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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-
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-