Polyelectrolyte behavior of carrageenans in aqueous solutions

Abstract

SynopsisOsmotic coefficients of sodium, potassium, and calcium counterions have been determined in aqueous solutions on kappa-, iota-, and lambda-carrageenans a t 25OC. The experimental results are correlated with the calculated ones from the limiting law of Manning. An ordered secondary structure exists in kappa-and iota-carrageenans. Its stability is discussed as a function of temperature, ionic strength, and the nature of the counterions.

Unravelling Secondary Structure Changes on Individual Anionic Polysaccharide Chains by Atomic Force Microscopy

“…[3] The sequence motif of lambda-carrageenan has been suggested to prevent the formation of any secondary structure and thus gel formation, whereas iota-carrageenan has been reported to be capable of undergoing a coil-helix transition as a first event of gelation. [4] For their thermoreversible gelation in aqueous solution, a two-step process involving an initial ion-induced helix formation followed by association into networks is generally accepted. Nonetheless, the mechanisms governing the conformational transition, ion-specificity effects, and the mode of molecular association into a percolating gel are still highly debated.…”

“…Nonetheless, the mechanisms governing the conformational transition, ion-specificity effects, and the mode of molecular association into a percolating gel are still highly debated. [2] An ordered dimeric double helix with 1.3 nm diameter was initially proposed for iota-carrageenan based on fiber X-ray diffraction results, [5a] which was further supported by osmometry, [5b] stopped-flow polarimetry, [5c] sizeexclusion chromatography combined with light scattering, [5d, e] and differential scanning calorimetry.[5f] Strong indication for a single-stranded iota-carrageenan helix as the ordered conformation emerged, however, from other osmometry studies combined with measurements of optical rotation [4] and intrinsic viscosity, [6a] which were substantiated by light scattering data, [6b] leaving the nature of the ordered state a highly controversial issue.This study focuses on resolving the disorder-order conformational transition in molecular solutions of these anionic polysaccharides by atomic force microscopy (AFM) imaging. The conformational change from disordered carrageenans in the random coil state [7] to ordered, helical chains, is expected to modulate the rigidity of individual polyelectrolyte chains [8] which will be assessed by applying polymer physics concepts to the AFM polymer traces.…”

“…Conditions of no added salt (0 mm) and ambient temperature imply a disordered carrageenan conformation. [4] The polymers appear to …”

“…[5f] Strong indication for a single-stranded iota-carrageenan helix as the ordered conformation emerged, however, from other osmometry studies combined with measurements of optical rotation [4] and intrinsic viscosity, [6a] which were substantiated by light scattering data, [6b] leaving the nature of the ordered state a highly controversial issue.…”

“…[4] For their thermoreversible gelation in aqueous solution, a two-step process involving an initial ion-induced helix formation followed by association into networks is generally accepted. Nonetheless, the mechanisms governing the conformational transition, ion-specificity effects, and the mode of molecular association into a percolating gel are still highly debated.…”