Single-conformation ultraviolet and infrared spectroscopy of model synthetic foldamers

β-peptides Ac-β3-hPhe-NHMe and Ac-β3-hTyr-NHMe

Esteban E. Baquero, William H. James, Hyuk Choi Soo, Samuel H. Gellman, Timothy S. Zwier

Research output: Contribution to journalArticle

53 Citations (Scopus)

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 languageEnglish
Pages (from-to)4784-4794
Number of pages11
JournalJournal of the American Chemical Society
Volume130
Issue number14
DOIs
Publication statusPublished - 2008 Apr 9

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Ultraviolet spectroscopy
Peptides
Conformations
Infrared spectroscopy
Spectrum Analysis
Phenol
Infrared radiation
Photons
Discrete Fourier transforms
Amides
Molecules
Ions
Phenols
Ionization
Spectroscopy
Geometry
Experiments

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Baquero, Esteban E. ; James, William H. ; Soo, Hyuk Choi ; Gellman, Samuel H. ; Zwier, Timothy S. / Single-conformation ultraviolet and infrared spectroscopy of model synthetic foldamers : β-peptides Ac-β3-hPhe-NHMe and Ac-β3-hTyr-NHMe. In: Journal of the American Chemical Society. 2008 ; Vol. 130, No. 14. pp. 4784-4794.
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title = "Single-conformation ultraviolet and infrared spectroscopy of model synthetic foldamers: β-peptides Ac-β3-hPhe-NHMe and Ac-β3-hTyr-NHMe",
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.",
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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 journalArticle

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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

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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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