The Experts below are selected from a list of 101940 Experts worldwide ranked by ideXlab platform
Y.f. Cheng - One of the best experts on this subject based on the ideXlab platform.
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understand the ac induced pitting corrosion on pipelines in both high Ph and Neutral Ph carbonate bicarbonate solutions
Corrosion Science, 2014Co-Authors: D Kuang, Y.f. ChengAbstract:Abstract In this work, the alternating current (AC) induced corrosion and pitting corrosion of X65 pipeline steel was studied in both high Ph and Neutral Ph carbonate/bicarbonate solutions. A real-time AC/DC (direct current) signal data acquisition technique coupled with polarization curve measurements and surface characterization was used for mechanistic studies. Pitting corrosion can be initiated on the steel at sufficiently high AC current densities in both solutions. Mechanistic models are proposed to illustrate the pitting initiation in the presence of AC, where AC can affect passive film or corrosion product layer formed on the steel as well as the charge distribution in double layer charge. In the high and Neutral Ph solutions, the critical AC current densities to initiate pitting are approximately 0.03 A/cm 2 and 0.02 A/cm 2 , respectively.
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mechanistic aspect of near Neutral Ph stress corrosion cracking of pipelines under cathodic polarization
Corrosion Science, 2012Co-Authors: Zhiyong Liu, Y.f. ChengAbstract:Abstract This paper investigates mechanistically stress corrosion cracking (SCC) of an X70 pipeline steel that is under cathodic protection (CP) in a near-Neutral Ph solution. It was found that there is a critical potential range, i.e., −730 and −920 mVSCE, where the steel is in a non-equilibrium electrochemical state, and anodic dissolution (AD) reaction may occur when the steel is polarized cathodically. When the applied potential is more positive than this range, SCC is AD-based; while the applied potential is more negative, SCC of pipelines is under hydrogen embrittlement (HE) mechanism. When the polarization potential is within the range, SCC of the steel is under the combined effect of AD and HE. Therefore, AD may still occur on pipeline steel that is under CP with the potential within this critical range, contributing to the cracking process.
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electrochemical corrosion behavior of x80 pipeline steel in a near Neutral Ph solution
Materials and Corrosion-werkstoffe Und Korrosion, 2010Co-Authors: H B Xue, Y.f. ChengAbstract:In this work, the electrochemical corrosion behavior of X80 pipeline steel was investigated in a near-Neutral Ph solution using electrochemical impedance spectroscopy (EIC) and Photo-electrochemical (PEC) measurements as well as X-ray Photo-electron spectroscopy (XPS) technique. The effects of hydrogen-charging and stress were considered. The results show that the steel is in an active dissolution state, and a layer of corrosion product is formed and deposited on the electrode surface, which is subjected to further oxidation to form ferric oxide and hydroxide. Photo-illumination enhances anodic dissolution of the steel when it is under anodic polarization due to destroying of the corrosion product film. When the steel is under cathodic polarization, the cathodic current density decreases upon laser illumination due to the Photo-oxidation of hydrogen atoms generated during cathodic reactions, which behaves as an anodic reaction to offset the cathodic current density. Hydrogen-charging and stress decrease the corrosion resistance of the steel and enhance the dissolution rate of the steel.
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micro electrochemical characterization of corrosion of welded x70 pipeline steel in near Neutral Ph solution
Corrosion Science, 2009Co-Authors: Guoan Zhang, Y.f. ChengAbstract:Abstract The local corrosion behavior of welded X70 pipeline steel in near-Neutral Ph solution was studied by micro-electrochemical measurements, including scanning vibrating electrode and local electrochemical impedance spectroscopy. The microstructure of the welded steel was observed by optical microscopy and scanning electron microscopy. It is demonstrated that the microstructure of weld metal consists of acicular ferrite and grain boundary ferrite, while that of heat-affected zone is a mixture of acicular ferrite, bainitic ferrite and a few martensite/austenite microconstituents. The microstructure of base steel is typically ferrite and pearlite. Electrochemical corrosion mechanism of welded X70 steel does not experience change upon hydrogen-charging, or stressing, or both. Hydrogen-charging is capable of enhancing the local anodic dissolution of the steel. The resistance of corrosion product layer decreases with hydrogen-charging, and heat-affected zone has the largest dissolution current upon hydrogen-charging. The increase of applied stress enhanced the anodic dissolution of welded X70 steel, especially the heat-affected zone, in near-Neutral Ph solution. Maximum current is observed in heat-affected zone, and increases with the increase of applied stresses. The total synergistic effect of hydrogen-charging (10 mA/cm 2 ) and applied stress (550 MPa) on anodic dissolution of welded X70 steel in near-Neutral Ph solution is determined to be within the range of 5.7 and 6.5, with a maximum value encountering in heat-affected zone.
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effects of corrosion product deposit on the subsequent cathodic and anodic reactions of x 70 steel in near Neutral Ph solution
Corrosion Science, 2008Co-Authors: G Z Meng, C. Zhang, Y.f. ChengAbstract:Abstract The effects of corrosion product deposit on the subsequent anodic and cathodic reactions of X-70 steel in a near-Neutral Ph solution were investigated by localized electrochemical impedance spectroscopy (LEIS), scanning vibrating micro-electrode (SVME) and macroscopic EIS measurements as well as surface analysis technique. It is found that the deposit layer formed on the steel surface is porous, non-compact in nature. The presence of a corrosion product layer would enhance adsorption, but significantly inhibit absorption and permeation of hydrogen atoms into steel. It is due to the porous structure of the deposit that generates a spatial separation of cathodic and anodic reaction sites, resulting in an increased effective surface area for hydrogen adsorption and, simultaneously, a “blocking” effect on hydrogen absorption and permeation. The deposit enhances greatly anodic dissolution of the steel, which is attributed to the adsorption of the intermediate species and the resultant “self-catalytic” mechanism for corrosion of the steel in near-Neutral Ph solution. In the presence of corrosion product deposit on the pipeline steel surface, pipeline corrosion, especially pitting corrosion, is expected to be enhanced. Stress corrosion cracks could initiate from the corrosion pits that form under deposit. However, deposit does not contribute to hydrogen permeation, although the hydrogen evolution is enhanced.
Ryuhei Nakamura - One of the best experts on this subject based on the ideXlab platform.
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regulating proton coupled electron transfer for efficient water splitting by manganese oxides at Neutral Ph
Nature Communications, 2014Co-Authors: Akira Yamaguchi, Riko Inuzuka, Toru Hayashi, Toshihiro Takashima, Kazuhito Hashimoto, Ryuhei NakamuraAbstract:Manganese oxides are extensively investigated as analogues of nature's oxygen-evolving complex, but they rarely function at Neutral Ph. Here, the authors investigate the induction and regulation of the proton-coupled electron-transfer mechanism involved in water oxidation by manganese oxides.
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regulating proton coupled electron transfer for efficient water splitting by manganese oxides at Neutral Ph
Nature Communications, 2014Co-Authors: Akira Yamaguchi, Riko Inuzuka, Toru Hayashi, Toshihiro Takashima, Kazuhito Hashimoto, Ryuhei NakamuraAbstract:Manganese oxides have been extensively investigated as model systems for the oxygen-evolving complex of Photosystem II. However, most bioinspired catalysts are inefficient at Neutral Ph and functional similarity to the oxygen-evolving complex has been rarely achieved with manganese. Here we report the regulation of proton-coupled electron transfer involved in water oxidation by manganese oxides. Pyridine and its derivatives, which have pKa values intermediate to the water ligand bound to manganese(II) and manganese(III), are used as proton-coupled electron transfer induction reagents. The induction of concerted proton-coupled electron transfer is demonstrated by the detection of deuterium kinetic isotope effects and compliance of the reactions with the libido rule. Although proton-coupled electron transfer regulation is essential for the facial redox change of manganese in Photosystem II, most manganese oxides impair these regulatory mechanisms. Thus, the present findings may provide a new design rationale for functional analogues of the oxygen-evolving complex for efficient water splitting at Neutral Ph.
Hironobu Naiki - One of the best experts on this subject based on the ideXlab platform.
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heating during agitation of β2 microglobulin reveals that supersaturation breakdown is required for amyloid fibril formation at Neutral Ph
Journal of Biological Chemistry, 2019Co-Authors: Masahiro Noji, Hironobu Naiki, Kenji Sasahara, Keiichi Yamaguchi, Kazumasa Sakurai, Jozsef Kardos, Yuji GotoAbstract:Amyloidosis-associated amyloid fibrils are formed by denatured proteins when supersaturation of denatured proteins is broken. β2-Microglobulin (β2m) forms amyloid fibrils and causes dialysis-related amyloidosis in patients receiving long-term hemodialysis. Although amyloid fibrils of β2m in patients are observed at Neutral Ph, formation of β2m amyloids in vitro has been difficult to discern at Neutral Ph because of the amyloid-resistant native structure. Here, to further understand the mechanism underlying in vivo amyloid formation, we investigated the relationship between protein folding/unfolding and misfolding leading to amyloid formation. Using thioflavin T assays, CD spectroscopy, and transmission EM analyses, we found that β2m efficiently forms amyloid fibrils even at Neutral Ph by heating with agitation at high-salt conditions. We constructed temperature- and NaCl concentration-dependent conformational Phase diagrams in the presence or absence of agitation, revealing how amyloid formation under Neutral Ph conditions is related to thermal unfolding and breakdown of supersaturation. Of note, after supersaturation breakdown and following the law of mass action, the β2m monomer equilibrium shifted to the unfolded state, destabilizing the native state and thereby enabling amyloid formation even under Physiological conditions with a low amount of unfolded precursor. The amyloid fibrils depolymerized at both lower and higher temperatures, resembling cold- or heat-induced denaturation of globular proteins. Our results suggest an important role for heating in the onset of dialysis-related amyloidosis and related amyloidoses.
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low concentrations of sodium dodecyl sulfate induce the extension of β2 microglobulin related amyloid fibrils at a Neutral Ph
Biochemistry, 2004Co-Authors: Suguru Yamamoto, Itaru Yamaguchi, Kazuhiro Hasegawa, Shinobu Tsutsumi, Yuji Goto, Fumitake Gejyo, Jozsef Kardos, Hironobu NaikiAbstract:In β2-microglobulin-related (Aβ2M) amyloidosis, partial unfolding of β2-microglobulin (β2-m) is believed to be prerequisite to its assembly into Aβ2M amyloid fibrils in vivo. Although low Ph or 2,2,2-trifluoroethanol at a low concentration has been reported to induce partial unfolding of β2-m and subsequent amyloid fibril formation in vitro, factors that induce them under near Physiological conditions have not been determined. Using fluorescence spectroscopy with thioflavin T, circular dichroism spectroscopy, and electron microscopy, we here show that at low concentrations, sodium dodecyl sulfate (SDS) converts natively folded β2-m monomers into partially folded, α-helix-containing conformers. Surprisingly, this results in the extension of Aβ2M amyloid fibrils at Neutral Ph, which could be explained basically by a first-order kinetic model. At low concentrations, SDS also stabilized the fibrils at Neutral Ph. These SDS effects were concentration-dependent and maximal at approximately 0.5 mM, around the cr...
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glycosaminoglycans enhance the trifluoroethanol induced extension of beta 2 microglobulin related amyloid fibrils at a Neutral Ph
Journal of The American Society of Nephrology, 2004Co-Authors: Suguru Yamamoto, Itaru Yamaguchi, Kazuhiro Hasegawa, Shinobu Tsutsumi, Yuji Goto, Fumitake Gejyo, Hironobu NaikiAbstract:beta(2)-Microglobulin-related (A beta 2M) amyloidosis is a frequent and serious complication in patients on long-term dialysis, and beta(2)-microglobulin is a major structural component of A beta 2M amyloid fibrils. Several biologic molecules inhibiting the depolymerization of A beta 2M amyloid fibrils at a Neutral Ph were found recently. The effect of trifluoroethanol and glycosaminoglycans (GAG) on the extension of the fibrils at a Neutral Ph was investigated with the use of fluorescence spectroscopy with thioflavin T, circular dichroism spectroscopy, and electron microscopy. Trifluoroethanol at concentrations of up to 20% (vol/vol) caused fibril extension of heparin-stabilized seeds, inducing a subtle change in the tertiary structure of beta(2)-microglobulin and stabilizing the fibrils at a Neutral Ph. This extension reaction followed a first-order kinetic model. In addition, some GAG, especially heparin, dose-dependently enhanced the fibril extension. These results suggest that some GAG, especially heparin, may bind to the fibrils and enhance their deposition in vivo. Thus, the experimental system described here should be useful to search for the factors that accelerate A beta 2M amyloid deposition in vivo. In addition, the interference of the binding of GAG to A beta 2M amyloid fibrils may be an attractive therapeutic modality.
Sheena E. Radford - One of the best experts on this subject based on the ideXlab platform.
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a systematic study of the effect of Physiological factors on β2 microglobulin amyloid formation at Neutral Ph
Biochemistry, 2006Co-Authors: Sarah L Myers, Thomas R Jahn, Isobel J Morten, Glenys A Tennent, Eric W Hewitt, Susan Jones, Sheena E. RadfordAbstract:β2-microglobulin (β2m) forms amyloid fibrils that deposit in the musculo-skeletal system in patients undergoing long-term hemodialysis. How β2m self-assembles in vivo is not understood, since the monomeric wild-type protein is incapable of forming fibrils in isolation in vitro at Neutral Ph, while elongation of fibril-seeds made from recombinant protein has only been achieved at low Ph or at Neutral Ph in the presence of detergents or cosolvents. Here we describe a systematic study of the effect of 11 Physiologically relevant factors on β2m fibrillogenesis at Ph 7.0 without denaturants. By comparing the results obtained for the wild-type protein with those of two variants (ΔN6 and V37A), the role of protein stability in fibrillogenesis is explored. We show that ΔN6 forms low yields of amyloid-like fibrils at Ph 7.0 in the absence of seeds, suggesting that this species could initiate fibrillogenesis in vivo. By contrast, high yields of amyloid-like fibrils are observed for all proteins when assembly is see...
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a systematic study of the effect of Physiological factors on β2 microglobulin amyloid formation at Neutral Ph
Biochemistry, 2006Co-Authors: Sarah L Myers, Thomas R Jahn, Isobel J Morten, Glenys A Tennent, Eric W Hewitt, Susan Jones, Sheena E. RadfordAbstract:Beta(2)-microglobulin (beta(2)m) forms amyloid fibrils that deposit in the musculo-skeletal system in patients undergoing long-term hemodialysis. How beta(2)m self-assembles in vivo is not understood, since the monomeric wild-type protein is incapable of forming fibrils in isolation in vitro at Neutral Ph, while elongation of fibril-seeds made from recombinant protein has only been achieved at low Ph or at Neutral Ph in the presence of detergents or cosolvents. Here we describe a systematic study of the effect of 11 Physiologically relevant factors on beta(2)m fibrillogenesis at Ph 7.0 without denaturants. By comparing the results obtained for the wild-type protein with those of two variants (DeltaN6 and V37A), the role of protein stability in fibrillogenesis is explored. We show that DeltaN6 forms low yields of amyloid-like fibrils at Ph 7.0 in the absence of seeds, suggesting that this species could initiate fibrillogenesis in vivo. By contrast, high yields of amyloid-like fibrils are observed for all proteins when assembly is seeded with fibril-seeds formed from recombinant protein at Ph 2.5 stabilized by the addition of heparin, serum amyloid P component (SAP), apolipoprotein E (apoE), uremic serum, or synovial fluid. The results suggest that the conditions within the synovium facilitate fibrillogenesis of beta(2)m and show that different Physiological factors may act synergistically to promote fibril formation. By comparing the behavior of wild-type beta(2)m with that of DeltaN6 and V37A, we show that the Physiologically relevant factors enhance fibrillogenesis by stabilizing fibril-seeds, thereby allowing fibril extension by rare assembly competent species formed by local unfolding of native monomers.
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role of the n and c terminal strands of beta 2 microglobulin in amyloid formation at Neutral Ph
Journal of Molecular Biology, 2003Co-Authors: Susan Jones, David P Smith, Sheena E. RadfordAbstract:Beta 2-microglobulin (β2m) is known to form amyloid fibrils de novo in vitro under acidic conditions (below Ph 4.8). Fibril formation at Neutral Ph, however, has only been observed by deletion of the N-terminal six residues; by the addition of pre-assembled seeds; or in the presence of Cu2+. Based on these observations, and other structural data, models for fibril formation of β2m have been proposed that involve the fraying of the N and C-terminal β-strands and the consequent loss of edge strand protective features. Here, we examine the role of the N and C-terminal strands in the initiation of fibrillogenesis of β2m by creating point mutations in strands A and G and comparing the properties of the resulting proteins with variants containing similar mutations elsewhere in the protein. We show that truncation of buried hydroPhobic side-chains in strands A and G promotes rapid fibril formation at Neutral Ph, even in unseeded reactions, and increases the rate of fibril formation under acidic conditions. By contrast, similar mutations created in the remaining seven β-strands of the native protein have little effect on the rate or Ph dependence of fibril formation. The data are consistent with the view that perturbation of the N and C-terminal edge strands is an important feature in the generation of assembly-competent states of β2m.
Yuji Goto - One of the best experts on this subject based on the ideXlab platform.
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heating during agitation of β2 microglobulin reveals that supersaturation breakdown is required for amyloid fibril formation at Neutral Ph
Journal of Biological Chemistry, 2019Co-Authors: Masahiro Noji, Hironobu Naiki, Kenji Sasahara, Keiichi Yamaguchi, Kazumasa Sakurai, Jozsef Kardos, Yuji GotoAbstract:Amyloidosis-associated amyloid fibrils are formed by denatured proteins when supersaturation of denatured proteins is broken. β2-Microglobulin (β2m) forms amyloid fibrils and causes dialysis-related amyloidosis in patients receiving long-term hemodialysis. Although amyloid fibrils of β2m in patients are observed at Neutral Ph, formation of β2m amyloids in vitro has been difficult to discern at Neutral Ph because of the amyloid-resistant native structure. Here, to further understand the mechanism underlying in vivo amyloid formation, we investigated the relationship between protein folding/unfolding and misfolding leading to amyloid formation. Using thioflavin T assays, CD spectroscopy, and transmission EM analyses, we found that β2m efficiently forms amyloid fibrils even at Neutral Ph by heating with agitation at high-salt conditions. We constructed temperature- and NaCl concentration-dependent conformational Phase diagrams in the presence or absence of agitation, revealing how amyloid formation under Neutral Ph conditions is related to thermal unfolding and breakdown of supersaturation. Of note, after supersaturation breakdown and following the law of mass action, the β2m monomer equilibrium shifted to the unfolded state, destabilizing the native state and thereby enabling amyloid formation even under Physiological conditions with a low amount of unfolded precursor. The amyloid fibrils depolymerized at both lower and higher temperatures, resembling cold- or heat-induced denaturation of globular proteins. Our results suggest an important role for heating in the onset of dialysis-related amyloidosis and related amyloidoses.
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low concentrations of sodium dodecyl sulfate induce the extension of β2 microglobulin related amyloid fibrils at a Neutral Ph
Biochemistry, 2004Co-Authors: Suguru Yamamoto, Itaru Yamaguchi, Kazuhiro Hasegawa, Shinobu Tsutsumi, Yuji Goto, Fumitake Gejyo, Jozsef Kardos, Hironobu NaikiAbstract:In β2-microglobulin-related (Aβ2M) amyloidosis, partial unfolding of β2-microglobulin (β2-m) is believed to be prerequisite to its assembly into Aβ2M amyloid fibrils in vivo. Although low Ph or 2,2,2-trifluoroethanol at a low concentration has been reported to induce partial unfolding of β2-m and subsequent amyloid fibril formation in vitro, factors that induce them under near Physiological conditions have not been determined. Using fluorescence spectroscopy with thioflavin T, circular dichroism spectroscopy, and electron microscopy, we here show that at low concentrations, sodium dodecyl sulfate (SDS) converts natively folded β2-m monomers into partially folded, α-helix-containing conformers. Surprisingly, this results in the extension of Aβ2M amyloid fibrils at Neutral Ph, which could be explained basically by a first-order kinetic model. At low concentrations, SDS also stabilized the fibrils at Neutral Ph. These SDS effects were concentration-dependent and maximal at approximately 0.5 mM, around the cr...
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glycosaminoglycans enhance the trifluoroethanol induced extension of beta 2 microglobulin related amyloid fibrils at a Neutral Ph
Journal of The American Society of Nephrology, 2004Co-Authors: Suguru Yamamoto, Itaru Yamaguchi, Kazuhiro Hasegawa, Shinobu Tsutsumi, Yuji Goto, Fumitake Gejyo, Hironobu NaikiAbstract:beta(2)-Microglobulin-related (A beta 2M) amyloidosis is a frequent and serious complication in patients on long-term dialysis, and beta(2)-microglobulin is a major structural component of A beta 2M amyloid fibrils. Several biologic molecules inhibiting the depolymerization of A beta 2M amyloid fibrils at a Neutral Ph were found recently. The effect of trifluoroethanol and glycosaminoglycans (GAG) on the extension of the fibrils at a Neutral Ph was investigated with the use of fluorescence spectroscopy with thioflavin T, circular dichroism spectroscopy, and electron microscopy. Trifluoroethanol at concentrations of up to 20% (vol/vol) caused fibril extension of heparin-stabilized seeds, inducing a subtle change in the tertiary structure of beta(2)-microglobulin and stabilizing the fibrils at a Neutral Ph. This extension reaction followed a first-order kinetic model. In addition, some GAG, especially heparin, dose-dependently enhanced the fibril extension. These results suggest that some GAG, especially heparin, may bind to the fibrils and enhance their deposition in vivo. Thus, the experimental system described here should be useful to search for the factors that accelerate A beta 2M amyloid deposition in vivo. In addition, the interference of the binding of GAG to A beta 2M amyloid fibrils may be an attractive therapeutic modality.
