Temperature-dependent gas-surface chemical kinetic model for methane ignition catalyzed by in situ generated palladium nanoparticles

A temperature-dependent gas-surface kinetic model for methane oxidation over palladium is proposed. Thermodynamic data for the surface species (O, H, OH, H₂O, and CO) are derived from statistical mechanic analysis using literature heats of desorption and vibrational frequencies. The rate parameters in the model also satisfy thermo-kinetic constraints. The hydrogen oxidation submodel is validated against literature stagnation flow reactor experiments at 1300 K and 13 Pa. The current model is further tested against catalytic methane ignition in a laminar flow reactor at atmospheric pressure, and with time-resolved measurements of the size distribution of palladium nanoparticles generated in situ from an aerosol containing palladium acetate. The improved gas-surface model predicts closely the experimental data. The role of palladium nanoparticles in enhancing methane ignition is attributed to heat release due to catalytic methane oxidation over distributed nanoparticle surfaces, leading to a temperature rise and thus an accelerated gas-phase chain-branching process.     

Aggregation behavior of organic‐soluble semi‐aromatic polyimides in N‐methylpyrrolidone systems

Aggregation behavior of the organic‐soluble semi‐aromatic polyimides, whose degrees of imidization range from 69 to 96%, obtained using 4,4′‐oxydianiline, 4,4′‐diamino‐3,3′dihydroxybiphenyl, and bicyclo[2.2.2]‐oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA) in N‐methylpyrrolidone (NMP), NMP/cyclohexanone, and NMP/γ‐butyrolactone (BCDA‐based polyimides) were studied by static light scattering (SLS) and dynamic light scattering (DLS). The DLS analyses for the multirelaxation modes demonstrated the specific character unlike flexible polymers that the single BCDA‐based polyimide chains first associate with each other to form small clusters in the dilute region, and then expand to large aggregates by the entanglements between the small clusters with an increasing concentration into the semi‐dilute region. Given the semi‐aromatic structure of BCDA‐based polyimides weakening the charge transfer (CT) interaction between the diamine and the dianhydride unit, it is concluded that the unique aggregation behavior of BCDA‐based polyimides is dominated by the balance between the driving force for the “organic solubility” given by both the increase in bulkiness and the decrease in the CT interaction, and that for the “organic insolubility” derived from both the hydrogen‐bonded interaction of the phenolic hydroxyl groups and the π–π interaction of the phenyl rings. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis of molecular‐weight‐controlled polyfluorene with boronate at one end

We investigated the synthesis of polyfluorene with a pinacol boronate (PinB) moiety at one end and with controlled molecular weight by means of Suzuki–Miyaura coupling polymerization of pinacol (7‐bromo‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)boronate ( 1 ) with a palladium(0) precatalyst in the presence of pinacol 4‐trifluoromethylphenylboronate ( 2 ) as a chain terminator and CsF/18‐crown‐6 as a base. When we used AmPhos Pd G2, which has a propensity for intramolecular catalyst transfer on a π‐electron face, polyfluorene with the PinB moiety at one end and PhCF₃ (derived from 2 ) at the other end was obtained, and the molecular weight increased in proportion to the feed ratio of [ 1 ]₀/[catalyst]₀, though the molecular weight distribution was broad. Since the molecular weight also linearly increased with respect to the conversion of 1 until the middle stage of polymerization, the polymerization appears to involve chain‐growth polymerization through intramolecular catalyst transfer from the Pd catalyst inserted into the C? Br bond of 1 . The broad molecular weight distribution might be mainly due to slow initiation and slow termination with 2 , rather than polymer–polymer coupling. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2498–2504     

Biradical processes in reactions between benzyne and tropone

The title reactions were investigated experimentally and theoretically. The benzyne--tropone pair has been known to give a Diels?CAlder [4+2] cycloadduct. However, in the present experiment using two sources of benzyne, many unexpected products were obtained. In particular, a zwitterion with a C?CCl bond is strikingly a major product, the structure of which was determined by the X-ray analysis. The bond is formed by quenching the Cl atom from the solvent CH₂Cl₂, which demonstrates that the reactions proceed via radical processes. DFT calculations revealed the elementary processes of the reactions. The presence of the novel zwitterion in the solid state has been interpreted in terms of the permanent dipole?Cdipole attractions/interactions/stabilization.     

Synthesis of jadomycin A and related jadomycin aglycons: structural re-examination of jadomycins S and T may be needed

Jadomycin A and related jadomycin M and W aglycons were synthesized. Easy re-construction of 4-(hydroxymethyl)-1,3-oxazolidin-5-one system into an isomeric 1,3-oxazolidine-4-carboxylic acid system during the synthetic trial of jadomycin S aglycon requests us to more precisely re-examine the structures proposed for jadomycins S and T, derived from hydroxyl-containing amino acids of l-serine and l-threonine, respectively.     

Clinical value of routine use of thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique for internal derangements of the knee joint at 3T

PurposeTo determine the clinical value of routine use of thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique for internal derangements of the knee joint at 3 T.Method and MaterialsThirty-four knees in 34 patients suspected of having internal derangements of the knee joint were included. Following standard 2D MRI protocol including sagittal PDWI, T1WI and T2*WI, coronal fat-suppressed PDWI, and axial fat-suppressed PDWI with 3-4 mm thicknesses, fat-suppressed and water-excitation PDWI using 3D FSE sequences with a variable flip angle technique with 0.6 mm thickness were obtained in coronal plane and the three major planes with 1 mm thickness (3D MRI) was reformatted. The standard 2D MRI protocol and reformatted 3D MRI protocol (three sagittal 2D sequence images plus 3D MRI) were independently analyzed by two radiologists concerning presence or absence of lesions in the menisci, cartilage, and ligament. Interobserver agreements in both the MRI protocols were assessed by weighted-kappa coefficients. Regarding diagnostic accuracy, areas under the receiver operating characteristic curves (Az values) of both the MRI protocols were compared.ResultsThirty-eight meniscal lesions, 39 cartilage lesions, and 20 ligamentous lesions were surgically detected. Excellent interobserver agreements (kappa = 0.91–0.98) were seen in both the MRI protocols, with a slightly better tendency in the reformatted 3D MRI protocol. Average Az values in detection of the meniscal, cartilage, and ligamentous lesions were significantly higher in the reformatted 3D MRI protocol than in the standard 2D MRI protocol (p < 0.01 or p < 0.001).ConclusionRoutine use of reformatted thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique may improve diagnostic accuracy and confidence in detection of internal derangements of the knee joint.     

Unexpected high regiocontrol in Heck reaction of fluorine-containing electron-deficient olefins—Highly regio- and stereoselective synthesis of β-fluoroalkyl-α-aryl-α,β-unsaturated ketones

Treatment of (E)-4,4,4-trifluoro-1-aryl-2-buten-1-one with various aryldiazonium salts in the presence of palladium catalyst gave the corresponding α-arylated Heck adducts with high regio- and stereoselectivity in good to high yields.     

Solid phase extraction of zinc(II) using a PVC-based polymer inclusion membrane with di(2-ethylhexyl)phosphoric acid (D2EHPA) as the carrier

A polymer inclusion membrane (PIM) is reported consisting of 45% (m/m) di(2-ethylhexyl)phosphoric acid (D2EHPA) immobilized in poly(vinyl chloride) (PVC) for use as a solid phase absorbent for selectively extracting Zn(II) from aqueous solutions in the presence of Cd(II), Co(II), Cu(II), Ni(II) and Fe(II). Interference from Fe(III) in the sample is eliminated by precipitation with orthophosphate prior to the extraction of Zn(II). Studies using a dual compartment transport cell have shown that the Zn(II) flux (2.58 × 10⁻⁶ mol m⁻² s⁻¹) is comparable to that observed for supported liquid membranes. The stoichiometry of the extracted complex is shown to be ZnR₂·HR, where R is the D2EHPA anion.     

Regularity estimates for convex multifunctions

The main result of the paper contains an exact formula for the rate of regularity of a set-valued mapping with a convex graph. As a consequence we find an exact expression for the rate of regularity of set-valued mappings associated with so-called constraint systems. It turns out that the rate is equal to the upper bound of Robinson-type estimates over all norms in the graph space of the homogenized mapping majorizing the norm of the underlying space. We further introduce a concept of a perfectly regular mapping and find some criteria for perfect regularity.