The use of sodium hydride in a ring closure

The use of sodium hydride for the synthesis of 1,5-methano-3-benzazocine derivatives, which involves the intramolecular acylation of the α-methylene group of tetralone by methylene isocyanate substituents, is discussed in detail.     

The morphology of nascent polyethylene prepared with the soluble catalyst (C5H5)2TiCl2-R2AlCl

Summary Polyethylene was prepared with the solubleZiegler-Natta catalyst bis-(cyclopentadienyl)-titanium dichloride-dialkylaluminum chloride under various polymerization conditions. The morphology and properties of the nascent polymer samples were studied by electron microscopy, fuming nitric acid oxidation and differential scanning calorimetry. The observations show that the polymer has a chain-folded lamellar structure. The morphology of this polymer contrasts with the fibrillar texture of nascent poly(α-olefins) prepared with heterogeneousZiegler-Natta catalysts. It is suggested that inZiegler-Natta polymerizations the morphology of the nascent polymer is determined by the physical state of the catalyst in the polymerization medium.

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Zusammenfassung Poly?thylen wurde unter verschiedenen Polymerisierungsbedingungen mit dem l?slichenZiegler-Natta-Katalysator Bis-(cyclopentadienyl)-Titandichlorid-Dialkylaluminiumchlorid hergestellt. Die Morphologie und Eigenschaften der naszierenden Polymerproben (imstatus nascendi) wurden durch Elektronenmikroskopie, Oxidation mit rauchender Salpeters?ure und kalorische Messungen untersucht. Die Beobachtungen zeigen, da? die polymere Substanz eine kettengefaltete lamellare Struktur hat. Die Morphologie dieses Polymeren unterscheidet sich von der fibrillaren Textur der naszierenden Poly(α-olefine) die durch heterogeneZiegler-Natta-Katalysatoren hergestellt wurden. Es wird vorgeschlagen, da? man fürZiegler-Natta-Polymerisate die Morphologie durch den physikalischen Zustand des Katalysators im Polymerisierungsmedium imstatus nascendi untersucht.

     

On the accuracy of EPI-based phase contrast velocimetry

For over a decade, echo-planar imaging (EPI) has been used in both the medical and applied sciences to capture velocity fields of fluid flows. However, previous studies have not rigorously confirmed the accuracy of the measurements or sought to understand the limitations of the technique. In this study, a bipolar gradient was added to a flow-compensated EPI pulse sequence to obtain rapid phase contrast images of steady and unsteady flows through two step stenoses. For steady Re = 100 and 258 flows, accuracy was measured through systematic comparisons with CFD simulations, mass flow rate measurements, and spin echo phase contrast images. On average, the EPI image data exhibited velocity errors of 5 to 10 percent, while mass was conserved to within 5.6 percent at each axial position. Compared to spin-echo phase contrast images, the EPI images have 50 percent lower signal-to-noise ratio, larger local velocity errors, and similar mass conservation characteristics. An unsteady flow was then examined by starting a pump and allowing it to reach a steady Re = 100 flow. Accuracy in this case was measured by the consistency between mass flow rate measurements at different axial positions. Images taken at 0.3 s intervals captured the velocity field evolution and showed that 50 to 100 percent errors occur when the flow changes on a time scale faster than the image acquisition time.     

Cyclic plate bearing tests

A series of circular and square plate-bearing tests are reported, the load-displacement curves for which can be fitted quite closely by a three parameter curve of modified exponential form. The characteristics features of the response of such plates to loading and unloading cycles are then demonstrated and it is shown that their behaviour can be accurately modelled by a simple modification of the first-load response equation which requires three further parameters to be introduced.The six parameters, from which the cyclic load behaviour of plates of any size can be predicted, can be determined from two in situ tests: a conventional plate test and a single-load-level cyclic plate test.     

An integral equation approach to self-similar plane-elastodynamic crack problems

The elastodynamic problem of an expanding crack under homogeneous polynomialform loading was reduced to the solution of a Cauchy singular integral equation. In this manner the solution of the original problem can be obtained by using well-known numerical treatments available for Cauchy SIEs. The procedure was accomplished by means of the Busemann-Chaplygin similarity technique and complex variable methods. The analysis has been restricted to the subsonic case.     

A versatile annulation protocol toward novel constrained phosphinic peptidomimetics

The development of a novel 3-center 2-component annulation reaction between alpha,omega-carbamoylaldehydes and suitably monoalkylated phosphinic acids is reported. Depending on the starting alpha,omega-carbamoylaldehyde, diverse phosphinic scaffolds varying in the size of their rigidity element, the nature and stereochemistry of substituents, and the participation of heteroatoms in the azacyclic ring system can be obtained in one synthetic step and in high yield. In addition, this methodology allows the synthesis of Fmoc-protected constrained aminophosphinic acids that can be easily converted to suitable pseudodipeptide building blocks compatible with the requirements of peptide synthesis on the solid phase. Finally, the careful choice of both substituents and protecting groups can provide functionally diverse, orthogonally protected constrained scaffolds for extended derivatization of the target phosphinic peptidomimetic structures.     

Practical Synthesis of Phosphinic Dipeptides by Tandem Esterification of Aminophosphinic and Acrylic Acids under Silylating Conditions

In this report, a synthetic protocol for the preparation of phosphinic dipeptides of type 5 is presented. These compounds serve as valuable building blocks for the development of highly potent phosphinopeptidic inhibitors of medicinally relevant Zn-metalloproteases and aspartyl proteases. The proposed method is based on the tandem esterification of α-aminophosphinic and acrylic acids under silylating conditions in order to subsequently participate in a P-Michael reaction. The scope of the transformation was investigated by using a diverse set of readily available acrylic acids and (R)-α-aminophosphinic acids, and high yields were achieved in all cases. In most examples reported herein, the isolation of biologically relevant (R,S)-diastereoisomers became possible by simple crystallization from the crude products, thus enhancing the operational simplicity of the proposed method. Finally, functional groups corresponding to acidic or basic natural amino acids are also compatible with the reaction conditions. Based on the above, we expect that the practicality of the proposed protocol will facilitate the discovery of pharmacologically useful bioactive phosphinic peptides.     

Balance laws and energy release rates for cracks in dipolar gradient elasticity

It is the purpose of this work to derive the balance laws (in the Günther–Knowles–Sternberg sense) pertaining to dipolar gradient elasticity. The theory of dipolar gradient (or grade 2) elasticity derives from considerations of microstructure in elastic continua [Mindlin, R.D., 1964. Microstructure in linear elasticity. Arch. Rational Mech. Anal. 16, 51–78] and is appropriate to model materials with periodic structure. According to this theory, the strain–energy density assumes the form of a positive-definite function of the strain (as in classical elasticity) and the gradient of both strain and rotation (additional terms). The balance laws are derived here through a more straightforward procedure than the one usually employed in classical elasticity (i.e. Noether’s theorem). Indeed, the pertinent balance laws are obtained through the action of the standard operators of vector calculus (grad, curl and div) on appropriate forms of the Hamiltonian of the system under consideration. These laws are directly related to the energy release rates in the processes of crack translation, rotation and self-similar expansion. Under certain conditions, they are identified with conservation laws and path-independent integrals are obtained.     

Alaninyl­tryptophan hydrate,glycyl­tryptophan dihydrate and tryptophyl­glycine hydrate

The crystal structures of the title tryptophan‐containing dipeptides, C₁₄H₁₇N₃O₃·H₂O, (I), C₁₃H₁₅N₃O₃·2H₂O, (II), and C₁₃H₁₅N₃O₃·H₂O, (III), respectively, contain at least one water mol­ecule of solvation. As a result, the crystal packing of these compounds is composed of regions of water‐mediated hydrogen bonding and tryptophan ring‐to‐ring stacking separated by the length of the mol­ecule. The tryptophan rings stack in a continuous layer that, when viewed edge‐on from the outermost part of the tryptophan ring, exhibits a herring‐bone motif. However, owing to the lack of direct overlap of adjacent rings, no degree of π contact or long‐range delocalization of ring systems is possible here. The overall molecular conformations of (I) and (III) contain a folding of one peptide over the other, such that a minimum in molecular volume occurs without any intramolecular hydrogen bonding. In these two dipeptides, extensive hydrogen bonding is observed to and from the single water mol­ecule of solvation. In the crystal structure of (II), however, an extended mol­ecule conformation complements a more extensive hydrogen‐bonding scheme involving two water mol­ecules of solvation per dipeptide.