Francisco TarazonaVasquez, Perla B' Balbuena

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Ab-initio calculation of PAMAM-G0 dendrimer-ion
binding energies
Francisco Tarazona-Vasquez, Perla B.
Balbuena University of South Carolina, Department
of Chemical Engineering
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Introduction

• In the present work EDA-core PAMAM-G0 NH2
  terminated dendrimer is studied by means of
  ab-initio calculations which permit us to
  reproduce not only the IR spectra but also get
  an insight in understanding the binding of
  transition metals being studied experimentally at
  USC Nanocenter.
• Ab-initio studies also will assess results from
  future MD simulations with the same systems under
  the same conditions

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Methodology

• Gaussian98 package was used through this work.
• Optimization with Quadratic convergence was used
  to find the stationary points.
• Hartree Fock level of theory was used to compute
  binding energies.
• A 3-21g basis set was used for light atoms and
  LANL2DZ with pseudopotentials for transition
  metals.
• Wave function stability analysis was performed to
  check the nature of the minima found as well as
  frequency calculations in each case.

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G0-NH2 building procedure
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Dendrimer Conformations
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EDA IR Spectra

• n(NH2 wagging) 875-750 cm-1
• n(C-N stretching) 1050-1200 cm-1
• n(NH2 scissors) 1620 cm-1
• n(CH2 ) 2939 cm-1
• n(NH2 stretching) 3300-3400 cm-1

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Vibrational spectrum PAMAM G0-NH2

• n(NH wagging) 810 cm-1
• n(amide band II) 1534 cm-1
• n(C0) amide band I 1634 cm-1
• n(CH2 stretching) 2964 cm-1
• n(NH2 stretching) 3430 cm-1

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Vibrational spectrum PAMAM G0-OH
n(NH wagging) 730 cm-1 n(C-C-O stretching)1066
cm-1 n(C-N stretching) 1185 cm-1 n(CH2
twisting) 1270 cm-1 n(CH2 wagging) 1372 cm-1
n(amide band II) 1540 cm-1 n(C0) amide band I
1630 cm-1 n(CH2 stretching) 2872 cm-1 n(OH
stretching) 3460 cm-1

• n(NH wagging) 730 cm-1
• n(C-C-O stretching)1066 cm-1
• n(C-N stretching) 1185 cm-1
• n(CH2 twisting) 1270 cm-1
• n(CH2 wagging) 1372 cm-1

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Transition-metals ground state energies

• (1) calculated in this work
• (2) experimental data in R.V.Parish, The Metallic
  Elements, Longman, NY, 1st Ed. 1977.
• M, Mn in hartrees, (1) and (2) in kcal/mol.

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The branch-core fragment approach
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Cu2 and G0-NH2 (1 branch)

• Site amide
• Site core.
• Site amine
• prefers to bind to core site.

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Pt2 and G0-NH2 (1 branch)

• Same sites than before.
• Pt prefers to adsorb at core also.

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Binding sites in a PAMAM N-core

• Ottaviani et al. J.Phys. Chem. B. 1997, 101,
  158-166

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Fragment-ion binding energies
Energies given en kcal/mol
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• Energy binding calculations in a amide site for
  Cu(II) and Pt(II) with the whole dendrimer show
  preference for Cu(II) instead of Pt(II) (-364 and
  -352 kcal/mol respectively).

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Fragmentmetal binding energies
Energies given en kcal/mol
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Conclusions

• The transition-metal ions bound to dendrimer
  sites according to the trend Au(III) gt
  Pt(II)Cu(II) gt Ag(I)
• The uncharged metal atoms do not follow a well
  defined trend as observed in ions
• Core sites are the most probable sites of
  sorption/complexation but also the terminal
  groups, which in higher generation dendrimers
  could lead to high sorption in the amine terminal
  groups.

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Ongoing Research

• Determination of C6 parameters to describe van
  der Waals nonbonded interactions in MD
• Calculations at HF/3-21g level of theory in a two
  branch-core approach.

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Cu(II) and G0-NH2 (two branch approach)

• Left Cu-O 1.9 A Cu-N(core) 4.2 A
• Right Cu-O 2.2 A Cu-N(core) 2.2 A (Most
  stable)
• DE 1.6 kcal/mole

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Further Research

• MD simulations for PAMAM G0, G1, and G2
  dendrimers solvent effects and dendrimer-metal
  cluster interactions

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Acknowledgments

• Financial support from the National Science
  Foundation
• Computational time from NERSC, NCSA and ARL