Synthetic Bilayer Membranes: Molecular Design,Self-Organization,and Application

Lipid bilayers are a most central building block of the biological molecular organization. Their two-dimensional self-assembly is essential to the generation of biological shapes and sizes on the molecular level. The observation that a totally synthetic amphiphile in water is spontaneously assembled to a bilayer structure suggested that bilayer formation is a general physicochemical phenomenon that is not restricted to particular structures of biolipid molecules. Bilayer formation is now observed for a large variety of synthetic amphiphiles which contain one, two, three, or four alkyl tails. The flexible alkyl tail may be replaced by perfluoroalkyl chains. The supramolecular structures obtained therefrom can be related to the component's molecular structure in many cases. The structural variety and the ease of molecular design make the synthetic bilayer an attractive vehicle for organizing covalently bound functional units and guest molecules. In addition, stable monolayers on water, planar lipid membranes (BLM), and free-standing cast films are obtainable because of the self-assembling property of bilayer-forming compounds. These molecular organizations display common supramolecular features. The use of the cast film as a molecular template provides exciting potential for the production of novel two-dimensional materials.     

Electrode Materials for Desalination of Water via Capacitive Deionization

Recent years have seen the emergence of capacitive deionization (CDI) as a promising desalination technique for converting sea and wastewater into potable water, due to its energy efficiency and eco-friendly nature. However, its low salt removal capacity and parasitic reactions have limited its effectiveness. As a result, the development of porous carbon nanomaterials as electrode materials have been explored, while taking into account of material characteristics such as morphology, wettability, high conductivity, chemical robustness, cyclic stability, specific surface area, and ease of production. To tackle the parasitic reaction issue, membrane capacitive deionization (mCDI) was proposed which utilizes ion-exchange membranes coupled to the electrode. Fabrication techniques along with the experimental parameters used to evaluate the desalination performance of different materials are discussed in this review to provide an overview of improvements made for CDI and mCDI desalination purposes     

The Myelin Membrane of the Central Nervous System—Essential Macromolecular Structure and Function

The neural sheaths that surround the nerve fibers (axons) are composed of myelin-specific complex lipids and are assembled during the myelination phase either by the oligodendrocytes in the central nervous system (CNS) or by the Schwann cells in the peripheral nervous system. These multilayered myelin membranes insulate the axons and permit a rapid, saltatory conduction of excitation and a reduced axon diameter in comparison with noninsulated axons. Myelination was hence the decisive evolutionary event in miniaturization of the central nervous system (brain and spinal cord). The morphology of the myelin membrane has been studied in detail mainly by electron microscopy. Most of its biochemistry has been elucidated in recent years by molecular-level analysis of both the lipid components (cholesterol, phospholipids and sphingolipids) and the constituent proteins. The multilamellar system is distinguished by a characteristic periodicity due to the 5-nm-thick bilayer formed by the myelin-specific lipids. The bilayer interacts with the myelin basic protein (MBP) on the cytosolic side of the plasma membrane process, while the integral membrane protein proteolipid protein (PLP) has hydrophilic domains exposed on both the cytosolic and extracytosolic faces of the bilayer. Numerous protein-chemical and -immunotopochemical findings have been summarized in a model of the myelin membrane. Through molecular biological studies, the genetic structure and chromosomal location of the myelin proteins have been determined. By employing techniques of molecular and cell biology together, it is now possible to analyze the process of myelinogenesis, the time- and location-specific expression of myelin-specific genes in the brain. Gene-technological methods have been used to define the mutations in the models jimpy mouse and myelin-deficient rat. These are animal models that correspond to genetically determined myelin defects (dysmyelinoses) in humans. Using them, it will be possible to study the cell death of oligodendrocytes on a molecular level; this process is the result of expression of mutant myelin proteins and is incompatible with life. Oligodendrocytes and the myelin structures they synthesize are the target structures of cytotoxic lymphocytes (T_c). In the course of the demyelination process in multiple sclerosis, these cause the breakdown of the myelin sheaths, in gradually appearing inflammations. T_c lymphocytes recognize myelin structures as epitopes and destroy them. The picture of the myelin membrane's molecular composition, which we are now perfecting, will also lead to a better understanding of demyelination on a molecular level, and hence to new therapeutic possibilities.     

Principles of Osmotic Desalination

Salt solutions can be separated into pure water and concentrated salt solution by reverse osmosis using semipermeable membranes. The distinct features and limitations of osmotic separations are developed from a consideration of the pertinent solution properties and the conditions inherently to be met by the membranes, seen as interacting barrier phase in a process which substantially separates water from water.     

金属有机骨架材料/聚酰亚胺混合基质膜的制备及气体分离性能

合成了3种不同结构、 粒径和气体吸附性能的金属有机骨架材料(MOFs): 微米级Cu₃(BTC)₂、 亚微米级ZIF-8和S-Cu₃(BTC)₂. 氮气吸附等温线分析结果表明, ZIF-8和Cu₃(BTC)₂具有较大比表面积(1653和1439 m²/g), S-Cu₃(BTC)₂的比表面积为171.4 m²/g. 用共混法将MOFs直接引入聚酰亚胺中制备了MOFs/聚酰亚胺混合基质膜(MMMs). X射线衍射(XRD)和全反射红外光谱(FTIR-ATR)分析结果表明, MOFs在混合基质膜中保持物理和化学稳定. 气体渗透测试结果表明, MOFs的加入使膜的气体渗透分离性能明显提高, S-Cu₃(BTC)₂使渗透系数增加了1.75倍; ZIF-8和Cu₃(BTC)₂使渗透系数增加了3倍左右; 同时, 膜的气体分离系数变化很小.     

Mechanisms of Biological Ion Transport — Carriers,Channels, and Pumps in Artificial Lipid Membranes

The cell membrane contains specific systems for passive and active transport of ions between the cytoplasm and the extracellular medium. For a number of small and medium-sized transport molecules like valinomycin and gramicidin A, extensive structural and kinetic data are available and it is possible in these cases to understand the transport function on the basis of their molecular structure. Incorporation into artificial bimolecular lipid membranes opens up the possibility of studying the kinetic properties of biological transport systems in detail.     

Modeling the Selectivity of Potassium Channels with Synthetic,Ligand‐Assembled π Slides

A supramolecular ion channel model mediates transmembrane ion transport (shown schematically) with a selectivity topology similar to that of K⁺ channels. This supports the biological significance of flexible arene arrays as selective cation binding sites.     

Tertiary Amine and N‐Heterocyclic Carbene Coordinated Haloalanes—Synthesis,Structure, and Application

The preparation of several tertiary amine and N‐heterocyclic carbene coordinated chloro‐ and bromoalanes has been studied and routes to their gram‐scale synthesis optimized. This provides a catalogue of well‐characterized, thermally stable haloalanes for future application. All complexes have been investigated by spectroscopy (IR, NMR) and, where possible, single‐crystal X‐ray diffraction structure determination. A particular focus of this article is the relative thermal stabilities of the complexes, which provides a useful handle for the aerobic stability of Group 13 hydride complexes. These thermal data have been elucidated in full and rationalized relative to one another on the basis of Lewis base donation, steric shielding, and relative inductive halide strengthening of the aluminum hydride bonds by halides. All of the four‐coordinate complexes reported exist as distorted tetrahedra in the solid state with aluminum to N/C‐donor bonds that shorten with the increasing Lewis acidity of the aluminum Lewis acid. The five‐coordinate complexes [AlBrH₂(Quin)₂] and [AlBr₂H(Quin)₂] (Quin=quinuclidine) exist in a trigonal‐bipyramidal geometry in the solid state with the amine donors situated in the apical positions. Five chloroalanes; [AlClH₂(Quin)], [AlClH₂(Quin)₂], [AlCl₂H(Quin)₂], [AlClH₂(IMes)], and [AlCl₂H(IMes)] (IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene), the latter two of which are aerobically stable, have been applied to the hydroalumination of carbonyl and heterocycle substrates and their chemo‐, regio‐, and stereoselectivities compared to those of Group 13 hydride reagents cited in the literature. Overall, the reactivities of these species are comparable to non‐halogenated alane complexes with the additional benefit of aerobic stability, non‐pyrophoricity, and enhanced regioselectivity borne out of greater Lewis acidity.     

Asymmetric Membranes: Preparation and Applications

The separation of molecular mixtures by semipermeable membranes under the driving force of hydrostatic pressure has assumed major importance in recent years. Among other factors the development of membranes with asymmetric structure which, while having the same separating properties, afford a filtration output many times greater than that of the previously known symmetrical membranes, was decisive for this method. In the present progress report the structures of asymmetric membranes are discussed, as well as their preparation from various polymers and their application to the separation of molecular mixtures.     

Semiconductor Photocatalysis—Mechanistic and Synthetic Aspects

Preceding work on photoelectrochemistry at semiconductor single‐crystal electrodes has formed the basis for the tremendous growth in the three last decades in the field of photocatalysis at semiconductor powders. The reason for this is the unique ability of inorganic semiconductor surfaces to photocatalyze concerted reduction and oxidation reactions of a large variety of electron‐donor and ‐acceptor substrates. Whereas great attention was paid to water splitting and the exhaustive aerobic degradation of pollutants, only a small amount of research also explored synthetic aspects. After introducing the basic mechanistic principles, standard experiments for the preparation and characterization of visible light active photocatalysts as well as the investigation of reaction mechanisms are discussed. Novel atom‐economic C? C and C? N coupling reactions illustrate the relevance of semiconductor photocatalysis for organic synthesis, and demonstrate that the multidisciplinary field combines classical photochemistry with electrochemistry, solid‐state chemistry, and heterogeneous catalysis.     

Electrochemical Interfacial Polymerization toward Ultrathin COF Membranes for Brine Desalination

Ultrathin covalent organic framework (COF) membranes are urgently demanded in molecular/ionic separations. Herein, we reported an electrochemical interfacial polymerization strategy to fabricate ultrathin COF membranes with thickness of 85 nm, by actively manipulate self-healing effect and self-inhibiting effect. The resulting COF membrane exhibited superior performance in brine desalination with the permeation flux of 92 kg m⁻² h⁻¹ and the rejection of 99.96 %. Our electrochemical interfacial polymerization strategy enriches the fabrication approach of COF membranes and facilitates the rational design of ultrathin membranes.     

分级纳米材料的结构、制备及其应用

纳米材料因其独特的表面效应、体积效应和量子效应等特点,在化工、生物工程、医学和能源等领域有着广阔的应用。 由简单的低维纳米结构作为主要的构建单元并按照特定的排列方式组装成规整有序的三维结构,即分级纳米结构,已经开展了许多的研究。 本文综述了分级纳米结构的制备方法和微观结构,及其在污水处理、超级电容器、太阳能电池以及光催化等领域的应用。     

Preparation and Synthetic Application of Naproxen-Containing Diaryliodonium Salts

The synthesis of naproxen-containing diaryliodonium salts has been realized from naproxen methyl ester and ArI(OH)OTs activated by trimethylsilyl trifluoromethanesulfonate (TMSOTf) in a solvent mixture comprising dichloromethane and 2,2,2-trifluoroethanol (TFE). Those iodonium salts have been successfully used in the functionalization of an aromatic ring of naproxen methyl ester, including fluorination, iodination, alkynylation, arylation, thiophenolation, and amination and esterification reactions. Moreover, further hydrolysis of the obtained 5-iodo-naproxen methyl ester afforded 5-iodo-naproxen.     

Polymer Alloys—Their Structure,Morphology, and Properties

Polymeric materials with novel properties for new technological applications are increasingly obtained by combining existing polymers, while the synthesis of new monomers has receded into the background. These polymer combinations or “alloys” (polyblends) are characterized by their chemical composition, the conformation of the chain molecules, and the morphology, i.e. the state of order at supramolecular level. Multiphase constitution is a typical characteristic of these substances, with a decisive influence on their macroscopic properties. The morphology of multiphase polymer alloys can be controlled to a limited extent via the chemical composition of their components when homopolymers are mixed in the melt or as dispersions. Graft copolymerization, on the other hand, makes it possible to achieve the desired morphology at a given chemical composition. Furthermore, transprent two-phase polymer alloys can be obtained under certain conditions. In multiphase polymers the reduction of stress without fracture, caused by mechanical loading will be treated using models. Certain combinations of properties such as hardness and toughness are connected with the coexistence of disperse and continuous phases. Equilibrium thermodynamical criteria for liquid mixtures wil be used to explain demixing phenomena in polymers. In the last few years it has become possible to determine the chain conformation experimentally using neutron scattering.     

Preparation and Properties of Nanoporous Triblock Copolymer Membranes

“ Unplug those pores!” could be a slogan common to cosmetologists and polymer chemists. Membranes with nanochannels can be obtained by first forming a film by casting a solution of a triblock and homopolymer mixture, then selectively cross-linking domains in the film by photolysis, and finally forming nanochannels through removal of the homopolymer by solvent extraction. Such membranes are not liquid permeable but have gas-permeability constants about six orders of magnitude higher than that of low-density polyethylene films.