Local Chain Mobility of Gellan in Aqueous Systems Studied by Fluorescence Depolarization

Abstract

The local chain mobility of a gellan, an electrolyte polysaccharide, in aqueous systems was examined with respect to the effect of the temperature, the concentration of gellan (c(G)), and the concentration of added salt (c(S)). The relaxation time of local motion was estimated for fluorescein isothiocyanate (FITC)-labeled-gellan by the fluorescence depolarization technique, and the chain mobility was discussed. The relaxation time increased with decreasing temperature, in particular when accompanying the coil-helix transition due to the great difference in chain mobility between the coil and the helical conformations. The effect of c(G) was observed for gellan solutions even below the critical concentration of chain entanglement (2 wt.-%) for well-expanded nonelectrolyte polymers with size similar to that of the gellan. This suggests that the actual excluded volume of gellan is larger than that of nonelectrolyte polymers due to the electrostatic repulsion between segments. The relaxation time for 0.2 wt.-% systems of gellan in coil conformation is independent of c(S), whereas a c(S) dependence of the relaxation time is clearly observed for 0.5 wt.-% systems. The degree of expansion of the gellan chain is independent of the shielding effect of cations on the electrostatic repulsion between gellan segments due to the stiffness of gellan chain. On the other hand, the c(G) as well as the c(S) dependence of the chain mobility is clearly observed for gellan in the helical conformation, examined over the concentration range, probably due to the partial aggregation of helices induced by the attractive interaction between gellan segments.

Chain Mobility of Pectin in Aqueous Solutions Studied by the Fluorescence Depolarization Method

“…However, the cation species coexisting with pectin chains in an aqueous solution have no effect on the chain mobility. Recently, similar results have been obtained for gellan 16 sthe chain mobility of the random-coiled gellan in aqueous solutions was not affected by the addition of a cation species, although the coil-helix transition temperature as well as the gelation temperature for gellan changed with the concentration of the cation species. These results imply that cation species do not affect the chain mobility of anionic polysaccharides.…”

“…The labeling reaction was assessed using fluorescence techniques. 16 We compared the fluorescence spectra as well as r j between an aqueous solution of labeled-pectin and an unlabeled pectin containing a trace of free An-MeOH. The fluorescence spectrum for the solution of labeled-pectin was 5 nm red-shifted from that for the solution of unlabeled pectin while maintaining the fingerprint characteristics of the anthryl group.…”

Pre-gel solution properties of gellan polysaccharides: Effect of potassium and calcium ions on chain associations

“…The sample concentrations used in the present study were selected based on a previous study by Nickerson and Paulson (2004) who found C * at 25°C for gellan solutions to be 0.44% (w/w) in the absence of added ions, and 0.25% (w/w) and 0.20% (w/w) in the presence of added K + (0.5 mM) and Ca 2+ (0.25 mM), respectively. Values were comparable to those determined by Nickerson, Paulson, and Speers (2003) and Horinaka, Kani, Honda, Uesaka, and Kawamura (2004) for similar systems. Overlap concentrations were lower than critical gelation concentrations determined using percolation theory corresponding to levels of 0.77% (w/w) for samples without added salts, and 0.42% (w/w) and 0.28% (w/w) with added K + (0.5 mM) and Ca 2+ (0.25 mM), respectively.…”

In situ formation of silvernanostructures within a polysaccharide film and application as a potential biocompatible fluorescence sensing medium

“…6, also shows increased emission in the exposed areas. The increase in the observed intensity at the exposed areas was $2.3 times (¼ G Q , eqn (12)) that outside of the areas (Fig. 6a).…”

“…7,10,11 Cations help to crosslink gellan's negatively charged polysaccharide helices, forming helix-helix aggregates. 6 Most work has made use of rheology to monitor changes in the bulk viscosity, although there is a report of fluorescence anisotropy employed to monitor chain conformation, 12 as well as calorimetry. 13 Previously we have made use of changes in the fluorescence lifetime of a hydrophilic probe, DASPMI (4-(4-(dimethylamino)styryl)-N-methyl-pyridiniumiodine) to elucidate this viscosity variation.…”