Pulse Radiolysis and Ultra‐High‐Performance Liquid Chromatography/High‐Resolution Mass Spectrometry Studies on the Reactions of the Carbonate Radical with Vitamin B₁₂ Derivatives

Abstract

The reactions of the carbonate radical anion (CO3 (.) (-) ) with vitamin B12 derivatives were studied by pulse radiolysis. The carbonate radical anion directly oxidizes the metal center of cob(II)alamin quantitively to give hydroxycobalamin, with a bimolecular rate constant of 2.0×10(9) M(-1) s(-1) . The reaction of CO3 (.) (-) with hydroxycobalamin proceeds in two steps. The second-order rate constant for the first reaction is 4.3×10(8) M(-1) s(-1) . The rate of the second reaction is independent of the hydroxycobalamin concentration and is approximately 3.0×10(3) s(-1) . Evidence for formation of corrinoid complexes differing from cobalamin by the abstraction of two or four hydrogen atoms from the corrin macrocycle and lactone ring formation has been obtained by ultra-high-performance liquid chromatography/high-resolution mass spectrometry (UHPLC/HRMS). A mechanism is proposed in which abstraction of a hydrogen atom by CO3 (.) (-) from a carbon atom not involved in the π conjugation system of the corrin occurs in the first step, resulting in formation of a Co(III) C-centered radical that undergoes rapid intramolecular electron transfer to form the corresponding Co(II) carbocation complex for about 50 % of these complexes. Subsequent competing pathways lead to formation of corrinoid complexes with two fewer hydrogen atoms and lactone derivatives of B12 . Our results demonstrate the potential of UHPLC combined with HRMS in the separation and identification of tetrapyrrole macrocycles with minor modifications from their parent molecule.

Biochemistry of Peroxynitrite and Protein Tyrosine Nitration

“…Carbonate radical can also react with hypotaurine, nucleotides, nucleosides, and nucleic acids, specifically guanine is rapidly oxidized . Moreover, CO 3 •– can oxidize a variety of metal complexes, including for example, the reaction with the metal center of cob­(II)­alamin to give hydroxycobalamin; with hemeproteins such as, Fe­(II)-cytochrome c , metmyoglobin, or methemoglobin; and with nonheme proteins, for example aconitase . These fast reactions indicate that CO 3 •– can be a significantly damaging agent in vivo.…”

“…•− can oxidize a variety of metal complexes, including for example, the reaction with the metal center of cob(II)alamin to give hydroxycobalamin; 476 with hemeproteins such as, Fe(II)cytochrome c, 477 metmyoglobin, or methemoglobin; 478 and with nonheme proteins, for example aconitase. 243 These fast reactions indicate that CO 3…”

Detection and quantification of nitric oxide–derived oxidants in biological systems

“…Carbonate anion radical promotes proteinprotein (particularly ditryptophan) or DNA-DNA crosslinks (265,266). It also rapidly reacts with transition metal centers or organic cofactors (267)(268)(269). Interestingly, bicarbonate enhanced the susceptibility of bacterial suspensions to ionizing radiation, which implies extracellular HO ⅐ (252).…”

Picosecond Pulse Radiolysis of Highly Concentrated Carbonate Solutions

“…The carbonate radical CO 3 •– plays an important role in biological, environmental, and chemical systems. − In biological systems, the carbonate radical which can be produced by peroxidase activity oxidizes amino acids and proteins by one electron oxidation . It can also oxidize the metal center of organometallic compounds in the human body . As the bicarbonate ion is abundant in biological systems, and also the carbonate radical can be produced through oxidation of CO 2 by nitrogen oxide radical, the study of the carbonate radical is a mandatory issue for the understanding of oxidative damages to biological tissues .…”

“…4 It can also oxidize the metal center of organometallic compounds in the human body. 5 As the bicarbonate ion is abundant in biological systems, and also the carbonate radical can be produced through oxidation of CO 2 by nitrogen oxide radical, the study of the carbonate radical is a mandatory issue for the understanding of oxidative damages to biological tissues. 6 Although the presence of carbonate radicals in the atmosphere is not important, its concentration can reach high values in surface waters.…”