CL-140151
Received: February 26, 2014 | Accepted: April 17, 2014 | Web Released: April 24, 2014
Synthesis and Antibacterial Activity of Silver Nanoparticles Capped
with a Carboxylic Acid-terminated Generation 1 Oleodendrimer
Rahul S. Kalhapure,1 Krishnacharya G. Akamanchi,2 Chunderika Mocktar,1 and Thirumala Govender*1
1Discipline of Pharmaceutical Sciences, School of Health Sciences, University of KwaZulu-Natal,
Private Bag X54001, Durban 4000, South Africa
2Department of Pharmaceutical Sciences and Technology, Institute of Chemical Technology,
Matunga (E), Mumbai 400019, India
(E-mail: govenderth@ukzn.ac.za)
This study investigated the potential of a novel carboxylic
acid-terminated generation 1 oleodendrimer (E1A) as a novel
biocompatible capping agent for the synthesis of silver nano-
particles (E1A@Ag). Synthesized E1A@Ag particles were
spherical with an average size of 9 « 3 nm and displayed
antimicrobial activity against Staphylococcus aureus, meth-
icillin-resistant Staphylococcus aureus, and Escherichia coli.
The current study, therefore, establishes E1A as an effective
biocompatible material for the synthesis of silver nanoparticles.
Figure 1. Structure of (A) oleodendrimer E1A; (B) bicephalous
dianionic surfactant: E1ANa.
Historically, though Ag compounds and ions have been
extensively used for both hygienic and healing purposes,1 their
use as anti-infectious agents has reduced due to the advent of
antibiotics and other disinfectants, as well as because the
mechanism of their toxic effects is poorly understood.2 How-
ever, the surge in bacterial resistance against antibiotics at the
end of the 20th century has given impetus for the return toward
usage of Ag’s antibacterial properties.3 Ag in the form of
nanoparticles (AgNPs), especially for medical applications, has
become a promising alternative to Ag salts and bulk metals
because salts may release Ag too quickly and uncontrollably,
while the bulk metal is too inefficient as a releasing material.4
To circumvent the major challenge of controlling particle
size, morphology, and agglomeration of AgNPs, organic capping
agents (CAs) also known as stabilizing or protecting agents are
usually required.5 There is a wide selection of stabilizing agents
that are available, including ligands and polymers that contain
functional groups such as thiol (-SH), cyano (-CN), carboxy
(-COOH), amino (-NH2), and fatty acids.2 Amongst fatty acids,
oleic acid (OA) has been widely used.4-6 This may be due to
OA being nontoxic, inexpensive, easy to use, and harmless
to environment materials.4 The unique properties and diverse
applications of OA has prompted our group toward development
of OA-based materials for pharmaceutical applications,7 includ-
ing a recently reported synthesis of oleodendrimers as pene-
tration enhancers.8 Herein, we report the application of one of
these oleodendrimers, i.e., carboxylic acid-terminated generation
1 oleodendrimer (E1A) (Figure 1A) for its use in combination
with bicephalous dianionic surfactant (E1ANa) (Figure 1B) as
an efficient CA to synthesize stable AgNPs (E1A@Ag) as well
as the in vitro cytotoxicity study thereof.
-COOH group without any tertiary nitrogen in the structure,
whereas E1A has two -COOH groups. Although E1A has more
-COOH groups than OA, it is, in comparison, much less than
those in PAA, and in addition, it has a tertiary nitrogen in the
structure unlike OA and PAA. E1A, therefore, combines the
properties of CAs with -COOH groups as well as CAs with a
tertiary nitrogen in a single molecule. Hence, it was hypothe-
sized that E1A would be an efficient CA with the optimal
number of functional groups necessary for the formation of
well-dispersed AgNPs. Moreover, utilization of AgNPs in the
medical field would ideally require a noncytotoxic CA; E1A
owing to its biocompatibility meets this requirement. The aim
of the study was, therefore, to prepare AgNPs using E1A as
a biocompatible CA and to evaluate its antibacterial activity
against both sensitive and resistant bacteria.
E1A and E1ANa were synthesized as per the procedures
previously reported by our group (Supporting Information).7,8,10
In vitro cytotoxicity study of E1A was performed on a human
cervix cancer cell line (HeLa) by sulforhodamine B (SRB) assay
¹1
at concentrations ranging from 10 to 80 ¯g mL (Supporting
Information).11 Adriamycin, a potent anticancer drug widely
used as a control for cytotoxicity studies, was used as a positive
control in this study due to its clearly defined toxicity profiles.
Parameters calculated were growth inhibition of 50% (GI50),
total growth inhibition (TGI), and the net loss of cells following
treatment (LC50).
E1A@Ag was synthesized through a liquid-solid-solution
process.12 E1ANa (0.208 mmol) and the mixture of E1A (0.206
mmol) and ethanol (1.5 mL) were added to a solution of silver
nitrate (AgNO3) (0.41 mmol) in milli-Q water (3 mL) (Millipore
Corp., USA) in a capped tube under stirring. The system was
kept at 100 °C for 3 h. E1A@Ag that had settled at the bottom of
the container was collected by filtration, washed with distilled
water, and dried in a vacuum desiccator for 24 h. Synthesized
E1A@Ag can be easily dispersed into nonpolar solvents like
The number of -COOH groups in a CA is an important
factor governing properties of AgNPs. CAs with higher number
of -COOH groups such as poly(acrylic acid) (PAA) result in
the formation of particle agglomerates due to interaction with
adjacent -COOH groups.5 Also, tertiary nitrogen in a CA
participates in the formation of AgNPs.9 OA has only one
© 2014 The Chemical Society of Japan