The oxidation of L-proline (Pro) by HO radical in water and the influence of transition metal ions on this process has been revisited by using the density functional theory (DFT) method at the M05-2X/6-311 + + G(3df,3pd)//M05-2X/6-311 + + G(d,p) level of theory at the temperature of 298.15 K. The main reactive sites of the HO-initiated oxidation of Pro via hydrogen atom transfer (HAT) reactions are at the β- and γ-carbon, with the branching ratios being 44.6% and 39.5%, respectively. The overall rate constant at 298.15 K is 6.04 × 10 M s. In addition, Pro tends to form stable complexes with both Fe and Cu ions via the -COO functional group of dipole-salt form. The most stable Cu(II)-Pro complexes have high oxidant risks in enhancing the HO formation in the presence of reducing agents. Besides this, the high oxidation state metal complexes, i.e. Fe(III)-Pro and Cu(II)-Pro, may be oxidized by HO radical via HAT reactions but with a lower rate constant than that of free-Pro. By contrast, the low oxidation state metal complexes (i.e. Fe(II)-Pro and Cu(I)-Pro) have higher oxidation risks than the free ligands, and thus, the complexation enhances the oxidation of Pro amino acid.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC10245202PMC
http://dx.doi.org/10.1098/rsos.230114DOI Listing

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