Single-chain Nanoparticles Research Articles

Effect of Molecular Crowding on Conformation and Interactions of Single-Chain Nanoparticles

Single-chain nanoparticles (SCNPs) are soft disordered nano-objects synthesized by intra-molecular bonding of linear polymer chains with a finite fraction of reactive groups allowing internal crosslinking of the molecule. They may be investigated as a mimick of, e.g., intrinsically disordered proteins, in particular with respect to the effect of the crowded cellular environment on macromolecular properties. Here the conformation of synthetic SCNPs in presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders[1]. A model describing the scattering of aggregating polydisperse SCNPs (see Figure 1) has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Two different crowders – of low and high molecular weight, respectively – are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and is hoped to contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects, and in particular the effect of crowding on biomacromolecules. Figure 1: Schematic representation of the aggregation process of two SCNPs of monomer numbers i1 and i2 described by the addition of their individual SCNP masses, and obeying the same local chain statistics.

Polymeric "Clickase" Accelerates the Copper Click Reaction of Small Molecules, Proteins, and Cells.

Recent work has shown that polymeric catalysts can mimic some of the remarkable features of metalloenzymes by binding substrates in proximity to a bound metal center. We report here an unexpected role for the polymer: multivalent, reversible, and adaptive binding to protein surfaces allowing for accelerated catalytic modification of proteins. The catalysts studied are a group of copper-containing single-chain polymeric nanoparticles (CuI-SCNP) that exhibit enzyme-like catalysis of the copper-mediated azide-alkyne cycloaddition reaction. The CuI-SCNP use a previously observed "uptake mode", binding small-molecule alkynes and azides inside a water-soluble amphiphilic polymer and proximal to copper catalytic sites, but with unprecedented rates. Remarkably, a combined experimental and computational study shows that the same CuI-SCNP perform a more efficient click reaction on modified protein surfaces and cell surface glycans than do small-molecule catalysts. The catalysis occurs through an "attach mode" where the SCNPs reversibly bind protein surfaces through multiple hydrophobic and electrostatic contacts. The results more broadly point to a wider capability for polymeric catalysts as artificial metalloenzymes, especially as it relates to bioapplications.

Mechanical Unfolding and Thermal Refolding of Single-Chain Nanoparticles Using Ligand-Metal Bonds.

Covalent macromolecules tend to fragment under mechanical stress through the mechanochemical scission of covalent bonds in the backbone. However, linear polymers that have been intramolecularly collapsed by covalent bonds show greater mechanochemical stability compared to other thermoplastics. Here, rhodium-π bonds are used for intramolecular collapse in order to show that mechanical stress can be removed from the polymer backbone and focused on weaker intramolecular cross-links, leading to polymer unfolding instead of mechanochemical events at the backbone. Moreover, given rhodium-π bonds form spontaneously, by changing the time interval between ultrasound pulses, we demonstrate that entropic spring effects can lead to polymer refolding and reformation of the previously cleaved metal-ligand bonds, effectively repairing the intramolecular noncovalent cross-links. These findings provide the first example of an intramolecular repairing mechanism in synthetic molecules in solution, allowing for restoration of chemical bonds after mechanochemical events.

Self-Assembly of Single Chain Janus Nanoparticles with Tunable Liquid Crystalline Properties from Stilbene-Containing Block Copolymers

Functional particles self-assembled from polymer single chain nanoparticles have potential applications in various fields, but functionality incorporation is difficult due to their ultrasmall sizes. Here, the preparation and self-assembly of amphiphilic polymer single chain Janus nanoparticles (SCJNPs) with tunable liquid crystalline (LC) properties are reported via intrachain photo-cross-linking stilbene-containing amphiphilic block copolymers (BCPs). The cross-linking degree can be controlled by varying UV irradiation time, which affects the LC properties and the size of the resulting SCJNPs accordingly. The self-assembly behavior of the LC-SCJNPs in solution was further investigated systematically. The morphology transition from nonspherical assemblies, including tubular, doughnut-like, and saddle-shaped, to spherical nanoparticles was observed by changing UV irradiation time and the composition of BCPs. Furthermore, the assemblies display a smectic phase with clear ordering stripes under TEM observation. The LC properties gradually diminish with the increasing UV irradiation time. The internal LC ordering has an important effect on the morphology transition from nonspheres to spheres. This work provides a facile approach to polymer particles with tunable functionalities that can be used for advanced materials by remote light manipulation.

Glass-Transition Dynamics of Mixtures of Linear Poly(vinyl methyl ether) with Single-Chain Polymer Nanoparticles: Evidence of a New Type of Nanocomposite Materials.

Single-chain polymer nanoparticles (SCNPs) obtained through chain collapse by intramolecular cross-linking are attracting increasing interest as components of all-polymer nanocomposites, among other applications. We present a dielectric relaxation study on the dynamics of mixtures of poly(vinyl methyl ether) (PVME) and polystyrene (PS)-based SCNPs with various compositions. Analogous dielectric measurements on a miscible blend of PVME with the linear precursor chains of the SCNPs are taken as reference for this study. Both systems present completely different behaviors: While the blend with the linear precursor presents dynamics very similar to that reported for PVME/PS miscible blends, in the PVME/SCNP mixtures there are an appreciable amount of PVME segments that are barely affected by the presence of SCNPs, which nearly vanishes only for mixtures with high SCNP content. Interestingly, in the frame of a simple two-phase system, our findings point towards the existence of a SCNP-rich phase with a constant PVME fraction, regardless of the overall concentration of the mixture. Moreover, the dynamics of the PVME segments in this SCNP-rich phase display an extreme dynamic heterogeneity, a signature of constraint effects.

Mapping the Compaction of Discrete Polymer Chains by Size Exclusion Chromatography Coupled to High-Resolution Mass Spectrometry

We introduce a powerful approach based on the combination of size exclusion chromatography with high-resolution mass spectrometry to selectively follow the compaction of discrete polymer chains that have uniform elemental composition. Single-chain nanoparticles (SCNP) have attracted considerable interest for a wide range of applications associated with their adjustable morphology. However, the precise characterization of morphological changes during the compaction is still challenging using existing analysis techniques. We employ a polystyrene backbone functionalized with tetrazole and fumarate moieties to utilize the nitrile imine-mediated tetrazole-ene cycloaddition for compaction. As every compaction step is associated with an elimination of one nitrogen molecule, it can be monitored via high-resolution electrospray ionization mass spectrometry. The combination with size exclusion chromatography enables the direct correlation of changes in mass with changes in morphology associated with the compaction. By establishing a calibration between the retention time and the hydrodynamic radius, ion chromatograms of discrete chains can be directly applied to determine the reduction in hydrodynamic radius associated with each cross-linking event. Therefore, accessing the compaction of discrete polymer chains becomes possible for the first time.

Brushes of elastic single-chain nanoparticles on flat surfaces

Single-chain polymer nanoparticles (SCNPs) are individual intrachain cross-linked polymer chains -typically with a size < 20 nm-which can be considered as emerging building blocks for bionanotechnology. Very recently, surfaces displaying molecular recognition motifs have been decorated with brushes of responsive SCNPs and transformed into a cross-linked polymeric monolayer, thus paving the way to controlled nanofilm formation around bioactive surfaces (e.g., virus capsids). In this work, the structural properties of brushes formed by topologically complex SCNPs on flat surfaces are investigated as a function of SCNP size and intrachain cross-linking degree. A detailed comparison is performed to the structural features displayed by brushes of other macromolecular architectures, thus revealing the tunable, unique properties of brushes comprising elastic SCNPs. Remarkably, this work paves the way to the potential design of brushes of SCNPs with drug delivery characteristics based on stimulus-mediated rupture of intrachain cross-links.

Facile Access to Completely Deuterated Single-Chain Nanoparticles Enabled by Intramolecular Azide Photodecomposition.

Access to completely deuterated single-chain nanoparticles (dSCNPs) has remained an unresolved issue. Herein, the first facile and efficient procedure to produce dSCNPs is reported, which comprises: i) the use of commercially available perdeuterated cyclic ether monomers as starting reagents, ii) a ring-opening copolymerization process performed in bulk to produce a neat dSCNP precursor, iii) a standard azidation reaction to decorate this precursor with azide moieties, and iv) a facile intramolecular azide photodecomposition step carried out under UV irradiation at high dilution providing with highly valuable, completely deuterated soft nano-objects from the precursor. dSCNPs are used to investigate by means of neutron-scattering measurements the form factor (radius of gyration, scaling exponent) of polyethylene oxide (PEO) chains in nanocomposites with different amounts of dSCNPs. Moreover, to illustrate the possibilities offered by the synthetic route disclosed in this communication for potential applications, the significant reduction in viscosity observed in a pure melt of polyether-based single-chain nanoparticles when compared to a melt of the corresponding linear polymer chains is shown.

Single-Chain Nanoparticles under Homogeneous Shear Flow

Single-chain nanoparticles (SCNPs) are a new class of macromolecular objects, synthesized through purely intramolecular cross-linking of single polymer chains. We use a multi-scale hydrodynamics simulation approach to study, for the first time, SCNPs under shear flow. We investigate the case of irreversible SCNPs (permanent cross-links) in dilute solution. SCNPs emerge as a novel class of macromolecular objects with response to shear distinct from other systems such as linear chains, star polymers, rings or dendrimers. This is evidenced by the observed set of scaling exponents for the shear rate dependence of the SCNP static and dynamic properties. Surprisingly these exponents are, at most, marginally dependent on the specific topology of the SCNP (globular or sparse), suggesting that they are inherently related to the network-like character of the molecular architecture and not to its specific connectivity. At high Weissenberg numbers the dynamics of the sparse SCNPs is dominated by tumbling motion, whereas tank-treading predominates for the most globular SCNPs.

Controlling Chain Coupling and Single-Chain Ligation by Two Colours of Visible Light.

While photochemical synthesis offers access to spatiotemporal reaction control, its potential to selectively address specific reactions by the colour of light is usually limited by ubiquitous spectral absorption overlaps of the reactive groups. Herein, a new concept is introduced that actively suppresses one ligation reaction by triggering the cycloreversion of the [2+2] cycloaddition of styrylpyrene. Combination of the photoreversible styrylpyrene chemistry with the [4+4] cycloaddition of 9-triazolylanthracene makes it possible to initially induce chain coupling using UV light and to subsequently ligate the formed single-chain nanoparticle (SCNP) with a second polymer chain using blue light. Seizing upon the first sequence-independent λ-orthogonal reactivity established here, the same macromolecular architecture was obtained in reverse irradiation sequence, by blue and subsequent violet light irradiation-completely foregoing high-energy UV light.

Fluorescent Heterotelechelic Single-Chain Polymer Nanoparticles: Synthesis, Spectroscopy, and Cellular Imaging

The folding and collapse of individual polymer chains into single-chain polymer nanoparticles (SCPNs) is a versatile and emerging platform for biological applications such as diagnostics, imaging, and therapy, where components for two or more of these functions can be combined onto a single polymer carrier. Here, we prepare heterotelechelic polymers with three sets of separately addressable chemical handles at their α-terminus and ω-terminus, and along their backbone. As a model system, the α- and ω-termini are conjugated with a targeting ligand (folic acid or biotin) and therapeutic drug cargo (camptothecin), respectively, and the backbone is grafted with pendant fluorescent dye molecules, poly(ethylene glycol) oligomers, and benzene-1,3,5-tricarboxamide. These polymers fold in water to give fluorescent SCPNs, which are characterized with respect to their physical and photophysical properties. The latter reveals a relationship between polymer folding, quantum yield, and resistance to photobleaching. The ...

Preparation of single chain nanoparticles via photoinduced radical coupling process

This contribution introduces a straightforward method for preparing well-defined polymeric nanoparticles using radical coupling process of ketyl moieties resulted from triplet excitation of pendant benzophenone groups. In the first step, poly(styrene-co-chloromethylstyrene) is synthesized by thermally initiated controlled radical copolymerization technique and subsequently, pendant chloride groups undergo post-modification with 4–hydroxybenzophenone. Achieved well-defined side–chain benzophenone containing copolymers generate ketyl radicals in the presence of excess hydrogen donor molecule upon UV-light irradiation and intramolecularly crosslinked nanoparticles are formed by radical coupling process in dilute regime. Resulting single chain nanoparticles and intermediates are characterized by 1H NMR, gel permeation chromatography, differential scanning calorimetry, UV–Vis spectrometry and electron microscopy techniques.

Controllable Self-Assembly of Amphiphilic Tadpole-Shaped Polymer Single-Chain Nanoparticles Prepared through Intrachain Photo-cross-linking.

We report the use of intramolecular cross-linking chemistry as a tool to control the self-assembly of amphiphilic diblock copolymers (di-BCPs). Two amphiphilic di-BCPs of poly( N, N'-dimethylacrylamide)- block-polystyrene (PDMA- b-PS) with photo-cross-linkable cinnamoyl groups in either hydrophobic or hydrophilic blocks were prepared using reversible addition-fragmentation chain transfer polymerization. Intramolecular photo-cross-linking of cinnamoyl groups led to the formation of tadpole-shaped polymer single-chain nanoparticles (SCNPs) consisting of a self-collapsed block as the "head" and an un-cross-linked block as the "tail". When intramolecular photo-cross-linking was carried out in hydrophobic PS blocks, a clear morphological transition from branched cylindrical micelles (for the linear di-BCP) to completely spherical micelles at a dimerization degree of ∼63% was observed. A pattern of morphological transitions from cylindrical micelles to spherical micelles is observed through stepwise downsizing the length of cylindrical micelles when increasing the self-collapse degree of PS blocks, whereas, in case of photo-cross-linking carried out in hydrophilic PDMA blocks, the size of micelles showed a dramatic increase due to the shift of hydrophobic-to-hydrophilic balance. When the cross-linking degree of PDMA blocks reached >60%, tadpole-shaped SCNPs assembled into nonconventional aggregates with a nonsmooth surface. Our results illustrate the impact of chain topologies on the self-assembly outcomes of amphiphilic di-BCPs, which likely opens a door to control the micellar morphologies from just one parent linear di-BCP, rather than resynthesizing BPCs with different volume fractions of the two blocks.

Preparation and Preliminary Evaluation of Povidone Single-Chain Nanoparticles as Potential Drug Delivery Nanocarriers

One of the key areas in nanomedicine is the use of nanometer-sized materials as nanocarriers for therapeutic and diagnostic (theranostic) purposes. In particular, nanoparticles (NPs) have attracted a considerable attention due to their small size that confers the ability to be transported more easily through the body. Ideally, nanocarriers would be biocompatible and biodegradable so the involvement of soft matter-based NPs is an interesting approach. Folding individual polymer chains to single-chain nanoparticles (SCNPs) endows the resulting soft nano-objects with promising prospects for drug encapsulation and subsequent controlled delivery. In this work, we report on the preparation and preliminary (in vitro) evaluation of Povidone SCNPs as potential drug delivery nanocarriers. We select Povidone (polyvinylpyrrolidone) as a water-soluble polymer with a large commercial use in medicine, which is biocompatible and non-antigenic as well as safe for oral and topical applications. For evaluation of Povidone SCNPs as drug delivery nanocarriers, we select two drugs with reported anti-cancer activity: (i) Cisplatin, a widely used hydrophilic anticancer agent for treatment of a variety of cancer cells; and (ii) Lovastatin, a lipophilic compound with in vitro anti-proliferative, pro-apoptotic and anti-invasive effects in different cancer cell lines. After showing release of these drugs from Povidone SCNPs, we demonstrate that these nanoparticles can be rendered fluorescent in combination with functional aggregation-induced emission (AIE) fluorophore molecules paving the way to the potential development of theranostic Povidone SCNPs.

Self-catalysed folding of single chain nanoparticles (SCNPs) by NHC-mediated intramolecular benzoin condensation

A self-catalysed folding strategy to form single chain nanoparticles (SCNPs) was developed via an intramolecular N-heterocyclic carbene (NHC)-mediated benzoin condensation.

M24+ paddlewheel clusters as junction points in single-chain nanoparticles

A straightforward approach to incorporate copper and molybdenum dimetallic clusters into well-defined single-chain nanoparticles, featuring unique paddlewheel structures as junction points, is introduced.

Counting loops in sidechain-crosslinked polymers from elastic solids to single-chain nanoparticles.

The vast differences in material properties accessible via crosslinking of sidechain-functionalized polymers are driven by topology. For example, vulcanized rubbery networks feature intermolecular connections and loop topologies of various orders while single-chain nanoparticles (SCNPs) are comprised, in principle, entirely of primary loops. Despite this fact, precise quantification of loops in sidechain crosslinked polymers has not been accomplished. Here, it is demonstrated that by introducing cleavable linkers and mass labels onto the pendant functional groups of reactive polymers, the number of primary loops in sidechain crosslinked materials ranging from rubbery networks (gels) to soluble SCNPs can be precisely quantified. This study sheds new light on the topology of sidechain-crosslinked networks, providing design principles for augmenting the properties of this industrially and academically important class of materials through topological control.

Valuable structure-size relationships for tadpole-shaped single-chain nanoparticles with long and short flexible tails unveiled.

Tadpole-shaped single-chain nanoparticles (TSCNPs) are useful soft building blocks for nanotechnology composed of a flexible polymer chain tethered to an intramolecularly folded single-chain nanoparticle. We disclose herein valuable structure-size relationships for a priori TSCNP design depending on tail length, which are validated by experimental data from multiple TSCNP systems, allowing, for the first time, the prediction of TSCNP size before synthesis.

Strengths and limitations of size exclusion chromatography for investigating single chain folding – current status and future perspectives

Synthetic approaches for Single-Chain Nanoparticles (SCNPs) developed rapidly during the last decade, opening a multitude of avenues for the design of functional macromolecular chains able to collapse into defined nanoparticles. However, the analytical evaluation of the SCNP formation process still requires critical improvements.

Associative properties of poly(ethylene glycol)-poly(vinyl acetate) comb-like graft copolymers in water.

The self-assembly of amphiphilic graft copolymers is generally reported for polymer melts or polymers deposited onto surfaces, while a small number of cases deal with binary mixtures with water. We report on the associative properties of poly(ethylene glycol)-graft-poly(vinyl acetate) (PEG-g-PVAc) comb-like copolymers in water, demonstrating the existence of a percolative behaviour when increasing the PEG-g-PVAc content. Rheology, light- and small-angle X-ray scattering experiments, together with dissipative particle dynamics simulations, reveal a progressive transition from spherical polymer single-chain nanoparticles (SCNPs) towards hierarchically complex structures as the weight fraction of the polymer in water increases. The ability of PEG-g-PVAc to attain different nano- and microstructures is of great importance in numerous applications such as in the fields of cosmetics, detergency and drug delivery.