Interchain Interactions Research Articles

Modulation of α-synuclein aggregation amid diverse environmental perturbation.

Intrinsically disordered protein α-synuclein (αS) is implicated in Parkinson's disease due to its aberrant aggregation propensity. In a bid to identify the traits of its aggregation, here we computationally simulate the multi-chain association process of αS in aqueous as well as under diverse environmental perturbations. In particular, the aggregation of αS in aqueous and varied environmental condition led to marked concentration differences within protein aggregates, resembling liquid-liquid phase separation (LLPS). Both saline and crowded settings enhanced the LLPS propensity. However, the surface tension of αS droplet responds differently to crowders (entropy-driven) and salt (enthalpy-driven). Conformational analysis reveals that the IDP chains would adopt extended conformations within aggregates and would maintain mutually perpendicular orientations to minimize inter-chain electrostatic repulsions. The droplet stability is found to stem from a diminished intra-chain interactions in the C-terminal regions of αS, fostering inter-chain residue-residue interactions. Intriguingly, a graph theory analysis identifies small-world-like networks within droplets across environmental conditions, suggesting the prevalence of a consensus interaction patterns among the chains. Together these findings suggest a delicate balance between molecular grammar and environment-dependent nuanced aggregation behavior of αS.

Transition metal centers with anharmonic elastic interactions in one-dimensional spin-crossover solids

An exact examination of a one-dimensional (1D) anharmonic elastic model describing the thermodynamic properties of spin-crossover (SCO) solids is presented. This elastic model incorporates both intra-chain and mean field inter-chain interactions, providing a more understanding of 1D SCO materials. Numerical findings for a linear chain of spins unveil intriguing features, such as a two-step-like transition. Extending the model to interacting chains leads to an additional term in the effective ligand field of the system’s Hamiltonian, thereby enhancing its predictive power by accounting for more elastic constants of interactions. This augmentation reinforces the model’s validity in capturing the spin-crossover phenomenon. Numerical results in this extended framework elucidate clearer two-step-like spin crossover transitions, with the HS_LS fraction of spins approaching maximum values at equilibrium temperature Teq.

Synthesis of a copolymer with a dynamic disulfide network and its application to a lithium-ion capacitor polymer electrolyte

Polymer electrolytes are being actively researched in energy storage applications because of their large operating potential range and cycle stability. Among them, poly(ethylene glycol) (PEG) is most commonly used to take advantage of the high ionic conductivity generated by polar functional groups in the structure. However, the polar functional group in the PEG structure has limitations that not only interfere with the movement of ions through interchain interaction, but also prevent the penetration of the polymer structure into the electrode material. In this paper, a copolymer into which a dynamic disulfide bonding network was introduced based on PEG was synthesized to control the polar functional effect of the polymer chain. The copolymer was then applied as a lithium-ion hybrid capacitor electrolyte. Due to the disconnection of the dynamic disulfide bond, the viscosity of the polymer electrolyte was reduced, allowing smooth penetration into the electrode material. The copolymer-based polymer electrolyte showed better energy storage performance and shorter relaxation time than a commercial PEG-based device (225 F g−1/5.18 × 10−5 s for copolymer and 166 F g−1/7.96 × 10−3 s for PEG). In addition, the copolymer not only preserved excellent ionic conductivity of PEG at a certain level (from 6.3 × 10−4 S cm−1 to 3.73 × 10−4 S cm−1) but also decreased the polarity of the material due to the presence of the nonpolar disulfide chain, thereby reducing crystallinity and dielectric permittivity (from 1460 to 246).

Human ferritin nanocarriers for drug-delivery: A molecular view of the disassembly process

Ferritins are natural proteins which spontaneously self-assemble forming hollow nanocages physiologically deputed to iron storage and homeostasis. Thanks to their high stability and easy production in vitro, ferritins represent an intriguing system for nanobiotechnology. Here we investigated the mechanism of disassembly and reassembly of a human recombinant ferritin constituted by the heavy chain (hHFt) exploiting a new procedure which involves the use of minimal amounts of sodium dodecyl sulfate (SDS) and assessed its effectiveness in comparison with two commonly used protocols based on pH shift at highly acidic and alkaline values. The interest in this ferritin as drug nanocarrier is related to the strong affinity of the human H-chain for the transferrin receptor TfR-1, overexpressed in several tumoral cell lines. Using different techniques, like NMR, TEM and DLS, we demonstrated that the small concentrations of SDS can eliminate the nanocage architecture without detaching the monomers from each other, which instead remain strongly associated. Following this procedure, we encapsulated into the nanocage a small ruthenium complex with a remarkable improvement with respect to previous protocols in terms of yield, structural integrity of the recovered protein and encapsulation efficiency. In our opinion, the extensive network of interchain interactions preserved during the SDS-based disassembly procedure represents the key for a complete and correct hHFt reassembly.

Association of Thermoresponsive Diblock Copolymer PDEGMA-b-PDIPAEMA in Aqueous Solutions: The Influence of Terminal Groups.

Aqueous solutions of a thermoresponsive diblock copolymer poly(di-[ethylene glycol] methyl ether methacrylate)-b-poly(2-[diisopropylamino] ethyl methacrylate) (PDEGMA-b-PDIPAEMA) were studied by static, dynamic and electrophoretic light scattering, small-angle X-ray scattering and differential scanning calorimetry. Thermoresponsive behavior of PDEGMA-b-PDIPAEMA was investigated at two pH values, pH = 2, at which the terminal carboxylic group of the PDEGMA chain and the PDIPAEMA block are protonated, and pH = 7, where the carboxyl terminal group is ionized while the PDIPAEMA block is partially deprotonated and more hydrophobic. Both at pH = 2 and 7, PDEGMA-b-PDIPAEMA copolymer underwent extensive association (the size of the aggregates was between 100 and 300 nm), indicating strong interchain interactions. While the measurements confirmed thermoresponsive behavior of PDEGMA-b-PDIPAEMA at pH = 7, no changes in the association with temperature were observed at pH 2 as the thermoresponsivity of PDEGMA was suppressed by hydrogen bonding between carboxylic groups and PDEGMA segments, as well as due to the increased hydrophilicity of the PDIPAEMA block. Fluorescence measurements with pyrene as a fluorescent probe showed that both at pH = 2 and pH = 7 the associates were able to solubilize hydrophobic substances.

Molecular simulation on structural and molecular properties of polymer-blend nanoparticles

Structural and molecular properties of homopolymer and polymer-blend nanoparticles were studied via Monte Carlo simulation of coarse-grained polyethylene-like models with different interchain interactions. For stronger interchain interaction, homopolymer nanoparticles become more compacted structures accompanied by higher bulk densities with sharper surface profiles. For polymer-blend nanoparticles, chain components with weaker/stronger interchain interaction tend to stay in the surface/bulk region and their density profiles exhibit uneven distribution. Near the surface, end/middle monomers are more segregated/depleted for stronger interchain interaction., Both bond and chain exhibit relatively random orientation in the bulk region, but they have noticeably anisotropic orientation, especially near the surface. Compared to the homopolymer nanoparticles, chain components in polymer-blend structures have more distortion, mostly near the surface. For stronger interchain interaction, polymers gain a larger fraction of gauche conformation in the bulk region and nanoparticles become denser packed structures.

Histidine Protonation Behaviors on Structural Properties and Aggregation Properties of Aβ(1-42) Mature Fibril: Approaching by Edge Effects.

The histidine behavior plays a crucial role in the structural and aggregation properties of protein folding and misfolding. Understanding the histidine behavior at the edge of the protein structure is critical for finding ways to disrupt fibril elongation and growth, but this impact remains poorly understood. In the current study, we used molecular dynamics simulations to investigate the edge substitution effect of histidine protonation on the structural and aggregation properties. Our data showed that ΔG1 contributed the most to binding affinity compared to ΔG2 and ΔG3. The different protonation states at the edge chain significantly impacted the secondary structure properties of the edge chain. Specifically, we found that such protonation behavior significantly affected specific regions, particularly the N-terminus (G9-Q15) and C-terminus (K28-A30). Further analysis confirmed that H6, H13, and H14 were directly involved in H-bonding networks with the C1_H14//C2_H13 interchain interactions critical for maintaining the interchain stability. Furthermore, we confirmed that H6, H13, and H14 were directly involved in the loss of the carbon skeleton contact in the N-terminus. Our findings indicate that the edge condition is more susceptible to changes in structural properties than the middle condition. The current study is helpful for understanding the histidine behavior hypothesis in related misfolding diseases.

A High-Performance Organic Photovoltaic System with Versatile Solution Processability.

Recently developed organic photovoltaic (OPV) materials have simultaneously closed the gaps in efficiency, stability, and cost for single-junction devices. Nonetheless, the developed OPV materials still pose big challenges in meeting the requirements for practical applications, especially regarding the prevalent issues of solution processability. Herein, a highly efficient polymer donor, named DP3, incorporating an electron-rich benzo[1,2-b:4,5-b']dithiophene unit as well as two similar and simple acceptor units is presented. Its primary objective is to enhance the interchain and/or intrachain interactions and ultimately fine-tune bulk-heterojunction microstructure. The DP3:L8-BO system demonstrates the highest power conversion efficiency (PCE) of 19.12%. This system also exhibits high-performance devices with over 18% efficiencies for five batches with various molecular weights (23.6-80.8KDa), six different blend thicknesses (95-308nm), differenced coating speeds (3.0-29.1mmin-1), with promising PCEs of 18.65% and 15.53% for toluene-processed small-area (0.029cm2) cells and large-area (15.40cm2) modules, thereby demonstrating versatile solution processability of the designed DP3:L8-BO system that is a strong candidate for commercial applications.

Cu(II) Specifically Disassembles Insulin Amyloid Nanostructures via Direct Interaction with Cross-β Fibrils.

In this work, we demonstrate direct evidence of the antiamyloid potential of Cu(II) ions against amyloid formation of insulin. The Cu(II) ions were found to efficiently disassemble the preformed amyloid nanostructures into soluble species and suppress monomer fibrillation under aggregation-prone conditions. The direct interaction of Cu(II) ions with the cross-β structure of amyloid fibrils causes substantial disruption of both the interchain and intrachain interactions, predominantly the H-bonds and hydrophobic contacts. Further, the Cu(II) ions show a strong affinity for the aggregation-prone conformers of the protein and inhibit their spontaneous self-assembly. These results reveal the possible molecular mechanism for the antiamyloidogenic potential of Cu(II) which could be important for the development of metal-ion specific therapeutic strategies against amyloid linked complications.

Accumulation of Hydrogen Bonds and van der Waals Interactions Determines Force Response between Two Parallel Cellulose Chains: Steered Molecular Dynamics Simulations.

We investigated the response forces between two parallel cellulose chains during the shearing and tearing processes by using steered molecular dynamics simulations. It was found that there are two logarithmic dependencies between response force and pulling speed in shearing processes but only one in tearing, according to Bell's equation by fitting the f-ln v curve. The mechanism is that there are 2-fold interactions determining the force response between two parallel cellulose chains resisting chain separation during a shearing process. Our results indicate that hydrogen bonds dominate the interchain interactions in the fast pull mode (FPM) for shearing, while van der Waals interactions dominate in the slow pull mode (SPM). For tearing, the one-by-one breaking of hydrogen bonds and van der Waals interactions plays a main role.

Imaging tunable Luttinger liquid systems in van der Waals heterostructures.

One-dimensional (1D) interacting electrons are often described as a Luttinger liquid1-4 having properties that are intrinsically different from those of Fermi liquids in higher dimensions5,6. In materials systems, 1D electrons exhibit exotic quantum phenomena that can be tuned by both intra- and inter-1D-chain electronic interactions, but their experimental characterization can be challenging. Here we demonstrate that layer-stacking domain walls (DWs) in van der Waals heterostructures form a broadly tunable Luttinger liquid system, including both isolated and coupled arrays. We have imaged the evolution of DW Luttinger liquids under different interaction regimes tuned by electron density using scanning tunnelling microscopy. Single DWs at low carrier density are highly susceptible to Wigner crystallization consistent with a spin-incoherent Luttinger liquid, whereas at intermediate densities dimerized Wigner crystals form because of an enhanced magneto-elastic coupling. Periodic arrays of DWs exhibit an interplay between intra- and inter-chain interactions that gives rise to new quantum phases. At low electron densities, inter-chain interactions are dominant and induce a 2D electron crystal composed of phased-locked 1D Wigner crystal in a staggered configuration. Increased electron density causes intra-chain fluctuation potentials to dominate, leading to an electronic smectic liquid crystal phase in which electrons are ordered with algebraical correlation decay along the chain direction but disordered between chains. Our work shows that layer-stacking DWs in 2D heterostructures provides opportunities to explore Luttinger liquid physics.

Simultaneously enhancing the mechanical and thermoelectric properties of diketopyrrolopyrrole-thiophene based conjugated polymers through dynamic hydrogen-bonding

Remarkable progress has been made in the development of thermoelectric materials based on diketonepyrrolopyrrole-thiophene (DPPT). However, achieving DPPT polymers with both high thermoelectric and mechanical properties remain a challenge. In this study, thymine groups, which are beneficial for the formation of intermolecular hydrogen bonds, were introduced into the side chains of DPPT, and a series of polymers (PDPPT-x) with different amount of thymine groups (x is the molar ratio of thymine side chains) were synthesized and characterized. The introducing thymine groups can regulate the self-assembly of conjugated polymers, effectively enhancing the crystallinity and molecular packing order, and thereby improve the charge carrier mobility. Additionally, the formed dynamic hydrogen-bonding networks by the thymine groups possess a moderate strength that can alleviate applied pressure and enhance the flexibility. Among these polymers, PDPPT-5 exhibited superior performance with excellent flexibility demonstrated by its elongation at break (up to 19.8 %), surpassing that of PDPPT-0 by a power factor of 2.2. In addition, the incorporation of 5 % amount of thymine groups can enhance the interchain interactions, thereby improving the crystallinity of the polymers and consequently enhancing the carrier mobility (4.26 × 10-3 cm2 V−1 s−1 for PDPPT-5 compared to 1.14 × 10-3 cm2 V−1 s−1 for PDPPT-0). Upon doping with FeCl3 at room temperature, the power factor of PDPPT-5 is about twice that of PDPPT-0. These results suggest that incorporating hydrogen bonding is a highly effective strategy for enhancing both the thermoelectric and mechanical properties of conjugated polymer-based thermoelectric materials.

Strategic design of degradable polyurethanes: Site-specific depolymerization, film-forming behavior, and reprocessability

This paper reports on the rational design of linear sustainable polyurethanes with on-demand depolymerization capabilities and film-forming properties. In this molecular approach, self-immolative urethane motifs are engineered to not only induce rapid degradation in response to an external stimulus via sequential elimination but also provide sufficient inter-chain interactions to yield nanofibers or free-standing films. Amalgamation with various isocyanate or polyol components results in a range of degradable polyurethanes, while doping with europium complexes or carbon black leads to the formation of free-standing hybrid films with photoluminescent or conductive properties, respectively. These films can be reversibly cast using a facile dissolution process, and the predetermined depolymerization products can then be used to generate upcycled materials such as polyurea or polyacrylate films. We believe that our conceptual design for sustainable polyurethanes can be advanced further when combined with conventional engineering techniques to meet industrial and environmental requirements and create desirable materials for contemporary applications.

Have a Cake and Eat it Too: A Nanofluidic Hybrid Membrane with Both High Stability and Ionic Conductivity

AbstractTwo‐dimensional nanofluidic membranes are promising candidates for various applications, such as energy conversion and ionic sensing. However, simultaneously achieving high stability and high ion transport in a nanofluidic membrane remains a great challenge. Herein, a robust and durable aramid nanofiber/carboxylated aramid nanofiber (ANF/cANF) nanofluidic hybrid membrane is designed with high ion conductivity and selectivity via surface grafting engineering and hybridization strategies. Due to the inherent ordered and asymmetric molecular structure, the strong interchain interactions of the ANF and the strong interfacial interactions between the ANF and cANF enable the membrane to exhibit robust structural stability in a wet state. Meanwhile, the enhanced surface charge enabled by the surface functionalization of carboxyl groups on the ANF results in excellent ion transport. As a result, the conductivity of the membrane is 5 and 36 times higher than the ANF membrane and bulk solution, respectively. Importantly, the ionic conductivity and mechanical strength of the membrane remain unchanged even after immersing in water for 90 days, demonstrating favorable underwater application potential. Moreover, the membrane is recyclable and has superior processability, allowing for large‐scale processing. This work provides a new strategy for designing durable and high‐ion‐transporting nanofluidic membranes for ion sensing and energy conversion.

Uniaxial extending neural probes for bleeding-absent implantation

Implantable neural probes, essential for brain electrophysiological research, have advanced with ultra-flexible designs to mitigate immune responses and postoperative complications. Strategies of shuttle-assisted implantation and temporary stiffening address issues in penetrating these probes into the target region, avoiding undesired bending. However, the risk of intraoperative bleeding remains due to these implants’ necessary rigidity during insertion. Here, we describe a neural probe with mechanical compliance accompanying self-implantation along the principal axis in the absence of bleeding. Crucial to the behavior is its anisotropic relaxation, which is dominated by the cross-sectional in-plane deformation inhibition due to interchain interactions between the parallel backbones in the globally aligned polymer system. We observed the ensured upright insertion of the probe into the brain while avoiding angiorrhexis with a two-photon microscope and a high-speed camera. The probes permit electrophysiological studies with minimal foreign body responses and imageological compatibility, underscoring their clinical potential.

Direct computations of viscoelastic moduli of biomolecular condensates.

In vitro facsimiles of biomolecular condensates are formed by different types of intrinsically disordered proteins including prion-like low complexity domains (PLCDs). PLCD condensates are viscoelastic materials defined by time-dependent, sequence-specific complex shear moduli. Here, we show that viscoelastic moduli can be computed directly using a generalization of the Rouse model and information regarding intra- and inter-chain contacts that is extracted from equilibrium configurations of lattice-based Metropolis Monte Carlo (MMC) simulations. The key ingredient of the generalized Rouse model is the Zimm matrix that we compute from equilibrium MMC simulations. We compute two flavors of Zimm matrices, one referred to as the single-chain model that accounts only for intra-chain contacts, and the other referred to as a collective model, that accounts for inter-chain interactions. The single-chain model systematically overestimates the storage and loss moduli, whereas the collective model reproduces the measured moduli with greater fidelity. However, in the long time, low-frequency domain, a mixture of the two models proves to be most accurate. In line with the theory of Rouse, we find that a continuous distribution of relaxation times exists in condensates. The single crossover frequency between dominantly elastic versus dominantly viscous behaviors is influenced by the totality of the relaxation modes. Hence, our analysis suggests that viscoelastic fluid-like condensates are best described as generalized Maxwell fluids. Finally, we show that the complex shear moduli can be used to solve an inverse problem to obtain distributions of relaxation times that underlie the dynamics within condensates.

Electrochemiluminescence enhanced by molecular engineering linear π-conjugated polymer: An ingenious ECL emitter for the construction of exosome sensing platform

Linear π-conjugated polymers (LCPs) with π-electron conjugation system have many remarkable optical characteristics such as fluorescence and electrochemiluminescence (ECL). However, the extremely strong interchain interaction and π-π stacking limit the luminescence efficiency. In this work, 1H-1,2,4-triazole-3,5-diamine was chosen as the polymer monomer and reacted with terephthalaldehyde via simple Schiff base condensation to synthesize LCPs. Subsequently, molecular engineering strategy was adopted to construct zirconium-based LCPs (MLCPs), which not only prevented π-π stacking but also ensured that extended π-coupling was maintained in the LCPs, thus effectively promoting charge transport and achieving strong luminescence. Second, the coreactant polyethyleneimine (PEI) was assembled onto the MLCPs (MLCPs@PEI) to further promote the emission of ECL. To further explore the potential of the obtained MLCPs@PEI as emerging ECL emitter, colorectal cancer exosome was chosen as model biomarker, and an innovative ECL ratiometric system based on MLCPs@PEI and luminol was designed to improve the validity and accuracy of the sensors. This research provides a fresh nanoplatform for exosome detection and broadens the application of LCPs in ECL immunoassay.

Mechanochemical synthesis of a red luminescent coordination polymer from a polydentate quinoline ligand with large conjugation

Abstract A red luminescent coordination polymer has been prepared from a polydentate 8-hydroxyquinoline ligand via mechanochemical synthesis. The obtained coordination polymer is micro/nano spherical and can suspend stably in organic solvents after ultrasonic treatment. Due to the large conjugation of the ligand with a strong polar s-triazine core, the coordination polymer shows a largely red-shifted emission relative to the ligand. The photoluminescence peak of the coordination polymer in organic solvent is at 613 nm, while a largely red-shifted photoluminescence peak at 675 nm and a shoulder peak at 770 nm are found in the photoluminescence spectrum of the coordination polymer in solid due to the strong interchain interaction.

Influence of swelling on the elasticity of polymer networks cross-linked in the melt state: Test of the localization model of rubber elasticity.

The elasticity of polymer networks, formed by cross-linking high molecular mass polymers in the melt state and then swollen by a solvent, involves contributions from both the presence of cross-link network junctions and the interchain interactions associated with the combined effect of excluded volume interactions and topological constraints that become modified when the network is swollen. We test the capacity of the previously developed localization model of rubber elasticity, a mean field "tube model," to describe changes in elasticity observed in classical experimental studies of the mechanical properties of this type of network. In order to obtain a satisfactory comparison to the experiments, it was found to be necessary to account for the independently observed tendency of the network junctions to become localized in the network with appreciable swelling, as well as the interchain interactions emphasized in previous discussions of the localization model.

Effect of enzymatic modification on the structure and rheological properties of diluted alkali-soluble pectin fraction rich in RG-I

This study focuses on pectin covalently linked in cell walls from two sources, apples and carrots, that was extracted using diluted alkali, and it describes changes in the rheological properties of diluted alkali-soluble pectin (DASP) due to enzymatic treatment. Given DASP’s richness of rhamnogalacturonan I (RG-I), RG-I acetyl esterase (RGAE), rhamnogalacturonan endolyase (RGL), and arabinofuranosidase (ABF) were employed in various combinations for targeted degradation of RG-I pectin chains. Enzymatic degradations were followed by structural studies of pectin molecules using atomic force microscopy (AFM) as well as measurements of rheological and spectral properties. AFM imaging revealed a significant increase in the length of branched molecules after incubation with ABF, suggesting that arabinose side chains limit RG-I aggregation. Structural modifications were confirmed by changes in the intensity of bands in the pectin fingerprint and anomeric region on Fourier transform infrared spectra. ABF treatment led to a decrease in the stability of pectic gels, while the simultaneous use of ABF, RGAE, and RGL enzymes did not increase the degree of aggregation compared to the control sample. These findings suggest that the association of pectin chains within the DASP fraction may rely significantly on intermolecular interactions. Two mechanisms are proposed, which involve side chains as short-range attachment points or an extended linear homogalacturonan conformation favoring inter-chain interactions over self-association.