Gaseous nitric oxide reacted with the dianionic hexanuclear
ruthenium carbide cluster
[PPN]2[Ru6C(CO)16]
(PPN = (PPh3)2N) to give the monoanionic
nitrosyl complex [PPN][Ru6C(CO)15(NO)] (2) in good yield. On
further reaction with gaseous NO, 2 gave a
neutral
pentanuclear complex with NO and NO2 ligands,
Ru5C(CO)14(NO)(NO2),
the structure of
which was confirmed by X-ray analysis of the phosphine derivative
Ru5C(CO)13(PPh3)(NO)(NO2) (4). A monoanionic allyl derivative of
the hexanuclear ruthenium cluster,
[PPN][Ru6C(CO)15(C3H5)], reacted with NO
to give neutral hexa- and pentanuclear allyl complexes
with
NO (and NO2) ligands,
Ru6C(CO)14(C3H5)(NO)
(6) and
Ru5C(CO)11(C3H5)(NO)2(NO2)
(7).
Addition of gaseous NO to 6 gave rise to another
pentanuclear complex
Ru5C(CO)13(C3H5)(NO2) (8) which did not react further with NO.
The solid state structures of the new NO
and NO2 complexes 4 and 6−8 are
reported.
An extremely thermostable [4Fe-4S] ferredoxin was isolated under anaerobic conditions from a hyperthermophilic archaeon Thermococcus profundus, and the ferredoxin gene was cloned and sequenced. The nucleotide sequence of the ferredoxin gene shows the ferredoxin to comprise 62 amino acid residues with a sequence similar to those of many bacterial and archaeal 4Fe (3Fe) ferredoxins. The unusual Fe-S cluster type, which was identified in the resonance Raman and EPR spectra, has three cysteines and one aspartate as the cluster ligands, as in the Pyrococcus furiosus 4Fe ferredoxin. Under aerobic conditions, a ferredoxin was purified that contains a [3Fe-4S] cluster as the major Fe-S cluster and a small amount of the [4Fe-4S] cluster. Its N-terminal amino acid sequence is the same as that of the anaerobically-purified ferredoxin up to the 26th residue. These results indicate that the 4Fe ferredoxin was degraded to 3Fe ferredoxin during aerobic purification. The aerobically-purified ferredoxin was reversibly converted back to the [4Fe-4S] ferredoxin by the addition of ferrous ions under reducing conditions. The anaerobically-purified [4Fe-4S] ferredoxin is quite stable; little degradtion was observed over 20 h at 100 degrees C, while the half-life of the aerobically-purified ferredoxin is 10 h at 100 degrees C. Both the anaerobically- and aerobically-purified ferredoxins were found to function as electron acceptors for the pyruvate-ferredoxin oxidoreductase purified from the same archaeon.
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