Improving the Gas-Separation Properties of PVAc-Zeolite 4A Mixed-Matrix Membranes through Nano-Sizing and Silanation of the Zeolite.

Mixed-matrix membranes containing synthesised nano-sized zeolite 4A and PVAc were fabricated to investigate the effect of zeolite loading on membrane morphology, polymer-filler interaction, thermal stability and gas separation properties. SEM studies revealed that, although the membranes with 40 wt % nano-sized zeolite particles were distributed uniformly through the polymer matrix without voids, the membranes with 15 wt % zeolite loading showed agglomeration. With increasing zeolite content, the thermal stability improved, the permeability decreased and the selectivity increased. The effect of silanation on dispersion of 15 wt % zeolite 4A nanoparticles through PVAc was investigated by post-synthesis modification of the zeolite with 3-Aminopropyl(diethoxy)methylsilane. Modification of the nanoparticles improved their dispersion in PVAc, resulting in higher thermal stability than the corresponding unmodified zeolite membrane. Modification also decreased the rigidity of the membrane. Partial pore blockage of the modified zeolite nanoparticles after silanation caused a further decrease in permeability, compared to the 15 wt % unmodified zeolite membrane.

The Effect of Thermal Treatment on the Hydrogen-Storage Properties of PIM-1.

There has been recent interest in polymers of intrinsic microporosity (PIMs) for solid-state hydrogen-storage materials; however, the gas-sorption properties and conditions for hydrogen uptake are relatively unexplored. PIM-1 has been synthesised using the condensation reaction between 3,3,3,3-tetramethyl-1,1-spirobisindane-5,5,6,6-tetraol and 2,3,5,6-tetrafluorophthalonitrile as precursors. The synthesised PIM-1 was annealed at different temperatures for varying times and then characterised for hydrogen uptake at both ambient and cryogenic temperatures. The excess hydrogen PCT isotherms have been measured to high pressure (320 bar) for the first time and the effect of different annealing conditions on the hydrogen capacity is reported.

Role of oxygen-containing functional groups in forest fire-generated and pyrolytic chars for immobilization of copper and nickel.

Char as a carbon-rich material, can be produced under pyrolytic conditions, wildfires or prescribed burn offs for fire management. The objective of this study was to elucidate mechanistic interactions of copper (Cu2+) and nickel (Ni2+) with different chars produced by pyrolysis (green waste, GW; blue-Mallee, BM) and forest fires (fresh-burnt by prescribed fire, FC; aged char produced by wild fire, AC). The pyrolytic chars were more effective sorbents of Cu2+ (∼11 times) and Ni2+ (∼5 times) compared with the forest fire chars. Both cross-polarization (CPMAS-NMR) and Bloch decay (BDMAS-NMR) 13C NMR spectroscopies showed that forest fire chars have higher woody components (aromatic functional groups) and lower polar groups (e.g. O-alkyl C) compared with the pyrolytic chars. The polarity index was greater in the pyrolytic chars (0.99-1.34) than in the fire-generated chars (0.98-1.15), while aromaticity was lower in the former than in the latter. Fourier transform infrared (FTIR) and Raman spectroscopies indicated the binding of carbonate and phosphate with both Cu2+ and Ni2+ in all chars, but with a greater extent in pyrolytic than forest fire-generated chars. These findings have demonstrated the key role of char's oxygen-containing functional groups in determining their sorption capacity for the Cu2+ and Ni2+ in contaminated lands.

Yellow-Emitting Carbon Nanodots and Their Flexible and Transparent Films for White LEDs.

We report carbon nanodots that can be utilized as effective color converting phosphors for the production of white light-emitting diodes (LEDs). Blue-excitable and yellow-emitting carbon nanodots, functionalized with 3-(imidazolidin-2-on-1-yl)propylmethyldimethoxysilane (IPMDS)-derived moieties (IS-CDs), are synthesized by a novel one-pot reaction in which the products from the initial reaction occurring between urea and 3-(2-aminoethylamino)propylmethyl-dimethoxysilane (AEPMDS) are further treated with citric acid. Distinctive from the majority of carbon nanodots reported previously, IS-CDs emit at 560 nm, under 460 nm excitation, with a quantum yield of 44%. Preliminary toxicity studies, assessed by the Artemia franciscana nauplii (brine shrimp larvae) bioassay, indicate that IS-CDs are largely nontoxic. Furthermore, the IS-CDs form flexible and transparent films without the need of encapsulating agents, and the solid films retain the optical properties of solvated IS-CDs. These features indicate an immense potential for the IS-CDs as an environmental-friendly, blue-excitable carbon nanodot-based phosphor in solid-state lighting devices.

Direct Mitsunobu monoesterification of N-protected tobramycin competes with intramolecular pyrrolidine formation in ester prodrug synthesis.

Unlike the related aminoglycoside neomycin B, N-protected tobramycin can be selectively esterified at its sole, primary hydroxyl group under Mitsunobu conditions. However, depending on the reaction conditions, the reaction can take a different course with intramolecular cyclization of an N-Boc amine leading to formation of an unusual tobramycin pyrrolidine derivative as the major reaction product.

Dicyclo-hexyl-ammonium (S)-2-azido-3-phenyl-propano-ate.

The asymmetric unit of the title compound, C(12)H(24)N(+)·C(9)H(8)N(3)O(2) (-), consists of two dicyclo-hexyl-ammonium cations linked to two (S)-2-azido-3-phenyl-propano-ate anions by four short N-H⋯O hydrogen bonds with N⋯O distances in the range 2.712 (3)-2.765 (3) Å. The dicyclo-hexyl-ammonium cations and the aryl and carboxyl-ate groups of the anion are related by a pseudo-inversion centre, with overall crystallographic inversion symmetry for the structure broken by the chirality of the α-C atoms of the anions.

Crystallographic characterization of the first reported crystalline form of the potent hallucinogen (R)-2-amino-1-(8-bromobenzo[1,2-b;5,4-b']difuran-4-yl)propane or 'bromodragonfly': the 1:1 anhydrous proton-transfer compound with 3,5-dinitrosalicylic acid.

The 1:1 proton-transfer compound of the potent substituted amphetamine hallucinogen (R)-2-amino-1-(8-bromobenzo[1,2-b;5,4-b']difuran-4-yl)propane (common trivial name 'bromodragonfly') with 3,5-dinitrosalicylic acid, namely 1-(8-bromobenzo[1,2-b;5,4-b']difuran-4-yl)propan-2-aminium 2-carboxy-4,6-dinitrophenolate, C(13)H(13)BrNO(2)(+).C(7)H(3)N(2)O(7)(-), forms hydrogen-bonded cation-anion chain substructures comprising undulating head-to-tail anion chains formed through C(8) carboxyl-nitro O-H...O associations and incorporating the aminium groups of the cations. The intrachain cation-anion hydrogen-bonding associations feature proximal cyclic R(3)(3)(8) interactions involving both an N(+)-H...O(phenolate) and the carboxyl-nitro O-H...O associations and aromatic pi-pi ring interactions [minimum ring centroid separation = 3.566 (2) A]. A lateral hydrogen-bonding interaction between the third aminium H atom and a carboxyl O-atom acceptor links the chain substructures, giving a two-dimensional sheet structure. This determination represents the first of any form of this compound and is in the (R) absolute configuration. The atypical crystal stability is attributed both to the hydrogen-bonded chain substructures provided by the anions, which accommodate the aminium proton-donor groups of the cations and give crosslinking, and to the presence of the cation-anion aromatic ring pi-pi interactions.

3α-Azido-5-cholestene.

The crystal structure of the title compound, C(27)H(45)N(3), has been determined as part of our investigation into the hydro-phobic modification of amino-glycoside anti-biotics. The isopropyl group showed disorder for the tertiary carbon (equal occupancies), with high thermal motion for the peripheral atoms of the isopropyl and azide groups also apparent in the structure. The axial disposition of the azide group is consistent with the clean inversion of stereochemistry at C-3 under Mitsunobu conditions.

Multisite modification of neomycin B: combined Mitsunobu and click chemistry approach.

The aminoglycoside antibiotic neomycin B has been converted into several novel building blocks that can be used for the specific modification of three of the four ring systems. Under carefully controlled conditions, the Mitsunobu reaction can be used to selectively dehydrate the ido ring to give the talo epoxide. Subsequently however, under more forcing conditions, the 2-deoxy streptamine ring undergoes Mitsunobu dehydration to give an aziridine. An unusual remote neighboring group effect was observed. When the primary hydroxyl of the ribose ring was blocked, aziridine formation on the deoxystreptamine ring did not occur. Both the epoxide and epoxide-aziridine neomycin building blocks can be ring-opened with azide and subjected to "click" type chemistry with terminal alkynes to generate a series of new neomycin analogues. These reactions can all be carried out without recourse to O-protecting groups. A detailed conformational analysis by NMR revealed some unexpected conformer preferences in these systems.

Mitsunobu dehydration of N-Boc neomycin B.

Reaction of hexa-N-Boc neomycin B with TPP and DIAD in toluene results in the formation of an epoxide in ring IV, not an aziridine or azetidine as previously reported.

Structural and solid state 31P NMR studies of the four-coordinate copper(I) complexes [Cu(PPh3)3X] and [Cu(PPh3)3(CH3CN)]X.

The tris(triphenylphosphine)copper(I) complexes [(PPh3)3CuX] for X = Cl (1), Br (2), I (3), ClO4 (4), BF4 (5), [(PPh3)3CuCl].CH3CN (1a), [Cu(PPh3)3(CH3CN)]X for X = ClO4 (6), BF4 (7), and [Cu(PPh3)3(CH3CN)]X.CH3CN for X = SiF5 (8), PF6 (9) have been studied by solid state 31P CP/MAS NMR spectroscopy together with single crystal X-ray diffraction for compounds (6)-(9), the latter completing the availability of crystal structure data for the series. Compounds (1)-(5) form an isomorphous series in space group P3 (a approximately 19, c approximately 11 A) with three independent molecules in the unit cell, all disposed about 3-fold symmetry axes. Average values (with estimated standard deviations) for the P-Cu-P, P-Cu-X bond angles and Cu-P bond lengths in compounds (1)-(3) are 110.1(6) degrees, 108.8(6) degrees and 2.354(8)A and 115.2(6) degrees, 102.8(9) degrees and 2.306(9)A for compounds (4) and (5). For the acetonitrile solvated compound (1a), the corresponding parameters are 115(4) degrees, 103(3) degrees and 2.309(3)A. The solid state 31P CP/MAS NMR quadrupole distortion parameters, dnu Cu, for (1)-(3) and (1a) are all less than 1 x 10(9) Hz2, despite the changes in donor properties of the halide in (1)-(3), and the coordination geometry of the P3CuX core in (1a). Change of anion to ClO4- and BF4- in compounds (4) and (5) results in a significant increase of dnu Cu to 4.4-5.2 10(9) Hz2 and 5.2-6.0 x 10(9) Hz2, respectively. Compounds (6) and (7) crystallise as isomorphous [Cu(PPh3)3(CH3CN)]X salts in space group Pbca, (a approximately 17.6, b approximately 22.3, c approximately 24.2 A), while compounds (8) and (9) crystallize as isomorphous acetonitrile solvated salts [Cu(PPh3)3(CH3CN)]X.CH3CN in space group P1(a approximately 10.5, b approximately 13.0, c approximately 19.5 A, alpha approximately 104, beta approximately 104, gamma approximately 94 degrees). The P3CuN angular geometries in all four compounds are distorted from tetrahedral symmetry with average P-Cu-P, P-Cu-N angles and Cu-P bond lengths of 115(4) degrees, 103(4) degrees and 2.32(1)A, with dnu Cu ranging between 1.3 and 2.5 x 10(9) Hz2. The solid state 29Si CP/MAS NMR spectrum of the pentafluorosilicate anion in compound (8) is also reported, affording 1J(29Si, 19F) = 146 Hz.

Translational Isomerism in Some Two- and Three-Station [2]Rotaxanes.

The template-directed syntheses of three [2]rotaxanes are described. They all have dumbbell components, with both hydroquinone and resorcinol rings inserted into polyether chains terminated by tetraarylmethane stoppers, that become encircled during the key self-assembly processes by the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), with its two pi-electron deficient bipyridinium units. It has been demonstrated by low-temperature (1)H NMR spectroscopy that the pi-electron deficient tetracationic cyclophane has a remarkably high preference to reside around the hydroquinone ring in these molecular shuttles. This observation illustrates how a very small constitutional difference-hydroquinone versus resorcinol recognition sites-can lead to the overwhelming preference for one translational isomer over another in this particular range of [2]rotaxanes.

Recognition of Bipyridinium-Based Derivatives by Hydroquinone- and/or Dioxynaphthalene-Based Macrocyclic Polyethers: From Inclusion Complexes to the Self-Assembly of [2]Catenanes.

A range of pi-electron-rich macrocyclic polyethers incorporating dioxybenzene (hydroquinone) and/or dioxynaphthalene units have been synthesized in good yields by simple two-step procedures. These macrocycles are able to bind bipyridinium-based guests as a result of a series of cooperative noncovalent bonding interactions. These molecular recognition events can be extended to the self-assembly of [2]catenanes incorporating the bipyridinium-based cyclophane, cyclobis(paraquat-p-phenylene), and the macrocyclic polyethers incorporating dioxybenzene and -naphthalene units. The efficiencies of these self-assembly processes were found to depend upon the stereoelectronic features of the pi-electron-rich macrocycles-namely, the nature and the substitution pattern of the aromatic units. X-ray crystallographic analysis of some of these [2]catenanes proved unequivocally the relative geometries of the interlocked components. In addition, in the case of those asymmetric [2]catenanes incorporating two different aromatic units within their macrocyclic polyether components, only one of the expected two translational isomers was observed in the solid state. In particular, in all the structures examined, the 1,4-dioxybenzene and 1,5-dioxynaphthalene units are located within the cavity of the tetracationic cyclophane component in preference to other regioisomeric dioxynaphthalene units that reside alongside. Variable-temperature (1)H NMR spectroscopic investigation of the geometries adopted by these [2]catenanes in solution revealed the same selectivity that was observed for one translational isomer over another in the solid state.