SURVEYING THE HYDROGEN BONDING LANDSCAPE OF AN ACHIRAL, α-AMINO ACID: CONFORMATION SPECIFIC IR AND...
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SURVEYING THE HYDROGEN BONDING LANDSCAPE OF AN ACHIRAL, α-AMINO ACID: CONFORMATION SPECIFIC IR AND UV SPECTROSCOPY OF 2-AMINOISOBUTYRIC ACID TD02 Joseph R. Gord, Daniel M. Hewett, Matthew A. Kubasik, and Timothy S. Zwier
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The Big Picture
Transcript of SURVEYING THE HYDROGEN BONDING LANDSCAPE OF AN ACHIRAL, α-AMINO ACID: CONFORMATION SPECIFIC IR AND...
SURVEYING THE HYDROGEN BONDING LANDSCAPE OF AN ACHIRAL, α-AMINO ACID: CONFORMATION SPECIFIC IR AND
UV SPECTROSCOPY OF 2-AMINOISOBUTYRIC ACID
TD02
Joseph R. Gord, Daniel M. Hewett, Matthew A. Kubasik, and Timothy S. Zwier
Introduction• a-aminoisobutyric Acid
(Aib)n forms 310 helices– (i → i+3)– 3 residues/turn
• f and y angles are typically -60º and -30º, respectively
• How does the choice for capping agent influence structure?
• How does length influence structure?
O NH
O
OH
O
φ ψ
(n)
Timothy Zeko; Steven F. Hannigan; Timothy Jacisin; Matthew J. Guberman-Pfeffer; Eric R. Falcone; Melissa J. Guildford; Christopher Szabo; Kathryn E. Cole; Jessica Placido; Erin Daly; Matthew A. Kubasik; J. Phys. Chem. B 2014, 118, 58-68.DOI: 10.1021/jp408818gCopyright © 2013 American Chemical Society
The Big Picture
O NH
O
HN
O
OH
O
O NH
O
OH
O
O NH
O
HN
O
NH
O
HN
OH
O
O
O NH
O
HN
O
NH
O
HN
NH
O
O
HN
O
OH
O
R O
O
R O
O
Methods
s0
sn
Ion
R2PI IR-UV HB
s0
sn
Ion
200 ns
s0
sn
Ion
RIDIRS
200 ns
S0
A
A
A
A
B
BB
B
C
C
C
C
A BC
A
B
C
A BC
CA B
Z-Aib-OH (Major)
Molecule Relative Energy (kJ/mol)
1 3.512 4.47
C5, g+ 0.004 3.525 8.817 6.00
C5, anti 2.80Z-Aib-OH C5, g+ Z-Aib-OH C5, anti
A
B
A = 37602 cm-1
B = 37576 cm-1
*
*
Z-Aib-OH C5, g+
Z-Aib-OH C5, anti
C5
C5
Free
OH
Possible Assignments (Minor)
Molecule Relative Energy (kJ/mol)
1 3.512 4.47
C5, g+ 0.004 3.52
C5*, 8.817 6.00
C5, anti 2.80
OH-1
OH-2
Conf A
OH-4
Z-Aib-OH C5
OH-7
(Conf A) OH-2
OH-1
OH-4OH-7 Z-Aib-OH C5
Z-Aib-OH vs Z-Gly-OH
Published in: Jacob C. Dean; Evan G. Buchanan; Timothy S. Zwier; J. Am. Chem. Soc. 2012, 134, 17186-17201.DOI: 10.1021/ja306652cCopyright © 2012 American Chemical Society
A
B
Z-Aib-OH C5, g+ [0.0 kJ/mol]
A = 37602 cm-1
B = 37576 cm-1
A = 37601 cm-1
B = 37598 cm-1
Z-Aib-OH (2) [4.5 kJ/mol]
Molecule Ring φ ψ Bond TypeZ-Aib-OH C5, g+ 83 -180 -180 C5Z-Aib-OH C5, anti 180 180 -180 C5Z-Gly-OH C5, g- -84 179 180 C5
Z-(Aib)2-OH
3434 cm-1
3272 cm-1
3427 cm-1
3574 cm-1
*
*
*
*Z-(Aib)2-OH C5, g- Fr
ee O
H
Z-(Aib)2-OH C5, g- [+ 4.27]Free
NH
C5
NH
MoleculeRelative Energies(kJ/mol)
OH Orientation Phenyl Phi Psi Phi2 Psi2 Bond Distance
Z-(Aib)2-OH C5, g- 4.27 Cis -78 58 32 172 -178 2.13Z-(Aib)2-OH g- 7.18 Cis -70 55 -140 -49 -42
Z-(Aib)2-OH C7, g- 12.7 Cis -76 77 -36 -170 33 2.02Z-(Aib)2-OH C7, g+ 4.38 Trans 80 -60 -34 -68 56 1.7
Z-(Aib)2-OH C7/C7, g- 7.14 Trans -71 72 -64 -71 53 1.7, 1.9 Z-(Aib)2-OH C10, g+ 0 Trans 74 -58 -31 -60 -24 1.9
Additional Assignments
C7
C7 C7
NH
C5
C10
Z-(Aib)2-OH g-
Z-(Aib)2-OH C5/7, g-
Z-(Aib)2-OH C7, g+
Z-(Aib)2-OH C7/C7, g-
Z-(Aib)2-OH C10, g+
Z-(Aib)2-OMe
Z-(Aib)2-OMe C5/7, g- [+ 4.31]
*
3418 cm-1
3342 cm-1
3407 cm-1
MoleculeRelative Energies(kJ/mol)
Structure Bond Members Phenyl Phi Psi Phi2 Psi2 Bond Length
C5, g- 1.74 C5 NH···O=C -76 63 24 -54 141 2.3
C5/7, g- 4.31 C5, C7 NH···O=C,NH···O=C -77 72 -70 -180 -179 2.1, 2.2
C5, g- 2.60 C5 NH···O=C -86 -64 -31 -174 -176 2.14Stack, g+ 6.88 Stack? 84 68 87 -51 -38
17 9.67 ? 70 -49 133 -50 -44
Z-(Aib)2-OMe C5, g- [+ 2.60]
**
*
C7 + C5 NH
Free
Free
C5
Z-(Aib)2-OtBu
Z-(Aib)2-OtBu C5, g+ [+ 3.53]
Z-(Aib)2-OtBu C5/7, g- [+ 10.3]MoleculeRelative Energies(kJ/mol)
Structure Phenyl Phi Psi Phi2 Psi2
C5, g+ 3.53 C5 81 -61 -34 -177 -176C5/7, g- 10.3 C5/7 -83 74 -64 180 -174
C7 + C5 NH
Free
Free
C5
Conclusions• Z-Aib-OH vs Z-Gly-OH
– Side chain seems to have very little influence on the electronic spectrum
• With only 2 Aib residues, there is not enough H-bonding potential to see helix formation– Dihedral angles do appear to indicate the beginning of helix
formation• OH vs OMe vs OtBu
– Caps have significant influence on the hydrogen bonding (OH)– OtBu proved very difficult to work with
• There is still much to be learned!
Future Work
O NH
O
HN
O
OH
O
O NH
O
OH
O
O NH
O
HN
O
NH
O
HN
OH
O
O
O NH
O
HN
O
NH
O
HN
NH
O
O
HN
O
OH
O
R O
O
R O
O ?
Acknowledgements
• Prof. Timothy S. Zwier• Prof. Matthew A. Kubasik• Prof. Hyuk Kang• Dr. Jacob C. Dean• Zwier Group Members– Daniel Hewett
Additional Talks:TD01, TD02, TD05, TG08, TG11,
WI10, RB03, FD06, FE12
