Strong Physical Interaction Research Articles

Influence of enhanced dispersity of chemically treated MWNTs on physical properties of MWNTs/PVDF films

In this study, multi-walled carbon nanotubes (MWNTs) were treated chemically with ethylene glycol (EG) to improve their dispersion in the polymer matrix. Poly(vinylidene fluoride) (PVDF) films with different EGMWNT contents were prepared by solution casting and the surface characteristics of EG-MWNTs and interaction between the EG-MWNTs and PVDF matrixes were investigated. Using XPS and Zeta potential values compared to those of pristine MWNTs, the surface characteristics of the EG-MWNTs were determined by the increase in the number of oxygen groups. The ΔHm and XC of the PVDF films increased slightly with increasing EG-MWNT content. In addition, the tensile strength of the pure PVDF film increased significantly with increasing EG-MWNTs addition; its maximum value was observed at a 1.0 wt% EG-MWNT loading, and was 62% higher than that of a pure PVDF film. This was attributed to the improved dispersability of EG-MWNTs in the PVDF matrix, leading to strong physical interactions between the EG-MWNTs and PVDF matrix.

GAP43 shows partial co-localisation but no strong physical interaction with prolyl oligopeptidase

It has recently been proposed that prolyl oligopeptidase (POP), the cytosolic serine peptidase with neurological implications, binds GAP43 (Growth-Associated Protein 43) and is implicated in neuronal growth cone formation, axon guidance and synaptic plasticity. We investigated the interaction between GAP43 and POP with various biophysical and biochemical methods in vitro and studied the co-localisation of the two proteins in differentiated HeLa cells. GAP43 and POP showed partial co-localisation in the cell body as well as in the potential growth cone structures. We could not detect significant binding between the recombinantly expressed POP and GAP43 using gel filtration, CD, ITC and BIACORE studies, pull-down experiments, glutaraldehyde cross-linking and limited proteolysis. However, glutaraldehyde cross-linking suggested a weak and transient interaction between the proteins. Both POP and GAP43 interacted with artificial lipids in our in vitro model system, but the presence of lipids did not evoke binding between them. In native polyacrylamide gel electrophoresis, GAP43 interacted with one of the three forms of a polyhistidine-tagged prolyl oligopeptidase. The interaction of the two proteins was also evident in ELISA and we have observed co-precipitation of the two proteins during co-incubation at higher concentrations. Our results indicate that there is no strong and direct interaction between POP and GAP43 at physiological conditions.

Influence of Surface Treatment of Multi-walled Carbon Nanotubes on Interfacial Interaction of Nanocomposites

In this work, the effect of aminized multi-walled carbon nanotubes (NH-MWNTs) on the mechanical interfacial properties of epoxy nanocomposites was investigated by means of fracture toughness, critical stress intensity factor (KIC), and impact strength testing, and their morphology was examined by scanning electron microscope (SEM). It was found that the incorporation of amine groups onto MWNTs was confirmed by the FT-IR and Raman spectra. The mechanical interfacial properties of the epoxy nanocomposites were remarkably improved with increasing the NH-MWNT content. It was probably attributed to the strong physical interaction between amine groups of NH-MWNTs and epoxide groups of epoxy resins. The SEM micrographs showed that NH-MWNTs were uniformly embed and bonded with epoxy resins, resulted in the prevention of the deformation and crack propagation in the NH-MWNTs/epoxy nanocomposites.

Large Strain and Fracture Properties of Poly(dimethylacrylamide)/Silica Hybrid Hydrogels

The synthesis and mechanical characterization of novel, tough poly(N,N-dimethylacrylamide) (PDMA)−silica hydrogel hybrids are presented to understand the role played by strong physical interactions between silica nanoparticles and the PDMA polymer on the properties of chemically cross-linked highly swollen PDMA networks. A detailed comparison of the hybrids with unmodified PDMA gels indicates that the incorporation of silica nanoparticles in the hydrogel increases the compression strength and the fracture toughness of notched samples up to an order of magnitude while increasing its modulus by a factor of 6 with a volume fraction of particles of the order of only 7%. The hybrid gels present a strain-dependent hysteresis but no permanent damage or residual strain upon unloading even after repeated cycling, a very unique property for such tough hydrogels. The reason for this exceptional increase in toughness is attributed mainly to the combined effect of breakable silica/polymer bonds and of a wide distribution of elastic chain lengths.

The Surface Characteristics and Reactivity of Residual Carbon in Coal Gasification Slag†

In a slagging entrained-flow coal gasifier, a large portion of the inorganic matter will form liquid slag that may have strong physical and chemical interactions with char. Understanding the char-slag interaction is important for improving the modeling and design of gasifiers. This paper reports the characteristics of residual carbon in both coarse and fine slag from a typical entrained-flow coal water slurry gasifier. The surface characteristics of slag and residual carbon in slag were evaluated by scanning electron microscopy and energy dispersive X-ray spectroscopy. The reactivity of the residual carbon in slag was compared through thermal gravimetric analysis. It was observed that fine inorganic matters in the slag tend to exist in spherical shape whereas residual carbons tend to stay as loose floccule. A melting test on fine carbon-slag mixture validated that inorganic matters have a tendency to agglomerate into large carbon-free spheres when melting in a carbon powder matrix due to surface tension change. It was also found that the reactivity of the carbon in fine slag was lower than carbon in coarse slag, which implies the formations of the carbon in fine and coarse slag are different.

Effects of riparian vegetation on the structure of the marginal aquatic habitat and the associated fish assemblage in a tropical Brazilian reservoir

Riparian zones represent areas of strong biological, physical and chemical interaction between terrestrial and aquatic ecosystems. These areas are usually typified by high diversity of fauna, flora and environmental processes. The present study evaluates the littoral habitat structure and its fish fauna related to associations between presence and absence of natural riparian vegetal cover, in a reservoir in northeastern Brazil. Sampling was performed on marginal areas where riparian vegetation was present and where it had been removed for the plantation of sugar cane. For each type of marginal area three replicate sites were sampled during the wet season. Data on the habitat structure (submerged elements and substrate composition), fish and water quality were collected. The data was analyzed using Shannon-Wiener's diversity index and Pielou's equitability. Non-metric Multidimensional Scaling and the Multi-Response Permutation Procedure were used to evaluate similarities between sites. The structure of the habitat was more diverse in sites were natural riparian vegetation was still present. Muddy substrate was more abundant in areas with riparian vegetation whereas sandy substrate was more abundant in areas where riparian vegetation had been removed. Measured physico-chemical parameters and nutrients remained nearly constant across all sites. Metynnis lippincottianus and Crenicichla menezesi were more associated with the habitat in areas where riparian vegetation was removed, whereas Cichlasoma orientale and Cichla ocellaris were strongly correlated to forested areas.

RGMb controls aggregation and migration of Neogenin-positive cells in vitro and in vivo

The proliferation, migration and differentiation of dentate gyrus stem and precursor cells have aroused keen interest. Neogenin and RGMb are expressed in non-overlapping compartments of the developing dentate gyrus. While Neogenin is expressed in migrating and proliferating dentate precursors, RGMb is localized in structures bordering the developing dentate, such as cornus ammonis cells and Cajal–Retzius cells in the marginal zone including the hippocampal fissure. Co-immunoprecipitation and binding assays indicate a strong physical interaction. In vitro and in vivo migration of dentate neuroepithelial cells is abolished by RGMb, and cell adhesion is reduced when cells expressing Neogenin comes into contact with cells expressing RGMb. Ectopic expression of RGMb in organotypic slice cultures and after in utero electroporation in the hippocampus modifies precursor cell migration. Our results imply that Neogenin-RGMb interaction might be involved in neuronal migration in the dentate gyrus.

A systematic characterization of Cwc21, the yeast ortholog of the human spliceosomal protein SRm300

Cwc21 (complexed with Cef1 protein 21) is a 135 amino acid yeast protein that shares homology with the N-terminal domain of human SRm300/SRRM2, a large serine/arginine-repeat protein shown previously to associate with the splicing coactivator and 3'-end processing stimulatory factor, SRm160. Proteomic analysis of spliceosomal complexes has suggested a role for Cwc21 and SRm300 at the core of the spliceosome. However, specific functions for these proteins have remained elusive. In this report, we employ quantitative genetic interaction mapping, mass spectrometry of tandem affinity-purified complexes, and microarray profiling to investigate genetic, physical, and functional interactions involving Cwc21. Combined data from these assays support multiple roles for Cwc21 in the formation and function of splicing complexes. Consistent with a role for Cwc21 at the core of the spliceosome, we observe strong genetic, physical, and functional interactions with Isy1, a protein previously implicated in the first catalytic step of splicing and splicing fidelity. Together, the results suggest multiple functions for Cwc21/SRm300 in the splicing process, including an important role in the activation of splicing in association with Isy1.

When Segregation Hangs by a Thread

When Segregation Hangs by a Thread

Stimuli‐Responsive Polymersomes as Nanocarriers for Drug and Gene Delivery

Polymeric formulations (micelles, vesicles etc.) have emerged as versatile drug carriers due to their increased stability, site specificity, blood circulation resistance and thus overall potential therapeutic effects compared to liposomes. Furthermore, stimuli-responsive systems have been developed whose properties change after applying certain external triggers. Polymersomes are mainly composed of amphiphilic block copolymers that are held together in water due to strong physical interactions between the insoluble hydrophobic blocks, thus forming a bilayer morphology or, in the case of triblock copolymers, a bilayer-like morphology. Formation and destabilization of these assemblies is a consequence of external stimuli (temperature, pH, oxidation/reduction conditions etc.). This review focuses on recent developments concerning stimuli- responsive polymersomes made of amphiphilic block copolymers and their potential applications within the biomedical field.

Two ~35 day clocks in Hercules X-1: evidence for neutron star free precession

We present evidence for the existence of two ∼35 day clocks in the Her X-1/HZ Her binary system. ∼35 day modulations are observed 1) in the Turn-On cycles with two on- and two off-states and 2) in the changing shape of the pulse profiles which re-appears regularly. The two ways of counting the 35 day cycles are generally in synchronization. This synchronization did apparently break down temporarily during the long Anomalous Low (AL3), which Her X-1 experienced in 1999/2000, in the sense that there must have been one extra Turn-On cycle. Our working hypothesis is that there are two clocks in the system, both with a period of about ∼35 days: precession of the accretion disk (the less stable “Turn-On clock”) and free precession of the neutron star (the more stable “Pulse profile clock”). We suggest that free precession of the neutron star is the master clock and that the precession of the accretion disk is basically synchronized to that of the neutron star through a feedback mechanism in the binary system. However, the Turn-On clock can slip against its master when the accretion disk has a very low inclination, as is observed to be the case during AL3. We take the apparent correlation between the histories of the Turn-Ons ,o f theAnomalous Lows and of the pulse period evolution, with a 5 yr quasi-periodicity, as evidence for strong physical interaction and feedback between the major components in the system. We speculate that the 5 yr (10 yr) period is due either to a corresponding activity cycle of HZ Her or a natural ringing period of the physical system of coupled components. The question of whether free precession really exists in neutron stars is very important for understanding matter with supra-nuclear density.

Progesterone regulation of RUSH/SMARCA3/HLTF includes DNA looping

RUSH/SMARCA3 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily A, member 3) is capable of sequence-selective DNA binding and ATP-dependent DNA unwinding. In rabbit uterine epithelial cells, RUSH-1alpha (113 kDa) is the progesterone-dependent splice variant and RUSH-1beta (95 kDa) is the oestrogen-dependent splice variant. Rabbit RUSH/SMARCA3 mRNA is primarily regulated at the proximal promoter (-162/+90) via a PRE (progesterone-response element) half-site/overlapping Y-box domain (-38/-26) and two Sp (specificity protein) 3 sites centred at -128 and -58. We investigated hormone regulation by exploring binding of transcription factors to a putative RUSH/SMARCA3 site (-616/-611) and the distal Sp3 (-131/-126) site. In response to progesterone, RUSH-1alpha binds the RUSH site and the Sp3 site becomes a functional binding site for Egr-1 (early growth-response gene product 1)/Sp (specificity protein)1/3/MAZ (Myc-associated zinc-finger protein)/MZF1 (myeloid zinc finger 1)/c-Rel. TransSignal TF-TF Interaction Arrays, supershift assays and ChIP (chromatin immunoprecipitation) analyses confirmed strong physical interactions between RUSH and Egr-1/c-Rel. Higher-order long-range interactions between RUSH and the Egr-1/c-Rel derivative of the anisotropic flexibility of the intervening DNA sequence were shown with 3C (chromosome conformation capture) assays. Transient transfection assays with mutant constructs showed the co-operative interaction between RUSH and Egr-1 mediates repression by c-Rel. Thus DNA-bound RUSH/SMARCA3 communicates with its own proximal promoter by looping the intervening DNA. Moreover, progesterone-dependent DNA looping is an adjunct to progesterone induction of the RUSH/SMARCA3 gene because the availability of RUSH isoforms and relevant binding partners is progesterone-regulated.

Carbon Nanotube Triggered Self‐Assembly of Oligo(p‐phenylene vinylene)s to Stable Hybrid π‐Gels

Gel self-assembly: Addition of small amounts of carbon nanotubes (CNTs) to a solution of oligo(p-phenylene vinylene) OPV1 in toluene triggers their self-assembly to form a composite gel (see picture) with higher stability and better rheological properties than the OPV1 gel. Strong physical interactions between the species allow the encapsulation of CNTs into self-assembled tapes of OPV1, reinforcing the 3D gel network.

Poly(phenylene sulfide) magnetic composites. II. Crystallization, thermal, and viscoelastic properties

AbstractPoly(phenylene sulfide)/ferrosoferric oxide composites (PPS/Fe3O4) with various loading levels were prepared by melt compounding. The crystallization, thermal, and viscoelastic properties were characterized respectively by the DSC, DMA, TGA and parallel plate rheometer. The results reveal that the well‐dispersed Fe3O4 particle restricts the segmental motion of polymer chain, leading to a remarkable increase of the glass transition temperature and thermal stability of the PPS due to the strong physical association and interactions between particles and matrix. The presence of the Fe3O4 particles, however, can not facilitate crystallization of PPS, because the particles only play the role of inert filler and have no heterogeneous nucleating effect. The crystallization kinetics, as a result, decreases with increasing particles loadings due to the increasing restriction of the chain mobility and high viscosity. In addition, the rheological percolated network of the Fe3O4 particles is very sensitive to the steady shear deformation, and also to the temperature. The network structure is easily broken by the steady shear flow due to the sharply reduced particle–particle interactions. However, the percolation threshold reduces with increase of temperature, because those interactions are temperature‐dependent. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

RHEOLOGICAL BEHAVIORS AND MECHANICAL PROPERTIES OF GLUTEN-STARCH-GLYCEROL COMPOSITES

研究了甘油增塑谷朊粉/淀粉混合体系的动态流变行为与单轴拉伸力学性能,考察了淀粉与水含量的影响.研究结果表明,含水量10%的混合体系储能模量(G′)随淀粉含量增大而增大,并在100℃出现橡胶平台.增塑谷朊粉在30℃呈现凝胶特性,在80℃出现交联网络结构.淀粉粒子可与小麦蛋白质形成复杂相互作用,阻碍蛋白质链段运动,导致模量与强度增加,断裂伸长率降低.含水量为20%与25%时,水份在淀粉粒子与蛋白质网络间起稀释和润滑作用,拉伸强度与断裂伸长率随淀粉含量的增高而降低.

Progesterone-Dependent Deoxyribonucleic Acid Looping between RUSH/SMARCA3 and Egr-1 Mediates Repression by c-Rel

Steroids regulate alternative splicing of RUSH/SMARCA3. The full-length, progesterone-dependent alpha-isoform and the 3'-truncated, estrogen-dependent beta-isoform have identical DNA-binding domains, nuclear localization signals, and RING fingers. Transcription of RUSH/SMARCA3 is mediated by a bipartite progesterone receptor half-site/overlapping Y-box combination (-38/-26), where progesterone activation is attenuated by nuclear factor Y binding. Regulation also involves two GC-rich sequences in the proximal promoter (-162/+90) and a RUSH/SMARCA3 site (-616/-611) in the 5'-untranslated region. Isoform-specific binding to the RUSH/SMARCA3 site is dictated by the hormonal milieu, as is the availability of factors that bind to the distal GC-rich site (-131/-126), a composite binding site for Egr-1/specific protein-1/3/Myc-associated zinc finger protein/myeloid zinc finger-1/c-Rel, and the proximal GC-rich site (-62/-53), which binds only Sp1/3. TransSignal TF-TF interaction arrays, supershift assays, and chromatin immunoprecipitation analyses confirmed strong physical interactions between RUSH/Egr-1 and RUSH/c-Rel that were visualized with fluorescent microscopy. Higher-order, long-range interactions between RUSH and Egr-1/c-Rel derivative of the anisotropic flexibility of the intervening DNA sequence were shown by Chromosome Conformation Capture assay. Glutathione S-transferase pull-downs confirmed that the RING finger is the protein-binding domain, suggesting that the RUSH isoforms have equivalent potential for protein interactions. Transient transfection assays showed that the cooperative interaction between RUSH and Egr-1 mediates repression by c-Rel. Thus, progesterone-induced transcription is fine-tuned by isoform-specific autoregulation, in which newly synthesized RUSH-1alpha binds DNA and interacts physically with liganded Egr-1 in the proximal promoter via a DNA-looping mechanism to mediate repression by c-Rel. In the absence of progesterone induction, RUSH-1beta replaces RUSH-1alpha binding, Egr-1 and c-Rel are unavailable as molecular ties, and DNA looping is disfavored.

Cadherin-11 is Expressed in Detrusor Smooth Muscle Cells and Myofibroblasts of Normal Human Bladder

ObjectivesIt has recently been found that detrusor smooth muscle cells and myofibroblasts are coupled via gap junctions. However, gap junctions cannot account for strong physical interaction between cells, which has prompted the search for intercellular adhesion molecules. Cadherin-11 is a candidate for such a molecule, since it mediates the interaction of dermal myofibroblasts in contractile wound granulation tissue. We therefore hypothesised that the physical adhesion between detrusor smooth muscle cells and myofibroblasts is mediated by cadherin-11. The aim of this study was to test this hypothesis. MethodsBladder biopsies from eight radical cystectomy specimens were snap-frozen, sectioned, and stained for E-cadherin; cadherin-11; α-catenin; β-catenin; γ-catenin; and smooth muscle cell/myofibroblast markers connexin-43, vimentin, desmin, smooth muscle actin, and smoothelin. Specimens were analysed by using binocular epifluorescent and confocal laser-scanning microscopy. ResultsSpecific positive membranous expression of all adhesion complex molecules except E-cadherin was detected in detrusor suburothelial tissue. All biopsies showed a similar punctate pattern of expression for cadherin-11 within bundles of smooth muscle cells and a suburothelial layer of cells. Cadherin-11 was specifically located at the cell membrane, in distinct linear domains. ConclusionsTo our knowledge this is the first time evidence has been provided for cadherin-mediated smooth muscle and suburothelial myofibroblast cell–cell interaction in the human bladder. Cadherin-11 most probably plays an important role in the intercellular physical coupling of detrusor smooth muscle cells and also of myofibroblasts.

Resistance to alkyl-lysophospholipid-induced apoptosis due to downregulated sphingomyelin synthase 1 expression with consequent sphingomyelin- and cholesterol-deficiency in lipid rafts

The ALP (alkyl-lysophospholipid) edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine; Et-18-OCH3) induces apoptosis in S49 mouse lymphoma cells. To this end, ALP is internalized by lipid raft-dependent endocytosis and inhibits phosphatidylcholine synthesis. A variant cell-line, S49AR, which is resistant to ALP, was shown previously to be unable to internalize ALP via this lipid raft pathway. The reason for this uptake failure is not understood. In the present study, we show that S49AR cells are unable to synthesize SM (sphingomyelin) due to down-regulated SMS1 (SM synthase 1) expression. In parental S49 cells, resistance to ALP could be mimicked by small interfering RNA-induced SMS1 suppression, resulting in SM deficiency and blockage of raft-dependent internalization of ALP and induction of apoptosis. Similar results were obtained by treatment of the cells with myriocin/ISP-1, an inhibitor of general sphingolipid synthesis, or with U18666A, a cholesterol homoeostasis perturbing agent. U18666A is known to inhibit Niemann-Pick C1 protein-dependent vesicular transport of cholesterol from endosomal compartments to the trans-Golgi network and the plasma membrane. U18666A reduced cholesterol partitioning in detergent-resistant lipid rafts and inhibited SM synthesis in S49 cells, causing ALP resistance similar to that observed in S49AR cells. The results are explained by the strong physical interaction between (newly synthesized) SM and available cholesterol at the Golgi, where they facilitate lipid raft formation. We propose that ALP internalization by lipid-raft-dependent endocytosis represents the retrograde route of a constitutive SMS1- and lipid-raft-dependent membrane vesicular recycling process.

Probing Genuine Strong Interactions and Post-translational Modifications in the Heterogeneous Yeast Exosome Protein Complex

The characterization of heterogeneous multicomponent protein complexes, which goes beyond identification of protein subunits, is a challenging task. Here we describe and apply a comprehensive method that combines a mild affinity purification procedure with a multiplexed mass spectrometry approach for the in-depth characterization of the exosome complex from Saccharomyces cerevisiae expressed at physiologically relevant levels. The exosome is an ensemble of primarily 3' --> 5' exoribonucleases and plays a major role in RNA metabolism. The complex has been reported to consist of 11 proteins in molecular mass ranging from 20 to 120 kDa. By using native macromolecular mass spectrometry we measured accurate masses (around 400 kDa) of several (sub)exosome complexes. Combination of these data with proteolytic peptide LC tandem mass spectrometry using a linear ion trap coupled to a FT-ICR mass spectrometer and intact protein LC mass spectrometry provided us with the identity of the different exosome components and (sub)complexes, including the subunit stoichiometry. We hypothesize that the observed complexes provide information about strongly and weakly interacting exosome-associated proteins. In our analysis we also identified for the first time phosphorylation sites in seven different exosome subunits. The phosphorylation site in the Rrp4 subunit is fully conserved in the human homologue of Rrp4, which is the only previously reported phosphorylation site in any of the human exosome proteins. The described multiplexed mass spectrometry-based procedure is generic and thus applicable to many different types of cellular molecular machineries even if they are expressed at endogenous levels.

Thermal, Dynamic Mechanical and Dielectric Behavior of Liquid-Crystalline Linear and Crosslinked Polyurethanes with Mesogenic Group in Side Chains

This paper describes DSC, dielectric and dynamic mechanical behavior of linear and crosslinked liquid crystalline (LC) polyurethanes based on LC diols with a mesogenic group in the side chain, diisocyanates of various flexibility and two triols. From our investigations it follows: a) Linear polymers prepared from diols with simple end side chain substituents (as hydrogen, nitro and nitril group) exhibit only amorphous behavior regardless of the structure of used diisocyanate; generally, the most pronounced LC behavior exhibited polymers prepared from a diol with phenyl substituent. b) Investigation of the curing reaction showed that rheological power-law parameters, which are characteristic of the structure at the gel point, are dependent on the initial ratio of the reactants (amount of LC diol in EANCs). c) Strong physical interactions between the mesogens support the cyclization in the course of crosslinking reaction. d) Introduction of chemical junctions (amount of triols) suppresses LC ordering in the networks.