Metal‐Ion‐Coordinating Properties of a Viral Inhibitor, a pyrophosphate analogue, and a herbicide metabolite, a glycinate analogue: The solution properties of the potentially five‐membered chelates derived from phosphonoformic acid and (aminomethyl)phosphonic acid

Abstract

The pyrophosphoric-acid-analogue phosphonoformic acid (pfa) and the amino-acid-analogue (aminomethy1)phosphonic acid (ampa) both form, in the deprotonated state, i.e., as -0OC-PO;-and H2N-CH2-PO:-, respectively, five-membered chelate rings with metal ions. pfa inhibits both phosphate transport and virus replication, while ainpa is a metabolic product of the common herbicide glyphosate ( = N-(phosphonomethy1)glycine). The acidity constants of H,pfa-and H2ampa* as well as the stability constants of the [M(Hpfa)], [M(pfa)]-, [M(Hampa)]+, and fM(ampa)] complexes, where M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, C~(2,2'-bipyridyl)*~, Cu( I , 10-phenantbroline)2+, Zn2+, or Cd2', have been determined by potentiometric pH titrations in aqueous solution at 25" and I = 0 . l~ (NaNO,). The structures of isomeric complexes and the connected intramolecular equilibria are deduced and evaluated based on the equilibrium constants measured and those calculated via the pK, values of the above mentioned ligands and previously established log K 1's. pK, straight-line plots ( H . Sigel et ul., Helv. Chim. Acra 1992, 75, 2634) for a simple phosphonate-M2+ coordination. pfa forms stronger complexes than ampa with all the above mentioned metal ions, with the single exception of "&(ampa)] which is slightly more stable than [Cu(pfa)]-. In neutral solutions, more precisely at pH of ca. 6, pfa complexes of alkaline-earth-metal ions retain one phosphonate-bound proton, [M(Hpfa)], whilc those of the transition-metal ions chelate with the trianionic ligand, pfa'? In accord with increasing ligand-basicity, the stability-constant order for all metal-ion complexes is oxalate < pfa < pyrophosphate but, owing to proton competition in pyrophosphate, in neutral solutions metal-ion complexation of pfa3-competes with P20$-. With ampa alkaline-earth-metal ions interact only with the phosphonate group of even the dianionic ligand (though Mg" appears to form a low fraction of a [Mg(ampa)] chelate) while transition-metal ions form chelates which are comparable in stability to those of glycinate.

Stabilities and coordination modes of glycinephosphonic acid in copper(II) heteroligand complexes with ethylenediamine, diethylenetriamine or N,N,N′,N′,N″-pentamethyldiethylene triamine in aqueous solution

“…-Me 5 dien [21,23,34] and Cu 2? -Gly(P) [31,33,36,37] are in good agreement with the literature data. Table 1 Cumulative formation constants (logb), derived equilibrium constants (logK) and characteristic parameters for the stability of complexes formed in the ternary systems Cu 2?…”

A comparison of three bacterial phosphonoacetate hydrolases from different environmental sources

“…Phosphonoformic acid, 2-phosphonopropionic acid and 3phosphonopropionic acid represent the closest organophosphonate structural analogues of phosphonoacetate, differing only in the number of methyl groups separating the carboxylic acid and phosphonic acid moieties. Phosphonoformic acid is a potent inhibitor of all three phosphonoacetate hydrolase enzymes (although this may be in part attributable to the chelation of Zn 2+ by phosphonoformic acid (Bin Song et al 1994)). The phosphonoacetate hydrolase of Pseudomonas sp.…”

Glyphosate, a chelating agent—relevant for ecological risk assessment?

“… Stability constants were measured by potentiometric pH titration at a ionic strength of 1 I = 0; 2 I = 0.1 M KNO 3 ; 3 information not given a From Duke et al ( 2012 ) b From http://www.coldcure.com/html/stability_constants.html#what c From Bunting and Thong 1970 d From Perkins 1952 e Values taken from several sources: Chen et al ( 1994 ), Hernlem et al ( 1996 ) 2 , Shenker et al ( 1996 ) 2 , Kraemer ( 2004 ) 1 , Parker et al ( 2004 ) 1 f Taken from Madsen et al ( 1978 ) g From Song et al ( 1994 ) …”