For the technological integration of molecular switches in electronic devices, self-assembling nanomaterials of such switches are highly sought after. The syntheses of a new tetrapyridyl ligand... Show moreFor the technological integration of molecular switches in electronic devices, self-assembling nanomaterials of such switches are highly sought after. The syntheses of a new tetrapyridyl ligand bearing a C12 alkyl chain and two N-H bridges (compound 1) and of its iron(II) complex [Fe(1)(NCS)(2)] (compound 2), are described. Magnetic susceptibility data for bulk samples of 2 confirmed their gradual spin-crossover properties. The self-assembly of 1 and 2 on highly ordered pyrolytic graphite surfaces (HOPG) was investigated by Scanning Tunneling Microscopy (STM). Both compounds 1 and 2 formed ordered monolayers after deposition by drop casting. The patterns of the two compounds are very different, which is attributed to the fundamentally different hydrogen bonding networks before and after coordination of Fe(NCS)(2) to the tetradentate chelate. Two possible models for the self-assembly of 1 and 2 are provided. This work suggests that it is possible to design molecular switches that self-assemble on surfaces in highly ordered monolayer films. This is a significant step in the development of spin-switching materials, which may streamline the integration of molecular switches in for example memory and sensing devices. Show less
Coronavirus genome replication is associated with virus-induced cytosolic double-membrane vesicles, which may provide a tailored microenvironment for viral RNA synthesis in the infected cell.... Show moreCoronavirus genome replication is associated with virus-induced cytosolic double-membrane vesicles, which may provide a tailored microenvironment for viral RNA synthesis in the infected cell. However, it is unclear how newly synthesized genomes and messenger RNAs can travel from these sealed replication compartments to the cytosol to ensure their translation and the assembly of progeny virions. In this study, we used cellular cryo-electron microscopy to visualize a molecular pore complex that spans both membranes of the double-membrane vesicle and would allow export of RNA to the cytosol. A hexameric assembly of a large viral transmembrane protein was found to form the core of the crown-shaped complex. This coronavirus-specific structure likely plays a key role in coronavirus replication and thus constitutes a potential drug target. Show less
Cryo-focused ion beam (FIB)-milling of biological samples can be used to generate thin electron-transparent slices from cells grown or deposited on EM grids. These so called cryo-lamellae allow... Show moreCryo-focused ion beam (FIB)-milling of biological samples can be used to generate thin electron-transparent slices from cells grown or deposited on EM grids. These so called cryo-lamellae allow high-resolution structural studies of the natural cellular environment by in situ cryo-electron tomography. However, the cryo-lamella workflow is a low-throughput technique and can easily be hindered by technical issues like the bending of the lamellae during the final cryo-FIB-milling steps. The severity of lamella bending seems to correlate with crinkling of the EM grid support film at cryogenic temperatures, which could generate tensions that may be transferred onto the thin lamella, leading to its bending and breakage. To protect the lamellae from such forces, we milled "micro-expansion joints" alongside the lamellae, creating gaps in the support that can act as physical buffers to safely absorb material motion. We demonstrate that the presence of micro-expansion joints drastically decreases bending of lamellae milled from eukaryotic cells grown and frozen on EM grids. Furthermore, we show that this adaptation does not create additional instabilities that could impede subsequent parts of the cryolamella workflow, as we obtained high-quality Volta phase plate tomograms revealing macromolecules in their natural structural context. The minimal additional effort required to implement micro-expansion joints in the cryo-FIB-milling workflow makes them a straightforward solution against cryo-lamella bending to increase the throughput of in situ structural biology studies. Show less
Spin-crossover compounds showing thermal hysteresis exhibit magnetic and colourmetric bistablility, which is of interest for a number of applications such as information storage and optical... Show moreSpin-crossover compounds showing thermal hysteresis exhibit magnetic and colourmetric bistablility, which is of interest for a number of applications such as information storage and optical displays. Mononuclear iron(II) complexes hold considerable potential in this field, and their cooperative properties may suffer less from size reduction effects than polymeric SCO materials because the coordination environment remains well defined throughout the material. In this thesis, 13 new mononuclear spin-transition materials based on the bapbpy scaffold are described. One of these compounds, [Fe(bbpya)(NCS)2], shows one of the highest transition temperatures (418 K) recorded among known mononuclear SCO complexes. Most interestingly, it keeps a large hysteresis cycle of 21 K in spite of its high transition temperature. Meanwhile, metal dilution study on [Fe(bapbpy)(NCS)2] clearly shows that the two steps and the hysteresis cycles of the SCO are two consequences of the same phenomenon: intermolecular interactions between spin-switching molecules. Finally, a new bapphen-based ligand bearing a 12-carbon alkyl chain at the back of the tetrapyridyl ligand was prepared, which allowed self-assembling the corresponding iron(II) complex on a highly oriented pyrolytic graphite (HOPG) surface. The stable and highly ordered 2D patterns observed by STM are promising for the future study of cooperative spin crossover at surfaces. Show less
![Spatially resolved investigation and control of the bistability in single crystals of the [Fe(bbpya)(NCS)2] spin crossover complex](/sites/all/modules/custom/islandora_solr_search/images/defaultimg.png?solr_nav%5Bid%5D=08778aa8373387114011&solr_nav%5Bpage%5D=0&solr_nav%5Boffset%5D=5)
