Competitive reactions in solutions of DNA and water‐soluble interpolyelectrolyte complexes

The reaction of competitive binding of two polyanions—DNA and synthetic fluorescence‐tagged poly(methacrylate) (PMA*)—with the polycation‐quencher poly(N‐ethyl‐4‐vinyl‐pyridinium) (PEVP) was studied by fluorescence quenching technique. It was found that ability of DNA to displace PMA *from the water‐soluble nonstoichiometric interpolyelectrolyte complex (NPEC) formed by PMA* and PEVP—NPEC(PMA*‐PEVP)—and to form water‐soluble NPEC(DNA‐PEVP)\documentclass{article}\pagestyle{empty}\begin{document}$$ NPEC(PMA^{*}\hbox{-}PEVP) + DNA \Leftrightarrow NPEC(DNA\hbox{-}PEVP) + PMA^{*}$$\end{document} can be determined by the parameter Ψ = P PMA * / P PEVP where P PMA * and P PEVP are the degrees of polymerization of PMA* and PEVP, respectively. In the case of Ψ < 1 the decrease of Ψ leads to the shift of the reaction equilibrium to the right, which can be explained by the gain of entropy due to the increase of the total number of polymeric particles in the solution. Introduction of alkali metal cations into the reaction mixture results in the shift of the reaction equilibrium, and according to their ability to shift the equilibrium to the right the cations can be arranged in the series Na + > K + > Li + . The substitution of native DNA by denatured DNA practically does not affect the reaction equilibrium in solutions of NaCl and KCl but considerably shifts it to the right in solutions of LiCl. The data obtained are in accordance with the differences in the selectivity of alkali cations binding with competitive polyanions. © 1995 John Wiley & Sons, Inc.