Rates of cytidine amino mercuration by methylmercury(II) determined by 1H NMR saturation recovery

Saturation recovery of the amino 1H resonance is a useful and necessary alternative to line-shape analysis for the determination of rates of cytidine amino mercuration by methylmercury. Reciprocal lifetimes of the free ligand could be obtained by correction of recovery data for dipolar contributions, which were determined from the temperature dependence of recovery in D2O-H2O mixtures. Reciprocal lifetimes fall in the range of 2-11 s-1 and are influenced by two separate rate processes: At high levels of total CH3HgOH they are a measure of the forward rate constant of amino mercuration, k1 = 1.2 +/- 0.1 x 103 s-1 M-1 (free CH3HgOH), and conform to an activation energy of 17 +/- 2 kcal mol-1; at low total [CH3HgOH], they reflect an additional amino-to-water proton exchange mechanism under conditions associated with significant concentrations of N3-protonated Cyd (free amino ligand). This latter route is proportional to total cytidine concentration