Polyelectrolyte Complexes Formed by Calf Thymus DNA and Aliphatic Ionenes: Unexpected Change in Stability upon Variation of Chain Length of Ionenes of Different Charge Density

Abstract

The formation of polyelectrolyte complexes (PECs) between aliphatic 2,4- and 2,8-ionenes and calf thymus DNA in water–salt solutions is monitored by a fluorescence-quenching technique using an ethidium bromide probe. As expected, the tolerance of PEC to dissociation in water–salt solutions increased with an increase in both the number of charged groups, i. e., degree of polymerization of the ionenes (DP), and in the charge density of their chains. However, the latter tendency weakened markedly upon the lengthening of the ionenes chains and ceased to hold at DP ≈ 25. Comparison of the stability of PECs formed by DNA and poly(methacrylate) anion, respectively, with the ionenes, disclosed that relatively short ionene chains formed noticeably less stable DNA-containing PECs, whereas upon lengthening of the ionenes the difference in the stability of the PEC successively decreased and evened out at DP ≈ 25, in the case of 2,8-ionene. All these findings imply that in such systems the role of charge–charge conformity of the partners in DNA-containing PECs is evident only for rather short ionenes. The unexpected changes in PEC stability revealed suggest that the short chains of the ionenes are of special interest for the design of self-assembling polyelectrolyte systems with controllable stability attractive for biomedical applications and bioseparation.