Formation of Se0 Nanoparticles in an Aqueous Cationic Polyelectrolyte

Article abstract of DOI:10.1023/A:1026042227091

The nanostructures formed by reduction of Se(IV) in the selenite-ascorbate redox system in an aqueous solution of supermacromolecular polycation, poly[trimethyl(methacryloyloxyethyl)ammonium] methyl sulfate, were studied by static and dynamic optical scat

Full text of DOI:10.1023/A:1026042227091

Russian Journal of Applied Chemistry, Vol. 76, No. 5, 2003, pp. 818 821. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 5,
003, pp. 847 850.
Original Russian Text Copyright
2
2003 by Kopeikin, Valueva, Kipper, Filippov, Khlebosolova, Borovikova, Lavrent’ev.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
0
Formation of Se Nanoparticles in an Aqueous
Cationic Polyelectrolyte
V. V. Kopeikin, S. V. Valueva, A. I. Kipper, A. P. Filippov, E. N. Khlebosolova,
L. N. Borovikova, and V. K. Lavrent’ev
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received December 23, 2002
Abstract The nanostructures formed by reduction of Se(IV) in the selenite ascorbate redox system in an
aqueous solution of supermacromolecular polycation, poly[trimethyl(methacryloyloxyethyl)ammonium]
methyl sulfate, were studied by static and dynamic optical scattering and flow birefringence.
Formation of uncharged metal nanoparticles of
100 nm size, which have energy-saturated surface
and exhibit certain anomalies in physicochemical
properties, is extensively studied [1].
As shown in [10], the reduction of sodium selenite
with glutathione in aqueous solution of bovine serum
albumin (BSA) yields red nano-a-Se , which is weak-
1
0
ly toxic but retains the biologically active properties
typical for ionic selenium species. It was found that
However, such metal nanoparticles are unstable in
aqueous solutions in the absence of stabilizing agents.
One of the most promising procedures for preparing
stable metal nanoparticles is reduction of their ionic
species in polymer solutions. In the course of the
pseudo-template synthesis, macromolecules and form-
ing nanoparticles recognize each other, which allows
control of the nanoparticle size by varying the struc-
ture and molecular weight of the polymer [2].
0
these nano-a-Se particles are predominantly stabilized
by adsorption processes, in which the noncovalent
(
poorly understood at present) interactions of the BSA
macromolecules with nanoparticles play the decisive
role.
To reveal the nature of these interactions and their
0
contribution to stabilization of nano-a-Se , we studied
formation of selenium(0) nanoparticles in the presence
of a synthetic polybase and analyzed the morphologi-
cal characteristics of the resulting adsorbates by vari-
ous optical methods.
Such polymer-stabilized nanoparticles are of par-
ticular importance as highly selective catalytic sys-
tems and adsorption matrices for immunoassay, and,
due to the rapid development of the biological nano-
technologies, as active components of drugs and trans-
port systems for biologically active compounds [3 5].
EXPERIMENTAL
0
In our work we studied nanoparticles of a-Se pre-
pared by reduction of selenious acid (SA) with ascor-
bic acid in the presence of a polymer and without it.
However, much less attention was given to non-
metal nanoparticles, especially those of amorphous
selenium(0) (nano-a-Se ), which, in contrast to metal
0
The reagent purity was no less than 99.99%. The
reduction kinetics was studied at the SA concentration
of 1.7 mM at 20 C on a Specord M40 spectrophotom-
eter ( 320 nm).
nanoparticles, can be described as an inorganic poly-
mer containing predominantly the Se and Se ring
6
8
fragments bound by the Se Se covalent bonds [6].
0
Nano-a-Se exhibits unique photoelectric and semi-
As a polymeric stabilizer we used supermacromolec-
ular poly[trimethyl(methacryloyloxyethyl)ammonium]
conductor properties and X-ray sensitivity; it is used
as highly sensitive biological sensor for immunoassay
6
methyl sulfate [polybase (PB)] with M 9 10 and
w
[7] and chromatographically mobile affine reagent [8].
21
1
intrinsic viscosity in 1 M NaNO [ ] = 4.5 dl g :
3
Moreover, selenium is an imperative element for
CH3
normal vital activity, it exhibits antioxidantive, anti-
mutagenic, immunnostimulating, and detoxication
activity [9]. Therefore, selenium and its compounds
are of particular interest as potential drugs.
[
CH CH ]n
2
+
O=C O (CH ) N(CH ) CH SO
4
2
2
3 3
3
1
070-4272/03/7605-0818$25.00 2003 MAIK Nauka/Interperiodica

FORMATION OF Se0 NANOPARTICLES
819
The nanocomposites of PB and elemental Se in the
0 : 10 weight ratio were prepared by reduction of
Se(IV) in solutions with a selenium concentration
of 0.01%.
f(p), tabulated function of the ratio of axes of a rigid
(impermeable for solvent) ellipsoid approximating
a particle [11].
9
Thus, for macromolecular flexible-chain and
moderately rigid-chain polymers (A < 5 nm) with in-
significant optical anisotropy and low molecular
The variation of the apparent viscosity of PB solu-
tion with time in the course of SA reduction was
monitored on a Brookfield rheoviscometer at a rotor
rotation rate of 12 rpm.
weight of the monomeric unit, [n] [n] , which al-
f
lows direct determination of the parameter p from the
experimental FBR values [11].
The relative viscosity
was determined on an
r
Ostwald capillary viscometer with a water outflow
time of 120 0.2 s at 21 C.
Using the elastic (static) light scattering method
[12], we evaluated the molecular weight M and the
w
size R of nanoparticles in question, and also their
Using the flow birefringence (FBR) procedure [11],
we evaluated the molecular dispersity of the resulting
adsorbates in solutions using the gradient dependence
of the FBR value n.
g
affinity for water solvent (from the second virial coef-
ficient A ). The amount of macromolecules adsorbed
2
on the selenium nanoparticle surface was determined
from the ratios of M for PB and its adsorbates. The
w
The FBR value n was determined in relation to
the gradient of the rotor rotation rate g and PB con-
centration c at fixed concentration of selenium. We
used a titanium dynamo-optimeter equipped with an
internal rotor (4 cm high, with a 0.3 mm gap between
the rotor and stator). All the measurements were
carried out in the temperature-controlled solutions at
reduced intensity of the solution scattering R was
determined using a Fica photogoniodiffusometer.
The wavelength of the incident vertically polarized
light was 546.1 nm. The measurements were per-
formed at the scattering angles
= 30 150 . The
solutions and solvents were purified by centrifuging at
3
1
5 10 rpm for 1.0 1.5 h. The refractive index in-
2
1 C to exclude changes in the viscosity and optical
crements dn/dc were determined with an IRF-23
refractometer.
density due to the temperature gradient. The experi-
mental setup was calibrated using phenylethyl alcohol
The experimental data on the light scattering were
treated with the Zimm procedure by double extrapola-
tion (to c = 0, = 0) of the dependences of Kc/R on
with high FBR ( n/g 17 10 12) and the polystyrene
bromoform system. The error in the FBR determina-
tion [n] = limg
( n/gc ) ( 0 is the solvent
2
0, c
0
0
sin ( /2) + kc (K is the calibration constant, and k is
viscosity) did not exceed 10%. The measurements
a numerical constant).
were performed at g < g , where g is the velocity
k
k
The average hydrodynamic parameters of the par-
ticles RH were determined by the quasi-elastic (dy-
namic) light scattering method [13]. The parameter *
characterizing the nanostructure conformation [14 17]
gradient at which the flow becomes turbulent.
In the general case (dn/dc 0, where dn/dc is an
increment of the solution refraction index, which
0
comprised 0.155 and 0.214 for PB H O and PB Se
2
was determined from the experimental ratio of R and
g
H O systems, respectively), the experimental [n]
0
2
RH for the PB Se adsorbate.
value includes three effects: [n] = [n] + [n] + [n] ,
e
fs
f
The optical section of the unit for measurements of
the dynamic light scattering was equipped with an
ALV-SP goniometer (Germany) and an He Ne laser
632.8 nm, 20 mW). The correlation function of
the scattered light intensity was evaluated with a
88-channel Photo Cor-FC correlator (Anteks Joint-
Stock Company, Russia). The experimental data were
treated by the Tikhonov’s methods of cumulants and
normalization using appropriate software.
where [n] is the intrinsic anisotropy and [n] and [n]
e
fs
f
are the micro- and macroform effects, respectively
[
11]. The total segmental anisotropy [n] + [n]fs is
e
(
determined by the equilibrium rigidity of the polymer
chain A and by the structure of a polymer unit, where-
2
as [n] is related to the asymmetry of the macromole-
f
cule (or particle) p by the following expression:
2
2
2
[
n] = [(n + 2)/3] [M (dn/dc) f (p)]/(30 RTn )
f s w s
In reduction of SA with ascorbic acid, the first-
order rate constant with respect to SA was 1.56
2
=
constM (dn/dc) f (p),
9
3
1
3
1
10
s , and it increased to 2.1 10
s
in the pres-
0
where M is the molecular weight of the adsorbate
macromolecule; n , refractive index of the solvent;
T, absolute temperature; R, universal gas constant; and
ence of PB. Without PB, the resulting Se nanopar-
ticles were unstable and formed aggregates in 3
4 days, which then precipitated. In the presence of
w
s
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 5 2003

820
KOPEIKIN et al.
0
the polymer stabilizer, the nano-a-Se particles were
aggregation-stable for at least 6 months.
This is confirmed by the n = f(g) dependences: at
g < g , for any c, these dependences are well approxi-
k
mated by straight lines passing through the origin.
The apparent viscosity of the PB solution remained
constant for 1 day, comprising about 200 cPs, and
then it sharply decreased to 30 cPs, which suggests
that the total number of the particles in the solution
decreased owing to the adsorption of macromolecules
on the surface of selenium nanoparticles. As seen
from the comparison of the intrinsic viscosity of the
initial PB and PB nano-a-Se adsorbate, the estimated
] value decreased from 55 to 12 dl g . At the same
time, M for the adsorbate determined from the data
In the [n] [n] approximation for the PB Se0
f
H O system, our calculations of the parameter p
2
showed nonspherical conformation of the nanostruc-
ture; p = 2.1, which corresponds to the conformation
of the Gaussian ball [11]. However, the absence of
the concentration dependence of the reduced optical
0
0
anisotropy in the PB Se H O system indicates that
2
1
[
the parameter p tends to 1, i.e., the conformation tends
to spherical [11]. Since, even in the case of such rigid
macromolecule as DNA, the shape of macromolecule
w
6
of the static light scattering was 100 10 , i.e., it in-
creased by a factor of 11 as compared to the free PB
macromolecules.
adsorbates on metal nanoparticles is close to spherical
0
[19], the [n]
[n] approximation for the PB Se
f
H O system is inadequate. In this case, a major con-
The second virial coefficient A for this system is
2
2
tribution to the observed optical anisotropy is made by
the segmental optical anisotropy probably related to
high hydrophobicity of the PB monomer unit [20],
and specifically the hydrophobic interactions of non-
polar macromolecule fragments with nano-Se0 are
responsible for adsorption.
very small (0.1 10 4 cm mol g ); it shows that the
3
1
thermodynamic state of solution is close to ideal.
In aqueous solutions, the average hydrodynamic
radius RH for free PO macromolecules is 540 nm,
whereas for selenium nanoparticles prepared in the
absence of polymeric stabilizer it comprises 170 nm.
Assuming nearly spherical conformation of the
nanostructure, its packing coefficient k can be de-
scribed by the following equation [21]:
0
The size of the PB-Se adsorbate, evaluated from the
dynamic and static light scattering data, is consider-
ably smaller [R (rms radius of inertia) 70 nm, R
g
H
7
0 nm]. In this case, * = R /R = 1, which suggests
g H
k = NMw*
V /v*M ,
(2)
i
i
0
almost ideal spherical shape of the adsorbate formed
14 17].
[
3
where
Vi = 253
[21] is the van der Waals
i
To determine the radius of the core selenium nano-
volume of the monomeric unit, which is the sum of
the van der Waals volume increments of the separate
0
particles in the adsorbate, the aqueous PB-Se solu-
tion was lyophilically dried, and the dry product was
pelletized and studied by small-angle X-ray diffraction
analysis. It was found that the radius of the spherical
atoms in this unit; M*, molecular weight of the par-
w
ticle; N, number of the adsorbed polymer macromole-
cules; M , molecular weight of the monomeric unit;
0
0
3
Se particle was about 15 nm, i.e., it was smaller by
and v*, adsorbate volume [4 /3(R*) ].
nearly an order of magnitude than that of the particles
prepared without polymeric stabilizer. Thus, in aque-
ous solution the thickness of the polymeric coating on
The R* value is the rms radius of inertia or the
average hydrodynamic radius of an adsorbate, which
are equal under the experimental conditions studied.
0
the Se nanoparticles is about 55 nm, i.e., macro-
molecules are strongly compacted upon adsorption.
The parameter k was 0.7, which is typical for
globular proteins (k 0.6 0.8). Thus, the adsorbate can
be described as a compact approximately spherical
nanostructure.
The data on the optical properties of PB suggest
that in aqueous solutions it is an impermeable strong-
ly asymmetric swollen ball with asymmetry p >2 [18].
On passing from the PB H O system to the PB Se0
Our data are of particular interest for deeper under-
standing of the biological and catalytic processes
occurring in the nature with participation of nanopar-
ticles of elements. We found that such nanoparticles
are adsorption matrices for biological polymers and
chemical reagents, which provides high local concen-
trations of these compounds and can strongly accele-
rate biochemical and catalytic processes.
2
H O system, the optical anisotropy decreased from
2
4
2
2
1
0000 to 6000 cm s g , which is probably due to
the changes in the macromolecule conformation.
It should be noted that, in the entire concentration
0
(
c) range studied, the PB H O and PB Se H O sys-
2
2
tems retain the molecular-dispersion state of solutions.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 5 2003

FORMATION OF Se0 NANOPARTICLES
8. US Patent 5120643.
821
CONCLUSIONS
9
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1
0. Zhang, J.S., Gao, X.Y., Zhang, L.D., and Bao, Y.P.,
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(
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0
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