Dynamic assembly of macromolecules in biological systems is one of the fundamental processes that facilitates life. Although such assembly most commonly uses noncovalent interactions, a set of dynamic reactions involving reversible covalent bonding is actively being exploited for the design of functional materials, bottom-up assembly, and molecular machines. This Minireview highlights recent implementations and advancements in the area of tunable orthogonal reversible covalent (TORC) bonds for these purposes, and provides an outlook for their expansion, including the development of synthetically encoded polynucleotide mimics.

The nanoscale self-assembly of four amphiphilic rod–coil di- and triblock copolymers with chiral, rodlike poly­(N-1-phenethyl-N′-methyl­carbodiimide) (PPMC) segments and random coil, hydrophilic PEG blocks has been investigated using dynamic light scattering (DLS) and tapping-mode atomic force microscopy (AFM). This self-assembly proved to be highly tunable simply upon altering the concentration and chemical structure of the hydrophilic selective solvent and/or blending the copolymers with polycarbodiimide homopolymer. When spin-coated from dilute (c = 0.5 mg/mL) THF/H2O solutions, these interesting polymers adopted either simple spherical micelles or spherical polymersomes depending on the relative amount of H2O used for dissolution. Switching selective solvent from H2O to MeOH induced changes in aggregation behavior, as evidenced by DLS and AFM, with interesting nanoworm and nanomaggot micelle assemblies observed when spin-coated from dilute THF/MeOH solutions. Blending high-MW PPMC homopolymer with the block copolymers and spin-coating from dilute THF/25 vol % MeOH solutions resulted in the formation of long, interconnected nanofibers with several different observed tangling pathways including parallel packing, perpendicular wrapping, and helical twisting of nanofibers. Additionally, a large number of toroid nanostructures were also identified by AFM when spin-coated from these conditions. Finally, spin-coating copolymer/homopolymer blends from THF/25 vol % EtOH induced the nanoscale formation of long, bundled superhelical nanofibers with defined helical structures depending on the homopolymer–copolymer chiral pairing (i.e., (R)-(R) pairing formed P superhelical nanofibers and M superhelix for (S)-(S) pairing). The highly tunable nature of these polymeric nanostructures offers new opportunities for the formation of nanoparticles with variable shapes and sizes simply upon altering the solvent combinations opening up new applications as biological mimics and drug delivery agents.

Polymer topology dictates dynamic and mechanical properties of materials. For most polymers, topology is a static characteristic. In this article, we present a strategy to chemically trigger dynamic topology changes in polymers in response to a specific chemical stimulus. Starting with a dimerized PEG and hydrophobic linear materials, a lightly cross-linked polymer, and a cross-linked hydrogel, transformations into an amphiphilic linear polymer, lightly cross-linked and linear random copolymers, a cross-linked polymer, and three different hydrogel matrices were achieved via two controllable cross-linking reactions: reversible conjugate additions and thiol−disulfide exchange. Significantly, all the polymers, before or after topological changes, can be triggered to degrade into thiol-or amine-terminated small molecules. The controllable transformations of polymeric morphologies and their degradation herald a new generation of smart materials.

The new polymerization of carbodiimides using two, simple [bis(triphenylphosphino)aryl]nickel(II) bromide complexes has been discovered to occur in a controlled, living fashion. These initiators are substantially more air and moisture stable compared to their titanium(IV) counterparts making them significantly easier to synthesize, purify, and utilize. The polymerization is initiated via aryl ligand transfer to the electrophilic center carbon of the carbodiimide. Sequential insertions of the carbodiimide π-bond into the nickel−nitrogen amidinate coordination bond propagates the polymer chain in a living chain growth manner as evident by the linear relationship in the plots of percent conversion vs M n , ln ([M] o /[M]) vs time, and monomer: initiator ratio vs M n . The transferred aryl ligand was confirmed to be appended to the terminus of the polymer chain by MALDI−TOF and 19 F NMR. This added control element offers new opportunities to end functionalize rigid-rod, helical polycarbodiimides. This new technique also provides the ability to generate the active Ni(II) initiation sites on potentially any aryl bromide species for the facile incorporation of rod-like, helical polycarbodiimides into such systems as block copolymers, graft copolymer, polymer functionalized surfaces, etc. To demonstrate this, poly(4-bromostyrene) was employed as a polymer-supported aryl bromide source to generate the active [bis(triphenylphosphino)aryl]nickel(II) bromide macroinitiator. The "grafting from" reaction was then carried out upon addition of the chiral (S)-PEMC monomer forming the excess single-handed helical polycarbodiimide appended graft copolymer. The morphology of this novel polymer system was studied using TMAFM, revealing nanofibular aggregation behavior when spin coated from dilute CHCl 3 solutions.

Extensive use of per-and polyfluoroalkyl substances (PFAS) has caused their ubiquitous presence in natural waters. One of the standard practices for PFAS removal from water is adsorption onto granular activated carbon (GAC); however, this approach generates a new waste stream, i.e., PFAS-laden GAC. Considering the recalcitrance of PFAS molecules in the environment, inadequate disposal (e.g., landfill or incineration) of PFAS-laden GAC may let PFAS back into the aquatic cycle. Therefore, developing approaches for PFAS-laden GAC management present unique opportunities to break its forever circulation within the aqueous environment. This comprehensive review evaluates the past two decades of research on conventional thermal regeneration of GAC and critically analyzes and summarizes the literature on regeneration of PFAS-laden GACs. Optimized thermal regeneration of PFAS-laden GACs may provide an opportunity to employ existing regeneration infrastructure to mineralize the adsorbed PFAS and recover the spent GAC. The specific objectives of this review are (i) to investigate the role of physicochemical properties of PFAS on thermal regeneration, (ii) to assess the changes in regeneration yield as well as GAC physical and chemical structure upon thermal regeneration, and (iii) to critically discuss regeneration parameters controlling the process. This literature review on the engineered regeneration process illustrates the significant promise of this approach that can break the endless environmental cycle of these forever chemicals, while preserving the desired physicochemical properties of the valuable GAC adsorbent.

Photo-controlled atom transfer radical polymerization (PhotoATRP) was implemented, for the first time, to accomplish polymerization induced self-assembly (PISA) mediated by UV light (λ = 365 nm) using ppm levels (ca. < 20 ppm) of copper catalyst at ambient temperature. Using CuII Br 2 /tris(pyridin-2-ylmethyl)amine (TPMA) catalyst systems, PISA was per-formed all in one-pot starting from synthesis of solvophilic poly(oligo(ethylene oxide) methyl ether methacrylate) (POEGMA) blocks to core-crosslinked nanoparticles (NPs) utilizing poly(glycidyl methacrylate) (PGMA) and N,N-cystamine bismethacrylamide (CBMA) as the solvophobic copolymer and crosslinking agent, respectively. Sequential chain-extensions were performed for PGMA demonstrating capabilities for accessing multi-block copolymers with temporal control via switching the UV light on and off. Further, core-crosslinking of PISA nanoparticles was performed via the slow incorporation of the CBMA enabling one-pot crosslinking during the PISA process. Finally, the disulfide installed in the CBMA core-crosslinks allowed for the stimuli-triggered dissociation of nanoparticles using DL-dithiothreitol at acidic pH. File list (2)download file view on ChemRxiv One-pot PhotoATR-PISA_Macromolecules_Final.docx (2.88 MiB) download file view on ChemRxiv Supporting Information_PhotoATR-PISA _Macromolecule...

Naturally occurring peptides and proteins often use dynamic disulfide bonds to impart defined tertiary/quaternary structures for the formation of binding pockets with uniform size and function. Although peptide synthesis and modification are well established, controlling quaternary structure formation remains a significant challenge. Here, we report the facile incorporation of aryl aldehyde and acyl hydrazide functionalities into peptide oligomers via solid-phase copper-catalysed azide-alkyne cycloaddition (SP-CuAAC) click reactions. When mixed, these complementary functional groups rapidly react in aqueous media at neutral pH to form peptide-peptide intermolecular macrocycles with highly tunable ring sizes. Moreover, sequence-specific figure-of-eight, dumbbell-shaped, zipper-like and multi-loop quaternary structures were formed selectively. Controlling the proportions of reacting peptides with mismatched numbers of complementary reactive groups results in the formation of higher-molecular-weight sequence-defined ladder polymers. This also amplified antimicrobial effectiveness in select cases. This strategy represents a general approach to the creation of complex abiotic peptide quaternary structures.

The thermo- and solvo-driven chiroptical switching process observed in specific polycarbodiimides occurs in a concerted fashion with large deviations in specific optical rotation (OR) and CD Cotton effect as a consequence of varying populations of two distinct polymer conformations. These two conformations are clearly visible in the (15)N NMR and IR spectra of the (15)N-labeled poly((15)N-(1-naphthyl)-N'-octadecylcarbodiimide) (Poly-3) and poly((15)N-(1-naphthyl)-(15)N'-octadecylcarbodiimide) (Poly-5). Using van't Hoff analysis, the enthalpies and entropies of switching (ΔHswitching; ΔSswitching) were calculated for both Poly-3 and Poly-5 using the relative integrations of both peaks in the (15)N NMR spectra at different temperatures to measure the populations of each state. The chiroptical switching (i.e., transitioning from state A to state B) was found to be an endothermic process (positive ΔHswitching) for both Poly-3 and Poly-5 in all solvents studied, meaning the conformation correlating with the downfield chemical shift (ca. 148 ppm, state B) is the higher enthalpy state. The compensating factor behind this phenomenon has been determined to be the large increase in entropy in CHCl3 as a result of the switching. Herein, we propose that the increased entropy in the system is a direct consequence of increased disorder in the solvent as the switching occurs. Specifically, the chloroform solvent molecules are very ordered around the polymer chains due to favorable solvent-polymer interactions, but as the switching occurs, these interactions become less favorable and disorder results. The same level of solvent disorder is not achieved in toluene, causing the chiroptical switching process to occur at higher temperatures.