Conformational properties and aggregation of homo‐oligomeric β³(R)‐valine peptides in organic solvents

Abstract

The conformational characteristics of protected homo-oligomeric Boc-[β (R)Val] -OMe, n = 1, 2, 3, 4, 6, 9, and 12 have been investigated in organic solvents using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) absorption spectroscopy and circular dichroism (CD) methods. The detailed H NMR analysis of Boc-[β (R)Val] -OMe reveals that the peptide aggregates extensively in CDCl , but is disaggregated in 20%, (v/v) dimethyl sulfoxide (DMSO) in CDCl and in CD OH. Limited assignment of the N-terminus NH groups, together with solvent dependence of NH chemical shifts and temperature coefficients provides evidence for 14-helix conformation in the 12-residue peptide. FTIR analysis in CHCl establishes that the onset of folding and aggregation, as evidenced by NH stretching bands at 3375 cm (intramolecular) and 3285 cm (intermolecular), begins at the level of the tetrapeptide. The observed CD bands, 214 nm (negative) and 198 nm (positive), support 14-helix formation in the 9 and 12 residue sequences. The folding and aggregation tendencies of homo-oligomeric α-, β-, and γ- residues is compared in the model peptides Boc-[ωVal] -NHMe, ω = α, β, and γ and n = 1, 2, and 3. Analysis of the FTIR spectra in CHCl , establish that the tendency to aggregate at the di and tripeptide level follows the order β > α∼γ, while the tendency to fold follows the order γ > β > α.

Coordination crosslinking of helical substituted oligoamide nanorods with Cu(II)

“…[18,19] FT-IR is regularly used for the characterization of the secondary structures of peptides and proteins. [26][27][28][29][30][31] The extensive knowledge base created around peptide FT-IR vibrations can be applied with ease to these substituted oligoamides due to their overarching similarities to natural peptides. [26,32] The most common bands seen in peptide FT-IR are vibrations modes of the amide groups of the peptide backbone.…”

“…[26][27][28][29][30][31] The extensive knowledge base created around peptide FT-IR vibrations can be applied with ease to these substituted oligoamides due to their overarching similarities to natural peptides. [26,32] The most common bands seen in peptide FT-IR are vibrations modes of the amide groups of the peptide backbone. [30,31,33] The amide I and II bands are common diagnostic tools for determining the secondary structures of peptides as both bands strongly absorb, making them easily identifiable.…”

“…[30,31,33] The amide I and II bands are common diagnostic tools for determining the secondary structures of peptides as both bands strongly absorb, making them easily identifiable. [26,[29][30][31][32][33][34] The amide I band (predominantly C=O stretch) occurs between 1600 and 1700 cm -1 and is highly sensitive to its local environment, and hence overall secondary structure of the molecule, however its contribution can be influenced by the vibrational bands from water. [26,[29][30][31]34] The amide II band (N-H stretch and C-N bend) found between 1510 and 1580 cm -1 is free from water contribution but is less sensitive to changes in secondary structure.…”

“…[26,[29][30][31][32][33][34] The amide I band (predominantly C=O stretch) occurs between 1600 and 1700 cm -1 and is highly sensitive to its local environment, and hence overall secondary structure of the molecule, however its contribution can be influenced by the vibrational bands from water. [26,[29][30][31]34] The amide II band (N-H stretch and C-N bend) found between 1510 and 1580 cm -1 is free from water contribution but is less sensitive to changes in secondary structure. [31,33] Amide bands appearing from 1200 to 1350 cm -1 are known as the amide III bands and can serve as a particularly sensitive diagnostic tool for secondary structure identification and are not impacted by any residual water bands.…”

“…A recent study on β 3 amino acid based substituted oligoamide systems reported the amide I and II peaks at 1645 cm -1 and 1548 cm -1 , respectively, in 14-helix secondary structures, whereas in random unfolded state the amide I and II bands occur at 1657 and 1502 cm -1 , respectively. [26] Further diagnostic features include the N-H bands commonly found around 3450 cm -1 that shift down to 3285 cm -1 when participating in the hydrogen bonding motif of the 14-helix, and the terminal carboxyl group that was identified at the vibrational frequency of 1720 cm -1 when in the 14-helix secondary structure. [26,28,30,32] Amide III band locations have not been reported for the 14-helix secondary structures.…”