The PmoB subunit of particulate methane monooxygenase (pMMO) in Methylococcus capsulatus (Bath): The CuI sponge and its function.

In this study, we describe efforts to clarify the role of the copper cofactors associated with subunit B (PmoB) of the particulate methane monooxygenase (pMMO) from Methylococcus capsulatus (Bath) (M. capsulatus). This subunit exhibits strong affinity toward CuI ions. To elucidate the high copper affinity of the subunit, the full-length PmoB, and the N-terminal truncated mutants PmoB33-414 and PmoB55-414, each fused to the maltose-binding protein (MBP), are cloned and over-expressed into Escherichia coli (E. coli) K12 TB1 cells. The Y374F, Y374S and M300L mutants of these protein constructs are also studied. When this E. coli is grown with the pmoB gene in 1.0 mM CuII, it behaves like M. capsulatus (Bath) cultured under high copper stress with abundant membrane accumulation and high CuI content. The recombinant PmoB proteins are verified by Western blotting of antibodies directed against the MBP sub-domain in each of the copper-enriched PmoB proteins. Cu K-edge X-ray absorption near edge spectroscopy (XANES) of the copper ions confirms that all the PmoB recombinants are CuI proteins. All the PmoB proteins show evidence of a "dicopper site" according to analysis of the Cu extended X-ray absorption edge fine structure (EXAFS) of the membranes. No specific activities toward methane and propene oxidation are observed with the recombinant membrane-bound PmoB proteins. However, significant production of hydrogen peroxide is observed in the case of the PmoB33-414 mutant. Reaction of the dicopper site with dioxygen produces hydrogen peroxide and leads to oxidation of the CuI ions residing in the C-terminal sub-domain of the PmoB subunit.

Dioxygen activation of a trinuclear Cu(I)Cu(I)Cu(I) cluster capable of mediating facile oxidation of organic substrates: competition between O-atom transfer and abortive intercomplex reduction.

The dioxygen activation of a series of Cu(I)Cu(I)Cu(I) complexes based on the ligands (L) 3,3'-(1,4-diazepane- 1,4-diyl)bis(1-{[2-(dimethylamino)ethyl](methyl)amino}propan-2-ol)(7-Me) or 3,3'-(1,4-diazepane-1,4-diyl)bis(1-{[2-(diethylamino)ethyl](ethyl)amino}propan-2-ol)(7-Et) forms an intermediate capable of mediating facile O-atom transfer to simple organic substrates at room temperature. To elucidate the dioxygen chemistry, we have examined the reactions of 7-Me, 7-Et, and 3,3'-(1,4-diazepane-1,4-diyl)bis[1-(4-methylpiperazin-1-yl)propan-2-ol] (7-N-Meppz) with dioxygen at -80, -55, and -35 °C in propionitrile (EtCN) by UV-visible, 77 K EPR, and X-ray absorption spectroscopy, and 7-N-Meppz and 7-Me with dioxygen at room temperature in acetonitrile (MeCN) by diode array spectrophotometry. At both -80 and -55 °C, the mixing of the starting [Cu(I)Cu(I)Cu(I)(L)](1+) complex (1) with O(2)-saturated propionitrile (EtCN) led to a bright green solution consisting of two paramagnetic species: the green dioxygen adduct [Cu(II)Cu(II)(µ-η(2):η(2)-peroxo)Cu(II)(L)](2+) (2) and the blue [Cu(II)Cu(II)(µ-O)Cu(II)(L)](2+) species (3). These observations are consistent with the initial formation of [Cu(II)Cu(II)(µ-O)(2)Cu(III)(L)](1+)(4), followed by rapid abortion of this highly reactive species by intercluster electron transfer from a second molecule of complex 1 to give the blue species 3 and subsequent oxygenation of the partially oxidized [Cu(II)Cu(I)Cu(I)(L)](2+)(5) to form the green dioxygen adduct 2. Assignment of 2 to [Cu(II)Cu(II)(µ-η(2):η(2)-peroxo)Cu(II)(L)](2+) is consistent with its reactivity with water to give H(2)O(2) and the blue species 3, as well as its propensity to be photoreduced in the X-ray beam during X-ray absorption experiments at room temperature. In light of these observations, the development of an oxidation catalyst based on the tricopper system requires consideration of the following design criteria: 1) rapid dioxygen chemistry; 2) facile O-atom transfer from the activated cluster to substrate; and 3) a suitable reductant to rapidly regenerate complex 1 to accomplish efficient catalytic turnover.

Transformation and structural discrimination between the neutral {Fe(NO)2}10 dinitrosyliron complexes (DNICs) and the anionic/cationic {Fe(NO)2}9 DNICs.

Reaction of Fe(CO)2(NO)2 and sparteine/tetramethylethylenediamine (TMEDA) in tetrahydrofuran afforded the electron paramagnetic resonance (EPR)-silent, neutral {Fe(NO)2}10 dinitrosyliron complexes (DNICs) [(sparteine)Fe(NO)2] (1) and [(TMEDA)Fe(NO)2] (2), respectively. The stable and isolable anionic {Fe(NO)2}9 DNIC [(S(CH2)3S)Fe(NO)2]- (4), with a bidentate alkylthiolate coordinated to a {Fe(NO)(2)} motif, was prepared by the reaction of [S(CH2)3S]2- and the cationic {Fe(NO)2}9 [(sparteine)Fe(NO)2]+ (3) obtained from the reaction of complex 1 and [NO][BF4] in CH(3)CN. Transformation from the neutral complex 1 to the anionic complex 4 was verified via the cationic complex 3. Here complex 3 acts as an {Fe(NO)2}-donor reagent in the presence of thiolates. The EPR spectra of complexes 3 and 4 exhibit an isotropic signal with g = 2.032 and 2.031 at 298 K, respectively, the characteristic g value of {Fe(NO)2}9 DNICs. On the basis of N-O/Fe-N(O) bond lengths of the single-crystal X-ray structures of the {Fe(NO)2}9/{Fe(NO)2}10 DNICs, the oxidation level of the {Fe(NO)2} core of DNICs can be unambiguously assigned. The mean N-O distances falling in the range of 1.214(6)-1.189(4) A and the Fe-N(O) bond distances in the range of 1.650(7)-1.638(3) A are assigned as the neutral {Fe(NO)(2)}(10) DNICs. In contrast, the mean N-O bond distances ranging from 1.178(3) to 1.160(6) A and the mean Fe-N(O) bond distances ranging from 1.695(3) to 1.661(4) A are assigned as the anionic/neutral/cationic {Fe(NO)2}9 DNICs. In addition, an EPR spectrum in combination with the IR nu(NO) (the relative position of the nu(NO) stretching frequencies and their difference Deltanu(NO)) spectrum may serve as an efficient tool for discrimination of the existence of the anionic/cationic/neutral {Fe(NO)2}9 DNICs and the neutral {Fe(NO)2}10 DNICs.