Combining Ion Mobility Spectrometry with Hydrogen-Deuterium Exchange and Top-Down MS for Peptide Ion Structure Analysis

The gas-phase conformations of electrosprayed ions of the model peptide KKDDDDIIKIIK have been examined by ion mobility spectrometry (IMS) and hydrogen deuterium exchange (HDX)-tandem mass spectrometry (MS/MS) techniques. [M+4H]⁴⁺ ions exhibit two conformers with collision cross sections of 418 Ų and 471 Ų. [M+3H]³⁺ ions exhibit a predominant conformer with a collision cross section of 340 Ų as well as an unresolved conformer (shoulder) with a collision cross section of ~367 Ų. Maximum HDX levels for the more compact [M+4H]⁴⁺ ions and the compact and partially-folded [M+3H]³⁺ ions are ~12.9, ~15.5, and ~14.9, respectively. Ion structures obtained from molecular dynamics simulations (MDS) suggest that this ordering of HDX level results from increased charge-site/exchange-site density for the more compact ions of lower charge. Additionally, a new model that includes two distance calculations (charge site to carbonyl group and carbonyl group to exchange site) for the computer-generated structures is shown to better correlate to the experimentally determined per-residue deuterium uptake. Future comparisons of IMS-HDX-MS data with structures obtained from MDS are discussed with respect to novel experiments that will reveal the HDX rates of individual residues. Graphical Abstract

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Microwave‐Assisted Aromatization of 1,3,5‐Trisubstituted 2‐Pyrazolines by Bi(NO3)3 · 5H2O,as a Novel and Convenient Oxidizing Agent

Abstract

Bismuth(III) nitrate pentahydrate, Bi(NO₃)₃?·?5H₂O, has been used as a mild, efficient, and inexpensive oxidant for the oxidative aromatization of several 1,3,5‐trisubstituted 2‐pyrazolines to pyrazoles in acetic acid under microwave irradiation with good to excellent yields.     

Terahertz wave switch based on photonic crystal ring resonators

In this paper, we have presented a compact and integrated terahertz wave switch design based on photonic crystal ring resonators. The photonic crystal structure with square lattice is investigated and applied for design of ring resonators. The switching mechanism of this novel switch is based on the variation of the resonant frequency of the ring resonator inserted between two parallel waveguides. The refractive index of the holes of the structure filled with polyaniline electrorheological fluids are varied by applied external electric field, the result of which is the variation of the ring resonant frequency. The proposed device is analyzed by using finite difference time domain method. Numerical simulation results show that this switch has high extinction ratio, small size, low voltage and advantages of selectivity of coupling THz wave to different output ports.     

Heat transfer and fluid flow of pseudo-plastic nanofluid over a moving permeable plate with viscous dissipation and heat absorption/generation

Journal of Thermal Analysis and Calorimetry - The purpose of the present study is investigating the heat transfer of non-Newtonian pseudo-plastic nanofluid flow on a moving permeable flat plate...     

Synthesis of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives via a one-pot four-component reaction

A one-pot four-component reaction of an aliphatic or aromatic amine, diketene, an aromatic aldehyde and 1,3-diphenyl-1H-pyrazol-5-amine in the presence of p-toluenesulfonic acid as a catalyst has been developed. In this reaction, a new class of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives is produced under mild reaction conditions and in good yields at ambient temperature.     

Application of micellar enhanced ultrafiltration (MEUF) for arsenic (v) removal from aqueous solutions and process optimization

In this study, the removal of arsenic was evaluated using micellar-enhanced ultrafiltration process. Response surface methodology and Box-Behnken matrix methods were also applied to design the experiments and determine the optimum conditions. Therefore, the main operational parameters including pH (4–10), initial concentration of arsenic (20–80?µg/L), and concentration of Cetyltrimethylammonium bromide (CTAB) (1–3?mM) were investigated. The results of analysis of variance revealed a good agreement between experimental data and the built model with the determination coefficient (R²) of 0.99. Accordingly, the removal efficiency obtained was about 94.8% at the optimal condition (pH?=?6.73, the initial concentration of arsenic?=?29.44?µg/L, and CTAB concentration of 2.83?mM).     

Expedient Catalytic Access to Knöevenagel Condensation Using Sr<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript> Nanocomposite in Room Temperature

Sr₃Al₂O₆ nanocomposite was prepared by sol gel method using aluminum isopropoxide, strontium nitrate, acetylacetone and polyethylene glycol as template, followed by calcination at 900 °C. This nanocomposite was characterized by various techniques including X-ray powder diffraction, infrared spectroscopy, elemental analysis, scanning transmission microscope and transmission electron microscope. It was found that Sr₃Al₂O₆ nanocomposite successfully catalyzes the Knöevenagel condensation of aromatic aldehydes with malononitrile in room temperature in ethanol. Expedient access to the corresponding Knöevenagel adducts in moderate to high yields within 6 min is promising. The recovered catalyst was reused for three times without significant loss of activity.     

Landau-Levich menisci

As shown by Landau, Levich and Derjaguin, a plate withdrawn out of a wetting bath at low capillary numbers deforms the very top of the liquid reservoir. At this place, a dynamic meniscus forms, whose shape and curvature select the thickness of the film entrained by the plate. In this paper, we measure accurately the thickness of the entrained film by reflectometry, and characterize the dynamic meniscus, which is found to decay exponentially towards the film. We show how this shape is modified when reversing the motion: as a plate penetrates the bath, the dynamic meniscus can "buckle" and present a stationary wavy profile, which we discuss.     

Effect of pH on the Behavior of Hyaluronic Acid in Dilute and Semidilute Aqueous Solutions

Summary : Viscosity, asymmetric flow field-flow fractionation (AFFFF) methods, and dynamic light scattering (DLS) experiments were used to characterize the effect of pH on the behavior of dilute and semidilute aqueous buffered solutions of hyaluronic acid (HA). It is shown that degradation of HA occurs at pH < 4 and pH > 11, and in the domain 4 < pH < 11 virtually no disruption of the HA chains occurs. The pH-induced scission of HA is attributed to the cleavage of glycosidic bonds. In dilute solutions, intramolecular rupture of HA chains occurs and in the semidilute concentration regime network-fragmentation is observed at low and high pH values. The degree of degradation of HA is most marked at high pH. From the molecular weight and radius of gyration obtained from AFFFF at different pH values, it is clear that the degradation of HA starts at early times after preparation of the solution, and continues for a couple of days. The kinetics of degradation of HA is fastest at high pH.     

On the Regularity and Koszulness of Modules Over Local Rings

Koszul modules over Noetherian local rings R were introduced by Herzog and Iyengar and they possess good homological properties, for instance their Poincaré series is rational. It is an interesting problem to characterize classes of Koszul modules. Following the idea traced by Avramov, Iyengar, and Sega, we take advantage of the existence of special filtration on R for proving that large classes of R-modules over Koszul rings are Koszul modules. By using this tool we reprove and extend some results obtained by Fitzgerald.