Face-to-face arene-arene binding energies: dominated by dispersion but predicted by electrostatic and dispersion/polarizability substituent constants

Parallel face-to-face arene-arene complexes between benzene and substituted benzenes have been investigated at the MP2(full)/6-311G** and M05-2X/6-311G** levels of theory. A reasonably good correlation was found between the binding energies and the ∑|σ(m)| values of the substituted aromatics. It is proposed that a substituent |σ(m)| value informs on both the aromatic substituent dispersion/polarizability and the effect the substituent has on the aromatic electrostatics. Supporting this hypothesis, a combination of electrostatic (∑σ(m)) and dispersion/polarizability (∑M(r)) substituent constant terms gives an excellent, and statistically significant, correlation with the benzene-substituted benzene binding energy. Symmetry adapted perturbation theory energy decomposition calculations show the dominant attractive force is dispersion; however, the sum of all nonelectrostatic forces is essentially a constant, while the electrostatic component varies significantly. This explains the importance of including an electrostatic term when predicting benzene-substituted benzene binding energies.     

Microfluidic sorting system based on optical force switching

We report a versatile, and automatic method for sorting cells and particles in a three dimensional polydimethylsiloxane (PDMS) structure consisting of two cross-microchannels. As microspheres or yeast cells are fed continuously into a lower channel, a line shaped focused laser beam is applied (perpendicular to the direction of flow) at the crossing junction of the two channels. The scattering force of the laser beam was employed to push microparticles matching specific criteria upwards from one channel to another. The force depends on the intrinsic properties of the particles such as their refractive index and size, as well as the laser power and the fluid flow speed. The combination of these parameters gives a tunable selection criterion for the effective and efficient sorting of the particles. The introduction of the cylindrical lens into the optical train allows for simultaneous manipulation of multiple particles which has significantly increased the efficiency and throughput of the sorting. A high aspect ratio microchannel (A.R.=1.6) was found to enhance the sorting performance of the device. By careful control of the microparticle flow rate, near 100% sorting efficiency was achieved.     

Supercontinuum radiation for applications in chemical sensing and microscopy

The advent of compact, high brightness supercontinuum radiation sources employing solid core photonic crystal fibres is beginning to make an impact across the field of applied spectroscopy research. In this article we focus on the use of supercontinuum sources to construct novel instrumentation for chemical sensing. A brief overview is given on the mechanisms of supercontinuum generation in solid core photonic crystal fibres, and then we review recent, and present new, results from our own research. We present examples on gas phase sensing applications, permitting wide bandwidth molecular spectra to be gathered at ultrahigh speed. Furthermore we demonstrate the design and construction of a wide bandwidth microscope for wavelength flexible hyperspectral confocal imaging. We conclude with an outlook and a summary of where and how we think the field may develop over coming years. PACS  07.07.Df; 42.62.Fi; 87.64.mk; 87.64.-t     

Quadrupole transitions in 20Ne

Untruncated shell model calculations in the 1s-0d shell using Chung-Wildenthal effective interactions have been performed for ²⁰Ne and the electron scattering form factors for elastic scattering and for the excitation of 2₁⁺, 2₁⁺ and 2₃⁺ states have been examined. Saxon-Woods wave functions and a phase-shift analysis have been used. It is shown that within the limited space of the 1s-0d shell, it is possible to obtain vastly different momentum transfer dependence for the electro-excitation of ΔJ^π = 2⁺ transitions. The 2₁⁺ and 2₂⁺ states are seen to be adequately described by the wave functions obtained in this calculation, but 2₃⁺ is not described well.     

A base induced fragmentation of tetramisole

The exposure of dl-2,3,5,6-tetrahydro-6-phenylimidazo[2,1-6 Jthiazole (tetramisole) to lithium diisopropylamide in tetrahydrofuran ruptures the thiazole ring to give, following the introduction of primary or secondary alkyl halides, 1-(2′-alkylthio)ethyl-4-phenylimidazoles. Conclusive evidence for the thiazole ring opening was obtained by a single crystal x-ray diffraction study of 1-(2′-p-bromobenzylthio)ethyl-4-phenylimidazole.