Trace Cu(II) as an Efficient Electron-Transfer Shuttle for Reductive Deiodination of Refractory Iodinated Contrast Media Compounds

Iodinated contrast media compounds (ICMs) are intensively applied in medical diagnostic radiology and have received wide environmental concerns due to formation potential of iodinated disinfection byproducts. Conventional water/wastewater treatment processes cannot effectively remove ICMs; reducing their total organic iodine concentration is even more difficult. The source control or elimination of ICMs thus becomes necessary. We report here that the refractory ICMs (5 mu M) can be efficiently deiodinated by ascorbate/ascorbic acid (AA) (200 mu M) coupled with a trace amount of Cu-(II) (5 mu M) through catalytic reduction but not oxidation, contrary to the conventional concept of AA/Cu-(II) coupling, which produces reactive oxygen species. Taking diatrizoate (DTZ, a refractory ICM) as an example, the coupling completely deiodinated DTZ without destroying its molecular structure. High-performance liquid chromatography inductively coupled plasma mass spectrometry analysis revealed that ternary complexes form between Cu-(II), ascorbate, and the anilide moiety of DTZ. Cu-(II) in the ternary complex works as an efficient electron-transfer shuttle to convey electrons from ascorbate to the target compound, inducing sequential and complete deiodination. Both DTZ and the nonionic ICMs can be effectively deiodinated even in human urine. Thus, AA coupled with trace Cu-(II) could be potentially useful for the source elimination of organic iodine of ICMs.