α-Triazolylboronic Acids: A Promising Scaffold for Effective Inhibitors of KPCs

Boronic acids are known reversible covalent inhibitors of serine β-lactamases. The selectivity and high potency of specific boronates bearing an amide side chain that mimics the β-lactam's amide side chain have been advanced in several studies. Herein, we describe a new class of boronic acids in which the amide group is replaced by a bioisostere triazole. The boronic acids were obtained in a two-step synthesis that relies on the solid and versatile copper-catalyzed azide–alkyne cycloaddition (CuAAC) followed by boronate deprotection. All of the compounds show very good inhibition of the Klebsiella pneumoniae carbapenemase KPC-2, with K_i values ranging from 1 nM to 1 μM, and most of them are able to restore cefepime activity against K. pneumoniae harboring bla_KPC-2. In particular, compound 1 e , bearing a sulfonamide substituted by a thiophene ring, proved to be an excellent KPC-2 inhibitor (K_i=30 nM); it restored cefepime susceptibility in KPC-Kpn cells (MIC=0.5 μg/mL) with values similar to that of vaborbactam (K_i=20 nM, MIC in KPC-Kpn 0.5 μg/mL). Our findings suggest that α-triazolylboronates might represent an effective scaffold for the treatment of KPC-mediated infections.     

Synthesis and characterization of nanocomposites of thermoplastic polyurethane with both graphene and graphene nanoribbon fillers

Thermoplastic polyurethane (TPU) nanocomposites containing graphene and graphene nanoribbons were obtained by polymerizing 1,4-butanediol with two diisocyanates (namely, 1,6-hexane diisocyanate or isophorone diisocyanate), in which the nanofillers were previously dispersed. Raman spectroscopy and Transmission Electron Microscopy demonstrated the formation of few-layer graphene and graphene nanoribbons dispersed in the monomers. At variance to the methods commonly reported in literature, that used in this work consists of the direct exfoliation of graphite without any chemical manipulation. Apart from the obvious cost and ease advantages, the so-obtained graphene does not contain any carboxy or alkoxy groups formed during the exfoliation process, which, at variance, are typically present in the most commonly reported methods. This finding paves the way toward the large-scale production of graphene and its nanoribbons, which are considered even more interesting than graphene itself for many potential applications. The obtained nanocomposites show a peculiar thermal and rheological behavior due to the presence of the nanofillers and to their reinforcing or plasticizing effect exerted on the TPU matrices.     

Metal recovery from jarosite waste – A resin screening study

Work has been carried out screening hydrometallurgical resins for application in the valorization of industrially produced jarosite. Of the seven resins tested, anion exchange resins performed poorly for valuable metal recovery. Purolite S950+ and S957, along with a strong acid resin, show good extraction properties, but are selective for Fe³⁺ over the other (divalent) metals. Purolite S930+ (iminodiacetic acid-functionalized resin) demonstrates selectivity for Cu²⁺ over Fe³⁺, but poor selectivity for Ni²⁺, Zn²⁺, and Co²⁺. Dowex M4195 (bispicolylamine-functionalized resin) demonstrates promise for extracting metals of value away from a mixed metal pregnant liquor solution (PLS). A three-stage column-based recovery process is proposed for jarosite leachate treatment.     

Effects of the degree of undercooling on flow induced crystallization in polymer melts

This study investigates the coupled effects of mild shear flow and temperature on the crystallization behavior of two thermoplastic polymers, namely, an isotactic polypropylene and an isotactic poly(1-butene). Rheological experiments are used to measure the crystallization induction time under isothermal, steady shear flow conditions. The experimental results clearly show the effects of the degree of undercooling on flow-induced crystallization (FIC). As temperature decreases, the corresponding increase in chain orientation at a given shear rate leads to an absolutely faster crystallization. At the same time, however, a temperature decrease makes the flow-induced driving force to crystallization relatively less influent with respect to the intrinsic kinetics. A FIC model based on the Doi-Edwards micro-rheological theory is shown to successfully describe the quantitative details of the observed experimental behavior.     

Oligomeric Composition of Polyols From Fatty Acid Methyl Ester: The Effect of Ring‐Opening Reactants of Epoxide Groups

Commercial availability of fatty acid methyl ester (FAME) from palm oil targeted for biodiesel offers a good feedstock for the production of structurally well‐defined polyols for polyurethane applications. The effect of molecular weight (MW), odd and even carbon numbers, and the linear and branched structure reactants used in the ring‐opening reaction of epoxidized fatty acid methyl ester (E‐FAME) on the properties of polyols was investigated. Conversions of E‐FAME to PolyFAME polyols were confirmed by Fourier transform infrared analysis, oxirane oxygen content, and hydroxyl number. Gel permeation chromatography (GPC) calibrated against polyether polyols as a standard and vapor pressure osmometry were used for MW determination. GPC chromatograms of PolyFAME polyols clearly demonstrated the formation of oligomers during ring‐opening reactions. MW, and odd and even carbon numbers in a structure of linear diols and branched diol used in the syntheses of PolyFAME polyols did not have an effect on crystallinity, glass transition, or melt temperatures measured using Differential scanning calorimetry (DSC). PolyFAME polyols ring‐opened with water, methanol, and 1,2‐propanediol contained secondary hydroxyl groups, whereas PolyFAME polyols ring‐opened with linear diols contained a mixture of primary and secondary hydroxyl groups. It was found that the concentration of primary hydroxyl groups increased significantly by increasing the number of carbons from C2 to C3 in the linear diols. The viscosity of PolyFAME polyols also increased with the MW of linear diols used in the E‐FAME ring‐opening reaction. These findings would be beneficial for formulators in choosing the most cost effective polyols for polyurethane formulations.     

Formulation Optimization of a Palm-Based Nanoemulsion System Containing Levodopa

Response surface methodology (RSM) was utilized to investigate the influence of the main emulsion composition; mixture of palm and medium-chain triglyceride (MCT) oil (6%–12% w/w), lecithin (1%–3% w/w), and Cremophor EL (0.5%–1.5% w/w) as well as the preparation method; addition rate (2–20 mL/min), on the physicochemical properties of palm-based nanoemulsions. The response variables were the three main emulsion properties; particle size, zeta potential and polydispersity index. Optimization of the four independent variables was carried out to obtain an optimum level palm-based nanoemulsion with desirable characteristics. The response surface analysis showed that the variation in the three responses could be depicted as a quadratic function of the main composition of the emulsion and the preparation method. The experimental data could be fitted sufficiently well into a second-order polynomial model. The optimized formulation was stable for six months at 4 °C.     

Inhibitive and adsorption behaviour of carboxymethyl cellulose on mild steel corrosion in sulphuric acid solution

Chemical methods were used to assess the inhibitive and adsorption behaviour of carboxymethyl cellulose (CMC) for mild steel in H₂SO₄ solution at 30-60 °C. Results obtained show that CMC act as inhibitor for mild steel in H₂SO₄. The inhibition efficiency was found to increase with increase in CMC concentration but decreased with rise in temperature, which is suggestive of physical adsorption mechanism. The adsorption of the CMC onto the mild steel surface was found to follow Langmuir and Dubinin-Radushkevich adsorption isotherm models. The inhibition mechanism was further corroborated by the values of activation parameters obtained from the experimental data.     

Synthesis,Characterization, and Spectroscopic Analysis of NdxY1−xTiNbO6 Microwave Ceramics

Solid solutions of Nd_xY_1−xTiNbO₆ ceramics were prepared through the solid-state ceramic route. The materials were calcined at 1250°C and sintered in the range 1400–1550°C. The structure of the system was analyzed using the X-ray diffraction and vibrational spectroscopic analysis. The morphology and the sintering behavior of the samples were analyzed using scanning electron microscopy. The dielectric constant (ɛ_r), temperature coefficient of resonant frequency (τ_f), and the unloaded quality factor (Q_u) were measured in the microwave frequency region using the cavity resonator method. The ɛ_r and τ_f increased with an increase in the concentration of Nd in the solid solutions. Nearly zero temperature coefficient of resonant frequency was obtained for the Nd_0.6Y_0.4TiNbO₆ ceramic. Samples are of high quality factor and are useful for microwave applications.     

Thermal stability of metal-supported catalysts for reduction of cold-start emissions in a wood-fired domestic boiler

The aim of the present work is to develop a catalyst based on a mixture of manganese oxides and platinum supported on a metallic monolith for abatement of emissions from wood combustion, particularly during the cold-start phase. The activity and the thermal stability of the catalysts have been studied in the laboratory, before performing tests in a wood-stove. The effect of the hydrothermal treatment at 900°C on the adherence of the washcoat onto a metallic substrate was studied using scanning electronic microscope. It revealed well-adhering washcoat onto the metallic support due to the growth of the alumina whiskers during the treatment. The influence of the amount of washcoat, as well as the influence of the concentration of manganese oxides in it (Mn: 5 to 20 mol%/Al₂O₃) on the activity of fresh and hydrothermally-treated catalysts were studied. The activity tests were carried out using a mixture of carbon monoxide, naphthalene and methane in the presence of air, steam and carbon dioxide to resemble the flue gases from wood combustion. On the fresh catalysts, containing the same total amount of manganese, a high concentration of manganese oxides in the washcoat favoured the oxidation of carbon monoxide and naphthalene, whereas a lower concentration of manganese oxides in the washcoat gave higher activity for the oxidation of methane. An increased total amount of manganese oxides in the catalysts, which had the same amount of washcoat, resulted in an increase in activity for the oxidation of the three combustibles. After thermal treatment at 900°C for 270 h in steam, most of the manganese oxide catalysts were activated for the oxidation of carbon monoxide and naphthalene while only being slightly deactivated for the oxidation of methane. The addition of manganese oxides in the washcoat, however, lowers the temperature of the γ- to -alumina phase transformation. Platinum (0.5 mol%) was added to the manganese oxide (10 mol%) catalyst to improve its activity. A platinum catalyst was also tested for comparison. The platinum and the mixed catalysts showed similar activity for the oxidation of carbon monoxide and naphthalene, while the mixed catalysts were more active for the oxidation of methane. A similarly mixed MnO_x–Pt (10–0.5 mol%) catalyst supported on Al₂O₃ stabilised with 3% lanthanum, but at larger scale, was tested in a wood-stove. The possibility of pre-heating the catalyst during the start-up phase was studied. The tests revealed a strong decrease of the carbon monoxide and unburned hydrocarbons emissions during the start-up phase when the catalyst was pre-heated with hot air compared with no pre-heating or no catalyst.     

Sulfolobus solfataricus protein disulphide oxidoreductase: insight into the roles of its redox sites

Sulfolobus solfataricus protein disulphide oxidoreductase (SsPDO)contains three disulphide bridges linking residues C⁴¹XXC⁴⁴,C¹⁵⁵XXC¹⁵⁸, C¹⁷³XXXXC¹⁷⁸. To get information on the role playedby these cross-links in determining the structural and functionalproperties of the protein, we performed site-directed mutagenesison Cys residues and investigated the changes in folding, stabilityand functional features of the mutants and analysed the resultswith computational analysis. The reductase activity of SsPDOand its mutants was evaluated by insulin and thioredoxin reductaseassays also coupled with peroxiredoxin Bcp1 of S. solfataricus.The three-dimensional model of SsPDO was constructed and correlatedwith circular dichroism data and functional results. Biochemicalanalysis indicated a key function for the redox site constitutedby Cys155 and Cys158. To discriminate between the role of thetwo cysteine residues, each cysteine was mutagenised and thebehaviour of the single mutants was investigated elucidatingthe basis of the electron-shuffling mechanism for SsPDO. Finally,cysteine pK values were calculated and the accessible surfacefor the cysteine side chains in the reduced form was measured,showing higher reactivity and solvent exposure for Cys155.