Artificial [FeFe]-hydrogenase: On resin modification of an amino acid to anchor a hexacarbonyldiiron cluster in a peptide framework

Article abstract of DOI:10.1002/ejic.201000979

A general method for immobilization of synthetic analogues of the [FeFe]-hydrogenase in designed peptides via on resin modification of an amino acid side chain with a dithiol functional group is described. Utilizing a unique amine side chain as anchor, the dithiol unit is coupled to the peptide via formation of an amide. This dithiol unit precisely positions the two required sulfur atoms for the formation of a [(μ-SRS){Fe-(CO)₃} ₂] cluster on reaction with [Fe₃(CO)₁₂]. UV/Vis and FTIR spectroscopy demonstrate formation of the desired complex.

Full text of DOI:10.1002/ejic.201000979

FULL PAPER
DOI: 10.1002/ejic.201000979
Artificial [FeFe]-Hydrogenase: On Resin Modification of an Amino Acid to
Anchor a Hexacarbonyldiiron Cluster in a Peptide Framework
Souvik Roy,[a,b] Sandip Shinde,[a,b] G. Alexander Hamilton, Hilairy E. Hartnett,
[a]
[a,b,c]
and
Anne K. Jones*[
a,b]
Keywords: Bioinorganic chemistry / Bioorganometallic chemistry / Enzyme models / Hydrogenase / Peptidomimetics /
Designed peptide
A general method for immobilization of synthetic analogues
of the [FeFe]-hydrogenase in designed peptides via on resin
modification of an amino acid side chain with a dithiol func-
tional group is described. Utilizing a unique amine side chain
tion of an amide. This dithiol unit precisely positions the two
required sulfur atoms for the formation of a [(μ-SRS){Fe-
(CO)
3 2 3
} ] cluster on reaction with [Fe (CO)12]. UV/Vis and
FTIR spectroscopy demonstrate formation of the desired
as anchor, the dithiol unit is coupled to the peptide via forma- complex.
Introduction
progress in understanding the mechanism of this enzyme
has been achieved via synthesis of relevant model com-
Hydrogen is an energy currency in both biological and
industrial settings, and hydrogenases are the biological cata-
lysts for the interconversion of protons and hydrogen. This
reaction is at the heart of hydrogen’s usage as a fuel. Un-
like industrial catalysts that rely on precious metals to cata-
lyze hydrogen activation, biology takes advantage of the
earth-abundant metals nickel and iron. FTIR and X-ray
crystallographic studies have shown that both [NiFe]- and
[14–20]
pounds.
[
1]
Scheme 1. [FeFe]-hydrogenase active site and first-generation
model compound utilizing a propanedithiol ligand.
[
FeFe]-hydrogenases contain unusual, organometallic active
sites utilizing biologically unprecedented CO and CN as in-
[
2–9]
trinsic ligands.
Despite the wealth of biomimetic chemistry that has been
The structure of the active site of [FeFe]-hydrogenases reported, there still exist several important functional differ-
Scheme 1) consists of an unusual [Fe S ] subunit bridged ences between synthetic model compounds and [FeFe]-hy-
(
2
2
to an ordinary [4Fe4S] cubane via a single cysteinyl sulfur drogenases. Model compounds cycle through the more re-
I
0
atom. The diiron subsite contains two features that are re- duced Fe -Fe redox state during electrocatalytic reduction
markable from a biological perspective: (1) the aforemen- of protons whereas [FeFe]-hydrogenases are believed to uti-
II
I
[14]
tioned diatomic ligands and (2) a dithiol organic bridging lize the Fe -Fe state.
Similarly, model compounds re-
molecule that has been alternatively proposed to contain quire substantial overpotentials to catalyze the reduction of
[
10–13]
carbon, nitrogen or oxygen at its central position.
From a synthetic chemistry perspective, the active site of zymes. Finally, none of the [FeFe]-hydrogenase models is
FeFe]-hydrogenases has remarkable structural similarities able to oxidize hydrogen while the enzymes are known to
to many known iron carbonyl compounds, and considerable perform reversible catalysis.
Increasingly, attention is being focused on generation of
protons at slower rates than can be achieved by the en-
[
functional [FeFe]-hydrogenase model complexes that can
perform electrocatalysis or photocatalysis. In these investi-
gations, a number of synthetic strategies have been devel-
oped for coupling relevant diiron models to electrode sur-
[
a] Department of Chemistry and Biochemistry, Arizona State
University,
Tempe, AZ 85287-1604, USA
Fax: +1-4809652747
E-mail: jonesak@asu.edu
[
21–25]
[
[
b] Center for Bioenergy and Photosynthesis, Arizona State
University,
faces, redox cofactors, or photoactive centers.
In par-
allel, strategies for investigating the impact of second coor-
Tempe, AZ 85287-1604, USA
c] School of Earth and Space Exploration, Arizona State Univer- dination sphere interactions and burial of the active site in
sity,
superstructures isolated from bulk solvent are starting to
Tempe, AZ 85287-1404, USA
[
22,26–32]
emerge.
On the other hand, relatively little attention
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000979.
has been paid to developing strategies for attachment of
1050
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 1050–1055

Artificial [FeFe]-Hydrogenase
[
28,33–35]
diiron models to amino acids
folds
or peptidic scaf- form a stable amide. After modification of the lysine, the
[
36,37]
– this, despite the fact that evidence continues to rest of the peptide can be simultaneously deprotected and
build indicating that the enzyme tertiary structure plays a cleaved from the resin via standard trifluoroacetic acid
crucial role in tuning the properties of the active site to methods and purified before incorporation of the diiron
achieve near diffusion-limited, bidirectional catalysis.
De novo designed proteins have proven an invaluable
unit via reaction with [Fe (CO) ].
3 12
Reactions with peptides can present unique challenges
tool in the study of complex oxidoreductases and have been relative to reactions with small, organic ligands. First, pep-
designed to bind a number of both naturally occurring and tides are not usually soluble in the organic solvents tradi-
artificial metallocofactors.[
38–43]
The construction of minia- tionally utilized for organometallic synthesis. Second, the
turized, peptidic systems coordinating hydrogenase-related number and diverse composition of functional groups pres-
metallocenters presents unique synthetic challenges. One ent in a peptide require carefully orchestrated protection/
approach has been utilization of the naturally occurring deprotection to avoid side products. To demonstrate the ef-
amino acid cysteine as an anchor for construction of a ficacy of this synthetic approach, a simple variant of the N-
[36]
[
(μ-SRS){Fe(CO) } ] cluster. This strategy has the disad- terminal sequence of the nickel-superoxide dismutase
3 2
vantage of relying on the correct placement of two distinct (SODA) from Streptomyces coelicolor was utilized. The
cysteines to form the desired complex. A second synthetic SODA peptide, ACDLPCG, binds nickel, is soluble and
route involves modification of an amino acid to create an monomeric in aqueous solution, is spectroscopically well
artificial amino acid ligand for the desired metal complex. characterized, and retains some of the catalytic activity of
[
45]
In this report, we present a method to modify a peptide still the complete enzyme.
Three variations in this sequence
attached to its resin support in order to create an artificial were introduced. First, the two cysteine residues were ex-
derivative of a lysine bearing a propanedithiol unit. The changed for serines to eliminate competition from these thi-
appended sulfur side chain posesses two sulfurs poised to ols for interaction with iron while maintaining the approxi-
anchor a covalently attached [Fe (SRS)(CO) ] unit. This mate length and polarity of the side chain. Second, the as-
2
6
approach can serve as a general method for modification of partic acid was exchanged for a lysine as an attachment
a wide range of designer synthetic peptides to probe interac- point for the iron cluster. Finally, a tryptophan residue was
tions between amino acids and [FeFe]-hydrogenase small introduced at the N-terminus to facilitate quantification of
models.
the peptide, yielding the final sequnce, WASKLPSG.
Figure 1 shows the analytical HPLC and Figure 2 the
NMR spectra from (A) deprotected, unmodified peptide,
Results and Discussion
(B) peptide modified with the dithiol acid, and (C) peptide
Scheme 2 shows the general strategy for synthesis of an modified with the diiron cluster. The HPLC traces demon-
Fe (SRS)(CO) ] unit appended to a dithiol-modified lysine strate that with each additional modification the peptide
[
2
6
residue. First, the desired peptide is constructed via stan- became more hydrophobic, eluting at a higher percentage
dard Fmoc/tBu solid-phase peptide synthesis. During syn- of acetonitrile. These changes in hydrophobicity facilitated
thesis, an orthogonally protected amino acid residue, in this efficient purification to yield high quality products as
case lysine, is introduced that serves as the site for dithiol shown in the NMR spectra. The peaks of peptide modified
incorporation. The dithiol unit is provided by 3-(acet- with the dithiol acid can clearly be observed after coupling
ylthio)-2-(acetylthiomethyl)propanoic acid.[44] This prop- to the lysine at 1.10 (t, 2 H), 2.4–2.55 (1 H) and 3.0–3.15 (4
anoic acid derivative can be coupled to a primary amine to H). These peaks are then shifted after incorporation of the
Scheme 2. Synthetic strategy for modification of a unique lysine with a dithiol functional unit and incorporation of an {Fe
The sphere represents the resin bead utilized for solid phase peptide synthesis.
2
(CO)
6
} unit.
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S. Roy, S. Shinde, G. A. Hamilton, H. E. Hartnett, A. K. Jones
FULL PAPER
diiron unit to overlap with the resonances of the ε-H of the that the products have the expected composition and the
lysine residue. Meanwhile, the peaks for all other protons iron cluster is coordinated via a single peptide monomer.
in the peptide can be accounted for and are virtually unaf-
The UV/Vis and FTIR spectra of Fe (CO) -modified
2 6
fected by the modifications of the peptide (complete assign- peptide are shown in Figure 3. The UV/Vis spectrum con-
ment can be found in the Supporting Information). ESI sists of three notable features: an absorption at 334 and a
mass spectrometry has also been utilized to demonstrate shoulder at 465 nm both associated with the Fe-S core, and
the characteristic absorbance of the tryptophan residue at
280 nm. The ratio of the extinction coefficients of these fea-
tures is similar to that observed previously for incorpora-
tion of cluster into peptide via cysteine, providing ad-
ditional evidence for nearly stoichiometric incorporation of
[
36]
cluster in the purified product.
the Fe (CO) -modified peptide has three bands at 2075,
2
The FTIR spectrum of
2
6
035 and 1999 cm–1 arising from the coupled CO vi-
brational modes of the complex. These confirm the pres-
ence of the carbonyls on each iron. Furthermore, the close
agreement between these values and those observed for
[
{μ-S(CH ) S}{Fe(CO) } ] suggests that, as expected, the
2 3 3 2
iron complex is completely exposed to solution when at-
tached to the peptide. Finally, ESI-MS data of Fe (CO) -
2
6
modified peptide also implies the presence of the CO li-
gands since ions formed by loss of CO ligands [complex-
CO, complex-(CO) and complex-(CO) ] could clearly be
3
6
identified (Supporting Information).
The complex [{μ-S(CH ) S}Fe (CO) ] is an unremark-
2
3
2
6
able catalyst, but it can undergo substitution of the carbon-
yls by a number of different types of ligands such as cyanide
[
14]
or phosphanes to form more active species.
Fe (CO) -modified peptide is also able to undergo substitu-
Similarly,
2
6
tion reactions. As shown in Figure 3, addition of excess
PMe to an acetonitrile solution of the peptide, results in a
3
uniform shifting of the frequencies of the ν(CO) bands to
approximately 100 cm–1 lower wavenumbers (1974, 1939,
and 1894). The compound [{μ-S(CH ) S}{Fe(CO) -
2
3
2
(
PMe )} ] is reported to have ν(CO) bands at 1979, 1942,
3 2
–1 [46]
and 1898 cm .
Thus, the observed data is consistent
with formation of a disubstituted phosphane derivative and
indicates that the cluster is accessible for ligand exchange.
Conclusions
We have demonstrated the ability to incorporate a
[
(μ-SRS)Fe (CO) ] model of [FeFe]-hydrogenases into a
2 6
peptide via on resin construction of a modified amino acid.
This synthetic scheme is general and allows covalent con-
nection of the diiron unit to any unique primary amine.
Importantly, the synthesis can be performed in water/meth-
anol mixtures yielding a water-soluble product in high
yield.
This approach provides a convenient method for con-
structing peptide-based models of [FeFe]-hydrogenases.
Figure 1. Analytical HPLC traces from (A) WASKLPSG, (B) pep- Through variation of the peptide scaffold, it will be possible
tide with dithiol side-chain modification WAS(Dt)LPSG and (C) to construct complexes in carefully tailored cavities de-
2
peptide modified with both a dithiol side-chain and the {Fe -
signed to incorporate selected aspects of the enzyme active
site. The 3-(acetylthio)-2(acetylthiomethyl)propanoic acid
unit may also be utilized as a handle to construct other
sulfur-ligated metallocenters.
(
0
CO)
6
} cluster. HPLC gradient 1% acetonitrile/min; flow rate
.25 mL/min. The higher amplitude signal in each case is ab-
sorbance at 220 nm (peptide bond) and the lower at 280 nm (tryp-
tophan).
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Artificial [FeFe]-Hydrogenase
1
Figure 2. H NMR spectra from (A) WASKLPSG, (B) peptide with dithiol side-chain modification WAS(Dt)LPSG and (C) both a dithiol
2 6 2
side-chain and the {Fe (CO) } cluster. NMR spectra were obtained in D O.
Figure 3. Characterization of [Fe
and (C) FTIR spectrum of [peptide-Fe
2
(CO)
6
] complex coordinated to dithiol-modified peptide via (A) UV/Vis and (B) FTIR spectroscopy
(CO) (PMe ]. UV/Vis spectrum was obtained in a 1:1 mixture of water/acetonitrile. For FTIR
2
4
3 2
)
experiments, sample was applied to a single CaF
Experiments were then performed with the film.
2
window as a methanolic solution and dried under a vacuum to form a thin film.
Experimental Section
Instrumentation: MALDI-MS (matrix assisted laser desorption/
General: All reactions were performed under an atmosphere of ni-
trogen. Unless otherwise specified, all chemicals were of the highest
purity available from Sigma–Aldrich. Fmoc protected amino acids
ionization mass spectrometry) characterization of peptides was per-
formed on a Voyager DE STR in the Proteomics and Protein
Chemistry Laboratory at Arizona State University. ESI-MS (elec-
and peptide coupling reagents were obtained from Protein Technol- trospray ionization mass spectrometry) was performed using a
ogies (Tucson, AZ, USA). Solvents including DMF, acetonitrile,
Thermo Quantum Discovery Max triple-quadrupole mass spec-
trometer in the Environmental Biogeochemistry Laboratory at Ari-
zona State University. Measurements were conducted in positive
3 2
methanol, ethyl acetate, hexanes, ether CDCl and D O were ob-
tained from Sigma Aldrich.
Eur. J. Inorg. Chem. 2011, 1050–1055
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1053

S. Roy, S. Shinde, G. A. Hamilton, H. E. Hartnett, A. K. Jones
FULL PAPER
(
(
+) and negative (–) ionization modes using a methanol/water
50:50 by volume) mobile phase at a flow rate of 10 mL min and
yl], was used for solid-phase peptide synthesis so that the side-chain
amino group of lysine can be selectively deprotected and modified.
Following synthesis, the peptide was acetylated at the N-terminus
[1:1 (v/v) acetic anhydride: N-methylmorpholine for 20 min, two
times].
–
1
the following ionization conditions: spray voltage, 4000 (+, –); cap-
illary temperature, 270 °C; sheath gas pressures, 25 (+) and 15 (–);
auxiliary gas pressure, 2 (+, –). NMR spectra were recorded at
1
4
00 or 500 MHz ( H) on Varian Liquid-State NMR instruments in
Coupling of 3-(Acetylthio)-2-(acetylthiomethyl)propanoic Acid to
Peptide and Purification: Resin-bound peptide (64 mg, 0.033 mmol)
was treated with 2% hydrazine in DMF (10 mL) for 45 min at room
temperature under nitrogen to remove the protecting group from
lysine. Following deprotection, 3-(acetylthio)-2-(acetylthiomethyl)-
propanoic acid (35 mg, 0.15 mmol), HATU [2-(1H-7-azabenzotri-
azol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate meth-
anaminium] (55 mg, 0.14 mmol) and DIEA [N,N-diisopropyl-
ethylamine] (30 μL, 0.16 mmol) dissolved in 5 mL of DMF were
added to the resin under nitrogen and stirred at room temperature
for 30 min. This coupling reaction was repeated. The resin was then
washed with DMF (5ϫ2 mL). The thioacetal groups were reduced
to thiol by treatment with 2–3% hydrazine in DMF (10 mL) under
nitrogen for 40 min. Then the peptide was simultaneously depro-
tected and cleaved from the resin using 95:2.5:2.5 trifluoroacetic
acid (TFA)/water/triisopropylsilane (TIPS) for 2 h and 15 min. The
crude cleavage solution was filtered and the residual resin was
washed with neat TFA (3ϫ1 mL). The TFA solution of peptide
was concentrated under reduced pressure to a light yellow colored
liquid (ca. 0.5–1 mL). The crude peptide was precipitated by adding
cold diethyl ether (–20 °C). Followed by incubation with four
equivalents TCEP, the crude peptide was purified by reverse-phase
HPLC on a Waters 600E HPLC system with a photodiode array
detector (3ϫ250 mm C-18 column for analytical and PrepLC
3
CDCl solutions containing 0.1% TMS (tetramethylsilane) unless
otherwise mentioned. UV/Vis measurements were performed on a
Hewlett–Packard 8453 spectrophotometer using quartz cuvettes
with a 1 cm pathlength. Peptide concentrations were determined
–
1
–1
via absorbance of the tryptophan residue (ε280 = 5600 m cm ).
FTIR spectra were recorded on a Thermo Nicolet Avatar-360 spec-
trometer as a dry film on a CaF
average of 1024 scans collected under nitrogen at 1 cm–1 resolution.
The clean CaF window was used as a reference.
2
window. Each spectrum is an
2
2-(Bromomethyl)propenoic Acid: Diethyl bis(hydroxymethyl)malon-
ate (13 g, 0.058 mmol) was dissolved in HBr (25 mL of 48% aque-
ous solution, ca. 0.2 mol) and was heated at 120–125 °C in an oil
bath for 45 min. On cooling the solution to –80 °C, white crystals
appeared. The crystals were removed by filtration and the filtrate
was heated again to 120–125 °C for 45 min. This solution was again
cooled to –80 °C and additional crystals were filtered off. This pro-
cess was repeated a third time. All the white crystals were collected
and dissolved in 30 mL of dichloromethane, washed with
2
ϫ10 mL of 1 n HCl, dried with anhydrous MgSO
4
and concen-
trated under reduced pressure to yield a white crystalline solid
1
(
2.8 g, 29.4%). H NMR (400 MHz): δ = 6.48 (s, 1 H), 6.09 (s, 1
H), 4.17 (s, 2 H) ppm.
3
-(Acetylthio)-2-(acetylthiomethyl)propanoic Acid: To a stirred sus-
pension of 2-(bromomethyl)propenoic acid (2.8 g, 0.017 mol) in
0 mL of water at 0 °C was added an aqueous solution of sodium
25 mm module C-18 column for semi-preparative HPLC) using
aqueous acetonitrile gradients containing 0.1% TFA (v/v). Molecu-
lar weight of the peptide was confirmed by matrix-assisted laser
desorption/ionization time-of-flight (MALDI-TOF MS) mass
5
carbonate (3.1 g, 0.029 mol in 15 mL) in small portions. To the
resulting mixture, thiolacetic acid (1.25 mL, 0.017 mol) was added
dropwise, and the solution was stirred at 0 °C for 2 hours. The
solution was acidified with 6 m HCl, and the white precipitate was
extracted with ethyl acetate (3ϫ25 mL). The EtOAc layer was
spectrometry. [M]+ calcd. 1020.99; found 1043.3 [(M + Na – H)+].
Cluster Incorporation Into Peptide: Dodecacarbonyltriiron (5 mg,
0.01 mmol) in methanol (1.5 mL) and 0.16 mm aqueous solution of
peptide (1 mL) were combined and refluxed for 1.5 hours resulting
in a color change from green to pale red. The reaction mixture was
concentrated under reduced pressure and was extracted with 3 mL
of water. The complex was purified by reverse phase HPLC using
aqueous-acetonitrile gradients.
4
dried with anhydrous MgSO and concentrated under reduced
pressure to yield a colorless oil. With this colorless oil, the reaction
was repeated (as 1H NMR of the oil indicated the presence of
about 33% unreacted starting material, 2-(bromomethyl)propenoic
acid) to produce pure 2-(acetylthiomethyl)acrylic acid as a colorless
1
oil (3 g). H NMR (400 MHz): δ = 6.38 (s, 1 H), 6.02 (s, 1 H), 3.75 Substitution of Carbon Monoxide Ligands with Trimethylphosphane:
(s, 2 H), 2.32 (s, 3 H) ppm. To this 2-(acetylthiomethyl)acrylic acid
Trimethylphosphane (4 μL, 0.038 mmol) was added to a 0.02 mm
acetonitrile solution of [peptide-{μ-S Fe (CO) }] complex (1 mL)
was added thiolacetic acid (2 mL, 0.027 mol) and stirred at room
2
2
6
1
temperature. After 36 hours, H NMR spectra of the reaction mix-
under N2 in the dark and stirred at room temperature for 1.5 h
resulting in color change to red. The FTIR of the crude reaction
ture showed no olefinic peaks. The unreacted thiolacetic acid was
removed from the reaction mixture under reduced pressure and the
yellow oil like residue was purified by column chromatography on
silica gel with hexane/ethyl acetate (3:1) as eluent followed by hex-
ane/ethyl acetate (2:1) giving 3-(acetylthio)-2-(acetylthiomethyl)-
–
1
mixture showed ν(CO) bands at 1974, 1939, 1894 cm .
Supporting Information (see also the footnote on the first page of
1
this article): Assignments of peptide H NMR spectra, ESI-MS for
2 6
the Fe (CO) -modified peptide.
f
propanoic acid as a white solid (2.8 g, 70%). R = 0.2 (3:1 hexane/
1
ethyl acetate). H NMR (400 MHz): δ = 3.19 (m, 4 H), 2.91 (p, 1
H), 2.35 (s, 6 H) ppm.
Acknowledgments
Peptide Synthesis: The eight amino acid containing peptide
Financial support for this research was provided by the US Air
Force Office of Scientific Research (AFOSR) under award FA9550-
(
WASKLPSG) was synthesized on a Protein Technologies PS3
automated peptide synthesizer using the standard Fmoc/tBu
Fmoc, 9-fluorenylmethoxycarbonyl) protection strategy and
08-1-0116. Additionally, SS was supported by the US National Sci-
(
ence Foundation (CAREER award number 0449842). Giovanna
Ghirlanda and Arnab Dutta are thanked for helpful discussions.
HBTU (o-benzotriazole-N,N,NЈ,NЈ-tetramethyluronium hexafluo-
rophosphate) as coupling reagent on Fmoc-Gly wang resin
25]
(
Aapptec 0.54 mmol/g, 100–200 mesh) at 0.1 mmol scale.[ Lysine
with an orthogonally protected side chain, Fmoc-Lys(ivDde)-OH
ivDde, 1-(4,4-dimethyl-2,6-dioxocyclohex-1-ylidene)-3-methylbut-
[1] R. Cammack, M. Frey, R. Robson, Hydrogen as a Fuel: Learn-
ing from Nature, Taylor & Francis, London, 2001.
[
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Eur. J. Inorg. Chem. 2011, 1050–1055

Artificial [FeFe]-Hydrogenase
[
[
[
[
[
2] A. Volbeda, M. H. Charon, C. Piras, E. C. Hatchikian, M.
Frey, J. C. Fontecilla-Camps, Nature 1995, 373, 580–587.
3] J. C. Fontecilla-Camps, A. Volbeda, C. Cavazza, Y. Nicolet,
Chem. Rev. 2007, 107, 4273–4303.
4] J. W. Peters, W. N. Lanzilotta, B. J. Lemon, L. C. Seefeldt, Sci-
ence 1998, 282, 1853–1858.
[25] C. Tard, X. M. Liu, I. S. K. M. Bruschi, L. De Gioia, S. C.
Davies, X. Yang, L. S. Wang, G. Sawers, C. J. Pickett, Nature
2005, 433, 610–613.
[26] K. N. Green, J. L. Hess, C. M. Thomas, M. Y. Darensbourg,
Dalton Trans. 2009, 4344–4350.
[
27] M. L. Singleton, J. H. Reibenspies, M. Y. Darensbourg, J. Am.
Chem. Soc. 2010, 132, 8870–8871.
5] Y. Nicolet, C. Piras, P. Legrand, E. C. Hatchikian, J. C.
Fontecilla-Camps, Structure with Folding Des. 1999, 7, 13–23.
6] Y. Nicolet, A. De Lacey, X. Vernede, V. M. Fernandez, E. C.
Hatchikian, J. C. Fontecilla-Camps, J. Am. Chem. Soc. 2001,
[
28] U.-P. Apfel, C. R. Kowol, Y. Halpin, F. Kloss, J. Kubel, H.
Goris, J. G. Vos, B. K. Keppler, E. Morera, G. Lucente, W. Wei-
gand, J. Inorg. Biochem. 2009, 103, 1236–1244.
[
29] A. D. Wilson, R. K. Shoemaker, A. Miedaner, J. T. Mucker-
123, 1596–1601.
man, D. L. DuBois, M. R. DuBois, Proc. Natl. Acad. Sci. USA
[
[
[
[
[
[
[
7] R. Happe, W. Roseboom, A. J. Pierik, S. P. J. Albracht, K. A.
2
007, 104, 6951–6956.
Bagley, Nature 1997, 385, 126.
[
[
30] M. R. DuBois, D. L. DuBois, Chem. Soc. Rev. 2009, 38, 62–72.
31] S. Ezzaher, J.-F. Capon, F. Gloaguen, F. Y. Petillon, P.
Schollhammer, J. Talarmin, Inorg. Chem. 2009, 48, 2–4.
8] K. A. Bagley, E. C. Duin, W. Roseboom, S. P. J. Albracht,
W. H. Woodruff, Biochemistry 1995, 34, 5527–5535.
9] A. J. Pierik, M. Hulstein, W. R. Hagen, S. P. J. Albracht, Eur.
J. Biochem. 1998, 258, 572–578.
10] A. Silakov, B. Wenk, E. Reijerse, W. Lubitz, Phys. Chem. Chem.
Phys. 2009, 11, 6592–6599.
11] A. S. Pandey, T. V. Harris, L. J. Giles, J. W. Peters, R. K. Szila-
gyi, J. Am. Chem. Soc. 2008, 130, 4533–4540.
12] S. Zilberman, E. I. Stiefel, M. H. Cohen, R. Car, Inorg. Chem.
[
[
[
32] S. Ezzaher, A. Gogoll, C. Bruhn, S. Ott, Chem. Commun. 2010,
4
6, 5775–5777.
33] L.-C. Song, J. Yan, Y.-L. Li, D.-F. Wang, Q.-M. Hu, Inorg.
Chem. 2009, 48, 11376–11381.
34] C. He, M. Wang, X. Zhang, Z. Wang, C. Chen, J. Liu, B. Aker-
mark, L. Sun, Angew. Chem. Int. Ed. 2004, 43, 3571–3574.
[35] X. de Hatten, E. Bothe, K. Merz, I. Huc, N. Metzler-Nolte,
Eur. J. Inorg. Chem. 2008, 4530–4537.
2
007, 46, 1153–1161.
13] M. T. Olsen, B. E. Barton, T. B. Rauchfuss, Inorg. Chem. 2009,
8, 7507–7509.
[36] A. K. Jones, B. R. Lichtenstein, A. Dutta, G. Gordon, P. L.
Dutton, J. Am. Chem. Soc. 2007, 129, 14844–14845.
[37] U.-P. Apfel, M. Rudolph, C. Apfel, C. Robl, D. Langenegger,
D. Hoyer, B. Jaun, M.-O. Ebert, T. Alpermann, D. Seebach,
W. Weigand, Dalton Trans. 2010, 39, 3065–3071.
[38] R. T. M. de Rosales, M. Faiella, E. Farquhar, L. Que, C. And-
reozzi, V. Pavone, O. Maglio, F. Nastri, A. Lombardi, J. Biol.
Inorg. Chem. 2010, 15, 717–728.
[39] J. G. Saven, Curr. Opin. Colloid Interf. Sci. 2010, 15, 13–17.
[40] J. L. R. Anderson, R. L. Koder, C. C. Moser, P. L. Dutton, Bio-
chem. Soc. Trans. 2008, 36, 1106–1112.
[41] M. Faiella, C. Andreozzi, R. T. M. de Rosales, V. Pavone, O.
Maglio, F. Nastri, W. F. DeGrado, A. Lombardi, Nat. Chem.
Biol. 2009, 5, 882–884.
[42] A. F. A. Peacock, O. Iranzo, V. L. Pecoraro, Dalton Trans.
2009, 2271–2280.
[43] V. Nanda, R. L. Koder, Nature Chem. 2010, 2, 15–24.
[44] R. Singh, G. M. Whitesides, J. Am. Chem. Soc. 1990, 112,
1190–1197.
[45] J. Shearer, L. M. Long, Inorg. Chem. 2006, 45, 2358–2360.
[46] X. Zhao, I. P. Georgakaki, M. L. Miller, J. C. Yarbrough, M. Y.
Darensbourg, J. Am. Chem. Soc. 2001, 123, 9710–9711.
Received: September 15, 2010
4
[
[
14] C. Tard, C. J. Pickett, Chem. Rev. 2009, 109, 2245–2274.
15] A. Jablonskyte, J. A. Wright, C. J. Pickett, Dalton Trans. 2010,
39, 3026–3034.
[
[
[
[
[
[
16] C. M. Thomas, T. B. Liu, M. B. Hall, M. Y. Darensbourg, In-
org. Chem. 2008, 47, 7009–7024.
17] B. E. Barton, T. B. Rauchfuss, Inorg. Chem. 2008, 47, 2261–
2263.
18] T. B. Liu, M. Y. Darensbourg, J. Am. Chem. Soc. 2007, 129,
7008–7009.
19] B. E. Barton, M. T. Olsen, T. B. Rauchfuss, Curr. Opin. Bio-
technol. 2010, 21, 292–297.
20] F. Gloaguen, T. B. Rauchfuss, Chem. Soc. Rev. 2009, 38, 100–
108.
21] A. M. Kluwer, R. Kapre, F. Hartl, M. Lutz, A. L. Spek, A. M.
Brouwer, P. W. N. M. van Leeuwen, J. N. H. Reek, Proc. Natl.
Acad. Sci. USA 2009, 106, 10460–10465.
[22] X. Ru, X. Zeng, Z. Li, D. J. Evans, C. Zhan, Y. Tang, L. Wang,
X. Liu, J. Polym. Sci.: Part A 2010, 48, 2410–2417.
[23] D. Streich, Y. Astuti, M. Orlandi, L. Schwartz, R. Lomoth, L.
Hammarstrom, S. Ott, Chem. Eur. J. 2010, 16, 60–63.
[24] H.-Y. Wang, W.-G. Wnag, G. Si, F. Wang, C.-H. Tung, L.-Z.
Wu, Langmuir 2010, 26, 9766–9771.
Published Online: November 17, 2010
Eur. J. Inorg. Chem. 2011, 1050–1055
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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