Triisopropyltriazacyclononane copper(II): an efficient phosphodiester hydrolysis catalyst and DNA cleavage agent

A 6000-fold rate enhancement has been observed for the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the presence of 0.2 mM Cu(i-Pr(3)9]aneN(3))(2+) at pH 9.2 and 50 degrees C. In a direct comparison, the rate of hydrolysis of BNPP is accelerated at least 60-fold over the previously reported catalyst Cu(9]aneN(3))(2+). As observed for Cu(9]aneN(3))(2+), hydrolysis is selective for diesters over monoesters. Hydrolysis of BNPP by Cu(i-Pr(3)9]aneN(3))(2+) is catalytic, exhibiting both rate enhancement and turnover. The reaction is inhibited by both p-nitrophenyl phosphate and inorganic phosphate. The reaction is first-order in substrate and half-order in metal complex, with a k(1.5) of 0.060 +/- 0.004 M(-1/2) s(-1) at 50 degrees C. The temperature dependence of the rate constant results in a calculated activation enthalpy (Delta H(++) of 51 +/- 2 kJ mol(-1) and activation entropy (Delta S(++)) of -110 +/- 6 J mol(-1) K(-1). The kinetic pK(a) of 7.8 +/- 0.2 is close to the thermodynamic pK(a) of 7.9 +/- 0.2, consistent with deprotonation of a coordinated water molecule in the active form of the catalyst. The active catalyst Cu(i-Pr(3)9]aneN(3))(OH)(OH(2))](+) is in equilibrium with an inactive dimer, and the formation constant for this dimer is between 216 and 1394 M(-1) at pH 9.2 and 50 degrees C. Temperature dependence of the dimer formation constant K(f) indicates an endothermic enthalpy of formation for the dimer of 27 +/- 3 kJ mol(-1). The time course of anaerobic DNA cleavage by Cu(i-Pr(3)9]aneN(3))(2+) is presented over a wide range of concentrations at pH 7.8 at 50 degrees C. The concentration dependence of DNA cleavage by Cu(9]aneN(3))(2+) and Cu(i-Pr(3)9]aneN(3))(2+) reveals a maximum cleavage efficiency at sub-micromolar concentrations of cleavage agent. DNA cleavage by Cu(i-Pr(3)9]aneN(3))(2+) is twice as efficient at pH 7.8 as at pH 7.2.