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• W2055784070 endingPage "6590" @default.
• W2055784070 startingPage "6574" @default.
• W2055784070 abstract "Resonant two-photon ionization (R2PI), UV hole-burning (UVHB), and resonant ion-dip infrared (RIDIR) spectroscopies have been used to record single-conformation infrared and ultraviolet spectra of three model synthetic foldamers with heterogeneous backbones, α/β-peptides Ac-β3-hAla-l-Phe-NHMe (βαL), Ac-β3-hAla-d-Phe-NHMe (βαD), and Ac-l-Phe-β3-hAla-NHMe (αβL), isolated and cooled in a supersonic expansion. βαL and βαD are diastereomers, differing only in the configuration of the α-amino acid residue; βαL and αβL contain the same residues, but differ in residue order. In all three α/β-peptides the β3-residue has S absolute configuration. UVHB spectroscopy is used to determine that there are six conformers of each molecule and to locate and characterize their S0−S1 transitions in the origin region. RIDIR spectra in the amide NH stretch region reflect the number and strength of intramolecular H-bonds present. Comparison of the RIDIR spectra with scaled, harmonic vibrational frequencies and infrared intensities leads to definite assignments for the conformational families involved. C8/C7eq double-ring structures are responsible for three conformers of βαL and four of βαD, including those with the most intense transitions in the R2PI spectra. This preference for C8/C7eq double rings appears to be dictated by the C7eq ring of the α-peptide subunit. Three of the conformers of βαL and βαD form diastereomeric pairs (A/A′, C/C′, and G/G′) that have nearly identical S0−S1 origin positions in the UV and belong to the same conformational family, indicating no significant change associated with the change in chirality of the α-peptide subunit. However, βαL favors formation of a C6/C5 conformer over C11, while the reverse preference holds in βαD. Calculations indicate that the selective stabilization of the lowest-energy C11(g+) structure in βαD occurs because this structure minimizes steric effects between the β2 methylene group and C=O(1). In the α/β-peptide αβL, two conformers dominate the spectrum, one assigned to a C5/C8 bifurcated double-ring, and the other to a C5/C6 double-ring structure. This preference for C5 rings in the α/β-peptide occurs because the C5 ring is further stabilized by an amide NH···π interaction involving an NH group on the adjacent amide, as it is in the α-peptides. Comparison of the NH stretch spectra of C8/C7eq structures in βαL with their C7eq/C8 counterparts in αβL shows that the central amide NH stretch is shifted to lower frequency by some 50−70 cm−1 due to cooperative effects associated with the central amide accepting and donating a H-bond to neighboring amide groups. This swaps the ordering of the C8 and C7 NH stretch fundamentals in the two molecules." @default.
• W2055784070 created "2016-06-24" @default.
• W2055784070 creator A5012750468 @default.
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• W2055784070 creator A5055277847 @default.
• W2055784070 creator A5073899338 @default.
• W2055784070 date "2009-04-14" @default.
• W2055784070 modified "2023-09-25" @default.
• W2055784070 title "Single-Conformation and Diastereomer Specific Ultraviolet and Infrared Spectroscopy of Model Synthetic Foldamers: α/β-Peptides" @default.
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• W2055784070 doi "https://doi.org/10.1021/ja901051v" @default.
• W2055784070 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/19366210" @default.
• W2055784070 hasPublicationYear "2009" @default.
• W2055784070 type Work @default.

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