Material Properties of Traditional Handmade Paper Samples Fabricated from Cellulosic Fiber of Lokta Bushes.

Handmade papers (HPs) are fabricated from fibrous biomass of Lokta bushes and other plant species following traditional eco-friendly method in Nepal. Although HP fabricated from Lokta bushes is believed to be durable and resistant to bugs and molds, material properties of this paper are not reported in literature. In this study, we measured several material properties of 10 handmade Lokta paper samples collected from local enterprises and paper industries. The mean caliper, grammage, apparent density, equilibrium moisture content, Cobb 60, brightness, opacity, tensile strength, and tensile index values in the paper samples ranged from ∼90 to 700 µm, 50 to 150 g/m2, 0.2 to 0.4 g/cm3, 4 to 7%, 50 to 400 g/m2, 56 to 67%, 83 to 98%, 30 to 2900 N/m, and 1 to 27 Nm/g, respectively. These properties suggested that the HPs are lightweight papers with intermediate to high strength. The tensile strength was found to be significantly higher along the length direction (p < 0.05). Characteristic features of cellulose, hemicellulose, and lignin were observed in FTIR spectra. The crystalline and amorphous phases were also identified in X-ray diffraction (XRD) data. Electron microscopy images revealed a nicely cross-linked network of intact fibers having almost parallel arrangement of microfibrils. These features could provide strength and durability to the paper samples. Understanding the material properties of HPs down to the sub-microscopic level may help improve the paper quality and find novel applications in the future.

Tuning the Magnetic Properties of Two-Dimensional MXenes by Chemical Etching.

Two-dimensional materials based on transition metal carbides have been intensively studied due to their unique properties including metallic conductivity, hydrophilicity and structural diversity and have shown a great potential in several applications, for example, energy storage, sensing and optoelectronics. While MXenes based on magnetic transition elements show interesting magnetic properties, not much is known about the magnetic properties of titanium-based MXenes. Here, we measured the magnetic properties of Ti3C2Tx MXenes synthesized by different chemical etching conditions such as etching temperature and time. Our magnetic measurements were performed in a superconducting quantum interference device (SQUID) vibrating sample. These data suggest that there is a paramagnetic-antiferromagnetic (PM-AFM) phase transition and the transition temperature depends on the synthesis procedure of MXenes. Our observation indicates that the magnetic properties of these MXenes can be tuned by the extent of chemical etching, which can be beneficial for the design of MXenes-based spintronic devices.

Intermediate Sr2Co1.5Fe0.5O6-δ Tetragonal Structure between Perovskite and Brownmillerite as a Model Catalyst with Layered Oxygen Deficiency for Enhanced Electrochemical Water Oxidation.

The generation of hydrogen in an environmentally benign way is highly essential to meet future energy demands. However, in the process of splitting water electrochemically, sluggish kinetics of the oxygen evolution reaction (OER) curtails its applicability, as it drags energy input. Herein, we synthesized Sr-Co-Fe-O oxides to optimize their OER activity by varying the Co/Fe ratio. Among them, Sr2Co1.5Fe0.5O6-δ exhibited the best OER catalytic activity in the series, with an overpotential of 318 mV at 10 mA cm-2 and Tafel slope of 44.8 mV dec-1. High-resolution neutron powder diffraction analysis identified an intermediate structure between the perovskite and brownmillerite, with alternating layers of disorderly orientated oxygen-deficient tetrahedra and fully stoichiometric octahedra. The unique stacking of tetrahedral and octahedral units facilitates desired interactions between the electrode surface and electrolyte. Theoretical calculations revealed that increased covalency of Co 3d and O 2p in Sr2Co1.5Fe0.5O6-δ oxide is another primary contributor to its augmented water oxidation ability. As a model for developing catalysts with such an intermediate structure, the synergetic effect of oxygen vacancy and hybridization between Co 3d and O 2p assured the Sr2Co1.5Fe0.5O6-δ oxide as a better catalyst for its enhanced OER activity.

Aggregation Controlled Charge Generation in Fullerene Based Bulk Heterojunction Polymer Solar Cells: Effect of Additive.

Optimization of charge generation in polymer blends is crucial for the fabrication of highly efficient polymer solar cells. While the impacts of the polymer chemical structure, energy alignment, and interface on charge generation have been well studied, not much is known about the impact of polymer aggregation on charge generation. Here, we studied the impact of aggregation on charge generation using transient absorption spectroscopy, neutron scattering, and atomic force microscopy. Our measurements indicate that the 1,8-diiodooctane additive can change the aggregation behavior of poly(benzodithiophene-alt-dithienyl difluorobenzotriazole (PBnDT-FTAZ) and phenyl-C61-butyric acid methyl ester (PCBM)polymer blends and impact the charge generation process. Our observations show that the charge generation can be optimized by tuning the aggregation in polymer blends, which can be beneficial for the design of highly efficient fullerene-based organic photovoltaic devices.

DJ-1, a Parkinson's disease related protein, aggregates under denaturing conditions and co-aggregates with α-synuclein through hydrophobic interaction.

BACKGROUND: DJ-1, a small ubiquitously expressed protein implicated in several pathways associated with Parkinson's disease pathogenesis, has been found to interact with α-synuclein and modulate its aggregation, yet the exact mechanisms remain unclear. METHODS: The stability and aggregation properties of wild-type DJ-1 under denaturing conditions, such as low pH, high temperature, presence of denaturants were investigated. The interaction between DJ-1 and α-synuclein was tested by SDS-PAGE gel and native gel electrophoresis and by size-exclusion HPLC. Fibrillization was monitored by thioflavin T fluorescence assays and amorphous aggregation was followed by light scattering measurements. The morphology of aggregated species was observed by transmission electron microscopy and atomic force microscopy. Protein secondary structures were characterized by far-UV circular dichroism. RESULTS: DJ-1 fibrillization was first observed at low pH or by adding denaturants. Amorphous aggregates formed at neutral pH, and the aggregation was dramatically accelerated by elevated temperature and the presence of α-synuclein. Aggregation of DJ-1 were enhanced by heating and perturbed by the co-occurrence of α-synuclein but strong interactions between the two proteins were not found. CONCLUSIONS: Varying environmental factors led to different aggregation pathways of DJ-1 although a simulated physiological condition would not lead to fibrillization. DJ-1 co-aggregating with α-synuclein may result from weak hydrophobic interaction and DJ-1 exhibited chaperon-like activity in the initial time of α-synuclein aggregation at high temperature. GENERAL SIGNIFICANCE: This research on DJ-1 presented its aggregation behavior under denaturing conditions and interaction mechanism with α-synuclein that may help to decipher its potential neuroprotective or neurotoxic role in Parkinson's disease.

Oxidized quercetin inhibits α-synuclein fibrillization.

BACKGROUND: α-Synucein is a small (14 kDa), abundant, intrinsically disordered presynaptic protein, whose aggregation is believed to be a critical step in Parkinson's disease (PD). Oxidative stress is reported to be a risk factor for dopamine cell degeneration in PD. Flavonoids are suggested to be important antioxidant against oxidative stress. Flavonoids were reported to inhibit fibrillization and disaggregate the preformed fibrils of α-synucein, but the molecular mechanism was still not clear. METHODS: Quercetin, a well-recognized flavonoid antioxidant, was tested for its inhibition of α-synucein aggregation by thioflavin T assay, light scattering measurement, size-exclusion high performance liquid chromatography, atomic force microscopy, etc. RESULTS: The pre-incubated quercetin exhibited a noticeably stronger inhibition behavior to the fibril formation than that of the freshly prepared. The inhibition is significant in the presence of ortho- and para-benzenediol isomers and inconsiderable in the presence of meta-isomer. The oxidized quercetin species (i.e., chalcantrione, benzyfuranone, quercetinchinone, and other derivatives) cause stronger inhibition than quercetin does because of the elevated polarity and hydrophilicity. Presence of quercetin disaggregates α-synucein fibrils, rather than oligomers and amorphous aggregations. CONCLUSIONS: Instead of the antioxidant activity, the 1:1 covalent binding of quercetin with α-synucein, and the increased hydophilicity of the covalently modified α-synucein oligomers or monomers, account for the inhibition of α-synucein fibrillation. GENERAL SIGNIFICANCE: Clarification of the molecular mechanism of the inhibition and disaggregation may help to screen safer and more effective flavonoid therapeutic in combating PD.

Aggregation pathways of the amyloid ß(1-42) peptide depend on its colloidal stability and ordered ß-sheet stacking.

Amyloid ß (Aß) fibrils are present as a major component in senile plaques, the hallmark of Alzheimer's disease (AD). Diffuse plaques (nonfibrous, loosely packed Aß aggregates) containing amorphous Aß aggregates are also formed in brain. This work examines the influence of Cu(2+) complexation by Aß on the aggregation process in the context of charge and structural variations. Changes in the surface charges of Aß molecules due to Cu(2+) binding, measured with a ζ-potential measurement device, were correlated with the aggregate morphologies examined by atomic force microscopy. As a result of the charge variation, the "colloid-like" stability of the aggregation intermediates, which is essential to the fibrillation process, is affected. Consequently, Cu(2+) enhances the amorphous aggregate formation. By monitoring variations in the secondary structures with circular dichroism spectroscopy, a direct transformation from the unstructured conformation to the ß-sheet structure was observed for all types of aggregates observed (oligomers, fibrils, and/or amorphous aggregates). Compared to the Aß aggregation pathway in the absence of Cu(2+) and taking other factors affecting Aß aggregation (i.e., pH and temperature) into account, our investigation indicates that formations of amorphous and fibrous aggregates diverge from the same ß-sheet-containing partially folded intermediate. This study suggests that the hydrophilic domain of Aß also plays a role in the Aß aggregation process. A kinetic model was proposed to account for the effects of the Cu(2+) binding on these two aggregation pathways in terms of charge and structural variations.

Characterization of the non-fibrillar α-synuclein oligomers.

Under certain in vitro conditions, α-Synuclein is an abundant 14 kDa presynaptic intrinsically disordered protein, involved in the pathogenesis of Parkinson's disease (PD) forms amyloid fibrils which resemble those found in Lewy bodies of PD patients. However, a substantial fraction of α-synuclein molecules (10-20 %) does not form fibrils during fibrillation and exists in a form of soluble oligomers. In this study, we examined these soluble oligomers by a variety of biophysical techniques including atomic force microscopy (AFM), circular dichroism, Fourier-transform infrared spectroscopy and thioflavin T fluorescence. We observed that the fibrillation kinetics is affected by the variation in salt and protein concentrations. Although both high salt and high protein concentrations noticeably accelerated α-synuclein fibrillation, the amount of non-fibrillar oligomers is independent of the salt content. The oligomers formed at low salt concentration adopt more ß-sheet structure and are smaller in size than those formed at high salt concentration. AFM analysis shows that the low salt oligomers represent a mixture of small oligomers and some amorphous aggregates, whereas oligomers formed at high salt concentrations are noticeably larger, more homogenous, and are mostly spherical in shape. All the late stage non-fibrillar oligomers do not form fibrils even when seeded with pre-formed fibrils, are characterized by negligible rates of dissociation, likely due to their intertwined structure, and are able to disrupt the integrity of the biological membrane. These findings suggest that these soluble oligomers are important players in the multi-pathway aggregation of α-synuclein and should be taken into account in studies on the molecular mechanisms of this protein fibrillation.

Role of different regions of alpha-synuclein in the assembly of fibrils.

Elucidating the details of the assembly of amyloid fibrils is a key step to understanding the mechanism of amyloid deposition diseases including Parkinson's disease. Although several models have been proposed, based on analyses of polypeptides and short peptides, a detailed understanding of the structure and mechanism of alpha-synuclein fibrillation remains elusive. In this study, we used trypsin and endoproteinase GluC to digest intact alpha-synuclein fibrils and to analyze the detailed morphology of the resultant fibrils/remnants. We also created three mutants of alpha-synuclein, in which the N-terminal and C-terminal regions were removed, both individually and in combination, and investigated the detailed morphology of the fibrils from these mutants. Our results indicate that the assembly of mature alpha-synuclein fibrils is hierarchical: protofilaments --> protofibrils --> mature fibrils. There is a core region of approximately 70 amino acids, from residues approximately 32 to 102, which comprises the beta-rich core of the protofilaments and fibrils. In contrast, the two terminal regions show no evidence of participating in the assembly of the protofilament core but play a key role in the interactions between the protofilaments, which is necessary for the fibril maturation.

GM1 specifically interacts with alpha-synuclein and inhibits fibrillation.

The aggregation of alpha-synuclein is believed to be a key step in the etiology of Parkinson's disease. Alpha-synuclein is found in the cytosol and is associated with membranes in the presynaptic region of neurons and has recently been reported to be associated with lipid rafts and caveolae. We examined the interactions between several brain sphingolipids and alpha-synuclein and found that alpha-synuclein specifically binds to ganglioside GM1-containing small unilamellar vesicles (SUVs). This results in the induction of substantial alpha-helical structure and inhibition or elimination of alpha-synuclein fibril formation, depending on the amount of GM1 present. SUVs containing total brain gangliosides, gangliosides GM2 or GM3, or asialo-GM1 had weak inhibitory effects on alpha-synuclein fibrillation and induced some alpha-helical structure, while all other sphingolipids studied showed negligible interaction with alpha-synuclein. alpha-Synuclein binding to GM1-containing SUVs was accompanied by formation of oligomers of alpha-synuclein. The familial mutant A53T alpha-synuclein interacted with GM1-containing SUVs in an analogous manner to wild type, whereas the A30P mutant showed minimal interaction. This is the first detailed report showing a direct association between GM1 and alpha-synuclein, which is attributed to specific interaction between helical alpha-synuclein and both the sialic acid and carbohydrate moieties of GM1. The recruitment of alpha-synuclein by GM1 to caveolae and lipid raft regions in membranes could explain alpha-synuclein's localization to presynaptic membranes and raises the possibility that perturbation of GM1/raft association could induce changes in alpha-synuclein that contribute to the pathogenesis of PD.

Effect of 4-hydroxy-2-nonenal modification on alpha-synuclein aggregation.

Several observations have implicated oxidative stress and aggregation of the presynaptic protein alpha-synuclein in the pathogenesis of Parkinson disease. alpha-Synuclein has been shown to have affinity for unsaturated fatty acids and membranes enriched in polyunsaturated fatty acids, which are especially sensitive to oxidation under conditions of oxidative stress. One of the most important products of lipid oxidation is 4-hydroxy-2-nonenal (HNE), which has been implicated in the pathogenesis of Parkinson disease. Consequently, we investigated the effects of the interaction of HNE with alpha-synuclein. Incubation of HNE with alpha-synuclein at pH 7.4 and 37 degrees C resulted in covalent modification of the protein, with up to six HNE molecules incorporated as Michael addition products. Fourier transform infrared and CD spectra indicated that HNE modification of alpha-synuclein resulted in a major conformational change involving increased beta-sheet. HNE modification of alpha-synuclein led to inhibition of fibrillation in an HNE concentration-dependent manner. This inhibition of fibrillation was shown to be due to the formation of soluble oligomers based on size exclusion high pressure liquid chromatography and atomic force microscope data. Small angle x-ray scattering analysis indicated that the HNE-induced oligomers were compact and tightly packed. Treatment with guanidinium chloride demonstrated that the HNE-induced oligomers were very stable with an extremely slow rate of dissociation. Addition of 5 mum HNE-modified oligomers to primary mesencephalic cultures caused marked neurotoxicity because the integrity of dopaminergic and GABAergic neurons was reduced by 95 and 85%, respectively. Our observations indicate that HNE modification of alpha-synuclein prevents fibrillation but may result in toxic oligomers, which could therefore contribute to the demise of neurons subjected to oxidative damage.

Polyelectrolyte-mediated assembly of copper-phthalocyanine tetrasulfonate multilayers and the subsequent production of nanoparticulate copper oxide thin films.

An approach to producing films of nanometer-sized copper oxide particulates, based on polyelectrolyte-mediated assembly of the precursor, copper(II)phthalocyanine tetrasulfonate (CPTS), is described. Multilayered CPTS and polydiallyldimethylammonium chloride (PDADMAC) were alternately assembled on different planar substrates via the layer-by-layer (LbL) procedure. The growth of CPTS multilayers was monitored by UV-visible spectrometry and quartz crystal microbalance (QCM) measurements. Both the UV-visible spectra and the QCM data showed that a fixed amount of CPTS could be attached to the substrate surface for a given adsorption cycle. Cyclic voltammograms at the CPTS/PDADMAC-covered gold electrode exhibited a decrease in peak currents with the layer number, indicating that the permeability of CPTS multilayers on the electrodes had diminished. When these CPTS multilayered films were calcined at elevated temperatures, uniform thin films composed of nanoparticulate copper oxide could be produced. Ellipsometry showed that the thickness of copper oxide nanoparticulate films could be precisely tailored by varying the thickness of CPTS multilayer films. The morphology and roughness of CPTS multilayer and copper oxide thin films were characterized by atomic force microscopy. X-ray diffraction (XRD) measurements indicated that these thin films contained both CuO and Cu2O nanoparticles. The preparation of such copper oxide thin films with the use of metal complex precursors represents a new route for the synthesis of inorganic oxide films with a controlled thickness.

The flavonoid baicalein inhibits fibrillation of alpha-synuclein and disaggregates existing fibrils.

The aggregation of alpha-synuclein has been implicated as a critical step in the development of Parkinson's disease. Parkinson's disease is a progressive neurodegenerative disorder caused by the loss of dopaminergic neurons from the substantia nigra; currently, no cure exists. Baicalein is a flavonoid with antioxidant properties; upon oxidation, it forms several products including quinones. We show here that low micromolar concentrations of baicalein, and especially its oxidized forms, inhibit the formation of alpha-synuclein fibrils. In addition, existing fibrils of alpha-synuclein are disaggregated by baicalein. The product of the inhibition reaction is predominantly a soluble oligomer of alpha-synuclein, in which the protein molecules have been covalently modified by baicalein quinone to form a Schiff base with a lysine side chain in alpha-synuclein. The binding of baicalein was abolished by conversion of the Tyr residues into Phe, demonstrating that Tyr is involved in the interaction of alpha-synuclein with baicalein. In disaggregation baicalein causes fragmentation throughout the length of the fibril. These observations suggest that baicalein and similar compounds may have potential as therapeutic leads in combating Parkinson's disease and that diets rich in flavonoids may be effective in preventing the disorder.

Annular oligomeric amyloid intermediates observed by in situ atomic force microscopy.

Amyloidoses and related protein deposition diseases involve the transformation of normally soluble proteins into insoluble deposits, usually fibrillar in nature. Although it was originally assumed that the fibrils were the toxic species, this assumption has recently been called into question. Accumulating evidence in several systems suggests that oligomeric intermediates on the aggregation pathway may be toxic. In the present study we used in situ atomic force microscopy to monitor aggregation in aqueous solution in real time. The sample used was an amyloidogenic immunoglobulin light chain, involved in AL or light chain amyloidosis. The nature of the observed oligomeric intermediates was dependent on the conditions of incubation, especially pH and ionic strength. Several different aggregation intermediates with a variety of morphologies, including annular or torus-shaped species, were observed. The data indicate that protein aggregation can be very complex, involving a variety of different oligomeric intermediates whose population will be determined by the kinetic and thermodynamic competition between them.

Electrochemical polymerization of aniline monomers infiltrated into well-ordered truncated eggshell structures of polyelectrolyte multilayers.

The use of nanosphere lithography to construct two-dimensional arrays of polystyrene (PS) particles coated with multilayered polyelectrolyte (PE) shells and truncated eggshell structures composed of PE thin layers is reported. The truncated eggshell PE structures were produced by extraction of the PS particle cores with toluene. The core-extraction process ruptures the apex of the PE coating and causes a slight expansion of the PE thin layers. Aniline hydrochloride was infiltrated into the PE shells and subsequently electropolymerized to yield an array of a composite containing polyaniline (PAni) and PE thin shells. Voltammetric, quartz crystal microbalance, and reflectance Fourier transform infrared spectroscopic measurements indicate that aniline monomers were confined within the thin PE shells and the electropolymerization occurred in the interior of the PE shell. The PE thickness governs the amount of infiltrated monomer and the ultimate loading of the PAni in the truncated eggshell structure. Surface-structure imaging by atomic force microscopy and scanning electron microscopy, carried out after each step of the fabrication process, shows the influence of the PE thickness on the organization and dimensions of the arrays. Thus, the PE thin shells composed of different layers can function as nanometer-sized vessels for the entrapment of charged species for further construction of composite materials and surface modifications. This approach affords a new avenue for the synthesis of new materials that combine the unique properties of conductive polymers and the controllability of template-directed surface reactions.

Formation of disulfide bond in p53 correlates with inhibition of DNA binding and tetramerization.

The p53 tumor suppressor protein is susceptible to oxidation, which prevents it from binding to its DNA response element. The goal of the current research was to determine the nature of the cysteine residue thiol oxidation that prevents p53 from binding its DNA target and its effect on p53 structure. Recombinant p53, purified in the presence of the reducing agent dithiothreitol (DTT), contains five free thiol groups on the surface of the protein. In the absence of DTT, p53 contains only four thiol groups, indicating that an average of one surface thiol group is readily susceptible to oxidation. Sulfite-mediated disulfide bond cleavage followed by reaction with 2-nitro-5-thiosulfobenzoate showed that oxidized p53 contains a single disulfide bond per monomer. By atomic force microscopy, we determined that reduced p53 binds to a double-stranded DNA containing the p53 promoter element of the MDM2 gene. The DNA-bound reduced p53 has an average cross-sectional diameter of 8.61 nm and a height of 4.12 nm. The amount of oxidized p53 that bound to the promoter element was ninefold lower, and it has an 18% larger average cross-sectional diameter. Electromobility shift assays showed that binding of oxidized p53 to DNA was enhanced upon addition of DTT, indicating that oxidation is reversible. The possibility that oxidized p53 contained significant amounts of sulfenic (-SOH), sulfinic (-SO2H), or sulfonic acid (-SO3H) was ruled out. Gel filtration chromatography indicated that oxidation increases the percentage of p53 monomers and high-molecular-weight oligomers (>1,000 kDa) relative to tetrameric p53. Protein modeling studies suggest that a mixed disulfide glutathione adduct on Cys182 could account for the observed stoichiometry of oxidized thiols and structural changes. The glutathione adduct may prevent proper helix-helix interaction within the DNA binding domain and contribute to tetramer dissociation.