Condensation Step Research Articles

Foam Silica Films Synthesized by Calcium Chloride-Assisted Emulsification

The development of porous films with an accessible high specific surface area is important for designing new adsorbents, sensors, or catalyst supports. Here, we describe a simple method to prepare a silica foam coating using a calcium chloride-assisted evaporation-induced emulsification method. An alcoholic silica sol containing calcium chloride and a poly(ethylene oxide)-based polymer is deposited on a substrate by dipping. The evaporation of the alcohol induces a phase separation between the silica-rich phase and the calcium-rich one. The size of the droplets increases via a coalescence process until the gelation of the sol, which determines the final pore size between 100 nm and 3 μm. Thermal analysis and monitoring of droplet evaporation confirm that the departure of the solvent is delayed by the presence of calcium chloride in the sol. The influence of the nature of the polymer on the porosity is discussed. The use of a block copolymer such as the Pluronic F-127, which strongly stabilizes the emulsion, allows to reach a low pore size (400 nm), while on the contrary, we propose to use a short poly(ethylene glycol) (PEG) such as PEG-400, which weakly stabilizes it, leading to larger pores (2-3 μm). Furthermore, we show that the addition of a zirconium salt (ZrOCl2·8H2O) to the silica sol accelerates the condensation step of the silica and leads to the decrease in the pore size.

Improvement of condensation step of water vapor in solar desalination of seawater and the development of three-ply membrane system

Seawater desalination using sunlight is a sustainable freshwater production, which contributes the solution of global water shortage. This solar desalination has generally three steps; conversion of solar energy to heat, vaporization of seawater by the heat and condensation of water vapor to form freshwater. We have studied a seawater desalination using two-ply membrane system, where a dye modified hydrophilic membrane is put on a hydrophobic one. When seawater loaded on the system is exposed to sunlight, desalinated water is obtained under the hydrophobic membrane by the membrane permeation of water vapor. This paper reports the improvement of the third step, condensation of water vapor, of our process, which is indispensable for the efficient production of freshwater. When Al petri dish, heatsink and cooling plate were equipped under the two-ply membrane system, the recovery of the vaporized water was remarkably improved by promoting the condensation of water vapor using those devices. Next, capillary action with hydrophilic membrane wick was applied for long term operation of the process with continuous supply of seawater. Finally, a three-ply membrane system, where black light-absorbing sheet, hydrophilic membrane wick and PTFE membrane were stacked, was found to be effective for the mass production of freshwater.

One-pot amination of cyclohexanone-to-secondary amines over carbon-supported Pd: Unraveling the reaction mechanism and kinetics

• Catalytic transformation of cyclohexanone into secondary amines. • A reaction map for the catalytic amination of cyclohexanone is proposed. • A kinetic model describing the amination of cyclohexanone is elucidated. • The effect of temperature, reactant concentrations and H 2 -equivalents is assessed. The liquid phase amination of the cyclohexanone (CyO) with aniline (PhNH 2 ) was studied on a Pd/C catalyst using NaCO 2 H as a H-donor. Catalytic tests were performed in batch reactors by varying reactant concentrations (0, 0.1, 0.2 and 0.4 mol/L), the temperature (80–160 °C) and H 2 -equivalents availability (0, 2 and 4 H 2 -equivalents with respect to CyO). The results indicate that, the use of NaCO 2 H barely affect the reactivity (measured as initial reaction rate) while it does influence the selectivity to secondary amines. This effect was ascribed to the limited effectivity of the H 2 transfer, which was controlled by the water formed after the condensation of the CyO with the PhNH 2 , hydrogen solubility in toluene, and the mass transfer from the liquid to the catalyst surface. The experimental observations were consistent with a multi-step mechanism consisting in: a first step of condensation of the ketone and the amine to form an imine, followed by the disproportionation of the imine into secondary amines. The kinetic measurements at initial rate conditions were well interpreted by a Langmuir Hinshelwood (L-H) kinetic model, which suggest that the surface reaction to form the intermediary imine is the rate limiting step (R.L.S).

Crystal structures of hydroxymethylbilane synthase complexed with a substrate analog: a single substrate-binding site for four consecutive condensation steps.

Hydroxymethylbilane synthase (HMBS), which is involved in the heme biosynthesis pathway, has a dipyrromethane cofactor and combines four porphobilinogen (PBG) molecules to form a linear tetrapyrrole, hydroxymethylbilane. Enzyme kinetic study of human HMBS using a PBG-derivative, 2-iodoporphobilinogen (2-I-PBG), exhibited noncompetitive inhibition with the inhibition constant being 5.4 ± 0.3 µM. To elucidate the reaction mechanism of HMBS in detail, crystal structure analysis of 2-I-PBG-bound holo-HMBS and its reaction intermediate possessing two PBG molecules (ES2), and inhibitor-free ES2 was performed at 2.40, 2.31, and 1.79 Å resolution, respectively. Their overall structures are similar to that of inhibitor-free holo-HMBS, and the differences are limited near the active site. In both 2-I-PBG-bound structures, 2-I-PBG is located near the terminus of the cofactor or the tetrapyrrole chain. The propionate group of 2-I-PBG interacts with the side chain of Arg173, and its acetate group is associated with the side chains of Arg26 and Ser28. Furthermore, the aminomethyl group and pyrrole nitrogen of 2-I-PBG form hydrogen bonds with the side chains of Gln34 and Asp99, respectively. These amino acid residues form a single substrate-binding site, where each of the four PBG molecules covalently binds to the cofactor (or oligopyrrole chain) consecutively, ultimately forming a hexapyrrole chain. Molecular dynamics simulation of the ES2 intermediate suggested that the thermal fluctuation of the lid and cofactor-binding loops causes substrate recruitment and oligopyrrole chain shift needed for consecutive condensation. Finally, the hexapyrrole chain is hydrolyzed self-catalytically to produce hydroxymethylbilane.

A dual responsive probe based on bromo substituted salicylhydrazone moiety for the colorimetric detection of Cd2+ ions and fluorometric detection of F‒ ions: Applications in live cell imaging

A dual responsive probe based on bromo substituted salicylhydrazone moiety for the colorimetric detection of Cd2+ ions and fluorometric detection of F‒ ions: Applications in live cell imaging

Effect of Pore Size Distribution on Capillary Condensation in Nanoporous Media

The occurrence of capillary condensation is often ignored in many naturally occurring nanoporous media, such as shale rock, simply because their isotherms do not adhere to the prescribed shapes presented in the literature. In particular, it is apparent from the literature that most shale isotherms do not display a clear capillary condensation step, which is commonly observed for much simpler adsorbents, such as MCM-41. We contend that the absence of this step from the isotherms for natural adsorbents is not due to the absence of nanoconfinement-induced phase behavior. Rather, it is due to the broad pore size distribution characteristic of such materials. By mechanically mixing different sizes of MCM-41 together and measuring isotherms for propane and n-butane in them at a variety of temperatures, we show that phase behavior in different pore sizes is additive and suppresses the commonly observed appearance of capillary condensation. By comparing the isotherms in the mixtures of MCM-41 to those measured in single pore sizes of MCM-41, we develop correlations, using the Lorentzian function, that make the determinations of porosity and fluid density from the mixture isotherms straightforward.

Effect of zinc substitution on the growth morphology of ZnO-CuO tenorite solid solutions

ZnxCu1−xO nanoparticles were synthesized by microwave heating of hydroxide mixtures to form single-phase tenorite crystallites with compositions of up to x ≈ 0.12 zinc concentration, after which formation of wurtzite ZnO was also observed. The lattice parameters, determined by Reitveld refinement of the x-ray diffraction data, showed a linear relationship in zinc concentration, a phenomenon known as Vegard’s Law which is generally taken as an indication of homogeneous cation distribution. Substitution of zinc for copper in the tenorite structure affects the particle growth kinetics, which results in a morphological change from plate-like in pure CuO to smaller, needle-like crystallites for compositions emerging at approximately Zn0.025Cu0.975O. The needle-like particles form as a result of imperfect oriented attachment in two dimensions, with the third dimension controlled by the initial hydroxide condensation step. When the concentration of zinc is increased to x = 0.075, imperfect oriented attachment occurs in three dimensions, which yields particles with flower morphologies.

B2O3 katkılı TiO2 ve katkısız ince filmlerin yüzey özelliklerinin Sol-jel yöntemi ile karşılaştırılması

Titanium dioxide (TiO2) is a widely used material in nanotechnological applications. Especially in photocatalytic and optical applications, TiO2 thin films are an indispensable material. Metal-doped thin films are of interest to researchers for the development of these properties. In this study, the effect of boron oxide (B2O3) additive on surface properties in coating TiO2 thin films on soda-lime glasses was investigated. In the experimental study, alkoxide solutions with a source of boron and titanium were used. TiO2 sol was prepared with Sol-Gel method. In addition, the sol was prepared by adding Triisopropyl borate. Condensation and polymerization steps were completed in acid catalysis and the solution was obtained. In the home-made dip coater device, the solution is coated on the surface. The surface properties of dried thin films have been characterized by applying morphological analysis and contact angle measurement tests. As a result, the B2O3-doped TiO2 coated surface was found to have better hydrophilic properties than the non-doped TiO2 surface. It has been observed that the boron oxide-doped TiO2 coated glass material has a superhydrophilic value.

Highly efficient and selective one-pot tandem imine synthesis via amine-alcohol cross-coupling reaction catalysed by chromium-based MIL-101 supported Au nanoparticles

One-pot tandem synthesis of imines from alcohols and amines is regarded as an effective, economic and green approach under mild conditions. In this work, Au nanoparticles (NPs) dispersed on MIL-101 (Au/MIL-101) were demonstrated as highly active and selective bifunctional heterogeneous catalyst for production of various imine derivatives with excellent yields, via amine-alcohol cross-coupling reaction at 343 K in an open flask under an Ar atmosphere. Various physicochemical techniques, including inductively coupled plasma optical emission spectroscopy (ICP-OES), powder X-ray diffraction (P-XRD), X-ray photoelectron spectroscopy (XPS) transmission electron microscopy (TEM) and N2 adsorption-desorption, were used to characterize of the Au/MIL-101 catalyst. The obtained bifunctional catalyst is highly active and selective towards one-pot imine formation and exhibited the highest TOF (30.15-51.47 h−1) among all the ever-reported MOF-supported Au catalysts. The reaction mechanism of the imine formation from alcohol and amine over Au/MIL-101 catalyst was proposed. Mechanism experiment results demonstrate that Au NPs highly effective in activating oxidation of benzyl alcohol to benzaldehyde while the Lewis acid sites on MIL-101 catalyzed the second condensation step without interfering with the oxidation step. As a result, the excellent catalytic performance of Au/MIL-101 can be ascribed to the synergistic effect between Au NPs with Lewis acid sites in MIL-101.

Topography of the free energy landscape of Claisen-Schmidt condensation: solvent and temperature effects on the rate-controlling step.

Recent studies have found that hydroxide elimination and the C[double bond, length as m-dash]C bond formation step in base-promoted aldol condensation have a strong influence on the overall rate of the reaction, in contrast to the well-accepted first enolization or C-C bond formation step. Here, applying theoretical models to the prototypical reaction of chalcone formation, the complete free energy profile of Claisen-Schmidt condensation is assessed, revealing how a protic solvent and a slight increase in temperature can induce the second enolization as the rate-controlling step (RCS). It is also observed: i) the nonexistence of a step with a much higher energetic barrier than the others, making the concept of RCS debatable; and ii) that the overall inverse kinetic isotopic effect does not exclude second enolization as a RCS in protic continuum medium. We expect that these results can expand the understanding of the decisive role of physicochemical factors on the choose of the RCS in the aldol condensation.

Synthesis of quinolines via sequential addition and I2-mediated desulfurative cyclization.

An efficient one-pot approach for the synthesis of quinolines from o-aminothiophenol and 1,3-ynone under mild conditions is disclosed. With the aid of ESI-MS analysis and parallel experiments, a three-step mechanism is proposed—a two-step Michael addition–cyclization condensation step leading to intermediate 1,5-benzothiazepine catalyzed by zirconocene amino acid complex Cp2Zr(η1-C9H10NO2)2, followed by I2-mediated desulfurative step.

Nano ZnO@PEG catalyzed one-pot green synthesis of pyrano[2,3-d]pyrimidines in ethanol via one-pot multicomponent approach

A facile one-pot multicomponent protocol for the synthesis of bio-active Pyrano[2,3-d]pyrimidine derivatives by a one- step condensation reaction of substituted aldehyde, malononitrile/methyl cyanoacetate, barbituric acid has been demonstrated using nano [email protected] as a catalyst at room temperature. The present approach offers several advantages, such as shorter reaction time, higher yields, and environmental friendliness. Easy isolation of products, absence of column chromatographic purification, use of commercially available low-cost starting materials and reusability of the catalyst make the methodology viable in organic synthesis.

Experimental study of fast pyrolysis vapors fractionation through different staged condensation configurations

The quality of biocrudes from fast pyrolysis of lignocellulosic biomass can be improved by optimizing the downstream condensation systems to separate and concentrate selected classes of compounds, thus operating different technological solutions and condensation temperatures in multiple condensation stages. Scientific literature reports that fractional condensation can be deployed as an effective and relatively affordable step in fast pyrolysis. It consists in a controlled multiple condensation approach, which aims at the separated collection of classes of compounds that can be further upgraded to bio-derived chemicals through downstream treatments. In this study, fractional condensation has been applied to a fast pyrolysis reactor of 1 kg h-1 feed, connected to two different condensation units: one composed by a series of two spray condensers and an intensive cooler; a second by an electrostatic precipitator and an intensive cooler too. Fast pyrolysis of pinewood was conducted in a bubbling fluidized bed reactor at 500 °C, while condensable vapours were collected by an interchangeable series of condensers. Using the first configuration, high boiling point compounds – such as sugars and lignin-derived oligomers – were condensed at higher temperatures in the first stage (100 – 170 °C), while water soluble lighter compounds and most of the water were condensed at lower temperatures and so largely removed from the bio-oil. In the first two condensing stages, the bio-oil water content remained below 7 wt % (resulting in 20 MJ kg-1 of energy content) maintaining about 43% of the liquid yield, compared to the 55% of the single step condensation runs. The work thus generated promising results, confirming the interest on upscaling the fractional condensation approach to full scale biorefinering.

Synthesis of 1,3-butadiene from ethanol/acetaldehyde over ZrO2-MgO-SiO2 catalyst: The thermodynamics and reaction kinetics analysis

The catalytic conversion of ethanol into 1,3-butadiene has once again attracted widely attention. However, the kinetics of 1,3-butadiene synthesis from ethanol are rarely reported. In this work, the kinetics of 1,3-butadiene synthesis from ethanol and acetaldehyde over ZrO2-MgO-SiO2 catalyst developed by our research group were studied. The study was carried out in an isothermal integral reactor at temperatures of 573–613 K with various space velocity. The kinetics of two main side reactions, dehydration of ethanol to ethylene and ether, were also measured. It was assumed that the aldol condensation rate determining step followed the Langmuir-Hinshelwood mechanism and the Eley-Rideal mechanism respectively, from which the corresponding kinetics models were derived. The results showed that the aldol condensation step followed the Langmuir-Hinshelwood mechanism over ZrO2-MgO-SiO2 catalyst, and the activation energy was calculated to be 54.6 kJ/mol. The obtained kinetics models were verified under the conditions of different ethanol/acetaldehyde molar ratio. The discrepancy between calculated outlet flow rates of key components and the experimental values was within ± 16%, indicating the validity of the obtained kinetics models. The research results can provide some theoretical guidance for the reactor design of 1,3-butadiene synthesis from ethanol.

Positioning Bacillus subtilis as terpenoid cell factory.

SummaryIncreasing demands for bioactive compounds have motivated researchers to employ micro‐organisms to produce complex natural products. Currently, Bacillus subtilis has been attracting lots of attention to be developed into terpenoids cell factories due to its generally recognized safe status and high isoprene precursor biosynthesis capacity by endogenous methylerythritol phosphate (MEP) pathway. In this review, we describe the up‐to‐date knowledge of each enzyme in MEP pathway and the subsequent steps of isomerization and condensation of C5 isoprene precursors. In addition, several representative terpene synthases expressed in B. subtilis and the engineering steps to improve corresponding terpenoids production are systematically discussed. Furthermore, the current available genetic tools are mentioned as along with promising strategies to improve terpenoids in B. subtilis, hoping to inspire future directions in metabolic engineering of B. subtilis for further terpenoid cell factory development.

Computational Approaches to Identify Molecules Binding to Mycobacterium tuberculosis KasA.

Tuberculosis is caused by Mycobacterium tuberculosis (Mtb) and is a deadly disease resulting in the deaths of approximately 1.5 million people with 10 million infections reported in 2018. Recently, a key condensation step in the synthesis of mycolic acids was shown to require β-ketoacyl-ACP synthase (KasA). A crystal structure of KasA with the small molecule DG167 was recently described, which provided a starting point for using computational structure-based approaches to identify additional molecules binding to this protein. We now describe structure-based pharmacophores, docking and machine learning studies with Assay Central as a computational tool for the identification of small molecules targeting KasA. We then tested these compounds using nanoscale differential scanning fluorimetry and microscale thermophoresis. Of note, we identified several molecules including the Food and Drug Administration (FDA)-approved drugs sildenafil and flubendazole with Kd values between 30–40 μM. This may provide additional starting points for further optimization.

A nested hybridizable discontinuous Galerkin method for computing second-harmonic generation in three-dimensional metallic nanostructures

We develop a nested hybridizable discontinuous Galerkin (HDG) method to numerically solve the Maxwell's equations coupled with a hydrodynamic model for the conduction-band electrons in metals. The HDG method leverages static condensation to eliminate the degrees of freedom of the approximate solution defined in the elements, yielding a linear system in terms of the degrees of freedom of the approximate trace defined on the element boundaries. This article presents a computational method that relies on a degree-of-freedom reordering such that the HDG linear system accommodates an additional static condensation step to eliminate a large portion of the degrees of freedom of the approximate trace, thereby yielding a much smaller linear system. For the particular metallic structures considered in this article, the resulting linear system obtained by means of nested static condensations is a block tridiagonal system, which can be solved efficiently. We apply the nested HDG method to compute second harmonic generation on a triangular coaxial periodic nanogap structure. This nonlinear optics phenomenon features rapid field variations and extreme boundary-layer structures that span a wide range of length scales. Numerical results show that the ability to identify structures which exhibit resonances at ω and 2ω is essential to excite the second harmonic response.

Lack of Specificity of Phenotypic Screens for Inhibitors of the Mycobacterium tuberculosis FAS-II System.

Phenotypic screening of inhibitors of the essential Mycobacterium tuberculosis FAS-II dehydratase HadAB led to the identification of GSK3011724A, a compound previously reported to inhibit the condensation step of FAS-II. Whole-cell-based and cell-free assays confirmed the lack of activity of GSK3011724A against the dehydratase despite evidence of cross-resistance between GSK3011724A and HadAB inhibitors. The nature of the resistance mechanisms is suggestive of alterations in the FAS-II interactome reducing access of GSK3011724A to KasA.

Structure and kinetics of indole-3-glycerol phosphate synthase from Pseudomonas aeruginosa: Decarboxylation is not essential for indole formation

In tryptophan biosynthesis, the reaction catalyzed by the enzyme indole-3-glycerol phosphate synthase (IGPS) starts with a condensation step in which the substrate's carboxylated phenyl group makes a nucleophilic attack to form the pyrrole ring of the indole, followed by a decarboxylation that restores the aromaticity of the phenyl. IGPS from Pseudomonas aeruginosa has the highest turnover number of all characterized IGPS enzymes, providing an excellent model system to test the necessity of the decarboxylation step. Since the 1960s, this step has been considered to be mechanistically essential based on studies of the IGPS–phosphoribosylanthranilate isomerase fusion protein from Escherichia coli. Here, we present the crystal structure of P. aeruginosa IGPS in complex with reduced CdRP, a nonreactive substrate analog, and using a sensitive discontinuous assay, we demonstrate weak promiscuous activity on the decarboxylated substrate 1-(phenylamino)-1-deoxyribulose-5-phosphate, with an ∼1000× lower rate of IGP formation than from the native substrate. We also show that E. coli IGPS, at an even lower rate, can produce IGP from decarboxylated substrate. Our structure of P. aeruginosa IGPS has eight molecules in the asymmetric unit, of which seven contain ligand and one displays a previously unobserved conformation closer to the reactive state. One of the few nonconserved active-site residues, Phe201 in P. aeruginosa IGPS, is by mutagenesis demonstrated to be important for the higher turnover of this enzyme on both substrates. Our results demonstrate that despite IGPS's classification as a carboxy-lyase (i.e. decarboxylase), decarboxylation is not a completely essential step in its catalysis.

Iridium complexes with a new type of N^N′‐donor anionic ligand catalyze the N‐benzylation of amines via borrowing hydrogen

The development of efficient and eco‐friendly methods for the synthesis of elaborate amines is highly desired as they are valuable chemicals. The catalytic alkylation of amines using alcohols as alkylating agents, through the so‐called borrowing hydrogen process, satisfies several of the principles of green chemistry. In this paper, four neutral half‐sandwich complexes of Ru(II), Rh(III), and Ir(III) have been synthesized and tested as catalysts in the N‐benzylation of amines with benzyl alcohol. The new derivatives contain a N^N′ anionic ligand derived from 5‐(pyridin‐2‐ylmethylene)hydantoin (Hpyhy) that has never been tested in metal complexes with catalytic applications. In particular, the Ir derivatives, [(Cp*)IrX(pyhy)] (X = Cl or H), exhibit high activity along with good selectivity in the process. Indeed, the scope of the optimized protocol has been proved in the benzylation of several primary and secondary amines. The selectivity towards monoalkylated or dialkylated amines has been tuned by adjusting the amine:alcohol ratio and the reaction time. Experimental results support a mechanism consisting of three consecutive steps, two of which are Ir catalyzed, and a favorable condensation step without the assistance of the catalyst. Moreover, an unproductive competitive pathway can operate when the reaction is performed in open‐air vessels, due to the irreversible release of H2. This route is hampered when the reaction is carried out in close vessels, likely because the release of H2 is reversed through metal‐based heterolytic cleavage. From our viewpoint, these results show the potential of the new catalysts in a very attractive and promising methodology for the synthesis of amines.