Faraday Discussions最新文献

Self-assembling peptide hydrogels (SAPHs) are increasingly recognised for their potential in biomedical and bioelectronic applications, with recent work focusing on exploiting the understanding of molecular self-assembly across the length scales. The resulting soft hydrogel materials are typically formulated by exploiting the self-assembly of short peptides into fibrillar aggregates that entangle and associate into networks. As more complex systems are thought to be needed to accommodate the needs of various applications, the mixing of peptides to form mixed SAPHs has come to the fore as a potential approach to design new systems with tailored and functional properties. This strategy has raised the question of whether mixing peptides with different chemical structures results in co-assembly or the formation of distinct fibrillar aggregates. In this work, we have used the FITC/Dabcyl FRET pair to investigate the co-assembly of a set of amphipathic short peptides. Our results show that the occurrence of co-assembly is affected the peptides’ physicochemical properties, in particular solubility and hydrophobic residue side-group nature.

Observational data collected in December 2014 at the base camp of Mount Everest, Nepal, indicated frequent new particle formation events of pure biogenic origin. Those events were speculated to be controlled by the along-valley winds forming in the valley connecting the Indo-Gangetic plain to the observational site, the Nepal Climate Observatory-Pyramid. The valley winds funnel highly oxygenated organic molecules of biogenic origin to higher elevations where they nucleate. The mechanism was referred to as “The Himalayan aerosol factory”. Its geographical extent and climate implications are currently unknown. In view of this, we conducted numerical chemical model simulations to corroborate the presence of the mechanism, and to quantify its geographical extent. Our numerical simulations confirmed that biogenic emissions located in the valleys can be converted into ultra-low volatility organic compounds, transported to the observational site by the along-valley winds, and therein nucleate. The overall time scale of the process, from the release of biogenic emissions to the conversion to ultra-low volatile organic compounds to the arrival time at the observational site, was found to be around 4 hours, consistent with the predicted along-valley winds intensity and the geographical distribution of biogenic emissions. A first estimation of the maximum injection height of biogenic particles, and highly oxygenated organic molecules, indicated the presence of efficient nucleating gases and biogenic particles at an elevation as high as 5000–6000 m a.s.l. These results suggest that the Himalayan chain, under specific weather conditions, is a main contributor to the biogenic aerosol loads in the free troposphere. Considering these findings, field campaigns, especially at the entrance of the valley’s floors, and research consortia supporting atmospheric research in Asian mountain regions, are highly encouraged.

A biomimetic peptide (P₁₁-4), which is predominantly negatively-charged, facilitates the nucleation of hydroxyapatite (HAp). P₁₁-4 self-assembles into fibrils via β-sheet formation, creating a 3D-gel-network. Here, X-ray nanoimaging and correlative scanning electron microscopy (SEM) investigated P₁₁-4's surface chemistry and its ability to nucleate HAp in the absence of the 3D-gel-network. P₁₁-4 was deposited on silicon nitride (SiN) windows, which were immersed in a mineralising solution (MS) and then mapped using nano-X-ray fluorescence (n-XRF) and differential phase contrast imaging at the hard X-ray nanoprobe beamline (I14) at Diamond Light Source. Elemental calcium and phosphorus maps were extracted using n-XRF, and compared with and without P₁₁-4. The windows were subsequently mapped using SEM and Energy Dispersive Spectroscopy (EDS) to confirm the morphology and elemental compositions of the formed structures. The calcium : phosphorus ratios were calculated to identify the phases formed. P₁₁-4 increased the calcium and phosphorus signals with time in MS compared to the control (without P₁₁-4). After 12 hours in MS, calcium ions accumulated on the deposited β-sheets, attracting phosphorus ions at later time points. From the morphology in the images and EDS analysis, the spherical calcium phosphate (CaP) structures appeared to be amorphous, indicating the formation of precursors, likely amorphous CaP, at early time points. In the presence of P₁₁-4, these structures grew and fused into larger CaP formations over time, unlike in the control. Nano-imaging techniques highlighted that P₁₁-4's surface chemistry accelerates the kinetics and controls the initial CaP crystallisation process, resulting in an amorphous CaP phase.

Shark teeth are considered excellent bio-archives because of their high abundance and preservation potential. Chemical proxies recorded by the teeth enameloid layers are used to interpret ecological and environmental parameters throughout the geological record. The use of these proxies relies on the assumption that biomineralization processes for enameloid formation have remained constant during shark evolution. Here, we test such an assumption by comparing the chemical composition at the nanoscale, using the technique of atom probe tomography (APT), of enameloid in modern and fossil shark teeth. Results indicate that there are clear differences in the chemistry at the core and inter-crystalline grain boundaries of fluorapatite crystals. These boundaries are enriched in strontium in all shark teeth, whereas there are differences in the distribution of magnesium, sodium, and iron. Teeth of the modern shark Isurus oxyrinchus have magnesium and sodium distributed at the inter-crystalline grain boundaries. Teeth of Eocene fossil sharks, Striatolamia macrota and Macrorhizodus praecursor, have a unique distribution of iron, at the inter-crystalline boundaries, and sodium, at the core of the crystals. This observation may indicate that biomineralization processes resulting in enameloid formation are not constant across the phylogeny of sharks. Overall, our findings strongly suggest that the enameloid content and distribution of magnesium, iron, strontium, and sodium are highly controlled by biomineralization processes. The role of magnesium and sodium seems to be similar in mammalian enamel and shark enameloid formation. Yet, nanoscale chemical differences, such as the presence of strontium in tooth enameloid, are likely associated to functional morphology.

Bone contains diverse structures. In fast-growing large animals, fibrolamellar bone is formed first and is then gradually replaced by remodelled bone with secondary osteons. Using position-resolved X-ray diffraction and X-ray fluorescence as a 2D multimodal microscopy technique, the nature of biomineral nanocrystals is investigated in bovine bone. Systematic spatial variations are found, for example, with the crystallite size increasing with distance from the bone growth front. The growth front is found to be sharply enriched in Zn, which is speculated to be related to the presence of metal-containing enzymes. Upon remodelling, the formed secondary osteons have a lower degree of mineralization, different lattice constants, and smaller nanocrystal sizes than the primary bone. The results underline the need for spatially resolved techniques for understanding bone biomineralization.

At the nanoscale, lamellar bone tissue mineralization ensues via heteronucleation of small mineral foci within the osteoid. The foci grow to produce a mature, volume-filling tessellation pattern at the micrometer-scale. Mineralization-inhibiting osteopontin (OPN) mediates this bone mineralization pathway and, eventually, the microscale properties of bone tissue. Using 2D and 3D electron microscopy, here we have assessed how the abundance of OPN can affect nanoscale mineralization, mineral ripening, and microscale patterning of mineral in normal wild-type mouse bone, and we compare that to mutant mouse models having elevated OPN (Fgf23^−/− and Hyp mice). When OPN is elevated, volume-filling mineral tessellation was incomplete (showing a four-fold increase in mineral surface area in the vicinity of the mineralization front in Hyp bone). Immunogold labeling showed excessive OPN in the foci, suggesting an arrest of their growth and an interruption of the pathway towards microscale tessellation. In Fgf23^−/− mice, electron tomography and 3D focused ion beam–scanning electron microscopy (FIB-SEM) imaging of mineral foci show instances of core–shell morphology with crystalline mineral confined to the focus interior, and an amorphous nanogranular texture persisting in the outer shell. Electron energy-loss spectroscopy, which is sensitive to nanoscale elemental composition, showed a lower Ca/P ratio at the periphery of Hyp foci, consistent with a more amorphous mineral character, suggesting that OPN may play a role in delaying the amorphous-to-crystalline transition. These aspects of nanoscale mineral maturation in mutant mice having elevated OPN implicate this protein as a fine-tuning regulator of mineralization kinetics, mineral composition, and mechanical properties of bone.

Bone mineralization during embryonic development requires the transport and deposition of an enormous amount of mineral precursors. In avian embryos, blood vessels play a dual role in this context: facilitating the demineralization of the eggshell to supply calcium and other minerals on the one hand, and mediating their deposition into the developing skeleton on the other. Understanding the interface between blood vessels and the surrounding tissues is therefore crucial for unraveling the mechanisms underlying biomineralization. However, visualizing this interface poses significant challenges and requires imaging methods that preserve the ultrastructure in a close-to-native state. Here we present a detailed methodology for a cryogenic correlative light and electron microscopy (cryo-CLEM) workflow to investigate the transport of mineral precursors in blood vessels of the femur of quail embryos during bone development. To achieve this, we use a fluorophore-conjugated antibody to label endothelial cells, which form the inner lining of blood vessels and which mediate exchanges between the bloodstream and developing tissues. This approach enables precise localization of blood vessels through fluorescence microscopy, which is subsequently correlated with 3D high-resolution electron microscopy using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM). This methodology allows imaging of a sufficient volume to observe both the lumen of the blood vessels and the surrounding matrix, providing deeper insights into calcium transport and bone mineralization during quail embryogenesis.

Coccolithophore microalgae intracellularly produce nanostructured calcitic platelets, known as coccoliths, through a biologically-controlled mineralization process. Mature coccoliths are secreted to the cell surface and assembled into a shell that envelops the cell. The large-scale global production of coccoliths, followed by their sedimentation to the ocean floor, significantly contributes to carbon cycling. Despite progress in understanding the biomineralization pathway of coccoliths, we are still limited in our ability to predict how future climate conditions will impact coccolith formation and thus ocean carbon fluxes. Investigating coccolith biomineralization at the single-cell level is therefore critical to advance our understanding but remains challenging since current imaging techniques lack the combined spatial and temporal resolution coupled with element-specific detection to follow processes in situ. In light of this gap, nanobeam-scanning X-ray fluorescence microscopy (nano-XRF) in the hard X-ray regime is employed here to investigate the intracellular elemental distribution of the coccolithophore Gephyrocapsa huxleyi (formerly Emiliania huxleyi) achieving a resolution of 100 nm and elemental detection from phosphorus (P) to zinc (Zn). Calcium- and phosphorus-rich intracellular bodies, previously proposed to be involved in coccolith biomineralization, were observed in cells initially prepared ex situ by drying. Interestingly, nano-XRF imaging reveals metal species (e.g., Mn, Fe, Zn) within these bodies that were not detected in earlier studies, suggesting multiple biological roles for these structures. Moving towards native-state imaging, G. huxleyi was then imaged in the hydrated state using a dedicated liquid cell device. Measurements were performed on G. huxleyi cells both with and without coccolith shell in sea water medium and compared to those of dried cells, demonstrating comparable image quality. The future potential and limitations of liquid cell nano-XRF imaging for coccolithophores and other microorganisms are further discussed.

We present a highly sensitive coherent Raman microscopy approach, which allows for the tridimensional (3D) imaging of a series of carbonate polymorphs in marine organisms. CaCO₃ biomineralization occurs from the transformation of metastable amorphous precursors and other crystalline phases into a final crystalline phase. Understanding biomineralization pathways requires identifying this physico-chemical temporal sequence. Our approach exploits the different vibrational signatures of amorphous calcium carbonate, aragonite, calcite, Mg-calcite or hemi-hydrated calcium carbonate. This optical method enables the production of spatially and spectrally resolved images of the different compounds. When applied on the growing edge of post-mortem samples of both Pinctada margaritifera pearl oyster shell and Stylophora pistillata coral, it allows for inferring a temporal crystallisation sequence. We thus highlight the existence of intermediate crystalline phases, involving magnesian calcite or hemi-hydrated calcium carbonate, respectively.