Synthesis and theoretical analysis of samarium nanoparticles: Perspectives in nuclear medicine

Article abstract of DOI:10.1021/jp0460083

The use of lanthanides as radionuclides in nuclear medicine is well-known, because they can be used for detecting and treating cancerous tumors. Due to the fact that the doses are directly related to the number of unstable atoms involved, the possibility of obtaining controlled-size lanthanide nanoparticles opens a wide scope for their application in nuclear medicine. In this work, we report the synthesis of anew samarium nanoparticle by using the bioreduction method, where the pH conditions play an important role in the size control of the produced clusters. The nanoparticles were characterized by using an transmission electron microscope, in addition to the use of a quantum mechanical method to relate the atomic and electronic structures to the chemical selectivity, which allows us to predict a direct coordination between the DTPA-bis-biotin molecules with the samarium nanoparticles larger than 55 atoms. This work involves experimental and theoretical methods to propose a totally new application for nanotechnology in nuclear medicine.

Full text of DOI:10.1021/jp0460083

8806
J. Phys. Chem. B 2005, 109, 8806-8812
Synthesis and Theoretical Analysis of Samarium Nanoparticles: Perspectives in Nuclear
Medicine
Jorge A. Ascencio,*,†,‡ Ana C. Rincon,‡ and Gerardo Canizal§
Instituto Mexicano del Petroleo, Eje Central La´zaro Ca´rdenas 152, Col. San Bartolo Atepehuacan,
C.P. 07730, Me´xico D.F., Mexico, Facultad de Quimica, UniVersidad Autonoma del Estado de Mexico,
Paseo Colon esq. Paseo Tollocan, C.P. 50110, Toluca, Me´xico, and Instituto Polite´cnico Nacional, Centro de
Educacio´n Continu´a y a Distancia (Unidad Allende), Allende No. 38, Centro, Me´xico D.F. 06010, Me´xico
ReceiVed: September 4, 2004; In Final Form: January 18, 2005
The use of lanthanides as radionuclides in nuclear medicine is well-known, because they can be used for
detecting and treating cancerous tumors. Due to the fact that the doses are directly related to the number of
unstable atoms involved, the possibility of obtaining controlled-size lanthanide nanoparticles opens a wide
scope for their application in nuclear medicine. In this work, we report the synthesis of anew samarium
nanoparticle by using the bioreduction method, where the pH conditions play an important role in the size
control of the produced clusters. The nanoparticles were characterized by using an transmission electron
microscope, in addition to the use of a quantum mechanical method to relate the atomic and electronic structures
to the chemical selectivity, which allows us to predict a direct coordination between the DTPA-bis-biotin
molecules with the samarium nanoparticles larger than 55 atoms. This work involves experimental and
theoretical methods to propose a totally new application for nanotechnology in nuclear medicine.
1. Introduction
of radionuclide atoms fixed to selective peptides, which seek
out the cancer tumors.
Multiple efforts are actually focused on the detection and
treatment of cancer tumors from the first stages. Development
of new materials and molecular manipulation are strongly
involved in the goal of improving health. In the nuclear medicine
field, the discovery and development of molecules characterized
by their high avidity for both avidin and streptavidin allows
the localization of tumors. Particularly, the use of DTPA-bis-
biotin, which has been demonstrated to exist in low concentra-
tions in the blood, has been labeled with 153SmIII to produce a
contrast in the region where there is a tumor.1 For the purpose
of radionuclide labeling, the use of selective molecules appears
to be a promising method for radiation, showing that most
tumors act as peptide collectors. Somatostatin is considered as
the universal inhibitor of hormone release from several organs,
this peptide being a 14 amino acid hormone. The pharmacologi-
cal properties of somatostatin have been replicated by ocreotide,
which is an 8 amino acid peptide. This peptide has been labeled
with 99mTc, 123I, 111Inm and 90Y, and it has proven to be useful
for tumor detection and therapy.2-7 Besides, it was reported that
the 90Y- and 111In-radiolabeled DOTA-lanreotide has been used
for treatment of somatostatin-receptor-expressing tumors.8-10
Also, the labeling of â-naphthyl-peptide with 188Re to study its
biodistribution in normal and tumor-bearing nude mice has been
reported.11 Besides, human studies have also identified the use
of 188Re-â-naphthyl-peptide and a similar complex as potential
therapeutic agents.11 However, the doses produced for these
complex pharmaceutical products depend directly on the number
At the same time, the accelerated development of nanometric
clusters of different elements, structures, and sizes,12 where the
control of these variables has become greater, and the use of
different theoretical13,14 and experimental15-17 methods allows
a better knowledge of the small particles and their use in the
design of new materials and pharmaceuticals. This way,
nanoparticles have become quite important in medicine during
the past few years, since small metal clusters for producing
contrast and other applications in disease evaluation and
treatment18-21 started to be used.
Besides, the use of quicker calculations allows a faster and
more carefully controlled dosage with less damage to nearby
healthy tissues.22 These tools have become important to evaluate
the doses with high precision, which involves the necessity for
a well-controlled number of radionuclide atoms. To achieve this
goal, it is indispensable to produce small nanoparticles of a well-
controlled size, which directly implies having control over the
number of atoms and the controlled radiation delivery. This
entails the additional difficulty of reducing the possible physical
stimulation of the materials to avoid risks when the atoms are
unstable, so the synthesis method must also be an eco-friendly
method to produce samarium nanoparticles without toxic
chemicals.
Samarium has five different stable isotopes and several
unstable isotopes. The most used radionuclide among them is
153Sm, which is well-known for nuclear medicine applications,
because of its properties (half-life of 46.284 h and a decay of
energy of 0.808 MeV). Even when the physical properties are
different, chemical selectivity and possible reactions between
them are similar, so the chemical synthesis methods can be
developed in a similar manner for the different isotopes. The
samarium has two different crystal structures, rhombohedral at
low energy and a cubic system when the material is obtained
* Author to whom correspondence should be addressed. Phone: 52 55
91758055. Fax: 52 55 91756429. E-mail: ascencio@imp.mx; jascencio@
yahoo.com.
† Instituto Mexicano del Petroleo.
‡ Facultad de Quimica, Universidad Autonoma del Estado de Mexico.
§ Instituto Polite´cnico Nacional, Centro de Educacio´n Continu´a y a
Distancia (Unidad Allende).
10.1021/jp0460083 CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/06/2005

Synthesis and Analysis of Sm Nanoparticles
J. Phys. Chem. B, Vol. 109, No. 18, 2005 8807
at higher temperatures (up to 917 °C). However, at a nanometric
scale, surface energy controls the configuration of metal
particles, and face-centered-cubic (fcc)-like clusters used to be
the most stable ones because of their tendency to be spherically
shaped.12,13
These characteristics of Sm allow prediction of an aggregation
process of Sm atoms into a low-energy cluster configuration;
in fact, there are already reported results that have demonstrated
the production of small nanoparticles of lanthanides in a
bimetallic form EuAu23 and for Yb.24 In both cases, the
bioreduction method has been successful. Due to the fact that
this method fulfills the proposed chemical conditions, we use
it for the synthesis of Sm nanoparticles. The electronic structure
of the nanoparticles was calculated by a density functional theory
method (DFT) to evaluate the possibility to fix the Sm
nanoparticles to the DTPA-bis-biotin molecule, identified as a
peptide collectable by the cancer tumor.
structures, a thermal occupancy was fixed at 0.05 au, which
involves a small numerical mistake but keeps the physical
meaning and band-gap proportion in relation to the number of
atoms and the lowest-energy configuration. Similar calculations
were also made for the peptide model, to apply the Pearson
theory,30 which predicts the interaction between a donor and
an acceptor based on the hardness or softness of the molecular
species. To understand the chemical interaction, we obtained a
model for the DTPA-bis-biotin molecular structure and also for
the lowest-energy configurations of the smallest clusters of Sm
atoms up to 55 atoms. Considering rhombohedral and fcc-like
configurations, the minimal-energy structures were determined
for the selected number of atoms (2-9, 12, 13, 19, 38, and 55)
by means of geometry optimization based on the DFT method.
In all cases, the geometry optimization was followed by a single-
point energy calculation for obtaining the electrostatic potential,
highest occupied and lowest unoccupied molecular orbitals
(HOMO and LUMO respectively), and Fukui function distribu-
tions.
2. Methods and Techniques
Experimental Methods. By means of a bioreduction method,
which has been proven for gold25 and ytterbium24 nanoparticles,
gold nanorods,26 and even AuEu bimetallic clusters,23 the
samarium nanoparticles were synthesized. We used samarium
nitrate (Sm(NO3)3‚5H2O) at a 3 × 10-4 M concentration,
considering the next equilibrium conditions: M ) n/V, n )
m/MW, and m ) MVMW. So MW ) 426.4 g/mol, V ) 100 mL,
and then m ) 0.01279 g/100 mL. Consequently, we used 0.1279
g of Sm(NO3)3‚5H2O dissolved in 100 mL of deionized water.
To obtain the nanoparticles, we prepared an alfalfa (Medicago
satiVa) powder, whuch was washed, dried, ground, washed with
0.01 M HCl, and dried. A suspension of alfalfa powder in
deionized water was prepared to a concentration of 5 mg/mL
and placed in an ultrasonic bath to homogenize the suspension
for 15 min. Samples were titrated to pH ) 4, 6, 7, and 8 by
means of buffer solutions of biphthalates and phosphates,
returning the suspension to the ultrasonic bath for 15 min. Then,
the suspensions were allowed to rest for 5 min and centrifuged
for 15 min, and at once the solution is added to Sm(NO3)3‚
5H2O with a concentration of 3 × 10-4 M (where the samarium
acquires an oxidation state of 3+); the reaction mixture is placed
in an ultrasonic bath for homogenization for 20 min. Subse-
quently, it is incubated in a bath at 25 °C for 4 h and centrifuged
for 30 min at 2000 rpm. The reaction mixture is decanted, and
the obtained liquid is allowed to rest for 72 h. The production
of nanoparticles is based on the synthesis of metals from aqueous
solutions, with the Sm cation and the tanins from the alfalfa
biomass to produce the typical reduction reaction of a transition
metal cation Mn + ne- f M0, which corresponds to a oxidation
process, and it depends on a free energy change that must be
favorable as is well-supported in the review work of Cushing
et al.27
Drops of the produced samples are deposited on the grid for
the corresponding analysis by transmission electron microscopy
(TEM). Samples were characterized by TEM for studying their
size and distribution, while energy dispersive spectroscopy
(EDS) allowed us to identify the composition of the samples.
These data were obtained using a JEOL JEM2010 microscope
with analytical equipment attached.
Theoretical Methods. To calculate the minimum energy
configuration of a Sm cluster, we used the DMol3 software by
Accelrys,28 which is based on a DFT approximation and the
local density approximation (LDA) with the Perdew-Wang
(PW) functional29 with a field-consistent tolerance of 1 × 10-6
au. However, because of the complexity to converge to Sm
3. Results and Discussion
Synthesis of Sm Nanoparticles. The synthesis of nano-
particles was carried out at different pH values (4, 6, 7, and 8)
to identify the best conditions to reduce the sizes of the
nanoparticles. There is an important influence of the alfalfa
origin on the optimum conditions for the synthesis, so a
compositional analysis of the biomass was also made. In Figure
1, three different EDS spectra are shown for (a) the biomass
and the samples prepared at (b) pH ) 4 and (c) pH ) 6. It is
clear that the biomass over the copper grid (where the samples
are placed to be analyzed by TEM) has the common organic
elements and a contribution from Ca, Si, and K, which are
observed in all of the samples with and without Sm. Besides,
the sample with Sm obtained at pH ) 4 shows small peaks at
5.8 and 6.3 keV, while the sample prepared at pH ) 6 shows
peaks at 5.8, 6.3, 6.7, and 7.3 keV. The low-level signal is
associated with the amount of Sm in the analyzed zone of the
matrix. For the other cases of pH ) 7 and pH ) 8, no evidence
of Sm was distinguished in the analyses, presenting similar
spectra to the pure biomass sample; since we could not find
aggregation of Sm atoms, it was impossible to find clusters and
consequently enough characteristic X-ray counts in the EDS
spectra. Multiple zones were analyzed, and none showed the
signal from Sm, which is directly related to a dispersed
distribution of the Sm atoms, which implies that considering
the preparation at pH ) 7 and pH ) 8 there is no successful
production of nanoparticles and the Sm atoms must be coor-
dinated to the biomass without the option to aggregate into
metallic clusters.
In Figure 2, common TEM images of the obtained nano-
particles obtained in the samples are shown. In Figure 2a,
clusters of approximately 10 nm are observed, they have a well-
defined and a regular profile, and the distribution observed
presents a kind of partial array with rounded-like nanoparticles.
It is also evident that they show a thickness effect and defects,
as is shown in the particle marked with an arrow; nanoparticles
overlapping are also observed. These observed characteristics
allow understanding of a low interaction between nanoparticles
and biomass. Besides, the nanoparticles formed in the samples
obtained at pH ) 6 show a strong interaction with the biomass,
which produces an agglomeration mechanism and a diffused
contrast over the images, as can be observed in Figure 2b. The
shapes of the clusters for the pH ) 6 samples are quite irregular,
and the size is widely variable. It is also clear that the samples

8808 J. Phys. Chem. B, Vol. 109, No. 18, 2005
Ascencio et al.
Figure 1. EDS spectra for the (a) biomass and sample with Sm prepared at (b) pH ) 4 and (c) pH)6.
Figure 2. TEM images of Sm nanoparticles in samples synthesized
at (a) pH ) 4 and (b) pH ) 6.
Figure 3. TEM analysis of dispersed particles from samples synthe-
sized at (a) pH ) 4 and (b) pH ) 6.
produce multiple scattering, which reduces the possibility to
distinguish between heavy elements and zones of dense biomass.
This contrast is associated with the strong interaction between
the biomass and the lanthanide nanoparticles. In the cases of
the pH ) 7 and pH ) 8 samples, there was no contrast from
the nanoparticles as was expected from the EDS analysis, so
we can identify an important influence of the pH on the
possibility to aggregate Sm atoms and to reduce the interaction
between the biomass and the Sm. In fact, this agrees with the
effect observed in the pH ) 6 samples, where there is an effect
of biomass interaction with the lanthanide atoms, while for the
pH ) 4 samples the interaction is reduced until well-defined
shapes with more free surface are produced, with the secondary

Synthesis and Analysis of Sm Nanoparticles
J. Phys. Chem. B, Vol. 109, No. 18, 2005 8809
Figure 4. Size distribution of Sm nanoparticles for samples synthesized at pH ) 4 and pH ) 6. The corresponding values for the plot and density
are also shown in the figure.
effects of twins common in metallic nanoparticles in many other
methods reduced.
atoms, which can be used for medicine applications. However,
the application of Sm nanoparticles in nuclear medicine depends
on the possibility to fix Sm atoms to the peptide (that is the
selective agent in the detection and treatment of cancer tumors),
so we analyzed the chemical selectivity of the peptide based
on Pearson’s theory, which considers the characteristic hardness
that involves the HOMO-LUMO gap with the preferential
interaction of molecular systems.31 And we also analyzed the
geometrical and exposed sites distributions in both the peptide
and Sm aggregate, which must match the donor zones of the
peptide with the acceptor atoms of the Sm nanoparticles, which
can be identified by means of the electrophilic f(-) and
nucleophilic f(+) Fukui fields.31
Chemical selectivity behavior is based on the chemical
potential of the systems µ, which measures the tendency of
electrons to escape from a molecular species, and it is known
as the chemical thermodynamic potential or electronegativity.32
This potential is related to the energy of the system by means
of
In another stage of analysis and after a longer ultrasonic bath
treatment, smaller nanoparticles are found in the pH ) 4 sample,
as shown in Figure 3a, where many particles around 1-3 nm
are found; the spherical shape is evident, but no atomistic
resolution can be distinguished for any particle. Similarly, in a
more dispersed pH ) 6 sample, multiple particles are found in
the range of 2-8 nm (Figure 3b); however, high-resolution
contrast was impossible to be observed. It must be mentioned
that when the electron beam current was increased by trying to
improve the resolution the cluster images oscillated, so we can
relate the poor resolution and the oscillating effect to the strong
magnetic behavior of Sm particles at this range.
A detailed study with more than 40 micrographs of each kind
of sample, size distribution, and a density study was made.
Results of this analysis are shown in Figure 4, where the plot
for the percentage of nanoparticles for each size is presented
for both pH conditions. In the figure, the density values and
the data for each size range are also shown for clarity. It is
clear that even when the amount of nanoparticles produced for
pH ) 4 is lower (782 p/µm2) than in the case of pH ) 6 samples
(1092 np/µm2), the size distribution of the Sm clusters obtained
with pH ) 4 is preferably found in the region of particles smaller
than 6 nm (∼63%), while the size distribution for the obtained
clusters at pH ) 6 is more dispersed and they tend to be larger
than 8 nm (∼71.4%). These data correspond to an evaluation
of more than 500 particles in each kind of sample, with a linear
extrapolation to establish the corresponding density per square
micrometer.
∂E
∂N υ
µ )
(1)
(
)
where E corresponds to the energy of the system and N to the
number of atoms considering a constant volume (υ). The
corresponding changes in the electronegativity µ ) µ(N,υ) are
related directly to the reactivity features and conditions. In that
way, Pearson theory allows for a numerical relation of the
chemical selectivity with the calculation of the frontier orbital
eigenvalues as
ꢀLUMO - ꢀHOMO
Coordination Analysis between Sm Nanoparticles and
DTPA-bis-biotin Molecules. This report shows the real pos-
sibility of obtaining Sm nanoparticles with a small quantity of
η )
(2)
2
which is directly related to the observed selectivity.25

8810 J. Phys. Chem. B, Vol. 109, No. 18, 2005
Ascencio et al.
Figure 5. Theoretical analysis of (a) 2, (b) 4, (c) 13, and (d) 55 Sm atoms. In each case, the distribution and sites of the electrostatic potential (EP)
and the corresponding electrophilic (f (-)) and nucleophilic (f (+)) fields are provided.
To study the chemical selectivity and the corresponding
options to coordinate the Sm clusters with the peptides, the
electronic effects of the size of the nanoparticles in the
electrostatic potential and Fukui fields are shown in Figure 5.
These parameters are displayed for the structures formed for
the two-atom interaction (Figure 5a), where the electrostatic
potential (EP) distribution shows a well-defined polarization
around both atoms, while the electrophilic (f (-)) and nucleo-
philic (f (+)) fields have no differences in their distribution
isosurfaces. This behavior is associated with the undefined
preferential zones of movement of electrons around the atoms.
In the four-atom-cluster case (Figure 5b), the atoms form a
homogeneous geometry with a tetrahedron structure with a
symmetric electrostatic potential (EP) and Fukui field isosur-
faces, which are located around all of the atoms with no
preference for any of them. So then, we need to evaluate

Synthesis and Analysis of Sm Nanoparticles
J. Phys. Chem. B, Vol. 109, No. 18, 2005 8811
Figure 6. Theoretical analysis of a DTPA-bis-biotin molecule, its (a) electrostatic potential, (b) HOMO, (c) LUMO, and (d) nucleophilic field
distributions are shown.
structures with larger shell configurations, as those formed by
fcc-like structures, which proved to be the most stable ones for
more than 13 atoms, which represents the smallest configuration
with a central atom and an external shell of 12 exposed atoms.
In Figure 5c, the electronic structure for the 13 Sm atom fcc-
like particle is shown. It is clear that electrostatic potential (EP),
electrophilic (f (-)) and nucleophilic (f (+)) distributions are
homogeneously found on the surface of the cluster; in the case
of Fukui fields, the highest intensity is located at the vertex
atoms. Basically, even when the numerical values could be
different between f (-) and f (+), the distribution zones are
similar, and no preferential atoms can be associated with
possible coordination to the peptide. The case of the Sm cluster
with 55 atoms (42 external) is shown in Figure 5d; while the
electrostatic potential is very homogeneous, the Fukui fields
show different zones for interacting with donor and acceptor
structures. It is clear that the external atoms are defined as
electrophilic sites, mainly those located in the center of the
{001} faces; similarly, the nucleophilic sites are identified inside
the cluster, so there are no exposed f (+) atoms. In fact, the
Sm nanoparticles with more than two shells show active sites,
specifically electrophilic ones, which can be coordinated to
nucleophilic sites in nearby molecules. The site of the active
atoms also implies an interaction with more than one atom for
each larger cluster. So larger Sm clusters with {001} faces will
have more active sites to fix donor molecules.
To evaluate the possibility of a real coordination of the
nanoparticles with the peptide, the corresponding analysis was
made for the DTPA-bis-biotin molecular structure.
In Figure 6, the electrostatic potential, HOMO, LUMO, and
nucleophilic sites for the peptide minimum-energy configuration
are shown. The minimum-energy structure matches the previ-
ously reported values,1 and the electrostatic potential (Figure
6a) denotes why the selective zones are related to the rings in
the extremities of the molecules, where a polarization is defined
the same as for the oxygen atoms in the middle of the molecule,
as it was identified to be coordinated to the 153Sm and 188Re
atoms.1,11 Besides, the main distributions of the HOMO and
LUMO are shown in Figures 6b and 6c, respectively, and both
are located around the rings that have sulfur atoms. Finally,
because we can recognize the preferential donor behavior of
the peptide to share electrons with the Sm, in the Figure 6d the
nucleophilic field is shown; it is clear that the molecule presents
an interesting behavior of f (+) distribution zones in the central

8812 J. Phys. Chem. B, Vol. 109, No. 18, 2005
Ascencio et al.
TABLE 1: Values of HOMO, LUMO, Gap, and Hardness
for the Minimum-Energy Configurations
Besides, an interesting magnetic effect has been observed in
the smallest nanoparticles of Sm; since the electron beam of
the electron microscope could not be fixed to acquire an image,
the magnitude of the magnetic field must be significant for future
applications in different devices that require a high magnetic
field produced by small sources.
structure
HOMO (eV) LUMO (eV) gap (eV)
η (eV)
2 Sm atoms
3 Sm atoms
4 Sm atoms
5 Sm atoms
6 Sm atoms
7 Sm atoms
9 Sm atoms
13 Sm atoms
38 Sm atoms
55 Sm atoms
DTPA
-20.176762 -3.274639 16.902123 8.4510615
-20.201333 -3.573850 16.627483 8.3137415
-3.963592 -3.396354
-4.096897 -3.423319
-4.334340 -3.468952
-4.405551 -3.545959
-4.532571 -3.793251
-3.911210 -3.544299
-3.988626 -3.712925
-4.008870 -3.879129
-4.937442 -4.843564
0.567238 0.2836193
0.673578 0.3367891
0.865388 0.4326941
0.859592 0.4297962
0.739320 0.3696601
0.366911 0.1834555
0.275701 0.1378505
0.129741 0.0648705
0.093878 0.0469392
Acknowledgment. We are indebted to L. Rendon for his
technical support in the transmission electron microscopy and
to C. Zorrilla for his help in technical activities.
References and Notes
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OH groups and the exposed rings, where we had also identified
the HOMO and LUMO distributions.
Therefore, the nanoparticles must be coordinated with the
sites that were identified in the molecule, and apart from the
identification of the possible coordinated atoms, the chemical
selectivity based on the mentioned hardness is associated with
eqs 1 and 2. The numerical value of the LUMO-HOMO gap
can be found in Table 1, where the hardness has lower values
when the size is increased up to a value close to the DTPA-
bis-biotin (DTPA) molecule.
The values allow identifying the largest configuration ana-
lyzed, which has {001} faces and more than one shell as the
optimum requirements to be used for coordination to the DTPA-
bis-biotin molecule. Even when the calculations are not accurate
enough to predict measurable data, both the behavior and the
influence of the size, especially of the second shell of atoms
that induce an extra influence of the core atoms on the exposed
ones, are clearly defined.
While the size of the nanoparticles is significantly smaller
when the synthesis is made at pH ) 4, when the particles are
obtained at conditions of pH ) 6, the size control is lower.
This is a very important parameter to be used in nanotechnology.
It is evident that the electronic structure of the clusters implies
the possibility of fixing clusters to the peptide molecule. This
can be analyzed in the identification of the active sites in Figures
4 and 5 for the Sm clusters and the corresponding sites for the
peptide, but it may also be analyzed with the help of the hardness
values reported in Table 1.
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C.; Thomas, P. J. Pure Appl. Chem. 2000, 72, 21.
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85, 2200.
4. Conclusions
The development of this kind of nanoparticle added to the
corresponding interaction study allows us to identify the
parameters for the application of these nanostructures as
nanobots in nuclear medicine. In fact, it provides the conditions
for having a sensor, a smart control to determine the region by
chemical selectivity (given by the peptide), and a well-controlled
dose or manipulation tool, which is the task of the Sm
nanoparticles in this proposed system for nuclear medicine.
We can conclude that it is possible to synthesize particles of
just a few samarium atoms by using the bioreduction method.
The pH condition is the main parameter to be considered in the
synthesis of Sm nanoparticles, because the nanoparticles can
be formed just at pH ) 4 and pH ) 6 conditions, but also the
size and electronic structure depend directly on this. The effect
of the pH conditions could be also observed in the plausible
interaction with the biomass for lower pH values, since pH )
6 produces nanoparticles with a high interaction with the
biomass and in the cases of pH ) 7 and pH ) 8 the interaction
must be so high that it makes it impossible to aggregate pure
lanthanide atoms to produce nanoparticles.
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The molecular simulation calculations showed an important
molecular chemical selectivity for fixing the cluster to the
peptide in particles with at least 55 Sm atoms.