Open Access

Show Abstract ▼

Abstract: Magnesium is attractive for the application as a temporary bone implant due to its inherent biodegradability, non-toxicity and suitable mechanical properties. The degradation process of magnesium in physiological environments is complex and is thought to be a diffusion-limited transport problem. We use a multi-scale imaging approach using micro computed tomography and transmission X-ray microscopy (TXM) at resolutions below 40 nm. Thus, we are able to evaluate the nanoporosity of the degradation layer and infer its impact on the degradation process of pure magnesium in two physiological solutions. Magnesium samples were degraded in simulated body fluid (SBF) or Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS) for one to four weeks. TXM reveals the three-dimensional interconnected pore network within the degradation layer for both solutions. The pore network morphology and degradation layer composition are similar for all samples. By contrast, the degradation layer thickness in samples degraded in SBF was significantly higher and more inhomogeneous than in DMEM+10%FBS. Distinct features could be observed within the degradation layer of samples degraded in SBF, suggesting the formation of microgalvanic cells, which are not present in samples degraded in DMEM+10%FBS. The results suggest that the nanoporosity of the degradation layer and the resulting ion diffusion processes therein have a limited influence on the overall degradation process. This indicates that the influence of organic components on the dampening of the degradation rate by the suppression of microgalvanic degradation is much greater in the present study.

Show Abstract ▼

Abstract: Ceria (cerium oxide) based materials have been widely used for catalytic applications including; fluid catalytic cracking, water gas shift reactions, solid oxide fuel cells and automotive catalytic after-treatment. It has often been the material of choice for supporting precious metals in many of the applications previously mentioned, as it can provide a high surface area and has excellent redox properties. This enables ceria to absorb oxygen into its structure and release it again, to facilitate oxidation reactions. Cerium is also one of the most abundant rare earth metals, making it a relatively cost effective material to use in industrial applications. For these reasons, cerium oxide remains to be a material of high interest for the development of cost-effective industrial catalysts and is, therefore, the focal material for this work. Modern internal combustion engine technology is being directed towards lean burn operation, involving higher air-fuel ratios in order to improve thermal efficiency. In turn, the operating temperature of modern engines is being reduced, providing less of the heat energy required to activate the catalysts in the after-treatment system. Therefore, in order to mitigate the emission from efficient lean burn engines and comply with emission regulations, the requirement for low temperature automotive catalysts is apparent. The objective of this work is to develop effective ceria based materials for the application of modern automotive after-treatment catalysis. The first approach is the use of a novel method for the preparation of a mixed oxide catalysts, which show high activity for CO and HC oxidation at low temperature. The preparation of ceria/manganese mixed oxide catalysts using a novel synthesis method has been studied and the materials were characterised to gain insights of their structure and morphology. Temperature programmed reactions using a complex mixture of reactants, before and after hydrothermal aging, were carried out to investigate their application for automotive emission control. The results from these studies were compared with more conventional ceria based materials that are often used for automotive after-treatment. A second approach used in this work is a post synthesis technique for the surface modification of ceria catalysts using ion bombardment. This technique was carried out on a commercially sourced, model catalyst. A Pt-CeO2/ZrO2 was treated with nitrogen ion irradiation and the effects of the adjustable parameters of the ion beam were investigated by carrying out temperature programmed reactions. The samples were also extensively characterised using XAFS and XPS techniques to understand the effects of the ion beam treatment on the structure, morphology and Pt dispersion of the materials.

Show Abstract ▼

Abstract: Obtaining well diffracting crystals of membrane proteins is often challenging, but chances can be improved by crystallizing them in lipidic conditions that mimic their natural membrane environments. One approach is the high lipid–detergent (HiLiDe) method, which works by mixing the target protein with high concentrations of lipid and detergent prior to crystallization. Although this approach is convenient and flexible, understanding the effects of systematically varying lipid/detergent ratios and a characterization of the lipid phases that form during crystallization would be useful. Here, a HiLiDe phase diagram is reported for the model membrane protein MhsT, which tracks the precipitation and crystallization zones as a function of lipid and detergent concentrations, and is augmented with data on crystal sizes and diffraction properties. Additionally, the crystallization of SERCA1a solubilized directly with native lipids is characterized as a function of detergent concentration. Finally, HiLiDe crystallization drops are analysed with transmission electron microscopy, which among other features reveals liposomes, stacked lamellae that may represent crystal precursors, and mature crystals with clearly discernible packing arrangements. The results emphasize the significance of optimizing lipid/detergent ratios over broad ranges and provide insights into the mechanism of HiLiDe crystallization.

Show Abstract ▼

Abstract: β-Galactosidases catalyse the hydrolysis of lactose into galactose and glucose; as an alternative reaction, some β-galactosidases also catalyse the formation of galactooligosaccharides by transglycosylation. Both reactions have industrial importance: lactose hydrolysis is used to produce lactose-free milk, while galactooligosaccharides have been shown to act as prebiotics. For some multi-domain β-galactosidases, the hydrolysis/transglycosylation ratio can be modified by the truncation of carbohydrate-binding modules. Here, an analysis of BbgIII, a multidomain β-galactosidase from Bifidobacterium bifidum, is presented. The X-ray structure has been determined of an intact protein corresponding to a gene construct of eight domains. The use of evolutionary covariance-based predictions made sequence docking in low-resolution areas of the model spectacularly easy, confirming the relevance of this rapidly developing deep-learning-based technique for model building. The structure revealed two alternative orientations of the CBM32 carbohydrate-binding module relative to the GH2 catalytic domain in the six crystallographically independent chains. In one orientation the CBM32 domain covers the entrance to the active site of the enzyme, while in the other orientation the active site is open, suggesting a possible mechanism for switching between the two activities of the enzyme, namely lactose hydrolysis and transgalactosylation. The location of the carbohydrate-binding site of the CBM32 domain on the opposite site of the module to where it comes into contact with the catalytic GH2 domain is consistent with its involvement in adherence to host cells. The role of the CBM32 domain in switching between hydrolysis and transglycosylation modes offers protein-engineering opportunities for selective β-galactosidase modification for industrial purposes in the future.

Open Access

Show Abstract ▼

Abstract: An estimated half of all proteins contain a metal, with these being essential for a tremendous variety of biological functions. X-ray crystallography is the major method for obtaining structures at high resolution of these metalloproteins, but there are considerable challenges to obtain intact structures due to the effects of radiation damage. Serial crystallography offers the prospect of determining low-dose synchrotron or effectively damage free XFEL structures at room temperature and enables time-resolved or dose-resolved approaches. Complementary spectroscopic data can validate redox and or ligand states within metalloprotein crystals. In this opinion, we discuss developments in the application of serial crystallographic approaches to metalloproteins and comment on future directions.