A DNA-templated catalyst: The preparation of metal-DNA nanohybrids and their application in organic reactions

Article abstract of DOI:10.1039/c0cc02632h

Different kinds of metal-DNA nanohybrids are synthesized from cheap natural DNA on a large scale. These air-stable M-DNA nanohybrids maintain the advantages of both DNA and the metal nanoparticles, which exhibit reversible solubility and high catalytic activities. Moreover, the M-DNA nanohybrids could be easily reused for several cycles.

Full text of DOI:10.1039/c0cc02632h

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A DNA-templated catalyst: the preparation of metal-DNA nanohybrids
and their application in organic reactionsw
Ye Wang, Guanghui Ouyang, Jintang Zhang and Zhiyong Wang*
Received 17th July 2010, Accepted 6th September 2010
DOI: 10.1039/c0cc02632h
Different kinds of metal-DNA nanohybrids are synthesized from
cheap natural DNA on a large scale. These air-stable M-DNA
nanohybrids maintain the advantages of both DNA and the
metal nanoparticles, which exhibit reversible solubility and high
catalytic activities. Moreover, the M-DNA nanohybrids could
be easily reused for several cycles.
borohydride was employed to reduce Pd2+ in the presence
of DNA and a dense homogeneous black solution was
obtained. No precipitation or aggregation were observed even
after centrifugation with 10 000 rpm. This indicated the
material was highly dispersed in water with the aid of the
DNA template. Moreover, the solution was air-stable, which
could be placed in air for several days remaining homo-
geneous. The amount of the preparation could be scaled up
to hundreds of millilitres easily at a time.
Recently, heterogenous catalysts of nanoscale particles
immobilized on various templates caught wide interests.1
Many inorganic solids and polymers have been used as
templates, showing great impact on the physical and chemical
character of nano-catalysts.2 As an important biopolymer
with many unique features, DNA has been well demonstrated
to be a suitable template for many metal and metal oxide
nanoparticles (NPs).3 Considering the sophisticated geometric
structures of DNA-templated NPs and potential functions of
DNA,4,5 we attempted to use DNA-templated metal NPs as
heterogeneous catalysts in organic reactions. On the other
hand, we attempted to make use of DNA chirality6 since the
metal NPs bind to the base pairs of DNA. However, few
reports involved DNA-templated metal NPs in organic reactions
perhaps due to the complicated technologies and small amount
of production of DNA-templated nanomaterials. Meanwhile,
natural DNA extracted from living creatures has attracted
much attention since it is quite plentiful and cheap in the real
world.7 Herein, by using natural fish sperm DNA as a new
kind of template, we synthesized different metal-DNA
(M-DNA) nanohybrids (M = Pd, Au, Ag and Pt) on a large
scale, and employed them as the catalysts for organic reactions.
The reactions proceeded efficiently and the catalysts could be
reused for several times. To the best of our knowledge, this is
the first example of the DNA-templated metal nanomaterials
acting as catalysts for organic reactions.
The as-synthesized solution (inset of Fig. 1A) was
characterized in detail. TEM image and XRD pattern
(Fig. 1A and ESIw) showed that this homogeneous solution
contained nano scale Pd0 particles with an average diameter of
about 7-8 nm. Then, the UV-Vis spectra of pure DNA,
Pd2+-DNA and Pd-DNA (Fig. 2) clearly indicated the inter-
actions between Pd NPs and DNA and thus verified the
formation of new hybrid material. IR and 31P NMR of
Pd-DNA were further investigated to enhance this conclusion.8
After successful synthesis of Pd-DNA, taking the same
method, KAuCl4, AgNO3 and K2PtCl6 were used to replace
K2PdCl4 respectively and in all cases homogeneous solutions
(inset of Fig. 1B–D) were synthesized smoothly. Similar
measurement of TEM, XRD and UV-Vis (Fig. 1B–D and
ESIw) indicated that the corresponding M-DNA (M = Au, Ag
and Pt) nanohybrids were also obtained.
The as-prepared M-DNA nanohybrids maintain the
characteristics of both the DNA molecules and the metal
NPs. Firstly, in accordance with the pure DNA, the
M-DNA nanohybrids could be precipitated from aqueous
media by the addition of alcohol, and redispersed smoothly
in water as shown in Fig. 3. After this redispersion, these
M-DNA were purified, and the accurate metal concentrations
In all kinds of DNA-templated metal NPs, the preparation
of palladium-DNA has been well researched.3a,4b,c In our
experiments, K2PdCl4 and fish sperm DNA were chosen as
the starting materials to synthesize nanohybrid in Tris buffer
(Tris(hydroxymethyl)-aminomethane, 10 mM, pH = 7.4). As
shown in the ESIw, the dosage of DNA template and the
selection of suitable reductants had a great influence on
the fabrication of nanohybrid. After optimization, sodium
Hefei National Laboratory for Physical Sciences at Microscale,
CAS Key Laboratory of Soft Matter Chemistry and Department of
Chemistry, University of Science and Technology of China, Hefei,
230026, P. R. China. E-mail: zwang3@ustc.edu.cn;
Fax: (+86) 551-360-3185
w Electronic supplementary information (ESI) available: Experimental
details, characterization of M-DNA before and after recycling,
reaction optimization and characterization of 2a–2j. See DOI:
10.1039/c0cc02632h/
Fig. 1 TEM images of different M-DNA nanohybrids: (A) Pd-DNA;
(B) Au-DNA; (C) Ag-DNA; (D) Pt-DNA.
c
7912 Chem. Commun., 2010, 46, 7912–7914
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Table 1 Reduction of aromatic nitro compounds catalyzed by
Pd-DNAa
Entry
R1
Time/h
EtOH
Product
Yield (%)b
1
2
3
4
5
6
1-H
2-Me
4-Me
4-OMe
4-COOH
4-COOEt
4-OTs
3-NO2
3-NH2
2-CHO
4
8
8
6
8
8
8
6
8
6
—
—
—
2 ml
—
2 ml
2 ml
—
2a
2b
2c
2d
2e
2f
2g
2h
2h
2i
95
80
89
97
97
99
80
94
83
83
Fig. 2 Normalized UV-Vis spectra of different solution: red line: DNA
in Tris; blue line: Pd2+-DNA in Tris; green line: Pd-DNA in Tris.
7
8c
9
2 ml
2 ml
10
a
Reaction conditions: 1 (1 mmol), Pd-DNA in Tris (4 ml, 1.8 mol%),
b
c
H2 balloon, 25 1C. Isolated yield. 1h (0.5 mmol) was used.
hardly reduced even under vigorous stirring (Table 1, entries 4,
6, 7, 9, 10). To solve this problem, addition of organic solvents
were tested. It was found adding 1/2 volume of EtOH could
maintain the homogeneous Pd-DNA solutions and enhance
the reaction yields. The addition of other solvents such as ethyl
acetate, THF, ether and acetone could generally destroy the
homogeneous Pd-DNA solutions during the reduction and
result in the formation of Pd black. The catalytic reactivity of
this Pd-DNA nanohybrid was also compared with other
hydrogenation catalysts, as shown in Table ESI-2w.8 Only
Pd-DNA catalyst led to both high chemoselectivity and high
conversion, which indicated the great efficiency of Pd-DNA
nanohybrid as catalyst.
Fig. 3 (A) As-synthesized M-DNA nanohybrid solution. (B) After
addition of 2–3 times volume of EtOH and placement still for 0.5 h.
(C) Precipitate after pouring out the colorless solution. (D) Homo-
geneous solution after addition of Tris buffer back to the precipitate.
of the M-DNA nanohybrids (M = Pd, Au, Ag and Pt) could
be determined by direct ICP-OES measurement. The concen-
tration of all the starting metal ions was 5 mM. After
purification, ICP-OES indicated that concentrations of different
elements were turned out to be 4.6 mM for Pd, 4.8 mM for Au,
3.9 mM for Ag and 3.4 mM for Pt respectively. Moreover,
different buffers of different pH such as MES (4-morpholine-
ethanesulfonic acid hydrate, 10 mM, pH = 5.5) and NaH-
CO3–Na2CO3 (pH = 10.5) could also redissolve the M-DNA
nanohybrids well besides Tris. Surprisingly, even in the solutions
of strong bases like NaOH and tBuOK, these M-DNA could
also dissolve smoothly and remain homogeneously, which
proved the high stability of these M-DNA nanohybrids.
Subsequently, the M-DNA nanohybrids were used as efficient
catalysts for organic reactions. Firstly, the hydrogenation of
nitrophenyl compounds to aniline derivatives under H2 was
investigated.9 The hydrogenation of nitrobenzene was studied
as a model reaction. After optimization,8 Pd-DNA was found to
be the best catalyst for the reduction. Under the same conditions
Pt-DNA was less reactive while Au-DNA and Ag-DNA showed
little catalytic activity for this hydrogenation. 1.8 mol% of
redissolved Pd-DNA in Tris was used to catalyze the hydro-
genation of nitrobenzene into aniline, affording the corres-
ponding product with an isolated yield of 95% (Table 1, entry 1).
Then different reaction substrates were employed. As shown in
Table 1, various aromatic nitro compounds, bearing electron-
deficient, electron-rich and neutral groups, can be reduced into
aniline derivatives smoothly with the catalyst of Pd-DNA nano-
hybrid at 25 1C (Table 1, entries 2–4, 8). Moreover, substrates
with sensitive functional groups such as aldehyde, carboxylic acid
and ester also survived the reaction (Table 1, entries 5–7, 10). It
was noted that the solubility of the reaction substrates affected
the reaction remarkably. The water-insoluble substrates were
Secondly, the M-DNA nanohybrids were employed as
catalysts for oxidation reactions.10 The aerobic oxidation of
1-phenylethynol to acetophenone was chosen as a model
reaction. Experimental results indicated that Au-DNA exhibited
the highest catalytic reactivity.8 After optimization of bases,8
the oxidation proceeded well under quite mild conditions.
1.9 mol% of Au-DNA nanohybrid, which was purified and
redissolved in 2 equivalents of LiOHÁH2O solution, was used
as the catalyst with oxygen balloon at 25 1C for 12 h.
Under these conditions, the substrate scope was investigated.
1-phenylethynol completely converted to acetophenone
(Table 2, entry 1). Electronic effect had little influence on this
oxidation (Table 2, entries 2–3). Substrate with steric effect
was also oxidized quantitatively at 50 1C (Table 2, entry 5).
When the phenyl ring was replaced with pyridine, the reaction
yield was decreased which may be due to the strong coordination
between N and Au NPs (Table 2, entry 6). For solid substrate
with poor solubility in water, the yield was lower (Table 2,
entry 4) and even EtOH was needed (Table 2, entry 7).
Aliphatic alcohol was oxidized to afford the corresponding
ketone smoothly (Table 2, entry 8). Cyclohexanol can be a
substrate in this oxidation in spite of a moderate yield
(Table 2, entry 9). Notably, the Au-DNA nanohybrid was
stable and kept homogeneous solution before and after the
reaction.
c
This journal is The Royal Society of Chemistry 2010
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Table 2 Oxidation of alcohols to ketones catalyzed by Au-DNAa
Table 4 Recycling of Au-DNA for oxidation of 1-phenylethynola
Run
1
2
3
4
5
6
7
Substrate
T/1C
25
>99
25
>99
25
93
25
89
50
>99
50
95
50
90
Yield (%)b
R2
R3
Entry
Yield (%)b
a
Reaction conditions: 3a (0.5 mmol), Au-DNA (initially 1.9 mol%)
redissolved in 2 ml solution of 1 mmol of LiOHÁH2O, O2 balloon,
1
2
3
4
5
6
7
8
9
Ph
Me
Me
Me
Me
Me
Me
Ph
>99
>99
>99
87
4-Me-Ph
4-F-Ph
4-NO2-Ph
2-Me-Ph
2-Py
b
12 h. Determined by GC-MS analysis with internal standard.
>99c
60c
facilitated the purification and phase separation. Most of these
M-DNA nanohybrids were efficient catalysts in different
organic reactions in aqueous media. The M-DNA nano-
hybrids can be well reused with combined unique features of
DNA and metal nanoparticles. The preparation of other
M-DNA nanohybrids and their applications including
asymmetric catalysis are in progress in our laboratory.
We are grateful to the National Natural Science Foundation
of China (20628202, 90813008, 20972144, 20772118 and
20932002) and the Graduate Innovation Fund of USTC.
Ph
82c,d
>99
60
1,2,3,4-Tetrahydro-1-naphthol
Cyclohexanol
a
Reaction conditions: 3 (0.5 mmol), Au-DNA (2 ml, 1.9 mol%)
redissolved in 2 ml solution of 1 mmol LiOHÁH2O, O2 balloon,
b
25 1C, 12 h. Determined by GC-MS analysis with internal standard.
c
d
50 1C. 1 ml EtOH was added.
Combining the unique features of DNA and metal nano-
particles, M-DNA nanohybrids could act as reusable catalysts
for organic reactions. In both reduction and oxidation, 2
volume of EtOH was added to the reaction mixture after the
reaction and the catalysts were precipitated on the bottom
while the products were dissolved in the solution. The catalyst
can be easily recovered by a simple phase separation,
redissolved in solvents and directly reused for the next round.
The hydrogenation of ethyl 4-nitrobenzoate was selected as
an example. The results are listed in Table 3. At the fifth
round, the reaction time was extended and the reaction yield
was reduced to 80%. TEM image and UV-Vis spectra of the
Pd-DNA8 indicated that Pd-DNA was partially destroyed and
Pd0 was aggregated and gradually leached into Pd2+ to bind
with the DNA, resulting in the decrease of catalytic activity.
Better results were gained when employing the oxidation of
1-phenylethynol to test the reusability of Au-DNA as shown
in Table 4. Au-DNA nanohybrid could be reused without
significant loss of activity up to 7 times with a mild heating at
the 5th–7th runs. Similar aggregation of Au NPs was also
detected after recycling.8
Notes and references
1 For recent reviews, see: (a) A. Corma and H. Garcia, Chem. Soc.
Rev., 2008, 37, 2096; (b) Juan M. Campelo, D. Luna, R. Luque,
Jose M. Marinas and Antonio A. Romero, ChemSusChem, 2009, 2,
´
18; (c) J. M. Fraile, J. I. Garcia, C. I. Herrerias, J. A. Mayoral and
E. Pires, Chem. Soc. Rev., 2009, 38, 695; (d) J. Lu and P. H. Toy,
Chem. Rev., 2009, 109, 815; (e) S. J. Wang, Z. Y. Wang and
Z. G. Zha, Dalton Trans., 2009, 9363; (f) R. J. White, R. Luque,
V. L. Budarin, J. H. Clark and D. J. Macquarrie, Chem. Soc. Rev.,
2009, 38, 481.
2 For examples see: (a) P. D. Stevens, G. F. Li, J. D. Fan, M. Yen
and Y. Gao, Chem. Commun., 2005, 4435; (b) A. Corma and
P. Serna, Science, 2006, 313, 332; (c) David J. Mihalcik and
W. Lin, Angew. Chem., Int. Ed., 2008, 47, 6229; (d) S. Benyahya,
F. Monnier, M. W. C. Man, C. Bied, F. Ouazzani and M. Taillefer,
Green Chem., 2009, 11, 1121; (e) S. Wang, X. He, L. Song and
Z. Wang, Synlett, 2009, 447; (f) M.-J. Jin and D.-H. Lee,
Angew. Chem., Int. Ed., 2010, 49, 1119; (g) C. A. Witham,
W. Y. Huang, C. K. Tsung, J. N. Kuhn, G. A. Somorjai and
F. D. Toste, Nat. Chem., 2010, 2, 36; (h) B. Z. Yuan, Y. Y. Pan,
Y. W. Li, B. L. Yin and H. F. Jiang, Angew. Chem., Int. Ed., 2010,
49, 4054.
3 (a) J. Richter, R. Seidel, R. Kirsch, M. Mertig, W. Pompe,
J. Plaschke and H. K. Schackert, Adv. Mater., 2000, 12, 507;
(b) M. Mertig, L. C. Ciacchi, R. Seidel, W. Pompe and A. De Vita,
Nano Lett., 2002, 2, 841; (c) W. U. Dittmer and F. C. Simmel,
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A. Ivanisevic, Langmuir, 2007, 23, 3886; (e) H. Wang, R. Yang,
L. Yang and W. Tan, ACS Nano, 2009, 3, 2451; (f) C. T. Wirges,
J. Timper, M. Fischler, A. S. Sologubenko, J. Mayer, U. Simon
and T. Carell, Angew. Chem., Int. Ed., 2009, 48, 219.
In summary, different M-DNA nanohybrids (M = Pd, Au,
Ag and Pt) were prepared from a cheap natural DNA under
mild conditions. Detailed characterizations indicated that
there was interaction between metal NPs and DNA which
stabilized the metal NPs. The as-synthesized M-DNA revealed
both the unique features of DNA and metal nanoparticles.
Dramatic solubility of M-DNA nanohybrids like pure DNA
4 (a) K. Keren, R. S. Berman, E. Buchstab, U. Sivan and E. Braun,
Science, 2003, 302, 1380; (b) Y. Hatakeyama, M. Umetsu,
S. Ohara, F. Kawadai, S. Takami, T. Naka and T. Adschiri,
Adv. Mater., 2008, 20, 1122; (c) K. Nguyen, M. Monteverde,
A. Filoramo, L. Goux-Capes, S. Lyonnais, P. Jegou, P. Viel,
M. Goffman and J. P. Bourgoin, Adv. Mater., 2008, 20, 1099.
5 H. A. Becerril and A. T. Woolley, Chem. Soc. Rev., 2009, 38, 329.
6 A. J. Boersma, R. P. Megens, B. L. Feringa and G. Roelfes, Chem.
Soc. Rev., 2010, 39, 2083.
Table 3 Recycling of Pd-DNA for reduction of ethyl 4-nitrobenzoatea
Run
1
2
3
4
5
7 X. D. Liu, H. Y. Diao and N. Nishi, Chem. Soc. Rev., 2008, 37, 2745.
8 See the ESIw for details.
9 For examples of hydrogenation catalyzed by nano-catalysts, see ref. 1f.
10 For examples of oxidation catalyzed by nano-catalysts, see:
H. Miyamura, R. Matsubara, Y. Miyazaki and S. Kobayashi,
Angew. Chem., Int. Ed., 2007, 46, 4151. and ref. 1a.
Time/h
Yield (%)b
8
99
9.5
99
11
96
13
90
20
80
a
Reaction conditions: 1f (1 mmol), Pd-DNA (initially 1.8 mol%) in
b
4 ml Tris, EtOH (2 ml), H2 balloon, 25 1C. Isolated yield.
c
7914 Chem. Commun., 2010, 46, 7912–7914
This journal is The Royal Society of Chemistry 2010