Association of κ-Carrageenan Induced by Cs⁺ Ions in Iodide Aqueous Solution:  A Light Scattering Study

Abstract

Light scattering (LS) investigations have additionally confirmed the intramolecular nature of the fundamental ordered conformation (single helix) of κ-carrageenan in aqueous 0.1 M NaI. The partial replacement of sodium with cesium ions induces a (thermoreversible) intermolecular association of the polysaccharide in the ordered conformation. The association-inducing effect can be observed already at the lowest investigated concentration of the cation. We found no significant change of the thermodynamic properties related to an alleged composition threshold value in the range of the cesium equivalent fraction, X Cs, from 0.12 to 0.40. The extent and the rate of the association process strongly increase with the concentration of cesium. Equilibrium values for the association constant could be obtained except for the case of X Cs = 0.40, where the process is too massive to allow long-time LS investigation. In the latter condition, some additional stiffening of the chain was noticed.

Isotropic−Nematic Phase Equilibrium and Phase Separation of κ-Carrageenan in Aqueous Salt Solution: Experimental and Theoretical Approaches

“…If we apply the theoretical model discussed previously by Vroege and accept that the hardcore diameter of KC is of 14 Å (based on the fact that the radius of the helix of KC in 0.1 M NaI is 7 Å as found from neutron and X-ray scattering measurements, Ramzi et al, unpublished), the effective diameter was calculated to be 37.81 Å (see Appendix). Considering that the κ-carrageenan in 0.1 M NaI has a persistence length of 35.6 nm, 25 we estimate the weight fraction for the isotropic-nematic transition at 4.7 wt % -4.8 wt %, respectively (see also Appendix). Indeed, these values are in the close agreement with the value that we found experimentally.…”

“…24 Recently it has been found that κ-carrageenan helix in 0.1 M NaI has a persistence length of 35.6 nm. 25 Despite the progress made, the properties of liquid crystalline polymers are not fully understood yet theoretically. Liquid crystalline polymers (LCP's) can be approached theoretically with the basic model of the rigid rod.…”

Characterization of α-carrageenan solution behavior by field-flow fractionation and multiangle light scattering

“…The gelation mechanism of k-and i-carrageenans has been previously described and investigated (Cuppo, Reynaers, & Paoletti, 2002;Mangione, Giacomazza, Bulone, Martorana, & San Biagio, 2003;Viebke, Borgstro¨m, Carlsson, Piculell, & Williams, 1998;Yuguchi, Tha`nh, Urakawa, & Kajiwara, 2002); l-carrageenan appears not to gel in aqueous systems. Briefly, a random coil to helix conformational transition proceeds with aggregation of helical segments to rigid rod bundles, eventually forming a gel network.…”

Non-equilibrium processes of interchain association induced by Cs+ ions in κ-carrageenan aqueous solutions

“…127H1222) of weight-average molar mass M w = 1.79(±0.02) × 10 5 g mol −1 (as determined by wide-angle light scattering) was purified as previously described [6]. Aqueous solutions in mixed NaI/CsI salt (with constant 0.1 M iodide concentration and varying cesium mole fraction, the latter being defined as X Cs = [CsI]/([CsI] + [NaI]) were prepared according to a standard procedure [6]. A peristaltic pump in a closed circuit was used to filter the solutions (Millipore membrane, pore size 0.22 m) directly in the light scattering cell.…”

“…In our previous work [3,5], we stressed the fundamental role of the preparative procedures in order to obtain reproducible and reliable results when dealing with -carrageenan, due to the extreme sensitivity of the biopolymer to the physicochemical parameters applied and, in particular, because of the very marked tendency towards macromolecular aggregation. Recently [6], we demonstrated, by use of static light scattering, the possibility to accurately control the process of intermolecular association in -carrageenan solutions, ranging from conditions of very limited cluster formation up to conditions of extensive, time-dependent association. To this purpose, we applied the mixed-counterion method firstly employed by Borgström et al [7].…”