Anion Coordination Chemistry: Polyguanidinium Salts as Anion Complexones

Abstract

SummaryThe synthesis of a series of polyguanidinium salts of potential interest as anion complexones is described. Among the various synthetic methods investigated, the polyguanidinium salts were found to be most conveniently prepared from polyamines via polypitroguanidine intermediates. The complexation of phosphate and carboxylate anions by these complexones and by related polyammonium salts were studied by analysis of pH-metric titration data. The ligands studied form relatively stable complexes (log K,= 2.0-4.0 for PO:-in water) which also present good selectivities in some cases. Both the stability and the selectivity of complexation are primarily governed by electrostatic forces and thus depend on charge accumulation in the interacting species; structural effects are also observed. Since the binding is primarily electrostatic, polyammonium salts form more stable complexes (at a given charge) than do polyguanidinium salts. However, whereas the complexation properties of the latter are independent of pH, the complexes of the former are observed only in the limited ranges of pH where both the protonated polyamine and the anion of interest can coexist. The polycationic ligands may, in principle, form chelate type anion complexes. Comparison with the corresponding single binding sites reveals an increase in complexation constant of about two or three orders of magnitude; this may be considered as a thermodynamic indication of a chelate effect for the polydentate ligands (by analogy with the well known effects displayed by cation complexones); however, structural data on the formation of chelate 'rings' are not yet available. The nature of the complexes and the prospects of anion complexones in various fields are discussed.

Membrane transport systems. I. Synthesis and characterization of carriers for a proton driven alkali metal cation pump

“…K,,. The results of these determinations are reported in Table 1 (logPlol = -pKaandlogPlll =logK, +pKa).Ina fashion analogous to that previously described with respect to the complexation of anions by polyguanidinium salts (31), computer analysis of the pHmetric titration curves obtained at various ratios of L/M gave a set of Pl , , which described the system, from which values of K, and K2 were calculated.…”

Membrane transport systems. VI. Complexation of cations by lipophilic crown ether carboxylic acids

“…These results appear in parentheses where appropriate in Table 1. The complexes of ammonium are proton ambiguous in a fashion similar to polyammonium and polyguanidinium/anion complexes (15); the overall stoichiometry of the complex is known but it is not known if the proton is associated with the ligand or the ammonia. For the dicarboxylate carriers it is productive to assume that the complex whose P I , , is calculated refers to NH,' + L2-rather than NH3 + LH-.…”

Cleavage of Phosphodiesters and of DNA by a Bis(guanidinium)naphthol Acting as a Metal‐Free Anion Receptor

“…In this concentration range, the polyanionic EDTA is expected to interfere with DNA binding of the cationic naphthols 11 and 12. [19] Only minor gains in plasmid cleavage resulted from the addition of 1-10 mm Mg 2 + ions. The reac- Figure 1.…”