Metal complexes of taurine. The first reported solution equilibrium studies for complex formation by taurine at physiological pH; the copper(II)-glycylglycinate-taurine and the copper(II)-glycylaspartate-taurine systems

The first solution studies at physiological pH for the formation of metal c omplexes of taurine, +NH3CH2CH2SO3-, one of the most abundant low molecular weight organic compounds in the animal kingdom, are reported. The complexe s Cu(Gly-GlyH(-1)) (1) and [Cu(Gly-AspH(-1))](-) (2) react with taurine to give the ternary complexes [Cu(Gly-GlyH(-1))taurine](-) (3) (log K = 2.95 /- 0.03, I = 0.2 M, T = 25.0 degrees C) and [Cu(Gly-AspH(-1))taurine](2-) ( 4) (log K = 2.68 +/- 0.02) in which taurine acts as an N-donor ligand, most likely monodentate, without involvement of the sulphonate group in coordin ation. The results of the pH-metric studies are confirmed by visible and EP R spectrophotometric studies. The taurine complexes are less stable than th e analogous complexes of beta-alanine due to the decreased basicity of the amino group in the former ligand, and in the case of the Cu(Gly-GlyH(-1)) c omplexes due to involvement of the carboxylate group of beta-alanine in axi al coordination. (C) 1999 Elsevier Science Inc. All rights reserved.