Prenormative verification and validation of a protocol for measuring magnetite-maghemite ratios in magnetic nanoparticles

An important step in establishing any new metrological method is a prenormative interlaboratory study, designed to verify and validate the method against its stated aims. Here, the 57Fe Mössbauer spectrometric 'centre of gravity' (COG) method was tested as a means of quantifying the magnetite/maghemite (Fe3O4/γ-Fe2O3) composition ratio in biphasic magnetic nanoparticles. The study involved seven laboratories across Europe and North and South America, and six samples—a verification set of three microcrystalline mixtures of known composition, and a validation set of three nanoparticle samples of unknown composition. The spectra were analysed by each participant using in-house fitting packages, and ex post facto by a single operator using an independent package. Repeatability analysis was performed using Mandel's h statistic and modified Youden plots. It is shown that almost all (83/84) of the Mandel h statistic values fall within the 0.5% significance level, with the one exception being borderline. Youden-based pairwise analysis indicates the dominance of random uncertainties; and in almost all cases the data analysis phase is only a minor contributor to the overall measurement uncertainty. It is concluded that the COG method is a robust and promising candidate for its intended purpose

Genome-wide methylation is modified by caloric restriction in<i> Daphnia magna</i>

Background The degradation of epigenetic control with age is associated with progressive diseases of ageing, including cancers, immunodeficiency and diabetes. Reduced caloric intake slows the effects of ageing and age-related disease in vertebrates and invertebrates, a process potentially mediated by the impact of caloric restriction on epigenetic factors such as DNA methylation. We used whole genome bisulphite sequencing to study how DNA methylation patterns change with diet in a small invertebrate, the crustacean Daphnia magna. Daphnia show the classic response of longer life under caloric restriction (CR), and they reproduce clonally, which permits the study of epigenetic changes in the absence of genetic variation. Results Global cytosine followed by guanine (CpG) methylation was 0.7–0.9%, and there was no difference in overall methylation levels between normal and calorie restricted replicates. However, 333 differentially methylated regions (DMRs) were evident between the normally fed and CR replicates post-filtering. Of these 65% were hypomethylated in the CR group, and 35% were hypermethylated in the CR group. Conclusions Our results demonstrate an effect of CR on the genome-wide methylation profile. This adds to a growing body of research in Daphnia magna that demonstrate an epigenomic response to environmental stimuli. Specifically, gene Ontology (GO) term enrichment of genes associated with hyper and hypo-methylated DMRs showed significant enrichment for methylation and acyl-CoA dehydrogenase activity, which are linked to current understanding of their roles in CR in invertebrate model organisms

A Closer Look at Fe(II) Passivation of Goethite

Our understanding of how Fe(II) reacts with Fe(III) oxides has evolved based on evidence for electron transfer at the oxide-water interface and Fe(II)-catalyzed recrystallization. There is, however, some evidence that these, and other processes, such as microbial reduction, cease after continued contact with Fe(II) as the Fe oxide becomes "passivated". Here, we explore the mechanism of oxide passivation by measuring whether exposure to Fe(II) inhibits Fe(II)-goethite electron transfer, and whether this inhibition is reversible. To quantify the extent of electron transfer, we used selective isotope labeling with Fe Mössbauer spectroscopy. We provide experimental evidence that pre-exposure to Fe(II) alters the products formed and inhibits the extent of electron transfer between goethite and Fe(II). We demonstrate that the goethite surface can accumulate a passivation layer of sorbed Fe(II) and that further electron transfer between Fe(II) and goethite is inhibited. Importantly, however, electron transfer can be partially restored upon removal of the layer of Fe(II) by extraction or oxidation. Our results suggest that in environments that are commonly subjected to transient geochemical fluctuations, electron transfer between Fe(II) and Fe oxides, and processes linked to it are likely to be relevant beyond just short time scales. 5