Synthesis and characterisation of 8-hydroxyquinoline bovine serum albumin conjugates as metal ion chelating proteins

A derivative of 8-hydroxyquinoline (8-quinolinol, oxine) with a linking bri dge containing a carboxylic group was covalently coupled to bovine serum al bumin by the N-hydroxysuccinimide method to obtain stable monomeric conjuga tes with oxine to protein mole ratios up to 37. These conjugates were chara cterised spectrophotometrically and their complexation properties were conf irmed by spectral analysis with and without the addition of Al(m), Cd(IT), Co(II), Cu(II), Hg(II), Mn(II), Ni(II), Pb(II), V(IV), U(VI) and Zn(II) ion s added. The maximum number of ions bound by these chelating proteins was d etermined spectrophotometrically by titration with metal ions at pH 6.0. Th e conjugates with a substitution ratio (moles of 8-hydroxyquinoline bound/m ole of albumin) less than about 8 showed 1:1 binding with metal ions, while conjugates with higher substitution ratios were able to complex with 2:1 r atio of 8-hydroxyquinoline to metal ion. Association and dissociation kinet ics of complexation with copper(II) ions showed a complex mechanism. The sp ectral and binding properties of these metal ion-binding proteins confirm t hat the coupling of the 8-hydroxyquinoline derivative to bovine serum album in gives stable, water soluble, macromolecular chelating agents that retain the complexing ability of the original ligand. (C) 1999 Elsevier Science B .V. All rights reserved.