Direct Observations of Amyloid β Self-Assembly in Live Cells Provide Insights into Differences in the Kinetics of Aβ(1–40) and Aβ(1–42) Aggregation

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α/β-Selectivity in Hydrolyses of α- or β- Naphthyl Acetates in the Presence of Cycloamyloses.

Cyclohexaamylose hydrolyzed α-naphthyl acetates more rapidly than the corresponding β-isomers, a phenomenon termed “α-selectivity”, while cyclooctaamylose showed “β-selectivity” and the selectivity of cycloheptaamylose fell between those of cyclohexa- and cyclooctaamyloses.     

Kinetics and Mechanism of 4-Nitrotoluene Oxidation with Ozone in an Acetic Acid Solution in the Presence of a Metal–Bromide Catalyst

The kinetics and mechanism of a reaction between ozone and 4-nitrotoluene in an acetic acid solution in the presence of a cobalt–bromide catalyst were studied at 100°. Under these conditions, 4-nitrobenzoic acid was the main reaction product (96.6%). The rate of oxidation exhibited a first order with respect to the substrate, ozone, and the catalyst and a zero order with respect to oxygen. The main stages of the catalytic cycle were considered. It is believed that the selective oxidation of 4-nitrotoluene at the methyl group in the presence of a catalyst occurs as a nonchain ion–radical process, in which the role of ozone is reduced to the generation of an active catalyst species (Co³⁺Br^– Co²⁺Br^·). This species involves 4-nitrotoluene in the oxidation process at a high rate.     

A Convenient Synthesis Of 1-Acyl Indolizines by 1,3-Dipolar Cycloaddition Reactions of Pyridinium Ylides and α,β-Unsaturated Aldehydes or Ketones in the Presence of Tetrakis-Pyridine Cobalt Dichromate

In the presence of tetrakispyridine cobalt dichromate (CoPy₄(HCrO₄)₂), pyridinium ylides and α,β-unsaturated aldehydes or ketones undergo 1,3-dipolar cycloaddition reactions followed by in situ aromatization to give 1-acyl substituted indolizines in moderate to good yields.     

Kinetics and Mechanism of 2,3,6-Trimethylphenol Oxidation by Hydrogen Peroxide in the Presence of TiO2–SiO2 Aerogel

The product and kinetics studies of 2,3,6-trimethylphenol (TMP) oxidation by 30% aqueous ₂₂ in the presence of a heterogeneous catalyst, TiO₂–SiO₂ aerogel, are performed in an MeCN medium. The main reaction products are 2,3,5-trimethyl-1,4-benzoquinone and 2,2",3,3",6,6"-hexamethyl-4,4"-biphenol. The reaction is first-order in ₂₂ and fractional order (1–0) in TMP. The reaction rate is proportional to the catalyst amount and depends on the water concentration in the reaction mixture in a complex manner. The results suggest the formation of an active intermediate on the titanium center. In this intermediate containing both a TMP molecule and the hydroperoxide group, inner-sphere one-electron oxidation of TMP occurs to give the phenoxyl radical.     

Assessment of the Stability of a Mercury Film on a Glass–Ceramic Carbon Electrode when Determining Zinc in the Presence of Manganese by Anodic Stripping Voltammetry

The possibility of assessing the stability of operation of a mercury film graphite electrode in anodic stripping voltammetry using Shewhart control charts (CCs) is shown. The offered technique allows significantly increasing the efficiency of the voltammetric determination of zinc and manganese and taking measurements of analytes in samples during a working day without replacing the mercury film on the electrode surface.     

Characterization of Alkylphenol Components in Ginkgo biloba Sarcotesta by Thermochemolysis–Gas Chromatography/Mass Spectrometry in the Presence of Trimethylsulfonium Hydroxide

A method to determine alkylphenols in Ginkgo biloba sarcotesta, especially focusing on polyunsaturated ginkgolic acid components, was developed on the basis of thermochemolysis–gas chromatography/mass spectrometry with a DB-23 column in the presence of trimethylsulfonium hydroxide [(CH₃)₃SOH]. By using this technique, powder sample of Ginkgo biloba sarcotesta can be directly analyzed without any tedious and time-consuming pretreatment. On the resulting chromatograms, seven kinds of ginkgolic acids including polyunsaturated ginkgolic acid GA17:2 and two kinds of ginkgols were clearly observed as their methyl derivative. Based on the peak areas, the ginkgolic acid compositions are in good agreement with these obtained by a high-performance liquid chromatography method dedicated to analysis of ginkgolic acid.     

A Novel Method for the Synthesis of High Hindered Iminoesters by the Reaction of Decomposition of Phenyldiazoacetate in the Presence of Rh2(OAc)4 with Arylamines and DEAD

It is well known that iminoesters were condensed by ketoesters with amines, but the procedure to ketoesters require harsh reaction conditions and multi steps. Herein we report a mild and practical one-step approach for the synthesis of iminoesters, especially for the high steric hindered iminoesters. Decomposition of phenyl diazoacetate catalyzed by rhodium acetate with amines to give N-H insertion product has been reported.     

Polymerization of Methyl Methacrylate by the System Ribonucleic Acid–Water in the Presence of Carbon Tetrachloride and Copper(11) Ion

Polymerization of methyl methacrylate (MMA) was carried out in the presence of ribonucleic acid (RNA), water, carbon tetrachloride, and copper(II) ion. The overall activation energy for the polymerization is proportional to the square root of the amount of RNA. The rate increased at first with the amount of MMA, but then became independent of the amount of MMA.

Polymerization was inhibited by the presence of air. Carbon tetrachloride and copper(II) ion are able to give RNA the ability to initiate polymerization. Conversion of MMA is accelerated by the addition of tertiary amine derivatives instead of carbon tetrachloride.     

On the Role Played by Dimers of Radical Cations in the Process of Electrochemical Oxidation–Reduction of Polyaniline: The Data that Were Obtained Using the Method of Cyclic Voltabsorptometry in the Presence of Counteranions of a Diverse Nature

The electrochemical oxidation–reduction of films of polyaniline is studied in the presence of various counteranions. The differential cyclic voltabsorptometric (DCVA) curves (dA/dt relative to potential, where A is the optical absorption) are recorded at characteristic wavelengths corresponding to individual spectrum components previously isolated with the Alentsev–Fok method. The DCVA curves for aqueous solutions of HCl, HClO₄, and H₂SO₄ at different potential scan rates are compared to traditional cyclic voltammograms. For the DCVA curves obtained at 665 nm discovered is one broad peak of dA/dt in the region of potentials between the first and second stages of polyaniline oxidation (0.6 V vs. Ag/AgCl). An assumption is made about a chemical nature of the process of generation of absorption in this spectral region, which, more likely than not, is connected with the emergence of dimers of radical cations of polyaniline. It is discovered that the electrochemical processes in the region of potentials that correspond to the first stage of oxidation give rise to variations in the absorption inside several regions of spectrum: 435 nm (radical cations) and 755 nm (localized polarons). An assumption is made that the first peak of the current corresponds to several successive processes that occur in a polyaniline molecule in the course of oxidation as well as to the existence of heterogeneous regions where the generation of localized polarons proceeds at different rates.     

When is a molecule properly solvated by a continuum model or in a cluster ansatz? A first-principles simulation of alanine hydration

In order to test the validity of the cluster ansatz approach as well as of the continuum model approach and to learn about the solvation shell, we carried out first-principles molecular dynamics simulations of the alanine hydration. Our calculations contained one alanine molecule dissolved in 60 water molecules. Dipole moments of individual molecules were derived by means of maximally localized Wannier functions. We observed an average dipole moment of about 16.0 D for alanine and of about 3.3 D for water. In particular, the average water dipole moment in proximity of alanine's COO(-) group decayed continously with increasing distance, while, surprisingly, close to the CH3 and NH3+ group, the dipole moment first rose before its value dropped. In a cluster ansatz approach, we considered snapshots of alanine surrounded by different water molecule shells. The dipole moments from the cluster approaches utilizing both maximally localized Wannier functions as well as natural population analysis served to approximate the dipole moments of the total trajectory. Sufficient convergence of the cluster ansatz approach is found for either of the two solvent shells around the polar groups and one solvent shell around the apolar groups or two solvent shells around the polar groups surrounded by a dieletric continuum.     

Physicochemical and Catalytic Properties of Ni,H/ZSM-5 and Ni,H/ZSM-5–Binder Catalysts Prepared in the Absence and in the Presence of Binder

Kinetics and Catalysis - Physicochemical and catalytic properties of H/ZSM-5 and Ni,H/ZSM-5 along with Ni,H/ZSM-5–Al2O3 (1 : 1) systems were examined. The systems with a binder were prepared...     

Heck Arylation of Cyclohexene Promoted by Ultrasonic and Micro wave in Ionic Liquid： a Novel Method of the Synthesis of 3-Naphthylcyclohexene

Palladium catalyzed arylation or vinylation of olefins by aryl halides are well known as the Mizoroki-Heck reaction and have proved to be of genuine synthetic utility for C-C bond formation1. Although a lot of progress has been made in Heck coupling react…     

A Green and Efficient Synthesis of Xanthenedione Derivatives Promoted by InCl_3·4H_2O in Ionic Liquid

Xanthenedione derivatives have held considerable interests in recent years, since theyconstitute a structural unit in a number of natural products1 and have been used asversatile synthons because of the inherent reactivity of the inbuilt pyran ring2. Usually,poly-hydrogenated xanthenediones (3, Scheme 1) can be obtained through the acid orbase catalyzed condensation of appropriate active methylene carbonyl compounds withaldehydes. But this method is not very satisfactory because of the prolong…     

A new methodology for simultaneous quantification of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 by column-switching LC/MS/MS

This article details the development of a novel method that overcomes the drawbacks of sandwich ELISA (sELISA) and allows reliable evaluation of simultaneous quantification of the amyloid (Aβ)-peptides, total-Aβ, Aβx-38, Aβx-40, and Aβx-42, in rat brain by optimized sample purification and column-switching liquid chromatographic-tandem mass spectrometry (LC/MS/MS). This method provides accurate analyses of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 with a linear calibration range between 0.05 and 45 ng/mL. Verification for accuracy and precision of biological samples were determined by a standard addition and recovery test, spiked with synthetic Aβ1-38, Aβ1-40, and Aβ1-42 into the rat brain homogenate. This method showed <20% relative error and relative standard deviation, indicating high reproducibility and reliability. The brain concentrations of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 after oral administration of flurbiprofen in rats were measured by this method. Aβx-42 concentrations (4.57 ± 0.69 ng/g) in rats administered flurbiprofen were lower than those in untreated rats (6.48 ± 0.93 ng/g). This was consistent with several reports demonstrating that NSAIDs reduced the generation of Aβ. We report here a method that allows not only the quantification of specific molecular species of Aβ but also simultaneous quantification of total-Aβ, Aβx-38, Aβx-40, and Aβx-42, thus overcoming the drawbacks of sELISA.     

Formation and Extraction of Niobium(V) Complex with Xylenol Orange in the Presence of a 4-Pyridone Derivative

Xylenol orange (XO) is a suitable reagent for the spectrophotometric determination of niobium in a weakly acidic medium. The present study shows that the addition of 3-hydroxy-2-methyl-1-phenyl-4-pyridone (HX) influences the complex formation as well as the spectroscopic properties of this colored system. To prevent formation of niobium(V) hydrolyzed species in water, tartaric acid was used when preparing the niobium stock solution. The red-violet colored complex formed by heating niobium(V) with xylenol orange (XO) in the presence of HX at pH=3 has a maximum absorption wavelength at 565 nm. The complex can be extracted by a chloroform solution of tetraphenylphosphonium (TPP) chloride. The optimum reaction conditions and other parameters for complex formation have been evaluated. The mechanism of extraction is probably based on the formation of the associated ion pair between the tetraphenylphosphonium cation and the mixed Nb(V)-XO-HX anion. The extracted complex in chloroform showed a maximum absorbance at 585 nm with the corresponding molar absorption coefficient being 3.72×10⁴ L⋅mol⁻¹⋅cm⁻¹, and obeys Beer’s law in the range 3×10⁻⁶ to 3×10⁻⁵ mol⋅L⁻¹.     

The Synthesis of a Multiple D–A Conjugated Macrocycle and Its Application in Organic Photovoltaic

As a novel class of materials, D–A conjugated macrocycles hold significant promise for chemical science. However, their potential in photovoltaic remains largely untapped due to the complexity of introducing multiple donor and acceptor moieties into the design and synthesis of cyclic π-conjugated molecules. Here, we report a multiple D–A ring-like conjugated molecule ( RCM ) via the coupling of dimer molecule DBTP-C3 as a template and thiophenes in high yields. RCM exhibits a narrow optical gap (1.33 eV) and excellent thermal stability, and shows a remarkable photoluminescence yield (Φ_PL) of 11.1 % in solution, much higher than non-cyclic analogues. Organic solar cell (OSC) constructed with RCM as electron acceptor shows efficient charge separation at donor-acceptor band offsets and achieves a power conversion efficiency (PCE) of 14.2 %-approximately fourfold higher than macrocycle-based OSCs reported so far. This is partly due to low non-radiative voltage loss down to 0.20 eV and a high electroluminescence yield (Φ_EL) of 4×10⁻⁴. Our findings emphasize the potential of D–A cyclic conjugated molecules in advancing organic photovoltaic technology.