Green synthesis of silver nanoparticles using green alga (Chlorella vulgaris) and its application for synthesis of quinolines derivatives

Article abstract of DOI:10.1080/00397911.2019.1610776

Nanoparticles have been used century ago but have regained their importance in recent years being simple, ecofriendly, pollutant free, nontoxic, low-cost approach, and due good atom economy. In this report, we have demonstrated the synthesis of silver nanoparticles using green algae (Chlorella vulgaris) which in turn was used for synthesis of biologically important quinolines. Algal extract was prepared and treated with silver nitrate solution for the synthesis of silver nanoparticles. Synthesized nanoparticles were characterized with the help of analytical tools like UV, FTIR, X-ray, and SEM and used as a catalyst for the synthesis of quinolines.

Full text of DOI:10.1080/00397911.2019.1610776

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Green synthesis of silver nanoparticles using green
alga (Chlorella vulgaris) and its application for
synthesis of quinolines derivatives
Akhil Mahajan, Anju Arya & Tejpal Singh Chundawat
To cite this article: Akhil Mahajan, Anju Arya & Tejpal Singh Chundawat (2019) Green
synthesis of silver nanoparticles using green alga (Chlorellaꢀvulgaris) and its application
for synthesis of quinolines derivatives, Synthetic Communications, 49:15, 1926-1937, DOI:
10.1080/00397911.2019.1610776
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2019, VOL. 49, NO. 15, 1926–1937
https://doi.org/10.1080/00397911.2019.1610776
Green synthesis of silver nanoparticles using green alga
(Chlorella vulgaris) and its application for synthesis of
quinolines derivatives
Akhil Mahajan, Anju Arya, and Tejpal Singh Chundawat
Department of Applied Sciences, The North Cap University, Gurugram, Haryana, India.
ABSTRACT
ARTICLE HISTORY
Received 28 November 2018
Nanoparticles have been used century ago but have regained their
importance in recent years being simple, ecofriendly, pollutant free,
nontoxic, low-cost approach, and due good atom economy. In this
report, we have demonstrated the synthesis of silver nanoparticles
using green algae (Chlorella vulgaris) which in turn was used for syn-
thesis of biologically important quinolines. Algal extract was pre-
pared and treated with silver nitrate solution for the synthesis of
silver nanoparticles. Synthesized nanoparticles were characterized
with the help of analytical tools like UV, FTIR, X-ray, and SEM and
used as a catalyst for the synthesis of quinolines.
KEYWORDS
Biocatalyst; Chlorella
vulgaris; green synthesis;
quinolines; silver
nanoparticles
GRAPHICAL ABSTRACT
Introduction
Metal nanoparticles have been synthesized extensively for a variety of applications in
the areas such as chemistry, physics, life science, material science, medical science,
CONTACT Tejpal Singh Chundawat
chundawatchem@yahoo.co.in, tejpal@ncuindia.edu
Department of Applied
Sciences, The North Cap University, Sector 23-A, Gurugram, Haryana, 122017, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2019 Taylor & Francis Group, LLC

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SYNTHETIC COMMUNICATIONSV
1927
nanomedicine, and engineering due to size and shape dependable properties.
Nanoparticles possess unique optical, magnetic, electronic and catalytic properties along
with their distinctive feature of size and shape.[1–2] Chemical synthesis of the metal
nanoparticles requires a chemical reducing agent to convert metal ion into metal nano-
particles which involve the use of aggressive and hazardous chemicals.[3] In contrast to
the chemical synthesis, green synthesis uses eco-friendly reagents as reducing agents in
place of hazardous and toxic chemicals. The emphasis of green synthesis of metal nano-
particles is due to minimal impact on the ecosystem.[4] There are three criteria for green
synthesis as (i) The selection of the environmental friendly solvent system. (ii) An eco-
friendly reducing agent. (iii) A nanoparticle stabilizing capping agent.[5] The biological
systems used for green synthesis include bacteria, fungi, plants, algae, and some other
microorganisms.[6]
Green algae are considered as a source of bioactive compounds such as proteins, lip-
ids, carbohydrates, carotenoids, vitamins, and other secondary metabolites with a range
of biological activities.[7,8] Quinoline derivatives are known to have a broad scope in
therapeutic, bioorganic, modern science and in the field of engineered natural science.
Quinoline derivatives have been found to exhibit different therapeutic activities such as
antimalarial,[9–12] antibacterial,[13,14] antifungal,[15,16] antiplatelet,[17] anticancer,[18,19]
[20]
antitubercular
etc. Quinolines scaffold being useful for the preparation of biologic-
ally active molecules, the newer methods for their synthesis has always been explored.
Although several methods are already available for the synthesis of quinolines, there is
always a scope to develop simpler and cost-effective synthetic methods. In the present
study, we have explored the catalytic usage of silver nanoparticles, obtained by green
synthesis, for the synthesis of quinolines. This newer method of synthesis provides a
one-pot route of synthesis for quinolines directly from 2-aminobenzylalcohol utilizing
the catalytic efficiency of synthesized novel silver nanoparticles from green alga C. vul-
garis. Different algal strains like red algae, brown algae, and green algae have been used
to synthesize silver nanoparticles.[21] To the best of our knowledge and understanding,
there are no reports on the use of silver nanoparticles (AgNPs) synthesized from C. vul-
garis as a catalyst for this conversion.
Results and discussion
This report discusses the synthesis of silver nanoparticles from green algae C. vulgaris.
The synthesized silver nanoparticles were explored for the catalytic activity in the syn-
thesis of quinolines. The complete process of the algal extract preparation and synthesis
of silver nanoparticles are given in (Fig. 1c). Algal extract of green alga C. vulgaris was
used as a potential source of reducing, capping and stabilizing agent in place of harsh
chemical reagents such as sodium borohydride. The results obtained in this study are
discussed in this section. Change in the color of the solution from colorless to brown,
after mixing of an algal extract with 1 mM silver nitrate solution, confirmed the synthe-
sis of silver nanoparticles. It was observed that the color intensity of the solution
increases with the time of incubation. Best time for harvesting the test alga C.vulgaris
with respect to growth was observed to be on the 15th day (Fig. 1a,b).[22,23]

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A. MAHAJAN ET AL.
Figure 1. (a) Chlorella vulgaris. (b) Growth of Chlorella vulgaris nutrient medium. (c) Experimental
procedure for synthesis of silver nanoparticles using Chlorella vulgaris.

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In this work, PMI (process mass intensity) was also calculated to quantify the green-
ness in terms of metrics. The green metrics related to nanoparticles synthesis was
related to PMI and it was defined as:
PMI ¼ material input kg ꢀ product output kg
ð Þ
ð
Þ
The PMI of synthesized nanoparticles was found to be 1.22 and yield of synthesized
nanoparticles was 82%. The ideal value of PMI is 1 when PMI increases mean waste
increases.[24]
The extract of green alga C. vulgaris was treated with the aqueous silver nitrate solu-
tion. The formation of silver nanoparticles was then characterized by visual observation
means a color change from light pale yellow to reddish brown indicating the reduction
of silver ions into silver nanoparticles (Fig. 1c). In this reduction process, silver nano-
particles scatter and absorb light at certain wavelength due to the resonate collective
excitations of charges density at the interface between a conductor and an insulator,
phenomena called Surface Plasmon Resonance (SPR).[25]
UV-visible spectrum of the silver nanoparticles synthesized by C. vulgaris exhibited
an absorption peak around 490 nm (Fig. 2a). This peak has already been recorded for
various metal nanoparticles which ranged from 2 to 100 nm in size.[26] The synthesized
silver nanoparticles covered with biomolecules are well dispersed in solutions and fairly
stable up to 3 months as indicated by retention of the brown color of the solution.
FTIR spectrum showed peaks at 3435.88 and 2092.30 cmꢁ1 due to N–H and O–H
stretching vibrations.[27] 1637.82 cmꢁ1peak is characteristic of N–Hꢁb1ending vibrations
in amide of the protein as capping agent.[28] The peak at 1559.61 cm showed the pres-
ence of carboxyl group and a weak band at 1414.42 and 618.16 cmꢁ1 due to COOꢁ in
the amino acid residue of the protein.[1,29] C–H bending vibrations by carbohydrates
(glucose residue by C–OH bond) showed the peak at 1037.17 cmꢁ1. The results of the
present study have shown that hydroxyl groups have a strong ability to interact with
nanoparticles (Fig. 2b). The main peaks existing in the spectrum of alga are also present
in the spectrum of synthesized silver nanoparticles with lower intensities and slight
shift. Therefore, it may be evidenced that proteins, polysaccharides, amides and long
chain fatty acids are responsible biomolecules for bioreduction, capping, and stabiliz-
ing agents.
Scanning electron microscopy showed the synthesis of cubical, spherical, and trun-
cated triangular shaped silver nanoparticles. Size of the synthesized silver nanoparticles
was found to be in the range of 40–90 nm (Fig. 2c). These results of SEM were con-
firmed by reference.[30,31]
The X-ray diffraction (XRD) analysis explained the structure of silver nanoparticles.
XRD measured between 2h of 20–80 (Fig. 2d). It is indexed by JCPDS card no (04-
0783). Indexing of 2h values for 33, 36, 42, 62, 73 are 110, 111, 200, 220, 311, respect-
ively.[27,32] Silver nanoparticles were crystalline in nature with face-centered cubic
structure. Average crystalline size calculated by Debye Scherer equation was found to
be 89 nm.
The synthesized silver nanoparticles were explored for the catalytic activity since there
are a number of reports.[33,34] Quinoline synthesis could not be accomplished in the
absence of the silver nanoparticles. This motivated us to design a direct synthesis of qui-
nolines from 2-aminobenzylalcohol and acetyl derivatives (Scheme 1). Utilizing this

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A. MAHAJAN ET AL.
Figure 2. (a) UV-Visible absorbance peak at 490 nm. (b) FTIR spectrum at 3435.88 and 2092.30 cmꢁ1
due to N–H and O–H stretching vibrations, 1637.82 cmꢁ1 peak of N–H bending vibrations in amide of
protein. (c) Scanning electron microscopy showed the presence of cubical, spherical and truncated tri-
angular with size range 40–90 nm. (d) XRD measured between 2h of 20 and 80.

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Figure 2. Continued.
synthetic scheme (Scheme 1), 19 substituted quinolines analogs were synthesized (as
shown in Table 1). Progress of the reaction was checked on TLC (5% ethyl acetate/hex-
ane as mobile phase, seen on UV light). Formation of products (4a-s) was confirmed by
1H NMR, 13C NMR, and electron ionization mass spectra.
Experimental
Culturing and extraction of green algae
Green algae C. vulgaris was isolated from cement tank, central park, Delhi, India by ser-
ial dilution method, followed by plating on Chu-10 nutrient medium solidified by 1.5%
agar-agar. The colonies appearing after three weeks of incubation were isolated and ino-
culated into liquid medium. For growth experiments, algal species were grown in an
incubator at 27 1ꢂC, 1.2 0.2 Klux light intensity and 16:8 hr light: dark cycle in a
nutrient medium.
For chlorophyl extraction the culture was centrifuged to obtain algal pellets, which
were then treated with the same volume of 90% methanol, followed by heating in a
water bath at 60 ꢂC for half an hour. Total chlorophyl was estimated by measuring the
absorbance of the supernatant thus obtained at 652 and 665 nm using UV-Vis
spectrophotometer
The algal biomass was shade dried. 10 g of algal biomass was taken in 500 ml
Erlenmeyer flask along with 200 ml of distilled water. The mixture was boiled in an
autoclave for 15 min and filtered hot through filter paper (Whatman No.1). The filtered
extract was centrifuged and the supernatant was used as a reducing agent for preparing
nanoparticles.

1932
A. MAHAJAN ET AL.
Scheme 1. Silver catalyzed synthesis of quinoline.
Synthesis of silver nanoparticles
About 10 ml of algal extract was mixed with 90 ml of 1 mM AgNO3 aqueous solution in
250 ml Erlenmeyer flask and stirred at room temperature for 3 h. Simultaneously, posi-
tive control of silver nitrate aqueous solution, algal extract and a negative control con-
taining only silver nitrate aqueous solution were maintained under the same conditions.
The reaction progress was regularly monitored by observing color change and recording
UV-visible spectrum. In positive control the initial light pale yellow solution turned to
reddish brown, indicating the formation of silver nanoparticles but in negative control,
no change in color was found. After the reaction reached saturation the solution was
centrifuged for 20 min and the obtained pellets were washed with deionized water to
remove impurities. This process of centrifugation and washing was repeated thrice to
get better isolation of nanoparticles. The obtained silver nanoparticles were then oven
dried at 55 ꢂC for 5 h.
General experimental procedure for synthesis of substituted quinolines (4a–4s)
To a solution of compound 2-aminobenzyl alcohol (250 mg, 1eq) in Toluene (5 ml) was
added acetyl derivatives (1.5eq) followed by addition of potassium hydroxide (2eq) and
Ag nanoparticles (0.05eq). Whole reaction mass was heated at 80 ꢂC for 24 h. Progress
of the reaction was monitored by TLC. After completion of the reaction, as confirmed
by TLC, the reaction mass was brought to room temperature and quenched with water.
Ethyl acetate/water work up was done. Organic layer was separated and the aqueous
layer was once again extracted with ethyl acetate. All the organic layers were combined
and dried over Na2SO4 and concentrated under reduced pressure to obtain crude mater-
ial, which was purified by column chromatography to obtain desired material using

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Table-1. Silver catalyzed synthesis of quinoline derivatives.
S.No
CH3COR
Product
Yield (%)
State
1
75
Liquid
2a
4a
2
3
77
80
Liquid
Liquid
2b
2c
4b
4c
4
5
6
78
85
84
Liquid
Liquid
Liquid
2d
2e
2f
4d
4e
4f
7
88
Solid
2g
4g
8
9
87
78
82
Solid
Solid
2h
2i
4h
4i
White
solid
10
2j
4j
Off white
solid
11
75
2k
4k

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A. MAHAJAN ET AL.
Table-1. Continued.
White
solid
12
13
78
81
2l
4l
White
solid
2m
4m
White
solid
14
65
2n
2o
4n
4o
15
16
53
78
Solid
White
solid
4p
4q
2p
2q
Brown
solid
17
85
Brown
solid
18
19
83
81
2r
2s
4r
4s
Brown
solid
ethyl acetate/hexane as a mobile phase. Formation of the desired product was confirmed
1
by H NMR, 13C NMR, and electron ionization mass spectra.
2-butylquinoline (4a)
1
Liquid; B.P (105–120 ꢂC, 0.1 torr); H NMR (400 MHz,DMSO-d6) d 8.26 (d, J ¼ 8.00 Hz,
1 H), 7.92 (t, J ¼ 7.24 Hz, 2 H), 7.70 (t, J ¼ 7.96 Hz, 1 H), 7.52 (t, J ¼ 7.60 Hz, 1 H), 7.44
(d, J¼ 8.4 Hz, 1 H), 2.92 (t, J ¼ 7.60 Hz, 2 H), 1.78–1.70 (m, 2 H), 1.40–1.31 (m, 2 H),
0.93 (t, J ¼ 7.32 Hz, 3 H); 13C NMR (100 MHz, CDCl3) d 163.00, 147.38, 136.62, 129.57,
128.44, 127.49, 126.72, 125.82, 121.38, 38.80, 32.17, 22.67, 13.98; Anal. Calcd for

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C13H15N: C, 84.28, H, 8.16; N, 7.26. Found: C, 84.23; H, 8.14; N, 7.24. MS (m/z)
[Mþ ]þ: 186.22; HRMS [M þ H]þ measured: 186.2258.
Plausible mechanism
Initially, 2-aminobenzyl alcohol A reacts with AgNPs in the presence of base to form
intermediate B which results in formation of H-AgNPs C and 2-aminobenzaldehyde D
whereas as 2-aminobenzaldehyde D further reacts with acetyl derivative E in the pres-
ence of base to form intermediate F which finally undergo cyclization resulting in for-
mation of desired quinoline G with elimination of water molecule.
Conclusion
This study demonstrated that the aqueous extract of green alga C. vulgaris can reduce
silver ions into silver nanoparticles and have the potential to stabilize them. The novel
method for synthesis of silver nanoparticles was explored and found to be efficient for
the synthesis of substituted quinolines. This provides a greener catalytic approach for
the synthesis of silver nanoparticles from alga C. vulgaris and its application is a newer
synthetic approach for biocatalytic, one-pot conversion of 2-aminobenzyl alcohol to bio-
logically important substituted quinolines. Although this method is cheap and does not
generate a toxic or harsh waste whose elimination else would have been a tedious job.
Synthesis of quinoline by this method is similar to the traditional method, but when the
multi-substituted 2-aminobenzyl alcohol was used, yield were either low or no product
formation was observed. Industrial scale application of this method would be worth
exploring taking sustainable measure into account, but it would require process
optimization.
Characterization data of compounds 4a–4s associated with this manuscript are found
in the Supporting Information file.
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