Filtern
Erscheinungsjahr
- 2022 (29) (entfernen)
Dokumenttyp
- Zeitschriftenartikel (29)
Sprache
- Englisch (29)
Referierte Publikation
- ja (29) (entfernen)
Schlagworte
- Mechanochemistry (13)
- In situ (3)
- Metal-organic-frameworks (3)
- Cocrystal (2)
- Crystallization (2)
- Materials (2)
- Nanoparticles (2)
- SAXS (2)
- XRD (2)
- Anticancer (1)
Organisationseinheit der BAM
- 6 Materialchemie (29)
- 6.3 Strukturanalytik (26)
- 6.0 Abteilungsleitung und andere (25)
- 1 Analytische Chemie; Referenzmaterialien (4)
- 1.4 Prozessanalytik (3)
- 6.1 Oberflächen- und Dünnschichtanalyse (3)
- 4 Material und Umwelt (2)
- 4.2 Material-Mikrobiom Wechselwirkungen (2)
- 6.2 Material- und Oberflächentechnologien (2)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (2)
Paper des Monats
- ja (1)
Flexible organic crystals (elastic and plastic) are important materials for optical waveguides, tunable optoelectronic devices, and photonic integrated circuits. Here, we present highly elastic organic crystals of a Schiff base, 1-((E)-(2,5-dichlorophenylimino)methyl)naphthalen-2-ol (1), and an azine molecule, 2,4-dibromo-6-((E)-((E)-(2,6-dichlorobenzylidene)hydrazono)methyl)phenol (2). These microcrystals are highly flexible under external mechanical force, both in the macroscopic and the microscopic regimes. The mechanical flexibility of these crystals arises as a result of weak and dispersive C−H⋅⋅⋅Cl, Cl⋅⋅⋅Cl, Br⋅⋅⋅Br, and π⋅⋅⋅π stacking interactions. Singly and doubly-bent geometries were achieved from their straight shape by a micromechanical approach using the AFM cantilever tip. Crystals of molecules 1 and 2 display a bright-green and red fluorescence (FL), respectively, and selective reabsorption of a part of their FL band. Crystals 1 and 2 exhibit optical-path-dependent low loss emissions at the termini of crystal in their straight and even in extremely bent geometries. Interestingly, the excitation position-dependent optical modes appear in both linear and bent waveguides of crystals 1 and 2, confirming their light-trapping ability.
We demonstrate here using a disulfide system the first example of reversible, selective, and quantitative transformation between three crystalline polymorphs by ball mill grinding. This includes the discovery of a previously unknown polymorph. Each polymorph is reproducibly obtained under well-defined neat or liquid-assisted grinding conditions, revealing subtle control over the apparent thermodynamic stability. We discovered that the presence of a contaminant as low as 1.5% mol mol−1 acting as a template is required to enable all these three polymorph transformations. The relative stabilities of the polymorphs are determined by the sizes of the nanocrystals produced under different conditions and by surface interactions with small amounts of added solvent. For the first time, we show evidence that each of the three polymorphs is obtained with a unique and reproducible crystalline size. This mechanochemical approach gives access to bulk quantities of metastable polymorphs that are inaccessible through recrystallisation.
Industrial and agricultural waste streams (waste water, sludges, tailings, etc.) which contain high concentrations of NH4+, PO43–, and transition metals are environmentally harmful and toxic pollutants. At the same time, phosphorous and transition metals constitute highly valuable resources. Typically, separate pathways have been considered to extract hazardous transition metals or phosphate independently from each other. Investigations on the simultaneous removal of multiple components have been carried out only to a limited extent. Here, we report the synthesis routes for Ni- and Co-struvites (NH4MPO4·6H2O, M = Ni2+ and Co2+), which allow for P, ammonia, and metal co-precipitation. By evaluating different reaction parameters, the phase and stability of transition metal struvites as well as their crystal morphologies and sizes could be optimized. Ni-struvite is stable in a wide reactant concentration range and at different metal/phosphorus (M/P) ratios, whereas Co-struvite only forms at low M/P ratios. Detailed investigations of the precipitation process using ex situ and in situ techniques provided insights into the crystallization mechanisms/crystal engineering of these materials. M-struvites crystallize via intermediate colloidal amorphous nanophases, which subsequently aggregate and condense to final crystals after extended reaction times. However, the exact reaction kinetics of the formation of a final crystalline product varies significantly depending on the involved metal cation in the precipitation process: several seconds (Mg) to minutes (Ni) to hours (Co). The achieved level of control over the morphology and size makes precipitation of transition metal struvites a promising method for direct metal recovery and binding them in the form of valuable phosphate raw materials. Under this paradigm, the crystals can be potentially up-cycled as precursor powders for electrochemical or (electro)catalytic applications, which require transition metal phosphates.
Phosphotyrosine residues are essential functional switches in health and disease. Thus, phosphotyrosine biomimetics are crucial for the development of chemical tools and drug molecules. We report here the discovery and investigation of pentafluorophosphato amino acids as novel phosphotyrosine biomimetics. A mild acidic pentafluorination protocol was developed and two PF5-amino acids were prepared and employed in peptide synthesis. Their structures, reactivities, and fluorine-specific interactions were studied by NMR and IR spectroscopy, X-ray diffraction, and in bioactivity assays. The mono-anionic PF5 motif displayed an amphiphilic character binding to hydrophobic surfaces, to water molecules, and to protein-binding sites, exploiting charge and H−F-bonding interactions. The novel motifs bind 25- to 30-fold stronger to the phosphotyrosine binding site of the protein tyrosine phosphatase PTP1B than the best current biomimetics, as rationalized by computational methods, including molecular dynamics simulations.
he mutual influence of F and OH groups in neighboring sites in topaz (Al2SiO4(F,OH)2) was investigated using magic angle spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy. The splitting of 19F and 1H NMR signals, as well as the OH Raman band, provides evidence for hydrogen bond formation within the crystal structure. Depending on whether a given OH group has another OH group or fluoride as its neighbor, two different hydrogen bond constellations may form: either OH···O···HO or F···H···O. The proton accepting oxygen was determined to be part of the SiO4 tetrahedron using 29Si MAS NMR. Comparison of the MAS NMR data between an OH-bearing and an OH-free topaz sample confirms that the 19F signal at −130 ppm stems from F− ions that take part in H···F bonds with a distance of ∼ 2.4 Å, whereas the main signal at −135 ppm belongs to fluoride ions with no immediate OH group neighbors. The Raman OH sub-band at 3644 cm−1 stems from OH groups neighboring other OH groups, whereas the sub-band at 3650 cm−1 stems from OH groups with fluoride neighbors, which are affected by H···F bridging. The integrated intensities of these two sub-bands do not conform to the expected ratios based on probabilistic calculations from the total OH concentration. This can be explained by a difference in the polarizability of the OH bond between the different hydrogen bond constellations or partial order or unmixing of F and OH, or a combination of both. This has implications for the quantitative interpretation of Raman data on OH bonds in general and their potential use as a probe for structural (dis-)order. No indication of tetrahedrally coordinated Al was found with 27Al MAS NMR, suggesting that the investigated samples likely have nearly ideal Al/Si ratios, making them potentially useful as high-density electron microprobe reference materials for Al and Si, as well as for F.
Changes in the global bulk and local structures, of three different barium compounds (BaZrO3, BaF2, and BaFCl),were induced by mechanical milling and followed using X-ray powder diffraction (PXRD), subsequent microstructure analysis, and 137Ba solid state NMR spectroscopy. Harder materials like BaZrO3 experience significantly higher structural changes upon milling than softer materials like BaF2. Moreover, soft materials with layered structures, like BaFCl, show a pronounced structural change during the milling process. By combining PXRD and solid state NMR, detailed information on the changes to the global and local structures were obtained, which are of interest for mechanochemical synthesis, mechanically treated catalysts or ionic conductors.
Mechanochemistry has become a sustainable and attractive cost-effective synthetic technique, largely used within the frame of crystal engineering. Cocrystals, namely, crystalline compounds made of different chemical entities within the same crystal structure, are typically synthesized in bulk via mechanochemistry; however, whereas the macroscopic aspects of grinding are becoming clear, the fundamental principles that underlie mechanochemical cocrystallization at the microscopic level remain poorly understood. Time-resolved in situ (TRIS) monitoring approaches have opened the door to exceptional detail regarding mechanochemical reactions. We here report a clear example of cocrystallization between two solid coformers that proceeds through the formation of a metastable low melting binary eutectic phase. The overall cocrystallization process has been monitored by time-resolved in situ (TRIS) synchrotron X-ray powder diffraction with a customized ball milling setup, currently available at μ Spot beamline at BESSY-II, Helmholtz-Zentrum Berlin. The binary system and the low melting eutectic phase were further characterized via DSC, HSM, and VT-XRPD.
Two isomorphous crystals are reported based on a naphthylvinylpyridine coformer. The crystals are mechanically flexible and exhibit photosalient response to UV irradiation. We therefore show how multiple mechanical phenomena can be simultaneously designed into a single material by cocrystallization.
Unintended Rate Enhancement in Mechanochemical Kinetics by Using Poly(methyl methacrylate) Jars
(2022)
Time-resolved in situ (TRIS) X-ray diffraction has changed how mechanochemical transformations are studied but requires the use of X-ray transparent jars often made from poly(methyl methacrylate) (PMMA). However, using PMMA jars can alter the apparent kinetics of mechanochemical polymorphism by an order of magnitude, questioning the interpretability of established TRIS methods. Our results suggest that rate enhancement in PMMA jars may not be dominated by chemical effects of the polymer, but rather a result of different equilibrium temperatures within the jar. These features must be better understood before control over mechanochemical reactions can be achieved.
Fluorescent plastically bendable crystals are a promising alternative to silicon-based materials for fabricating photonic integrated circuits, owing to their optical attributes and mechanical compliance. Mechanically bendable plastic organic crystals are rare. Their formation requires anisotropic intermolecular interactions and slip planes in the crystal lattice. This work presents three fluorescent plastically bendable crystalline materials namely, 2-((E)-(6-methylpyridin-2-ylimino)methyl)-4-chlorophenol (SB1), 2-((E)-(6-methylpyridin-2-ylimino)methyl)-4-bromophenol (SB2), and 2-((E)-(6-Bromopyridin-2-ylimino)methyl)-4-bromophenol (SB3) molecules. The crystal plasticity in response to mechanical stress facilitates the fabrication of various monolithic and hybrid (with a tip-to-tip coupling) photonic circuits using mechanical micromanipulation with an atomic force microscope cantilever tip. These plastically bendable crystals act as active (self-guiding of fluorescence) and passive waveguides both in straight and extremely bent (U-, J-, and O-shaped) geometries. These microcircuits use active and passive waveguiding principles and reabsorbance and energy-transfer mechanisms for their operation, allowing input-selective and direction-specific signal transduction.
Lake Magadi, East African Rift Valley, is a hyperalkaline and saline soda lake highly enriched in Na+, K+, CO32–, Cl–, HCO3–, and SiO2 and depleted in Ca2+ and Mg2+, where thick evaporite deposits and siliceous sediments have been forming for 100 000 years. The hydrogeochemistry and the evaporite deposits of soda lakes are subjects of growing interest in paleoclimatology, astrobiology, and planetary sciences. In Lake Magadi, different hydrates of sodium carbonate/bicarbonate and other saline minerals precipitate. The precipitation sequence of these minerals is a key for understanding the hydrochemical evolution, the paleoenvironmental conditions of ancient evaporite deposits, and industrial crystallization. However, accurate determination of the precipitation sequence of these minerals was challenging due to the dependency of the different hydrates on temperature, water activity, pH and pCO2, which could induce phase transformation and secondary mineral precipitation during sample handling. Here, we report a comprehensive methodology applied for monitoring the evaporitic mineral precipitation and hydrochemical evolution of Lake Magadi. Evaporation and mineral precipitations were monitored by using in situ video microscopy and synchrotron X-ray diffraction of acoustically levitated droplets. The mineral patterns were characterized by ex situ Raman spectroscopy, X-ray diffraction, and scanning electron microscopy. Experiments were coupled with thermodynamic models to understand the evaporation and precipitation-driven hydrochemical evolution of brines. Our results closely reproduced the mineral assemblages, patterns, and textural relations observed in the natural setting. Alkaline earth carbonates and fluorite were predicted to precipitate first followed by siliceous sediments. Among the salts, dendritic and acicular trona precipitate first via fractional crystallization─reminiscent of grasslike trona layers of Lake Magadi. Halite/villiaumite, thermonatrite, and sylvite precipitate sequentially after trona from residual brines depleted in HCO3–. The precipitation of these minerals between trona crystals resembles the precipitation process observed in the interstitial brines of the trona layers. Thermonatrite precipitation began after trona equilibrated with the residual brines due to the absence of excess CO2 input. We have shown that evaporation and mineral precipitation are the major drivers for the formation of hyperalkaline, saline, and SiO2-rich brines. The discrepancy between predicted and actual sulfate and phosphate ion concentrations implies the biological cycling of these ions. The combination of different in situ and ex situ methods and modeling is key to understanding the mineral phases, precipitation sequences, and textural relations of modern and ancient evaporite deposits. The synergy of these methods could be applicable in industrial crystallization and natural brines to reconstruct the hydrogeochemical and hydroclimatic conditions of soda lakes, evaporite settings, and potentially soda oceans of early Earth and extraterrestrial planets.
Formation Mechanism of a Nano-Ring of Bismuth Cations and Mono-Lacunary Keggin-Type Phosphomolybdate
(2022)
A new hetero-bimetallic polyoxometalate (POM) nano-ring was synthesized in a one-pot procedure. The structure consists of tetrameric units containing four bismuth-substituted monolacunary Keggin anions including distorted [BiO8] cubes. The nano-ring is formed via self-assembly from metal precursors in aqueous acidic medium. The compound (NH4)16[(BiPMo11O39)4] ⋅ 22 H2O; (P4Bi4Mo44) was characterized by single-crystal X-ray diffraction, extended X-ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG-DSC-MS). The formation of the nano-ring in solution was studied by time-resolved in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L3 edge indicating a two-step process consisting of condensation of Mo-anions and formation of Bi−Mo-units followed by a rapid self-assembly to yield the final tetrameric ring structure.
Catalysts derived from pyrolysis of metal organic frameworks (MOFs) are promising candidates to replace expensive and scarce platinum-based electrocatalysts commonly used in polymer electrolyte membrane fuel cells. MOFs contain ordered connections between metal centers and organic ligands. They can be pyrolyzed into metal- and nitrogen-doped carbons, which show electrocatalytic activity toward the oxygen reduction reaction (ORR). Furthermore, metal-free heteroatom-doped carbons, such as N-F-Cs, are known for being active as well. Thus, a carbon material with Co-N-F doping could possibly be even more promising as ORR electrocatalyst. Herein, we report the mechanochemical synthesis of two polymorphs of a zeolitic imidazole framework, Co-doped zinc 2-trifluoromethyl-1H-imidazolate (Zn0.9Co0.1(CF3-Im)2). Time-resolved in situ X-ray diffraction studies of the mechanochemical formation revealed a direct conversion of starting materials to the products. Both polymorphs of Zn0.9Co0.1(CF3-Im)2 were pyrolyzed, yielding Co-N-F containing carbons, which are active toward electrochemical ORR.
Herein we report the synthesis of a zeolitic imidazolate framework (ZIF-8) by an easy “mix and wait” procedure. In a closed vial, without any interference, the mixture of 2-methylimidazole and basic zinc carbonate assembles into the crystalline product with approx. 90% conversion after 70 h. The reaction exhibits sigmoidal kinetics due to the self-generated water which accelerates the reaction.
Mechanochemical transformations offer environmentally benign synthesis routes, whilst enhancing both the speed and selec-tivity of reactions. In this light, mechanochemistry promises to trans-form the way in which chemistry is done in both academia and indus-try but is greatly hindered by a current lack in mechanistic understand-ing. The continued development and use of time-resolved in situ(TRIS) approaches to monitor mechanochemical reactions provides a new dimension to elucidatethese fascinating transformations. We here discuss recent trends in method development that have pushed the boundaries of mechanochemical research. New features of mech-anochemical reactions obtained by TRIS techniques are subse-quently discussed, shedding light on how different TRISapproaches have beenused. Emphasis is placed on the strength of combining complementary techniques. Finally, we outline our views for the po-tential of TRIS methods in mechanochemical research, towards es-tablishing a new, environmentally benign paradigm in the chemical sciences
n situ monitoring of mechanochemical reactions between dicyandiamide (DCD) and CuX2 salts (X = Cl−, NO3−), for the preparation of compounds of agrochemical interest, showed the appearance of a number of phases. It is demonstrated that milling conditions, such as the amount of water added in wet grinding and/or the milling frequency, may affect the course of the mechanochemical reactions, and drive the reaction towards the formation of different products. It has been possible to discover by in situ monitored experiments two novel crystalline forms, namely the neutral complexes [Cu(DCD)2(OH2)2(NO3)2] (2) and [Cu(DCD)2(OH2)Cl2]·H2O (4), in addition to the previously known molecular salt [Cu(DCD)2(OH2)2][NO3]2·2H2O (1, DIVWAG) and neutral complex [Cu(DCD)2(OH2)Cl2] (3, AQCYCU), for which no synthesis conditions were available. Compounds 2 and 4 were fully characterized via a combination of solid-state techniques, including X-ray diffraction, Raman spectroscopy and TGA.
A facile and efficient methodology is described for the solvothermal synthesis of size-tunable, stable, and uniform NiCu core–shell nanoparticles (NPs) for application in catalysis. The diameter of the NPs is tuned in a range from 6 nm to 30 nm and to adjust the Ni:Cu ratio from 30:1 to 1:1. Furthermore, the influence of different reaction parameters on the final NPs is studied. The NPs are structurally characterized by a method combination of transmission electron microscopy, anomalous small-angle X-ray scattering, X-ray absorption fine structure, and X-ray photoelectron spectroscopy. Using these analytical methods, it is possible to elucidate a core–shell–shell structure of all particles and their chemical composition. In all cases, a depletion from the core to the shell is observed, with the core consisting of NiCu alloy, surrounded by an inner Ni-rich shell and an outer NiO shell. The SiO2-supported NiCu core–shell NPs show pronounced selectivity of >99% for CO in the catalytic reduction of CO2 to CO using hydrogen as reactant (reverse water–gas shift reaction) independent of size and Ni:Cu ratio.
Mechanochemistry offers a unique opportunity to modify and manipulate crystal forms, often providing new products as compared with conventional solution methods. While promising, there is little known about how to control the solid form through mechanochemical means, demanding dedicated investigations. Using a model organic cocrystal system (isonicotinamide:glutaric acid), we here demonstrate that with mechanochemistry, polymorphism can be induced in molecular solids under conditions seemingly different to their conventional thermodynamic (thermal) transition point.
Whereas Form II converts to Form I upon heating to 363 K, the same transition can be initiated under ball milling conditions at markedly lower temperatures (348 K). Our results indicate that mechanochemical techniques can help to reduce the energy barriers to solid form transitions, offering new insights into controlling polymorphic forms. Moreover, our results suggest that the nature of mechanochemical transformations could make it difficult to interpret mechanochemical solid form landscapes using conventional equilibrium-based tools.
The debate on the mechanisms which underpin mechanochemical reactions via ball mill grinding is still open. Our ability to accurately measure the microstructural (crystal size and microstrain) evolution of materials under milling conditions as well as their phase composition as a function of time is key to the in-depth understanding of the kinetics and driving forces of mechanochemical transformations. Furthermore, all ball milling reactions end with a steady state or milling equilibrium – represented by a specific phase composition and relative microstructure – that does not change as long as the milling conditions are maintained. The use of a standard sample is essential to determine the instrumental contribution to the X-ray powder diffraction (XRPD) peak broadening for time-resolved in situ (TRIS) monitoring of mechanochemical reactions under in operando conditions. Using TRIS-XRPD on a ball milling setup, coupled with low-energy synchrotron radiation, we investigated different data acquisition and analysis strategies on a silicon standard powder. The diffraction geometry and the microstructural evolution of the standard itself have been studied to model the instrumental contribution to XRPD peak broadening throughout the grinding activity. Previously proposed functions are here challenged and further developed. Importantly, we show that minor drifts of the jar position do not affect the instrumental resolution function significantly. We here report and discuss the results of such investigations and their application to TRIS-XRPD datasets of inorganic and organic ball mill grinding reactions.
Water-stable metal−organic frameworks (MOFs) with proton-conducting behavior have attracted great attention as promising materials for proton-exchange membrane fuel cells. Herein, we report the mechanochemical gram-scale synthesis of three new mixed-ligand phosphonate-based MOFs, {Co(H2PhDPA)(4,4′-bipy)H2O)·2H2O}n (BAM-1), {Fe(H2PhDPA)(4,4′-bipy) (H2O)·2H2O}n (BAM-2), and {Cu(H2PhDPA)(dpe)2(H2O)2·2H2O}n (BAM-3) [where H2PhDPA = phenylene diphosphonate, 4,4′-bipy = 4,4′-bipyridine, and dpe = 1,2-di(4-pyridyl)ethylene]. Single-crystal X-ray diffraction measurements revealed that BAM-1 and BAM-2 are isostructural and possess a three-dimensional (3D) network structure comprising one-dimensional (1D) channels filled with guest water molecules. Instead, BAM-3 displays a 1D network structure extended into a 3D supramolecular structure through hydrogenbonding and π−π interactions. In all three structures, guest water molecules are interconnected with the uncoordinated acidic hydroxyl groups of the phosphonate moieties and coordinated water molecules by means of extended hydrogen-bonding interactions. BAM-1 and BAM-2 showed a gradual increase in proton conductivity with increasing temperature and reached 4.9 × 10−5 and 4.4 × 10−5 S cm−1 at 90 °C and 98% relative humidity (RH). The highest proton conductivity recorded for BAM-3 was 1.4 × 10−5 S cm−1 at 50 °C and 98% RH. Upon further heating, BAM-3 undergoes dehydration followed by a phase transition to another crystalline form which largely affects its performance. All compounds exhibited a proton hopping (Grotthuss model) mechanism, as suggested by their low activation energy.
The ternary sulfido bismuthate K3[BiS3] is synthesized in quantitative yields. The material exhibits nonlinear optical properties with strong second harmonic generation properties at arbitrary wavelengths in the infrared spectral range and a notable laser-induced damage threshold of 5.22 GW cm−2 for pulsed laser radiation at a wavelength of 1040 nm, a pulse duration of 180 fs, and a repetition rate of 12.5 kHz. K3[BiS3] indicates semiconductivity with a direct optical band gap of 2.51 eV. Dielectric and impedance characterizations demonstrate κ values in the range of 6−13 at 1 kHz and a high electrical resistivity. A strong diamagnetic behavior with a susceptibility of −2.73 × 10−4 m3 kg−1 at room temperature is observed. These results suggest it is a promising nonlinear optical candidate for the infrared
region. The synergic physical characteristics of K3[BiS3] provide insight into the correlation of optical, electrical, and magnetic properties.
We obtained three 4-(1-Napthylvinyl) pyridine based cocrystals ( 1–3 ) and studied its structure mechan- ical property correlation which aimed towards various applications for photo switches, mechanical ac- tuators etc. Selection of coformer molecules is important in fine tuning mechanical property outcome of synthesized cocrystals. Amongst three cocrystals, cocrystal 1 is mechanically flexible and its mechani- cal property is attributed to underlying crystal packing features which is in line with existing elastically bendable crystals while other two cocrystals ( 2, 3 ) are brittle in nature. Hirshfeld analysis was carried out to illustrate structure-property correlation particularly in terms of number as well as types of non- covalent interactions in the lattice and further to corroborate the space of the molecules in the lattice.
Designing the shape and size of catalyst particles, and their interfacial charge, at the nanometer scale can radically change their performance. We demonstrate this with ceria nanoparticles. In aqueous media, nanoceria is a functional mimic of haloperoxidases, a group of enzymes that oxidize organic substrates, or of peroxidases that can degrade reactive oxygen species (ROS) such as H2O2 by oxidizing an organic substrate. We show that the chemical activity of CeO2−x nanoparticles in haloperoxidase- and peroxidaselike reactions scales with their active surface area, their surface charge, given by the ζ-potential, and their surface defects (via the Ce3+/Ce4+ ratio). Haloperoxidase-like reactions are controlled through the ζ-potential as they involve the adsorption of charged halide anions to the CeO2 surface, whereas peroxidase-like reactions without charged substrates are controlled through the specific surface area SBET. Mesoporous CeO2−x particles, with large surface areas, were prepared via template-free hydrothermal reactions and characterized by small-angle X-ray scattering. Surface area, ζ-potential and the Ce3+/Ce4+ ratio are controlled in a simple and predictable manner by the synthesis time of the hydrothermal reaction as demonstrated by X-ray photoelectron spectroscopy, sorption and ζ-potential measurements. The surface area increased with synthesis time, whilst the Ce3+/Ce4+ ratio scales inversely with decreasing ζ-potential. In this way the catalytic activity of mesoporous CeO2−x particles could be tailored selectively for haloperoxidase- and peroxidase-like reactions. The ease of tuning the surface properties of mesoporous CeO2x particles by varying the synthesis time makes the synthesis a powerful general tool for the preparation of nanocatalysts according to individual needs.
The mechanism of mixed-ligand metal–organic framework (MOF) formation, and the possible role of intermediate single-ligand metal complexes during mechanosynthesis, have not been explored yet. For the first time, we report here in situ real-time monitoring of the mechanochemical formation mechanism of mixed-ligand MOFs. Our results show that binary phases can act as intermediates or competing products in one-pot and stepwise synthesis.
Clerodin was isolated from the medicinal plant Clerodendrum infortunatum, and CSD search showed the first crystal structure of clerodin by a single-crystal X-ray diffraction study. We checked its binding potential with target proteins by docking and conducted network pharmacology analysis, ADMET analysis, in silico pathway analysis, normal mode analysis (NMA), and cytotoxic activity studies to evaluate clerodin as a potential anticancer agent. The cell viability studies of clerodin on the human breast carcinoma cell line (MCF-7) showed toxicity on MCF-7 cells but no toxicity toward normal human lymphocyte cells (HLCs). The anticancer mechanism of clerodin was validated by its enhanced capacity to produce intracellular reactive oxygen species (ROS) and to lower the reduced glutathione content in MCF-7 cells.
Metal nanoparticles have a substantial impact across diferent felds of science, such as photochemistry, energy conversion, and medicine. Among the commonly used nanoparticles, silver nanoparticles are of special interest due to their antibacterial properties and applications in sensing and catalysis. However, many of the methods used to synthesize silver nanoparticles often do not result in well-defned products, the main obstacles being high polydispersity or a lack of particle size tunability. We describe an automated approach to on-demand synthesis of adjustable particles with mean radii of 3 and 5 nm using the polyol route. The polyol process is a promising route for silver nanoparticles e.g., to be used as reference materials. We characterised the as-synthesized nanoparticles using small-angle X-ray scattering, dynamic light scattering and further methods, showing that automated synthesis can yield colloids with reproducible and tuneable properties.
X-ray absorption spectroscopy (XAS) provides a unique, atom-specific tool to probe the electronic structure of solids. By surmounting long-held limitations of powder-based XAS using a dynamically averaged powder in a Resonant Acoustic Mixer (RAM), we demonstrate how time-resolved in situ (TRIS) XAS provides unprecedented detail of mechanochemical synthesis. The use of a custom-designed dispersive XAS (DXAS) setup allows us to increase the time resolution over existing fluorescence measurements from ∼15 min to 2 s for a complete absorption spectrum. Hence, we here establish TRIS-XAS as a viable method for studying mechanochemical reactions and sampling reaction kinetics. The generality of our approach is demonstrated through RAM-induced (i) bottom-up Au nanoparticle mechanosynthesis and (ii) the synthesis of a prototypical metal organic framework, ZIF-8. Moreover, we demonstrate that our approach also works with the addition of a stainless steel milling ball, opening the door to using TRIS-DXAS for following conventional ball milling reactions. We expect that our TRIS-DXAS approach will become an essential part of the mechanochemical tool box.