Single Polymer Chain Research Articles

Single-Chain Polymer Nanoparticles Targeting the Ookinete Stage of Malaria Parasites.

Malaria is an infectious disease transmitted by mosquitos, whose control is hampered by drug resistance evolution in the causing agent, protist parasites of the genus Plasmodium, as well as by the resistance of the mosquito to insecticides. New approaches to fight this disease are, therefore, needed. Research into targeted drug delivery is expanding as this strategy increases treatment efficacies. Alternatively, targeting the parasite in humans, here we use single-chain polymer nanoparticles (SCNPs) to target the parasite at the ookinete stage, which is one of the stages in the mosquito. This nanocarrier system provides uniquely sized and monodispersed particles of 5-20 nm, via thiol-Michael addition. The conjugation of succinic anhydride to the SCNP surface provides negative surface charges that have been shown to increase the targeting ability of SCNPs to Plasmodium berghei ookinetes. The biodistribution of SCNPs in mosquitos was studied, showing the presence of SCNPs in mosquito midguts. The presented results demonstrate the potential of anionic SCNPs for the targeting of malaria parasites in mosquitos and may lead to progress in the fight against malaria.

Study of the Dynamic Viscoelasticity of Single Poly(N-isopropylacrylamide) Chains Using Atomic Force Microscopy

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) is of great interest in the fields of medicine and pharmacology because its lower critical solubility temperature (LCST) is close to the physiological temperature. The understanding of the phase transfer mechanism of PNIPAM near the LCST is of great significance for the design, development, and application of its derivatives. In this study, a dynamic single-molecule force spectroscopy (SMFS) approach was used to quantitatively assess the dynamic viscoelasticity of single PNIPAM chains at different temperatures. We found that the relationship between the viscoelasticity coefficient of a single polymer chain in the low elongation region and the number of chain segments below the LCST was in accordance with the prediction of the Kirkwood model. Above the LCST, the PNIPAM chains exhibited different viscoelastic behaviors that were determined by their conformations. Importantly, the characterization of dynamic viscoelasticity allowed us to observe the phase transition behavior of single polymer chains in the low elongation region where they are similar to random coils, which helped us to understand the microscopic mechanism of their temperature response. In particular, above the LCST, the PNIPAM chains no longer underwent purely entropic elastic behavior but instead displayed enthalpic viscoelastic behavior dominated by intramolecular hydrogen bonds.

Formation of zinc phthalocyanine on polymethyl methacrylate chain: Its nanographene‐based composite, thermal, electrical and optical behaviors

AbstractPoly[4‐((4‐vinylbenzyl)oxy) phthalonitrile‐co‐methyl methacrylate] [P(VBOPN10.7%‐co‐MMA)] was prepared by atom transfer radical polymerization (ATRP) method at 110°C. Green colored single chain polymer molecule via intramolecular formation of zinc phthalocyanine (SCP‐ZnPc) on polymer chain was synthesized using VBOPN as a precursor copolymer under conditions of dilute cyclohexanol and at 140–150°C. The successful formation of zinc phthalocyanine on a single chain molecule was confirmed using Fourier‐transform infrared spectroscopy (FT‐IR) and UV/Vis spectroscopy techniques. Nanogaphene‐based SCP‐ZnPc composite was prepared to employ 6 weight (wt)% of total weight and were investigated its thermal, electrical, dielectric and optical properties. The dielectric and DC electrical conductivity of SCP‐ZnPc/NG 6 wt% nanocomposite were found to increase depending upon temperature. And the conduction obeyed the Arrhenius relationship with the activation energy, Ea values for I. and II. regions were 0.345 eV and 0.275 eV, respectively. The optical constants (refractive index, real value of optical dielectric constant) and the optical band gap of SCP‐ZnPc/NG 6 wt% were estimated. The direct band gap and refractive index of SCP‐ZnPc/NG 6 wt% were estimated, and its direct band gap was estimated as 2.7 eV.

Color-Tunable Binary Copolymers Manipulated by Intramolecular Aggregation and Hydrogen Bonding.

Construction of color-tunable luminescent polymeric materials with enhanced emission intensity and room-temperature phosphorescence (RTP) performance regulated by a single chromophore component is highly desirable in the scope of photoluminescent materials. Herein, a set of binary copolymers were facilely synthesized using free radical polymerization by selecting different types of polymer matrix and N-substituted naphthalimides (NPA) as chromophores. Surprisingly, the fluorescence emission of copolymers could be remarkably enhanced, because of the intramolecular aggregation of NPA manipulated by a single polymer chain in both solution and solid state. Moreover, RTP signals of binary copolymers were all clearly observed in the air without any processing procedure, because of the embedding of phosphors into hydrogen bonding networks after copolymerization with vinyl-based acrylamide monomers. Taking advantages of the synergistic effect of copolymerization-induced aggregation and copolymerization-induced rigidification to promote optical performance, UV stimulus-responsive luminescent polymer films with processability, flexibility, and adjustable emission wavelength were simply prepared using a drop-casting method in large scale, the setting of which is the basis for application in the fields of organic optoelectronics, information security, and bioimaging/sensing.

Enhancing Cellular Internalization of Single-Chain Polymer Nanoparticles via Polyplex Formation.

Intracellular delivery of nanoparticles is crucial in nanomedicine to reach optimal delivery of therapeutics and imaging agents. Single-chain polymer nanoparticles (SCNPs) are an interesting class of nanoparticles due to their unique site range of 5-20 nm. The intracellular delivery of SCNPs can be enhanced by using delivery agents. Here, a positive polymer is used to form polyplexes with SCNPs, similar to the strategy of protein and gene delivery. The size and surface charge of the polyplexes were evaluated. The cellular uptake showed rapid uptake of SCNPs via polyplex formation, and the cytosolic delivery of the SCNPs was presented by confocal microscopy. The ability of SCNPs to act as nanocarriers was further explored by conjugation of doxorubicin.

Molecular dynamics study on the thermal conductivity of a single polyethylene chain: Strain dependence and potential models’ effect

The thermal conductivity of a single polymer chain, which is an important factor in the rational design of polymer-based thermal management materials, is strongly affected by the strain state of the chain. In the present study, using non-equilibrium molecular dynamics simulations, the thermal conductivity of a single polyethylene chain, representing a typical polymer chain, was calculated as a function of strain. To investigate the effect of different modeling of covalent bonds, the results were compared for reactive and non-reactive potential models, the AIREBO and NERD potentials, respectively. When the strain ε was as small as ε < −0.03, i.e., under slight compression, the thermal conductivity values were similar regardless of the potential model and increased with increasing strain. However, the two potential models showed qualitatively different behaviors for larger strains up to ε < 0.15: the thermal conductivity calculated by the non-reactive potential continually grows with increasing strain, whereas that by the reactive potential model is saturated. The analysis of internal stress and vibrational density of states suggested that the saturation behavior is due to the weakening of the covalent bond force as the C–C bond elongates, and thus, the result of the reactive model is likely more realistic. However, for ε > 0.1, the reactive potential also produced unphysical results due to the effect of the switching function, describing the formation and breaking of covalent bonds. The present results indicate that careful selection of the potential model and deformation range is necessary when investigating the properties of polymers under tensile strain.

Single-Chain Polymer Nanoparticles for Addressing Morphologies and Functions at the Nanoscale: A Review

This review discusses recent advances concerning morphologies and functions obtained from single-chain nanoparticles (SCNPs). SCNPs are unimolecular, soft nano-objects consisting of individual polymer chains collapsed to a certain degree by means of intramolecular bonding. Many of potential applications of SCNPs rely on their peculiar molecular morphology adopted in solution. SCNPs coming from random or block copolymers can yield ordered structures by self-assembly in a wide range of morphologies including spheres, cylinders, bicontinuous structures, lamellae, vesicles, and many other complex or hierarchical assemblies. These nanocomposites can provide practical applications, still in their infancy, in several fields. The classification of SCNPs according to their morphologies will help to link their function to the specific applications.

Freely jointed chain models with extensible links.

Analytical relations for the mechanical response of single polymer chains are valuable for modeling purposes, on both the molecular and the continuum scale. These relations can be obtained using statistical thermodynamics and an idealized single-chain model, such as the freely jointed chain model. To include bond stretching, the rigid links in the freely jointed chain model can be made extensible, but this almost always renders the model analytically intractable. Here, an asymptotically correct statistical thermodynamic theory is used to develop analytic approximations for the single-chain mechanical response of this model. The accuracy of these approximations is demonstrated using several link potential energy functions. This approach can be applied to other single-chain models, and to molecular stretching in general.

Single-chain models illustrate the 3D RNA folding shape during translation

The three-dimensional conformation of RNA is important in the function and fate of the molecule. The common conformation of mRNA is formed based on the closed-loop structure and internal base pairings with the activity of the ribosome movements. However, recent reports suggest that the closed-loop structure might not be formed in many mRNAs. This implies that mRNA can be considered as a single polymer in the cell. Here, we introduce the Three-dimensional RNA Illustration Program (TRIP) to model the three-dimensional RNA folding shape based on single-chain models and angle restriction of each bead component from previously reported single-molecule fluorescence in situ hybridization (smFISH) experimental data. This simulation method was able to recapitulate the mRNA conformation change of the translation activity and three-dimensional positional interaction between an organelle and its localized mRNAs as end-to-end distances. Within the analyzed cases, base-pairing interactions only have minor effects on the three-dimensional mRNA conformation, and instead single-chain polymer characteristics have a more significant impact on the conformation. This top-down method will be used to interpret the aggregation mechanism of mRNA under different cellular conditions such as nucleolus and phase-separated granules.

Conformation Dynamics of Single Polymer Strands in Solution.

Conformational changes in macromolecules significantly affect their functions and assembly into high-level structures. Despite advances in theoretical and experimental studies, investigations into the intrinsic conformational variations and dynamic motions of single macromolecules remain challenging. Here, liquid-phase transmission electron microscopy enables the real-time tracking of single-chain polymers. Imaging linear polymers, synthetically dendronized with conjugated aromatic groups, in organic solvent confined within graphene liquid cells, directly exhibits chain-resolved conformational dynamics of individual semiflexible polymers. These experimental and theoretical analyses reveal that the dynamic conformational transitions of the single-chain polymer originate from the degree of intrachain interactions. In situ observations also show that such dynamics of the single-chain polymer are significantly affected by environmental factors, including surfaces and interfaces.

Neutralization of ionic interactions by dextran-based single-chain nanoparticles improves tobramycin diffusion into a mature biofilm

The extracellular matrix protects biofilm cells by reducing diffusion of antimicrobials. Tobramycin is an antibiotic used extensively to treat P. aeruginosa biofilms, but it is sequestered in the biofilm periphery by the extracellular negative charge matrix and loses its efficacy significantly. Dispersal of the biofilm extracellular matrix with enzymes such as DNase I is another promising therapy that enhances antibiotic diffusion into the biofilm. Here, we combine the charge neutralization of tobramycin provided by dextran-based single-chain polymer nanoparticles (SCPNs) together with DNase I to break the biofilm matrix. Our study demonstrates that the SCPNs improve the activity of tobramycin and DNase I by neutralizing the ionic interactions that keep this antibiotic in the biofilm periphery. Moreover, the detailed effects and interactions of nanoformulations with extracellular matrix components were revealed through time-lapse imaging of the P. aeruginosa biofilms by laser scanning confocal microscopy with specific labeling of the different biofilm components.

Single-chain polymer nanoparticles-encapsulated chiral bifunctional metal-organic frameworks for asymmetric sequential reactions

• Pd(II) was stably loaded in the channels of MOFs using Pd(II) cross-linked single-chain nanoparticles. • A bifunctional catalyst Pd-SCNP@DUT-67-Pro was prepared by the “one-pot” method. • The catalyst was used for Suzuki coupling/asymmetric aldol sequential reactions. • The catalyst can be used for 3 cycles without activity loss and structural changes. Among multitudinous development methods of the active sites of MOFs, the encapsulation method is widely used. However, metal ions with excellent catalytic performance are not suitable for being directly encapsulated in MOFs. Because metal ions are much smaller than the pore sizes of MOFs, they will move in and out of the channels of MOFs haphazardly rather than being stably loaded in the channels like that of enzymes and metal nanoparticles. Here, to solve the above-mentioned problem, the metal ion Pd(II) was introduced into the single-chain polymer nanoparticles (SCNP) to form Pd(II) cross-linked SCNP (Pd-SCNP). A bifunctional heterogeneous catalyst Pd-SCNP@DUT-67-Pro was prepared by introducing Pd-SCNP and chiral proline into the channels and on the Zr-clusters of DUT-67, respectively. The catalyst displayed excellent enantioselectivity and good coupling performance in Suzuki coupling/asymmetric aldol sequential reactions. Besides, Pd-SCNP@DUT-67-Pro still retained good catalytic activity within three cycles of reuse.

Manipulation of a Single Polymer Chain: From the Nanomechanical Properties to Dynamic Structure Evolution

Manipulation of a Single Polymer Chain: From the Nanomechanical Properties to Dynamic Structure Evolution

Organized states arising from compression of single semiflexible polymer chains in nanochannels.

We use molecular dynamics simulation to probe the nonequilibrium physics of single nanochannel-confined semiflexible polymers in a homogeneous flow field. The flow field compresses the polymer against the end of the nanochannel, simulating an experiment of a nanochannel confined chain compressed against a slit barrier. The flow-based compression gives rise to a packing of the chain against the channel end that possesses a striking organization, consisting of interweaving of folds and circular coils. For stiff chains at low flow, we find that the organization is dominated by repeated hairpin folds. For stiff chains at higher flow, we observe that circular coils arise along with the folds, with folding and coiling domains becoming interwoven at the highest flow speeds. Chain organization is retained even when the chain persistence length is on order of the channel width. We show that the global polymer organization, consisting of a number of defined folds and coiled loops, arises from the minimization of the total chain free energy.

Forming a Double-Helix Phase of Single Polymer Chains by the Cooperation between Local Structure and Nonlocal Attraction.

Double-helix structures, such as DNA, are formed in nature to realize many unique functions. Inspired by this, researchers are pursuing strategies to design such structures from polymers. A key question is whether the double helix can be formed from the self-folding of a single polymer chain without specific interactions. Here, using Langevin dynamics simulation and theoretical analysis, we find that a stable double-helix phase can be achieved by the self-folding of single semiflexible polymers as a result of the cooperation between local structure and nonlocal attraction. The critical temperature of double-helix formation approximately follows T^{cri}∼ln(k_{θ}) and T^{cri}∼ln(k_{τ}), where k_{θ} and k_{τ} are the polymer bending and torsion stiffness, respectively. Furthermore, the double helix can exhibit major and minor grooves due to symmetric break for better packing. Our results provide a novel guide to the experimental design of the double helix.

Preparation of AIE Functional Single-Chain Polymer Nanoparticles and Their Application in H2 O2 Detection through Intermolecular Heavy-Atom Effect.

Single-chain polymer nanoparticles (SCNPs) are soft matter constructed by intrachain crosslinks, with promising prospects in detection and catalysis. Herein, a fluorescent core (SCNPs) with aggregation-induced emission (AIE) is prepared, applying for H2 O2 detection through intermolecular heavy-atom effect. In detail, the SCNPs precursors are synthesized by ring-opening copolymerization. Then the SCNPs are prepared by intramolecularly cross-linking via olefin metathesis. Imitating the structure of AIE dots, SCNPs are encapsulated by H2 O2 -responsive polymers. Probably due to the stable secondary structure of SCNPs, the obtained micelles show stable fluorescence performance. Furthermore, as the heavy-atom, tellurium is introduced into the carriers to construct the heavy-atom effect. In this micelle-based system, the SCNPs act as the fluorescent core, and the stimuli-responsive polymer acts as the carrier and the fluorescent switch. The hydrophilicity of the tellurium-containing segment is affected by the concentration of H2 O2 , resulting in a change in the distance from the SCNPs, which ultimately leads to a change in the fluorescence intensity. Furthermore, tellurium is particularly sensitive to H2 O2 , which can detect low concentrations of H2 O2 . The SCNPs are merged with AIE materials, with the hope of exploring new probe designs.

Single-chain chiral Ru-Cu star polymers for highly efficient catalytic aqueous asymmetric transfer hydrogenation

It is of great research value to design simulated enzyme catalysts with high catalytic activity, high selectivity and that are reusable in water. In this work, a star-shaped thermal responsive polymer-Ru/diamine functional intelligent chiral catalyst was synthesized by controlled atom transfer radical polymerization (ATRP). Polymerization can be controlled through self-catalysis of chiral monomers and polymers. Because of the complex that forms between the chiral polymer and Cu2+, the synthesized star polymer experiences a chiral amplification effect. At the same time, the star Ru-Cu catalyst can be assembled into single-chain polymers in water, which showed better catalytic activity and selectivity than the Ru catalyst for aqueous asymmetric reactions, and can be recycled up to six times. Our work provides a new method for controllable synthesis of chiral polymers without additional ligands and the need to remove Cu2+ at the end of the reaction, making the method green and more cost-effective. In summary, bimetallic nanocatalysts were controllably constructed by star chiral polymers through the ATRP pathway. This method significantly aids the development of helical chiral polymers and the preparation of high-efficiency enzyme catalysts.

Vibrations Responsible for Luminescence from HJ-Aggregates of Conjugated Polymers Identified by Cryogenic Spectroscopy of Single Nanoparticles.

A single polymer chain can be thought of as a covalently bound J-aggregate, where the microscopic transition-dipole moments line up to emit in phase. Packing polymer chains into a bulk film can result in the opposite effect, inducing H-type coupling between chains. Cofacial transition-dipole moments oscillate out of phase, canceling each other out, so that the lowest-energy excited state turns dark. H-aggregates of conjugated polymers can, in principle, be coaxed into emitting light by mixing purely electronic and vibronic transitions. However, it is challenging to characterize this electron-phonon coupling experimentally. In a bulk film, many different conformations exist with varying degrees of intrachain J-type and interchain H-type coupling strengths, giving rise to broad and featureless aggregate absorption and emission spectra. Even if single nanoparticles consisting of only a few single chains are grown in a controlled fashion, the luminescence spectra remain broad, owing to the underlying molecular dynamics and structural heterogeneity at room temperature. At cryogenic temperatures, emission from H-type aggregates should be suppressed because, in the absence of thermal energy, internal conversion drives the aggregate to the lowest-energy dark state. At the same time, electronic and vibronic transitions narrow substantially, facilitating the attribution of spectral signatures to distinct vibrational modes. We demonstrate how to distinguish signatures of interchain H-type aggregate species from those of intramolecular J-type coupling. Whereas all dominant vibronic modes revealed in the photoluminescence (PL) and surface-enhanced resonance Raman scattering spectra of a single chromophore within a single polymer chain are identified in the J-type aggregate luminescence spectra, they are not all present at once in the H-type spectra. Universal spectral features are found for the luminescence from strongly HJ-coupled chains, clearly resolving the vibrations responsible for the nonadiabatic excited-state molecular dynamics that enable light emission. We discuss the possible combinations of vibrational modes responsible for H-type aggregate PL and demonstrate that only one, mainly the lowest energy one, of the three dominant vibrational modes contributes to the 0-1 transition, whereas combinations of all three are found in the 0-2 transition. From this analysis, we can distinguish between energy shifts due to either J-type intrachain coupling or H-type interchain interactions, offering a means to directly discriminate between structural and energetic disorder.

All-Atom Molecular Dynamics Simulations on a Single Chain of PET and PEV Polymers.

Polyethylene vanillic (PEV), a bio-based material, has mechanical and thermal properties similar to polyethylene terephthalate (PET), the most common polymer used in industries. The present study aimed to investigate and compare their structural dynamics and physical data using a computational approach. The simple model of a single-chain polymer containing 100 repeating units was performed by all-atom molecular dynamics (MD) simulations with refined OPLS–AA force field parameters. As a result, the flexibility of the PEV structure was greater than that of PET. PET and PEV polymers had the predicted glass transition temperature Tg values of approximately 345 K and 353 K, respectively. PEV showed a slightly higher Tg than PET, consistent with current experimental evidence.

Hyaluronan homeostasis and its role in pain and muscle stiffness.

Hyaluronan (HA) is a glycosaminoglycan that consists of single-chain polymers of disaccharide units of glucuronic acid and N-acetylglucosamine. It is a chief constituent of the extracellular matrix. About 27% of the total HA in the body is expressed in the skeleton and connective tissue, while 8% is expressed in muscles. In physiological conditions, HA functions as a lubricant and viscoelastic shock absorber. Additionally, HA is part of complex cellular signaling which modulates nociception and inflammation. This study aims to understand the role that HA plays in the musculoskeletal system, specifically in muscles and the surrounding fascia. This review is also intended to further understand HA homeostasis and the process of its synthesis, degradation, and clearance from the local tissue. The authors examined muscle pain and stiffness as pathological conditions associated with HA accumulation.