We have tested the ability of the OPLS–AA models (optimized potentials for liquid simulations) of alkanes and perfluoroalkanes recently developed by Jorgensen and co-workers to represent the unusual mixing behavior of alkane+perfluoroalkane systems. We find that these all-atom Lennard-Jones (6-12)+Coulomb representations, together with the usual Lorentz–Berthelot combining rules, fail to reproduce the weaker-than-anticipated interactions between these two classes of molecules. Systematic disagreements with experiment are found in the case of second pressure virial coefficients, gas solubilities, and liquid–liquid mixing properties. These discrepancies are not specific to the choice of OPLS–AA potentials, but are rather linked to the failure of the geometric mean combining rule for relating unlike atom interactions. In all cases examined, a reduction in the strength of cross H+F interactions by ∼25% relative to the geometric mean is required in order to achieve reasonable agreement with experiment. Several less commonly used combining rules were also examined. Although some of these rules are able to provide a reasonable description of the interactions among perfluoroalkane and alkane species, they fail to provide a consistent treatment when atoms other than C, H, and F are considered, as is necessary for modeling the interaction of the former molecules with rare-gas atoms.

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.

Data from prior simulation and experimental studies (a total of 52 solute/solvent pairs) are collected and analyzed in an attempt to relate the extent of local density augmentation in supercritical fluids to the strength of intermolecular interactions. For this purpose, intermolecular potential functions consisting of pairwise additive atom-atom potentials, with parameters either taken from literature sources or derived from quantum chemical calculations, are constructed and tested against experimental second-pressure virial coefficient data. For the solute-solvent combinations of interest in supercritical systems near room temperature, such potentials are found to reproduce experimental second-pressure virial coefficient data with reasonable accuracy. On the basis of these potentials, a variety of characteristics of solute-solvent and solvent-solvent interactions are computed and compared to simulated and experimental measures of density augmentation. It is found that the extent of augmentation is strongly correlated to measures of the free energy of solute-solvent interaction. However, simulated and experimental augmentation data apparently follow distinct correlations with these free energies, indicating the presence of a widespread error in either the measurement or the interpretation of density augmentation in supercritical solvents.

Artificial water channels are synthetic molecules that aim to mimic 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 clusters

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The outstanding capacity of aquaporins (AQPs) for mediating highly selective superfast water transport 1-7 has inspired recent development of supramolecular monovalent ion-excluding artificial water channels (AWCs). AWC-based bioinspired membranes are proposed for desalination, water purification, and other separations applications [8][9][10][11][12][13][14][15][16][17][18] . While some recent progress has been made in synthesizing AWCs that approach the water permeability and ion selectivity of AQPs, a hallmark feature of AQPshigh water transport while excluding protons has not been reproduced. We report on a class of biomimetic, helically folded pore-forming polymeric foldamers, that can serve as long sought-after highly selective ultrafast water-conducting channels exceeding those of AQPs (1.1 × 10 10 H2O molecules/s for AQP1 7 ), with high water over monovalent ion transport selectivity (~10 8 water molecules over Clion) conferred by the modularly tunable hydrophobicity of the interior pore surface. The best-performing AWC reported here delivers water transport at an exceptionally high rate, 2.5 times that of AQP1, while concurrently rejecting salts (NaCl and KCl) and even protons.

Aquaporins (AQPs) are naturally occurring water channel proteins. They can facilitate water molecule translocation across cellular membranes with exceptional selectivity and high permeability that are unmatched in synthetic membrane systems. These unique properties of AQPs have led to their use as functional elements in membranes in recent years. However, the intricate nature of AQPs and concerns regarding their stability and processability have encouraged researchers to develop synthetic channels that mimic the structure and properties of AQPs and other biological water-conducting channels. These channels have been termed artificial water channels. This article reviews current progress and provides a historical perspective as well as an outlook toward developing scalable membranes based on artificial water channels.

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