The amide oxygen donor. Metal ion coordinating properties of the ligand nitrilotriacetamide. A thermodynamic and crystallographic study.

The metal ion coordinating properties of ntam (nitrilotriacetamide) are reported. The protonation constant (pK) for ntam is 2.6 in 0.

Factors controlling metal-ion selectivity in the binding sites of calcium-binding proteins. The metal-binding properties of amide donors. A crystallographic and thermodynamic study.

The metal-ion complexing properties of the ligand EDTAM (ethylenediamine-N,N,N',N'-tetraacetamide) are investigated as a model for the role of amide oxygen donors in the binding sites of Ca-binding proteins. The structures of the complexes [Ca(EDTAM)NO3]NO3 (1), [La(EDTAM)(H2O)4](NO3)3.H2O (2), and [Cd(EDTAM)(NO3)]NO3 (3) are reported: 1 monoclinic, P2(1)/c, a = 10.

Possible insights into metal ion recognition in calcium-binding proteins provided by complexing properties of ligands containing amide oxygen donors.

The formation constants of the ligand N,N,N',N'-tetrakis(carbamoylmethyl)-ethylenediamine suggest that the amide oxygen is a stronger Lewis base in water than the alcoholic oxygen, or water, and that part of the selectivity for Ca2+ over Mg2+ shown by calcium-binding proteins such as calmodulin or annexin may be due to the higher affinity of Ca2+ for the O-donor of the Ca-binding amide groups present in such proteins.