Theoretical study on the origin of enantioselectivity in the primary amine–Brønsted acid catalyzed epoxidation of cyclic enones

Computational studies to determine the origin of enantioselectivity in the (1R,2R)-1,2-diphenylethane-1,2-diamine (DEPN)–Brønsted acid catalyzed epoxidation of 2-cyclohexen-1-one have been performed using density functional theory. Transition states for conjugate addition and ring closure steps of the epoxidations catalyzed by three different catalyst systems were characterized. Our calculations show that the C_sp2H?O H-bond interaction between the benzene ring of the catalyst and H₂O is mainly responsible for the chiral discrimination observed. The Brønsted acid counterion plays a very important role in ensuring high enantioselectivity by improving the rigidity of the transition state structures to allow the efficient formation of the C_sp2H?O H-bond. Moreover, we explain why these two diamine catalysts (1S,2S)-DACH and (1R,2R)-DPEN display consistent enantioselectivities in the catalytic epoxidation of 2-cyclohexen-1-one when combining with three different cocatalysts; achiral TFA, and chiral (R)- and (S)-TRIP.     

Mean curvature flow with free boundary – Type 2 singularities

In this paper we give sufficient conditions that guarantee the mean curvature flow with free boundary on a pinched cylinder develops a Type 2 curvature singularity. We additionally prove that Type 0 singularities may only occur at infinity.     

An Efficient Steric Controlled Photo-Fries Rearrangement in the Naphthalene Series

For the work on the synthesis of 2-acyl-5-methoxynaphthoquinones as tricyclic analogues of daunomycinone¹, we wanted to develop an efficient regioselective synthesis of 5-methoxy-2-acyl-1-naphthols without using Lewis acids. This requirement precluded the use of the thermal Fries but not the photo-Fries rearrangement. Although the mechanistic aspects of the photo reaction have received much study², the reaction has been little used preparatively³ because it usually gives poor yields of hydroxy ketones even when only one product is possible.     

Small-scale fracture toughness of ceramic thin films: the effects of specimen geometry,ion beam notching and high temperature on chromium nitride toughness evaluation

For the implementation of thin ceramic hard coatings into intensive application environments, the fracture toughness is a particularly important material design parameter. Characterisation of the fracture toughness of small-scale specimens has been a topic of great debate, due to size effects, plasticity, residual stress effects and the influence of ion penetration from the sample fabrication process. In this work, several different small-scale fracture toughness geometries (single-beam cantilever, double-beam cantilever and micro-pillar splitting) were compared, fabricated from a thin physical vapour-deposited ceramic film using a focused ion beam source, and then the effect of the gallium-milled notch on mode I toughness quantification investigated. It was found that notching using a focused gallium source influences small-scale toughness measurements and can lead to an overestimation of the fracture toughness values for chromium nitride (CrN) thin films. The effects of gallium ion irradiation were further studied by performing the first small-scale high-temperature toughness measurements within the scanning electron microscope, with the consequence that annealing at high temperatures allows for diffusion of the gallium to grain boundaries promoting embrittlement in small-scale CrN samples. This work highlights the sensitivity of some materials to gallium ion penetration effects, and the profound effect that it can have on fracture toughness evaluation.     

Stereoelectronic Basis for the Kinetic Resolution of N‐Heterocycles with Chiral Acylating Reagents

The kinetic resolution of N‐heterocycles with chiral acylating agents reveals a previously unrecognized stereoelectronic effect in amine acylation. Combined with a new achiral hydroxamate, this effect makes possible the resolution of various N‐heterocycles by using easily prepared reagents. A transition‐state model to rationalize the stereochemical outcome of this kinetic resolution is also proposed.     

Maze exploration and learning in C. elegans

The soil dwelling nematode, Caenorhabditis (C.) elegans, is a popular model system for studying behavioral plasticity. Noticeably absent from the C. elegans literature, however, are studies evaluating worm behavior in mazes. Here, we report the use of microfluidic mazes to investigate exploration and learning behaviors in wild-type C. elegans, as well as in the dopamine-poor mutant, cat-2. The key research findings include: (1)C. elegans worms are motivated to explore complex spatial environments with or without the presence of food/reward, (2) wild-type worms exhibit a greater tendency to explore relative to mutant worms, (3) both wild-type and mutant worms can learn to make unconditioned responses to food/reward, and (4) wild-type worms are significantly more likely to learn to make conditioned responses linking reward to location than mutant worms. These results introduce microfluidic mazes as a valuable new tool for biological behavioral analysis.     

Reactive ligand influence on initiation in phenylene catalyst‐transfer polymerization

Synthesizing conjugated polymers via catalyst‐transfer polymerization (CTP) has led to unprecedented control over polymer sequence and molecular weight. Yet many challenges remain, including broadening the monomer scope and narrowing the molecular weight dispersities. Broad polymer dispersities can arise from nonliving pathways as well as slow initiation. Previously, slow initiation was observed in Ni‐mediated CTP of phenylene monomers. Although precatalysts with faster initiation rates have been reported, the rates still do not exceed propagation. Herein a second‐ and third‐generation of reactive ligands are described, along with a simple method for measuring initiation rates. A precatalyst with an initiation rate that exceeds propagation is now reported, however, the resulting polymer samples still exhibit broad dispersities, suggesting that slow initiation is not the most significant contributing factor in Ni‐mediated phenylene polymerizations. In addition, initiation rates measured under authentic polymerization conditions revealed that both exogenous triphenylphosphine and an ortho‐trifluoroethoxy substituent on the reactive ligand have a strong influence. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1530–1535     

On the uniqueness of solutions to the displacement problem in linear elastodynamics

In recent separate investigations, Kirchhoff's classical uniqueness theorem of elastodynamics has been extended in two ways. Gurtin and Toupin generalized the theorem to encompass bodies possessing an elasticity tensor that obeys the semi-strong ellipticity condition, whereas the author has extended the theorem to unbounded regions. These two results are brought together in the present paper.

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Resume Dans deux études récentes, le champ d'application du théoréme classique de Kirchhoff sur l'unicité de l'élastodynamique a été élargi de deux manières différentes. Gurtin et Toupin l'ont généralisé pour inclure les corps possédant un tenseur d'élasticité obéissant à la condition d'ellipticité demi-forte, alors que le présent auteur l'a étendu aux régions non finies. Ces deux résultats ont été combinés dans la présente communication.