Biomimetic artificial photosynthesis by light-harvesting synthetic wood

Article abstract of DOI:10.1002/cssc.201100074

Tree of a kind: An integrated artificial photosynthetic system is developed by reassembling raw materials from plants as support matrix for the encapsulation of porphyrins. The hybrids allow visible-light-driven regeneration of NADH and production of fine chemicals. The synthetic wood not only provides a microenvironment for porphyrin encapsulation but also makes the photosynthesis more effective due to the redox-active lignin component.

Full text of DOI:10.1002/cssc.201100074

DOI: 10.1002/cssc.201100074
Biomimetic Artificial Photosynthesis by Light-Harvesting Synthetic Wood
Minah Lee,[a] Jae Hong Kim,[a] Sang Hyun Lee,[b] Sahng Ha Lee,[a] and Chan Beum Park*[a]
In green plants, solar energy is collected by chlorophyll mole-
cules and is passed on to photosynthetic reaction centers
where it is used for oxygen evolution and carbon fixation.[1]
During natural photosynthesis the energy, obtained from pho-
tons, of excited electrons generates a reducing power in the
form of pyridine nucleotide cofactor, NAD(P)H, whose role as
electron carrier is essential in reduction and oxidation reactions
for photosynthetic cellular functions. The light-driven reduction
of CO2 to organic compounds occurs through the Calvin cycle,
in which photochemically regenerated NAD(P)H is consumed
by redox enzymes.[2] Inspired by natural photosynthesis, many
efforts have been made towards the development of biomim-
etic artificial light-harvesting assemblies for making use of the
practically unlimited supply of solar energy, and its conversion
to chemical energy in different forms.[3–5] In particular, the
light-induced cofactor recycling system has been regarded as a
blueprint for biocatalytic reactions because NAD(P)+/NAD(P)H-
dependent redox reactions can be used to produce valuable
fine chemicals.[6] Although redox enzymes are powerful biocat-
alysts for chemical synthesis, with high selectivity and catalytic
efficiency under mild conditions, their applicability is limited
by the high costs involved in supplying stoichiometric
amounts of cofactor for industrial processes.[7–9] Several photo-
chemical approaches, using “free” colloidal nanomaterials (e.g.,
p-doped TiO2,[10] W2Fe4Ta2O17,[11] quantum dots[12]), have been
reported for the visible-light-driven regeneration of NADH, but
low efficiency and limited photostability due to reactive free
radicals have hindered their practical application.[13]
duction of fine chemicals by NAD(P)H-dependant enzymes and
mimicking the natural photosystem (Figure 1A).
The porphyrins are a class of organic molecules that have a
macrocyclic tetrapyrrole core that can be functionalized with
Attempts to integrate photosynthetically active components
within support materials, mimicking light-harvesting pigments
embedded within thylakoid membranes of chloroplasts, have
been reported.[14–17] The supporting matrix for encapsulation
(or immobilization) of photosynthetic materials can assist in
the organization of the guest materials and protect them by
providing a stable microenvironment.[18] Furthermore, the ap-
proach allows easier handling of photoactive materials and fa-
cilitates recycling from the reaction mixture.[19] Herein, we pro-
vide the first report on light-harvesting synthetic wood (LSW)
for biomimetic artificial photosynthesis. LSW can harness solar
radiation for the regeneration of NAD(P)H, allowing the pro-
Figure 1. (A) Illustration of the light-harvesting system of green plants (left)
and that of light-harvesting synthetic wood (LSW) (right). In both systems,
light-driven cofactor regeneration takes place followed by NAD(P)H-depend-
ant enzymatic reaction. (B) Molecular structures of light-harvesting pigment
in plants (left) and LSW (right). (C) Molecular structures of structural compo-
nents including cellulose, xylan, and lignin (tentative structure) common for
plants and LSW.
different substituents. They exhibit remarkable photochemical,
catalytic, electrochemical, and biochemical properties. The por-
phyrins include chlorophyll; the natural light-harvesting pig-
ment (Figure 1B).[20] In our LSW, porphyrins serve as light-har-
vesting pigments encapsulated within a porous lignocellulosic
support. Encapsulation was achieved through simultaneous re-
actions: lignocellulose coagulation and porphyrin reprecipita-
tion. The porous lignocellulosic support (SW) was a composite
of three major structural components of plant cells: cellulose,
hemicellulose, and lignin (Figure 1C). In plant cells, crystalline
cellulose microfibrils, which encapsulate cells in a mesh-like
structure, are linked to hemicelluloses to provide strength as
[a] M. Lee, J. H. Kim, S. H. Lee, Prof. C. B. Park
Department of Materials Science and Engineering
Korea Advanced Institute of Science and Technology
335 Science Road, Daejeon 305–701 (Korea)
Fax: (+82)42-869-3310
E-mail: parkcb@kaist.ac.kr
[b] Prof. S. H. Lee
Department of Microbial Engineering
Konkuk University
Seoul, 143–701 (Korea)
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201100074.
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581

well as extensibility, and lignin, a complex phenolic polymer,
penetrates the voids, conferring mechanical strength to cell
walls.[21] The all-wood composite is environmentally friendly
and highly suitable for replacing nonrenewable, petroleum-
based synthetic polymers. Furthermore, we found that the in-
corporation of lignin into SW is important for enhancing elec-
tron transfer in artificial photosynthesis.
ed that the SW is mostly mesoporous, with a relatively broad
pore-size distribution centered at ca. 20 nm (Figure 2B). The
FTIR spectrum of the SW sample shows peaks typical for cellu-
lose, xylan, and lignin (Figure 2C). The lignin peaks at
1513 cmÀ1 and 1596 cmÀ1 correspond to the aromatic skeletal
vibration and the aromatic skeletal vibration breathing with C=
O stretching, respectively.[25]
The practical use of lignocellulosic materials has drawn
much attention in response to growing environmental aware-
ness, but their poor solubility in water has limited their appli-
cation.[22] We used an ionic liquid to dissolve the unmodified
lignocellulosic materials. Ionic liquids are chemically/thermally
stable, nonflammable, and nonvolatile, so they have been con-
sidered as “green solvents.”[23] The ionic liquid used in this
study, 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc), in
particular is known to have a low toxicity, low corrosiveness,
and good biodegradability.[24] We obtained a SW gel film by re-
moving [C2mim]OAc from a preformed film of a viscous SW so-
lution. As the film coagulated upon water treatment,
[C2mim]OAc was extracted from the film while the wood com-
ponents barely dissolved in water, affording a translucent
brown-colored gel (Figure 2A, inset). To characterize the inside
structure of the SW film while minimizing collapse of the gel
network, we removed water by freeze-drying. According to
analysis by scanning electron microscopy (SEM) the SW has an
interconnected macro- and mesoporous structure, which may
lead to efficient mass transport during photosynthesis (Fig-
ure 2A). The pore-size distribution, obtained by Brunauer–
Emmett–Teller (BET) analysis using N2 adsorption, also indicat-
LSW capable of performing photosynthesis was prepared by
encapsulating a hydrophobic porphyrin as photosensitizing
pigment. We successfully incorporated water-insoluble por-
phyrins into SW by virtue of the strong solvating power of
[C2mim]OAc. Water was added to a porphyrin–SW solution,
which was then casted as a film onto a glass plate to coagu-
late the lignocellulosic support. The hydrophobic porphyrins
dissolved in [C2mim]OAc were simultaneously entrapped in the
SW gel through reprecipitation.
We tested six types of hydrophobic porphyrins, with differ-
ent functionalities and metal centers (Figure 1B), for the visi-
ble-light-driven regeneration of NADH from NAD+. Porphyrins
with different substituents resulted in differential conversion
yields (Figure 3A), and among the porphyrins, mTHPP showed
the highest conversion yield of NADH; thus, mTHPP was
chosen as a model porphyrin for further experiments. We did
not observe leakage of the encapsulated mTHPP during im-
mersion for more than 2 h in the reaction medium, according
to changes in the absorbance spectra of the solution (Fig-
ure 3C, inset). This makes the LSW suitable for photoenzymatic
reactions. We compared UV/vis absorption spectra of an
mTHPP–SW solution and film to an SW solution and SW film
(Figure 3C). The Soret band of
the mTHPP–SW film was broad-
er than that of mTHPP–SW solu-
tion. The lmax value (427 nm) of
the Soret band of mTHPP–SW
film was red-shifted by 5 nm
compared to mTHPP–SW solu-
tion (422 nm) in [C2mim]OAc.
The small red-shift and broaden-
ing of the Soret band suggest
changes in the molecular inter-
actions of mTHPP entrapped in
the film; a phenomenon com-
monly observed in spectroscop-
ic studies on self-assembled
monolayers[26–28] or supramolec-
ular assemblies of porphyrins.[29]
According to literature reports,
the spectral change should be
caused by the formation of J-ag-
gregate-like, partially stacked
structures that are adsorbed to
the support by noncovalent in-
teractions. Stacked face-to-face
Figure 2. Characterization of the SW film. (A) SEM images of the SW film, showing its macro-/mesoporous struc-
ture. The inset is a photograph of the SW film, showing a translucent material (the sample has a brown color).
(B) Nitrogen adsorption (open symbols) and desorption (filled symbols) isotherms, and Barrett–Joyner–Halenda
(BJH) mesopore size distribution of SW (C) FTIR spectra of SW and its components (cellulose, xylan, and lignin).
porphyrin aggregation (i.e.,
sandwich-type H-aggregates) is
well-known to result in a spec-
tral blue-shift relative to the mo-
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mance of porphyrins that demonstrated relatively high NADH
regeneration efficiencies (TPyP, CoTMPP, and mTHPP, according
to Figure 3A) in two different supports: SW film and cellulose
film. As shown in Figure 4A, porphyrin–SW was much more ef-
ficient in NADH regeneration than porphyrin–cellulose. To in-
vestigate this difference, we measured photocurrents of
mTHPP–SW film and mTHPP–cellulose film, each formed on
ITO glass, in a 0.1m phosphate buffer containing 15 w/v% trie-
thanolamine (TEOA) over time intervals of 10 s by exposure to
the light source. In response to the ON/OFF cycling of the light
source, a stable, reproducible photocurrent was observed (Fig-
ure 4B). Furthermore, an increase in the net anodic photocur-
rent with an increase of positive bias to ITO electrode was ob-
served (Figure 4C). These results indicate that the transfer of
photoexcited electrons from mTHPP to the ITO electrode took
place yielding the photocurrent generation, and the resulting
oxidized mTHPP recaptured electrons from TEOA, an electron
donor. From the photocurrent transients of the two films, we
found that a higher photo-to-dark current ratio, as well as a
faster response time, especially in the rise time, was achieved
in the mTHPP–SW film. We attribute this result to improved
charge transfer efficiency[38] by the introduction of lignin to the
Figure 3. (A) NADH regeneration by water-insoluble porphyrins encapsulat-
ed in SW. mTHPP showed the highest NADH conversion yield. (B) Change in
fluorescence of an mTHPP–SW film in the presence of M at various concen-
trations. (C) Absorption spectra collected from mTHPP–SW solution, mTHPP-
SW film, SW solution, and SW film. The inset shows the amount of mTHPP
leakaged from SW film over incubation time.
nomer excited-state level, whereas side-by-side porphyrin ag-
gregation (i.e., J-aggregates) leads to a red-shift.[30] The rela-
tively small red-shift of the Soret band compared to other por-
phyrin aggregates indicates moderate interaction among por-
phyrin molecules.[31,32]
For the visible-light driven NAD(P)H regeneration using
mTHPP-SW, we used a rhodium-based organometallic com-
pound, M ([Cp*Rh(bpy)H2O]2+), as a hydride transfer mediator,
instead of ferredoxin-NADP+ reductase that works for NADPH
photogeneration in natural photosynthesis. M is known to be
capable of efficient regeneration of enzymatically active NADH
as well as NADPH,[33–35] unlike ferredoxin-NADP+ reductase
which has specificity only for NADPH. For the SW–porphyrin
hybrid material to facilitate artificial photosynthesis, the photo-
induced electron-transfer reaction from porphyrin to M should
occur efficiently, followed by a rapid reduction of NAD(P)H by
M. To investigate the donor–acceptor relationship between
mTHPP and M, we tracked changes in the fluorescence spec-
trum of mTHPP-SW film in the presence of M. As shown in Fig-
ure 3B, we observed a gradual decrease of the mTHPP fluores-
cence intensity with the increasing concentration of M. The
emission quenching indicates that the presence of M inhibits
the radiative decay of excited electrons in mTHPP, which
should be due to the electron transfer from excited porphyrin
to the electron acceptor M.[36,37] A detailed mechanism of
NADH regeneration by M is shown in Figure S1 (Supporting In-
formation).
Figure 4. (A) Comparison between porphyrin–SW and porphyrin–cellulose
films for photochemical NADH regeneration. (B,C) Photoelectrochemical
properties of each film. The porphyrin–SW film shows enhanced perfor-
mance in NADH conversion and photocurrent generation with a high
photo-to-dark current ratio and a faster response time.
To observe the effect of the SW composite on cofactor re-
generation compared to pure cellulose, we tested the perfor-
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composite, which should be responsible for the enhanced
NADH regeneration by the porphryin–SW film. Lignin contains
free phenolic groups that enable the polymer to undergo oxi-
dation–reduction reactions.[39] These phenolic groups in lignin
can be oxidized into electroactive quinine functionalities, facili-
tating reversible proton-coupled two-electron redox cycling ac-
cording to a recent report.[40] Furthermore, Barsberg et al. also
suggested the existence of donor–acceptor interactions be-
tween the substructures in disordered lignin polymers.[41] Thus,
similar to the protein environment of the natural photosyn-
thetic reaction center in the thylakoid membrane containing
electron donor and acceptor assemblies, such as plastoquinon
and tyrosin residue involved in electron transfer,[42] the local
environment of encapsulated porphyrin in LSW comprising
lignin may energetically contribute to efficient charge transfer
for biomimetic artificial photosynthesis.
À4.2 eV[7]) in one step (Figure S1). The electrochemical activa-
tion of the complex is achieved by two reduction steps fol-
lowed by protonation.[44] Meanwhile, a sacrificial electron
donor TEOA (E~À5.37 eV) reduces the oxidized porphyrin to
avoid photodegradation of the dye. The regenerated cofactor
NADH in an enzymatically active form is then consumed by
GDH for the conversion of a-ketoglutarate to l-glutamate. It
was observed that while the enzymatic synthesis of l-gluta-
mate hardly occurred under dark stage, a gradual increase of
conversion yield up to 18% was observed with the light on in
8 h (Figure 5B). The turnover frequency of mTHPP encapsulat-
ed in LSW was estimated to be ca. 1.25 hÀ1, indicating a better
efficiency than inorganic materials (e.g., p-doped TiO2,[10]
W2Fe4Ta2O17,[11] quantum dots[12]) reported for photochemical
NADH regeneration. As expected, a control experiment with
SW without encapsulating mTHPP did not show l-glutamatic
synthesis (Figure S3). We found that the photoenzymatic con-
version yield was affected by the composition of SW (Fig-
ure 5C). The conversion yield increased with increasing
amounts of lignin, whereas hemicellulose did not show any
notable effect on the synthetic reaction. This supports that
lignin is involved in the electron transfer, improving the light-
harvesting reaction. Taken together, our results show that SW
can not only act as a supporting matrix for light-harvesting
pigments, but can also enhance the photosynthetic reaction
by the presence of lignin. LSW exhibited a high structural sta-
bility (Figure S4) and photostability (Figure S5), indicating that
LSW is active for the overall photosynthetic reaction.
As a mimic of the organic synthesis in the Calvin cycle by
NAD(P)H-dependent redox enzymes, we combined a redox en-
zymatic reaction by l-glutamate dehydrogenase (GDH), a
NADH-dependent oxidoreductase, with visible-light-driven co-
factor regeneration facilitated by using LSW. An energy level
diagram of our artificial photosynthesis system is illustrated in
Figure 5A. The highest occupied molecular orbital (HOMO) (E~
À5.90 eV) and lowest unoccupied molecular orbital (LUMO)
(E~À3.69 eV) levels of mTHPP were estimated from cyclic vol-
tammograms of mTHPP in DMSO (Figure S2). Visible-light-
driven electron transfer reaction from the porphyrin to the
electrochemical mediator (M) (E~À3.96 eV[43]) results in activa-
tion of M, which can transfer one hydride ion to NAD(P)+ (E~
In summary, we demonstrated the development of an inte-
grated artificial photosynthetic system by reassem-
bling raw materials from plants as a support for the
encapsulation of light-harvesting pigments. Similar
to the natural light-harvesting by chloroplasts, water-
insoluble porphyrins encapsulated in a lignocellulosic
matrix enabled the utilization of light energy to-
wards the photochemical regeneration of NADH co-
factors and enzymatic chemical synthesis. The
porous SW composite provides a microenvironment
for porphyrin encapsulation and also allows an effec-
tive photosynthesis because of the inclusion of the
redox-active lignin component. This work hints at a
rational design of an artificial photosynthetic system
by allowing the use of renewable natural biopoly-
mers, facile fabrication under mild conditions, and an
environmentally friendly process.
Experimental Section
Materials: All chemicals, apart from porphyrins, were
purchased from Sigma–Aldrich (St. Louis, MO, USA) and
were used without further purification. Porphyrins in-
cluding
5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-
Figure 5. (A) Schematic energy-level diagram of the biomimetic artificial photosynthesis
system. Under visible-light irradiation, photo-excited electrons of mTHPP encapsulated in
LSW are transferred to M, generating reduction potentials for NAD(P)H regeneration. The
dotted arrows refer to photo-induced electron transfer. (B) Time-profile of l-glutamate
conversion yield under dark stage for 6 h, followed by a light stage for 8 h. (C) Effect of
synthetic wood composition on l-glutamate conversion. The result shows a significant
role of lignin in the photosynthesis of l-glutamate.
porphine (pTHPP), 5,10,15,20-tetrakis(3-hydroxyphenyl)-
21H,23H-porphine (mTHPP), 5,10,15,20-tetrakis(4-me-
thoxyphenyl)-21H,23H-porphine cobalt(II) (CoTMPP),
5,10,15,20-tetraphenyl-21H,23H-porphine
5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (TPyP), and
5,10,15,20-tetraphenyl-21H,23H-porphine zinc (ZnTPP)
(TPP),
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ChemSusChem 2011, 4, 581 – 586

were obtained from Frontier Scientific (Logan, UT, USA). The organ-
ometallic rhodium complex M, pentamethylcyclopentadienyl-2,20-
bipyridine-chloro-rhodium(III), was synthesized according the
method by Kolle and Gratzel.[33–35]
Enzymatic photosynthesis: The photosynthesis of l-glutamate was
performed under visible light (l>400 nm) in an enzymatic reaction
solution containing NAD+ (0.2 mm), M (500 mm), a-ketoglutarate
(5 mm), ammonium sulphate (100 mm), TEOA (15 w/v%), and l-glu-
tamate dehydrogenase (40 unit) in a 100 mm phosphate buffer
(pH 7.4). A constant flow of argon gas was supplied to the solu-
tion. For the quantitative analysis of l-glutamate, high-perfor-
mance liquid chromatography (LC-20 A prominence, Shimadzu Co.,
Japan), using an Inertsil C18 column (ODS-3 V, length, 150 mm),
was used. Samples were eluted by using phosphoric acid (0.05%)
at the flow rate of 1.0 mLminÀ1 and detected at 214 nm.
Synthetic wood film formation: SW components including cellulose
(2.5%, w/w), xylan (1.5%, w/w), and lignin (1%, w/w) were added
*
to [C2mim]OAc. The mixture was heated on a hot plate at 70 C
with vigorous magnetic stirring for more than 3 h to ensure the
formation of a homogeneous solution. After complete dissolution,
the resulting solution was spread on a glass plate and cast into a
thin film with a thickness at 500 mm by a blade coating method.
Deionized water was sprayed on the surface of the film to fix the
shape. The sample was further immersed in water to precipitate a
SW gel, followed by thorough washing for the complete removal
of [C2mim]OAc. For the synthesis of porphyrin-encapsulated SW
films, or LSW, porphyrin solutions were prepared by dissolving por-
phyrins in [C2mim]OAc at a concentration of 5 mgmLÀ1 and mixed
with the SW solution in the ratio of one to two. The resultant solu-
tion was stirred vigorously to ensure a homogenous distribution of
porphyrin. Then, LSW films were formed using the solution accord-
ing to the same method described above.
Acknowledgements
This study was supported by the National Research Foundation
via National Research Laboratories (R0A-2008–000–20041–0),
Converging Research Center (2009–0082276), and Engineering Re-
search Center (2008–0062205) programs, Korea. This research
was also partially supported by the EEWS initiative (KAIST).
Characterization: The morphology of SW film was examined by
using an S-4800 field-emission scanning electron microscope (SEM)
(Hitachi High-technologies Co., Japan) at an acceleration voltage of
10 kV after Pt-coating by a SCD005 Pt-coater (Bal-Tec AG., Liechten-
stein). Nitrogen adsorption-desorption isotherms were obtained by
using a Surface Area and Porosity Analyzer ASAP2020 (Micromerit-
ics, USA) at 77 K. Specific surface areas were calculated by using
the BET equation in a relative pressure range between P/P0 =0.05–
0.3. The pore-size distribution was estimated from the desorption
branch of the isotherm by using the BJH method. FTIR spectra
were obtained for the samples in KBr pellets by using a FT/IR-6100
(JASCO, Japan) at a resolution of 4 cmÀ1 by taking 100 scans per
spectrum. UV/vis absorption spectra of film or solution were mea-
sured by using a V-650 spectrophotometer (JASCO, Japan). Spec-
trofluorometric experiments were performed by using RF-5301PC
(Shimadzu Co., Japan) with excitation wavelength of 430 nm.
Keywords: biomimetic synthesis · hybrid materials · natural
products · photosynthesis · porphyrins
[1] W. Kuhlbrandt, D. N. Wang, Nature 1991, 350, 130–134.
[2] J. M. Berg, J. L. Tymoczko, L. Stryer, Biochemistry, 6th ed. W. H. Freeman,
New York, 2007, pp. 541–551.
[3] T. Nakashima, N. Kimizuka, Adv. Mater. 2002, 14, 1113–1116.
[4] K. Sugiyasu, N. Fujita, S. Shinkai, Angew. Chem. 2004, 116, 1249–1253;
Angew. Chem. Int. Ed. 2004, 43, 1229–1233.
[5] A. Ajayaghosh, V. K. Praveen, C. Vijayakumar, Chem. Soc. Rev. 2008, 37,
109–122.
[6] R. Wichmann, D. Vasic-Racki, Adv. Biochem. Engin. Biotechnol. 2005, 92,
225–260.
[7] H. K. Chenault, G. M. Whitesides, Appl. Biochem. Biotechnol. 1987, 14,
147–197.
[8] A. Schmid, J. S. Dordick, B. Hauer, A. Kiener, M. Wubbolts, B. Witholt,
Nature 2001, 409, 258–268.
Photochemical cofactor regeneration: The photochemical regener-
ation of NADH was conducted in a quartz reactor at room temper-
ature under visible light. We used a 450 Watt Xe-lamp (Oriel Co.)
equipped with a 400 nm cut-off filter as a light source. The reac-
tion solution was composed of 1 mm NAD+, 0.25 mm M, 15 w/v%
TEOA in a 100 mm phosphate buffer (pH 7.4). LSW film prepared
on a glass substrate was immersed in the reaction solution for
NADH regeneration. The concentration of regenerated NADH was
measured according to the increase in the absorbance of NADH at
340 nm by using BioSpec-mini spepctrophotometer (Shimadzu Co.,
Japan). Photocurrents were obtained by using a potentiostat/gal-
vanostat (WonATech, Model: WMPG1000, Korea) with the predeter-
mined applied potential (vs. Ag/AgCl) under the irradiation of a
450 Watt Xe-lamp equipped with the 400 nm cut-off filter. A 3-elec-
trode system including mTHPP-SW or mTHPP-cellulose coated
indium tin oxide (ITO) glass (working electrode), Ag/AgCl (refer-
ence electrode, 0.197 V versus normal hydrogen electrode), and a
platinum wire (counter electrode) were connected to a multi-chan-
nel potentiostat/galvanostat. A phosphate buffer (100 mm, pH 7.4)
with 15 w/v% TEOA was used as an electrolyte solution. Cyclic vol-
tammograms of mTHPP was obtained with the same system
except the working electrode, a glassy carbon disk (working diam-
eter 2 mm), and the supporting electrolyte, a solution of 0.10m
TBAP in DMSO.
[9] H. Zhao, W. A. van der Donk, Curr. Opin.Biotechnol. 2003, 14, 583–589.
[10] Q. Shi, D. Yang, Z. Jiang, J. Li, J. Mol. Catal. B: Enzym. 2006, 43, 44–48.
[11] C. B. Park, S. H. Lee, E. Subramaniam, B. B. Kale, S. M. Lee, J. O. Baeg,
Chem. Commun. 2008, 5423–5425.
[12] D. H. Nam, S. H. Lee, C. B. Park, Small 2010, 6, 922–926.
[13] F. Hollmann, I. W. C. E. Arends, K. Buehler, ChemCatChem 2010, 2, 762–
782.
[14] C.-J. Liu, S.-G. Li, W.-Q. Pang, C.-M. Che, Chem. Commun. 1997, 65–66.
[15] B. T. Holland, C. Walkup, A. Stein, J. Phys. Chem. B 1998, 102, 4301–
4309.
[16] T. Itoh, K. Yano, Y. Inada, Y. Fukushima, J. Am. Chem. Soc. 2002, 124,
13437–13441.
[17] K. Okeyoshi, R. Yoshida, Adv. Funct. Mater. 2010, 20, 708.
[18] J. C. Rooke, C. Meunier, A. Leonard, B.-L. Su, Pure Appl. Chem. 2008, 80,
2345–2376.
[19] S. L. Jain, J. K. Joseph, F. E. Kuhn, O. Reiser, Adv. Synth. Catal. 2009, 351,
230–234.
[20] X. Gong, T. Milic, C. Xu, J. D. Batteas, C. M. Drain, J. Am. Chem. Soc.
2002, 124, 14290–14291.
[21] T. T. Teeri, H. Brumer, G. Daniel, P. Gatenholm, Trends Biotechnol. 2007,
25, 299–306.
[22] A. Pinkert, K. N. Marsh, S. Pang, M. P. Staiger, Chem. Rev. 2009, 109,
6712–6728.
[23] T. Torimoto, T. Tsuda, K. Okazaki, S. Kuwabata, Adv. Mater. 2010, 22,
1196-.1221.
[24] N. Sun, M. Rahman, Y. Qin, M. L. Maxim, H. Rodrguez, R. D. Rogers,
Green Chem. 2009, 11, 646–655.
[25] S. Kubo, J. F. Kadla, Biomacromolecules 2005, 6, 2815–2821.
ChemSusChem 2011, 4, 581 – 586
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
585

[26] H. Imahori, H. Norieda, Y. Nishimura, I. Yamazaki, K. Higuchi, N. Kato, T.
Motohiro, H. Yamada, K. Tamaki, M. Arimura, Y. Sakata, J. Phys. Chem. B
2000, 104, 1253–1260.
[27] Z. Zhang, T. Imae, Nano Lett. 2001, 1, 241–243.
[28] H. Yamada, H. Imahori, Y. Nishimura, I. Yamazaki, S. Fukuzumi, Adv.
Mater. 2002, 14, 892–895.
[29] M. Ohtani, P. V. Kamat, S. Fukuzumi, J. Mater. Chem. 2010, 20, 582–587.
[30] R. F. Khairutdinov, N. Serpone, J. Phys. Chem. B 1999, 103, 761–769.
[31] S. Okada, H. Segawa, J. Am. Chem. Soc. 2003, 125, 2792–2796.
[32] X. Li, Z. Zheng, M. Han, Z. Chen, G. Zou, J. Phys. Chem. B 2007, 111,
4342–4348.
[37] D. Baskaran, J. W. Mays, X. P. Zhang, M. S. Bratcher, J. Am. Chem. Soc.
2005, 127, 6916–6917.
[38] Y. Han, G. Wu, H. Li, M. Wang, H. Chen, Nanotechnology 2010, 21,
185708.
[39] E. Adler, Wood Sci. Technol. 1977, 11, 169–218.
[40] G. Milczarek, Electroanalysis 2007, 19, 1411–1414.
[41] S. Barsberg, T. Elder, C. Felby, Chem. Mater. 2003, 15, 649–655.
[42] K. N. Ferreira, T. M. Iverson, K. Maghlaoui, J. Barber, S. Iwata, Science
2004, 303, 1831–1838.
[43] F. Hollmann, A. Schmid, E. Steckhan, Angew. Chem. 2001, 113, 190–193;
Angew. Chem. Int. Ed. 2001, 40, 169–171.
[33] E. Steckhan, S. Herrmann, R. Ruppert, E. Dietz, M. Frede, E. Spika, Orga-
nometallics 1991, 10, 1568–1577.
[44] F. Hildebrand, C. Kohlmann, A. Franz, S. Lutz, Adv. Synth. Catal. 2008,
350, 909–918.
[34] H. C. Lo, C. Leiva, O. Buriez, J. B. Kerr, M. M. Olmstead, R. H. Fish, Inorg.
Chem. 2001, 40, 6705–6716.
[35] F. Hollmann, B. Witholt, A. Schmid, J. Mol. Catal. B: Enzym. 2002, 19–20,
167–176.
[36] D. M. Guldi, G. M. A. Rahman, N. Jux, N. Tagmatarchis, M. Prato, Angew.
Chem. 2004, 116, 5642–5646; Angew. Chem. Int. Ed. 2004, 43, 5526–
5530.
Received: February 7, 2011
Published online on April 19, 2011
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