Dynamics of Single-Chain Nanoparticles under Crowding: A Neutron Spin Echo Study.

We present a neutron spin echo (NSE) investigation to examine the impact of macromolecular crowding on the dynamics of single-chain nanoparticles (SCNPs), serving as synthetic models for biomacromolecules with flexibility and internal degrees of freedom, such as intrinsically disordered proteins (IDPs). In particular, we studied the dynamics of a medium-size poly(methyl methacrylate) (PMMA)-based SCNP (33 kDa) in solutions with low- (10 kDa) and high- (100 kDa) molecular weight analogous deuterated PMMA linear crowders. The dynamic structure factors of the SCNPs in dilute solution show certain degrees of freedom, yet the analysis in terms of the Zimm model reveals high internal friction that effectively stiffens the chain-a phenomenon also observed for IDPs. Under crowding conditions, the internal dynamics remains essentially unchanged, but the center-of-mass diffusion slows down. The effective viscosity felt by the SCNPs at the timescales probed by NSE is lower than the macroscopic viscosity of the crowder solution, and it does not depend significantly on the molecular weight.

Structure of Single-Chain Nanoparticles under Crowding Conditions: A Random Phase Approximation Approach.

The conformation of poly(methyl methacrylate) (PMMA)-based single-chain nanoparticles (SCNPs) and their corresponding linear precursors in the presence of deuterated linear PMMA in deuterated dimethylformamide (DMF) solutions has been studied by small-angle neutron scattering (SANS). The SANS profiles were analyzed in terms of a three-component random phase approximation (RPA) model. The RPA approach described well the scattering profiles in dilute and crowded solutions. Considering all the contributions of the RPA leads to an accurate estimation of the single chain form factor parameters and the Flory-Huggins interaction parameter between PMMA and DMF. The value of the latter in the dilute regime indicates that the precursors and the SCNPs are in good solvent conditions, while in crowding conditions, the polymer becomes less soluble.

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 Extra Solvent Power of Ionic Liquids for Monomers, Polymers, and Dry/Wet Globular Single-Chain Polymer Nanoparticles.

Ionic liquids (ILs) have shown advantages in organic synthesis and catalysis, energy storage and conversion, and a variety of pharmaceutical applications. Understanding the miscibility behavior of IL/monomer, IL/polymer, and IL/polymer nanoparticle mixtures is critical for the use of ILs as green solvents in polymerization processes as well as to rationalize recent observations concerning the superior solubility of some proteins in ILs when compared to standard solvents. In this work, the most relevant results obtained in terms of extended three-component Flory-Huggins theory concerning the extra solvent power (ESP) of ILs when compared to traditional nonionic solvents for monomeric solutes (Case I), linear polymers (Case II), dry (i.e., without IL inside) globular single-chain polymer nanoparticles (SCNPs) (Case III), and wet (i.e., with IL inside) globular SCNPs (Case IV) are presented. Moreover, useful ESP maps are drawn for the first time for IL mixtures corresponding to Cases I, II, III, and IV at a constant temperature and pressure. Finally, a potential pathway to improve the miscibility of nonionic polymers in ILs is proposed.

Excellent Stability in Water of Single-Chain Nanoparticles against Chain Scission by Sonication.

In this study the superior stability against degradation induced by ultrasound irradiation of water-soluble single-chain polymer nanoparticles when compared to their parent precursor polymers is reported, and a loop scission mechanism in support of such behavior is suggested.

A Solvent-Based Strategy for Tuning the Internal Structure of Metallo-Folded Single-Chain Nanoparticles.

Controlling the spatial distribution of catalytic sites in metallo-folded single-chain nanoparticles (SCNPs) is a first step toward the rational design of improved catalytic soft nano-objects. Here an unexplored pathway is reported for tuning the internal structure of metallo-folded SCNPs. Unlike the conventional SCNP synthesis in good solvent (protocol I), the proposed new route (protocol II) is based on the use of amphiphilic random copolymers and transfer, after SCNP formation, from selective to good (nonselective) solvent conditions. The size and morphology of the SCNPs obtained by the two protocols, and the corresponding spatial distribution of the catalytic sites, have been determined by combining results from size exclusion chromatography with triple detection, small-angle X-ray scattering and molecular dynamics (MD) simulations. Remarkably, the use of these protocols allows the tuning of the internal structure of the metallo-folded SCNPs, as supported by MD simulations results. While the conventional protocol I yields a homogeneous distribution of the catalytic sites in the SCNP, these are arranged into clusters in the case of protocol II.

Advances in single chain technology.

The recent ability to manipulate and visualize single atoms at atomic level has given rise to modern bottom-up nanotechnology. Similar exquisite degree of control at the individual polymeric chain level for producing functional soft nanoentities is expected to become a reality in the next few years through the full development of so-called "single chain technology". Ultra-small unimolecular soft nano-objects endowed with useful, autonomous and smart functions are the expected, long-term valuable output of single chain technology. This review covers the recent advances in single chain technology for the construction of soft nano-objects via chain compaction, with an emphasis in dynamic, letter-shaped and compositionally unsymmetrical single rings, complex multi-ring systems, single chain nanoparticles, tadpoles, dumbbells and hairpins, as well as the potential end-use applications of individual soft nano-objects endowed with useful functions in catalysis, sensing, drug delivery and other uses.