Structure of the molybdenum site in YedY, a sulfite oxidase homologue from Escherichia coli.

YedY from Escherichia coli is a new member of the sulfite oxidase family of molybdenum cofactor (Moco)-containing oxidoreductases. We investigated the atomic structure of the molybdenum site in YedY by X-ray absorption spectroscopy, in comparison to human sulfite oxidase (hSO) and to a Mo(IV) model complex. The K-edge energy was indicative of Mo(V) in YedY, in agreement with X- and Q-band electron paramagnetic resonance results, whereas the hSO protein contained Mo(VI). In YedY and hSO, molybdenum is coordinated by two sulfur ligands from the molybdopterin ligand of the Moco, one thiolate sulfur of a cysteine (average Mo-S bond length of ∼2.4 Å), and one (axial) oxo ligand (Mo═O, ∼1.7 Å). hSO contained a second oxo group at Mo as expected, but in YedY, two species in about a 1:1 ratio were found at the active site, corresponding to an equatorial Mo-OH bond (∼2.1 Å) or possibly to a shorter Mo-O(-) bond. Yet another oxygen (or nitrogen) at a ∼2.6 Å distance to Mo in YedY was identified, which could originate from a water molecule in the substrate binding cavity or from an amino acid residue close to the molybdenum site, i.e., Glu104, that is replaced by a glycine in hSO, or Asn45. The addition of the poor substrate dimethyl sulfoxide to YedY left the molybdenum coordination unchanged at high pH. In contrast, we found indications that the better substrate trimethylamine N-oxide and the substrate analogue acetone were bound at a ∼2.6 Å distance to the molybdenum, presumably replacing the equatorial oxygen ligand. These findings were used to interpret the recent crystal structure of YedY and bear implications for its catalytic mechanism.

Tungsten's redox potential is more temperature sensitive than that of molybdenum.

The redox potentials of strictly analogous complexes of molybdenum and tungsten were studied using temperature dependent electrochemistry in order to evaluate a proposed influence of the potentials on the use of tungsten at thermophilic conditions and the use of molybdenum at mesophilic conditions in the molybdopterin dependent oxido reductases. Each pair of molybdenum and tungsten compounds was studied under identical conditions. The studies reveal that tungsten's redox potential is always more temperature sensitive than molybdenum's with a stronger shift of the potential upon temperature change in negative or positive direction depending on the ligand system. No exceptions to this different behaviour of molybdenum and tungsten were observed. The conducted experiments are described in detail and the relevance for the use of either metal is discussed. In addition a possible reason for this fundamental difference as part of the nature of molybdenum and tungsten is proposed.

Synthesis and reaction of monomeric germanium(II) and lead(II) dimethylamide and the synthesis of germanium(II) hydrazide by cleavage of one N-H bond of hydrazine.

The beta-diketiminate substituted germanium(II) and lead(II) dimethylamides, LGeNMe(2) (1) and LPbNMe(2) (2), [L = CH{(CMe)(2)(2,6-iPr(2)C(6)H(3)N)(2)}] have been synthesized by the reaction of LiNMe(2) with LGeCl and LPbCl respectively. Reaction of compound 1 with an equivalent amount of elemental sulfur leads to the germanium analogue of thioamide, LGe(S)NMe(2) (3). 2 reacts with 2-benzoyl pyridine (PhCOPy-2) to form the lead(II) alkoxide LPbOC(NMe(2))Ph(2-Py) (4) by nucleophilic addition of "NMe(2)" to the carbon oxygen double bond. The reaction of stable N-heterocyclic germylene L(1)Ge [L(1) = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}] with hydrazine yields the germanium(II) substituted hydrazide LGeNHNH(2) (5) by cleavage of one N-H bond of hydrazine. Finally, attempts to isolate lead(II) hydride LPbH from the reaction of 2 with phenylsilane (PhSiH(3)) failed, and instead LPbN(2,6-iPr(2)C(6)H(3)){C(CH(3))CHC(CH(3))=N(2,6-iPr(2)C(6)H(3))} (6) was obtained in very low yield. We are able to prove this only by single crystal X-ray structural analysis. Compounds 1, 2, 3, 4, and 5 were characterized by microanalysis, electron impact (EI) mass spectrometry, and multinuclear NMR spectroscopy. Furthermore compounds 1, 2, 5, and 6 were characterized by single crystal X-ray structural analysis, with the result that they are exhibiting monomeric structures in the solid state with trigonal-pyramidal environment at the metal center and a stereochemically active lone pair.

Lewis-base-stabilized dichlorosilylene: a two-electron sigma-donor ligand.

The first structurally described cobalt(I) Lewis-base-stabilized silylene complex [Co(CO)(3){SiCl(2)(IPr)}(2)](+)[CoCl(3)(THF)](-) [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] was prepared by applying the two-electron sigma-donor ligand SiCl(2)(IPr) through coordination with Co(2)(CO)(8). The bonding situation between ligand SiCl(2)(IPr) and the cobalt(I) metal center in [Co(CO)(3){SiCl(2)(IPr)}(2)](+) of 1 was investigated by (1)H NMR and IR spectroscopy, single-crystal X-ray structural analysis, and density functional theoretical calculations.

Facile access of stable divalent tin compounds with terminal methyl, amide, fluoride, and iodide substituents.

The stable beta-diketiminate tin(II) complexes LSnX [L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3] with terminal methyl, amide, fluoride, and iodide (X = Me, N(SiMe3)2, F, I) are described. LSnMe (2) is synthesized by salt metathesis reaction of LSnCl (1) with MeLi and can be isolated in the form of yellow crystals in 88% yield. Compound LSnN(SiMe3)2 (3) was obtained by treatment of LH with 2 equiv of KN(SiMe3)2 in THF followed by adding 1 equiv of SnCl2. Reaction of 2 and 3 respectively with Me3SnF in toluene provided the tin(II)fluoride LSnF (4) with a terminal fluorine as colorless crystals in 85% yield. 4 is highly soluble in common organic solvents. The reaction of LLi(OEt2) with 1 equiv of SnI2 in diethyl ether afforded the LSnI (5). Compounds 2, 3, 4, and 5 were characterized by microanalysis, multinuclear NMR spectroscopy, and X-ray structural analysis. Single crystal X-ray structural analyses indicate that all the compounds (2, 3, 4, 5) are monomeric and the tin center resides in a trigonal-pyramidal environment.