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1.
Influence of Aromatic Residues on the Material Characteristics of Aβ Amyloid Protofibrils at the Atomic Scale
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Amyloid fibrils, which cause a number of degenerative diseases, are insoluble under physiological conditions and are supported by native contacts. Recently, the effects of the aromatic residues on the Aβ amyloid protofibril were investigated in a ThT fluorescence study. However, the relationship between the material characteristics of the Aβ protofibril and its aromatic residues has not yet been investigated on the atomic scale. Here, we successfully constructed wild‐type (WT) and mutated types of Aβ protofibrils by using molecular dynamics simulations. Through principle component analysis, we established the structural stability and vibrational characteristics of F20L Aβ protofibrils and compared them with WT and other mutated models such as F19L and F19LF20L. In addition, structural stability was assessed by calculating the elastic modulus, which showed that the F20L model has higher values than the other models studied. From our results, it is shown that aromatic residues influence the structural and material characteristics of Aβ protofibrils. 相似文献
2.
Mingyan Dong Thomas J. Paul Zachary Hoffmann Prof. Dr. Kwaichow Chan Dingkun Hu Prof. Dr. Hongqi Ai Prof. Dr. Rajeev Prabhakar 《Chemphyschem》2016,17(16):2558-2566
In this study, structural and mechanical properties of a series of models of Aβ42 (one‐ and two‐fold) and Aβ40 (two‐ and three‐fold) fibrils have been computed by using all‐atom molecular dynamics simulations. Based on calculations of the twist angle (θ) and periodicity (v=360d/θ), oligomers formed by 20, 11, and 13 monomers were found to be the smallest realistic models of three‐fold Aβ40, one‐fold Aβ42, and two‐fold Aβ42 fibrils, respectively. Our results predict that the Aβ40 fibrils initially exist in two staggered conformations [STAG(+2) and STAG(+1)] and then undergo a [STAG(+2)→STAG(+1)] transformation in a size‐dependent manner. The length of the loop region consisting of the residues 23–29 shrinks with the elongation of both Aβ40 and Aβ42 fibrils. A comparison of the computed potential energy suggests that a two‐fold Aβ40 aggregate is more stable than its three‐fold counterpart, and that Aβ42 oligomers can exist only in one‐fold conformation for aggregates of more than 11 monomers in length. The computed Young′s modulus and yield strengths of 50 GPa and 0.95 GPa, respectively, show that these aggregates possess excellent material properties. 相似文献
3.
Vivian Cody Jia Q. Truong Bruce A. Holdsworth Jessica K. Holien Samantha J. Richardson David K. Chalmers David J. Craik 《Molecules (Basel, Switzerland)》2022,27(21)
Human transthyretin (hTTR) can form amyloid deposits that accumulate in nerves and organs, disrupting cellular function. Molecules such as tafamidis that bind to and stabilize the TTR tetramer can reduce such amyloid formation. Here, we studied the interaction of VCP-6 (2-((3,5-dichlorophenyl)amino)benzoic acid) with hTTR. VCP-6 binds to hTTR with 5 times the affinity of the cognate ligand, thyroxine (T4). The structure of the hTTR:VCP-6 complex was determined by X-ray crystallography at 1.52 Å resolution. VCP-6 binds deeper in the binding channel than T4 with the 3′,5′-dichlorophenyl ring binding in the ‘forward’ mode towards the channel centre. The dichlorophenyl ring lies along the 2-fold axis coincident with the channel centre, while the 2-carboxylatephenylamine ring of VCP-6 is symmetrically displaced from the 2-fold axis, allowing the 2-carboxylate group to form a tight intermolecular hydrogen bond with Nζ of Lys15 and an intramolecular hydrogen bond with the amine of VCP-6, stabilizing its conformation and explaining the greater affinity of VCP-6 compared to T4. This arrangement maintains optimal halogen bonding interactions in the binding sites, via chlorine atoms rather than iodine of the thyroid hormone, thereby explaining why the dichloro substitution pattern is a stronger binder than either the diiodo or dibromo analogues. 相似文献
4.
Ione Cendoya Daniel Lpez Angel Alegría Carmen Mijangos 《Journal of Polymer Science.Polymer Physics》2001,39(17):1968-1975
In this article we report on the investigation of the dynamics of poly(vinyl alcohol) (PVA) and PVA‐based composite films by means of dielectric spectroscopy and dynamic mechanical thermal analysis. Once the characterization of pure PVA was done, we studied the effect of a nanostructured magnetic filler (nanosized CoFe2O4 particles homogeneously dispersed within a sulfonated polystyrene matrix) on the dynamics of PVA. Our results suggest that the α‐relaxation process, corresponding to the glass transition of PVA, is affected by the filler. The glass‐transition temperature of PVA increases with filler content up to compositions of around 10 wt %, probably as a result of polymer–filler interactions that reduce the polymer chain mobility. For filler contents higher than 10 wt %, the glass‐transition temperature of PVA decreases as a result of the absorption of water that causes a plasticizing effect. The β‐ and γ‐relaxation processes of PVA are not affected by the filler as stated from both dynamic mechanical thermal analysis and dielectric spectroscopy. Nevertheless, both relaxation processes are greatly affected by the moisture content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1968–1975, 2001 相似文献
5.
Influence of the β‐Sheet Content on the Mechanical Properties of Aggregates during Amyloid Fibrillization
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Jae Sun Jeong Prof. Hilal A. Lashuel Prof. Raffaele Mezzenga Prof. Giovanni Dietler 《Angewandte Chemie (International ed. in English)》2015,54(8):2462-2466
Amyloid fibrils associated with neurodegenerative diseases, such as Parkinson’s and Alzheimer’s, consist of insoluble aggregates of α‐synuclein and Aβ‐42 proteins with a high β‐sheet content. The aggregation of both proteins occurs by misfolding of the monomers and proceeds through the formation of intermediate oligomeric and protofibrillar species to give the final fibrillar cross‐β‐sheet structure. The morphological and mechanical properties of oligomers, protofibrils, and fibrils formed during the fibrillization process were investigated by thioflavin T fluorescence and circular dichroism in combination with AFM peak force quantitative nanomechanical technique. The results reveal an increase in the Young’s modulus during the transformation from oligomers to mature fibrils, thus inferring that the difference in their mechanical properties is due to an internal structural change from a random coil to a structure with increased β‐sheet content. 相似文献
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Iwan H. Sahputra Alessio Alexiadis Michael J. Adams 《Journal of Polymer Science.Polymer Physics》2019,57(8):454-464
A hybrid molecular mechanics–molecular dynamics simulation method has been performed to study the effects of moisture content on the mechanical properties of microcrystalline cellulose (MCC) and the mobility of the water molecules. The specific volume and diffusion coefficient of the water increase with increasing moisture content in the range studied of 1.8–25.5 w/w%, while the Young's modulus decreases. The simulation results are in close agreement with the published experimental data. Both the bound scission and free‐volume mechanisms contribute to the plasticization of MCC by water. The Voronoi volume increases with increasing moisture content. It is related to the free volume and the increase enhances the mobility of the water molecules and thus increases the coefficient of diffusion of the water. Moreover, with increasing moisture content, the hydrogen bonding per water molecule between MCC–water molecules decreases, thus increasing the water mobility and number of free water molecules. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 454–464 相似文献
8.
By employing molecular dynamics simulations, the evolution of deformation of a monolayer graphene sheet under a central transverse loading are investigated. Dependence of mechanical responses on the symmetry (shape) of the loading domain, on the size of the graphene sheet, and on temperature, is determined. It is found that the symmetry of the loading domain plays a central role in fracture strength and strain. By increasing the size of the graphene sheet or increasing temperature, the tensile strength and fracture strain decrease. The results have demonstrated that the breaking force and breaking displacement are sensitive to both temperature and the symmetry of the loading domain. In addition, we find that the intrinsic strength of graphene under a central load is much smaller than that of graphene under a uniaxial load. By examining the deformation processes, two failure mechanisms are identified namely, brittle bond breaking and plastic relaxation. In the second mechanism, the Stone–Wales transformation occurs. 相似文献
9.
Molecular composites have been prepared by dispersing rigid‐rod molecules of ionically‐modified poly(p‐phenylene terephthalamide) (PPTA anion) in a polar poly(4‐vinylpyridine) (PVP) matrix. For concentrations up to 5 wt % of the rigid‐rod reinforcement, the resulting composites are transparent and possess a single glass transition temperature that increases with concentration of the PPTA anion. The mechanical properties of the molecular composites are found to increase with concentration and to attain maximum values at about 5 wt % of the PPTA anion. The enhancement in properties, and the miscibility induced between the two component polymers, is attributed to the development of specific interactions between the ionic groups of the PPTA anion and the polar units of the PVP matrix. When such interactions are not present, as in composites reinforced with non‐ionic PPTA, the samples are opaque and their properties are significantly reduced compared to those of the PPTA anion/PVP composites. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2201–2209, 1999 相似文献
10.
W. H. S. Brandão A. L. Aguiar L. A. Ribeiro D. S. Galvão J. M. De Sousa 《Chemphyschem》2021,22(7):701-707
Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( and ) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( ). Moreover, it was obtained that Young's modulus (YMod) (750–900 GPa) and ultimate strength (σUS) (120–150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. YMod values obtained for PopNTs are not significantly temperature-dependent. While the σUS values for the showed a quasi-linear dependence with the temperature, the exhibited no clear trends. 相似文献
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K. Wang S. Y. Yang L. Fan M. Sh. Zhan J. G. Liu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):1997-2006
A series of molecular‐weight‐controlled fluorinated aromatic polyimides were synthesized through the polycondensation of a fluorinated aromatic diamine, 1,4‐bis(4′‐amino‐2′‐trifluoromethylphenoxy)benzene, with 4,4′‐oxydiphthalic anhydride in the presence of phthalic anhydride as the molecular‐weight‐controlling and end‐capping agent. Experimental results demonstrated that the resulting polyimides could melt at temperatures of 250–300 °C to give high flowing molten fluids, which were suitable for melt molding to give strong and flexible polyimide sheets. Moreover, the aromatic polyimides also showed good solubility both in polar aprotic solvents and in common solvents. Polyimide solutions with solid concentrations higher than 25 wt % could be prepared with relatively low viscosity and were stable in storage at the ambient temperature. High‐quality polyimide films could be prepared via the casting of the polyimide solutions onto glass plates, followed by baking at a relatively low temperature. The molten behaviors and organosolubility of the molecular‐weight‐controlled aromatic polyimides depended significantly on the polymer molecular weights. Both the melt‐molded polyimide sheets and the solution‐cast polymer films exhibited outstanding combined mechanical and thermal properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1997–2006, 2006 相似文献
13.
Molecular composites were prepared from several types of ionically modified, poly(p‐phenylene terephthalamide) (PPTA) dispersed in a poly(4‐vinylpyridine) matrix. Optical clarity tests indicated that the component polymers of the composite were miscible, at least at low concentrations of the rodlike reinforcement. In composites containing ionic PPTA, where ionic sulfonate groups were attached as side groups either to PPTA chains or to PPTA anion chains, the glass‐transition temperature (Tg) was increased by l0 °C or more, at 5 wt % reinforcement. At concentrations of 10–15 wt % of the ionic polymer, Tg values leveled off or decreased slightly. This suggested that some aggregation of the rigid‐rod molecules occurred. In composites containing ionic PPTA, where the ionic sulfonate groups were directly attached to the phenylene rings of PPTA chains, not only was Tg shifted significantly to higher temperatures, but the rubbery plateau modulus retained high values up to temperatures of 250 °C or above. Observed effects were considered to be the result of strong ionic interactions between the ionic reinforcement polymer and the polar matrix polymer. The possible effects of the counterion on Tg and the storage modulus are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1110–1117, 2002 相似文献
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15.
Myung Eun Suk 《Molecules (Basel, Switzerland)》2021,26(13)
By using the advantages of carbon nanotubes (CNTs), such as their excellent mechanical properties and low density, CNT-reinforced metal matrix composites (MMCs) are expected to overcome the limitations of conventional metal materials, i.e., their high density and low ductility. To understand the behavior of composite materials, it is necessary to observe the behavior at the molecular level and to understand the effect of various factors, such as the radius and content of CNTs. Therefore, in this study, the effect of the CNT radius and content on the mechanical properties of CNT-Al composites was observed using a series of molecular dynamics simulations, particularly focusing on MMCs with a high CNT content and large CNT diameter. The mechanical properties, such as the strength and stiffness, were increased with an increasing CNT radius. As the CNT content increased, the strength and stiffness increased; however, the fracture strain was not affected. The behavior of double-walled carbon nanotubes (DWNTs) and single-walled carbon nanotubes (SWNTs) was compared through the decomposition of the stress–strain curve and observations of the atomic stress field. The fracture strain increased significantly for SWNT-Al as the tensile force was applied in the axial direction of the armchair CNTs. In the case of DWNTs, an early failure was initiated at the inner CNTs. In addition, the change in the elastic modulus according to the CNT content was predicted using the modified rule of mixture. This study is expected to be useful for the design and development of high-performance MMCs reinforced by CNTs. 相似文献
16.
The aim of the last part of this general study is to analyze the influence of the interfacial properties and, more precisely, the adhesion energy, between carbon fibers and PEEK on the final performance of unidirectional composites. A set of mechanical properties, i.e. interlaminar shear strength, longitudinal tensile and compressive and transverse tensile properties, of different unidirectional laminates with the same content (60% by volume) of carbon fibers is determined. It is first shown that the interlaminar shear strength is constant, whatever the type of materials. Therefore, this test is not appropriate to characterize the strength of the fiber–matrix interface in PEEK-based composites. On the contrary, in agreement with previous work on other systems, it appears that the ultimate properties (longitudinal tensile and compressive as well as transverse tensile strengths and strains) of the laminates increase with the interfacial adhesion energy, whereas the stiffness of these composites remains unaffected in all cases. 相似文献
17.
Rachele Pucciariello Loredana Tammaro Vincenzo Villani Vittoria Vittoria 《Journal of Polymer Science.Polymer Physics》2007,45(8):945-954
Novel composites based on poly(ε‐caprolactone) (PCL) and an organically modified layer double hydroxide (LDH) obtained using the melt‐extrusion technique have been characterized through structural, thermal, and mechanical analyses. Although exfoliation has not been achieved and despite the very low content of filler (from 1 to 3% by weight), significant enhancements are obtained in the physical and mechanical properties of the composites with respect to neat PCL. As a consequence, LDHs can substitute other nanofillers, in particular, cationic clays for polymeric matrices. They can be modified by a large number of organic anions, generally more numerous than the cationic ones, and can be mixed in very simple ways with polymers. This makes such nanofillers suitable to obtain new hybrid materials for a series of applications, from active food packaging to intelligent materials for biomedical device, for example, controlled drug release. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 945–954, 2007 相似文献
18.
Single‐Point Remote Control of Flapping Motion in Clothespin‐Shaped Bimetallic Palladium Complexes Based on the N(sp2)–N(sp3) Interconversion in Amide Functionalities
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Ryo Inoue Dr. Soichiro Kawamorita Prof. Dr. Takeshi Naota 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(16):5712-5726
The synthesis, structure, and flapping motion of clothespin‐shaped binuclear trans‐bis(salicylaldiminato)palladium(II) complexes (anti‐ 1 ) with 4‐azaheptamethylene linkers bearing amide ( a – g ), urethane ( h ), or urea ( i ) functionalities are described in this report. Various 2D 1H NMR experiments and XRD analyses indicate that the amide‐ and urethane‐linked anti‐ 1 a , b , d – h complexes exist as equilibrated mixtures of major and minor conformers I and II in CDCl3, whereas the complexes anti‐ 1 c and i were observed as a single species. The mapping of NOESY cross‐peaks between conformers I and II revealed that the equilibration of the major and minor conformers of anti‐ 1 a , b , d – h proceeds by two pathways, namely a nonrotatory flapping motion of the coordinated blades and a nonflapping rotation of C?N bonds, whereas the equilibration of anti‐ 1 c proceeds by simultaneous flapping and rotation motions. Kinetic studies carried out by means of 1H–1H EXSY experiments revealed that 1) the ΔG≠298K values for the flapping motion are controlled remotely by the steric and electronic effects of the RCON functionalities and 2) the activation parameters for the nonrotatory flapping process are identical to those for the nonflapping peptide rotation in the complexes anti‐ 1 a,b,d – h , which indicates that the present multistep conformational transformation induced by the flapping motion is controlled by the rate‐determining pyramidalization/depyramidalization (i.e., sp2/sp3 interconversion) of the nitrogen atoms of the functionalities. The static and controllable molecular mobility of anti‐ 1 bearing peptide linkers has been discussed by comparison with the dynamic behavior of its analogues anti‐ 2 – 4 with flexible polymethylene linkers. 相似文献
19.
四组分高能体系结合能和力学性能的分子动力学模拟 总被引:7,自引:0,他引:7
用分子动力学(MD)方法模拟研究了下列4种四组分高能混合体系的结合能和力学性能: 聚叠氮缩水甘油醚(GAP)/硝化甘油(NG)/1,2,4-丁三醇硝酸酯(BTTN)/二硝基偶氮氧化二呋咱(DNOAF)、GAP/ NG/ BTTN/三氢化铝(AlH3)、聚乙二醇(PEG)/NG/BTTN/DNOAF和PEG/NG/BTTN/AlH3. 结果表明, 在三组分粘合剂中加进DNOAF和AlH3, 结合能均较大, 依次为45.35, 56.02, 48.75和65.96 kJ/kg, 预示体系稳定性和相容性均较好. 组分间的相互作用主要是非键力, 且含AlH3体系的静电力更大, 其余体系以van der Waals力较大. 静态力学分析表明, 在4种混合体系中, PEG/NG/BTTN/AlH3的拉伸模量、体模量(K)、剪切模量(G)、K/G 和柯西压(C12-C44)值均较大, 预示该体系的刚性、塑性和延展性均较好, 这可能与PEG的醚O和AlH3的缺电子桥键之间存在特殊的配位键作用有关. 相似文献
20.
Tatiana Sukhanova Vladimir Bershtein Mimi Keating Galina Matveeva Milana Vylegzhanina Victor Egorov Nina Peschanskaya Pavel Yakushev Edmund Flexman Stefan Greulich Bryan Sauer Kathleen Schodt 《Macromolecular Symposia》2004,214(1):135-146
Comparative WAXD/SAXS/SEM/DSC structural studies of a series of semi-crystalline poly(oxymethylene) (POM) engineering plastics, including the commercial products, homopolymer Delrin® and typical poly(oxymethylene-co-oxyethylene)s, and a few lab-made POM compositions, were performed. The latter differed in their content of functional additives (present in low concentrations) and POM molecular weight characteristics. In parallel, their densities, thermal behavior/laser-interferometric creep rate spectra (DSC/CRS) at 20-180 °C, as well as long-term creep resistance (LTCR) at 20 °C were studied. It has been found that introducing the nucleating agents and oxyethylene units resulted in formation of more fine spherulitic or practically non-spherulitic structure with close- or loose-packed lamellar stacks. The presence of both “thick” (5-10 nm) and “thin” (1.5-3 nm) lamellae in the weight ratio of ∼3:1 was shown in all cases. Close values of real POM crystallinities, not exceeding 50%, were obtained by WAXD and DSC. A predominant role of “straightened out” or slightly bent tie chains in disordered layers of isotropic POMs was presumed, resulting in segmental dynamics differently constrained by crystallites (DSC/CRS data). As a result, certain morphology - density - creep resistance correlations were found. 相似文献