Nitrogen-oxygen donors

Figure 3 Schematic illustration of a hybrid hydrogel system—genetically engineered coiled-coil protein domains used to crosslink synthetic water-soluble polymers. Divalent transition metal ions are shown to form complexes with nitrogen-oxygen-donor ligands on the synthetic polymer side chains and the terminal histidine residues in the coiled coils.

Macrocyclic polyamines that can be fully or nearly fully protonated in the neutral pH range appear to be the best ligands for the biologically important carboxylate and adenosine phosphate anions because the formation of these anions occurs in these pH regions. Lehn and Dietrich and their coworkers have synthesized macrocyclic polyamines [24]N(,(53) and [32]N8(54), based on propylene units (Dietrich et al., 1981), and macrocycles with mixed nitrogen-oxygen donor atoms connected by ethylene units, [27]Nft03(55) (Dietrich et al., 1981) and [24]N(,02(56) (Hosseini and Lehn, 1987 Hosseini et al., 1983). These macrocycles are similar to those found in natural systems. 

Plutonium(III), (IV), and (VI) complex stabiUty constants have been determined for some oxygen-donor (carboxylate) (114) and a few nitrogen-donor (115,116) ligands. Complexes of plutonium with natural complexants such as humic acids have also been studied extensively (89). 

Titanium triiodide can be made by direct combination of the elements or by reducing the tetraiodide with aluminum at 280°C in a sealed tube. Til reacts with nitrogen, oxygen, and sulfur donor ligands to give the corresponding adducts (148). 

Structural aspects and coordination chemistry of metal porphyrin complexes with emphasis on axial ligand binding to carbon donors and mono- and di-atomic nitrogen and oxygen donors. P. D. Smith, B. R. James and D. H. Dolphin, Coord. Chem. Rev., 1981,39, 31-75 (170). 

---