Synthesis of tryptophans by Lewis acid promoted ring-opening of aziridine-2-carboxylates: optimization of protecting group and Lewis acid

The preparation of tryptophan derivatives through the Lewis acid promoted substitution of aziridine carboxylates with indole was found to be accompanied by a ring-expansion reaction to generate an oxazolidinone byproduct. The ratio of tryptophan to oxazolidinone products can be optimized through a judicious choice of Lewis acid and N-protecting group.     

Multinuclear NMR studies of end-groups in polymers—III. Search for abnormal end-groups derived from azoisobutyronitrile

Samples of azoisobutyronitrile (AIBN), labelled with deuterium and nitrogen-15, have been used to initiate polymerizations and copolymerizations of styrene and methyl methacrylate. As in the case of [¹³C]-AIBN, the chemical shift associated with an end-group labelled with a particular isotope depends upon the nature of the attached monomer unit but there is no evidence of more than one type of end-group.     

Tip-clearance and other three-dimensional effects in axial flow fans

Zusammenfassung Es wird die an einem Axialventilator durchgeführte Untersuchung der Auswirkung des Schaufelspaltes auf Laufradstr?mung und Leistung beschrieben. Das Laufrad, mit einem Durchmesser von 305 mm, war für ausgepr?gt dreidimensionale Str?mung entworfen. Die in solchen F?llen bestehenden Einschr?nkungen der Gültigkeit von zweidimensionalen Berechnungsunterlagen aus Windkanalversuchen werden besprochen. Es zeigte sich, dass die radial nach aussen gerichtete Querstr?mung durch Zentrifugalwirkung und die nach innen gerichtete Querstr?mung durch Vergr?sserung des Spaltspieles hervorgerufen wird. Vergr?sserung der Spaltweite beeinflusst die Str?mungsverh?ltnisse nicht nur in der N?he der Schaufelspitze, sondern über die ganze radiale Erstreckung der Schaufel. Dadurch wird die Druckziffer verkleinert, und die Abreissbedingungen ver?ndern sich. Unter diesen Verh?ltnissen ist es wesentlich, die ?nderung der Axialgeschwindigkeit im Laufrad korrekt in Rechnung zu setzen. Der wesentlichste Parameter scheint die Gr?ssec _2m /u zu sein. Dabei zeichnet sich bei gleichen Eintrittsverh?ltnissen, aber stark verschiedenen Querstr?mungen ein eindeutiger Zusammenhang zwischenc _2u /c _2m undc _2m /u für beliebige Schaufelgeometrien ab. Es mag daher von Vorteil sein, den aus Messungen am zweidimensionalen Windkanal erhaltenen Unterlagen in dieser Form den Vorzug vor den üblichen Einzelflügel- und Gitterparametern zu geben, die durch Querstr?mung merklich beeinflusst werden.      

Cu2+ Coordination of Covalently Cross-linked β-Amyloid Dimers

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by deposition of extracellular amyloid plaques comprised from fibrillar aggregates of the amyloid-β peptide (Aβ). Cu²⁺ interactions with Aβ appear to be involved in both the production of reactive oxygen species and the misfolding of Aβ into oligomeric intermediates including covalently cross-linked dimers. We have previously investigated the Cu²⁺ coordination of Aβ monomers in detail, whilst others have shown that Aβ fibrils coordinate Cu²⁺ in a similar manner to Aβ monomers. However, the coordination of low-molecular-weight Aβ species, which are believed to be responsible for neuronal dysfunction in AD, has not been widely investigated. Here, we report the first study of Cu²⁺ coordination by synthetic Aβ dimers containing an artificial diaminopimelic acid (DAP) or a dityrosine cross-link at residue 10. Our preliminary findings show that dityrosine cross-linking imparts unique structural constraints, resulting in Cu²⁺ coordination distinct from Aβ monomers and fibrils, which may be relevant to the greater toxicity of low-molecular-weight Aβ oligomers in AD.     

DEA-based predictors for estimating fleet size changes when modelling the introduction of rights-based management

The introduction of individual transferable quotas (ITQs) into a fishery is going to change not only the amount of catch a fleet can take, but often also changes the fleet structure, particularly if total allowable catches are decreased. This can have an impact on the economic, social and environmental outcomes of fisheries management. Management Strategy Evaluation (MSE) modelling approaches are recognised as the most appropriate method for assessing impacts of management, but these require information as to how fleets may change under different management systems. In this study, we test the applicability of data envelopment analysis (DEA) based performance measures as predictors of how a fishing fleet might change under the introduction of ITQs and also at different levels of quota. In particular, we test the assumption that technical efficiency and capacity utilisation are suitable predictors of which boats are likely to exit the fishery. We also consider scale efficiency as an alternative predictor. We apply the analysis to the Torres Strait tropical rock lobster fishery that is transitioning to an ITQ-based management system for one sector of the fishery. The results indicate that capacity utilisation, technical efficiency and scale efficiency are reasonable indicators of who may remain in the fishery post ITQs. We find that the use of these measures to estimate the impacts of lower quota levels provides consistent fleet size estimates at the aggregate level, but which individual vessels are predicted to exit is dependent on the measure used.     

A review of intercombination lines in beryllium-like ions

Theoretical and experimental results for the 2s^{2 1}S₀-2s2p³P₁ intercombination line in beryllium-like ions are reviewed and revised, and some new data are presented. The uncertainty in the resulting transition rate is estimated, by using convergence of systematic calculations, accuracy of energy properties and theoretical tests, and is used to evaluate the accuracy of present and other calculations, and arrive at a recommended theoretical value, with uncertainty estimates.     

Studies with dithizone: Part 33. effect of temperature on the spectrum in chloroform

The position and relative intensity of the two peaks in the visible absorption spectrum of dithizone dissolved in chloroform do not change on cooling from room temperature to ?48°C. Thus either the two absorption peaks cannot be ascribed to two discrete species (thiol and thione tautomers), or the enthalpy of their interconversion is zero.     

On using the weissenberg rheogoniometer to measure normal stresses in lubricating greases as examples of materials which have a yield stress

Summary Some years ago it was desired to measure normal stress components in viscometric flows of lubricating greases since it was thought that flow elasticity might be a relevant property in grease lubrication processes. An attempt at measurement was made with the cone-and-plate configuration of theWeissenberg rheogoniometer. Since greases are prone to fracture in this device the initial tests were carried out at very low rates of shear to avoid fracture. These tests revealed the existence of unusual effects which are ascribed to interactions between the instrument and the yield stress property. At high rates of shear it is possible to show the existence of normal stresses in greases but their measurement cannot be carried out accurately. Fracture and shear degradation occur; furthermore, the zero of the normal stress measurement is uncertain to within an amount proportional to the yield stress. Procedures for minimizing inaccuracies are discussed.

---

Zusammenfassung Vor einigen Jahren entstand der Wunsch, die Normalspannungskomponenten in Schichtenströmungen (Viskosimeterströmungen) bei Schmierfetten zu messen, da man vermutete, daß die Elastizität eine wichtige Eigenschaft beim Schmierprozeß darstellen würde. Es wurde daher der Versuch unternommen, solche Messungen mit einer Kegel-Platte-Einrichtung imWeissenberg-Rheogoniometer durchzuführen. Da Schmierfette bei dieser Anordnung zum Bruch neigen, wurden die ersten Versuche bei sehr niedrigen Schergeschwindigkeiten gefahren. Diese Versuche erwiesen die Existenz von ungewöhnlichen Effekten, die der Wechselwirkung zwischen dem Gerät und Fließspannungs-Eigenschaften zuzuschreiben sind. Bei hohen Schergeschwindigkeiten ist es möglich, die Existenz von Normalspannungen in Fetten nachzuweisen, aber diese Messungen können nur mit geringer Genauigkeit durchgeführt werden. Es treten Bruch- und Scherabbauerscheinungen auf. Außerdem ist der Nullpunkt der Normalspannungsmessung um einen Betrag ungenau, welcher der Fließspannung proportional ist. Verfahren zur Verkleinerung dieser Ungenauigkeiten werden diskutiert.

---

---

Presented at a joint meeting of the British Society of Rheology and the Italian Society of Rheology, Shrivenham, 8–11 th April 1975.

---

With 11 figures     

The enantioselective synthesis of APTO and AETD: polyhydroxylated beta-amino acid constituents of the microsclerodermin cyclic peptides

The polyhydroxylated beta-amino acids (2S,3R,4S,5S,7E)-3-amino-8-phenyl-2,4,5-trihydroxyoct-7-enoic acid (APTO) and (2S,3R,4S,5S,7E,9E)-3-amino-10-(4-ethoxyphenyl)-2,4,5-trihydroxydeca-7,9-dienoic acid (AETD) are key components of the microsclerodermin family of anti-fungal cyclic peptides. They have been synthesised in protected form in twelve steps using a unified strategy, with the introduction of the unsaturated sidechain in the final step of the synthesis from a common aldehyde intermediate. The synthesis features the ordered application of asymmetric aminohydroxylation and dihydroxylation reactions to efficiently introduce the stereochemistry of the targets with high selectivity.