Hydrophobic mesoporous silicon dioxide for improving foam stability

In this study, mesoporous SiO₂ nanoparticles (MSNs) were synthesized via a sol–gel method and modified with (3-chloropropyl) trimethoxysilane to make them hydrophobic (MMSNs). The material was characterized via SEM, TEM, FT-IR, DLS, BET and contact angle measurements. The MMSNs have good foam stability, so that the foam properties of the added particles have been increased by 38.4% in an oil/SDS solution. Simultaneously, it becomes a promising material for foam stabilization in order to enhance the oil recovery because it is bio-compatibile and environment friendly. Also, it provides a novel application-stable foam for mesoporous materials.

In this study, mesoporous SiO₂ nanoparticles (MSNs) were synthesized via a sol–gel method and modified with (3-chloropropyl) trimethoxysilane to make them hydrophobic (MMSNs).     

Patterned nanofiber air filters with high optical transparency,robust mechanical strength,and effective PM2.5 capture capability

PM_2.5, due to its small particle size, strong activity, ease of the attachment of toxic substances and long residence time in the atmosphere, has a great impact on human health and daily production. In this work, we have presented patterned nanofiber air filters with high optical transparency, robust mechanical strength and effective PM_2.5 capture capability. Here, to fabricate a transparency air filter by a facile electrospinning method, we chose three kinds of patterned wire meshes with micro-structures as negative receiver substrates and directly electrospun polymer fibers onto the supporting meshes. Compared with randomly oriented nanofibers (named “RO NFs” in this paper) and commercially available facemasks, the patterned air filters showed great mechanical properties, and the water contact angles on their surfaces were about 122–143° (the water contact angle for RO NFs was 81°). In addition, the patterned nanofibers exhibited high porosity (>80%), and their mean pore size was about 0.5838–0.8686 μm (the mean pore size of RO NFs was 0.4374 μm). The results indicate that the transparent patterned air filters have the best PM_2.5 filtration efficiency of 99.99% at a high transmittance of ∼69% under simulated haze pollution.

PM_2.5, due to its small particle size, strong activity, ease of the attachment of toxic substances and long residence time in the atmosphere, has a great impact on human health and daily production.     

Fabrication of CS/GA/RGO/Pd composite hydrogels for highly efficient catalytic reduction of organic pollutants

In this study, natural polymer material chitosan (CS) and graphene oxide (GO) with large specific surface area were used to prepare a new CS/RGO-based composite hydrogel by using glutaraldehyde (GA) as cross-linking agent. In addition, a CS/GA/RGO/Pd composite hydrogel was prepared by loading palladium nanoparticles (Pd NPs). The morphologies and microstructures of the prepared hydrogels were characterized by SEM, TEM, XRD, TG, and BET. The catalytic performance of the CS/GA/RGO/Pd composite hydrogel was analyzed, and the experimental results showed that the CS/GA/RGO/Pd composite hydrogel had good catalytic performance for degradation of p-nitrophenol (4-NP) and o-nitroaniline (2-NA). Therefore, this study has potential application prospect in wastewater treatment and provides new information for composite hydrogel design.

New functional CS/GA/RGO/Pd composite hydrogels are prepared via a self-assembly process, demonstrating potential applications in catalysis as well as composite materials.     

Effect of polyethylene glycol on crystal growth and photocatalytic activity of anatase TiO2 single crystals

In order to evaluate the effect of polyethylene glycol (PEG) on the growth of TiO₂ crystals, anatase TiO₂ crystals with different morphologies and structures were synthesized by controlling the content and type of PEG in a solvothermal system. Then, their morphology and structure were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Characterization results show that hydrofluoric acid can promote the formation of high activity (001) facets. Experiments on the effect of PEG on crystal growth show that the low molecular weight PEG (PEG400) can accelerate crystal differentiation and relieve the agglomeration of crystals in the presence of hydrofluoric acid. Besides, according to the experimental results, we found that PEG400 can reduce the agglomeration size and number of TiO₂ polycrystalline particles. Research on the photocatalytic activity proposed that the independence of single crystal and the integrity of (001) facets are the critical factors in advanced oxidation reaction. The resultant anatase TiO₂ single crystals could produce more hydroxyl radicals (˙OH) in the photocatalytic system, which exhibited remarkable photocatalytic performance for the degradation of Acid Red B.

Anatase TiO₂ crystals with different structures were synthesized. Experiments on the effect of polyethylene glycol show that the low molecular weight PEG (PEG400) can accelerate crystal differentiation and relieve the agglomeration of crystals.     

A nitronyl nitroxide and its two 1D chain Cu–Tb complexes: synthesis,structures, and magnetic properties

A new nitronyl nitroxide, namely NIT-Ph-p-OCH₂trz (1), and two types of one-chain Cu–Tb complexes, namely [TbCu(hfac)₅NIT-Ph-p-OCH₂trz·0.5C₆H₁₄]_n (2a) and [LnCu(hfac)₅NIT-Ph-p-OCH₂trz]_n (2b) (NIT-Ph-p-OCH₂trz = 2-(4-((1H-1,2,4-triazol-1-yl)methoxy)phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate), have been successfully synthesized simultaneously through reacting nitronyl nitroxide radical NIT-Ph-p-OCH₂trz with Cu(hfac)₂ and Ln(hfac)₃, and the molecular structures have been elucidated via single-crystal X-ray structural analysis. 2a features a ‘ladder-like’ chain structure, while 2b displays a linear chain structure built up by Ln(hfac)₃ units bridged with the NO groups of radical ligands. The additional Cu(ii) ions are coordinated to the nitrogen atoms of the triazole units. Nonzero out-of-phase signals are observed for the Tb derivatives (2a and 2b) and they exhibit frequency-dependent out-of-phase signals indicating a single-chain magnet behavior.

A new nitronyl nitroxide and two types of one-chain Cu–Tb complexes have been successfully synthesized, and the molecular structures have been elucidated via single-crystal X-ray structural analysis.     

Synthetic progress toward the marine natural product zamamiphidin A

An asymmetric synthetic approach to the octahydrofuro[3,4-b]pyridine framework of marine natural product zamamiphidin A has been described. The key steps include an asymmetric Michael addition of (R)-N-tert-butanesulfinyl imidate with enamidomalonate to install the C10 stereocenter, an intramolecular alkoxide exchange/Michael addition/hydrogenation sequence to construct the bicyclic ring system.

An asymmetric synthetic approach to the octahydrofuro[3,4-b]pyridine framework of marine natural product zamamiphidin A has been described.

Marine natural products have been recognized as an important source of potential lead compounds.¹ Recently, the growing attention on innovative drug discovery has propelled the identification of numerous marine-derived bioactive compounds with superior chemical novelty.² In 2013, Kobayashi and co-workers isolated a new macrocyclic diamine alkaloid zamamiphidin A (1, Fig. 1A) from an Okinawan marine sponge Amphimedon sp. (SS-1231),³ along with its biogenetically related manzamine alkaloids such as ircinic acid (2) and manzamine A (3). In the isolation work, the authors also demonstrated that compound 1 exhibited moderate antibacterial activity against Staphylococcus aureus (MIC, 32 μg mL⁻¹).³ Architecturally, zamamiphidin A was characterized by an unprecedented heptacyclic framework, comprising a highly fused pentacyclic caged core, two 11-membered rings and seven contiguous stereocenters including one all-carbon quaternary center. More specifically, the fusion of 7-oxa-2-azabicyclo[2.2.1]heptane (4, Fig. 1B), azabicyclo[3.3.1]nonane (5) and octahydrofuro[3,4-b]pyridine (6) fragments as well as the presence of quaternary ammonium salt render zamamiphidin A unique among other macrocyclic diamine alkaloids.⁴ To the best of our knowledge, the chemical synthesis of 1 has yet to be disclosed. Herein, we report our recent synthetic efforts toward zamamiphidin A (1).Open in a separate windowFig. 1Structures of (A) zamamiphidin A (1), its related manzamine alkaloids (2 and 3) and (B) fragments 4–6 of 1.From a retrosynthetic perspective (Scheme 1), we envisioned that zamamiphidin A would arise from the advanced intermediate 7 through late-stage formation of two 11-membered rings.^4,5 Central to the synthesis of the target molecule (1) would be the construction of the pentacyclic and cage-like backbone 7. Structural analysis suggested the diazapentacyclic core of 7 could be simplified as a fully substituted tetrahydrofuran moiety containing two amine functionalities at C3 and C10 (Scheme 1, in blue), which thus could be traced back to the precursor 10. Specifically, disconnecting the C1–N2 bond in 7 revealed ketone 8; and the azabicyclo[3.3.1]nonane unit in 8 could be formed by a Mannich reaction and an intramolecular Dieckmann condensation from bicycle 9. Disassembly of the piperidine ring in 9 through an intramolecular Michael addition led back to the functionalized tetrahydrofuran 10. Based on our previous studies,⁶10 could be easily traced back to the chiral malonate 12 bearing a pendant N-tert-butanesulfinyl imidate motif, relying on an intramolecular alkoxide exchange to forge the tetra-hydrofuran ring (11 to 10) and a Davis oxidation to install the C9 hydroxyl group (12 to 11). In turn, 12 could be accessed via a diastereoselective Michael addition of N-tert-butanesulfinyl imidate 13 to enamidomalonate 14.Open in a separate windowScheme 1Retrosynthetic analysis of zamamiphidin A.Our synthetic approach started from the preparation of the chiral malonate 12 (Scheme 2). First, condensation of the known primary amine 15⁷ with dimethyl methoxymethylenemalonate (16) in refluxing toluene delivered enamine 17 (92% yield), which was subsequently protected with Boc to give compound 14. The key asymmetric Michael addition of (R)-N-tert-butanesulfinyl imidate 13 to enamidomalonate 14 proceeded smoothly by employing LiHMDS as base,^6,8–10 providing adduct 12 as the major diastereomer in 72% yield (d.r. = 7 : 1 at C10). We supposed that the addition would preferentially take place through Ts-18 to avoid the significant steric repulsion between the tert-butyl group of 13 and the N-Boc side chain of 14, thus favoring the generation of 12. The configuration of the newly generated C10 stereocenter in 12 could be confirmed later by further transformations (vide infra). As far as we knew, this example represents the first asymmetric conjugate addition of N-tert-butanesulfinyl metalloenamines by using enamidomalonate as the Michael acceptor, which would be useful for the preparation of β-amino acid.¹¹Open in a separate windowScheme 2Synthesis of the chiral malonate 12.With malonate 12 available, we next sought to construct the octahydrofuro[3,4-b]pyridine ring system of zamamiphidin A (Scheme 3). To this end, our first task was to introduce a hydroxyl group at C9 in 12. After exploring various oxidative conditions such as Mn(OAc)₃/AcOH,¹² IBX/DMSO/H₂O,¹³ and O₂/I₂/NaOAc,¹⁴ we found that a Davis protocol¹⁵ (Davis'' oxaziridine/NaH/THF, −50 °C) was successful to convert 12 to 11 with 82% yield. Formation of the tetrahydrofuran ring from 11 proceeded in the presence of Et₃N/toluene at reflux temperature via an intramolecular alkoxide exchange, resulting in 19 (71% yield). Desilylation of 19 with HF afforded the primary alcohol 20 (85% yield). The latter then underwent a two-step synthetic sequence including oxidation of the hydroxyl group to aldehyde and Wittig olefination of the resulting aldehyde with methyl(triphenylphosphoranylidene)acetate (21), providing enoate 10 in 64% overall yield. Upon treating 10 with NaH in the presence of HMPA at −20 °C, an intramolecular Michael addition reaction occurred to enable the coupling of C4 and C4a, leading to the formation of the bicyclic intermediate 22 (72% yield). The structure of 22 was determined through extensive interpretation of the NMR data of its deprotected derivative 23. Unfortunately, we found that the configuration of the newly formed C4a stereocenter was opposite to that in the natural product zamamiphidin A. Inversion of the C4a stereochemistry through generation of the C4–C4a double bond (22 to 24) followed by hydrogenation (24 to 25) was investigated. When compound 22 was treated with LDA and PhSeCl followed by oxidation and spontaneous elimination under the conditions of H₂O₂/pyridine/CHCl₃, the above reaction gave a complex mixture, with only 5–10% yield of the desired product 24 isolated. We attempted to improve this transformation by employing various bases (e.g., LiHMDS, NaHMDS, KHMDS, LiTMP) and different oxidants (e.g., m-CPBA, NaIO₄, AcOOH), which all proved to be unsuccessful. These failures impeded further transformations.Open in a separate windowScheme 3Synthesis of the tricyclic compound 28.On the other hand, we investigated the construction of the oxazolidine ring starting from the bicyclic intermediate 22 (Scheme 3). Thus, reduction of the imine double bond in 22 with borane dimethyl sulfide afforded sulfinamide 26 in 55% yield. Subjecting 26 to the conditions of HCl/MeOH¹⁶ followed by treatment of the resulting primary amine with 2-hydroxypyridine in refluxing toluene¹⁷ furnished an unexpected tricyclic compound 28. The structure of 28 was determined unambiguously through X-ray crystallographic analysis, which again confirmed the C4a stereochemistry generated in the aforementioned intramolecular Michael addition reaction (10 to 22). Formation of the undesired 28 was due to the lactamization occurred at C18 rather than at C1 that was initially envisaged to establish the oxazolidine ring. These results indicated that the correct configuration of C4a might be crucial for the subsequent synthesis.In our revised synthetic approach, a propiolate group was employed to replace the originally used enoate for the Michael addition. We envisioned that hopefully reduction of the double bond generated in the Michael addition of the corresponding propiolate would secure the right configuration at the C4a position. As shown in Scheme 4, the known propargyl alcohol 29 was prepared on a decagram scale from 3-butyl-1-ol over two steps.¹⁸ After acylation of 29 and subsequent deprotection of the TBS group with TBAF, the resulting primary alcohol 30 was converted into phthalimide 31via a Mitsunobu reaction in the presence of phthalimide/PPh₃/DIAD (64% overall yield for three steps). Deacylation of 31 followed by silylation of the resulting primary alcohol with TBSCl/Et₃N/DMAP provided 32 in 36% yield over two steps. Exposure of 32 to hydrazine hydrate in refluxing methanol resulted in removal of the phthalimide group and delivered a free amine, which was directly condensed with 16 to afford the secondary enamine 33 in 80% overall yield. Further protection of the amino group in 33 with Boc produced intermediate 34. Next, compound 34 underwent a similar three-step transformation to that performed on enamidomalonate 14, involving asymmetric 1,4-conjugate addition with imidate 13, Davis oxidation to install the C9 hydroxyl group (35 to 36), and cyclization with Et₃N to assemble the tetrahydrofuran ring, yielding the intermediate 37 smoothly. To reach propiolate 39, the precursor of the key Michael addition for forming C4–C4a bond, further functional group manipulations of 37 were conducted. These included desilyation with HF (37 to 38), Dess–Martin oxidation, Pinnick oxidation, and esterification (38 to 39). Gratifyingly, upon treating 39 with LDA and HPMA in THF at −20 °C, compound 24 was formed with 42% yield through an intramolecular Michael addition and spontaneous migration of the double bond from C4a–C8a to C4–C4a.Open in a separate windowScheme 4Synthesis of compound 24.With compound 24 in hand, selective reduction of the C4–C4a double bond was carried out under catalytic hydrogenation conditions (RANEY® Ni/H₂) and furnished 25 (70% yield) as a single diastereomer with correct C4 and C4a configurations (Scheme 5). Ensuing reduction of the imine group in 25 using borane dimethyl sulfide delivered the tert-butyl sulfonamide 40 with excellent diastereoselectivity (single isomer, 72% yield). The structures of both 25 and 40 were extensively interpreted by NMR spectroscopy. As a consequence, the configurations at C3, C4, C4a and C10 were found to be consistent with the ones in zamamiphidin A.¹⁹ Furthermore, transformations of 25 or 40 into the core of the target zamamiphidin A were investigated. Subjecting 25 to various conditions (NaH, NaOMe, t-BuOK, LDA, LiHMDS, AlCl₃, TiCl₄, etc.) for a Dieckmann condensation failed to construct the C1–C8a bond and give the desired product 41. Instead, ring-opening of the tetrahydrofuran unit in 25 was observed under some circumstances, leading to the byproduct 42via a retro-Michael reaction.Open in a separate windowScheme 5Synthesis of 25 and attempted further transformations.Meanwhile, attempts to synthesize the tricyclic β-keto ester 43 or lactam 44 from compound 40 were also unsuccessful. Most of these experiments suffered from either no reaction or decomposition of the starting materials.In conclusion, we have established a synthetic approach to the octahydrofuro[3,4-b]pyridine core of the complex natural product zamamiphidin A. The synthesis features an intermolecular asymmetric Michael addition (compounds 34 to 35) to form the first chiral center at C10 and a Michael addition/hydrogenation sequence (compounds 39 to 25) to secure the correct configurations at C4 and C4a. The highly functionalized bicyclic intermediate (i.e., 40) prepared in the present work contains four contiguous stereocenters and all the requisite heteroatoms at the right positions. While further transformations of related intermediates to zamamiphidin A were unfruitful, efforts to develop a feasible strategy for total synthesis of the target molecule are ongoing in our laboratory.     

Simulation-guided nanofabrication of high-quality practical tungsten probes

Micro/nanoscale tungsten probes are widely utilized in the fields of surface analysis, biological engineering, etc. amongst several others. This work performs comprehensive dynamic simulations on the influences of electric field distribution, surface tension and the bubbling situation on electrochemical etching behaviors, and then the tip dimension. Results show that the etching rate is reliant on the electric field distribution determined by the cathode dimension. The necking position lies in the meniscus rather than at the bottom of the meniscus. A bubble-free condition is mandatory to stabilize the distribution of OH⁻ and WO₄²⁻ ions for a smooth tungsten probe surface. Such simulation-guidance enables the nanofabrication of probes with a high aspect ratio (10 : 1), ultra-sharp tip apex (40 nm) and ultra-smooth surface. These probes have been successfully developed for high-performance application with Scanning Tunneling Microscopy (STM). The acquired decent atomic resolution images of epitaxial bilayer graphene robustly verify the feasibility of the practical level application of these nanoscale probes. Therefore, these nanoscale probes would be of great benefit to the development of advanced analytical science and nano-to-atomic scale experimental science and technology.

Dynamic simulation is employed to reveal the mechanism of electrochemical nanofabrication of nanoscale probes for atomic resolution imaging in STM.     

Pharmacokinetic–pharmacodynamic modeling for Moutan Cortex/Moutan Cortex charcoal and the contributions of the chemical component using support vector regression with particle swarm optimization

Moutan Cortex (MC) and Moutan Cortex charcoal (MCC) are two kinds of Chinese medicinal materials widely used in traditional Chinese medicine (TCM) with opposite drug efficacy. And the contributions of the chemical component to the drug efficacy are still not clear. In our study, a support vector regression (SVR) model with particle swarm optimization (PSO) has been developed for simultaneously characterizing the pharmacokinetics (PK) and pharmacodynamics (PD) of MC/MCC. Then the contributions of the chemical component to the drug efficacy of MC/MCC are calculated by the weight analysis of SVR. The experimental results show that the effective substances found by the PSO-SVR model in MC and MCC are consistent with TCM theory. And the PSO-SVR model is a better model for PK–PD compared with the back-propagation neural network (BPNN). In conclusion, the PSO-SVR is a valuable tool that linked PK and PD profiles of MC/MCC with multiple components and identified the contributions of multiple therapeutic materials to the drug efficacy.

Moutan Cortex (MC) and Moutan Cortex charcoal (MCC) are two kinds of Chinese medicinal materials and effective substances are still unclear. A PK-PD model for MC/MCC is proposed using the support vector regression with particle swarm optimization.     

Catalytic oxidation of NO over MnOx–CoOx/TiO2 in the presence of a low ratio of O3/NO: activity and mechanism

In order to broaden the temperature range of NO oxidation reaction in flue gas and maintain high oxidation efficiency, various loading amounts of MnO_x–CoO_x/TiO₂ mesoporous catalysts were tested in the catalytic oxidation of NO. It was found that 15%MnO_x–CoO_x(2 : 1)/TiO₂ demonstrated the best adsorption performance to oxygen species and contained more oxygen vacancies, as well as the best surface oxygen mobility, thus exhibiting excellent NO catalytic oxidation activity. O₃ (O₃/NO < 1) combined with 15%MnO_x–CoO_x(2 : 1)/TiO₂ improved the oxidation efficiency of NO at 50–400 °C, especially below 250 °C. When the temperatures were less than 250 °C, the oxidation efficiencies of NO by O₃ over 15%MnO_x–CoO_x(2 : 1)/TiO₂ were 5–13% higher than the calculated theoretical efficiencies. This indicated that there was a synergistic effect between O₃ and 15%MnO_x–CoO_x(2 : 1)/TiO₂ below 250 °C. Based on the results of in situ DRIFTS studies, it was deduced that monodentate nitrates were the main intermediates that produced a synergistic effect due to the introduction of O₃. In addition, O₃ accelerated the transformation between nitrate species, decreased the decomposition temperature of nitrate species, and inhibited the accumulation of nitrate ions, thus improving the oxidation efficiency of NO.

O₃ promotes the formation of monodentate nitrates at low temperature, thus improving the efficiency of NO oxidation.     

Enhanced sintering resistance of bimetal/SBA-15 catalysts with promising activity under a low temperature for CO methanation

According to its thermodynamic equilibrium analysis and strong exothermic characteristics, the major challenge of syngas methanation is to develop a high-efficient low-temperature catalyst with superior sintering resistance. In this study, bimetal-based SBA-15 catalysts were prepared via a citric acid-assisted impregnation method and applied in CO methanation. The obtained catalysts were characterized via X-ray diffraction, N₂ adsorption–desorption, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction and other techniques. Combining the structural characterization of the fresh and used catalyst, the function of the organic additive and metal promoters was revealed. The catalysts exhibited superior low-temperature activity and excellent sintering resistance owing to the electron migration from the additive metal to Ni, strong interaction between the metal and support and the confinement effect of the support. The catalyst with Mo as a promotor exhibited the best dispersion and the largest surface concentration of nickel, which resulted in its highest catalytic activity among the catalysts. The design and preparation of a highly effective catalyst can provide novel insight into the preparation of other catalysts.

Well-dispersed bimetallic catalysts with confinement effects and strong interaction lead to superior low-temperature activity and excellent thermostability.