Negative Temperature Sensitive Hydrogels in Controlled Drug Delivery

Summary: PVP/PNIPAAm copolymers exhibit a temperature sensitive nature that makes them an attractive candidate for controlled drug delivery devices. Diclofenac sodium was added to the monomeric mixture, which included an initiator and crosslinking agent (where appropriate), prior to UV photopolymerisation. It was found that the xerogels retained similar properties as the original samples (not containing drug) at lower levels of drug integration. In all cases, drug dissolution analysis showed that the active agent was released at a slower rate at temperatures above the Lower Critical Solution Temperature (LCST). Interestingly, the drug release trends were almost identical for both the physically and chemically crosslinked hydrogels, when the decrease in transition temperature caused by the incorporated crosslinking agent is taken into consideration. It is believed that both types of copolymers reached a constant maximum swollen weight at a set of temperatures above their transition temperatures. When this swollen plateau is attained, the hydrophilic-hydrophobic interactions are balanced, thus the gel does not swell or shrink further and the drug diffuses out at a constant rate.     

Coherent and incoherent π0 photoproduction from the deuteron

Differential cross-sections for the reactions d (γ,π⁰)d and d (γ,π⁰)pn have been measured at MAMI with the TAPS detector setup in the energy range 140 MeV < E _γ < 306 MeV. By use of the Glasgow tagging spectrometer an 0.8 MeV energy resolution for photons incident on the target was achieved. The π⁰ missing energy resolution was sufficient for a reliable separation of coherent and incoherent channels. The data for the break-up channel exhibit very strong final state interaction effects, whereas the observed angular dependence of the inclusive process d (γ,π⁰)X is in quantitative agreement with predictions for a quasi-free process. The observed absolute d (γ,π⁰)X cross-sections, on the other hand, are significantly smaller than predicted by the quasi-free process for E _γ >∼ 250 MeV. Associating this failure with the π⁰ photoproduction on the neutron would suggest that its cross-section is up to 25% below the presently believed value. Received: 13 February 2001 / Accepted: 13 April 2001     

On Bruck-Reilly extensions

We present a generalization for the procedure of taking Bruck-Reilly extensions, and we characterize abstractly the regular semigroups which can be obtained in this way. We shall in particular characterize the regular semigroups which can be obtained by considering the usual Bruck-Reilly extensions. Our procedure generalizes Munn’s construction [3] which in its turn combines ideas used by Bruck [1] and Reilly [4].     

Early stages of silicon oxidation

Experiments have shown that the early stages of silicon oxidation proceed layer by layer, so that one layer is essentially complete before another develops. Other experiments show that the mechanism does not involve step growth, the most obvious mechanism. We use a new approach to modelling the growth to show that these two observations can be understood when there is a rate-determining step which depends strongly on the local oxide thickness. The rate in question might be the sticking probability, or the rate of incorporation of adsorbed oxygen species into the oxide network. Such mechanisms are possible when transport by an ionic species dominates, contrary to the situation for thicker films. Our modelling suggests the mechanisms are driven by the image interaction, as in earlier suggestions by Stoneham and Tasker, rather than an effect of the electric field central to the Mott-Cabrera mechanism.     

O-Heterocycles by the cyclization of side-chain bromomethoxylated 2′-acetoxychalcones

Summary The title chalcone derivatives react with aqueous sodium hydroxide of various concentrations to form aurones as the major product, together with small amounts of flavones. However, the introduction of 4-nitro or 4-chloro substituents resulted in the formation of flavones as the major product.

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O-Heterocyclen mittels Cyclisierung von an der Seitenkette brommethoxylierten 2-Acetoxychalconen

Zusammenfassung Die im Titel genannten Chalconderivate reagieren mit Natronlauge in verschiedenen Konzentrationen, wobei Aurone zusammen mit geringen Mengen an Flavonen entstehen. Die Einführung von 4-Nitro- oder 4-Chlor-Substituenten führte jedoch zur bevorzugten Bildung von Flavonen.

     

Perfluorocyclobutane aromatic ether polymers

Novel polymers containing alternating perfluorocyclobutane and aromatic ether subunits are prepared from aryl poly(trifluorovinyl ether) monomers via the thermal [2π + 2π] dimerization of the trifluorovinyl ether functionality. A model study is described, which probes the nature of the perfluorocyclobutane rings formed during the polymerization reaction. The bifunctional monomer 4,4′-bis(trifluorovinyloxy) biphenyl and the trifunctional monomer 1,1,1-tris(4-trifluorovinyloxyphenyl)ethane are prepared and polymerized to provide thermoplastic and thermoset polymers, respectively. Characterization of the mechanical and dielectric properties of these new polymers is presented. © 1993 John Wiley & Sons, Inc.     

Determination of deoxynivalenol (vomitoxin) by high-performance liquid chromatography with electrochemical detection

A rapid method for the analysis of deoxynivalenol (DON) was developed using high-performance liquid chromatography (HPLC) with reductive electrochemical detection (ED). Deoxynivalenol produced by Fusarium roseum growing on solid cornmeal and rice substrates and from naturally contaminated wheat was extracted and quantitated via ED. DON levels in wheat were verified by gas chromatography and structurally confirmed by mass spectrometry. DON was optimally resolved by HPLC employing a radially compressed octadecylsilane column and a mobile phase of deoxygenated methanol-40 mM borate buffer (35:65) at a flow-rate of 1.0 ml/min. Under these conditions DON exhibited an average retention time of 3.6 min. Reductive ED (-1.4 V) allowed a 12-fold increase in sensitivity and greater selectivity than classical UV absorption at 224 nm. A detection limit for DON of 25 pg/microliter was achieved under these conditions. The determination of DON in crude grain extracts was hindered by extractable interfering substances, whereas ED was more functional-group selective (i.e. reduction of the carbonyl moiety). ED permits a direct quantitation of DON from crude grain extracts and may facilitate the determination of this agent and associated metabolites in biological samples.