Quantum Mechanical Calculations on Novel Actinide Chelating Agents Aisha Mehmood, Maria Benavides, PhD Department of Natural Sciences www.uhd.edu/academic/colleges/sciences/ns/ Abstract: Plutonium is produced in significant amounts as the isotope 239Pu during nuclear reactor operations. The use of actinides such as Pu in energy and weapons production has resulted in major environmental and health concerns. In the event of actinide release it is critical to have the means to treat large number of people in a very short time. Chelation therapy is the approach currently used to treat actinide poisoning because it reduces the deposition of actinides in the internal organs. In order to effectively respond and treat actinide poisoning on a massive scale it is crucial to have access to effective, nontoxic chelating agents that can be orally administered, that are easily produced and safely stored at any location. Specific sequestering agents have been designed and synthesized to bind actinides. Our study focuses on determining the structures and molecular properties of four hydroxypyridinone (HOPO)-based sequestering agents 2,2-Dime-3LI(1,2-HOPO), 3LI-(1,2-HOPO), 4LI(1,2-HOPO) and 5LI(1,2-HOPO) which have been shown to strongly and specifically bind plutonium at physiological pH. Our calculations were carried out using density functional theory (DFT) with the B3LYP functional applied in conjunction with three increasingly larger basis sets (3-21G, 6-31G, and 6-311G) to obtain the equilibrium geometries, vibrational frequencies, and IR spectra for all four ligands. The highest occupied molecular orbital (HOMO) – lowest occupied molecular orbital (LUMO) energy gap values for all four compounds are greater than 4 eV suggesting that the ligands are chemically stable. Two hydrogen bonds are observed in each compound which we suspect contribute to their chemical stability. The four compounds exhibit dipole moments ranging between 3 to 4 Debye which indicates they possess polar character. Our computed vibrational frequencies were found in excellent agreement with the experimental frequencies, suggesting our proposed models are good representations of the actual molecular structures. Introduction: Over the past years concern for harm caused by radiation in human body has increased. Recent disaster such as Fukushima Daiichi nuclear reactor accident in Japan has raised red flags for radiation safety. Such events are not common; however once the damage has happened, it is large and capable of destroying many lives. Nuclear fissions release significant amount of several different actinides that can enter human body through radiation or radioactive substances. All actinides are radioactive and bind with human internal tissue. Chelation therapy has shown positive results for reducing internal human actinide contamination. Plutonium (Pu) is an alpha emitter that is known to have the greatest retention in the human body among actinides. Our studies focuses ...

1. Quantum Mechanical Calculations on Novel Actinide Chelating
Agents
Aisha Mehmood, Maria Benavides, PhD
Department of Natural Sciences
www.uhd.edu/academic/colleges/sciences/ns/
Abstract: Plutonium is produced in significant amounts as the
isotope 239Pu during nuclear reactor operations. The use of
actinides such as Pu in energy and weapons production has
resulted in major environmental and health concerns. In the
event of actinide release it is critical to have the means to treat
large number of people in a very short time. Chelation therapy
is the approach currently used to treat actinide poisoning
because it reduces the deposition of actinides in the internal
organs. In order to effectively respond and treat actinide
poisoning on a massive scale it is crucial to have access to
effective, nontoxic chelating agents that can be orally
administered, that are easily produced and safely stored at any
location. Specific sequestering agents have been designed and
synthesized to bind actinides. Our study focuses on determining
the structures and molecular properties of four
hydroxypyridinone (HOPO)-based sequestering agents 2,2-
Dime-3LI(1,2-HOPO), 3LI-(1,2-HOPO), 4LI(1,2-HOPO) and
5LI(1,2-HOPO) which have been shown to strongly and
specifically bind plutonium at physiological pH. Our
calculations were carried out using density functional theory
(DFT) with the B3LYP functional applied in conjunction with
three increasingly larger basis sets (3-21G, 6-31G, and 6-311G)
to obtain the equilibrium geometries, vibrational frequencies,
and IR spectra for all four ligands. The highest occupied
molecular orbital (HOMO) – lowest occupied molecular orbital

2. (LUMO) energy gap values for all four compounds are greater
than 4 eV suggesting that the ligands are chemically stable.
Two hydrogen bonds are observed in each compound which we
suspect contribute to their chemical stability. The four
compounds exhibit dipole moments ranging between 3 to 4
Debye which indicates they possess polar character. Our
computed vibrational frequencies were found in excellent
agreement with the experimental frequencies, suggesting our
proposed models are good representations of the actual
molecular structures.
Introduction: Over the past years concern for harm caused by
radiation in human body has increased. Recent disaster such as
Fukushima Daiichi nuclear reactor accident in Japan has raised
red flags for radiation safety. Such events are not common;
however once the damage has happened, it is large and capable
of destroying many lives. Nuclear fissions release significant
amount of several different actinides that can enter human body
through radiation or radioactive substances. All actinides are
radioactive and bind with human internal tissue. Chelation
therapy has shown positive results for reducing internal human
actinide contamination. Plutonium (Pu) is an alpha emitter that
is known to have the greatest retention in the human body
among actinides. Our studies focuses on four actinide
sequestering agent, namely, 2,2-Dime-3 linkage(1-hydroxy-2-
pyridinone), 3 linkage(1-hydroxy-2-pyridinone), 4 linkage(1-
hydroxy-2-pyridinone) and 5 linkage(1-hydroxy-2-pyridinone)
shown to bind Pu [1].The main objective of our studies is to
predict their structures as well as other molecular properties so
that we gain an understanding of their chemical nature.
Method: The chelating agent ligands were modeled using
GaussView[4]. The calculations consisted first of a geometry
optimization routine that yielded a molecular structure. This
calculation was then followed by a frequency calculation that

3. yielded harmonic frequencies that produced the corresponding
IR spectrum. The frequency calculation serves as well to
confirm that the optimized structure corresponds to the
equilibrium geometry, which in turn corresponds to the most
stable structure. If no imaginary frequencies are generated
during the frequency calculation indicating that the optimized
geometry is truly the equilibrium geometry. All calculations
were performed using density functional theory (DFT) in
combination with the B3LYP hybrid functional. Three sets of
basis sets (3-21G, 6-31G, and 6-311G ) were used for each
compound in order to assess the effect of the basis set size. All
calculations were performed using the Gaussian 09 codes [3].
Results and Discussion:
Geometries:
2,2-Dime-3LI(1,2-HOPO), 3LI-(1,2-HOPO), 4LI(1,2-HOPO)
Good structures and dipole moments were obtained for 2,2-
Dime-3LI(1,2-HOPO), 3LI-(1,2-HOPO), 4LI(1,2-HOPO). DFT
calculations predicted that 2,2-Dime-3LI(1,2-HOPO). The
computed equilibrium geometries have suitable orientation for
actinide sequestering (see figures 1 - 3).
5LI(1,2-HOPO)
The optimized structure for 5LI(1,2-HOPO) was surprisingly
rotated invertible (figure 4), which means that the most stable
structure is in the trans configuration with respect to the other
three compounds. This behavior was only observed in the case
of the 5 linkage, this may be due its longer chain of carbon
connecting the two hydroxypyridinone groups as compare to the
chain lengths of the other compounds.
B. Vibrational analysis:
An amide and carbonyl group stretch at 1650 cm-1 was reported
by David, et al, for the 1,2-HOPO molecule[6]. Under the 6-
311G basis sets, all four sequestering agents 2,2-Dime-3LI(1,2-

4. HOPO), 3LI-(1,2-HOPO), 4LI(1,2-HOPO) and 5LI(1,2-HOPO)
have an amide stretch ranging in values between 1665 and 1658
cm-1 . The ratio of the theoretical and experimental frequency
is near unity and our calculated values agree with the
experimental values within 1.0%
C. HOMO-LUMO energy gaps
HOMO-LUMO energy gaps are excellent indicators of chemical
stability [5]. HOMO-LUMO energy gaps calculated with 6-
321G, 6-331 and 6-311G basis sets are greater than 3 eV for all
four compounds, indicating these molecules possess high
chemical stability.
D. Hydrogen Bonding
Multiple hydrogen bonding is observed in the cases of 2,2-
Dime-3LI(1,2-HOPO), 3LI-(1,2-HOPO), and 4LI(1,2-HOPO)
molecules. The hydrogen bonding appears between the hydrogen
located in two hydroxyl groups on each ring and the oxygen
atoms bonded to the nitrogen atoms.
Due to the trans configuration of the 5LI(1,2-HOPO) compound,
no hydrogen bonding is observed in this molecule.
The dipole moment is also lower as there is less interaction
between the tetradentate HOPOs.
E. Dipole moments
All four compounds exhibit large values of dipole moments,
ranging from 3 to 6 eV. This suggests all four compounds are
highly polar in nature. This is consistent with the presence of
various electronegative atoms such as O and N atoms and the
fact that these compounds are not symmetrical. Interestingly,
the 5LI(1,2-HOPO) compound has the lowest dipole moment
value among the four compounds which may be due to the lack
of interaction between the tetradentate HOPOs.
Conclusion: The calculated dipole moment, large HOMO-
LUMO gaps, and hydrogen bonding all indicate that these
ligands are highly chemically stable. The results indicate that
these molecules possess the necessary chemical properties,
molecular geometry and spatial orientation for effective actinide

5. binding.
Future Work: In order to broaden the scope this work, it would
be of interest to conduct similar studies on Me-3,2-HOPO
molecules.
Acknowledgements: We would like to thank the Nuclear
Regulatory Commission for their generous support of this
research (U.S. Nuclear Regulatory Commission (SDB-27-10-
1121)).
References:
[1] Gorden, A. E., Xu, J., Raymond, K. N., & Durbin, P. (2003).
Rational Design of Sequestering Agents for Plutonium and
Other Actinides. Chemical Reviews, 103(11), 4207-4282.
[2] Durbin, P. W., Kullgren, B., Ebbe, S. N., Xu, J., &
Raymond, K. N. (2000). Chelating Agents for Uranium(VI): 2,
Efficacy and Toxicity of Tetradentate Catecholate and
Hydroxypyridinonate Ligands in Mice. Health Physics, 78(5),
511-521.
[3] Frisch, M. E., et al. (2009). Gaussian 09, Revision A.01.
Wallingford, CT: Gaussian, Inc.
[4] Frisch, A. E., Dennington, R. D., Keith, T. A., Neilsen, A.
B. and Holder, A. J. (2003) GaussView, revision 3.0.9,
Gaussian, Inc., Pittsburgh PA
[5] Aihara, J. (1999) Reduced HOMO-LUMO gaps as index of
kinetic stability for polycyclic aromatic hydrocarbons. J. Phys.
Chem. A. 103, 7487-7496
[6] David L. White., et al. (1986). Specific Sequestering Agents
for the Actinides. J Med. Chem. A. 31, 12-14
Figure 1: 2,2-Dime-3LI(1,2-HOPO)
Figure 2: 3LI-(1,2-HOPO),
Figure 4: 5LI(1,2-HOPO)

6. Figure 5: IR spectrum for 2,2-Dime-3LI(1,2-HOPO)
Figure 6: IR spectrum for 5-LI(1,2-HOPO).
Figure 7: IR spectrum for 4LI(1,2-HOPO).
Table 1: Calculated dipole moment of all chelating agent
Table 2: HOMO-LUMO Energy Gap
Figure 3: 4LI(1,2-HOPO)
Table 3: Frequency data comparison for the Amide and ring
Carbonyl group using 6-311G basis set
Figure 6: IR spectrum for 3-LI(1,2-HOPO).Basis
SetHydoxypyridinone Chelating Agent Dipole Moment2,2-
Dime-3LI(1,2-HOPO)3LI-(1,2-HOPO)4LI(1,2-HOPO)5LI(1,2-
HOPO)6-21G 4.02624.81392.12991.55926-
31G4.81394.95663.09822.68786-
311G6.99375.18123.25782.7187Basis SetHydoxypyridinone
Chelating Agent HOMO-LUMO Energy Gap2,2-Dime-3LI(1,2-
HOPO)3LI-(1,2-HOPO)4LI(1,2-HOPO)5LI(1,2-HOPO)3-
21G4.3794.3403.4264.3676-31G4.3354.1664.4736-
311G4.4774.2884.1674.489Basis SetHydoxypyridinone
Chelating Agent Frequency Calculations for the Amide and
Ring Carbonyl Group2,2-Dime-3LI(1,2-HOPO)3LI-(1,2-
HOPO)4LI(1,2-HOPO)5LI(1,2-HOPO)Experimental Frequency
1650165016501650Computational Frequency
166516351658Ratio Near Unity1.000.991.00
*

7. 84 5-LIO (Me-3, 2-HOPO) ^337
51 5-LICAM(S) ^157
30 5-LICAM(S) ^157
Sandra C. Balanga, Maria Benavides, PhD
Department of Natural Sciences
www.uhd.edu/academic/colleges/Sciences/ns
Abstract : This study focuses on determining the structures and
molecular properties of three compounds currently used as
ligands in the preparation of magnetic resonance imaging (MRI)
contrast agents (DTPA-N-MA, DTPA-N’-MA, and DTPA-
cs124). Calculations were performed using density functional
theory (DFT) with B3LYP functional applied in combination
with a basis set of (3-21G and 6-311G to obtain equilibrium
geometries, vibration frequencies, and IR spectra for the
chelates. The highest occupied molecular orbital (HOMO) –
lowest occupied molecular orbital (LUMO) energy gap values
for the three compounds range between 3.5 to 4.5 eV,
suggesting that the ligands are chemically stable. The
compounds exhibit dipole moments ranging between 4.5 to 7.8
Debye indicating they possess polar character.
Introduction
Over the past years MRI exams including the use of contrast
agents has considerably increased. MRI has important clinical
applications, and its successful use in radiology practice and
medical diagnostics has revolutionized medicine as a whole.

8. Gadolinium(III) ion is an element of choice in MRI due to its
very unique magnetic properties. Gadolinium(III) ion is known
to be a potential toxic metal ion, but when appropriate ligands
are attached to it, they stay chelated in the body and are
excreted intact1. Thus active investigations in the chemical
structure and stability of complex agents have to be thoroughly
study. Previous studies have shown that DTPA form strong
complexes with gadolinium for the period that the complex
agent is in the body1. The main focus of our study is to use
computational process to predict the structures as well as the
molecular properties of three potential gadolinium chelating
agents (DTPA-N-MA, DTPA-N’-MA, DTPA-cs124), used in the
preparation of MRI contrast agents.
Methods
The three compounds were modeled using GaussView 5.02.
First, geometry optimization calculations were performed to
obtain an optimized and most stable molecular structure along
with the dipole moment values of the compounds. The
optimized structures were then used to run frequency
calculations to obtain harmonic frequencies with corresponding
IR spectra. The frequency calculation serves as well to confirm
that the optimized structure corresponds to the equilibrium
geometry, which in turn corresponds to the most stable
structure. The optimized geometries are considered as true
equilibrium geometries of the compounds only when no
imaginary frequencies are generated during the frequency
calculation. All calculations were performed using Gaussian 09
codes3 along with density functional theory (DFT) in
combination with the B3LYP hybrid functional. Two basis sets
(3-21G, and 6-311G ) were used to run optimization and
frequency calculations for each compound.
Results and DiscussionGeometries
The computed equilibrium geometries of DTPA-N-MA, DTPA-
N’-MA, and DTPA-cs124 correspond to structures that have
suitable orientations for binding to Gadolinium (III) (figures 1-
3).

9. B. Vibrational analysis
According to a study conducted by Darras, et al4, bands in the
IR spectrum of DTPA corresponding to the C=O bending and
stretching of CO2H are observed at 1730 and 1696 cm-1, and
the bending of the OH group in CO2H is observed at about
1100cm-1. Under the 6-311G basis set, the computational
frequency values corresponding to the C=O bending/stretching
for the three ligands ranged between 1700 to 1705 cm-1 and
1716 to 1721 cm-1, and the experimental values were 1696 cm-
1 and 1730 cm-1, respectively (Table 3). The computational
frequencies corresponding to the vibration motion of OH in
CO2H for the three compounds ranged in values between 1100.1
and 1110.4 cm-1.The ratio of the computational and
experimental frequency of the ligands is near unity, indicating
that our proposed models are good representations of the actual

10. molecular structures.
C. HOMO-LUMO energy gaps
HOMO-LUMO energy gaps are excellent indicators of chemical
stability; a value greater than 1 eV suggests a compound is
chemically stable5. HOMO-LUMO energy gaps resulting from
calculations using 6-311G basis sets ranged between 3.5 to 4.5
eV, for all three compounds, indicating these molecules possess
high chemical stability.
D. Hydrogen Bonding
Multiple hydrogen bonding are observed for DTPA-N-MA,
DTPA-N’-MA, and DTPA-cs124 molecules. The hydrogen
bonding appears mostly between the hydrogen attached to the
nitrogen and the oxygen atoms of the carbonyl group. Hydrogen
bonding between hydrogen attached to carbon atoms and the
oxygen atoms of the carbonyl group is also observed.
E. Dipole moments
All three compounds exhibit large dipole moment values,
ranging from 4.5 to 7.8 eV. This suggests all three compounds
are highly polar in nature. This is consistent with the presence
of various electronegative atoms such as O and N atoms and the
fact that these compounds are not symmetrical. Interestingly,
the DTPA-cs124 compound has the lowest dipole moment value
among the three compounds which may be due to the presence
of benzene rings and increased molecular weight.
Conclusion
The presence of multiple hydrogen bonding and large HOMO-
LUMO energy gaps indicate that these ligands are highly
chemically stable. The results indicate that these molecules
possess the necessary chemical properties and molecular
geometry to be used as chelating agents in the productions of
MRI contrast agents.

11. Future Work: In order to broaden the scope of this work, it
would be of great interest to study other ligands.
Acknowledgements: Special thanks to the Welch Foundation
(grant no. BJ-0027)27). Thanks to my research advisor Dr.
Maria Benavides for her valuable advices and endless support
throughout this enriching research experience.
References:Caravan, P., Ellison, J. J., McMurry, T. J., &
Randall, B. L. (1999). Gadolinium(III) Chelates as MRI
Contrast Agents: Structure, Dynamics, and Applications.
Chemical Reviews, 99, 2293-2352.Dennington, R., Keith, T.,
A., Millam, J. (2009). GaussView Version 5. Semichem, Inc.,
Shawnee Mission KS.Frisch, M. E., et al. (2009). Gaussian 09,
Revision A.01. Wallingford, CT: Gaussian, Inc.Darras, V.,
Nelea, M., Winnik, F. M., & Buschmann, M. D. (2010).
Chitosan Modified with Gadolinium
Diethylenetriaminepentaacetic Acid for Magnetic Resonance
Imaging of DNA/Chitosan Nanoparticles. Carbohydrate
Polymers, 80, 1137-1146.Aihara, J. (1999) Reduced HOMO-
LUMO gaps as index of kinetic stability for polycyclic aromatic
hydrocarbons. J. Phys. Chem. A. 103, 7487-7496.
Figure 1: DTPA-N-MA
Figure 2: DTPA-N’-MA
Figure 3: DTPA-cs124
Table 1: Calculated dipole moment of all chelating agent
Table 2: HOMO-LUMO Energy Gap
Table 3: Frequency data comparison for the carboxylic acid and
hydroxyl group using 6-311G basis set
Figure 4: IR spectrum for DTPA-N-MA
Figure 5: IR spectrum for DTPA-N’-MA
Figure 6: IR spectrum for DTPA-cs124Basis SetChelating Agent
Dipole Moment (Debye)DTPA-N-MADTPA-N’-MADTPA-
cs1243-21G 5.01086.38134.5616-
311G4.53487.83754.5022Basis SetChelating Agent HOMO-
LUMO Energy Gap (eV) DTPA-N-MADTPA-N’-MADTPA-
cs1243-21G5.1135.0233.4766-
311G4.5114.3443.568CompoundComputational Frequency (cm-

12. 1 )Experimental Frequency (cm-1)Ratio Near UnityDTPA-N-
MABending/Stretching COOH1703.516961.001719.217301.00
Bending OH group1107.511000.99DTPA-N’-MA
Bending/Stretching COOH1700.316961.001716.417300.99
Bending OH group1100.111000.99DTPA-cs124
Bending/Stretching COOH1705.916961.001721.917300.99
Bending OH group1110.411000.99

13. *
30 graph 1
51 graph 2
84 graph 3
Abstract :
Plutonium is produced in significant amounts as the isotope
239Pu during nuclear reactor operations. The use of actinides
such as Pu in energy and weapons production has resulted in
major environmental and health concerns. In the event of
actinide release it is critical to have the means to treat large
number of people in a very short time. Chelation therapy is the
approach currently used to treat actinide poisoning because it
reduces the deposition of actinides in the internal organs. In

14. order to effectively respond and treat actinide poisoning on a
massive scale it is crucial to have access to effective, nontoxic
chelating agents that can be orally administered, that are easily
produced and safely stored at any location. Specific
sequestering agents have been designed and synthesized to bind
actinides. This study focuses on determining the structures and
molecular properties of three compounds currently used as
ligands in the preparation of magnetic resonance imaging (MRI)
contrast agents (5-LICAM(S)^157, 5-LICAM(C)^157, and
5LIO(Me-3,2-HOPO^337). Calculations were performed using
density functional theory (DFT) with B3LYP functional applied
in combination with two basis sets (3-21G and 6-311G) to
obtain equilibrium geometries, vibration frequencies, and IR
spectra for the chelates. The highest occupied molecular orbital
(HOMO) – lowest occupied molecular orbital (LUMO) energy
gap values for the three compounds range between 4.01 to 5.05
eV, suggesting that the ligands are chemically stable. The
compounds exhibit dipole moments ranging between 4.5 to 7.6
Debye indicating they possess polar character.
Methods used:
The three compounds were modeled using GaussView 5.02.
First, geometry optimization calculations were performed to
obtain an optimized and most stable molecular structure along
with the dipole moment values of the compounds. The
optimized structures were then used to run frequency
calculations to obtain harmonic frequencies with corresponding
IR spectra. The frequency calculation serves as well to confirm
that the optimized structure corresponds to the equilibrium
geometry, which in turn corresponds to the most stable
structure. The optimized geometries are considered as true
equilibrium geometries of the compounds only when no
imaginary frequencies are generated during the frequency
calculation. All calculations were performed using Gaussian 09
codes3 along with density functional theory (DFT) in
combination with the B3LYP hybrid

15. From the HOMO-LUMO energy gaps the relative chemical
stability of each of the contrast agents could be determined. The
HOMO-LUMO energy gaps were calculated using both basis
sets. For the 3-21G basis set, 5-LICAM(S)^157, 5-
LICAM(C)^157, and 5LIO(Me-3,2-HOPO^337 have HOMO-
LUMO energy gaps of 5.774 eV, 1111 eV, and 5.281 eV. Using
the 6-311G basis set, the HOMO-LUMO gaps were calculated to
be 5.498 eV, 1111 eV, and 5.015 eV, respectively. With such
large values it can be noted that these compounds are
exceptionally stable.
Hydrogen Bonding
There are multiple hydrogen bonds observed in the cases
5-LICAM(S)^157, 5-LICAM(C)^157, and 5LIO(Me-3,2-
HOPO^337 molecules. The hydrogen bonding appears between
the hydrogen in the three hydroxyl group substituents in each
molecule. There’s also hydrogen bonding resulting from the two
carbonyl groups in each molecule. The presence of hydrogen
bonding is known to increase chemical stability. Because of the
numerous hydrogen bonds, this aids in high stability of these
compounds as shown by the HOMO-LUMO energy gaps.
Dipole Moments
Each compound has a large magnitude value for the dipole
moments. For each compound the dipole moment for each basis
set was calculated. For the 3-21G basis set 5-LICAM(S)^157, 5-
LICAM(C)^157, and 5LIO(Me-3,2-HOPO^337 have dipole
moments of (____ Debye), ____ Debye, and ____Debye. Using
the 6-311G basis set, the dipole moments were determined to be
____Debye, ____ Debye, and _____ Debye, respectively. From

16. these values, it can be noted that each molecule is polar. This
can be shown by the presence of highly electronegative atoms
oxygen and nitrogen.
For 5-LICAM(S)^157, the HOMO-LUMO energy gaps for
both basis sets were averaged at approximately 4.01 eV. For 5-
LICAM(C)^157, these gaps averaged 5.6 eV. In the largest
compound 5LIO(Me-3,2-HOPO^337, the energy gaps were
averaged at about 4.5 eV. These values suggested that all three
compounds were significantly stable. From the trend in the
dipole moments it can be noted that the dipole moment
decreased as a result of hydrogen bonding as the size of the
molecules were increased.
Conclusion
The various calculations in the two basis sets provided a
variety of information about each compound. From the
calculations, it was determined that the equilibrium for each
compound had been determined. The geometries were found in
good agreement with the reported IR spectra. This confirms that
our proposed models are good representations of the structures
for these compounds. (please add more)
Acknowledgements:
I would like to thank Dr. Maria Benavides for the opportunity to
participate and her support throughout this research. I would
also like to acknowledge University of Houston-Downtown for
the opportunity to work in the laboratory and use the
university’s resources in order to achieve my goals.
References
[1] Darras, V., Nelea, M., Winnik, F., & Buschmann, M. (2010).
Chitosan Modified with Gadolinium
Diethylenetriaminepentaacetic Acid for Magnetic Resonance
Imaging of DNA/Chitosan Nanoparticles. Carbohydrate
Polymers, 80, 1137-1146.
[2] Dennington, R., Keith, T., A., Millam, J. (2009). GaussView
Version 5. Semichem, Inc., Shawnee Mission KS.

17. [3]Caravan, P., Ellison, J., Lauffer, R., McMurry, T. (1999).
Gadolinium (III) Chelates as MRI Contrast Agents: Structure,
Dynamics, and Applications. Chemical Reviews, 99, 2293-
2352.
[4] Frisch, M. E., et al. (2009). Gaussian 09, Revision A.01.
Wallingford, CT: Gaussian, Inc.