Circadian clocks generate slow and ordered cellular dynamics but consist of fast-moving bio-macromolecules; consequently, the origins of the overall slowness remain unclear. We identified the adenosine triphosphate (ATP) catalytic region [adenosine triphosphatase (ATPase)] in the amino-terminal half of the clock protein KaiC as the minimal pacemaker that controls the in vivo frequency of the cyanobacterial clock. Crystal structures of the ATPase revealed that the slowness of this ATPase arises from sequestration of a lytic water molecule in an unfavorable position and coupling of ATP hydrolysis to a peptide isomerization with high activation energy. The slow ATPase is coupled with another ATPase catalyzing autodephosphorylation in the carboxyl-terminal half of KaiC, yielding the circadian response frequency of intermolecular interactions with other clock-related proteins that influences the transcription and translation cycle.

The structure of vesicles formed by anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in brine solution (1.5 wt% NaCl) at 20°C, in the diluted region of the phase diagram, has been characterized by cryogenic transmission electron microscopy (cryo-TEM) and the combination of three scattering techniques (Small Angle X-ray Scattering (SAXS), Dynamic Light Scattering (DLS) and Multi-angle light scattering (MALS)). Resultsshow a polydisperse vesicle size system. The distribution is mainly composed of small vesicles (14 nm diameter) and there is no micelles in solution. The determination of the form factor indicates the presence of only spherical vesicles (no other morphologies, such as tubular vesicles, were observed). The bilayer structure of the vesicles was characterized by SAXS and the membrane thickness measured at 2.7 nm. This thickness is shorter than twice the AOT molecule extended length indicating a non-negligible interpenetration of the hydrophobic tails.

The structure of adsorbed surfactant layers at equilibrium state has already been investigated using various experimental techniques. However, the comprehension of the formation of structural intermediates in non-equilibrium states and the resulting adsorption kinetics still remains a challenging task. The temporal characterization of these intermediate structures provides further understanding of the layer structure at equilibrium and of the main interactions involved in the adsorption process. In this article, we studied adsorption kinetics of AOT vesicles on silica at different pH at ambient temperature. AOT vesicles were formed in a brine solution. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to obtain information on the kinetics of surfactant adsorption and on the structure of the adsorbed layer at the equilibrium state.Additionally, neutron reflectivity experiments were performed to provide a detailed description of the mean surfactant concentration profile normal to the surface at equilibrium. Results suggest that vesicles in the bulk influence the adsorption mechanisms. In acidic conditions, after a time dependent structural rearrangement step followed by the rupture of initially adsorbed vesicles, the formation of a bilayer was observed. At intermediate and basic pH, in spite of the electrostatic repulsion between the negatively charged surfactants and silica, results demonstrated the existence of an adsorbed layer composed of AOT vesicles. Vesicles are more or less closely packed depending on the pH of the solution. Results show non-negligible influence of NaCl addition at pH values where adsorption is initially inhibited. Vesicle adsorption at intermediate and basic pH is probably due to the combination of attractive van der Waals interactions promoted in high ionic strength systems and the formation of hydrogen bonds. Interpretation of adsorption kinetics gave insight into adsorption mechanisms in an electrostatic repulsion environment.

In comparison to condensed matter, soft matter is subject to several interplaying effects (surface heterogeneities, swelling effect…) that influence transport at the nanoscale. In consequence, transport in soft and compliant materials is coupled to adsorption and deformation phenomena. The permeance of the material, i.e. the response of the material to a pressure gradient, is dependent on the temperature, the chemical potential and the external constraint. Therefore, the characterization of water dynamics in soft porous materials, that we address here, becomes much more complex. In this paper, the development of an original setup for scattering measurements of a radiation in the transmitted geometry in oedometric conditions is described. A specially designed cell enables a uniaxial compression of the investigated material, PIM-1 (Polymers of Intrinsic Microporosity), in the direction perpendicular to the applied hydraulic pressure gradient (up to 120 bars). High pressure boosting of the circulating water is performed with a commercially available high-pressure pump Karcher. This particular setup is adapted to Quasi-elastic neutron scattering technique, which enables to probe diffusion and relaxation phenomena with characteristic times of 10 -9 -10 -12 s. Moreover, it can easily be modified for other scattering techniques.