Abstract
The conformational properties of kappa-carrageenan in 0.2M LiI and
iota-carrageenan in 0.2M LiCl were analyzed by size exclusion chromatography
combined with low-angle laser light seat tering. Fractionated samples
with narrow molecular weight distributions (M-w/M-n similar to 1.4)
were used, and M-w in the disordered states were 35,000 (kappa-35)
and 200,000 (kappa-200) for kappa-carrageenan and 65,000 (iota-65)
and 170,000 (iota-170) for iota-carrageenan, respectively. The analyses
were performed across a temperature range where the conformational
transitions occurred, and at extremely low concentrations (2-50 mu
g/mL) due to low amounts of sampler injected and the subsequent dilution
occurring during the separation. The results indicate that a twofold
increase of the molecular weight (M-w) occurs for kappa-carrageenan
upon inducing the ordered conformation. For iota-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 kappa- and iota-carrageenan
are double (or multiple) stranded in their ordered conformations,
within the concentration range studied here. (C) 1999 John Wiley
& Sons, Inc.
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