Competitive counterion binding to poly(alkylene phosphate)s related to natural teichoic acids. The Poisson‐Boltzmann approach

Abstract

The problem of competitive metal ion binding to poly(alkylene phosphate)s, considered as synthetic models of natural teichoic acids, was analysed theoretically applying the Poisson‐Boltzmann (PB) equation to a cylindrical cell model. There were calculated the radial distribution functions as well as the degree of ion binding of mono‐and divalent metal ions to polyphosphate ions in solutions of different concentrations ranging from 10−5 M to 10−2 M and containing different amounts of M⊕ and M2+ counterions. For comparison, analogous calculations were performed also for poly(styrenesulfonate)s. The results indicate the preferential binding of divalent metal ions to polyphosphate ions over monovalent ones. The selectivity for M2+ ions is concentration dependent and increases with decreasing the polymer solution concentration. It results from PB calculations, that condensation of divalent metal ions at the surface of polyion chains seems to be responsible for preferential binding of biologically important metal ions, for example magnesium, to natural teichoic acids and their synthetic analogues.

Interaction of sodium and calcium ions with poly(alkylene phosphate)—a synthetic analogue of natural teichoic acids

“…A common feature of deÐnitions (iÈiii) above is the more or less arbitrary division of the ion distribution functions and an assumption of di †erent values of "" binding radius ÏÏ that leads to di †erent numerical values of obtained from eqns. (9) or f bi (10). On the other hand, an expression of the degree of ion binding in terms of counterion concentrations at the boundary of the polyion cell and their average values as in Katchalsky treatment [deÐnition (iv)] brings us to another numerical value of f bi .…”