Large Polymer Research Articles

Characterizing HP1-Driven Chromatin Compaction using Nuclear Magnetic Resonance Spectroscopy

Eukaryotes package their DNA by wrapping it around a histone protein core to form a structure known as the nucleosome. The nucleosomes form large polymers called chromatin which separate into two distinct compartments in the nucleus. In constitutive heterochromatin compartments, chromatin displays dense compaction and dampened gene expression. Heterochromatin protein 1 (HP1) is a multivalent chromatin binding protein enriched at these heterochromatin sites. It is known that HP1 is capable of compacting single chromatin strands and cross-linking separate strands. Here we map the structural and biophysical properties of HP1 in vitro as it interacts with differentially modified semi-synthetic chromatin. Nuclear magnetic resonance spectroscopy provides the selectivity to study HP1 in dense chromatin networks while resolving residue-specific biophysical changes. These results provide insight into the function of HP1 in near-physiological chromatin environments.

Synthesis and Aggregation of a Porphyrin-Cored Hyperbranched Polyglycidol and Its Application as a Macromolecular Photosensitizer for Photodynamic Therapy.

Macromolecules are potentially useful delivery systems for cancer drugs, as their size allows them to utilize the enhanced permeability and retention effect (EPR), which facilitates selective delivery to (and retention within) tumors. In addition, macromolecular delivery systems can prolong circulation times as well as protect and solubilize toxic and hydrophobic drug moieties. Overall, these properties and abilities can result in an enhanced therapeutic effect. Photodynamic therapy (PDT) combines the use of oxygen and a photosensitizer (PS), which become toxic upon light irradiation. We proposed that a PS encapsulated within a water-soluble macromolecule could exploit the EPR effect and safely and selectively deliver the PS to a tumor. In this paper, we describe the synthesis of a porphyrin-cored hyperbranched polymer that aggregated into larger micellar structures. DLS and TEM indicated that these aggregated structures had diameters of 45 and 20 nm for the solvated and nonsolvated species, respectively. The porphyrin-cored HBP (PC-HBP), along with the nonencapsulated porphyrin (THPP), were screened against EJ bladder carcinoma cells in the dark and light. Both THPP and PC-HBP displayed good toxicity in the light, with LD50 concentrations of 0.5 and 1.7 μM, respectively. However, in the dark, the nonincorporated porphyrin (THPP) displayed significant toxicity, generating an LD50 of 4 μM. On the other hand, no dark toxicity was observed for the polymer system (PC-HBP) at concentrations of 100 μM or less. As such, incorporation within the large polymer aggregate serves to eliminate dark toxicity while maintaining excellent toxicity when irradiated.

Temperature-responsive star-shaped poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) with central thiacalix[4]arene fragments: structure and properties in solutions

Temperature-responsive star-shaped poly(2-ethyl-2-oxazoline) (star-PETOX) and poly(2-isopropyl-2-oxazoline) (star-PIPOX) with arms grafted to the lower rim of thiacalix[4]arene were studied in solutions by viscometry, sedimentation velocity, light scattering, and small-angle neutron scattering. The experiments were carried out in water and tetrahydrofuran solutions. It was revealed that in tetrahydrofuran, the studied polymers were present only as individual molecules, while in aqueous solutions, in addition to individual molecules, large polymer aggregates were found. Molecular characteristics of the star-PETOX and star-PIPOX samples were estimated; their behavior in tetrahydrofuran and water was studied over a wide temperature range. It was established that a cloud point of the aqueous solution of star-PETOX (67 °C) is higher than that of a solution of star-PIPOX (35 °C). Comparison of the data obtained by dynamic light scattering and small-angle neutron scattering turned out to be fruitful in revealing all the structural levels of the organization of star-PETOX and star-PIPOX in aqueous solutions. They include the level of the individual macromolecules and the level of supramolecular organization with a star-like architecture.

Electrospray ionization-ion mobility spectrometry-high resolution tandem mass spectrometry with collision-induced charge stripping for the analysis of highly multiply charged intact polymers.

Polymers with large molecular weight are difficult to interpret using electrospray ionization-mass spectrometry (ESI-MS) due to the generation of various highly multiply charged analytes. Although ESI-ion mobility spectrometry (IMS)-MS is effective in reducing the complexity of the mass spectrum, this approach is insufficient for analyzing highly multiply charged polymers. In this study, we propose a method combining tandem mass spectrometry (quadrupole and high-resolution time-of-flight MS, QMS/TOFMS), IMS, and collision-induced charge stripping (CICS) for analyzing large intact polymers (∼40 kDa), which are highly multiply charged. The number of charges can be estimated from a Fourier transform power spectrum of a mass spectrum when the charge number is less than approximately 20. Interpretations of the spectra of poly(ethylene oxide)s (PEOs) weighing 20 kDa, poly(methyl methacrylate)s weighing 22 kDa, and methoxy-PEO-maleimide weighing 40 kDa were successfully demonstrated with isotope level and polymerization degree level separations, respectively. In the proposed method, a mixture can be analyzed for relatively small (a few kDa) and large (a few tens of kDa) polymers simultaneously without any sample pretreatment.

Changes in protein compositions and textural properties of the muscle of skate fermented at 10°C

ABSTRACT Chemical properties such as pH, ammonia nitrogen, total volatile base nitrogen, trimethylamine nitrogen, protein composition, and free amino acids composition and textural property were investigated for skate muscle subjected to fermentation at 10°C for 14 days. The values of pH, TVBN, TMAN, and ammonia nitrogen content significantly increased in skate muscle. Principal component analysis indicated a high correlation between changes in textural profiles and ammonia flavor and changes in muscle protein composition. In addition, SDS-PAGE of protein fractions showed that myofibrillar tended to aggregate into large polymers during fermentation. On the other hand, changes in trichloroacetic acid-soluble peptides and free amino acid content during fermentation indicated intensive degradation of muscle proteins. The variations in chemical properties and protein composition of skate muscle during fermentation reveal that decomposition and degradation of muscle proteins are important factors that influence the chemical composition and textural property of skate during fermentation at 10°C.

Can one determine the density of an individual synthetic macromolecule?

Dendronized polymers (DPs) are large and compact main-chain linear polymers with a cylindrical shape and cross-sectional diameters of up to ∼15 nm. They are therefore considered molecular objects, and it was of interest whether given their experimentally accessible, well-defined dimensions, the density of individual DPs could be determined. We present measurements on individual, deposited DP chains, providing molecular dimensions from scanning and transmission electron microscopy and mass-per-length values from quantitative scanning transmission electron microscopy. These results are compared with density values obtained from small-angle X-ray scattering on annealed bulk specimen and with classical envelope density measurements, obtained using hydrostatic weighing or a density gradient column. The samples investigated comprise a series of DPs with side groups of dendritic generations g = 1-8. The key findings are a very large spread of the density values over all samples and methods, and a consistent increase of densities with g over all methods. While this work highlights the advantages and limitations of the applied methods, it does not provide a conclusive answer to the question of which method(s) to use for the determination of densities of individual molecular objects. We are nevertheless confident that these first attempts to answer this challenging question will stimulate more research into this important aspect of polymer and soft matter science.

Evaluation of localization systems for CNC machining of large FRPC parts

In machining of large fiber-reinforced polymer composite (FRPC) parts, the part must be precisely located before machining. The exact location and geometry are usually determined by the probing systems employing a touch probe integrated with a CNC machine. When measuring a large number of points, touch probing consumes a significant amount of time and adversely affects the utilization of the CNC machine in serial production. To increase the probing speed and acquire additional details, an optical probing operating on the laser triangulation measuring principle is developed. The paper deals with the integration of the optical system with the existing CNC machine employing touch probing. The integration was performed in serial production of FRPC parts for wind industry, resulting in a reduction of time necessary to machine the FRPC part. The system enables measurement of workpiece location and geometry before and after machining and therefore ensures workpiece geometry traceability.

Understanding the Spontaneous Reactions between Oxide-Free Silicon and Lithium-Battery Electrolytes

Here, we studied for the first time the kinetics of the chemical reactions between oxide-free silicon and electrolytes and the composition and morphology of the surface film formed during these reactions. We found that the kinetics of these reactions is swift; a few nm passivating film is formed during a few milliseconds and a complete passivation takes place in about 30 seconds. XPS study show a passivating film consisting of large organic molecules or polymers containing C-O, C=O, C-Fx and O-C-F moieties, SiFx, SiOxFy, some SiO2 and small amounts of LiF. Containing only traces of Li, it cannot serve as an SEI and may lead to lesser uniformity of the SEI formed on top of it.

Unusual crowding-induced chain looping kinetics in hard-sphere fluids: a contrastive study with polymer solutions.

A theoretical framework is developed to investigate the looping kinetics of a chain in hard-sphere (HS) fluids, based on a generalized Smoluchowski diffusion-reaction equation. A contrastive study with polymer solutions is performed. The crowding-associated effective viscosity and collapse effects are properly taken into account, which obey different scaling relations in HS and polymer fluids. We examine the dependence of the looping time on both concentration and size of crowders, demonstrating unusual and distinct discrepancies in the two crowded media. Firstly, in the solution of large polymers, the looping rate grows monotonically with polymer concentration. On the other hand, in the solution of large HSs, a caging regime can be observed, where the looping time tends to the value in the absence of crowders. Secondly, polymers in moderate size generally impede chain looping due to the enhanced viscosity. However, in HS fluids, the looping time exhibits a rather complicated variation with increasing HS size. We show a possible mechanism where in the case of small crowders with a relatively strong compaction in the probed chain, the looping kinetics can be facilitated. As the crowder size increases, the collapse effect is reduced and looping is dominated by viscosity-induced inhibition. Simultaneously, our theory rationalizes another possibility of the mechanism observed by recent simulation work. We conclude that the looping kinetics in specific systems actually should be governed by the critical competition between the two crowding factors. By giving reasonable measurements of effective viscosity and collapse, our theoretical framework can provide a unified strategy to analyze crowding effects on the looping rate in a systematic manner.

Pore structure of affected zone around saturated and large superabsorbent polymers in cement paste

Superabsorbent polymer (SAP) has been widely used as internal curing agent for cement-based materials, duo to its high internal curing efficiency. Pore structure of affected zone around SAP is important for understanding the internal curing mechanism. This paper presents a study of the pore structure evolution of affected zone around SAP in cement paste with water/cement ratio 0.24 and 0.30 from 3 up to 28 days. Pore structure of affected zone and matrix was tested by mercury intrusion porosimetry and nitrogen adsorption and desorption. Surface fractal dimensions were determined using two different fractal models. Results indicated that SAP had no effect on the pore shape of affected zone, excluding the pore volume and pore diameter at early and late ages. Higher critical pore diameter but lower pore volume were found in affected zone at late ages. All the samples showed a multi-fractal property at micro- and macro-fractal scale, and the surface fractal dimension of affected zone was always larger than the matrix, showing a higher pore complexity. Some new findings on internal curing were achieved from an affected zone perspective. The calculated mechanical strength and permeability of affected zone from the pore structure parameters were found higher than the matrix. These new findings may give insight into the effect of internal curing with SAP from the perspective of affected zone.

Click Chemistry in Macromolecular Design: Complex Architectures from Functional Polymers

This contribution reviews the applications of click chemistry reactions in design and synthesis of various macromolecular architectures that hold key aspects in polymer science. By considering the emerging concepts that shape how synthetic polymer chemistry and macromolecular engineering utilize ‘reactions’ in ‘fabrication’, in the last decade, the click chemistry methodologies have been pioneered the chemical approaches that allow to access diverse complex macromolecules. The common and leading features of click chemistry reactions rely on efficient, fast, selective and easy to implement chemical transformations giving very high to quantitative coupling efficiencies. These are essential virtues that provide triumphing in macromolecular engineering, since the building blocks are usually large polymer chains. For the efficient building of complex macromolecules via click reactions, properly functionalized polymers are key components in which special design is required to successful installation of ‘clickable’ reactive groups on polymer end groups or side chains. In this report, the synthetic methods encompassing various click chemistry reactions in fabrication and applications of a range of complex macromolecular architectures have been reviewed.

Engineered cell-to-cell signalling within growing bacterial cellulose pellicles.

SummaryBacterial cellulose is a strong and flexible biomaterial produced at high yields by Acetobacter species and has applications in health care, biotechnology and electronics. Naturally, bacterial cellulose grows as a large unstructured polymer network around the bacteria that produce it, and tools to enable these bacteria to respond to different locations are required to grow more complex structured materials. Here, we introduce engineered cell‐to‐cell communication into a bacterial cellulose‐producing strain of Komagataeibacter rhaeticus to enable different cells to detect their proximity within growing material and trigger differential gene expression in response. Using synthetic biology tools, we engineer Sender and Receiver strains of K. rhaeticus to produce and respond to the diffusible signalling molecule, acyl‐homoserine lactone. We demonstrate that communication can occur both within and between growing pellicles and use this in a boundary detection experiment, where spliced and joined pellicles sense and reveal their original boundary. This work sets the basis for synthetic cell‐to‐cell communication within bacterial cellulose and is an important step forward for pattern formation within engineered living materials.

Depleting Depletion: Maintaining Single-Walled Carbon Nanotube Dispersions after Graft-To Polymer Functionalization.

Grafting polymers onto single-walled carbon nanotubes (SWCNTs) usefully alters properties but does not typically yield stable, solvated species directly. Despite the expectation of steric stabilization, a damaging (re)dispersion step is usually necessary. Here, poly(vinyl acetate)s (PVAc's) of varying molecular weights are grafted to individualized, reduced SWCNTs at different concentrations to examine the extent of reaction and degree of solvation. The use of higher polymer concentrations leads to an increase in grafting ratio (weight fraction of grafted polymer relative to the SWCNT framework), approaching the limit of random sequentially adsorbed Flory "mushrooms" on the surface. However, at higher polymer concentrations, a larger percentage of SWCNTs precipitate during the reaction; an effect which is more significant for larger weight polymers. The precipitation is attributed to depletion interactions generated by ungrafted homopolymer overcoming Coulombic repulsion of adjacent like-charged SWCNTs; a simple model is proposed. Larger polymers and greater degrees of functionalization favor stable solvation, but larger and more concentrated homopolymers increase depletion aggregation. By using low concentrations (25 μM) of larger molecular weight PVAc (10 kDa), up to 65% of grafted SWCNTs were retained in solution (at 65 μg mL-1) directly after the reaction.

Red blood cell adhesion can be reduced by non-reactive macromolecules.

To date, the mechanisms behind red blood cell (RBC) adhesion remain unclear. However, polymer depletion at the red cell surface has been shown to play a significant role. Interestingly, most previous studies have focused on the adhesion-promoting effects of one type of large polymer or plasma protein. However, the situation in vivo is more complex in that one needs to consider a mixture of various bio-macromolecules. To explore this complexity, Interference Reflection Microscopy was used to investigate how mixtures of various polymers affect RBC adhesion. RBC adhesion to albumin-coated glass coverslips was studied in the presence of two pro-adhesion polymers [dextran70 kDa and 35 kDa poly(ethylene glycol) (PEG 35)] with and without three types of smaller polymers: dextran 10 kDa, PEG 10 kDa and Poloxamer 188. Our findings show that the presence of small polymers can inhibit the adhesion-promoting effects of dextran 70 and PEG 35, with a more pronounced reduction for heterogeneous mixtures. Interpretation of our results in terms of the depletion model appears appropriate, in that our findings are consistent with the assumption that this reduction occurs because of an increase of small molecules in the depletion region. This study thus suggests that depletion interaction can control cell-cell interactions in complex environments (e.g., in vivo), and indicates that considering the interplay of all plasma constituents is important in order to understand the pathophysiology of diseases associated with cell adhesion and vascular complications.

Self-Assembly of a Structurally Defined Chiro-Optical Peptide-Oligothiophene Hybrid Material.

Conducting polymers are routinely used in optoelectronic biomaterials, but large polymer polydispersity and poor aqueous compatibility complicate integration with biomolecular templates and development of discrete and defined supramolecular complexes. Herein, we report on a chiro-optical hybrid material generated by the self-assembly of an anionic peptide and a chemically defined cationic pentameric thiophene in aqueous environment. The peptide acts as a stereochemical template for the thiophene and adopts an α-helical conformation upon association, inducing optical activity in the thiophene π–π* transition region. Theoretical calculations confirm the experimentally observed induced structural changes and indicate the importance of electrostatic interactions in the complex. The association process is also probed at the substrate–solvent interface using peptide-functionalized gold nanoparticles, indicating that the peptide can also act as a scaffold when immobilized, resulting in structurally well-defined supramolecular complexes. The hybrid complex could rapidly be assembled, and the kinetics of the formation could be monitored by utilizing the local surface plasmon resonance originating from the gold nanoparticles. We foresee that these findings will aid in designing novel hybrid materials and provide a possible route for the development of functional optoelectronic interfaces for both biomaterials and energy harvesting applications.

Independent and combined effects of elevated CO2 and post-anthesis heat stress on protein quantity and quality in spring wheat grains.

Spring wheat plants were grown under two CO2 concentrations (380 and 550 μmol mol-1) and two temperature treatments (ambient and post-anthesis heat stress) to investigate the effects of elevated CO2 and heat stress on grain protein quality. Contents of protein components, glutenin macropolymers (GMP) and amino acids in grains decreased due to elevated CO2, while increased by high temperature. The combination of elevated CO2 and heat stress increased the contents of total protein and albumin, but decreased the contents of gliadin and glutenin, while the content and particle size distribution of GMP as well as the contents of amino acids were not significantly affected. Furthermore, we found that the content and particle size distribution of GMP were not only determined by the contents of proteins and high-molecular-weight glutenin subunits, but also related to the contents of amino acids containing disulfide bonds, which favor the formation of large insoluble polymers.

Flexible Distributed Bragg Refractors: Cost‐Effective, Flexible, Hydrophobic, and Tunable Structural Color Polymeric Bragg Reflector Metastructures (Advanced Optical Materials 21/2018)

Inspired by Nature, Marisol Martín-González and co-workers (article number 1800408) explore the fabrication of flexible distributed Bragg refractors from commodity thermoplastic polymers like polyethylene, creating a hydrophobic metamaterial with consistent structural colour in different view directions. These large three-dimensional polymer networks open new possibilities for the use in sensing, photonics, filtering or as scaffold for other materials.

Planar deposition flow modeling of fiber filled composites in large area additive manufacturing

The rapid transition of the Fused Filament Fabrication (FFF) Additive Manufacturing (AM) process from small scale prototype models to large scale polymer deposition has been driven, in part, by the addition of short carbon fibers to the polymer feedstock. The addition of short carbon fibers improves both the mechanical and thermal properties of the printed beads. The improvements to the anisotropic mechanical and thermal properties of the polymer feedstock are dependent on the spatially varying orientation of short carbon fibers which is itself a function of the velocity gradients in the flow field throughout the nozzle and in the extrudate during deposition flow. This paper presents a computational approach for simulating the deposition flow that occurs in the Large Area Additive Manufacturing (LAAM) process and the effects on the final short fiber orientation state in the deposited polymer bead and the resulting bead mechanical and thermal properties. The finite element method is used to evaluate Stokes flow for a two-dimensional planar flow field within a Strangpresse Model 19 LAAM polymer deposition nozzle. A shape optimization method is employed to compute the shape of the polymer melt flow free surface below the nozzle exit as the bead is deposited on a moving print platform. Three nozzle configurations are considered in this study. Fiber orientation tensors are calculated throughout the fluid domain using the Folgar-Tucker fiber interaction model. The effective bulk mechanical properties, specifically the longitudinal and transverse moduli, and the coefficient of thermal expansion, are also calculated for the deposited bead based on the spatially varying fiber orientation tensors. Fiber orientation is found to be highly aligned along the deposition direction of the resulting bead and the computed properties through the thickness of the bead are found to be affected by nozzle height during deposition.

Optical probing for CNC machining of large parts made from fiber-reinforced polymer composite materials

In machining of large fiber-reinforced polymer (FRP) composite parts, the part must be precisely located before machining. The exact location and shape are usually determined by the probing systems employing a touch probe integrated with a CNC machine. When measuring a large number of points, touch probing consumes a significant amount of time and adversely affects the utilization of the CNC machine in serial production. In order to increase the probing speed and acquire additional details, a new optical probing operating on the laser triangulation measuring principle is developed. The paper describes the measuring principle, system integration, neural network as the measuring system transfer function, and the calibration process. When measuring polyester or epoxy resin-based materials, the laser light penetrates into the part and reflects back inside of the part. This interference is successfully neutralized by the calibration body made from the same FRP material as the measured part. Verification of the calibration body and the machine coordinate system alignment is demonstrated by comparison of corrections determined with the optical and touch probing.

A nearly uniform distributional pattern of heterotrophic bacteria in the Mariana Trench interior

The uniqueness of hadal trench environment and its potential role in global carbon sequestration allows for a detailed study of microbially driven carbon cycle of the trench system. Limited studies on microbiology by far have suggested that the hadal-sphere generally hosts a heterotrophic microbial community that is mostly fed by surface-sinking organic matter or re-suspended and laterally transported organic matter from sediments. However, temporal dynamics in trench microbial community in connection to surface and sediment organic carbon exports is still beyond our knowledge. In this study, we conducted vertical sampling and analysis of the microbial community from the epipelagic zone down to the hadal zone at the Mariana Trench. 16S rRNA gene composition showed high variations at the first 1000 m below surface (mbs); however, a nearly uniform microbial community composition (Jaccard dissimilarity less than 73%) was observed below 1000 mbs and down into the bottom of the trench. The deep-sea bacteria were generally chemoheterotrophs characterized by Erythrobacter, Rhodovulum, Alteromonas, some Marinobacter, etc., which were also present at the ocean surface. Several deep-sea-enriched but surface-depleted bacteria include Glaciecola, Oceanicola and Oleibacter were potential degraders of large organic polymers. In spite of consistent community composition, enhanced chromophoric dissolved organic matter proportions in the hadal zone of the trench might imply intensified microbial activity compared to the water column above. These observations suggest an unusual transitory state of the Mariana Trench water columns and extend our understanding of the dynamics of the hadal microbial community.