Structural comparison of alkylated derivatives of (bmmp-dmed)Ni and (bmmp-dmed)Zn

Grapperhaus, Craig A.; Mullins, Christopher S.; Mashuta, Mark S.

doi:10.1016/j.ica.2004.09.035

Cited by 13 publications

(23 citation statements)

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“…The XANES spectrum shows a resolved maximum near 8336 eV that is associated with a 1s → 4p z electronic transition that is diagnostic for four-coordinate planar coordination, and is also observed for dithionite-reduced WT-NiSOD , The expected peak associated with a 1s → 3d transition was not observed; however, it has very low intensity in many 4-coordinate complexes, including some where it is not detected . EXAFS arising from first-coordination sphere scattering atoms was best fit with 2 N-donor atoms @ 1.98(2) Å and 2 S-donor atoms @ 2.14(2) Å (see SI) and is similar to dithionite-reduced WT-NiSOD (NiN = 1.91(1) Å; NiS = 2.160(4) Å), only with a slightly longer average NiN distance, as well as to the distances found in planar NiN 2 S 2 complexes (NiN = 1.90–1.99 Å; NiS = 2.14–2.20 Å). , …”

Section: Resultsmentioning

confidence: 91%

“…31 EXAFS arising from first-coordination sphere scattering atoms was best fit with 2 N-donor atoms @ 1.98(2) Å and 2 S-donor atoms @ 2.14(2) Å (see SI) and is similar to dithionite-reduced WT-NiSOD (NiN = 1.91(1) Å; NiS = 2.160(4) Å), 9 only with a slightly longer average NiN distance, as well as to the distances found in planar NiN 2 S 2 complexes (NiN = 1.90− 1.99 Å; NiS = 2.14−2.20 Å). 32,33 3.3. Electronic Structure.…”

Section: Resultsmentioning

confidence: 99%

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A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site

Campeciño

Dudycz

Tumelty³

et al. 2015

J. Am. Chem. Soc.

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Computational investigations have implicated the amidate ligand in nickel superoxide dismutase (NiSOD) in stabilizing Ni-centered redox catalysis and in preventing cysteine thiolate ligand oxidation. To test these predictions, we have used an experimental approach utilizing a semisynthetic scheme that employs native chemical ligation of a pentapeptide (HCDLP) to recombinant S. coelicolor NiSOD lacking these N-terminal residues, NΔ5-NiSOD. Wild-type enzyme produced in this manner exhibits the characteristic spectral properties of recombinant WT-NiSOD and is as catalytically active. The semisynthetic scheme was also employed to construct a variant where the amidate ligand was converted to a secondary amine, H1*-NiSOD, a novel strategy that retains a backbone N-donor atom. The H1*-NiSOD variant was found to have only ∼1% of the catalytic activity of the recombinant wild-type enzyme, and had altered spectroscopic properties. X-ray absorption spectroscopy reveals a four-coordinate planar site with N2S2-donor ligands, consistent with electronic absorption spectroscopic results indicating that the Ni center in H1*-NiSOD is mostly reduced in the as-isolated sample, as opposed to 50:50 Ni(II)/Ni(III) mixture that is typical for the recombinant wild-type enzyme. The EPR spectrum of as-isolated H1*-NiSOD accounts for ∼11% of the Ni in the sample and is similar to WT-NiSOD, but more axial, with gz < gx,y. (14)N-hyperfine is observed on gz, confirming the addition of the apical histidine ligand in the Ni(III) complex. The altered electronic properties and implications for redox catalysis are discussed in light of predictions based on synthetic and computational models.

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Section: Resultsmentioning

confidence: 91%

Section: Resultsmentioning

confidence: 99%

A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site

Campeciño

Dudycz

Tumelty³

et al. 2015

J. Am. Chem. Soc.

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“…In an effort to obtain insight into the S-alkylation mechanism of these Zn(II) metalloenzymes, the reactivity of synthetic mononuclear thiolate Zn II complexes has been investigated in numerous studies. − Generally, S-alkylation reactions can follow two different pathways: (i) a dissociative mechanism, in which the metal–sulfur bond is split, followed by a S N 2 reaction involving the free thiolate and (ii) an associative mechanism, in which the reaction occurs via a S N 2 reaction involving the bound thiolate. It has been demonstrated that for anionic tetrathiolate Zn complexes a dissociative mechanism is operative, , while for neutral thiolate Zn complexes and for the Ada protein an associative mechanism is most likely. − ,− …”

Section: Introductionmentioning

confidence: 99%

“…Even if none of the Ni thiolate-containing enzymes achieve S-oxygenation or S-alkylation reaction, synthetic mononuclear thiolate Ni complexes have also been extensively investigated because of their efficient reactions with dioxygen ,− or alkyl ,− transfer agent. It appears from these studies that series of mononuclear Ni II and Zn II thiolate complexes synthesized with the same ligand exhibit different reactivity toward S-alkylation.…”

Section: Introductionmentioning

confidence: 99%

Experimental and Computational Investigation of Thiolate Alkylation in Ni^II and Zn^II Complexes: Role of the Metal on the Sulfur Nucleophilicity

et al. 2011

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The biologically relevant S-alkylation reactions of thiolate ligands bound to a transition metal ion were investigated with particular attention paid to the role of the metal identity: Zn(II) versus Ni(II). The reactivity of two mononuclear diamine dithiolate Zn and Ni complexes with CH(3)I was studied. With the [ZnL] complex (1) (LH(2) = 2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1-diphenylethanethiolate)), a double S-methylation occurs leading to [ZnL(Me2)I(2)] (1(Me2)), while with [NiL] (2), only the mono-S-methylated product [NiL(Me)]I (2(Me)) is formed. Complexes 1 and 1(Me2) have been characterized by X-ray crystallography, while the structures of 2 and 2(Me) have been previously described. The kinetics of the first S-methylation reaction, investigated by (1)H NMR, is found to follow a second-order rate law, and the activation parameters, ΔH(‡) and ΔS(‡), are similar for both 1 and 2. S K-edge X-ray absorption spectroscopy measurements have been carried out on 1, 2, and 2(Me), and a TD-DFT approach was employed to interpret the data. The electronic structures of 1 and 2 calculated by DFT reveal that the thiolate-metal bond is predominantly ionic in 1 and covalent in 2. However, evaluation of the molecular electrostatic potential minima around the lone pairs of the thiolate sulfur atoms gives similar values for 1 and 2, suggesting a comparable nucleophilicity. The DFT-optimized structures of the mono-S-methylation products have been calculated for the Zn and Ni complexes. Molecular electrostatic potential analysis of these products shows that (i) the nucleophilicity of the remaining thiolate sulfur atom is partly quenched for the Ni complex while it is conserved in the Zn complex and, more importantly, (ii) that the accessibility for the methyl transfer agent to the remaining thiolate is favored for the mono-S-methylated Zn complex compared to the Ni one. This explains the absence of a double S-methylation process in the case of the Ni complex at room temperature.

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“…The significantly strong dπ-pπ interactions between metal and sulfur imparts distribution of spin density on metal and sulfur center. [42][43][44] The highly reactive thiyl radical is stabilized by the metal center in a controlled fashion leading to their exploitation as selective catalysts for the functionalization of unsaturated hydrocarbons.…”

Section: An Introduction To Metal-stabilized Thiyl Radicalsmentioning

confidence: 99%

Evaluating ligand assisted activation of small molecules through proton reduction and alcohol oxidation.

Jain¹

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Structural comparison of alkylated derivatives of (bmmp-dmed)Ni and (bmmp-dmed)Zn

Cited by 13 publications

References 36 publications

A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site

A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site

Experimental and Computational Investigation of Thiolate Alkylation in Ni^II and Zn^II Complexes: Role of the Metal on the Sulfur Nucleophilicity

Evaluating ligand assisted activation of small molecules through proton reduction and alcohol oxidation.

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Structural comparison of alkylated derivatives of (bmmp-dmed)Ni and (bmmp-dmed)Zn

Cited by 13 publications

References 36 publications

A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site

A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site

Experimental and Computational Investigation of Thiolate Alkylation in NiII and ZnII Complexes: Role of the Metal on the Sulfur Nucleophilicity

Evaluating ligand assisted activation of small molecules through proton reduction and alcohol oxidation.

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Product

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Experimental and Computational Investigation of Thiolate Alkylation in Ni^II and Zn^II Complexes: Role of the Metal on the Sulfur Nucleophilicity