Bulk Poly Research Articles

Synthesis and anticorrosion property of poly(2,3-dimethylaniline)/organic-attapulgite nanofibers via self-assembling and graft polymerization

Core–shell poly(2,3-dimethylaniline)/organic-attapulgite (P(2,3-DMA)/APTES-ATP) nanofibers were prepared by self-assembling and graft polymerization in the presence of organically modified attapulgite, based on the encapsulation of attapulgite (ATP) template with P(2,3-DMA) after the surface modification with γ-aminopropyltriethoxysilane (APTES) to form a self-assembled layer on the surface of ATP rod-shaped particle (APTES-ATP). Structure, morphology and thermal stability of the nanocomposites were characterized by XRD, FTIR, SEM, TEM and TGA measurements, respectively. The anticorrosion property of the as-prepared nanocomposites was evaluated by open circuit potential (OCP) and impedance spectroscopy (EIS) in 3.5 wt% NaCl aqueous solution. Experimental results indicated that P(2,3-DMA)/APTES-ATP had a more higher thermal stability and anti-corrosion properties compared with the bulk poly(2,3-dimethylaniline) (P(2,3-DMA)).

Study of the morphology of network material obtained by the catalytic polymerization of 2-hydroxyethyl methacrylate

The vanadyl ion complex VO(DMSO)5(ClO4)2 (I) exhibits high catalytic activity in the polymerization of 2-hydroxyethyl methacrylate (HEMA) in both aerobic and anaerobic conditions. A feature of I is the formation of a network structure capable of swelling in aqueous medium. On the grounds of studying the elastic properties of hydrogels, the concentrations of elastically active chains nc in a network of bulk poly(HEMA) is determined. An increase in the cross-link density is observed with increasing concentration of I. The topological structure and morphology of poly(HEMA) are investigated; structural manifestations of the bifunctional nature of the catalyst and two directions of polymerization initiation are found.

Polymer dynamics near the surface and in the bulk of poly(tetrafluoroethylene) probed by zero-field muon-spin-relaxation spectroscopy.

The results of many experiments on polymers such as polystyrene indicate that the polymer chains near a free surface exhibit enhanced dynamics when compared with the bulk. We have investigated whether this is the case for poly(tetrafluoroethylene) (PTFE) by using zero-field muon-spin-relaxation spectroscopy to characterize a local probe, the F-Mu(+)-F state, which forms when spin-polarized positive muons are implanted in PTFE. Low-energy muons (implantation energies from 2.0 to 23.0 keV) were used to study the F-Mu(+)-F state between ∼ 23 and 191 nm from the free surface of PTFE. Measurements were also made with surface muons (4.1 MeV) where the mean implantation depth is on the order of ∼ 0.6 mm. The relaxation rate of the F-Mu(+)-F state up to ∼ 150 K was found to be significantly higher for muons implanted at 2.0 keV than for higher implantation energies, which suggests that the polymer chains in a region on the order of a few tens of nanometers from the free surface are more mobile than those in the bulk.

Anomalous temperature dependence of speed of sound of bulk poly(N-isopropylacrylamide) hydrogels near the phase transition

Bulk Poly(N-isopropylacrylamide) (PNIPAm) hydrogels are thermally responsive polymers that undergo a sharp volumetric phase transition around its lower critical solution temperature of 33°C. The physical characteristics of bulk, micro-, and nano-form PNIPAm hydrogel have been well-studied, and have applications ranging from biomedical devices to mechanical actuators. An important physical characteristics which reveals lack of available information is speed of sound. Prior studies have utilized Brillouin scattering, multi-echo reflection ultrasound spectroscopy, the sing-around method, and others in measuring the speed of sound. We use a planar resonant cavity with bulk PNIPAm hydrogel in aqueous solution to determine the temperature dependent speed of sound around the lower critical solution temperature. The results show sharp nonmonotonic behavior of the sound velocity in vicinity of the phase transition.

Preparation and properties of poly(2,3-dimethylaniline)/organic–kaolinite nanocomposites via in situ intercalative polymerization

Abstract Poly(2,3-dimethylaniline)/kaolinite nanocomposites (P(2,3-DMA)/K2) were prepared by in situ intercalative polymerization in the presence of organically modified kaolinite, based on the intercalation modification of crude kaolinite with dimethylsulfoxide (DMSO) and methanol system. Intercalation extent of kaolinite, Structure, Morphology and Thermal stability of the nanocomposites were characterized by XRD, FTIR, SEM and TGA–DTA, respectively. The electrochemical behavior of the as-prepared nanocomposites was evaluated by open circuit potential (OCP), tafel polarization curves (TAF) and impedance spectroscopy (EIS) in 3.5 wt% NaCl aqueous solution. Experimental results indicated that the clay layers of kaolinite in P(2,3-DMA)/K2 were well intercalated and exfoliated, and the P(2,3-DMA)/K2 had a more higher thermal stability and anticorrosion properties relative to the bulk poly(2,3-dimethylaniline) (P(2,3-DMA)) and the P(2,3-DMA)/crude kaolinite composites (P(2,3-DMA)/K0).

The Human Nuclear Poly(A)-Binding Protein Promotes RNA Hyperadenylation and Decay

Control of nuclear RNA stability is essential for proper gene expression, but the mechanisms governing RNA degradation in mammalian nuclei are poorly defined. In this study, we uncover a mammalian RNA decay pathway that depends on the nuclear poly(A)-binding protein (PABPN1), the poly(A) polymerases (PAPs), PAPα and PAPγ, and the exosome subunits RRP6 and DIS3. Using a targeted knockdown approach and nuclear RNA reporters, we show that PABPN1 and PAPα, redundantly with PAPγ, generate hyperadenylated decay substrates that are recognized by the exosome and degraded. Poly(A) tail extension appears to be necessary for decay, as cordycepin treatment or point mutations in the PAP-stimulating domain of PABPN1 leads to the accumulation of stable transcripts with shorter poly(A) tails than controls. Mechanistically, these data suggest that PABPN1-dependent promotion of PAP activity can stimulate nuclear RNA decay. Importantly, efficiently exported RNAs are unaffected by this decay pathway, supporting an mRNA quality control function for this pathway. Finally, analyses of both bulk poly(A) tails and specific endogenous transcripts reveals that a subset of nuclear RNAs are hyperadenylated in a PABPN1-dependent fashion, and this hyperadenylation can be either uncoupled or coupled with decay. Our results highlight a complex relationship between PABPN1, PAPα/γ, and nuclear RNA decay, and we suggest that these activities may play broader roles in the regulation of human gene expression.

The Rubber Elasticity of Poly(<i>N</i>-isopropylacrylamide) Hydrogel Networks

We report here on the characterization of classical bulk poly (N-isopropylacrylamide) (PNIPAAm) hydrogel networks. The classical PNIPAAm hydrogels were prepared from N-isopropylacrylamide (NIPAAm) as a main monomer and N,N-methylenebisacrylamide (MBAAm) as a crosslinker. The viscoelastic character of bulk hydrogels was examined using rheological measurements under frequency sweep mode (20 °C). A range of frequency, ω from 0.1 to 100 rad/s, was employed as this is a typical range for rubber plateau. Within this range, almost frequency independent of storage moduli (G'; ~ 104 Pa as a function of hydrogel compositions were obtained. Indeed, the perfect soft-rubbery behaviour of PNIPAAm hydrogels could be confirmed and thus enabled the estimation of mesh size. Interestingly, the mesh size rubbery hydrogels determined from rheological data was in a good agreement to that from swelling experiments (~ 4 to 9 nm).

Modeling Photoinduced Charge Transfer Across π-Conjugated Heterojunctions

The adapted Su−Schrieffer−Heeger (aSSH) model Hamiltonian is extended in this work to incorporate the interchain π−π stacking and dynamical electron−phonon coupling effects so that the photoinduced charge-transfer mechanism can be directly probed at the π-conjugated heterojunction interfaces. It is found that excitons generated in the bulk poly(p-phenylene vinylene) (PPV) phase require an activation energy of 0.23 eV to reach the heterojunction interfaces before getting their charges separated. Electron transfers from the D1 state of PPV to the t1u state of C60 follow the nonadiabatic mechanism, which is accelerated by three major factors including the 0.95 eV energy drop between the two states, close vicinity of the electron-donating D1 state to the C60 phase, and suppressed inversion symmetry of C60 at the interfaces. The irreversible phonon relaxation energy associated with the nonadiabatic electron transfer is estimated to be 0.3 eV, which explains the widely accepted empirical energy offsets between the measured open-circuit voltage and the theoretical built-in potential.

191st ENMC International Workshop: Recent advances in oculopharyngeal muscular dystrophy research: From bench to bedside 8-10 June 2012, Naarden, The Netherlands

This workshop hosted a group of 19 clinicians and basic scientist from 5 countries (France, USA, Canada, Denmark and The Netherlands). Recent research developments and possible collaboration in advancing therapies for oculopharyngeal muscular dystrophy (OPMD), a late onset, rare and progressive neurodegeneration disorder were discussed in this meeting. The disease is caused by alanine expansion mutations in the gene encoding for poly(A)-binding protein nuclear 1 (PABPN1), resulting in accumulation of mutant PABPN1 in the cell nucleus and the formation of insoluble aggregates. Therefore, OPMD is categorized together with neurodegenerative disorders that are caused by single amino acid repeats. While the genetic cause for those disorders is often recognized, the molecular basis for symptoms is still obscure. PABPN1 is ubiquitously expressed and it is not known why symptoms develop only after midlife and initially only in subsets of skeletal muscles [1,2]. While the genetic cause for OPMD was reported in 1998 and good surgical treatments exist for major early symptoms, there are currently no medical options for the more general skeletal muscle involvement, no validated biomarkers and no clinical severity scale.

The Ccr4-Not deadenylase complex constitutes the major poly(A) removal activity inC. elegans

Post-transcriptional regulatory mechanisms are widely used to control gene expression programs of tissue development and physiology. Controlled 3' poly(A) tail-length changes of mRNAs provide a mechanistic basis of such regulation, affecting mRNA stability and translational competence. Deadenylases are a conserved class of enzymes that facilitate poly(A) tail removal, and their biochemical activities have been mainly studied in the context of single-cell systems. Little is known about the different deadenylases and their biological role in multicellular organisms. In this study, we identify and characterize all known deadenylases of Caenorhabditis elegans, and identify the germ line as tissue that depends strongly on deadenylase activity. Most deadenylases are required for hermaphrodite fertility, albeit to different degrees. Whereas ccr-4 and ccf-1 deadenylases promote germline function under physiological conditions, panl-2 and parn-1 deadenylases are only required under heat-stress conditions. We also show that the Ccr4-Not core complex in nematodes is composed of the two catalytic subunits CCR-4 and CCF-1 and the structural subunit NTL-1, which we find to regulate the stability of CCF-1. Using bulk poly(A) tail measurements with nucleotide resolution, we detect strong deadenylation defects of mRNAs at the global level only in the absence of ccr-4, ccf-1 and ntl-1, but not of panl-2, parn-1 and parn-2. Taken together, this study suggests that the Ccr4-Not complex is the main deadenylase complex in C. elegans germ cells. On the basis of this and as a result of evidence in flies, we propose that the conserved Ccr4-Not complex is an essential component in post-transcriptional regulatory networks promoting animal reproduction.

Visualization of Endoplasmic Reticulum Localized mRNAs in Mammalian Cells

In eukaryotes, most of the messenger RNAs (mRNAs) that encode secreted and membrane proteins are localized to the surface of the endoplasmic reticulum (ER). However, the visualization of these mRNAs can be challenging. This is especially true when only a fraction of the mRNA is ER-associated and their distribution to this organelle is obstructed by non-targeted (i.e. "free") transcripts. In order to monitor ER-associated mRNAs, we have developed a method in which cells are treated with a short exposure to a digitonin extraction solution that selectively permeabilizes the plasma membrane, and thus removes the cytoplasmic contents, while simultaneously maintaining the integrity of the ER. When this method is coupled with fluorescent in situ hybridization (FISH), one can clearly visualize ER-bound mRNAs by fluorescent microscopy. Using this protocol the degree of ER-association for either bulk poly(A) transcripts or specific mRNAs can be assessed and even quantified. In the process, one can use this assay to investigate the nature of mRNA-ER interactions.

The preparation of poly(vinyl phosphonic acid) hydrogels as new functional materials for in situ metal nanoparticle preparation

Bulk poly(vinyl phosphonic acid) (p(VPA)) hydrogels were synthesized via a photo polymerization technique using polyethylene glycol diacrylate with different molecular weights as crosslinker. The prepared hydrogel was also used as template for in situ metal nanoparticle preparations of Co, Ni and Cu, by loading the corresponding metal ions from aqueous solution into the p(VPA) hydrogel networks and then reducing the metal ions with sodium boron hydride (NaBH4) within the hydrogel matrices. The amount of metal in hydrogel composites was determined by atomic absorption spectroscopy (AAS) and thermogravimetric analysis (TGA) measurements. Moreover, p(VPA)–M (M: Co, Ni, Cu, etc) were used as a soft reactor for the generation of hydrogen by hydrolysis of NaBH4,and in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). P(VPA)–Co composite demonstrated the best catalytic performance and its activation energy was calculated as 23.01kJmol−1 which is comparable and mostly better than similar work in the literature.

Severe Heat Shock Induces Nucleolar Accumulation of mRNAs in Trypanosoma cruzi

Several lines of evidence have shown that, besides its traditional function in ribosome biogenesis, the nucleolus is also involved in regulating other cellular processes such as mRNA metabolism, and that it also plays an important role as a sensor and coordinator of the stress response. We have recently shown that a subset of RNA Binding Proteins and the poly(A)+ RNA are accumulated into the Trypanosoma cruzi nucleolus after inducing transcription inhibition with Actinomycin D. In this study, we investigated the behaviour of the T. cruzi mRNA population in parasites subjected to severe heat shock, an environmental stress that also decreases the rate of RNA synthesis. We found that the bulk of poly(A)+ RNA is reversibly accumulated into the nucleolus when exposing T. cruzi epimastigote forms to severe heat shock. However, the Hsp70 mRNA was able to bypass such nucleolar accumulation. Together, these data reinforce the idea about the involvement of the T. cruzi nucleolus in mRNA metabolism during an environmental stress response. Interestingly, T. brucei procyclic forms did not induce nucleolar accumulation of poly(A)+ RNA under such stress condition, suggesting that different trypanosomatids have adopted different responses to deal with the same stress conditions.

Rheological studies on PNIPAAm hydrogel synthesis via in situ polymerization and on resulting viscoelastic properties

Bulk poly(N-isopropylacrylamide) hydrogels were prepared via free radical polymerization. Two different initiation methods were studied: redox- and photoinitiation. It was demonstrated that the desired final properties of resulting hydrogels, i.e., high monomer conversion (>95%) and adjustable swelling were only obtained by selecting best suited initiation conditions. For redox polymerization, this was achieved by tuning the ratio of accelerator N,N,N′,N′-tetramethylethylenediamine to initiator ammonium persulfate. The key parameters for achieving optimum photopolymerization conditions were photoinitiator concentration and UV irradiation time. With help of in situ rheological measurements, optimum conditions could be further verified and quantified by monitoring the liquid-to-gel transition. Overall, photoiniated crosslinking copolymerization was postulated to offer better options for in situ preparation of tailored functional hydrogels, in particular for the integration of smart soft matrices within membrane pores or other microsystems via a rapid reaction. Rheology was also used to investigate the hydrogel after ex situ preparation, revealing “perfect” soft-rubbery behavior. A good correlation between the mesh sizes determined from swelling and rheology was also found. In conclusion, rheology has been found to be a powerful tool because it provides valuable data on polymerization and gelation kinetics as well as information about the hydrogels microstructure based on their viscoelastic character.

Enhancement of photochemical response in bulk poly(methyl methacrylate) photopolymer dispersed organometallic compound

The enhancement of photochemical response is investigated in Zinc methylacrylate organometallic compound and phenathrenequinone doped poly(methyl methacrylate) photopolymer experimentally and theoretically. In experiments, the improvement in photosensitivity due to ZnMA compound is presented quantitatively. The dynamics parameters, quantum yield and initiation rate of PQ molecules, are determined by nonlinear fitting the experimental curves. The theoretical model with nonlocal effect is proposed to explain the contribution of actual chemical process to the enhancement of photochemical response. The comparison of theoretical and experimental results is finally described. Two significant roles of ZnMA compound, as a catalyst to accelerate the photochemical reaction and as a reactant to participate in the photoattachment with PQ molecules, are demonstrated quantitatively. The time constant of grating formation 20.9s and the photosensitivity 2.3×10−5cm2/J are experimentally obtained in an optimized 0.1wt% ZnMA doped PQ-PMMA sample. This study contributes the physical mechanism for improvement of photosensitivity and provides significant theoretical foundation for advance the properties of materials in holographic memory.

A novel p(AAm-co-VPA) hydrogel for the Co and Ni nanoparticle preparation and their use in hydrogel generation from NaBH4

A novel bulk poly(acrylamide-co-vinyl phosphonic acid) (p(AAm-co-VPA)) hydrogels were synthesized via a photo polymerization technique in macro dimension. Ni and Co nanoparticles inside p(AAm-co-VPA) hydrogel were also prepared by reduction of the metal ions loaded into the hydrogel network from the corresponding metal salt solution in water. The reduction of these bound metal ions within hydrogel matrices were done by treating hydrogel-laden metal ions with NaBH4 to produce novel hydrogel-metal composite catalyst systems. Furthermore, these soft hydrogel composite catalyst systems were employed in the generation of hydrogen from the hydrolysis of sodium boron hydride (NaBH4) in a basic medium. Thermogravimetric analysis (TGA) and atomic absorption spectroscopy (AAS) measurements were employed to determine the metal particle content of p(AAm-co-VPA)-M (M: Co, Ni) composite hydrogels. The effects of different parameters such as the amount of catalyst, the reaction temperature, the type of the metal, the initial concentration of NaBH4 and reusability of the prepared catalyst systems were investigated, and the activation energy for hydrolysis of NaBH4 by p(AAm-co-VPA) was found as 23.68kЈ/mol.

Fluorocarbon thin film with superhydrophobic property prepared by pyrolysis of hexafluoropropylene oxide

A fluorocarbon thin film with superhydrophobic property was prepared by chemical vapor deposition (CVD) method at low temperature (200–300°C) via pyrolysis hexafluoropropylene oxide (HFPO). The experiment results indicated the morphology and structure of fluorocarbon films were strongly dependent on the pyrolysis temperature. As shown through atomic force microscope (AFM), the surface morphology of the films ranged from rodlike grains to sheets. Fourier transform infrared (FTIR) spectroscopy revealed that all the films contained the vibrational frequencies of linear CF2 chains, which were also characteristic of bulk poly tetrafluoroethylene (PTFE). X-ray photoelectron spectroscopy (XPS) analysis showed that CF2 structures were predominant in the films with high order. The film deposited at 300°C exhibited a superhydrophobic surface with contact angle up to 172.7°.

P180 Promotes the Ribosome-Independent Localization of a Subset of mRNA to the Endoplasmic Reticulum

Author SummaryMessenger RNAs (mRNAs) that encode secreted or membrane-bound proteins must be delivered to, and then maintained on, the surface of the endoplasmic reticulum (ER). These mRNAs encode a short polypeptide that targets the mRNA/ribosome/nascent protein complexes to the ER surface during translation; however, recent studies support the existence of additional ER-localization signals that might be present within the mRNA molecules themselves. Here, we demonstrate that a fraction of these mRNAs, whose encoded proteins are destined for secretion, contain information that targets and anchors them to the ER independently of their encoded polypeptide or their association to ribosomes. We identify proteins on the ER that may serve as receptors for these mRNAs. We then show that one of these candidate membrane-bound receptors, p180, is required for the maintenance of certain mRNAs on the surface of the ER even after their translation into protein is disrupted. We also demonstrate that p180 contains a region that binds directly to RNA and likely mediates the anchoring of mRNA to the ER. Our study thus provides the first mechanistic details of an alternative pathway used to ensure that secretory mRNAs, and their encoded proteins, reach their proper destination in the ER.

Polymer Nanoparticles via Living Radical Polymerization in Aqueous Dispersions: Design and Applications

In the past decade, living radical polymerization (LRP) has revolutionized academic research in the fields of free-radical polymerization and materials design. Sophisticated macromolecular architectures, designed for a variety of applications and end-use properties, can now be synthesized using relatively simple LRP chemistries that do not require stringent oxygen or moisture free environments, subzero reaction temperatures, or highly purified reagents. Publications abound not only in the fundamentals of LRP but also its use in designing tailor-made polymers and polymer–hybrid composites. Corporate research organizations have also been actively involved in LRP, with numerous patents being issued annually. Despite the intense research interest, however, comparatively few products have been commercialized, with high process costs being a primary factor. Most commercial free-radical polymerizations are conducted in aqueous dispersions due to significantly lower process costs compared to bulk or solution poly...

SELF-TRAPPING OF OPTICAL VORTEX BY USING THE MOLECULAR REORIENTATION IN PHOTOSENSITIVE POLYMERIC MATERIALS

Amorphous bulk composites were prepared by doping azo-dye Disperse Red 13 (DR13) in poly(methyl methacrylate) (PMMA) matrices. Photo-induced anisotropy of such kind of bulk polymer material was investigated experimentally by measuring the birefringence when irradiating it with linearly polarized green light. We report the first observation of self-trapping of an optical vortex based on such effect in bulk poly(methyl methacrylate) materials containing photosensitive azo-dye molecules. The dependence of the average core width of a single-charge optical vortex versus time and input power was investigated in detail.