Blockable Zn10L15 Ion Channels through Subcomponent Self‐Assembly

Metal–organic anion channels based on Zn₁₀L₁₅ pentagonal prisms have been prepared by subcomponent self‐assembly. The insertion of these prisms into lipid membranes was investigated by ion‐current and fluorescence measurements. The channels were found to mediate the transport of Cl⁻ anions through planar lipid bilayers and into vesicles. Tosylate anions were observed to bind and plug the central channels of the prisms in the solid state and in solution. In membranes, dodecyl sulfate blocked chloride transport through the central channel. Our Zn₁₀L₁₅ prism thus inserts into lipid bilayers to turn on anion transport, which can then be turned off through addition of the blocker dodecyl sulfate.     

Experimental and Computational Analysis of the Solvent‐Dependent O2/Li+‐O2− Redox Couple: Standard Potentials,Coupling Strength,and Implications for Lithium–Oxygen Batteries

Understanding and controlling the kinetics of O₂ reduction in the presence of Li⁺‐containing aprotic solvents, to either Li⁺‐O₂⁻ by one‐electron reduction or Li₂O₂ by two‐electron reduction, is instrumental to enhance the discharge voltage and capacity of aprotic Li‐O₂ batteries. Standard potentials of O₂/Li⁺‐O₂⁻ and O₂/O₂⁻ were experimentally measured and computed using a mixed cluster‐continuum model of ion solvation. Increasing combined solvation of Li⁺ and O₂⁻ was found to lower the coupling of Li⁺‐O₂⁻ and the difference between O₂/Li⁺‐O₂⁻ and O₂/O₂⁻ potentials. The solvation energy of Li⁺ trended with donor number (DN), and varied greater than that of O₂⁻ ions, which correlated with acceptor number (AN), explaining a previously reported correlation between Li⁺‐O₂⁻ solubility and DN. These results highlight the importance of the interplay between ion–solvent and ion–ion interactions for manipulating the energetics of intermediate species produced in aprotic metal–oxygen batteries.     

Metal‐Chelated Polymer Nanodiscs for NMR Studies

Paramagnetic relaxation enhancement (PRE) is commonly used to speed up spin lattice relaxation time (T₁) for rapid data acquisition in NMR structural studies. Consequently, there is significant interest in novel paramagnetic labels for enhanced NMR studies on biomolecules. Herein, we report the synthesis and characterization of a modified poly(styrene‐co‐maleic acid) polymer which forms nanodiscs while showing the ability to chelate metal ions. Cu²⁺‐chelated nanodiscs are demonstrated to reduce the T₁ of protons for both polymer and lipid‐nanodisc components. The chelated nanodiscs also decrease the proton T₁ values for a water‐soluble DNA G‐quadruplex. These results suggest that polymer nanodiscs functionalized with paramagnetic tags can be used to speed‐up data acquisition from lipid bilayer samples and also to provide structural information from water‐soluble biomolecules.     

Identification of Key Reversible Intermediates in Self‐Reconstructed Nickel‐Based Hybrid Electrocatalysts for Oxygen Evolution

The oxygen evolution reaction (OER) has been explored extensively for reliable hydrogen supply to boost the energy conversion efficiency. The superior OER performance of newly developed non‐noble metal electrocatalysts has concealed the identification of the real active species of the catalysts. Now, the critical active phase in nickel‐based materials (represented by NiNPS) was directly identified by observing the dynamic surface reconstruction during the harsh OER process via combining in situ Raman tracking and ex situ microscopy and spectroscopy analyses. The irreversible phase transformation from NiNPS to α‐Ni(OH)₂ and reversible phase transition between α‐Ni(OH)₂ and γ‐NiOOH prior to OER demonstrate γ‐NiOOH as the key active species for OER. The hybrid catalyst exhibits 48‐fold enhanced catalytic current at 300 mV and remarkably reduced Tafel slope to 46 mV dec^?1, indicating the greatly accelerated catalytic kinetics after surface evolution.     

A Dimeric Bis(melamine)‐Substituted Bispidine for Efficient Transmembrane H+/Cl− Cotransport

A 3,7‐diazabicyclo[3.3.1]nonane linking to two melamines is a unique transmembrane H⁺/Cl⁻ carrier. In the solid state, the V‐shaped compound forms a HCl‐bound zig‐zag network through cooperative protonation and hydrogen bond interactions. In the lipid membrane, the receptor forms a dimeric self‐assembly involving multiple H⁺ and Cl⁻ leading to the efficient transport of the acid. The pH‐dependent Cl⁻ efflux observed for the compound was rationalized based on a gradual protonation model that confers an active transmembrane carrier at physiological pH.     

Ca2+ induced Fe(CN)63−/4− electron transfer at Pt supported BLM electrode

The effect of Ca²⁺ on the electron transfer of Fe(CN)₆^3−/4− couple at Pt supported lecithin (PC)/cholesterol (CH) bilayer lipid membrane (BLM) electrode has been studied by voltammetry and ac impedance spectroscopy. Experimental results suggest that the interaction of Ca²⁺ with the BLM can open some kind of channel for Fe(CN)₆^3−/4− ions, allowing increased access of the redox couple to the electrode surface. This phenomenon may be related to the Ca²⁺ regulation or activation effect of ion channel in some biomembranes.     

A Bottom‐Up Proteomic Approach to Identify Substrate Specificity of Outer‐Membrane Protease OmpT

Identifying peptide substrates that are efficiently cleaved by proteases gives insights into substrate recognition and specificity, guides development of inhibitors, and improves assay sensitivity. Peptide arrays and SAMDI mass spectrometry were used to identify a tetrapeptide substrate exhibiting high activity for the bacterial outer‐membrane protease (OmpT). Analysis of protease activity for the preferred residues at the cleavage site (P1, P1′) and nearest‐neighbor positions (P2, P2′) and their positional interdependence revealed FRRV as the optimal peptide with the highest OmpT activity. Substituting FRRV into a fragment of LL37, a natural substrate of OmpT, led to a greater than 400‐fold improvement in OmpT catalytic efficiency, with a k _cat/K _m value of 6.1×10⁶ L mol⁻¹ s⁻¹. Wild‐type and mutant OmpT displayed significant differences in their substrate specificities, demonstrating that even modest mutants may not be suitable substitutes for the native enzyme.     

Scandium‐Catalyzed Self‐Assisted Polar Co‐monomer Enchainment in Ethylene Polymerization

Direct coordinative copolymerization of ethylene with functionalized co‐monomers is a long‐sought‐after approach to introducing polyolefin functionality. However, functional‐group Lewis basicity typically depresses catalytic activity and co‐monomer incorporation. Finding alternatives to intensively studied group 4 d⁰ and late‐transition‐metal catalysts is crucial to addressing this long‐standing challenge. Shown herein is that mono‐ and binuclear organoscandium complexes with a borate cocatalyst are active for ethylene + amino olefin [AO; H₂C=CH(CH₂)_nNR₂] copolymerizations in the absence of a Lewis‐acidic masking reagent. Both activity (up to 4.2×10² kg mol⁻¹⋅h^−1> atm^−1>) and AO incorporation (up to 12 % at 0.2 m [AO]) are appreciable. Linker‐length‐dependent (n) AO incorporation and mechanistic probes support an unusual functional‐group‐assisted enchainment mechanism. Furthermore, the binuclear catalysts exhibit enhanced AO tolerance and enhanced long chain AO incorporation.     

Tip penetration through lipid bilayers in atomic force microscopy

In studies of solid supported lipid bilayers with atomic force microscopes (AFM) the force between tip and bilayer is routinely measured. During the approach of the AFM tip in aqueous electrolyte first a short-range repulsive force is observed. For many solid-like and some liquid-like lipid bilayers a subsequent break-through is observed. We observe such a break-through also for dioleoyloxypropyl-trimethylammonium chloride (DOTAP) which is expected to be liquid-like. Here we describe a model which assumes that the jump reflects the penetration of the AFM tip through the lipid bilayer. The model predicts a logarithmical dependence of the break-through force on the approaching velocity of the AFM tip. Two parameters are introduced: The ratio A/αV, α being a geometric factor, A being the area over which pressure is exerted on the bilayer, V the activation volume, and k₀, the rate of spontaneous formation of a hole in the lipid bilayer that is big enough to allow the break-through of the tip. Experiments with bilayers consisting of DOTAP and dioleoylphosphatidylserine (DOPS) show that the break-through forces behave in the predicted way. For DOTAP we obtain ratios A/αV of about 58 nm⁻¹ and rates k₀ ranging from 1.9×10⁻⁸ to 2.5×10⁻⁴ s⁻¹. For DOPS the corresponding values are 162 nm⁻¹ and 2.0 s⁻¹.     

Molecular Swings as Highly Active Ion Transporters

Ions are transported across membrane mostly via carrier or channel mechanisms. Herein, a unique class of molecular‐machine‐inspired membrane transporters, termed molecular swings is reported that utilize a previously unexplored swing mechanism for promoting ion transport in a highly efficient manner. In particular, the molecular swing, which carries a 15‐crown‐5 unit as the ion‐binding and transporting unit, exhibits extremely high ion‐transport activities with EC₅₀ values of 46 nm (a channel:lipid molar ratio of 1:4800 or 0.021 mol % relative to lipid) and 110 nm for K⁺ and Na⁺ ions, respectively. Remarkably, such ion transport activities remain high in a cholesterol‐rich environment, with EC₅₀ values of 130 (0.045 mol % relative to lipid/cholesterol) and 326 nm for K⁺ and Na⁺ ions, respectively.     

Temperature‐Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

The rate coefficients for gas‐phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240–340 K. The rate coefficients k(CH₂OO + CF₃COOH)=(3.4±0.3)×10⁻¹⁰ cm³ s⁻¹ and k((CH₃)₂COO + CF₃COOH)=(6.1±0.2)×10⁻¹⁰ cm³ s⁻¹ at 294 K exceed estimates for collision‐limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre‐reactive complex. Fits to a model incorporating this complex formation give k [cm³ s⁻¹]=(3.8±2.6)×10⁻¹⁸ T² exp((1620±180)/T) + 2.5×10⁻¹⁰ and k [cm³ s⁻¹]=(4.9±4.1)×10⁻¹⁸ T² exp((1620±230)/T) + 5.2×10⁻¹⁰ for the CH₂OO + CF₃COOH and (CH₃)₂COO + CF₃COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.     

Molecular mechanics simulation studies of dienoic hydrocarbons: From alkenes to 1-Palmitoyl-2-linoleoyl-phosphatidylcholines

Although no crystal structures of mixed-chain phosphatidylcholines with unsaturated sn-2 acyl chains exist, the force field method in conjunction with the experimentally determined structure of saturated identical-chain phosphatidylcholine can be applied to simulate molecular structure for mixed-chain phosphatidylcholines. In this study, the packing models of mixed-chain 1-palmitoyl-2-linoleoyl-phosphatidylcholines in bilayers at temperatures below the gel-liquid crystalline phase transition temperature or T < T_m are simulated by using Allinger's MM3(92) force field. Our results indicate that the unsaturated sn-2 acyl chains of the mixed-chain lipid can fold into two energy-minimized topologies: the crankshaftlike and the U-shaped motifs. The folded region in the crankshiftlike sn-2 acyl chain is characterized by a sequence s⁻ Δs⁺s⁺Δs⁻, and the U-shaped chain arises from the characteristic sequence s⁻Δs⁺s⁻Δs⁺, where s^± denotes the ± skew conformation and Δ the cis carbon-carbon double bond. These modeled structures of 1-palmitoyl-2-linoleoyl-phosphatidylcholines in the bilayer at T < T_m should not be regarded as highly rigid structures, since torsion angles of carbon-carbon bonds associated with sequences s Δs⁺s⁺Δs and s Δs⁺s⁻Δ s⁺ can fluctuate somewhat without appreciably affecting the steric energy of the corresponding lipid bilayer. © 1996 by John Wiley & Sons, Inc.     

An Ultrastable and Easily Regenerated Hydrogen‐Bonded Organic Molecular Framework with Permanent Porosity

A robust hydrogen‐bonded organic framework HOF‐TCBP (H₄TCBP=3,3′,5,5′‐tetrakis‐(4‐carboxyphenyl)‐1,1′‐biphenyl) has been successfully constructed and structurally characterized. It possesses a permanent 3D porous structure with a 5‐fold interpenetrated dia topological network. This activated HOF‐TCBP has a high BET surface area of 2066 m² g⁻¹ and is capable of highly selective adsorption and separation of light hydrocarbons under ambient conditions. It shows excellent thermal stability, as demonstrated by PXRD experiments and N₂ adsorption tests. Practical use of HOF‐TCBP is facilitated by the ease of its preparation and renewal through rotary evaporation.     

Ion Channel Behavior of a Supported Bilayer Lipid Membrane Composed of 5,5－Ditetradecyl－2－ （2－trimethyl－ammonioethyl）－l, 3－dioxane Bromide Modified Glassy Carbon Electrode

A synthetic cationic surfactant, 5,5-ditetradecyl-2-(2-trimethyl-ammonioethyl)-l,3-dioxane bromide (DTDB), was used to construct a supported bilayer lipid membrane (s-BLM) coatedon an underlying glassy carbon electrode (GCE). Electrochemical impedance spectroscopy (EIS), small-angle X-ray diffraction (SAXD) and cyclic voltammetry were used to characterize the s-BLM. Both EIS and SAXD data indicated that the synthetic lipid exists as a well-oriented bilayer in the membrane.The voltammetric study showed that the lipid membrane can open ion channels in the presence of ClO4^- stimulant with Ru(bpy)3^2 as marker ions and give distinct channel currents.The channels can be dosed and open up again many times by removing or introducing ClO4^- anions.     

Nanoscale Surface Modification of Lithium‐Rich Layered‐Oxide Composite Cathodes for Suppressing Voltage Fade

Lithium‐rich layered oxides are promising cathode materials for lithium‐ion batteries and exhibit a high reversible capacity exceeding 250 mAh g⁻¹. However, voltage fade is the major problem that needs to be overcome before they can find practical applications. Here, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LLMO) oxides are subjected to nanoscale LiFePO₄ (LFP) surface modification. The resulting materials combine the advantages of both bulk doping and surface coating as the LLMO crystal structure is stabilized through cationic doping, and the LLMO cathode materials are protected from corrosion induced by organic electrolytes. An LLMO cathode modified with 5 wt % LFP (LLMO–LFP5) demonstrated suppressed voltage fade and a discharge capacity of 282.8 mAh g⁻¹ at 0.1 C with a capacity retention of 98.1 % after 120 cycles. Moreover, the nanoscale LFP layers incorporated into the LLMO surfaces can effectively maintain the lithium‐ion and charge transport channels, and the LLMO–LFP5 cathode demonstrated an excellent rate capacity.     

Water Transport with Ultralow Friction through Partially Exfoliated g‐C3N4 Nanosheet Membranes with Self‐Supporting Spacers

Two‐dimensional (2D) graphitic carbon nitride (g‐C₃N₄) nanosheets show brilliant application potential in numerous fields. Herein, a membrane with artificial nanopores and self‐supporting spacers was fabricated by assembly of 2D g‐C₃N₄ nanosheets in a stack with elaborate structures. In water purification the g‐C₃N₄ membrane shows a better separation performance than commercial membranes. The g‐C₃N₄ membrane has a water permeance of 29 L m⁻² h⁻¹ bar⁻¹ and a rejection rate of 87 % for 3 nm molecules with a membrane thickness of 160 nm. The artificial nanopores in the g‐C₃N₄ nanosheets and the spacers between the partially exfoliated g‐C₃N₄ nanosheets provide nanochannels for water transport while bigger molecules are retained. The self‐supported nanochannels in the g‐C₃N₄ membrane are very stable and rigid enough to resist environmental challenges, such as changes to pH and pressure conditions. Permeation experiments and molecular dynamics simulations indicate that a novel nanofluidics phenomenon takes place, whereby water transport through the g‐C₃N₄ nanosheet membrane occurs with ultralow friction. The findings provide new understanding of fluidics in nanochannels and illuminate a fabrication method by which rigid nanochannels may be obtained for applications in complex or harsh environments.     

Synthetic Nanosheets of Natural van der Waals Heterostructures

Creation of new van der Waals heterostructures by stacking different two dimensional (2D) crystals on top of each other in a chosen sequence is the next challenge after the discovery of graphene, mono/few layer of h ‐BN, and transition‐metal dichalcogenides. However, chemical syntheses of van der Waals heterostructures are rarer than the physical preparation techniques. Herein, we demonstrate the kinetic stabilization of 2D ultrathin heterostructure (ca. 1.13–2.35 nm thick) nanosheets of layered intergrowth SnBi₂Te₄, SnBi₄Te₇, and SnBi₆Te₁₀, which belong to the Sn_m Bi_2n Te_{3n +m} homologous series, by a simple solution based synthesis. Few‐layer nanosheets exhibit ultralow lattice thermal conductivity (κ _lat) of 0.3–0.5 W m⁻¹ K⁻¹ and semiconducting electron‐transport properties with high carrier mobility.     

From Discrete Molecular Cages to a Network of Cages Exhibiting Enhanced CO2 Adsorption Capacity

We have adopted the concept of “cage to frameworks” to successfully produce a Na–N connected coordination networked cage Na‐NC1 by using a [3+6] porous imine‐linked organic cage NC1 (Nanjing Cage 1) as the precursor. It is found that Na‐NC1 exhibits hierarchical porosity (inherent permanent voids and interconnected channel) and gas sorption measurements reveal a significantly enhanced CO₂ uptake (1093 cm³ g⁻¹ at 23 bar and 273 K) than that of NC1 (162 cm³ g⁻¹ under the same conditions). In addition, Na‐NC1 exhibits very low CO₂ adsorption enthalpy making it a good candidate for porous materials with both high CO₂ storage and low adsorption enthalpy.     

Microporous Cyclic Titanium‐Oxo Clusters with Labile Surface Ligands

By using ethylene glycol and monocarboxylic acid as surface ligands, a series of cyclic Ti‐oxo clusters (CTOC) with permanent microporosity are successfully synthesized. With a cyclic {Ti₃₂O₁₆} backbone made of eight connected Ti₄ tetrahedral cages that are arranged in a zigzag fashion, the clusters have a “donut” shape with an inner diameter of 8.3 Å, outer diameter of 26.9 Å and height of 10.4 Å. While both inner and outer walls of the “donut” clusters are modified by double‐deprotonated ethylene glycolates, their upper and lower surfaces are bound by carboxylates and mono‐deprotonated ethylene glycolates. The clusters are readily packed into one‐dimensional tubes which are further arranged in two different modes into crystalline microporous solids with surface areas over 660 m² g⁻¹, depending on the surface carboxylates. The solid with olefin‐bearing carboxylates exhibits a superior CO₂ adsorption capacity of 40 cm³ g⁻¹ at 273 K under 1 atm. Moreover, the mono‐deprotonated ethylene glycolates on the clusters are demonstrated to be highly exchangeable by other alcohols, providing a nice platform for creating microporous solids or films with a wide variety of surface functionalities.