Single‐Particle Spectroscopy on Large SAPO‐34 Crystals at Work: Methanol‐to‐Olefin versus Ethanol‐to‐Olefin Processes

The formation of hydrocarbon pool (HCP) species during methanol‐to‐olefin (MTO) and ethanol‐to‐olefin (ETO) processes have been studied on individual micron‐sized SAPO‐34 crystals with a combination of in situ UV/Vis, confocal fluorescence, and synchrotron‐based IR microspectroscopic techniques. With in situ UV/Vis microspectroscopy, the intensity changes of the λ=400 nm absorption band, ascribed to polyalkylated benzene (PAB) carbocations, have been monitored and fitted with a first‐order kinetics at low reaction temperatures. The calculated activation energy (E_a) for MTO, approximately 98 kJ mol^?1, shows a strong correlation with the theoretical values for the methylation of aromatics. This provides evidence that methylation reactions are the rate‐determining steps for the formation of PAB. In contrast for ETO, the E_a value is approximately 60 kJ mol^?1, which is comparable to the E_a values for the condensation of light olefins into aromatics. Confocal fluorescence microscopy demonstrates that during MTO the formation of the initial HCP species are concentrated in the outer rim of the SAPO‐34 crystal when the reaction temperature is at 600 K or lower, whereas larger HCP species are gradually formed inwards the crystal at higher temperatures. In the case of ETO, the observed egg‐white distribution of HCP at 509 K suggests that the ETO process is kinetically controlled, whereas the square‐shaped HCP distribution at 650 K is indicative of a diffusion‐controlled process. Finally, synchrotron‐based IR microspectroscopy revealed a higher degree of alkylation for aromatics for MTO as compared to ETO, whereas high reaction temperatures favor dealkylation processes for both the MTO and ETO processes.     

Dual‐Pore Mesoporous Carbon@Silica Composite Core–Shell Nanospheres for Multidrug Delivery

Monodispersed mesoporous phenolic polymer nanospheres with uniform diameters were prepared and used as the core for the further growth of core–shell mesoporous nanorattles. The hierarchical mesoporous nanospheres have a uniform diameter of 200 nm and dual‐ordered mesopores of 3.1 and 5.8 nm. The hierarchical mesostructure and amphiphilicity of the hydrophobic carbon cores and hydrophilic silica shells lead to distinct benefits in multidrug combination therapy with cisplatin and paclitaxel for the treatment of human ovarian cancer, even drug‐resistant strains.     

Carbon Nanotubes Decorated with CoP Nanocrystals: A Highly Active Non‐Noble‐Metal Nanohybrid Electrocatalyst for Hydrogen Evolution

The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. The strongly acidic conditions in proton exchange membranes create a need for acid‐stable HER catalysts. A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low‐temperature phosphidation of a Co₃O₄/CNT precursor. As a novel non‐noble‐metal HER catalyst operating in acidic electrolytes, the nanohybrid exhibits an onset overpotential of as low as 40 mV, a Tafel slope of 54 mV dec^?1, an exchange current density of 0.13 mA cm^?2, and a Faradaic efficiency of nearly 100 %. This catalyst maintains its catalytic activity for at least 18 hours and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm^?2, respectively.     

Study of the base-catalysed oxidation of the anti-bacterial and anti-protozoal agent metronidazole by permanganate ion in alkaline medium

The mechanism of dismutation of MnO₄ ^2? via the complex [MTZ–MnO₄·OH]^2?, formed during the oxidation of metronidazole (MTZ), has been investigated spectrophotometrically at different temperatures. The stoichiometry of the reaction is 1:1, i.e. 1 mol MTZ reacts with 1 mol Mn(VII).The reaction is first order in permanganate, less than first order in [MTZ] and [alkali]. The effects of added products and the dielectric constant and ionic strength of the reaction medium were investigated. The main products were identified by spot test and FT-IR. A mechanism involving a free radical has been proposed. In the equilibrium step MTZ binds to the MnO₄ ^? species to form a complex (C). Investigation of the reaction at different temperatures enabled determination of the activation data for the slow step of proposed mechanism. The proposed mechanism and the derived rate laws are consistent with the observed kinetics.     

A mechanophysical phase transition provides a dramatic example of colour polymorphism: the tribochromism of a substituted tri(methylene)tetrahydrofuran-2-one

Background

Derivatives of fulgides have been shown to have interesting photochromic properties. We have synthesised a number of such derivatives and have found, in some cases, that crystals can be made to change colour on crushing, a phenomenon we have termed “tribochromism”. We have studied a number of derivatives by X-ray crystallography, to see if the colour is linked to molecular structure or crystal packing, or both, and our structural results have been supported by calculation of molecular and lattice energies.

Results

A number of 5-dicyanomethylene-4-diphenylmethylene-3-disubstitutedmethylene-tetrahydrofuran-2-one compounds have been prepared and structurally characterised. The compounds are obtained as yellow or dark red crystals, or, in one case, both. In two cases where yellow crystals were obtained, we found that crushing the crystals gave a deep red powder. Structure determinations, including those of the one compound which gave both coloured forms, depending on crystallisation conditions, showed that the yellow crystals contained molecules in which the structure comprised a folded conformation at the diphenylmethylene site, whilst the red crystals contained molecules in a twisted conformation at this site. Lattice energy and molecular conformation energies were calculated for all molecules, and showed that the conformational energy of the molecule in structure IIIa (yellow) is marginally higher, and the conformation thus less stable, than that of the molecule in structure IIIb (red). However, the van der Waals energy for crystal structure IIIa, is slightly stronger than that of structure IIIb – which may be viewed as a hint of a metastable packing preference for IIIa, overcome by the contribution of a more stabilising Coulomb energy to the overall more favourable lattice energy of structure IIIb.

Conclusions

Our studies have shown that the crystal colour is correlated with one of two molecular conformations which are different in energy, but that the less stable conformation can be stabilised by its host crystal lattice.

Open image in new window

Graphical abstract Graphical representation of the structural and colour change in the tribochromic compound (III).

     

Effect of Sodium Dodecylbenzenesulfonate on the Association Behavior of Promethazine Hydrochloride in Aqueous/Electrolyte Solutions at Different Temperatures

The interaction between the amphiphilic phenothiazine drug promethazine hydrochloride (PMT) and an anionic surfactant sodium dodecylbenzenesulfonate has been investigated using the conductometric technique in the absence and presence of an inorganic salt (50 mmol·kg^?1 NaCl) at five different compositions and temperatures. PMT is employed for the cure of allergic symptoms. Different physicochemical parameters such as critical micellar concentration (cmc), thermodynamic, and micellar composition are evaluated and discussed in detail using regular solution theory (RST). The addition of salt decreased the surface charge of micelles, lowering the cmc values of the amphiphile. The interaction parameter (β) is negative at all temperatures and compositions indicating attractive interactions. Due to the presence of NaCl in mixed systems the attractive interaction (β) was further increased (β values more negative). The negative values of Gibbs energy (\( \Delta G^{0}_{\text{m}} \)) of mixing revealed the stability of the solution. Owing to the presence of NaCl, the \( \Delta G^{0}_{\text{m}} \) values are found to be more negative suggesting that the driving force for interaction was significantly increased and micellization more thermodynamically favorable.     

Thermodynamic properties of ibuprofen sodium salt in aqueous/urea micellar solutions at 298.15 K

Thermodynamic, surface and micellar properties of anti-inflammatory drug sodium 2-(4-isobutylphenyl) propionate (sodium salt of ibuprofen (NaIBF)) in aqueous/urea solution were studied by surface tension measurements at 298.15 K in the presence of anionic surfactant sodium dodecylsulfate (SDS). Critical micelle concentration (cmc), surface tension at cmc (γcmc), maximum Gibbs surface excess (Γ_max), minimum surface area per surfactant molecule at the air/water interface (A _min) etc. were determined in pure water as well as in aqueous urea solution. The theories of Clint, Rosen and Rubingh have been applied to describe the interactions between these amphiphiles at the interface and in the micellar solution. Various thermodynamic parameters have been calculated and discussed in detail.     

A facile and mild Pd-catalyzed one-pot process for direct hydrodeoxygenation (HDO) phenols to arenes through a ArOSO2F intermediates transformation

A practical one-pot process for hydrodeoxygenation (HDO) of phenolic derivatives to their corresponding arenes was developed. This method provided a facile route to upgrading bio-oil. The substrate scope of this protocol was wide, complicated and multi-phenolic compounds were also smoothly hydrodeoxygenated to their corresponding arenes.     

Long-range electronic interactions at a high temperature: bromine adatom islands on Cu(111)

Long-range electronic interactions between Br adatom islands, which are formed at approximately 600 K, on Cu(111) are mediated by substrate surface-state electrons at that elevated temperature. Using scanning tunneling microscopy at 4 K, we have quantified nearest neighbor island separations and found favored spacings to be half-multiples of the Fermi wavelength of Cu(111). The strong interaction potential and decay length of the interisland interactions are discussed in terms of the interaction of Br with the substrate surface state.     

Synthesis,Crystal Structure and Spectroscopic Properties of 1,2-Benzothiazine Derivatives:An Experimental and DFT Study

1,2-Benzothiazine derivatives methyl 3-methoxy-4-oxo-3,4-dihydro-2H-benzo[e] [1,2]thiazine-3-carboxylate 1,1-dioxide(1) and methyl 2-ethyl-3-hydroxy-4-oxo-3,4-dihydro-2Hbenzo[e][1,2]thiazine-3-carboxylate 1,1-dioxide(2) were synthesized, and characterized by spectroscopic techniques; 1H-NMR and infrared(IR) spectroscopy. Crystals of 1 and 2 were grown by slow evaporation of methanol and ethyl acetate, respectively and their crystal structures were investigated by single-crystal X-ray diffraction analysis. Geometric properties were calculated by the B3 LYP method of density functional theory(DFT) at the 6-31G+(d) basis set to compare with the experimental data. Simulated properties were found in strong agreement with the experimental ones. Intermolecular forces have also been modeled in order to investigate the strength of packing and strong hydrogen bonding was observed in both compounds 1 and 2. Electronic properties such as Ionization Potential(IP), Electron Affinities(EA) and coefficients of the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of com- pounds 1 and 2 were simulated for the first time.