Analysis of the conformational properties of κ‐ and ι‐carrageenan by size‐exclusion chromatography combined with low‐angle laser light scattering

The conformational properties of κ‐carrageenan in 0.2M LiI and ι‐carrageenan in 0.2M LiCl were analyzed by size exclusion chromatography combined with low‐angle laser light scattering. Fractionated samples with narrow molecular weight distributions (M_w/M_n ∼ 1.4) were used, and M_w in the disordered states were 35,000 (κ‐35) and 200,000 (κ‐200) for κ‐carrageenan and 65,000 (ι‐65) and 170,000 (ι‐170) for ι‐carrageenan, respectively. The analyses were performed across a temperature range where the conformational transitions occurred, and at extremely low concentrations (2–50 μg/mL) due to low amounts of samples injected and the subsequent dilution occurring during the separation. The results indicate that a twofold increase of the molecular weight (M_w) occurs for κ‐carrageenan upon inducing the ordered conformation. For ι‐carrageenan an additional increase in M_w may take place, which is attributed to the strong tendency for aggregation of ordered chains especially at high molecular weights. The results thus suggest that both κ‐ and ι‐carrageenan are double (or multiple) stranded in their ordered conformations, within the concentration range studied here. © 1999 John Wiley & Sons, Inc. Biopoly 49: 71–80, 1999