Generalized gradient approximation adjusted to transition metals properties: Key roles of exchange and local spin density

Perdew-Burke-Ernzerhof (PBE) and PBE adapted for solids (PBEsol) are exchange-correlation (xc) functionals widely used in density functional theory simulations. Their differences are the exchange, μ, and correlation, β, coefficients, causing PBEsol to lose the Local Spin Density (LSD) response. Here, the μ/β two-dimensional (2D) accuracy landscape is analyzed between PBE and PBEsol xc functional limits for 27 transition metal (TM) bulks, as well as for 81 TM surfaces. Several properties are analyzed, including the shortest interatomic distances, cohesive energies, and bulk moduli for TM bulks, and surface relaxation degree, surface energies, and work functions for TM surfaces. The exploration, comparing the accuracy degree with respect experimental values, reveals that the found xc minimum, called VV, being a PBE variant, represents an improvement of 5% in mean absolute percentage error terms, whereas this improvement reaches ~11% for VVsol, a xc resulting from the restoration of LSD response in PBEsol, and so regarded as its variant.     

Analytical potential of a laser ablation–glow discharge–optical emission spectrometry system for the analysis of conducting and insulating materials

The analytical capabilities of a glow discharge (GD) as a secondary source for excitation/ionization of the material provided by laser ablation (LA) have been compared to conventional laser induced breakdown spectroscopy (LIBS). In LA–GD both sources can be independently adjusted to optimize the sampling process and then its subsequent excitation. This could involve a number of analytical performance advantages, such as reduced matrix dependence, greater precision and sensitivity than those encountered in LIBS. For such purpose, an ablation chamber design including two electrodes to generate the GD discharge has been built and assayed. A comparison between LIBS and LA–GD–OES has been carried out, both, under reduced argon and helium atmospheres. Different sets of samples (conducting reference materials, glass and fluorine pellets) have been used to evaluate the novel coupled technique. The LA–GD coupled system has shown to provide lower detection limits. In addition, best linear correlations between intensities and concentrations and lower matrix effects have also been found using the coupled system. Moreover, special advantages of the LA–GD–OES have also been demonstrated for the analysis of fluorine.     

指向学习体验的物质及其转化复习的教学实践——以“钠及其化合物”为例

学习体验是学生对学习内容、过程、方法、意义的自我感受和评估,对学生学习志趣、学习素养提升有积极正向作用。以钠及其化合物复习为例,将各类别物质间转化关系的构建、物质制备原理和条件的优选作为学习体验对象,依据学习体验的内在发展历程设计学习任务及活动,引导学生亲身体验学科认知方式、学科思维方法、学科应用价值,评价体验结果,激励学生自主学习发生。     

离子色谱法测定蓝藻培养液中有机酸和无机阴离子

建立了一种利用阴离子交换色谱柱分离,电导检测器同时测定17种有机酸和7种阴离子的方法。采用Ionpac AS11-HC阴离子交换柱,KOH溶液作为淋洗液,梯度洗脱,流量为1.0mL/min,柱温为30℃,进样体积为25μL。24种分析物测定结果的相对标准偏差在0.31%~2.67%之间,线性相关系数均大于0.996,平均加标回收率在80.3%~108.5%之间。该方法可用于微生物培养液中有机酸和阴离子的同时测定。     

DFT studies on coordination models for adsorption essays of Cu(II) and Ni(II) solutions in modified silica gel with iminodiacetic groups

Research in functionalized inorganic supports faces special challenges regarding the inmobilization of organic chains and efficient computational methods for the quantum chemical modeling of coordination compounds. The silylant 3-cloropropyltriethoxysilyl (R1) was anchored over silica gel in anhydrous conditions, in order to react with diethyl Iminodiacetate (DIDA) to obtain modified silica gel (R2), which was hydrolized in basic conditions previously synthesized and characterized by S _BET, TGA and FTIR spectroscopy to obtain iminodiacetic acid groups IDA to prepare an modified inorganic support (R3) that is able to get hands on metals from the first transition series such as copper and nickel. The obtained experimental values showed that the functionalized grade of R3 corresponds to 0.1598 mmol of the nitrogen indicated that the adsorbed Cu(II) or Ni(II) have the stoichiometry for both cation of 1:1. Based on this relation, the three different structures were proposed to carry out the computational studies using density functional theory (DFT) in its LDA and PW91 with the TZP slater type basis set. The primary coordination sphere of copper(II) or nickel (II) ion in R3 are optimized, structural parameters are calculated, vibrational bands are assigned and energy gaps of frontier orbital (HOMO–LUMO) have been calculated. The calculated results reproduced the experimental data with good agreement. An energy decomposition analysis (EDA) of the different models proposed here was performed and suggest a 1:1 coordination form.     

Higher regularity of the free boundary in the parabolic Signorini problem

We show that the quotient of two caloric functions which vanish on a portion of an \(H^{k+ \alpha }\) regular slit is \(H^{k+ \alpha }\) at the slit, for \(k \ge 2\). In the case \(k=1\), we show that the quotient is in \(H^{1+\alpha }\) if the slit is assumed to be space-time \(C^{1, \alpha }\) regular. This can be thought of as a parabolic analogue of a recent important result in De Silva and Savin (Boundary Harnack estimates in slit domains and applications to thin free boundary problems, 2014), whose ideas inspired us. As an application, we show that the free boundary near a regular point of the parabolic thin obstacle problem studied in Danielli et al. (Optimal regularity and the free boundary in the parabolic Signorini problem. Mem. Am. Math. Soc., 2013) with zero obstacle is \(C^{\infty }\) regular in space and time.     

A Safety Strategy for Producing Poly(Acrylic Acid) of Low Molar Mass

The synthesis of poly(acrylic acid) (PAA) of low molar mass under safe conditions is difficult due to the high polymerization rate of acrylic acid (AA) and the fast heat generation. The aqueous‐solution “semibatch” polymerization of non‐ionized AA in almost starved conditions involves high initiator loads when low molar masses are required. This article proposes the simultaneous feeding of AA and nonconventional chain transfer agents (CTA) as a strategy aimed at controlling both the molar masses and the generated heat rate. Three CTAs are investigated: 2‐mercaptoethanol, thioglycolic acid, and isopropyl alcohol. Even when PAA of relatively low molar mass can be produced by adequately selecting the flow rates and concentrations of both AA and CTA, it is found that the nature of CTA can have a significant effect on the polymerizations kinetics. The mechanisms responsible for these effects are discussed with the help of a representative mathematical model.

     

Modulating Protein–Protein Interactions by Cyclic and Macrocyclic Peptides. Prominent Strategies and Examples

Cyclic and macrocyclic peptides constitute advanced molecules for modulating protein–protein interactions (PPIs). Although still peptide derivatives, they are metabolically more stable than linear counterparts, and should have a lower degree of flexibility, with more defined secondary structure conformations that can be adapted to imitate protein interfaces. In this review, we analyze recent progress on the main methods to access cyclic/macrocyclic peptide derivatives, with emphasis in a few selected examples designed to interfere within PPIs. These types of peptides can be from natural origin, or prepared by biochemical or synthetic methodologies, and their design could be aided by computational approaches. Some advances to facilitate the permeability of these quite big molecules by conjugation with cell penetrating peptides, and the incorporation of β-amino acid and peptoid structures to improve metabolic stability, are also commented. It is predicted that this field of research could have an important future mission, running in parallel to the discovery of new, relevant PPIs involved in pathological processes.     

SYNTHESIS,IDENTIFICATION AND SURFACE ACTIVITY OF 2-AMINE-2-DEOXY-3-O-n-OCTYL-D-GLUCOPYRANOSE HYDROCHLORIDE

The synthesis and identification of this product are described. Variations of surface tension of its aqueous solutions versus concentration (ranged between 3 and 95 mmol/L) and temperature (ranged between 20.0 and 47.5°C) are studied.

The isothermal plots of surface tension versus the logarithm of the concentration show a continous decrease, with a sharp change of slope at a concentration about 6.5 mmol/L, for all the studied temperatures. A second change of slope, less pronounced, appears for a higher concentration. This concentration value increases from 28 to 42 mmol/L when temperature is raised from 20.0 to 47.5°C.

The changes of slope can be attributed mainly to micellization of neutral amine molecules resulting from hydrolysis of surface active cations, which present a weak electrolytic character.