Furanyl cyclic amines: a diastereoselective synthesis of 2,6-syn-disubstituted piperidines under thermodynamic control

Utilising the propensity of the 2-furanyl group to facilitate equilibration of an adjacent tosylamide chiral centre, a diastereoselective route to 2,6-syn-piperidines was developed that proceeds with high levels of thermodynamic stereocontrol. X-ray crystallography structures suggest that, as seen in similar systems, pseudo-allylic strain between the N-tosyl group and the substituents at the 2 and 6 positions dominates stereochemical preference, overriding 1,3 diaxial interactions.     

Pattern formation in a simple chemical system with general orders of autocatalysis and decay. I. Stability analysis

In this preliminary paper we introduce a mathematical model based on an autocatalytic reaction scheme with termination, and general reaction orders. Rigorous stability analysis and numerical solutions are presented which illustrate that the problem can for certain parameter values admit a stable stationary pattern in the concentration of the autocatalyst and reactant. This pattern forms at the rear of a permanent form travelling wave or pulse solution.     

Symmetry and singularity properties of second-order ordinary differential equations of Lie's type III

We extend the work of Abraham-Shrauner [B. Abraham-Shrauner, Hidden symmetries and linearization of the modified Painlevé-Ince equation, J. Math. Phys. 34 (1993) 4809-4816] on the linearization of the modified Painlevé-Ince equation to a wider class of nonlinear second-order ordinary differential equations invariant under the symmetries of time translation and self-similarity. In the process we demonstrate a remarkable connection with the parameters obtained in the singularity analysis of this class of equations.     

Turbulent diffusion of a buoyant layer at a wall

Summary When a light fluid is injected at a steady rate at the roof of a tunnel in which there is a turbulent main flow of a heavier fluid, the turbulent diffusion of the light layer may be considerably reduced due to buoyancy. For large Richardson numbers turbulent mixing ceases altogether.The equations of motion and diffusion were solved by introducing an eddy diffusivity which is dependant on the Richardson number. Experiments were made on brine (floor) layers in a water flow, and on methane (roof) layers in an air flow. Results were essentially in agreement with theory.The motion and mixing of the layers depend mainly on the inclination of the tunnel and on a dimensionless combination of main-flow velocity, gravity, relative density difference, volume input rate of layer fluid, and tunnel width. Values of the dimensionless parameter are suggested to overcome the effects of buoyancy on mixing, and to prevent layers from moving up a slope against the main flow.     

Creating permanent 3D arrangements of isolated cells using holographic optical tweezers

We report the creation of permanent 3D configurations of cells, at predefined positions, within a gelatin matrix. The technique used holographic optical tweezers to manipulate individual E. coli within a solution comprising monomer precursors. The matrix was then set and after the laser beam was removed, we were able to demonstrate that the structures remained intact for many days. We were also able to demonstrate that, in the presence of appropriate nutrients, the E. coli survived within the gelatin matrix for several days. The technique could have a number of potential future applications, including the arrangement of a variety of different cell types in complex architectures, as motifs for promoting tissue differentiation and growth within the field of cell engineering.     

The ene reactions of nitroso compounds involve polarized diradical intermediates

The ene reactions of nitroso compounds were studied with B3LYP/6-31G* geometry optimizations and energy calculations, along with single point energy evaluations using CASPT2/6-31G** and UCCSD(T)/6-311+G* methods. Reactions of HNO with propene and of MeNO and p-NO2C6H4NO with propene or substituted alkenes were also studied. The reaction mechanism is stepwise and involves a polarized diradical intermediate. The electronic structure of this intermediate is between that of a closed shell polar species and that of a pure diradical, and it is stabilized by polar solvents. A weak C-N bonding interaction combined with a CH-O hydrogen bond leads to heightened barriers to rotation about formally single bonds compared to conventional diradicals. Consequently, rotation is slower than hydrogen abstraction and cyclization to form an aziridine N-oxide. This aziridine N-oxide does not lead to ene products without subsequent ring opening but provides a mechanism for the RNO moiety to translate from one end of the alkene to the other. B3LYP calculations are also able to reproduce kinetic isotope effects and regioselectivity.