Chemical Fixation Creates Nanoscale Clusters on the Cell Surface by Aggregating Membrane Proteins

Chemical fixations have been thought to preserve the structures of the cells or tissues. However, given that the fixatives create crosslinks or aggregate proteins, there is a possibility that these fixatives create nanoscale artefacts by aggregation of membrane proteins which move around freely to some extent on the cell surface. Despite this, little research has been conducted about this problem, probably because there has been no method for observing cell surface structures at the nanoscale. In this study, we have developed a new method to observe cell surfaces stably and with high resolution using atomic force microscopy and a microporous silicon nitride membrane. We demonstrate that the size of the protrusions on the cell surface is increased after treatment with three commonly used fixatives and show that these protrusions were created by the aggregation of membrane proteins by fixatives. These results call attention when observing fixed cell surfaces at the nanoscale.

The dielectric response of phenothiazine-based glass-formers with different molecular complexity

We examined a series of structurally related glass-forming liquids in which a phenothiazine-based tricyclic core (PTZ) was modified by attaching n-alkyl chains of different lengths (n = 4, 8, 10). We systematically disentangled the impact of chemical structure modification on the intermolecular organization and molecular dynamics probed by broadband dielectric spectroscopy (BDS). X-ray diffraction (XRD) patterns evidenced that all PTZ-derivatives are not ‘ordinary’ liquids and form nanoscale clusters. The chain length has a decisive impact on properties, exerting a plasticizing effect on the dynamics. Its elongation decreases glass transition temperature with slight impact on fragility. The increase in the medium-range order was manifested as a broadening of the dielectric loss peak reflected in the lower value of stretching parameter βKWW. A disagreement with the behavior observed for non-associating liquids was found as a deviation from the anti-correlation between the value of βKWW and the relaxation strength of the α-process. Besides, to explain the broadening of loss peak in PTZ with the longest (decyl) chain a slow Debye process was postulated. In contrast, the sample with the shortest alkyl chain and a less complex structure with predominant supramolecular assembly through π–π stacking exhibits no clear Debye-mode fingerprints. The possible reasons are also discussed.

Excitation of Surface Electromagnetic Waves at the Silver/NaCl Aqueous Solution Interface

The results of a study of the dynamics of the excitation angle of a surface electromagnetic wave (SEW) at the interface between a silver/NaCl aqueous solution of concentrations 10−3, 10−4, 10−6 and 10−10 M are presented. It is shown that the rate of change in the excitation angle of SEW is proportional to the concentration of the solution up to a dilution of 10−10 M. The observed effect is explained by the formation of silver chloride on the surface of the silver film as a result of the interaction of solution ions with nanoscale clusters of the silver film. The proposed technique for measuring the dynamics of the excitation angle of SEW can be used for a comparative analysis of the concentrations of highly dilute solutions, as well as for studying the formation and dynamics of transition layers and physicochemical processes in the near-surface regions.

Heterostructured CoOx–TiO2 Mesoporous/Photonic Crystal Bilayer Films for Enhanced Visible-Light Harvesting and Photocatalysis

Heterostructured bilayer films, consisting of co-assembled TiO2 photonic crystals as the bottom layer and a highly performing mesoporous P25 titania as the top layer decorated with CoOx nanoclusters, are demonstrated as highly efficient visible-light photocatalysts. Broadband visible-light activation of the bilayer films was implemented by the surface modification of both titania layers with nanoscale clusters of Co oxides relying on the chemisorption of Co acetylacetonate complexes on TiO2, followed by post-calcination. Tuning the slow photon regions of the inverse opal supporting layer to the visible-light absorption of surface CoOx oxides resulted in significant amplification of salicylic-acid photodegradation under visible and ultraviolet (UV)–visible light (Vis), outperforming benchmark P25 films of higher titania loading. This enhancement was related to the spatially separated contributions of slow photon propagation in the inverse opal support layer assisted by Bragg reflection toward the CoOx-modified mesoporous P25 top layer. This effect indicates that photonic crystals may be highly effective as both photocatalytically active and backscattering layers in multilayer photocatalytic films.

The geochemical and geochronological implications of nanoscale trace-element clusters in rutile

The geochemical analysis of trace elements in rutile (e.g., Pb, U, and Zr) is routinely used to extract information on the nature and timing of geological events. However, the mobility of trace elements can affect age and temperature determinations, with the controlling mechanisms for mobility still debated. To further this debate, we use laser-ablation–inductively coupled plasma–mass spectrometry and atom probe tomography to characterize the micro- to nanoscale distribution of trace elements in rutile sourced from the Capricorn orogen, Western Australia. At the >20 µm scale, there is no significant trace-element variation in single grains, and a concordant U-Pb crystallization age of 1872 ± 6 Ma (2σ) shows no evidence of isotopic disturbance. At the nanoscale, clusters as much as 20 nm in size and enriched in trace elements (Al, Cr, Pb, and V) are observed. The 207Pb/206Pb ratio of 0.176 ± 0.040 (2σ) obtained from clusters indicates that they formed after crystallization, potentially during regional metamorphism. We interpret the clusters to have formed by the entrapment of mobile trace elements in transient sites of radiation damage during upper amphibolite facies metamorphism. The entrapment would affect the activation energy for volume diffusion of elements present in the cluster. The low number and density of clusters provides constraints on the time over which clusters formed, indicating that peak metamorphic temperatures are short-lived, <10 m.y. events. Our results indicate that the use of trace elements to estimate volume diffusion in rutile is more complex than assuming a homogeneous medium.

Polyoxometalate clusters in minerals: review and complexity analysis

Most research on polyoxometalates (POMs) has been devoted to synthetic compounds. However, recent mineralogical discoveries of POMs in mineral structures demonstrate their importance in geochemical systems. In total, 15 different types of POM nanoscale-size clusters in minerals are described herein, which occur in 42 different mineral species. The topological diversity of POM clusters in minerals is rather restricted compared to the multitude of moieties reported for synthetic compounds, but the lists of synthetic and natural POMs do not overlap completely. The metal–oxo clusters in the crystal structures of the vanarsite-group minerals ([As3+V4+ 2V5+ 10As5+ 6O51]7−), bouazzerite and whitecapsite ([M 3+ 3Fe7(AsO4)9O8–;n (OH) n ]), putnisite ([Cr3+ 8(OH)16(CO3)8]8−), and ewingite ([(UO2)24(CO3)30O4(OH)12(H2O)8]32−) contain metal–oxo clusters that have no close chemical or topological analogues in synthetic chemistry. The interesting feature of the POM cluster topologies in minerals is the presence of unusual coordination of metal atoms enforced by the topological restraints imposed upon the cluster geometry (the cubic coordination of Fe3+ and Ti4+ ions in arsmirandite and lehmannite, respectively, and the trigonal prismatic coordination of Fe3+ in bouazzerite and whitecapsite). Complexity analysis indicates that ewingite and morrisonite are the first and the second most structurally complex minerals known so far. The formation of nanoscale clusters can be viewed as one of the leading mechanisms of generating structural complexity in both minerals and synthetic inorganic crystalline compounds. The discovery of POM minerals is one of the specific landmarks of descriptive mineralogy and mineralogical crystallography of our time.

Nanoscale Pb clustering and multi-domain Pb-mobility in zircon

<p>Uranium-Lead dating of zircon remains one of the most widely utilized and most reliable temporal records throughout Earth history. This stems from the mineral’s widespread occurrence, pristine zircon being both physically and chemically robust, and the ability to evaluate the presence of open system behavior (i.e. “concordance”) through comparison of the independent <sup>238</sup>U→<sup>206</sup>Pb, <sup>235</sup>U→<sup>207</sup>Pb, and <sup>232</sup>Th→<sup>208</sup>Pb decay chains. The phenomenon of discordance is well documented in zircon, and is typically (though not always) associated with radiation damage accumulation and Pb-loss. Despite a long history of research, the nanoscale controls on Pb mobility and Pb loss (i.e. the relative rates of radiation damage, annealing, and Pb diffusion) remain poorly defined. The unique characterization capabilities of atom probe tomography (APT) provide a novel means to study U-Pb systematics on the scale of the radiation damage, annealing and diffusion processes. APT studies have documented nanoscale heterogeneity in trace elements, Pb, and Pb isotope ratios, and correlated the <sup>207</sup>Pb/<sup>206</sup>Pb ratios within clusters to transient thermal episodes in the history of a zircon.</p><p> </p><p>This work seeks to provide a foundation for multi-scale U-Pb characterization, including how differential Pb mobility at the nanoscale can influence micron- to- grain-scale U-Pb systematics. Historically, concordia diagrams have used simple Pb-loss models to extract temporal information about the timing of Pb mobility/loss; however, these models assume <sup>207</sup>Pb and <sup>206</sup>Pb are uniformly disturbed within a grain and lost in equal proportions at the time of Pb loss. Our previous studies suggest that radiogenic Pb can be concentrated and immobilized in nanoscale clusters, leading to differential retention of Pb in clusters vs. matrix domains, and requiring a more complex treatment of isotopic shifts during any post-clustering Pb loss. This “multi-domain element (Pb) mobility” (MDEM or MDPM) influences subsequent Pb-loss trajectories on concordia diagrams, manifesting in systematic offsets for discordia as a function of the zircon crystallization age, the timing of cluster formation, and the timing of Pb mobility. These results highlight that (1) traditional interpretations of discordia in the presence of cryptic nanoscale clustering can lead to inaccuracies, and (2) multi-scale U-Pb characterization offers a means to both study discordance and to extract additional temporal information from zircon with otherwise ambiguous and/or complex Pb-loss patterns.</p>

Monodisperse Polymer Melts Crystallize via Structurally Polydisperse Nanoscale Clusters: Insights from Polyethylene

This study demonstrates that monodisperse entangled polymer melts crystallize via the formation of nanoscale nascent polymer crystals (i.e., nuclei) that exhibit substantial variability in terms of their constituent crystalline polymer chain segments (stems). More specifically, large-scale coarse-grain molecular simulations are used to quantify the evolution of stem length distributions and their properties during the formation of polymer nuclei in supercooled prototypical polyethylene melts. Stems can adopt a range of lengths within an individual nucleus (e.g., ∼1–10 nm) while two nuclei of comparable size can have markedly different stem distributions. As such, the attainment of chemically monodisperse polymer specimens is not sufficient to achieve physical uniformity and consistency. Furthermore, stem length distributions and their evolution indicate that polymer crystal nucleation (i.e., the initial emergence of a nascent crystal) is phenomenologically distinct from crystal growth. These results highlight that the tailoring of polymeric materials requires strategies for controlling polymer crystal nucleation and growth at the nanoscale.

Agglomeration of Silicon Dioxide Nanoscale Colloids in Chemical Mechanical Polishing Wastewater: Influence of pH and Coagulant Concentration

Chemical mechanical polishing (CMP) wastewater generated from semiconductor manufacturing industries is known to contain residual organic and inorganic contaminants, i.e. photoresists, acids, including silicon dioxide (SiO2), nanoparticles (NPs) and others. Nanoscale colloids in CMP wastewater have strong inclination to remain in the suspension, leading to high turbidity and chemical oxygen demand (COD). Although various types of pre-treatment have been implemented, these nanoparticles remain diffused in small clusters that pass through the treatment system. Therefore, it is crucial to select suitable pH and coagulant type in the coagulation treatment process. In this research zeta potential and dynamic light scattering measurements are applied as preliminary step aimed at determining optimum pH and coagulant dosage range based on the observation of inter particle-particle behavior in a CMP suspension. The first phase of the conducted study is to analyze nanoscale colloids in the CMP suspension in terms of zeta potential and z-average particle size as a function of pH within a range of 2 to 12. Two types of coagulants were investigated - polyaluminum chloride (PACl) and ferrous sulfate heptahydrate (FeSO4·7H2O). Similar pH analysis was conducted for the coagulants with the same pH range separately. The second phase of the study involved evaluating the interaction between nanoscale colloids and coagulants in the suspension. The dynamics of zeta potential and corresponding particle size were observed as a function of coagulant concentration. Results indicated that CMP wastewater is negatively charged, with average zeta potential of -59.8 mV and 149 d.nm at pH value of 8.7. The interaction between CMP wastewater and PACl showed that positively charged PACl rapidly adsorbed colloids in the wastewater, reducing the negative surface charge of nanoscale clusters. The interaction between CMP wastewater and FeSO4·7H2O showed that larger dosage is required to aggregate nanoscale clusters, due to its low positive value to counter negative charges of CMP wastewater.