Abstract
The conformational preferences and infrared and ultraviolet spectral signatures of two model β-peptides, Ac-β3-hPhe-NHMe (1) and Ac-β3-hTyr-NHMe (2), have been explored under jet-cooled, isolated molecule conditions. The mass-resolved, resonant two-photon ionization spectra of the two molecules were recorded in the region of the S 0-S1 origin of the phenyl or phenol ring substituents, respectively. UV-UV hole-burning spectroscopy was used to determine that two conformations of 1 are present, with the transitions due to conformer A, with S0-S1 origin at 34431 cm-1, being almost 20 times larger than those due to conformer B, with S0-S1 origin at 34404 cm-1. Only one conformation of 2 was observed. Resonant ion-dip infrared spectroscopy provided single-conformation infrared spectra in the 3300-3700 cm-1 region. The spectra of conformer A of both molecules have H-bonded and free amide NH stretch infrared transitions at 3400 and 3488 cm-1, respectively, while conformer B of 1 possesses bands at 3417 and 3454 cm-1. For comparison with experiment, full optimizations of all low-lying minima of 1 were carried out at the DFT B3LYP/6-31+G* and RIMP2/aug-cc-pVDZ levels of theory, and single point MP2/6-31+G* calculations at the DFT geometries. On the basis of the comparison with previous studies in solution and the calculated results, conformer A of 1 and 2 were assigned to a C6 conformer, while conformer B of 1 was assigned to a unique C8 structure with a weak intramolecular H-bond. The reasons for the preference for C6 over C8 structures and the presence of only two conformations in the jet-cooled spectrum are discussed in light of the predictions from calculations.
| Original language | English |
|---|---|
| Pages (from-to) | 4784-4794 |
| Number of pages | 11 |
| Journal | Journal of the American Chemical Society |
| Volume | 130 |
| Issue number | 14 |
| DOIs | |
| Publication status | Published - 2008 Apr 9 |
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All Science Journal Classification (ASJC) codes
- Catalysis
- Chemistry(all)
- Biochemistry
- Colloid and Surface Chemistry
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Single-conformation ultraviolet and infrared spectroscopy of model synthetic foldamers : β-peptides Ac-β3-hPhe-NHMe and Ac-β3-hTyr-NHMe. / Baquero, Esteban E.; James, William H.; Soo, Hyuk Choi; Gellman, Samuel H.; Zwier, Timothy S.
In: Journal of the American Chemical Society, Vol. 130, No. 14, 09.04.2008, p. 4784-4794.Research output: Contribution to journal › Article
TY - JOUR
T1 - Single-conformation ultraviolet and infrared spectroscopy of model synthetic foldamers
T2 - β-peptides Ac-β3-hPhe-NHMe and Ac-β3-hTyr-NHMe
AU - Baquero, Esteban E.
AU - James, William H.
AU - Soo, Hyuk Choi
AU - Gellman, Samuel H.
AU - Zwier, Timothy S.
PY - 2008/4/9
Y1 - 2008/4/9
N2 - The conformational preferences and infrared and ultraviolet spectral signatures of two model β-peptides, Ac-β3-hPhe-NHMe (1) and Ac-β3-hTyr-NHMe (2), have been explored under jet-cooled, isolated molecule conditions. The mass-resolved, resonant two-photon ionization spectra of the two molecules were recorded in the region of the S 0-S1 origin of the phenyl or phenol ring substituents, respectively. UV-UV hole-burning spectroscopy was used to determine that two conformations of 1 are present, with the transitions due to conformer A, with S0-S1 origin at 34431 cm-1, being almost 20 times larger than those due to conformer B, with S0-S1 origin at 34404 cm-1. Only one conformation of 2 was observed. Resonant ion-dip infrared spectroscopy provided single-conformation infrared spectra in the 3300-3700 cm-1 region. The spectra of conformer A of both molecules have H-bonded and free amide NH stretch infrared transitions at 3400 and 3488 cm-1, respectively, while conformer B of 1 possesses bands at 3417 and 3454 cm-1. For comparison with experiment, full optimizations of all low-lying minima of 1 were carried out at the DFT B3LYP/6-31+G* and RIMP2/aug-cc-pVDZ levels of theory, and single point MP2/6-31+G* calculations at the DFT geometries. On the basis of the comparison with previous studies in solution and the calculated results, conformer A of 1 and 2 were assigned to a C6 conformer, while conformer B of 1 was assigned to a unique C8 structure with a weak intramolecular H-bond. The reasons for the preference for C6 over C8 structures and the presence of only two conformations in the jet-cooled spectrum are discussed in light of the predictions from calculations.
AB - The conformational preferences and infrared and ultraviolet spectral signatures of two model β-peptides, Ac-β3-hPhe-NHMe (1) and Ac-β3-hTyr-NHMe (2), have been explored under jet-cooled, isolated molecule conditions. The mass-resolved, resonant two-photon ionization spectra of the two molecules were recorded in the region of the S 0-S1 origin of the phenyl or phenol ring substituents, respectively. UV-UV hole-burning spectroscopy was used to determine that two conformations of 1 are present, with the transitions due to conformer A, with S0-S1 origin at 34431 cm-1, being almost 20 times larger than those due to conformer B, with S0-S1 origin at 34404 cm-1. Only one conformation of 2 was observed. Resonant ion-dip infrared spectroscopy provided single-conformation infrared spectra in the 3300-3700 cm-1 region. The spectra of conformer A of both molecules have H-bonded and free amide NH stretch infrared transitions at 3400 and 3488 cm-1, respectively, while conformer B of 1 possesses bands at 3417 and 3454 cm-1. For comparison with experiment, full optimizations of all low-lying minima of 1 were carried out at the DFT B3LYP/6-31+G* and RIMP2/aug-cc-pVDZ levels of theory, and single point MP2/6-31+G* calculations at the DFT geometries. On the basis of the comparison with previous studies in solution and the calculated results, conformer A of 1 and 2 were assigned to a C6 conformer, while conformer B of 1 was assigned to a unique C8 structure with a weak intramolecular H-bond. The reasons for the preference for C6 over C8 structures and the presence of only two conformations in the jet-cooled spectrum are discussed in light of the predictions from calculations.
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U2 - 10.1021/ja078271y
DO - 10.1021/ja078271y
M3 - Article
VL - 130
SP - 4784
EP - 4794
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 14
ER -