Shifting Native Chemical Ligation into Reverse through N→S Acyl Transfer

Peptide thioester synthesis by N→S acyl transfer is being intensively explored by many research groups the world over. Reasons for this likely include the often straightforward method of precursor assembly using Fmoc-based chemistry and the fundamentally interesting acyl migration process. In this review we introduce recent advances in this exciting area and discuss, in more detail, our own efforts towards the synthesis of peptide thioesters through N→S acyl transfer in native peptide sequences. We have found that several peptide thioesters can be readily prepared and, what's more, there appears to be ample opportunity for further development and discovery.     

Chemical Corrosion Mechanisms of Magnesite-chrome Bricks by Converter Slag

The corrosion resistance of four kinds magnesitechrome bricks against converter salg was investigated by static crucible slag tests. The microstructures of the asdelivered and tested refractories were analyzed by means of SEM and EDS. The results showed that： Different magnesite-chrome bricks have different slag resistances. Generally, the slag resiantance sequence is as follows： rebounded fused magnesite-chrome brick 〉 semi-reboun- ded magnesite-chrome brick 〉 direct-bonded magnesitechrome brick 〉 silicate bonded magnesite-chrome brick. Slag reacts with the periclase of magnesite-chrome refractories, which results in the dissoving of periclase in fayalite slag. However, the complex spinels have superior slag resistance.     

Separation Science—A Vital Tool of the Chemical Engineer

Abstract

Separation attempts reach back into the earliest history of mankind. Motivated by necessity, man developed methods of separation which, although crude by our standards, represented ingenious progress. Thus, food and condiment preparation had much to do with the development of processes such as leaching, solvent extraction, crystallization, evaporation, and the like.     

Chemical modification of styrene–butadiene–styrene co-polymer by grafting of N-carbamyl maleamic acid

A styrene–butadiene–styrene (SBS) block co-polymer was functionalized using different amounts of N-carbamyl maleamic acid (NCMA) and benzoyl peroxide as initiator. NCMA, which is a bifunctional monomer, was synthesized in our laboratories. The concentration of NCMA used in the functionalization of SBS ranged from 0.5 to 3% (w/w) based on the co-polymer mass. Benzoyloxy radicals generated from the thermal decomposition of benzoyl peroxide initiated the grafting reaction. The concentration of the initiator was kept constant at 0.076% (w/w). FT-IR spectroscopy was used to determine the amount of NCMA effectively grafted onto the SBS. The maximum amount of monomer grafted was about 0.3% (w/w) when the SBS was modified with 1% (w/w) NCMA. The effect of grafting on the surface properties and the adhesion to polyurethane adhesive of the modified SBS were evaluated. Contact angle values were obtained using liquid droplets. When the concentration of the NCMA used in the grafting reaction was 1% (w/w), the contact angles with water on original and modified SBS were 95° and 77°, respectively. Adhesion properties were evaluated by standard peel tests employing a commercial polyurethane adhesive. The modified SBS having the largest amount of NCMA displayed a T-peel strength value 5-times higher than the corresponding value measured with the original SBS.     

Chemical Stability of ZnO–Na2O–SO3–P2O5 Glasses

We report on chemical stability and corrosion behavior of highly depolymerized sulfophosphate glasses from the system ZnO–Na₂O–SO₃–P₂O₅ in aqueous solution, providing data on weight loss, ion release rates, and modifications of surface topology as a function of time, temperature and pH value. Observations seem consistent with the previously developed structural model of chemical heterogeneity, where cations Na⁺ and Zn²⁺ cluster selectively in the vicinity of sulfate and phosphate anions, respectively.     

Stimulation of Phospholipase A2 by Toxic Main Group Heavy Metals: Partly Dependent on G-proteins?

Organometals induce platelet aggregation and inorganic metal ions such as Cd(2+) or Pb(2+) sensitise human blood platelets to aggregating agents and this action is associated with the liberation of arachidonic acid and eicosanoid formation. The same mechanism is observed using human leukaemia cells (HL-60) when treated with MeHgCl or Et(3)PbCl. The fatty acid liberation within human platelets and HL-60 cells could only be inhibited with phospholipase A(2) inhibitors of different specificity.Preincubation of the cells with pertussis toxin reduces the activation induced by Et(3)PbCl to a great extent. The non-catalytic B subunit, that only mediates the binding of the toxin to the cell membranes, has no effect at all. When summarised, these results suggest that one possible mechanism for the stimulation of phospholipase A(2) by Et(3)PbCl functions via a G-protein dependent pathway.     

Synthesis of O＇-SiAION-BN Composite by Reaction Sintering

By using micron α-SisN4, SiO2, Al2O3 and h-BN as starting materials, O＇ -SiAION-BN （ Si2-z AlzO1 ＋z N2-z, z= 0. 3） composite was synthesized by reaction sintering. According to theoretical proportion ratio： n（ SiO2）/n（ α-Si3N4） = 1, the effects of two sintering aid composites, Y2O3 ＋ B2O3 and Y2O3 ＋ TiO2 at 1700℃ for 2h, were studied. The results indicate that Y2 O3 ＋ TiO2 as sintering aid can accelerate reaction sintering of O＇ -SiAION-BN more effectively than Y2O3 ＋ B2O3, and the relative density of the composites declined with the increase of BN addition （10%, 20% and 30% respectively）; XRD analysis found that excessive β-Si3N4 existed in the O＇ -SiAION-BN composite. Therefore, in order to get more pure O＇ -SiAION and BN phases in the composites ore SiO2 is needed. When Y2O3 ＋ TiO2 was used as sintering aid and addition of BN was 10%, the result of cross experiment on condition of A- n（SiO2）/n（α-Si3N4） was 1.05, 1.1 and 1.2; B-- addition of sintering aid was 2%, 4% and 6% ; C-- firing temperature was 1600℃, 1650℃ and 1700℃ ; D--soaking time was 1h, 2h and 3h, shows that the sintering properties were influenced by factors of firing temperature, soaking time, addition of sintering aid and n（ SiO2 ）/n（α-SisN4） in order of importance. In addition, the technical parameter A s B 3 C s D3 can achieve the highest relative density. Besides, using Pattern Recognition method, the optimized parameter range to form pure O＇ -SiAION and BN without β-Si3N4 remained was determined as Y 〉 1024X^2 - 230. 400X ＋ 11.088 （ X = 0. 9999A -0. 0006C - 0. 0163D, Y = 0. 0163A ＋ 0. 009B -0. 0014C ＋0. 9999D）.     

Synthesis of O’-SiAlON-BN Composite by Reaction Sintering

1 IntroductionO’-SiAlON is a solid solution made from Si2N2Oand Al2O3, and its crystal structure is similar toSi2N2O. Chemical formula of O’-SiAlON can be ex-pressed as Si2 -ZAlZO1 ZN2 -Z, which solid solubilitychanges depending on temperature, e.g. z …     

A Review of Ozone Systems Costs for Municipal Applications. Report by the Municipal Committee – IOA Pan American Group

Ozone has proven effective in improving water treatment plant performance, increasing customer satisfaction, and meeting increasingly stringent regulatory requirements. The benefits include disinfection; reducing chlorine disinfection by-products; micro-coagulation; enhanced filter performance; biological filtration; oxidation of iron, manganese, sulfide, taste- and odor-causing compounds, pharmaceuticals and personal care products (PPCPs), and endocrine disrupting compounds (EDCs). Despite the effectiveness of ozone in water treatment, a perception remains that ozone may be too expensive for consideration at many water treatment facilities. This paper presents an evaluation by the Municipal Committee of the International Ozone Association (IOA-MC) that aims to provide a realistic assessment of the current capital and operating costs of ozone in the North American water treatment practice. A general strategy is proposed for developing preliminary estimates of ozone capital and operating costs that could be used by engineers and/or owners for planning purposes. The information presented may benefit utilities, managers, and engineers engaged in the evaluation of treatment options.     

A Metabolomic Approach to Identifying Chemical Mediators of Mammal–Plant Interactions

Different folivorous marsupials select their food from different subgenera of Eucalyptus, but the choices cannot be explained by known antifeedants, such as formylated phloroglucinol compounds or tannins, or by nutritional quality. Eucalypts contain a wide variety of plant secondary metabolites so it is difficult to use traditional methods to identify the chemicals that determine food selection. Therefore, we used a metabolomic approach in which we employed ¹H nuclear magnetic resonance spectroscopy to compare chemical structures of representatives from the two subgenera and to identify chemicals that consistently differ between them. We found that dichloromethane extracts of leaves from most species in the subgenus Eucalyptus differ from those in Symphyomyrtus by the presence of free flavanones, having no substitution in Ring B. Although flavanoids are known to deter feeding by certain insects, their effects on marsupials have not been established and must be tested with controlled feeding studies.     

The Association of Two “Frustrated” Lewis Pairs by State-of-the-Art Quantum Chemical Methods

State-of-the-art quantum chemical methods have been applied to describe the association of two frustrated Lewis pairs (FLPs), B(C₆F₅)₃/PR₃ ( 1 : R=2,4,6-Me₃C₆H₂; 2 : R=CMe₃), with different steric demands of the base component. Interaction energies are calculated at the dispersion-corrected DFT, MP2 (second-order Møller-Plesset), and DLPNO-CCSD(T) (domain-based local pair natural orbital-coupled cluster, including single, double and perturbative triple excitations) levels of theory, combined with extended triple- or quadruple-ζ AO (atom-centered orbital) basis sets. Thermostatistical contributions to the free binding energy are calculated from harmonic frequencies at the efficient HF-3c (minimal basis Hartree-Fock with three corrections) level, while solvation effects in benzene are accounted for by the COSMO-RS (conductor-like screening model for realistic solvents) continuum model. Comparison with the recently measured experimental value for the free association energy of the FLP 1 reveals agreement between theory and experiment within the estimated error bars. The computed gas phase interaction energies for both FLPs are similar (about −13 kcal mol⁻¹), with only small variations (about ±3 kcal mol⁻¹) for various quantum chemical methods, when London dispersion interactions are accounted for properly. The association of the more “frustrated” FLP 1 is mainly driven by nondirectional dispersion forces, resulting in non-preferential orientations, which is in agreement with experimental results. On the other hand, in FLP 2 with the “smaller” base, the boron and phosphorous atoms face each other in the favored complex structure, indicating a weak P B donor-acceptor interaction. This conformation of 2 seems to be more suitable for small molecule (e.g., H₂) activations.     

Transformation of the Β-Triketone Pesticides Tembotrione and Sulcotrione by Reactions with Ozone: Kinetic Study,Transformation Products,Toxicity and Biodegradability

Rate constants between ozone and triketone herbicides, tembotrione and sulcotrione, were determined between pH 2 and 12. Both compounds are completely transformed within seconds by ozone under real water treatment conditions. A reaction pathway was proposed based on the identification of transformation products. Toxicity evaluation using Vibrio fischeri test showed that a residual toxicity remained even after degradation of the major by-products, but biodegradation significantly increased from 50% to 70% for molar ozone to pesticide ratios from 0 to 2. Thus, ozonation coupled with biological treatment would drastically reduce the risk associated to the presence of triketone herbicides.     

Measurement of the t→m and m→t transformations in Ce–TZP by dilatometry and impedance spectroscopy

The thermally induced t→m and m→t phase transformation of 9 mol% CeO₂-stabilized ZrO₂ with mean grain sizes varying from 1.2 to 2.7 μm has been characterized by dilatometry, XRD and impedance spectroscopy. XRD analysis indicates an increase in the volume fraction of the monoclinic phase from 0.69 to 0.89 with increasing grain size, which could be quantitatively correlated with the impedance spectra of the materials. Based on these findings, the m→t retransformation could be studied in situ by impedance spectroscopy in the temperature range from 20–350 °C. Depending on the grain size, the changes in the capacitive and resistive parts of the electrical impedance correlate well with the retransformation ranges obtained by dilatometry. Therefore, impedance spectroscopy is a useful analytical tool to study the transformation behaviour of zirconia ceramics.     

On modelling of surface tension of CMC-α-Fe2O3 nanoparticles by fuzzy-hybrid approach: A comparison study

Surface tension is one of the most important rheological parameters of nanoliquids. It influences the thermophysical and mass transfer properties of nanostructures. Accurate estimation of the surface tension from operating variables is critical for determining optimal production processes. However, the challenges of producing nanoparticles and measuring their properties introduce experimental errors in the data used for mathematical modelling. Crisp regression approaches provide adequate representation of the data, but they do not provide information about the experimental uncertainty. In this study, a fuzzy-hybrid approach is proposed for mathematical modelling of surface tension of carboxymethyl cellulose/chitosan-α-Fe₂O₃ nanoparticles. Then, the proposed model is compared with a crisp model from a previous study. Error analysis is conducted to validate the constructed fuzzy model. It is observed that the fuzzy-hybrid modelling approach has yielded significantly lower error values (a 60%–90% improvement in all error metrics on average), and thus, it is superior to the crisp approach. This study contributes to the subject of modelling rheological properties. It is shown that the fuzzy-hybrid approach has impressive potential to be utilized for modelling the rheological properties of nanostructures.     

Chemical Treatment of Silica Nanoparticles by Diethanolamine and γ-Glycidoxypropyltrimethoxysilane and Application of Modified Nanoparticles in Epoxy-Based Composites

In order to prepare silica nanoparticles that are more compatible with epoxy resin's media, nano SiO₂ was reacted with γ-glycidoxypropyltrimethoxysilane as a coupling agent in addition with diethanolamine. Formation of modified nano particles provided better dispersion condition in the epoxy-based nanocomposite. Thermal and mechanical characteristics of epoxy nanocomposites were investigated by several methods. A dramatic improvement was observed. Scanning electron microscope was applied to study the microscopic condition of nanocomposites in break surfaces.     

Chemical Recognition of Partner Plant Species by Foundress Ant Queens in Macaranga–Crematogaster Myrmecophytism

The partnership in the Crematogaster–Macaranga ant–plant interaction is highly species-specific. Because a mutualistic relationship on a Macaranga plant starts with colonization by a foundress queen of a partner Crematogaster species, we hypothesized that the foundress queens select their partner plant species by chemical recognition. We tested this hypothesis with four sympatric Macaranga species and their Crematogaster plant-ant species. We demonstrated that foundress Crematogaster queens can recognize their partner Macaranga species by contact with the surface of the seedlings, that they can recognize compounds from the stem surface of seedlings of their partner plant species, and that the gas chromatographic profiles are characteristic of the plant species. These findings support the hypothesis that foundress queens of the Crematogaster plant-ant species select their partner Macaranga species by recognizing nonvolatile chemical characteristics of the stem surfaces of seedlings.     

Oxidation of Herbicides in Groundwater by the Fenton Process: A Realistic Alternative for O3/H2O2 Treatment?

Oxidation with O₃/H₂O₂ and Fe²⁺/H₂O₂ are optional for the degradation of herbicides and pesticides in water. The choice of which process will be applied depends upon the degree of degradation of organic micropollutants and the process conditions related to the formation of oxidation by-products, and also on the total costs and the safety and reliability of the process. Under real conditions, atrazine and some phenylureaherbicides were oxidized with O₃/H₂O₂. Comparable experiments under conditions of different pH, iron and DOC content were performed with Fe²⁺/H₂O₂, in order to gain information on the influence of these parameters. The oxidation results of both processes as well as the formation of bromate as one of the oxidation by-products are described. It was found that 80% of atrazine and >99% of some phenylureaherbicides could be degraded with O₃/H₂O₂ at pH 7.8 (H₂O₂/O₃ ratio 3.7 g/g). Under these conditions, bromate was formed up to 5 μg/1. Comparable results were obtained with Fe²⁺/H₂O₂ at a pH value of 5.5, whereas the formation of bromate was kept below 0.2 μg/L.