title: Revised coordination model and stability constants of Cu(II) complexes of tris buffer.
abstract: 2-Amino-2-hydroxymethyl-propane-1,3-diol, or tris(hydroxymethyl)aminomethane (Tris), is probably the most common biochemical buffer used alone or in combination with other buffers because it is stable, unreactive, and compatible with most proteins and other biomolecules. Being nontoxic, it has even found applications in medicine. Tris is known, however, to coordinate transition metal ions, Cu(II) among them. Although often ignored, this feature affects interactions of Cu(II) ions with biomolecules, as Tris is usually used in high molar excess. Therefore, it is important to have precise knowledge on the stoichiometry, stability, and reactivity of cupric Tris complexes. The literature data are incoherent in this respect. We reinvestigated the complex formation in the Tris-Cu(II) system by potentiometry, UV-vis, ESI-MS, and EPR at a broad range of concentrations and ratios. We found, contrary to several previous papers, that the maximum stoichiometry of Tris to Cu(II) is 2 and at neutral pH, dimeric complexes are formed. The apparent affinity of Tris buffer for Cu(II), determined by the competitivity index (CI) approach [Krężel, A.; Wójcik, J.; Maciejczyk, M.; Bal, W. Chem. Commun. 2003, 6, 704-705] at pH 7.4 varies between 2 × 10(6) and 4 × 10(4) M(-1), depending on the Tris and Cu(II) concentrations and molar ratio.
authors.affiliation: Faculty of Chemistry, University of Wroclaw , Wroclaw, Poland.
authors.forename: Justyna
authors.initials: J
authors.lastname: Nagaj
authors.forename: Kamila
authors.initials: K
authors.lastname: Stokowa-Sołtys
authors.forename: Ewa
authors.initials: E
authors.lastname: Kurowska
authors.forename: Tomasz
authors.initials: T
authors.lastname: Frączyk
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Jeżowska-Bojczuk
authors.forename: Wojciech
authors.initials: W
authors.lastname: Bal
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry; D004355:Drug Stability; D008958:Models, Molecular; D021241:Spectrometry, Mass, Electrospray Ionization; D014325:Tromethamine
chemical_list: D056831:Coordination Complexes; D014325:Tromethamine; D003300:Copper