Electroanalytical applications of boron-doped diamond microelectrode arrays

The electrochemical characteristics of a novel all diamond fabricated boron-doped diamond microelectrode array (BDD-MEA) are critically appraised. The voltammetric response of simple electron transfer processes has been investigated and found to generate sigmoidal voltammetric curves. Furthermore, the device has been utilized for various analytical applications including, the direct detection of 4-nitrophenol over the concentration range 1.8-9.2 μM, manganese over the range 0.1-4.8 μM and the indirect determination of sulfide producing a limit of detection of 23 μM.     

The reaction of 4-amino-2-oxazolines with isocyanates and isothiocyanates. Synthesis and X-ray structures of polysubstituted 2-imidazolidinones, 1,3-oxazolidines and 1,3-thiazolidines

Reactions of 4-alkylamino-2-phenyl-2-oxazolines 1 with isocyanates and isothiocyanates provide unprecedented efficient and regioselective heterocycle-heterocycle transformations. Compounds 1 reacted rapidly with tosyl isocyanate yielding directly 3-alkyl-4-benzamido-1-tosyl-2-imidazolidinones 4 in almost quantitative yields. The corresponding ureido intermediates 2 were not isolable species. However, the reactions with non-sulfonylated isocyanates or isothiocyanates were slower, leading to the expected ureido and thioureido derivatives 5, which were easily and efficiently transformed to either polysubstituted 2-imino-1,3-oxazolidine or 2-imino-1,3-thiazolidine hydrochlorides 7, respectively, by treatment with hydrochloric acid. The possible reasons for this disparity in chemical behaviour are discussed. X-ray crystallographic structures for 4-benzamido-3-methyl-1-tosyl-2-imidazolidinone 4b, 4-[1-isopropyl-3-(4-nitrophenyl)ureido]-2-phenyl-2-oxazoline 5e, (Z)-3-benzyl-4-benzamido-2-phenylimino-1,3-oxazolidine hydrochloride 7a and (Z)-3-benzyl-4-benzamido-2-phenylimino-1,3-thiazolidine hydrochloride 7b have been determined.     

A compact broadband cavity enhanced absorption spectrometer for detection of atmospheric NO(2) using light emitting diodes

A compact and low power detector has been developed for the in situ measurement of atmospheric NO(2) using broadband cavity enhanced absorption spectroscopy. Absorption by the O(2)-O(2) collisional pair was used to determine the cavity mirror reflectivity, thus enabling the retrieval of absolute absorber concentrations by differential spectral fitting techniques. Quantitative amounts of ambient NO(2) (between 3 and 32 parts per billion) were retrieved from spectra recorded in the presence of ambient aerosol with statistical uncertainties approaching 100 ppt for a 60 s averaging period. The instrument's response was compared to that of a commercial chemiluminescence detector and was found to agree to within 6%.     

Air-stable titanium alkoxide based metal-organic framework as an initiator for ring-opening polymerization of cyclic esters

An air-stable titanium-organic framework, prepared from Ti(OiPr)4 and 1,4-butanediol, has been characterized via single-crystal X-ray diffraction, revealing a unique supramolecular structure. Its functionality as a highly active initiator for the ring-opening polymerization of cyclic esters is demonstrated. A discrete titanium trimer containing the related ligand (2R,3R)-2,3-butanediol has also been prepared, and it shows analogous activity as a polymerization initiator.     

Cobalt-catalyzed aziridination with diphenylphosphoryl azide (DPPA): direct synthesis of N-phosphorus-substituted aziridines from alkenes

A new catalytic aziridination system that consists of cobalt(II) tetraphenylporphyrin [Co(TPP)] as the catalyst and diphenylphosphoryl azide (DPPA) as the nitrene source has been developed. The cobalt-based catalytic system allows direct synthesis of N-phosphorus-substituted aziridines from alkenes with dinitrogen as the byproduct. Cobalt ion seems essential to the catalytic aziridination with DPPA as no or only trace amounts of the desired products were observed with other metal complexes of tetraphenylporphyrin.     

Evolution of an open-access quantitative bioanalytical mass spectrometry service in a drug discovery environment

Increased demand for assays for compounds at the early stages of drug discovery within the pharmaceutical industry has led to the need for open-access mass spectrometry systems for performing quantitative analysis in a variety of biological matrices. The open-access mass spectrometers described here are LC/MS/MS systems operated in 'multiple reaction monitoring' (MRM) mode to obtain the sensitivity and specificity required to quantitate low levels of pharmaceutical compounds in an excess of biological matrix. Instigation of these open-access systems has resulted in mass spectrometers becoming the detectors of choice for non-expert users, drastically reducing analytical method development time and allowing drug discovery scientists to concentrate on their core expertise of pharmacokinetics and drug metabolism. Setting up an open-access facility that effectively allows a user with minimal mass spectral knowledge to exploit the MS/MS capability of triple quadrupole mass spectrometers presents a significantly different challenge from setting up qualitative single stage mass spectrometry systems. Evolution of quantitative open access mass spectrometry within a pharmaceutical drug metabolism and pharmacokinetics group, from its beginnings as a single generic system to a series of specialist fully integrated walk-up facilities, is described.     

High-spectral-resolution coherent anti-Stokes Raman scattering with interferometrically detected broadband chirped pulses

To achieve high-spectral-resolution multiplex coherent anti-Stokes Raman scattering (CARS), one typically uses a narrowband pump pulse and a broadband Stokes pulse. This is to ensure a correspondence between anti-Stokes and vibrational frequencies. We obtain high-resolution CARS spectra of isopropanol, using a broadband chirped pump pulse and a broadband Stokes pulse, by detecting the anti-Stokes pulse with spectral interferometry. With the temporally resolved anti-Stokes signal, we can remove the chirp of the anti-Stokes pulse and restore high spectral resolution while also rejecting nonresonant scattering.     

Anomalous thermal denaturing of proteins adsorbed to nanoparticles

We have used localized surface plasmon resonance (LSPR) to monitor the structural changes that accompany thermal denaturing of bovine serum albumin (BSA) adsorbed onto gold nanospheres of size 5nm-60nm. The effect of the protein on the LSPR was monitored by visible extinction spectroscopy. The position of the resonance is affected by the conformation of the adsorbed protein layer, and as such can be used as a very sensitive probe of thermal denaturing that is specific to the adsorbed protein. The results are compared to detailed calculations and show that full calculations can lead to significant increases in knowledge where gold nanospheres are used as biosensors. Thermal denaturing on spheres with diameter > 20 nm show strong similarity to bulk calorimetric studies of BSA in solution. BSA adsorbed on nanospheres with d ⩽ 15nm shows a qualitative difference in behavior, suggesting a sensitivity of denaturing characteristics on local surface curvature. This may have important implications for other protein-nanoparticle interactions.     

Sex-related differences in vocal responses to pitch feedback perturbations during sustained vocalization

The present study assessed the effect of sex on voice fundamental frequency (F(0)) responses to pitch feedback perturbations during sustained vocalization. Sixty-four native-Mandarin speakers heard their voice pitch feedback shifted at ± 50, ± 100, or ± 200 cents for 200 ms, five times during each vocalization. The results showed that, as compared to female speakers, male speakers produced significantly larger but slower vocal responses to the pitch-shifted stimuli. These findings reveal a modulation of vocal response as a function of sex, and suggest that there may be a differential processing of vocal pitch feedback perturbations between men and women.     

Large Eddy Simulation of Turbulent Confined Highly Swirling Annular Flows

The present paper discusses the Large Eddy Simulation of a confined non-reacting annular swirling jet. The configuration corresponds to a well investigated flow studied experimentally by Sheen (1993). The flow field is characterised by a high swirl number resulting in relatively complex features. The challenging behaviour of the flow is governed by the interaction of several recirculation zones. The central recirculation zone formed by the swirling jet is strongly affected by the cylindrical centre body which acts as a bluff body. The flow features coherent structures such as Precessing Vortex Cores (PVCs), which create regions with high velocity fluctuations. The simulations presented comprise a detailed investigation of the parameters controlling the inert flow and a thorough comparison with the experimental data.