Reactivity of ferrate(VI) and ferrate(V) with amino acids
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The oxidation of the essential amino acids by ferrate(VI) (Fe(VI)) and ferrate(V) (Fe(V)) has been studied by stopped-flow and pulse radiolysis techniques at pH 12.4 and 23-24 °C. FeO43- was formed in these studies by reduction of Fe(VI) with radiation-generated reducing radicals. Both Fe(VI) and Fe(V) react preferentially with amino acids in which the α-amino group is protonated (RCH(NH3+)COO-). Rate constants (k5) for reactions of Fe(VI) with RCH(NH3+)COO- range from 10 to 103 M-1s-1. The corresponding k6 values for Fe(V) are orders of magnitude higher: k6 = (0.01-5.0) × 107 M-1 s-1. Cysteine, a reducing species, reacts with Fe(VI) at a rate of k = 760 ± 49 M-1 s-1 and with FeO43- at a nearly diffusion-controlled rate of k = (4.0 ± 0.8) × 109 M-1 s-1; both rates were computed on the basis of [cysteine] tot. The ratio k6/k5 varies from 5 × 103 to 3 × 105; for cysteine this ratio is 5 × 106. The oxidation process of amino acids initiated by Fe(V) proceeds in presence of Fe(VI) by a chain reaction in which amino acid free radicals and Fe(V) are the chain carriers. © 1991, American Chemical Society. All rights reserved.
author list (cited authors)
Sharma, V. K., & Bielski, B.