idaho seminar

8/8/2019 Idaho Seminar

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Intramolecular H-bonding Effects

on Ion Binding by AromaticAmides: An Ab Initio StudyRubn D. Parra, Ph.D

DePaul UniversityChicago, IL


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I. IntroductionII. F- - amide InteractionsIII. Li+- amide Interactions

IV. Cooperativity in Ion-Pair BindingV. Summary and OutlookVI. ReferencesVII, QuestionsVIII. Acknowledgments


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Introduction

The functional group of an amide is anacyl group (RCO-) bonded to a nitrogenatom.In particular, the amide RCO-NHRexhibits amphiphilic properties. T he C=O group is suitable to interact with

other groups, atoms, or ions deficient inelectrons. T he N-H group is suitable for interacting with

electron-rich units.


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Introduction

Ion binding is the process by which amolecule, 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 neededbecause non-covalent interactions aregenerally weak.


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IntroductionCh elate effect

Ni2+

+ 6 NH3 [Ni(NH3)6]2+

( G = -51.7 kj/mol

Ni2+ + 3 NH2CH

2CH

2NH

2[Ni(NH2CH2CH2NH2)3]2+( G = -101.1 kj/mol


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Introduction

M acrocyclic EffectZn2+ + A [ZnA]2+ ( G = -64.2 kJ/mol

Zn2+ + B [ZnB]2+ ( G = -87.5 kJ/mol A B


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Introduction

Amide-containing ligands have proven valuable in catioand anion binding.T he amide group exhibits amphiphilicproperties with the carbonyl group serving as a suitablebinding site for metal ions, and the N-H group serving a

a binding site for anions.Natural and syntethic amides are used for the transportof ions across bilayer membranes.

The great solubility in organic solvents usuallyaccompanied by a diminished solubility in aqueoussolution makes amides appealing for applications in thefield of ion-selective electrodes and liquid-liquidseparations Additionally, the hydrogen bonding capabilities of amidare known to be crucial in many relevant systemsincluding enzymes and proteins.


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Introduction

P ositive C ooperativityHost compounds containing at least two spatiall

separated binding sites can show cooperativitydue to conformational coupling between sites.Comparatively few cases of amphi-receptorshave been reported which show binding

properties to both cations and anions.


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Introduction

The conventional H bond is usually defined asX-H Y

X and Y are typically O, N, F, ClH-bonds are ubiquitous in nature.T hey areresponsible for the unusual properties of water,are mediators of chemical reactions, provide fordrug-molecule interactions in the body, and areimportant in the structure of DNA.


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F- - Amide InteractionsR1 = H or NHC=OR2 = H or NHC=O

N N

O O

H H

R2R1

X-


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F--Binding Amides

DA tA T A


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Li+-Binding Amides

DA tA T A


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DA


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DA


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DA_F


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DA_F


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tA_F


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T A_F


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DA


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DA


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DA_Li


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tA_Li


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T A


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T A_Li


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T A_Li


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T A_LiF


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Binding Energies (kcal/mol)

Li+

BindingDi-amide -109 Tri-amide -107 Tetra-amide -107

F-BindingDi-amide -114

Tri-amide -120 Tetra-amide -127

LiF Binding Tetra-amide -294

C

C

H


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H22O 11

Li+

Binding Tri-amide1.779 (1.789 )

Tetra-amide1.751 (1.773 )

F- Binding Tri-amide

1.721 (1.773 ) Tetra-amide

1.717 (1.773 )LiF Binding

Tetra-amide1.696 (1.773 )

C

O

H H

C

O11

HH

H

H22

OH

H

O

H


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N BO analysis

lpO11W

*H22NLi+ 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)

C

N

H H

C

N

HH

H

NH22

H

NH

H


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N BO Ch argesLi+ Binding

Tri-amideqO11 = -0.69 (-0.70)qH22= +0.50 (+0.47)

Tetra-amideqO11 = -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)

C

O

N

H H

C

O11

N

HH

H

NH

22

C

OH

NH

C

OH


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D ipole M oments ( D ebye)Li+ BindingDi-amide 0.9

Tri-amide 6.2 Tetra-amide 3.6

F- BindingDi-amide 2.9

Tri-amide 4.3 Tetra-amide 1.1

LiF Binding Tetra-amide 11.3

C

O

N

H H

C

O

N

HH

H

N

C

OH

NH

C

OH

H


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N -H Stretc h ing FrequenciesLi+ Binding

Di-amideRN-H22 = 3769 (3800 cm-1)

Tri-amideRN-H22 = 3517 (3608 cm-1)

Tetra-amideRN-H22 = 3487 (3608 cm-1)

F-Binding Tri-amide

RN-H22 = 3457 (3617 cm-1) Tetra-amide

RN-H22 = 3295 (3608 cm-1)LiF Binding

RN-H22 = 3287 (3608 cm-1)

C

O

N

H H

C

O 11

N

HH

H

NH22

C

OH

NH

C

OH


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F- BindingHF Di-amide 1.649

Tri-amide 1.561 ; 1.679 Tetra-amide 1.585

Li+ BindingOLiDi-amide 1.771

Tri-amide 1.762 ; 1.780 Tetra-amide 1.775

LiF BindingHF 1.588 OLi 1.770

C

O

N

H H

C

O

N

HH

H

N

C

OH

NH

C

OH

H


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F- BindingNCCC (degs.)

Di-amide 7 Tri-amide 5 Tetra-amide 4

Li+

BindingCNCC (degs.)Di-amide 47

Tri-amide 31, 34 Tetra-amide 22

LiF BindingNCCC 9CNCC 24

C

O

N

H H

C

O

N

HH

H

N

C

OH

NH

C

OH

H


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NBO analysis: E2 (kcal/mol)Lp F- W* N-H,W* C-H


Li+ BindingLp O Li+


LiF BindingLp F- W* N-H,W* C-H 204Lp O Li+ 48

C

O

N

H H

C

O

N

HH

H

N

C

OH

NH

C

OH

H


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Symmetric Stretching frequenciesF- Binding

RN-H +RC-HDi-amide 3304 cm-1

Tri-amide 3327 cm-1 Tetra-amide 3205 cm-1

Li+ BindingRC=O

Di-amide 1813 cm-1 Tri-amide 1814 cm-1 Tetra-amide 1801 cm-1

LiF BindingRN-H +RC-H 3216 cm-1RC=O 1784 cm-1

C

O

N

H H

C

O

N

HH

H

N

C

OH

NH

C

OH

H


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Summary

Anion (F-) and cation (Li+) binding througharomatic amides has been presented.Ion binding results in substantial changes in the

equilibrium conformation of the amide modelsystems.Binding affinity of the anion is greater than thatof the cation.

Intramolecular H-bonding enhances F-binding,but has negligible effect on the binding energy o

Li+.


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Summary The presence of either ion induces significant

polarization on the ligand.T here is charge transfer fromthe anion to the ligand, and from the ligand to the metalion.

Charge separation is notorious in the ion-pair bindingwhich presents the largest dipole moment.Evidence of positive cooperativity is presented, wherebinding of an ion at one site enhances significantly theaffinity of the ligand for the other ion at thecorresponding binding site.Binding of one ion induces conformational changesalong with polarization of the ligand, which is transmittto the second binding site.


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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, JeffreyG. 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.M etals and Ligand Reactivity (VCH Publishers, NewYork, 1996).Desiraju,G. R.; Steiner,T ., The Weak Hydrogen Bond In Structural Chemistry and Biology ; Oxford University Press, 1999.Wheeler, O. H.; Rosado, O. inThe Chemistry of Amides , IntersciencePublishers, 1970, p. 352.Schneider, H-J; Yatsimirsky, A.Principles and Methods inSupramolecular Chemistry ; Wiley, Chichester, 2000.Steed, J. W.; Atwood, H. L.;Supramolecular Chemistry ; Wiley,Chichester, 2000.


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Acknowledgments

Megan Ghorbanpour Michael P. Wemhoff Paul D. KofoedLucia Petkovic and Idaho National Laboratoryfor the invitation

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