6,332 publications from this institution
Amyloid fibrils comprising primarily the peptides Aβ40 and Aβ42 are a defining feature of the Alzheimer's disease (AD) brain, and convergent evidence suggests that the process of their formation plays a central role in the AD pathogenic pathway. Elucidation of fibril assembly is critical for the discovery of potential AD diagnostics and therapeutics, since the pathogenic entity is not necessarily the product fibril, but could be a precursor species whose formation is linked to fibrillogenesis in vivo. Atomic force microscopy allowed the identification of an unanticipated intermediate in in vitro fibril formation, the Aβ amyloid protofibril. This manuscript describes studies of the structure of the Aβ40 protofibril and its in vitro assembly and disassembly using atomic force microscopy (AFM). The Aβ40 protofibril has a height of ca. 4.3 ± 0.5 nm and a periodicity of ca. 20 ± 4.7 nm. The rate of its elongation depends on the total concentration of Aβ40, the temperature, and ionic strength of the medium. Aβ42 and Aβ40 protofibrils elongate at a comparable rate. Statistical analysis of AFM data reveals a decrease in the number of protofibrils with time, indicating that coalescence of smaller protofibrils contributes to protofibril elongation. Similar analysis reveals that protofibrils shorten while the number of protofibrils also decrease following dilution, indicating that protofibril disassembly does not proceed by a reverse of the assembly process. These investigations provide systematic data defining factors affecting Aβ fibrillization and, thus, should be valuable in the design of high-throughput assays to identify agents which alter Aβ protofibril assembly.
The Young's modulus, strength, and toughness of nanostructures are important to proposed applications ranging from nanocomposites to probe microscopy, yet there is little direct knowledge of these key mechanical properties. Atomic force microscopy was used to determine the mechanical properties of individual, structurally isolated silicon carbide (SiC) nanorods (NRs) and multiwall carbon nanotubes (MWNTs) that were pinned at one end to molybdenum disulfide surfaces. The bending force was measured versus displacement along the unpinned lengths. The MWNTs were about two times as stiff as the SiC NRs. Continued bending of the SiC NRs ultimately led to fracture, whereas the MWNTs exhibited an interesting elastic buckling process. The strengths of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values. Because of buckling, the ultimate strengths of the stiffer MWNTs were less than those of the SiC NRs, although the MWNTs represent a uniquely tough, energy-absorbing material.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDirect measurement of interfacial interactions between semispherical lenses and flat sheets of poly(dimethylsiloxane) and their chemical derivativesManoj K. Chaudhury and George M. WhitesidesCite this: Langmuir 1991, 7, 5, 1013–1025Publication Date (Print):May 22, 1991Publication History Published online1 May 2002Published inissue 22 May 1991https://doi.org/10.1021/la00053a033RIGHTS & PERMISSIONSArticle Views3278Altmetric-Citations555LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts
Clamped-clamped compressed wide metal columns with length to thickness ratios such that they undergo plastic buckling are considered. Further, the thickness of the columns is assumed to be in the range of microns to tens of microns, typical of elements comprising some of the small-scale lattice materials currently being produced. The strengthening effects associated with plastic strain gradients are expected to influence buckling behavior, and the columns are analyzed using several versions of the available strain gradient plasticity theories. The columns are assumed to be infinitely wide and subject to plane strain deformations. Approximate one-dimensional and exact two-dimensional analyses are presented. The primary focus is the onset of plastic buckling as predicted by bifurcation from the state of uniform compression. However, a numerical post-buckling study is carried out for one class of strain gradient theories for columns with initial imperfections to ascertain if the buckling predictions stemming from this class of theory are realistic. The paper highlights the fact that one class of strain gradient theories does not appear to be adequate for analyzing plastic buckling.
This paper describes the synthesis of the trivalent hapten molecule 1, containing three 2,4-dinitrophenyl (2,4-DNP) groups, and the use of this molecule to aggregate three molecules of anti-2,4-DNP IgG into a complex with 3:2 stoichiometry (IgG312). The equilibrium product IgG312 was generated in ∼90% yield upon mixing IgG and 1; during incubation, thermodynamically unstable, high-molecular-weight aggregates (>104 nm in diameter) form first and convert subsequently to IgG312. The thermodynamics and the kinetics of the formation of aggregates were studied using size-exclusion high-performance liquid chromatography (SE-HPLC), dynamic light scattering (DLS), and analytical ultracentrifugation (AUC). An analytical model based on multiple species in equilibrium was developed and used to interpret the SE-HPLC data. The aggregate IgG312 was more stable thermodynamically and kinetically than monomeric aggregates of this IgG with monomeric derivatives of 2,4-DNP; this stability suggests potential applications of these aggregates in biotechnology.
Mode I, quasi-static, steady-state crack growth is analyzed for rate dependent materials under plane strain conditions in small scale yielding. The solid is characterized by an elastic–viscoplastic constitutive law and the plane ahead of the crack tip is embedded with a rate dependent fracture process zone. The macroscopic work of fracture of the material is computed as a function of the crack velocity and the parameters characterizing the fracture process zone and the solid. With increasing crack velocity a competition exists between the strain rate hardening of the solid, which causes elevated tractions ahead of the crack tip that tend to drive crack propagation, and the rate strengthening of the fracture process zone which tends to resist fracture. Results for material parameters characteristic of polymers show that the toughness of the material can either increase or decrease with increasing crack velocity. To motivate the model, the cohesive zone parameters are discussed in terms of failure mechanisms such as crazing and void growth ahead of the crack tip. The toughness of rubber modified epoxies is explained by employing the fracture model along with micromechanical void cell calculations.
