Mucopolysaccharides in aqueous solutions: effect of ionic strength on titration curves.
We study the changes taking place in hyaluronic acid, chondroitin 4-sulfate (C4-S) and condroitin 6-sulfate (C6-S), at ionic strengths of 0.10, 0.15, and 0.20 in NaCl, in a neutralization process in aqueous solution. We apply the equation of Henderson Hasselbalch modified for polyelectrolytes and evaluate the changes in the electrostatic free energy starting from the pK curves as a function of the dissociation degree. For a dissociation degree next to 0.4 corresponding to the -COOH group of the hyaluronic acid, we observed a change in the conformation of the three glycosaminoglycans studied. This conformational change takes place as a consequence of the break of intramolecular links and the beginning of the ionization process. The macromolecules in solution show a structure of random coil sufficiently expanded so that the interaction among the close ionizable groups is negligible.
Rueda
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C
Departamento de Fisicoquímica Farmacéutica, Facultad de Farmacia, Universidad Complutense, Ciudad Universitaria, Madrid, Spain. crueda@eucmax.sim.ucm.es
Arias
C
C
Galera
P
P
López-Cabarcos
E
E
Yagüe
A
A
D000465:Algorithms; D004563:Electrochemistry; D006025:Glycosaminoglycans / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011199:Potentiometry; D012996:Solutions
D006025:Glycosaminoglycans; D012996:Solutions