Probing the Influence of Local Coordination Environment on the Properties of Fe-Type Nitrile Hydratase Model Complexes

Jackson, Henry L.; Shoner, Steven C.; Rittenberg, Durrell K.; Cowen, J. A.; Lovell, Scott; Barnhart, David M.; Kovacs, Julie A.

doi:10.1021/ic001271d

Cited by 37 publications

(80 citation statements)

References 57 publications

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“…This is most likely caused by H-bonding interactions between the protic solvent and thiolate lone-pairs. 76 The relative intensities of the two bands in Figure 6 are in contrast to the electronic absorption properties of the cupredoxins (blue copper proteins). Cupredoxins display a significantly more intense transition (ε ~ 3000 -6000 M −1 cm −1 ) near 600 nm, and a much less intense (ε < 1000 M −1 cm −1 ) transition near 400 nm.…”

Section: A Perturbed Green Copper Protein Site Analoguementioning

confidence: 99%

Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [M^II(S^Me2N₄(tren))]⁺ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable Cu^II−Thiolate

et al. 2007

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A series of five-coordinate thiolate-ligated complexes [M II (tren)N 4 S Me2 ] + (M = Mn, Fe, Co, Ni, Cu, Zn; tren = tris(2-aminoethyl)amine) are reported, and their structural, electronic, and magnetic properties are compared. Isolation of dimeric [Ni II (SN 4 (tren)-RS dang )] 2 ("dang"= dangling, uncoordinated thiolate supported by H-bonds) using the less bulky [(tren)N 4 S] 1− ligand, pointed to the need for gem-dimethyls adjacent to the sulfur in order to sterically prevent dimerization. All of the gem-dimethyl derivatized complexes are monomeric, and with the exception of [Ni II (S Me2 N 4 (tren)] + , are isostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. The nickel complex uniquely adopts an approximately ideal square pyramidal geometry, and resembles the active site of Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structures are observed. The M II -S thiolate bonds systematically decrease in length across the series (Mn-S > Fe-S > Co-S > Ni-S ~ Cu-S < Zn-S) with exceptions occurring upon the occupation of σ* orbitals. The copper complex, [Cu II (S Me2 N 4 (tren)] + , represents a rare example of a stable Cu II -thiolate, and models the perturbed "green" copper site of nitrite reductase. In contrast to the intensely colored, low-spin Fe (III)-thiolates, the M(II)-thiolates described herein are colorless to moderately colored, and highspin (in cases where more than one spin-state is possible), reflecting the poorer energy match between the metal d-and sulfur-orbitals upon reduction of the metal ion. As the d-orbitals drop in energy proceeding across the across the series M 2+ (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metal charge transfer transition moves into the visible region, and the redox potentials cathodically shift. The reduced M +1 oxidation state is only accessible with copper, and the more oxidized M +4 oxidation state is only accessible for manganese.

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Section: A Perturbed Green Copper Protein Site Analoguementioning

confidence: 99%

Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [M^II(S^Me2N₄(tren))]⁺ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable Cu^II−Thiolate

et al. 2007

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“…45,56 Like the NHase active site, 7,11 complex 3 is low-spin (S = ½) over a wide temperature range, stabilized in the 3+ oxidation state (E 1/2 = −1.01 V vs SCE), and intense green in color (λ max = 718 (2500) nm). A low spin state is unexpected for non-heme iron, especially when ligated by π-donors such as RS − , which tend to decrease 10Dq.…”

Section: Synthesis and Structure Of Singly Oxygenated [Fe III -(Adit)mentioning

confidence: 99%

“…The blue-shift caused by oxygen atom addition is similar in direction to that induced by Hbonding between the thiolates of 3 and protic solvents; 56 however, it is considerably larger in magnitude for oxygen atom addition (3463.7 cm −1 (9.9 kcal/mol) versus H-bonding (502.4 cm −1 (1.44 kcal/mol); Table 5). 56 …”

Section: Changes To the Electronic Structure Upon Single Oxygen Atom mentioning

confidence: 99%

“…As shown by the redox potential obtained from the CV of Figure 8, the oxygenated sulfenate/thiolate ligand stabilizes iron in the 3+ oxidation state, as does the dithiolate ligand of 3 (E 1/2 = −1.01 vs SCE). 45,56 Although there is a slight cathodic shift upon oxygen atom addition, the magnitude of this shift (75 mV = 1.73 kcal/mol) is less than one might have anticipated, had there not been a second …”

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“…Two of the three coordinated cysteinate sulfurs are oxidized (post-translationally modified) in NHase -one to a sulfenic acid ( 114 Cys-S-(OH)) and the other to a sulfinate 112 CysSO 2 −.3, 21 The third cysteinate sulfur, which is trans to the inhibitor/substrate binding site and less accessible to solvent, remains unmodified. 3, S-sensitive vibrations, attributed to the doubly and singly oxygenated ν S=O stretches, are seen in the FT-IR spectra of NHase (from Rhodococcus N-771) 24 at 1140, 1030, and 910 cm −1 , which shift slightly upon deuteration, providing evidence that at least one of the sulfenate or sulfinate oxygens is either protonated or H-bonded, perhaps to the conserved Arg 56 and/or Arg 141 residues. One would expect a metal-bound sulfenate oxygen (RS-(OH)) to be highly acidic.…”

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How Does Single Oxygen Atom Addition Affect the Properties of an Fe−Nitrile Hydratase Analogue? The Compensatory Role of the Unmodified Thiolate

et al. 2006

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Nitrile hydratase (NHase) is one of a growing number of enzymes shown to contain posttranslationally modified cysteine sulfenic acids (Cys-SOH). Cysteine sulfenic acids have been shown to play diverse roles in cellular processes, including transcriptional regulation, signal transduction, and the regulation of oxygen metabolism and oxidative stress responses. The function of the cysteine sulfenic acid coordinated to the iron active site of NHase is unknown. Herein we report the first example of a sulfenate-ligated iron complex, [Fe III (ADIT)(ADIT-O)] + (5), and compare its electronic and magnetic properties with those of structurally related complexes in which the sulfur oxidation state and protonation state have been systematically altered. Oxygen atom addition was found to decrease the unmodified thiolate Fe-S bond length and blue-shift the ligand-to-metal charge-transfer band (without loss of intensity). S K-edge X-ray absorption spectroscopy and density functional theory calculations show that, although the modified RS-O − fragment is incapable of forming a π bond with the Fe III center, the unmodified thiolate compensates for this loss of π bonding by increasing its covalent bond strength. The redox potential shifts only slightly (75 mV), and the magnetic properties are not affected (the S = ½ spin state is maintained). The coordinated sulfenate S-O bond is activated and fairly polarized (S + -O − ). Addition of strong acids at low temperatures results in the reversible protonation of sulfenateligated 5. An X-ray structure demonstrates that Zn 2+ binds to the sulfenate oxygen to afford [Fe III HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript unmodified NHase thiolate, involving its ability to "tune" the electronics in response to protonation of the sulfenate (RS-O − ) oxygen and/or substrate binding, is discussed.Nitrile hydratases (NHases) are non-heme iron enzymes that convert nitriles to less toxic amides cleanly, and rapidly, under mild conditions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] It is unusual for a hydrolytic metalloenzyme to incorporate iron, as opposed to zinc, 17,18 presumably because, unlike other metal ions, Zn 2+ is not complicated by redox chemistry. Iron, on the other hand, can promote unwanted side reactions with dioxygen (i.e., Fenton chemistry involving OH · radicals) upon reduction to the Fe 2+ oxidation state. 19,20 The NHase iron site is, however, redox inactive and stabilized in the 3+ oxidation state. The stabilization of Fe 3+ is accomplished by placing the iron in an electron-rich environment consisting of five anionic ligands-two deprotonated peptide amides and three cysteinates (Figure 1). Two of the three coordinated cysteinate sulfurs are oxidized (post-translationally modified) in NHase -one to a sulfenic acid ( 114 Cys-S-(OH)) and the other to a sulfinate 112 CysSO 2 −.3,21 The third cysteinate sulfur, which is trans to the inhibitor/substrate binding site and less accessible to solvent, remains unmodifie...

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Nitrile Hydratase

Shearer¹,

Kovacs²

2002

Encyclopedia of Catalysis

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Nitrile hydratases (NHases) are metalloenzymes, found in soil bacteria, first isolated from toxic wate sites, which catalyze the hydration of nitrile to amides. These contain either a mononuclear non‐heme Fe 3+ or a non‐corrinoid Co 3+ . Initial spectroscopic studies demonstrated that both the metal centers are low spin ( S = 1/2 for Fe 3+ and S = 0 Co 3+ ). Two crystal structures of Fe‐NHase from Rhodococcus R312 have shown that the iron center is ligated by three cysteinates in a fac configuration, two amide nitrogens from the peptide backbone, and a hydroxide (active form) or NO (inactive form) in a site trans to a cysteinate. The electronic spectrum of the active form of Fe‐NHase is dominated by an intense π‐sulfur‐to‐metal charge transfer band near 700 nm. The EPR and electronic absorption spectra of Fe‐NHase are both substrate‐ and pH‐dependent. NHase has been used industrially in the multi‐kiloton production of commodity amides, has been utilized to a limited extent as a reagent for organic synthesis, and may find use in the field of chemical waste treatment. Model compounds, in combination with biochemical and biophysical techniques, have proven useful in answering fundamental questions concerning NHase, but several key issues remain unresolved. For examle, the mechanism of NHase catalysis remains to be elucidated, and the involvement of low spin, rather than the more reactive high spin metal ions (Co 3+ , Fe 3+ ) in these reactions has yet to be explained.

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Probing the Influence of Local Coordination Environment on the Properties of Fe-Type Nitrile Hydratase Model Complexes

Cited by 37 publications

References 57 publications

Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [M^II(S^Me2N₄(tren))]⁺ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable Cu^II−Thiolate

Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [M^II(S^Me2N₄(tren))]⁺ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable Cu^II−Thiolate

How Does Single Oxygen Atom Addition Affect the Properties of an Fe−Nitrile Hydratase Analogue? The Compensatory Role of the Unmodified Thiolate

Nitrile Hydratase

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Probing the Influence of Local Coordination Environment on the Properties of Fe-Type Nitrile Hydratase Model Complexes

Cited by 37 publications

References 57 publications

Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [MII(SMe2N4(tren))]+ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable CuII−Thiolate

Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [MII(SMe2N4(tren))]+ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable CuII−Thiolate

How Does Single Oxygen Atom Addition Affect the Properties of an Fe−Nitrile Hydratase Analogue? The Compensatory Role of the Unmodified Thiolate

Nitrile Hydratase

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Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [M^II(S^Me2N₄(tren))]⁺ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable Cu^II−Thiolate

Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [M^II(S^Me2N₄(tren))]⁺ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable Cu^II−Thiolate