Reaction of Hydroxyl Radicals with the Ferrous and Ferric Iron Chelates of Diethylenetriamine-N,N,N′,N″,N″-Pentaacetate

Abstract

Reactions of the hydroxyl radical with ferrous and ferric diethylenetriamine-N,N,N′,N″,N″-pentaacetate (DTPA) complexes in neutral aqueous solution were studied using a ⁶⁰Co-γ radiolysis source for radical production. Hydroxyl radicals oxidize the ferrous chelate of DTPA to the ferric chelate, as determined by changes in the optical absorbance. In the presence of equimolar concentrations of ferric and ferrous chelates, HO- is “trapped“ by Fe(III)DTPA^2– and yields of Fe(III)DTPA^2– are substantially reduced. Both tert-butyl alcohol and methanol react efficiently with hydroxyl radicals. tert-Butyl alcohol produces unreactive radicals, and is thus an effective scavenger. However, the reducing hydroxymethyl radical produced upon reaction of HO- with methanol effectively reduces Fe(III)DTPA^2– present in the system, so that solutions initially containing the more absorbing Fe(III)DTPA^2– are bleached. These results with alcoholic hydroxyl radical scavengers illustrate possible complications from scavengers such as methanol which produce reactive products which may themselves stimulate further reaction.

Key Words:

• Hydroxyl radicals
• hydroxyl radical scavengers
• tert-butyl alcohol
• methanol. iron chelates
• diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA)