An electronic conference proceeding. A tetrakisphosphonate receptor mol. well sol. in polar solvents such as methanol and water, but insol. in DMSO and acetonitrile was prepd. as a macrocyclic host for lysine and histidine. To check the complex stoichiometries with lysine, arginine, ornithine and histidine, Job-Plots were taken for each of the amino acid-complexes. The result showed that the smaller amino acids histidine, ornithine and arginine produced a clear 2:1-stoichiometry, but lysine was bound in a clean 1:1-complex. NMR titrns. was also performed for each of the four complexes in methanol and the resulting binding curves were analyzed by nonlinear regression. Thus, prepd. tetrakisphosphonate receptor mol. is moderately selective for lysine in water.