Ion binding by X-537A. Rates of complexation of Ni2+ and Mn2+ in methanol

The rates of complexation are studied through the effects of the paramagnetic ions upon the magnetic resonances of three of the proton species in X-537A = XH. For the dissociation of the complex MX+ leads to M2+ + X- at 25 degrees the rate is (2.4 plus or minus 0.4) x 10(2) sec-1 for Ni2+ and in the range from 2 x 10(4) to 1 x 10(6) sec-1 for Mn2+. For the Ni2+ complex the activation parameters are also determined and discussed in terms of the details of the process. The difference in rate constants found here is much greater than the difference in the dissociation constants.