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Etude Potentiométrique de l'α‐Poly(acide‐ L ‐glutamique) et de ses Oligomères. II
Author(s) -
Rinaudo M.,
Domard A.
Publication year - 1973
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.1973.360121003
Subject(s) - chemistry , counterion , potentiometric titration , polyelectrolyte , ionic bonding , ion , counterion condensation , polymer , crystallography , thermodynamics , physics , organic chemistry
Potentiometric neutralization of oligomers represented by the general formula shown was studied.The intrinsic p K of carboxyl function was found to be 4.40 at 25°C; the variation of the apparent p K a , Δ K (α), was studied as a function of the degree of neutralization: the influence of the degree of neutralization on the accumulation of ionic sites along the chain is clearly shown. The experimental curves of polyglutamic acid allowed us to deduce the sequence of ionic selectivity and the energy of conformational transition. The theoretical interpretation of the results was proposed in terms of the rod like model from Katchalsky's theory. The intrinsic p K o for the polymer was set equal to the value experimentally obtained on oligomers. By activity measurements on Na + and Ca 2+ counterions in salt‐free solutions, the free fraction of counterions was deduced on the different samples. The results were interpreted with the electrostatic model previously proposed; in this view, the oligomers are assimilated to imaginary polyelectrolytes. This allowed us to determine the values of Δp K and the fraction of free ions at the same time.