Supramolecular chemistry based on cyclodextrin receptors as second-sphere ligands contribute to developing non-covalent materials with synergistic functionalities. Herein, we comment on a recent ...investigation of this concept, describing selective gold recovery through a hierarchical host-guest assembly specifically built from β-CD.
Cobalt-aluminum-layered double hydroxides containing carboxymethyl β-cyclodextrin (CMβCD) were synthesized by coprecipitation and evaluated as a cobalt source for the 4-nitrophenol reduction in an ...aqueous medium. Several physicochemical techniques (XRD, FTIR, TGA) indicated the intercalation of the anionic cyclodextrin without damages to the hydrotalcite-type structure. These lamellar cobalt-aluminum hybrid materials (CoAl_CMβCD) were evaluated in the 4-nitrophenol reduction and showed higher activities in comparison with the CMβCD-free standard material (CoAl_CO3). To rationalize these results, a set of experimental controls going from physical mixtures of CoAl_CO3 with different cyclodextrins to other cobalt-based materials were investigated, highlighting the beneficial effects of both the layered double hydroxide and CMβCD-based hybrid structures. CMβCD also showed a beneficial effect as an additive during the 4-nitrophenol reduction. CoAl_CO3, dispersed in a fresh CMβCD solution could be re-used for five successive cycles without the loss of activity.
The present protocol reports the ultrasound assisted synthesis of NiO nanoparticles(NPs) using benzylamine as a base and different types of cyclodextrins (CDs) as capping agents. The use of α-CD, ...β-CD or γ-CD leads to different morphologies of NiO NPs. In particular, NiO nanosheets obtained using β-CD as the capping agent. The synthesized NPs were characterized by FEG-SEM, TEM, XRD and EDS analysis. They showed high catalytic activity towards synthesis of different trisubstituted imidazoles under solvent free conditions. In addition, NiO NPs could be recycled and reused consecutively up to four recycle runs without much loss of their catalytic activity.
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•Ultrasound assisted synthesis of NiO NPs using different capping agents of CD's.•Mechanism of interaction of CD with benzylamine was investigated.•Study of change in morphology of NPs with change in capping agnets.•Catalytic activity of NiO NPs for the synthesis of substituted imidazoles.
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•CD-assisted Ni-Pd bimetallic catalysts were prepared by different impregnation routes.•The best method involves the pre-adsorption of CD on Al2O3 before adding metal salts.•High ...dispersion of surface Ni nanoparticles (5–6 nm) along with surface Pd enrichment.•A 71% yield to n-octylamine was achieved in the reaction of 1-octanol with ammonia.
This paper reports the use of β-cyclodextrin as a pre-shaping agent for the preparation of low-metal xNi-yPd/Al2O3 catalysts (x = 2, 5 wt% and y = 0.2, 0.5, 1.0 wt%) targeting the direct amination of 1-octanol with ammonia. Six different preparation methods were used aiming at tuning the Ni-Pd interaction. The catalysts were finely characterized by XRD, H2-TPR, CO pulse chemisorption, STEM-EELS/EDS-SDD and XPS, while the elementary interaction between Ni-Pd-cyclodextrin was assessed by marrying ESI-MS experiments with DFT calculations. Among the different methods studied, the most outstanding effect was obtained when β-cyclodextrin was pre-adsorbed on γ-Al2O3 before impregnating the Ni and Pd nitrate precursors. At such conditions, the best formulation (5Ni-0.5Pd/Al-CD_M4) afforded 90% conversion and 71% yield to 1-octylamine (TON = 93) in the amination of 1-octanol with ammonia at 160 °C for 4 h, which places it among the most active and selective Ni catalysts reported in the literature.
In this paper, we present a versatile template-directed colloidal self-assembly method for the fabrication in aqueous phase of composition-tuned mesoporous RuO2@TiO2-SiO2 catalysts. Randomly ...methylated β-cyclodextrin/Pluronic F127 supramolecular assemblies were used as soft templates, TiO2 colloids as building blocks, and tetraethyl orthosilicate as a silica source. Catalysts were characterized at different stages of their synthesis using dynamic light scattering, N2-adsorption analysis, powder X-ray diffraction, temperature programmed reduction, high-resolution transmission electron microscopy, high-angle annular bright-field and dark-field scanning transmission electron microscopy, together with EDS elemental mapping. Results revealed that both the supramolecular template and the silica loading had a strong impact on the pore characteristics and crystalline structure of the mixed oxides, as well as on the morphology of the RuO2 nanocrystals. Their catalytic performance was then evaluated in the aqueous phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) under mild conditions (50 °C, 50 bar H2). Results showed that the cyclodextrin-derived catalyst displayed almost quantitative LA conversion and 99% GVL yield in less than one hour. Moreover, this catalyst could be reused at least five times without loss of activity. This work offers an effective approach to the utilization of cyclodextrins for engineering the surface morphology of Ru nanocrystals and pore characteristics of TiO2-based materials for catalytic applications in hydrogenation reactions.
α-, β-, and γ-cyclodextrins (CDs) were modified on their secondary face by mechanosynthesis at room temperature using a laboratory-scale ball-mill. Mono-2-tosylated α-, β-, and γ-CDs were obtained in ...good yield from mixtures of native α-, β-, and γ-CDs, respectively, N-tosylimidazole, and an inorganic base, with each of them being in the solid state. The yields appeared to be dependent upon the nature of the base and the reaction time. A kinetic monitoring by 1H NMR spectroscopy demonstrated that the highest yields in mono-2-tosyl-CDs were measured using KOH as a base in very short reaction times (up to 65% in 80 s). Mono-(2,3-manno-epoxide) α-, β-, and γ-CDs were subsequently synthesized by ball-milling a mixture of monotosylated α-, β-, and γ-CDs, respectively, and KOH. The characterization of the modified CDs was carried out by X-ray diffraction, mass spectrometry, solid-state NMR, and diffuse reflectance UV–vis (DR UV–vis) spectroscopies. Clues to the supramolecular arrangement of the molecules in the solid state provide information on the reaction mechanism.
Surface modification plays a key role in the fabrication of highly active and stable enzymatic nanoreactors. In this study, we report for the first time the effect of various functional groups ...(epoxy, amine, trimethyl, and hexadecyl) on the catalytic performance of lipase B from
(CALB) incorporated within a monolithic supramolecular hydrogel with multiscale pore architecture. The supramolecular hydrogel formed by host-guest interactions between α-cyclodextrin (α-CD) and Pluronic F127 was first silicified to provide a hierarchically porous material whose surface was further modified with different organosilanes permitting both covalent anchoring and interfacial activation of CALB. The catalytic activity of nanoreactors was evaluated in the liquid phase cascade oxidation of 2,5-diformylfuran (DFF) to 2,5-furandicarboxylic acid (FDCA) under mild conditions. Results showed that high FDCA yields and high efficiency conversion of DFF could be correlated with the ability of epoxy and amine moieties to keep CALB attached to the carrier, while the trimethyl and hexadecyl groups could provide a suitable hydrophobic-hydrophilic interface for the interfacial activation of lipase. Cationic cross-linked β-CD was also evaluated as an enzyme-stabilizing agent and was found to provide beneficial effects in the operational stability of the biocatalyst. These supramolecular silicified hydrogel monoliths with hierarchical porosity may be used as promising nanoreactors to provide easier enzyme recovery in other biocatalytic continuous flow processes.
Cinchonidine-functionalized β-cyclodextrin was used as stabilizing agent for platinum nanoparticles dispersed in water, but also as chiral modifier for the asymmetric hydrogenation of ethyl pyruvate ...at 30 °C under 40 bar of hydrogen. This functionalized cyclodextrin allowed getting more stable, more catalytically active and also more enantioselective Pt nanoparticles compared to control catalytic systems. NMR and MALDI-MS analyses clearly showed the reduction of the vinyl group of the cinchonidine graft during the nanoparticles preparation. Under hydrogen pressure, the hydrogenation of the quinolinic moiety was also proven and can be responsible for the difficulties encountered during the recycling study.
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•Cinchonidine-grafted β-cyclodextrin stabilizes platinum nanoparticles in water.•Ethyl pyruvate was hydrogenated with an enantiomeric excess of 63%.•The cinchonidine graft is required to obtain the asymmetric induction.•Concomitant hydrogenation of the cinchonidine graft of the stabilizer was proven.
A Pd/CeO2 catalyst with a prominent reversible H2 storage capacity revealed a high activity and selectivity in the direct amination of benzyl alcohol with aniline and ammonia via the borrowing ...hydrogen mechanism.
Got to pump it up! A Pd/CeO2 catalyst with a prominent reversible H2 storage capacity revealed a high activity and selectivity in the direct amination of benzyl alcohol with aniline and ammonia via the borrowing hydrogen mechanism.
A water-soluble β-cyclodextrin polymer synthesized by crosslinking β-cyclodextrin with epichlorohydrin and glycidyltrimethylammonium chloride allowed the stabilization of ruthenium nanoparticles not ...only in basic aqueous medium but also in acidic medium. The aqueous ruthenium colloidal suspensions obtained with this polymer were active as catalysts for the hydrogenation of a large variety of unsaturated compounds including aromatic or fatty acids. The recycling of this catalytic system was attested through ten consecutive runs without loss of stability and activity, demonstrating its robustness.
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