Mechanical Characterization of Amyloid Fibrils Using Coarse‐Grained Normal Mode Analysis

Recent experimental studies have shown that amyloid fibril formed by aggregation of β peptide exhibits excellent mechanical properties comparable to other protein materials such as actin filaments and microtubules. These excellent mechanical properties of amyloid fibrils are related to their functional role in disease expression. This indicates the necessity of understanding how an amyloid fibril achieves the remarkable mechanical properties through self‐aggregation with structural hierarchy. However, the structure‐property–function relationship still remains elusive. In this work, the mechanical properties of human islet amyloid polypeptide (hIAPP) are studied with respect to its structural hierarchies and structural shapes by coarse‐grained normal mode analysis. The simulation shows that hIAPP fibril can achieve the excellent bending rigidity via specific aggregation patterns such as antiparallel stacking of β peptides. Moreover, the length‐dependent mechanical properties of amyloids are found. This length‐dependent property has been elucidated from a Timoshenko beam model that takes into account the shear effect on the bending of amyloids. In summary, the study sheds light on the importance of not only the molecular architecture, which encodes the mechanical properties of the fibril, but also the shear effect on the mechanical (bending) behavior of the fibril.     

Triacetyluridine (TAU) decreases depressive symptoms and increases brain pH in bipolar patients.

Eleven patients with bipolar depression were given doses of up to 18 g per day of triacetyluridine (TAU) over 6 weeks to test the effect of uridine on symptoms of depression via Montgomery-Asberg Depression Rating Scale (MADRS; Asberg, Montgomery, Perris, Schalling, & Sedvall, 1978) scores and on cellular bioenergetics using phosphorus magnetic resonance spectroscopic imaging (31P-MRSI). All patients and comparison participants (n = 9) completed baseline 31P-MRSI scans, and 9 patients completed posttherapy scans. The percentage changes for MADRS scores (Week 2, -23.8; Week 3, -34.9; Week 4, -42.5) and the time effects of TAU on MADRS scores (Week 2, z = -2.07, p = .039; Week 3, z = -4.28, p     

Kinetic Study of the Quenching Reaction of Singlet Oxygen by Common Synthetic Antioxidants (tert-Butylhydroxyanisol, tert-di-Butylhydroxytoluene, and tert-Butylhydroquinone) as Compared with α-Tocopherol

ABSTRACT: Effects of synthetic phenolic antioxidants (BHA, BHT, and TBHQ) on the methylene blue (MB) sensitized photooxidation of linoleic acid as compared with that of α‐tocopherol have been studied. Their antioxidative mechanism was studied by both ESR spectroscopy in a 2,2,6,6‐tetramethylpiperidone (TMPD)‐methylene blue (MB) system and spectroscopic analysis of rubrene oxidation induced by a chemical source of singlet oxygen. Total singlet oxygen quenching rate constants (k_ox?Q+k_q) were determined using a steady state kinetic equation. TBHQ showed the strongest protective activity against the MB sensitized photooxidation of linoleic acid, followed by BHA and BHT. TBHQ (1 × 10^?3 M) exhibited 86.5% and 71.4% inhibition of peroxide and conjugated diene formations, respectively, in linoleic acid photooxidation after 60‐min light illumination. The protective activity of TBHQ against the photosensitized oxidation of linoleic acid was almost comparable to that of α‐tocopherol. The data obtained from ESR and rubrene oxidation studies clearly showed the strong singlet oxygen quenching ability of TBHQ. The k_ox?Q+k_q of BHA, BHT, and TBHQ were determined to be 3.37 × 10⁷, 4.26 × 10⁶, and 1.67 × 10⁸ M^?1 s^?1, respectively. The k_ox?Q+k_q of TBHQ was within the same order of magnitude of that of α‐tocopherol, a known efficient singlet oxygen quencher. There was a high negative correlation (r² = ?0.991) between log (k_ox?Q+k_q) and reported oxidation potentials for the synthetic antioxidants, indicating their charge‐transfer mechanism for singlet oxygen quenching. This is the 1st report on the kinetic study on k_ox?Q+k_q of TBHQ in methanol as compared with other commonly used commercial synthetic antioxidants and α‐tocopherol.     

All-fiber add-drop wavelength-division multiplexer based onintermodal coupling

We demonstrate a novel all-fiber add-drop multiplexer by using a tilted Bragg grating written on a two-mode fiber and a mode-selective coupler. The device can be made potentially with low loss and low cost, useful for add-drop of a small number of channels in wavelength-division-multiplexing (WDM) communication systems     

Lamellar silica mesostructures assembled from a new class of Gemini surfactants: alkyloxypropyl-1,3-diaminopropanes

Abstract  

Representative members of a new class of commercially available Gemini surfactants, namely, the alkyloxypropyl-1,3-diaminopropanes, are shown to template the direct assembly of mesoporous silicas with lamellar framework structures. The hydrolysis of tetraethylorthosilicate in the presence of a derivative with a straight hydrophobic chain, C _n H_2n+1O(CH₂)₃NH(CH₂)₃NH₂ with n = 8 and 10 (Tomah3 DA1214), afforded a layered mesophase with a surface area of 464 m²/g, a pore volume of 0.39 cm³/g, a pore size of 3.6 nm and a vesicular hierarchical structure. The introduction of electrostatic forces into the assembly process through the protonation of up to 33% of the amine centers improves the quality of the lamellar framework order as evidenced by increases in X-ray diffraction and textural properties. Also, the vesicular hierarchical structure formed under electrically neutral assembly conditions is replaced by well dispersed multilamellar nanoparticles upon surfactant protonation. Chain branching in the hydrophobic segment of Gemini derivative i-C₁₀H₂₁O(CH₂)₃NH(CH₂)₃NH₂ (Tomah3 DA14) compromises the quality of the lamellar framework structure, but affords higly dispersed nanoparticles with hierarchical coiled slab to vesicular motifs depending on the degree of surfactant protonation. In addition to providing unusual lamellar framework structures, these Gemini surfactants afford hierarchical nanoparticle motifs of relatively uniform size (50–200 nm) and a very high degree of dispersion for a potential use in a variety of materials applications.     

Synthesis and Characterization of Red‐Emitting Iridium(III) Complexes for Solution‐Processable Phosphorescent Organic Light‐Emitting Diodes

A new series of highly efficient red‐emitting phosphorescent Ir(III) complexes, (Et‐CVz‐PhQ)₂Ir(pic‐N‐O), (Et‐CVz‐PhQ)₂Ir(pic), (Et‐CVz‐PhQ)₂Ir(acac), (EO‐CVz‐PhQ)₂Ir(pic‐N‐O), (EO‐CVz‐PhQ)₂Ir(pic), and (EO‐CVz‐PhQ)₂Ir(acac), based on carbazole (CVz)‐phenylquinoline (PhQ) main ligands and picolinic acid N‐oxide (pic‐N‐O), picolinic acid (pic), and acetylacetone (acac) ancillary ligands, are synthesized for phosphorescent organic light‐emitting diodes (PhOLEDs), and their photophysical, electrochemical, and electroluminescent (EL) properties are investigated. All of the Ir(III) complexes have high thermal stability and emit an intense red light with an excellent color purity at CIE coordinates of (0.65,0.34). Remarkably, high‐performance solution‐processable PhOLEDs were fabricated using Ir(III) complexes with a pic‐N‐O ancillary ligand with a maximum external quantum efficiency (5.53%) and luminance efficiency (8.89 cd A^?1). The novel use of pic‐N‐O ancillary ligand in the synthesis of phosphorescent materials is reported. The performance of PhOLEDs using these Ir(III) complexes correlates well with the results of density functional theory calculations.     

Direct preparation of dichloropropanol from glycerol and hydrochloric acid gas in a solvent-free batch reactor: Effect of experimental conditions

Solvent-free direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas was carried out in a batch reactor with a variation of reaction conditions (agitation speed, reaction time, reaction temperature, and reaction pressure), amount of H₃PW₁₂O₄₀ catalyst, and amount of water absorbent (silica gel blue). The reaction was conducted at high agitation speed in order to avoid mass transfer limitation between glycerol and hydrochloric acid gas. In the direct preparation of DCP from glycerol and hydrochloric acid gas, DCP formation was increased with increasing reaction time, reaction temperature, and reaction pressure. Chlorination of glycerol occurred via the following consecutive reaction steps: glycerol→monochloropropanediol (MCPD)→dichloropropanol (DCP)→trichloropropane (TCP). Reaction rate decreased in the order of first-step reaction>second-step reaction>third-step reaction. The presence of H₃PW₁₂O₄₀ catalyst and water absorbent (silica gel blue) enhanced the formation of DCP. DCP formation was increased with increasing the amount of H₃PW₁₂O₄₀ catalyst and water absorbent (silica gel blue). Strong Brönsted acid site of H₃PW₁₂O₄₀ catalyst and water removal from the reaction system favorably served in improving DCP formation.     

A performance evaluation method of preformed joint sealant: Slip-down failure

Various preformed joint sealants (PJS) can be used for joint concrete pavement (JCP) to prevent the JCP from distresses such as pumping and faulting. Even though PJS have an important role in concrete pavement structures, most of the test methods that assess PJS focus on evaluating their basic mechanical and chemical properties rather than performance-related properties. In this study, a tester for PJS is developed and utilized to determine the resistant stiffness, which is considered to be a performance-related parameter, of PJS in transverse joints. The resistant stiffness is determined by dividing the peak force by the displacement; and the normalized value, which is used to simplify the relationship between the joint width and the sealant width, is determined by dividing the joint width by the sealant width. From laboratory tests performed on the developed tester, it is found that the resistant stiffness and normalized value are representative parameters that can be used to recommend the proper width of the joint, regardless of the joint width and joint type. Also, the relationship between the slip-down distress and the joint width, which is obtained from field survey results, can be utilized to recommend a minimum width for PJS.     

Exploring Nanomechanical Behavior of Silicon Nanowires: AFM Bending Versus Nanoindentation

Despite many efforts to advance the understanding of nanowire mechanics, a precise characterization of the mechanical behavior and properties of nanowires is still far from standardization. The primary objective of this work is to suggest the most appropriate testing method for accurately determining the mechanical performance of silicon nanowires. To accomplish this goal, the mechanical properties of silicon nanowires with a radius between 15 and 70 nm (this may be the widest range ever reported in this research field) are systematically explored by performing the two most popular nanomechanical tests, atomic force microscopy (AFM) bending and nanoindentation, on the basis of different analytical models and testing conditions. A variety of nanomechanical experiments lead to the suggestion that AFM bending based on the line tension model is the most appropriate and reliable testing method for mechanical characterization of silicon nanowires. This recommendation is also guided by systematic investigations of the testing environments through finite element simulations. Results are then discussed in terms of the size‐dependency of the mechanical properties; in the examined range of nanowire radius, the elastic modulus is about 185 GPa without showing significant size dependency, whereas the nanowire strength dramatically increases from 2 to 10 GPa as the radius is reduced.