Solution of the Fokker-Planck equation for the shock wave problem

An eigenexpansion solution of the time-independent Brownian motion Fokker-Planck equation is given for a situation in which the external acceleration is a step function. The solution describes the heavy-species velocity distribution function in a binary mixture undergoing a shock wave, in the limit of high dilution of the heavy species and negligible width of the light-gas internal shock. The diffusion solution is part of the eigenexpansion. The coefficients of the series of eigenfunctions are obtained analytically with transcendentally small errors of order exp(–1/M), whereM 1 is the mass ratio. Comparison is made with results from a hypersonic approximation.     

Crystal Structures of the Lithium Cryptates of Two Macrobicyclic Ligands Containing Pyridine,Bipyridine, and Biisoquinoline Units

The crystal structures of the LiBr complexes of two macrobicyclic ligands, [py.py.bpy] 1 and [py.biqi.biqi] 2 , have been determined. They confirm the cryptate nature of these species. In 3 , the Li⁺ cation is bound in the shallow cavity of a ligand of flattened shape, whereas in 4 , it is buried inside the macrobicycle and surrounded by its three bridges.     

The Lattice Solid Model to Simulate the Physics of Rocks and Earthquakes: Incorporation of Friction

The particle-based lattice solid model developed to study the physics of rocks and the nonlinear dynamics of earthquakes is refined by incorporating intrinsic friction between particles. The model provides a means for studying the causes of seismic wave attenuation, as well as frictional heat generation, fault zone evolution, and localisation phenomena. A modified velocity–Verlat scheme that allows friction to be precisely modelled is developed. This is a difficult computational problem given that a discontinuity must be accurately simulated by the numerical approach (i.e., the transition from static to dynamical frictional behaviour). This is achieved using a half time step integration scheme. At each half time step, a nonlinear system is solved to compute the static frictional forces and states of touching particle-pairs. Improved efficiency is achieved by adaptively adjusting the time step increment, depending on the particle velocities in the system. The total energy is calculated and verified to remain constant to a high precision during simulations. Numerical experiments show that the model can be applied to the study of earthquake dynamics, the stick–slip instability, heat generation, and fault zone evolution. Such experiments may lead to a conclusive resolution of the heat flow paradox and improved understanding of earthquake precursory phenomena and dynamics.     

The Singular Molecular Conformation of Humic Acids in Solution Influences Their Ability to Enhance Root Hydraulic Conductivity and Plant Growth

Some studies have reported that the capacity of humic substances to improve plant growth is dependent on their ability to increase root hydraulic conductivity. It was proposed that this effect is directly related to the structural conformation in solution of these substances. To study this hypothesis, the effects on root hydraulic conductivity and growth of cucumber plants of a sedimentary humic acid and two polymers—polyacrylic acid and polyethylene glycol—presenting a molecular conformation in water solution different from that of the humic acid have been studied. The results show that whereas the humic acid caused an increase in root hydraulic conductivity and plant growth, both the polyacrylic acid and the polyethylene glycol did not modify plant growth and caused a decrease in root hydraulic conductivity. These results can be explained by the different molecular conformation in water solution of the three molecular systems. The relationships between these biological effects and the molecular conformation of the three molecular systems in water solution are discussed.     

A hydrodynamic injection approach for capillary electrophoresis using rotor–stator valves

Sample injection is a critical step in a capillary electrophoresis (CE) analysis. Electrokinetic injection is the simplest approach and is often selected for implementation in portable CE instruments. However, in order to minimize the effect of sample matrix upon the results of a CE analysis, hydrodynamic injection is preferred. Although portable CE instruments with hydrodynamic injection have been reported, injection has always been performed at the grounded end of the capillary. This simplifies fluidic handling but limits coupling with electrochemical detectors and electrospray ionization–mass spectrometry (ESI–MS). We demonstrated previously that injection at the high-voltage (HV) end of the capillary could be performed using an HV-compatible rotary injection valve (fixed-volume injection). However, the mismatch between the bore sizes of the channels on the rotor–stator valve and the separation capillary caused peak tailing and undesired mixing, impairing analytical performance. In this work, we present an HV-compatible hydrodynamic injection approach that overcomes the issues associated with the fixed-volume injection approach reported previously. The performance of the CE instrument was demonstrated by analyzing a mixture of 13 amino acids by CE coupled to laser-induced fluorescence, which showed relative standard deviations for peak area and migration time below 5% and 1%, respectively, for triplicate analysis. Additionally, replicate measurements of a mixture of amino acids, peptides, nucleobases, and nucleosides by CE coupled to electrospray ionization–mass spectrometry (CE–ESI–MS) were performed to evaluate peak tailing, and results were similar to those obtained with a commercial CE–ESI–MS setup.     

Strategies for solving matrix effects in the analysis of sulfathiazole in honey samples using three-way photochemically induced fluorescence data

A widely employed compound for honey treatment, sulfathiazole (ST), was determined in commercial honey samples, employing a combination of photochemically induced fluorescence excitation-emission matrices (EEMs) and chemometric processing of the recorded second-order data. Parallel Factor Analysis (PARAFAC) and Self-Weighted Alternating Trilinear Decomposition (SWATLD) methods were used for calibration. An appropriately designed calibration with a set of standards composed of 18 samples, coupled to the use of the second-order advantage offered by the applied chemometric techniques, allowed quantitation of sulfathiazole in spiked commercial honey samples. No previous separation or sample pretreatment steps were required. The results were compared with other calibration methods such as N-PLS and PLS-1 that produced good results on synthetic samples but not on the investigated commercial honey samples.     

A Chirally Stable,Atropoisomeric, Cα‐Tetrasubstituted α‐Amino Acid: Incorporation into Model Peptides and Conformational Preference

A variety of model peptides, including four complete homologous series, to the pentamer level, characterized by the recently proposed binaphthyl‐based, axially chiral, C^α‐tetrasubstituted, cyclic α‐amino acid Bin, in combination with Ala, Gly, or Aib residues, was synthesized by solution methods and fully characterized. The solution conformational propensity of these peptides was determined by FT‐IR absorption and ¹H‐NMR techniques. Moreover, the molecular structures of the free amino acid (S)‐enantiomer and an N^α‐acylated dipeptide alkylamide with the heterochiral sequence ‐(R)‐Bin‐Phe‐ were assessed in the crystal state by X‐ray diffraction. Taken together, the results point to the conclusion that β‐bends and 3₁₀ helices are preferentially adopted by Bin‐containing peptides, although the fully extended conformation would also be adopted in solution by the short oligomers to some extent. We also confirmed the tendency of (R)‐Bin to fold a peptide chain into right‐handed bend and helical structures. The absolute configuration of the Bin residue(s) was correlated with the typically intense exciton‐split Cotton effect of the ¹B_b binaphthyl transition near 225 nm.     

ACE-Inhibitory and Antioxidant Activities of Peptide Fragments Obtained from Tomato Processing By-Products Fermented Using <Emphasis Type="Italic">Bacillus subtilis</Emphasis>: Effect of Amino Acid Composition and Peptides Molecular Mass Distribution

The effects of amino acid composition and peptide molecular mass on ACE-inhibitory and antioxidant activities of protein fragments obtained from tomato waste fermented using Bacillus subtilis were evaluated. The addition of B. subtilis increased the relative amounts of aromatic and positively-charged amino acids which have been described to influence the biological activities of peptide fragments. IC₅₀ values of hydrolysates for ACE-inhibitory and 2, 2′-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities were found to be 1.5 and 8.2 mg/mL, respectively. Size-exclusion chromatography (SEC) pattern of the hydrolysate indicated the breakdown of parent proteins to smaller peptides with molecular weights mainly below 1400 Da. MALDI-TOF mass spectrometry analysis revealed that the highest ACE-inhibitory activity was due to peptides showing molecular mass range 500–800 Da, while the most active antioxidant peptides were found to be mainly at the two different peptide weight ranges 500–800 Da and 1200–1500 Da.     

Staudinger–Vilarassa reaction versus Huisgen reaction for the control of surface hydrophobicity and water adhesion

Surface modifications are keys for a great number of applications. In order to perfectly control the surface properties, it is important to control the modification pathways. Two general pathways can be described in order to introduce modification on surfaces: the post‐strategies and the ante‐strategies. In this work, we focus on the comparison between the Huisgen and the Staudinger–Vilarrasa reaction for both post‐surface and ante‐surface modifications. Here, we focused on the possibility to use both two reactions to obtain superhydrophobic and oleophobic properties. This work includes monomer synthesis, surface modifications with alkyl, aryl or perfluoroalkyl chain. Copyright © 2016 John Wiley & Sons, Ltd.