Metal-Surface Interactions and Surface Heterogeneity in ‘Well-Defined’ Silica-Supported Alkene Metathesis Catalysts: Evidences and Consequences

Here we present our observations on a peculiar kinetic behavior observed at low catalyst loadings for the metathesis of internal olefins on a highly active silica-supported tungsten oxo alkylidene prepared through surface organometallic chemistry (SOMC). The observed kinetic profile is comprised of two consecutive regimes, which support the presence of two different active sites on the surface of such catalysts. We propose that the more active site is operational in the beginning of the reaction but deactivates very fast, and the second one initiates over time due to the presence of ethylene formed subsequently under the reaction conditions. A combination of spectroscopic techniques and computations was used to identify the possible nature of these sites. Solid-state NMR, EXAFS and DFT calculations are consistent with the esence of two distinct surface species that likely originate from the occurrence of slightly different local environments on the surface, that is, metal sites with a different number of nearby siloxane bridges. This data highlights the effects that may arise from the amorphous nature of the supports like silica and the difficulties to obtain truly single-site catalysts – one of the ultimate goals of SOMC.     

Synthesis and Catalytic Applications of Sulfonic Acid Group–Functionalized Nano- and Microsilica Structures

Sulfonic acid group–functionalized nano- and microsilica with different sizes and shapes were synthesized. Silica nanospheres with an average size of 225 nm, silica microtubes, and fine silica gel were prepared and functionalized by sulfonic acid. Their catalytic activity was investigated in the three-component Biginelli reaction for the synthesis of dihydropyrimidinones.     

Preparation and Surface Modification of Novel Vesicular Nano-Particle “Cerasome” with Liposomal Bilayer and Silicate Surface

A novel class of nano-hybrid materials, Cerasome, bearing a liposomal bilayer structure and a ceramic surface, has been developed by a sol-gel reaction of a double-chain proamphiphile having an trialkoxysilane in the head moiety and followed self-assembling. In the present work, we developed new methods for preparation of the Cerasomes forming under various pH conditions and their surface modification by employing appropriate alkoxysilane compounds. When the proamphiphilic alkoxysilane was hydrolyzed in an acidic ethanol and then injected into an aqueous media at various pH, the morphologically stable Cerasomes were obtained in a wide pH range. On the other hand, an acid treatment of the proamphiphile in ethanol in the presence of tetraethoxysilane gave the Cerasome with highly developed siloxane networks on its vesicular surface. Surface modification of the Cerasome with amino groups was readily achieved in the similar manner by replacing tetraethoxysilane to 3-aminopropyltriethoxysilane. The Cerasomes thus prepared were characterized by means of dynamic light scattering and zeta potential measurements.     

Redox-Neutral Tetrafluoroethylation of Aryl Alkynes with 1,1,2,2-Tetrafluoroethane Sulfonic Acid Leading to α-Tetrafluoroethylated Acetophenones

The redox-neutral tetrafluoroethylation of alkynes with 1,1,2,2-tetrafluroroethanesulfonic acid (TFESA) and azobis(isobutyronitrile) (AIBN) proceeds via the formation of vinyl tetrafluoroethanesulfonates followed by a radical tetrafluoroethylation. Experimental and theoretical results support an intermolecular reaction.     

Composites of Polystyrene Sulfonic Acid (PSSA)‐Polyaniline and Montmorillonite Clay: Synthesis and Characterization

Polystyrene sulfonic acid (PSSA) doped water‐soluble polyaniline (PANI)/montmorillonite (MMT) clay composites were synthesized by intercalation polymerization in aqueous medium. The properties of the composites were characterized by X‐ray diffraction (XRD), transmission electron microscope (TEM), Fourier‐transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS) and conductivity measurement. The results show that the composite has a mixed nanomorphology and exfoliated silicate nanolayers of MMT clay dispersed in the polyaniline matrix. This composite is more thermal stable than that without clay samples and results in good stable temperature‐dependent dc conductivity [σ_dc(T)] as temperature changed.     

α-Amino-iso-Butyric Acid Foldamers Terminated with Rhodium(I) N-Heterocyclic Carbene Catalysts

To investigate how remotely induced changes in ligand folding might affect catalysis by organometallic complexes, dynamic α-amino-iso-butyric acid (Aib) peptide foldamers bearing rhodium(I) N-heterocyclic carbene (NHC) complexes have been synthesized and studied. X-ray crystallography of a foldamer with an N-terminal azide and a C-terminal Rh(NHC)(Cl)(diene) complex showed a racemate with a chiral axis in the Rh(NHC) complex and a distorted 3₁₀ helical body. Replacing the azide with either one or two chiral L-α-methylvaline (L-αMeVal) residues gave diastereoisomeric foldamers that each possessed point, helical and axial chirality. NMR spectroscopy revealed an unequal ratio of diastereoisomers for some foldamers, indicating that the chiral conformational preference of the N-terminal residue(s) was relayed down the 1 nm helical body to the axially chiral Rh(NHC) complex. Although the remote chiral residue(s) did not affect the stereoselectivity of hydrosilylation reactions catalysed by these foldamers, these studies suggest a potential pathway towards remote conformational control of organometallic catalysts.     

Surface and Antimicrobial Properties of N-Palmitoyl Amino Acid–Based Surfactants

Synthesized sodium N-pamitoyl amino acids were evaluated for surface and antimicrobial properties and compared with sodium lauryl sulfate (SLS). Emulsion stability of the amino acid surfactants and calcium tolerance of the sodium N-palmitoyl isoleucine were better as compared to SLS. Wetting ability and foaming properties of the palmitic acid-based surfactants were inferior to SLS. N-Acyl amino acids exhibited better antibacterial activity compared to sodium salts of N-acyl amino acids and standard compounds against Staphylococcus aureus MLS-16 and Bacillus subtilis. These studies revealed that the palmitoyl amino acid surfactants can be exploited in household, skin care formulations, and industrial applications.     

Crystal Structures of β-Cyclodextrin Complexes with Formic Acid and Acetic Acid

β-Cyclodextrin (β–CD)-formic acid (1) andβ-CD–acetic acid (2) inclusion complexes crystallizeas β-CD...0.3HCOOH...7.7H₂O andβ-CD...0.4CH₃COOH...7.7H₂O in themonoclinic space group P2₁ with comparable unit cell constants.Anisotropic refinement of atomic parameters against X-ray diffractiondata with F_o ² > 2σ (F_o ²) (986/8563 and 991/8358)converged at R-factors of 0.051 and 0.054 for 1 and 2,respectively. In both complexes, the β-CD molecularconformation, hydration pattern and crystal packing are similar,but the inclusion geometries of the guest molecules are different.The β-CD macrocycles adopt a ``round'' conformationstabilized by intramolecular, interglucose O3(n)...O2(n + 1)hydrogen bonds and their O6–H groups are systematically hydratedby water molecules. In the asymmetric unit, each complex contains oneβ-CD, 0.3 formic acid (or 0.4 acetic acid), and 7.7 water moleculesthat are distributed over 9 positions. Water sites located in theβ-CD cavity hydrogen bond to the guest molecule. In thecrystal lattice, β-CD molecules are packed in a typical ``herringbone'' fashion. In 1, the formic acid (occupancy 0.3) is entirely included in the β-CD cavity such that its C atom is shifted from the O4-plane center to the β-CD O6-side by 2.90 Å and C=O, C–-O bonds point to this side. In 2, the acetic acid (occupancy 0.4) is completely embedded in the β-CD cavity, in which the carboxylic C atom is displaced from the O4-plane centerto the β-CD O6-side by 0.87 Å; the C=O bond directsto the β-CD O6-side and makes an angle of 15°to the β-CD molecular axis. Furthermore, bothdimethyl-β-CD-acetic acid and β-CD-acetic acidcomplexes form a cage structure, showing that the small guestsenclosed entirely in the cavity either in β-CD or indimethyl-β-CD do not affect the packing of the host macrocycles.     

Synthesis and Acid-Base Properties of Tetraphenylporphine Derivatives with Amino Acid “Anchor” Groups

Russian Journal of General Chemistry - Asymmetrically substituted 5,10,15,20-tetraphenylporphyrin derivatives such as 5-(4-aminophenyl)10,15,20-triphenylporphine,...     

p-Toluene Sulfonic Acid–Catalyzed,Solvent-Free Synthesis of Symmetrical Bisamides by Reaction Between Aldehydes and Amides

Reaction between aldehydes and amides catalyzed by p-toluene sulfonic acid in solvent-free conditions provided a simple and efficient one-pot route for the synthesis of symmetrical bisamide derivatives in excellent yields.     

Preparation and Analysis of Acylated Insulin with Dehydrocholic Acid

Insulin was chemically modified with dehydrocholic acid without the use of protecting agents and the main monoacylated insulin, ε-N^BZ9-Dehydrocholyl insulin was obtained selectively and analyzed by PAGE, HPLC and MALDI-TOF-MS.     

Influence of the Br?nsted and Lewis Acid Sites in Platinum/Solid Acid Catalysts on the Hydrogenation of Benzene and Toluene

The hydrogenation of benzene and toluene was investigated over US-SSY, -Al₂O₃, and Ha1-MCM-41 supported platinum catalysts. The acidity of catalyst supports was measured by IR spectra of pyridine adsorption. On the Brönsted acid supported catalyst, both the hexacyclic saturation product and the pentacyclic one, the hydroisomerization product, were observed, and these two products were revealed to be primary reaction products. The two products were proposed to be formed competitively on Brönsted acid sites with carbonium ions as the reaction intermediate. By contrast, no hydroisomerization product was found on Lewis acid supported catalysts. It was inferred that the electron-deficient reaction intermediate formed on Lewis acids could not undertake any skeletal isomerization process to give a pentacyclic saturation product.     

Synthesis and Characterization of the Terpolymer of Itaconic Acid with Acrylamide and 2-Acrylamido-2-methylpropanesulfonic Acid

The thermal stability of the polymer is of great significance in paper, ceramics and oil industry1. Conventional polymers such as polyanionic cellulose can not meet high temperature limitations2-4. Aggour5-6 and Collette7 etc. have conducted extensive research on synthesis and characterizations of the copolymer or terpolymer containing 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS). Till now, very few research works have been reported on the terpolymer of itaconic acid (IA), acrylamid…     

Nanoweb Surface-Mounted Metal–Organic Framework Films with Tunable Amounts of Acid Sites as Tailored Catalysts

Metal–organic frameworks (MOFs) are a promising class of materials for many applications, due to their high chemical tunability and superb porosity. By growing MOFs as (thin-)films, additional properties and potential applications become available. Here, copper (II) 1,3,5-benzenetricarboxylate (Cu-BTC) metal–organic framework (MOF) thin-films are reported, which were synthesized by spin-coating, resulting in “nanowebs”, that is, fiber-like structures. These surface-mounted MOFs (SURMOFs) were studied by using photoinduced force microscopy (PiFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The optimal concentration of precursors (10 mm ) was determined that resulted in chemically homogeneous, pure nanowebs. Furthermore, the morphology and (un)coordinated Cu sites in the web were tuned by varying the rotation speed of the spin-coating process. X-ray diffraction (XRD) analysis showed that rotation speeds ≥2000 rpm (with precursors in a water/ethanol solution) generate the catena-triaqua-μ-(1,3,5-benzenetricarboxylate)-copper(II), or Cu(BTC)(H₂O)₃ coordination polymer. X-ray photoelectron spectroscopy (XPS) highlighted the strong decrease in number of (defective) Cu⁺ sites, as the nanowebs mainly consist of coordinated Cu²⁺ Lewis acid sites (LAS) and organic linker–linker, for example, hydrogen-bonding, interactions. Finally, the Lewis-acidic character of the Cu sites is illustrated by testing the films as catalysts in the isomerization of α-pinene oxide. The higher number of LAS (≥3000 rpm), result in higher campholenic aldehyde selectivity reaching up to 87.7 %. Furthermore, the strength of a combined micro- and spectroscopic approach in understanding the nature of MOF thin-films in a spatially resolved manner is highlighted.     

Dielectric Relaxation of the β-Cyclodextrin Complexes with Tridecanoic Acid and 1,13-Tridecanedioic Acid

The frequency and temperature dependence of the real (') and imaginary (') parts of the dielectric permittivity of the polycrystalline complex-cyclodextrin-tridecanoic acid in two hydration forms (with 16.2 and 10.7 water molecules) and -cyclodextrin-1,13-tridecanedioic acid with 16.4 and 10.5 water molecules have been investigated, in the frequency range 0.1–100 kHz and temperature range 120–310 K. The dielectric behavior is described well by Debye-type relaxation dispersion. All systems except for the complex of partially dehydrated monocarboxylic acid, exhibit an additional -dispersion, at low frequencies (f < 1000 Hz). Only one-step was found in the ' vs. Tplots of both complexes in the two hydration forms, a fact indicating that the watermolecules cannot be divided into strongly bound and easily movable molecules. The'vs. T plots, at a fixed frequency (200 Hz), show the characteristic peakattributed to a transition between ordered and disordered -CD hydroxyl groupsand water molecules. The transition temperature was 202.7 K for all systems examinedexcept for the complex -CD-tridecanoic acid.16.2 H₂O (214.5 K). This means that the order to disorder transformation process was unaffected by the dehydration process in the case of the dicarboxylic acid complex, whereas in the case of the monocarboxylic acid, it was unexpectedly facilitated. The relaxation time varies with temperature, in a like curve (in the range 8–14 s), with maximum values located at the corresponding order-disorder transition temperatures. The activation energies of the fully hydrated complexes have absolute values of 5 kJ/mol in the range 1.98–3.82 K_{BT transition} which are higher than the corresponding values of :2 kJ/mol of the dehydrated complexes. A thermal hysteresis observed in all complexes is a result of the order-disorder transformation.     

Approximate Quantitation of Ascorbic Acid in Citrus and Tomato Juices with “Sandwich”-Indicator Sticks

Abstract

A rapid field-test of ascorbic acid content in fruit juices is feasible by the application of indicator papers capable for approximate quantitation.     

Gas-Phase Alkylation of Pyridine and Phenol with Alcohols Over Halide Clusters of Group 5–7 Transition Metals as Solid Acid Catalysts

Pyridine is allowed to react with methanol under a hydrogen stream in the presence of (H₃O)₂[(W₆Cl₈)Cl₆]·6H₂O supported on silica gel. When the temperature is raised above 200 °C, the catalytic activity of the cluster appears. Methylation of pyridine proceeds yielding 2-methylpyridine in 61% selectivity at 400 °C. The corresponding hexanuclear chloride clusters of niobium, molybdenum, and tantalum also catalyze the reaction. Ethanol affords the corresponding 2-ethylpyridine. When phenol is allowed to react with methanol in the presence of (H₃O)₂[(Mo₆Cl₈)Cl₆]·6H₂O supported on silica gel in the same manner, selective O-methylation proceeds yielding anisole in 57% selectivity at 150–200 °C. Above 250 °C, C-methylation predominates and provides o-cresol with 67% selectivity at 300 °C. The corresponding clusters of niobium, tantalum, and tungsten also catalyze the reaction. Ethanol and 1-propanol afford the corresponding 2-alkylphenols. Alkyl cations produced over weak Brønsted acid sites (H ₀ ≈ +1.3) developed on the clusters are assumed as intermediates for both reactions.