2]Pseudorotaxanes, [2]rotaxanes and metal-organic rotaxane frameworks containing tetra-substituted dibenzo[24]crown-8 wheels

[2]Pseudorotaxanes, [2]rotaxanes and metal-organic rotaxane framework materials that utilise DB24C8 as the wheel component are well known and structural variations based on changing the axle component are common. Studies in which the DB24C8 wheel is structurally modified are much more limited. Herein, is described the synthesis of symmetrical DB24C8 analogues containing four CH(2)OR (R = CH(2)CH(2)CH(3), CH(2)(C(6)H(5)), C(6)H(5) and C(6)H(4)(4-COOEt)) substituents on the 4 and 5 positions of the aromatic rings. The effect of these molecular appendages on the stability and structures of the interpenetrated and interlocked molecules derived from these new wheels is described. The major effects are an increase in association constants for the formation of [2]pseudorotaxanes relative to DB24C8, the crystal packing of [2]rotaxanes and a change on the internal structure of a 2D MORF (R = C(6)H(5)) compared to DB24C8.     

A new route to aerogels: Monolithic silica cryogels

We have explored several different gel syntheses and drying procedures for producing silica cryogels with similar properties to those of silica aerogels, particularly in terms of monolithicity, density, porosity and surface area. These materials could be a suitable alternative to silica aerogels and ambigels. Some successful preparation methods are presented and properties of the corresponding cryogels are discussed, including comparison of these materials to supercritically dried products and an assessment of the effects of the experimental variables in the preparation process on the properties of the resultant cryogels. Two routes for the preparation of cryogels are highlighted, one of which is especially attractive as it has the advantage (compared to the known syntheses of APD aerogels) of not requiring any solvent exchange step.     

Hagedorn Wavepackets in Time-Frequency and Phase Space

The Hermite functions are an orthonormalbasis of the space of square integrable functions with favourable approximation properties. Allowing for a flexible localization in position and momentum, the Hagedorn wavepackets generalize the Hermite functions also to several dimensions. Using Hagedorn’s raising and lowering operators, we derive explicit formulas and recurrence relations for the Wigner and FBI transform of the wavepackets and show their relation to the Laguerre polyomials.     

Gas-phase reactions of halogenated radical carbene anions with sulfur and oxygen containing species

The reactivities of mono- and dihalocarbene anions (CHCl⁻, CHBr⁻, CF₂⁻, CCl₂⁻, and CBrCl⁻) were studied using a tandem flowing afterglow-selected ion flow tube instrument. Reaction rate constants and product branching ratios are reported for the reactions of these carbene anions with six neutral reagents (CS₂, COS, CO₂, O₂, CO, and N₂O). These anions were found to demonstrate diverse chemistry as illustrated by formation of multiple product ions and by the observed reaction trends. The reactions of CHCl⁻ and CHBr⁻ occur with similar efficiencies and reactivity patterns. Substitution of a Cl atom for an H atom to form CCl₂⁻ and CBrCl⁻ decreases the rate constants; these two anions react with similar efficiencies and reactivity trends. The CF₂⁻ anion displays remarkably different reactivity; these differences are discussed in terms of its lower electron binding energy and the effect of the electronegative fluorine substituents. The results presented here are compared to the reactivity of the CH₂⁻ anion, which has previously been reported.     

First X‐Ray Structure Analyses of Rhodium(III) η1‐Allyl Complexes and a Mechanism for Allylic Isomerization Reactions

Metal‐to‐metal allyl transfer : Using the first structurally characterized rhodium η¹‐allyl complexes it is shown that the σ‐bound allyl substituent can be transferred from the Rh^III complex to a Rh^I complex in a fast equilibrium. This process may account for the decrease in regioselectivity observed in allylic alkylation reactions in which complex 1 is used as a catalyst.

     

Intracellular Degradation of Elastin by Cathepsin K in Skin Fibroblasts— A Possible Role in Photoaging

Solar elastosis is observed in the dermis of photoaged skin and is characterized by an accumulation of abnormal elastin in the extracellular space. Several proteases that degrade elastin in the extracellular space have been implicated in its formation. The lysosomal protease cathepsin K (catK) has recently been described to be highly expressed in skin fibroblasts under certain pathologic conditions. As cat K is one of the most potent mammalian elastases, we hypothesized that catK-mediated intracellular elastin degradation may play a role in the formation of solar elastosis. Immunostaining of cultured skin fibroblasts incubated with labeled elastin demonstrated internalization of extracellular elastin to lysosomes and its degradation by catK. Induction of catK expression in fibroblasts was observed both in vitro and in vivo after exposure to longwave UVA. In contrast to fibroblasts from young donors, cells from old donors failed to activate catK in response to UVA. These data suggest a role of intracellular elastin degradation by catK in the formation of solar elastosis. We propose that an age-related decline in catK activity, in particular after UV exposure, may promote the formation of actinic elastosis through a decline of orderly intracellular elastin degradation and subsequent accumulation of elastin in the extracellular space.     

In situ derivatization reaction and determination of ibuprofen in water samples using headspace generation-programmed temperature vaporization-gas chromatography-mass spectrometry

The aim of the present work is to propose a method for the determination of ibuprofen, as a typical representative of pharmaceutical compounds, in aqueous samples. To do so, an in situ derivatization reaction in aqueous medium was employed in the vial of a headspace sampler (HS), after which instrumental measurements were made with gas chromatography-mass spectrometry (GC-MS). As the injection system we propose a programmed temperature vaporizer (PTV) where, in solvent vent mode, better results can be obtained than with the conventional split and splitless injection modes. Since the derivatization reaction takes place in the HS vial, after the mixing of reagents and the sealing of the vial, the whole process takes place on-line, with no need for intermediate steps. The simplicity and speed of the method – analysis throughput: 10.5 min – together with the limit of detection obtained (0.23 μg/L), bearing in mind that no preconcentration step or later clean-up step are required, make this a good method for the analysis of ibuprofen in aqueous samples of urban waste water.     

Synthesis of a three-member array of cycloadducts in a glass microchip under pressure driven flow

The synthesis of a series of cycloadduct products carried out in a glass microchip under pressure driven flow is presented. Initially, four different compounds were synthesized individually with conversions similar to those obtained in the corresponding batch macroscale reactions. Using identical experimental conditions for all four compounds, the results were highly predictable and reproducible, without the need for individual optimization. A multi-reaction experiment was then carried out in a single chip achieving the synthesis of a three-member array in a single run.     

Screening method for polycyclic aromatic hydrocarbons in soil using hollow fiber membrane solvent microextraction

A fast, inexpensive screening method for polycyclic aromatic hydrocarbons in soil has been developed. Using hollow fiber membrane solvent microextraction, 8 microl of octane extraction solvent was placed inside a porous, polypropylene fiber. Following an 8 min analyte preconcentration step, 4 microl of extract was injected into a gas chromatograph. Separation was achieved in less than 10 min with a detection limit of 0.13 mg/kg for 2-methylnaphthalene. Results of both spiked and real soil samples are presented.