A. Pandya et al. / Journal of Molecular Catalysis A: Chemical 380 (2013) 78–83
79
waste and consume far less energy than chemical synthesis routes
which reduce the production cost of AuNPs.
Nowadays, bio mineralization processes exploit the specific
rials, thus favouring controlled and efficient synthesis [23].
Previously, different types of micro-organisms, several biomolecule
and green chemical methods for biosynthesis of gold or sil-
ver nanoparticles are also reported [24–31]. In comparison with
traditional chemical synthesis, biomolecule assisted synthesis of
noble metal nanomaterials have a number of advantages to other
microorganisms. Since biomolecule assisted synthesis are carried
input is reduced and the solvents or agents used are nontoxic fac-
tors that minimize environmental damage resulting higher yield
of nanoparticles. Thus, the dissimilatory metal-reducing capabil-
ity can be used for rapid and eco-friendly biosynthesis of metal
nanoparticles [32].
Fig. 1. UV–vis spectra of AuNPs synthesized by protein egg albumin at various times
under microwave heating (reaction conditions: Temp. – 80 ◦C, P – 50 W, reaction
time – 2–5 min).
In this study, we used cell-free egg albumin protein both as a
reducing and a stabilizing agent for AuNPs synthesis. At this junc-
ture, we account the egg albumin protein mediated green synthesis
of gold nanocatalyst and catalytic application of this gold nanobio-
catalyst (AuNBC) in the manufacture of sodium benzoate from
benzyl alcohol which is significantly environmental-friendly pro-
cess, non-toxic, and energy efficient one due to the mild reaction
condition and recyclability of catalyst. To the best of our knowledge,
no work has been reported on the synthesis of sodium benzoate
using AuNBC elsewhere. Hence, in the present investigation, it was
proposed to prepare gold nanocatalyst through green route and to
apply this gold nanobiocatalyst for the synthesis of sodium ben-
zoate from benzyl alcohol.
pale yellow to pink red to yield protein stabilized AuNPs with par-
ticle size of 39 5 nm. On completion of the reaction, AuNBC were
separated by centrifugation at 5000 rpm for 30 min. The solid par-
ticles were collected and dissolved in deionised water. For catalytic
activity, AuNBC suspensions were separated by centrifugation. Pel-
lets were collected, washed with ultra pure water to remove any
unreacted gold and finally resuspended in ultra pure water.
2.2. Catalytic activity of AuNBC
The catalytic activity of AuNBC was studied using oxidation of
benzyl alcohol as a model system and further it was carried out
by microwave synthesizer. In a typical experiment, the reactions
were carried out in dry 25 ml microwave reaction open vessel with
air condenser equipped with a magnetic stir bar containing, 2 ml
benzyl alcohol (1.5 M), 3 ml NaOH (0.1 M), 3.5 ml AuNBC (0.55 mM)
and air as the oxidant under ambient pressure, stirred vigorously
in a CEM microwave (90 ◦C, 80 W) for 8 min and kept for cooling.
After that the reaction mixture was centrifuged to isolate the solid
product and recrystallized with ethanol. White solid of sodium ben-
zoate was obtained with high purity (>99%) checked using GC, HPLC
and M.P. 302 ◦C using DSC experiment (Fig. S2, see ESI). In addi-
tion, the aqueous solution was acidified by HCl until the pH value
was decreased to 3.0, the mixture was filtered and then white solid
of benzoic acid was obtained with purity >99%, M.P. 122 ◦C and
confirmed with GC and DSC respectively (Fig. S2 and S3, see ESI).
Further, the remaining AuNBC catalyst was separated from the solid
products using centrifugation and was reused.
2. Materials and methods
All chemicals used are of analytical grade or of the highest purity
available. HAuCl4·3H2O, Egg albumin powder and the other pure
chemicals and biochemical were purchased from Sigma Aldrich.
Working standard solutions were prepared daily in deionised
water. Ultrapure Millipore water was used in all AuNPs biosyn-
thesis experiments. UV–vis absorption spectra were acquired on a
Jasco V-570. IR spectra were measured with a Bruker Tensor-27.
High resolution transmission electron micrograph (HR-TEM) was
recorded by JEOL, JEM-2100 (200 kV). 1H NMR was carried out using
scanned on 400 MHz, FT-NMR Bruker Avance-400 in CDCl3 (TMS
for standard). DLS measurements were performed using Nanotrac
(NPA 150/250). pH measurement was made by using model EQ-
664 (Equip-tronics). Microwave synthesizer (CEM Discover) was
used for the purpose of synthesis. The melting point was deter-
mined Shimadzu DSC 60 with a heating rate of 10.0 ◦C min−1
.
ESI-Mass spectra were taken on a Shimadzu GCMS-QP 2000A.Gas
chromatography (Shimadzu) and HPLC (Chrompack) was used to
check the purity.
2.1. Synthesis of gold nanoparticles by protein white egg albumin
Prior to the synthesis of nanoparticles, all the glassware was
washed with aqua regia (3:1 HCl–HNO3) and then thoroughly
rinsed with deionised water. Synthesis of gold nano-bio-conjugate
(AuNBC) was carried out by microwave synthesizer under spe-
cific condition. The synthesis was carried out in a modified (CEM
Discover) microwave using single mode and continuous power at
2.45 GHz. The reactions were carried out in sealed reaction ves-
sel containing 3 ml of 0.60 mM HAuCl4 solution, 2 ml white egg
albumin protein (2 mg protein/ml) was mixed with 0.2 M sodium
phosphate buffer (pH 7.0) with vigorous stirring and was heated at
80 ◦C at a power up to 50 W for 5 min. The solution changed from
Fig. 2. FT-IR spectra of egg albumin protein before (A) and after (B) interaction with
HAuCl4.