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Journal of the American Chemical Society

The use of Metal-Organic Frameworks as crystalline matrices for the synthesis of multiple component or multivariate solids by the combination of different linkers into a single material has emerged as a versatile route to tailor the properties of single-component phases or even access new functions. This approach is particularly relevant for Zr6-MOFs due to the synthetic flexibility of this inorganic node. However, the majority of materials are isolated as polycrystalline solids, which are not ideal to decipher the spatial arrangement of parent and exchanged linkers for the formation of homogeneous structures or heterogeneous domains across the solid. Here we use high-throughput methodologies to optimize the synthesis of single crystals of UiO-68 and UiO-68-TZDC, a photoactive analogue based on a tetrazine dicarboxylic derivative. The analysis of the single linker phases reveals the necessity of combining both linkers to produce multivariate frameworks that combine efficient light sensitization, chemical stability, and porosity, all relevant to photocatalysis. We use solvent-assisted linker exchange reactions to produce a family of UiO-68-TZDC% binary frameworks, which respect the integrity and morphology of the original crystals. Our results suggest that the concentration of TZDC in solution and the reaction time control the distribution of this linker in the sibling crystals for a uniform mixture or the formation of core-shell domains. We also demonstrate how the possibility of generating an asymmetric distribution of both linkers has a negligible effect on the electronic structure and optical band gap of the solids but controls their performance for drastic changes in the photocatalytic activity toward proton or methyl viologen reduction.

March 26, 2021
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Polymers Journal

The automated dialysis of polymers in synthetic robots is described as a first approach for the purification of polymers using an automated protocol. For this purpose, a dialysis apparatus was installed within a synthesis robot. Therein, the polymer solution could be transferred automatically into the dialysis tube. Afterwards, a permanent running dialysis could be started, enabling the removal of residual monomer. Purification efficiency was studied using chromatography and NMR spectroscopy, showing that the automated dialysis requires less solvent and is faster compared to the classical manual approach.

March 15, 2021
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Journal of Drug Delivery Science and Technology

The use of poly (vinyl alcohol) (PVA) and a PVA-sodium dodecyl sulfate mixture (PVA-SDS) for the colloidal stabilization of poly (DL-lactide) (PDLLA) and poly (DL-lactide-co-glycolide) (PLGA) nanoparticles (NPs) loaded with paclitaxel (PTX) was investigated. During the preparation of PDLLA and PLGA NPs via a single emulsion method, electrosteric-like stabilization imparted by the PVA-SDS led to the formation of smaller average particle diameter (Dp) than using only PVA which provided steric stabilization. It was found that, with the polymer composition of the NPs, the release profile can be tuned also, depending on whether PVA-SDS or PVA alone was used as stabilizer. The mechanism of the NP degradation and PTX release was studied as a function of time. The results obtained during 28 days were discussed in detail based on the evolutions of Dp, polymer molecular weight and its polydispersity index including the role of the electrosteric-like and steric stabilizers on the phenomenology involved.

March 1, 2021
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European Polymer Journal

Pentafluorophenyl methacrylate (PFPMA) and pentafluorophenyl acrylate (PFPA) are frequently used monomers to produce advanced materials for biomedical applications via (co)polymerization reactions. This contribution reports kinetic investigations of the reversible addition fragmentation chain transfer (RAFT) copolymerization of PFPMA and methyl methacrylate (MMA) mediated by a dithiobenzoate chain transfer agent (CTA) at 70 °C in dimethyl formamide (DMF). Control with respect to the molar mass of the copolymers was observed for initial PFPMA monomer feeds ≤40 mol%. The rate of PFPMA incorporation decreased with increasing initial PFPMA feed ratios. Reactivity ratios were estimated with a nonlinear regression that utilizes a visualization of the sum of squares space method (rPFPMA = 1.06 and rMMA = 0.44). The slight preference for MMA-type radicals to add PFPMA monomers increased the rate of consumption of PFPMA especially in low initial PFPMA monomer feeds. In addition, kinetic investigations of the RAFT homopolymerization of PFPA revealed an induction period and poor control on the polymer molar mass in the polar solvents acetonitrile and DMF using a dithiobenzoate CTA. A better control using the same CTA was observed in 1,4-dioxane. Polymerizations carried out in the presence of a trithiocarbonate CTA were less affected by the solvent polarity and a good control on the polymer molar mass was achieved in acetonitrile and 1,4-dioxane even at high monomer conversion (>95%, dispersity value (Ð) ≤ 1.19).

February 24, 2021
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The Collaborative Research Centre PolyTarget is developing polymer-based, nanoparticulate carrier materials for the targeted application of active pharmaceutical ingredients. In the foreground are systems that are suitable for the treatment of diseases and syndromes whose morbidity is significantly characterized by an inflammatory reaction. The collaborative research centre PolyTarget is funded by the German Research Foundation (DFG). Spokesman is Prof. Dr. Ulrich S. Schubert.

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Der Sonderforschungsbereich (SFB) PolyTarget // The Collaborative Research Centre PolyTarget

February 16, 2021
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ChemPlusChem Journal

The assembly of complex molecules, such as organic cages, can be achieved through supramolecular and dynamic covalent strategies. Their use in a range of applications has been demonstrated, including gas uptake, molecular separations, and in catalysis. However, the targeted design and synthesis of new species for particular applications is challenging, particularly as the systems become more complex. High-throughput computation-only and experiment-only approaches have been developed to streamline the discovery process, although are still not widely implemented. Additionally, combined hybrid workflows can dramatically accelerate the discovery process and lead to the serendipitous discovery and rationalisation of new supramolecular assemblies that would not have been designed based on intuition alone. This Minireview focuses on the advances in high-throughput approaches that have been developed and applied in the discovery of supramolecular organic cages. 

February 1, 2021
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International Journal of Hydrogen Energy Journal

Mono-metallic Pt and Rh catalysts supported on both CeO2 and TiO2 were prepared and tested for water-gas shift activity in a Flowrence, high-throughput reactor system. The feed composition mimicked a typical fuel processor, steam methane reformer outlet stream. The Pt/CeO2 catalyst showed the best metal activity of ∼3.8 E-07 moles CO converted·gPt-1 s-1, at a Pt loading of 0.5 wt%, activity decreasing with increasing metal loading. Furthermore, the Pt/CeO2 catalyst produced almost no methane while the Rh based catalysts led to substantial methanation.

January 18, 2021
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Applied Catalysis B: Environmental Journal

Pd-Pt/Al2O3 and Pd-Pt/CeO2-ZrO2-Y2O3-La2O3 methane oxidation catalysts were investigated under typical lean-burn gas engine conditions with respect to sulfur poisoning and during reactivation, particularly under the most efficient rich conditions. Sulfation of the noble metal and the support material led to pronounced catalyst deactivation. A pronounced transfer of sulfates to the support, particularly alumina, only partially protects the noble metal. In situ X-ray absorption spectroscopy gave insight into the nature and evolution of Pd species during regenerative treatment. Although palladium sulfate that formed during poisoning is decomposed at approximately 200°C in oxygen-free conditions, support regeneration requires higher temperatures, which result in PdS formation above 400°C. Despite its high stability under rich conditions, PdS decomposition by oxidation in lean atmosphere leads to the recovery of the activity. In addition, water vapor that is present during the rich regeneration exhibited a beneficial effect on the regeneration with higher catalytic activity after regeneration.

January 15, 2021
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Nature Catalysis Journal

Platinum single sites are highly attractive due to their high atom economy and can be generated on CeO2 by an oxidative high-temperature treatment. However, their location and activity are strongly debated. Furthermore, reaction-driven structural dynamics have not been addressed so far. In this study, we were able to evidence platinum-induced CeO2 surface restructuring, locate platinum single sites on CeO2 and track the variation of the active state under reaction conditions using a complementary approach of density functional theory calculations, in situ infrared spectroscopy, operando high-energy-resolution fluorescence detected X-ray absorption spectroscopy and catalytic CO (as well as C3H6 and CH4) oxidation. We found that the onset of CO oxidation is linked to the migration of platinum single sites from four-fold hollow sites to form small clusters containing a few platinum atoms. This demonstrates that operando studies on single sites are essential to assess their fate and the resulting catalytic properties.

January 6, 2021
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Nature Catalysis Journal

Platin-Einzelplätze sind aufgrund ihrer hohen Atomökonomie sehr attraktiv und können auf CeO2 durch eine oxidative Hochtemperaturbehandlung erzeugt werden. Ihr Standort und ihre Aktivität sind jedoch stark umstritten. Darüber hinaus wurde die reaktionsgetriebene Strukturdynamik bisher noch nicht behandelt. In dieser Studie konnten wir die Platin-induzierte CeO2 Oberflächenrestrukturierung, lokalisieren Platin-Einzelplätze auf CeO2 und verfolgen die Variation des aktiven Zustands unter Reaktionsbedingungen mit Hilfe eines komplementären Ansatzes aus Dichtefunktionaltheorieberechnungen, in situ-Infrarotspektroskopie, operando-Fluoreszenz mit hoher Energieauflösung, Röntgenabsorptionsspektroskopie und katalytischer CO (sowie C3H6 und CH4) Oxidation. Wir fanden heraus, dass der Beginn der CO-Oxidation mit der Migration von Platin-Einzelstellen von Vierfach-Hohlstellen zu kleinen Clustern mit wenigen Platinatomen verbunden ist. Dies zeigt, dass Operando-Studien an einzelnen Stellen unerlässlich sind, um deren Schicksal und die daraus resultierenden katalytischen Eigenschaften zu beurteilen.

January 6, 2021