Equimolar Conditions Research Articles

Determining Structures of Layer-by-Layer Spin-Coated Zinc Dicarboxylate-Based Metal-Organic Thin Films.

Thin films of crystalline solids with substantial free volume built from organic chromophores and metal secondary building units (SBUs) are promising for engineering new optoelectronic properties through control of interchromophore coupling. Zn-based SBUs are especially relevant in this case because they avoid quenching the chromophore's luminescence. We find that layer-by-layer spin-coating using Zn acetate dihydrate and benzene-1,4-dicarboxylic acid (H2BDC) and biphenyl-4,4'-dicarboxylic acid (H2BPDC) linkers readily produces crystalline thin films. However, analysis of the grazing-incidence wide-angle X-ray scattering (GIWAXS) data reveals the structures of these films vary significantly with the linker, and with the metal-to-linker molar ratio used for fabrication. Under equimolar conditions, H2BPDC creates a type of structure like that proposed for SURMOF-2, whereas H2BDC generates a different metal-hydroxide-organic framework. Large excess of Zn2+ ions causes the growth of layered zinc hydroxides, irrespective of the linker used. Density functional theory (DFT) calculations provide structural models with minimum total energy that are consistent with the experimentally observed diffractograms. In the broader sense, this work illustrates the importance in this field of careful structure determination, e. g., by utilizing GIWAXS and DFT simulations to determine the structure of the obtained crystalline metal-organic thin films, such that properties can be rationally engineered and explained.

Large-scale computational screening of metal–organic frameworks for D2/H2 separation

Deuterium (D 2 ) is one of the important fuel sources that power nuclear fusion reactors. The existing D 2 /H 2 separation technologies that obtain high-purity D 2 are cost-intensive. Recent research has shown that metal–organic frameworks (MOFs) are of good potential for D 2 /H 2 separation application. In this work, a high-throughput computational screening of 12,020 Computation-Ready Experimental MOFs is carried out to determine the best MOFs for hydrogen isotope separation application. Meanwhile, the detailed structure-performance correlation is systematically investigated with the aid of machine learning. The results indicate that the ideal D 2 /H 2 adsorption selectivity calculated based on Henry coefficient is strongly correlated with the 1/Δ AD feature descriptor; that is, inverse of the adsorbility difference of the two adsorbates. Meanwhile, the machine learning (ML) results show that the prediction accuracy of all the four ML methods is significantly improved after the addition of this feature descriptor. In addition, the ML results based on eXtreme Gradient Boosting model also revealed that the 1/Δ AD descriptor has the highest relative importance compared to other commonly-used descriptors. To further explore the effect of hydrogen isotope separation in binary mixture, 1,548 MOFs with ideal adsorption selectivity greater than 1.5 are simulated at equimolar conditions. The structure-performance relationship shows that high adsorption selectivity MOFs generally have smaller pore size (3–5 Å, 1 Å=0.1 nm) and lower surface area. Among the top 200 performers, the materials mainly have the sql, pcu, cds, hxl, and ins topologies. Finally, three MOFs with high D 2 /H 2 selectivity and good D 2 uptake are identified as the best candidates, of all which had one-dimensional channel pore. The findings obtained in this work may be helpful for the identification of potentially promising candidates for hydrogen isotope separation.

New mescaline-related N-acylhydrazone and its unsubstituted benzoyl derivative: Promising metallophores for copper-associated deleterious effects relief in Alzheimer's disease

Alzheimer's disease (AD) is related to the presence of extracellular aggregated amyloid-β peptide (Aβ), which binds copper(II) with high affinity in its N-terminal region. In this sense, two new 1-methylimidazole-containing N-acylhydrazonic metallophores, namely, X1TMP and X1Benz, were synthesized as hydrochlorides and characterized. The compound X1TMP contains the 3,4,5-trimethoxybenzoyl moiety present in the structure of mescaline, a natural hallucinogenic protoalkaloid that occurs in some species of cacti. Single crystals of X1Benz, the unsubstituted derivative of X1TMP, were obtained. The experimental partition coefficients of both compounds were determined, as well as their apparent affinity for Cu2+ in aqueous solution. Ascorbate consumption assays showed that these N-acylhydrazones are able to lessen the production of ROS by the Cu(Aβ)-system, and a short-time scale aggregation study, measured through turbidity and confirmed by TEM images, revealed their capacity in preventing Aβ fibrillation at equimolar conditions in the presence and absence of copper. 1H15N HSQC NMR experiments demonstrated a direct interaction between Aβ and X1Benz, the most soluble of the compounds. The Cu2+ sequestering potential of this hydrazone towards Aβ was explored by 1H NMR. Although increasing amounts of X1Benz were unexpectedly not efficient at removing the metal-induced perturbations in Aβ backbone amides, the broadening effects observed on the compound's signals indicate the formation of a ternary Aβ‑copper-X1Benz species, which can be responsible for the observed ROS-lessening and aggregation-preventing activities. Overall, the N-acylhydrazones X1TMP and X1Benz have shown promising prospects as agents for the treatment of AD.

A Prediction for the Conversion Performance of H2S to Elemental Sulfur in an Ionic-Liquid-Incorporated Transition Metal Using COSMO-RS

In the present study, the conversion performance of hydrogen sulfide (H2S) to elemental sulfur in ionic-liquid-incorporated transition metals (ILTMs) is predicted using a conductor-like screening model for realistic solvents (COSMO-RS). The predictions were made via the establishment of a correlation between the conversion performance and solubility of H2S in ionic liquids (ILs). All molecules involved were optimized at the DFT/TZVP/M06 computational level and imported on the COSMOtherm program at equimolar conditions. For validation purposes, the solubility of ILs was predicted at 1 bar pressure. Simple regression analysis was used to establish a relationship between the solubility and conversion performance of H2S. The results indicate that the solubility prediction of ILs is accurate (R2 = 93.40%) with a p-value of 0.0000000777. Additionally, the conversion performance is generally found to be dependent on the solubility value. Furthermore, 1-butyl-3-methylimidazolium chloride [bmim][Cl] was chosen as the base IL for incorporating the transition metal, owing to its solubility and selectivity to H2S. The solubility trend of ILTMs is found to follow the following order: [bmim][NiCl3] > [bmim][FeCl4] > [bmim][CoCl3] > [bmim][CuCl3]. According to the viscosity measurements of ILTMs, [bmim][NiCl3] and [bmim][FeCl4] exhibited the highest and lowest viscosity values, respectively. Therefore, [bmim][FeCl4] is a promising ILTM owing to its higher solubility and low viscosity for the application studied.

Understanding butanol recovery and coupling effects in pervaporation of Acetone-Butanol-Ethanol (ABE) solutions: A modelling and experimental study

The sustainable downstream recovery of bio-butanol from multicomponent fermentation broths through organophilic pervaporation is still challenged, in part, by a limited knowledge on the effect of by-products ethanol and acetone on final butanol recovery. This study therefore involves an experimental and theoretical inquisition on extraction of butanol and coupling effects involved between the various components. A commercial polydimethylsiloxane membrane was used for pervaporation of binary and ternary model solutions. Modified solution-diffusion based models were then customized to emulate temperature and concentration dependence of permeation. Membrane performance and coupling were found to be functions of the concentration of both organic components involved as well as temperature of the feed. The membrane was observed to be most intrinsically selective towards butanol in all systems. In ternary mixtures, the presence of second organic component positively enhanced coupling effects in favor of butanol recovery but lead to a decreased membrane plasticization by butanol itself. Ultimately permeance based coupling factors revealed that membrane permselectivity towards butanol was best benefited by coupling at lower butanol to ethanol/acetone concentration ratios in feed. In contrast, minimal coupling was experienced at equimolar conditions and multicomponent pervaporation in such cases could be satisfactorily modelled as binary mixture separation.

Mesoporous silica-encaged ultrafine ceria–nickel hydroxide nanocatalysts for solar thermochemical dry methane reforming

Reforming of methane to produce synthesis gas for the Fischer–Tropsch process provides an alternative to fossil fuels. Silica-encaged ceria–nickel hydroxide catalysts were produced by an in situ synthesis method to obtain ultrafine bimetallic species dispersed evenly within the mesoporous silica matrix. Dry reforming and reduction-oxidation cycling was undertaken with the materials. Catalysts with high content of nickel showed good activity during dry reforming, with conversions rates close to equilibrium in equimolar conditions. Insignificant deactivation of the catalysts was observed over 5 h and 50 h of reaction at 900 °C. Syngas production via reduction–oxidation cycling was shown to be insignificant as compared to continuous catalytic reforming.

Perturbative Cauchy theory for a flux-incompressible Maxwell-Stefan system

<p style='text-indent:20px;'>Recently, the authors proved [<xref ref-type="bibr" rid="b2">2</xref>] that the Maxwell-Stefan system with an incompressibility-like condition on the total flux can be rigorously derived from the multi-species Boltzmann equation. Similar cross-diffusion models have been widely investigated, but the particular case of a perturbative incompressible setting around a non constant equilibrium state of the mixture (needed in [<xref ref-type="bibr" rid="b2">2</xref>]) seems absent of the literature. We thus establish a quantitative perturbative Cauchy theory in Sobolev spaces for it. More precisely, by reducing the analysis of the Maxwell-Stefan system to the study of a quasilinear parabolic equation on the sole concentrations and with the use of a suitable anisotropic norm, we prove global existence and uniqueness of strong solutions and their exponential trend to equilibrium in a perturbative regime around any macroscopic equilibrium state of the mixture. As a by-product, we show that the equimolar diffusion condition naturally appears from this perturbative incompressible setting.</p>

Disulfides as mercapto-precursors in nucleophilic ring opening reaction of polymeric epoxides: establishing equimolar stoichiometric conditions in a thiol-epoxy 'click' reaction.

The base-catalyzed oxirane ring opening reaction with thiol nucleophiles is frequently employed for post-polymerization modification of polymeric glycidyl scaffolds. Due to various beneficial attributes, it is often referred to as a 'click' reaction. However, the tendency of the free thiol molecules to undergo oxidative dimerization through the formation of a disulfide bond under ambient conditions results in partial consumption of the sulfhydryl precursors. Therefore, an excess of the thiol precursors is typically used to counterbalance the side-reaction. This violates the equimolar stoichiometry conditions required for 'click' reactions in the context of polymer synthesis. Here, we show that commercially available disulfides can be used to generate the necessary thiolate nucleophiles in situ through the reduction of the SS-bond with sodium borohydride. Such activation strategy eliminates the sulfhydryl oxidation mechanism to disulfides and ensures that the post-synthesis functionalization of epoxy polymers can be performed under equimolar 'click' conditions.

Ion foam flotation of neodymium: From speciation to extraction

Ion foam flotation of neodymium (Nd3+) was studied using a pH-sensitive surfactant, the nonaoxyethylene oleylether carboxilic acid, which has the peculiarity of remaining water soluble in the presence of multivalent cations. The flotation efficiency factors were determined as a function of pH and for two different (surfactant/Nd) molar ratios, equimolar (1/1) or stoichiometric (3/1). An opposite trend was observed, showing low (<30%) and high (>95%) ion extraction yields respectively for equimolar and stoichiometric conditions. We show that i) the determination of the surfactant/Nd speciation solutions is essential to understand the very different behaviors between equimolar and stoichiometric experiments and ii) the ion extraction process is mainly driven by interfacial mechanisms. In terms of applications we show that once the ion extraction is efficiently performed for pH values between 5 and 7, the recovery of the surfactant is possible by performing a second flotation process at lower pH (2.5). Moreover ion foam flotation using this pH sensitive surfactant was shown to be highly efficient for the removal of traces and ultra-traces of metal ions. Therefore the results presented here suggest that the development of a continuous process, for example in the context of waste water treatment, is feasible.

PEGylation and Dimerization of Expressed Proteins under Near Equimolar Conditions with Potassium 2-Pyridyl Acyltrifluoroborates.

The covalent conjugation of large, functionalized molecules remains a frontier in synthetic chemistry, as it requires rapid, chemoselective reactions. The potassium acyltrifluoroborate (KAT)–hydroxylamine amide-forming ligation shows promise for conjugations of biomolecules under aqueous, acidic conditions, but the variants reported to date are not suited to ligations at micromolar concentrations. We now report that 2-pyridyl KATs display significantly enhanced ligation kinetics over their aryl counterparts. Following their facile, one-step incorporation onto the termini of polyethylene glycol (PEG) chains, we show that 2-pyridyl KATs can be applied to the construction of protein–polymer conjugates in excellent (>95%) yield. Four distinct expressed, folded proteins equipped with a hydroxylamine could be PEGylated with 2–20 kDa 2-pyridyl mPEG KATs in high yield and with near-equimolar amounts of coupling partners. Furthermore, the use of a bis 2-pyridyl PEG KAT enables the covalent homodimerization of proteins with good conversion. The 2-pyridyl KAT ligation offers an effective alternative to conventional protein–polymer conjugation by operating under aqueous acidic conditions well suited for the handling of folded proteins.

Mixed micelles of oppositely charged poly(N-isopropylacrylamide) diblock copolymers

Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N-isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two-dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D 1H NMR NOESY), dynamic light scattering, and small angle X-ray scattering measurements. Well-defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D 1H NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1457–1469

Effects of gadolinium-based contrast agent concentrations (0.5 M or 1.0 M) on the diagnostic performance of magnetic resonance imaging examinations: systematic review of the literature.

Background To date there is no agreement as to what is the optimal concentration for gadolinium-based contrast agents (GBCAs). Purpose To assess whether diagnostic performance differences exist between 0.5 M and 1.0 M GBCAs used for magnetic resonance imaging (MRI). Material and Methods A PubMed literature search identified 21 clinical studies published between 2005 and 2013 which evaluated the diagnostic efficacy of both types of GBCAs. Study design, type of procedure, GBCA administration mode, imaging performances, impact on patient management, study limitations, and biases were analyzed. No statistical test was performed on pooled data. Results Sixteen comparative and five non-comparative studies were analyzed, involving 2183 patients who underwent MRI procedures for various indications. In 67% of the studies, 0.5 M and 1.0 M GBCAs were injected at equimolar gadolinium amounts per kg body weight. Only 33% applied the same molar flow rate for delivery of the GBCAs. No significant differences between GBCAs were reported for 23 out of 27 qualitative endpoints (mainly image quality, lesion, and vessel visualization) and 29 out of 40 quantitative endpoints. Three out of four studies with non-equimolar delivery rates showed better contrast-to-noise and signal-to-noise ratios for 1.0 M gadobutrol, without showing an impact on diagnostic performance. Methodological biases were identified in several studies impairing the interpretation of comparisons. Conclusion Imaging differences between 0.5 M and 1.0 M GBCAs were essentially observed under non-equimolar delivery rates. However, they did not result into greater diagnostic efficacy when performed under equimolar conditions.

Performance of basic mixed oxides for aqueous-phase 5-hydroxymethylfurfural-acetone aldol condensation

This paper is focused on the study of the catalytic activity of MgAl and MgZr mixed oxides in the aqueous-phase aldol-condensation of 5-hydroxymethylfurfural (5-HMF) and acetone. The experiment is carried out in a stirred batch reactor. It considers the effect of reaction conditions (namely temperature, reactant concentration and catalyst loading) on catalyst performance. It also looks into the stability of the materials (catalyst reusability in subsequent reaction cycles), as well as into the development and validation of a simplified kinetic model. MgZr catalyst provides the best yield to aldol condensation products, especially for the formation of the second adduct (C15). This material high activity results from its optimum acid/basic sites ratio, mainly medium-strength. Retroaldolization, promoted by stronger basic sites, was identified as an important side-reaction, whereas adsorption effects and oligomerization reactions (evaluated using thermogravimetric analysis and temperature-programmed oxidation of the spent catalysts) determine catalyst stability. Concerning the effect of operation conditions, the best results were obtained working with 0.5g of MgZr, at 323K. The highest C15 yield was reached with 5-HMF excess (2:1) (16.1%), whereas the whole yield is maximized at equimolar conditions (37%).

Kinetic Modeling of Ethylene Glycol Monoesterification

ABSTRACTThe monoesterification of ethylene glycol under isothermal conditions was conducted using benzoic acid in methane‐sulfonic acid/Al2O3 as a catalyst. Using this reagent, glycol was selectively monoesterified with high yield. The reactions were performed within an automated batch reactor under equimolar conditions, constant rotational frequency of the stirrer, and within the temperature range from 65 to 85°C. The rate constant related to this reaction and to the corresponding reverse reaction, activation energy, and preexponential factor was derived from experimental data. It has been concluded that under these conditions the formation of dibenzoate was successfully prevented.

Macromolecular surface design: photopatterning of functional stable nitrile oxides.

The efficient trapping of photogenerated thioaldehydes with functional shelf-stable nitrile oxides in a 1,3-dipolar cycloaddition is a novel and versatile photochemical strategy for polymer end-group functionalization and surface modification under mild and equimolar conditions. The modular ligation in solution was followed in detail by electrospray ionization mass spectrometry (ESI-MS). X-ray photoelectron spectroscopy (XPS) was employed to analyze the functionalized surfaces, whereas time-of-flight secondary-ion mass spectrometry (ToF-SIMS) confirmed the spatial control of the surface functionalization using a micropatterned shadow mask. Polymer brushes were grown from the surface in a spatially confined regime by surface-initiated atom transfer radical polymerization (SI-ATRP) as confirmed by TOF-SIMS, XPS as well as ellipsometry.

Pure hydrogen-generating “doped” sodium hydrazinidoborane

In this work, we present the performance of “doped” sodium hydrazinidoborane NaN2H3BH3 as hydrogen carrier. It was prepared by ball-milling hydrazine borane N2H4BH3 and sodium hydride NaH in cold conditions, with an excess of 5 wt% of NaH. Such an excess is essential for the generation of pure hydrogen, i.e. free from the undesired by-products NH3 and N2H4 under heating, whereas for a material prepared in equimolar conditions non negligible amounts of ammonia NH3 are detected. Our main results, i.e. characterization of “doped” sodium hydrazinidoborane, dehydrogenation experiments, analysis of the purity of H2, and characterization of the solid residue, are presented and discussed herein. The potential of “doped” sodium hydrazinidoborane as solid-state chemical hydrogen storage material is finally discussed.

Study of the recovery of phosphorus from struvite precipitation in supernatant line from anaerobic digesters of sludge

The goal of this work was to study the effective recovery of phosphorus from the supernatant of anaerobic digestion of sewage sludge by precipitation as struvite. The formation of struvite is envisioned as a promising process for nutrient removal and subsequent recovery, thus providing a strong incentive for its implementation, since the sewage is a renewable source of phosphorus. Struvite precipitation was obtained by controlled addition of Mg(OH)2 or MgCl2. We evaluated the removal of ammonia and phosphate under equimolar conditions of magnesium and magnesium stoichiometric excess of 100–200% relative to the limiting reagent, under a stirring speed of 300 rpm at pH 8, 9 and 10. MgCl2 in 1:1 molar ratio to phosphate, considering the stoichiometric ratio [PO43−]:[NH4+] of 0.13 (presented by raw sample). The results show the best cost–benefit ratio, removal of phosphate of 90.6% and ammonium removal of 29%, resulting in 23 mg l−1 PO43− and 265 mg l−1 NH4+ concentration in effluent.

Study of the recovery of phosphorus from struvite precipitation in supernatant line from anaerobic digesters of sludge

The goal of this work was to study the effective recovery of phosphorus from the supernatant of anaerobic digestion of sewage sludge by precipitation as struvite. The formation of struvite is envisioned as a promising process for nutrient removal and subsequent recovery, thus providing a strong incentive for its implementation, since the sewage is a renewable source of phosphorus. Struvite precipitation was obtained by controlled addition of Mg(OH)2 or MgCl2. We evaluated the removal of ammonia and phosphate under equimolar conditions of magnesium and magnesium stoichiometric excess of 100 to 200% relative to the limiting reagent, under a stirring speed of 300 rpm at pH 8, 9 and 10. The best condition was MgCl2 in 1:1 molar ratio to phosphate, considering the stoichiometric ratio [PO4(3-)]:[NH4(+)] of 0.13 (presented by raw sample). The results show the best cost-benefit ratio, removal of phosphate of 90.6% and ammonium removal of 29%, resulting in 23 mg l(-1) PO4(3-) and 265 mg l(-1) NH4(+) concentration in effluent.

Amphiphilic Properties of Dodecylammonium Chloride/4‐(1‐Pentylheptyl) Benzene Sodium Sulfonate Aqueous Mixtures and Study of the Catanionic Complex

AbstractSurfactants are often used in supramolecular chemistry, due to their ability to self‐organize. Surfactant molecules aggregate spontaneously and reversibly to adopt a defined intermolecular arrangement. In this work, general phase behavior, adsorption and association in aqueous mixtures of dodecylammonium chloride, DACl and sodium 4‐(1‐pentylheptyl) benzenesulfonate, NaDBS, were studied by a combination of techniques including surface tension and conductivity measurements, light scattering and optical microscopy. The strong synergistic properties of the system were brought out with the Regular Solution Theory. Various colloidal objects are observed in wide range of composition: conventional small vesicles, large giant multilamellar or multivesicular vesicles. An excess of NaDBS provides extremely large tubular and elongated multilamellar vesicles. The new catanionic 1:1 complex, dodecylammonium‐4‐(1‐pentylheptyl) benzenesulfonate, formed in the equimolar conditions is a result of intramolecular charge neutralization. The thermal properties of this solid compound were examined by thermal polarizing microscopy, differential scanning calorimetry, and X‐ray diffraction. The most probable ion‐pair amphiphilic cluster of the crystal smectic phase, at room temperature, consists of ionic groups formed in ordered layers with dodecyl chains packed into somewhat disordered layers, tilted to the layer plane.

Efficient [2+2] photocycloadditions under equimolar conditions by employing a continuous UV-flow reactor

Abstract The [2 + 2] photocycloaddition between maleimide and various alkenes was optimized in a simple custom-made UV flow reactor. While complete maleimide conversion is only achieved with excesses of at least 10 eq. of alkene and reaction times of 12–24 h in batch, complete reactions with yields in the range >98% could be obtained in 5 min in the flow reactor under strictly equimolar conditions. Functional alkenes carrying allyl, alcohol, amine and ether moieties were successfully conjugated in good yields under optimized reaction conditions. As is demonstrated, the reaction gains in flow most characteristics of a high-efficient reaction, making the process highly valuable for upscaled synthesis of maleimide conjugates.