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 (p n BA) with M n ≈ 38 000. RAFT polymerization is used to synthesize conjugates possessing p n BA 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 β-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 β-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 p n BA blocks in the conjugates.