Effect of Inhibitors on the Catalyzed Dehydration of HCO 3 - by Copper(II) Complexes Re-Evaluated Rudi van Eldik* Institute for Inorganic Chemistry, UniVersity of Erlangen-Nu ¨rnberg, Egerlandstr. 1, 91058 Erlangen, Germany Received November 24, 2003 In a recent paper by Cheng and co-workers (Sun, Y.-J.; Zang, L. Z.; Cheng, P.; Lin, H.-K.; Yan, S.-P.; Sun, W.; Liao, D.-Z.; Jiang, Z.-H.; Shen, P.-W. Inorg. Chem. 2003, 42, 508-515), kinetic evidence for inhibitor effects of specific ligands on the catalyzed dehydration of HCO 3 - by copper(II) complexes of the type [Tp Ph ]- CuX (X - ) OH - ,N 3 - , and NCS - ) was reported. The analysis of the kinetic data is not correct, and a re-evaluation shows that the claimed catalytic activity of the studied complexes on the dehydration reaction of bicarbonate is indeed questionable. Furthermore, the apparent inhibitor effect of specific selected ligands in the Cu(II) complexes does not seem to exist at all and is based on a wrong interpretation of the kinetic data. Introduction Cheng and co-workers recently reported in this journal 1 a kinetic study of the effect of inhibitors on the catalyzed dehydration of HCO 3 - by a series of Cu(II) complexes of the type [Tp Ph ]CuX, where [Tp Ph ] ) hydrotris(3-phenyl- pyrazolyl)borate and X ) OH - (1), N 3 - (2), and NCS - (3). The analysis of the kinetic data, on which basis the effect of the inhibitors X and the catalytic role of the Cu(II) complexes was interpreted, is unfortunately not correct and calls for a re-evaluation of the data in order to prevent further misin- terpretation of this and related reports in the literature. Furthermore, the reported data is of fundamental importance to the understanding of the catalytic function of carbonic anhydrase, 2,3 and could be misleading to chemists not familiar with the kinetic details of such studies. Our experience in this area, 2,4-11 especially with the handling and interpretation of kinetic data for such reactions, has made us aware of the potential importance of the reported findings 1 and encouraged the composition of this Communication. Cheng and co-workers 1 studied the dehydration rate of HCO 3 - as a function of the concentration of the selected Cu(II) complexes, and found that the observed first-order dehydration rate constant depends on the concentration and nature of the selected Cu(II) complex. From this concentra- tion dependence, they estimated rate constants for the catalytic process. A careful inspection of their results (Figure 4 in ref 1) shows that the plots of k obs versus [Cu(II)] not only exhibit the mentioned concentration dependence, but also shows a significant intercept at zero Cu(II) concentration. In fact, the observed acceleration (i.e., increase in k obs with increasing [Cu(II)]) is indeed very small as compared to the large intercepts observed for the three studied complexes. Furthermore, the slopes of the plots are so similar that the three complexes exhibit virtually the same catalytic activity within the error limits of such kinetic measurements. It is only the intercepts of the plots, i.e., a contribution from a Cu(II) complex independent pathway, that show some dependence on the nature of the complex. The authors do not comment on the intercepts at all and conclude that the dehydration rate constant varies linearly with the total Cu- (II) concentration, which is only true if one ignores the large intercepts in the plots. In order to demonstrate this point, the data as presented by the authors are plotted in Figure 1, and the same data are plotted in Figure 2 on a scale selected to show the importance of the ignored intercepts. It is quite clear from Figure 2 that the apparently observed catalytic effect is indeed very small within the experimental error limits of such measurements. * E-mail: vaneldik@chemie.uni-erlangen.de. (1) Sun, Y.-J.; Zang, L. Z.; Cheng, P.; Lin, H.-K.; Yan, S.-P.; Sun, W.; Liao, D.-Z.; Jiang, Z.-H.; Shen, P.-W. Inorg. Chem. 2003, 42, 508. (2) Palmer, D. A.; van Eldik, R. Chem. ReV. 1983, 83, 651. (3) Acharya, A. N.; Das, A.; Dash, A. C. AdV. Inorg. Chem. Vol. 55, in press. (4) Zhang, X.; van Eldik, R.; Koike, T.; Kimura, E. Inorg. Chem. 1993, 32, 5749. (5) Zhang, X.; van Eldik, R. Inorg. Chem. 1995, 34, 5606. (6) Zhang, X.; Hubbard, C. D.; van Eldik, R. J. Phys. Chem. 1996, 100, 9161. (7) Hartmann, M.; Merz, K. M., Jr.; van Eldik, R.; Clark, T. J. Mol. Model. 1998, 4, 355. (8) Mao, Z.-W.; Liehr, G.; van Eldik, R. J. Am. Chem. Soc. 2000, 122, 4839. (9) Mao, Z.-W.; Liehr, G.; van Eldik, R. J. Chem. Soc., Dalton Trans. 2001, 1593. (10) Mao, Z.-W.; Heinemann, F. W.; Liehr, G.; van Eldik, R. J. Chem. Soc., Dalton Trans. 2001, 3652. (11) Erras-Hanauer, H.; Mao, Z.-W.; Liehr, G.; Clark, T.; van Eldik, R. Eur. J. Inorg. Chem. 2003, 1562. Inorg. Chem. 2004, 43, 2756-2758 2756 Inorganic Chemistry, Vol. 43, No. 9, 2004 10.1021/ic0353561 CCC: $27.50 © 2004 American Chemical Society Published on Web 04/03/2004