Organisation and association of kappa-carrageenan helices under different salt conditions.
Mixtures of the added salts NaI and CsI can be used to gradually 'tune' the propensity of kappa-carrageenan (KC) helices to aggregate in solution. We show that this method can be used to resolve the molecular events by which helix formation, under certain conditions, leads to gelation. We also present an overview of the various states of aggregation and organisation that appear for helical KC (non-degraded or ultrasonically degraded) when the NaI/CsI ratio and the concentration of KC are varied. A transition to rigid, superhelical rods is found above a well-defined fraction of cesium. This transition is reflected in a range of experimental measurements, such as cryo-transmission electron microscopy, optical rotation, viscometry and small deformation oscillatory measurements. The superhelical-rod state also seems essential for the association of KC with locust bean gum, and locust bean gum is found to stabilise this state. Novel states of KC alone have been found at cesium contents below the transition threshold. Non-degraded KC forms weak gels at sufficiently high concentrations (> ca. 1%). In contrast, ultrasonically degraded KC forms a chiral nematic liquid crystalline phase at sufficiently high concentrations (> ca. 5%) under these salt conditions.
Piculell
L
L
Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, Sweden. Lennart.Piculell@fkem1.lu.se
Borgström
J
J
Chronakis
I S
IS
Quist
P O
PO
Viebke
C
C
D002236:Carbohydrate Conformation; D002351:Carrageenan / Q000737:chemistry*; D002586:Cesium / Q000737:chemistry; D005690:Galactose / Q000031:analogs & derivatives; D005782:Gels; D007454:Iodides / Q000737:chemistry; D008351:Mannans / Q000737:chemistry; D012212:Rheology / Q000379:methods; D012492:Salts / Q000737:chemistry*; D012974:Sodium Iodide / Q000737:chemistry
D005782:Gels; D007454:Iodides; D008351:Mannans; D012492:Salts; C012990:galactomannan; D002586:Cesium; D002351:Carrageenan; D012974:Sodium Iodide; C040050:cesium iodide; D005690:Galactose