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Phase separation of intrinsically disordered proteins (IDPs) is a remarkable feature of living cells to dynamically control intracellular partitioning. Despite the numerous new IDPs that have been identified, progress towards rational engineering in cells has been limited. To address this limitation, we systematically scanned the sequence space of native IDPs and designed artificial IDPs (A-IDPs) with different molecular weights and aromatic content, which exhibit variable condensate saturation concentrations and temperature cloud points in vitro and in cells. We created A-IDP puncta using these simple principles, which are capable of sequestering an enzyme and whose catalytic efficiency can be manipulated by the molecular weight of the A-IDP. These results provide a robust engineered platform for creating puncta with new, phase-separation-mediated control of biological function in living cells.Artificial intrinsically disordered proteins (A-IDPs) have now been shown to form exclusionary, intracellular droplets that can be designed using simple principles that are based on the aromatic/aliphatic ratio and molecular weight. Droplets that sequester an enzyme and modulate enzyme efficiency on the basis of the molecular weight of the A-IDPs were also engineered using A-IDPs as a minimal condensate scaffold.

Anion effects on the cloud-point temperature for the liquid-liquid phase transition of lysozyme were investigated by temperature gradient microfluidics under a dark field microscope. It was found that protein aggregation in salt solutions followed 2 distinct Hofmeister series depending on salt concentration. Namely, under low salt conditions the association of anions with the positively charged lysozyme surface dominated the process and the phase transition temperature followed an inverse Hofmeister series. This inverse series could be directly correlated to the size and hydration thermodynamics of the anions. At higher salt concentrations, the liquid-liquid phase transition displayed a direct Hofmeister series that correlated with the polarizability of the anions. A simple model was derived to take both charge screening and surface tension effects into account at the protein/water interface. Fitting the thermodynamic data to this model equation demonstrated its validity in both the high and low salt regimes. These results suggest that in general positively charged macromolecular systems should show inverse Hofmeister behavior only at relatively low salt concentrations, but revert to a direct Hofmeister series as the salt concentration is increased.

On planet Earth, water is everywhere: the majority of the surface is covered with it; it is a key component of all life; its vapour and droplets fill the lower atmosphere; and even rocks contain it and undergo geomorphological changes because of it. A community of physical scientists largely drives studies of the chemistry of water and aqueous solutions, with expertise in biochemistry, spectroscopy and computer modelling. More recently, however, supramolecular chemists -- with their expertise in macrocyclic synthesis and measuring supramolecular interactions -- have renewed their interest in water-mediated non-covalent interactions. These two groups offer complementary expertise that, if harnessed, offer to accelerate our understanding of aqueous supramolecular chemistry and water writ large. This Review summarizes the state-of-the-art of the two fields, and highlights where there is latent chemical space for collaborative exploration by the two groups.

Artificial water channels are synthetic molecules that aim to mimic the structural and functional features of biological water channels (aquaporins). Here we report on a cluster-forming organic nanoarchitecture, peptide-appended hybrid[4]arene (PAH[4]), as a new class of artificial water channels. Fluorescence experiments and simulations demonstrated that PAH[4]s can form, through lateral diffusion, clusters in lipid membranes that provide synergistic membrane-spanning paths for a rapid and selective water permeation through water-wire networks. Quantitative transport studies revealed that PAH[4]s can transport >109 water molecules per second per molecule, which is comparable to aquaporin water channels. The performance of these channels exceeds the upper bound limit of current desalination membranes by a factor of ~104, as illustrated by the water/NaCl permeability–selectivity trade-off curve. PAH[4]’s unique properties of a high water/solute permselectivity via cooperative water-wire formation could usher in an alternative design paradigm for permeable membrane materials in separations, energy production and barrier applications.Cooperative water wires formed by clustering of artificial water channels enhance membrane permselectivity.

Synthetic polymer membranes, critical to diverse energy-efficient separations, are subject to permeability-selectivity trade-offs that decrease their overall efficacy. These trade-offs are due to structural variations (e.g., broad pore size distributions) in both nonporous membranes used for Angstrom-scale separations and porous membranes used for nano to micron-scale separations. Biological membranes utilize well-defined Angstrom-scale pores to provide exceptional transport properties and can be used as inspiration to overcome this trade-off. Here, we present a comprehensive demonstration of such a bioinspired approach based on pillar[5]arene artificial water channels, resulting in artificial water channel-based block copolymer membranes. These membranes have a sharp selectivity profile with a molecular weight cutoff of ~ 500 Da, a size range challenging to achieve with current membranes, while achieving a large improvement in permeability (~65 L m −2  h −1  bar −1  compared with 4–7 L m −2  h −1  bar −1 ) over similarly rated commercial membranes. Synthetic polymeric membranes used for separations suffer from permeability-selectivity trade-offs. Here the authors demonstrate how a bioinspired pillar[5]arene artificial water channel embedded in a copolymer membrane can improve selectivity while still achieving high permeability.

Research efforts related to the Hofmeister series of salt ions have waxed and waned during its long and storied history. The past few decades have, however, witnessed a renaissance in its study, and the importance of the related solvation science is becoming ever more apparent.

Abstract Hydrophobic hydration, whereby water spontaneously structures around hydrophobic and amphiphilic molecules, plays a key role in the process of surfactant micelle formation and micellar oil solubilization. Using vibrational Raman multivariate curve resolution spectroscopy, we characterized changes in the hydrophobic hydration occurring within nonionic alkylphenol ethoxylate surfactant Tergitol NP‐12 micelles as a function of oil solubilization. We report trends in the changes of hydrophobic hydration depending on the chain length of the oil as well as the presence of a halogen atom in the oil chemical structure. Changes in hydrophobic hydration directly correlate to changes in the physical properties of the micellar solution, including cloud point and micelle hydrodynamic diameter. We compare hydrophobic hydration of Tergitol NP‐12 to nonionic linear alkyl ethoxylate surfactant Makon TD‐12 and ionic sodium dodecyl sulfate and observe similar trends; the molecular structure of the oil has the largest impact on the hydrophobic hydration. We believe these studies contribute to a fundamental understanding of the importance of hydrophobic hydration in surfactant and oil aggregates, especially as it relates to micellar oil solubilization, and provide insight into how the molecular solubilizate can impact micellar structure, size, and stability.

We have developed a microfluidic assay for bacterial chemotaxis in which a gradient of chemoeffectors is established inside a microchannel via diffusion between parallel streams of liquid in laminar flow. The random motility and chemotactic responses to L-aspartate, L-serine, L-leucine, and Ni2+of WT and chemotactic-mutant strains of Escherichia coli were measured. Migration of the cells was quantified by counting the cells accumulating in each of 22 outlet ports. The sensitivity of the assay is attested to by the significant response of WT cells to 3.2 nM L-aspartate, a concentration three orders of magnitude lower than the detection limit in the standard capillary assay. The response to repellents was as robust and easily recorded as the attractant response. A surprising discovery was that L-leucine is sensed by Tar as an attractant at low concentrations and by Tsr as a repellent at higher concentrations. This assay offers superior performance and convenience relative to the existing assays to measure bacterial tactic responses, and it is flexible enough to be used in a wide range of different applications.

The ability of cells or cell components to move in response to chemical signals is critical for the survival of living systems. This motion arises from harnessing free energy from enzymatic catalysis. Artificial model protocells derived from phospholipids and other amphiphiles have been made and their enzymatic-driven motion has been observed. However, control of directionality based on chemical cues (chemotaxis) has been difficult to achieve. Here we show both positive or negative chemotaxis of liposomal protocells. The protocells move autonomously by interacting with concentration gradients of either substrates or products in enzyme catalysis, or Hofmeister salts. We hypothesize that the propulsion mechanism is based on the interplay between enzyme-catalysis-induced positive chemotaxis and solute–phospholipid-based negative chemotaxis. Controlling the extent and direction of chemotaxis holds considerable potential for designing cell mimics and delivery vehicles that can reconfigure their motion in response to environmental conditions.

Weakly hydrated anions help to solubilize hydrophobic macromolecules in aqueous solutions, but small molecules comprising the same chemical constituents precipitate out when exposed to these ions. Here, this apparent contradiction is resolved by systematically investigating the interactions of NaSCN with polyethylene oxide oligomers and polymers of varying molecular weight. A combination of spectroscopic and computational results reveals that SCN − accumulates near the surface of polymers, but is excluded from monomers. This occurs because SCN − preferentially binds to the centre of macromolecular chains, where the local water hydrogen-bonding network is disrupted. These findings suggest a link between ion-specific effects and theories addressing how hydrophobic hydration is modulated by the size and shape of a hydrophobic entity. Weakly hydrated anions solubilize macromolecules but cause small molecules that are made from identical chemical constituents to precipitate out of aqueous solutions. Now, this phenomenon has been understood by demonstrating that the binding of anions to polymers is regulated by molecular curvature and interfacial water structure.