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Intramolecular H-bonding Effects on Ion Binding by Aromatic Amides: An Ab Initio Study. Rub é n D. Parra, Ph.D DePaul University Chicago, IL. I. Introduction II. F - - amide Interactions III. Li + - amide Interactions IV. Cooperativity in Ion-Pair Binding V. Summary and Outlook

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intramolecular h bonding effects on ion binding by aromatic amides an ab initio study

Intramolecular H-bonding Effects on Ion Binding by Aromatic Amides: An Ab Initio Study

Rubén D. Parra, Ph.D

DePaul University

Chicago, IL

slide2
I. Introduction
  • II. F- - amide Interactions
  • III. Li+ - amide Interactions
  • IV. Cooperativity in Ion-Pair Binding
  • V. Summary and Outlook
  • VI. References
  • VII, Questions
  • VIII. Acknowledgments
introduction
Introduction
  • The functional group of an amide is an acyl group (RCO-) bonded to a nitrogen atom.
  • In particular, the amide RCO-NHR’ exhibits amphiphilic properties.
    • The C=O group is suitable to interact with other groups, atoms, or ions deficient in electrons.
    • The N-H group is suitable for interacting with electron-rich units.
introduction4
Introduction
  • Ion binding is the process by which a molecule, called the host, provides one or more sites to bind an ion, called the guest, by means of non-covalent interactions.
  • Multiple binding sites are usually needed because non-covalent interactions are generally weak.
introduction5
Introduction

Chelate effect

Ni2+ + 6 NH3 [Ni(NH3)6]2+

DG = -51.7 kj/mol

Ni2+ + 3 NH2CH2CH2NH2 [Ni(NH2CH2CH2NH2)3] 2+

DG = -101.1 kj/mol

introduction6
Introduction

Macrocyclic Effect

Zn2+ + A  [ZnA]2+ DG = -64.2 kJ/mol

Zn2+ + B  [ZnB]2+ DG = -87.5 kJ/mol

A B

introduction7
Introduction
  • Amide-containing ligands have proven valuable in cation and anion binding. The amide group exhibits amphiphilic properties with the carbonyl group serving as a suitable binding site for metal ions, and the N-H group serving as a binding site for anions.
  • Natural and syntethic amides are used for the transport of ions across bilayer membranes.
  • The great solubility in organic solvents usually accompanied by a diminished solubility in aqueous solution makes amides appealing for applications in the field of ion-selective electrodes and liquid-liquid separations
  • Additionally, the hydrogen bonding capabilities of amides are known to be crucial in many relevant systems including enzymes and proteins.
introduction8
Introduction

Positive Cooperativity

Host compounds containing at least two spatially separated binding sites can show cooperativity due to conformational coupling between sites.

Comparatively few cases of amphi-receptors have been reported which show binding properties to both cations and anions.

introduction9
Introduction
  • The conventional H bond is usually defined as

X-H … Y

X and Y are typically O, N, F, Cl

  • H-bonds are ubiquitous in nature. They are responsible for the unusual properties of water, are mediators of chemical reactions, provide for drug-molecule interactions in the body, and are important in the structure of DNA.
f amide interactions
F- - Amide Interactions
  • R1 = H or NHC=O
  • R2 = H or NHC=O
slide27
Binding Energies (kcal/mol)

Li+ Binding

Di-amide -109

Tri-amide -107

Tetra-amide -107

F- Binding

Di-amide -114

Tri-amide -120

Tetra-amide -127

LiF Binding

Tetra-amide -294

slide28
H22…O11

Li+ Binding

Tri-amide

1.779 Ǻ (1.789 Ǻ)

Tetra-amide

1.751Ǻ (1.773 Ǻ)

F- Binding

Tri-amide

1.721 Ǻ (1.773 Ǻ)

Tetra-amide

1.717Ǻ (1.773 Ǻ)

LiF Binding

Tetra-amide

1.696 Ǻ (1.773 Ǻ)

slide29
NBO analysis

lpO11 s*H22N

Li+ Binding

Tri-amide

30 (30 kcal/mol)

Tetra-amide

34 (29 kcal/mol)

F- Binding

Tri-amide

42 (27 kcal/mol)

Tetra-amide

42 (29 kcal/mol)

LiF Binding

Tetra-amide

48 (29 kcal/mol)

slide30
NBO Charges

Li+ Binding

Tri-amide

qO11 = -0.69 (-0.70)

qH22 = +0.50 (+0.47)

Tetra-amide

qO11 = -0.69 (-0.69)

qH22 = +0.50 (+0.47)

F- Binding

Tri-amide

qO11 = -0.76 (-0.69)

qH22 = +0.48 (+0.47)

Tetra-amide

qO11 = -0.76 (-0.69)

qH22 = +0.47 (+0.47)

LiF Binding

qO11 = -0.75 (-0.69)

qH22 = +0.50 (+0.47)

slide31
Dipole Moments (Debye)

Li+ Binding

      • Di-amide 0.9
      • Tri-amide 6.2
      • Tetra-amide 3.6

F- Binding

      • Di-amide 2.9
      • Tri-amide 4.3
      • Tetra-amide 1.1

LiF Binding

      • Tetra-amide 11.3
slide32
N-H Stretching Frequencies

Li+ Binding

Di-amide

nN-H22 = 3769 (3800 cm-1)

Tri-amide

nN-H22 = 3517 (3608 cm-1)

Tetra-amide

nN-H22 = 3487 (3608 cm-1)

F- Binding

Tri-amide

nN-H22 = 3457 (3617 cm-1)

Tetra-amide

nN-H22 = 3295 (3608 cm-1)

LiF Binding

nN-H22 = 3287 (3608 cm-1)

slide33
F- Binding

H…F

Di-amide 1.649 Ǻ

Tri-amide 1.561 Ǻ; 1.679 Ǻ

Tetra-amide 1.585 Ǻ

Li+ Binding

O…Li

Di-amide 1.771 Ǻ

Tri-amide 1.762 Ǻ; 1.780 Ǻ

Tetra-amide 1.775 Ǻ

LiF Binding

H…F 1.588 Ǻ

O…Li 1.770 Ǻ

slide34
F- Binding

NCCC (degs.)

Di-amide 7

Tri-amide 5

Tetra-amide 4

Li+ Binding

CNCC (degs.)

Di-amide 47

Tri-amide 31, 34

Tetra-amide 22

LiF Binding

NCCC 9

CNCC 24

slide35
NBO analysis: E2 (kcal/mol)

Lp F-  s* N-H, s* C-H

Di-amide 197

Tri-amide 187

Tetra-amide 193

Li+ Binding

Lp O Li+

Di-amide 45

Tri-amide 43

Tetra-amide 41

LiF Binding

Lp F-  s* N-H, s* C-H 204

Lp O Li+ 48

slide36
Symmetric Stretching frequencies

F- Binding

nN-H + nC-H

Di-amide 3304 cm-1

Tri-amide 3327 cm-1

Tetra-amide 3205 cm-1

Li+ Binding

nC=O

Di-amide 1813 cm-1

Tri-amide 1814 cm-1

Tetra-amide 1801 cm-1

LiF Binding

nN-H + nC-H 3216 cm-1

nC=O 1784 cm-1

summary
Summary
  • Anion (F-) and cation (Li+) binding through aromatic amides has been presented.
  • Ion binding results in substantial changes in the equilibrium conformation of the amide model systems.
  • Binding affinity of the anion is greater than that of the cation.
  • Intramolecular H-bonding enhances F- binding, but has negligible effect on the binding energy of Li+.
summary38
Summary
  • The presence of either ion induces significant polarization on the ligand. There is charge transfer from the anion to the ligand, and from the ligand to the metal ion.
  • Charge separation is notorious in the ion-pair binding which presents the largest dipole moment.
  • Evidence of positive cooperativity is presented, where binding of an ion at one site enhances significantly the affinity of the ligand for the other ion at the corresponding binding site.
  • Binding of one ion induces conformational changes along with polarization of the ligand, which is transmitted to the second binding site.
references
References
  • R. D. Parra, B. Yoo, M. Wemhoff,   J. Phys. Chem. A. 110, 4487 (2006).
  • Bianchi, A.; Bowman-James, K.; Garcia-Espana, E., Eds. Supramolecular Chemistry of Anions; Wiley-VCH: New York, 1997.
  • Saenger, Jeffrey G. A. Hydrogen Bonding in Biological Structures; Springer-Verlag: Berlin, 1991.
  • Kavallieratos, K.; Bertao, C. M.; Crabtree, R. H. J. Org. Chem., 1999, 64, 1675.
  • Constable, E. C. Metals and Ligand Reactivity (VCH Publishers, New York, 1996).
  • Desiraju, G. R.; Steiner, T., The Weak Hydrogen Bond In Structural Chemistry and Biology; Oxford University Press, 1999.
  • Wheeler, O. H.; Rosado, O. in The Chemistry of Amides, Interscience Publishers, 1970, p. 352.
  • Schneider, H-J; Yatsimirsky, A. Principles and Methods in Supramolecular Chemistry; Wiley, Chichester, 2000.
  • Steed, J. W.; Atwood, H. L.; Supramolecular Chemistry; Wiley, Chichester, 2000.
acknowledgments
Acknowledgments
  • Megan Ghorbanpour
  • Michael P. Wemhoff
  • Paul D. Kofoed
  • Lucia Petkovic and Idaho National Laboratory for the invitation