Tetra-2-methoxyethyl phenylene-1,4-di(benzyloaminomethanephosphonate) a new ligand for metal ions and amino acids. Electrospray ionization mass spectrometric and NMR studies

Formation of stable complexes between tetra-2-methoxyethyl phenylene-1,4-di(benzyloaminomethanephosphonate) (receptor) and monovalent (Li+, Na+, K+, Rb+, and Cs+) and divalent metal cations (Mg2+, Ca2+, Ba2+) in acetonitrile has been studied by means of ESI-MS technique. Additionally the chelating properties of the phosphonate towards amino acids (2 × HCl∗Arg, 2 × HCl∗Lys) in methanol and water have been evaluated. Crown ether-like esters of the phosphonate do not bind ammonium cations of these basic amino acids and instead of that proton transfer from carboxylic group of amino acids to amino moiety of the receptor, governed by surprisingly low basicity of its amino moiety (pK = 4), was observed.