Bimetallic Au–Pd alloy nanoparticles supported on MIL-101(Cr) as highly efficient catalysts for selective hydrogenation of 1,3-butadiene

Gold–palladium (Au–Pd) bimetallic nanoparticle (NP) catalysts supported on MIL-101(Cr) with Au : Pd mole ratios ranging from 1 : 3 to 3 : 1 were prepared through coimpregnation and H₂ reduction. Au–Pd NPs were homogeneously distributed on the MIL-101(Cr) with mean particle sizes of 5.6 nm. EDS and XPS analyses showed that bimetallic Au–Pd alloys were formed in the Au(2)Pd(1)/MIL-101(Cr). The catalytic performance of the catalysts was explored in the selective 1,3-butadiene hydrogenation at 30–80 °C on a continuous fixed bed flow quartz reactor. The bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) presented improved catalytic performance. The as-synthesized bimetallic Au(2)Pd(1)/MIL-101(Cr) with 2 : 1 Au : Pd mole ratio showed the best balance between the activity and butene selectivity in the selective 1,3-butadiene hydrogenation. The Au–Pd bimetallic-supported catalysts can be reused in at least three runs. The work affords a reference on the utilization of a MOF and alloy nanoparticles to develop high-efficiency catalysts.

Bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) showed high activity and butene selectivity for 1,3-butadiene hydrogenation reaction.     

Breaking thiacalix[4]arene into pieces – a novel synthetic approach to higher calixarenes bearing mixed (–S–, –CH2–) bridges

A novel approach to calix[5–7]arenes possessing mixed (S and CH₂) bridges within the skeleton is based on the reaction of thiacalix[4]arene monosulfoxide with BuLi leading to a linear phenolic tetramer in essentially quantitative yield. This key intermediate is then cyclized with suitable building blocks to give macrocyclic calixarene analogues. Compared to the traditional stepwise construction of similar systems, this procedure based on thiacalixarene cleavage represents a scalable, robust, and straightforward synthesis and enables the preparation of larger calixarenes on a gram scale. As shown by ¹H NMR and UV-vis titration experiments, the mixed-bridge calix[7]arene is able to recognize fullerenes C₆₀ and C₇₀, thus showing possible applications of such systems. The structures of the mixed bridge systems were confirmed by single crystal X-ray analysis, and the behavior of novel macrocyclic skeletons in solution was studied using dynamic NMR techniques.

A novel approach is based on the cleavage of thiacalix[4]arene monosulfoxide with BuLi providing a linear tetramer in an essentially quantitative yield which is used as a building block for further cyclization.     

Na–Ga–Si type-I clathrate single crystals grown via Na evaporation using Na–Ga and Na–Ga–Sn fluxes

Single crystals of a Na–Ga–Si clathrate, Na₈Ga_5.70Si_40.30, of size 2.9 mm were grown via the evaporation of Na from a Na–Ga–Si melt with the molar ratio of Na : Ga : Si = 4 : 1 : 2 at 773 K for 21 h under an Ar atmosphere. The crystal structure was analyzed using X-ray diffraction with the model of the type-I clathrate (cubic, a = 10.3266(2) Å, space group Pm$\bar{3}$n, no. 223). By adding Sn to a Na–Ga–Si melt (Na : Ga : Si : Sn = 6 : 1 : 2 : 1), single crystals of Na₈Ga_xSi_46−x (x = 4.94–5.52, a = 10.3020(2)–10.3210(3) Å), with the maximum size of 3.7 mm, were obtained via Na evaporation at 723–873 K. The electrical resistivities of Na₈Ga_5.70Si_40.30 and Na₈Ga_4.94Si_41.06 were 1.40 and 0.72 mΩ cm, respectively, at 300 K, and metallic temperature dependences of the resistivities were observed. In the Si L_2,3 soft X-ray emission spectrum of Na₈Ga_5.70Si_40.30, a weak peak originating from the lowest conduction band in the undoped Si₄₆ was observed at an emission energy of 98 eV.

Single crystals of a Na–Ga–Si clathrate, Na₈Ga_4.94Si_41.06, of size 3.7 mm were grown via the evaporation of Na from a Na–Ga–Si–Sn melt with the molar ratio of Na : Ga : Si : Sn = 6 : 1 : 2 : 1 at 873 K for 3 h under an Ar atmosphere.     

Synthesis of a novel resorcin[4]arene–glucose conjugate and its catalysis of the CuAAC reaction for the synthesis of 1,4-disubstituted 1,2,3-triazoles in water

The Cu(i)-catalyzed azide–alkyne cycloaddition (CuAAC) in aqueous media using resorcin[4]arene glycoconjugate (RG) is reported. The eight β-d-glucopyranoside moieties constructed on the resorcin[4]arene upper rim provide a pseudo-saccharide cavity that offers a suitable host environment for water-insoluble hydrophobic azido and/or alkyne substrates in water. The utility of RG was established as an efficient inverse phase transfer catalyst for the CuAAC in water as a green approach for the synthesis of 1,4-disubstituted 1,2,3-triazole species. The catalytic utility of RG (1 mol%) was demonstrated in a multicomponent one-pot CuAAC for various azido/alkyne substrates. The RG acts as a molecular host and a micro-reactor resulting in the 1,4-disubstituted 1,2,3-triazoles in excellent yield.

The Cu(i)-catalyzed azide–alkyne cycloaddition (CuAAC) in aqueous media using resorcin[4]arene glycoconjugate (RG) is reported.     

Risk profile,antithrombotic treatment and clinical outcomes of patients in Nordic countries with atrial fibrillation – results from the GARFIELD-AF registry

AimsThe objective was to evaluate the clinical characteristics, management and two-year outcomes of patients with newly diagnosed non-valvular atrial fibrillation at risk for stroke in Nordic countries.MethodsWe examined the baseline characteristics, antithrombotic treatment, and two-year clinical outcomes of patients from four Nordic countries.ResultsA total of 52,080 patients were enrolled in the GARFIELD-AF. Out of 29,908 European patients, 2,396 were recruited from Nordic countries. The use of oral anticoagulants, alone or in combination with antiplatelet (AP), was higher in Nordic patients in all CHA₂DS₂-VASc categories: 0–1 (72.8% vs 60.3%), 2–3 (78.7% vs 72.9%) and ≥4 (79.2% vs 74.1%). In Nordic patients, NOAC ± AP was more frequently prescribed (32.0% vs 27.7%) and AP monotherapy was less often prescribed (10.4% vs 18.2%) when compared with Non-Nordic European patients. The rates (per 100 patient years) of all-cause mortality and non-haemorrhagic stroke/systemic embolism (SE) were similar in Nordic and Non-Nordic European patients [3.63 (3.11–4.23) vs 4.08 (3.91–4.26), p value = .147] and [0.98 (0.73–1.32) vs 1.02 (0.93–1.11), p value = .819], while major bleeding was significantly higher [1.66 (1.32–2.09) vs 1.01 (0.93–1.10), p value < .001].ConclusionNordic patients had significantly higher major bleeding than Non-Nordic-European patients. In contrast, rates of all-cause mortality and non-haemorrhagic stroke/SE were comparable. Clinical Trial RegistrationUnique identifier: NCT01090362. URL: http://www.clinicaltrials.gov. Key MessageNordic countries had significantly higher major bleeding than Non-Nordic-European countries. Rates of mortality and non-haemorrhagic stroke/SE were similar .     

Computational study on palladium-catalyzed alkenylation of remote δ-C(sp3)–H bonds with alkynes: a new understanding of mechanistic insight and origins of site-selectivity

Palladium-catalyzed alkenylation of δ-C(sp³)–H bonds with alkynes was conducted by density functional theory calculations. The present study shows that the dimeric Pd₂(OAc)₄ mechanism reproduces experimental observations well, including regioselectivity and provides a deep mechanistic insight complementing the monomeric Pd(OAc)₂ mechanism recently reported by Chen''s group. In addition, the economical heterodimeric Ni–Pd(OAc)₄ was predicted to be a potential species for such alkenylation of δ-C(sp³)–H bonds.

Palladium-catalyzed alkenylation of δ-C(sp³)–H bonds with alkynes was conducted by DFT calculations, showing that the dimeric Pd₂(OAc)₄ mechanism reproduces experimental observations well.     

Viologen–cucurbituril host/guest chemistry – redox control of dimerization versus inclusion

Two calix[4]arene systems, C23⁴⁺ and C24⁴⁺ – where 2 corresponds to the number of viologen units and 3–4 corresponds to the number of carbon atoms connecting the viologen units to the macrocyclic core – have been synthesized and led to the formation of [3]pseudorotaxanes when combined with either CB[7] or CB[8]. The [3]pseudorotaxanes spontaneously dissociate upon reduction of the bipyridinium units as the result of intramolecular dimerization of the two face-to-face viologen radical cations. CB[7] and CB[8]-based [2]pseudorotaxanes containing monomeric viologen guest model compounds, MC3²⁺ and MC⁴⁺, do not undergo decomplexation and dimerization following electrochemical reduction of their bipyridinium units.

Two calix[4]arenes with two viologen units separated by 3 or 4 carbon atoms from the macrocyclic core were synthesized and led to the formation of [3]pseudorotaxanes when combined with CB[7] or CB[8].     

Continuous syntheses of carbon-supported Pd and Pd@Pt core–shell nanoparticles using a flow-type single-mode microwave reactor

Continuous syntheses of carbon-supported Pd@Pt core–shell nanoparticles were performed using microwave-assisted flow reaction in polyol to synthesize carbon-supported core Pd with subsequent direct coating of a Pt shell. By optimizing the amount of NaOH, almost all Pt precursors contributed to shell formation without specific chemicals.

Continuous syntheses of carbon-supported Pd@Pt core–shell nanoparticles were performed using flow processes including microwave-assisted Pd core–nanoparticle formation.

Continuous flow syntheses have attracted attention as a powerful method for organic, nanomaterial, and pharmaceutical syntheses because of various features that produce benefits in terms of efficiency, safety, and reduction of environmental burdens.^1–7 Advances of homogeneous heating and mixing techniques in continuous flow reactors have engendered further developments for precise reaction control, which is expected to create innovative materials through combination with multiple-step flow syntheses.Microwave (MW) dielectric heating has been recognized as a promising methodology for continuous flow syntheses because rapid or selective heating raises the reaction rate and product yield.^8–18 For the last two decades, most MW apparatus has been batch-type equipped with a stirring mechanism in a multi-mode cavity. Therefore, conventionally used MW-assisted flow reactors have been mainly of the modified batch-type. Results show that the electromagnetic field distribution can be spatially disordered, causing inhomogeneous heating of the reactor.^19–25 Improvements of reactors suitable for flow-type work have been studied actively in recent years to improve their energy efficiency and to make irradiation of MW more homogeneous.^26–37We originally designed a MW flow reactor system that forms a homogeneous heating zone through generation of a uniform electromagnetic field in a cylindrical single-mode MW cavity.^26,30 The temperatures of flowing liquids in the reactor were controlled precisely via the resonance frequency auto-tracking function. Continuous flow syntheses of metal nanoparticle, metal-oxide, and binary metal core–shell systems with uniform particle size have been achieved using our MW reactor system.^26,38,39 Furthermore, large-scale production necessary for industrial applications can be achieved through integration of multiple MW reactors.³⁰Carbon-supported metal catalysts are widely used in various chemical transformations and fine organic syntheses. Particularly, binary metal systems such as Pd@Pt core–shell nanoparticles have attracted considerable interest for electro-catalysis in polymer electrolyte membrane fuel cells (PEMFC) because of their enhanced oxygen reduction activity compared to a single-use Pt catalyst. Binary metal systems also contribute to minimization of the usage of valuable Pt.^40–51 Earlier studies of carbon-supported Pd@Pt syntheses involved multiple steps of batch procedures such as separation, washing and pre-treatment of core metal nanoparticles, coating procedures of metal shells, and dispersion onto carbon supports. Flow-through processes generally present advantages over batch processes in terms of simplicity and high efficiency in continuous material production.We present here a continuous synthesis of carbon-supported Pd and Pd@Pt core–shell nanoparticles as a synthesis example of a carbon-supported metal catalyst using our MW flow reactor. This system incorporates the direct transfer of a core metal dispersion into a shell formation reaction without isolation. Nanoparticle desorption is prevented by nanoparticle synthesis directly on a carbon support. The presence of protective agents that are commonly used in nanoparticle syntheses, such as poly(N-vinylpyrrolidone), can limit the chemical activity of the catalyst. Nevertheless, this system requires no protective agent. Moreover, this system is a simple polyol synthesis that uses no strong reducing agent. It therefore imposes little or no environmental burden. For this study, the particle size and distribution of metals in Pd and Pd@Pt core–shell nanoparticles were characterized using TEM, HAADF-STEM observations, and EDS elemental mapping. From electrochemical measurements, the catalytic performance of Pd@Pt core–shell nanoparticles was evaluated.A schematic view of the process for the continuous synthesis of carbon-supported Pd@Pt core–shell nanoparticles is presented in Fig. 1. Details of single-mode MW flow reactor are described in ESI.^† We attempted to conduct a series of reactions coherently in a flow reaction system, i.e., MW-assisted flow reaction for the synthesis of carbon supported core Pd nanoparticles with subsequent deposition of the Pt shell. Typically, a mixture containing Na₂[PdCl₄] (1–4 mM) in ethylene glycol (EG), carbon support (Vulcan XC72, 0.1 wt%), and an aqueous NaOH solution were prepared. This mixture was introduced continuously into the PTFE tube reactor placed in the center of the MW cavity. Here, EG works as the reaction solvent as well as the reducing agent that converts Pd(ii) into Pd(0) nanoparticles. The MW heating temperature was set to 100 °C with the flow rate of 80 ml h^−l, which corresponds to residence time of 4 s. The carbon-supported Pd nanoparticles were transferred directly to the Pt shell formation process without particle isolation. The dispersed solution was introduced into a T-type mixer and was mixed with a EG solution of H₂[PtCl₆]·6H₂O (10 mM). The molar ratio of Pd : Pt was fixed to 1 : 1. Subsequently, after additional aqueous NaOH solution was mixed at the second T-mixer, the reaction mixture was taken out of the mixer and was let to stand at room temperature (1–72 h) for Pt shell growth.Open in a separate windowFig. 1Schematic showing continuous synthesis of carbon-supported Pd and Pd@Pt core–shell nanoparticles. The Pd nanoparticles were dispersed on the carbon support by MW heating of the EG solution. The solution was then transferred directly to Pt shell formation.Rapid formation of Pd nanoparticles with average size of 3.0 nm took place at the carbon-support surface during MW heating in the tubular reactor (Fig. 2a). Most of the Pd(ii) precursor was converted instantaneously to Pd(0) nanoparticles and was well dispersed over the carbon surface. Fig. 2b shows the time profile of the outlet temperature and applied MW power during continuous synthesis of carbon-supported Pd nanoparticles. The solution temperature rose instantaneously, reaching the setting temperature in a few seconds. This temperature was maintained with high precision (±2 °C) by the continuous supply of ca. 18 W microwave power. No appreciable deposition of metal was observed inside of the PTFE tube. It is noteworthy that Pd of 98% or more was supported on carbon by heating for 4 s at 100 °C from ICP-OES measurement. Our earlier report described continuous polyol (EG) synthesis of Pd nanoparticles as nearly completed with 6 s at 200 °C.³⁹ The reaction temperature in polyol synthesis containing the carbon was considerably low, suggesting that selective reduction reaction occurs on the carbon surface, which is a high electron donating property.Open in a separate windowFig. 2(a) TEM image of carbon-supported Pd nanoparticles synthesized using the MW flow reactor. The average particle size was 3.0 nm. (b) The time profile of the temperature at the reactor outlet and applied microwave power during continuous synthesis of carbon-supported Pd nanoparticles. Na₂[PdCl₄] = 2 mM, NaOH = 10 mM.The concentrations of Na₂[PdCl₄] precursor and NaOH affect the Pd nanoparticle size. Results show that the Pd particle size increased as the initial concentration of Na₂[PdCl₄] increased (Fig. S1a and b^†). Change of NaOH concentration exerted a stronger influence on the particle size. Nanoparticles of 12.3 nm were observed without addition of NaOH, whereas 2.6 nm size particles were deposited at the concentration of 20 mM (Fig. S1c and d^†). The higher NaOH concentration led to instantaneous nucleation and rapid completion of reduction. The Pd nanoparticle surface is equilibrated with Pd–O⁻ and Pd–OH depending on the NaOH concentration. The surface is more negative at high concentrations of NaOH because of the increase of the number of Pd–O⁻, which inhibits the mutual aggregation and further particle growth. Furthermore, to control the Pd nanoparticle morphology, we conducted synthesis by adding NaBr, which has been reported as effective for cubic Pd nanoparticle synthesis.⁵² However, because reduction of the Pd precursor derives from electron donation from both the polyol and the carbon support, morphological control was not achieved (Fig. S2^†). That finding suggests that morphological control is difficult to achieve by adding surfactant agents to the polyol.For Pt shell formation, carbon supported Pd nanoparticles (3.0 nm average particle size) were mixed with H₂[PtCl₆]·6H₂O solution with the molar ratio of Pd : Pt = 1 : 1. Then additional NaOH solution was mixed. As described in earlier reports,³⁹ alkaline conditions under which base hydrolysis and reduction of [PtCl₆]²⁻ to [Pt(OH)₄]²⁻ takes place are necessary for effective Pt shell formation. It is noteworthy that the added Pt precursor was almost entirely supported on carbon within 24 h in cases where an appropriate amount of additional NaOH (5 mM) was mixed by the second T-mixer (Fig. 3a). However, for 10 mM, nucleation and growth of single Pt nanoparticles were enhanced in place of core–shell formation. Consequently, a mixture of Pd@Pt and single Pt nanoparticles was formed on the carbon support (Fig. 3b). Very fine Pt nanoparticles were observed in the supernatant solution.Open in a separate windowFig. 3(a) Time profiles of residual ratio of Pt in the mixed solutions. Horizontal axis was left standing time. Carbon-support in the mixed solution after added the Pt precursor was precipitated by centrifugation. The supernatant solution was measured by ICP-OES. Concentrations of additional NaOH were 0, 5, and 10 mM. (b) TEM image of carbon-supported Pd@Pt core–shell nanoparticles. The synthesis conditions of Pd nanoparticles were Na₂[PdCl₄] (2 mM) and NaOH (10 mM). The molar ratio of Na₂[PdCl₄] : H₂[PtCl₆]·6H₂O was 1 : 1, and additional NaOH concentration was 10 mM. After left standing for 72 h, the mixture of Pd@Pt and single Pt nanoparticles (1–2 nm) was formed on carbon-support. Fig. 4a portrays a TEM image of carbon supported Pd@Pt core–shell nanoparticles. The average particle size of Pd@Pt core–shell nanoparticles was 3.6 nm after being left to stand for 24 h: larger than the initial Pd nanoparticles (3.0 nm). Fig. 4b shows the HAADF-STEM image of Pd@Pt core–shell nanoparticles supported on carbon. The core–shell structure of the particles can be ascertained from the contrast of the image. The Z-contrast image shows the presence of brighter shells over darker cores. Actually, the contrast is strongly dependent on the atomic number (Z) of the element.⁵³ The Z values of Pt (Z = 78) and Pd (Z = 46) differ considerably. Therefore, the image shows the formation of Pd@Pt core–shell structure with the uniform elemental distribution. Elemental mapping images by STEM-EDS show that both Pd and Pt metals were present in all the observed nanoparticles (Fig. 4c). Based on the atomic ratio (Pd : Pt = 49 : 51), they show good agreement with the designed values. The Pt shell thickness was estimated as about 0.6 nm, which corresponds to 2–3 atomic layer thickness of Pt encapsulating the Pd core metal, indicating good agreement with Fig. 4b image. For an earlier study, uniform Pt shells were formed by dropwise injection of the Pt precursor solution because the Pt shell growth rate differs depending on the crystal plane of the Pd nanoparticle.⁴⁶ For more precise control of shell thickness in our system, the Pt precursor solution should be mixed in multiple steps.Open in a separate windowFig. 4(a) TEM image and (b) HAADF-STEM image of carbon-supported Pd@Pt core–shell nanoparticles and the line profile of contrast. (c) Elemental mapping image of carbon-supported Pd@Pt core–shell nanoparticles, where Pd and Pt elements are displayed respectively as red and green. The EDS atomic ratio of Pd : Pt was 49 : 51. The synthesis conditions of Pd nanoparticles were Na₂[PdCl₄] (2 mM) and NaOH (10 mM). The molar ratio of Na₂[PdCl₄] : H₂[PtCl₆]·6H₂O was 1 : 1. The concentration of additional NaOH were 5 mM. It was left standing for 24 h.A comparison of the catalytic performance of the carbon-supported Pd@Pt core–shell and Pt nanoparticles is shown in Fig. S3.^† For this experiment, carbon-supported Pt nanoparticles with Pt 2 mM were prepared as a reference catalyst using a similar synthetic method. The initial Pt mass activities of the carbon-supported Pd@Pt and Pt nanoparticles were, respectively, 0.39 and 0.24 A mg_Pt⁻¹, improving by the core–shell structure. In addition, durability tests for carbon-supported Pd@Pt nanoparticles show that the reduction rate of Pt mass activity after 5000 cycles was only 2%. The catalytic activities of carbon-supported Pd@Pt nanoparticles were superior in terms of durability, suggesting that the Pt shell was firmly formed.     

An active and stable multifunctional catalyst with defective UiO-66 as a support for Pd over the continuous catalytic conversion of acetone and hydrogen

The one-pot synthesis of methyl isobutyl ketone (MIBK) and methyl isobutyl methanol (MIBC) from acetone and hydrogen is a typical cascade reaction comprised of aldol condensation-dehydration-hydrogenation. Pd loss and aggregation during long term operation are typical problems in industrial application. In this paper, an active and stable catalyst was achieved with defective UiO-66 as a support for Pd, which was synthesized with the ratio 15 : 1 of ZrOCl₂·8H₂O to ZrCl₄ as Zr-precursors. The resultant Pd catalyst remained active for at least 1000 h with a MIBK + MIBC selectivity of 84.87–93.09% and acetone conversion of 45.26–53.22% in a continuous trickle-bed reactor. Besides the increased Brønsted acid amount generated by the defect sites was favorable for the activity, the cavity confinement in the UiO-66 (R = 15 : 1) structure also efficiently prevented Pd loss and aggregation during the long term run. The contrast of the characterization of the fresh and used Pd/UiO-66 (R = 15 : 1) indicated that the deactivation of the catalyst was attributed to carbonaceous accumulation on the catalyst surface, which could be easily regenerated by calcination. This work supplied a new alternative for the design and utilization of industrial catalysts for MIBK and MIBC synthesis.

The one-pot synthesis of methyl isobutyl ketone (MIBK) and methyl isobutyl methanol (MIBC) from acetone and hydrogen is a typical cascade reaction comprised of aldol condensation-dehydration-hydrogenation.     

A novel donor–π–acceptor halochromic 2,6-distyrylnaphthalene chromophore: synthesis,photophysical properties and DFT studies

In this study a new 2,6-distyryl naphthalene [2-((4-((E)-2-(6-((E)-2,4-bis(methylsulfonyl)styryl)naphthalen-2-yl)vinyl)phenyl)(ethyl)amino)ethan-1-ol; ASDSN] was synthesized successfully using Heck chemistry as the main reaction. The ASDSN compound is a donor–pi–acceptor (D–π–A) conjugated system with amino as electron donating and sulfonyl as electron withdrawing groups. The UV-vis absorption of ASDSN was observed in the range of 403–417 nm with high molar extinction coefficients (ε = 15 300–56 200 M⁻¹ cm⁻¹) in some different solvents. This new fluorescent 2,6-distyryl naphthalene compound emits in the yellow region of the visible spectrum (557 nm) with Stokes shifts of 5930 cm⁻¹. ASDSN is a pH-responsive fluorescence compound that shows yellow fluorescence in neutral form and blue fluorescence in the protonated form. A white light emission (WLE) for the chromophore was observed at pH = 3.0. The ASDSN chromophore presented a satisfactory white light quantum yield (Φ) of 13% which was desirable for producing white light emitting devices. Density functional theory (DFT) and time-dependent (TD)-DFT were applied to study structural and electronic properties of the chromophore.

A new pH-responsive fluorescence chromophore with white light emission at pH = 3 was synthesized which has high potential application in the preparation of high-performance lighting devices.     

Cinnamaldehyde–cucurbituril complex: investigation of loading efficiency and its role in enhancing cinnamaldehyde in vitro anti-tumor activity

This study aimed to clarify the physico-chemical properties of cucurbit[7]uril (CB[7]) and cinnamaldehyde (Cinn) inclusion complexes (CB[7]–Cinn) and their resulting antitumor activity. CB[7]–Cinn inclusion complexes were prepared by a simple experimental approach and fully characterized for their stoichiometry, formation constant, particle size and morphology. Quantum chemical calculations were performed to elucidate the stable molecular structures of the inclusion complexes and their precursors and to investigate the probable stoichiometry and direction of interaction using three different DFT functionals at the 6-31G(d,p) basis set. The UV-vis spectrophotometric titrations as well as the Job plot, based on ¹H NMR spectroscopy, suggested 1 : 1 and 1 : 2 stoichiometries of CB[7] : Cinn. The formation constants of the complexes were calculated using Benesi–Hildebrand equations and non-linear fittings. Moreover, the theoretical calculations confirmed the potential formation of 1 : 1 and 1 : 2 stoichiometries and clarify the orientation of binding from the Cinn phenyl moiety. The nanoparticles'' TEM images showed a crystal-like spherical shape, smooth surface, with a small tendency to agglomerate. CB[7]–Cinn inclusion complexes were analyzed for their antitumor activity against MDA-MB-231 breast cancer and U-87 glioblastoma cell lines. The IC₅₀ values were calculated after 72 hours of incubation with different concentrations of CB[7]–Cinn inclusion complexes and compared to free Cinn and free CB[7]. The IC₅₀ values for free Cinn and CB[7]–Cinn inclusion complexes were 240.17 ± 32.46 μM and 260.47 ± 20.83 μM against U-87 cells and 85.93 ± 3.35 μM and 176.3 ± 7.79 μM against MDA-MB-231 cells, respectively, despite the enhanced aqueous solubility. No significant cytotoxicity was noticed for the free CB[7].

This study aimed to clarify the physico-chemical properties of cucurbit[7]uril (CB[7]) and cinnamaldehyde (Cinn) inclusion complexes (CB[7]–Cinn) and their resulting antitumor activity.     

1,2,3-Triazole framework: a strategic structure for C–H⋯X hydrogen bonding and practical design of an effective Pd-catalyst for carbonylation and carbon–carbon bond formation

1,2,3-Triazole is an interesting N-heterocyclic framework which can act as both a hydrogen bond donor and metal chelator. In the present study, C–H hydrogen bonding of the 1,2,3-triazole ring was surveyed theoretically and the results showed a good agreement with the experimental observations. The click-modified magnetic nanocatalyst Pd@click-Fe₃O₄/chitosan was successfully prepared, in which the triazole moiety plays a dual role as both a strong linker and an excellent ligand and immobilizes the palladium species in the catalyst matrix. This nanostructure was well characterized and found to be an efficient catalyst for the CO gas-free formylation of aryl halides using formic acid (HCOOH) as the most convenient, inexpensive and environmentally friendly CO source. Here, the aryl halides are selectively converted to the corresponding aromatic aldehydes under mild reaction conditions and low Pd loading. The activity of this catalyst was also excellent in the Suzuki cross-coupling reaction of various aryl halides with phenylboronic acids in EtOH/H₂O (1 : 1) at room temperature. In addition, this catalyst was stable in the reaction media and could be magnetically separated and recovered several times.

The C–H hydrogen bonding of a 1,2,3-triazole framework was studied. An Fe₃O₄–chitosan core–shell incorporating a triazole/Pd complex was investigated as a nanocatalyst in carbonylation and C–C coupling.     

Hydrodesulfurization of dibenzothiophene using Pd-promoted Co–Mo/Al2O3 and Ni–Mo/Al2O3 catalysts coupled with ionic liquids at ambient operating conditions

Sulfur compounds in fuel oils are a major source of atmospheric pollution. This study is focused on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) via the coupled application of 0.5 wt% Pd-loaded Co–Mo/Al₂O₃ and Ni–Mo/Al₂O₃ catalysts with ionic liquids (ILs) at ambient temperature (120 °C) and pressure (1 MPa H₂). The enhanced HDS activity of the solid catalysts coupled with [BMIM]BF₄, [(CH₃)₄N]Cl, [EMIM]AlCl₄, and [(n-C₈H₁₇)(C₄H₉)₃P]Br was credited to the synergism between hydrogenation by the former and extractive desulfurization and better H₂ transport by the latter, which was confirmed by DFT simulation. The Pd-loaded catalysts ranked highest by activity i.e. Pd–Ni–Mo/Al₂O₃ > Pd–Co–Mo/Al₂O₃ > Ni–Mo/Al₂O₃ > Co–Mo/Al₂O₃. With mild experimental conditions of 1 MPa H₂ pressure and 120 °C temperature and an oil : IL ratio of 10 : 3.3, DBT conversion was enhanced from 21% (by blank Ni–Mo/Al₂O₃) to 70% by Pd–Ni–Mo/Al₂O₃ coupled with [(n-C₈H₁₇)(C₄H₉)₃P]Br. The interaction of polarizable delocalized bonds (in DBT) and van der Waals forces influenced the higher solubility in ILs and hence led to higher DBT conversion. The IL was recycled four times with minimal loss of activity. Fresh and spent catalysts were characterized by FESEM, ICP-MS, EDX, XRD, XPS and BET surface area techniques. GC-MS analysis revealed biphenyl as the major HDS product. This study presents a considerable advance to the classical HDS processes in terms of mild operating conditions, cost-effectiveness, and simplified mechanization, and hence can be envisaged as an alternative approach for fuel oil processing.

Synergistic application of ionic liquids with Pd loaded Co–Mo@Al₂O₃ and Ni–Mo@Al₂O₃ catalysts for efficient hydrodesulfurization of dibenzothiophene at ambient conditions.     

Copper–ligand clusters dictate size of cyclized peptide formed during alkyne–azide cycloaddition on solid support

Peptide and peptidomimetic cyclization by copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction have been used to mimic disulfide bonds, alpha helices, amide bonds, and for one-bead-one-compound (OBOC) library development. A limited number of solid-supported CuAAC cyclization methods resulting in monomeric cyclic peptide formation have been reported for specific peptide sequences, but there exists no general study on monocyclic peptide formation using CuAAC cyclization. Since several cyclic peptides identified from an OBOC CuAAC cyclized library has been shown to have important biological applications, we discuss here an efficient method of alkyne–azide ‘click’ catalyzed monomeric cyclic peptide formation on a solid support. The reason behind the efficiency of the method is explored. CuAAC cyclization of a peptide sequence with azidolysine and propargylglycine is performed under various reaction conditions, with different catalysts, in the presence or absence of an organic base. The results indicate that piperidine plays a critical role in the reaction yield and monomeric cycle formation by coordinating to Cu and forming Cu–ligand clusters. A previously synthesized copper compound containing piperidine, [Cu₄I₄(pip)₄], is found to catalyze the CuAAC cyclization of monomeric peptide effectively. The use of 1.5 equivalents of CuI and the use of DMF as solvent is found to give optimal CuAAC cyclized monomer yields. The effect of the peptide sequence and peptide length on monomer formation are also investigated by varying either parameter systemically. Peptide length is identified as the determining factor for whether the monomeric or dimeric cyclic peptide is the major product. For peptides with six, seven, or eight amino acids, the monomer is the major product from CuAAC cyclization. Longer and shorter peptides on cyclization show less monomer formation. CuAAC peptide cyclization of non-optimal peptide lengths such as pentamers is affected significantly by the amino acid sequence and give lower yields.

We report the heterogeneous controlled formation of monomeric cyclic peptides by CuAAC reaction using cooper–piperidine complexes.     

Synergetic effect over flame-made manganese doped CuO–CeO2 nanocatalyst for enhanced CO oxidation performance

CuO–CeO₂ nanocatalysts with different amounts of Mn dopping (Mn/Cu molar ratios of 0.5 : 5, 1 : 5 and 1.5 : 5) were synthesized by flame spray pyrolysis (FSP) method and tested in the catalytic oxidation of CO. The physicochemical properties of the synthesised samples were characterized systematically, including using X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), oxygen-temperature programmed desorption (O₂-TPD), hydrogen-temperature programmed reduction (H₂-TPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The results showed that the 1Mn–Cu–Ce sample (Mn/Cu molar ratio of 1 : 5) exhibited superior catalytic activity for CO oxidation, with the temperature of 90% CO oxidation at 131 °C at a high space velocity (SV = 60 000 mL g⁻¹ h⁻¹), which was 56 °C lower than that of the Cu–Ce sample. In addition, the 1Mn–Cu–Ce sample displays excellent stability with prolonged time on CO stream and the resistance to water vapor. The significantly enhanced activity was correlated with strong synergetic effect, leading to fine textual properties, abundant chemically adsorbed oxygen and high lattice oxygen mobility, which further induced more Cu⁺ species and less formation of carbon intermediates during the CO oxidation process detected by in situ DRIFTS analysis. This work will provide in-depth understanding of the synergetic effect on CO oxidation performances over Mn doped CuO–CeO₂ composite catalysts through FSP method.

The synergetic effect is promoted on Mn doped CuO–Ce O₂ catalyst to induce less carbon intermediates to enhance CO oxidation performance.     

Palygorskite-anchored Pd complexes catalyze the coupling reactions of pyrimidin-2-yl sulfonates

In this work, an anchored Pd complex (PGS–APTES–Pd(OAc)₂) was prepared via simple and green steps from the natural clay mineral palygorskite and was well characterized by XPS, XRD, IR, SEM, and EDX. This complex was further utilized as a fine catalyst for the C–C/C–N coupling reactions of pyrimidin-2-yl sulfonates. Subsequently, the cyclic utilization test indicated the high stability and sustainability of this PGS–APTES–Pd(OAc)₂ catalyst, and no activation was required in the recycling process, providing an applicable and reusable catalyst in organic synthesis.

PGS–APTES–Pd(OAc)₂ was prepared through simple and green steps from the natural clay mineral palygorskite. Obviously, the stability and reusability of PGS–APTES–Pd(OAc)₂ were superior to those of the PGS–Pd catalyst (prepared by the impregnation method) in recycling test.     

Synthesis of novel calix[4]arene p-benzazole derivatives and investigation of their DNA binding and cleavage activities with molecular docking and experimental studies

In this study, novel p-benzimidazole-derived calix[4]arene compounds with different structures, and a benzothiazole-derived calix[4]arene compound, were synthesized by a microwave-assisted method and their structures were determined by FTIR, ¹H NMR, ¹³C NMR, MALDI-TOF mass spectroscopy, and elemental analysis. The effects of functional calixarenes against bacterial (pBR322 plasmid DNA) and eukaryotic DNA (calf thymus DNA = CT-DNA) were investigated. The studies with plasmid DNA have shown that compounds 6 and 10 containing methyl and benzyl groups, respectively, have DNA cleavage activity at the highest concentrations (10 000 μM). Interactions with plasmid DNA using some restriction enzymes (BamHI and HindIII) were also investigated. The binding ability of p-substituted calix[4]arene compounds towards CT-DNA was examined using UV-vis and fluorescence spectroscopy and it was determined that some compounds showed efficiency. In particular, it was observed that the functional compounds (10 and 5) containing benzyl and chloro-groups had higher activity (K_b binding constants were found to be 7.1 × 10³ M⁻¹ and 9.3 × 10² M⁻¹ respectively) on DNA than other compounds. Competitive binding experiments using ethidium bromide also gave an idea about the binding properties. Docking studies of the synthesized compounds with DNA were performed to predict the binding modes, affinities and noncovalent interactions stabilizing the DNA–compound complexes at the molecular level. Docking results were in good agreement with the experimental findings on the DNA binding activities of compounds. Based on these results, this preliminary study could shed light on future experimental antibacterial and/or anticancer research.

In this study, p-benzazole-derived calix[4]arene compounds with aromatic structures are synthesized and their DNA cleavage/binding properties are investigated.     

C(acyl)–C(sp2) and C(sp2)–C(sp2) Suzuki–Miyaura cross-coupling reactions using nitrile-functionalized NHC palladium complexes

Application of N-heterocyclic carbene (NHC) palladium complexes has been successful for the modulation of C–C coupling reactions. For this purpose, a series of azolium salts (1a–f) including benzothiazolium, benzimidazolium, and imidazolium, bearing a CN-substituted benzyl moiety, and their (NHC)₂PdBr₂ (2a–c) and PEPPSI-type palladium (3b–f) complexes have been systematically prepared to catalyse acylative Suzuki–Miyaura coupling reaction of acyl chlorides with arylboronic acids to form benzophenone derivatives in the presence of potassium carbonate as a base and to catalyse the traditional Suzuki–Miyaura coupling reaction of bromobenzene with arylboronic acids to form biaryls. All the synthesized compounds were fully characterized by Fourier Transform Infrared (FTIR), and ¹H and ¹³C NMR spectroscopies. X-ray diffraction studies on single crystals of 3c, 3e and 3f prove the square planar geometry. Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), metal mapping analyses and thermal gravimetric analysis (TGA) were performed to get further insights into the mechanism of the Suzuki–Miyaura cross coupling reactions. Mechanistic studies have revealed that the stability and coordination of the complexes by the CN group are achieved by the removal of pyridine from the complex in catalytic cycles. The presence of the CN group in the (NHC)Pd complexes significantly increased the catalytic activities for both reactions.

Nitrile-functionalized Pd(ii) complexes have evaluated for the Suzuki–Miyaura cross-coupling reactions. The highest TON value was reached for the acylative Suzuki–Miyaura cross-coupling reaction of acyl chlorides with phenylboronic acids.     

Host–guest modes and supramolecular frameworks of complexes of tetramethyl cucurbit[6]uril with 4-chloroaniline and 4,4′-diaminostilbene

Since the first reportal on decamethylcucurbit[5]uril (Me₁₀Q[5]) in 1992, substituted cucurbit[n]urils have attracted considerable research interest. In this study, the host–guest modes between the tetramethyl cucurbit[6]uril (TMeQ[6]) as a host and 4-chloroaniline and 4,4′-diaminostilbene (G1 and G2) as guests were investigated by single-crystal X-ray diffraction, NMR, ITC, UV-Vis spectrum, and MALDI-TOF mass spectrometry analyses. The experimental results showed that TMeQ[6] formed a 1 : 1 inclusion compound with G1, and the carbonyl portal of TMeQ[6] formed a 1 : 1 self-assembly with G2. Further, multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H⋯π interactions, ion–dipole interactions, and dipole–dipole interactions).

Two TMeQ[6]-based multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H... π interactions, ion–dipole interactions, and dipole–dipole interactions).     

Access to indolines from primary phenylethylamines by an unexpected palladium-catalyzed C–H functionalization process

A new method for the preparation of 2,2-disubstituted indolines from 2-phenylethylamines was developed under Pd catalysis and PhI(OAc)₂ as oxidant. Imines derived from 2-pyridinecarboxaldehyde were formed in situ to direct a C–H activation process. The resulting imines were also oxidized to the corresponding amides in the same Pd-catalyzed process to obtain the final indoline as a picolinamide.

A new method for the preparation of 2,2-disubstituted indolines from 2-phenylethylamines was developed under Pd catalysis and PhI(OAc)₂ as oxidant.