Cross-linking of Polymer of Intrinsic Microporosity (PIM-1) via nitrene reaction and its effect on gas transport property

Polymer of Intrinsic Microporosity (i.e. PIM-1) has been crosslinked thermally via nitrene reaction using polyethylene glycol biazide (PEG-biazide) as a crosslinker. The crosslinking temperature was optimized using TGA coupled with FT-IR spectroscopy. The dense membranes containing different ratios of PIM-1 to PEG-biazide were cast from chloroform solution. Crosslinking of PIM-1 renders it insoluble even in excellent solvents for the uncrosslinked polymer. The resulting crosslinked membranes were characterized by FT-IR spectroscopy, TGA and gel content analysis. The influence of crosslinker content on the gas transport properties of PIM-1, its density and fractional free volume (FFV) were investigated. Compared to the pure PIM-1 membrane, the crosslinked PIM-1 membranes showed better gas separation performance especially for CO₂/N₂, CO₂/CH₄ and propylene/propane (C₃H₆/C₃H₈) gas pairs and as well as suppressed penetrant-induced plasticization under high CO₂ pressure.     

An in vitro experiment on the interaction of charcoal or wheat bran with 11-nor-9-carboxy-Δ9-tetrahydrocannabinol and its glucuronide

The rather long yet variable terminal half-lives and detection times since last use of urinary cannabinoids may partly be attributed to their enterohepatic circulation which generally can be interrupted or restricted by chemical adsorbents. Therefore, an in vitro experiment was performed to study the adsorption/binding of 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (THC-COOH) and its glucuronide to activated charcoal and wheat bran; remaining concentrations were determined by liquid chromatography/tandem mass spectrometry. Adsorption/binding of 1,000 ng/mL of free or conjugated THC-COOH was complete using as little as 5 mg of charcoal whereas adsorption/binding to wheat bran increased with increasing amounts. Taking of remedies affecting enterohepatic recycling of THC-COOH and its glucuronide may challenge interpretation of cannabinoid concentrations used to detect or assess frequency of drug use or the time since last drug consumption.

New synthetic routes for N-substituted 1,n-diamines. II. Synthesis of selectively N-substituted tetra- and pentamethylenediamines from ω-alkanoic acid derivatives

A new approach for the synthesis of selectively N-substituted tetra- and pentamethylenediamines 1 (n = 4,5) is described. The method uses N-substituted ω-haloalkanamides 2 as precursors and involves the microwave-promoted conversion into ω-azidocarboxamides 3 and later the reduction of both azido and carboxamide groups with diborane.     

Telomerisation of buta-1,3-diene and methanol: superiority of chromanyl-type phosphines in the Dow process for the industrial production of 1-MOD

Butadiene and methanol were telomerised in the presence of palladium catalysts with ligands containing 8-diphenylphosphinochromane-like substituents at phosphorus. MonoXantphos and monoSPANphos afforded the most active, stable and selective catalysts known to date under commercially relevant production conditions for 1-methoxyocta-2,7-diene, the precursor to oct-1-ene.     

Continuous-wave EPR at 275GHz: application to high-spin Fe(3+) systems

The 275GHz electron-paramagnetic-resonance spectrometer we reported on in 2004 has been equipped with a new probe head, which contains a cavity especially designed for operation in continuous-wave mode. The sensitivity and signal stability that is achieved with this new probe head is illustrated with 275GHz continuous-wave spectra of a 1mM frozen solution of the complex Fe(III)-ethylenediamine tetra-acetic acid and of 10mM frozen solutions of the protein rubredoxin, which contains Fe(3+) in its active site, from three different organisms. The high quality of the spectra of the rubredoxins allows the determination of the zero-field-splitting parameters with an accuracy of 0.5GHz. The success of our approach results partially from the enhanced absolute sensitivity, which can be reached using a single-mode cavity. At least as important is the signal stability that we were able to achieve with the new probe head.     

Direct hydride transfer in the reaction mechanism of quinoprotein alcohol dehydrogenases: a quantum mechanical investigation

Oxidation of alcohols by direct hydride transfer to the pyrroloquinoline quinone (PQQ) cofactor of quinoprotein alcohol dehydrogenases has been studied using ab initio quantum mechanical methods. Energies and geometries were calculated at the 6-31G(d,p) level of theory. Comparison of the results obtained for PQQ and several derivatives with available structural and spectroscopic data served to judge the feasibility of the calculations. The role of calcium in the enzymatic reaction mechanism has been investigated. Transition state searches have been conducted at the semiempirical and STO-3G(d) level of theory. It is concluded that hydride transfer from the Calpha-position of the substrate alcohol (or aldehyde) directly to the C(5) carbon of PQQ is energetically feasible. Copyright 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1732-1749, 2001     

The structure and conformation of dichloroacetyl chloride as determined by gas-phase electron diffraction

The structure and conformation of dichloroacetyl chloride have been determined by gas-phase electron diffraction at nozzle temperatures of 20 and 119°C. The molecules exist as a mixture of two conformers with the hydrogen and oxygen atoms syn and gauche to each other. The composition (mole fraction of syn form) of the vapor was found to be 0.72 ± 0.06 and 0.73 ± 0.12 at 20 and 119°C, respectively, corresponding to almost equal energy for the two forms. The results for the distance (r_g), angle ∠α and r.m.s. amplitude (l) parameters obtained at the two temperatures are entirely consistent. At 20°C the more important parameters, with estimated uncertainties of 3σ are: r(C-H) = 1.062(0.049)Å, r(C0) = 1.189(0.003)Å, r(C-C) = 1.535(0.008)Å, r(CO-Cl) = 1.752 (0.009)Å, r(CHCl-Cl) = 1.771(0.004)Å, ∠C-CO = 123.3(1.3)°, ∠C-CO-Cl = 113.9 (5.9)°, ∠C-CHCl—Cl = 109.5(1.5)°, ∠C1-C-Cl = 111.7(0.5)°, ∠Cl-C-H = 108.0(1.5), φ₁ (HCCO torsion angle in the syn conformer) = 0.0° (assumed), φ₂ (HCCO torsion angle in the gauche conformer) = 138.2(5.1)°.     

Metastable ion studies: Ethyl(methoxy)(chloro)silanes

Metastable ion scanning was used to investigate the fragmentation patterns of ethyl(trimethoxy)silane, ethyl(dimethoxy)chlorosilane and ethyl(methoxy)dichlorosilane, their deuterated counterparts and ethyltrichlorosilane. For these compounds the molecule ion has a low abundance using 70 eV electron impact ionization. In all cases the base peak corresponds to the loss of neutral C₂H₅. When chemical ionization is employed with isobutane, usable peaks representative of the molecule ions are observed.     

Core Halogenation as a Construction Principle in Tuning the Material Properties of Tetraazaperopyrenes

A detailed study on the effects of core halogenation of tetraazaperopyrene (TAPP) derivatives is presented. Its impact on the solid structure, as well as the photophysical and electrochemical properties, has been probed by the means of X‐ray crystallography, UV/Vis and fluorescence spectroscopy, high‐resolution electron energy loss spectroscopy (HREELS), cyclic voltammetry (CV), and DFT modeling. The aim was to assess the potential of this approach as a construction principle for organic electron‐conducting materials of the type studied in this work. Although halogenation leads to a stabilization of the LUMOs compared to the unsubstituted parent compound, the nature of the halide barely affects the LUMO energy while strongly influencing the HOMO energies. In terms of band‐gap engineering, it was demonstrated that the HOMO–LUMO gap is decreased by substitution of the TAPP core with halides, the effect being found to be most pronounced for the iodinated derivative. The performance of the recently reported core‐fluorinated and core‐iodinated TAPP derivatives in organic thin‐film transistors (TFTs) was investigated on both a glass substrate, as well as on a flexible plastic substrate (PEN). Field‐effect mobilities of up to 0.17 cm² Vs^?1 and on/off current ratio of >10⁶ were established.