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We have investigated the adsorption of Pb atoms on the (100) surface of an orthorhombic Al13Co4 crystal at 300 and 573K substrate temperatures. This complex metallic alloy is an approximant to the decagonal Al-Ni-Co quasicrystal. At submonolayer coverage and at 300 K, Pb adatoms remain highly mobile and adsorb preferentially within the hollow site situated in between adjacent Al pentagonal clusters present at the surface. These experimental findings are supported by ab initio calculations based on density functional theory (DFT). For both temperature regimes, Pb adsorption leads to the formation of pseudomorphic monolayers above which the high adsorbate mobility prohibits the growth of additional layers. For the high-temperature deposition, we propose a structural model for the Pb film and discuss its relationship with the underneath substrate. [ABSTRACT FROM AUTHOR]

Abstract: Using plastic deformation tests and high-energy X-ray scattering, we examined the anelastic strain and structural anisotropy in a binary Cu64.5Zr35.5 metallic glass deformed homogeneously under uniaxial compression at 425°C, which is approximately 60°C below the glass transition temperature. For a sample quenched immediately after deformation, we find that the atomic structure observed by X-ray scattering is anisotropic with the average bond length parallel to the loading axis being smaller than that of an undeformed, structurally relaxed reference sample, while the average bond length normal to the loading axis is dilated relative to the same reference sample. For a different sample annealed at 425°C for 500s immediately following deformation, the magnitude of the structural anisotropy decreases as anelastic strain is recovered. The relationship between the atomic-scale structural rearrangements that occur during annealing and the macroscopic anelastic strain recovery is discussed. [Copyright &y& Elsevier]

Abstract: We present the results of 27Al nuclear magnetic resonance (NMR) experiments on the phase Co4Al13. These results are compared to a recent structure model [1], which demonstrates a unique bonding for Al atoms in the Co–Al–Co molecular groups. In our measurement, two 27Al signals were identified. The first one originates from Al atoms forming cages. The second signal corresponds to Al sites with exceptionally large almost axially symmetric quadrupole coupling. This finding is in perfect agreement with isolated Co–Al–Co molecular groups in accordance to Ref. [1]. [Copyright &y& Elsevier]

Abstract: The β-Al3Mg2 complex metallic alloy comprises about 1168 atoms in the giant-unit cell, making this material excellent candidate to investigate how the exceptional structural complexity and the coexistence of two different length scales – one defined by the unit-cell parameters and the other by the cluster substructure – affect physical properties of a metallic material. We have investigated magnetic, electrical, thermal transport and thermoelectric properties of a monocrystalline and a polycrystalline Al3.26Mg2 sample in a mixed β–β′ phase, grown by the Czochralski technique. Electrical resistivity is in the range ρ ≈30–40μΩcm and exhibits T 2 dependence at low temperatures and T at higher temperatures, resembling nonmagnetic amorphous alloys. Magnetic susceptibility χ measurements revealed that the samples are Pauli paramagnets with significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperature. Combined analysis of the ρ(T) and χ(T), together with the independent determination of the Pauli susceptibility via the NMR Knight shift suggests that the observed temperature dependence originates from the mean-free-path effect on the orbital susceptibility. The electronic density of states (DOS) at the Fermi energy E F was estimated by NMR and was found to amount about 90% of the DOS of the fcc Al metal. Thermal conductivity contains electronic, Debye and hopping of localized vibration terms, whereas the thermopower is small and negative. High structural complexity of the β-Al3Mg2 complex metallic alloy does not result in high complexity of its electronic structure. We found no evidence for the existence of a pseudogap in the DOS at E F. [Copyright &y& Elsevier]

Ultrasmall silver nanoparticles (2 nm) were prepared by reduction with sodium borohydride (NaBH 4 ) and stabilized by the ligand glutathione (a tripeptide: glycine-cysteine-glutamic acid). NMR spectroscopy and optical spectroscopy (UV and fluorescence) revealed that these particles initially consist of silver nanoparticles and fluorescing silver nanoclusters, both stabilized by glutathione. Over time, the silver nanoclusters disappear and only the silver nanoparticles remain. Furthermore, the capping ligand glutathione eliminates hydrogen sulfide (H 2 S) from the central cysteine and is released from the nanoparticle surface as tripeptide glycine-dehydroalanine-glutamic acid. Hydrogen sulfide reacts with the silver core to form silver sulfide. After four weeks in dispersion at 4 °C, this process is completed. These processes cannot be detected by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), or differential centrifugal sedimentation (DCS) as these methods cannot resolve the mixture of nanoparticles and nanoclusters or the nature of the nanoparticle core. X-ray photoelectron spectroscopy showed the mostly oxidized state of the silver nanoparticle core, Ag(+I), both in freshly prepared and in aged silver nanoparticles. These results demonstrate that ultrasmall nanoparticles can undergo unnoticed changes that considerably affect their chemical, physical, and biological properties. In particular, freshly prepared ultrasmall silver nanoparticles are much more toxic against cells and bacteria than aged particles because of the presence of the silver clusters.

Ultrasmall nanoparticles (diameter 2 nm) of silver, platinum, and bimetallic nanoparticles (molar ratio of Ag:Pt 0:100; 20:80; 50:50; 70:30; 100:0), stabilized by the thiolated ligand glutathione, were prepared and characterized by transmission electron microscopy, differential centrifugal sedimentation, X-ray photoelectron spectroscopy, small-angle X-ray scattering, X-ray powder diffraction, and NMR spectroscopy in aqueous dispersion. Gold nanoparticles of the same size were prepared as control. The particles were fluorescently labeled by conjugation of the dye AlexaFluor-647 via copper-catalyzed azide-alkyne cycloaddition after converting amine groups of glutathione into azide groups. All nanoparticles were well taken up by HeLa cells. The cytotoxicity was assessed with an MTT test on HeLa cells and minimal inhibitory concentration (MIC) tests on the bacteria Escherichia coli and Staphylococcus xylosus . Notably, bimetallic AgPt nanoparticles had a higher cytotoxicity against cells and bacteria than monometallic silver nanoparticles or a physical mixture of silver and platinum nanoparticles. However, the measured release of silver ions from monometallic and bimetallic silver nanoparticles in water was very low despite the ultrasmall size and the associated high specific surface area. This is probably due to the surface protection by a dense layer of thiolated ligand glutathione. Thus, the enhanced cytotoxicity of bimetallic AgPt nanoparticles is caused by the biological environment in cell culture media, together with a polarization of silver by platinum.

Machine learning approaches for image analysis require extensive training datasets for an accurate analysis. This also applies to the automated analysis of electron microscopy data where training data are usually created by manual annotation. Besides nanoparticle shape and size distribution, their internal crystal structure is a major parameter to assess their nature and their physical properties. The automatic classification of ultrasmall gold nanoparticles (1-3 nm) by their crystallinity is possible after training a neural network with simulated HRTEM data. This avoids a human bias and the necessity to manually classify extensive particle sets as training data. The small size of these particles represents a significant challenge with respect to the question of internal crystallinity. The network was able to assign real particles imaged by HRTEM with high accuracy to the classes monocrystalline, polycrystalline, and amorphous after being trained with simulated datasets. The ability to adjust the simulation parameters opens the possibility to extend this procedure to other experimental setups and other types of nanoparticles., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Ultrasmall gold nanoparticles were functionalized with peptides of two to seven amino acids that contained one cysteine molecule as anchor via a thiol-gold bond and a number of alanine residues as nonbinding amino acid. The cysteine was located either in the center of the molecule or at the end (C-terminus). For comparison, gold nanoparticles were also functionalized with cysteine alone. The particles were characterized by UV spectroscopy, differential centrifugal sedimentation (DCS), high-resolution transmission electron microscopy (HRTEM), and small-angle X-ray scattering (SAXS). This confirmed the uniform metal core (2 nm diameter). The hydrodynamic diameter was probed by 1 H-DOSY NMR spectroscopy and showed an increase in thickness of the hydrated peptide layer with increasing peptide size (up to 1.4 nm for heptapeptides; 0.20 nm per amino acid in the peptide). 1 H NMR spectroscopy of water-dispersed nanoparticles showed the integrity of the peptides and the effect of the metal core on the peptide. Notably, the NMR signals were very broad near the metal surface and became increasingly narrow in a distance. In particular, the methyl groups of alanine can be used as probe for the resolution of the NMR spectra. The number of peptide ligands on each nanoparticle was determined using quantitative 1 H NMR spectroscopy. It decreased with increasing peptide length from about 100 for a dipeptide to about 12 for a heptapeptide, resulting in an increase of the molecular footprint from about 0.1 to 1.1 nm 2 .

Metallic nanoparticles were analysed with respect to size and shape by a machine learning approach. This involved a separation of particles from the background (segmentation), a separation of overlapping particles, and the identification of individual particles. An algorithm to separate overlapping particles, based on ultimate erosion of convex shapes (UECS), was implemented. Finally, particle properties like size, circularity, equivalent diameter, and Feret diameter were computed for each particle of the whole particle population. Thus, particle size distributions can be easily created based on the various parameters. However, strongly overlapping particles are difficult and sometimes impossible to separate because of an a priori unknown shape of a particle that is partially lying in the shadow of another particle. The program is able to extract information from a sequence of images of the same sample, thereby increasing the number of analysed nanoparticles to several thousands. The machine learning approach is well-suited to identify particles at only limited particle-to-background contrast as is demonstrated for ultrasmall gold nanoparticles (2 nm)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Introduction: Macrophages are the preferential target of Mycobacterium avium subsp. paratuberculosis (MAP), the etiologic agent of ruminant paratuberculosis. Uptake of pathogens by intestinal macrophages results in their trafficking through endosomal compartments, ultimately leading to fusion with an acidic lysosome to destroy the pathogen. MAP possesses virulence factors which disrupt these endosomal pathways. Additionally, levels of serum vitamin D 3 have proven relevant to host immunity. Dynamics of endosomal trafficking and vitamin D 3 metabolism have been largely unexplored in bovine paratuberculosis., Methods: This study aimed to characterize expression of early and late endosomal markers Rab5 and Rab7, respectively, within CD68+ macrophages in frozen mid-ileum sections harvested from cows at different stages of natural paratuberculosis infection. Additionally, factors of vitamin D 3 signaling and metabolism were characterized through expression of vitamin D 3 activating enzyme 1α-hydroxylase (CYP27B1), vitamin D 3 inactivating enzyme 24-hydroxylase (CYP24A1), and vitamin D 3 receptor (VDR) within CD68+ ileal macrophages., Results and Discussion: Cows with clinical paratuberculosis had significantly greater macrophage and MAP burden overall, as well as intracellular MAP. Total expression of Rab5 within macrophages was reduced in clinical cows; however, Rab5 and MAP colocalization was significantly greater in this group. Intracellular Rab7 colocalization with MAP was not detected in subclinical or Johne's Disease negative (JD-) control cows but was present in clinical cows. Additionally, macrophage CYP27B1 expression was significantly reduced in clinical cows. Taken together, the results from this study show disparate patterns of expression for key mediators in intracellular MAP trafficking and vitamin D metabolism for cows at different stages of paratuberculosis., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Wherry, Heggen, Shircliff, Mooyottu and Stabel.)

Liquid methanol has the potential to be the hydrogen energy carrier and storage medium for the future green economy. However, there are still many challenges before zero-emission, affordable molecular H 2 can be extracted from methanol with high performance. Here, we present noble-metal-free Cu-WC/W plasmonic nanohybrids which exhibit unsurpassed solar H 2 extraction efficiency from pure methanol of 2,176.7 µmol g -1  h -1 at room temperature and normal pressure. Macro-to-micro experiments and simulations unveil that local reaction microenvironments are generated by the coperturbation of WC/W's lattice strain and infrared-plasmonic electric field. It enables spontaneous but selective zero-emission reaction pathways. Such microenvironments are found to be highly cooperative with solar-broadband-plasmon-excited charge carriers flowing from Cu to WC surfaces for efficient stable CH 3 OH plasmonic reforming with C 3 -dominated liquid products and 100% selective gaseous H 2 . Such high efficiency, without any CO x emission, can be sustained for over a thousand-hour operation without obvious degradation.

Azide-terminated ultrasmall gold nanoparticles (2 nm gold core) were covalently functionalized with alkyne-terminated small-interfering siRNA duplexes by copper-catalyzed azide-alkyne cycloaddition (CuAAC; click chemistry). The nanoparticle core was visualized by transmission electron microscopy. The number of attached siRNA molecules per nanoparticle was determined by a combination of atomic absorption spectroscopy (AAS; for gold) and UV-Vis spectroscopy (for siRNA). Each nanoparticle carried between 6 and 10 siRNA duplex molecules which corresponds to a weight ratio of siRNA to gold of about 2.2 : 1. Different kinds of siRNA were conjugated to the nanoparticles, depending on the gene to be silenced. In general, the nanoparticles were readily taken up by cells and highly efficient in gene silencing, in contrast to free siRNA. This was demonstrated in HeLa-eGFP cells (silencing of eGFP) and in LPS-stimulated macrophages (silencing of NF-κB). Furthermore, we demonstrated that nanoparticles carrying antiviral siRNA potently inhibited the replication of Herpes simplex virus 2 (HSV-2) in vitro . This highlights the strong potential of siRNA-functionalized ultrasmall gold nanoparticles in a broad spectrum of applications, including gene silencing and treatment of viral infections, combined with a minimal dose of gold., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Recently proposed bimetallic octahedral Pt-Ni electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) cathodes suffer from particle instabilities in the form of Ni corrosion and shape degradation. Advanced trimetallic Pt-based electrocatalysts have contributed to their catalytic performance and stability. In this work, we propose and analyse a novel quaternary octahedral (oh-)Pt nanoalloy concept with two distinct metals serving as stabilizing surface dopants. An efficient solvothermal one-pot strategy was developed for the preparation of shape-controlled oh-PtNi catalysts doped with Rh and Mo in its surface. The as-prepared quaternary octahedral PtNi(RhMo) catalysts showed exceptionally high ORR performance accompanied by improved activity and shape integrity after stability tests compared to previously reported bi- and tri-metallic systems. Synthesis, performance characteristics and degradation behaviour are investigated targeting deeper understanding for catalyst system improvement strategies. A number of different operando and on-line analysis techniques were employed to monitor the structural and elemental evolution, including identical location scanning transmission electron microscopy and energy dispersive X-ray analysis (IL-STEM-EDX), operando wide angle X-ray spectroscopy (WAXS), and on-line scanning flow cell inductively coupled plasma mass spectrometry (SFC-ICP-MS). Our studies show that doping PtNi octahedral catalysts with small amounts of Rh and Mo suppresses detrimental Pt diffusion and thus offers an attractive new family of shaped Pt alloy catalysts for deployment in PEMFC cathode layers., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The mammalian microbiome encodes numerous secondary metabolite biosynthetic gene clusters; yet, their role in microbe-microbe interactions is unclear. Here, we characterized two polyketide synthase gene clusters (fun and pks) in the gut symbiont Limosilactobacillus reuteri. The pks, but not the fun, cluster encodes antimicrobial activity. Forty-one of 51 L. reuteri strains tested are sensitive to Pks products; this finding was independent of strains' host origin. Sensitivity to Pks was also established in intraspecies competition experiments in gnotobiotic mice. Comparative genome analyses between Pks-resistant and -sensitive strains identified an acyltransferase gene (act) unique to Pks-resistant strains. Subsequent cell-wall analysis of wild-type and act mutant strains showed that Act acetylates cell-wall components, providing resistance to Pks-mediated killing. Additionally, pks mutants lost their competitive advantage, while act mutants lost their Pks resistance in in vivo competition assays. These findings provide insight into how closely related gut symbionts can compete and co-exist in the gastrointestinal tract., Competing Interests: Declaration of interests J.-P.V.P. received unrestricted funds from BioGaia AB, a probiotic-producing company. J.-P.V.P. is the founder of the consulting company Next-Gen Probiotics. J.W. has received grants and honoraria from several food and ingredient companies, including companies that produce probiotics. J.W. is a co-owner of Synbiotic Solutions, and is on the Scientific Advisory Board of Alimentary Health. M.Ö. was an employee of DuPont Nutrition and Biosciences. J.C. is a Scientific Advisor for Seed Health, Inc., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Core-shell particles with thin noble metal shells represent an attractive material class with potential for various applications ranging from catalysis to biomedical and pharmaceutical applications to optical crystals. The synthesis of well-defined core-shell architectures remains, however, highly challenging. Here, we demonstrate that atomically-thin and homogeneous platinum shells can be grown via a colloidal synthesis method on a variety of gold nanostructures ranging from spherical nanoparticles to nanorods and nanocubes. The synthesis is based on the exchange of low binding citrate ligands on gold, the reduction of platinum and the subsequent kinetically hindered growth by carbon monoxide as strong binding ligand. The prerequisites for homogeneous growth are low core-binding ligands with moderate fast ligand exchange in solution, a mild reducing agent to mitigate homonucleation and a strong affinity of a second ligand system that can bind to the shell's surface. The simplicity of the described synthetic route can potentially be adapted to various other material libraries to obtain atomically smooth core-shell systems., (© 2022. The Author(s).)

Two ways to deliver ultrasmall gold nanoparticles and gold-bovine serum albumin (BSA) nanoclusters to the colon were developed. First, oral administration is possible by incorporation into gelatin capsules that were coated with an enteric polymer. These permit the transfer across the stomach whose acidic environment damages many drugs. The enteric coating dissolves due to the neutral pH of the colon and releases the capsule's cargo. Second, rectal administration is possible by incorporation into hard-fat suppositories that melt in the colon and then release the nanocarriers. The feasibility of the two concepts was demonstrated by in-vitro release studies and cell culture studies that showed the easy redispersibility after dissolution of the respective transport system. This clears a pathway for therapeutic applications of drug-loaded nanoparticles to address colon diseases, such as chronic inflammation and cancer.

Ultrasmall silver nanoparticles were prepared by reduction with NaBH 4 and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with 13 C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ 1 H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver-sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL -1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag ∼250 GSH ∼155 .

The invention of silicon drift detectors has resulted in an unprecedented improvement in detection efficiency for energy-dispersive X-ray (EDX) spectroscopy in the scanning transmission electron microscope. The result is numerous beautiful atomic-scale maps, which provide insights into the internal structure of a variety of materials. However, the task still remains to understand exactly where the X-ray signal comes from and how accurately it can be quantified. Unfortunately, when crystals are aligned with a low-order zone axis parallel to the incident beam direction, as is necessary for atomic-resolution imaging, the electron beam channels. When the beam becomes localized in this way, the relationship between the concentration of a particular element and its spectroscopic X-ray signal is generally nonlinear. Here, we discuss the combined effect of both spatial integration and sample tilt for ameliorating the effects of channeling and improving the accuracy of EDX quantification. Both simulations and experimental results will be presented for a perovskite-based oxide interface. We examine how the scattering and spreading of the electron beam can lead to erroneous interpretation of interface compositions, and what approaches can be made to improve our understanding of the underlying atomic structure.

Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO 2 to methanol, open questions still remain regarding the role and the dynamic nature of the active sites formed at the metal-oxide interface. Here, we apply high-pressure operando spectroscopy methods to well-defined Cu and Cu 0.7 Zn 0.3 nanoparticles supported on ZnO/Al 2 O 3 , γ-Al 2 O 3 and SiO 2 to correlate their structure, composition and catalytic performance. We obtain similar activity and methanol selectivity for Cu/ZnO/Al 2 O 3 and CuZn/SiO 2 , but the methanol yield decreases with time on stream for the latter sample. Operando X-ray absorption spectroscopy data reveal the formation of reduced Zn species coexisting with ZnO on CuZn/SiO 2 . Near-ambient pressure X-ray photoelectron spectroscopy shows Zn surface segregation and the formation of a ZnO-rich shell on CuZn/SiO 2 . In this work we demonstrate the beneficial effect of Zn, even in diluted form, and highlight the influence of the oxide support and the Cu-Zn interface in the reactivity.

A strategy toward epitope-selective functionalized nanoparticles is introduced in the following: ultrasmall gold nanoparticles (diameter of the metallic core about 2 nm) were functionalized with molecular tweezers that selectively attach lysine and arginine residues on protein surfaces. Between 11 and 30 tweezer molecules were covalently attached to the surface of each nanoparticle by copper-catalyzed azide alkyne cycloaddition (CuAAC), giving multiavid agents to target proteins. The nanoparticles were characterized by high-resolution transmission electron microscopy, differential centrifugal sedimentation, and 1 H NMR spectroscopy (diffusion-ordered spectroscopy, DOSY, and surface composition). The interaction of these nanoparticles with the model proteins hPin1 (WW domain; hPin1-WW) and Survivin was probed by NMR titration and by isothermal titration calorimetry (ITC). The binding to the WW domain of hPin1 occurred with a K D of 41 ± 2 μM, as shown by ITC. The nanoparticle-conjugated tweezers targeted cationic amino acids on the surface of hPin1-WW in the following order: N-terminus (G) ≈ R17 > R14 ≈ R21 > K13 > R36 > K6, as shown by NMR spectroscopy. Nanoparticle recognition of the larger protein Survivin was even more efficient and occurred with a K D of 8 ± 1 μM, as shown by ITC. We conclude that ultrasmall nanoparticles can act as versatile carriers for artificial protein ligands and strengthen their interaction with the complementary patches on the protein surface.