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Abstract: Electron tomography is a unique technique for imaging the microstructure of materials with a nanometer resolution. The signal-to-noise ratio of electron tomograms is, however, often too low for a reliable segmentation-based image analysis. We derive a general relation between the grey-tone correlation function of the tomograms and the 2-point correlation function of the morphology, which enables us to analyse quantitatively the grey-tone correlation function with a morphological model of the material. The methodology is applied to SBA-15 ordered mesoporous silica. The three-dimensional grey-tone correlation function obtained from electron tomography is analysed in terms of a hexagonal array of Gaussian independent pores. The model enables us to relate the morphology obtained from the 2-point correlation function to macroscopic characterization data of the material, notably small-angle X-ray scattering and nitrogen adsorption. [Copyright &y& Elsevier]

Abstract: Increased computer speed has helped to proliferate tomography throughout the geosciences. Although best known from the medical CATscan, tomography is also a powerful tool for geological problems. Whereas qualitative tomography is widely used, quantitative data from tomograms are not so commonly available. Presented here are two programs, Electron Tomography Segmentation, surface Area, and Volume (ETSAV) and Electron Tomography CUTter (ETCut), that were written to obtain quantitative volume and surface-area data from tomograms. Based on a specified threshold value, ETSAV distinguishes objects within a tomogram and then returns volume and surface-area data for each object. If object separation is unsatisfactory using a single threshold, ETCut is called to digitally separate objects that appear connected in the tomogram, allowing ETSAV to perform its functions. By knowing the nature of the object of interest, error can be corrected to, on average, less than 5% for a single object; combined volumes of many particles of different sizes may result in lesser errors. A section of the Brenham pallasite meteorite was examined using the programs. Olivine comprises 67.2% of the volume (50.4%wt%), followed by FeNi metal at 23.1% (39.3%wt%), troilite at 4.4% (4.8%wt%), and schreibersite at 3.4% (5.5%wt%). In all, 56.1% and 44.7% of the troilite and schreibersite surface areas, respectively, border olivine, suggesting that they wet olivine. Since the programs can be applied to any tomogram, from any field, there are many potential applications. [Copyright &y& Elsevier]

In a recent letter to the editor Prof Khosravi-Darani responded to our paper ''Unravelling mechanisms of protein and lipid oxidation in mayonnaise at multiple length scales". In our work, we observed liposomes in the continuous phase of mayonnaise. In the letter the objection was made that liposomes cannot be formed in a non-aqueous phase which, however, was not argued in our publication. As mayonnaise is an oil-in-water (O/W) emulsion and its continuous phase is aqueous, liposomes may be observed in this phase. Therefore, the objection from Prof Khosravi-Darani does not apply to our work. [ABSTRACT FROM AUTHOR]

• LDL particles engage in multi-scale aggregation in the continuous phase of mayonnaise. • Micronscale localisation of protein free radicals with a fluorescent spintrap. • Local protein oxidation induced by local lipid oxidation • At the droplet interface dispersed proteins undergo lipid-radical induced oxidation. • Protein oxidation also occurs in LDL particles in the continuous phase. In mayonnaise, lipid and protein oxidation are closely related and the interplay between them is critical for understanding the chemical shelf-life stability of mayonnaise. This is in particular the case for comprehending the role of low-density lipoprotein (LDL) particles acting as a main emulsifier. Here, we monitored oxidation and the concomitant aggregation of LDLs by bright-field light microscopy and cryogenic transmission electron microscopy. We further probed the formation of protein radicals and protein oxidation by imaging the accumulation of a water-soluble fluorescent spin trap and protein autofluorescence. The effect of variation of pH and addition of EDTA on the accumulation of the spin trap validated that protein radicals were induced by lipid radicals. Our data suggests two main pathways of oxidative protein radical formation in LDL particles: (1) at the droplet interface, induced by lipid free radicals formed in oil droplets, and (2) in the continuous phase induced by an independent LDL-specific mechanism. [ABSTRACT FROM AUTHOR]

Many food emulsions, such as mayonnaise or infant formula, are stabilized by combinations of proteins and phospholipids that are concomitantly present at the oil-water interface. It is expected that the physical, as well as the oxidative stability of emulsions are affected by the interfacial composition. Controlling the interfacial composition can therefore be a means to improve emulsion stability, and in particular lipid oxidation. In this work, we varied the ratio of pea protein and sunflower phosphatidylcholine and investigated the resulting interfacial composition and oxidative stability of oil-in-water (O/W) emulsions prepared at fixed pea protein concentration. Increasing the phospholipid concentration led to a monotonic decrease in the adsorbed proteins and to an increase in the adsorbed phospholipids. Cryo-transmission electron microscopy revealed a slight decrease in interfacial thickness, measuring 2.8 nm for pea protein alone, compared to 2.3 nm at the highest phosphatidylcholine-to-pea protein ratio (PC/sPPI) of 0.8 (w/w), and a slight decrease in interfacial roughness, albeit that the differences are small. The oxidative stability of the emulsions globally increased with increasing the PC/sPPI ratio, with the exception of the system with a PC/sPPI ratio of 0.6, which was more sensitive to oxidation than all the other PC-containing emulsions. This peculiar behavior is discussed in the context of model interfacial films of comparable mixed compositions, which exhibit discrete spherical structures and strands. Our results suggest that the PC/sPPI ratio determines the specific interfacial structure that is formed (i.e., packing and patchiness), and it can be expected that thereby the oxidative stability of O/W emulsions stabilized by proteins and phospholipids is modulated. [Display omitted] • For all emulsifier ratios, the emulsions were stable to coalescence. • Phosphatidylcholine (PC)-containing emulsions resisted flocculation. • Interfacial heterogeneity decreased with increasing PC/pea protein (PP) ratio. • At high PC/PP ratio, PC became dominant at the oil-water interface. • This ratio non-monotonically affects oxidative stability and interfacial structure. [ABSTRACT FROM AUTHOR]

Abstract: The structural details of a bifunctional Pt/USY catalyst were studied using electron tomography. As a part of a fundamental study on the synthesis of Pt/USY catalyst, H2PtCl6 precursor was used for the impregnation of USY zeolite support as a source of negatively charged PtCl6 2− ions in order to restrict interaction with acidic sites of USY zeolite. After heat treatments, it was visualized in 3D that some Pt particles were 3–4nm in size, while the majority maintained the size of 1.2–1.5nm which corresponds to the diameter of the zeolite Y micropore cavities (1.2nm). Electron tomography further revealed that 3–4nm Pt particles seem to be entrapped in the zeolite crystal, without preferential location in mesopores or at the surface of the crystals. Quantitative image analysis provided the diameters (compared with EXAFS results) and the nearest neighbor distances of hundreds of imaged Pt particles. [Copyright &y& Elsevier]

Sampling limitations in electron microscopy questions whether the analysis of a bulk material is representative, especially while analyzing hierarchical morphologies that extend over multiple length scales. We tackled this problem by automatically acquiring a large series of partially overlapping (S)TEM images with sufficient resolution, subsequently stitched together to generate a large-area map using an in-house developed acquisition toolbox ( TU/e Acquisition ToolBox ) and stitching module ( TU/e Stitcher ). In addition, we show that quantitative image analysis of the large scale maps provides representative information that can be related to the synthesis and process conditions of hierarchical materials, which moves electron microscopy analysis towards becoming a bulk characterization tool. We demonstrate the power of such an analysis by examining two different multi-phase materials that are structured over multiple length scales. [ABSTRACT FROM AUTHOR]

In electron tomography, the fidelity of the 3D reconstruction strongly depends on the employed reconstruction algorithm. In this paper, the properties of SIRT, TVM and DART reconstructions are studied with respect to having only a limited number of electrons available for imaging and applying different angular sampling schemes. A well-defined realistic model is generated, which consists of tubular domains within a matrix having slab-geometry. Subsequently, the electron tomography workflow is simulated from calculated tilt-series over experimental effects to reconstruction. In comparison with the model, the fidelity of each reconstruction method is evaluated qualitatively and quantitatively based on global and local edge profiles and resolvable distance between particles. Results show that the performance of all reconstruction methods declines with the total electron dose. Overall, SIRT algorithm is the most stable method and insensitive to changes in angular sampling. TVM algorithm yields significantly sharper edges in the reconstruction, but the edge positions are strongly influenced by the tilt scheme and the tubular objects become thinned. The DART algorithm markedly suppresses the elongation artifacts along the beam direction and moreover segments the reconstruction which can be considered a significant advantage for quantification. Finally, no advantage of TVM and DART to deal better with fewer projections was observed. [ABSTRACT FROM AUTHOR]

Phosvitins is a key egg yolk protein and can often be found in food emulsions. It is highly phosphorylated and hence phosvitins contain a large number of negatively charged amino acid groups, for pH > pI. Due to the presence of these phophoserines, phosvitins bind to positively charged multivalent ions. Its amphipolar structure makes phosvitin also an efficient emulsion stabilizer. The ion binding and emulsifying abilities of phosvitins are influenced by environmental conditions such as pH and ionic strength. Various physicochemical properties of phosvitins such as size and charge under various conditions, and how they self-assemble via multivalent ions are not well-understood. To gain more insight into these physical characteristics, we performed high brilliance synchrotron small angle X-ray scattering (SAXS) on phosvitin solutions. The structure factor S (q) obtained from the SAXS profiles showed that the double layer interactions between charged phosvitin assemblies are strongly affected by pH and ionic strength of the buffer. The effects of multivalent ions (Mg2+, Fe3+) on the size and structure of phosvitin were also investigated. Our results revealed that the aggregation of phosvitin mediated by metal ions is induced by electrostatic attraction and only occurs beyond a threshold cation concentration, where phosvitin loses long-range electrostatic double layer repulsions. These findings help understanding the effects of metal ions and pH on phosvitin in more complex environments such as food emulsions. [Display omitted] • The physicochemical properties of phosvitins such as size and charge were measured using scattering. • An improved purification method was developed to prepare high-purity phosvitins. • SAXS yielded the structure factor S (q), showing phosvitins behave as charged colloidal spheres. • Adding multivalent cations can induce aggregation of phosvitins. • A threshold cation concentration is needed to initiate phosvitin aggregation. [ABSTRACT FROM AUTHOR]

Abstract: Cells of Synechocystis sp. PCC 6803 lacking photosystem I (PSI-less) and containing only photosystem II (PSII) or lacking both photosystems I and II (PSI/PSII-less) were compared to wild type (WT) cells to investigate the role of the photosystems in the architecture, structure, and number of thylakoid membranes. All cells were grown at 0.5μmol photons m−2 s−1. The lumen of the thylakoid membranes of the WT cells grown at this low light intensity were inflated compared to cells grown at higher light intensity. Tubular as well as sheet-like thylakoid membranes were found in the PSI-less strain at all stages of development with organized regular arrays of phycobilisomes on the surface of the thylakoid membranes. Tubular structures were also found in the PSI/PSII-less strain, but these were smaller in diameter to those found in the PSI-less strain with what appeared to be a different internal structure and were less common. There were fewer and smaller thylakoid membrane sheets in the double mutant and the phycobilisomes were found on the surface in more disordered arrays. These differences in thylakoid membrane structure most likely reflect the altered composition of photosynthetic particles and distribution of other integral membrane proteins and their interaction with the lipid bilayer. These results suggest an important role for the presence of PSII in the formation of the highly ordered tubular structures. [Copyright &y& Elsevier]

Abstract: Electron-holographic tomography (EHT), that is, the combination of off-axis electron holography with electron tomography, was successfully applied for the quantitative 3D mapping of electrostatic potentials at the nanoscale. Here we present the first software package (THOMAS) for semi-automated acquisition of holographic tilt series, a prerequisite for efficient data collection. Using THOMAS, the acquisition time for a holographic tilt series, consisting of object and reference holograms, is reduced by a factor of five on average, compared to the previous, completely manual approaches. Moreover, the existing software packages for retrieving amplitude and phase information from electron holograms have been extended, now including a one-step procedure for holographic tilt series reconstruction. Furthermore, a modified SIRT algorithm (WSIRT) was implemented for the quantitative 3D reconstruction of the electrostatic potential from the aligned phase tilt series. Finally, the application of EHT to a polystyrene latex sphere test-specimen and a pn-doped Ge ‘needle’-shaped specimen are presented, illustrating the quantitative character of EHT. For both specimens the mean inner potential (MIP) values were accurately determined from the reconstructed 3D potential. For the Ge specimen, additionally the ‘built-in’ voltage across the pn junction of 0.5V was obtained. [Copyright &y& Elsevier]

The multiscale pore structure of mesoporous silica microspheres plays an important role for tuning mass transfer kinetics in technological applications such as liquid chromatography. While local analysis of a pore network in such materials has been previously achieved, multiscale quantification of microspheres down to the nanometer scale pore level is still lacking. Here we demonstrate for the first time, by combining low convergence angle scanning transmission electron microscopy tomography (LC-STEM tomography) with image analysis and lattice Boltzmann simulations, that the multiscale pore network of commercial mesoporous silica microspheres can be quantified. This includes comparing the local tortuosity and intraparticle diffusion coefficients between different regions within the same microsphere. The results, spanning more than two orders of magnitude between nanostructures and entire object, are in good agreement with bulk characterization techniques such as nitrogen gas physisorption and add valuable local information for tuning mass transfer behavior (in liquid chromatography or catalysis) on the single microsphere level. Image 1 • Imaging and analysis workflow for materials with a complex hierarchical ordering. • Quantitative analysis of the 3D pore network of mesoporous silica microspheres. • Bulk porosity and pore size distribution match properties of a single microsphere. • Local variations between different regions within the same sphere are observed. • Effective diffusion coefficient is simulated in different regions of the particle. [ABSTRACT FROM AUTHOR]