Self-assembly of poly(ethylene oxide)-block-poly(acrylic acid) induced by CaCl2: mechanistic study

The interaction between CaCl 2 and double hydrophilic block copolymer, poly(ethylene oxide) 45- block-poly(acrylic acid) 70, PEO 45- b-PAA 70, was investigated. At a stoichiometric ratio of Ca2+:COO (-) = 0.5, Ca2+ ions were bound to COO (-) groups on PAA segments via electrostatic interaction. Small particles of 4-8 nm in diameter were observed, suggesting the formation of coil-like polymeric globule induced by charge neutralization. At Ca2+:COO (-) >or= 2.5, monodispersed aggregates of average hydrodynamic diameter of 52.0 +/- 7.4 nm were produced. The ISE, ITC, surface tension and fluorescence spectroscopic data confirmed that the formation of these aggregates is not the result of interaction between excess Ca2+ ions and the polymer, but rather it is due to changes in the water activity that triggers the structural rearrangement of Ca2+/PEO 45- b-PAA 70 complex.     

Fast analysis of decabrominated diphenyl ether using low-pressure gas chromatography-electron-capture negative ionization mass spectrometry

This paper reports the applicability of low-pressure gas chromatography-mass spectrometry operated in electron-capture negative ionization mode (LP-GC-ECNI-MS) for the analysis of decabrominated diphenyl ether (BDE-209). Particular attention was paid to find optimal injector and oven conditions for minimal thermal degradation of BDE-209. The analytical characteristics were compared for LP-GC columns (10 m x 0.53 mm) with different film thicknesses (d(f) 0.15 microm versus 0.25microm) and for a conventional GC column (15 m x 0.25 mm, 0.10 microm d(f)). Short residence times (6.5 and 9.8 min) of BDE-209 were found for the LP-GC systems with 0.15 and 0.25microm d(f), respectively, resulting in a low elution temperature and minimal degradation. Additionally, baseline separation of 22 polybrominated diphenyl ether (PBDE) congeners (major components of PBDE technical mixtures) was possible in less than 12 min using the LP-GC-ECNI-MS system with 0.15microm d(f). The optimized method was applied for the determination of PBDEs in Belgian indoor dust samples. The obtained concentrations of BDE-209 (range 8-292 ng/g dry weight) were in the same range or lower than concentrations in dust from other European countries.     

Spin hamiltonian for which the chiral spin liquid is the exact ground state

We construct a Hamiltonian that singles out the chiral spin liquid on a square lattice with periodic boundary conditions as the exact and, apart from the twofold topological degeneracy, unique ground state.     

A weak cation-exchange monolith as stationary phase for the separation of peptide diastereomers by CEC

A CEC weak cation-exchange monolith has been prepared by in situ polymerization of acrylamide, methylenebisacrylamide and 4-acrylamidobutyric acid in a decanol-dimethylsulfoxide mixture as porogen. The columns were evaluated by SEM and characterized with regard to the separation of diastereomers and α/β-isomers of aspartyl peptides. Column preparation was reproducible as evidenced by comparison of the analyte retention times of several columns prepared simultaneously. Analyte separation was achieved using mobile phases consisting of acidic phosphate buffer and ACN. Under these conditions the peptides migrated due to their electrophoretic mobility but the EOF also contributed as driving force as a function of the pH of the mobile phase due to increasing dissociation of the carboxyl groups of the polymer. Raising the pH of the mobile phase also resulted in deprotonation of the peptides reducing analyte mobility. Due to these mechanisms each pair of diastereomeric peptides displayed the highest resolution at a different pH of the buffer component of the mobile phase. Comparing the weak-cation exchange monolith to an RP monolith and a strong cation-exchange monolith different elution order of some peptide diastereomers was observed, clearly illustrating that interactions with the stationary phase contribute to the CEC separations.     

A model for enhanced coal bed methane recovery aimed at carbon dioxide storage

Numerical simulations on the performance of CO₂ storage and enhanced coal bed methane (ECBM) recovery in coal beds are presented. For the calculations, a one-dimensional mathematical model is used consisting of mass balances describing gas flow and sorption, and a geomechanical relationship to account for porosity and permeability changes during injection. Important insights are obtained regarding the gas flow dynamics during displacement and the effects of sorption and swelling on the ECBM operation. In particular, initial faster CH₄ recovery is obtained when N₂ is added to the injected mixture, whereas pure CO₂ allows for a more effective displacement in terms of total CH₄ recovery. Moreover, it is shown that coal swelling dramatically affects the gas injectivity, as the closing of the fractures associated with it strongly reduces coal’s permeability. As a matter of fact, injection of flue gas might represent a useful option to limit this problem.     

Triflimide-catalyzed allyl-allyl cross-coupling: a metal-free allylic alkylation

A highly efficient metal-free intermolecular C(sp3)-C(sp3) allyl-allyl cross-coupling protocol between allyl acetates and allyltrimethylsilanes, which proceeded smoothly in the presence of catalytic triflimide to form 1,5-dienes with good to excellent regioselectivity, has been developed.     

3D Mapping of Gas Physisorption for the Spatial Characterisation of Nanoporous Materials

Nanoporous materials used in industrial applications (e. g., catalysis and separations) draw their functionality from properties at the nanoscale (1–10 Å). When shaped into a technical form these solids reveal spatial variations in the same properties over much larger length scales (1 μm–1 cm). The multiscale characterization of these systems is impaired by the trade-off between sample size and image resolution that is bound to the use of most imaging techniques. We show here the application of X-ray computed tomography for the non-invasive spatial characterization of a zeolite/activated carbon adsorbent bed across three orders of magnitude in scale. Through the unique combination of gas adsorption isotherms measured locally and their interpretation by physisorption analysis, we determine three-dimensional maps of the specific surface area and micropore volume. We further use machine learning to identify and locate the materials within the packed bed. This novel ability to reveal the extent of heterogeneity in technical porous solids will enable a deeper understanding of their function in industrial reactors. Such developments are essential towards bridging the gap between material research and process design.     

Protonation of phosphovanadomolybdates H(3+x)PV(x)Mo(12-x)O40: computational insight into reactivity

Protonated phosphovanadomolybdates of the Keggin structure, H(3+x)PV(x)Mo(12-x)O(40) where x = 0, 1, 2, and derivatives with surface defects formed by loss of constitutional water were studied using high-level DFT calculations toward determination of the most stable species and possible active forms in oxidation catalysis in both the gas phase and in polar solutions. The calculations demonstrate that protonation at bridging positions is energetically much more favorable than protonation of terminal oxygen atoms. The preferential protonation site is determined by the stability of the metal-oxygen bond rather than the negative charge on the oxygen atom. In H(3)PMo(12)O(40), maximum distances between protons at bridging oxygen atoms are energetically favored. In contrast, for H(4)PVMo(11)O(40) and H(5)PV(2)Mo(10)O(40) protons prefer nucleophilic sites adjacent to vanadium atoms. Up to three protons are bound to the nucleophilic sites around the same vanadium atom in the stable isomeric forms of H(5)PV(2)Mo(10)O(40) that result in strong destabilization of oxo-vanadium(V) bonding to the Keggin unit. Such behavior arises from the different nature of the Mo-O and V-O bonds that can be traced to the different sizes of the valence d orbitals of the metals. Coordination of two protons at the same site yields water and an oxygen defect as a result of its dissociation. The energetic cost for the formation of surface defects decreases in the order: O(t) ? O(c) ? O(e) and is lower for the sites adjacent to vanadium atoms. Vanadium atoms near defects also have a significant contribution to the LUMO. Thus, vanadium-substituted polyoxometalates with defects near and, especially, between vanadium atoms present a plausible active form of polyoxometalates in oxidation reactions.     

High‐Field Pulsed EPR Spectroscopy for the Speciation of the Reduced [PV2Mo10O40]6− Polyoxometalate Catalyst Used in Electron‐Transfer Oxidations

An in‐depth spectroscopic EPR investigation of a key intermediate, formally notated as [PV^IVV^VMo₁₀O₄₀]^6? and formed in known electron‐transfer and electron‐transfer/oxygen‐transfer reactions catalyzed by H₅PV₂Mo₁₀O₄₀, has been carried out. Pulsed EPR spectroscopy have been utilized: specifically, W‐band electron–electron double resonance (ELDOR)‐detected NMR and two‐dimensional (2D) hyperfine sub‐level correlation (HYSCORE) measurements, which resolved ⁹⁵Mo and ¹⁷O hyperfine interactions, and electron–nuclear double resonance (ENDOR), which gave the weak ⁵¹V and ³¹P interactions. In this way, two paramagnetic species related to [PV^IVV^VMo₁₀O₄₀]^6? were identified. The first species (30–35 %) has a vanadyl (VO²⁺)‐like EPR spectrum and is not situated within the polyoxometalate cluster. Here the VO²⁺ was suggested to be supported on the Keggin cluster and can be represented as an ion pair, [PV^VMo₁₀O₃₉]^8?[V^IVO²⁺]. This species originates from the parent H₅PV₂Mo₁₀O₄₀ in which the vanadium atoms are nearest neighbors and it is suggested that this isomer is more likely to be reactive in electron‐transfer/oxygen‐transfer reaction oxidation reactions. In the second (70–65 %) species, the V^IV remains embedded within the polyoxometalate framework and originates from reduction of distal H₅PV₂Mo₁₀O₄₀ isomers to yield an intact cluster, [PV^IVV^VMo₁₀O₄₀]^6?.     

Collective Synthesis of 4‐Hydroxy‐2‐pyridone Alkaloids and Their Antiproliferation Activities

A collective synthesis of 4‐hydroxy‐2‐pyridone alkaloids—specifically, pretenellin B, prebassianin B, farinosone A, militarione D, pyridovericin, and torrubiellone C—has been achieved. Key steps include using a strategic convergent method to synthesize the densely substituted pyridone key intermediate by Suzuki–Miyaura cross‐coupling reaction, a divergent synthesis approach of target molecules by aldol condensation of pyridone intermediate with homologous aldehydes, and an iterative synthesis of homologous aldehydes with all‐trans‐polyene backbones. Interestingly, among the six tumor cell lines investigated, torrubiellone C was found to induce potent and apoptotic inhibitory activities on Jurkat T cells with IC₅₀ values of 7.05 μM . Hence, this approach could potentially contribute to the synthesis of bioactive small‐molecule libraries as well as drug discovery.