Synthesis of diacetylene-containing peptide building blocks and amphiphiles, their self-assembly and topochemical polymerization in organic solvents.
A series of functional iodoacetylenes was prepared and converted into the corresponding diacetylene-substituted amino acids and peptides via Pd/Cu-promoted sp-sp carbon cross-coupling reactions. The unsymmetrically substituted diacetylenes can be incorporated into oligopeptides without a change in the oligopeptide strand's directionality. Thus, a series of oligopeptide-based, amphiphilic diacetylene model compounds was synthesized, and their self-organization as well as their UV-induced topochemical polymerizability was investigated in comparison to related polymer-substituted macromonomers. Solution-phase IR spectroscopy, gelation experiments, and UV spectroscopy helped to confirm that a minimum of five N-H...O=C hydrogen-bonding sites was required in order to obtain reliable aggregation into stable beta-sheet-type secondary structures in organic solvents. Furthermore, the non-equidistant spacing of these hydrogen-bonding sites was proven to invariably lead to beta-sheets with a parallel beta-strand orientation, and the characteristic IR-spectroscopic signatures of the latter in organic solution was identified. Scanning force micrographs of the organogels revealed that compounds with six hydrogen-bonding sites gave rise to high aspect ratio nanoscopic fibrils with helical superstructures but, in contrast to the related macromonomers, did not lead to uniform supramolecular polymers. The UV-induced topochemical polymerization within the beta-sheet aggregates was successful, proving parallel beta-strand orientation and highlighting the effect of the number and pattern of N-H...O=C hydrogen-bonding sites as well as the hydrophobic residue in the molecular structure on the formation of higher structures and reactivity.
Jahnke
Eike
E
Department of Materials, ETH Zurich, Wolfgang-Pauli Str. 10, HCI H515, 8093 Zürich, Switzerland.
Weiss
Jan
J
Neuhaus
Sonja
S
Hoheisel
Tobias N
TN
Frauenrath
Holger
H
D000114:Acetylene / Q000737:chemistry*; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D018625:Microscopy, Atomic Force; D008970:Molecular Weight; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry; D010293:Pargyline / Q000031:analogs & derivatives / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D011437:Propylamines / Q000737:chemistry; D012997:Solvents / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013501:Surface-Active Agents / Q000138:chemical synthesis* / Q000737:chemistry
D009842:Oligopeptides; D011108:Polymers; D011437:Propylamines; D012997:Solvents; D013501:Surface-Active Agents; C009054:propargylamine; D010293:Pargyline; D000114:Acetylene