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Nickel hydride hydrogenases

Nickel-iron hydrogenases [NiFe] (Figure 8.2) are present in several bacteria. Their structure is known [22, 23] to be a heterodimeric protein formed by four subunits, three of which are small [Fe] and one contains the bimetallic active center consisting of a dimeric cluster formed by a six coordinated Fe linked to a pentacoordinated Ni (III) through two cysteine-S and a third ligand whose nature changes with the oxidation state of the metals in the reduced state it is a hydride, H, whereas in the oxidized state it may be either an oxo, 0, or a sulfide,... [Pg.276]

Barton BE, Rauchfuss TB (2010) Hydride-containing models for the active site of the nickel-iron hydrogenases. J Am Chem Soc 132(42) 14877-14885. doi 10.1021/jal05312p... [Pg.265]

A similar reaction can be written for the [Fe] hydrogenases with a Fe-[4Fe-4S] complex replacing the nickel. Note that the nickel atom in the NiFe cluster, and the Fe-[4Fe-4S] sites are nearest to the electron carrier [4Fe-4S] clusters, indicating that electron transfer occurs through these atoms. The other atom in each of the centres is an iron atom with -CN and -CO ligands, and it seems likely that this is a binding site for hydride (Fig. 8.1). [Pg.185]

Fig. 10. Hypothetical reaction cycle for D. gigas hydrogenase, based on the EPR and redox properties of the nickel (Table II). Only the nickel center and one [4Fe-4S] cluster are shown. Step 1 enzyme, in the activated conformation and Ni(II) oxidation state, causes heterolytic cleavage of H2 to produce a Ni(II) hydride and a proton which might be associated with a ligand to the nickel or another base in the vicinity of the metal site. Step 2 intramolecular electron transfer to the iron-sulfur cluster produces a protonated Ni(I) site (giving the Ni-C signal). An alternative formulation of this species would be Ni(III) - H2. Step 3 reoxidation of the iron-sulfur cluster and release of a proton. Step 4 reoxidation of Ni and release of the other proton. Fig. 10. Hypothetical reaction cycle for D. gigas hydrogenase, based on the EPR and redox properties of the nickel (Table II). Only the nickel center and one [4Fe-4S] cluster are shown. Step 1 enzyme, in the activated conformation and Ni(II) oxidation state, causes heterolytic cleavage of H2 to produce a Ni(II) hydride and a proton which might be associated with a ligand to the nickel or another base in the vicinity of the metal site. Step 2 intramolecular electron transfer to the iron-sulfur cluster produces a protonated Ni(I) site (giving the Ni-C signal). An alternative formulation of this species would be Ni(III) - H2. Step 3 reoxidation of the iron-sulfur cluster and release of a proton. Step 4 reoxidation of Ni and release of the other proton.
For the Ru system the thiol hydride could not be detected, while for the Rh system and also [IrH2(HS(CH2)3SH)(PCy3)2]+(which similarly catalyzes D2/H + exchange (79)), the H2 complex could not be seen but is a transient. A related system, Ni(NHP Pr3)(S3) clearly shows that heterolysis of D2 can also occur at nickel sites, which may be relevant to H2 activation in [FeNi] hydrogenases (78). [Pg.144]

Barton BE, Whaley CM, Rauchfuss TB, Gray DF. Nickel-iron dithiolato hydrides relevant to the [NiFe]-hydrogenase active site. J Am Chem Soc. 2009 131(20) 6942-3. [Pg.223]

Treatment of the amino-phosphine complex with H2 generates a hydrido nickel complex with a pendant ammonium substituent. Catalysis, which was established electrochemicaUy, is proposed to involve oxidation of the Ni(ll) hydride to a Ni(III) hydride, a process which enhances the acidity of the hydrido ligand sufficiently to allow its deprotonation by the pendant amine (Fig. 12.12). This proton transfer gives an easily oxidized Ni(I) intermediate. Catalysis of the H2 oxidation by mononuclear nickel complexes foreshadows the preparation of related bimetallic species exhibiting hydrogenase reactivity. [Pg.417]


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See also in sourсe #XX -- [ Pg.314 ]




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Hydride hydrogenase

Hydrogenase

Hydrogenases nickel

Nickel hydride

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