A double septin ring accompanies cytokinesis in yeasts and mammalian cells. In budding yeast, reorganisation of the septin collar at the bud neck into a dynamic double ring is essential for actomyosin ring constriction and cytokinesis. Septin reorganisation requires the Mitotic Exit Network (MEN), a kinase cascade essential for cytokinesis. However, the effectors of MEN in this process are unknown. Here we identify the F-BAR protein Hof1 as a critical target of MEN in septin remodelling. Phospho-mimicking HOF1 mutant alleles overcome the inability of MEN mutants to undergo septin reorganisation by decreasing Hof1 binding to septins and facilitating its translocation to the actomyosin ring. Hof1-mediated septin rearrangement requires its F-BAR domain, suggesting that it may involve a local membrane remodelling that leads to septin reorganisation. In vitro Hof1 can induce the formation of intertwined septin bundles, while a phosphomimetic Hof1 protein has impaired septin-bundling activity. Altogether, our data indicate that Hof1 modulates septin architecture in distinct ways depending on its phosphorylation status.

Poly(N-isopropylacrylamide) (PNIPAM) is one of the most well studied thermoresponsive polymers and its microgels undergo a reversible volume phase transition (VPT) at temperatures close to that of the human body. Coupling this property with the unique optical properties of single-walled carbon nanotubes (SWCNT) in the near infrared (NIR) leads to interesting nanohybrids that could be used as multi-responsive sensors/actuators for biological applications.We show the synthesis of thermoresponsive SWCNT/PNIPAM hybrids using two different non-covalent strategies, preserving the nanotube optical properties such as fluorescence. The first strategy involves the dispersion of the SWCNT in water with sodium dodecyl sulfate (SDS), and subsequent in situ synthesis of PNIPAM microgels inside the SDS coatings around the nanotubes. The second strategy starts with modifying the nanotubes with a pyrene derivative, which in turn is used as the starting point for the in situ polymerization of the PNIPAM microgels, thus ensuring that the polymer grows around the nanotubes. In both cases, we obtain hybrids showing a phase transition at temperatures close to that of the human body, with the absorption and fluorescence spectra of the hybrids in the NIR changing in response to the changing dielectric environment. These systems could be used as actuators/sensors in biological systems.

ContextSingle-wall carbon nanotubes (SWCNT) dispersed in water with the help of sodium dodecyl sulfate (SDS) surfactants exhibit a temperature dependent near infrared (NIR) exciton spectrum. Due to their biocompatibility and NIR spectrum falling within the transparent window for biological tissue, SWCNTs hold potential for sensing temperature inside cells. Here, we seek to elucidate the mechanism responsible for this temperature dependence, focusing on changes in the water coverage of the SWCNT as the surfactant structure changes with temperature. We compare optical absorption spectra in the UV–Vis-IR range and fully atomistic molecular dynamics (MD) simulations. The observed temperature dependence of the spectra for various SWCNTs may be attributed to changes in the dielectric environment and its impact on excitons. MD simulations reveal that the adsorbed SDS molecules effectively shield the SWCNT, with ~ 70% of water molecules removed from the first two adlayers; this coverage shows a modest temperature dependence. Although we are not able to directly demonstrate how this influences the NIR spectrum, this represents a potential pathway given the strong influence of the water environment on the excitons in SWCNTs.MethodsOptical absorption measurements were carried out in the UV–Vis-NIR range using a Varian Cary 5000 spectrophotometer in a temperature-controlled environment. PeakFit™ v. 4.06 was used as peak-fitting program in the spectral range 900–1400 nm (890–1380 meV) as a function of the temperature. Fully atomistic molecular dynamics simulations were conducted using the NAMD2 package. The CHARMM force field comprising two-body bond stretching, three-body angle deformation, four-body dihedral angle deformation, and nonbonded interactions (electrostatic and Lennard–Jones 6–16 potentials) was employed.

Mesoporous systems are ubiquitous in membrane science and applications due to their high internal surface area and tunable pore size. A new synthesis pathway of hydrolytic ionosilica films with mesopores formed by ionic liquid (IL) templating is proposed and compared to the traditional non-hydrolytic strategy. For both pathways, the multi-scale formation of pores has been studied as a function of IL content, combining results of thermogravimetric analysis (TGA), nitrogen sorption, and small-angle X-ray scattering (SAXS). The combination of TGA and nitrogen sorption provides access to ionosilica and pore volume fractions, with contributions of meso- and macropores. We then elaborate an original and quantitative geometrical model to analyze the SAXS data based on small spheres (Rs = 1 – 2 nm) and cylinders (Lcyl = 10 – 20 nm) with radial polydispersity provided by the nitrogen sorption isotherms. As a main result, we found that for a given incorporation of templating IL, both synthesis pathways produce very similar pore geometries, but the better incorporation efficacy of the new hydrolytic films provides a higher mesoporosity. Our combined study provides a coherent view of mesopore geometry, and thereby an optimization pathway of porous ionic membranes in terms of accessible mesoporosity contributing to the specific surface. Possible applications include electrolyte membranes of improved ionic properties, e.g., in fuel cells and batteries, as well as molecular storage.

We use molecular dynamics simulations to study the structural and mechanical properties of bead-spring polymer networks. In this study we deal with systems which are biologically-relevant as they result from the action of enzymes, i.e. biological catalysts. The latter convert repulsive monomers into attractive ones and hence, starting from a polymer solution, trigger the formation of a physically-crosslinked polymer network. This gel has a remarkably regular mesostructure in the form of a cluster phase. We simulate uniaxial tension of these networks. The evolution of their structural and mechanical properties during deformation is monitored by computing quantities such as the anisotropic pair correlation functions, Poisson's ratio, elastic moduli and stress-strain curves, and the effects of temperature and system composition (i.e. fraction of attractive monomers) are investigated.

Abstract Creating amorphous solid states by randomly bonding an ensemble of dense liquid monomers is a common procedure that is used to create a variety of materials, such as epoxy resins, colloidal gels, and vitrimers. However, the properties of the resulting solid do a priori strongly depend on the preparation history. This can lead to substantial aging of the material; for example, properties such as mechanical moduli and transport coefficients rely on the time elapsed since solidification, which can lead to a slow degradation of the material in technological applications. It is therefore important to understand under which conditions random monomer bonding can lead to stable solid states, that is, long-lived metastable states whose properties do not change over time. This work presents a theoretical and computational analysis of this problem and introduces a random bonding procedure that ensures the proper equilibration of the resulting amorphous states. Our procedure also provides a new route to investigate the fundamental properties of glassy energy landscapes by producing translationally invariant ultrastable glassy states in simple particle models.