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Complex capsules were fabricated by combining the polymerization of dopamine with hydrogen-bonding layer-by-layer assembly (LbL) of dopamine-modified poly(acrylic acid) (PAA-dopa) and poly(vinylpyrrolidone) (PVPON). PDA(PAA-dopa/PVPON) n shell was cross-linked by dismutation reaction among catechol groups of polydopamine (PDA) and PAA-dopa. During LbL assembly, PAA-dopa and PVPON diffuse in the robust PDA pre-layer, and hence the complex capsules become soft and flexible. With the change of environmental pH value, the hydrogen bonds in PDA(PAA-dopa/PVPON) n capsules would dissociate or reconstruct, and thus the complex capsules exhibit pH-responsive swelling–shrinking behavior. With only one assembled bilayer, PDA(PAA-dopa/PVPON) 1 capsules show a volume swelling ratio of 1.34 from pH 2.0 to pH 8.5. In addition, the complex capsules display controlled loading and release of Rhodamine 6G (R6G) as pH value changed, which can be considered as a potential candidate for drug delivery. [ABSTRACT FROM AUTHOR]

Superoxide dismutases (SODs) are enzymes that play a key role in protecting cells from toxic oxygen metabolites by disproportionation of two molecules of superoxide into molecular oxygen and hydrogen peroxide via cyclic reduction and oxidation at the active site metal. The azide anion is a potent competitive inhibitor that binds directly to the metal and is used as a substrate analog to superoxide in studies of SOD. The crystal structure of human MnSOD-azide complex was solved and shows the putative binding position of superoxide, providing a model for binding to the active site. Azide is bound end-on at the sixth coordinate position of the manganese ion. Tetrameric electrostatic surfaces were calculated incorporating accurate partial charges for the active site in three states, including a state with superoxide coordinated to the metal using the position of azide as a model. These show facilitation of the anionic ligand to the active site pit via a ‘valley’ of positively-charged surface patches. Surrounding ridges of negative charge help guide the superoxide anion. Within the active site pit, Arg173 and Glu162 further guide and align superoxide for efficient catalysis. Superoxide coordination at the sixth position causes the electrostatic surface of the active site pit to become nearly neutral. A model for electrostatic-mediated diffusion, and efficient binding of superoxide for catalysis is presented. [ABSTRACT FROM AUTHOR]

The effects of methanol space velocity and inlet methanol partial pressure on lifetime and selectivity of methanol-to-olefins catalysis are examined and interpreted to elucidate reaction parameters and propose intermediates and reactions relevant to catalyst deactivation. The propensity of active centers in HSSZ-13 to turn over for methanol-to-olefins catalysis increases when the methanol partial pressure local to organic co-catalysts confined within the inorganic chabazite cages is lower either by decreasing methanol space velocity or inlet methanol partial pressure. High initial methane selectivity reveals methanol disproportionation, to methane and formaldehyde, a primary reaction, and continual methane formation implicates persistent participation of methanol in bimolecular hydrogen transfer reactions throughout the catalyst lifetime. Methane selectivity correlates positively with inlet methanol partial pressure reflecting enhanced relative rates of formaldehyde formation with increasing methanol partial pressure. Subsequent alkylation reactions of olefins- and aromatics-based C C chain growth carriers by formaldehyde accelerate the relative rates of hydrogen transfer and proliferate, apparently, the precursors mediating the transformation of active hydrocarbon pool participants to those inducing catalyst deactivation. [ABSTRACT FROM AUTHOR]

La 1/3 Ca 2/3 FeO 3 with unusually-high-valence Fe 3.67+ was synthesized at a high pressure and high temperature. The compound crystallizes in a √2 a ×2 a ×√2 a perovskite cell in which the La and Ca ions at the A site are disordered. At 217 K the Fe 3.67+ shows charge disproportionation to Fe 3+ and Fe 5+ in a ratio of 2:1, and this disproportionation is accompanied by transitions in magnetic and transport properties. The charge-disproportionated Fe 3+ and Fe 5+ are arranged along the <111> direction of the cubic perovskite cell. The local electronic and magnetic environments of Fe in La 1/3 Ca 2/3 FeO 3 are quite similar to those of Fe in La 1/3 Sr 2/3 FeO 3 , and the 2:1 charge disproportionation pattern of Fe 3+ and Fe 5+ in La 1/3 Ca 2/3 FeO 3 is also the same as that in La 1/3 Sr 2/3 FeO 3 . [ABSTRACT FROM AUTHOR]

While 1,2,4-trimethylbenzene (TMB) disproportionation is one of the potential technologies for p -xylene production, its reaction intermediates have been neither experimentally observed nor identified yet. Here we present GC–MS evidence that not only pentamethylated diphenylmethane (5mDPM) derivatives but also hexamethylated diphenylmethane (6mDPM) ones are serving as key reaction intermediates of 1,2,4-TMB disproportionation over large-pore zeolites. We also propose a new bimolecular diphenylmethane-mediated reaction pathway for the formation of tetramethylbenzenes (TeMBs) and xylenes over large-pore zeolites based on the GC–MS results obtained. Comparison with the GC–MS results from LaNa-Y after transalkylation reactions of three different TeMB isomers with three xylene and three TMB isomers, respectively, allows us to rationally identify most of the seven 5mDPM and three 6mDPM derivatives at their isomer level. A combination of GC–MS and DFT calculation results demonstrates that the bimolecular 1,2,4-TMB disproportionation over LaNa-mordenite, a practically one-dimensional 12-ring zeolite with regard to this reaction, is a new example of transition state shape selectivity in zeolite catalysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] Adsorption of NO on Cu-ZSM-5 causes disproportionation of Cu2+ to Cu+ and Cu3+ ions. [•] The process occurs with participation of associated [Cu–O–Cu]2+ sites even at 100K. [•] The Cu3+ ions form two kinds of mononitrosyl species (1960 and 1947cm−1). [•] The Cu3+–NO species can accept a second NO molecule thus forming dinitrosyls. [•] At ambient temperature, Cu3+ ions are reduced by NO to Cu+ and Cu2+. [ABSTRACT FROM AUTHOR]

Highlights: [•] New zeolite catalyst has been created where only a portion is developed for strong acid sites. [•] Selective creation of strong acid sites occurs via Al replacement for B in parts of the structure. [•] The novel large pore (but short path) zeolite is contrasted with ZSM-11 and SSZ-57. [•] Reactions studied are Constraint Index, hydroisomerization of n-hexane, and isomerization and disproportionation of diethylbenzene. [Copyright &y& Elsevier]

Abstract: Researchers at Chevron recently discovered a route for making high silica stilbite (STI), a zeolite with intersecting 10- and 8-ring channels. This zeolite, named SSZ-75, provides an interesting comparison to two other two-dimensional 10/8-ring zeolites, namely, ferrierite (FER) and ZSM-57 (MFS). The catalytic properties of these zeolites are characterized here using the Constraint Index test, adsorption measurements, and toluene disproportionation and its alkylation with isopropyl alcohol. Results are then compared to ZSM-5 (a well-characterized 3-dimensional 10-ring zeolite) and TON (a 1-dimensional 10-ring zeolite). While the micropore volumes for several of these five materials are similar, the Constraint Index, which considers the competitive cracking of n-hexane and 3-methylpentane, differs greatly. On the other hand, toluene conversions along with selectivity to p-xylene for MFI and STI are remarkably similar. This indicates that the reaction volume available at the intersections of the 10- and 8-ring channels in STI is comparable with that of the 10-ring channel intersections in MFI. However, in toluene alkylation with isopropyl alcohol, differences in intersection volume between MFI and STI are revealed. These results nicely demonstrate how the size of the pores and geometry of the channel intersections (rather than just the size of the individual pores) impact the catalytic properties of zeolites with multidimensional channel systems. [Copyright &y& Elsevier]

Abstract: Micro/mesoporous materials with different contribution of micro/mesoporosity have been studied in cumene disproportionation. The materials were prepared by recrystallization of mordenite and characterized by X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, infrared spectroscopy, and temperature-programmed desorption of ammonia. Micro/mesoporous materials with a low degree of recrystallization showed remarkably high activity and stability with respect to the parent and desilicated mordenites. The enhanced catalytic activity is due to a high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by uniform and homogeneously distributed intracrystalline mesopores. The high catalyst resistance to deactivation is due to two reasons: i) the improved transport of bulky products, which prevents the catalyst from the formation of “soft” coke inside the zeolite pores; ii) the coating of the zeolite with a mesoporous layer, which prevents the formation of “hard” coke on the external surface of the crystal. [Copyright &y& Elsevier]

Abstract: The catalytic oxidation of dichloromethane (DCM, 1000ppm) in wet air was carried out in a fixed bed reactor over a range of Pt/γ-Al2O3 catalysts. The dichloromethane oxidation occurs following a bifunctional mechanism. DCM is disproportionated over γ-Al2O3 into a 1/1/3molar mixture of CO, CH3Cl, and HCl; the DCM transformation is followed by CH3Cl and CO oxidation into CO2. A mechanism of DCM disproportionation is proposed involving, as intermediates, formate species as well as alumina hydroxyl groups formed by water adsorption. [Copyright &y& Elsevier]