title: Thermodynamics of conformational ordering of iota-carrageenan in KCl solutions using high-sensitivity differential scanning calorimetry.
abstract: Thermodynamic properties of aqueous solutions of iota-carrageenan as affected by KCl (0.15-1.2 M) or iota-carrageenan (0.5-6 mg/mL) content were studied by high-sensitivity differential scanning calorimetry. The polysaccharide was found to undergo two consecutive cooperative conformational transitions, which can be represented by the scheme: [H2]2<-->2H2<-->4C where C is the random coil, H2 is the double helix, and [H2]2 is the double helix dimer. The first transition follows by the "all or none" mechanism. The profile of the second transition resembles that of a second-order phase transition. The parameter sigma (of order 1), estimated for this latter transition, suggests that the stacking effect in helices of iota-carrageenan is rather small. The cooperativity of the transition is mainly defined by the loop factor. Free energies of both transitions at 273 K were calculated as a function of salt concentration. These experimental data were found to agree with Manning's theory.
authors.affiliation: Institute of Biochemical Physics, Russian Academy of Sciences, Vavilov St. 28, 117813 Moscow GSP-1, Russia. grinberg@ineos.ac.ru
authors.forename: V Y
authors.initials: VY
authors.lastname: Grinberg
authors.forename: N V
authors.initials: NV
authors.lastname: Grinberg
authors.forename: A I
authors.initials: AI
authors.lastname: Usov
authors.forename: N P
authors.initials: NP
authors.lastname: Shusharina
authors.forename: A R
authors.initials: AR
authors.lastname: Khokhlov
authors.forename: K G
authors.initials: KG
authors.lastname: de Kruif
mesh_terms: D002152:Calorimetry, Differential Scanning / Q000379:methods / Q000706:statistics & numerical data; D002236:Carbohydrate Conformation; D002351:Carrageenan / Q000737:chemistry*; D046911:Macromolecular Substances; D011189:Potassium Chloride; D012680:Sensitivity and Specificity; D012996:Solutions; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D046911:Macromolecular Substances; D012996:Solutions; D011189:Potassium Chloride; D002351:Carrageenan