Merging Molecular Recognition and Gold(I) Catalysis with Triphoscalix[6]arene Ligands

We report the synthesis and characterization of novel triphosphine calix[6]arene ligands. These supramolecular wheels, with recognition features governed by the hydrogen-bonding domain, were employed to synthesize multitasking trinuclear gold(I) complexes as a new platform for the synthesis of interwoven (pseudo)rotaxane species. In parallel, the multivalent, metal-bonded upper rim displayed catalytic features promoting highly selective gold-catalyzed cycloisomerization reactions of 1,6-enynes.     

Predicting Deliquescence Relative Humidities of Crystals and Crystal Mixtures

The presence of water in the form of relative humidity (RH) may lead to deliquescence of crystalline components above a certain RH, the deliquescence RH (DRH). Knowing the DRH values is essential, e.g., for the agrochemical industry, food industry, and pharmaceutical industry to identify stability windows for their crystalline products. This work applies the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) to purely predict the DRH of single components (organic acids, sugars, artificial sweeteners, and amides) and multicomponent crystal mixtures thereof only based on aqueous solubility data of the pure components. The predicted DRH values very well agree with the experimental ones. In addition, the temperature influence on the DRH value could be successfully predicted with PC-SAFT. The DRH prediction also differentiates between formation of hydrates and anhydrates. PC-SAFT-predicted phase diagrams of hydrate-forming components illustrate the influence of additional components on the hydrate formation as a function of RH. The DRH prediction via PC-SAFT allows for the determining of the stability of crystals and crystal mixtures without the need for time-consuming experiments.     

Single-Sided Portable NMR Investigation to Assess and Monitor Cleaning Action of PVA-Borax Hydrogel in Travertine and Lecce Stone

In this work, we investigated the potential of PVA-borax hydrogel for cleaning limestones and the dependence of the cleaning on the porosity of the rock and on the action time of the hydrogel treatment. Towards this goal, we used a nuclear magnetic resonance (NMR) spectrometer, developed for non-invasive and non-destructive applications on cultural heritage. T₂-NMR parameters were quantified on different samples of Lecce stone and Travertine cut perpendicular (Pe) and parallel (Pa) to the bedding planes under different experimental conditions: untreated samples, treated with Paraloid B72 and cleaned with PVA-PEO-borax hydrogel applied for 4 min and 2 h. The T₂ results suggest that the effectiveness of the cleaning strongly depended on the porosity of the stones. In Lecce stone, the hydrogel seemed to eliminate both the paramagnetic impurities (in equal measure with 4 min and 2 h treatment) and Paraloid B72. In Travertine Pe, characterized by a smaller pore size compared to Lecce stone, no significant effects were found regarding both the cleaning and the treatment with Paraloid B72. In Travertine Pa, characterized by a larger pore size than the other two samples, the hydrogel seemed to clean the paramagnetic agents (it worked better if applied for a longer time) but it did not appear to have any effect on Paraloid B72 removal.     

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Indoles from Alkynes and Aryl Azides: Scope and Theoretical Assessment of Ruthenium Porphyrin-Catalyzed Reactions

A symbiotic experimental/computational study analyzed the Ru(TPP)(NAr)₂-catalyzed one-pot formation of indoles from alkynes and aryl azides. Thirty different C₃-substituted indoles were synthesized and the best performance, in term of yields and regioselectivities, was observed when reacting ArC≡CH alkynes with 3,5-(EWG)₂C₆H₃N₃ azides, whereas the reaction was less efficient when using electron-rich aryl azides. A DFT analysis describes the reaction mechanism in terms of the energy costs and orbital/electronic evolutions; the limited reactivity of electron-rich azides was also justified. In summary, PhC≡CH alkyne interacts with one NAr imido ligand of Ru(TPP)(NAr)₂ to give a residually dangling C(Ph) group, which, by coupling with a C(H) unit of the N-aryl substituent, forms a 5+6 bicyclic molecule. In the process, two subsequent spin changes allow inverting the conformation of the sp² C(Ph) atom and its consequent electrophilic-like attack to the aromatic ring. The bicycle isomerizes to indole via a two-step outer sphere H-migration. Eventually, a ′Ru(TPP)(NAr)′ mono-imido active catalyst is reformed after each azide/alkyne reaction.     

Synthesis,Structure, Solid-State NMR Spectroscopy,and Electronic Structures of the Phosphidotrielates Li3AlP2 and Li3GaP2

The lithium phosphidoaluminate Li₉AlP₄ represents a promising new compound with a high lithium ion mobility. This triggered the search for new members in the family of lithium phosphidotrielates, and the novel compounds Li₃AlP₂ and Li₃GaP₂, obtained directly from the elements via ball milling and subsequent annealing, are reported here. It was unexpectedly found through band structure calculations that Li₃AlP₂ and Li₃GaP₂ are direct band gap semiconductors with band gaps of 3.1 and 2.8 eV, respectively. Rietveld analyses reveal that both compounds crystallize isotypically in the orthorhombic space group Cmce (no. 64) with lattice parameters of a=11.5138(2), b=11.7634(2) and c=5.8202(1) Å for Li₃AlP₂, and a=11.5839(2), b=11.7809(2) and c=5.8129(2) Å for Li₃GaP₂. The crystal structures feature TrP₄ (Tr=Al, Ga) corner- and edge-sharing tetrahedra, forming two-dimensional layers. The lithium atoms are located between and inside these layers. The crystal structures were confirmed by MAS-NMR spectroscopy.     

Dissipative Dynamic Covalent Chemistry (DDCvC) Based on the Transimination Reaction

This work reports that the composition of a dynamic library (DL) of interconverting imines can be controlled over time in a dissipative fashion by the addition of an activated carboxylic acid used as a chemical fuel. When the fuel is added to the DL, which is initially under thermodynamic equilibrium, the composition of the mixture dramatically changes and a new, dissipative (out of equilibrium) state is reached that persists until fuel exhaustion. Thus, a transient dissipative dynamic library (DDL) is generated that, eventually, reverts back to the initial DL when the fuel is consumed, closing a DL→DDL→DL cycle. The larger the amount of added fuel, the longer the time spent by the system in the DDL state. The transimination reaction is shown to be an optimal candidate for the realization of a dissipative dynamic covalent chemistry (DDCvC).     

SiO2-Coated ZnO Nanoflakes Decorated with Ag Nanoparticles for Photocatalytic Water Oxidation

Many strategies have been adopted to improve the photoinduced features of zinc oxide nanostructures for different application fields. In this work, zinc oxide has been synthesised and decorated by plasmonic metal nanoparticles to enhance its photocatalytic activity in the visible range. Furthermore, an insulating layer of SiO₂ has been grown between the surface of zinc oxide nanoflakes and silver nanoparticles. A synthetic procedure that allows the accurate modulation of the insulating layer thickness in the range 5–40 nm has been developed. Evidences highlight the crucial role of the SiO₂ layer in dramatically increasing photocatalytic water oxidation promoted by the nanostructure under both UV and visible illumination. An ideal thickness value of about 10 nm has been demonstrated to guarantee the plasmon-induced resonance energy-transfer process and to quench the Förster resonance energy-transfer mechanism; thus, optimising the local surface plasmon resonance effect and water oxidation properties.     

Impact of rock fabric,thermal behavior,and carbonate decomposition kinetics on quicklime industrial production and slaking reactivity

This paper deals with thermal analyses, burning trials and reactivity tests on 15 carbonate rocks, i.e., pure and impure carbonates, mud-supported and grain-supported limestones, crystalline marbles, and dolomites, used for the production of different lime products in industrial vertical shaft kilns worldwide. In particular, thermogravimetric and differential thermogravimetric analysis (TG–DTG) on massive (80–120 g) fine-grained (< 3.35 mm) samples allowed the extrapolation of the Arrhenius kinetic parameters, i.e., the (apparent) activation energy (E_a) and the pre-exponential or frequency factor (A). Other calcination parameters, i.e., the duration time, starting and ending calcination times and temperatures, and peaks of maximum calcination rate were also extrapolated in order to enhance their relationships with quicklime reactivity. Moreover, thermal analyses (TG–DTG–DTA) were repeated on powders (90 mg) using a more accurate analyzer to compare results. The study is completed by a thorough chemical–physical and mineralogical–petrographic characterization of carbonate rocks and derived burnt products. Results pointed out that medium-to-coarse crystalline materials, i.e., grain-supported limestones, diagenetic dolomites, and granoblastic marbles presented the highest activation energy, burnability and slaking reactivity. Conversely, microcrystalline carbonates with the highest micrite-to-sparite ratio, i.e., mud-supported limestones, and impure carbonates, enriched in quartz, clay minerals, and other subordinated non-carbonate impurities, presented the lowest activation energy, burnability, and slaking reactivity. This study also investigated the effect of BET-specific surface area and real density, depending on specific sintering tendency, on quicklime reactivity. Results from this multidisciplinary research activity put further constraints on carbonate rocks calcination kinetics and their suitability in the lime industry.