Kinetic Stereoselectivity in Complexation Reactions of Histidine with Bivalent Metal Ions in Aqueous Solution

Abstract

Using temperature jump method, rate constants of the following type reactions were obtained,
(M2 + is metal ion and L-, D- are L- and D-form of histidine anion). At 25° C and ionic strength of 0.1, rate constants were: nickel(II), k2= 4.1 X 10 mol-.1. sec-1, k_2= 0.059 sec-', k3=4.3 X 105 mol-1.1. sec-1, 2 k_3=0.027 sec-1; cobalt, k2 1.4 x 106 mol-l./ . sec-1, k2=5.7 sec', ks= 1.2 x 106 mol-1.1. sec-1, 2 k_3=2.9 sec'; zinc(JI), k2= 6.0 X 10' mol-l / sec-', k₂=190 sec', k3= 5.2 x 107 mol- .1. sec-1, 2 k_3=96 sec'; cadmium(II), k2 7 x 107 mol-l./ .sec-% k 2 4 × 103 sec' (the coefficient 2 of k, is the statistical factor).
The formation rate constants k2 and k, were equal within experimental error for nickel TO, cobalt10, and zinc(II), but 2 k, was about half of k2. The effect of optical activity of his- tidine on complexation reactions appeared kinetically on the dissociation reactions of bihistidine complexes. The results of formation rate constants agreed with the two step mechanism involving water dissociation from the inner hydration shell of the ion ML⁺.