HYDROLYSIS OF PHOSPHODIESTERS WITH NI(II), CU(II), ZN(II), PD(II), AND PT(II) COMPLEXES

The hydrolysis of bis(4-nitrophenyl) phosphate (1) is catalyzed by Ni(tren)2+ in aqueous solution at 75 °C. The activity of the catalyst remains constant for 85 turnovers and thereafter decreases. Antitumor complexes of Pd(II) and Pt(II) were also examined but did not show turnover in the hydrolysis of ethyl 4-nitrophenyl phosphate (2). Catalytic rate enhancement in the hydrolysis of 1 by Ni(tren)(OH)(OH2)+ was 1200 at pH 8.6 and of 2 by 1 × 1CT4 M Pd(bpy)2+ was 49 at pH 6.0 over spontaneous hydrolysis under the same conditions. The pH-rate profile of Ni(tren)2+-catalyzed hydrolysis of 1 shows a pH-dependent region from pH 8.0 to pH 10.8 and a pH-independent region from pH 6.0 to pH 8.0. Ni(II) complexes of tren and bpy were compared to their corresponding Cu(II) and Zn(II) analogues. The pH–rate profile of the Pd(II)-and Pt(II)-accelerated hydrolysis of 2 shows a pH dependence from pH 6.0 to pH 7.5. The rate enhancement becomes negligible with respect to spontaneous hydrolysis at alkaline pH, which is attributed to the formation of hydroxy-bridged polymers. A mechanism involving intramolecular hydroxide attack on a metal-bound phosphate is proposed. Of the M(bpy)2+ and M(tren)2+ complexes examined (M = Ni2+, Cu2+, Zn2+) only the Cu(bpy)2+ complex was effective in nicking supercoiled plasmid DNA. The inhibition of DNA nicking by Ce4+ for the latter complex suggests that nicking occurs by a redox process rather than by hydrolysis. © 1990, American Chemical Society. All rights reserved.