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Thermodynamics of conformational transition and chain association of ι‐carrageenan in aqueous solution: Calorimetric and chirooptical data
Author(s) -
Denef B.,
Gamini A.,
Delben F.,
Paoletti S.,
Reynaers H.,
Vanneste K.
Publication year - 1998
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/(sici)1097-0282(199802)45:2<105::aid-bip2>3.0.co;2-w
Subject(s) - chemistry , enthalpy , isothermal microcalorimetry , aqueous solution , thermodynamics , electrolyte , counterion , differential scanning calorimetry , calorimetry , enthalpy of fusion , isothermal process , salt (chemistry) , polymer , dilution , ion , organic chemistry , physics , electrode
Isothermal microcalorimetry, differential scanning calorimetry (DSC), and chirooptical data obtained for ι‐carrageenan in NaCl, LiCl, and NaI aqueous solutions are presented. The experiments have been performed as a function of concentration both for the polymer and for the simple salt as a cosolute. The experimental findings consistently show the occurrence of a salt‐induced disorder‐to‐order transition. From microcalorimetric experiments the exothermic enthalpy of transition Δ H tr is obtained as the difference between the theoretical, purely electrostatic Δ H el enthalpy change and the actual mixing enthalpy Δ H mix , measured when a ι‐carrageenan salt‐free solution at constant polymer concentration is mixed with a 1:1 electrolyte solution of variable concentration. In the case of added NaCl, the absolute values of enthalpy changes |Δ H tr | are in good agreement with those obtained for the opposite process, at comparable polymer and salt concentrations, from DSC melting curves. The microcalorimetric results show that the negative maximum value of Δ H tr corresponding to the interaction of Li + counterion with ι‐carrageenan polyion results to be significantly lower than the corresponding values obtained for Na + counterion. At variance with the microcalorimetric data, chirooptical results show that the salt‐induced disorder‐to‐order transition, occurring in the 0.02–0.2 M salt concentration range, appears to be complete at a concentration of about 0.08–0.1 M of the simple ion, irrespective of the polymer concentration and of the nature of added electrolyte. © 1998 John Wiley & Sons, Inc. Biopoly 45: 105–117, 1998