Tsai-Te Lu

Relative Binding Affinity of Thiolate, Imidazolate, Phenoxide, and Nitrite Toward the {Fe(NO)2} Motif of Dinitrosyl Iron Complexes (DNICs): The Characteristic Pre-Edge Energy of {Fe(NO)2}9 DNICs

The synthesis, characterization, and transformation of the anionic {Fe(NO)(2)}(9) dinitrosyl iron complexes (DNICs) [(NO)(2)Fe(ONO)(2)](-) (1), [(NO)(2)Fe(OPh)(2)](-) (2), [(NO)(2)Fe(OPh)(C(3)H(3)N(2))](-) (3) (C(3)H(3)N(2) = imidazolate), [(NO)(2)Fe(OPh)(-SC(4)H(3)S)](-) (4), [(NO)(2)Fe(p-OPhF)(2)](-) (5), and [(NO)(2)Fe(SPh)(ONO)](-) (6) were investigated. The binding affinity of ligands ([SPh](-), [-SC(4)H(3)S](-), [C(3)H(3)N(2)](-), [OPh](-), and [NO(2)](-)) toward the {Fe(NO)(2)}(9) motif follows the ligand-displacement series [SPh](-) approximately [-SC(4)H(3)S](-) > [C(3)H(3)N(2)](-) > [OPh](-) > [NO(2)](-). The findings, the pre-edge energy derived from the 1s --> 3d transition in a distorted T(d) environment of the Fe center falling within the range of 7113.4-7113.8 eV for the anionic {Fe(NO)(2)}(9) DNICs, implicate that the iron metal center of DNICs is tailored to minimize the electronic changes accompanying changes in coordinated ligands. Our results bridging the ligand-substitution reaction study and X-ray absorption spectroscopy study of the electronic richness of the {Fe(NO)(2)}(9) core may point the way to understanding the reasons for natures choice of combinations of cysteine, histidine, and tyrosine in protein-bound DNICs and rationalize that most DNICs characterized/proposed nowadays are bound to the proteins almost through the thiolate groups of cysteinate/glutathione side chains in biological systems.

Discrimination of mononuclear and dinuclear dinitrosyl iron complexes (DNICs) by S K-edge X-ray absorption spectroscopy: insight into the electronic structure and reactivity of DNICs.

In addition to probing the formation of dinitrosyl iron complexes (DNICs) by the characteristic Fe K-edge pre-edge absorption energy ranging from 7113.4 to 7113.8 eV, the distinct S K-edge pre-edge absorption energy and pattern can serve as an efficient tool to unambiguously characterize and discriminate mononuclear DNICs and dinuclear DNICs containing bridged-thiolate and bridged-sulfide ligands. The higher Fe-S bond covalency modulated by the stronger electron-donating thiolates promotes the Fe → NO π-electron back-donation to strengthen the Fe-NO bond and weaken the NO-release ability of the mononuclear DNICs, which is supported by the Raman ν(Fe-NO) stretching frequency. The Fe-S bond covalency of DNICs further rationalizes the binding preference of the {Fe(NO)(2)} motif toward thiolates following the trend of [SEt](-) > [SPh](-) > [SC(7)H(4)SN](-). The relative d-manifold energy derived from S K-edge XAS as well as the Fe K-edge pre-edge energy reveals that the electronic structure of the {Fe(NO)(2)}(9) core of the mononuclear DNICs [(NO)(2)Fe(SR)(2)](-) is best described as {Fe(III)(NO(-))(2)}(9) compared to [{Fe(III)(NO(-))(2)}(9)-{Fe(III)(NO(-))(2)}(9)] for the dinuclear DNICs [Fe(2)(μ-SEt)(μ-S)(NO)(4)](-) and [Fe(2)(μ-S)(2)(NO)(4)](2-).

Anionic Roussin’s Red Esters (RREs) syn-/anti-[Fe(µ-SEt)(NO)2]2−: the Critical Role of Thiolate Ligands in Regulating the Transformation of RREs into Dinitrosyl Iron Complexes and the Anionic RREs

The anionic syn-/ anti-[Fe(mu-SEt)(NO) 2] 2 (-) ( 2a) were synthesized and characterized by IR, UV-vis, EPR, and X-ray diffraction. The geometry of the [Fe(mu-S) 2Fe] core is rearranged in going from [{Fe(NO) 2} (9)-{Fe(NO) 2} (9)] Roussins red ester [Fe(mu-SEt)(NO) 2] 2 ( 1a) (Fe...Fe distance of 2.7080(5) A) to the [{Fe(NO) 2} (9)-{Fe(NO) 2} (10)] complex 2a (Fe...Fe distance of 2.8413(6) A) to minimize the degree of Fe...Fe interaction to stabilize complex 2a. On the basis of X-ray absorption (Fe K- and L-edge), EPR and SQUID, complex 2a is best described as the anionic [{Fe(NO) 2} (9)-{Fe(NO) 2} (10)] Roussins red ester with the fully delocalized mixed-valence core. The complete bridged-thiolate cleavage yielded DNIC [(EtS) 2Fe(NO) 2] (-) ( 3a) in the reaction of 2 equiv of [EtS] (-) and complex 1a, whereas reaction of 2 equiv of [(t)BuS] (-) with [Fe(micro-S (t)Bu)(NO) 2] 2 (1b) gave DNIC [((t)BuS) 2Fe(NO) 2] (-) (3b) and the anionic Roussins red ester [Fe(mu-S (t)Bu)(NO) 2] 2 (-) (2b) through bridged-thiolate cleavage in combination with reduction. In contrast to the inertness of DNIC 3b toward complex 1b, nucleophile DNIC 3a induces the reduction of complex 1a to produce the anionic Roussins red ester 2a. Interestingly, dissolution of complex 3a in MeOH at 298 K finally led to the formation of a mixture of complexes 2a and 3a, in contrast to the dynamic equilibrium of complexes 3b and 1b observed in dissolution of complex 3b in MeOH. These results illustrate the aspect of how the steric structures of nucleophiles ([EtS] (-) vs [ (t)BuS] (-) and [(EtS) 2Fe(NO)2](-) vs [((t)BuS) 2Fe(NO)2] (-)) function to determine the reaction products.

Anionic Mixed Thiolate-Sulfide-Bridged Roussin's Red Esters [(NO)2Fe(μ-SR)(μ-S)Fe(NO)2]- (R = Et, Me, Ph): A Key Intermediate for Transformation of Dinitrosyl Iron Complexes (DNICs) to [2Fe-2S] Clusters

Transformations of dinitrosyl iron complex (DNIC) [(NO)(2)Fe(SEt)(2)](-) and the anionic Roussins red ester (RRE) [(NO)(2)Fe(mu-SEt)(2)Fe(NO)(2)](-) into [2Fe-2S] clusters facilitated by HSCPh(3)/Me(2)S(3) and [Fe(SEt)(4)](-), respectively, via an intermediate anionic mixed thiolate-sulfide-bridged RRE [(NO)(2)Fe(mu-SEt)(mu-S)Fe(NO)(2)](-) through the reassembling process ([(NO)(2)Fe(SEt)(2)](-) (2)/[(NO)(2)Fe(mu-SEt)(2)Fe(NO)(2)](-) (4) --> [(NO)(2)Fe(mu-SEt)(mu-S)Fe(NO)(2)](-) (3-Et) --> [(NO)(2)Fe(mu-S)(2)Fe(NO)(2)](2-) (5) --> [(SEt)(2)Fe(mu-S)(2)Fe(SEt)(2)](2-) (1)) were demonstrated. The anionic mixed thiolate-sulfide-bridged RRE 3-Et was characterized by IR, UV-vis, electron paramagnetic resonance, (1)H NMR, cyclic voltammetry, and single-crystal X-ray diffraction. In contrast to the nucleophilicity displayed by complex 2, the inertness of [(NO)(2)Fe(SPh)(2)](-) toward HSCPh(3) implicates how the reducing ability of the coordinated thiolates of DNICs modulate the release of sulfide from HSCPh(3) via reduction and the conversion of DNICs into the anionic mixed sulfide-thiolate-bridged complex. The reversible interconversion between complex 3-Et and complex [(NO)(2)Fe(mu-SPh)(mu-S)Fe(NO)(2)](-) (3-Ph) via protonation and a bridged-thiolate exchange reaction, respectively, demonstrates that the [{Fe(NO)(2)}(9)-{Fe(NO)(2)}(9)] motif displays a preference for the stronger electron-donating alkylthiolate-bridged ligand over the phenylthiolate-bridged ligand. This study may signify that the anionic mixed thiolate-sulfide-bridged RREs act as a key intermediate in the transformation of DNICs into [2Fe-2S] clusters. Also, the thiolate-coordinate DNICs serve as not only the thiolate/electron carrier activating the incorporation of sulfide of HSCPh(3) (Me(2)S(3)) to assemble the [Fe(mu-S)(2)Fe] core but also the Fe source in the biosynthesis of the [2Fe-2S] and [4Fe-4S] iron-sulfur clusters.

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

Release of the distinct NO redox-interrelated forms (NO(+), *NO, and HNO/NO(-)), derived from reaction of the dinitrosyl iron complex (DNIC) [(NO)(2)Fe(C(12)H(8)N)(2)](-) (1) (C(12)H(8)N=carbazolate) and the substitution ligands (S(2)CNMe(2))(2), [SC(6)H(4)-o-NHC(O)(C(5)H(4)N)](2) ((PyPepS)(2)), and P(C(6)H(3)-3-SiMe(3)-2-SH)(3) ([P(SH)(3)]), respectively, was demonstrated. In contrast to the reaction of (PyPepS)(2) and DNIC 1 in a 1:1 stoichiometry that induces the release of an NO radical and the formation of complex [PPN][Fe(PyPepS)(2)] (4), the incoming substitution ligand (S(2)CNMe(2))(2) triggered the transformation of DNIC 1 into complex [(NO)Fe(S(2)CNMe(2))(2)] (2) along with N-nitrosocarbazole (3). The subsequent nitrosation of N-acetylpenicillamine (NAP) by N-nitrosocarbazole (3) to produce S-nitroso-N-acetylpenicillamine (SNAP) may signify the possible formation pathway of S-nitrosothiols from DNICs by means of transnitrosation of N-nitrosamines. Protonation of DNIC 1 by [P(SH)(3)] triggers the release of HNO and the generation of complex [PPN][Fe(NO)P(C(6)H(3)-3-SiMe(3)-2-S)(3)] (5). In a similar fashion, the nucleophilic attack of the chelating ligand P(C(6)H(3)-3-SiMe(3)-2-SNa)(3) ([P(SNa)(3)]) on DNIC 1 resulted in the direct release of [NO](-) captured by [((15)NO)Fe(SPh)(3)](-), thus leading to [((15)NO)((14)NO)Fe(SPh)(2)](-). These results illustrate one aspect of how the incoming substitution ligands ((S(2)CNMe(2))(2) vs. (PyPepS)(2) vs. [P(SH)(3)]/[P(SNa)(3)]) in cooperation with the carbazolate-coordinated ligands of DNIC 1 function to control the release of NO(+), *NO, or [NO](-) from DNIC 1 upon reaction of complex 1 and the substitution ligands. Also, these results signify that DNICs may act as an intermediary of NO in the redox signaling processes by providing the distinct redox-interrelated forms of NO to interact with different NO-responsive targets in biological systems.

New members of a class of dinitrosyliron complexes (DNICs): the characteristic EPR signal of the six-coordinate and five-coordinate {Fe(NO)2}9 DNICs.

Compared to the tetrahedral {Fe(NO)(2)}(9) dinitrosyliron complexes (DNICs) [(L)(2)Fe(NO)(2)](-) (L=SR, imidazolate) displaying EPR signal g=2.03, the newly synthesized six-/five-coordinate {Fe(NO)(2)}(9) DNICs [(TPA)Fe(NO)(2)][BF(4)] (1-TPA) (TPA=2-[CH(2)-C(5)H(4)N](3)N), [((iPr)PDI)Fe(NO)(2)][BF(4)] (2-(iPr)PDI) ((iPr)PDI=2,6-[2,6-(i)Pr(2)-C(6)H(3)N=CMe](2)C(5)H(3)N) and [(PyImiS)Fe(NO)(2)] (4-PyImiS) (PyImiS=2-[2-(C(5)H(4)N)CMe=N]C(6)H(4)S) exhibit the distinct EPR signal g=2.015-2.018. The Fe K-edge pre-edge energy (7113.4-7113.6eV) derived from the 1s→3d transition in the octahedral and square-pyramidal environment of the Fe center, falling within the range of 7113.4-7113.8eV for the tetrahedral {Fe(NO)(2)}(9) DNICs, implicates that the iron cores of DNICs 1-TPA, 2-(iPr)PDI and 4-PyImiS are tailored to minimize the electronic changes accompanying changes in coordination geometry. In contrast to the thermally stable 1-TPA, 2-(iPr)PDI and 4-PyImiS, the spontaneous transformation of the proposed thermally unstable five-coordinate {Fe(NO)(2)}(9) DNIC [(PyPepS-H)Fe(NO)(2)](-) (6-PyPepS) (PyPepS-H=[SC(6)H(4)-o-NC(O)(C(5)H(4)N)]) into the {Fe(NO)}(7)-{Fe(NO)}(7) [(μ-PyPepS-H)Fe(NO)](2) (7) along with release of nitroxyl demonstrates that the distinct electron-donating ability of the coordinated ligands ([PyPepS-H]>[PyImiS]~[TPA]>[(iPr)PDI]) regulates the stability and geometric structure of {Fe(NO)(2)}(9) DNICs. This study also shows the aspect of how the geometric structure of {Fe(NO)(2)}(9) DNICs imposed by the electron-donating ability and conformation of the coordinated ligands (tridentate [(iPr)PDI] vs tridentate [PyImiS] vs tetradentate [TPA] vs tridentate [PyPepS-H] vs bidentate [SC(6)H(4)-o-NC(O)Ph](2-)) regulates the Fe-NO bonding of {Fe(NO)(2)}(9) DNICs and presumably the release of nitroxyl from DNICs.

Transformation of dinitrosyl iron complexes [(NO)2Fe(SR)2]- (R = Et, Ph) into [4Fe-4S] Clusters [Fe4S4(SPh)4]2-: relevance to the repair of the nitric oxide-modified ferredoxin [4Fe-4S] clusters.

Transformation of dinitrosyl iron complexes (DNICs) [(NO)(2)Fe(SR)(2)](-) (R = Et, Ph) into [4Fe-4S] clusters [Fe(4)S(4)(SPh)(4)](2-) in the presence of [Fe(SPh)(4)](2-/1-) and S-donor species S(8) via the reassembling process ([(NO)(2)Fe(SR)(2)](-) --> [Fe(4)S(3)(NO)(7)](-) (1)/[Fe(4)S(3)(NO)(7)](2-) (2) --> [Fe(4)S(4)(NO)(4)](2-) (3) --> [Fe(4)S(4)(SPh)(4)](2-) (5)) was demonstrated. Reaction of [(NO)(2)Fe(SR)(2)](-) (R = Et, Ph) with S(8) in THF, followed by the addition of HBF(4) into the mixture solution, yielded complex [Fe(4)S(3)(NO)(7)](-) (1). Complex [Fe(4)S(3)(NO)(7)](2-) (2), obtained from reduction of complex 1 by [Na][biphenyl], was converted into complex [Fe(4)S(4)(NO)(4)](2-) (3) along with byproduct [(NO)(2)Fe(SR)(2)](-) via the proposed [Fe(4)S(3)(SPh)(NO)(4)](2-) intermediate upon treating complex 2 with 1.5 equiv of [Fe(SPh)(4)](2-) and the subsequent addition of 1/8 equiv of S(8) in CH(3)CN at ambient temperature. Complex 3 was characterized by IR, UV-vis, and single-crystal X-ray diffraction. Upon addition of complex 3 to the CH(3)CN solution of [Fe(SPh)(4)](-) in a 1:2 molar ratio at ambient temperature, the rapid NO radical-thiyl radical exchange reaction between complex 3 and the biomimetic oxidized form of rubredoxin [Fe(SPh)(4)](-) occurred, leading to the simultaneous formation of [4Fe-4S] cluster [Fe(4)S(4)(SPh)(4)](2-) (5) and DNIC [(NO)(2)Fe(SPh)(2)](-). This result demonstrates a successful biomimetic reassembly of [4Fe-4S] cluster [Fe(4)S(4)(SPh)(4)](2-) from NO-modified [Fe-S] clusters, relevant to the repair of DNICs derived from nitrosylation of [4Fe-4S] clusters of endonuclease III back to [4Fe-4S] clusters upon addition of ferrous ion, cysteine, and IscS.

Molecular structure of the red isomeric (5, 7, 7, 12, 14, 14-hexamethyl-1, 4, 8, 11-tetra-azacyclotetradeca-4, 11-diene) copper(II) perchlorate☆

Abstract A red crystal of [Cu(trans-[14] diene)]2+ (ClO4−)2 was crystallized from a methanol-water or acetone-water solution by slow evaporation of the solvent. This crystal has the chemical formula C16H32N4Cu(II) (ClO4)2, FW = 542.92. Using a Syntex P 1 auto-diffractometer, the crystal data were determined: monoclinic, P2l/c, a = 10.487(9), b = 16.971(15), c = 13.855(13) A , β = 105.17(7)°, Z = 4, V = 2379.9 A 3 , D c = 1.52, D m = 1.52 g cm −3 (by flotation), μ = 38.23 cm−1 for CuKα. The structure was mainly solved by heavy atom method and difference Fourier synthesis. The hydrogen atoms attached to the nitrogen atoms in the trans-diene are on the same side (cis) of the macrocyclic plane. The two perchlorate ions form hydrogen bonds with the NH groups and therefore are located in the cis configuration as hydrogen atoms are. The copper atom and four nitrogen atoms are coplanar within 0.05 A.