High catalytic activities of artificial peroxidases based on supramolecular hydrogels that contain heme models

Article abstract of DOI:10.1002/chem.200702010

Composed of a supramolecular hydrogel and a heme model compound, a new type of artificial peroxidase shows high catalytic activity in organic media. The activity of this new type of artificial enzyme is significantly higher than that of the heme model compounds alone. Changes in the distal substituents above the coordinated-metal centers of the model compounds directly modulate catalytic activity. This supramolecular-hydrogelbased artificial enzyme is most active in toluene, reaching about 90% of the nascent activity of horseradish peroxidase. Moreover, this study confirms that the incorporation of the heme models into the nanofibers of gelators accounts for most of the enhancement of catalytic activity.

Full text of DOI:10.1002/chem.200702010

FULL PAPER
DOI: 10.1002/chem.200702010
High Catalytic Activities of Artificial Peroxidases Based on Supramolecular
Hydrogels That Contain Heme Models
Qigang Wang, Zhimou Yang, Manlung Ma, Chi K. Chang,* and Bing Xu*[a]
Abstract: Composed of a supramolec-
ular hydrogel and a heme model com-
pound, a new type of artificial perox-
idase shows high catalytic activity in or-
ganic media. The activity of this new
type of artificial enzyme is significantly
higher than that of the heme model
compounds alone. Changes in the
distal substituents above the coordinat-
ed-metal centers of the model com-
pounds directly modulate catalytic ac-
tivity. This supramolecular-hydrogel-
based artificial enzyme is most active
in toluene, reaching about 90% of the
nascent activity of horseradish perox-
idase. Moreover, this study confirms
that the incorporation of the heme
models into the nanofibers of gelators
accounts for most of the enhancement
of catalytic activity.
Keywords:
catalysis
·
enzyme
mimics · gelators · heme models ·
hydrogels · nanofibers
Introduction
ing the stabilities of the catalytic intermediates, the activities
of various hemes likely depends on the nature of the distal
groups above the coordinating centers in the heme model
compounds.
This paper describes the evaluation of the catalytic activity
of artificial enzymes composed of a supramolecular hydro-
gel[1,2,3] and
a
group of synthetic heme model com-
Supramolecular hydrogels of amphiphilic oligopeptides[8,9]
or other small molecules[10–12] are being explored for various
important applications, such as scaffolds for tissue engineer-
ing,[8] media for screening inhibitors,[11,13] matrices for bio-
mineralization,[14] and biomaterials for wound healing.[12]
Similar to the natural selection of peptide chains in en-
zymes, self-assembled nanofibers of derivatives of amino
acids allow the incorporation of heme model compounds as
the prosthetic group to mimic peroxidases.[3] In the artificial
enzymes reported in this work, the hydrogels serve at least
two functions: as the skeleton of the artificial enzyme to aid
the function of the active site in organic solvent and as im-
mobilization carriers to facilitate their various applications.
We have demonstrated that the nanofibers in supramolec-
ular hydrogels protect a hemin monomer by preventing its
dimerization and degradation and facilitate its catalytic ac-
tivity by providing nanoporous diffusion channels, which
possess unique flexibility to allow the transport of sub-
strates. As a result, the hemin chloride encapsulated in a
supramolecular hydrogel reaches about 60% catalytic activi-
ty in toluene relative to that of native horseradish perox-
idase (HRP) in water.[2] The excellent performance of this
enzyme mimic system made of a supramolecular hydrogel
prompted us to evaluate whether supramolecular hydrogels
could serve as a general platform for the combination of
other synthetic heme model compounds and for the deter-
pounds.[4,5,6] It is well-known that the spatial arrangement of
atoms or groups near the active center determines the activ-
ities of hemoproteins.[7] To understand the activities of
hemes, Chang et al. have synthesized a series of heme
models modified by a range of groups that have varying
dipole moments and are positioned near the coordinated
heme center. From studies on these models, Chang et al. re-
ported that dipolar forces and hydrogen bonding should
play a significant role in regulating the oxygen affinities of
heme proteins.[5,6] In particular, it was observed that the off-
rates of O2 were governed by the dipole moments in the
model molecules equipped with aprotic groups. For the
heme-model compounds modified with protic groups, the
off-rates of O2 were determined by hydrogen bonding inter-
actions with the O2 located at their coordinated centers.
Since the off-rates of O2 from the heme groups in proteins
are related to their ability to catalyze peroxidation by affect-
[a] Dr. Q. Wang, Dr. Z. Yang, M. Ma, Prof. C. K. Chang, Prof. B. Xu
Department of Chemistry
The Hong Kong University of Science & Technology
Clear Water Bay, Hong Kong (China)
Fax : (+852)2358-1594
E-mail: chang@ust.hk
chbingxu@ust.hk
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mination of factors that govern or contribute to the catalytic
activity in such systems. More specifically, we expected that,
similar to the case for the hemoprotein and the trends in
catalytic activities observed in the series of model com-
pounds themselves, the distal substituents above the iron
centers of the heme model compounds would have a signifi-
cant influence on the catalytic activities of the supramolec-
ular-hydrogel-based artificial peroxidases.
In this work, we found that changes in the distal substitu-
ents above the active centers of the heme model compounds
also determined the activities of the supramolecular-hydro-
gel-based artificial enzymes. The highest catalytic activity of
the hydrogel-based artificial enzyme (I; Scheme 1) in tolu-
ene reached about 90% of the activity of HRP in water. By
removing water from the hydrogels, we obtained lyophilized
artificial enzymes (II), which were examined to determine
their catalytic activities in organic solvent (toluene). The
catalytic activities of the lyophilized enzymes reached up to
75% of that of I in organic solvent. These results confirm
that supramolecular hydrogels are an excellent platform for
making artificial enzymes and verifies the possibility of fine
tuning the activity of the artificial peroxidases by changing
the distal substituents near the active center of the heme
model compounds. This novel approach may provide impor-
tant guidance for the development of artificial enzymes.
lyophilized powder (II) containing the nanofibers of 1 and 2,
and the heme model. We characterized both I and II and in-
vestigated their catalytic activities for oxidation.
As shown in the TEM images (Figure 1), the control hy-
drogel (i.e. that made of only 1 and 2) and Gel-6 (i.e. that
composed of 1, 2, and 6) have a similar morphology (we
chose Gel-6 as the representative example of Gels-3 to -6 as
they share the same features). The morphology of the con-
trol hydrogel consisted of nanofibers (ꢀ20 nm diameter) of
self-assembled 1 and 2, which were noncovalently entangled
to form 50~500 nm pores. Besides the relatively large pores,
the diameters of the nanofibers in Gel-6 are almost the
same as those in the control, which suggests that the nano-
fibers of Gel-6 mainly consist of 1 and 2. The gray area/dark
particles that surround the nanofibers are probably the
heme model compounds and the less-ordered aggregates of
1 and 2.[3] Moreover, the presence of the heme model com-
pounds in the outer layer of the nanofibers should facilitate
the diffusion of the substrates upon their subsequent catalyt-
ic application as artificial peroxidases.
Figure 2 shows the UV/Vis spectra of compound 6, Gel-6,
and HRP in an aqueous buffer (0.1m phosphate, pH 7.4).
The Soret peak of Gel-6 at 411 nm is the same as that of
pure 6, which indicates that the configuration of 6 in the ar-
tificial peroxidases is unchanged. The Soret peaks of the
other compounds (4, 5, 7 and 8) in the hydrogels are also
the same as their corresponding pure forms. However, the
Soret peak of compound 3 differs from that of pure 3 in the
aqueous buffer because 3 has no axial imidazole-containing
ligands for coordination to the iron center. Although it
exists in dimer form in the aqueous buffer, in the hydrogel,
compound 3 changes into its more active monomeric form
as a result of supramolecular interactions. A 1:1 mixture of
histidine and Gel 3 shows a redshift in the Soret band (from
Results and Discussion
Scheme 1 illustrates the typical procedure for making the ar-
tificial peroxidases by using supramolecular hydrogels. The
mixture of Fmoc-l-phenylalanine (1) (Fmoc: 9-fluorenylme-
thoxycarbonyl) and Fmoc-l-lysine (2) under slightly basic
conditions resulted in a suspension, which turned into a
clear solution upon heating to 333 K. The addition of one of
the heme model compounds 3–8[5] and subsequent cooling
afforded a brown, nontransparent hydrogel (I). After fast
cooling with liquid nitrogen, I was freeze-dried to give the
400 to 406 nm), which indicates the formation of a hemin–
[3]
histidine complex stabilized by a FeIII N bond. In the case
À
of model hemes 4–8, the direct introduction of an axial
ligand with imidazole at the meso position led to their mon-
Scheme 1. Procedure for making the supramolecular-hydrogel-based artificial enzymes by using hydrogelators and heme model compounds.
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Artificial Peroxidases Based on Supramolecular Hydrogels
FULL PAPER
signed heme model compounds.[15] Gel-6 displays another
strong peak at 265nm, which is the characteristic absorb-
ance of the Fmoc groups in 1 and 2. The absorbance of Gel-
6 at about 295nm originates from the phenylalanine of the
hydrogel. The tryptophan and/or tyrosine residues in HRP
lead to the weakly absorbing peak at 280–300 nm.
Using the oxidation of pyrogallol as a model reaction, we
monitored the catalytic activities of the artificial peroxidases
(Gels-3 to -8) formed by the heme model compounds (3–8)
and the supramolecular hydrogel. As shown in Table 1 and
Figure 3, these supramolecular-hydrogel-based, artificial per-
oxidases all exhibit relatively high activities in toluene that
are close to the activities of native peroxidases in water.
Relative to Gel-3, the artificial enzymes made of Gels-4 to
-8 have significantly higher activities in toluene. Among
them, the activity of Gel-6 in toluene can reach 90% of that
of native HRP in aqueous buffer. These results suggest that
hydrogel-encapsulated compounds 4–8 have a greater struc-
tural similarity to native HRP than Gel-3, which is in agree-
ment with the data obtained from their UV/Vis spectra.
The kinetic data in Table 1 indicate that the kcat of Gel-3
in toluene (370.7 minÀ1) is 136 times that of free 3 in toluene
(2.7 minÀ1). For model hemes 4–8, the values of kcat for the
free forms in toluene are 8.1, 7.5, 9.8, 3.7, and 9.3 minÀ1, re-
spectively. Compared with the activities of Gels-4 to -8 in
toluene (1212.2, 1063.6, 1556.9, 545.1, and 1481 minÀ1), the
activity enhancements of the model hemes 4–8 after hydro-
gel immobilization are times 148.6, 140.8, 157.9, 146.3, and
158.3, respectively. The 130–160-fold enhancement of activi-
ty for Gels-3 to -8 indicates the influence of the novel supra-
molecular hydrogel skeleton on the artificial peroxidases.
Such an effect should be divided into two parts, the effect of
Figure 1. TEM images of the nanofiber matrices in A) the hydrogel made
of 1 and 2 without heme model compounds and B) the hydrogel made of
1 and 2 with the addition of compound 6 (Gel-6) after cryo-drying.
Figure 2. UV/Vis spectra of 4 mm Gel-6 (d), free 6 (c), and free
HRP in pH 7.4 buffer (a).
omeric forms and produced a redshift of the Soret band rel-
ative to that of heme 3. As a result, the model heme 6 and
Gel-6 have the same Soret band at about 411 nm as that of
HRP, which has a similar heme group to that of the de-
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5075

B. Xu, C. K. Chang et al.
Table 1. The activity data and ratios of various catalytic systems in differ-
ent solvents.[a]
ers that mimic the molecular environment around the active
center in a natural enzyme.
kcat in buffer
kcat in toluene
kcat in toluene
after
Activity
ratio[c]
Figure 4 shows the time-course plots of the catalytic reac-
tions over 15minutes for Gels- 3 to -8 in water. These data
indicate that the activities of artificial peroxidases with dif-
[minÀ1
]
[minÀ1
]
lyophilizing
[b]
[minÀ1
]
Free 3
Gel-3
Gel-3
+histidine
Gel-4
Gel-5
Gel-6
Gel-7
Gel-8
HRP
2.4
19.9
49.7
2.7
370.7
1045.3
2.7
255.6
710.6
1.00
1.45
1.47
59.8
56.6
90.3
44.4
88.6
1212.2
1063.6
1556.9
545.1
1481.4
1.8
776.5
685.4
1146.9
406.5
979.51.5
1.8
1.56
1.55
1.35
1.34
1
1740.0
1.00
[a] The backgrounds of all carriers without heme model compounds have
been subtracted. [b] The samples were lyophilized to form a powder
before assaying the activities. [c] The ratio of the activity of the artificial
enzyme versus the lyophilized artificial enzymes (i.e. dried hydrogels con-
taining heme models).
Figure 4. Time-course plots (over 15minutes) of the reaction of pyrogal-
lol (10.0 mm) and H2O2 (40.0 mm) in 0.01m phosphate buffer at pH 7.4
catalyzed by 5 mm Gel-3 (&), Gel-4 (&), Gel-5 (~), Gel-6 (~), Gel-7
(*), and Gel-8 (*).
ferent heme model compounds depends on the distal groups
above the coordinated iron atoms and reveals that the order
of their catalytic abilities in the aqueous buffer is Gel-6>
Gel-8>Gel-4>Gel-5>Gel-7>Gel-3. Figure 5shows the
time-course plots of the catalytic reactions over 15minutes
for Gels-3 to -8 in toluene, which showed the same order of
catalytic activity as in water. Therefore, the order of the ac-
tivities of the artificial peroxidases is Gel-6>Gel-8>Gel-
4>Gel-5>Gel-7>Gel-3. As shown in Figures 5and 4, the
artificial systems have activities in the order of Gels-6, -8,
-4, -5, -7@Gel-3 in water and Gels-6, -8, -4, and -5@Gels-7
and -3 in toluene. The major reason for the different reactiv-
ities of Gel-7 in toluene and water is that the hydrophobic
alkyl chain on the thioester of 7 is a poor facilitator of hy-
Figure 3. Catalytic activities of the artificial enzymes, heme model com-
pound 3, and HRP under three different reaction conditions.
the supramolecular nanofibers and that of the phase equilib-
rium of reactants and products between the hydrophobic
toluene solution and the aqueous environment.
By measuring the activities of the lyophilized artificial en-
zymes in organic media, we can separate the contribution of
the amphiphilic nanofibers from the effect of the phase
transfer that originates from the organic media and water in
the hydrogel. In the case of 3, the activity of lyophilized
Gel-3 in toluene is about 12 times the activity of Gel-3 in
the aqueous buffer (Table 1). At the same time, the activity
of the artificial enzyme (i.e., Gel-3) in toluene is about 19
times higher than that of Gel-3 in the aqueous buffer.
Therefore, the effect of phase transfer may contribute to
about a 1.5fold increase in the enhanced activity of the arti-
ficial peroxidases in toluene. This enhancement is quite con-
sistent for all the artificial peroxidases. When the heme
model compounds are incorporated into the hydrogel, all of
the enhancement ratios from phase transfer are about 1.5.
Thus, the high activities of the artificial peroxidases in or-
ganic solvent mainly originate from the amphililic nanofib-
Figure 5. Time-course plots (over 15 minutes) of the reaction of pyrogal-
lol (10.0 mm) and H2O2 (40.0 mm) in toluene catalyzed by 5 mm Gel-3
(&), Gel-4 (&), Gel-5 (~), Gel-6 (~), Gel-7 (*), and Gel-8 (*).
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Artificial Peroxidases Based on Supramolecular Hydrogels
FULL PAPER
drogen bonding with the iron-bound oxygen atom. When
the solvent is water, sufficient water molecules are present
to aid the formation of hydrogen bonds on the oxygen
atom, thus assisting the catalytic reaction.
As a result, the FeV=O species from heme models 4 and 5
should have higher activation energies compared with those
of heme models 6 and 8. The higher activation energy of
heme model 5 than that of 4 may also be ascribed to in-
creased steric hindrance in its molecular structure. For heme
model 7, the distal alkyl chains from the thioester do not
bear lone pair electrons that could act as hydrogen-bond ac-
ceptors. Therefore, the intermediate species in 7 has the
highest activation energy among the heme models 4–8.
Among the artificial peroxidases, Gels-4 to -8, the order of
activation energy for their intermediates is Gel-7>Gel-5>
Gel-4>Gel-8>Gel-6, which agrees with the order of activi-
ty: Gel-6>Gel-8>Gel-4>Gel-5>Gel-7.
It is well-known that during catalysis peroxidases react
first with hydrogen peroxide to form intermediate species
(FeV=O–porphyrins).[16] In native HRP, the proximal histi-
dine coordinates to the iron in heme, which can effectively
reduce the energy level of the FeV=O–porphyrin by electron
donation from the imidazole group. Therefore, the inter-
mediate species in HRP has lower activation energy and
higher activity in the peroxidation reaction. Thus, in an arti-
ficial peroxidase, a ligand containing imidazole can have the
same positive effect as the histidine group in HRP. This
mechanism explains the higher activities of Gels-4 to -8 than
that of Gel-3. The intermediates of the artificial peroxidases
formed by the heme model compounds 4–8 with an axial
ligand containing imidazole might also effectively lower the
activation energy.
To explain how the distal groups in heme model com-
pounds can influence the activities of the corresponding arti-
ficial peroxidases, we need to examine how the distal groups
above the porphyrin ring of the heme model compounds
may affect the hydrogen bond formed by the iron–oxo spe-
cies. The heme model compounds 4–8 can be divided into
two types. The first type, which includes compounds 6–8
(Scheme 2A), has meta-substituted benzamides with the
Conclusions
The combination of a supramolecular hydrogel with various
heme model compounds that act as the active center affords
artificial peroxidases with high catalytic activities. The activi-
ty of the artificial peroxidases can be tailored by changing
the distal substituents above the coordinated centers of the
heme model compounds, which is independent of the supra-
molecular hydrogel. Although the effect of phase transfer at
the interface of the organic solvent and water in the supra-
molecular hydrogel provides a certain enhancement, the
high activities of the artificial peroxidases in organic sol-
vents are mainly due to the unique features of the amphi-
philic nanofibers. Moreover, by using the principles illustrat-
ed in this work, it may be possible to tune the activities of
the artificial peroxidases by changing the distal substituents
or the structure of the hydrogelators. Our future work will
expand this general strategy to a variety of artificial en-
zymes.
Experimental Section
Fmoc-l-phenylalanine (50 mmol), Fmoc-l-lysine (50 mmol), and sodium
carbonate (100 mmol) were added to water (1 mL) to afford a suspension,
which turned into a clear solution after heating to 333 K. Then, the pow-
dered heme model (10 mmol) was rapidly dissolved in the peptide solu-
tion. A hydrogel composite with hemin (Gels-3 to -8) formed after about
10 min. After rapid cooling with liquid nitrogen, I was freeze-dried to
give the lyophilized powder (II). By using the oxidation of pyrogallol
(10.0 mm) by H2O2 (40.0 mm) as a model reaction and by fixing the total
concentration of various hemins at 5 mM in the mixture, the activities of
the hemins were obtained by monitoring the absorbance (420 nm) of pur-
purogallin, the product of hemin-catalyzed oxidation of pyrogallol. The
activity constant kcat (Vmax/[E], in which Vmax is the velocity of the reac-
tion and [E] is the concentration of the enzyme) was measured by using
the initial reaction rate in the first minute at saturated concentration
(10.0 mm), which eliminates the effect from the concentration of sub-
strate and enzyme. Therefore, the kcat values in various systems represent
the basic kinetic activity.
Scheme 2. The orientations of the distal groups in A) compounds 6–8 and
B) compounds 4 and 5.
distal groups above the coordination site of the porphyrin
ring. The second type, represented by 4 and 5 (Scheme 2B),
has the simple o-anilide with the distal groups above the co-
ordination site of the porphyrin ring. In the first type, it is
apparent that the heme model 6 has distal OH groups and
heme model 8 has the tertiary amide near the iron–oxo site
of the intermediate. These groups bear lone-pair electrons
and may act as hydrogen bond acceptors to lower the activa-
tion energy of their intermediates. The higher activation
energy of heme model 8 than that of 6 may be ascribed to
increased steric hindrance in its molecular structure. For the
second type of heme model compound, the electron-defi-
cient distal groups in heme models 4 and 5 are located away
from the FeV=O porphyrin relative to heme models 6 and 8.
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B. Xu, C. K. Chang et al.
Kim, Chem. Commun. 2003, 2912; N. Sreenivasachary, J. M. Lehn,
Proc. Natl. Acad. Sci. USA 2005, 102, 5938; M. Suzuki, M. Yumoto,
M. Kimura, H. Shirai, K. Hanabusa, Chem. Commun. 2002, 884; S.
Tamaru, S. Kiyonaka, I. Hamachi, Chem. Eur. J. 2005, 11, 7294;
R. V. Ulijn, L. De Martin, L. Gardossi, P. J. Halling, Curr. Org.
Chem. 2003, 7, 1333; B. G. Xing, C. W. Yu, K. H. Chow, P. L. Ho,
D. G. Fu, B. Xu, J. Am. Chem. Soc. 2002, 124, 14846; Z. M. Yang,
H. W. Gu, D. G. Fu, P. Gao, K. J. K. Lam, B. Xu, Adv. Mater. 2004,
16, 1440; Z. M. Yang, H. W. Gu, Y. Zhang, L. Wang, B. Xu, Chem.
Commun. 2004, 208; Z. M. Yang, G. L. Liang, L. Wang, B. Xu, J.
Am. Chem. Soc. 2006, 128, 3038; Y. Zhang, Z. M. Yang, F. Yuan,
H. W. Gu, P. Gao, B. Xu, J. Am. Chem. Soc. 2004, 126, 15028; W.
Deng, H. Yamaguchi, Y. Takashima, A. Harada, Angew. Chem.
2007, 119, 5236; Angew. Chem. Int. Ed. 2007, 46, 5144; B. V. Shan-
kar, A. Patnaik, J. Phys. Chem. B 2007, 111, 9294; J. E. A. Webb,
M. J. Crossley, P. Turner, P. Thordarson, J. Am. Chem. Soc. 2007,
129, 7155; M. de Loos, A. Friggeri, J. van Esch, R. M. Kellogg, B. L.
Feringa, Org. Biomol. Chem. 2005, 3, 1631; A. Friggeri, C. van der
pol, K. J. C. van Bommel, A. Heeres, M. C. A. Stuart, B. L. Feringa,
J. van Esch, Chem. Eur. J. 2005, 11, 5353.
Acknowledgement
This work was supported by the Hong Kong Research Grant Council
(HKU2/05C, HKU2/06C, 604905, 600504, 603907).
[1] S. Sawada, Y. Nomura, Y. Aoyama, K. Akiyoshi, J. Bioact. Compat.
Polym. 2006, 21, 487; L. A. Estroff, A. D. Hamilton, Chem. Rev.
2004, 104, 1201; M. George, R. G. Weiss, Acc. Chem. Res. 2006, 39,
489; Z. M. Yang, G. L. Liang, B. Xu, Acc. Chem. Res. 2008, 41, 315;
P. Terech, R. G. Weiss, Chem. Rev. 1997, 97, 3133; R. G. Weiss, P.
Terech, Molecular gels: materials with self-assembled fibrillar net-
works, Springer, Dordrecht, 2006.
[2] Q. G. Wang, Z. M. Yang, L. Wang, M. L. Ma, B. Xu, Chem.
Commun. 2007, 1032.
[3] Q. G. Wang, Z. M. Yang, X. Q. Zhang, X. D. Xiao, C. K. Chang, B.
Xu, Angew. Chem. 2007, 119, 4363; Angew. Chem. Int. Ed. 2007, 46,
4285.
[4] C. K. Chang, T. G. Tralor, Proc. Natl. Acad. Sci. USA 1973, 70, 2647.
[5] C. K. Chang, B. Ward, R. Young, M. P. Kondylis, J. Macromol. Sci.
Chem. A 1988, 25, 1307.
[6] R. Young, C. K. Chang, J. Am. Chem. Soc. 1985, 107, 898.
[7] P. F. Chen, A. L. Tsai, K. K. Wu, J. Biol. Chem. 1994, 269, 25 062; S.
de Lauzon, D. Mansuy, J. P. Mahy, Eur. J. Biochem. 2002, 269, 470;
R. Ricoux, J. L. Boucher, D. Mansuy, J. P. Mahy, Biochem. Biophys.
Res. Commun. 2000, 278, 217; Y. Zhao, J. P. M. Schelvis, G. T. Bab-
cock, M. A. Marletta, Biochemistry 1998, 37, 4502.
[8] H. A. Behanna, J. J. J. M. Donners, A. C. Gordon, S. I. Stupp, J. Am.
Chem. Soc. 2005, 127, 1193; G. A. Silva, C. Czeisler, K. L. Niece, E.
Beniash, D. Harrington, J. A. Kessler, S. I. Stupp, Science 2004, 303,
1352; S. Vauthey, S. Santoso, H. Y. Gong, N. Watson, S. G. Zhang,
Proc. Natl. Acad. Sci. USA 2002, 99, 5355; S. G. Zhang, Nat. Bio-
technol. 2003, 21, 1171.
[11] S. Kiyonaka, K. Sada, I. Yoshimura, S. Shinkai, N. Kato, I. Hamachi,
Nat. Mater. 2004, 3, 58; I. Yoshimura, Y. Miyahara, N. Kasagi, H.
Yamane, A. Ojida, I. Hamachi, J. Am. Chem. Soc. 2004, 126, 12204.
[12] Z. M. Yang, K. M. Xu, L. Wang, H. W. Gu, H. Wei, M. J. Zhang, B.
Xu, Chem. Commun. 2005, 4414.
[13] Z. M. Yang, B. Xu, Chem. Commun. 2004, 2424.
[14] Z. A. C. Schnepp, R. Gonzalez-McQuire, S. Mann, Adv. Mater. 2006,
18, 1869.
[15] S. Nagano, M. Tanaka, K. Ishimori, Y. Watanabe, I. Morishima, Bio-
chemistry 1996, 35, 14251; E. S. Ryabova, A. Dikiy, A. E. Hesslein,
M. J. Bjerrum, S. Ciurli, E. Nordlander, J. Biol. Inorg. Chem. 2004,
9, 385; G. Smulevich, M. Paoli, G. DeSanctis, A. R. Mantini, F.
Ascoli, M. Coletta, Biochemistry 1997, 36, 640.
[16] P. R. O. Demontellano, Annu. Rev. Pharmacol. Toxicol. 1992, 32, 89;
Z. S. Farhangrazi, B. R. Copeland, T. Nakayama, T. Amachi, I. Ya-
mazaki, L. S. Powers, Biochemistry 1994, 33, 5647; M. A. Gilabert,
A. N. P. Hiner, P. A. Garcia-Ruiz, J. Tudela, F. Garcia-Molina, M.
Acosta, F. Garcia-Canovasa, J. N. Rodriguez-Lopez, BBA-Proteins
and Proteomics 2004, 1699, 235; R. S. Koduri, M. Tien, Biochemistry
1994, 33, 4225; J. N. Rodriguez-Lopez, D. J. Lowe, J. Hernandez-
Ruiz, A. N. P. Hiner, F. Garcia-Canovas, R. N. F. Thorneley, J. Am.
Chem. Soc. 2001, 123, 11838; A. T. Smith, S. A. Sanders, R. N. F.
Thorneley, J. F. Burke, R. R. C. Bray, Eur. J. Biochem. 1992, 207,
507.
[9] A. Aggeli, M. Bell, N. Boden, J. N. Keen, P. F. Knowles, T. C. B.
McLeish, M. Pitkeathly, S. E. Radford, Nature 1997, 386, 259; E.
Gazit, Chem. Soc. Rev. 2007, 36, 1263; N. Hendler, N. Sidelman, M.
Reches, E. Gazit, Y. Rosenberg, S. Richter, Adv. Mater. 2007, 19,
1485; A. R. Hirst, B. Q. Huang, V. Castelletto, I. W. Hamley, D. K.
Smith, Chem. Eur. J. 2007, 13, 2180; M. A. Kostiainen, G. Z. R. Szil-
vay, D. K. Smith, M. B. Linder, O. Ikkala, Angew. Chem. 2006, 118,
3618; Angew. Chem. Int. Ed. 2006, 45, 3538; P. D. Thornton, R. J.
Mart, R. V. Ulijn, Adv. Mater. 2007, 19, 1252; R. V. Ulijn, J. Mater.
Chem. 2006, 16, 2217.
[10] M. Ikeda, M. Takeuchi, S. Shinkai, Chem. Commun. 2003, 1354; H.
Kobayashi, M. Amaike, J. H. Jung, A. Friggeri, S. Shinkai, D. N.
Reinhoudt, Chem. Commun. 2001, 1038; S. M. Park, Y. S. Lee, B. H.
Received: December 20, 2007
Published online: April 9, 2008
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