Characterisation and proposed origin of mass spectrometric ions observed 30 Th above the ionised molecules of per-O-methylated carbohydrates

Derivatisation of carbohydrates by permethylation significantly improves the mass spectrometric intensity of carbohydrate-derived ions and allows more readily interpretable fragmentation; in addition, samples are conveniently separated from salts, and larger oligosaccharides are more readily ionised. It has previously been recognised that, in the mass spectra of permethylated carbohydrates, a series of ions indicating species 30 Da larger than the fully methylated carbohydrate molecules are also observed. These species have not been characterised in the literature despite their apparently ubiquitous occurrence in the mass spectra of permethylated carbohydrates. Tandem mass spectrometry (MS/MS) experiments were performed on permethylated carbohydrates and reduced permethylated carbohydrates that exhibit the artefact, demonstrating that the artefact is not reducing terminal specific, and that the artefact can be introduced at any hydroxyl residue. It was further demonstrated through the use of different alkylation reagents that the origin of this artefact group is the alkylating reagent itself. It is proposed that side reactions that occur between the permethylation reagents allow the production of small amounts of iodomethyl methyl ether. This reagent can then compete with methyl iodide for reaction with the carbohydrate -OH groups. The result is partial incorporation of a methoxymethyl moiety instead of a methyl group, detected as '+30' artefact ions.     

Recent advances in analytical construct resins

The area of solid-phase synthesis has witnessed exponential growth in the last fifteen years, but difficulties associated with the monitoring and analysis of resin-bound reactions and products have been apparent due to a limited number of analytical methods available. With the substrate tethered to an insoluble support traditional chromatographic monitoring is only possible after cleavage. In order to address this 'analytical bottleneck' Geysen, in 1996 elaborated Merrifield's initial dual linker strategy by incorporating an encoding system between two in-line linkers. These analytical construct resins represented a new approach for both the quality control of solid-phase combinatorial libraries and for the development of new synthetic sequences on solid-support. This review will summarize the development and application of analytical construct resins focusing on recent applications of the technology.     

Synthesis and application of crown ether tagged triarylphosphines

Crown ether tagged triarylphosphines 1 and 2 were synthesised and applied in Mitsunobu and Heck reactions, their reactivity being evaluated against triphenylphosphine- and polymer-bound triphenylphosphine. Purification of the reactions was effected by post-reaction sequestration onto an ammonium functionalised solid-phase.     

Phosphonyl radical addition to enol ethers. The stereoselective synthesis of cyclic ethers

Addition of diethyl phosphite or diethyl thiophosphite to enol ethers, in the presence of a radical initiator, results in the regioselective synthesis of organophosphonate or phosphonothioate derivatives, respectively, under mild conditions. This method can be applied to the stereoselective formation of substituted tetrahydrofurans and tetrahydropyrans, on cyclisation of vinyl ethers bearing unsaturated side chains.     

Integrated Josephson effect suppression electromagnets for sis receivers

We describe a method for integrating a Josephson current suppression electromagnet along with a superconductor-insulator-superconductor (SIS) mixer. In this technique, circuitry already in place for matching the SIS mixing device with the antenna is used as the conductor for an electromagnet. Reduced cost and size are among the advantages achieved by elimination of external magnets.     

Design and results for a 345 GHz sis focal plane array using planar technology

We describe a focal plane array using antenna elements and SIS junctions photo-etched on a quartz substrate. The etched antenna is of a new strip-line type in which a two-dimensional corrugated horn is phase-corrected with a strip-line lens. Good beam efficiency is indicated by the measured antenna patterns. A DSB receiver temperature of 225 K was obtained with a number of imperfections still present.     

Extraction of perfluorinated compounds from food matrices using fluorous solvent partitioning

Perfluorinated compounds (PFCs) such as perfluorooctane sulfonic acid (PFOS) have emerged as a new class of global environmental pollutant; they bioaccumulate and are persistent in the environment and in wildlife. Fluorine-fluorine interactions have been investigated as a means to isolate PFCs for mass spectrometric quantification. A novel sample extraction and cleanup procedure has been developed for fat-containing samples based on fluorous liquid-liquid extraction (F-LLE) in a triphasic solvent system consisting of hybrid:fluorous:organic solvent (trifluoroethanol:perfluorohexane/dichloromethane-saturated with water). This system partially separates fluorous from non-fluorous compounds, allowing removal of co-extractants, which had previously resulted in liquid chromatography mass spectrometry (LC-MS/MS) peak suppression preventing low-level detection of PFCs. The developed F-LLE was coupled with an existing extraction protocol allowing the limits of detection of PFCs to be lowered an order of magnitude for high fat samples. The developed workflow was used to show the absence of a range of eleven PFCs in nine UK and one Irish cheese samples. This representative application demonstrates a new application of fluorous-organic extraction in sample cleanup for measurement of fluorinated analytes in food, environment and broader analytical chemistry.     

Investigation of Parameters that Affect Resin Swelling in Green Solvents

The influence of various physical and chemical factors on the swelling of polystyrene and PEG based resins in greener organic solvents has been systematically investigated. In general, chemical factors: the nature of the functionality/linker and the degree of loading were found to have a far larger influence on the swelling of the resins than physical parameters such as bead size. The results are interpreted in terms of Hansen solubility parameters for the solvents and there is evidence that some solvents interact with the polymeric core of a resin whilst others interact with the functionality. The results are extended to a study of the changes in resin swelling observed during both deprotection and chain elongation reactions during solid phase peptide synthesis.     

2-Thiaadamantanes. Interconversions,degradations and spectroscopic analysis

Chemical and spectroscopic evidence is presented in proof of structure of the tricyclic products from acid-catalysed acetylation of 9-thiabicyclo[3,3,1]nonan-2,6-dione.