Oxidations mediated by biologically relevant complexes of manganese

The pathway of manganese, from its use in a gasoline additive, methylcyclopentadienyl manganese tricarbonyl (MMT), to its combustion, metabolism and biodistribution, is described. Biologically relevant, manganese-binding molecules, such as peptides and nucleotides, are presented.; The chemistry of some of these complexes with restriction fragment and plasmid DNA was examined. Manganese(II) in the presence of carbonate was observed to reduce H₂O₂ by one electron, producing ·OH and other radicals, as detected by electron paramagnetic resonance (EPR). These radicals damaged restriction fragment and plasmid DNA. In the presence of tri-peptides, phosphate, pyrophosphate and ATP, manganese(II) did not produce radicals or damage DNA.; In the presence of sulfite, manganese(III) also appeared to produce ·OH as observed by quenching reactions and DNA reactivity patterns, although EPR indicated that only sulfite radical was generated. It was proposed that Mn(III) trapped SO₅·, and the complex decomposed to release ·OH.; Salicylalanylhistidine carboxylic acid manganese(III) MnSalAH and derivative complexes are described. The ligand is a salicylimine conjugate of the N-terminal amine of a dipeptide. An x-ray crystal structure of MnSalAH was obtained. MnSalAH is an octahedral complex with two axial water molecules and a planar ligand coordinating environment.; Because these complexes bear structural features of both porphyrins and salen ligands, their reactivity was examined with respect to one- and two-electron transfer reactions that manganese porphyrins and salens are known to catalyze. The one electron reaction explored was the dismutation of superoxide catalyzed by the manganese(II)/(III) redox couple. A two-electron oxidation examined was the epoxidation of an olefin, carbamazepine (CBZ), using KHSO₅ or Na₂SO₃/O₂ as oxidant.; The dismutation of superoxide catalyzed by MnSalAH was examined by the nitroblue tetrazolium (NBT) assay. The assay indicated that MnSalAH and several derivatives catalyzed the dismutation reaction. Kinetic analysis with a stopped-flow apparatus did not support catalytic activity of the MnSalAH complexes.; Catalysis via a two-electron mechanism was explored to identify novel “green” catalysts. Manganese(III) meso-tetrakis-( N-methylpyridinium-2-yl)porphyrin (MnTMPyP), was observed to epoxidize CBZ in the presence of sulfite and oxygen. However, MnSalXH was observed to decompose instead of producing the Mn(V)-oxo species necessary for epoxidation.