ß-Sheet Structure Formation within Binary Blends of Two Spider Silk Related Peptides.

Intrinsically disordered proteins (IDPs) play an important role in molecular biology and medicine because their induced folding can lead to so-called conformational diseases, where ß-amyloids play an important role. Still, the molecular folding process into the different substructures, such as parallel/antiparallel or extended ß-sheet/crossed ß-sheet is not fully understood. The recombinant spider silk protein eADF4(Cx) consisting of repeating modules C, which are composed of a crystalline (pep-c) and an amorphous peptide sequence (pep-a), can be used as a model system for IDP since it can assemble into similar structures. In this work, blend films of the pep-c and pep-a sequences were investigated to modulate the ß-sheet formation by varying the molar fraction of pep-c and pep-a. Dichroic Fourier-transform infrared spectroscopy (FTIR), circular dichroism, spectroscopic ellipsometry, atomic force microscopy, and IR nanospectroscopy were used to examine the secondary structure, the formation of parallel and antiparallel ß-sheets, their orientation, and the microscopic roughness and phase formation within peptide blend films upon methanol post-treatment. New insights into the formation of filament-like structures in these silk blend films were obtained. Filament-like structures could be locally assigned to ß-sheet-rich structures. Further, the antiparallel or parallel character and the orientation of the formed ß-sheets could be clearly determined. Finally, the ideal ratio of pep-a and pep-c sequences found in the fibroin 4 of the major ampullate silk of spiders could also be rationalized by comparing the blend and spider silk protein systems.

Molecular origins of Epoxy-Amine/Iron oxide interphase formation.

HYPOTHESIS: Interphase properties in composites, adhesives and protective coatings can be predicted on the basis of interfacial interactions between polymeric precursor molecules and the inorganic surface during network formation. The strength of molecular interactions is expected to determine local segmental mobility (polymer glass transition temperature, Tg) and cure degree. EXPERIMENTS: Conventional analysis techniques and atomic force microscopy coupled with infrared (AFM-IR) are applied to nanocomposite specimens to precisely characterise the epoxy-amine/iron oxide interphase, whilst molecular dynamics simulations are applied to identify the molecular interactions underpinning its formation. FINDINGS: Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and high-resolution AFM-IR mapping confirm the presence of nanoscale under-cured interphase regions. Interfacial segregation of the molecular triethylenetetraamine (TETA) cross-linker results in an excess of epoxy functionality near synthetic hematite, (Fe2O3) magnetite (Fe3O4) and goethite (Fe(O)OH) particle surfaces. This occurs independently of the variable surface binding energies, as a result of entropic segregation during the cure. Thermal analysis and molecular dynamics simulations demonstrate that restricted segmental motion is imparted by strong interfacial binding between surface Fe sites in goethite, where the position of surface hydroxyl protons enables synergistic hydrogen bonding and electrostatic binding to Fe atoms at specific sites. This provides a strong driving force for molecular orientation resulting in significantly raised Tg values for the goethite composite samples.

Smart functional polymer coatings for paper with anti-fouling properties.

Cellulose, as the main component of paper, is becoming more and more important for several high tech applications because of its beneficial properties, such as abundance, low cost, renewability, mechanical robustness and biocompatibility. To make cellulose accessable for new applications it is necessary to introduce new properties, which can be done by surface modification e.g. grafting of polymers onto surfaces. In this work, two comb copolymers, poly[(2-methyl-2-oxazoline methacrylate)-co-glycidyl methacrylate] and poly[(2-methacryloyloxyethyl phosphorylcholine)-co-glycidyl methacrylate], were synthesized by free radical polymerization of glycidyl methacrylate and oligo(2-methyl-2-oxazoline) as well as 2-methacryloyloxyethyl phosphorylcholine. After extensive characterization the polymers were covalently attached to thin cellulose model layers and filter paper using a one-step grafting-to approach. For the comprehensive analysis of these layers, thin cellulose films were fabricated on silicon wafers by spin coating of trimethylsilyl cellulose followed by acid hydrolysis which resulted in homogeneous layers as substrates for the grafting process of the functional polymers. The layers were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDX). To demonstrate the high potential of such polymer-modified cellulose materials, protein repellance of the cellulose films, containing peptidomimetic 2-methyl-2-oxazoline and zwitterionic phosphorylcholine groups after successful functionalization, is shown. Cell adhesion experiments using Bacillus subtilis, Escherichia coli and Saccharomyces cerevisiae indicate the considerable anti-fouling capacity against both Gram-positive and Gram-negatve bacteria as well as the yeast fungus.

Temperature-Dependent Reinforcement of Hydrophilic Rubber Using Ice Crystals.

This is the first study on the impact of ice crystals on glass transition and mechanical behavior of soft cross-linked elastomers. A hydrophilic elastomer such as epichlorohydrin-ethylene oxide-allyl glycidyl ether can absorb about ∼40 wt % of water. The water-swollen cross-linked network exhibits elastic properties with more than 1500% stretchability at room temperature. Coincidently, the phase transition of water into solid ice crystals inside of the composites allows the reinforcement of the soft elastomer mechanically at lower temperatures. Young's modulus of the composites measured at -20 °C remarkably increased from 1.45 to 3.14 MPa, whereas at +20 °C, the effect was opposite and the Young's modulus decreased from 0.6 to 0.03 MPa after 20 days of water treatment. It was found that a part of the absorbed water, ∼74% of the total absorbed water, is freezable and occupies nearly 26 vol % of the composites. Simultaneously, these solid ice crystals are found to be acting as a reinforcing filler at lower temperatures. The size of these ice crystals is distributed in a relatively narrow range of 400-600 nm. The storage modulus (E') of the ice crystal-filled composites increased from 3 to 13 MPa at -20 °C. The glass transition temperature (-37 °C) of the soft cross-linked elastomer was not altered by the absorption of water. However, a special transition (melting of ice) occurred at temperatures close to 0 °C as observed in the dynamic mechanical analysis of the water-swollen elastomers. The direct polymer/filler (ice crystals) interaction was demonstrated by strain sweep experiments and investigated using Fourier transform infrared spectroscopy. This type of cross-linked rubber could be integrated into a smart rubber application such as in adaptable mechanics, where the stiffness of the rubber can be altered as a function of temperature without affecting the mechanical stretchability either below or above 0 °C (above the glass temperature region) of the rubber.

Plant pressure sensitive adhesives: similar chemical properties in distantly related plant lineages.

MAIN CONCLUSION: A mixture of resins based on aliphatic esters and carboxylic acids occurs in distantly related genera Peperomia and Roridula , serving different functions as adhesion in seed dispersal and prey capture. According to mechanical characteristics, adhesive secretions on both leaves of the carnivorous flypaper Roridula gorgonias and epizoochorous fruits of Peperomia polystachya were expected to be similar. The chemical analysis of these adhesives turned out to be challenging because of the limited available mass for analysis. Size exclusion chromatography and Fourier transform infrared spectroscopy were suitable methods for the identification of a mixture of compounds, most appropriately containing natural resins based on aliphatic esters and carboxylic acids. The IR spectra of the Peperomia and Roridula adhesive resemble each other; they correspond to that of a synthetic ethylene-vinyl acetate copolymer, but slightly differ from that of natural tree resins. Thus, the pressure sensitive adhesive properties of the plant adhesives are chemically proved. Such adhesives seem to appear independently in distantly related plant lineages, habitats, life forms, as well as plant organs, and serve different functions such as prey capture in Roridula and fruit dispersal in Peperomia. However, more detailed chemical analyses still remain challenging because of the small available volume of plant adhesive.

Identification of microplastics by FTIR and Raman microscopy: a novel silicon filter substrate opens the important spectral range below 1300 cm(-1) for FTIR transmission measurements.

The presence of microplastics in aquatic ecosystems is a topical problem and leads to the need of appropriate and reliable analytical methods to distinctly identify and to quantify these particles in environmental samples. As an example transmission, Fourier transform infrared (FTIR) imaging can be used to analyze samples directly on filters without any visual presorting, when the environmental sample was afore extracted, purified, and filtered. However, this analytical approach is strongly restricted by the limited IR transparency of conventional filter materials. Within this study, we describe a novel silicon (Si) filter substrate produced by photolithographic microstructuring, which guarantees sufficient transparency for the broad mid-infrared region of 4000-600 cm(-1). This filter type features holes with a diameter of 10 µm and exhibits adequate mechanical stability. Furthermore, it will be shown that our Si filter substrate allows a distinct identification of the most common microplastics, polyethylene (PE), and polypropylene (PP), in the characteristic fingerprint region (1400-600 cm(-1)). Moreover, using the Si filter substrate, a differentiation of microparticles of polyesters having quite similar chemical structure, like polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), is now possible, which facilitates a visualization of their distribution within a microplastic sample by FTIR imaging. Finally, this Si filter can also be used as substrate for Raman microscopy-a second complementary spectroscopic technique-to identify microplastic samples.

Spectroscopic examinations of hydrogen bonding in hydroxy-functionalized ADMET chemistry.

Wide-angle X-ray scattering (WAXS) and temperature-dependent Fourier transform infrared spectroscopy (FTIR) spectroscopy are used to study hydrogen bonding interactions of a hydroxyl-functionalized polyethylene (PE) prepared by acyclic diene metathesis (ADMET) chemistry. The hydroxyl polymer exhibits an orthorhombic unit cell structure with characteristic reflection planes at (110) and (200), comparable to pure crystalline PE. These data unequivocally demonstrate that the OH branch is excluded from the PE lamellae. Furthermore, the polymer melts 100 °C higher than all previous analogous polymers possessing precision placed long aliphatic branches that also are excluded from PE lamellae. Temperature-dependent FTIR spectroscopy from ambient to 150 °C, followed by cooling to 125 °C supports exclusion of the hydroxyl group from the crystalline lattice. It is concluded that these hydroxyl groups form stable physical networks in the amorphous region via hydrogen bonding and are important for the overall morphology of such polymers.

Platelet Janus particles with hairy polymer shells for multifunctional materials.

A novel approach is developed for the large-scale synthesis of Janus particles with platelet geometry and dense polymer shells by employing simultaneous "grafting from" of hydrophilic and hydrophobic polymers using surface-induced ATRP in emulsion. The method is based on the fabrication of an emulsion consisting of a water solution of a hydrophilic monomer and a solution of a hydrophobic monomer in an organic solvent, which is stabilized by initiator-modified kaolinite particles. Two polymers are grafted simultaneously on the opposite faces of the kaolinite particle during polymerization. The synthesized particles have a clear Janus character and are highly efficient for the stabilization of emulsions. Because of its simplicity, the method can readily be upscaled for the synthesis of large amounts of Janus particles, up to several grams.