C₁₂‐Helix Development in (αγ)_n Sequences – Spectroscopic Characterization of Boc–[Aib–γ⁴(R)Val]–OMe Oligomers

Abstract

The solution conformations of the αγ‐hybrid oligopeptides Boc–[Aib–γ4(R)Val]n–OMe (n = 1–8) in organic solvents have been probed by NMR, IR, and CD spectroscopic methods. In the solid state, this peptide series favors C12‐helical conformations, which are backbone‐expanded analogues of 310 helices in α‐peptide sequences. NMR studies of the six‐ (n = 3) and 16‐residue (n = 8) peptides reveal that only two NH protons attached the N‐terminus residues Aib(1) and γ4(R)Val(2) are solvent‐exposed. Sequential NiH–Ni+1H NOEs characteristic of local helical conformations are also observed at the α residues. IR studies establish that chain extension leads to a large enhancement in the intensities of the hydrogen‐bonded NH stretching bands (3343–3280 cm–1), which suggest elongation of intramolecularly hydrogen‐bonded structures. The development of C12‐helical structures upon lengthening of the αγ sequence is supported by the NMR and IR observations. The CD spectra of the (αγ)n peptides reveal a negative maximum at ca. 206 nm and a positive maximum at ca. 192 nm, spectral feature that are distinct from those of 310 helices in α‐peptides.

Self-assembly of diphenylalanine backbone homologues and their combination with functionalized carbon nanotubes

“…4a shows two defined N-H stretching bands at 3357 and 3324 cm −1 for peptide 1, and a band at 3351 with a shoulder at 3324 cm −1 for peptide 2, respectively. It is wellestablished that the non-hydrogen bonded N-H corresponds to a higher energy bands, while the lower energy bands are due to intramolecularly hydrogen bonded N-H. 36,37 In this context, the relatively higher band proportion at 3324 cm −1 of 1 in comparison to 2 may be due to a stronger intramolecular hydrogen bonding. This could be attributed to the observed highly ordered fibers in 1.…”

Novel layer-by-layer self-assembled peptide nanocarriers for siRNA delivery

“…Red shi on C]O absorbance at 1683 cm À1 to 1679 cm À1 , together with broadening of frequency and increase in intensity indicates hydrogen bonding of C]O. Amide A and B bands, demonstrating NH stretching frequency levels, are also important for the interpretation of the H-bonding ability of peptides. It is well established that the non-hydrogen bonded N-H is due to higher energy bands, while the lower energy bands correspond to intramolecularly hydrogen bonded N-H. 37,41 Large absorption peaks seen at amide A and B regions of FFA dimers and FFANP and low-frequency shoulders indicates the presence of hydrogen bonding of the N-H group. 35,42 Urea (CO(NH 2 ) 2 ), as a strong H-bonding donor, is commonly used as a hydrogen bonding inhibitor and protein denaturing agent.…”

Investigation of α/γ hybrid peptide self‐assembled structures with antimicrobial and antibiofilm properties

“…The amide I (C═O stretching) and amide II (N─H bending) frequencies were observed in the range of 1649 to 1656 cm −1 and 1523 to 1536 cm −1 , respectively. The observation of IR frequency at 1649 to 1656 cm −1 in peptides P1 to P3 may be due the formation of helical structure …”

“…31 In to 1656 cm −1 in peptides P1 to P3 may be due the formation of helical structure. 36 Further, we investigated the secondary structure and the molecular aggregation of hybrid peptides P1 to P3 by performing the CD experiments. The CD spectra of lyophilized powder in methanol are shown in Figure S14.…”