Comparison of AOAC 2005.06 LC official method with other methodologies for the quantitation of paralytic shellfish poisoning toxins in UK shellfish species

A refined version of the pre-column oxidation liquid chromatography with fluorescence detection (ox-LC-FLD) official method AOAC 2005.06 was developed in the UK and validated for the determination of paralytic shellfish poisoning toxins in UK shellfish. Analysis was undertaken here for the comparison of PSP toxicities determined using the LC method for a range of UK bivalve shellfish species against the official European reference method, the PSP mouse bioassay (MBA, AOAC 959.08). Comparative results indicated a good correlation in results for some species (mussels, cockles and clams) but a poor correlation for two species of oysters (Pacific oysters and native oysters), where the LC results in terms of total saxitoxin equivalents were found to be on average more than double the values determined by MBA. With the potential for either LC over-estimation or MBA under-estimation, additional oyster and mussel samples were analysed using MBA and ox-LC-FLD together with further analytical and functional methodologies: a post-column oxidation LC method (LC-ox-FLD), an electrophysiological assay and hydrophilic interaction liquid chromatography with tandem mass spectrometric detection. Results highlighted a good correlation among non-bioassay results, indicating a likely cause of difference was the under-estimation in the MBA, rather than an over-estimation in the LC results.     

Metabolic fingerprinting as a tool to monitor whole-cell biotransformations

Fourier transform infrared (FT-IR) spectroscopy was employed as a rapid high-throughput phenotypic typing technique to generate metabolic fingerprints of Escherichia coli MG1655 pDTG601A growing in fed-batch culture, during the dioxygenase-catalysed biotransformation of toluene to toluene cis-glycol. With toluene fed as a vapour, the final toluene cis-glycol concentration was 83 mM, whereas the product concentration was only 22 mM when the culture was supplied with liquid toluene. Multivariate statistical analysis employing cluster analysis was used to analyse the dynamic changes in the data. The analysis revealed distinct trends and trajectories in cluster ordination space, illustrating phenotypic changes related to differences in the growth and product formation of the cultures. In addition, partial least squares regression was used to correlate the FT-IR metabolic fingerprints with the levels of toluene cis-glycol and acetate, the latter being an indicator of metabolic stress. We propose that this high-throughput metabolic fingerprinting approach is an ideal tool to assess temporal biochemical dynamics in complex biological processes, as demonstrated by this redox biotransformation. Moreover, this approach can also give useful information on product yields and fermentation health indicators directly from the fermentation broth without the need for lengthy chromatographic analysis of the products.     

Influence of montmorillonite tactoid size on Na-Ca cation exchange reactions

The spatial organisation of swelling clay platelets in a suspension depends on the chemical composition of the equilibration solution. Individual clay platelets can be well dispersed, with surfaces entirely in contact with the external solution, or be stacked in tactoids, where part of the surfaces forms parallel alignments embedding interlayer water and cations. External and interlayer surfaces do not exhibit similar affinities for cations having different hydration and charge properties and the clay platelet stacking arrangement influences the clay affinity for these cations. This paper aims to establish the link between exchange properties and clay tactoid size and organisation for Na-Ca exchange on montmorillonite. Different montmorillonite samples behave differently with regards to Na-Ca exchange, from ideal to non-ideal exchange behaviour. A simple model coupling the tactoid stacking size to different Na/Ca relative affinities of the external and interlayer clay surfaces enables these differences to be reproduced.     

A one-pot oxidation/allylation/oxidation sequence for the preparation of β,γ-unsaturated ketones directly from primary alcohols

A one-pot oxidation/allylation/oxidation procedure has been developed for the conversion of primary alcohols into β,γ-unsaturated ketones. The methodology has been applied to a range of alcohols, and in some cases, isomerisation to produce the corresponding α,β-unsaturated ketones has been carried out.     

Combined effect of stacking and solvation on the spontaneous mutation in DNA

In DNA, base pairs are involved in two reciprocal interactions: interbase hydrogen bonds and stacking. Furthermore, base pairs also undergo the effects of the external entities present in the biological environment, such as water molecules and cations. In this contribution, the double spontaneous mutation has been studied with hybrid theoretical tools in a DNA-embedded guanine-cytosine model accounting for the impact of the first hydration shell. According to our findings, the combination of the neighboring base pairs and surrounding water molecules plays a crucial role in the double proton transfer. Indeed, as a consequence of these interactions, the double proton transfer (DPT) mechanism is altered: on the one hand, stacking and hydration strongly affect the geometry of base pairs, and, on the other hand, vicinal water molecules may play an active role in the tautomeric equilibrium by catalyzing the proton transfer reaction.     

Myosin-cross-reactive antigen (MCRA) protein from <Emphasis Type="Italic">Bifidobacterium breve</Emphasis> is a FAD-dependent fatty acid hydratase which has a function in stress protection

Background  

The aim of this study was to determine the catalytic activity and physiological role of myosin-cross-reactive antigen (MCRA) from Bifidobacterium breve NCIMB 702258. MCRA from B. breve NCIMB 702258 was cloned, sequenced and expressed in heterologous hosts (Lactococcus and Corynebacterium) and the recombinant proteins assessed for enzymatic activity against fatty acid substrates.     

Asymmetric copper-catalysed intramolecular C-H insertion reactions of α-diazo-β-keto sulfones

Asymmetric copper-catalysed intramolecular C-H insertion reactions of a series of α-diazo-β-keto sulfones are reported. Enantioselectivities of up to 82% ee were achieved in moderate to good yield. These results represent the highest level of enantiocontrol achieved to date for a copper-catalysed cyclopentanone synthesis via C-H insertion.