Rapid synthesis of carbohydrate derivatives, including mimetics of C-linked disaccharides and C-linked aza disaccharides, using the hetero-Diels-Alder reaction

In this work we demonstrate the value of performing a hetero-Diels-Alder reaction (HDAR) between Danishefsky's diene and a range of aldehydes or imines, under microwave irradiation. By using a range of aldehydes and imines, including those derived from carbohydrates, access to functionalized 2,3-dihydro-4H-pyran-4-ones or 2,3-dihydro-4-pyridinones in good to excellent synthetic yields is possible. A particular strength of the methodology is its ability to access mimetics of C-linked disaccharides and C-linked aza disaccharides, targets of current therapeutic interest, in a rapid, convenient, and diastereoselective manner. The effect of high pressure on the HDARs involving carbohydrate-derived aldehydes and imines is also explored, with enhancement in yields occurring for the aldehyde substrates. Finally, HDARs using carbohydrate derived ketones, enones, and enals are described under a range of conditions. Optimum results were obtained under high-pressure conditions, with highly functionalized carbohydrate derivatives being afforded, in good yields, in this way.     

Determination of anthelmintic drug residues in milk using ultra high performance liquid chromatography–tandem mass spectrometry with rapid polarity switching

A new UHPLC–MS/MS (ultra high performance liquid chromatography coupled to tandem mass spectrometry) method was developed and validated to detect 38 anthelmintic drug residues, consisting of benzimidazoles, avermectins and flukicides. A modified QuEChERS-type extraction method was developed with an added concentration step to detect most of the analytes at <1 μg kg⁻¹ levels in milk. Anthelmintic residues were extracted into acetonitrile using magnesium sulphate and sodium chloride to induce liquid–liquid partitioning followed by dispersive solid phase extraction for cleanup. The extract was concentrated into dimethyl sulphoxide, which was used as a keeper to ensure analytes remain in solution. Using rapid polarity switching in electrospray ionisation, a single injection was capable of detecting both positively and negatively charged ions in a 13 min run time. The method was validated at two levels: the unapproved use level and at the maximum residue level (MRL) according to Commission Decision (CD) 2002/657/EC criteria. The decision limit (CCα) of the method was in the range of 0.14–1.9 and 11–123 μg kg⁻¹ for drugs validated at unapproved and MRL levels, respectively. The performance of the method was successfully verified for benzimidazoles and levamisole by participating in a proficiency study.     

Qualities of examples in learning and teaching

In this paper, we theorise about the different kinds of relationship between examples and the classes of mathematical objects that they exemplify as they arise in mathematical activity and teaching. We ground our theorising in direct experience of creating a polynomial that fits certain constraints to develop our understanding of engagement with examples. We then relate insights about exemplification arising from this experience to a sequence of lessons. Through these cases, we indicate the variety of fluent uses of examples made by mathematicians and experienced teachers. Following Thompson’s concept of “didactic object” (Symbolizing, modeling, and tool use in mathematics education. Kluwer, Dordrecht, The Netherlands, pp 191–212, 2002), we talk about “didacticising” an example and observe that the nature of students’ engagement is important, as well as the teacher’s intentions and actions (Thompson avoids using a verb with the root “didact”. We use the verb “didacticise” but without implying any connection to particular theoretical approaches which use the same verb.). The qualities of examples depend as much on human agency, such as pedagogical intent or mathematical curiosity or what is noticed, as on their mathematical relation to generalities.     

The hydrological response of heavy clay grassland soils to rainfall in south‐west England using δ2H

Stable isotopes of water have been previously used in catchment studies to separate rain‐event water from pre‐event groundwater. However, there are a lack of studies at the smaller scale looking at the separation of event water from pre‐event water. This is particularly relevant for heavy clay soil systems through which the movement of water is uncertain but is thought to be rainwater‐dominated. The data presented here were collected at a rural site in the south‐west of England. The historic rainfall at the site was isotopically varied but similar to the global meteoric water line, with annual weighted means of ?37‰ for δ²H and ?5.7‰ for δ¹⁸O and with no seasonal variation. Drainage was sampled from the inter‐flow (surface runoff + lateral through‐flow) and drain‐flow (55 cm deep mole drains) pathways of two 1 ha lysimeters during two rainfall events, which had δ²H values of ?68‰ and ?92‰, respectively. The δ²H values of the lysimeter drainage water suggest that there was no contribution of event water during the first, small discharge (Q) event; however, the second larger event did show isotopic variation in δ²H values negatively related to Q indicating that rainwater was contributing to Q. A hydrograph separation indicated that only 49–58% of the inter‐flow and 18–25% of the drain‐flow consisted of event water. This was surprising given that these soil types are considered retentive of soil water. More work is needed on heavy clay soils to understand better the nature of water movement from these systems. Copyright © 2010 John Wiley & Sons, Ltd.     

An Application of Groupoids of Fractions to Inverse Semigroups

We describe an application of category theory to the theory of inverse semigroups: we prove the P-theorem for E-unitary inverse semigroups using groupoids of fractions of their associated division categories.     

Catalytic asymmetric hydrogenation of aromatic ketones in room temperature ionic liquids

Polar bisphosphonic acid-derived Ru(BINAP)(DPEN)Cl₂ precatalysts were synthesized and immobilized in room temperature ionic liquids (RTILs) for asymmetric hydrogenation of aromatic ketones with ee values of up to 98.7%. The performance of the Ru catalysts is highly dependent on the nature of imidazolium ILs. For the imidazolium ILs without acidic protons, both ILs and Ru catalysts were recycled by simple extraction and reused. Such a simple immobilization approach also prevented the leaching of Ru (and Ru catalysts) into the chiral secondary alcohol products, and should prove desirable for the production of pharmaceutical intermediates that are free from metal contaminants.     

Electrical properties of highly (111)-oriented lead zirconate thin films

Antiferroelectric PbZrO₃ thin films were grown on Pt/Ti/SiO₂/Si substrates with predominant (111) orientation using a sol-gel process. The Pt/PbZrO₃/Pt film capacitor showed well-saturated hysteresis loops at an applied voltage of 5 V with remanent polarisation (P_r) and coercive electric field (E_c) values of 8.97 μC/cm² and 162 kV/cm, respectively. The leakage current density of the highly (111)-oriented PbZrO₃ film was less than 1.0×10⁻⁷ A/cm² over electric field ranges from 0 to 105 kV/cm. The conduction current depended on the voltage polarity. The PbZrO₃/Pt interface forms a Schottky barrier at electric fields from 20 to 160 kV/cm. The dielectric relaxation current behaviour of Pt/PbZrO₃/Pt capacitor obeys the well-known Curie-Von Schweidler law at electric field of 20-80 kV/cm, the currents have contributions of both dielectric relaxation current and leakage current.