Peptide-guided organization of peptide-polymer conjugates:: Expanding the approach from oligo- to polymers

The synthesis and self-assembly behavior of a set of peptide-polymer conjugates is described. It is demonstrated that an oligopeptide segment, composing 3.5 wt % of a conjugate, can effectively direct the microstructure formation of a poly(n-butyl acrylate)-block (pnBA) with M-n approximate to 38 000. RAFT polymerization is used to synthesize conjugates possessing pnBA blocks with different block lengths (M-n=8000 - 38 000) but having the same peptide - aggregator domain. The high tendency of this peptide to adopt a beta-sheet is temporarily suppressed by switch and pseudoproline defects, allowing the ease of introduction of a RAFT chain-transfer moiety (CTA). The resulting peptide-CTA can effectively mediate the polymerization of n-butyl acrylate, leading to a conjugate with suppressed aggregation tendency. However, the undisturbed peptide segment is reestablished via a pH-controlled rearrangement in the defects, triggering peptide-directed microstructure formation. Atomic force microscopy (AFM) allows the visualization of fibrillar microstructures and frequently provides evidence for a left-handed superhelical fine structure. The peptide segments organize into P-sheets as proven by infrared spectroscopy (FT-IR) and electron diffraction coupled to transmission electron microscopy (SAED-TEM). Thus, peptide organization controls microstructure formation and both the dimensions of the fibrils and the approximated rates of self-assembly are correlated to the molecular weight of the pnBA blocks in the conjugates.