Isolation of a Reactive Tricoordinate α‐Oxo Gold Carbene Complex

The [(P,P)Au=C(Ph)CO₂Et]⁺ complex 3 [where (P,P) is an o‐carboranyl diphosphine ligand] was prepared by diazo decomposition at ?40 °C. It is the first α‐oxo gold carbene complex to be characterized. Its crystallographic structure was determined and DFT calculations have been performed, unraveling the key influence of the chelating (P,P) ligand. The gold center is tricoordinate and the electrophilicity of the carbene center is decreased. Complex 3 mimics transient α‐oxo gold carbenes in a series of catalytic transformations, and provides support for the critical role of electrophilicity in the chemoselectivity of phenol functionalization (O?H vs. C?H insertion).     

Ambident electrophilicity of 4-nitrobenzochalcogenadiazoles: Kinetic studies and structure-reactivity relationships

The kinetics of the reactions of 4-nitrobenzofurazane 1a , 4-nitrobenzothiadiazole 1b , and 4-nitrobenzoselenadiazole 1c with a series of 4-Y-substituted phenoxide anions 2a-e (Y = OMe, Me, H, Cl, and CN) in aqueous solution at 20°C were investigated photometrically. The derived second-order rate constants (k₂) have been combined with the nucleophilicity parameters values of these series of anions 2a-e to determine the electrophilicity parameters E of electrophiles 1a-c according to the linear free-energy relationship (log k₂)/s versus N. General reactivity of these electrophiles 1a-c is found to be fairly similar with E values ranging in −10.77 ± 0.61 < E < −7.53 ± 0.29. The comparison with structurally related neutral electron-deficient heteroaromatic and aromatic compounds revealed that 1a - c are more reactive than 1,3,5-trinitrobenzene, as benchmark aromatic electrophile used in nucleophilic addition or substitution processes. The rate constants for the reactions of 4-nitrobenzochalcogenadiazoles 1a-c with some other nucleophiles were measured and found to agree with those calculated from Mayr's equation. Finally, analysis of the rate data in terms of the Brønsted approach reveals that 1a-c exhibits especially low intrinsic reactivity in σ-adducts 3 forming reactions.     

A Green One-pot Synthesis of PDMS Bis-Macromonomers Using an Ecologic Catalyst (Maghnite-H+)

PDMS bis-macromonomers bearing methyl methacrylate end groups is a material mainly used for making extended-wear contact lenses. Silicon-based materials give a good oxygen passage and methyl methacrylate has biocompatibility and mechanical properties of the elastomer. The present study shows the synthesis of this material. The polymerization of hexamethylcyclotrisiloxane (D₃) catalyzed by Maghnite-H⁺ (Mag-H⁺), a montmorillonite sheet silicate clay exchanged with protons, an efficient catalyst for cationic polymerization of manyheterocyclic and vinylicmonomers. The structural compositions of “Maghnite” have already been determined. The effects of the amount of Mag-H⁺, temperature and the reaction time were studied. Moreover, we used a simple method, one step in solution to prepare Poly dimethyl siloxane (PDMS) and PDMS bis-macromonomers. The structure of the resulting products is characterized and established by ¹H and ¹³C-NMR, where the methacrylate end groups are clearly visible. The presence of unsaturated end group was also determined by UV and FTIR analysis. The influence of the amount of methacrylic anhydride on monomer conversion was studied. The polymerization yield and the molecular weight of PDMS macromonomers depend on the amount of methacrylic anhydride used.     

Hydrogel droplet microarrays with trapped antibody-functionalized beads for multiplexed protein analysis

Antibody microarrays are a powerful tool for rapid, multiplexed profiling of proteins. 3D microarray substrates have been developed to improve binding capacity, assay sensitivity, and mass transport, however, they often rely on photopolymers which are difficult to manufacture and have a small pore size that limits mass transport and demands long incubation time. Here, we present a novel 3D antibody microarray format based on the entrapment of antibody-coated microbeads within alginate droplets that were spotted onto a glass slide using an inkjet. Owing to the low concentration of alginate used, the gels were highly porous to proteins, and together with the 3D architecture helped enhance mass transport during the assays. The spotting parameters were optimized for the attachment of the alginate to the substrate. Beads with 0.2 μm, 0.5 μm and 1 μm diameter were tested and 1 μm beads were selected based on their superior retention within the hydrogel. The beads were found to be distributed within the entire volume of the gel droplet using confocal microscopy. The assay time and the concentration of beads in the gels were investigated for maximal binding signal using one-step immunoassays. As a proof of concept, six proteins including cytokines (TNFα, IL-8 and MIP/CCL4), breast cancer biomarkers (CEA and HER2) and one cancer-related protein (ENG) were profiled in multiplex using sandwich assays down to pg mL(-1) concentrations with 1 h incubation without agitation in both buffer solutions and 10% serum. These results illustrate the potential of beads-in-gel microarrays for highly sensitive and multiplexed protein analysis.     

Cationic Gold(III) Alkyl Complexes: Generation,Trapping, and Insertion of Norbornene

Migratory insertion of alkenes into gold–carbon bonds, a fundamental yet unprecedented organometallic transformation, has been investigated from a discrete (P,C) cyclometalated gold(III) dimethyl complex. Methide abstraction by B(C₆F₅)₃ is shown to generate a highly reactive cationic Au^III complex that evolves spontaneously by C₆F₅ transfer from boron. In the presence of norbornene, migratory insertion into the Au C bond proceeds readily. The resulting norbornyl complex is efficiently trapped with pyridines or chloride to give stable four‐coordinate adducts.     

Catalyst control of selectivity in the C–O bond alumination of biomass derived furans

Non-catalysed and catalysed reactions of aluminium reagents with furans, dihydrofurans and dihydropyrans were investigated and lead to ring-expanded products due to the insertion of the aluminium reagent into a C–O bond of the heterocycle. Specifically, the reaction of [{(ArNCMe)₂CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with furans proceeded between 25 and 80 °C leading to dearomatised products due to the net transformation of a sp² C–O bond into a sp² C–Al bond. The kinetics of the reaction of 1 with furan were found to be 1st order with respect to 1 with activation parameters ΔH^‡ = +19.7 (±2.7) kcal mol⁻¹, ΔS^‡ = −18.8 (±7.8) cal K⁻¹ mol⁻¹ and ΔG^‡_{298 K} = +25.3 (±0.5) kcal mol⁻¹ and a KIE of 1.0 ± 0.1. DFT calculations support a stepwise mechanism involving an initial (4 + 1) cycloaddition of 1 with furan to form a bicyclic intermediate that rearranges by an α-migration. The selectivity of ring-expansion is influenced by factors that weaken the sp² C–O bond through population of the σ*-orbital. Inclusion of [Pd(PCy₃)₂] as a catalyst in these reactions results in expansion of the substrate scope to include 2,3-dihydrofurans and 3,4-dihydropyrans and improves selectivity. Under catalysed conditions, the C–O bond that breaks is that adjacent to the sp²C–H bond. The aluminium(iii) dihydride reagent [{(MesNCMe)₂CH}AlH₂] (Mes = 2,4,6-trimethylphenyl, 2) can also be used under catalytic conditions to effect a dehydrogenative ring-expansion of furans. Further mechanistic analysis shows that C–O bond functionalisation occurs via an initial C–H bond alumination. Kinetic products can be isolated that are derived from installation of the aluminium reagent at the 2-position of the heterocycle. C–H alumination occurs with a KIE of 4.8 ± 0.3 consistent with a turnover limiting step involving oxidative addition of the C–H bond to the palladium catalyst. Isomerisation of the kinetic C–H aluminated product to the thermodynamic C–O ring expansion product is an intramolecular process that is again catalysed by [Pd(PCy₃)₂]. DFT calculations suggest that the key C–O bond breaking step involves attack of an aluminium based metalloligand on the 2-palladated heterocycle. The new methodology has been applied to important platform chemicals from biomass.

Non-catalysed and catalysed reactions of aluminium reagents with furans, dihydrofurans and dihydropyrans were investigated and lead to ring-expanded products due to the insertion of the aluminium reagent into a C–O bond of the heterocycle.     

A novel natural source Vicia faba L. membranes as colourant: development and optimisation of the extraction process using response surface methodology (RSM)

In this research paper, an eco-friendly extraction process of dyes from Vicia faba L. membranes was developed. In this regard, the influence of independent process factors like the weight of material, the extraction time, the temperature and the sodium hydroxide concentration on the natural dye extraction from Vicia faba membranes was investigated. The optimisation of the extraction conditions and the effect evaluation of the different operating parameters were carried out using a Box–Behnken design under response surface methodology. The optimum conditions were found to be 66 °C, 90 min, 5 g and 0.1628 mol·L^?1 for extraction temperature, time, mass of the material and sodium hydroxide concentration, respectively. The efficiency of this extraction process under these optimum conditions was evaluated by measuring the total phenolic content (TPC), the total flavonoid content and the relative colour yield (K/S). In these operating conditions, good fastness ratios were observed for the dyed fabrics.     

Cationic Gold(III) Alkyl Complexes: Generation,Trapping, and Insertion of Norbornene

Migratory insertion of alkenes into gold–carbon bonds, a fundamental yet unprecedented organometallic transformation, has been investigated from a discrete (P,C) cyclometalated gold(III) dimethyl complex. Methide abstraction by B(C₆F₅)₃ is shown to generate a highly reactive cationic Au^III complex that evolves spontaneously by C₆F₅ transfer from boron. In the presence of norbornene, migratory insertion into the Au? C bond proceeds readily. The resulting norbornyl complex is efficiently trapped with pyridines or chloride to give stable four‐coordinate adducts.     

Ultrathin-layer α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> deposited under hematite for solar water splitting

This work proposes a new strategy to prepare a hematite (α-Fe₂O₃) bilayer photoanode by hydrothermally depositing α-Fe₂O₃ (B) on the α-Fe₂O₃ (A) films prepared by electrochemical deposition. Compact smooth surfaced α-Fe₂O₃ (A) films were electrochemically deposited on FTO (SnO₂:F) substrates from an aqueous bath. The α-Fe₂O₃ (A), α-Fe₂O₃ (B), and α-Fe₂O₃/α-Fe₂O₃ bilayer films’ characteristics were defined by X-ray diffraction (XRD) measurements, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) spectroscopy. Pure crystalline α-Fe₂O₃ (B) films with a typical anisotropic-like nanoparticle formation, which exhibited nanostructured rods covering the substrate and formed the characteristic mesoporous film morphology, were hydrothermally deposited on α-Fe₂O₃ (A) films prepared by electrochemical depositing in a solution bath at 25 °C and a potential of ??0.15 V. The photocurrent measurements exhibited increased intrinsic surface states (or defects) at the α-Fe₂O₃ (A)/α-Fe₂O₃ (B) interface. The photoelectrochemical performance of the α-Fe₂O₃ (A)/α-Fe₂O₃ (B) structure was examined by chronoamperometry, which found that the α-Fe₂O₃ (A)/α-Fe₂O₃ (B) structure exhibited greater photoelectrochemical activity than the α-Fe₂O₃ (A) and α-Fe₂O₃ (B) thin films. The highest photocurrent density was obtained for the bilayer α-Fe₂O₃ (A)/α-Fe₂O₃ (B) films in 1 M NaOH electrolyte. This great photoactivity was ascribed to the highly active surface area, and to the externally applied bias that favored the transfer and separation of photogenerated charge carriers in α-Fe₂O₃ (A)/α-Fe₂O₃ (B). The improved photocurrent density was attributed to an appropriate band edge alignment of semiconductors and to enhanced light absorption by both semiconductors. The best performing samples were α-Fe₂O₃ (A)/α-Fe₂O₃ (B), which reached the maximum incident photon conversion efficiencies (IPCE) of 400 nm at the potential of 0.1 V. In this case, the IPCE values were 3-fold higher than those of the α-Fe₂O₃ (A) and α-Fe₂O₃ (B) films.