Conformational Study and Hydrogen Bonds Detection on Elastin-Related Polypeptides Using X-ray Photoelectron Spectroscopy

Influences of Absorbed Dose Rate on the Mechanical Properties and Fiber-Matrix Interaction of High-Density Polyethylene-Based Carbon Fiber Reinforced Thermoplastic Irradiated by Electron-Beam

In this study, a high-density polyethylene (HDPE)-based carbon fiber-reinforced thermoplastic (CFRTP) was irradiated by an electron-beam. To assess the absorbed dose rate influence on its mechanical properties, the beam energy and absorbed dose were fixed, while the absorbed dose rates were varied. The tensile strength (TS) and Young's modulus (YM) were evaluated. The irradiated CFRTP TS increased at absorbed dose rates of up to 6.8 kGy/s and decreased at higher rates. YM showed no meaningful differences. For CFRTPs constituents, the carbon fiber (CF) TS gradually increased, while the HDPE TS decreased slightly as the absorbed dose rates increased. The OH intermolecular bond was strongly developed in irradiated CFRTP at low absorbed dose rates and gradually declined when increasing those rates. X-ray photoelectron spectroscopy analysis revealed that the oxygen content of irradiated CFRTPs decreased with increasing absorbed dose rate due to the shorter irradiation time at higher dose rates. In conclusion, from the TS viewpoint, opposite effects occurred when increasing the absorbed dose rate: a favorable increase in CF TS and adverse decline of attractive hydrogen bonding interactions between HDPE and CF for CFRTPs TS. Therefore, the irradiated CFRTP TS was maximized at an optimum absorbed dose rate of 6.8 kGy/s.

Heparan sulfates facilitate harmless amyloidogenic fibril formation interacting with elastin-like peptides

Heparan sulfates (HSs) modulate tissue elasticity in physiopathological conditions by interacting with various matrix constituents as tropoelastin and elastin-derived peptides. HSs bind also to protein moieties accelerating amyloid formation and influencing cytotoxic properties of insoluble fibrils. Interestingly, amyloidogenic polypeptides, despite their supposed pathogenic role, have been recently explored as promising bio-nanomaterials due to their unique and interesting properties. Therefore, we investigated the interactions of HSs, obtained from different sources and exhibiting various degree of sulfation, with synthetic amyloidogenic elastin-like peptides (ELPs), also looking at the effects of these interactions on cell viability and cell behavior using in vitro cultured fibroblasts, as a prototype of mesenchymal cells known to modulate the soft connective tissue environment. Results demonstrate, for the first time, that HSs, with differences depending on their sulfation pattern and chain length, interact with ELPs accelerating aggregation kinetics and amyloid-like fibril formation as well as self-association. Furthermore, these fibrils do not negatively affect fibroblasts’ cell growth and parameters of redox balance, and influence cellular adhesion properties. Data provide information for a better understanding of the interactions altering the elastic component in aging and in pathologic conditions and may pave the way for the development of composite matrix-based biomaterials.

Characterisation of the electronic structure of galvinoxyl free radical by variable energy UPS, XPS and NEXAFS spectroscopy

UPS, XPS and NEXAFS spectra of persistent free radical galvinoxyl are assigned using theoretical ΔDFT and TDDFT methods.

Combined effects of solvation and aggregation propensity on the final supramolecular structures adopted by hydrophobic, glycine-rich, elastin-like polypeptides

Previous work on elastin-like polypeptides (ELPs) made of hydrophobic amino acids of the type XxxGlyGlyZzzGly (Xxx, Zzz = Val, Leu) has consistently shown that differing dominant supramolecular structures were formed when the suspending media were varied: helical, amyloid-like fibers when suspended in water and globules evolving into "string of bead" structures, poly(ValGlyGlyValGly), or cigar-like bundles, poly(ValGlyGlyLeuGly), when suspended in methyl alcohol. Comparative experiments with poly(LeuGlyGlyValGly) have further indicated that the interface energy plays a significant role and that solvation effects act in concomitance with the intrinsic aggregation propensity of the repeat sequence. Continuing our investigation on ELPs using surface (X-ray photoelectron spectroscopy, atomic force microscopy) and bulk (circular dichroism, Fourier transform infrared spectroscopy) techniques for their characterization, here we have compared the effect of suspending solvents (H(2)O, dimethylsulfoxide, ethylene glycol, and MeOH) on poly(ValGlyGlyValGly), the polypeptide most inclined to form long and well-refined helical fibers in water, searching for the signature of intermolecular interactions occurring between the polypeptide chains in the given suspension. The influence of sequence specificities has been studied by comparing poly(ValGlyGlyValGly) and poly(LeuGlyGlyValGly) with a similar degree of polymerization. Deposits on substrates of the polypeptides were characterized taking into account the differing evaporation rate of solvents, and tests on their stability in ultra high vacuum were performed. Finally, combining experimental and computational studies, we have revaluated the three-dimensional modeling previously proposed for the supramolecular assembly in water of poly(ValGlyGlyValGly). The results were discussed and rationalized also in the light of published data.

Roles of hydrocarbon chain-length in preparing graphene oxide from mildly-oxidized graphite with intercalating anionic aliphatic surfactants

The longer the length of carbon chain, the higher the yield of graphene oxide prepared.

An experimental NEXAFS and computational TDDFT and ΔDFT study of the gas-phase core excitation spectra of nitroxide free radical TEMPO and its analogues

Core excitation (NEXAFS) C 1s, N 1s, and O 1s gas-phase spectra of stable nitroxide free radical TEMPO and two of its amide-substituted analogues are assigned from the onset of the absorptions to the vicinity of the core-ionization thresholds using the theoretical TDDFT and ΔDFT methods.

A facile synthesis of a highly stable superhydrophobic nanofibrous film for effective oil/water separation

An oil/water separation film with excellent durability and stable recyclability is highly desired for the treatment of oil containing effluents, like industrial oily wastewater.

Hydrogen bonds of a novel resin cement contribute to high adhesion strength to human dentin

OBJECTIVE

The detachment of fiber posts from root canals is primarily caused by the loss of adhesion between dentin and cement; therefore, the purpose of this study was to formulate a novel resin cement that improves the bond strength of fiber posts to the dentin-cement interface.

METHODS

Three concentrations (30, 35, and 40wt.%) of bis[2-(methacryloyloxy)-ethyl] phosphate (2MP) were prepared as dentin bonding agent components. Isobornyl acrylate (IBOA) and ethylhexylacrylate (EHA) were used as key components to fabricate the resin cement (named IE cement). The adhesive strengths of IE cement to coronal and root canal dentin were tested after placement of specimens in a water bath at 100% humidity and 37°C for either 24h or 5 months. The microtensile bond test, the push-out bond test, and the fracture toughness test were performed. Four commercially available resin cements (Nexus(®) third generation (NX3), Variolink II, RelyX Unicem, and Panavia F 2.0) were used for comparisons. X-ray photoelectron spectroscopy (XPS) was used to analyze the interaction of collagen extracted from human dentin and 2MP as well as the fracture surfaces of the specimens submitted to the microtensile bond test.

RESULTS

The 35% concentration of 2MP, in combination with IBOA and EHA, was the most effective for improving the IE cement's bond strength to dentin. The XPS results revealed that the phosphate groups of 2MP formed hydrogen bonds with the collagen and that such bonds prominently decreased in number in the specimens that were stored for 5 months.

SIGNIFICANCE

The combination of 2MP, IBOA, and EHA can effectively increase the adhesive strength of IE cement to dentin via hydrogen bond formation.

Incorporation of a clot-binding peptide into polythiophene: properties of composites for biomedical applications

Biocomposites formed by a pentapeptide (CREKA), which recognizes clotted plasma proteins, entrapped into the poly(3,4-ethylenedioxythiophene) (PEDOT) matrix have been prepared using three very different procedures. X-ray photoelectron spectroscopy analyses indicate that PEDOT-CREKA films, prepared by chronoamperometry in basic aqueous solution (pH = 10.3) and deposited onto a PEDOT internal layer, present the higher concentration of peptide: one CREKA molecule per six polymer repeat units. The surface of this bilayered system shows numerous folds homogeneously distributed, which have been exhaustively characterized by scanning electron microscopy and atomic force microscopy. Indeed, the morphology and topography of such bilayered films is completely different from those of biocomposite-prepared acid aqueous and organic solutions as polymerization media. The impact of the entrapped peptide molecules in the electrochemical properties of the conducting polymer has been found to be practically negligible. In contrast, biocompatibility assays with two different cellular lines indicate that PEDOT-CREKA favors cellular proliferation, which has been attributed to the binding of the peptide to the fibrin molecules from the serum used as a supplement in the culture medium. The latter assumption has been corroborated examining the ability of PEDOT-CREKA to bind fibrin. The latter ability has been also used to explore an alternative strategy based on the treatment of PEDOT-CREKA with fibrin to promote cell attachment and growth. Overall, the results suggest that PEDOT-CREKA is appropriated for multiple biomedical applications combining the electrochemical properties of conducting polymer and the ability of the peptide to recognize and bind proteins.

Surface and adsorption characteristics of three elastin-like polypeptide coatings with varying sequence lengths

The surface properties of a family of elastin-like polypeptides (ELPs), differing in molecular weight and sequence length, were investigated to understand how the nature of the polypeptide film might contribute to their thrombogenic profile. Physical adsorption of the ELPs onto Mylar increased surface wettability as the sequence length decreased while X-ray spectroscopy analysis showed an increasing amide content with sequence length. Chemical force microscopy analysis revealed that the ELP-coated surfaces displayed purely hydrophilic adhesion forces that increased as the ELP sequence length decreased. Adsorption isotherms performed using the quartz crystal microbalance with dissipation, showed that the surface coverage increased with ELP sequence length. The longer polypeptides (ELP2 and ELP4) also displayed higher specific dissipation values indicating that they established films with greater structural flexibility and associated water content than the shorter polypeptide, ELP1. Additionally, the stability of the ELP coating was lower with the shorter polypeptides. This study highlights the different surface properties of the ELP coatings as well as the dynamic nature of the ELP adsorbed layer wherein the conformational state may be an important factor contributing to their blood response.

Influence of amino acid specificities on the molecular and supramolecular organization of glycine-rich elastin-like polypeptides in water

Elastin-like polypeptides adopt complex supramolecular structures, showing either a hydrophobic or a hydrophilic surface, depending on their surrounding environment and the supporting substrate. The preferred organization is important in many situations ranging from biocompatibility to bio-function. Here we compare the n-repeat pentamer LeuGlyGlyValGly (n = 7) with the analogue ValGlyGlyValGly (n = 5), as water suspensions and as deposits on silicon substrates. These sequences contain the repeat XxxGlyGlyZzzGly (Xxx, Zzz = Val, Leu) motif belonging to the hydrophobic glycine-rich domain of elastin and represent a simplified model from which to obtain information on molecular interactions functional to elastin itself. The compounds studied differ only by the presence of the -CH(2)- spacer in the Leu moiety and thus the work was aimed at revealing the influence of this spacer element on self assembly. Both polypeptides were studied under identical conditions, using combined techniques, to identify differences in their conformational states both at molecular (CD, FTIR) and supramolecular (XPS, AFM) levels. By these means, together with a Congo Red spectroscopic assay of β-sheet formation in water, a clear correlation between amino acid sequences (sequence specificity) and their kinetics and ordering of aggregation has emerged. The novel outcomes of this work are from the supplementary measurements, made to augment the AFM and XPS studies, showing that the significant step in the self assembly of both polypeptides takes place in the liquid phase and from the finding that the substitution of Val by Leu in the first position of the pentapeptide effectively inhibits the formation of amyloidal fibers.

Switchable wettability on cooperative dual-responsive poly-L-lysine surface

A cooperative dual-responsive polypeptide surface switching between superhydrophilic and superhydrophobic states is presented. This macroscopic phenomenon of surface originates from the combination of the cooperative unfolding/aggregation of the poly-L-lysine (PLL) immobilized on the substrate with micro/nanocomposite structure in response to pH and temperature. At pH lower than the pK(a) of PLL (approximately 11.0), PLL mainly adopts a random coil conformation, which corresponds to the superhydrophilic state on the rough surface substrate. Raising the pH to higher than the pK(a) allows the appearance of alpha-helix conformation, which also corresponds to the hydrophilic state. However, heating up the surface at pH higher than the pK(a) destabilizes the alpha-helix conformation and induces the formation of aggregated beta-sheet structures, which represents the superhydrophobic state. Lowering the pH and temperature simultaneously switches a reversible conversion from superhydrophobic to superhydrophilic states. In the switching process, the hydrophobicity and hydrophilicity can be "memorized" due to the cooperative pH and temperature stimuli-induced unfolding/aggregation behaviors of PLL. This provides a new exciting prospect for understanding surface properties of polypeptides and the design of smart material surfaces with potential applications in nanodevices, bioseparation, and biosensors.

On enhancers and inhibitors of elastin-derived amyloidogenesis

Aims: The main aim of this study is to better understand the self-aggregation mechanism of amyloid-like elastin-derived fibers in order to design and produce new powerful drugs that will inhibit the onset of ‘amyloidosis’. Materials & methods: Atomic force microscopy (AFM), Congo Red birefringence assay and Thioflavin T fluorescence measurements were used to demonstrate the amyloid-like behavior of some fragments of elastin protein (exon 30 [EX30] and exon 28 [EX28]). Turbidimetry on apparent absorbance technique was used to investigate the effect either of enhancers or of inhibitors on the amyloidogenic elastin-like peptides. Circular-dichroism spectroscopy was used to study the secondary structures of the peptides. Results & discussion: We used Congo Red birefringence assay, Thioflavin T fluorescence measurements and AFM measurements that are used commonly to demonstrate the formation of amyloids. The elastin fibrillogenesis is amyloid-like. Then, the elastin amyloidogenesis is inhibited by particular pentapeptides. Conclusions: We have reported herein that the fibrillogenesis of elastin-derived EX28 and EX30 polypeptides is facilitated significantly by the effect of sodium taurocholate bile salt and is inhibited by a classical inhibitor of Aβ-amyloid peptide, such as KLVFF, as well as by novel inhibitors, designed by us on the basis of some elastin sequences.

Cellular response to nanoscale elastin-like polypeptide polyelectrolyte multilayers

Ionic elastin-like polypeptide (ELP) conjugates are a new class of biocompatible, self-assembling biomaterials. ELPs composed of the repeat unit (GVGVP)(n) are derived from the primary sequence of mammalian elastin and produced in Escherichia coli. These biopolymers exhibit an inverse transition temperature that renders them extremely useful for applications in cell-sheet engineering. Cationic and anionic conjugates were synthesized by the chemical coupling of ELP to polyethyleneimine (PEI) and polyacrylic acid (PAA). The self-assembly of ELP-PEI and ELP-PAA using the layer-by-layer deposition of alternately charged polyelectrolytes is a simple, versatile technique to generate bioactive and biomimetic surfaces with the ability to modulate cell-substratum interactions. Our studies are focused on cellular response to self-assembled multilayers of ionic (GVGVP)(40) incorporated within the polymeric sequence H(2)N-MVSACRGPG-(GVGVP)(40)-WP-COOH. Angle-dependent XPS studies indicated a difference in the chemical composition at the surface ( approximately 10A below the surface) and subsurface regions. These studies provided additional insight into the growth of the nanoscale multilayer assembly as well as the chemical environment that the cells can sense. Overall, cellular response was enhanced on glass substrata coated with ELP conjugates compared with uncoated surfaces. We report significant differences in cell proliferation, focal adhesions and cytoskeletal organization as a function of the number of bilayers in each assembly. These multilayer assemblies have the potential to be successfully utilized in the rational design of coatings on biomaterials to elicit a desired cellular response.

Transformation of Amyloid-like Fibers, Formed from an Elastin-Based Biopolymer, into a Hydrogel: An X-ray Photoelectron Spectroscopy and Atomic Force Microscopy Study

Previous studies have revealed the propensity of elastin-based biopolymers to form amyloid-like fibers when dissolved in water. These are of interest when considered as "ancestral units" of elastin in which they represent the simplest sequences in the hydrophobic regions of the general type XxxGlyGlyZzzGly (Xxx, Zzz = Val, Leu). We normally refer to these biopolymers based on elastin or related to elastin units as "elastin-like polypeptides". The requirement of water for the formation of amyloids seems quite interesting and deserves investigation, the water representing the natural transport medium in human cells. As a matter of fact, the "natural" supramolecular organization of elastin is in the form of beaded-string-like filaments and not in the form of amyloids whose "in vivo" deposition is associated with some important human diseases. Our work is directed, therefore, to understanding the mechanism by which such hydrophobic sequences form amyloids and any conditions by which they might regress to a non-amyloid filament. The elastin-like sequence here under investigation is the ValGlyGlyValGly pentapeptide that has been previously analyzed both in its monomer and polymer form. In particular, we have focused our investigation on the apparent stability of amyloids formed from poly(ValGlyGlyValGly), and we have observed these fibers evolving to a hydrogel after prolonged aging in water. We will show how atomic force microscopy can be combined with X-ray photoelectron spectroscopy to gain an insight into the spontaneous organization of an elastin-like polypeptide driven by interfacial interactions. The results are discussed also in light of fractal-like assembly and their implications from a biomedical point of view.