Generalizing the effects of chirality on block copolymer assembly.

We explore the generality of the influence of segment chirality on the self-assembled structure of achiral-chiral diblock copolymers. Poly(cyclohexylglycolide) (PCG)-based chiral block copolymers (BCPs*), poly(benzyl methacrylate)-b-poly(d-cyclohexylglycolide) (PBnMA-PDCG) and PBnMA-b-poly(l-cyclohexyl glycolide) (PBnMA-PLCG), were synthesized for purposes of systematic comparison with polylactide (PLA)-based BCPs*, previously shown to exhibit chirality transfer from monomeric unit to the multichain domain morphology. Opposite-handed PCG helical chains in the enantiomeric BCPs* were identified by the vibrational circular dichroism (VCD) studies revealing transfer from chiral monomers to chiral intrachain conformation. We report further VCD evidence of chiral interchain interactions, consistent with some amounts of handed skew configurations of PCG segments in a melt state packing. Finally, we show by electron tomography [3D transmission electron microscope tomography (3D TEM)] that chirality at the monomeric and intrachain level ultimately manifests in the symmetry of microphase-separated, multichain morphologies: a helical phase (H*) of hexagonally, ordered, helically shaped tubular domains whose handedness agrees with the respective monomeric chirality. Critically, unlike previous PLA-based BCP*s, the lack of a competing crystalline state of the chiral PCGs allowed determination that H* is an equilibrium phase of chiral PBnMA-PCG. We compared different measures of chirality at the monomer scale for PLA and PCG, and argued, on the basis of comparison with mean-field theory results for chiral diblock copolymer melts, that the enhanced thermodynamic stability of the mesochiral H* morphology may be attributed to the relatively stronger chiral intersegment forces, ultimately tracing from the effects of a bulkier chiral side group on its main chain.

Chirality Effects in Peptide Assembly Structures.

Peptide assembly structures have been widely exploited in fabricating biomaterials that are promising for medical applications. Peptides can self-organize into various highly ordered supramolecular architectures, such as nanofibril, nanobelt, nanotube, nanowire, and vesicle. Detailed studies of the molecular mechanism by which these versatile building blocks assemble can guide the design of peptide architectures with desired structure and functionality. It has been revealed that peptide assembly structures are highly sequence-dependent and sensitive to amino acid composition, the chirality of peptide and amino acid residues, and external factors, such as solvent, pH, and temperature. This mini-review focuses on the regulatory effects of chirality alteration on the structure and bioactivity of linear and cyclic peptide assemblies. In addition, chiral self-sorting and co-assembly of racemic peptide mixtures were discussed.