Assessing structure/property relationships and synthetic protocols in the fabrication of poly(oxanorbornene imide) single-chain nanoparticles

Macromolecular Function Emerging from Intramolecular Peptide Stapling of Synthetic Polymers

Protein function results from the precise folding of polypeptides into bespoke architectures. Taking inspiration from nature, the field of single-chain nanoparticles (SCNPs), intramolecularly crosslinked synthetic polymers, emerged. In contrast to nature, the function of SCNPs is generally defined by the parent polymer or the applied crosslinker, rather than by the crosslinking process itself. This work explores the cyanopyridine-aminothiol click reaction to crosslink peptide-decorated polymers intra-macromolecularly to endow the resulting SCNPs with emerging functionality, resulting from the conversion of N-terminal cysteine units into pyridine-thiazolines. Dimethylacrylamide based polymers with different cysteine-terminated amino acid sequences tethered to their sidechains are investigated (P1 (C), P2 (GDHC), P3 (GDSC)) and intramolecularly crosslinked into SCNPs. Since the deprotection of the parent polymers yields disulfide-based SCNPs, a direct comparison between disulfide and pyridine-thiazolines crosslinked SCNPs is possible. This comparison revealed two emerging properties of the pyridine-thiazoline crosslinked SCNPs: 1) The formation of pyridine-thiazolines gave rise to metal binding sites within the SCNP, which complexed iron. 2) Depending on the peptide sequence in the precursor polymer, the hydrolytic activity of the peptide sequences is either increased (GDHC) or decreased (GDSC) upon pyridine-thiazoline formation compared to identical SCNPs based on disulfide crosslinks.

Rapid Identification of Cell Types and Phenotypic States Using a One-Polymer Multichannel Nanosensor Fabricated via Flash Nanoprecipitation

Cell state transitions are fundamental in biology, determining how cells respond to environmental stimuli and adapt to diseases and treatments. Cell surface-based sensing of geno/phenotypes is a versatile approach for distinguishing different cell types and states. Array-based biosensors can provide a highly sensitive platform for distinguishing cells based on the differential interactions of each sensing element with cell surface components. In this work, a highly modular polymer-based supramolecular multichannel sensor array (FNP sensor) was fabricated by encapsulating a hydrophobic dye (pyrene) into the monolayer of a positively charged fluorescent polymer through flash nanoprecipitation (FNP). We utilized this one-polymer sensor array to discriminate among cell types commonly found in tumors: 4T1 cancer cells, NIH/3T3 fibroblast cells, and RAW 264.7 macrophage cells. The sensor also successfully characterized varying ratios of NIH/3T3 cancer-associated fibroblasts (CAFs) and RAW 264.7 tumor-associated macrophages (TAMs). This single polymer-based sensor array provides effective discrimination and high reproducibility, providing a high-throughput tool for diagnostic screening of cell types and states associated with cancer progression.

Förster resonance energy transfer within single chain nanoparticles

Single chain nanoparticles (SCNPs) are a highly versatile polymer architecture consisting of single polymer chains that are intramolecularly crosslinked. Currently, SCNPs are discussed as powerful macromolecular architectures for catalysis, delivery and sensors. Herein, we introduce a methodology based on Förster Resonance Energy Transfer (FRET) to evidence the folding of single polymer chains into SCNPs via fluorescence readout. We initially introduce a molecular FRET pair based on a bimane and nitrobenzoxadiazole (NBD) moiety and study its fluorescence properties in different solvents. We subsequently construct a low dispersity polymer chain carrying NBD units, while exploiting the bimane units for intramolecular chain collapse. Upon chain collapse and SCNP formation - thus bringing bimane and NBD units into close proximity - the SCNPs report their folded state by a strong and unambiguous FRET fluorescence signal. The herein introduced reporting of the folding state of SCNPs solely relies on an optical readout, opening avenues to monitoring SCNP folding without recourse to complex analytical methodologies.

Unraveling Reactivity Differences: Room-Temperature Ring-Opening Metathesis Polymerization (ROMP) versus Frontal ROMP

In this study, we explore the distinct reactivity patterns between frontal ring-opening metathesis polymerization (FROMP) and room-temperature solventless ring-opening metathesis polymerization (ROMP). Despite their shared mechanism, we find that FROMP is less sensitive to inhibitor concentration than room-temperature ROMP. By increasing the initiator-to-monomer ratio for a fixed inhibitor/initiator quantity, we find reduction in the ROMP background reactivity at room temperature (i.e., increased resin pot life). At elevated temperatures where inhibitor dissociation prevails, accelerated frontal polymerization rates are observed because of the concentrated presence of the initiator. Surprisingly, the strategy of employing higher initiator loading enhances both pot life and front speeds, which leads to FROMP rates exceeding prior reported values by over 5 times. This counterintuitive behavior is attributed to an increase in the proximity of the inhibitor to the initiator within the bulk resin and to whether the temperature favors coordination or dissociation of the inhibitor. A rapid method was developed for assessing resin pot life, and a straightforward model for active initiator behavior was established. Modified resin systems enabled direct ink writing of robust thermoset structures at rates much faster than previously possible.

Peptide based folding and function of single polymer chains

A modular synthetic strategy to fold single polymer chains upon deprotection of pendent cysteine terminal peptides is reported. The one step deprotection initiates both folding and catalytic activity of the macromolecular architectures.

100th Anniversary of Macromolecular Science Viewpoint: Re-examining Single-Chain Nanoparticles

Single-chain nanoparticles (SCNP) are a class of polymeric nanoparticles obtained from the intramolecular cross-linking of polymers bearing reactive pendant groups. The development of SCNP has drawn tremendous attention since the fabrication of SCNP mimics the self-folding behavior in natural biomacromolecules and is highly desirable for a variety of applications ranging from catalysis, nanomedicine, nanoreactors, and sensors. The versatility of novel chemistries available for SCNP synthesis has greatly expanded over the past decade. Significant progress was also made in the understanding of a structure-property relationship in the single-chain folding process. In this Viewpoint, we discuss the effect of precursor polymer topology on single polymer folding. We summarize the progress in SCNP of complex architectures and highlight unresolved issues in the field, such as scalability and topological purity of SCNP.