Selective Formation Research Articles

Low MWCO non-polyamide nanofiltration membranes synthesized in aqueous by coupling with catechol-amine chemistry and the oxidation-induced self-polymerization of m-phenylenediamine

Catechol-amine coatings offer versatile routes for surface modifications and nanofiltration (NF) membrane preparations. However, the formation of the selective layer is time-consuming and often deficient, rendering it unsuitable for large-scale applications. In this work, oxidation-induced self-polymerization and catechol-amine chemistry were combined to rapidly construct nanofiltration membranes in an aqueous medium. M-phenylenediamine (MPD) underwent oxidation and self-polymerized on a polysulfone (PSF) support. The addition of sodium periodate facilitated the subsequent tannic acid (TA) coating. The catechol-amine reaction between oxidized TA and poly-MPD forms crosslinked poly TA-MPD complexes, offering the resulting membrane a high selectivity. The role of NaIO4 in the selective layer formation and the influences of the synthesis parameters on the membrane performance were discussed. Utilizing the facile method enabled the achievement of a low molecular weight cut-off (MWCO) NF membrane (180 Da). The membrane exhibited a high water permeance (10.9 Lm−2h−1bar−1) and good salt rejections (93 % for Na2SO4). The filtration of the bovine serum acid (BSA) solution demonstrated the membrane has good antifouling performance with a flux recovery ratio (FRR) of 95.1 %. The proposed method offers a straightforward and rapid approach to fabricating low MWCO NF membranes in an aqueous medium, which has potential in large-scale applications.

CO2 Electroreduction by Engineering the Cu2O/RGO Interphase

In the present investigation, Cu2O-based composites were successfully prepared through a multistep method where cubic Cu2O nanoparticles (CU Cu2O) have been grown on Reduced Graphene Oxide (RGO) nanosheets. The structural and morphological properties of the materials have been studied through a comprehensive characterization, confirming the coexistence of crystalline Cu2O and RGO. Microscopical imaging revealed the intimate contact between the two materials, affecting the size and the distribution of Cu2O nanoparticles on the support. The features of the improved morphology strongly affected the electrochemical behavior of the composites, increasing the activity and the faradaic efficiencies towards the electrochemical CO2 reduction reaction process. CU Cu2O/RGO 2:1 composite displayed selective CO formation over H2, with higher currents compared to pristine Cu2O (−0.34 mA/cm2 for Cu2O and −0.64 mA/cm2 for CU Cu2O/RGO 2:1 at the voltage of −0.8 vs. RHE and in a CO2 atmosphere) and a faradaic efficiency of 50% at −0.9 V vs. RHE. This composition exhibited significantly higher CO production compared to the pristine materials, indicating a favorable *CO intermediate pathway even at lower voltages. The systematic investigation on the effects of nanostructuration on composition, morphology and catalytic behavior is a valuable solution for the formation of effective interphases for the promotion of catalytic properties providing crucial insights for future catalysts design and applications.

Highly Selective C-N and C-S Dual Functionalization of 1,3-Dicarbonyl Derivatives Using TBHP as an Oxidant.

A direct electrosynthesis/photocatalyst-free, atom-economical, and efficient method for the selective synthesis of (E)-3-amino-2-thiocyanato-α,β-unsaturated carbonyl compounds is described through a given protocol. The present approach features the use of inexpensive ammonium thiocyanate to achieve dual functionalization of 1,3-dicarbonyl compounds using TBHP as an oxidant, providing a rapid and practical route to the selective formation of both C-N and C-S bonds via a radical process. This method offers a broad substrate scope with excellent yield and allows for further exploration of the products to construct heterocyclic compounds and other functionalities.

Oxidative Syntheses of N,N-Dialkylhydroxylamines.

Despite the wide utility of hydroxylamines in organic synthesis, relatively few are commercially available, and there is a need for direct, efficient, and selective methods for their synthesis. Herein, we report two complementary methods to accomplish direct oxidation of secondary amines using UHP as an oxidant. The first method uses 2,2,2-trifluoroethanol (TFE) and a large excess of amine. Isolation of hydroxylamine products is enabled by selective salt formation, and recovery of excess amine is demonstrated. The second method uses hexafluoroacetone as an additive and is highlighted by the 1:1 stoichiometry between the oxidant and amine.

Selectivity switch via tuning surface static electric field in photocatalytic alcohol conversion

Photocatalysis has shown great potential in organic reactions, while controlling the selectivity is a long-standing goal and challenge due to the involvement of various radical intermediates. In this study, we have realized selectivity control in the photocatalytic conversion of alcohols via engineering the surface static electric field of the CdS semiconductor. By leveraging the Au-CdS interaction to adjust lattice strain, which influences the intensity of the surface static electric field, we altered the pathways of alcohol conversion. The increased intensity of the surface static electric field changed the activation pathways of the C-H/O-H bond, leading to the selective formation of targeted C/O-based radical intermediates and altering the selectivity from aldehydes to dimers. A wide range of alcohols, such as aromatic alcohol and thiophenol alcohol, were selectively converted into aldehyde or dimer. This work provides an effective strategy for selectively controlling reaction pathways by generating a surface electric field.

Organocatalytic Activation of Unsymmetrical 2,3‐Diketones towards Catalytic Asymmetric Domino Michael–Henry Reaction

In this study, we explored a method to distinguish between both enolizable regions of unsymmetrical 2,3‐diketones in organocatalytic domino reactions involving nitroalkenes. The selective formation of an enamine from only one side of the molecule was made possible by the use of optically pure 2‐(trifluoromethyl)pyrrolidine. This catalyst, remarkably enhancing the reaction, owes its efficacy to a unique interplay between basicity and nucleophilicity. These features caused the enolization of the substrate at the second possible site to be omitted. The approach resulted in excellent regio‐ diastereo‐ and enantioselectivity (91‐99% ee) across various nitroalkenes, leading to the synthesis of novel cyclopentanone derivatives with three contiguous stereogenic center.

Synthesis of adamantane appended supramolecular amphiphilic bullets: structural and spectral insights

The present manuscript reports the synthesis of two targeted amphiphilic bullets through a highly selective amide bond formation by competing parallel esterification. A simple reaction protocol was developed based on the usage of commercially available starting materials(1-Amino-3-adamantanol), reagents (DIPEA) and solvents (THF). Readily available materials were chosen in this regard. Out of the three reactions, two reactions resulted 100 % atom economy. All these reactions resulted more than 92 % yield of the targeted products via selective amide bond formation. All these reactions Milder reaction conditions such as room temperature and 3hours of reaction time were enough to carryout the process. All the novel products were charactezed by advanced analytical techniques such as 1H, 13C NMR, Infra Red and ESI-MS spectral data. DFT studies were carried out to predict relative stabilities and reactivities of all the three amides. The solavation energy of phthalimide derivative is having relatively higher solvation energy in comparison with that of other amides.In case of relative stabilities, BOC group containig amide is more stable. On the other hand, succinamide deravative is having higher energy gap in between HOMO and LUMO.

Contemporary Concepts of Adhesive Cementation of Glass-Fiber Posts: A Narrative Review.

(1) Background: Cementation of glass fiber posts to root canals has been associated with various failures, especially debonding. This narrative review aims to present the contemporary concepts concerning the adhesive cementation of glass fiber post and to discuss the optimal management of these factors. (2) Methods: Electronic search was performed in MEDLINE/Pub Med and Google Scholar using selected keywords examining the parameters post length, surface treatment of glass fiber posts, post space preparation and dentin pretreatment, resin cement selection, adhesive systems and hybrid layer formation, and clinical techniques. (3) Results: The search led to the selection of 44 articles. Epoxy resin-based endodontic sealers are recommended and the use of temporary cement in the root canal should be avoided. The minimum length of a glass fiber post adhesively cemented to a root canal is 5 mm. Irrigating the root canals with chlorhexidine, MTAD, or EDTA (alone or in combination with NaOCl) after post space preparation seems to enhance the bond strength. Silane application on the surface of the post seems to be beneficial. Concerning resin cements and adhesive systems, the results were rather inconclusive. Finally, resin cement should be applied inside the root canal with an elongation tip and photoactivation should be delayed. (4) Conclusions: Contemporary concepts of adhesive cementation of glass fiber posts can indeed improve the bond between glass fiber posts, resin cement, and root canal dentin, however, evidence coming from long-term randomized prospective clinical trials is needed in order to obtain safer conclusions.

Bimetallic Ru(II) Complex Catalysed β‐Alkylation of Secondary Alcohols and α‐Alkylation of Ketones: Selective Formation of Saturated Ketones

AbstractRu(II) bimetallic [(p‐cymene)2(RuCl)2L1]2X (X=BF4 (Cat2); X=PF6 (Cat3)) and monometallic [(p‐cymene)(RuCl)L2]BF4 (Cat4) (where L1=N,N’‐(3,3’,5,5’‐tetraisopropyl‐[1,1’‐biphenyl]‐4,4’‐diyl)bis(1‐(pyridin‐2‐yl)methanimine); L2=N‐(2,6‐diisopropyl‐phenyl)‐1‐(pyridin‐2‐yl)‐methanimine) catalyse selective synthesis of saturated ketones using β‐alkylation of secondary alcohol or α‐alkylation of ketones with primary alcohol. Notably, a single catalyst facilitates the oxidation of both secondary and primary alcohols followed by condensation and hydrogenation yielding α‐alkylated saturated ketones. Remarkably, this system allows catalyst loading as low as 0.01 mol% for β‐alkylation of secondary alcohols and 0.005 mol% for the α‐alkylation of ketone, delivering access to a wide array of α‐alkylated ketones derivatives with yields of ~97 %. Complex Cat2, in particular, orchestrates one‐pot alkylation reactions with a high turnover frequency (TOF) of 5.6 105 h−1 using as low as low catalyst loading of 0.0001 mol%. A comparative study between bimetallic and monometallic complexes reveals that complex Cat2 exhibits better selectivity for the formation of saturated ketones presumably owing to a cooperative effect between the metal centres. The scale‐up synthesis highlights the practical applicability of the catalytic approach. To delve into the plausible mechanisms, we conducted initial investigations through meticulously controlled experiments and spectroscopic analysis.

High-efficient acetylene synthesis by selective electrochemical formation of CO2-derived CaC2

Acetylene can be used as feedstock for various chemical products, but its raw material has been a fossil fuel, which poses an environmental challenge. One way to address the challenge is to form CaC2 from CO2, which reacts with water to form acetylene. This study demonstrated the selective formation of CaC2 from CO2 by an electrochemical process in NaCl-KCl-CaCl2-CaO melt at 823 K to produce C2H2 with high current efficiency. The CaC2 was formed through two reactions: the carbon electrodeposition from CO2-derived CO32− (Step 1) and the electrochemical reduction of Ca(II) ion on the carbon (Step 2). These two reactions could be controlled by conducting potentiostatic electrolysis under CO2 and Ar atmospheres, resulting in acetylene synthesis with a maximum current efficiency of 92 %. Each electrochemical reaction agreed with the thermodynamic electrode potential. The electrolysis on carbon electrodes revealed that the higher the crystallinity of carbon, the more selectively CaC2 was formed. The CaC2 formation was induced by the reduction of Ca(II) ions on the basal plane of the graphite layer rather than the edge plane. The unique interfacial phenomenon between high-temperature melt and a carbon electrode surface will contribute to realizing a highly efficient CO2 conversion process to acetylene.

Selective formation of glycolic acid by photocatalytic conversion of glycerol under sunlight with SnO2-based heterojunctions

Glycerol is a byproduct of biodiesel synthesis and is one of the most readily available platform molecules originating from biomass. Heterogeneous photocatalysis is a strategic approach, and reactions run under ambient conditions convert glycerol into industrially relevant molecules such as glycolic acid. The p-n type heterojunctions are useful photocatalysts because they can decrease the bandgaps and facilitate electron promotion between the bands of materials, thereby optimizing the formation of reactive oxygen species (ROS) and increasing reaction efficiencies. In this study, photocatalysts were synthesized via coprecipitation with a 5 % w/w mixture of Cu2+ and Ni2+ precursors, which produced the p-n heterojunctions SnO2/CuO-5 % and SnO2/NiO-5 %, respectively. Was observed an increase in the surface areas of the materials, which were ∼19 and 62 m2/g for SnO2/CuO-5 % and SnO2/NiO-5 %, respectively. The addition of metals to the heterojunctions enabled the use of solar light, due to the decrease of the bandgaps of the materials to 1.9 and 2.0 eV for SnO2/CuO-5 % and SnO2/NiO-5 %, respectively; these were lower than of SnO2 (2.54 eV). The photocatalytic activities of the heterojunctions were tested via glycerol oxidation, and after 4 h, the SnO2/CuO-5 % heterojunction exhibited the highest reaction efficiency (19 %), followed by 13 % and 11 % for SnO2/NiO-5 % and SnO2, respectively. The selectivities indicated the reaction pathway, in which glyceraldehyde and tartaric acid were intermediates for glycolic acid production; glycolic acid is the precursor to polyglycolic acid (PGA), for which production levels are increasing. The results of this study point to new technological pathways enabling responsible use of the resources present in nature and reuse of their byproducts, as with the conversion of glycerol to economically attractive molecules and contribute to a sustainable economy.

Ultrasonication‐Assisted Preparation of Au‐Pt/ZrO2 Catalysts for the Selective Base‐Free Oxidation of Glucose to Glucaric Acid

AbstractSelective catalytic oxidation of glucose to glucaric acid is still challenging due to the potential formation of a large range of by‐products. ZrO2 supported AuPt catalysts are very efficient for this reaction under base‐free conditions, in aqueous phase. Different preparation methods were tested and the catalysts synthesized by co‐impregnation using NaBH4 as reductant gave the most promising results. We demonstrated that the presence of a pure AuPt alloy is critical for the selective formation of glucaric acid. We have shown that when ultrasonication was used during preparation, less by‐products were formed, increasing significantly final yield of glucaric acid, up to 71 %. The Au/Pt ratio affects the catalytic results and an optimal ratio around 1.1 was determined. Finally, the catalyst is stable up to 196 h in continuous reactor.

Mild and selective synthesis of imines and N-Heterocyclic compounds via formic acid-mediated reductive coupling strategy over Nitrogen-Coordinated cobalt Single-Atom catalysts

The selective formation of C = N bonds through the formic acid-mediated reductive coupling of nitro groups with carbonyl groups over heterogeneous catalysts poses challenges due to the corrosion of metal catalysts by formic acid and the rapid further hydrogenation of C = N into C-N bonds. In this study, we demonstrate that nitrogen-coordinated cobalt single-atom catalysts exhibit robust activity in this transformation. Various imines and N-heterocyclic compounds, including benzimidazoles, quinazolines, and pyrroles, can be synthesized at a modest temperature of only 70 °C. The high catalytic activity is attributed to the synergistic roles of nitrogen and cobalt atoms, serving as basic and active sites, respectively. Experimental data, complemented by density functional theory (DFT) calculations, clearly indicate that the transfer hydrogenation of nitrobenzene preferentially proceeds via the “direct” pathway rather than the “condensation” pathway. Moreover, the reduction of C = N bonds into C-N bonds demands much higher energy than the reduction of nitro groups, thereby enabling high selectivity towards C = N bonds. The findings of this study are expected to provide a novel approach for selective C = N bond formation and contribute to a deeper understanding of the mechanism underlying the reductive amination process.

Electrocatalytic and Selective Oxidation of Glycerol to Formate on 2D 3d-Metal Phosphate Nanosheets and Carbon-Negative Hydrogen Generation.

In the landscape of green hydrogen production, alkaline water electrolysis is a well-established, yet not-so-cost-effective, technique due to the high overpotential requirement for the oxygen evolution reaction (OER). A low-voltage approach is proposed to overcome not only the OER challenge by favorably oxidizing abundant feedstock molecules with an earth-abundant catalyst but also to reduce the energy input required for hydrogen production. This alternative process not only generates carbon-negative green H2 but also yields concurrent value-added products (VAPs), thereby maximizing economic advantages and transforming waste into valuable resources. The essence of this study lies in a novel electrocatalyst material. In the present study, unique and two-dimensional (2D) ultrathin nanosheet phosphates featuring first-row transition metals are synthesized by a one-step solvothermal method, and evaluated for the electrocatalytic glycerol oxidation reaction (GLYOR) in an alkaline medium and simultaneous H2 production. Co3(PO4)2 (CoP), Cu3(PO4)2 (CuP), and Ni3(PO4)2 (NiP) exhibit 2D sheet morphologies, while FePO4 (FeP) displays an entirely different snowflake-like morphology. The 2D nanosheet morphology provides a large surface area and a high density of active sites. As a GLYOR catalyst, CoP ultrathin (∼5 nm) nanosheets exhibit remarkably low onset potential at 1.12 V (vs RHE), outperforming that of NiP, FeP, and CuP around 1.25 V (vs RHE). CoP displays 82% selective formate production, indicating a superior capacity for C-C cleavage and concurrent oxidation; this property could be utilized to valorize larger molecules. CoP also exhibits highly sustainable electrochemical stability for a continuous 200 h GLYOR operation, yielding 6.5 L of H2 production with a 4 cm2 electrode and 98 ± 0.5% Faradaic efficiency. The present study advances our understanding of efficient GLYOR catalysts and underscores the potential of sustainable and economically viable green hydrogen production methodologies.

Interplay between the Formation of Colloidal Clathrate and Cubic Diamond Crystals.

Controlling the valency of directional interactions of patchy particles is insufficient for the selective formation of target crystalline structures due to the competition between phases of similar free energy. Examples of such are stacking hybrids of interwoven hexagonal and cubic diamonds with (i) its liquid phase, (ii) arrested glasses, or (iii) clathrates, all depending on the relative patch size, despite being within the one-bond-per-patch regime. Herein, using molecular dynamics simulations, we demonstrate that although tetrahedral patchy particles with narrow patches can assemble into clathrates or stacking hybrids in the bulk, this behavior can be suppressed by the application of external surface potential. Depending on its strength, the selective growth of either cubic diamond crystals or empty sII clathrate cages can be achieved. The formation of a given ordered network depends on the structure of the first adlayer, which is commensurate with the emerging network.

Synthesis of Metastable Calcium Carbonate Using Long-Chain Bisphosphonate Molecules.

Cementation in construction materials primarily relies on the aqueous precipitation of minerals such as carbonates and silicates. The kinetics of nucleation and growth play a critical role in the development of strength and durability, yet our understanding of the kinetic controls governing phase formation and porosity reduction in cements remains limited. In this study, we synthesized bisphosphonate molecules with varying alkyl chain lengths and functional groups to investigate their impact on calcium carbonate precipitation. Through conductivity measurements, infrared spectroscopy, and thermogravimetric analysis, we uncovered the selective formation of polymorphs and the specific incorporation of these molecules within the carbonate matrix. Further, in situ atomic force microscopy revealed that these molecules influenced the morphology of the precipitates, indicating a possible effect on the ionic organization through sorption mechanisms. Interestingly, amorphous calcium carbonate (ACC), when formed in the presence of bisphosphonates, showed metastability for at least seven months without inhibiting further calcium carbonate precipitation. Our research sheds light on the diverse mechanisms by which organic additives can modify mineral nucleation and growth, offering valuable insights for the control and enhancement of carbonate-based cementation processes.

The “4 + 1” strategy fabrication of iron single-atom catalysts with selective high-valent iron-oxo species generation

Single-atom catalysts (SACs) with atomic dispersion active sites have exhibited huge potentials in peroxymonosulfate (PMS)-based Fenton-like chemistry in water purification. However, four-N coordination metal (MN4) moieties often suffer from such problems as low selectivity and narrow workable pH. How to construct SACs in a controllable strategy with optimized electronic structures is of great challenge. Herein, an innovative strategy (i.e., the "4 + 1" fabrication) was devised to precisely modulate the first-shell coordinated microenvironment of FeN4 SAC using an additional N (SA-FeN5). This leads to almost 100% selective formation of high-valent iron-oxo [Fe(IV)═O] (steady-state concentration: 2.00 × 10-8 M) in the SA-FeN5/PMS system. In-depth theoretical calculations unveil that FeN5 configuration optimizes the electron distribution of monatomic Fe sites, which thus fosters PMS adsorption and reduces the energy barrier for Fe(IV)═O generation. SA-FeN5 was then attached to polyvinylidene difluoride membrane for a continuous flow device, showing long-term abatement of the microcontaminant. This work furnishes a general strategy for effective PMS activation and selective high-valent metal-oxo species generation by high N-coordination number regulation in SACs, which would provide guidance in the rational design of superior environmental catalysts for water purification.

Selective α-Hydroxyketone Formation and Subsequent C–C Bond Cleavage by Cytochrome P450 Monooxygenase Enzymes

Selective α-Hydroxyketone Formation and Subsequent C–C Bond Cleavage by Cytochrome P450 Monooxygenase Enzymes

Unusual facet and co-catalyst effects in TiO2-based photocatalytic coupling of methane

Photocatalytic coupling of methane to ethane and ethylene (C2 compounds) offers a promising approach to utilizing the abundant methane resource. However, the state-of-the-art photocatalysts usually suffer from very limited C2 formation rates. Here, we report our discovery that the anatase TiO2 nanocrystals mainly exposing {101} facets, which are generally considered less active in photocatalysis, demonstrate surprisingly better performances than those exposing the high-energy {001} facet. The palladium co-catalyst plays a pivotal role and the Pd2+ site on co-catalyst accounts for the selective C2 formation. We unveil that the anatase {101} facet favors the formation of hydroxyl radicals in aqueous phase near the surface, where they activate methane molecules into methyl radicals, and the Pd2+ site participates in facilitating the adsorption and coupling of methyl radicals. This work provides a strategy to design efficient nanocatalysts for selective photocatalytic methane coupling by reaction-space separation to optimize heterogeneous-homogeneous reactions at solid-liquid interfaces.

Hydrogen‐Bond‐Mediated Formation of C−N or C=N Bond during Photocatalytic Reductive Coupling Reaction over CdS Nanosheets

AbstractReductive amination of carbonyl compounds and nitro compounds represents a straightforward way to attain imines or secondary amines, but it is difficult to control the product selectivity. Herein, we report the selective formation of C−N or C=N bond readily manipulated through a solvent‐induced hydrogen bond bridge, facilitating the swift photocatalytic reductive coupling process. The reductive‐coupling of nitro compounds with carbonyl compounds using formic acid and sodium formate as the hydrogen donors over CdS nanosheets selectively generates imines with C=N bonds in acetonitrile solvent; while taking methanol as solvent, the C=N bonds are readily hydrogenated to the C−N bonds via hydrogen‐bonding activation. Experimental and theoretical study reveals that the building of the hydrogen‐bond bridge between the hydroxyl groups in methanol and the N atoms of the C=N motifs in imines facilitates the transfer of hydrogen atoms from CdS surface to the N atoms in imines upon illumination, resulting in the rapid hydrogenation of the C=N bonds to give rise to the secondary amines with C−N bonds. Our method provides a simple way to control product selectivity by altering the solvents in photocatalytic organic transformations.