Etude Potentiométrique de l'α-Poly(acide-L-glutamique) et de ses Oligomères. II

✍ Scribed by M. Rinaudo; A. Domard

• Publisher: Wiley (John Wiley & Sons)
• Year: 1973
• Tongue: English
• Weight: 658 KB
• Volume: 12
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1973.360121003

✦ Synopsis

Abstract

Potentiometric neutralization of oligomers represented by the general formula shown was studied.
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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.