- Study of nitrosation of hexaammineruthenium(II): Crystal structure of trans-[RuNO(NH3)4Cl]Cl2
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The nitrosation of [Ru(NH3)6]2+ in hydrochloric acid and alkaline ammonia media has been studied; the patterns of interconversion of ruthenium complexes in reaction solutions have been proposed. In both cases, nitrogen(II) oxide acts as the nitrosation agent. The procedure for the synthesis of [Ru(NO)(NH3)5]Cl3 ? H2O (yield 75-80%), the main nitrosation product of [Ru(NH 3)6]2+, has been optimized. Thermolysis of [Ru(NO)(NH3)5]Cl3 ? H2O in a helium atmosphere has been studied; the intermediates have been identified. One of these products is polyamidodichloronitrosoruthenium(II) whose subsequent decomposition gives an equimolar mixture of ruthenium metal and dioxide. The structure of trans-[RuNO(NH3)4Cl]Cl2, formed in the second stage of thermolysis and as a by-product in the nitrosation of [Ru(NH3)6]Cl2, has been determined by X-ray diffraction. Nauka/Interperiodica 2007.
- Il'in,Emel'Yanov,Baidina,Alferova,Korol'Kov
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- Tuning the rate and pH accessibility of a conformational electron transfer gate
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Methods to fine-tune the rate of a fast conformational electron transfer (ET) gate involving a His-heme alkaline conformer of iso-1-cytochrome c (iso-1-Cytc) and to adjust the pH accessibility of a slow ET gate involving a Lys-heme alkaline conformer are described. Fine-tuning the fast ET gate employs a strategy of making surface mutations in a substructure unfolded in the alkaline conformer. To make the slow ET gate accessible at neutral pH, the strategy involves mutations at buried sequence positions which are expected to more strongly perturb the stability of native versus alkaline iso-1-Cytc. To fine-tune the rate of the fast His 73-heme ET gate, we mutate the surface-exposed Lys 79 to Ala (A79H73 variant). This mutation also simplifies ET gating by removing Lys 79, which can serve as a ligand in the alkaline conformer of iso-1-Cytc. To adjust the pH accessibility of the slow Lys 73-heme ET gate, we convert the buried side chain Asn 52 to Gly and also mutate Lys 79 to Ala to simplify ET gating (A79G52 variant). ET kinetics is studied as a function of pH using hexaammineruthenium(II) chloride (a6Ru 2+) to reduce the variants. Both variants show fast direct ET reactions dependent on [a6Ru2+] and slower gated ET reactions that are independent of [a6Ru2+]. The observed gated ET rates correlate well with rates for the alkaline-to-native state conformational change measured independently. Together with the previously reported H73 variant (Baddam, S.; Bowler, B. E. J. Am. Chem. Soc. 2005, 127, 9702-9703), the A79H73 variant allows His 73-heme-mediated ET gating to be fine-tuned from 75 to 200 ms. The slower Lys 73-heme (15-20 s time scale) ET gate for the A79G52 variant is now accessible over the pH range 6-8.
- Baddam, Saritha,Bowler, Bruce E.
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- Spin-trapping studies of the reduction of O2 and H2O2 by titanium(III), iron(II), and ruthenium(II) complexes
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The reductions of H2O2 and O2 by Ti(edta)(H2O)-, Ti(H2O)63+, Fe(edta)2-, Fe(H2O)62+, and Ru(NH3)62+ have been studied by the spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and N-tert-butyl-α-phenylnitrone (PBN) radical traps. The resultant radical adducts RDMPO? and RPBN? have been characterized by ESR spectroscopy in agreement with literature values. Ti(edta)(H2O)-, Fe(edta)2-, Fe(H2O)62+, and Ru(NH3)62+ reductions of H2O2 produce HO? identified by the HO-DMPO? and HO-PBN? spectra. HO? formed in these reductions may be intercepted by chemical mediators (CH3OH, C2H5OH, (CH3)2CO, (CH3)3COH) to provide more long-lived secondary carbon-centered radicals, which are trapped by DMPO or PBN. Excellent spectral matches for RDMPO? and RPBN? species are obtained for the Ti(edta)(H2O)-, Fe(edta)2-, Fe(H2O)62+, Ti(H2O)63+, and Ru(NH3)62+ reductants for H2O2 in the presence or absence of mediators. When O2 is used as the oxidant for Ru(NH3)62+, this reaction known to proceed outer sphere via O2-, only the dismutation/reduction product (HO?) is trapped at pH 6.86. Both HO2? and HO? are trapped at pH 2.57 in a 1.0:7.6 ratio. Ti(edta)(H2O)- is known to be oxidized inner sphere by O2 via coordinated O2-. No radical adducts for the Ti(edta)(H2O)-/O2/radical trap system are observed with or without mediators in the solvent cage. The reduction of O2 by either Fe(edta)2- or Fe2(ttha)2- proceeds by an inner-sphere pathway in which the coordinated O2- survives long enough to attack an adjacent carboxylate moiety, forming a trappable ligand-based carbon-centered radical, or to attack sacrificial mediators in the solvent cage.
- Johnson, Craig R.,Myser, Terry K.,Shepherd, Rex E.
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p. 1089 - 1095
(2008/10/08)
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