different from those of the native protein.The reaction of a5RuH202+ with sperm whale myoglobin was allowed to proceed for 24 h under anaerobic conditions at pH 7, and the Ru-labeled protein was then oxidized and purified by standard procedures, to give Ru3Mb. * Absences of the imidazole C-2 proton resonances of His-12, His-81, and His-113 in the high-field N M R spectrum of Ru3Mb pinpoint those residues as the sites of attachment of the a5Ru3+ groups (Figure l).**J3The three attached a5Ru3+ groups do not appear strongly to perturb the M b conformation, as judged by comparative measurements of electronic and vibrational spectra. The ability of the heme in Ru3Mb to bind anions, however, is enhanced greatly over that of the native protein. Cyanide, for example, binds strongly both to the Fe"' and Fe" forms of Ru3Mb.14 The electrostatic influence of the three aSRu3+ groups is likely responsible for this impressive change in anion affinity, as it is for the very high PI value (-9.2) for Ru3Mb.The reduction of O2 by a variety of organic substrates is catalyzed quite effectively by Ru3Mb. Good substrates for this L( synthetic oxidation-reduction enzyme" include ascorbate and durohydroquinone. Comparisons of reactivity parameters (K,,,,

Gaseous bis(trimethylsilyl)methyl-lithium (LiR) at ca. 413 K is a monomer with Li-C 2.03(6) A and the SiMe3 groups only slightly distorted from an eclipsed conformation with respect to each other; crystalline LiR is a polymer, having three 'molecules' of monomer in the asymmetric unit, the Li-C distances range from 2.14(3) to 2.27(2) A and average 2.19(5) A,

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Preparation and Properties of Some Bis(cyclopentadienyl)ytterbium(n)Complexes and the X-Ray Crystal and Molecular Structures of [Yb( q -C,H,SiMe,),(thf),l

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The crystal structure and the i.r. spectra reveal the nearly ideal C,, symmetry of the [ReNCIJ-ion. The force constant of the Re-N bond is in agreement with the observed ReZN length of 1.61 9(10) A. The Re-CI bond distance, 2.322(2) A, is the first to be reported for a ReV1 case. Unit-cell parameters are in close agreement with those of the other members of the isostructural series: a = 12.776(4), c = 7.778(3) A, Z = 2, and 0, = 1.90 g ~m -~ in the tetragonal space group P4/n. Least-squares refinement gave a final R value of 0.022 for 534 unique observed reflections.COMPLEXES of the [MNCl,]-ion are well known for the transition metals molybdenum, tungsten, ruthenium, and o s m i ~m . l -~ Some of their tetraphenylarsonium derivatives have been characterized by X-ray crystallographic determinations. The complexes contain metal-nitrogen triple bonds (symmetry &), as shown by the short metal-nitrogen bond lengths [MoSN, 1.66(1)

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