화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.133, No.11, 3981-3988, 2011
Single-Molecule Force Spectroscopy of beta-Peptides That Display Well-Defined Three-Dimensional Chemical Patterns
Oligomers of beta-amino acids ("beta-peptides") can be designed to fold into stable helices that display side chains with a diverse range of chemical functionality in precise arrangements. We sought to determine whether the predictable, three-dimensional side-chain patterns generated by beta-peptides could be used in combination with single-molecule force spectroscopy to quantify how changes in nanometer-scale chemical patterns affect intermolecular interactions. To this end, we synthesized beta-peptides that were designed to be either globally amphiphilic (GA), i.e., display a global segregation of side chains bearing hydrophobic and cationic functional groups, or non-globally amphiphilic (iso-GA), i.e., display a more uniform distribution of hydrophobic and cationic functional groups in three-dimensions. Single-molecule force measurements of beta-peptide interactions with hydrophobic surfaces through aqueous solution (triethanolamine buffer, pH 7.2) reveal that the GA and iso-GA isomers give rise to qualitatively different adhesion force histograms. The data are consistent with the display of a substantial nonpolar domain by the GA oligomer, which leads to strong hydrophobic interactions, and the absence of a comparable domain on the iso-GA oligomer. This interpretation is supported by force measurements in the presence of methanol, which is known to disrupt hydrophobic interactions. Our ability to associate changes in measured forces with changes in three-dimensional chemical nanopatterns projected from conformationally stable beta-peptide helices highlights a contrast between this system and conventional peptides (a-amino acid residues): conventional peptides are more conformationally flexible, which leads to uncertainty in the three-dimensional nanoscopic chemical patterns that underlie measured forces. Overall, we conclude that beta-peptide oligomers provide a versatile platform for quantifying intermolecular interactions that arise from specific functional group nanopatterns.