Disguise tactics: Peptide–polymer hybrid nanotubes are constructed in which self‐assembled cyclic peptides govern the structure, and a synthetic polymer coating determines the surface chemistry. Formation of the latter is initiated in situ from preorganized peptide building blocks. The picture shows an AFM image of nanotubes on a silicon wafer.

Peptide−polymer hybrid nanotubes (PPNT) were prepared by a combination of self-assembling functional cyclic peptides and in-situ surface-initiated atom transfer radical polymerization (ATRP). Cyclic peptides that consist of alternating d- and l-amino acids, carrying ATRP initiators in distinct side chains, were self-assembled into hollow nanotubes that expose all initiation moieties at the outer surface, thereby forming a cyclic peptide initiator nanotube (CP-ini). The CP-ini nanotubes were dispersed in 2-propanol, and a surface-initiated ATRP reaction has been performed using N-isopropylacrylamide (NIPAM) as monomer, tris[2(dimethylamino)ethyl]amine (Me6TREN) as ligand, and additional sacrificial (model) initiator. The molar mass of the resulting PNIPAM can be well controlled by adjusting the polymerization time (i.e., reaction conversion). The solvent-free height of the PNIPAM−PPNT, as measured by statistical analysis of cross sections of atomic force microscopy (AFM) height micrographs, increases with increasing molar mass of the attached PNIPAM chains in a well-controlled manner. The latter allows for the first time to tailor the outer diameter of self-assembled peptide nanotubes in a very precise way without changes to the primary sequence of the peptide ring. The length of the PNIPAM−PPNT remains almost constant with increasing polymerization time; however, at larger polymerization times, a decrease in absolute number of PPNT is observed, and smaller particles are increasingly present due to a breakup of the PNIPAM−PPNT into smaller peptide−polymer hybrid nanoobjects.

The external structure of polymer-wrapped nanotubes resembles that of small nanorods with a core/shell morphology, where the core consists of a self-assembled peptide nanotube surrounded by a soft polymeric coat. The length and the diameter of the nanorods are investigated as a function of the molar mass of the peptide-grafted macromolecules by statistical atomic force microscopy cross-section analysis of dry nanorods adsorbed to a solid substrate. With increasing molar mass of the grafted polymers, the height increases from less than 2 nm up to more than 10 nm, and the length of the objects decreases from about 120 nm to about 30 nm. Additional analysis suggests excluded volume interactions between the highly grafted polymer chains on the surface of the peptide nanotube to be the major driving force for the shortening of the nanotubes. The present findings may provide a base for fine tuning the dimensions of such novel bioinspired nanomaterials.

Peptide/polymer hybrid molecules consisting of poly(butylacrylate) chains, covalently attached to a cyclic D‐alt‐L‐octapeptide, were prepared by the in situ ATRP of butylacrylate using a cyclic peptide that was modified at three distinct positions with an initiator group. The apparent molar mass of the peptide/PBA hybrid molecules could be controlled through adjusting the reaction conversion. The hybrid molecule showed a solvent induced self‐assembly, which yielded rod‐like nanostructures having a core shell morphology with an internal beta‐sheet peptide assembly surrounded by a soft PBA exterior.

Umhüllungstaktik: Peptid‐Polymer‐Hybridnanoröhren wurden hergestellt, deren Struktur durch selbstorganisierte cyclische Peptide vorgegeben wird und deren Oberflächenchemie durch eine synthetische Polymerhülle eingestellt werden kann. Diese wird in situ mithilfe von Initiatoren erzeugt, die auf den cyclischen Peptiden gebunden sind (Bild: AFM‐Aufnahme von Peptid‐Polymer‐Hybridnanoröhren auf einem Siliciumwafer).