Thermodynamics of polysaccharide polyelectrolytes: Enthalpy changes in the

ABSTRACT- An approach, based entirely on Counterion Condensation (CC) polyelectrolyte theory and on thermodynamic consideration, is used to derive the ionic and the non-ionic energy contributions for processes involving the conformational transition of a linear polyelectrolyte. As an example of application, the conformational transition of the algal polysaccharide, K-carrageenan, is analysed. This anionic polymer undergoes a fhermoreversible disorder-order conformational transition which parallels specijk binding of cations (as K +, Cs+,...) and, quite unusually, of the iodide anion. Experimental data on the conformational process and on the binding process will be compared with the theoretical prediction. INTRO D UCTlO N The effect of ionic strength on the behavior of a polyelectrolyte chain is the most striking and universally accepted one in the study of the interactions between linear charged biopolymeric species and ions in solution. However, the computational handling of the long-range electrostatic interactions in polymorphic macromolecular chains still remains difficult, although under some simplified circumstances it can be reasonably treated. The range of validity of such conditions has restricted the application of the theoretical results to cases in which the univocity of the chain structure and the absence of variations due to "specific'&apos