Photochemistry of the Dinitrosyl Iron Complex [S₅Fe(NO)₂]^- Leading to Reversible Formation of [S₅Fe(μ-S)₂FeS₅]^2-:  Spectroscopic Characterization of Species Relevant to the Nitric Oxide Modification and Repair of [2Fe−2S] Ferredoxins

Abstract

[C(4)H(3)N(CH(2)NMe(2))-2]AlMe(2) (1) is prepared in 88% yield by the reaction of substituted pyrrole [C(4)H(4)N(CH(2)NMe(2))-2] with 1 equiv of AlMe(3) in methylene chloride. Reaction of compound 1 with 1 equiv of phenyl isocyanate in toluene generates a seven-membered cycloaluminum compound [C(4)H(3)N[CH(2)NPh(CONMe(2))]-2] AlMe(2) (2). The phenyl isocyanate was inserted into the aluminum and dimethylamino nitrogen bond and induced an unusual rearrangement which results in C-N bond breaking and formation. A control experiment shows that the reaction of substituted pyrrole [C(4)H(4)N(CH(2)NMe(2))-2] with 1 equiv of phenyl isocyanate in diethyl ether yields a pyrrolyl attached urea derivative [C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NHPh]-1] (3). The demethanation reaction of AlMe(3) with 1 equiv of 3 in methylene chloride at 0 degrees C afforded O-bounded and N-bounded aluminum dimethyl compounds [C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NPh]-1]AlMe(2) (4a) and [C(4)H(3)N(CH(2)NMe(2))-2-[CO(=NPh)]-1]AlMe(2) (4b) in a total 78% yield after recrystallization. Both 4a and 4b are observed in (1)H NMR spectra; however, the relative ratio of 4a and 4b depends on the solvent used. Two equivalents of AlMe(3) was reacted with 3 in methylene chloride to yield a dinuclear aluminum compound AlMe(3)[C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NPh]-1] AlMe(2) (5). Reaction of 5 with another equivalent of ligand 3 results in the re-formation of compounds 4a and 4b.

The Metal Core Structures in the Recombinant Escherichia coli Transcriptional Factor SoxR

“…In any case, these are transient species. Presumably, within a protein, sulfide released would form di‐ or persulfide species (S Cys S − ),27 or cysteine and sulfane (S 0 ),10a, 16, 21b or other sulfide (S 2− )10, 27a intermediates that could become readily available for subsequent repair of the [2 Fe2 S] clusters from the nitrosylated iron–sulfur cores 21b. 27b, c In recent studies on the reaction of the Rieske iron center in ToMOC and the [4 Fe4 S] center in WhiB‐like proteins with either DEANO or added NO gas, it was suggested that these cysteine‐coordinated iron–sulfur clusters within these proteins encountered cluster degradation to form RRE species primarily,10a, 11 as observed herein for mixed‐valence reduced SoxR in solution.…”

Formation of the Distinct Redox‐Interrelated Forms of Nitric Oxide from Reaction of Dinitrosyl Iron Complexes (DNICs) and Substitution Ligands

“…The released nitric oxide in the reaction of complex 1 and (PyPepS) 2 was trapped by complex [S 5 FeA C H T U N G T R E N N U N G (m-S) 2 FeS 5 ] 2À to produce the known [S 5 Fe(NO) 2 ] À . [24] The transformation of complex 1 into complex 4, carbazole, and NO (g) under the reaction of (PyPepS) 2 and 1 may be accounted for by the following reaction sequences: (PyPepS) 2 was oxidatively added to 1, thus leading to the formation of intermediate B www.chemeurj.org (Scheme 2). As shown in Scheme 2b, it is presumed that intermediate B prefers the intramolecular deprotonation of the proximal carboxamide-coordinated ligands by carbazolate followed by chelation of carboxamido and pyridine to result in the formation of carbazole and 4 along with the release of NO (g) as opposed to the elimination of N-nitrosocarbazole 3 observed in the reaction of 1 and (S 2 CNMe 2 ) 2 .…”

“…The formation of complex 4 was also characterized by single‐crystal X‐ray diffraction (Figure S4 in the Supporting Information), and the by‐product carbazole was identified by 1 H NMR spectroscopy. The released nitric oxide in the reaction of complex 1 and (PyPepS) 2 was trapped by complex [S 5 Fe(μ‐S) 2 FeS 5 ] 2− to produce the known [S 5 Fe(NO) 2 ] − 24. The transformation of complex 1 into complex 4 , carbazole, and NO (g) under the reaction of (PyPepS) 2 and 1 may be accounted for by the following reaction sequences: (PyPepS) 2 was oxidatively added to 1 , thus leading to the formation of intermediate B (Scheme ).…”

“…The IR n NO spectrum showed a strong absorption band at 1715 cm À1 (THF) assigned to the formation of the known complex [(NO)FeA C H T U N G T R E N N U N G (S 2 CNMe 2 ) 2 ] (2). [23] The solution in THF was filtered through Celite to remove the insoluble [PPN]- [24] In the meantime, hexane (20 mL) was added to the brown reaction solution kept in the small vial to result in the precipitation of the insoluble brown solid [PPN][FeA C H T U N G T R E N N U N G (PyPepS) 2 ] (4) (0.177 g, 84 %) characterized by IR (n CO = 1677 cm À1 (s) (CH 3 CN)) and UV/Vis (438, 520, 880 nm (DMF)). The upper solution (THF/hexane) was dried under vacuum to obtain carbazole as characterized by 1 H NMR spectroscopy.…”

Synthesis of dinitrosyl iron complexes (DNICs) with intramolecular hydrogen bonding

“…Darensbourg et al employed N 2 S 2 ligands mimicking the Cys-X-Cys motif to show that Fe(NO) 2 acts as an unit bound by different thiolate ligands [8]. Recently, Liaw and coworkers synthesized a series of LMW DNICs, [S 5 Fe(NO) 2 ] À and [(SR) 2 Fe(NO) 2 ] À (SR = thiolates) and showed the NO-releasing ability of DNICs modulated by the coordinated thiolates [9][10][11][12][13]. In addition to the NO-releasing ability regulation afforded by the coordinated ligands, the effect of hydrogen bonding commonly found in biology may further tune NO release.…”