Selective Binding of Glyphosate by a Ditopic Cyclic–Open‐Chain Polyazaligand in Aqueous Solution

Abstract

International audienceThis paper reports a study of the interaction between a ditopic cyclic–open-chain polyazaligand L1py and the herbicide glyphosate [N-(phosphonomethyl)glycine or PMG] by potentiometric titrations as well as calorimetry and NMR measurements. This nonsymmetrical ligand is composed of a cyclam unit (1,4,8,11-tetraazacyclotetradecane) and the linear tetraamine 1,4,8,11-tetraazaundecane linked by a 2,6-dimethylpyridine spacer. This ligand forms stable adducts with PMG. For comparison, two analogous symmetrical ditopic ligands, a bis-macrocycle L4py and a bis-tetraamine L5py, and two related anions, iminodiacetic acid (IDA) and iminobis(methylphosphonic acid) (IDP), were also investigated. The results unambiguously show that L1py selectively binds PMG, especially around neutral pH, whereas L4py and L5py exhibit a weaker affinity for this substrate. Calorimetic and 1H NMR measurements showed that the host–guest adducts are mainly stabilized by charge–charge interactions and hydrogen bonds involving the ammonium function of PMG and the nonprotonated nitrogen atom of the pyridine linker

Glyphosate and ATP binding by mononuclear Zn(ii) complexes with non-symmetric ditopic polyamine ligands

“…8). 21,23 This result supports the hypothesis of an interaction mode involving binding of the phosphonate moiety of PMG to Zn(II) and highlights the relevant role played by the metal centre in the recognition process. 23…”

“…Ligands L1py, L2py and L1para are synthesized according to previously described procedures. 22,23 A previous investigation on the L1py and L2py basicity properties showed that these ligands behave as polyprotic bases in aqueous solutions, forming a number of protonated species in the pH range 2-11. 22,23 For instance, at neutral pH, they form a tetraprotonated species, featuring two ammonium groups on the cyclam unit and the remaining couple on the open-chain tetraamine moiety.…”

“…22,23 A previous investigation on the L1py and L2py basicity properties showed that these ligands behave as polyprotic bases in aqueous solutions, forming a number of protonated species in the pH range 2-11. 22,23 For instance, at neutral pH, they form a tetraprotonated species, featuring two ammonium groups on the cyclam unit and the remaining couple on the open-chain tetraamine moiety. This investigation has been extended to L1para and the results are reported in ESI (Table S1 †); the values of the basicity constants are very similar to those obtained for L1py, confirming that the nitrogen atom of the pyridinyl linker is not protonated in the studied pH range.…”

“…In fact, previous studies on adducts formed by L1py with PMG have shown that the amine group of the substrate, when protonated at acidic pH values, can interact via hydrogen bonding with the pyridine nitrogen. 23 To provide more information on the interaction between ZnL1py and PMG, we performed 1 H, 31 P and 13 C NMR spectra of aqueous solutions containing equimolecular amounts of both receptor and substrate ([ZnL1py] = [PMG] = 10 −2 M) at different pH values. 1 H NMR spectra are too complex to be correctly interpreted.…”

“…We have recently shown that the ditopic cyclic-open chain ligand L1py (Chart 2) is an attractive chelator of biological anions such as ATP 22 and a selective receptor for PMG. 23 In fact, this polyamine contains two different binding domains, the rigid tetraazamacrocycle cyclam (1,4,8,11-tetraazacyclotetradecane) and the flexible linear tetraamine 1,4,8,11-tetraazaundecane, separated by a 2,6-dimethylpyridinyl linker, and forms highly protonated species at neutral pH, the cyclam and the tetraamine being respectively di-and fully protonated. The receptor strongly binds to ATP, enclosing its triphosphate chain within a cleft delimited by the two polyamine moieties.…”