Oxidative self-decomposition of the nickel(III) complexes of glycylglycyl-L-histidylglycine and glycylglycylhistamine, and, Rates of bromamine formation in basic solution
Abstract
The oxidative self-decompositions of the nickel(III) doubly-deprotonated peptide complexs of Gly2HisGly and G1y2Ha are investigated, where Gly is glycine, His is L-histidine, and Ha is histamine. Molar absorptivities of the divalent and trivalent nickel complexes are reported. The Ni(III) complexes undergo base-assisted oxidative self-decomposition at the α carbons of the N-terminal glycyl residues. At p[H+] 5.4–7.0, the major pathways are four- and two-electron oxidations for NiIII (H−2Gly2HisGly) and NiIII(H −2Gly2Ha)+, respectively. Ni III(H−2Gly2HisGly) also undergoes some C-terminal decarboxylation and NiIII(H−2Gly 2Ha)+ undergoes minor oxidation at the internal glycyl residue and histamine group as well. Above p[H+] 8.5, both Ni(III)-peptide complexes can form dinuclear oxo bridged Ni(III) species that react via double one-electron oxidations at the α carbons of the N-terminal glycyl residues to give crosslinked peptides. The resulting 2,3-diaminobutanedioic acid derivatives are unstable in atmospheric O2 and undergo oxidation to form 2,3-diaminobutenedioic acid derivatives. The formation of monobromamine from ammonia and hypobromous acid/hypobromite are studied in the p[H +] range 10.7–13.0. A phosphate buffer acceleration is observed that increases significantly with decreasing p[H+]. These data suggest that HPO42− assists the reaction as a general acid. The observed rate of the reaction also increases greatly from p[H+] 13.0 to 10.5 as the more rapid HOBr/NH3 pathway becomes more significant. The second-order rate constants for the reactions of HOBr and OBr− with NH3 were determined to be 2.6(5) × 107 M−1s−1 and 6.5(5) × 104 M−1s −1 for the HOBr and OBr− pathways, respectively.
Degree
Ph.D.
Advisors
Margerum, Purdue University.
Subject Area
Analytical chemistry|Chemistry|Biochemistry
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