Photoinduced hydrogen evolution with bisviologen-linked ruthenium(II) complexes and hydrogenase

Article abstract of DOI:10.1016/S1381-1169(99)00244-7

Bisviologen-linked ruthenium(II) complexes with different methylene chain length between ruthenium complex and viologen, Ru(bpy)₂(dcbpy)C(m)V(A)C(n)V(B)(m = 2, n = 3; m = 3, n = 4), were synthesized and characterized. From luminescence spectra, the photoexcited state of Ru(bpy)₂(dcbpy) moiety is oxidatively quenched by the bound viologen, and an intramolecular electron transfer occurs. Luminescence lifetime measurements show that the electron transfers from the photoexcited state of ruthenium(II) complex moiety to the bound bisviologen more rapidly than that of monoviologen-linked ruthenium(II) complexes. Ru(bpy)₂(dcbpy)C(m)V(A)C(n)V(B) were applied to the photoinduced hydrogen evolution in the system containing nicotinamide-adenine dinucleotide phosphate (reduced form, NADPH), Ru(bpy)₂(dcbpy)C(m)V(A)C(n)V(B) and hydrogenase under steady state irradiation. In the case of Ru(bpy)₂(dcbpy)C₃V(A)C₄V(B), the efficient photoinduced hydrogen evolution was observed. (C) 2000 Elsevier Science B.V.

Full text of DOI:10.1016/S1381-1169(99)00244-7

Ž
.
Journal of Molecular Catalysis A: Chemical 151 2000 7–15
www.elsevier.comrlocatermolcata
Photoinduced hydrogen evolution with bisviologen-linked
ž /
ruthenium II complexes and hydrogenase
)
Tomohiro Hiraishi, Toshiaki Kamachi, Ichiro Okura
Department of Bioengineering, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8501, Japan
Received 26 February 1999; accepted 10 May 1999
Abstract
Ž .
Bisviologen-linked ruthenium II complexes with different methylene chain length between ruthenium complex and
Ž
. Ž
.
Ž
.
viologen, Ru bpy dcbpy CmV CnVB ms2, ns3; ms3, ns4 , were synthesized and characterized. From luminescence
2
A
Ž
. Ž
.
spectra, the photoexcited state of Ru bpy dcbpy moiety is oxidatively quenched by the bound viologen, and an
2
intramolecular electron transfer occurs. Luminescence lifetime measurements show that the electron transfers from the
Ž .
photoexcited state of ruthenium II complex moiety to the bound bisviologen more rapidly than that of monoviologen-linked
Ž . . Ž
Ž
.
ruthenium II complexes. Ru bpy dcbpy CmV CnVB were applied to the photoinduced hydrogen evolution in the system
2
A
Ž
.
Ž
. Ž
.
containing nicotinamide-adenine dinucleotide phosphate reduced form, NADPH , Ru bpy dcbpy CmV CnVB and hydroge-
2
A
Ž
. Ž
.
nase under steady state irradiation. In the case of Ru bpy dcbpy C3VAC4VB, the efficient photoinduced hydrogen evolution
2
was observed. q 2000 Elsevier Science B.V. All rights reserved.
Ž .
Keywords: Photoinduced hydrogen evolution; Bisviologen-linked ruthenium II complexes; Hydrogenase; Intramolecular electron transfer
1. Introduction
extinction coefficients in the visible region, and
relatively long-lived excited states.In this reac-
tion, the reduction of electron carrier is one of
the important steps. In the four-component sys-
tem, however, the diffusional electron transfer
step from photoexcited photosensitizer to elec-
tron carrier occurs leading to the low yield of
charge separation state. To improve this system,
the longer lifetimes of charge separated states
between photosensitizer and electron carrier are
desired. Charge separation processes have been
extensively studied in acceptor-linked photosen-
Photoinduced hydrogen evolution from water
has been studied extensively using a system
composed of four components: electron donor
Ž .
Ž .
Ž .
D , photosensitizer P , electron carrier C and
w
x
catalyst as shown in Scheme 1 1–4 . Among
inorganic photosensitizers, ruthenium tris 2,2 -
X
Ž
.
bipyridine derivatives are the suitable com-
pounds for photoinduced hydrogen evolution
system, because ruthenium complexes possess
properties such as photostability in water, high
w
x
sitizer systems 5–15 . In these artificial sys-
Ž .
)
tems, such as a viologen-linked ruthenium II
Corresponding author. Tel.: q81-045-9245752; fax: q81-
complex, the intramolecular electron transfer
045-9245778; E-mail: iokura@bio.titech.ac.jp
1381-1169r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
Ž
.
PII: S1381-1169 99 00244-7

(
)
8
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
Scheme 1. Photoinduced hydrogen evolution system.
from ruthenium complex moiety to binding vio-
logen competes with the rapid back electron
transfer from acceptor to photosensitizer leading
the effective photoinduced hydrogen evolution
system, because photoinduced two-step electron
transfer from photoexcited ruthenium complex
moiety to acceptor may occur, and back elec-
tron transfer is suppressed.
w
x
to the shortlived charge separated state 12–14 .
To achieve the long-lived charge separated states
in the model systems, the suppression of the
back electron transfer is required. The charge
separation is stabilized by a multistep electron
transfer in a series of acceptors arranged in a
fashion analogous to the electron transfer chain
in photoreaction center. Among the viologen-
linked ruthenium complexes, bisviologen-linked
ruthenium complexes, in which two viologens
with different redox potentials are connected
covalently, are suitable compounds to establish
In this paper, bisviologen-linked ruthenium
Ž .
Ž
. Ž
.
Ž
II complexes, Ru bpy dcbpy CmV CnVB m
2
A
. Ž
s2, ns3; ms3, ns4 , the structures are
shown in Fig. 1 , were synthesized and charac-
.
terized by spectroscopic measurements. As the
reduction of NADP to NADPH occurs with the
concomitant oxygen evolution in photosynthe-
sis, NADPH was used as an electron donor in
the artificial photoinduced hydrogen evolution
Ž .
system. Bisviologen-linked ruthenium II com-
Ž
. Ž
.
Ž
. Ž
.
Fig. 1. Structures of Ru bpy dcbpy CmV CnVB and Ru bpy dcbpy CmV Cn.
2
A
2
A

(
)
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
9
w
x
plexes were applied to photoinduced hydrogen
evolution system containing NADPH, Ru
ture 20 . Protein concentration was determined
using the following molar absorption coeffi-
1
1
Ž
. Ž
.
bpy dcbpy CmV CnVB and hydrogenase.
cient: ´s155 mmoly dm3 cmy at 280 nm.
2
A
2.4. Spectroscopic measurements
2. Materials and methods
UV–vis absorption spectra were measured in
3
Ž
.
2.1. Materials
25 mmol dmy Tris–HCl buffer pH 7.4 using
a Shimadzu MultiSpec-1500 spectrometer.
1H-NMR spectra were recorded on a Varian
GEMINI-200. The chemical shifts were refer-
enced to the solvent peak calibrated against
All reagents were of analytical or of the
highest grade available. 4,4X-Dimethyl-2,2X-bi-
X
X
Ž
.
pyridine dmbpy , 4,4 -dicarboxy-2,2 -bipyridine
X
Ž
.
Ž
.
dcbpy , bisviologen-linked 4-carboxy-2,2 -bi-
tetramethylsilane TMS .
pyridine-4X-carbodiimide
dcbpy CmV CnVB
The luminescence spectra were measured in
ŽŽ
.
.
A
3
Ž
.
Ž
.
and Ru bpy Cl2 PnH2O were prepared as de-
25 mmol dmy Tris–HCl buffer pH 7.4 at
room temperature using a Hitachi F-4000 spec-
trometer. The absorbance at the excitation
wavelength was kept constant at 0.3 for all the
sample solutions in these experiments.
2
w
x
scribed previously 16–19 .
2.2. Preparation of bis- and monoÕiologen-lin-
ked ruthenium II complexes
( )
Luminescence lifetime measurements were
carried out by using time-correlated single-pho-
Ž
.
Ž .
The tris bipyridyl ruthenium II complexes
Ž
.
Ž
.
were prepared by refluxing Ru bpy Cl2 PnH2O
with either dcbpy C3VAC4VB or dcbpy -
ton-counting Horiba NAES-500 spectrometer
under argon.
2
Ž
.
Ž
.
C2V C3VB in 1:1 EtOH:H2O under argon. The
A
reaction was monitored by UV–vis spec-
2.5. Photoinduced hydrogen eÕolution under
steady state irradiation
Ž .
troscopy. The Ru II complexes were applied to
a neutral alumina column to remove the impu-
Ž
.
rity and starting material 1:1 acetone:ethanol .
The product was eluted as a orange band with
methanol eluent. After removal of solvent under
For the steady-state irradiation, the sample
solution in a Pyrex cell was irradiated using 200
Ž
.
W tungsten lamp Philips KP-8 at 308C. Light
of wavelength less than at 390 nm was removed
by Toshiba L-39 cut-off filter. The sample solu-
vacuum, the orange compound was dissolved in
25 mmol dmy Tris–HCl buffer Tris, tris hy-
3
Ž
Ž
y
3
.
. Ž
.
Ž
.
droxymethyl aminomethane pH 7.4 and ap-
plied to a SP Sepharose Fast Flow cation
tion containing NADPH 2.0 mmol dm
Ru bpy dcbpy CmV CnVB 10 mmol dm
,
.
y
3
Ž
. Ž
.
Ž
2
A
y
3
Ž
.
Ž
.
exchange column Pharmacia . The desired
product was eluted with a linear gradient from 0
and hydrogenase 0.15 mmol dm
in 3.0 ml
3
of 25 mmol dmy Tris–HCl buffer pH 7.4
Ž
.
to 1 mol dmy NaCl as a single peak. Monovio-
was deaerated by repeated freeze-pump-thaw
cycles and then incubated for 5 min under ar-
gon. Evolved hydrogen was detected by gas
3
Ž .
Ž
logen-linked ruthenium II complexes Ru-
Ž
. Ž
.
.
bpy dcbpy CmV Cn were synthesized analo-
gously to the preparation of bisviologen-linked
2
A
Ž
chromatography Shimadzu GC-14B, detector:
Ž .
.
ruthenium II complexes.
TCD, column: active carbon .
2.3. Purification of hydrogenase
2.6. Determination of kinetic parameters
Hydrogenase was purified from DesulfoÕib-
rio Õulgaris Miyazaki according to the litera-
Hydrogen evolution was measured in the
Ž
.
Ž
.
presence of dithionite-reduced Ru bpy -
2

(
)
10
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
Ž
.
dcbpy CmV CnVB in a 5-ml test tube sealed
A
with Septa at 308C under argon. The sample
Ž
. Ž
.
solutions contained Ru bpy dcbpy CmV CnVB
2
A
y
3
Ž
.
and dithionite 20 mmol dm
in 4 ml of 25
mmol dmy Tris–HCl buffer pH 7.4 . The
3
Ž
.
reaction was started by injecting a small volume
Ž
of hydrogenase solution final conc.; 37 nmol
3
dmy
.
.
3. Results and discussion
3.1. Photophysical properties of Ru bpy 2-
(
)
(
)
(
) (
)
dcbpy CmVACnVB and Ru bpy 2 dcbpy CmÕACn
Ž
. Ž
.
Ž .
Fig. 2. Absorption spectra of Ru bpy dcbpy C3V C4VB a ,
The absorption maxima of Ru bpy -
Ž
. Ž
.
Ž .
Ž
.2Ž
. Ž . A
Ž
.
2
Ru bpy dcbpy C3V C4 b and Ru bpy dcbpy c in 25 mmol
2
A
2
dmy3 Tris–HCl buffer pH 7.4 .
Ž
.
Ž
.
Ž
. Ž
.
dcbpy CmVACnVB , Ru bpy dcbpy CmVACn
and Ru bpy dcbpy are listed in Table 1. As
2
Ž
. Ž
.
2
an example, the absorption spectra of Ru
Ž
. Ž
.
Ž
. Ž
.
Ž
. Ž
.
action between the Ru bpy dcbpy site and the
bpy dcbpy C 3VAC 4VB , Ru bpy dcbpy
2
2
2
Ž
. Ž
.
bound bisviologen may occur in the ground
state. The absorption maximum of the
C3V C4 and Ru bpy dcbpy are shown in
A
2
Fig. 2. The absorption spectra of Ru
Ž . Ž .
dithionite-reducedRu bpy dcbpy CmVACnVB
2
Ž
. Ž
.
Ž
.
bpy dcbpy C mVAC nVB and Ru bpy
2
2
Ž .
was at 540 nm data not shown . In the case of
Ž
.
dcbpy C mVAC n are similar to that of
Ž . Ž .
the reduced Ru bpy dcbpy CmV Cn, the ab-
2 A
Ž
. Ž
.
Ru bpy dcbpy , with exception of the slightly
2
sorption maximum was at 605 nm. These results
suggest that the intramolecular interaction be-
tween VA and VB may occur. Similar observa-
broadening of MLCT band. Launikonis et al.
w
x
21 reported that the substitution of bpy to
dcbpy leads to the broadening of MLCT band
w
x
Ž
.
tion was demonstrated by Atherton et al. 22 . It
was examined that the intramolecular associa-
tion of covalently linked viologen radical via
methylene chain occurred.
in ruthenium complexes. In the Ru bpy -
2
Ž
.
Ž
. Ž
.
dcbpy C mVAC nVB and Ru bpy dcbpy -
2
CmV Cn, MLCT band may be broaden due to
A
Ž
.
the substitution of dcbpy to dcbpy CmV CnVB.
A
Ž
.
The photoexcited states of Ru bpy -
From the absorption spectra, no electronic inter-
2
Ž
.
Ž
. Ž
.
dcbpy CmVACnVB and Ru bpy dcbpy Cm-
2
VACn were studied using the luminescence emi-
ssion spectra. As an example, the luminescence
Table 1
Ž
. Ž
.
spectra of Ru bpy dcbpy C3VAC4VB, Ru
2
Ž
. Ž .
Wavelength of absorption maxima of Ru bpy dcbpy
2
Ž
. Ž
.
Ž
. Ž
. Ž
.
bpy dcbpy C3VAC4 and Ru bpy dcbpy
2
2
Ž
. Ž
.
Ž
. Ž
.
CmV CnVB, Ru bpy dcbpy CmV Cn and Ru bpy dcbpy
A
2
A
2
Ž
.
are shown in Fig. 3. For Ru bpy dcbpy CmV -
2
A
Compound
Wavelength of absorption
CnVB, the shapes of the luminescence spectra of
Ž
.
maxima nm
Ž
. Ž
.
Ru bpy dcbpy CmV CnVB were the same as
Ž
. Ž
.
.
.
.
.
Ru bpy dcbpy
244
249
254
255
255
287
285
285
284
283
458
452
454
454
455
2
A
Ž
.2Ž
Ž
. Ž
.
Ž
Ru bpy dcbpy C2V C3
that of Ru bpy dcbpy . However, the lumines-
cence intensity of Ru bpy dcbpy CmV CnVB
was lower than that of Ru bpy dcbpy . This
Ž
.2Ž
A
2
Ru bpy dcbpy C3V C4
Ž
.2Ž
A
. Ž
.
2
Ž
A
.
Ru bpy dcbpy C2V C3VB
Ž
.2Ž
2
A
. Ž
Ru bpy dcbpy C3V C4VB
2
A
result indicates that the photoexcited state of

(
)
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
11
listed in Table 2. As an example, the lumines-
Ž
. Ž
.
cence decays of Ru bpy dcbpy C3V C4VB
2
A
Ž
. Ž
.
and Ru bpy dcbpy C3V C4 are shown in Fig.
2
A
Ž
. Ž
.
4. For Ru bpy dcbpy , the luminescence de-
2
cay was first order kinetics and the excited
lifetime was determined as 507 ns. For the
mono- and bisviologen-linked ruthenium com-
plexes, the luminescence decays of Ru
Ž
. Ž
.
Ž
. Ž
.
bpy dcbpy CmV CnVB and Ru bpy dcbpy
2
A
2
CmV Cn were much shorter than that of
Ru bpy dcbpy due to the quenching of pho-
toexcited Ru bpy dcbpy moiety by the bound
Ž A . Ž
.
2
Ž
. Ž
.
2
viologen. This result also indicates that the ox-
idative quenching of photoexcited state of Ru
Ž
. Ž
.
bpy dcbpy site is the major deactivation
2
Ž
. Ž
.
Ž .
pathway of the photoexcited state. In the case of
mono- and bisviologen-linked ruthenium com-
plexes, the decays obeyed double exponential
kinetics. The reason of two components of life-
time is explained as follows. For the mono- and
bisviologen-linked ruthenium complexes, there
may be two conformers. In quinone-linked por-
phyrins and viologen-linked porphyrins, two
conformers are proposed by Siemiarczuk et al.
Fig. 3. Luminescence spectra of Ru bpy dcbpy C3V C4VB a ,
A
Ž
. Ž
.
Ž .
Ž
. 2Ž
. Ž .
Ru bpy dcbpy C3V C4 b and Ru bpy dcbpy c in 25 mmol
2
A
2
dmy3 Tris–HCl buffer pH 7.4 . The excitation wavelength was
Ž
.
450 nm. Inset shows the magnified Y-axis of Fig. 3.
Ž
. Ž
.
Ru bpy dcbpy site is oxidatively quenched by
the bound bisviologen due to an intramolecular
electron transfer and no electronic interaction
2
Ž
. Ž
.
occurs between the Ru bpy dcbpy moiety and
2
w
x
w x
the bound bisviologen in the photoexcited state.
In addition, the intensity of Ru bpy dcbpy
CmV CnVB was lower than that of Ru bpy -
dcbpy CmV Cn, indicating that the photoex-
cited ruthenium complex moiety in Ru bpy -
dcbpy CmV CnVB is more efficiently quenched
than that in Ru bpy dcbpy CmV Cn.
23 and Batteas et al. 24 . The proposed con-
Ž
. Ž
.
formation is as follows. The fast process may be
attributed to electron transfer between proximal
partners. In this conformation, the acceptor is
held in close proximity to porphyrin, so that
rapid process occurs. On the other hand, the
slow process may be associated with conforma-
tion in which the bound acceptor is kept some
distance away from the porphyrin.
2 Ž
.
A
2
Ž
.
A
Ž
.
2
Ž
.
A
Ž
. Ž
.
2
A
(
)
2
3.2. Luminescence lifetimes of Ru bpy -
(
)
dcbpy CmVACnVB
The shorter component of photoexcited life-
Ž .
Ž
. Ž
.
times ts of Ru bpy dcbpy CmV CnVB is
2
A
Ž
.
Ž
. Ž
.
The photoexcited state lifetime of Ru bpy -
shorter than that of Ru bpy dcbpy CmV Cn,
indicating that the photoexcited ruthenium com-
Ž . Ž .
plex moiety in Ru bpy dcbpy CmV CnVB is
2 A
2
2
A
Ž
.
dcbpy CmV CnVB was measured by time-corre-
lated single photon counting. The results are
A
Table 2
Ž
. Ž
.
Ž
. Ž
.
Luminescence lifetimes of Ru bpy dcbpy CmV CnVB and Ru bpy dcbpy CmV Cn
2
A
2
A
y9
y9
Ž
.
s
Ž
.
s
Compound
tmono 10
t bis 10
Ž
. Ž
.
.
.
.
Ž . Ž
Ž . Ž
ts: 3.7 83% , tl: 18.6 17%
.
.
Ru bpy dcbpy C2V C3
ts: 3.9 86% , tl: 11.6 14%
A
Ž
.2Ž
Ru bpy dcbpy C3V C4
A
Ž
.2Ž
Ž
.
.
Ž
.
Ru bpy dcbpy C2V C3VB
ts: 1.5 86% , tl: 6.9 14%
A
Ž
.2Ž
Ž
Ž
.
Ru bpy dcbpy C3V C4VB
ts: 1.2 76% , tl: 20.9 24%
2
A

(
)
12
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
Table 3
Ž
.
Ž
.
Intramolecular electron transfer rates of Ru bpy
dcbpy -
2
Ž
. Ž
.
CmV CnVB and Ru bpy dcbpy CmV Cn
A
2
A
8
8
koq1 10 sy1
koq2 10 sy1
Ž
.
Ž
.
Compound
Ž
. Ž
.
.
.
.
Ru bpy dcbpy C2V C3
2.54
2.68
A
Ž
.2Ž
Ru bpy dcbpy C3V C4
A
Ž
.2Ž
Ru bpy dcbpy C2V C3VB 2.54
4.10
5.63
A
Ž
.2Ž
Ru bpy dcbpy C3V C4VB 2.68
2
A
ruthenium complexes, respectively. The appar-
Ž
.
ent intramolecular electron transfer rate kbis in
Ž
. Ž
.
Ru bpy dcbpy CmV CnVB represents as fol-
lows, kb2is skoq1 qkoq2. As the koq1 value is the
A
same as the intramolecular electron transfer rate
Ž
. Ž
.
Ž .
Ž
. Ž
.
Fig. 4. Luminescence decays of Ru bpy dcbpy C3V C4VB
a
in Ru bpy dcbpy CmV Cn, koq1 represents as
2
A
2
A
in 25 mmol dmy3 Tris–HCl
. Ž Ž .
and Ru bpy dcbpy C3V C4 b
Ž
.
2
A
Ž .
shown in Eq. 2 . The intramolecular electron
transfer rate constants are given in Table 3.
The electrochemical measurements showed
that the two step electron transfer from the
photoexcited state of ruthenium complex to
bisviologen may occur 18 . On the other hand,
the luminescence lifetime measurements suggest
that the electron transfers from the photoexcited
Ž
.
buffer pH 7.4 . The excitation wavelength was 350 nm.
quenched by VA and VB as shown in Scheme 2,
q
w x
where Ru2 represents Ru bpy dcbpy moi-
Ž
. Ž
.
2
ety.
From Scheme 2, the intramolecular electron
ruthenium complex moiety to V and VB. These
Ž
.
A
transfer rate constants koq1, koq2 can be deter-
mined from the measured lifetime of photoex-
cited ruthenium complexes according to Eqs.
results indicate that the two step electron trans-
fer may occur with the concomitant electron
transfer from the photoexcited state of ruthe-
Ž .
Ž .
1 and 2 .
nium complex moiety to V and VB.
A
1
1
kbis skoq1 qkoq2
s
y
1
Ž .
t bis, s
td
3.3. Photoreduction of bound Õiologen in
Ru bpy 2 dcbpy CmVACnVB
(
) (
)
1
1
koq1
s
y
2
Ž .
tmono, s
td
When the solution containing NADPH and
Ž
. Ž
.
Ru bpy dcbpy CmV CnVB was irradiated, the
2
A
where td is the excited state lifetime of the
absorbance due to reduced bisviologen in-
creased. As an example, the absorption spec-
trum change of Ru bpy dcbpy C3V C4VB at
540 nm is shown in Fig. 5. The reaction was
Ž .
viologen free ruthenium II complex. tmono,s and
t bis,s are the shorter components of excited state
lifetimes of the mono- and bisviologen-linked
Ž
. Ž
.
2
A
completed within 6 min. On the other hand,
Ž
. Ž
.
when Ru bpy dcbpy CmV Cn was used, no re-
2
A
duction of the bound viologen was observed.
These results suggest that the bound bisviologen
Ž
. Ž
.
in Ru bpy dcbpy CmVACnVB molecule is
2
Ž
.
more easily reduced than that in Ru bpy -
2
Ž
.
dcbpy CmV Cn due to the suppression of the
Scheme 2.
A

(
)
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
13
Fig. 5. Time dependence of the absorption change of
. Ž
Fig. 6. Time dependence of photoinduced hydrogen evolution
under steady state irradiation. The solution contains 2.0 mmol
Ž
.
Ru bpy dcbpy C3V C4VB under steady-state irradiation moni-
2
A
tored at 540 nm. The solution contains 2.0 mmol dmy3 of
. Ž
dmy3 of NADPH, 10 mmol dmy3 of Ru bpy dcbpy C3V C4VB
Ž
. Ž
.
2
A
NADPH and 10 mmol dmy3 of Ru bpy dcbpy C3V C4VB in 25
and 0.15 mmol dmy3 of hydrogenase in 25 mmol dmy3 Tris–HCl
Ž
.
2
A
mmol dmy3 Tris–HCl buffer pH 7.4 .
buffer pH7.4 v . For the monoviologen linked ruthenium
Ž
.
Ž
. Ž .
complex system, the solution contains 2.0 mmol dmy3 of NADPH,
10 mmol dmy3 of Ru bpy dcbpy C3V C4 and 0.15 mmol dmy3
Ž
. Ž
.
2
A
Ž
.
of hydrogenase ' .
back electron transfer from reduced viologen to
the ruthenium complex moiety.
toinduced hydrogen evolution was accom-
Ž
. Ž
.
plished compared with the Ru bpy dcbpy Cm-
VACn system.
2
3.4. Photoinduced hydrogen eÕolution with hy-
drogenase
When the solution containing NADPH,
Ž
. Ž
.
Ru bpy dcbpy C3VAC4VB and hydrogenase
2
was irradiated, the photoinduced hydrogen evo-
lution was observed. Fig. 6 shows the time
dependence of the photoinduced hydrogen
Ž
. Ž
.
evolution. In the case of Ru bpy dcbpy -
2
C2V C3VB, however, no photoinduced hy-
A
drogen evolution was observed. For Ru
Ž
. Ž
.
bpy dcbpy C2V C3VB, as the distance be-
2
A
Ž
. Ž
.
tween Ru bpy dcbpy moiety and the bound
viologen is shorter than that of Ru bpy -
Ž
Ž
of Ru bpy dcbpy C3V C4VB. This result indi-
cates that Ru bpy dcbpy C3V C4VB may be
2
Ž
.
2
.
dcbpy C3V C4VB, the steric hindrance of Ru
A
. Ž
.
bpy dcbpy C2V C3VB may be larger than that
2
A
Ž
. Ž
.
2
A
Ž
. Ž
.
2
A
Fig. 7. Dependence of hydrogen evolution rate on the concentra-
Ž . Ž . Ž
the more suitable substrate for hydrogenase than
tion of dithionite-reduced Ru bpy dcbpy CmV CnVB B: ms2,
2
A
.
ns 3; v: ms 3, ns 4 . The sample solutions contains
Ž
. Ž
.
Ru bpy dcbpy C2V C3VB. By using the sys-
2
A
y3
Ž
. Ž
.
Ž
.
and hy-
Ru bpy dcbpy CmV CnVB, dithionite 20 mmol dm
2
A
Ž
. Ž
.
tem containing NADPH, Ru bpy dcbpy -
y3
y3
2
Ž
.
drogenase 37 nmol dm
in 4.0 ml of 25 mmol dm Tris–HCl
C3V C4VB and hydrogenase, the effective pho-
Ž
.
pH 7.4 .
A

(
)
14
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
Ž
. Ž
.
concentration of Ru bpy dcbpy CmVACnVB
2
and reached constant values. In the system
Ž
. Ž
.
containing dithionite-reduced Ru bpy dcbpy -
2
CmV CnVB and hydrogenase, the substrate
A
Ž
.
affinity constants Km , maximum velocity
Ž
.
Ž
.
Vmax , catalytic constants kcat and catalytic
Ž
.
efficiency kcatrKm were determined from the
double reciprocal plots as shown in Fig. 8. The
results are listed in Table 4. The kcatrKm value
Ž
. Ž
.
of Ru bpy dcbpy C3V C4VB is higher than
2
Ž
A
.
. Ž
that of Ru bpy dcbpy C2VAC3VB, indicating
2
Ž
. Ž
.
that Ru bpy dcbpy C3VAC4VB is more suit-
2
able compound for hydrogen evolution than Ru
Ž
. Ž
.
bpy dcbpy C2VAC3VB. From these results, as
2
Ž
. Ž
.
Ru bpy dcbpy C3V C4VB has high affinity for
hydrogenase compared with Ru bpy dcbpy
2
A
Fig. 8. Lineweaver–Burk plot for hydrogen evolution rate of
Ž
. Ž
.
2
Ž
. Ž
.
hydrogenase with dithionite-reduced Ru bpy dcbpy CmV CnVB
2
A
C2VAC3VB, the efficient hydrogen evolution
Ž
.
B: ms2, ns3; v: ms3, ns4 .
Ž
. Ž
.
proceeded by using Ru bpy dcbpy C3V C4VB.
2
A
This result coincides with that of photoinduced
hydrogen evolution in the system containing
Ž
. Ž
.
Ru bpy dcbpy CmV CnVB and hydrogenase.
2
A
(
)
2
3.5. Substrate affinity of Ru bpy -
Ž
. Ž
.
In the case of Ru bpy dcbpy C3V C4VB, as
2
A
(
)
dcbpy CmVaCnVB for hydrogenase
the distance between the ruthenium complex
moiety and the bound viologen is long enough,
the bound viologen can be easily away from the
ruthenium complex moiety leading to the higher
affinity for hydrogenase by little steric hin-
drance among the ruthenium complex moiety,
the bound viologen and hydrogenase. In the
For the more detailed information on pho-
toinduced hydrogen evolution using Ru
bpy dcbpy CmV CnVB and hydrogenase, ki-
netic studies were carried out. In the presence of
Ž
. Ž
.
2
A
Ž
. Ž
.
dithionite-reduced Ru bpy dcbpy C mVA-
2
Ž . Ž .
case of Ru bpy dcbpy C2V C3VB, on the other
2 A
CnVB, hydrogen evolution with hydrogenase
was observed. Hydrogen evolved linearly with
reaction time. Fig. 7 shows the dependence
of the initial rate of hydrogen evolution on
the concentration of dithionite-reduced Ru
hand, as the distance between ruthenium com-
plex moiety and the bound viologen is short, the
approach of bound viologen to ruthenium com-
plex moiety may be more easily than that of
Ž
. Ž
.
Ž
. Ž
.
bpy - dcbpy CmV CnVB. The initial rate of hy-
Ru bpy dcbpy C3V C4VB, so that steric hin-
2
A
2
A
drogen evolution increased with increasing the
drance is large.
Table 4
Kinetic parameters for hydrogen evolution with dithionite-reduced bisviologen linked ruthenium complexes and hydrogenase
Substrate
Kmy6
Vmax
Ž
kcyat1
kcatrKm
5
y7
10 mol dmy3
10 mol dmy3 sy1
10 moly1 dm3 sy1
8.67
Ž
.
.
Ž
s
.
Ž
.
Ž
. Ž
.
.
Ru bpy dcbpy C2V C3VB
6.77
3.30
2.16
4.24
5.87
11.5
A
Ž
.2Ž
Ru bpy dcbpy C3V C4VB
34.8
2
A
The kinetic parameters were determined by fitting to the Michaelis–Menten equation.

(
)
T. Hiraishi et al.rJournal of Molecular Catalysis A: Chemical 151 2000 7–15
15
w x
9
A. Osuka, S. Marumo, K. Maruyama, N. Mataga, Y. Tanaka,
S. Taniguchi, T. Okada, I. Yamazaki, Y. Nishimura, Bull.
Acknowledgements
Ž
.
Chem. Soc. Jpn. 68 1995 262.
w
x
10 D. Kuciauskas, P.A. Liddell, S.-C. Hung, S. Lin, S. Stone,
The present work is partly supported by a
Grant-in-Aid on Priority-Areas-Research from
the Ministry of Education, Science, Sports and
G.R. Seely, A.L. Moore, T.A. Moore, D. Gust, J. Phys.
Ž
.
Chem. B 101 1997 429.
w
w
x
11 Y. Amao, T. Hiraishi, I. Okura, J. Mol. Catal. A Chem. 126
Ž
.
Ž
.
Culture of Japan No. 10145211 .
1997 13.
x
12 E.H. Yonemoto, R.L. Riley, Y.H. Kim, S.J. Atherton, R.H.
Ž
.
Schmehl, T.E. Mallouk, J. Am. Chem. Soc. 114 1992 8081.
w
w
x
Ž
.
13 L.A. Kelly, M.A.J. Rodgers, J. Phys. Chem. 98 1994 6386.
x
14 T. Hiraishi, T. Kamachi, I. Okura, J. Mol. Catal. A Chem.
References
Ž
.
138 1999 107.
w
w
x
Ž
.
15 T.J. Rutherford, F.R. Keene, Inorg. Chem. 36 1997 2872.
w x
1
J.R. Darwent, P. Douglas, A. Harriman, G. Porter, M.C.
x
16 G. Sprintschnik, H.W. Sprintschnik, P.P. Kirsch, D.G. Whit-
Ž
.
Richoux, Coord. Chem. Rev. 44 1982 93.
Ž
.
ten, J. Am. Chem. Soc. 99 1977 4947.
w x
2
J. Kiwi, K. Kalyanasundaram, M. Graetzel, Struct. Bonding
w
w
x
x
Ž
.
17 L.A. Kelly, M.A.J. Rodgers, J. Phys. Chem. 98 1994 6377.
18 T. Hiraishi, T. Kamachi, I. Okura, J. Photochem. Photobiol.
Ž
.
49 1981 37.
w x
Ž
.
3
I. Okura, Coord. Chem. Rev. 68 1985 53.
Ž
.
A Chem. 116 1998 119.
w x
Ž
.
4
I. Okura, S. Aono, A. Yamada, J. Phys. Chem. 89 1985
w
x
19 D.P. Rillema, D.G. Taghdiri, D.S. Jones, C.D. Keller, L.A.
1593.
Ž
.
Worl, T.J. Meyer, H.A. Levy, Inorg. Chem. 26 1987 578.
w x
Ž
.
5
M.R. Wasielewski, Chem. Rev. 92 1992 435.
w
w
x
x
Ž
.
20 T. Yagi, J. Biochem. 68 1970 649.
21 A. Launikonis, P.A. Lay, A.W.-H. Mau, A.M. Sargeson,
w x
6
A. Osuka, S. Nakajima, K. Maruyama, N. Mataga, T. Asahi,
I. Yamazaki, Y. Nishimura, T. Ohno, K. Nozaki, J. Am.
Ž
.
W.H.F. Sasse, Aust. J. Chem. 39 1986 1053.
Ž
.
Chem. Soc. 115 1993 4577.
w
w
x
22 S.J. Atherton, K. Tsukahara, R.G. Wilkins, J. Am. Chem.
w x
7
M. Ohkohchi, A. Takahashi, N. Mataga, T. Okada, A. Osuka,
Ž
.
Soc. 108 1986 3380.
Ž
.
H. Yamada, K. Maruyama, J. Am. Chem. Soc. 115 1993
x
23 A. Siemiarczuk, A.R. McIntosh, T.-H. Ho, M.J. Stillman,
12137.
K.L. Roach, A.C. Weedon, J.R. Bolton, J.S. Connolly, J.
w x
8
D. Gust, T.A. Moore, A.L. Moore, S.-J. Lee, E. Bittersmann,
D.K. Luttrull, A.A. Rehms, J.M. DeGraziano, X.C. Ma, F.
Ž
.
Am. Chem. Soc. 105 1983 7224.
w
x
24 J.D. Batteas, A. Harriman, Y. Kanda, N. Mataga, A.K.
Ž
.
Gao, R.E. Belford, T.T. Trier, Science 248 1990 199.
Ž
.
Nowark, J. Am. Chem. Soc. 112 1990 126.