Premium
Physicochemical properties of pectic acid. I. Thermodynamic evidence of a pH‐induced conformational transition in aqueous solution
Author(s) -
Cesàro A.,
Ciana A.,
Delben F.,
Manzini G.,
Paoletti S.
Publication year - 1982
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/bip.360210214
Subject(s) - chemistry , aqueous solution , solvation , enthalpy , dissociation (chemistry) , dilution , polymer , thermodynamics , conformational change , crystallography , inorganic chemistry , organic chemistry , stereochemistry , molecule , physics
On the basis of measurements of enthalpy of dissociation and of dilution, an interamolecular conformational transition induced by pH change is shown for pectic acid in aqueous solution. Additional evidence is given by potentiometic, viscometric, and chiroptical results. The transition from a more rigid, probably H‐bonded, structure prevailing at low pH to a more extended one at around neutrality is accompanied by a Δ H value of about 500 cal/equiv and a Δ S value of 1.6 cal/equiv K in water at 25°C. The addition of salts increases the stability of the rigid conformation without changing the general features of the phenomenon. Dilatometric measurements suggest that the transition is accompanied by practically no change in the overall solvation of the polymer chain.