Equilibrium and dynamic studies of the disorder–order transition of kappa carrageenan
- 1 January 1983
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 79 (10) , 2489-2500
- https://doi.org/10.1039/f19837902489
Abstract
The equilibria and dynamics of the transition from disorder to order in the polysaccharide kappa carrageenan have been investigated over a range of KCl concentrations and temperatures. Kinetic observations can be explained by the following sequential mechanism for ordering of disaccharide residues following a salt-concentration jump: conformational change in disordered form C°→ C (II) dimerisation 2C ⇌ H2(III) aggregate formation xC +yH2⇌(H2)(½x+y)(IV) where C indicates a random coil and H a helix residue. Reaction (III) was investigated quantitatively using a stopped-flow polarimeter, and the rate equation shown to be that of a second-order forward, first-order reverse equilibration, consistent with double-helix formation. Forward rate constants extrapolate to zero at the transition midpoint, as expected for a cooperative transition. Rate and activation parameters for helix nucleation in 0.50 mol dm–3 KCl are k2(298 K)=(9±1)× 103 dm3 mol–1 s–1, ΔH*= 5±3 kJ mol–1 and ΔS*=–150±10J mol–1 K–1. Parallels are drawn with polynucleotide double-helix formation, and in particular the low value of ΔH* is consistent with a nucleation length of 1 or 2 disaccharides. A lower bound of 36±3 disaccharides is estimated for the cooperative length from equilibrium and d.s.c. data for the transition.Keywords
This publication has 0 references indexed in Scilit: