Modal and characteristics-based approaches for modeling elastic waves induced by time-dependent boundary conditions

In this paper, we present a characteristics-based approach for solving elastic wave problems with time-dependent traction boundary conditions. A generalized mathematical model for this important class of problems is expressed as a set of first-order, linear, hyperbolic partial differential equations. We analyze the mathematical structure of this first-order linear system, verify its hyperbolicity, derive its characteristic form, and deduce its eigenvalues, eigenvectors, and Riemann invariants. The eigenvalues correspond to the wave speeds, while the Riemann invariants are used to construct a solution by the method of characteristics.     

Asymmetric synthesis of β-fluoroaryl-β-amino acids

The conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to a range of β-fluoroaryl-α,β-unsaturated esters gave the corresponding β-amino esters with high diastereoselectivity and in good isolated yields. Sequential treatment of the resultant β-fluoroaryl-β-amino esters under optimised hydrogenolysis conditions, followed by ester hydrolysis with 2.0 M aq HCl, provided access to a range of β-fluoroaryl-β-amino acids in good yield.     

Development and Use of Antibodies in Surface Plasmon Resonance-Based Immunosensors for Environmental Monitoring

The interaction between antibody and antigen is characterised by relatively high affinity and specificity, making this type of reaction a prime candidate for use as an analytical tool. The interaction may be combined with biosensors in the production of immunosensors for environmental monitoring. Polyclonal and monoclonal antibodies have had a significant impact in analytical detection systems over the past few decades with antibody fragments becoming important in recent years. Production of antibodies to small haptens requires the initial conjugation of hapten to a larger carrier molecule. Once hapten-carrier conjugates have been produced, polyclonal, monoclonal and various antibody fragments may be produced by differing protocols. A critical step in the production of antibody fragments is the development of efficient screening procedures to identify suitable antibody-producing clones and this has been reviewed in this article. Various antibody types may then be used in the generation of immunosensors for the monitoring of environmental pollutants. The selection of the appropriate sensor technology applicable for the determination of an antibody-antigen interaction is of prime importance for immunosensor development. One example of such an application is surface plasmon resonance-based biosensors, as they provide real-time analysis of interactions between the antibody and antigen of interest.     

Photomechanical Actuation of Ligand Geometry in Enantioselective Catalysis

A catalyst that couples a photoswitch to the biaryl backbone of a chiral bis(phosphine) ligand, thus allowing photochemical manipulation of ligand geometry without perturbing the electronic structure is reported. The changes in catalyst activity and selectivity upon switching can be attributed to intramolecular mechanical forces, thus laying the foundation for a new class of catalysts whose selectivity can be varied smoothly and in situ over a useful range by controlling molecular stress experienced by the catalyst during turnover. Forces on the order of 100 pN are generated, thus leading to measurable changes in the enantioselectivities of asymmetric Heck arylations and Trost allylic alkylations. The differential coupling between applied force and competing stereochemical pathways is quantified and found to be more efficient for the Heck arylations.