Pollution trees: identifying similarities among complex pollutant mixtures in water and correlating them to mutagenicity

There are relatively few tools available for computing and visualizing similarities among complex mixtures and in correlating the chemical composition clusters with toxicological clusters of mixtures. Using the "intersection and union ratio (IUR)" and other traditional distance matrices on contaminant profiles of 33 specific water samples, we used "pollution trees" to compare these mixtures. The "pollution trees" constructed by neighbor-joining (NJ), maximum parsimony (MP), and maximum likelihood (ML) methods allowed comparison of similarities among these samples. The mutagenicity of each sample was then mapped to the "pollution tree". The IUR-distance-based measure proved effective in comparing chemical composition and compound level differences between mixtures. We found a robust "pollution tree" containing seven major lineages with certain broad characteristics: treated municipal water samples were different from raw water samples and untreated rural drinking water samples were similar with local water sources. The IUR-distance-based tree was more highly correlated to mutagenicity than were other distance matrices, i.e., MP/ML methods, sampling group, region, or water type. IUR-distance-based "pollution trees" may become important tools for identifying similarities among real mixtures and examining chemical composition clusters in a toxicological context.     

Near-infrared oximetry of three post-rigor skeletal muscles for following myoglobin redox forms

We investigated the response of frequency-domain multidistance (FDMD) near-infrared (NIR) tissue oximetry for detecting absolute amounts of myoglobin (Mb) redox forms and their relationship to meat colour stability. Four packaging formats were used to create different blends of Mb redox forms and meat colours during display. Changes in surface colour and subsurface pigment forms during simulated display time (0, 2, 4, and 10 d at 2 °C) were evaluated using surface reflecto-spectrophotometry (both L∗a∗b∗ and specific wavelengths) and FDMD NIR tissue oximetry. Data for both methods of direct measurement of oxymyoglobin and deoxymyoglobin were strongly related and accounted for 86–94% of the display variation in meat colour. Indirect estimates of metmyoglobin ranged from r² = 59–85%. It appears that NIR tissue oximetry has potential as a noninvasive, rapid method for the assessment of meat colour traits and may help improve our understanding of meat colour chemistry in post-rigor skeletal muscle.     

The use of atomic force microscopy to measure the efficacies of various chemical sanitizers in removing organic matter from glass surfaces

Improper washing and sanitizing of tableware items is a significant public health risk. Residual food soils left on food-contact surfaces can harbor pathogenic microorganisms and may even allow them to form biofilms. This study investigated the effect of various sanitizers (sodium hypochlorite, quaternary ammonium compound, neutral electrolyzed water and an acidic formulation) for removal of various milk-based products (whole, 2% reduced fat, chocolate low-fat and skim milk) from underlining glass surfaces. Atomic force microscopy (AFM) was used to determine the thicknesses of the milk films left after attempts to clean the glass surfaces. Results showed that PRO-SAN® (the acidic formulation) significantly reduced the amount of residual food soil when compared with the other sanitizers. This could be due to sodium dodecylbenzene sulfonate (a surfactant) being present in the acidic formulation. The data also showed that whole and chocolate milk would be more difficult to clean when compared with 2% and skim milk.     

The effects of freeze-thaw and sonication on mitochondrial oxygen consumption, electron transport chain-linked metmyoglobin reduction, lipid oxidation, and oxymyoglobin oxidation

Mitochondria potentially influence Mb redox stability in meat by (1) decreasing partial oxygen pressure via oxygen consumption, (2) mitochondrial electron transport chain (ETC)-linked reduction of MetMb, and/or (3) oxidation of mitochondrial membrane lipid. The objective of this study was to investigate the effect of freeze-thaw and sonication treatments on mitochondrial oxygen consumption, ETC-dependent MetMb reducing activity, lipid oxidation, and Mb redox stability. Mitochondria were frozen and thawed (-18°C for 2h and 4°C for 0.5h) for 3 cycles, or sonicated for 30s with a sonic dismembrator. State III oxygen consumption rate (OCR) was decreased by both treatments at pH 7.2, and by sonication only at pH 5.6 (P<0.05). There was no effect on state IV OCR (P>0.05). Respiratory control ratio (RCR) was decreased by freeze-thaw and sonication at pH 7.2 and 5.6 (P<0.05). Sonication increased mitochondrial lipid oxidation and MetMb formation (P<0.05); a similar effect was observed in sonicated samples in the presence of ascorbic acid and ferric chloride (P<0.05). Sonication also decreased mitochondrial ETC-dependent MetMb reduction (P<0.05). These results suggested that sonication treatment had the potential to affect Mb stability via mitochondrial lipid oxidation and/or ETC-mediated MetMb reduction, but the effect on myoglobin stability by freeze-thaw treatment was minimal.     

Four-dimensional spectral tomography of carbonaceous nanocomposites

There is considerable interest in the adhesion of polymers to carbon nanotubes for nanocomposite applications.(1-4) One example is multiwalled carbon nanotubes (MWCNTs) dispersed in nylon 6,6.(5) We will show that high-contrast tomographic reconstructions can be created from plasmon-loss electrons that show the three-dimensional structural complexity of the MWCNT-nylon composite at the nanoscale. Further, by recording a series of energy-loss images at successive tilts, it is possible to interrogate subvolumes to extract energy-loss spectra from the reconstructed "volume spectra".     

Image-spectroscopy--II. The removal of plural scattering from extended energy-filtered series by Fourier deconvolution.

The increased spectral information obtained by acquiring an EFTEM image-series over several hundred eV allows plural scattering to be removed from loss images using standard deconvolution techniques developed for the quantification of EEL spectra. In this work, both Fourier-log and Fourier-ratio deconvolution techniques have been applied successfully to such image-series. Application of the Fourier-log technique over an energy-loss range of several hundred eV has been achieved by implementation of a novel method that extends the effective dynamic range of EFTEM image-series acquisition by over four orders of magnitude. Experimental results show that the removal of plural scattering from EFTEM image-series gives a significant improvement in quantification for thicker specimen regions. Further, the recovery of the single-scattering distribution using the Fourier-log technique over an extended energy-loss range is shown to result in an increase in both the ionisation-edge jump-ratio and the signal-to-noise ratio.     

Assessment of an amperometric membrane probe for determining free residual chlorine in saline cooling waters

Cooling water at coastal and estuarine power stations is chlorinated to inhibit mussel growth in the intakes to the condensers and a means of automatically monitoring the free residual chlorine concentration is desired so that the dosage can be precisely maintained at 0.2 μg ml⁻¹ Cl₂. The Delta Scientific model 82124 amperometric membrane probe has been tested in the laboratory for its suitability for this application. The probe had a linear response to hypochlorous acid over the range 0–5 μg ml⁻¹, but was not specific for free residual chlorine, as chloramines also produced a response. The main product of the chlorination of sea water is bromine, to which the probe is about five times more sensitive than to hypochlorous acid. Although the probe can be calibrated with bromine, its response is then much noisier than that obtained with hypochlorous acid. The salinity of the sample influences the reading obtained at a given concentration of oxidant: increasing the salinity increases the reading obtained with hypochlorous acid but decreases that obtained with bromine.     

Insights to Carrier-Phonon Interactions in Lead Halide Perovskites via Multi-Pulse Manipulation

A fundamental understanding of the hot-carrier dynamics in halide perovskites is crucial for unlocking their prospects for next generation photovoltaics. Presently, a coherent picture of the hot carrier cooling process remains patchy due to temporally overlapping contributions from many-body interactions, multi-bands, band gap renormalization, Burstein–Moss shift etc. Pump-push-probe (PPP) spectroscopy recently emerges as a powerful tool complementing the ubiquitous pump-probe (PP) spectroscopy in the study of hot-carrier dynamics. However, limited information from PPP on the initial excitation density and carrier temperature curtails its full potential. Herein, this work bridges this gap in PPP with a unified model that retrieves these essential hot carrier metrics like initial carrier density and carrier temperature under the push conditions, thus permitting direct comparison with traditional PP spectroscopy. These results are well-fitted by the phonon bottleneck model, from which the longitudinal optical phonon scattering time τ_LO, for MAPbBr₃ and MAPbI₃ halide perovskite thin film samples are determined to be 240 ± 10 and 370 ± 10 fs, respectively.     

Characterization of Competitive Inhibitors of Plasmodium falciparum cGMP-Dependent Protein Kinase**

Plasmodium falciparum cGMP-dependent protein kinase (PfPKG) is an enticing antimalarial drug target. Novel chemotypes are needed because existing inhibitors have safety issues that may prevent further development. This work demonstrates isoxazole-based compounds are potent ATP competitive inhibitors of PfPKG and discloses a new analogue in this series. Isoxazoles 3 and 5 had K_i values that are comparable to a known standard, 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H pyrrol-3-yl] pyridine. They also exhibited excellent selectivity for PfPKG over the human orthologue and the gatekeeper mutant T618Q PfPKG, which mimics the less accessible binding site of the human orthologue. The human orthologue's larger binding site volume is predicted to explain the selectivity of the inhibitors for the P. falciparum enzyme.     

Kaleidoscope

Kaleidoscope - Lewisham Children and Young People's Centre brings together 23 health, social and educational services under a single roof in southeast London. Jeremy Melvin describes how van Heyningen and Haward Architects, after winning a high-profile CABE competition, rose to the bureaucratic and architectural challenges of the project. Copyright © 2007 John Wiley & Sons, Ltd.