Water is a unique solvent that is ubiquitous in biology and present in a variety of solutions, mixtures, and materials settings. It therefore forms the basis for all molecular dynamics simulations of ...biological phenomena, as well as for many chemical, industrial, and materials investigations. Over the years, many water models have been developed, and it remains a challenge to find a single water model that accurately reproduces all experimental properties of water simultaneously. Here, we report a comprehensive comparison of structural and dynamic properties of 30 commonly used 3-point, 4-point, 5-point, and polarizable water models simulated using consistent settings and analysis methods. For the properties of density, coordination number, surface tension, dielectric constant, self-diffusion coefficient, and solvation free energy of methane, models published within the past two decades consistently show better agreement with experimental values compared to models published earlier, albeit with some notable exceptions. However, no single model reproduced all experimental values exactly, highlighting the need to carefully choose a water model for a particular study, depending on the phenomena of interest. Finally, machine learning algorithms quantified the relationship between the water model force field parameters and the resulting bulk properties, providing insight into the parameter–property relationship and illustrating the challenges of developing a water model that can accurately reproduce all properties of water simultaneously.
Serial crystallography of membrane proteins often employs high‐viscosity injectors (HVIs) to deliver micrometre‐sized crystals to the X‐ray beam. Typically, the carrier medium is a lipidic cubic ...phase (LCP) media, which can also be used to nucleate and grow the crystals. However, despite the fact that the LCP is widely used with HVIs, the potential impact of the injection process on the LCP structure has not been reported and hence is not yet well understood. The self‐assembled structure of the LCP can be affected by pressure, dehydration and temperature changes, all of which occur during continuous flow injection. These changes to the LCP structure may in turn impact the results of X‐ray diffraction measurements from membrane protein crystals. To investigate the influence of HVIs on the structure of the LCP we conducted a study of the phase changes in monoolein/water and monoolein/buffer mixtures during continuous flow injection, at both atmospheric pressure and under vacuum. The reservoir pressure in the HVI was tracked to determine if there is any correlation with the phase behaviour of the LCP. The results indicated that, even though the reservoir pressure underwent (at times) significant variation, this did not appear to correlate with observed phase changes in the sample stream or correspond to shifts in the LCP lattice parameter. During vacuum injection, there was a three‐way coexistence of the gyroid cubic phase, diamond cubic phase and lamellar phase. During injection at atmospheric pressure, the coexistence of a cubic phase and lamellar phase in the monoolein/water mixtures was also observed. The degree to which the lamellar phase is formed was found to be strongly dependent on the co‐flowing gas conditions used to stabilize the LCP stream. A combination of laboratory‐based optical polarization microscopy and simulation studies was used to investigate these observations.
This is a study of the phase changes detected in monoolein samples under constant flow using a high‐viscousity injector. The sample behaviour was studied using X‐ray techniques while light microscopy and modelling studies were used to help interpret some of the effects observed in the data.
Femtoliter droplets at solid interfaces attract significant interest as the basic units in many physical and biological processes. One challenge in the application of these tiny droplets is their ...fast evaporation rate in air due to their large surface‐to‐volume ratio. Ionic liquids with low volatility present an opportunity to overcome this challenge. The advanced properties of ionic liquids (ILs) have enabled them to be widely applied in chemical reactions, biopolymers, molecular self‐assembly and separations. At interfaces, the wettability of ILs is pursued in next‐generation lubricants and battery technology. Previously, IL droplets at solid surfaces have been prepared by nanodispensing, micropipette, and solvent evaporation. Here, the solvent exchange protocol is extended to yield protic ionic liquid droplets at the interface with controlled size, distribution, location, and stability in both liquid and air surroundings. During growth, the droplets demonstrate an interesting dewetting dynamic. This behavior has not been observed for molecular liquids during solvent exchange and suggests interesting interfacial dynamics of the ionic liquid. One proof‐of‐concept application of using surface nanodroplets of the protic ionic liquid ethylammonium nitrate for compartmentalized reactions and templating SiO2 nanostructures is demonstrated. This work broadens and intertwines the opportunities of ILs and nanodroplets.
Protic ionic liquid ethylammonium nitrate nanodroplets at the interface can be formed by solvent exchange with controlled size, distribution, and stability in both liquid and air surroundings. These surface ethylammonium nitrate (EAN) nanodroplets are used as compartmentalized nanoreactors for templating SiO2 nanostructures. This work advances and intertwines the opportunities of ionic liquids and nanodroplets.
