DNA as a bioligand supported on magnetite for grafting palladium nanoparticles for cross-coupling reaction

Article abstract of DOI:10.1002/aoc.5357

The utilization of deoxyribonucleic acid (DNA) in nanotechnology is a promising area of research wherein the distinct properties of DNA are exploited for the design and development of new materials and applications. The biodegradability and natural profusion of DNA makes it highly suitable for use in various fields. In this report, we have treated DNA as a bioligand, supported on functionalized magnetite for the grafting of palladium (Pd) nanoparticles to make Pd-DNA bio-nanocatalyst. The Pd-DNA was subjected to Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Brunauer–Emmett–Teller, energy dispersive X-ray spectroscopy, vibrating sample magnetometry, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectrometry analysis. The prepared Pd-DNA was found to be highly efficient in catalyzing Suzuki–Miyaura cross-coupling reaction with excellent yields when compared with commercially available palladium-based catalysts. Also, the Pd-DNA could be easily recovered from the reaction mass using an external magnet and recycled up to six times without substantial loss of activity. Furthermore, Felbinac, a non-inflammatory drug, was synthesized in quantitative yields using the Pd-DNA bio-nanocatalyst.

Full text of DOI:10.1002/aoc.5357

Received: 14 August 2019
DOI: 10.1002/aoc.5357
Revised: 15 October 2019
Accepted: 22 October 2019
F U L L P A P E R
DNA as a bioligand supported on magnetite for grafting
palladium nanoparticles for cross-coupling reaction
Vishal Kandathil1 | Manjunatha Kempasiddaiah1
|
Sanna Kotrappanavar Nataraj1 | Sasidhar Balappa Somappa2 | Siddappa A. Patil1
1Centre for Nano and Material Sciences,
The utilization of deoxyribonucleic acid (DNA) in nanotechnology is a promis-
ing area of research wherein the distinct properties of DNA are exploited for
the design and development of new materials and applications. The biodegrad-
ability and natural profusion of DNA makes it highly suitable for use in vari-
ous fields. In this report, we have treated DNA as a bioligand, supported on
functionalized magnetite for the grafting of palladium (Pd) nanoparticles to
make Pd-DNA bio-nanocatalyst. The Pd-DNA was subjected to Fourier-trans-
form infrared spectroscopy, field-emission scanning electron microscopy,
transmission electron microscopy, X-ray powder diffraction, Brunauer–
Emmett–Teller, energy dispersive X-ray spectroscopy, vibrating sample magne-
tometry, X-ray photoelectron spectroscopy, and inductively coupled plasma
optical emission spectrometry analysis. The prepared Pd-DNA was found to be
highly efficient in catalyzing Suzuki–Miyaura cross-coupling reaction with
excellent yields when compared with commercially available palladium-based
catalysts. Also, the Pd-DNA could be easily recovered from the reaction mass
using an external magnet and recycled up to six times without substantial loss
of activity. Furthermore, Felbinac, a non-inflammatory drug, was synthesized
in quantitative yields using the Pd-DNA bio-nanocatalyst.
Jain University, Jain Global Campus,
Kanakapura, Ramanagaram, Bangalore,
562112, India
2Organic Chemistry Section, National
Institute for Interdisciplinary Science and
Technology (CSIR), Trivandrum, 695019,
India
Correspondence
Siddappa A. Patil, Centre for Nano and
Material Sciences, Jain University, Jain
Global Campus, Kanakapura,
Ramanagaram. Bangalore 562112, India.
Email: p.siddappa@jainuniversity.ac.in
K E Y W O R D S
bioligand, bio-nanocatalyst, magnetite, palladium nanoparticles, Suzuki–Miyaura cross-coupling
1 | INTRODUCTION
can catalyze multiple classes of organic transformations,
thereby making them feasible for commercial-scale pro-
Nanotechnology has become one of the most important
fields of research globally due to its widespread applica-
tions in an array of fields such as medicine,[1] electron-
ics,[2] energy,[3] water treatment,[4] sensors,[2] catalysis[5]
and so on. The particular role of each nanomaterial in its
respective field when compared with bulk materials is
associated with its size and morphology.[6] Nanocatalysis
is an emerging segment of nanotechnology in which
research is being directed to the synthesis of engineered
nanomaterials which possess high catalytic efficiency and
duction.[7] For this, the design of the nanocatalysts is of
utmost importance since this has a direct effect on the
sustainability of the nanocatalyst.
Recently, biomaterials have been shown to be useful
materials owing to their unique properties in the area of
bionanotechnology and catalysis.[8] Enzymes, lipids, and
nucleic acids are biomaterials that are of great interest
due to their distinctive properties, which can be fine-
tuned to suit the reaction requirements, and their envi-
ronmental friendliness, easy availability, and low
Appl Organometal Chem. 2020;e5357.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5357

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KANDATHIL ET AL.
toxicity.[9] Deoxyribonucleic acid (DNA) is especially sig-
nificant in the field of catalysis because of its ability to
act as a ligand system for metal complex formation or as
a support for metal nanoparticles.[10]
(smDNA) was purchased from TCI Chemicals (Karna-
taka, India) Pvt. Ltd. Palladium (II) acetate, aryl halides,
arylboronic acids, sodium sulfate, dichloromethane, ethyl
acetate, and n-hexane, bis[3-(trimethoxysilyl)propyl]
amine were purchased from Sigma-Aldrich, Karnataka,
India and Avra Chemical, Karnataka, India and were
used without further purification. Heating was accom-
plished by either a heating mantle or a silicone oil bath.
Reactions were monitored by thin-layer chromatography
(TLC) performed on 0.25 mm Merck TLC silica gel plates,
using UV light as a visualizing agent. Purification of reac-
tion products was carried out by flash column chroma-
tography using silica gel 60 (230–400 mesh). Yields refer
to chromatographically pure material. Concentration in
vacuo refers to the removal of volatile solvent using a
rotary evaporator attached to a dry diaphragm pump (10–
15 mmHg), followed by pumping to a constant weight
with an oil pump (<300 mTorr).
The phosphate groups and nitrogen-rich bases pre-
sent in DNA have high affinity for transition metals.
Amongst the transition metals, palladium (Pd) has huge
significance in synthetic organic chemistry due to its
excellent activity in various organic transformations.[11]
Palladium can catalyze diverse organic reactions in
which the Suzuki–Miyaura cross-coupling reaction is of
prime importance in carbon–carbon (C–C) bond forma-
tion.[12] The easy availability of starting materials, rela-
tively mild reaction conditions, and high functional
group tolerance are some of the key advantages of
Suzuki–Miyaura cross-coupling over other C–C coupling
reactions. The applications of Suzuki–Miyaura cross-cou-
pling reactions range from synthesis of various active
pharmaceutical ingredients to agrochemicals, and from
industrially important polymers to natural product syn-
thesis.[13] However, palladium is a noble metal there is a
high production cost associated with these commercially
important cross-coupled products. In order to tackle this,
scientists are constantly developing catalysts that are
highly active, easy to synthesize, and easily recoverable
from the reaction mass so that they can be recycled,
thereby drastically reducing the cost of production and
making the process economically viable and green.
In this report, we describe the design of a green and
sustainable bio-nanocatalyst in which the metal chelating
properties of DNA, supported on silane functionalized
magnetite, are exploited to graft palladium nanoparticles.
It is desirable to have provision for the easy recovery of
the catalyst even if the catalyst shows excellent activity
because then it is possible to use it for further cycles. The
presence of magnetite as a support makes the catalyst
easily recoverable from the reaction mass by simple mag-
netic attraction.[14] The bio-nanocatalyst prepared was
characterized by various spectroscopic, microscopic, and
surface analyses, and studied for catalytic activity in the
Suzuki–Miyaura cross-coupling reaction. The bio-
nanocatalyst can be easily recovered from the reaction
mass and recycled up to six times without considerable
loss of activity.
2.2 | Characterization
Fourier-transform infrared spectra were recorded with a
Perkin Elmer Spectrum Two, India. The elemental palla-
dium content in Pd-DNA and the reaction mass were deter-
mined using a Perkin Elmer Optima 5300 DV inductively
coupled plasma optical emission spectrometer. Brunauer–
Emmett–Teller (BET) surface areas were obtained by phy-
sisorption of N2 using a Microtrac BELSORP MAX, India
instrument. Transmission electron microscope images
were obtained using a Jeol/JEM 2100 microscope. A JEOL
JSM 7100F field-emission scanning electron microscope
fitted with energy dispersive X-ray spectroscopy (EDS) was
used to observe the morphology and elemental distribu-
tions of samples. X-ray powder diffraction patterns were
obtained using a Rigaku X-ray Diffraction Ultima-IV,
India. The magnetic properties of the samples were studied
at room temperature using a Lakeshore 7410S Vibrating
Sample Magnetometer, India. The surface chemistry of Pd-
DNA was analyzed using X-ray photoelectron spectroscopy
(XPS; PHI 5000 VersaProbe II, ULVAC-PHI Inc., USA)
equipped with micro-focused (200 μm, 15 kV) monochro-
matic Al-Kα X-Ray source (hν = 1486.6 eV). 1H NMR spec-
tra were recorded using an Agilent 400-MR DD2
System, India. 1H NMR coupling constants (J) are reported
in Hertz (Hz) and multiplicities are indicated as follows:
s (singlet), d (doublet), t (triplet), and m (multiplet).
2 | EXPERIMENTAL
2.1 | Materials
2.3 | Preparation of Fe3O4 magnetic
nanoparticles
Unless otherwise stated, all reactions were performed
under aerobic conditions in oven-dried glassware with
magnetic stirring. DNA sodium salt ex. salmon milt
Magnetic nanoparticles (MNP) were synthesized as per
our previous reports[15] following the chemical co-

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precipitation method. Here, FeCl3.6H2O (2.35 g,
8.7 mmol) and FeCl2.4H2O (0.86 g, 4.3 mmol) were mixed
and dissolved in deionized water (40 ml), followed by
sites present in DNA to form the bio-nanocatalyst. The
obtained bio-nanocatalyst was isolated by magnetic
decantation followed by water (2 × 20 ml) and ethanol
(20 ml) washes, and dried at 45 ꢀC for 12 hr.
ꢀ
stirring of the resultant solution for 30 min at 85 C to
completely dissolve both the reactants. Then ammonium
hydroxide (5 ml) solution was added slowly with vigorous
ꢀ
stirring at 85 C to generate a black solid. The reaction
2.7 | General procedure for Suzuki–
was continued for a further 30 min. The black magnetic
nanoparticles were isolated by using an external magnet,
washed repeatedly with deionized water until neutral
pH, further washed with methanol (2 × 20 ml), and dried
at 80 ꢀC in the oven.
Miyaura cross-coupling reaction
To a 25 ml round-bottomed flask containing 5 ml of etha-
nol:water (1:1) mixture were added aryl halide (1 equiv),
aryllboronic acid (1.1 equiv), K2CO3 (2.5 equiv), and Pd-
DNA (0.02 mol% Pd). The mixture was then stirred mag-
netically at room temperature for the required time. The
progress of the reaction was monitored by thin layer
chromatography (TLC). After reaction completion, Pd-
DNA was removed from the reaction mass using an
external magnet, washed with ethanol (1 × 5 ml) and
water (1 × 5 ml), and was reused without purifying fur-
ther. The product was extracted using dichloromethane
(2 × 10 ml) and the combined organic layer was subjected
to washing with water (2 × 10 ml) followed by drying of
the organic layer over Na2SO4. The dried organic layer
was concentrated in vacuo and the product was purified
by column chromatography using n-hexane and ethyl
acetate as eluents to afford the corresponding products in
good to excellent yields. All the coupled products were
known molecules and were confirmed by comparing with
the 1H NMR of authentic samples (see Supporting
Information).
2.4 | Synthesis of silyl functionalized
MNP
The MNP (2.0 g) were suspended in toluene (50 ml) by
ultrasonication for 10 min. Then bis[3-(trimethoxysilyl)
propyl]amine (4.0 g, 11.7 mmol) was added to the suspen-
sion dropwise under stirring and the stirring was contin-
ꢀ
ued at 45 C for 24 hr. The solution was cooled to room
temperature and the resultant dark-brown silyl chloride
functionalized MNP (SMNP) were isolated by magnetic
decantation, washed with deionized water and ethanol,
and dried at 50 ꢀC.
2.5 | DNA fixation on SMNP (DNA-
SMNP)
smDNA (200 mg) was added to 50 ml of phosphate buffer
solution (pH 7.2), and the mixture heated to 80 ꢀC to dis-
solve it completely. The temperature was brought down
to room temperature followed by the addition of SMNP
(200 mg) and ultrasonication for 2 min. The reaction
3 | RESULTS AND DISCUSSION
3.1 | Synthesis of the bio-nanocatalyst
Pd-DNA
ꢀ
mass was stirred for 2 hr at 80 C then cooled to room
temperature and the DNA-SMNP isolated by magnetic
decantation. The product was given water (2 × 20 ml)
and ethanol (20 ml) washes and dried at 45 ꢀC for 12 hr.
The proliferation of chelating sites present on the DNA
backbone enabled us to fabricate the DNA as a bioligand
for the grafting of Pd NPs. The biodegradability and low
toxicity of DNA are also advantages over other chemical
ligands. First, magnetite was synthesized by the chemical
co-precipitation method followed by functionalization
with bis[3-(trimethoxysilyl)propyl]amine to get SMNP
(Scheme 1). The DNA was then grafted onto the SMNP
2.6 | Synthesis of the bio-nanocatalyst
(Pd-DNA)
ꢀ
To 50 ml of ethylene glycol solvent, 150 mg of DNA-
SMNP and 150 mg of palladium(II) acetate were added.
The reaction mass was ꢀdispersed by ultrasonication for
2 min and heated to 85 C for 2–3 hr. During this period
the Pd(II) undergoes reduction to form the palladium
nanoparticles (Pd NPs) and the change in color of the
reaction mass from brown to black indicates the forma-
tion of Pd(0), which will be coordinated to the binding
by stirring at 80 C for 2 hr to form DNA-SMNP. The
MNPs interact with the phosphate groups present in the
backbone of DNA because of the strong affinity of phos-
phate groups towards iron oxide.[16] The silane prevents
the magnetite from agglomerating and at the same time
the amine group present on the silane acts as additional
coordinating site for the transition metals. The DNA-
SMNP was then taken in ethylene glycol solvent and

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KANDATHIL ET AL.
SCHEME 1 Graphical representation of
the steps involved in the synthesis of bio-
nanocatalyst
palladium(II) acetate was added. On heating, the palla-
dium salt undergoes a reduction process to form palla-
dium nanoparticles. The electron-rich nitrogen atoms on
the bases in DNA along with the phosphate groups coor-
dinate with the palladium nanoparticles formed. These
interactions are strong enough to prevent the leaching
out of palladium nanoparticles from the active bio-
nanocatalyst.
3.2 | Characterization of Pd-DNA
To understand the functional groups and the bonding
interactions of the newly prepared Pd-DNA bio-
nanocatalyst, Fourier-transform infrared spectroscopy
(FT-IR) analysis was carried out (Figure 1). The peaks at
3374 and 578 cm−1 were attributed to the O-H and Fe-O
stretching vibrations of the MNP (Figure 1a), respec-
tively. After the functionalization of MNPs with bis[3-
(triethoxysilyl)propyl]amine (Figure 1b), an additional
prominent peak at 1027 cm−1 was observed for Si-O bond
stretching along with peaks for C-H stretching at
2929 cm−1 and 2877 cm−1, confirming silane func-
tionalization. Apart from the peaks in the 3000–
3500 cm−1 range which belongs to N-H and C-H
stretching, the major peaks at 1695 cm−1 (C=O),
1657 cm−1 (C=N), and 1538 cm−1 (C=C) of DNA
FIGURE 1 FT-IR spectra of (a) MNP, (b) SMNP, (c) DNA,
(d) DNA-SMNP, and (e) Pd-DNA
from Figure 1d, wherein the peaks corresponding to both
DNA and SMNP are present with a slight shift in the
wavenumbers along with the disappearance of P-O-C
backbone stretching at 963 cm−1 and some stretching
and bending vibrations of groups in the nucleobases pre-
sent which may be due to interaction with Fe3O4. Again,
after the inclusion of Pd on DNA-SMNP, a peak shift is
observed when compared with the peaks of DNA-SMNP,
which is due to the interaction of Pd with DNA-SMNP
(Figure 1e). For instance, the peak at 1474 cm−1 is shifted
to 1489 cm−1 and the peak at 1367 cm−1 shifts to
nucleobases and peaks at 1239 cm−1 (asymmetric PO2
−
stretching), 1060 cm−1 (symmetric PO2 stretching), and
−
963 cm−1 (P-O-C backbone stretching) were observed[10]
in the FT-IR spectrum of DNA (Figure 1c). The successful
incorporation of DNA onto SMNP can be understood

BIONANOCATALYST
5 of 13
1388 cm−1. Another significant difference is that the sin-
gle peak at 1063 cm−1 is resolved into two peaks, one at
1060 cm−1 and the other at 1045 cm−1, which can be
attributed to the interaction of phosphate groups with Pd
nanoparticles.
(Figure 3). The TEM images show the successful metalli-
zation of DNA supported on MNP with Pd nanoparticles.
The Pd nanoclusters formed during the reduction step
are uniformly grafted onto the DNA resulting in masking
of DNA and the formation of a tangled chain-like struc-
ture. The size of the Pd-DNA from TEM was found to be
in the range 11–15 nm.
The surface morphology and topology of Pd-DNA
were further examined by field-emission scanning elec-
tron microscopy (FESEM) (Figure 4). The tangled chain-
like structure of DNA coated with Pd nanoparticles
supported on spherical MNP was confirmed with FESEM
analysis, which in turn corroborated the TEM results.
The Pd-DNA was then subjected to EDS analysis and ele-
mental mapping to determine and confirm the presence
and distribution of the elements present. The EDS analy-
sis showed the presence of the elements C, N, O, P, Si,
Fe, and Pd, confirming the successful formation of the
bio-nanocatalyst, and the elemental mapping (Figure 5)
showed the uniform distribution of all the elements pre-
sent. The palladium content was quantified by induc-
tively coupled plasma optical emission spectrometry
(ICP-OES) and was found to be 8.76% w/w.
The crystallinity and phase of MNP and the bio-
nanocatalyst were determined using X-ray powder dif-
fraction (XRD) analysis (Figure 2). The X-ray diffraction
pattern of MNP (Fe3O4) (Figure 2a) shows a cubic spinel
structure with an average crystallite size of 9.9 nm with
peaks at 2θ = 30.43ꢀ, 35.73ꢀ, 43.39ꢀ, 53.88ꢀ, 57.42ꢀ, and
62.97ꢀ corresponding to the reflection planes of (220),
(311), (400), (422), (511), and (440). The phase of MNP
remained unaltered after the preparation of Pd-DNA
with additional peaks observed at 2θ = 40.03ꢀ, 46.51ꢀ,
and 68.03ꢀ corresponding to lattice planes (111), (200),
and (220), respectively, of Pd(0) (Figure 2b). The average
crystallite size of Pd-DNA was found to be 13.2 nm calcu-
lated using the Scherrer equation.
The Pd-DNA was characterized by transmission elec-
tron microscopy (TEM) to find the morphology and size
BET analysis was performed to identify the surface
area of both MNP and the bio-nanocatalyst (Figure 6).
The nitrogen adsorption–desorption isotherms for the
MNP and Pd-DNA show a type II isotherm, which is
characteristic of the non-porous materials. The surface
area of MNP was found to be 103.32 m2 g−1 whereas the
surface area of Pd-DNA was 70.44 m2 g−1. The decrease
in the surface area can be attributed to the successful sur-
face modification of MNP.
The room temperature vibrating sample magnetome-
try (VSM) results for MNP and Pd-DNA are given in Fig-
ure 7. They show that the saturation magnetization
values for MNP and Pd-DNA are 42.92 and 21.48 emug−1
,
respectively. The decrease in the saturation magnetiza-
tion value in the case of Pd-DNA when compared with
MNP can be attributed to the successful functionalization
of MNP to form the bio-nanocatalyst Pd-DNA.
FIGURE 2 XRD patterns of (a) MNP and (b) Pd-DNA
FIGURE 3 TEM images of Pd-DNA at
different magnifications

6 of 13
KANDATHIL ET AL.
FIGURE 4 FESEM images of Pd-DNA
FIGURE 5 EDS spectrum and elemental mapping of Pd-DNA
To understand the chemical composition and surface
parameters, the bio-nanocatalyst was subjected to XPS
analysis. The XPS spectrum (Figure 8a) shows the
presence of all the elements (C1s, O1s, N1 s, P2p, Fe2p
and Pd3d) present in the Pd-DNA. Binding energy values
of 335.2 eV (Pd 3d5/2) and 340.7 eV (Pd 3d3/2) were

BIONANOCATALYST
7 of 13
FIGURE 6 Nitrogen adsorption–desorption curves for
(a) MNP and (b) Pd-DNA
FIGURE 8 XPS spectra of (a) fresh Pd-DNA and
(b) deconvulated Pd3d spectra of fresh Pd-DNA
observed, which correspond to Pd(0) nanoparticles
present in the catalyst. The presence of PdO from XPS
analysis can be attributed to the surface oxidation of
Pd(0) during the sampling procedures.
3.3 | Application of Pd-DNA in the
Suzuki–Miyaura cross-coupling reaction
Among the various C–C coupling reactions reported,
Suzuki-Miyaura cross-coupling has an ascendancy which
can be attributed to the mild reaction conditions,
FIGURE 7 Room temperature VSM magnetization curves for
SCHEME 2 Suzuki–Miyaura cross-coupling of
(a) MNP and (b) Pd-DNA
4-bromoanisole with phenylboronic acid

8 of 13
KANDATHIL ET AL.
relatively less toxic substrates, and the use of greener sol-
vents with excellent functional group tolerance. Thus,
after determining the various characteristics of the bio-
nanocatalyst Pd-DNA through various spectroscopic,
microscopic, and surface analyses, we proceeded to study
the activity of the prepared Pd-DNA in the Suzuki–
Miyaura cross-coupling reaction. The cross-coupling
between 4-bromoanisole and phenylboronic acid was
chosen as the model reaction for the optimization of reac-
tion conditions (Scheme 2).
Since our main focus was on adopting greener condi-
tions for the reaction, the solvent of choice was the etha-
nol:water system. Even though this solvent system was
preferred, we carried out the reaction in other solvent
systems, such as water, ethanol, methanol, methanol:
water, acetonitrile, toluene, N,N-dimethylformamide,
and acetone. The yields were high for the ethanol:water
and methanol:water system when compared with other
solvents (Table 1), which also justifies the use of a green
solvent system. Apart from the solvent system, the other
parameters studied for reaction optimization included
base selection, reaction temperature, quantity of catalyst,
and time required for maximum conversion and yield.
When the reaction was carried out using MNP, SMNP,
and DNA-SMNP, there was no product formation, which
confirms that the presence of palladium is necessary for
the reaction to happen. Among the bases used, carbonate
bases were found to be superior and among the carbonate
bases, potassium carbonate was exemplary. Use of
sodium hydroxide and potassium hydroxide resulted in
lower yield. The reaction temperature was fixed to be
room temperature because an increase in temperature
made no difference to the conversion and yield. The opti-
mal amount of palladium in the Pd-DNA in the reaction
TABLE 1 Optimization of Suzuki–Miyaura cross-coupling reaction conditions for the model reactiona
Entry
1c
2d
3e
4f
Base
Solvent
Temperature (ꢀC)
Pd (mol %)
-
Time (hr)
1
Yield (%)b
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Cs2CO3
NaOH
KOH
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH: H2O (1:1)
EtOH
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
40
-
-
-
1
-
1
-
-
1
-
5
0.01
0.02
0.025
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
1
80
92
92
92
75
86
88
60
55
82
90
76
80
83
76
90
84
92
92
6
0.50
0.50
1
7
8
9
0.25
0.50
0.50
0.25
0.25
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
10
11
12
13
14
15
16
17
18
19
20
21
22
23
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
DMF
H2O
MeOH
CH3CN
Toluene
MeOH: H2O (1:1)
Acetone
EtOH: H2O (1:1)
EtOH: H2O (1:1)
50
aReaction conditions: 4-bromoanisole (1 equiv), phenylboronic acid (1.1 equiv), base (2.2 equiv), and solvent (5 ml) in air.
bIsolated yield.
cReaction in the absence of bio-nanocatalyst.
dReaction in the presence of MNP.
eReaction in the presence of SMNP.
fReaction in the presence of DNA-SMNP.
Abbreviation: RT, room temperature.

BIONANOCATALYST
9 of 13
TABLE 2 Suzuki–Miyaura cross-coupling of different aryl halides with arylboronic acid using Pd-DNAa
(Continues)

10 of 13
KANDATHIL ET AL.
TABLE 2 (Continued)
aReaction conditions: aryl halide (1.0 equiv), phenylboronic acid (1.1 equiv), Pd-DNA (0.02 mol% Pd with respect to aryl halide), K2CO3 (2.2 equiv), and EtOH:
H2O (5 ml) in air. Yields given are isolated yield after column chromatography; average of two runs.
TABLE 3 Comparison of results for the Pd-DNA bio-nanocatalyst with other catalysts in the Suzuki–Miyaura cross-coupling reaction
between iodobenzene and phenylboronic acid
Entry
Catalyst
Solvent
Temperature (ꢀC)
Time (hr)
Yield (%)
Reference
1
2
3
4
AG22-Pd
Catalyst C2
DNA-G-Pd
Pd-DNA
EtOH:H2O (1:2)
Dioxane:H2O (1:1)
H2O
60
80
1
100
94
9b
[17]
4
[18]
100
RT
0.07
0.5
100
98
EtOH:H2O (1:1)
Present work
Abbreviation: RT, room temperature.
mixture was found to be 0.02 mol%. Increasing the palla-
dium mol% has no effect on the yield or conversion
whereas decreasing the palladium mol% resulted in lower
conversion and yield. The highest conversion and yield
were obtained after a reaction time of 30 min. When the
reaction was continued above 30 min there was no
increase in the conversion and yield, but a shorter reac-
tion time resulted in lower conversion and yield. Thus
the maximum yield for the Suzuki–Miyaura cross-cou-
pling reaction was obtained while employing potassium
carbonate base and 0.02 mol% of Pd in the catalyst at
room temperature in ethanol:water (1:1) as a solvent.
Under the optimized conditions, we studied the sub-
strate scope with varying substitutions on aryl halides as
well as arylboronic acids (Table 2). From the results
obtained it can be seen that the bio-nanocatalyst Pd-DNA
performs well with various substrates resulting in good to
excellent yields. Even though all the aryl halides with an
electron-donating group as well as an electron-withdraw-
ing group underwent the Suzuki–Miyaura cross-coupling
reaction to give good to excellent yield in the presence of
Pd-DNA, the time taken for reaction completion was
slightly higher for the former. Among aryl halides, aryl
iodides reacted in less time when compared with their
FIGURE 9 Recycling efficiency of Pd-DNA for the model
Suzuki–Miyaura cross-coupling reaction
FIGURE 10 FT-IR spectra of (a) fresh Pd-DNA and (b) Pd-
DNA after seven recycles

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FIGURE 11 FESEM images of Pd-DNA after seven recycles
bromide counterparts. It can also be seen from the results
that, irrespective of the substitution on the phenylboronic
acid, Pd-DNA can effectively catalyze the cross-coupling
reaction under optimized conditions. The use of mild
reaction conditions along with green solvents and easy
recovery of the nanocatalyst from the reaction mixture
using an external magnet are the major advantages of
this protocol. To check the applicability of Pd-DNA in
the synthesis of drug molecules, we synthesized a non-
inflammatory drug, Felbinac. Under the optimized reac-
tion conditions we could synthesize Felbinac in excellent
yield, which corroborates the applicability of our bio-
nanocatalyst (Table 2, 3k).
To examine the efficiency of the bio-nanocatalyst we
compared the yield obtained for similar reactions with
reported DNA-based catalysts, and the results are pres-
ented in Table 3. From the table it is clear that among
the reported DNA-based catalysts, Pd-DNA has the upper
hand in various aspects. Apart from the high yield, Pd-
DNA can be easily recovered and recycled, uses green
solvent for the reaction, and is able to catalyze the cross-
coupling at room temperature.
number of recycles because the palladium nanoparticles
are strongly interacted with the nitrogen present in the
DNA base as well as with the phosphate groups and also
with the nitrogen on the silane backbone.
After the seventh recycle, Pd-DNA was characterized
by FT-IR, FESEM, XRD, and XPS analyses to understand
the possible changes occurring in bio-nanocatalyst com-
position as well as on the surface. From the FT-IR analy-
sis of recycled Pd-DNA (Figure 10b), it is apparent that
there is no change in the chemical composition and the
wavenumbers match those of the fresh Pd-DNA (Fig-
ure 10a) with slight differences in the intensities of the
peaks. From FESEM analysis (Figure 11), it can be seen
that even after the seventh recycle Pd-DNA retains its
tangled chain-like morphology. The XRD analysis of Pd-
DNA after seven recycles (Figure 12b) further confirms
that there is no difference in the crystallinity or on the
phase of the recycled Pd-DNA when compared with fresh
3.4 | Recyclability of Pd-DNA in the
Suzuki–Miyaura cross-coupling reaction
Recyclability is an important feature that determines the
sustainability and greenness of any catalyst. In our case,
we chose the Suzuki-Miyaura cross-coupling reaction as
the model reaction for the recyclability study of the
nanocatalyst. From the results obtained (Figure 9), it can
be substantiated that the bio-nanocatalyst Pd-DNA is
highly efficient and recyclable without considerable loss
in activity for up to six cycles, although a drop in yield is
obtained thereafter. The use of milder and greener reac-
tion conditions is another advantage for the increased
FIGURE 12 XRD patterns of (a) fresh Pd-DNA and (b) Pd-DNA
after seven recycles

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KANDATHIL ET AL.
so it can be utilized on a commercial scale for different
applications. The prepared Pd-DNA was well character-
ized by various analytical techniques and the activity
study revealed that it is highly efficient and recyclable in
the Suzuki–Miyaura cross-coupling reaction. Further,
being green and sustainable, our approach can be utilized
for the binding of various transition metal nanoparticles
on DNA for their study in different applications.
ACKNOWLEDGMENTS
The authors thank Nano Mission, Ministry of Science &
Technology, Department of Science & Technology, Gov-
ernment of India, for financial support through Grant
SR/NM/NS-20/2014. Also, SKN thank DST-Government
of India for NANOMISSION PROJECT (SR/NM/NT-
1073/2016).
CONFLICTS OF INTEREST
The authors declare that they have no conflict of interests
concerning this article.
FIGURE 13 Deconvulated Pd3d spectra of Pd-DNA after
seven recycles
Pd-DNA (Figure 12a). The deconvulated Pd3d spectra of
the recycled Pd-DNA show that there is no change in the
oxidation state of the active centre of the bio-nanocatalyst
even after seven recycles, which further confirms that the
Pd-DNA is highly stable. Thus, it can be concluded that
the Pd-DNA is an easily recoverable, highly recyclable,
and efficient bio-nanocatalyst.
FUNDING INFORMATION
The authors thank Nano Mission, Ministry of Science &
Technology, Department of Science & Technology, Gov-
ernment of India, for financial support through Grant
SR/NM/NS-20/2014.
ORCID
Siddappa A. Patil https://orcid.org/0000-0002-2855-
5302
3.5 | Leaching study
To confirm the heterogeneity of the bio-nanocatalyst and
identify if there is any leaching out of palladium
nanoparticles into the reaction mass, we carried out a
leaching study. Here, we ran the model reaction and after
the reaction completion the bio-nanocatalyst was sepa-
rated by an external magnet and the reaction mass
obtained was analyzed by ICP-OES analysis. The palla-
dium content in the reaction mass was less than 0.1 ppm,
which rules out the possibility of any palladium leaching
into the reaction mass, proving that Pd-DNA is heteroge-
neous in nature and the interaction between palladium
nanoparticles and various groups present in DNA-SMNP
are strong enough to prevent palladium nanoparticles
from leaching out.
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
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How to cite this article: Kandathil V,
Kempasiddaiah M, Nataraj SK, Somappa SB,
Patil SA. DNA as a bioligand supported on
magnetite for grafting palladium nanoparticles for
cross-coupling reaction. Appl Organometal Chem.
2020;e5357. https://doi.org/10.1002/aoc.5357
[15] a) K. Vishal, B. D. Fahlman, B. Sasidhar, S. A. Patil, S. A. Patil,
Catal. Lett. 2017, 147, 900. b) V. Kandathil, B. D. Fahlman,