Search

Aggregation of amphiphilic polymers in block-selective solvents produces different nanostructures, which have been studied extensively for wide-ranging applications. Nevertheless, such immiscibility-driven aggregation does not endow them with the desired structural precision, predictability or surface functional group exposure, which significantly impact their functional applications. More recently, biomimetic folded structures of synthetic macromolecules (mostly oligomers) have come to the fore, but such studies have been limited to probe the secondary structures. In this article, we have collated hierarchical structures of foldamers, especially highlighting our recent contribution to the field of chain-folding regulated assembly of segmented polyurethanes (PUs) and their functional applications. A series of such PUs have been discussed, which contain a segmented hydrocarbon backbone and alternately placed pendant solvophilic groups. In either water or highly non-polar solvents (TCE, MCH), depending on the nature of the pendant group, they exhibit folded structures stabilized by intra-chain H-bonding. Hierarchical assembly of such folded chains by inter-chain H-bonding and/or π-stacking leads to the formation of well-defined nanostructures with functional applications ranging from organic optoelectronics to biomaterials. For example, a segmented PU with appended naphthalene-diimide (NDI) chromophores showed a pleated structure in MCH, which helped in organization of the NDI chromophores within π-stacking distance. Such folded polymer chains eventually produced nanotubular structures with excellent electron mobility. They also showed efficient intercalation of the pyrene (Py) donor by NDI–Py charge-transfer interaction and in this case the mixed nanotubular structure exhibited prominent room-temperature ferroelectricity. On the other hand, having cationic functionalities as the pendant groups such chain-folding regulated assembly produced unilamellar polymersomes with excellent antibacterial activity with very low minimum inhibitory concentrations (<10 μg mL−1). Replacing the pendant amine functionality with sulphate groups made these polyurethanes highly potent antiviral materials. In the absence of the alternating connectivity of the solvophobic and solvophilic segments or rigid hydrocarbon backbone, such folding propensity is destroyed, leading to structural collapse. While significant efforts have been made in correlating primary structures of wide-ranging polymers with their functional applications, this article demonstrates the direct correlation between the secondary structures of polymers and their functional properties. [ABSTRACT FROM AUTHOR]

Herein, we report the rich morphological and conformational versatility of a biologically active peptide (PEP‐1), which follows diverse self‐assembly pathways to form up to six distinct nanostructures and up to four different secondary structures through subtle modulation in pH, concentration and temperature. PEP‐1 forms twisted β‐sheet secondary structures and nanofibers at pH 7.4, which transform into fractal‐like structures with strong β‐sheet conformations at pH 13.0 or short disorganized elliptical aggregates at pH 5.5. Upon dilution at pH 7.4, the nanofibers with twisted β‐sheet secondary structural elements convert into nanoparticles with random coil conformations. Interestingly, these two self‐assembled states at pH 7.4 and room temperature are kinetically controlled and undergo a further transformation into thermodynamically stable states upon thermal annealing: whereas the twisted β‐sheet structures and corresponding nanofibers transform into 2D sheets with well‐defined β‐sheet domains, the nanoparticles with random coil structures convert into short nanorods with α‐helix conformations. Notably, PEP‐1 also showed high biocompatibility, low hemolytic activity and marked antibacterial activity, rendering our system a promising candidate for multiple bio‐applications. [ABSTRACT FROM AUTHOR]