Transcript Ion Affinity of a Model Macrocyclic tetraamide: an Ab

Ion Affinity of a Model Macrocyclic
Tetraamide: an Ab Initio Study
Rubén D. Parra, Ph.D
Department of Chemistry
DePaul University, Chicago
Ion Affinity of a Model Macrocyclic Tetraamide: an Ab
Initio Study
• I. Introduction
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II. Macrocyclic Tetraamides
III. Anion -Tetraamide Interactions
IV. Li+-Tetraamide Interactions
V. Cooperativity in Ion-Pair Binding
VI. Summary and Outlook
VII. References
VIII, Questions
IX. Acknowledgments
Host-Guest Complexation
• “A host-guest relationship involves a complementary
stereoelectronic arrangement of binding sites in host and
guest…The host component is defined as an organic
molecule or ion whose binding sites converge in the
complex…The guest component is any molecule or ion
whose binding sites diverge in the complex” Donald
Cram
• Multiple binding sites are needed because non-covalent
interactions are generally weak.
What is a macrocycle?
• In the context of molecular recognition or host-guest chemistry, a
macrocycle can be conveniently defined as a cyclic molecule with
convergent binding groups that are arranged to match the
functionality of the guest molecule.
• 18-Crown-6 Ether
Calixpyrroles
Chelate effect
complexes of polydentate ligands are
more stable than those containing an
equivalent number of monodentate
ligands.
Ni2+ + 6 NH3  [Ni(NH3)6]2+
DG = -51.7 kj/mol
Ni2+ + 3 NH2CH2CH2NH2  [Ni(NH2CH2CH2NH2)3] 2+
DG = -101.1 kj/mol
Macrocyclic effect
Macrocyclic effect: complexes with macrocyclic
ligands are more stable than those with
polydentate open ligands containing an equal
number of equivalent donor atoms.
Macrocyclic effect
Zn2+ + A  [ZnA]2+
Zn2+ + B  [ZnB]2+
A
DG = -64.2 kJ/mol
DG = -87.5 kJ/mol
B
Preorganization
• If a host does not undergo a significant conformational
change upon guest binding, it is said to be preorganized.
• 18-crown-6
Macrocyclic tetraamides
• Macrocyclic ligands containing four amide
(NHC=O) functionalities separated by
suitable bridging units.
B1
Amide
Amide
B4
B2
Amide
Amide
B3
Macrocyclic tetraamides
• In this work
B1 = B3 = phenyl ring
B2 = B4 = ethene group
• There are sixteen (16) possibilities to arrange the four
amide groups for a given set of bridging units, depending
on whether the amide group is attached to a bridging unit
through its amide nitrogen or carbon atom.
Macrocyclic tetraamides
studied in this work
cation binding
H
N
N
anion binding
O
H
O
N
O
O
O
O
N
N
H
N
H
O
N
H
H
H
H
N
O
Fluoride binding: Free ligand
Fluoride binding: Free ligand
Fluoride binding: Complex
Fluoride binding: Complex
Chloride binding: Complex
Chloride binding: Complex
Table 1: Anion binding energies (kcal/mol)
Complex
1 -1391.762256
2 -1391.762256
F-99.8596977
-99.8596977
Tetraamide
DE
-1291.743346 -103.30
-1291.751119 -95.21
Complex
-1752.12121
-1752.12121
Cl-460.274726
-460.274726
Tetraamide
-1291.73817
-1291.751119
1
2
1 geometry of the ligand as in the complex.
2 geometry of the ligand fully optimized.
Energies obtained at the B3LYP/6-31+G(d)//6-31G(d) level.
Total energies in Hartrees
DE
-67.97
-59.84
Table 2: Relevant structural parameters
N-H
C=O
N-C
C-H
N...N
N...N
N...N
N-H...X
N-H-C=O
C-H...X
Ligand
1.012
1.229
1.386
1.087
2.866
5.112
5.860
163
F1.029
1.233
1.375
1.084
2.955
4.875
5.701
1.840
166
176
1.931
151
Cl1.024
1.232
1.376
1.081
2.985
5.005
5.828
2.298
172
167
2.766
118
Distances in Angstroms, Angles in degrees.
Table 3: Mulliken charges and N-H symmetric
stretching modes
Ligand
-1
nN-H (cm )
charges (au)
X
C-H
N-H
F-
Cl-
3603 3388 3426
0.12
0.33
-0.49 -0.67
0.19 0.15
0.38 0.37
Lithium ion binding: Free ligand
Lithium binding: Free ligand
Lithium ion binding: Complex
Lithium ion binding: Complex
Table 2: Li+ binding energies (kcal/mol)
Complex
1 -1299.147904
2 -1299.147904
3 -1299.147904
Li+
Tetraamide
-7.28459325 -1291.679121
-7.28459325 -1291.70836
-7.28459325 -1291.735942
1 geometry of the ligand as in the complex.
2 geometry of the ligand fully optimized (saddle point).
3 geometry of the ligand fully optimized (minimum).
Energies obtained at the B3LYP/6-31+G(d)//6-31G(d) level.
Total energies in Hartrees
DE
-115.58
-97.23
-79.92
Table 4: Relevant structural parameters for Li+ binding
N-H (o)
N-H (i)
C=O (i)
C=O (o)
N-C (i)
N-C (o)
C-H
O...O
O...O
O...O
C=O...M
Ligand
1.024
1.012
1.236
1.228
1.369
1.365
1.083
4.560
6.398
4.435
C-H...M
N-H-C=O
180
Li+
1.014
1.237
1.370
1.071
2.655
3.125
4.100
2.050
121
2.486
103
179
Table 3: Mulliken charges and C=O symmetric
stretching modes
Ligand Li+ Complex
-1
nC=O (cm ) 1770
charges (au)
Li+
C-H
0.17
C=O (i)
-0.53
C=O(o)
-0.51
1743
0.39
0.27
-0.52
Ion-pair binding
NH
HN
O O
O O
H N
O
N
N
O
H
H
H
H
N H
O
N
N
O
Ion-pair binding: Free ligand
Ion-pair binding: Free ligand
Ion-pair binding: Ion-pair complex
Ion-pair binding: Li+ complex
Ion-pair binding: F- complex
Table 3: Ion-pair (Li+, F-) binding energies (kcal/mol)
Li_F
Li_noF
F_noLi
Complex
-2458.735173
-2358.621611
-2451.210135
Li+
-7.284593248
-7.284593248
F-99.8596977
-99.8596977
Energies obtained at the B3LYP/6-31+G(d)//6-31G(d) level.
Total energies in Hartrees
Tetraamide
-2351.172607
-2351.160798
-2351.183763
DE
-262.47
-110.58
-104.59
-47.30
Intramolecular H-bonding Effects
1
Intramolecular H-bonding Effects
2a
Intramolecular H-bonding Effects
2b
Intramolecular H-bonding Effects
2c
Intramolecular H-bonding Effects
3
Intramolecular H-bonding Effects
4
Table 4: H-bonding effects on F- binding energies
System DE(kcal/mol)* DE(kcal/mol)**
0
-103.30
-95.21
1
-107.61
-99.30
2a
-111.46
-104.28
2b
-111.76
-103.20
2c
-111.77
-103.31
3
-115.41
-106.66
4
-118.58
-109.69
* Geometry of ligand as in complex
** Fully optimized ligand
Table 5: Structural parameters and atomic charges for F- binding
charges (au)
F(N-)H
(N-)H total
distances (Ǻ)
N-H…F
0 HB
-0.485
0.384
0.384
0.384
0.384
1.536
1 HB
-0.485
0.390
0.381
0.383
0.386
1.540
2a HB
-0.485
0.390
0.390
0.383
0.383
1.546
2b HB
-0.484
0.388
0.388
0.385
0.385
1.546
2c HB
-0.484
0.391
0.391
0.381
0.381
1.544
3 HB
-0.484
0.387
0.389
0.391
0.382
1.549
4 HB
-0.484
0.388
0.388
0.388
0.388
1.552
1.839
1.795
1.811
1.841
1.876
1.791
1.792
1.844
1.843
1.828 1.78
1.829 1.78
1.813 1.867
1.814 1.867
1.768
1.802
1.822
1.841
1.799
1.799
1.799
1.799
Summary
• The two neutral macrocycle tetraamides studied
in this work exhibit pronounced affinity toward
cations (Li+) and anions(F-, Cl-) respectively.
• Size complementarity seems to determine
binding selectivity for the anions: Cl- anion is too
bulky to be included in the cavity, whereas the
smaller F- anion fits well.
• Conformational changes upon Li+ complexation
are far more pronounced than in F- or Clcomplexation.
Summary
• In particular, the free ligand (in the case of Li+
complexation) is stabilized by two N-H…O=C
intramolecular H-bonding interactions. Li+
complexation involves then the breaking of
these two intramolecular H-bonds.
• Intramolecular hydrogen bonds involving the
amide oxygens are shown to enhance Fbinding. A gain of about 4 kcal/mol in the
binding energy is obtained per H-bond added
in the macrocyle.
Summary
• The existence of two binding cavities, one for
anion and the other for cation binding, results
in a sizeable polarization of the ligand. This
polarization enhances cooperatively the ionpair binding of the ligand.
References
•
(1)
– (a) Lehn, J. –M. Supramolecular Chemistry; VCH: Weinheim, 1995.
– (b) Schneider, H-J; Yatsimirsky, A. Principles and Methods in
Supramolecular Chemistry; Wiley, Chichester, 2000.
– (c) Steed, J. W.; Atwood, H. L.; Supramolecular Chemistry; Wiley,
Chichester, 2000.
– (d) Dietrich, B.; Viout, P.; Lehn, J. –M.; Macrocyclic Chemistry; VCH,
Weinheim, 1993.
– (e) Bianchi, A.; Bowman-James, K.; Garcia-España, Enrique; Eds.
Supramolecular Chemistry of Anions, 1997.
•
(2) Chmielewski, M.; Szumna, A.; Jurczak, J. Tetrahedron Lett. 2004, 45,
8699
•
(3) Chmielewski, M.; Jurczak, J. Tetrahedron Lett. 2004, 45, 6007.
•
(4) Szumna, A.; Jurczak, J. Eur. J. Org. Chem.. 2001, 4031
Acknowledgments
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•
•
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Mr. Bryan Yoo
Mr. Mike Wemhoff
The Chemistry Department at DePaul University.
The Chemistry Department at Loyola for the
invitation
• Last but certainly not least, all of you who kindly
attended the presentation.