International Conference on Chemical and Environmental Sciences (ICCES'2012) June 16-17, 2012, Bangkok
Surface Capping of Magnetite Nanoparticles
with Carboxymethyl Starch Molecules
Phawinee. Nanta, Wanwisa. Sakolpap, and Kittiwut. Kasemwong
from in vivo environment, causing improvement of the
biocompatibility of MNPs. Furthermore, the adding surface
agents can enhance the ability to escape from
reticuloendothelial system (RES) and expand the half-life in
blood circulation.
This study was aimed to synthesize MNPs via
coprecipitation method and surface capped during the synthesis
with carboxymethyl starch that is one of anions biopolymer and
most important agent used in pharmaceutics [6]. The effect of
degree of substitution (DS) on the growth of MNPs crystal,
crystal size distribution and colloid stability were investigated
using zeta potential value.
Abstract— The magnetite nanoparticles (MNPs) were employed
as a new bio-diagnostic and therapeutic agents such as contrast agent
in MRI, thermoseed in hyperthermia and drug carrier in drug delivery
system. However, the limitation of synthesis of MNPs is the control of
suitable particle size and size distribution due to lack of understanding
of mechanism of growth of MNPs crystal. Surface capping MNPs is
commonly used to solve this problem. MNPs were prepared by
coprecipitation process between Fe2+ and Fe3+ and capped with
carboxymethyl starch (CMS) during reaction. In this study was to
investigate the influence of the degree of substitution (DS) of carboxyl
group on the crystal sizes, size distribution, and the surface electric
charge (zeta potential) of the particles. The particles size of bared
MNPs was approximately 8 nm measured by TEM. In addition,
CMS-MNPs with DS of 0.24 showed the highest negative surface
electric charge value.
II. MATERIALS AND METHODS
A. Materials
ferrous
chloride
Ferric
chloride
(FeCl 3 .6H 2 O),
(FeCl 2 .4H 2 O) and sodium hydroxide (NaOH) were purchased
from
Merck
(Darmstadt,
Germany).
Sodium
monochloroacetate (SMCA) was purchased from Sigma
Aldrich (Steinheim, Germany). Cassava starch was purchase
from Thai Wah Food Production Public Company Limited
(Bangkok, Thailand).
Keywords—Carboxymethyl starch, Degree of substitution,
Magnetite nanoparticles, Surface capping
I. INTRODUCTION
M
AGNETITE nanoparticles (MNPs) have been applied in
several areas such as petrochemical industry, catalysis,
agriculture, wastewater treatment, and especially in the
biomedical application. MNPs perform excellent properties
when their size is below a critical value. This size range, each
nanoparticle becomes a single magnetic domain and shows
superparamagnetic behavior [1], achieving its great potential
use. In biomedical applications, the biointerfacial
nanoparticles, colloidal stability in complex biological
environment, biocompatible, and norrow size distribution were
required. [2] - [5]
However, bared MNPs have high ratio of surface area to
volume causing lower surface energy. Subsequently, it leads to
agglomerates form of such particles. Moreover, magnetic core
is highly active and easily oxidized in air, resulting in loss of
magnetism and dispersibility [1]. In general, the addition of
chelating organic anions or polymer surface complexing agents
during or after synthesis was employed to avoid the problems.
These adding materials can be easily isolated the magnetic core
B. Preparation of Carboxymehtyl Starch
CMS was prepared by etherification of hydroxyl groups of
starch with sodium monochloroacetate (SMCA) in the
presence of sodium hydroxide. The DS was controlled by
adjusting the SMCA concentration. Starch (10% w/w) was
suspended in 100 cm3 of 85% isopropyl alcohol/water 90:10.
Some sodium hydroxide was dropped in the mixture with
vigorously stirring. Then, various amounts of SMCA (0.5 to 4
mole/mole of AGU) were added and the mixture was shaken
for 4 h at 40°C. The reaction was stopped by neutralizing the
mixture with CH 3 COOH and then, the mixture was washed
several times with ethanol until measurement of the filtrate
using silver nitrate test was negative. The obtained starch was
dried in vacuum oven at 40°C.
C. Preparation of Magnetite Nanoparticles
MNPs were prepared under nitrogen flushing as the
following procedure. First 15 cm3 of the iron solution
containing 7.5 cm3 0.1 M FeCl 2 .4H 2 O and 0.2 M FeCl 3 .6H 2 O
was added dropwise into 150 cm3 of deoxygenated 0.1 M
NaOH under mechanical stirring (4000 rpm) for 30 min at room
temperature. Then, the particles were collected and removed
from the solution by applying a magnet. Afterwords, the
Phawinee. Nanta is with the Department of Chemical Engineering,
Thammasat University, Pathumthani, CO 12120 Thailand (e-mail:
[email protected]).
Wanwisa. Skolpap is with the Department of Chemical Engineering,
Thammasat University, Pathumthani, CO 12120 Thailand (corresponding
author e-mail: [email protected]).
Kittiwut. Kasemwong is with the National Nanotechnology center, National
Science and Technology Development Agency, Pathumthani, CO 12120
Thailand (e-mail: [email protected]).
139
International Conference on Chemical and Environmental Sciences (ICCES'2012) June 16-17, 2012, Bangkok
particles were washed with deoxygenated water.
zeta-nanosizer (Malvern Instruments Ltd., UK) in deionized
water medium at 25°C.
D.Preparation of Magnetite Nanoparticles Capped with
CMS (CMS-MNPs)
80 mg of CMS was dissolved in 16 cm3 of deionized water at
80°C under magnetic stirring. Then, 4 cm3 of the iron solution
was poured into previously prepared starch solution under
vigorous stirring. The CMS and 20 cm3 of iron mixture was
added dropwise into 200 cm3 of deoxygenated 0.1 M NaOH
under mechanical stirring (4000 rpm) at 60°C for 2 h. The
remaining solution was cooled to room temperature and stood
for 12 h. After formation of gels, they were washed with
deoxygenate water until pH lower than 8.5. This procedure
could also be carried out under nitrogen flushing.
III.
RESULTS AND DISCUSSION
Fig. 1 shows the FT-IR spectrum of (a) bared MNPs, (b)
CMS, and (c) CMS-MNPs, respectively. This result showed
bounding of starch on the MNPs surface. The wide peak around
3400 cm-1 was characteristic of O-H strectching vibrations of
starch. The peaks at 1745, 1600, and 1418 cm-1 were distinctive
of C=O and COO- bonds in carboxylic salts in CMS structure.
For CMS-MNPs spectra, the O-H, C=O, and COO- peaks of
CMS and the Fe-O peak at 587 of starch and MNPs binding
were found.
E. Degree of substitution
The DS of CMS was determined by back titration method.
The prepared CMS presented in the salt form (Na-CMS).
Firstly, Na-CMS was treated with 6 M HCl to obtain the
H-CMS. Secondly, 0.5 g of H-CMS was dissolved in 20 cm3
of 0.2 M NaOH followed by the addition of 50 cm3 of distilled
water was added. The solution was transferred to a 100 cm3
volumetric flask, and then filled up with distilled water. The
solution was pipetted to an Erlenmeyer flask and diluted by
adding 50 cm3 of distilled water. The excess of NaOH was
back titrated with 0.05 M HCl using phenolphthalein as an
indicator. A blank was also titrated. The DS was calculated by
using (1).
(c)
2918.76
Transmittance
3383.3
586.547
(b)
1744.6
2934.12
1417.6
1600.49
3436.7
(a)
586.547
DS = 162nCOOH /( m ds − 58nCOOH )
(1)
4000
3000
2000
1000
-1
Wavenumber (cm )
nCOOH = 4(Vb − V ) ⋅ c HCl / 1000
(2)
Fig. 1 FT-IR spectra of (a) bared MNPs, (b) CMS, and (c) CMS-MNPs
where n COOH (mol) is the amount of COOH calculated by
using (2); m ds (g) is the mass of dry sample; V b (cm3) is the
volume of HCl used for titration of the blank; V (cm3) is
volume of HCl used for titration of the sample and c HCl
(mol/dm3) is the HCl concentration.
(a)
F. Characterization
A Fourier transforms infrared (FT-IR) spectra of native
cassava starch, CMS and CMS-MNPs were recorded in the
transmission mode on a Nicolet 6700 FT-IR microscope
model (Thermo Fisher Scientific Inc., USA) in KBr medium
at room temperature. A FEI TECNAI T20 transmission
electron microscope (TEM) was used to determine the crystal
size, morphology and size distribution of MNPs. The surface
electric charge of the particles was measured using Malvern
(c)
(b)
(d)
TABLE I
AVERAGE CRYSTAL SIZE AND ZETA POTENTIAL OF MNPS AND CMS-MNPS
WITH VARIOUS DEGREE OF SUBSTITUTION (DS)
DS
CRYSTAL SIZE (NM)
Zeta potential ζ (mV)
bared
0
0.13
0.24
0.40
1.42
7.73 ± 1.77
10 ± 2.78
6.10 ± 1.07
4.35 ± 0.91
7.63 ± 1.24
4.47 ± 1.10
16.2
4.49
-9.17
-34.43
-32.13
4.33
Fig. 2 TEM images of (a) bared MNPs and CMS-MNPs with DS (b) 0,
(c) 0.13, and (d) 0.24
140
International Conference on Chemical and Environmental Sciences (ICCES'2012) June 16-17, 2012, Bangkok
35
spherical in shape. The average crystal size of the particles
calculated from the statistical results shown in TABLE I and
size distribution shown in Fig. 3. Comparing histograms in
Fig. 3, MNPs capped with CMS showed smaller and narrower
size distribution than bared and MNPs capped with native
starch. However, their size did not always decrease with the
increase of amount of DS. DS of 0.24 is an appropriate value
for synthesis of magnetic particles with smallest crystal size
and highest negative surface electric charge value (shown in
TABLE I). The preparation of MNPs by coprecipitation
process shown in Fig. 4 has two stages (a) as follows a short
burst nucleation and a slow growth of nuclei by diffusion of
the solutes to the surface of crystals [7]. CMS-MNPs design
model illustrates in Fig. 4 (b). CMS can promote to hinderer
nucleation period or retard crystal growth. In other words,
starch molecule caused the steric repulsion that prevented iron
ion diffusion to the surface of nanoparticles yielding a small
particle. Meanwhile, carboxyl group caused electrostatic
repulsion that isolated each molecule resulting in
improvement of colloidal stability.
DS also was influential to particles stability. TABLE I
shows surface electric charge value or zeta potential of the
particles. The zeta potential trended to increase in negative
potential as DS increased until saturation point (DS 0.24).
Beyond saturation point, the value of DS became lower.
Furthermore, CMS-MNPs exhibited superparamagnetism
(data not show) and performed better magnetic behaviors. Fig.
5 shows the photographs of CMS-MNPs dispersed in
deoxygenated water. The particles are quite sufficient to
respond to an external magnetic field which was verified by
localization of the black particles.
(a)
30
25
20
15
10
5
300
(b)
25
Crystal size (nm)
20
15
10
5
0
50
(c)
X Data
40
30
%Intensity
20
10
400
(d)
30
20
10
400
(e)
X Data
30
(a)
20
10
400
(f)
(b)
X Data
30
20
10
0
5
10
15
Crystal size (nm)
Fig. 4 Schematic illustrations of (a) growth mechanism of magnetite
and (b) CMS-MNPs design model
Fig. 3 The corresponding particle size histograms of (a) bared MNPs,
and CMS-MNPs with DS (b) 0, (c) 0.13, (d) 0.24, (e) 0.40, and (f)
1.42
Fig. 2 shows TEM images of (a) bared MNPs and
CMS-MNPs with DS (b) 0, (c) 0.13, and (d) 0.24 taken from
the colloidal suspension. The nanoparticles are roughly
141
International Conference on Chemical and Environmental Sciences (ICCES'2012) June 16-17, 2012, Bangkok
Z. Stojanović, K. Jeremić, S. Jovanović, M. D. Lechner, “A Comparison
of Some Methods for the Determination of the Degree of Substitution of
Carboxymethyl Starch,” in Starch/Stärke, vol. 57, pp. 79-83, 2005.
[10] J. H. Huang, H. J. Parab, R. S. Liu, T. C. Lai, M. Hsiao, C. H. Chen, H. S.
Sheu, J. M. Chen, D. P. Tsai, and Y. K. Hwu, “Investigation of the Growth
Mechanism of Iron Oxide Nanoparticles via a Seed-Mediated Method and
Its Cytotoxicity Studies,” J. Phys. Chem. C, vol. 112, pp. 15684-15690,
July 2008.
[11] M. Mahmoudi, P. Stroeve, A. S. Milani, and A. S. Arbab,
Superparamagnetic Iron Oxide Nanoparticles: Synthesis, Surface
Engineering, Cytotoxicity and Biomedical Applications. New York: Nova
Science, 2011.
[12] S. P. Gubin, Magnetic Nanoparticles. Weinheim: WILEY-VCH, 2009.
[9]
Fig. 5 Photograph of CMS-MNPs dispersed in deoxygenated water
IV.
CONCLUSION
In summary, capping of CMS resulted of significant
decrease in the crystal size of MNPs and narrow size
distribution. CMS-MNPs with DS of 0.24 was the suitable
value for synthesis of magnetic particles with smallest crystal
size and highest negative surface electric charge value.
Capping system can enhance colloidal stability of particles due
to two repulsive forces as follows steric repulsion from starch
molecule and electrostatic repulsion from carboxyl group. So,
synthesized CMS-MNPs could improve colloidal stability,
biocompatible and norrow size distribution that was potential
used in biomedical applications.
ACKNOWLEDGMENT
This work was supported by the National Science and
Technology Development Agency (NSTDA) via the Thailand
Graduated Institute of Science and Technology (TGIST),
(TGIST01-53-073) and the National Nanotechnology Center
(NANOTEC), and the TEM instrument supported by Center of
Nanoimaging (CNI) via Faculty of Science Mahidol
University, Thailand.
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