Complexation of amphoteric copolymer of 2- methyl-5-vinylpyridine-acrylic acid with copper(ll) ions and catalase-like activity of polyampholyte-metal complexes E. A. Bekturov, S. E. Kudaibergenov and V. B. Sigitov Institute of Chem/ca/ Sciences, Academy of Sciences of the Kazakh SSR, A/ma-Ata 480100, Kras/n str. 106, USSR (Received22 April 1985; revised 17 January 1986) The interaction of polyampholyte based on 2-methyl-5-vinylpyridine and acrylic acid with copper(II) ions in aqueous solution has been investigated. Several types of complexes were formed, dependent on pH. The catalytic action of polyampholyte--copper(II) complex in hydrogen peroxide decomposition has been studied. The kinetic parameters and activation energy of this process were determined. The relation between the structure of complexes and their catalytic activity is also discussed. (Keywords: amphoteric copolymer of 2-methyl-5-vinylpyridin~acrylic acid; copper(II) complexes; catalase-like activity) INTRODUCTION The complexes of synthetic macromolecular ligands with transition metal ions have been widely investigatedl-a. In some recent publications 5'6 the possibility is noted of modelling the complexation of metal ions with biological ligands through synthetic macromolecular systems. Among the synthetic polyelectrolytes, amphoteric copolymers most closely resemble structure and behaviour of biopolymers 7. However, the complexation reaction between polyampholytes and metal ions has been little studied s- 11. In the present paper the complexation of the 2-methyl- 5-vinylpyridine-acrylic acid (2M5VPy-AA) polyam- pholyte with Cu 2 ÷ has been investigated by potentiometric and conductometric titration, u.v., e.s.r. and visible spectroscopy, and viscometry in aqueous solution. Also, the catalytic properties of polyampholyte- copper(II) complex have been studied in hydrogen peroxide decomposition. EXPERIMENTAL 2M5VPy-AA copolymer was synthesized as in ref. 12. ( CH2--CH )m ( CH2 CH )n COOH m : 60-'2mol0/. CH3 n = 40±2mo1"/0 It was purified by two-fold acetone precipitation from methanol solution. Copolymer composition was determined by elemental analysis and potentiometric and conductimetric titrations. The hydrodynamic-average molecular weight M~ of copolymer was 2x105. Potentiometric titration of 2M5VPy-AA was carried out on a OP-211/1 digital pH-meter and electroconductivity was measured on a OP-102/1 conductometer (Radelkis, Hungary). All experiments were conducted in a thermostatically controlled cell at 298 + 0.1 K. Visible and u.v. spectra of complexes were measured on a DU-8B spectrophotometer (Beckman, USA) at room tempera- ture. E.s.r. spectra of samples were determined on a 'Jeol ME3XESR' spectrometer (Japan) at 77 K. Solution viscosity was measured on a Ubbelohde viscometer at 298 _ 0.05 K. Ionic strength was adjusted to the indicated value by addition of KNOa. Reagent-grade CuSO4.5H20 was used. Hydrogen peroxide decomposition was carried out in a thermostatically controlled cell at 298 + 0.1 K. pH of the solution was maintained by borate buffer ~ = 0.5). The residual concentration of H20 2 was determined by titration of samples drawn from the reaction vessel. RESULTS AND DISCUSSION Structure of complexes Potentiometric titration curves of 2M5VPy-AA at various ionic strengths # are shown in Figure 1. In the presence of KNO 3 the curves are marked and have two distinct inflections. They arise from the step-by-step titration ofcarboxylic and pyridinium groups. The values of apparent dissociation constants pKa determined at p = 0.10 from the dependence of pH - log[0t/(1 - ~t)] on ct as 0t---,0 are 3.5 and 8.0 respectively. The strengthening of acidic and basic properties of polyampholyte can be explained by inductive influence of neighbouring groups13. The addition of Cu 2 ÷ to polyampholyte solution leads to a shift in the potentiometric titration curves, which involves formation of polyampholyte-copper(II) com- plex. Conductimetric and spectrophotometric data obtained in the pH interval 6.0-8.0 show that one copper(II) ion is able to bind four groups in the polyampholyte. The complex has absorption bands in the visible (2 = 730 nm) and u.v. (;~= 253 nm) regions (Figure 2). As seen from Figure 2 the absorption maximum of 0032-3861/86/081269~4503.00 © 1986 Butterworth & Co. (Publishers) Ltd. POLYMER, 1 986, Vol 27, August 1269