weight and polymer morphology in the aqueous solutions, which are closely related to the polymer properties and applications 1–6. Aggregations of amphiphilic nonionic polymers, block copolymers2, 4, 7, 8 and hydrophobically modified polyelectrolytes including block polyelectrolytes in organic solvents or aqueous solutions1, 3, 9 have been reported over the past 2 decades.…”

“…Aggregations of amphiphilic nonionic polymers, block copolymers2, 4, 7, 8 and hydrophobically modified polyelectrolytes including block polyelectrolytes in organic solvents or aqueous solutions1, 3, 9 have been reported over the past 2 decades. Because aggregation is mainly attributed to intermolecular hydrogen bonding4 and entanglement,10 control of aggregation behavior can be achieved by changing of such interchain interactions with methods of varying the solution temperature or modifying the aqueous solution quality with, for example, the addition of salts etc 1, 5…”