Mechanism of O-Atom Transfer from Nitrite: Nitric Oxide Release at Copper(II)

Molly Stau ﬀ er, Zeinab Sakhaei, Christine Greene, Pokhraj Ghosh, Je ﬀ ery A. Bertke,

Forum Article

Mechanism of O‑Atom Transfer from Nitrite: Nitric Oxide Release at

Copper(II)

and Timothy H. Warren *

Cite This: https://doi.org/10.1021/acs.inorgchem.1c00625

Read Online

ACCESS

Metrics & More

Article Recommendations

sı Supporting Information

ABSTRACT: Nitric oxide (NO) is a key signaling molecule in health and disease.

While nitrite acts as a reservoir of NO activity, mechanisms for NO release require

further understanding. A series of electronically varied β-diketiminatocopper(II) nitrite

complexes [Cu ](κ -O N) react with a range of electronically tuned triarylphosphines

PAr that release NO with the formation of OPAr . Second-order rate constants are

largest for electron-poor copper(II) nitrite and electron-rich phosphine pairs.

Computational analysis reveals a transition-state structure energetically matched with

experimentally determined activation barriers. The production of NO follows a pathway

that involves nitrite isomerization at Cu from κ -O N to κ -NO followed by O-atom

transfer (OAT) to form OPAr and [Cu ]-NO that releases NO upon PAr binding

at Cu to form [Cu ]-PAr . These ﬁndings illustrate important mechanistic

considerations involved in NO formation from nitrite via OAT.

INTRODUCTION

The oldest of these models, which dates to 1979, involves a

cobalt nitro complex supported by a dianionic tetraazacyle that

■

Nitric oxide (NO) serves as a signaling molecule involved in a

wide array of physiological functions, such as its role as a

vasodilator connected with blood pressure and cardiovascular

undergoes reduction by PPh to generate the corresponding

cobalt nitrosyl and OPPh . Most model complexes have

focused on iron/cobalt porphyrin complexes using a variety of

health. While endothelial nitrogen oxide synthase (NOS)

4−33

O-atom acceptors,

although other coordination motifs

produces NO from arginine, this enzyme loses activity when

the oxygen levels become low. Tightly regulated reduction of

nitrite to form NO can compensate for this loss of NOS

activity under hypoxia.

cytochrome c oxidase, and xanthine oxidase are each able to

act as nitrite reductases.

Cu-containing nitrite reductases are common in soil bacteria

where they perform a key denitriﬁcation step in the nitrogen

cycle by converting nitrite to NO. In mammalian biology, Cu

has been implicated in the reverse transformation, converting

NO to nitrite at the redox-active Cu site of ceruloplasmin.

Interestingly, a recent report indicates that the ubiquitous

carbonic anhydrase II enzyme may act as a nitrite reductase

when complexed with Cu rather than Zn, generating NO.

While one-electron reduction of nitrite to NO may occur in

2,21,34,35

have also been examined (Figure 1B).

These synthetic

models typically possess a nitrite ion bound through the N

−5

The enzymes deoxymyoglobin,

atom. As shown by computational studies with an iron

porphyrin system, [M](κ -NO ) structures can enable smooth

−9

conversion to a metal nitrosyl [M]-NO upon OAT with SMe

⧧

with modest barriers, ΔG (298 K), calculated in either the

−

absence (10.4 kcal mol ) or presence of an axial ligand L

−

(

17.8 kcal mol ; L = pyridine; Figure 1C).

Two recent reports document OAT from nitrite at Cu that

12,21

results in NO loss via OAT to PPh with reduction to Cu .

Importantly, these complexes each possess O-bound nitrite

with the [Cu ](κ -O N) binding mode. To better understand

OAT from nitrite at Cu, we examine herein the electronic role

of the Cu center and incoming O-atom acceptor through

kinetic studies supported by computational analysis to develop

the presence of proton sources to generate water, O-atom

transfer (OAT) pathways also exist. The former has been

3,14

a reaction pathway for NO release from nitrite at Cu .

well characterized in biological

and biomimetic sys-

5−19

tems;

however, OAT to nucleophiles is less stud-

Potential O-atom acceptors such as thiols RSH

,12,20−22

Special Issue: Renaissance in NO Chemistry

Received: March 1, 2021

ied.

and dialkyl sulﬁdes RSR′ are readily biologically available and

may be oxidized to sulfenic acids RS(O)H and sulfoxides

RS(O)R′ (Figure 1A).

A range of Fe, Co, and Cu biomimetic complexes

demonstrate OAT with a range of nucleophiles (Figure 1).

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Forum Article

Scheme 1. Synthesis of Copper(II) Nitrite Complexes 1−4

and X-ray Structure of Complex 2

Table 1. Reduction Potentials and OAT Activation

Parameters with P(Ar )₃for Copper(II) Nitrites 1−4

⧧

−1

⧧

E₁_/₂(V vs NHE)

ΔH

ΔS (cal

ΔG (298 K)

−1

[Cu]

in THF

(kcal mol⁻¹)

mol

)

(kcal mol

)

0.33

0.30

−0.02

−0.11

4.6 ± 0.7

5.7 ± 0.5

13.9 ± 0.5

13.1 ± 0.2

−38.5 ± 3.1

−34.5 ± 2.4

−13.3 ± 1.8

−18.5 ± 0.8

16.0 ± 1.2

16.0 ± 0.9

17.9 ± 0.8

18.6 ± 0.3

optically silent [Cu ]-PAr complexes (Scheme 2). The

reaction of 1 with 2 equiv of P(Ar )₃resulted in a yield of

2% [Cl NN ]Cu−P(Ar )₃by F NMR (Figure S19).

Demonstrating NO release, copper(II) nitrite 1 reacts with 2

equiv of PPh₃or P(Ar )₃in toluene to provide the

corresponding [Cu ]-PAr complex. Capture of NO by the

cobalt(II) porphyrin meso-tetra(4-methoxyphenyl)-

porphyrincobalt(II) [T(OMe)PP]Co gives the diamagnetic

Figure 1. (A) OAT reactions of metal complexes with nitrite. (B)

Metal scaﬀolds supporting OAT from nitrite. (C) Calculated OAT to

[T(OMe)PP]Co(NO) amenable to H NMR analysis, which

shows 64% and 59% yield respectively for PPh and P(Ar )₃

the SMe transition state.

(Scheme S2). Consistent with the 1:2 [Cu ](κ -O N)/PAr

2 3

stoichiometry, the reaction of [Cl NN ]Cu(κ -O N) (1) with

RESULTS AND DISCUSSION

■

1 equiv of P(Ar ) reduces the yields of [Cl NN ]Cu−

We previously demonstrated that the β-diketiminatocopper(II)

P(Ar )₃and NO to 46% and 51%, respectively. Because the

nitrite [ Pr NN ]Cu (κ -O N) reacts with PPh to release

NO that is released can react with copper(I) β-diketiminates

NO with the formation of [ Pr NN ]Cu (PPh ) and

[

Cu ] to reform copper(II) nitrites such as [Cu ](O N)[Cu ]

OPPh . To examine the electronic roles of the Cu center

and N O, this may represent a pathway that competes with

the trapping of [Cu ] by PAr .

and the phosphine that serves as the O-atom acceptor, we

sought to employ a range of sterically similar, yet electronically

diﬀerent, β-diketiminatocopper(II) nitrite complexes

Scheme 2. NO Release from Cu -Bound Nitrite 1

[

Cu ](κ -O N) and para-substituted triarylphosphines PAr .

To modulate the electronic environment of the copper(II)

nitrite complexes with minimal steric impact, we employed β-

diketiminate ligands with backbone substituents X = Me or

CF along with N-aryl o-Cl or o-Me substituents. The reaction

of copper(I) β-diketiminates [Cu ] with AgNO serves as a

reliable route to the corresponding copper(II) nitrites

To establish the rate law, we followed the reaction of

[

Cu ](κ -O N) (1−4; Scheme 1).

[

Me NN ]Cu(κ -O N) (2; ca. 2.0 mM) with excess P(Ar⁾3

Cyclic voltammetry experiments of the copper(II) nitrites

2 F 2

−4 performed in tetrahydrofuran (THF) reveal quasi-

in toluene by UV−vis spectroscopy by monitoring the loss of

reversible waves that correspond to a range of reduction

potentials that span 0.33 V (vs NHE) for 1 (backbone CF and

the band at λ = 600 nm for 2. We chose the electron-poor

max

phosphine P(Ar )₃to slow the reaction enough to enable a

study by straightforward UV−vis kinetics at −60 °C in the

presence of 25−50 equiv of phosphine. These studies reveal

N-aryl Cl substituents) to −0.11 V (vs NHE) for 4 (backbone

Me and N-aryl Me substituents) (Table 1). Copper(II) nitrite

complexes 1−4 are dark green in color, possessing UV−vis

pseudo-ﬁrst-order decay of 2 with observed rate constants k

obs

spectra in toluene with λ values around 600 nm. This can be

that vary linearly with [P(Ar ) ] (Figures S25 and S26) to

max

used to follow NO release upon reaction with PAr , which

results in reduction of the Cu center to give essentially

give the overall second-order rate law k[Cu(O N)][P(Ar )₃],

−

−1

where k(−60 °C) = 0.27(2) M s .

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Forum Article

⧧

−1

Figure 2. Free energies of activation ΔG (kcal mol ) at 298 K for

Figure 3. Hammett analysis of the reaction of copper(II) nitrite 3

the reaction of 1−4 with excess P(Ar ) versus reduction potential

with para-substituted triarylphosphines P(Ar ) .

⧧

of copper(II) nitrite. Bars represent standard errors in ΔG .

Direct attack of the phosphine P(Ar )₃on the copper(II)

nitrite 4 with a κ -O N nitrite binding mode led to a transition

Eyring analysis allowed for quantiﬁcation of the activation

parameters for each electronically diﬀerent copper nitrite

complex 1−4 (Figure 2). We obtained second-order rate

constants at various temperatures under pseudo-ﬁrst-order

conditions with 20 equiv of P(Ar⁾3 ⁽^F ⁱ ^g ^u ^r ^e ^S ² ⁷⁾^.^T^h^e^v^e^r^y

diﬀerent rates of the reaction require Eyring analysis over

diﬀerent temperature spans in order to conveniently follow

these reactions by UV−vis spectroscopy. For instance, we

employed a temperature range of −60 to −30 °C in the

reaction of 1, while we used a range of 15−45 °C for less

reactive 4. These studies reveal that the experimental enthalpy

and free energies of activation ΔH and ΔG (298 K) generally

increase with decreasing reduction potential of the copper(II)

nitrites 1−4 (Table 1 and Figures S29 and S30). The β-

diketiminato backbone substituent exerts the most prominent

eﬀect: ΔH increases from ca. 5 kcal mol (X = CF ) to 13−

4 kcal mol (X = Me). We observe a smaller range of free

⧧

state much higher in energy [ΔG (298 K) = 31.1 kcal

calc

−1

⧧

mol ] than experimentally determined [ΔG (298 K)

exp

−1

8.6(3) kcal mol ] (Figure S37 ). By starting with a κ -O N

bonding mode, OAT to phosphine most directly results in a

8,39

metastable [Cu]-ON isonitrosyl complex,

calculated to be

0.6 kcal mol higher in free energy than the corresponding

−1

three-coordinate nitrosyl [Cu ]-NO (Scheme S3).

There are several crystallographically determined binding

modes for nitrite at Cu centers, which include κ -O N, κ -

2,13,40,41

ONO, and κ -NO (Figure 4 ).

At copper(II)

⧧

−1

−

Figure 4. Nitrite bonding modes at Cu.

⧧

−1

energies of activation ΔG (298 K) = 16−19 kcal mol that

reﬂect more negative entropies of activation observed with X =

CF versus Me (Figure 2).

Employing compound 3 as a model along with a set of para-

substituted phosphines PAr , we monitored the electronic

complexes of lower coordination number, nitrite generally

prefers the κ -O N binding mode in both synthetic

21,42

complexes

as well as Cu-containing nitrite reductases.

Tetradentate supporting ligands, however, can lead to the κ -

ONO binding mode.

complexes typically display the κ -NO binding mode

inﬂuence on the rate of reaction. As can be seen from the

Hammett plot (Figure 3), electron-rich phosphines accelerate

the reaction [ρ = −1.5(6)]. Thus, the combination of an

electron-poor Cu center with an electron-rich phosphine favors

43,44

On the other hand, copper(I)

12,41

because of the availability of back-bonding into the NO π*

nitrite reduction at Cu . Among the phosphines studied, this

orbitals (Figure S75 ). While the β-diketiminatocopper(II)

eﬀect represents a nearly 20-fold increase in the second-order

rate constant.

nitrites in this study exhibit κ -O N binding modes in the solid

12,45

state,

a recent computational study indicates that both κ -

ONO and κ -NO binding modes are energetically accessible

at Cu in the presence of hydrogen bonding. Guided by

examples in iron porphyrin chemistry for which the [Fe](κ -

Guided by the experimental rate law and activation

parameters in the generation of NO from β-

diketiminatocopper(II) nitrites 1−4, we sought to uncover

further details of the reaction pathway through density

functional theory (DFT) computational analysis. We chose

to focus on the synthetic model 4 because its experimental

parameters had the lowest estimated errors. In accordance with

previous DFT complexes on copper β-diketiminato complexes,

we carried out calculations at the BP86+GD3BJ/6-311+

NO ) binding mode can enable direct transformation to the

corresponding [Fe]-NO nitrosyl complex upon OAT, we

were eager to consider this κ -NO binding mode as a possible

intermediate in OAT from nitrite at Cu .

Computationally examining nitrite isomerization in the

copper(II) complex 4, we ﬁnd that a distorted κ -NO binding

−

G(d,p)/SMD-toluene//BP86/6-311+G(d)/gas level of

mode is only 0.9 kcal mol higher in free energy than the κ -

O N ground state with a barrier of ΔG (298 K) = 8.1 kcal

⧧

theory.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Forum Article

Figure 5. Reaction coordinate diagram of OAT from [Me NN]Cu(κ -O N) (4) to P(Ar ) via [Me NN]Cu-NO (7). Free energies (bold) are in

kilocalories per mole at 298 K.

−

mol . This transition state resembles the κ -ONO binding

we ﬁnd that it does not undergo OAT with β-

mode, which in our model did not result in an optimized stable

diketiminatocopper(II) nitrites at room temperature or even

point (Figure S46 ). Curiously, this κ -NO binding mode is

with modest heating. DFT analysis that involves a κ -O N-to-

not symmetrical as found in the crystallographically charac-

κ -NO isomerization of copper(II) nitrites 1−4 prior to OAT

to SMe reveals calculated free energies of activation that range

from 33.0 to 42.1 kcal mol for the four copper nitrite

complexes (Scheme 3 and Figure S38 ). Thus, the ease of

oxidation of the incoming O-atom acceptor is a crucial feature

−

terized {[ Pr NN ]Cu(κ -NO )} in which the nitrite ONO

−

plane is orthogonal to the β-diketiminato backbone. Rather,

this κ -NO binding mode has a close Cu···O contact of 2.440

Å, which results in a highly distorted square-planar

coordination. This distortion unequally polarizes a modest

amount of unpaired electron density present at nitrite toward

of OAT from nitrite at Cu .

−

Scheme 3. Considering OAT from Copper(II) Nitrites 1−4

the proximal O atom (0.14 e ) at the expense of the distal O

−

^t^o^S^M^e2

atom (0.05 e ) (Figure S74 ).

A scan of the approach of the phosphine to the O atom with

greater spin density led to the optimization of a transition state

⧧

−1

with ΔG (298 K) = 19.1 kcal mol , extremely close to the

−

experimental value of 18.6(3) kcal mol . In this transition

state, which features κ -NO coordination, the nitrite has

twisted to become orthogonal to the β-diketiminato plane.

This primes an O atom (O1) for abstraction by the incoming

phosphine with N−O1 and P−O1 distances of 1.44 and 1.86

Å, respectively, in the transition state. Developing Cu-NO

character is apparent through a shortening of the Cu−N (1.85

Å) and N−O2 (1.23 Å) bonds that lead to copper(I) nitrosyl 7

with Cu−N (1.78 Å) and N−O2 (1.19 Å) distances, which are

slightly bent orthogonal to the β-diketiminato backbone with a

Cu−N−O2 angle of 157.9°. The conversion of copper(II)

Calculated free energies are in kilocalories per mole at 298 K.

CONCLUSIONS

■

Cu-containing nitrite reductases have reduction potentials in

the range of 0.17−0.28 V (vs NHE) at the type 2 Cu site,

0−54

similar to both copper(II) models 1 and 2, which exhibit

reduction potentials of 0.33 and 0.31 V (vs NHE) in THF.

This study reveals that increasing the reduction potential of a

copper(II) nitrite facilitates OAT from nitrite, a feature that

controls the rate of reaction at roughly isosteric models.

Moreover, the combination of an electron-poor Cu center with

an electron-rich O-atom acceptor proves optimal for OAT.

DFT studies benchmarked on the experimental free energy of

nitrite 4 and P(Ar ) reactants to copper nitrosyl 7 and

phosphine oxide OP(Ar ) is signiﬁcantly exergonic at

−

27.2 kcal mol . Moreover, the displacement of NO at Cu by

phosphine to give the copper(I) phosphine adduct [Cu ]-

P(Ar )₃is further downhill by another 6.7 kcal mol⁻¹in free

energy (Figure 5). This is congruent with our experimental

observation of [Cu ]-PPh in the reaction of [Cu ](κ -O N)

activation reveal that OAT requires isomerization of the nitrite

to a κ -NO binding mode, which enables eﬃcient transfer of a

complexes with 2 equiv of PPh (Scheme 2).

The identiﬁcation of a DFT transition state structure for

nitrite O atom from N to P to form OPAr along with the

OAT from the Cu -bound nitrite to a phosphine that matches

copper nitrosyl [Cu]-NO. In contrast to the strong binding of

the experimental activation energies encourages the consid-

eration of biologically relevant O-atom acceptors. For instance,

methionine residues are often found in the vicinity of Cu active

NO at iron(II) porphyrins, the more labile Cu−NO

interaction results in NO release, with an additional

equivalent of the incoming nucleophile that binds to the Cu

6−49

sites.

Employing SMe as a simple model, experimentally

center.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Siegler, M. A.; Ivanovic-Burmazovic, I.; Karlin, K. D. Nitrogen Oxide

Forum Article

These studies reveal higher thermodynamic and kinetic

barriers for OAT from copper(II) nitrites to more modest O-

atom acceptors such as dialkyl sulﬁdes. Nonetheless, turning

on the OAT pathways from nitrite to dialkyl sulﬁdes such as

methionine commonly found within the coordination sphere

of copper enzymes could represent a pathway to connect

nitrite and NO with oxidative methionine signaling, a post-

(3) Gladwin, M. T.; Schechter, A. N.; Kim-Shapiro, D. B.; Patel, R.

P.; Hogg, N.; Shiva, S.; Cannon, R. O.; Kelm, M.; Wink, D. A.; Espey,

M. G.; Oldfield, E. H.; Pluta, R. M.; Freeman, B. A.; Lancaster, J. R.;

Feelisch, M.; Lundberg, J. O. The Emerging Biology of the Nitrite

Anion. Nat. Chem. Biol. 2005, 1, 308−314.

(

4) Hematian, S.; Kenkel, I.; Shubina, T. E.; Durr, M.; Liu, J. J.;

Atom-Transfer Redox Chemistry; Mechanism of NO(g) to Nitrite

55−57

translational means to control protein activity.

III

Conversion Utilizing μ -oxo Heme-Fe −O −Cu (L) Constructs. J.

Am. Chem. Soc. 2015, 137, 6602−6615.

ASSOCIATED CONTENT

sı Supporting Information

(5) Hematian, S.; Garcia-Bosch, I.; Karlin, K. D. Synthetic Heme/

Copper Assemblies: Toward an Understanding of Cytochrome c

Oxidase Interactions with Dioxygen and Nitrogen Oxides. Acc. Chem.

Res. 2015, 48, 2462−2474.

■

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c00625.

(6) Basu, S.; Azarova, N. A.; Font, M. D.; King, S. B.; Hogg, N.;

Gladwin, M. T.; Shiva, S.; Kim-Shapiro, D. B. Nitrite Reductase

Experimental, characterization, and computational de-

tails (PDF)

Activity of Cytochrome c. J. Biol. Chem. 2008, 283, 32590−32597.

(7) Zhang, Z.; Naughton, D.; Winyard, P. G.; Benjamin, N.; Blake,

Accession Codes

D. R.; Symons, M. C. R. Generation of Nitric Oxide by a Nitrite

Reductase Activity of Xanthine Oxidase: A Potential Pathway for

Nitric Oxide Formation in the Absence of Nitric Oxide Synthase

Activity. Biochem. Biophys. Res. Commun. 1998, 249, 767−772.

CCDC 1875639, 1983021, and 2081113 contain the

supplementary crystallographic data for this paper. These

data can be obtained free of charge via www.ccdc.cam.ac.uk/

data_request/cif , or by emailing data_request@ccdc.cam.ac.

uk , or by contacting The Cambridge Crystallographic Data

Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44

(

8) Cosby, K.; Partovi, K. S.; Crawford, J. H.; Patel, R. P.; Reiter, C.

D.; Martyr, S.; Yang, B. K.; Waclawiw, M. A.; Zalos, G.; Xu, X.;

Huang, K. T.; Shields, H.; Kim-Shapiro, D. B.; Schechter, A. N.;

Cannon, R. O.; Gladwin, M. T. Nitrite Reduction to Nitric Oxide by

Deoxyhemoglobin Vasodilates the Human Circulation. Nat. Med.

223 336033.

2003, 9, 1498−1505.

AUTHOR INFORMATION

Corresponding Author

Timothy H. Warren − Department of Chemistry, Georgetown

University, Washington, D.C. 20057, United States;

orcid.org/0000-0001-9217-8890; Email: thw@

georgetown.edu

(9) Shiva, S.; Huang, Z.; Grubina, R.; Sun, J.; Ringwood, L. A.;

MacArthur, P. H.; Xu, X.; Murphy, E.; Darley-Usmar, V. M.; Gladwin,

M. T. Deoxymyoglobin Is a Nitrite Reductase That Generates Nitric

Oxide and Regulates Mitochondrial Respiration. Circ. Res. 2007, 100,

■

54−661.

10) Maia, L. B.; Moura, J. J. G. How Biology Handles Nitrite. Chem.

Rev. 2014, 114, 5273−5357.

11) Andring, J. T.; Kim, C. U.; McKenna, R. Structure and

(

Authors

Mechanism of Copper −Carbonic Anhydrase II: A Nitrite Reductase.

Molly Stauﬀer − Department of Chemistry, Georgetown

University, Washington, D.C. 20057, United States

Zeinab Sakhaei − Department of Chemistry, Georgetown

University, Washington, D.C. 20057, United States

Christine Greene − Department of Chemistry, Georgetown

University, Washington, D.C. 20057, United States

Pokhraj Ghosh − Department of Chemistry, Georgetown

University, Washington, D.C. 20057, United States

Jeﬀery A. Bertke − Department of Chemistry, Georgetown

University, Washington, D.C. 20057, United States;

orcid.org/0000-0002-3419-5163

IUCrJ 2020, 7, 287−293.

(12) Sakhaei, Z.; Kundu, S.; Donnelly, J. M.; Bertke, J. A.; Kim, W.

Y.; Warren, T. H. Nitric Oxide Release via Oxygen Atom Transfer

from Nitrite at Copper(II). Chem. Commun. 2017, 53, 549−552.

(13) Rose, S. L.; Antonyuk, S. V.; Sasaki, D.; Yamashita, K.; Hirata,

K.; Ueno, G.; Ago, H.; Eady, R. R.; Tosha, T.; Yamamoto, M.;

Hasnain, S. S. An Unprecedented Insight into the Catalytic

Mechanism of Copper Nitrite Reductase from Atomic-Resolution

and Damage-Free Structures. Sci. Adv. 2021, 7, eabd8523.

(14) Fukuda, Y.; Tse, K. M.; Nakane, T.; Nakatsu, T.; Suzuki, M.;

Sugahara, M.; Inoue, S.; Masuda, T.; Yumoto, F.; Matsugaki, N.;

Nango, E.; Tono, K.; Joti, Y.; Kameshima, T.; Song, C.; Hatsui, T.;

Yabashi, M.; Nureki, O.; Murphy, M. E. P.; Inoue, T.; Iwata, S.;

Mizohata, E. Redox-Coupled Proton Transfer Mechanism in Nitrite

Reductase Revealed by Femtosecond Crystallography. Proc. Natl.

Acad. Sci. U. S. A. 2016, 113, 2928−2933.

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.1c00625

Notes

(15) Cioncoloni, G.; Roger, I.; Wheatley, P. S.; Wilson, C.; Morris,

The authors declare no competing ﬁnancial interest.

R. E.; Sproules, S.; Symes, M. D. Proton-Coupled Electron Transfer

Enhances the Electrocatalytic Reduction of Nitrite to NO in a

Bioinspired Copper Complex. ACS Catal. 2018 , 8 , 5070 −5084.

ACKNOWLEDGMENTS

■

(16) Merkle, A. C.; Lehnert, N. Binding and Activation of Nitrite

T.H.W. acknowledges funding from the National Institutes of

Health (Grant R01GM126205).

and Nitric Oxide by Copper Nitrite Reductase and Corresponding

Model Complexes. Dalton Trans. 2012 , 41 , 3355 −3368.

(17) Moore, C. M.; Szymczak, N. K. Nitrite Reduction by Copper

REFERENCES

■

through Ligand-Mediated Proton and Electron Transfer. Chem. Sci.

2015, 6, 3373−3377.

(18) Matson, E. M.; Park, Y. J.; Fout, A. R. Facile Nitrite Reduction

in a Non-Heme Iron System: Formation of an Iron(III)-Oxo. J. Am.

(

1) Nitric Oxide: Biology and Pathobiology, 2nd ed.; Ignarro, L. J.,

Ed.; Elsevier/Academic Press: Amsterdam, The Netherlands, 2010.

2) De Pascali, F.; Hemann, C.; Samons, K.; Chen, C.-A.; Zweier, J.

L. Hypoxia and Reoxygenation Induce Endothelial Nitric Oxide

Synthase Uncoupling in Endothelial Cells through Tetrahydrobiop-

terin Depletion and S-Glutathionylation. Biochemistry 2014, 53,

Chem. Soc. 2014, 136, 17398−17401.

−

(19) Sanders, B. C.; Hassan, S. M.; Harrop, T. C. NO Activation

and Reduction to NO by a Nonheme Fe(NO ) Complex. J. Am.

679−3688.

Chem. Soc. 2014, 136, 10230−10233.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Forum Article

−

20) Cheng, R.; Wu, C.; Cao, Z.; Wang, B. QM/MM MD

(37) Sanders, B. C.; Hassan, S. M.; Harrop, T. C. NO Activation

Simulations Reveal an Asynchronous PCET Mechanism for Nitrite

and Reduction to NO by a Nonheme Fe(NO ) Complex. J. Am.

Reduction by Copper Nitrite Reductase. Phys. Chem. Chem. Phys.

Chem. Soc. 2014, 136, 10230 −10233.

(38) Bitterwolf, T. E. Photochemical Nitrosyl Linkage Isomerism/

020, 22, 20922−20928.

21) Maria, S.; Chattopadhyay, T.; Ananya, S.; Kundu, S. Reduction

Metastable States. Coord. Chem. Rev. 2006 , 250 , 1196 −1207.

(39) De La Cruz, C.; Sheppard, N. A Structure-Based Analysis of the

of Nitrite to NO at a Mononuclear Copper(II)-Phenolate Site. Inorg.

Chim. Acta 2020, 506, 119515.

Vibrational Spectra of Nitrosyl Ligands in Transition-Metal

Coordination Complexes and Clusters. Spectrochim. Acta, Part A

22) Horrell, S.; Kekilli, D.; Strange, R. W.; Hough, M. A. Recent

Structural Insights into the Function of Copper Nitrite Reductases.

011, 78, 7−28.

40) Boulanger, M. J.; Murphy, M. E. P. Directing the Mode of

Metallomics 2017, 9, 1470−1482.

Nitrite Binding to a Copper-Containing Nitrite Reductase from

Alcaligenes Faecalis S-6: Characterization of an Active Site Isoleucine.

Protein Sci. 2003, 12, 248−256.

23) Tovrog, B. S.; Diamond, S. E.; Mares, F. Oxygen Transfer from

Ligands: Cobalt Nitro Complexes as Oxygenation Catalysts. J. Am.

Chem. Soc. 1979, 101, 270−272.

(41) Chandra Maji, R.; Mishra, S.; Bhandari, A.; Singh, R.;

24) Khin, C.; Heinecke, J.; Ford, P. C. Oxygen Atom Transfer from

Olmstead, M. M.; Patra, A. K. A Copper(II) Nitrite That Exhibits

Change of Nitrite Binding Mode and Formation of Copper(II)

Nitrosyl Prior to Nitric Oxide Evolution. Inorg. Chem. 2018, 57,

Nitrite Mediated by Fe(III) Porphyrins in Aqueous Solution. J. Am.

Chem. Soc. 2008, 130, 13830−13831.

(

25) He, C.; Howes, B. D.; Smulevich, G.; Rumpel, S.; Reijerse, E. J.;

(

550−1561.

Lubitz, W.; Cox, N.; Knipp, M. Nitrite Dismutase Reaction

Mechanism: Kinetic and Spectroscopic Investigation of the

Interaction between Nitrophorin and Nitrite. J. Am. Chem. Soc.

42) Lehnert, N.; Cornelissen, U.; Neese, F.; Ono, T.; Noguchi, Y.;

Okamoto, K.; Fujisawa, K. Synthesis and Spectroscopic Character-

ization of Copper(II)−Nitrito Complexes with Hydrotris(Pyrazolyl)-

26) Heinecke, J.; Ford, P. C. Formation of Cysteine Sulfenic Acid

015, 137, 4141−4150.

by Oxygen Atom Transfer from Nitrite. J. Am. Chem. Soc. 2010, 132,

240−9243.

27) Heinecke, J. L.; Khin, C.; Pereira, J. C. M.; Suárez, S. A.;

(43) Hematian, S.; Siegler, M. A.; Karlin, K. D. Nitric Oxide (NO)

Generation from Heme/Copper Assembly Mediated Nitrite Reduc-

(

tase Activity. JBIC, J. Biol. Inorg. Chem. 2014, 19 (0), 515 −528.

(44) Hematian, S.; Garcia-Bosch, I.; Karlin, K. D. Synthetic Heme/

Iretskii, A. V.; Doctorovich, F.; Ford, P. C. Nitrite Reduction

Mediated by Heme Models. Routes to NO and HNO? J. Am. Chem.

Soc. 2013, 135, 4007−4017.

Copper Assemblies: Toward an Understanding of Cytochrome c

Oxidase Interactions with Dioxygen and Nitrogen Oxides. Acc. Chem.

Res. 2015, 48, 2462−2474.

(

28) Goodwin, J.; Kurtikyan, T.; Standard, J.; Walsh, R.; Zheng, B.;

(45) Kundu, S.; Kim, W. Y.; Bertke, J. A.; Warren, T. H. Copper(II)

Parmley, D.; Howard, J.; Green, S.; Mardyukov, A.; Przybyla, D. E.

Variation of Oxo-Transfer Reactivity of (Nitro)Cobalt Picket Fence

Porphyrin with Oxygen-Donating Ligands. Inorg. Chem. 2005, 44,

Activation of Nitrite: Nitrosation of Nucleophiles and Generation of

NO by Thiols. J. Am. Chem. Soc. 2017, 139 , 1045 −1048.

(46) Davis, A. V.; O ’Halloran, T. V. A Place for Thioether

Chemistry in Cellular Copper Ion Recognition and Trafficking. Nat.

Chem. Biol. 2008, 4, 148−151.

(47) Liu, J.; Chakraborty, S.; Hosseinzadeh, P.; Yu, Y.; Tian, S.;

Petrik, I.; Bhagi, A.; Lu, Y. Metalloproteins Containing Cytochrome,

Iron −Sulfur, or Copper Redox Centers. Chem. Rev. 2014, 114, 4366−

4469.

29) O ’Shea, S. K.; Wall, T.; Lin, D. Activation of Nitrite Ion by

215−2223.

Biomimetic Iron(III) Complexes. Transition Met. Chem. 2007, 32,

14−517.

30) Kurtikyan, T. S.; Hovhannisyan, A. A.; Iretskii, A. V.; Ford, P.

C. Six-Coordinate Nitro Complexes of Iron(III) Porphyrins with

Trans S-Donor Ligands. Oxo-Transfer Reactivity in the Solid State.

Inorg. Chem. 2009, 48, 11236−11241.

(48) Solomon, E. I.; Heppner, D. E.; Johnston, E. M.; Ginsbach, J.

W.; Cirera, J.; Qayyum, M.; Kieber-Emmons, M. T.; Kjaergaard, C.

H.; Hadt, R. G.; Tian, L. Copper Active Sites in Biology. Chem. Rev.

(

31) Goodwin, J.; Bailey, R.; Pennington, W.; Rasberry, R.; Green,

C.; Fromm, G.; Lyerly, S.; Watson, N.; Long, A.; De Nitto, N.

014, 114, 3659−3853.

T.; Shasho, S.; Yongsavanh, M.; Echevarria, V.; Tiedeken, J.; Brown,

Structural and Oxo-Transfer Reactivity Differences of Hexacoordinate

and Pentacoordinate (Nitro)(Tetraphenylporphinato)Cobalt(III)

Derivatives. Inorg. Chem. 2001, 40, 4217 −4225.

49) Wilson, T. D.; Yu, Y.; Lu, Y. Understanding Copper-Thiolate

Containing Electron Transfer Centers by Incorporation of Unnatural

Amino Acids and the CuA Center into the Type 1 Copper Protein

Azurin. Coord. Chem. Rev. 2013, 257, 260−276.

(50) Suzuki, S.; Kataoka, K.; Yamaguchi, K.; Inoue, T.; Kai, Y.

32) Munro, O. Q.; Scheidt, W. R. (Nitro)Iron(III) Porphyrins.

Structure −Function Relationships of Copper-Containing Nitrite

EPR Detection of a Transient Low-Spin Iron(III) Complex and

Structural Characterization of an O Atom Transfer Product. Inorg.

Chem. 1998, 37, 2308−2316.

Reductases. Coord. Chem. Rev. 1999, 190−192, 245−265.

(51) Suzuki, S.; Deligeer; Yamaguchi, K.; Kataoka, K.; Kobayashi, K.;

Tagawa, S.; Kohzuma, T.; Shidara, S.; Iwasaki, H. Spectroscopic

characterization and intramolecular electrontransfer processes of

native and type 2 Cu-depleted nitrite reductases. JBIC, J. Biol. Inorg.

Chem. 1997, 2, 265−274.

33) Castro, C. E.; O ’Shea, S. K. Activation of Nitrite Ion by

Iron(III) Porphyrins. Stoichiometric Oxygen Transfer to Carbon,

Nitrogen, Phosphorus, and Sulfur. J. Org. Chem. 1995, 60, 1922−

(52) Farver, O.; Eady, R. R.; Abraham, Z. H.; Pecht, I. The

923.

34) Tsai, F.-T.; Kuo, T.-S.; Liaw, W.-F. Dinitrosyl Iron Complexes

intramolecular electron transfer between copper sites of nitrite

reductase: a comparison with ascorbate oxidase. FEBS Lett. 1998,

DNICs) Bearing O-Bound Nitrito Ligand: Reversible Trans-

formation between the Six-Coordinate {Fe(NO)₂ } [(1-

MeIm) (H -ONO)Fe(NO) ] (g = 2.013) and Four-Coordinate

{

36, 239−242.

(53) Kobayashi, K.; Tagawa, S.; Deligeer; Suzuki, S. The pH-

Dependent Changes of Intramolecular Electron Transfer on Copper-

Containing Nitrite Reductase. J. Biochem. 1999, 126, 408−412.

Fe(NO) } [(1-MeIm)(ONO)Fe(NO) ] (g = 2.03). J. Am. Chem.

Soc. 2009, 131, 3426−3427.

35) Tsai, F.-T.; Lee, Y.-C.; Chiang, M.-H.; Liaw, W.-F. Nitrate-to-

Nitrite-to-Nitric Oxide Conversion Modulated by Nitrate-Containing

54) Pinho, D.; Besson, S.; Brondino, C. D.; de Castro, B.; Moura, I.

Copper-containing nitrite reductase from Pseudomonas chlororaphis

DSM 50135. Eur. J. Biochem. 2004, 271, 2361−2369.

(55) Lin, S.; Yang, X.; Jia, S.; Weeks, A. M.; Hornsby, M.; Lee, P. S.;

Nichiporuk, R. V.; Iavarone, A. T.; Wells, J. A.; Toste, F. D.; Chang,

C. J. Redox-Based Reagents for Chemoselective Methionine

Bioconjugation. Science 2017, 355, 597−602.

{

Fe(NO) } Dinitrosyl Iron Complex (DNIC). Inorg. Chem. 2013,

36) Conradie, J.; Ghosh, A. Iron(III)−Nitro Porphyrins:

2, 464−473.

Theoretical Exploration of a Unique Class of Reactive Molecules.

Inorg. Chem. 2006, 45, 4902−4909.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

M.; Barras, F.; Ezraty, B. Redox Controls RecA Protein Activity via

Forum Article

(

56) Henry, C.; Loiseau, L.; Vergnes, A.; Vertommen, D.; Mérida-

Floriano, A.; Chitteni-Pattu, S.; Wood, E. A.; Casadesus, J.; Cox, M.

Reversible Oxidation of Its Methionine Residues. eLife 2021, 10,

e63747.

57) Ezraty, B.; Gennaris, A.; Barras, F.; Collet, J.-F. Oxidative

Stress, Protein Damage and Repair in Bacteria. Nat. Rev. Microbiol.

017, 15, 385−396.