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Th. : Sci. : Strasbourg : 1875.

The principal organometallic products resulting from the reactions of Na[(ƞ⁵-C₅H₄R)Cr(CO)₃] (R = H or Me) with allyl chlorides in THF are the green, dimeric [(ƞ⁵-C₅H₄R)Cr(CO)₃]₂ complexes (51-67% yields). The red organometallic by-products usually formed during these conversions are novel (ƞ⁶-6-alkenylfulvene)Cr(C0)₃ complexes (5-8% yields) which have been characterized completely by conventional spectroscopic methods. Dark green [W(N0)₂Cl₂]n may be synthesized in high yields by two preparative methods. The first method involves treatment of WCl₆ in CH₂Cl₂ with an excess of NO, and it proceeds via the isolable intermediate complexes, dark violet c̲i̲̲s̲-W(N0)₂Cl₄ and bright green f̲a̲c̲-W(NO)₃Cl₃. The second method involves controlled reaction of W(CO)₆ with two equivalents of ClN0 in CH₂Cl₂. It is initiated by traces of oxidant and probably proceeds via a catalytic, radical-chain mechanism that is described. If either reaction is effected in the presence of two equivalents of CH₃CN, then yellow-green W(N0)Cl₃(CH₃CN)₂ is the only nitrosyl-containing product formed. Polymeric [W(N0)₂Cl₂]n may be cleaved by a variety of Lewis bases, L, and (n̲-Bu)₃Sn(C₅H₅) to form W(N0)₂Cl₂L₂ (L = phosphine, phosphite, CH₃CN, etc.) and CpW(N0)₂Cl (Cp - ƞ⁵-C₅H₅), respectively, in good yields. The synthesis of the electron-rich nitrosyl complexes CpM(NO)L₂ (M = Cr, Mo, or W; L = P(0Me)₃, PMePh₂, P(n̲-Bu)₃, SbPh₃ or 1/2 (dppe)) is described. They are preparable in moderate to high yields by the reduction of the iodo dimers [CpM(NO)In]₂ (M = Cr, n = 1; M = Mo or W, n = 2) with sodium amalgam in THF ln the presence of the appropriate Lewis base, L, and they exhibit metal-dependent trends in vNO (Cr » Mo > W), δ ³¹P (Cr > Mo » W), and ²J₃₁p (Cr < Mo < W). These reduction reactions proceed via a number of transient intermediates, some of which are isolable. A unified mechanism for these reductive syntheses is proposed. The novel complexes, CpMo(NO)(ƞ⁴-trans-diene) (diene = acyclic conjugated diene) and CpMo(NO)(ƞ⁴-c̲i̲s̲-2,3-dlmethyl-butadiene)t are preparable in moderate yields by the reduction of [CpMo(NO)I₂]₂ with sodium amalgam in THF in the presence of the appropriate diene. The reaction between [CpMo(NO)I₂]₂ and C₄H₆•Mg•2(THF) results in the formation of a green, isolable oligomeric complex CpMo(NO)I(ƞ³-C₃H₄R) (where R = CH₂MgI and the nitrosyl oxygen acts as a Lewis base towards Mg) that can be hydrolyzed to CpMo(NO)I(ƞ³-C₄H₇) or converted to CpMo(NO)(ƞ⁴+-t̲r̲a̲n̲s̲-C₄H₆). These diene complexes have been fully characterized by conventional spectroscopic techniques (extensive ¹H and ¹³C NMR spectra being particularly informative) and by single-crystal X-ray structural determinations of CpMo(NO)(ƞ⁴-t̲r̲a̲n̲s̲-2,5-dimethyl-2,4-hexadiene) and CpMo(N0)(ƞ⁴-c̲i̲s̲-2,3-dimethyl-butadlene). A molecular orbital rationale for the structural and spectrocopic properties and relative stabilities of these c̲i̲s̲- and t̲r̲a̲n̲s̲-diene complexes is then presented. / Science, Faculty of / Chemistry, Department of / Graduate

S-Nitrosation is a post-translational modification of protein cysteine residues, which occurs in response to cellular oxidative stress. Although it is increasingly being linked to physiologically important processes, the molecular basis for protein regulation by this modification remains poorly understood. Biophysical methods were used to elucidate the mechanism and molecular consequences of S-nitrosation of glutathione transferase (GST) P1-1, a ubiquitous homodimeric detoxification enzyme and important target for cancer therapeutics. Transient kinetic techniques, isothermal titration calorimetry and protein engineering were used to develop a minimal mechanism for S-nitrosation of GSTP1-1, the first for any protein. Cys47 of GSTP1-1 is S-nitrosated according to a conformational selection mechanism, with the chemical step limited by a pre-equilibrium between the open and closed conformations of a dynamic helix at the active site. Cys101, in contrast, is Snitrosated in a single step but is subject to negative cooperativity due to steric hindrance at the dimer interface. S-Nitrosation at Cys47 and Cys101 was found to reduce the detoxification activity of GSTP1-1 by 94%. Circular dichroism spectroscopy, acrylamide quenching and amide hydrogen-deuterium exchange mass spectrometry experiments revealed that the loss of activity is due to the introduction of local disorder at the active site. Furthermore, the modification destabilises domain 1 of GSTP1-1 against denaturation, smoothing the unfolding energy landscape of the protein and introducing a refolding defect. These data elucidate the physical basis for the regulation of GSTP1-1 by S-nitrosation, and provide general insight into the mechanism of S-nitrosation and its effect protein stability and dynamics.

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No description available.