Synthesis of CoII-NO- Complexes and Their Reactivity as a Source of Nitroxyl

Article abstract of DOI:10.1021/jacs.6b05896

Metal-nitroxyl (M-HNO/M-NO^-) coordination units are found in denitrification enzymes of the global nitrogen cycle, and free HNO exhibits pharmacological properties related to cardiovascular physiology that are distinct from nitric oxide (NO). To elucidate the properties that control the binding and release of coordinated nitroxyl or its anion at these biological metal sites, we synthesized {CoNO}⁸ (1, 2) and {CoNO}⁹ (3, 4) complexes that contain diimine-dipyrrolide supporting ligands. Experimental (NMR, IR, MS, EPR, XAS, XRD) and computational data (DFT) support an oxidation state assignment for 3 and 4 of high spin Co^II (S_Co = 3/2) coordinated to ³NO^- (S_NO = 1) for S_tot = 1/2. As suggested by DFT, upon protonation, a spin transition occurs to generate a putative low spin Co^II-¹HNO (S_Co = S_tot = 1/2); the Co-NO bond is ～0.2 ? longer, more labile, and facilitates the release of HNO. This property was confirmed experimentally through the detection and quantification of N₂O (～70% yield), a byproduct of the established HNO self-reaction (₂HNO → N₂O + H₂O). Additionally, 3 and 4 function as HNO donors in aqueous media at pH 7.4 and react with known HNO targets, such as a water-soluble Mn^III-porphyrin ([Mn^III(TPPS)]^3- TPPS = meso-tetrakis(4-sulfonatophenyl)porphyrinate) and ferric myoglobin (metMb) to quantitatively yield [Mn(TPPS)(NO)]^4- and MbNO, respectively.

Full text of DOI:10.1021/jacs.6b05896

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Article
II
–
Synthesis of Co-NO Complexes and Their Reactivity as a Source of Nitroxyl
Melody R. Walter, Stephen P. Dzul, Andria V. Rodrigues, Timothy L.
Stemmler, Joshua Telser, Jeanet Conradie, Abhik Ghosh, and Todd C. Harrop
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b05896 • Publication Date (Web): 26 Aug 2016
Downloaded from http://pubs.acs.org on August 26, 2016
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Journal of the American Chemical Society
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Synthesis of Co -NO Complexes and Their Reactivity as a Source
of Nitroxyl
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†
‡
‡
‡
§
Melody R. Walter, Stephen P. Dzul, Andria V. Rodrigues, Timothy L. Stemmler, Joshua Telser,
±
€
,†
Jeanet Conradie, Abhik Ghosh, and Todd C. Harrop*
†
Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia, 140 Cedar Street, Athens,
Georgia 30602, United States
‡
Departments of Pharmaceutical Sciences, Biochemistry and Molecular Biology, Wayne State University, Detroit, Michigan
4
§
8201, United States
Department of Biological, Chemical, and Physical Sciences, Roosevelt University, 430 South Michigan Avenue, Chicago,
Illinois 60605, United States
±
Department of Chemistry, University of the Free State, 9300 Bloemfontein, Republic of South Africa
€
Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, Nꢀ9037 Tromsø,
Norway
−
ABSTRACT: Metalꢀnitroxyl (MꢀHNO/MꢀNO ) coordination units are found in denitrification enzymes of the global nitrogen cyꢀ
cle, and free HNO exhibits pharmacological properties related to cardiovascular physiology that are distinct from nitric oxide (NO).
To elucidate the properties that control the binding and release of coordinated nitroxyl or its anion at these biological metal sites we
synthesized {CoNO} (1, 2) and {CoNO} (3, 4) complexes that contain diimineꢀdipyrrolide supporting ligands. Experimental
(NMR, IR, MS, EPR, XAS, XRD) and computational data (DFT) support an oxidation state assignment for 3 and 4 of high spin
8
9
II
3
−
Co (S = 3/2) coordinated to NO (S = 1) for S = 1/2. As suggested by DFT, upon protonation, a spin transition occurs to genꢀ
Co
NO
tot
II 1
erate a putative low spin Co ꢀ HNO (SCo = Stot = 1/2); the CoꢀNO bond is ~0.2 Å longer, more labile, and facilitates the release of
HNO. This property was confirmed experimentally through the detection and quantification of N O (~70% yield), a byproduct of
the established HNO selfꢀreaction (2HNO → N O + H O). Additionally, 3 and 4 function as HNO donors in aqueous media at pH
.4 and react with known HNO targets such as a waterꢀsoluble Mn ꢀporphyrin ([Mn (TPPS)] ; TPPS = mesoꢀtetrakis(4ꢀ
2
2
2
III
III
3−
7
4
−
sulfonatophenyl)porphyrinate) and ferric myoglobin (metMb) to quantitatively yield [Mn(TPPS)(NO)] and MbNO, respectively.
25ꢀ27
Introduction
vantages distinct from NO,
probably due to its preference
III
−
1
for thiols and Fe ꢀhemes. For example, HNO increases heart
muscle strength (positive cardiac inotrope; increases myocarꢀ
dial contractility) and plasma levels of calcitonin geneꢀrelated
peptide (CGRP), whose cardiovascular effects include vasodiꢀ
As a result, nitroxyl has been looked to as a promisꢀ
ing cardiovascular therapeutic. While the endogenous forꢀ
mation of HNO has yet to be firmly established, possible canꢀ
Metalꢀnitroxyl (HNO/NO , pK = 11.6 ) complexes repreꢀ
sent critical intermediates in the global nitrogen cycle and
inhibited states of metalloenzymes that lead to a variety of
disorders. For example, FeꢀHNO intermediates are generatꢀ
ed in the reduction of nitric oxide (NO) to nitrous oxide (N O),
a
2ꢀ4
26ꢀ27
lation.
2
5ꢀ7
8
a detoxification path in fungal and bacterial NO reductases.
9ꢀ10
Cytochrome c nitrite reductase (CcNiR) , responsible for the
2
8
−
didates include NO synthase (in the absence of its cofactor),
thiolꢀcontaining species such as H2S
sixꢀelectron reduction of NO2 to NH , goes through two Feꢀ
nitroxyl intermediates, designated as {FeNO} in the notation
by Enemark and Feltham. The extent of the FeꢀNO πꢀ
backbonding in CcNiR prevents the release of any NH O
HNOꢀbound myoglobin
(MbHNO) has also been well documented, likely due to its
In addition to Fe proteins, cobalamins
(Cbl), which serve as cofactors for vitamin B ꢀdependent
enzymes such as methionine synthase and methylmalonyl
CoAꢀmutase, are known to react with NO and HNO to form
the corresponding {CoNO} complex NOCbl.
inhibition and/or deficiency of Cbl, which results from interacꢀ
tions with NO amongst other reasons, has been shown to lead
3
29ꢀ31
− 32
8
or SSNO , and antiꢀ
33
11
oxidants such as tyrosine and ascorbate. Unfortunately, the
x
6
ꢀ1 ꢀ1 34
rapid selfꢀreaction (k = 10 M s ) of HNO to N O and H O
2
2
x
y
1
0
makes its detection challenging. Moreover, the instability of
HNO necessitates the use of donor molecules.
intermediates during catalysis.
35ꢀ37
1
2ꢀ13
uncommon stability.
Several classes of HNO donors, both organic and inorganic,
have been employed in research and even clinically. For exꢀ
1
2
ample, Angeli’s Salt (Na
N
O
), which generates HNO and
2
2
3
14
−
NO
donor.
an antiꢀalcoholism agent;
at physiological pH, is the most studied and utilized
2
8
15ꢀ19
23,35,38
Indeed,
Cyanamide (H NꢀC≡N) is a drug that is used as
2
39ꢀ40
it is oxidatively bioactivated by
−
catalase and releases HNO and CN as a byꢀproduct. The
mechanism of action is the inhibition of aldehyde dehydrogenꢀ
ase, an enzyme that is vital to metabolism of ethanol, resulting
in elevated blood acetaldehyde levels. Although a number of
such donors have been found effective, each is conditionꢀ
2
0ꢀ21
to megaloblastic anemia and neurological disorders.
In addition to representing intermediates in NO reduction,
x
22ꢀ24
the pharmacological roles of HNO are rapidly emerging.
Despite its structural similarity, nitroxyl has therapeutic adꢀ
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9
dependent and has limitations that hinder its widespread utiliꢀ
ty, including concomitant release of undesirable byꢀproducts
assignment. Entry into the relatively unknown {CoNO} state
will afford reactive complexes that are more capable of HNO
release, but less reactive than analogous Fe systems, due to
1
2
3
4
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1
1
1
1
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4
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4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
−
−
(e.g., NO , CN ), short halfꢀlives, or ineffective release of
2
2
3,26
III
‒
II
‒
HNO under physiological conditions.
Thus, there is a clear
Co ꢀNO → Co ꢀNO reduction. As such, CoꢀNO platforms
can shed fundamental insights into the effects of metal oxidaꢀ
tion state on coordinated NO reactivity. In addition, CoNO
complexes will provide answers regarding the efficacy of Cbl
and the potential use of NOCbl as
an HNO donor. The electronic structure of {CoNO} is also
more readily assessed by EPR hyperfine interactions with the I
7/2 Co nucleus (100% abundance), a feature that is lacking
in reactive and diamagnetic {FeNO} systems. Indeed, reꢀ
search and development of low molecular weight Co comꢀ
plexes has provided the community with materials utilized for
nitrite reduction
wastewater remediation and synthesis of reduced nitrogen
compounds), and the reductive activation of other small molꢀ
ecules of biological/environmental/industrial interest such as
and CO2, reactions typically carried out in nature by
Fe active sites.
Synthesis and Spectroscopy of {CoNO} Complexes. The
{CoNO} complexes [Co(LN )(NO)] (1) (LN4 = dianion of
(N E,N E)ꢀN ,N ꢀbis((1Hꢀpyrrolꢀ2ꢀyl)methylene)ꢀbenzeneꢀ1,2ꢀ
diamine) and [Co(LN4 )(NO)] (2) were synthesized in
~80% yield by direct purge of NO(g) into MeCN solutions of
the parent Co ꢀLN4 complexes. Peripheral variations on the
phenyleneꢀdiimine unit were made to explore ligand inductive
effects on the redox properties of the Coꢀnitrosyls. Their strucꢀ
ture and purity were confirmed by a variety of spectroscopic
techniques as well as elemental analysis and Xꢀray crystallogꢀ
2
6,35
need for more effective HNO delivery agents.
−
Given that metal sites appear to be both biological HNO
targets and potential HNO sources, our lab has initiated a proꢀ
gram aimed at elucidating the structural, electronic, and reacꢀ
tive properties of metalꢀcoordinated nitroxyls, formally
17ꢀ19
as an HNO scavenger
66
9
8
{MNO} , through the synthesis of coordination complexes
59
4
1ꢀ43
=
that resemble biological active sites.
The objectives herein
0
1
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8
are twoꢀfold: (i) to assess the ability of these systems to reꢀ
lease HNO under physiological conditions; and (ii) to provide
insight into the fundamental MꢀNO bonding properties in deꢀ
67ꢀ72
H2 evolution (alternative energy),
nitrifying enzymes that convert NO into reduced and bioaꢀ
x
(
vailable nitrogen compounds. We have previously communiꢀ
52
8
cated the fiveꢀcoordinate (5C)
{CoNO1}
complex,
PhCl
PhCl
2 1 2
[
Co(LN4 )(NO)] (LN4
= dianion of (N E,N E)ꢀN ,N ꢀ
73ꢀ74
75
N2
bis((1Hꢀpyrrolꢀ2ꢀyl)methylene)ꢀ4,5ꢀdichlorobenzeneꢀ1,2ꢀ
+
diamine, see Scheme 1), that exhibits H ꢀinduced release of
4
3
8
nitroxyl in organic solvents. To realize HNOꢀrelease in waꢀ
ter, we have synthesized and characterized the oneꢀelectron
8
Ph
Ph
4
9
1
2
1
2
reduced {CoNO} complexes in the present account (Scheme
8
41,43ꢀ54
53,55ꢀ
PhCl 43
1). While numerous {CoNO} complexes exist,
few
5
8
describe NO release prior to our work. Furthermore, the
{CoNO} state is rare, with the exception of a few isolated
tetrahedral complexes containing ligated carbonyls,
9
II
R
5
9ꢀ60
trisꢀ
tris(2ꢀ
and one complex bearing
6
1ꢀ62
pyrazolyl
borates,
63ꢀ64
diphenylphosphinoethyl)amines,
an Nꢀconfused porphyrin. However, the reaction chemistry
of {CoNO} systems is underexplored. Herein we report the
synthesis and properties of 5C {CoNO} complexes via a
6
5
8
/9
raphy (vide infra). For example, the FTIR spectrum of 1 disꢀ
9
ꢀ1
played a strong doubleꢀhumped ν band at 1667 cm and
NO
ꢀ
1
ꢀ1
ꢀ1
combined experimental and theoretical approach. Our results
1
656 cm (KBr) that shifted to 1641 cm (ꢀν : 26 cm ) and
NO
II 3
−
9
ꢀ1 ꢀ1
point to a high spin (HS) Co ꢀ NO assignment for {CoNO} ,
1
628 cm (ꢀνNO: 28 cm ) upon isotopic substitution with
NO(g) (see Figure S1 in the supporting information = SI).
The morphology of the νNO peak in 1 is attributed to a disorꢀ
dered nitrosyl, which is seen in the Xꢀray structure (Figure
II 1
1
5
which changes to low spin (LS) Co ꢀ HNO upon protonation
of the NO ligand. Most notably, the reported {CoNO} comꢀ
plexes demonstrate the release of nitroxyl to Mn ꢀP complexꢀ
es (P = porphyrin) and Fe ꢀmyoglobin (metMb) in water at
9
III
III
15
15
15
S4). The N NMR of the Nꢀlabeled complex (1- NO) in
15
pH 7.4.
THFꢀd exhibited one N peak at 675 ppm (vs. CH NO ) and
8
3
2
8
Scheme 1. Synthesis and Interconversion of {CoNO} and
is consistent with a bent metalꢀnitrosyl, i.e., CoꢀNꢀO of ~125°
(Figure S3). As noted with other 5C squareꢀpyramidal
these properties suggest a general
assignment of LSꢀCo (SCo = 0) coordinated to singlet nitroxyl
anion NO (S = 0) for an overall diamagnetic ground state.
We note that the resonance structure LSꢀCo ꢀ NO ↔ LSꢀ
Co ꢀNO• has also been evoked for the {CoNO} unit in
9
76
{CoNO} complexes. R = H for 1, 3; R = Cl for 2, 4.
8
41,43ꢀ54
{
CoNO} complexes,
III
1
‒
NO
III 1
‒
II
8
15
NOCbl.
8
{
CoNO} Structural Properties. Analogous to 2 and other
the structure of 1 indicates a
squareꢀpyramidal ( = 0.013 ) Co with a mostly planar N
ligand and an axially bound NO (Figure 1, Tables S1ꢀS2). Co
is displaced by 0.242 Å out of the plane of the N ligand with
CoꢀN(O) (1.804 Å) and NꢀO (1.162 Å) bond lengths typical
for this class of metalꢀnitrosyls. For comparison, the NꢀO bond
distance in 1 and 2 (1.162, 1.172 Å, respectively) is in beꢀ
8
41,43ꢀ54
5C {CoNO} complexes,
77
τ
Results and Discussion
4
Rationale. Addressing the structure and reaction chemistry
4
of wellꢀdefined, firstꢀrow metalꢀcoordinated nitroxyls has been
41ꢀ42
2
challenging. Indeed, previous work by us
and others (vide
8
II
infra) demonstrate that {FeNO} complexes, formally LSꢀFe ꢀ
NO , can be synthesized and generate coordinated HNO.
‒
1
tween NO• (1.15 Å) and HNO (1.21 Å) and suggests some
degree of delocalization in the CoꢀNꢀO bond. It appears that
However, these systems are very reactive as they are highly
susceptible to disproportionation, and thus necessitate the use
of in situ lowꢀtemperature measurements. Employing Co to
access coordinated nitroxyl or its anion provides a more conꢀ
trollable platform to explore and characterize biologically
44
the range of NꢀO bond lengths observed in the majority of 5C
8
−
pyramidal {CoNO} (1.15ꢀ1.20 Å) advocates for an NO oxiꢀ
dation state, which is reflected in the bent CoꢀNꢀO angle,
124.9°. The bent CoꢀNꢀO observed in the structure of 1 and
8
relevant MꢀHNO structure and bonding as {CoNO} complexꢀ
8
2
III
‒
other {CoNO} complexes is consistent with sp hybridization
es are stable and inert entities arising from the LSꢀCo ꢀNO
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of the nitrosyl nitrogen, which is also inꢀline with the solutionꢀ
state N NMR spectrum (vide supra).
{CoNO} analogs, a shift which is consistent with a Coꢀ
15
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
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3
3
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3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
centered reduction. In comparison, reduction of coordinated
NO generally results in a dramatic ν redꢀshift (~100ꢀ200 cm
ꢀ
NO
1
7
8 2,4,79ꢀ80
) as observed in the reduction of {FeNO} to {FeNO} .
Moreover, ligandꢀbased redox events to generate pyrrolide
8
1
radicals can be eliminated based on EPR data (vide infra).
High resolution mass spectrometry (HRMS) experiments proꢀ
vide additional evidence for the formation of 3 and 4. For exꢀ
−
ample, the molecular ion peak [M] for 3 is observed at m/z:
3
49.037 (calcd. m/z: 349.037) with the appropriate isotopic
15
distribution (Figure S11). HRMS on the N isotopologue 3-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
5
NO (calcd. m/z: 350.034; obsvd. m/z: 350.035) further supꢀ
ports the predicted formulation (Figure S12). HRMS also conꢀ
firm formation of 4 and 4- NO (Figures S13ꢀS14).
15
9
EPR of {CoNO} Complexes. Xꢀband (9.60 GHz) measꢀ
Figure 1. Xꢀray structure of one of two independent molecules in
the lattice of [Co(LN4 )(NO)] (1) at 50% thermal probability for
all nonꢀhydrogen atoms. Hydrogen atoms are omitted for clarity.
urements of 3 and 4 reveal an asymmetric coordination enviꢀ
ronment with significant nuclear hyperfine coupling (hfc)
from the Co nucleus (I = 7/2) whereas the N splitting is
minimal (Figure 2; Figure S15). The large Co hfc differs
from EPR of Co ꢀO complexes
where the unpaired electron (upe) is in the dz2 orbital, leading
Ph
59
14
59
Electrochemical Properties. The cyclic voltammogram
II
82ꢀ83
II
and from typical LSꢀCo
2
(
CV) of 1 was measured in MeCN and is reported versus the
+
ferrocene/ferrocenium (Fc/Fc ) couple. The CV of 1 displays a
reversible {CoNO
59
59
84ꢀ86
8
9
to g > g
∥
≈ 2.0, large A
∥
( Co), and small A ( Co).
For
}
/{CoNO} couple at ꢀ1.39 V (Figures S5ꢀ
⊥
⊥
II
example, the spin Hamiltonian parameters of [Co (OEP)L]
complexes (where OEP = octaethylporphyrin; L is a wide
range of Nꢀdonors, e.g., py, Im), in which the upe resides in
S7; E1/2 = ꢀ0.99 V vs. NHE). Other irreversible peaks observed
in the CV are attributed to ligandꢀbased redox events (Figure
S5). Comparisons can be made with related CoꢀNO complexes
and with metalꢀnitrosyls that also contain dianionic planar
ligands. For example, 1 exhibits an E1/2 value that is shifted by
the dz2 orbital, were reported with g
= 2.315 ± 0.010 with
⊥
59
A ( Co) = 225 ꢀ 240 MHz (~80 ꢀ 85 G) and g = 2.03 ± 0.01
where A ( Co) is small (< 10 MHz, 3 G) and unresolved.
∥
∥
ꢀ0.11 V from 2, which contains a more electronꢀdeficient N4
59
84
⊥
ligand. This result is consistent with the shift in the
7
8
Contrastingly, 3 and 4 exhibit g
⊥ ⊥
∥ ∥
> g (g = 2.270, g = 2.070,
{
FeNO} /{FeNO} couple observed in the Fe analogues reꢀ
42
ported previously by our lab.
Additionally, the
2.085; g = 2.278(2); g = 2.078(2), respectively) and both A⊥,∥
values are large (~200 MHz and, ~350 MHz, respectively)
(Figure 2). This result indicates the upe being predominantly
in the dx2ꢀy2 orbital, resembling what is commonly seen in
squareꢀplanar/pyramidal Cu complexes.
of a dx2ꢀy2 upe is shown in the proposed frontier MOs (vide
infra) and in comparison to other MꢀNO systems. In a cyclamꢀ
ligated {FeNO} complex, calculations of frontier MOs using
∥
⊥
8
9
{CoNO} /{CoNO} couple is readily modulated by changes
beyond the ligand periphery. Indeed, attachment of W(CO) to
4
87
the coordinated thiolates in a Co(N S )(NO) complex results
2
2
5
1
II 88ꢀ89
in a dramatic +0.49 V shift in E . Overall, the reversible
Further support
1
/2
8
/9
8
{
CoNO}
couple of 1, 2, and other {CoNO}
highlight the potential for accessing oneꢀ
electron reduced {CoNO} complexes.
4
1,43,51ꢀ52
complexes
9
6
*
9
9
spinꢀrestricted B3LYP suggest the NOꢀπ orbital is lower in
energy than the nearby d
{CoNO} Synthesis and Properties. {CoNO} complexes
9
0
orbital. In contrast to the
were synthesized by adding stoichiometric KC to a 2ꢀMeTHF
x2ꢀy2
8
6
*
{
FeNO} case, it is likely that the NOꢀπ orbital in 3 and 4 is
solution of 1 or 2 containing 18ꢀcrownꢀ6 ether (18C6)
9
(
[
[
Scheme 1). Accordingly, the {CoNO}
complexes
and
higher in energy than dx2ꢀy2 due to stronger πꢀbonding in CoꢀN
versus FeꢀN. Due to the high covalency of the CoꢀN(O) bond,
the effect of the equatorial Nꢀligands can be detected by inꢀ
spection of EPR linewidths. The Xꢀband EPR of the isotopoꢀ
logues 3- NO and 4- NO ( N, I = 1/2), exhibit no significant
effect from labeling on the Co hfc, although there is an inꢀ
crease in the EPR linewidths, indicative of unresolved
hfc. This is further indication that the majority of the spinꢀ
density is on Co.
Ph
K(18C6)][Co(LN4 )(NO)]
(3)
PhCl
K(18C6)][Co(LN4 )(NO)] (4) were obtained in analytically
91
pure form in 70 and 82% yields, respectively. The isolated
9
15
15
15
brown {CoNO} complexes could also be converted back to
8
59
the corresponding {CoNO} complexes 1 and 2 by addition of
+
14,15
oxidants such as Fc (Scheme 1). Similarly, air oxidation leads
N
8
primarily to {CoNO} with minor formation of Coꢀ
62
nitrite/nitrate complexes based on IR.
9
Spectroscopic analysis confirmed the {CoNO} assignment
for 3 and 4. The FTIR spectrum of 3 exhibited a ν band at
NO
ꢀ1
ꢀ1
15
ꢀ
1
609 cm that shifted to ~1580 cm in 3- NO (ꢀν = 28 cm
NO
1
ꢀ1
from 3; Figures S8ꢀS9) whereas 4 exhibited νNO at 1617 cm .
Values of ν for 3 and 4 resemble those reported for other
NO
9
52,59ꢀ65
15
{
CoNO} complexes.
The νNO of 4- NO overlaps signifꢀ
icantly with ligand C=N stretches making a definitive assignꢀ
ment difficult (Figure S10). Similar complications in identifyꢀ
8
ing νNO bands have also been observed in an {FeNO} porphyꢀ
7
8
rin complex due to overlapping ligand vibrations. Regardꢀ
ꢀ
1
less, νNO peaks of 3 and 4 are ~50 cm redꢀshifted from the
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9
(vide infra) probe the electronic structure of these {CoNO}
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
systems quantitatively.
8/9
X-ray Absorption Spectroscopy (XAS) of {CoNO}
Complexes. The XAS data confirm the crystallographic reꢀ
sults of 1 (Figures 3ꢀ4). XAS spectra are constructed of two
components: the Xꢀray absorption near edge spectrum
(XANES), which provides electronic and structural insight
regarding metal oxidation state and metalꢀligand coordination
symmetry, and the extended Xꢀray absorption fine structure
(EXAFS) region, which provides highly accurate metalꢀligand
bond length characterization (± 0.02 Å), metal ligand coordiꢀ
nation number (± 0.5) and ligand atom identity (± row of the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
95
periodic table). In the XANES spectrum for 1, the lowest
energy preꢀedge peak occurs at 7710.1 eV, which corresponds
to a symmetryꢀforbidden 1s→3d transition. The relatively
large area under this transition (0.44 eV) is consistent with an
increased distortion in bond symmetry that permits mixing of
96
3
d and 4p orbitals in the formation of a LS 5C Co complex.
The first inflection point of the XANES is shifted to higher
energy relative to the Co control, which is indicative of reꢀ
II
duced electron density on the metal and more consistent with a
III
Co oxidation state in 1. Simulations of the extended Xꢀray
absorption fine structure (EXAFS) region show an average
bond length in the nearest neighbor environment for 1 of 1.88
Å, constructed of five O/N ligands (spectral resolution: 0.12
Å) (Figure 4). This value compares well with the distances
determined from Xꢀray crystallography (avg: 1.89 Å, Table
Figure 2. Xꢀband EPR spectrum of 3 in 2ꢀMeTHF at 10 K (black)
with simulation (red). Spectrometer settings: microwave frequenꢀ
cy, 9.582 GHz; microwave power, 1.0 mW; modulation frequenꢀ
cy, 100 kHz; modulation amplitude, 6.48 G. Simulation parameꢀ
43
S2). The XAS of 2 is also comparable to 1.
59
ters: Stot = 1/2, g = [2.070, 2.085, 2.270], A ( Co) = 200, 180
⊥
59
MHz, A ( Co) = 355 MHz, single crystal Gaussian linewidths,
||
W = 80 MHz, W = 40 MHz (halfꢀwidth at halfꢀmaximum).
⊥
||
The Xꢀband EPR is modelled as very slightly rhombic; as
such, higher frequency EPR (Qꢀband; 35 GHz) spectra were
recorded in order to obtain better dispersion of the gꢀvalues
(which are fieldꢀdependent). However, the fieldꢀindependent
hfc is more readily determined from lower frequencies (Xꢀ
92
band, or even lower (Sꢀ or Lꢀband) EPR). This multifrequenꢀ
II
93
cy approach has been pervasive for Cu complexes, but only
II
94
recently applied to LSꢀCo species. The Qꢀband EPR corꢀ
roborates the Xꢀband measurement (Figure S16), and resoluꢀ
tion of slight rhombic splitting is attainable with the higher
frequency. The Qꢀband spectrum of 3 (200(10), 200(10),
59
345(5); W = 130 MHz) was simulated with similar A( Co)
values as in the Xꢀband data (200(5), 200(5), 355, Wxy = 80
8
9
Figure 3. XANES for {CoNO} 1 (normal), {CoNO} 3 (bold),
MHz), and the g obtained from the Xꢀband simulation ((2.070
⊥
II
and [Co (H O) ](NO ) (dotted). Inset: baseline subtracted expanꢀ
2
6
3 2
+
2.085)/2 = 2.078(2)) is exactly the average of the resolved
II
sion of 1s→3d preꢀedge features for 1, 3, and Co control (colorꢀ
ing same as full XANES).
Qꢀband gx,y values (2.06(1), 2.10(1)) (Figure S16). It is imꢀ
9
portant to note that even at Qꢀband, {CoNO} complexes 3
Ph
PhCl
and 4, comprising the two different ligands LN4 and LN4
,
respectively, give identical EPR spectra, indicating a negligiꢀ
ble effect of peripheral substitution on the Co center.
Overall, the multiꢀfrequency EPR studies demonstrate that
9
both {CoNO} complexes, 3 and 4, are Coꢀcentered paramagꢀ
nets, as opposed to nitroxyl radicals bound to essentially diaꢀ
magnetic metals. As seen by EPR, 3 and 4 have essentially
axial symmetry, as found e.g., in porphyrin complexes, which
is unsurprising given the roughly square planar N donor set
4
R
from LN , but the frontier molecular orbitals are opposite:
typical LS Co ꢀLax porphyrins have the upe in a dz2 orbital,
4
II
with dx2ꢀy2 unoccupied, while the ground state in 3 and 4 has
the upe in dx2ꢀy2 with dz2 unoccupied. Computational studies
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from EXAFS analysis of other Nꢀligated Co complexes, such
II
9
9
II
1
2
3
4
5
6
7
8
9
as Coꢀsubstituted ferric uptake regulatory protein and Co ꢀ
100
substituted alcohol dehydrogenase. The EXAFS also indiꢀ
cate there is an increase in the Coꢀligand distances between
8
9
{CoNO} 1 and {CoNO} 3 of 0.18 Å, a shift which is again
consistent with a metalꢀbased reduction. Similar metric changꢀ
es are also observed for 4 (see Table S3).
Theoretical modeling. Density functional theory (DFT)
calculations provide a satisfactory theoretical framework for
9
understanding many of the properties of the {CoNO} state
101ꢀ102
outlined above.
The assumption of C symmetry allowed
s
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
us to investigate at least two different states. Allꢀelectron ocꢀ
7
cupation 1 (α||β: A′ 61||60, A″ 45||45) corresponds to a LS d
II
th
th
Co state with the 8 and 9 electrons (EnemarkꢀFeltham
count) added to a ligand (NO π* or other) orbital (Figure
103
S19). Occupation 2 (α||β: A´ 60||60, A´´ 46||45) is described
II
–
as a HS Co –NO state with a singly occupied d
orbital
x2ꢀy2
(
Figures 5, 6). All functionals tested (BP86, OLYP, B3LYP)
indicate occupation 2 as the ground state, in agreement with
the EPR data, albeit by different margins of energy, relative to
occupation 1 (Figure S19). Some of the key calculated properꢀ
ties of occupation 2 follow.
Figure 4. Raw (panels A, C) and Fourier transformed EXAFS
(panels B, D) (black) of {CoNO} 1 (top) and {CoNO} 3 (botꢀ
tom) with best fit simulation (green).
8
9
Single occupancy of the dx2ꢀy2 orbital resulted in relatively
long equatorial CoꢀN distances of about 2.1 Å, relative to ocꢀ
8
The XAS of 3 shows distinct features that correspond to a
cupation 1 and the {CoNO} state (CoꢀN: 1.9 Å; see Figure
8
Coꢀcentered reduction when going from {CoNO} to
S20), in agreement with the EXAFS results. This orbital occuꢀ
pancy is also responsible for a substantial displacement of the
9
{CoNO} . The XANES region of the spectrum displays a 1s→
3d preꢀedge feature at 7709.7 eV for 3 (shifted ꢀ0.4 eV from 1)
metal (∼0.7 Å) above the N plane of the ligand, a structural
4
and the first inflection point of the edge feature aligns closely
effect that remains to be observed experimentally. The Coꢀ
N(O) bond length is 1.692 Å, essentially unchanged from the
II
II
in energy to the Co model (Figure 3), suggesting a Co center
8
in 3, consistent with EPR. The 1s→3d feature in this region
{CoNO} state. Another significant structural change is the
9
62
9
has also been observed in a tetrahedral {CoNO} complex
less bent nature of CoꢀNꢀO (144.9°) in {CoNO} , which exꢀ
II
96ꢀ97
and other 5C/6C Co complexes.
The area under this tranꢀ
plains the intensity change of the 1s→3d feature in the XAS.
sition is an indication of the symmetry about the Co center. In
general, more centrosymmetric complexes exhibit weaker
The spin density profile for occupation 2 is characterized by
a full unpaired electron in the dx2ꢀy2 orbital, smaller amounts of
positive spin density in the dxz and dyz orbitals, and a signifiꢀ
cant amount of negative spin density on the NO distributed in
a cylindrically symmetric manner about the NꢀO axis (Figures
1
s→ 3d transitions. Indeed, the area of the preꢀedge feature of
3
(0.18 eV) is less than in 1 (0.44 eV), which suggests a more
symmetric coordination environment in 3 versus 1 (Figure 3).
Either a change in coordination geometry (centrosymmetric,
e.g., octahedral or squareꢀplanar) or spinꢀstate could explain
the weaker preꢀedge intensity. However, EPR (vide supra) in
combination with EXAFS (vide infra), eliminate a geometry
II
X and 5). These spin populations are indicative of HS Co ,
2
2
1
1
1
(
SCo = 3/2) with a (d ) (d ) (d ) (d ) (d ) configuration,
xy z2 xz yz x2ꢀy2
–
antiferromagnetically coupled to an NO diradical (S = 1).
NO
The reader may verify this orbital occupancy from a careful
examination of the frontier MOs (Figure 6).
II
change. For example, octahedral and planar Co complexes
exhibit very weak 1s→ 3d peaks with areas ranging from
98
The spinꢀdensity profiles obtained with the three functionals
differ somewhat. As noted before, the hybrid functional
0.050ꢀ0.061 eV. As the EXAFS and computational (vide
infra) results confirm, a 5C coordination sphere is retained in 3
and 4. Thus, the symmetry difference between 1 and 3 is likely
B3LYP resulted in the largest separation of
α and β spin denꢀ
sity, the classic pure functional BP86 resulted in the smallest
such separation, and the comparatively newer OLYP functionꢀ
al separated the α and β spins to an intermediate degree. Deꢀ
spite the quantitative differences, the fact that all three funcꢀ
tionals indicate occupation 2 as the ground state may be
viewed as powerful evidence in support of our electronic
structural description. As mentioned, this description is fully
consistent with the conclusion from XAS and EPR.
associated with a change in the CoꢀNꢀO bond angle from bent
8
(
1
~125°) in {CoNO} (1, 2) to less bent but still not linear (140ꢀ
9
50°) in {CoNO} (3, 4).
A comparison of the EXAFS for 1 and 3 show completely
different wave patterns suggesting significant changes in the
metalꢀligand metrical parameters between these two moleꢀ
cules. Simulations of the EXAFS region of 3 show an average
bond length of 2.06 Å constructed of 4 ± 1 O/N ligands (Figꢀ
2
DFT (OLYP) calculations on the CoꢀHNO complex indicate
ure 4, Table S3). Based on the large DebyeꢀWaller factor (σ =
1
II
3
2
a lowꢀspin dz2 Co ground state axially coordinated to a
closed shell HNO (Figure 5). The singly occupied molecular
orbital (SOMO) represents a σꢀantibonding interaction beꢀ
4
.14 × 10 Å ) in the nearest neighbor fit for 3, there is a higher
level of metalꢀligand bond disorder for this system, which
explains the abnormally low apparent metalꢀligand coordinaꢀ
tion number. Furthermore, based on the chemical reversibility
of the 3ꢀtoꢀ1 conversion, a 5C Co is still expected in 3. This
average distance compares well with distances determined
tween the Co dz2 (43.4%) and NO p (17.7%). Such an elecꢀ
z
tronic description is consistent with a longer CoꢀN(O) (1.891
Å) and NꢀO (1.229 Å), and shorter equatorial CoꢀN (avg:
9
1
.937 Å), relative to the {CoNO} state (Figures 5, S21). The
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8
lengthening of CoꢀN(O) is important, as it primes the HNO for
dissociation and further reactivity, and reflects the relatively
weak πꢀacceptor ability of HNO (compared with NO) as well
as the antibonding nature of the SOMO. The calculations did
tified in the THF reaction were {CoNO} 1, as well as the
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
corresponding tetrahedral dinitrosyl cobalt complex
Ph
10
[Co(LN
H )(NO) ]BF (5, a {Co(NO) } complex; Figures
2 2 4 2
2ꢀ
4
S24ꢀS25) via protonation of the pyrrolideꢀNꢀdonors of LN
4
108
8
not reveal any other lowꢀenergy states for the CoꢀHNO comꢀ
.
Contrastingly, {CoNO} complexes (1, 2) are not reactive,
likely due to a lower HNO pK , and largely H Oꢀinsoluble,
precluding 1 or 2 from effectively releasing HNO in water.
II
plex; assumption of M = 3/2 led to a highꢀspin Co ~0.5 eV
a
2
S
1
09
above the ground state.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 7. Headspace IR of the reaction of HBF •Et O with 3
(black) or 3- NO (blue) (10:1) at t = 24 h. Conditions:
4
2
15
Figure 5. Selected OLYP/TZP results for the lowestꢀenergy
9
II
{
CoNO} (top) and Co ꢀHNO (bottom) states: optimized strucꢀ
DMSO/H O (1:9), RT. See Figure S23 for full spectrum.
2
tures on the left with distances (Å, black), angles (deg, blue), and
Mulliken spin populations (red); spin density profiles on right
To this point (2016), few firstꢀrow metalꢀnitroxyl complexes
demonstrating release of HNO have been reported. Tetrahedral
1
10
dinitrosyl iron complexes (DNICs) bearing Nꢀ
and Sꢀ
110ꢀ111
supporting
ligands exhibit HNOꢀtransfer capability to
III
III
Fe ꢀheme proteins and Fe ꢀporphyrins, however, no measꢀ
urements have been done to track the possibility of free HNO.
8
Lehnert synthesized a sterically protected {FeNO} porphyrin,
which forms an FeꢀHNO complex revealed by UVꢀvis at RT.
While this design prevented the disproportionation chemistry
1
12
often seen in Feꢀnitroxyls, HNO release was not observed.
RichterꢀAddo reported the in situ synthesis and characterizaꢀ
tion of an FeꢀHNO porphyrin that reacts with Ph P, a wellꢀ
3
113
114
known HNO trap, to yield Ph P=O and Ph P=NH. Howꢀ
3
3
ever, the phosphine products were not quantified and other
methods to test HNO release were not provided. Ultimately,
Figure 6. OLYP/TZP KohnꢀSham energy level diagram (vertical
7
9
this complex decomposes to the corresponding {FeNO} and
scale is in eV) for the frontier MOs of the {CoNO} system.
8
H even at ꢀ20 °C. Additionally two {FeNO} complexes have
2
been crystallized, yet addition of acid to these Feꢀnitroxyls
Nitroxyl-Relevant Reactivity in Water: (i) Reaction of
7
78,115
116
9
+
either leads to the {FeNO} and H
or no reaction
.
Mulꢀ
{
CoNO} Complexes with H and formation of HNO. Given
2
8
3
4
tinuclear Fe complexes release N O through an NORꢀlike
reaction (NOR: 2NO + 2e + 2H → N O + H O) via coupling
the fast selfꢀreaction of nitroxyl to form N O and water (vide
2
2
‒
+
supra), N O serves as an indirect marker for HNO, and its
2
2
2
of closelyꢀspaced coordinated nitroxyl ligands. Importantly,
mononuclear analogues of these Fe complexes do not generate
presence provides evidence of the formation and liberation of
1
04
HNO from the reported CoNO complexes. After addition of
9
N O emphasizing the necessity of such multinuclear entities.
HBF •Et O to {CoNO} (3) in H O (10:1), the reaction headꢀ
2
4
2
2
Most related to this work are two Co compounds that go
space revealed IR bands consistent with the Pꢀ and Rꢀbranches
9
52,65
ꢀ
1
ꢀ1
through putative {CoNO} intermediates to result in N O.
of N O at 2236 and 2208 cm that shift to 2167 and 2145 cm
2
2
9
15
8,105ꢀ106
The {CoNO} system with an Nꢀconfused porphyrin catalytiꢀ
cally generates N O via a bimolecular NOR mechanism;
when using the NO isotopologue (Figure 7).
Indeed,
65
the yield of N O from 3 was 63 ± 3%, quantified using a caliꢀ
2
2
dimerization of free HNO to N O was excluded based on MS
bration curve with N O produced from the HNO donor Piꢀ
2
2
107
evidence of the hyponitritoꢀbridged Coꢀdimer. Notably, none
of these studies collectively probe the HNO donor capacity of
the Feꢀ or Coꢀnitroxyls, and only one demonstrated HNO
transfer in water. These reports contrast with what we demonꢀ
strate here, viz., no evidence of a dimer to promote NꢀN couꢀ
loty’s Acid (Figure S22). These results were consistent with
+
9
the 4/H reaction. Thus, {CoNO} complexes produce HNO in
15
water. Notably, no other gaseous Nꢀcontaining species were
observed in the IR (Figure S23). Reaction of 3 with
HBF •Et O (1:7) in THF, a solvent in which other products are
4
2
readily identified, also produces N O. Additional species idenꢀ
2
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Journal of the American Chemical Society
pling via an NORꢀlike pathway that would be independent of
free HNO.
ii) Reaction of {CoNO} Complexes with a Nitroxyl
addition of
[Mn(TPPS)(NO)] in blue (t = 6.5 h).
3
(red solid;
5
equiv). Final trace of
4
−
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
8/9
8/9
(
(iii) Reaction of {CoNO} Complexes with a Biological
III
target (Mn -porphyrin). Based on the high affinity and suꢀ
Nitroxyl Target (metMb). Biological HNO targets were purꢀ
sued to assess whether HNO/NO coordination occurs with
known proteins under aqueous conditions. As such, the reacꢀ
tion of the Coꢀnitrosyls with equine skeletal metMb was invesꢀ
tigated in PBS (pH 7.4) at 310 K. The addition of {CoNO} 3
to metMb (5:1) afforded nitrosylated myoglobin (MbNO) over
1.5 h based on shifts in the Soret (409 nm → 420 nm) and Qꢀ
bands (503 nm, 637 nm → 545 nm, 582 nm; Figure 9). Using
the ε values of metMb
MbNO was found to be nearly quantitative with kobs = 4.88
III
117
perior selectivity of HNO for Mn ꢀP, HNO donor reactions
−
III
3−
were investigated using waterꢀsoluble [Mn (TPPS)] (TPPS
=
mesoꢀtetrakis(4ꢀsulfonatophenyl)porphyrinate; λmax = 467
9
nm) in phosphateꢀbuffered saline (PBS; pH 7.4) at 298 K.
III
3−
Indeed, the reaction of 3 with [Mn (TPPS)] (5:1) afforded
4
−
[Mn(TPPS)(NO)] (λmax = 424 nm) in 6.5 h with a pseudo
ꢀ
5
ꢀ1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
firstꢀorder rate constant (k ) of 9.00 ± 3.96 × 10 s (Figure
obs
8
123ꢀ124
125
8). In contrast, no reaction was observed between {CoNO} 1
and [Mn (TPPS)] over a 24 h period under identical condiꢀ
tions (Figure S26). As demonstrated by Doctorovich, the
reaction between [Mn (TPPS)] and a large excess of Anꢀ
(t : 117 min) at pH 7.
Additionally, they demonstrate that E (Mn /Mn ) of MnꢀP
and MbNO,
formation of
III
3−
126
117
ꢀ4 ꢀ1
± 0.72 × 10 s . Under similar conditions, the reaction of 4
III
3−
with metMb was complete within 3.5 h (Figure S28). The
ꢀ
2
ꢀ1
9
geli’s Salt occurs with kobs ~ 10
s
{CoNO} /metMb reaction is slower than the immediate
1/2
III
II
−
8
1/2
HNO/NO transfer that occurs with the analogous {FeNO}
41
influences the reaction mechanism with HNO donors, viz. an
MnꢀP with E½ > 0 accelerates decomposition of the donor
through a donor/MnꢀP bonding interaction, whereas an MnꢀP
with E1/2 < 0 reacts directly with free HNO after donor deꢀ
system. For reference, the reaction of Angeli’s Salt with
127
sperm whale metMb takes 15.5 min to go to completion,
and recently, a dinitrosyl iron complex (DNIC) was shown to
form MbNO in 10 min (both at 25 °C). The slower HNO
release of 3 is an advantageous kinetic control that we did not
have with the Fe systems. In contrast, there was no reaction
between 1 and metMb (Figure S29).
110
118ꢀ119
composition.
This mechanistic distinction may be faciliꢀ
tated by electrostatics, given the negative charge of HNO doꢀ
nors such as Angeli’s Salt and Piloty’s Acid. Indeed, when
III
Mn ꢀP and the HNO donor directly interact, t is on the order
1
/2
of seconds. In contrast, t1/2 is on the order of minutesꢀtoꢀhours
when donor decomposition/release of free HNO is the rateꢀ
III
limiting step. The latter occurs when the Mn ꢀP E is nega-
½
tive. Taken together, the clean reaction of
3
with
III
3−
[
{
Mn (TPPS)] (E1/2 = ꢀ0.16 V vs. NHE) to form the
6
MnNO} complex over 6.5 h is consistent with production of
9
free HNO from the {CoNO} platform in 3.
9
+
Given that one of the products of the {CoNO} 3/H reacꢀ
10
tion in THF is the corresponding {Co(NO)2} complex 5, we
III
3−
also probed the reaction between 5 and [Mn (TPPS)] (Figꢀ
ure S27). Based on UVꢀvis spectral monitoring, the reaction of
III
3−
5
with [Mn (TPPS)] (2.5/1) goes to completion in 21 h.
III
Thus, 5 is capable of reductively nitrosylating Mn ꢀP and is
an alternative HNO donor. This result draws parallels to thioꢀ
9
lateꢀligated {Fe(NO) } DNICs that have been demonstrated to
2
store and release NO equivalents in a protonꢀresponsive manꢀ
Figure 9. UVꢀvis spectrum of a 2.19 µM solution of equine skeleꢀ
tal muscle metMb before (red) and after 1.5 h (blue) reaction with
3 (5 equiv) at 310 K in PBS (pH 7.4; traces in grey represent 10
min intervals). Inset: expansion of the Qꢀband region for the iniꢀ
tial and final spectrum.
120ꢀ122
9
ner.
However, it appears that {CoNO} 3 reacts on a
slightly faster timescale than its dinitrosyl analogue and is thus
an unlikely HNO donor in the aforementioned reaction.
II
Mechanistically, there is no evidence of a reduced Fe ꢀMb
1
23
intermediate (Soret = 435 nm ), although the timescale with
which such an intermediate is formed and then nitrosylated
could be more rapid than the timescale with which the reaction
was monitored (< 1 min). To eliminate the possibility that
9
{
CoNO} reductively nitrosylates metMb by electronꢀtransfer
8
followed by NO• release from {CoNO} , we studied the reacꢀ
tion of {CoNO} 1 with ferrous myoglobin (deoxyMb). Interꢀ
estingly, complex 1 is capable of nitrosylating deoxyMb, to
form MbNO (Figure S31). However, this reaction is complete
8
soon after mixing the two compounds. If metMb reduction by
9
{
CoNO} occurred before nitrosylation, then the completion
time would likely be faster than the observed 1.5 h. Therefore,
these results, along with the Mn ꢀP assay, suggest free HNO
III
III
transfer from 3. In contrast to its reaction with Mn ꢀP,
Figure 8. UVꢀvis spectral monitor of a 9.90 µM PBS solution (pH
10
{
Co(NO)2} 5 is not capable of reductively nitrosylating
III
3−
7
.4, 298 K) of [Mn (TPPS)] (red dash) and immediately after
ACS Paragon Plus Environment

Journal of the American Chemical Society
metMb under identical conditions (24 h), likely a result of
Page 8 of 14
ꢀ
O
H
O
O
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
electrostatic repulsion between the positively charged metMb
and the cationic dinitrosyl (Figure S32).
N
N
N
eꢀ
+ H+
+
Co
Co
Co
1
Proposed Reaction Pathway. Spectroscopic evidence ( H
{CoNO}8
LSꢀCoIIIꢀ1NOꢀ
{CoNO}9
{CoHNO}9
+
NMR, IR, MS) of the 3/H reaction points to free HNO via
II
3
ꢀ
II
1
ꢀ
HSꢀCo ꢀ NO
LSꢀCo ꢀ NO
N O in addition to the presence of the Coꢀnitrosyl 1 and diꢀ
2
III
+
nitrosyl 5 as major products. A smaller amount of [Co L]
+ H
+
+ HNO target
aqueous
+
NO (n = 2+) OR
ꢀ
I
−
and [Co L] is also observed. Several paths that account for
these compounds are depicted in Scheme 2. In the absence of
an HNO target, three competing reactions occur. Reaction A
+ e , NO (n = 3+)
+
H
O
solv
N
+
HNO target
organic
produces free HNO which selfꢀreacts to form N O and H O.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
Con
+ HNOꢀmodified product
8
Co
An alternate reaction (B) produces one equiv of {CoNO} 1
with concurrent evolution of 0.5 equiv of H . Reactions analoꢀ
2
7
8,112,128
8
gous to B have been reported
with an {FeNO} comꢀ
plex to form H and the corresponding {FeNO} . Two of the
Scheme 3. Proposal of HNOꢀrelease. Compounds in brackets
represent intermediates not isolated or observed spectroscopiꢀ
cally in the reaction.
7
2
reactions (B and C) account for the observation of dinitrosyl 5.
We have previously demonstrated that {CoNO} and H are in
8
+
10
III
+
Conclusions
equilibrium with {Co(NO) } and [Co L] (Scheme 2, botꢀ
2
43
8
+
tom). The {CoNO} /H equilibrium favors the reactant side
under stoichiometric conditions. The other possibility (C) genꢀ
erates 5 with the concomitant production of a [Co L] monoanꢀ
ion. These three competing reactions explain the observed
product speciation, diamagnetism, as well as the relative quanꢀ
tities based on NMR integration. Path A is favored with excess
A combined structural (XAS), spectroscopic (FTIR, EPR,
MS) and theoretical (DFT) effort has shown that 5C {CoNO}
species exhibit rare electronic structural properties that change
upon the addition of H .
complexes (3, 4) are assigned as HSꢀCo coordinated to NO ,
while a putative LSꢀCo ꢀ HNO intermediate exists after H
addition. These protonated {CoNO} complexes liberate free
HNO in water as demonstrated by the detection and quantifiꢀ
9
I
−
+ 130ꢀ131
The isolated nitroxyl anion
II 3 ‒
II 1
+
+
9
H whereas B and C are favored under stoichiometric condiꢀ
tions. Assuming a pK of 11 for the Coꢀcoordinated NO,
129
a
nearly all (99.8%) of the complex is CoꢀHNO at pH 7.4 and
thus reaction A predominates under physiological conditions.
cation of N O via headspace gas IR. As a cautionary note,
experiments performed under limiting H conditions reveal
2
+
that several competing paths exist that could prevent the reꢀ
lease of HNO, one of which involves the formation of the corꢀ
1
0
responding dinitrosyl {Co(NO)2} complex 5 as a potential
dead end. However, this limitation is somewhat muted by the
fact that 5 may also generate HNO. Nitroxyl trapping experiꢀ
III
ments with Mn ꢀP and metMb conducted under physiological
conditions are consistent with free HNO being released from 3
II
and 4 with the Co ꢀHNO intermediate being generated along
the reaction path. The enhanced reactivity of 3 and 4 in water
is in stark contrast to the relative inertness of {CoNO} 1 and
8
2
and can be explained by the increased lability of the CoꢀNO
bond resulting from the primarily Coꢀcentered reduction in the
9
8
{CoNO} complexes. Numerous {CoNO} complexes have
been synthesized and the results presented here and
Scheme 2. Interconversions of Co nitrosyls upon protonation
43,55ꢀ56
in the absence of an HNO target. Path A is favored with exꢀ
elsewhere
suggest that many could be reasonable HNO
+
108
8
+
43
9
cess H . Grey represents {CoNO} /H path.
donors. However, their oneꢀelectron reduced {CoNO} anaꢀ
logues are even more promising, especially as HNO donors in
aqueous media. Taken together, this work provides the first
example of an extensively characterized set of {CoNO}
complexes and suggests that these types of molecules will
likely play a role in the development of HNO donors.
The first step towards free HNO is protonation of 3 to
form 3-HNO which, as suggested by DFT, changes the Co
8
/9
II 1
from HS to LS, i.e., LSꢀCo ꢀ HNO (Scheme 3). Protonation
leads to elongation of the CoꢀNO distance by 0.2 Å and laꢀ
bilizes this bond so that HNO can readily dissociate from the
In order to apply these complexes for biomedical HNOꢀ
release, several properties must still be optimized. For examꢀ
II
[
Co L] platform. HNO can then either (i) form N O and/or (ii)
2
3−
III
react with an HNO target, e.g., [Mn (TPPS)] or metMb.
Indeed, in the presence of an HNO target, the free HNO proꢀ
duced from 3 is captured (see Figures 7ꢀ9). As there is no
spectral evidence for any intermediates in the {CoNO} reacꢀ
tion with metMb or Mn ꢀP, and given the isosbestic behavior,
8
9
ple, the {CoNO} /{CoNO} potential is too negative (E ~ ꢀ1
1
/2
V vs. NHE) to be useful under physiological conditions and
the aqueous solubility of the complexes needs to be improved.
Based on the similarities in electronic structure and reactivity
between 3 and 4, it is clear that changes to the primary coordiꢀ
nation sphere (rather than peripheral ligand modifications)
must occur in order to significantly modulate the properties of
the MꢀNO unit. The fine tuning of these properties can be acꢀ
complished by judicious ligand design in future constructs.
For example, supporting ligands with neutral donors will: (i)
make the corresponding CoꢀNO complexes cationic, charged,
9
III
it is likely that free HNO dissociates from Co and reacts with
III
the M ꢀP center directly.
8
9
and thus more waterꢀsoluble in both {CoNO} and {CoNO}
ACS Paragon Plus Environment

Page 9 of 14
Journal of the American Chemical Society
9
states; (ii) increase E1/2 such that the {CoNO} state is accessiꢀ
Physical Methods. FTIR spectra were collected with a
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
ble and stable in the biological window, as this state is the
most likely HNO donor; and (iii) increase the lability of the
coordinated HNO by decreasing πꢀbackdonation from Co due
to reduced charge on the metal. Although dimerization is not
observed here, synthetic strategies that encourage HNO liberaꢀ
tion and prevent dimerization and subsequent nitroxyl couꢀ
pling reactions (i.e., NOR reaction) should be considered.
Secondaryꢀsphere modifications to protect the CoꢀNO pocket
should accomplish such a goal. Another design component to
consider is the use of pentacoordinate supporting ligands to
restrict NO chemistry to one specific coordination site and
prevent alternative reaction pathways (e.g, dinitrosyl forꢀ
Thermo Nicolet 6700 spectrophotometer running the OMNIC
software. Solidꢀstate samples were run as KBr pellets, while
solutionꢀstate spectra were obtained using a demountable airꢀ
tight liquid IR cell from GrasebyꢀSpecac with CaF
and 0.1 mm Teflon spacers. All FTIR samples were prepared
inside a glovebox under an inert atmosphere of purified N
windows
2
.
2
The closed liquid cell was taken out of the box and spectra
were acquired immediately. Xꢀband (9.60 GHz) EPR spectra
were obtained on a Bruker ESP 300E EPR spectrometer conꢀ
trolled with a Bruker microwave bridge at 10 K. The EPR was
equipped with a continuousꢀflow liquid He cryostat and a
temperature controller (ESR 9) made by Oxford Instruments
Inc. Continuous wave (CW) Qꢀband (35 GHz) EPR spectra
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
mation). On the other hand, the Co(LN )ꢀNO complexes preꢀ
4
137
sented here do not show any affinity for a sixth ligand due to
the strong trans influence of the NO axial ligand. It appears
that CoꢀNO complexes in biology are rather stable. Indeed,
were recorded at 2 K on a modified Varian spectrometer.
Under the experimental conditions employed here, which lead
138
to “rapidꢀpassage” effects, 35 GHz EPR spectra are obꢀ
served in the dispersion mode and appear as absorption lineꢀ
shapes, rather than the standard absorption mode detection and
first derivative presentation. Digital derivatives were taken to
allow conventional presentation. EPR simulations were perꢀ
II
8
ꢀ1 ꢀ1
NO has a high affinity for Co ꢀCbl (k = 5.0 × 10 M s ; k
on
off
ꢀ
1 132
8
= 3.0 s ) to generate the {CoNO} , comparable to ferrousꢀ
hemes, and labilizes the benzimidazole ligand (CoꢀNimidazole
2.35 Å). Similar kon values are observed with 5C baseꢀoff
133
:
134
139
Cbl and cobinamide (Cbi), but the back reaction is even less
formed using the program QPOW, as modified by J. Telser.
Electronic absorption spectra were run at 298 K or 310 K usꢀ
ing a Caryꢀ50 UVꢀvis spectrophotometer containing a Quanꢀ
tum Northwest TC 125 temperature control unit. The UVꢀvis
samples were prepared anaerobically in gasꢀtight screw cap
quartz cells with an optical pathlength of 1 cm. Electrochemisꢀ
ꢀ
1
135
ꢀ1
132
favored (koff = 1.7 s (baseꢀoff Cbl); koff = 0.019 s (Cbi)).
Collectively, these design elements are being tested and are
the subject of ongoing work in our lab.
Experimental
try measurements were performed with a PAR Model 273A
+
General Information. All reagents were purchased from
commercial suppliers and used as received unless otherwise
noted. Research grade nitric oxide gas (NO(g), UHP, 99.5%)
was obtained from Matheson TriꢀGas. The NO(g) was purified
potentiostat using a nonꢀaqueous Ag/Ag (0.01 M AgNO /0.1
3
n
M Bu NPF in MeCN) reference electrode, Ptꢀwire counter
4
6
electrode, and a Glassy Carbon working milliꢀelectrode (diamꢀ
eter = 2 mm) under an Ar atmosphere. Measurements were
performed at ambient temperature using 1.0ꢀ10.0 mM analyte

by passage through an Ascarite II (sodium hydroxideꢀcoated
n
silica, purchased from Aldrich) column and handled under
in MeCN containing 0.1 M Bu NPF as the supporting elecꢀ
4
6
1
5
15
anaerobic conditions. NO(g) ( N ≥ 98%) was procured from
Cambridge Isotope Labs and used as received. 18ꢀcrownꢀ6
ether (18C6) was obtained from Aldrich and used as received.
Piloty’s Acid (PA) was used as received from Cayman Chemꢀ
ical and stored at ꢀ20 °C. The Piloty’s acid solution used for
the N O calibration curve was prepared with milliꢀQ H O and
trolyte. Ferrocene (Fc) was used as an external standard and
+ 1
all potentials are reported relative to the Fc/Fc couple. H, and
1
5
N spectra were recorded in the listed deuterated solvent with
a 400 MHz Bruker BZH 400/52 NMR spectrometer or a Variꢀ
an Unity Inova 500 MHz NMR spectrometer at 298 K or RT
with chemical shifts internally referenced to TMS, CH
NO
2
2
3
2
15
adjusted with NaOH to pH 13.0. Acetonitrile (MeCN), tetraꢀ
hydrofuran (THF), dichloromethane (CH Cl ), and diethyl
( N), or the residual protio signal of the deuterated solvent as
140
previously reported. Low resolution ESIꢀMS data were colꢀ
lected on a Bruker Esquire 3000 plus ion trap mass spectromeꢀ
ter. High resolution ESIꢀMS data were collected using an Orꢀ
bitrap Elite system with CID for MSꢀMS with precision to the
third decimal place. Elemental microanalyses for C, H, and N
were performed by Environmental (formerly Columbia Anaꢀ
lytical Services) in Tucson, AZ or QTIꢀIntertek in
Whitehouse, NJ.
2
2
ether (Et O) were purified by passage through activated aluꢀ
2
mina columns using an MBraun MBꢀSPS solvent purification
system and stored over 3 Å molecular sieves under an N atꢀ
2
mosphere before use. Anhydrous 2ꢀmethyltetrahydrofuran (2ꢀ
MeTHF) and methanol (MeOH) were obtained by storage over
3
Å molecular sieves for 48 h, decanting from the sieves, and
136 1 2
storage under N . (Et N) [CoCl ], LN ꢀligands (N E,N E)ꢀ
N ,N ꢀbis((1Hꢀpyrrolꢀ2ꢀyl)methylene)ꢀbenzeneꢀ1,2ꢀdiamine
(LN H , where H = dissociable protons), (N E,N E)ꢀN ,N ꢀ
2
4
2
4
4
1
2
Computational methods. DFT calculations were carried
Ph
1
2
1
2
4
2
out with the ADF (Amsterdam Density Functional) 2013 proꢀ
141
bis((1Hꢀpyrrolꢀ2ꢀyl)methylene)ꢀ4,5ꢀdichlorobenzeneꢀ1,2ꢀ
gramme, with three different exchange correlation functionꢀ
PhCl 42
8
1
42
143ꢀ145
146ꢀ
diamine
(LN H
),
{CoNO}
complexes
4
2
als, including the pure functionals BP86
and OLYP,
Allꢀelectron STOꢀ
PhCl
)(NO)] (2) and [Co(LN4
PhCl 15
15 43
1
49
150ꢀ151
[
Co(LN4
)( NO)] (2- NO)
and the hybrid functional B3LYP.
were synthesized according to the published procedures. All
reactions were performed under an inert atmosphere of N2
TZP basis sets were employed throughout, along with a fine
mesh for numerical integration of matrix elements and tight
criteria for both SCF and geometry optimizations.
using standard Schlenk line techniques or in an MBraun
Unilab glovebox under an atmosphere of purified N . Reacꢀ
2
tions involving NO(g) and nitroxyl transfer were performed
with minimal light exposure by wrapping the reaction
flasks/vials with aluminum foil to avoid any photochemical
reactions.
Synthesis of Compounds
Ph
8
[Co(LN4 )(NO)], {CoNO} (1). To a batch of yellow
Ph
LN H2 (350.0 mg, 1.334 mmol) in 4 mL of MeCN, a 2 mL
4
MeCN slurry of NaH (72.1 mg, 3.00 mmol) was added. A
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 14
slightly heterogeneous dark yellow solution resulted from
(w), 736 (m), 687 (w), 610 (w), 592 (w), 583 (w), 525 (w),
477 (w), 450 (w), 419 (w). HRMSꢀESI (m/z): [M] calcd for
−
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
mixing the two reactants and H gas was evolved. This soluꢀ
2
tion stirred with quick vacuum for 30 min, following which a
5 mL blue MeCN slurry of (Et N) [CoCl ] (615.4 mg, 1.334
C H CoN O (relative abundance), 349.037 (100.0), 350.040
16
12
5
1
4
2
4
(17.3), 351.043 (1.2); found, 349.037 (100.0), 350.040 (14.4),
II
ꢀ1
ꢀ1
mmol) was added. Upon mixing the Co salt and the deprotoꢀ
nated ligand, the solution immediately turned deep redꢀbrown
and a light grey solid slowly precipitated. The reaction mixture
stirred at 60 °C with a water bath for 3 h. After cooling the
reaction to RT, the solution was filtered to remove NaCl and
washed with 3 mL of MeCN. The yellowꢀtinted dark brown
351.029 (0.8). UVꢀvis (THF, 298 K), λmax, nm (ε, M cm ):
317 (5,900), 365 (9,600), 451 (3,700), 498 (2,400). Anal.
Calcd. for C H CoKN O : C, 51.53; H, 5.56; N, 10.73.
28 36
5
7
Found: C, 51.05; H, 5.69; N, 10.21.
Ph 15
15
9
15
[K(18C6)][Co(LN4 )( NO)], {Co NO} (3- NO). The
15
isotopicallyꢀlabeled complex 3- NO was prepared analogousꢀ
Ph
1
5
MeCN filtrate containing (Et N) [Co(LN )Cl ] was then
4
2
4
2
ly to 3 except for using 50.0 mg (0.143 mmol) of 1- NO, 30.9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
purged with purified NO(g) for 1.5 min at 60 °C. Addition of
NO resulted in an immediate albeit slight color change; the
solution became darker brown (redꢀtinted) and a microcrystalꢀ
line precipitate was immediately observed. The reaction mixꢀ
ture stirred at 60 °C for 30 min under an NO atmosphere. The
solution was then cooled to RT and excess NO(g) was reꢀ
mg (0.229 mmol) of KC , and 75.5 mg (0.286 mmol) of 18C6.
8
Yield: 68.7 mg (0.105 mmol, 74% yield). FTIR (KBr matrix),
ꢀ
1
νNO (cm ): ~1580; overlaps with broad imine stretches (νC=N)
−
in the same region. HRMSꢀESI (m/z): [M] calcd for
15
C H CoN N O1 (relative abundance), 350.034 (100.0),
16
12
4
1
3
51.037 (17.3), 352.040 (1.4); found, 350.035 (100.0),
moved by pulling vacuum and refilling with N . The reaction
2
351.038 (17.3), 352.037 (1.2).
mixture was then placed in a ꢀ24 °C freezer overnight to inꢀ
duce further precipitation. The resulting microcrystalline solid
was filtered, washed (3 × 1 mL) with MeCN and dried under
PhCl
9
[K(18C6)][Co(LN4 )(NO)], {CoNO} (4). Solid KC8
(
25.9 mg, 0.191 mmol) was directly added to a 4 mL 2ꢀ
MeTHF solution of 2 (50.0 mg, 0.120 mmol) containing 18C6
63.2 mg, 0.239 mmol) and stirred for 1 h at RT. The color of
1
vacuum to afford 391.3 mg (1.120 mmol, 84%) of product. H
(
NMR (500 MHz, THF, δ from residual protio solvent): 8.13
the solution remained dark brown and the KC slowly changed
8
(s, 1H), 7.58 (br m, 1H), 7.51 (s, 1H), 7.08 (br m, 1H), 7.00 (s,
from gold to silver consistent with formation of graphite. The
reaction mixture was filtered with a medium porosity glass frit
to remove the insoluble silver graphite flakes. The resulting
dark brown filtrate was then stripped to dryness in vacuo leavꢀ
ing a sticky residue. This residue was stirred in ~10 mL of
1
3
1H), 6.33 (s, 1H). C NMR (125 MHz, THFꢀd , RT, δ from
8
solvent): 153.0 (CH=N), 147.5 (ArꢀC), 143.9 (ArꢀC), 142.4
(
ArꢀC), 126.7 (ArꢀC), 122.2 (ArꢀC), 116.4 (ArꢀC), 114.9 (Arꢀ
ꢀ1
C). FTIR (KBr matrix), νmax (cm ): 3293 (vw), 3059 (vw),
3
010 (vw), 1667 (sh, vs, νNO), 1656 (vs, νNO), 1582 (m), 1552
Et O for 20 min in order to remove the excess 18C6, which
2
(vs), 1507 (m), 1460 (m), 1446 (m), 1406 (w), 1380 (vs), 1326
(w), 1295 (vs), 1257 (s), 1196 (m), 1170 (w), 1154 (w), 1102
(w), 1076 (w), 1042 (s), 1033 (vs), 986 (m), 929 (w), 914 (w),
afforded 70.4 mg (0.0976 mmol, 82%) of a dark brown solid
after vacuum filtration and drying. FTIR (KBr matrix), ν
max
ꢀ1
(cm ): 3092 (w), 3079 (w), 2908 (m), 2892 (m), 2855 (m),
8
6
95 (m), 863 (w), 846 (w), 816 (w), 781 (w), 741 (vs), 729 (s),
2
823 (w), 2797 (w), 1617 (m, νNO), 1568 (vs), 1537 (s), 1455
77 (m), 648 (w), 627 (w), 603 (m), 532 (w), 480 (w). FTIR
(
(
m), 1380 (s), 1350 (m), 1292 (s), 1270 (m), 1249 (w), 1191
w), 1110 (vs), 1026 (m), 963 (m), 932 (w), 889 (w), 866 (w),
ꢀ1
(
1
solution, CaF windows, 0.1 mm spacers, RT), ν (cm ):
2
NO
668 (THF), 1670 (MeOH), 1668 (MeCN). UVꢀvis (THF, 298
8
5
38 (w), 808 (w), 760 (w), 741 (w), 685 (w), 673 (w), 608 (w),
ꢀ1 ꢀ1
K), λmax, nm (ε, M cm ): 318 (19,000), 364 (25,000), 453
12,000), 497 (9,600). Anal. Calcd for C H CoN O•0.5H O:
31 (w), 494 (w), 467 (w), 450 (w), 432 (w) 417 (w), 405 (w).
(
−
1
6
12
5
2
HRMSꢀESI (m/z): [M] calcd for C H Cl CoN O (relative
16
10
2
5
1
C, 53.64; H, 3.66; N, 19.55. Found: C, 53.75; H, 3.30; N,
19.23.
abundance), 416.959 (100.0), 417.963 (17.3), 418.956 (64.8),
19.959 (11.2), 420.953 (10.5), 421.957 (1.8); found, 416.960
(100.0), 417.980 (23.5), 418.957 (65.9), 419.977 (15.0),
20.954 (10.0), 421.973 (1.9). UVꢀvis (THF, 298 K), λmax, nm
4
Ph 15
15
8
15
[
Co(LN4 )( NO)], {Co NO} (1- NO). The isotopicallyꢀ
15
labeled complex 1- NO was prepared analogously to 1 except
for using 0.2000 g (0.7625 mmol) of LN H2 , 41.2 mg (1.72
4
Ph
ꢀ1
ꢀ1
4
(ε, M cm ): 324 (5,000), 370 (8,400), 460 (3,700), 510
(2,300). Anal. Calcd. for C H Cl CoKN O •H O: C, 45.47;
mmol) of NaH, 351.7 g (0.7625 mmol) of (Et N) [CoCl ], and
4
2
4
28
34
2
5
7
2
1
5
NO(g). Yield: 0.1421 g (0.4057 mmol, 53%). FTIR (KBr
matrix), ν (cm ): 1641 (ꢀν : 26 cm ), 1628 (ꢀνNO: 28 cm
). N NMR (50.7 MHz, THFꢀd , δ from CH NO ): 675.
H, 4.91; N, 9.47. Found: C, 45.40; H, 4.45; N, 9.27.
ꢀ
1
ꢀ1
ꢀ
PhCl 15
15
9
15
NO
NO
[
K(18C6)][Co(LN4
)( NO)], {Co NO} (4- NO). The
1
15
15
8
3
2
isotopicallyꢀlabeled complex 4- NO was prepared analogousꢀ
ly to 4 except for using 50.1 mg (0.120 mmol) of 2- NO, 25.9
Ph
9
15
[
K(18C6)][Co(LN4 )(NO)], {CoNO} (3). Solid KC (31.0
8
mg, 0.229 mmol) was directly added to a 4 mL 2ꢀMeTHF
solution of 1 (50.0 mg, 0.143 mmol) containing 18C6 (75.6
mg, 0.286 mmol) and stirred for 1 h at RT. The color of the
solution remained dark brown and the color of the insoluble
mg (0.192 mmol) of KC , and 63.2 mg (0.239 mmol) of 18C6.
8
Yield: 57.0 mg (0.0789 mmol, 66% yield). FTIR (KBr maꢀ
ꢀ
1
trix), νNO (cm ): ~1585, unable to definitively identify ν
15NO
due to broad imine stretches (ν ) in the same region. HRMSꢀ
C=N
−
15
KC slowly changed from gold to silver flakes. The reaction
8
ESI (m/z): [M] calcd for C H Cl CoN N O (relative
16 10 2 4 1 1
was filtered, yielding insoluble silver flakes (graphite) and a
dark brown filtrate, which was then dried in vacuo leaving a
abundance), 417.956 (100.0), 418.959 (17.3), 419.953 (63.9),
20.956 (11.1), 421.950 (10.2), 422.953 (1.8); found, 417.958
(100.0), 418.960 (17.8), 419.954 (67.8), 420.957 (11.3),
21.951 (10.9), 422.954 (1.7).
4
sticky residue. The sticky residue stirred in ~15 mL of Et O
2
for 2 h in order to remove the excess 18C6 and was then filꢀ
4
tered, affording 65.0 mg of 2 as a dark brown solid (0.0996
ꢀ1
mmol, 70%). FTIR (KBr matrix), νmax (cm ): 3078 (w), 2901
ASSOCIATED CONTENT
Supporting Information. Additional reactivity, structural and
spectroscopic data, CIF file for 1. This material is available free of
charge via the Internet at http://pubs.acs.org.
(m), 1609 (m, νNO), 1581 (s), 1557 (s), 1457 (m), 1382 (s),
1
1
351 (m), 1285 (s), 1253 (m), 1213 (w), 1187 (m), 1105 (vs),
025 (m), 961 (m), 920 (w), 867 (w), 836 (w), 784 (w), 759
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AUTHOR INFORMATION
Journal of the American Chemical Society
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13) Sulc, F.; Immoos, C. E.; Pervitsky, D.; Farmer, P. J. J. Am.
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Chem. Soc. 2004, 126, 1096.
Corresponding Author
*Email: tharrop@uga.edu
(14) Brown, K. L. Chem. Rev. 2005, 105, 2075.
(
(
15) Pallares, I. G.; Brunold, T. C. Inorg. Chem. 2014, 53, 7676.
16) Brouwer, M.; Chamulitrat, W.; Ferruzzi, G.; Sauls, D. L.;
Author Contributions
Weinberg, J. B. Blood 1996, 88, 1857.
17) Subedi, H.; Hassanin, H. A.; Brasch, N. E. Inorg. Chem. 2014,
53, 1570.
(
The manuscript was written through contributions of all authors.
All authors have given approval to the final version of the manuꢀ
script.
(
18) Subedi, H.; Brasch, N. E. Eur. J. Inorg. Chem. 2015, 2015,
3
825.
(
19) Subedi, H.; Brasch, N. E. Dalton Trans. 2016, 45, 352.
Notes
(20) Carmel, R.; Jacobsen, D. W., Homocysteine in Health and
0
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3
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9
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The authors declare no competing financial interest.
Disease. Cambridge University Press: Cambridge, U.K., 2001.
(21) Qureshi, G. A.; Memon, S. A.; Collin, C.; Parvez, S. H.
Biogenic Amines 2004, 18, 117.
ACKNOWLEDGMENT
(
22) Fukuto, J. M.; Carrington, S. J. Antioxid. Redox Sign. 2011,
4, 1649.
23) Paolocci, N.; Jackson, M. I.; Lopez, B. E.; Miranda, K.;
T.C.H. acknowledges financial support from the NSF, the Office
of the Vice President for Research (OVPR), and the Office of the
Provost at the University of Georgia (UGA). The authors also
acknowledge the work of Koustubh S. Dube (UGA) for the initial
report of 1. TLS and SPD acknowledge the NIH and the Ameriꢀ
can Heart Association/Friedreich’s Ataxia Research Alliance
1
(
Tocchetti, C. G.; Wink, D. A.; Hobbs, A. J.; Fukuto, J. M. Pharmacol.
Ther. 2007, 113, 442.
(
24) FloresꢀSantana, W.; Salmon, D. J.; Donzelli, S.; Switzer, C.
H.; Basudhar, D.; Ridnour, L.; Cheng, R.; Glynn, S. A.; Paolocci, N.;
Fukuto, J. M.; Miranda, K. M.; Wink, D. A. Antioxid. Redox Sign.
2011, 14, 1659.
(25) Moncada, S.; Higgs, E. A. Br. J. Pharmacol. 2006, 147, S193.
(26) Irvine, J. C.; Ritchie, R. H.; Favaloro, J. L.; Andrews, K. L.;
Widdop, R. E.; KempꢀHarper, B. K. Trends Pharmacol. Sci. 2008, 29,
601.
(DK068139 (TLS), DK101230 and 14PRE18830036 (SPD)) for
research funding. We thank Dr. Dennis R. Phillips and Dr. Chauꢀ
Wen Chou from the Proteomics and Mass Spectrometry Core
Facility (PAMS) at UGA for their assistance with MS experiꢀ
ments. Instrumentation was purchased in part with funds from
NIH Grant 1S10RR028859ꢀ01. Funds for PAMS facility operaꢀ
tions were provided by the UGA OVPR and the UGA Department
of Chemistry. We thank Prof. Brian M. Hoffman, Northwestern
University, for use of the Xꢀ and Qꢀband EPR spectrometers,
which is supported by the NIH (GM 111097 to B.M.H.). XAS
studies were performed at the Stanford Synchrotron Radiation
Lightsource (SSRL) and at the National Synchrotron Radiation
Laboratory (NSLS) on beamline X3b. SSRL is a national user
facility operated by Stanford University on behalf of the Departꢀ
ment of Energy (DOE), Office of Basic Energy Sciences. The
SSRL Structural Molecular Biology Program is supported by the
DOE, Office of Biological and Environmental Research, and by
the NIH, National Center for Research Resources, Biomedical
Technology Program. NSLS, located at Brookhaven National
Laboratory, is supported by the DOE, Division of Materials Sciꢀ
ences and Division of Chemical Sciences, under Contract No.
DEAC02ꢀ98CH10886.
(
27) Paolocci, N.; Saavedra, W. F.; Miranda, K. M.; Martignani,
C.; Isoda, T.; Hare, J. M.; Espey, M. G.; Fukuto, J. M.; Feelisch, M.;
Wink, D. A.; Kass, D. A. Proc. Natl. Acad. Sci. U.S.A. 2001, 98,
10463.
(28) Rosen, G. M.; Tsai, P.; Pou, S. Chem. Rev. 2002, 102, 1191.
(
29) Eberhardt, M.; Dux, M.; Namer, B.; Miljkovic, J.; Cordasic,
N.; Will, C.; Kichko, T. I.; de la Roche, J.; Fischer, M.; Suárez, S. A.;
Bikiel, D.; Dorsch, K.; Leffler, A.; Babes, A.; Lampert, A.; Lennerz,
J. K.; Jacobi, J.; Martí, M. A.; Doctorovich, F.; Högestätt, E. D.;
Zygmunt, P. M.; IvanovicꢀBurmazovic, I.; Messlinger, K.; Reeh, P.;
Filipovic, M. R. Nature Commun. 2014, 5, 4381.
(
30) Miljkovic, J. L.; Kenkel, I.; IvanovićꢀBurmazović, I.;
Filipovic, M. R. Angew. Chem. Int. Ed. 2013, 52, 12061
(31) Filipovic, M. R.; Eberhardt, M.; Prokopovic, V.; Mijuskovic,
A.; OrescaninꢀDusic, Z.; Reeh, P.; IvanovićꢀBurmazović, I. J. Med.
Chem. 2013, 56, 1499.
(32) Wedmann, R.; Zahl, A.; Shubina, T. E.; Dürr, M.; Heinemann,
F. W.; Bugenhagen, B. E. C.; Burger, P.; IvanovićꢀBurmazović, I.;
Filipovic, M. R. Inorg. Chem. 2015, 54, 9367.
REFERENCES
(1) Bartberger, M. D.; Liu, W.; Ford, E.; Miranda, K. M.; Switzer,
C.; Fukuto, J. M.; Farmer, P. J.; Wink, D. A.; Houk, K. N. Proc. Natl.
Acad. Sci. U.S.A. 2002, 99, 10958.
(
33) Suarez, S. A.; Neuman, N. I.; Muñoz, M.; Álvarez, L.; Bikiel,
D. E.; Brondino, C. D.; IvanovićꢀBurmazović, I.; Miljkovic, J. L.;
Filipovic, M. R.; Martí, M. A.; Doctorovich, F. J. Am. Chem. Soc.
2015, 137, 4720.
(
(
2) Speelman, A. L.; Lehnert, N. Acc. Chem. Res. 2014, 47, 1106.
3) Kumar, M. R.; Fukuto, J. M.; Miranda, K. M.; Farmer, P. J.
(
34) Shafirovich, V.; Lymar, S. V. Proc. Natl. Acad. Sci. U.S.A.
2
5
6
002, 99, 7340.
Inorg. Chem. 2010, 49, 6283.
(4) Lehnert, N.; Scheidt, W. R.; Wolf, M. W. Struct. Bond. 2014,
(
(
35) Miranda, K. M. Coord. Chem. Rev. 2005, 249, 433.
36) Kohout, F. C.; Lampe, F. W. J. Am. Chem. Soc. 1965, 87,
1
54, 155.
5) Shiro, Y.; Fujii, M.; Iizuka, T.; Adachi, S.ꢀi.; Tsukamoto, K.;
Nakahara, K.; Shoun, H. J. Biol. Chem. 1995, 270, 1617.
6) Daiber, A.; Nauser, T.; Takaya, N.; Kudo, T.; Weber, P.;
795.
(37) Smith, P. A. S.; Hein, G. E. J. Am. Chem. Soc. 1960, 82, 5731.
38) Angeli, A.; Angelico, F.; Scurti, F. Chem. Zentralbl. 1902, 73,
91.
39) DeMaster, E. G.; Redfern, B.; Nagasawa, H. T. Biochem.
Pharmacol. 1998, 55, 2007.
40) Nagasawa, H. T.; DeMaster, E. G.; Redfern, B.; Shirota, F. N.;
(
(
(
Hultschig, C.; Shoun, H.; Ullrich, V. J. Inorg. Biochem. 2002, 88,
343.
(
(
7) Obayashi, E.; Takahashi, S.; Shiro, Y. J. Am. Chem. Soc. 1998,
20, 12964.
8) Zheng, S.; Berto, T. C.; Dahl, E. W.; Hoffman, M. B.;
Speelman, A. L.; Lehnert, N. J. Am. Chem. Soc. 2013, 135, 4902.
9) Maia, L. B.; Moura, J. J. G. Chem. Rev. 2014, 114, 5273.
(
1
Goon, D. J. W. J. Med. Chem. 1990, 33, 3120.
(41) Patra, A. K.; Dube, K. S.; Sanders, B. C.; Papaefthymiou, G.
C.; Conradie, J.; Ghosh, A.; Harrop, T. C. Chem. Sci. 2012, 3, 364.
(
(
(
42) Sanders, B. C.; Patra, A. K.; Harrop, T. C. J. Inorg. Biochem.
013, 118, 115.
43) Rhine, M. A.; Rodrigues, A. V.; Bieber Urbauer, R. J.;
(10) Bykov, D.; Neese, F. Inorg. Chem. 2015, 54, 9303.
2
(11) Enemark, J. H.; Feltham, R. D. Coord. Chem. Rev. 1974, 13,
(
n
3
39. {MNO} where n = number of metal d + NO π* electrons.
Urbauer, J. L.; Stemmler, T. L.; Harrop, T. C. J. Am. Chem. Soc.
2014, 136, 12560.
(
12) Lin, R.; Farmer, P. J. J. Am. Chem. Soc. 2000, 122, 2393.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 14
(
44) McCleverty, J. A. Chem. Rev. 2004, 104, 403 and references
(76) Mason, J.; Larkworthy, L. F.; Moore, E. A. Chem. Rev. 2002,
102, 913.
(77) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.;
Verschoor, G. C. J. Chem. Soc. Dalton Trans. 1984, 1349.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
therein.
(
and references therein.
45) Wyllie, G. R. A.; Scheidt, W. R. Chem. Rev. 2002, 102, 1067
(
46) Wright, A. M.; Hayton, T. W. Comment Inorg. Chem. 2012,
3, 207 and references therein.
47) Ellison, M. K.; Scheidt, W. R. Inorg. Chem. 1998, 37, 382.
(78) Pellegrino, J.; Bari, S. E.; Bikiel, D. E.; Doctorovich, F. J. Am.
Chem. Soc. 2010, 132, 989.
(79) Sanders, B. C.; Rhine, M. A.; Harrop, T. C. Struct. Bond.
2014, 160, 57.
(80) Harrop, T. C. Adv. Inorg. Chem. 2015, 67, 243.
(81) Gautam, R.; Loughrey, J. J.; Astashkin, A. V.; Shearer, J.;
Tomat, E. Angew. Chem. Int. Ed. 2015, 54, 14894.
(82) Ramdhanie, B.; Telser, J.; Caneschi, A.; Zakharov, L. N.;
Rheingold, A. L.; Goldberg, D. P. J. Am. Chem. Soc. 2004, 126, 2515.
(83) Fujii, H.; Dou, Y.; Zhou, H.; Yoshida, T.; IkedaꢀSaito, M. J.
Am. Chem. Soc. 1998, 120, 8251.
(84) Little, R. G.; Hoffman, B. M.; Ibers, J. A. Bioinorg. Chem.
1974, 3, 207.
(85) Wayland, B. B.; Minkiewicz, J. V.; AbdꢀElmageed, M. E. J.
Am. Chem. Soc. 1974, 96, 2795.
(86) Wayland, B. B.; AbdꢀElmageed, M. E. J. Am. Chem. Soc.
1974, 96, 4809.
(87) McGarvey, B. R. Can. J. Chem. 1975, 53, 2498.
(88) Solomon, E. I.; Heppner, D. E.; Johnston, E. M.; Ginsbach, J.
W.; Cirera, J.; Qayyum, M.; KieberꢀEmmons, M. T.; Kjaergaard, C.
H.; Hadt, R. G.; Tian, L. Chem. Rev. 2014, 114, 3659.
(89) Garribba, E.; Micera, G. J. Chem. Ed. 2006, 83, 1229.
(90) García Serres, R.; Grapperhaus, C. A.; Bothe, E.; Bill, E.;
Weyhermüller, T.; Neese, F.; Wieghardt, K. J. Am. Chem. Soc. 2004,
126, 5138.
(91) Brown, T. G.; Hoffman, B. M. Mol. Phys. 1980, 39, 1073.
(92) Hori, H.; IkedaꢀSaito, M.; Froncisz, W.; Yonetani, T. J. Biol.
Chem. 1983, 258, 12368.
(93) Hyde, J. S.; Froncisz, W. Annu. Rev. Biophys. Bioeng. 1982,
11, 391.
(94) Liptak, M. D.; Fleischhacker, A. S.; Matthews, R. G.; Telser,
J.; Brunold, T. C. J. Phys. Chem. B. 2009, 113, 5245.
(95) Bencze, K. Z.; Kondapalli, K. C.; Stemmler, T.L., Xꢀray
Absorption Spectroscopy. In Applications of Physical Methods to
Inorganic and Bioinorganic Chemistry, Scott, R. A.; Lukehart, C. M.,
Eds. John Wiley & Sons, Ltd.: Chichester, UK, 2008; pp 513.
(96) Padden, K. M.; Krebs, J. F.; MacBeth, C. E.; Scarrow, R. C.;
Borovik, A. S. J. Am. Chem. Soc. 2001, 123, 1072.
(97) Wirt, M. D.; Sagi, I.; Chen, E.; Frisbie, S. M.; Lee, R.;
Chance, M. R. J. Am. Chem. Soc. 1991, 113, 5299.
(98) Padden, K. M.; Krebs, J. F.; Trafford, K. T.; Yap, G. P. A.;
Rheingold, A. H.; Borovik, A. S.; Scarrow, R. C. Chem. Mater. 2001,
13, 4305.
3
(
(48) Fujita, E.; Chang, C. K.; Fajer, J. J. Am. Chem. Soc. 1985,
07, 7665.
1
(
49) Franz, K. J.; Doerrer, L. H.; Spingler, B.; Lippard, S. J. Inorg.
Chem. 2001, 40, 3774.
50) Kozhukh, J.; Lippard, S. J. J. Am. Chem. Soc. 2012, 134,
1120.
(51) Hess, J. L.; Conder, H. L.; Green, K. N.; Darensbourg, M. Y.
Inorg. Chem. 2008, 47, 2056.
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
(
(
52) Uyeda, C.; Peters, J. C. J. Am. Chem. Soc. 2013, 135, 12023.
53) Kumar, P.; Lee, Y.ꢀM.; Hu, L.; Chen, J.; Park, Y. J.; Yao, J.;
Chen, H.; Karlin, K. D.; Nam, W. J. Am. Chem. Soc. 2016, 138, 7753.
54) Kumar, P.; Lee, Y.ꢀM.; Park, Y. J.; Siegler, M. A.; Karlin, K.
D.; Nam, W. J. Am. Chem. Soc. 2015, 137, 4284.
55) Doyle, M. P.; Pickering, R. A.; Dykstra, R. L.; Cook, B. R. J.
(
(
Am. Chem. Soc. 1982, 104, 3392. The species responsible for release
of the NO moiety may be a reduced cobalt nitrosyl given the presence
of excess reductant.
(
56) Doyle, M. P.; Van Doornik, F. J.; Funckes, C. L. Inorg. Chim.
III
Acta 1980, 46, L111. [Co(NH
3
)
5
(NO)]Cl
2
reacts with both Fe ꢀ and
II
Fe ꢀheme proteins.
(
57) Ungermann, C. B.; Caulton, K. G. J. Am. Chem. Soc. 1976,
9
8, 3862.
(
(
58) Caulton, K. G. J. Am. Chem. Soc. 1973, 95, 4076.
59) Blanchard, A. A.; Rafter, J. R.; Adams, W. B., Jr. J. Am.
Chem. Soc. 1934, 56, 16.
(60) Coleman, G. W.; Blanchard, A. A. J. Am. Chem. Soc. 1936,
5
8, 2160.
61) Thyagarajan, S.; Incarvito, C. D.; Rheingold, A. L.; Theopold,
K. H. Inorg. Chim. Acta 2003, 345, 333.
62) Tomson, N. C.; Crimmin, M. R.; Petrenko, T.; Rosebrugh, L.
(
(
E.; Sproules, S.; Boyd, W. C.; Bergman, R. G.; DeBeer, S.; Toste, F.
D.; Wieghardt, K. J. Am. Chem. Soc. 2011, 133, 18785.
(
63) Sacconi, L.; Ghilardi, C. A.; Mealli, C.; Zanobini, F. Inorg.
Chem. 1975, 14, 1380.
64) Di Vaira, M.; Ghilardi, C. A.; Sacconi, L. Inorg. Chem. 1976,
(
1
5, 1555.
(65) Chuang, C.ꢀH.; Liaw, W.ꢀF.; Hung, C.ꢀH. Angew. Chem. Int.
Ed. 2016, 55, 5190.
66) Broderick, K. E.; Alvarez, L.; Balasubramanian, M.; Belke, D.
(
D.; Makino, A.; Chan, A.; Woods, V. L., Jr.; Dillmann, W. H.;
Sharma, V. S.; Pilz, R. B.; Bigby, T. D.; Boss, G. R. Exp. Biol. Med.
007, 232, 1432. The species responsible for release of the NO
moiety may be a reduced cobalt nitrosyl given the presence of excess
reductant.
(99) Adrait, A.; Jacquamet, L.; Le Pape, L.; Gonzalez de Peredo,
A.; Aberdam, D.; Hazemann, J.ꢀL.; Latour, J.ꢀM.; MichaudꢀSoret, I.
Biochemistry 1999, 38, 6248.
2
(100) Kleifeld, O.; Rulíšek, L.; Bogin, O.; Frenkel, A.; Havlas, Z.;
Burstein, Y.; Sagi, I. Biochemistry 2004, 43, 7151.
(101) Reviews on quantum chemical studies on nitrosyls: (a)
Ghosh, A. Acc. Chem. Res. 2005, 38, 943. (b) Ghosh, A.; Hopmann,
K. H.; Conradie, J. in Computational Inorganic and Bioinorganic
Chemistry, eds. Solomon, E. I.; Scott, R. A.; King, R. B., John Wiley
& Sons Ltd: Chichester, UK, 2009, pp. 389− 410. (c) Goodrich, L.
E.; Paulat, F.; Praneeth, V. K. K.; Lehnert, N. Inorg. Chem. 2010, 49,
6293.
(102) DFT calculation on CoNO complexes: (a) Jaworska, M.
Chem. Phys. 2007, 332, 203. (b) Hopmann, K. H.; Conradie, J.;
Tangen, E.; Tonzetich, Z. J.; Lippard, S. J.; Ghosh, A. Inorg. Chem.
2015, 54, 7362.
(
67) McCrory, C. C. L.; Uyeda, C.; Peters, J. C. J. Am. Chem. Soc.
012, 134, 3164.
68) Stubbert, B. D.; Peters, J. C.; Gray, H. B. J. Am. Chem. Soc.
011, 133, 18070.
69) Valdez, C. N.; Dempsey, J. L.; Brunschwig, B. S.; Winkler, J.
R.; Gray, H. B. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 15589.
70) Zee, D. Z.; Chantarojsiri, T.; Long, J. R.; Chang, C. J. Acc.
Chem. Res. 2015, 48, 2027 and references therein.
71) Kelley, P.; Day, M. W.; Agapie, T. Eur. J. Inorg. Chem. 2013,
013, 3840.
72) Basu, D.; Mazumder, S.; Niklas, J.; Baydoun, H.;
2
2
(
(
(
(
2
(
Wanniarachchi, D.; Shi, X.; Staples, R. J.; Poluektov, O.; Schlegel, H.
B.; Verani, C. N. Chem. Sci. 2016, 7, 3264.
(103) The notation A´ 61||60 means that there are 61
α or spinꢀup
(
73) Ding, K.; Brennessel, W. W.; Holland, P. L. J. Am. Chem.
Soc. 2009, 131, 10804.
74) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003, 125,
0782.
(75) Chapovetsky, A.; Do, T. H.; Haiges, R.; Takase, M. K.;
Marinescu, S. C. J. Am. Chem. Soc. 2016, 138, 5765.
electrons and 60 or spinꢀdown electrons in the irreducible
β
representation A´ (C point group symmetry).
s
9
(
(104) The {CoNO} porphyrin in reference 65 functions as an NO
1
reductase model and liberates N O in THF mixtures with a protic
2
solvent (H O, MeOH, EtOH) via
2
2 2
a putative N O ꢀbridging
intermediate.
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(
105) Heinecke, J. L.; Khin, C.; Pereira, J. C. M.; Suárez, S. A.;
(137) Werst, M. M.; Davoust, C. E.; Hoffman, B. M. J. Am. Chem.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
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5
5
5
5
5
5
5
5
5
6
Iretskii, A. V.; Doctorovich, F.; Ford, P. C. J. Am. Chem. Soc. 2013,
Soc. 1991, 113, 1533.
(138) Mailer, C.; Taylor, C. P. S. Biochim. Biophys. Acta 1973,
322, 195.
1
35, 4007.
106) Łapiński, A.; SpangetꢀLarsen, J.; Waluk, J.; Radziszewski, J.
G. J. Chem. Phys. 2001, 115, 1757.
107) Hughes, M. N.; Cammack, R. Methods Enzymol. 1999, 301,
79.
(108) [Co (LN
(
(139) Belford, R. L.; Nilges, M. J., In EPR Symposium, 21st Rocky
Mountain Conference, Denver, Colorado. August, 1979.
(140) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H.
E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I.
Organometallics 2010, 29, 2176.
(141) Te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fenseca
Guerra, C.; Van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. J.
Comput. Chem. 2001, 22, 931.
(
2
III
Ph
+
I
Ph
ꢀ
4
)] and [Co (LN
)] disproportionation.
109) Reactions of 1 and 2 with HBF
the presence of trace N O by IR.
110) Tseng, Y.ꢀT.; Chen, C.ꢀH.; Lin, J.ꢀY.; Li, B.ꢀH.; Lu, Y.ꢀH.;
4
)] may be the products of
II
Ph
[
Co (LN
4
(
4
•Et
2
O (1:1.3) in THF reveal
2
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Lin, C.ꢀH.; Chen, H.ꢀT.; Weng, T.ꢀC.; Sokaras, D.; Chen, H.ꢀY.; Soo,
Y.ꢀL.; Lu, T.ꢀT. Chem. Eur. J. 2015, 21, 17570.
(142) For a comparison of different exchangeꢀcorrelation
functionals for transition metal systems, see, e.g.: (a) M. Reiher;
Salomon, O.; Hess, B. A. Theor. Chem. Acc. 2001, 107, 48. (b)
Ghosh, A.; Taylor, P. R. Curr. Opin. Chem. Biol. 2003, 7, 113. (c)
Conradie, J.; Swarts, J. C.; Ghosh, A. J. Phys. Chem. B 2004, 108,
452. (d) Swart, M.; Ehlers, A. W.; Lammertsma, K. Mol. Phys. 2004,
102, 2647. (e) Conradie, J.; Ghosh, A. J. Phys. Chem. B 2007, 111,
12621; (f) Hopmann, K. H.; Conradie J.; Ghosh, A. J. Phys. Chem. B
2009, 113, 10540; (g) Conradie, M. M.; Conradie, J.; Ghosh, A. J.
Inorg. Biochem. 2011, 105, 84.
(
111) Chiang, C.ꢀY.; Darensbourg, M. Y. J. Biol. Inorg. Chem.
006, 11, 359.
112) Goodrich, L. E.; Roy, S.; Alp, E. E.; Zhao, J.; Hu, M. Y.;
Lehnert, N. Inorg. Chem. 2013, 52, 7766.
113) Reisz, J. A.; Klorig, E. B.; Wright, M. W.; King, S. B. Org.
Lett. 2009, 11, 2719.
114) Abucayon, E. G.; Khade, R. L.; Powell, D. R.; Zhang, Y.;
RichterꢀAddo, G. B. J. Am. Chem. Soc. 2016, 138, 104.
2
(
(
(
(
(
115) Hu, B.; Li, J. Angew. Chem. Int. Ed. 2015, 54, 10579.
116) Kupper, C.; Rees, J. A.; Dechert, S.; DeBeer, S.; Meyer, F. J.
(143) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
(144) Perdew, J. P. Phys. Rev. B 1986, 33, 8822.
Am. Chem. Soc. 2016, 138, 7888.
(117) Martí, M. A.; Bari, S. E.; Estrin, D. A.; Doctorovich, F. J.
Am. Chem. Soc. 2005, 127, 4680.
(145) Erratum.; Perdew, J. P. Phys. Rev. B 1986, 34, 7406.
(146) Handy, N. C.; Cohen, A. J. Mol. Phys. 2001, 99, 403.
(147) Lee, C. H.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(148) Johnson, B. G.; Gill, P. M. W.; Pople, J. A. J. Chem. Phys.
1993, 98, 5612.
(149) Russo, T. V.; Martin, R. L.; Hay, P. J. J. Chem. Phys. 1994,
101, 7729.
(150) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(
118) Álvarez, L.; Suarez, S. A.; Bikiel, D. E.; Reboucas, J. S.;
BatinićꢀHaberle, I.; Martí, M. A.; Doctorovich, F. Inorg. Chem. 2014,
3, 7351.
119) Doctorovich, F.; Bikiel, D. E.; Pellegrino, J.; Suárez, S. A.;
5
(
Martí, M. A. Acc. Chem. Res. 2014, 47, 2907.
(120) Pereira, J. C. M.; Iretskii, A. V.; Han, R.ꢀM.; Ford, P. C. J.
Am. Chem. Soc. 2015, 137, 328.
(151) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M.
J. J. Phys. Chem. 1994, 98, 11623.
(
(
(
121) Fitzpatrick, J.; Kim, E. Acc. Chem. Res. 2015, 48, 2453.
122) Tran, C. T.; Kim, E. Inorg. Chem. 2012, 51, 10086.
123) Romberg, R. W.; Kassner, R. J. Biochemistry 1979, 18, 5387.
(124) Antonini, E.; Brunori, M., Hemoglobin and Myoglobin in
their Reactions with Ligands. NorthꢀHolland Publishing Company:
Amsterdam, 1971.
(
125) Andrei, D.; Salmon, D. J.; Donzelli, S.; Wahab, A.; Klose, J.
R.; Citro, M. L.; Saavedra, J. E.; Wink, D. A.; Miranda, K. M.;
Keefer, L. K. J. Am. Chem. Soc. 2010, 132, 16526.
(126) The calculated quantitative yield (99%) of MbNO may be
high because of lightꢀscattering from insoluble complex or denatured
protein, and/or contributing absorbance from the CoNO complex. The
latter is more likely as relatively low concentrations of CoNO
complex were used and no precipitation was observed. Secondly,
addition of the same volume of organic solvent to the metMb solution
did not change its UVꢀvis spectrum, thus eliminating any
denaturation.
(
127) Bazylinski, D. A.; Hollocher, T. C. J. Am. Chem. Soc. 1985,
07, 7982.
128) Choi, I.ꢀK.; Liu, Y.; Feng, D.; Paeng, K.ꢀJ.; Ryan, M. D.
Inorg. Chem. 1991, 30, 1832.
129) Gao, Y.; Toubaei, A.; Kong, X.; Wu, G. Angew. Chem. Int.
Ed. 2014, 53, 11547.
130) Lehnert, N.; Praneeth, V. K. K.; Paulat, F. J. Comput. Chem.
006, 27, 1338.
131) A similar trend has been observed upon protonation of a 6C
1
(
(
(
2
(
8
{
FeNO} complex with ~0.05 Å increases in FeꢀN(O) and NꢀO.
However, there is no spinꢀstate change. See reference 130.
(132) Sharma, V. S.; Pilz, R. B.; Boss, G. R.; Magde, D.
Biochemistry 2003, 42, 8900.
(
(
133) Ford, P. C.; Lorkovic, I. M. Chem. Rev. 2002, 102, 993.
134) Hassanin, H. A.; ElꢀShahat, M. F.; DeBeer, S.; Smith, C. A.;
Brasch, N. E. Dalton Trans. 2010, 39, 10626.
135) Wolak, M.; Zahl, A.; Schneppensieper, T.; Stochel, G.; van
(
Eldik, R. J. Am. Chem. Soc. 2001, 123, 9780.
(136) Gill, N. S.; Taylor, F. B. Inorg. Synth. 1967, 9, 136.
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