In-section Click-iT detection and super-resolution CLEM analysis of nucleolar ultrastructure and replication in plants.

Correlative light and electron microscopy (CLEM) is an important tool for the localisation of target molecule(s) and their spatial correlation with the ultrastructural map of subcellular features at the nanometre scale. Adoption of these advanced imaging methods has been limited in plant biology, due to challenges with plant tissue permeability, fluorescence labelling efficiency, indexing of features of interest throughout the complex 3D volume and their re-localization on micrographs of ultrathin cross-sections. Here, we demonstrate an imaging approach based on tissue processing and embedding into methacrylate resin followed by imaging of sections by both, single-molecule localization microscopy and transmission electron microscopy using consecutive CLEM and same-section CLEM correlative workflow. Importantly, we demonstrate that the use of a particular type of embedding resin is not only compatible with single-molecule localization microscopy but shows improvements in the fluorophore blinking behavior relative to the whole-mount approaches. Here, we use a commercially available Click-iT ethynyl-deoxyuridine cell proliferation kit to visualize the DNA replication sites of wild-type Arabidopsis thaliana seedlings, as well as fasciata1 and nucleolin1 plants and apply our in-section CLEM imaging workflow for the analysis of S-phase progression and nucleolar organization in mutant plants with aberrant nucleolar phenotypes.

Chiral Light Emission from a Hybrid Magnetic Molecule-Monolayer Transition Metal Dichalcogenide Heterostructure.

Hybrid layered materials assembled from atomically thin crystals and small molecules bring great promises in pushing the current information and quantum technologies beyond the frontiers. We demonstrate here a class of layered valley-spin hybrid (VSH) materials composed of a monolayer two-dimensional (2D) semiconductor and double-decker single molecule magnets (SMMs). We have materialized a VSH prototype by thermal evaporation of terbium bis-phthalocyanine onto a MoS2 monolayer and revealed its composition and stability by both microscopic and spectroscopic probes. The interaction of the VSH components gives rise to the intersystem crossing of the photogenerated carriers and moderate p-doping of the MoS2 monolayer, as corroborated by the density functional theory calculations. We further explored the valley contrast by helicity-resolved photoluminescence (PL) microspectroscopy carried out down to liquid helium temperatures and in the presence of the external magnetic field. The most striking feature of the VSH is the enhanced A exciton-related valley emission observed at the out-of-resonance condition at room temperature, which we elucidated by the proposed nonradiative energy drain transfer mechanism. Our study thus demonstrates the experimental feasibility and great promises of the ultrathin VSH materials with chiral light emission, operable by physical fields for emerging opto-spintronic, valleytronic, and quantum information concepts.

Thermal Traits of MNPs under High-Frequency Magnetic Fields: Disentangling the Effect of Size and Coating.

We investigated the heating abilities of magnetic nanoparticles (MNPs) in a high-frequency magnetic field (MF) as a function of surface coating and size. The cobalt ferrite MNPs were obtained by a hydrothermal method in a water-oleic acid-ethanol system, yielding MNPs with mean diameter of about 5 nm, functionalized with the oleic acid. By applying another cycle of hydrothermal synthesis, we obtained MNPs with about one nm larger diameter. In the next step, the oleic acid was exchanged for 11-maleimidoundecanoic acid or 11-(furfurylureido)undecanoic acid. For the heating experiments, all samples were dispersed in the same solvent (dichloroethane) in the same concentration and the heating performance was studied in a broad interval of MF frequencies (346-782 kHz). The obtained results enabled us to disentangle the impact of the hydrodynamic, structural, and magnetic parameters on the overall heating capabilities. We also demonstrated that the specific power absorption does not show a monotonous trend within the series in the investigated interval of temperatures, pointing to temperature-dependent competition of the Brownian and Néel contributions in heat release.

The use of sample positioning to control defect creation by oxygen plasma in isotopically labelled bilayer graphene membranes.

Monolayer and isotopically labelled bilayer graphene membranes were prepared on grids for transmission electron microscopy (TEM). In order to create defects in the graphene layers in a controlled way, we studied the sensitivity of the individual graphene layers to the oxygen plasma treatment. We tested samples with different configurations by varying the order of the transfer of layers and changing the orientation of the samples with respect to the plasma chamber. Using Raman spectroscopy, HRTEM and X-ray photoelectron spectroscopy, we demonstrated defect formation and determined the quantity and chemical composition of the defects. By keeping the sample structure and the setup of the experiment unchanged, the significant role of the sample orientation with respect to the chamber was demonstrated. The effect was accounted for by the variation of the accessibility of the sample surface for the reactive species. Therefore, this effect can be used to control the degree of damage in each layer, resulting in differing numbers of defects present on each side of the sample.

Towards Catalytically Active Porous Graphene Membranes with Pulsed Laser Deposited Ceria Nanoparticles.

Porous graphene with catalytically active ceria nanometre-size particles were prepared using pulsed laser deposition (PLD) on graphene produced through chemical vapour deposition (CVD). The reported process provided porous graphene containing ceria nanoparticles as confirmed by HR TEM and XPS. Isotopically labelled 13 C graphene was employed to study desorption of the species containing carbon. Methanol adsorption was utilised to probe the nature of the catalytic activity of prepared ceria decorated graphene. The important role of graphene support for the stabilization of reduced ceria nanoparticles was finally confirmed. Increased dehydrogenation activity of graphene with ceria nanoparticles leading to CO and H2 formation was demonstrated.

Surface-Confined Macrocyclization via Dynamic Covalent Chemistry.

Surface-confined synthesis is a promising approach to build complex molecular nanostructures including macrocycles. However, despite the recent advances in on-surface macrocyclization under ultrahigh vacuum, selective synthesis of monodisperse and multicomponent macrocycles remains a challenge. Here, we report on an on-surface formation of [6 + 6] Schiff-base macrocycles via dynamic covalent chemistry. The macrocycles form two-dimensional crystalline domains on the micrometer scale, enabled by dynamic conversion of open-chain oligomers into well-defined ∼3.0 nm hexagonal macrocycles. We further show that by tailoring the length of the alkyl substituents, it is possible to control which of three possible products-oligomers, macrocycles, or polymers-will form at the surface. In situ scanning tunneling microscopy imaging combined with density functional theory calculations and molecular dynamics simulations unravel the synergistic effect of surface confinement and solvent in leading to preferential on-surface macrocyclization.

Chemistry of 2,14-Dithiacalix[4]arene: Alkylation and Conformational Behavior of Peralkylated Products.

2,14-Dithiacalix[4]arene, prepared on a multigram scale, was alkylated using the reaction conditions well known from the chemistry of classical calixarenes or thiacalixarenes to study the specific conformational preferences and dynamic behavior of the corresponding tetraalkylated derivatives. As proved by the combination of the X-ray crystallography and dynamic NMR techniques, the presence of mixed bridges (-CH2- and -S- groups) within the basic skeleton brings about considerable changes in the mutual ratios of the individual conformers compared to the parent macrocycles. Interestingly, certain conformers, hardly accessible for common calixarenes/thiacalixarenes (e.g., 1,2-alternates) are easily prepared in very good yields in the case of 2,14-dithiacalix[4]arene, which makes this mixed-bridge system attractive as molecular scaffold for supramolecular applications.

Thermoreversible magnetic nanochains.

The reversible organization of nanomagnets into highly anisotropic assemblies is of considerable interest for many applications, including theragnostic strategies in vivo. The current preparation strategies lead to structures that are not stable without the permanent presence of an applied magnetic field (MF); otherwise, irreversible assemblies are produced with moderate shape anisotropy at nanoscales. Here, we present a new approach based on the thermoreversible Diels-Alder reaction in the presence of an external MF that enables the assembly of single-domain nanomagnets into narrow chains with lengths of several micrometers. The MF-assisted click chemistry approach included (i) the synthesis of nanoparticles through a modified hydrothermal method, (ii) their functionalization via ligand exchange, (iii) the MF-assisted formation of chains, and (iv) the linkage of the nanomagnets in the presence of the magnetic field. Moreover, the chains can be again disassembled at elevated temperatures through a retro-Diels-Alder reaction. We thus demonstrated for the first time that MF-assisted click chemistry is a convenient method for large-scale preparation of highly anisotropic assemblies of nanosized magnets that can be reversibly decomposed by thermal treatment.