title: Conformational energetics of interpolyelectrolyte complexation between ι-carrageenan and poly(methylaminophosphazene) measured by high-sensitivity differential scanning calorimetry.
abstract: The interaction of poly(methylaminophosphazene) hydrochloride (PMAP·HCl) of varying degrees of ionization (f) with the potassium salt of ι-carrageenan was studied by high-sensitivity differential scanning calorimetry at a KCl concentration of 0.15 M, which is included for the purpose of stabilizing the helix conformation of the polysaccharide up to 55 °C. The conditions of strong (pH 3.8, I = 0.15), moderate (pH 7.4, I = 0.15), and weak (pH 7.4, I = 0.25) electrostatic interactions of the polyelectrolytes were considered. The thermodynamic parameters of the helix-coil transition of ι-carrageenan were determined as a function of the polycation/polyanion ratio. We show that the interpolyelectrolyte reaction between PMAP·HCl and ι-carrageenan results in a complete unfolding of the polysaccharide helix under conditions of strong electrostatic interaction and increases its stability under conditions of medium and weak electrostatic interactions. The formation of stoichiometric PMAP-carrageenan interpolyelectrolyte complexes proceeded via a cooperative mechanism at pH 3.8 (f = 0.5) and pH 7.4 (f = 0.2) at an ionic strength of 0.15. In contrast, the complexation at pH 7.4 and an ionic strength of 0.25 could be considered to be a consecutive competitive binding of charged units of poly(methylaminophosphazene) to the oppositely charged polysaccharide matrix in the helix or coil conformation. Binding constants of the polycation to the helix and coil forms of ι-carrageenan were estimated. They revealed a preferential binding of the polycation to the helix form of the polysaccharide.
authors: N. M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St. 4, 119334 Moscow, Russian Federation. grinberg@ineos.ac.ru
authors: Valerij Y
authors: VY
authors: Grinberg
authors: Tatiana V
authors: TV
authors: Burova
authors: Natalia V
authors: NV
authors: Grinberg
authors: Alexander S
authors: AS
authors: Dubovik
authors: Dzidra R
authors: DR
authors: Tur
authors: Anatoly I
authors: AI
authors: Usov
authors: Vladimir S
authors: VS
authors: Papkov
authors: Alexei R
authors: AR
authors: Khokhlov