Pulse radiolytic study of the binding of highly charged counterions to a polyelectrolyte

Richard E. Sassoon, Joseph Rabani*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

The technique of pulse radiolysis was used in order to investigate the binding of ferrocyanide and ferricyanide ions to the positive polyelectrolyte polybrene in aqueous solution. Radicals of polybrene were prepared by reaction of OH radicals in an H atom abstraction reaction with polybrene. The rate constant of this reaction was measured to be (1.3 ± 0.3) × 109 M-1 s-1 by using the competition technique with phenol. From competition studies with ferrocyanide for OH radicals the ratio k(OH+Fe(CN)64-)/k(OH+PBH2) was measured to be about a third of the value expected from the independently obtained rate constants. This was suggested to be due to trapping of the ferrocyanide ion in the polyelectrolyte field. A second reaction between polybrene radicals and ferrocyanide was observed to take place in which the yield of ferricyanide was measured to be about 0.19 of the theoretical assuming a Poisson-type distribution of ferrocyanide ions among the polybrene molecules. Ferricyanide ions were found to react with polybrene radicals via two processes which were identified as a fast intrapolyelectrolyte reaction between polybrene radicals and ferricyanide ions which lie on them and a much slower interpolyelectrolyte reaction in which polybrene radicals react with ferricyanide ions lying on other polybrene molecules. The fraction of polybrene radicals taking part in each reaction and the kinetics of the system were found to be dependent on the coverage of the positive charges of polybrene by ferricyanide ions. No evidence for exchange of ferricyanide ions by their release into the bulk of solution was found under our experimental conditions. Aggregate formation was found to occur in solution in both the polybrene-ferrocyanide and the polybrene-ferricyanide systems above a certain coverage of positive charges of the polymer by the highly charged counterions. In order to study the polyelectrolytic effects of polybrene, reference experiments were carried out by using solutions of the n-butyltrimethylammonium cation.

Original languageEnglish
Pages (from-to)6389-6396
Number of pages8
JournalJournal of Physical Chemistry
Volume88
Issue number25
DOIs
StatePublished - 1984

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