The Ca:P ratio in a certified standard of hydroxyapatite was determined by Xray spectrometry (XRS), with the X-rays excited by both electrons and ions using energy dispersive spectroscopy on the scanning electron microscope (SEM-EDS) and particle induced X-ray emission (PIXE). The certified value of Ca:P was accurately verified by 3 MeV 4 He + Rutherford Backscattering Spectrometry (RBS).We show that the demonstrably rough surface of this sample does not cause perturbation of the Ca:P ratio within the uncertainties of each of the XRS measurements. Paper O4-8, EXRS

Porphyry-type deposits are the world’s main source of copper and molybdenum and provide a large proportion of gold and other metals. However, the mechanism by which mineralising fluids are extracted from source magmas and transported upwards into the ore-forming environment is not clearly understood. Here we use field, micro-textural and geochemical techniques to investigate field relationships and samples from a circa 8 km deep cross-section through the archetypal Yerington porphyry district, Nevada. We identify an interconnected network of relatively low-temperature hydrothermal quartz that is connected to mineralised miarolitic cavities within aplite dykes. We propose that porphyry-deposit-forming fluids migrated from evolved, more water-rich internal regions of the underlying Luhr Hill granite via these aplite dykes which contained a permeable magmatic crystal mush of feldspar and quartz. The textures we describe provide petrographic evidence for the transport of fluids through crystal mush dykes. We suggest that this process should be considered in future models for the formation of porphyry- and similar-type deposits.

"Total-IBA" implies the synergistic use of multiple IBA techniques. It has been claimed that Total-IBA inherits the accuracy of the most accurate IBA technique used. A specific example is now given of this where (in vacuo) EBS/PIXE of a glass sample uniform in depth is validated against absolutely calibrated EPMA of the same sample. The EPMA results had a mass closure gap of 2.0±0.6 wt%; the full PIXE analysis determined the composition of this missing 2 wt%. The PIXE calibration was against a single certified glass sample, with uncertainties per line ~10 %. Benchmarking also demonstrates ~10% underestimation of the Si scattering cross-section at proton energies ~3 MeV. But the Total-IBA determination of the silica content had a low standard uncertainty of about 2 %. This is due to the strong constraints of both the chemical prior and also the mass closure properties of the EBS. Irradiation-induced sodium migration in this soda-lime glass is explored.

Proton-induced X-ray emission combined with a scanning proton microprobe has been used to investigate the distribution of inorganic elements in silicifying macrohairs from the lemma of the grass Phalaris canariensis L. Results, presented in the form of X-ray spectra and two-dimensional elemental maps, showed that the inorganic elements Si, K, P, S and Cl were spatially organized within the macrohairs during the different stages of silicification. Much lower quantities of all elements except silicon were found in the mature macrohairs. It is suggested that these changes in the inorganic content of the macrohairs are related to a silicification process that is associated with cellular activity.

AbstractProtein aggregation is a widespread process leading to deleterious consequences in the organism, with amyloid aggregates being important not only in biology but also for drug design and biomaterial production. Insulin is a protein largely used in diabetes treatment and its amyloid aggregation is at the basis of the so-called insulin-derived amyloidosis. Here we uncover the major role of zinc in both insulin dynamics and aggregation kinetics at low pH, where the formation of different amyloid superstructures (fibrils and spherulites) can be thermally induced. Amyloid aggregation is accompanied by zinc release and the suppression of water-sustained insulin dynamics, as shown by particle-induced X-ray emission and X-ray absorption spectroscopy and by neutron spectroscopy, respectively. Our study shows that zinc binding stabilizes the native form of insulin by facilitating hydration of this hydrophobic protein and suggests that introducing new binding sites for zinc can improve insulin stability and tune its aggregation propensity.Statement of SignificanceLocalized amyloidosis occurs at insulin injection sites for diabetes treatment, leading to deleterious inflammations known as insulin-derived amyloidosis. Amyloid superstructures are also promising candidates in the field of biomaterials. Here we revealed that zinc, coordinated to insulin in the native form, is released upon amyloid aggregation, when insulin forms superstructures known as fibrils and spherulites. Zinc release leads to a full suppression of functionally essential protein dynamics through a modification of the protein’s hydration properties and completely modifies insulin amyloid kinetics. The results suggest that changes in protein hydration upon zinc binding/release modifies both stability and dynamics of insulin and might then be a general strategy to control protein stability and tune protein aggregation into amorphous and ordered superstructures.