Near-degenerate stereomorphs of the doubly-chiral hcp-{213̅1} surface

The surfaces of hcp crystals can show a variety of structural features and classes of symmetry that differ markedly from those of simpler fcc or bcc crystals. The hcp-{213?1} surface, for example, can occur in four distinct stereomorphs, interconverted by a combination of mirror operations (linking degenerate enantiomorphically related surfaces) and/or the removal of the outermost atomic layer (linking non-degenerate diamorphically related surfaces). The strict pattern of degeneracy amongst these stereomorphs is analogous to that found for molecules with two chiral centres, and hence it is possible to view this system as doubly-chiral. Simple nearest-neighbour bond-counting arguments, however, suggest that for {213?1} even the diamorphically related cases should be near-degenerate, despite the fact that they differ in having either a notably short or notably long interlayer spacing between the outermost layers (ideal spacing ratio 1:5). In the present work, this counterintuitive result is confirmed at the level of density functional theory, both for the ideal and relaxed {213?1} surfaces of Co, Ru and Re.     

Volume-based thermoelasticity: consequences of the (near) proportionality of isothermal compressibility to formula-unit volume

Groups of structurally related materials, including the alkali halides, exhibit a proportionality of isothermal compressibility to formula-unit volume. The relationship has recently been explored by Glasser and by Recio et al. In this paper, we present the consequences of such proportionality on the relationships of Born-Lande? and Born-Mayer parameters to the formula-unit volume. These relationships have then been tested separately on (i) alkali (excluding cesium) halides and (ii) cesium halides. We conclude that the equations fit the NaCl-type materials satisfactorily, but less well for the CsCl-type materials, and that the Born-Mayer equation is more applicable. These results confirm the conclusion that volume is intimately linked to thermodynamic quantities, as already demonstrated by our development of volume-based thermodynamics (VBT).     

Synthesis and characterization of luminescent bis-cyclometalated platinum(IV) complexes

Presented is the synthesis and characterization of a series of luminescent heteroleptic bis-cyclometalated platinum(IV) complexes. An oxidation-facilitated cyclometalation is employed to convert platinum(II) pendant species into bis-cyclometalated platinum(IV) dichlorides, which are transformed into the tris-chelated diimine complexes through ligand substitution. The structure-property relationship is probed by judiciously varying substituents on both the C(∧)N and the N(∧)N ligands resulting in a family of complexes exhibiting blue emission, long excited-state lifetimes, and highly efficient oxygen quenching. Excited-state properties are corroborated by static and time-dependent density-functional theory calculations of both the singlet and the triplet state.     

An unexpected ring contraction of two nitroaryl pro-drugs: conversion of N-(nitroaryl)-3-chloropiperidine derivatives into N-(nitroaryl)-2-chloromethylpyrrolidines

Treatment of the N-nitroaryl-3-hydroxypiperidine derivatives 12 and 13 with thionyl chloride afforded the corresponding N-aryl-2-chloromethylpyrrolidines 5 and 15 via a ring-contraction process involving an intermediate aziridinium ion.     

The use of 35S and Tnos expression elements in the measurement of genetically engineered plant materials

An online survey was conducted by the International Life Sciences Institute, Food Biotechnology Committee, on the use of qualitative and quantitative polymerase chain reaction (PCR) assays for cauliflower mosaic virus 35S promoter and Agrobacterium tumefaciens Tnos DNA sequence elements for the detection of genetically engineered (GE) crop plant material. Forty-four testing laboratories around the world completed the survey. The results showed the widespread use of such methods, the multiplicity of published and in-house methods, and the variety of reference materials and calibrants in use. There was an interest on the part of respondents in validated quantitative assays relevant to all GE events that contain these two genetic elements. Data are presented by testing two variations each of five published real-time quantitative PCR methods for 35S detection on eight maize reference materials. The results showed that two of the five methods were not suitable for all the eight reference materials, with poor linear regression parameters and multiple PCR amplification products for some of the reference materials. This study demonstrates that not all 35S methods produce satisfactory results, emphasizing the need for method validation.     

Oxazoles XXI. Three Ester Ammonium Salts Resulting from the Rupture of an Oxazoline Ring

Abstract  

The synthesis and characterisation of three ammonium salts that are formed via a ring opening of a 2-oxazoline (i.e., a 4,5-dihydro-1,3-oxazole) are described. Compound 1, derived from 2-phenyl-2-oxazoline (Phox), was isolated as a major reaction product during an unrelated synthesis using Phox which was being carried out in the presence of NO₃ ⁻ ions. The isolated compound is identified as the nitrate salt of the terminal ammonium ester [H₃NCH₂CH₂OC(=O)Ph]⁺ (1). The X-ray crystal structure (C₉H₁₂N₂O₅) of 1 is revealed to be orthorhombic (space group Pna2₁) with a = 21.1304(8), b = 7.5975(2) and c = 6.8629(3)?. The analogous material 2a, obtained from the related oxazole 4,4-dimethyl-2-phenyl-2-oxazoline (MePhox) under identical conditions to that of 1, contains the [H₃NCMe₂CH₂OC(=O)Ph]⁺ cation. The X-ray crystal structure (C₁₁H₁₆N₂O₅) of 2a is monoclinic with a = 6.1270(3), b = 6.3603(3), c = 16.1632(8)? and β = 90.662(3)o and of space group P2₁. Chiral derivative 2b, was isolated from a wet CH₂Cl₂/THF solution upon treatment of MePhox with (S)-mandelic acid. This material was shown to also contain the [H₃NCMe₂CH₂OC(=O)Ph]⁺ cation, a lattice water molecule and an (S)-mandalate anion. The X-ray crystal structure of 2b (C₁₉H₂₃NO₅·H₂O) is orthorhombic (space group P2₁2₁2₁) with a = 6.4733(3), b = 11.4661(5) and c = 24.5791(11)?. One proposed mechanism by which all three materials are formed was first presented in seminal work by Deslongchamps. The compounds reported herein are representatives of a class of rarely isolated intermediates in heterocyclic ring opening reactions and they are also the first examples of (ω-ammoniumethyl)(aryl) esters to be structurally characterised.     

Coherent control of nanoscale light localization in metamaterial: creating and positioning isolated subwavelength energy hot spots

We show the strong optically induced interactions between discrete metamolecules in a metamaterial system and coherent monochromatic continuous light beam with a spatially tailored phase profile can be used to prepare a subwavelength scale energy localization. Well-isolated energy hot spots of a fraction of a wavelength can be created and positioned on the metamaterial landscape offering new opportunities for data storage and imaging applications.     

Wavelength division (de)multiplexing based on dispersive self-imaging

We proposed and experimentally demonstrated wavelength division (de)multiplexers (WDMs) utilizing the wavelength dispersive nature of self-imaging multimode interferometers. Proof-of-principle devices fabricated on the silicon-on-insulator platform operated as 4-channel WDMs with a free spectral range of >90 nm, an averaging cross talk of <-20 dB for a 1 nm band, and an insertion loss of <2.0 dB. The potential for higher channel counts and smaller channel wavelength spacing was also predicted. This type of WDM is easy to design and fabricate. The underlying concept is applicable to all planar waveguide platforms.     

On the parameter choice in grad-div stabilization for the Stokes equations

Standard error analysis for grad-div stabilization of inf-sup stable conforming pairs of finite element spaces predicts that the stabilization parameter should be optimally chosen to be $\mathcal O(1)$ . This paper revisits this choice for the Stokes equations on the basis of minimizing the $H^{1}(\Omega )$ error of the velocity and the $L^{2}(\Omega )$ error of the pressure. It turns out, by applying a refined error analysis, that the optimal parameter choice is more subtle than known so far in the literature. It depends on the used norm, the solution, the family of finite element spaces, and the type of mesh. In particular, the approximation property of the pointwise divergence-free subspace plays a key role. With such an optimal approximation property and with an appropriate choice of the stabilization parameter, estimates for the $H^{1}(\Omega )$ error of the velocity are obtained that do not directly depend on the viscosity and the pressure. The minimization of the $L^{2}(\Omega )$ error of the pressure requires in many cases smaller stabilization parameters than the minimization of the $H^{1}(\Omega )$ velocity error. Altogether, depending on the situation, the optimal stabilization parameter could range from being very small to very large. The analytic results are supported by numerical examples. Applying the analysis to the MINI element leads to proposals for the stabilization parameter which seem to be new.