Cyclohexane Rings Reduce Membrane Permeability to Small Ions in Archaea‐Inspired Tetraether Lipids

Extremophile archaeal organisms overcome problems of membrane permeability by producing lipids with structural elements that putatively improve membrane integrity compared to lipids from other life forms. Herein, we describe a series of lipids that mimic some key structural features of archaeal lipids, such as: 1) single tethering of lipid tails to create fully transmembrane tetraether lipids and 2) the incorporation of small rings into these tethered segments. We found that membranes formed from pure tetraether lipids leaked small ions at a rate that was about two orders of magnitude slower than common bilayer‐forming lipids. Incorporation of cyclopentane rings into the tetraether lipids did not affect membrane leakage, whereas a cyclohexane ring reduced leakage by an additional 40 %. These results show that mimicking certain structural features of natural archaeal lipids results in improved membrane integrity, which may help overcome limitations of many current lipid‐based technologies.     

Effect of the Structure of Cholesterol‐Based Tethered Bilayer Lipid Membranes on Ionophore Activity

Tethered bilayer lipid membranes (tBLM) are formed on 1) pure tether lipid triethyleneoxythiol cholesterol (EO₃C) or on 2) mixed self‐assembled monolayers (SAMs) of EO₃C and 6‐mercaptohexanol (6MH). While EO₃C is required to form a tBLM with high resistivity, 6MH dilutes the cholesterol content in the lower leaflet of the bilayer forming ionic reservoirs required for submembrane hydration. Here we show that these ionic reservoirs are required for ion transport through gramicidin or valinomycin, most likely due to the thermodynamic requirements of ions to be solvated once transported through the membrane. Unexpectedly, electrochemical impedance spectroscopy (EIS) shows an increase of capacitance upon addition of gramicidin, while addition of valinomycin decreases the membrane resistance in the presence of K⁺ ions. We hypothesise that this is due to previously reported phase separation of EO₃C and 6MH on the surface. This results in ionic reservoirs on the nanometre scale, which are not fully accounted for by the equivalent circuits used to describe the system.     

膜片电极支撑自组装双层脂膜中短杆菌肽离子通道的形成

通过一个两步程序在膜片电极尖端形成自组装双层脂膜：（1）膜片电极尖端沾取成膜液；（2）将吸附成膜液的尖端浸入电解液中，排除尖端多余的成膜液，通过电学方法监测双层脂膜的形成。将短杆菌肽通道蛋白分散在成膜液和电解质溶液中，在制备膜片电极支撑双层脂膜过程中，短杆菌肽重组到双层脂膜中形成离子通道，对通道的一般特性进行了研究，并观察到通道开放和关闭的现象。     

The Effect of Bacterial Signal Indole on the Electrical Properties of Lipid Membranes

Indole is an important biological signalling molecule produced by many Gram positive and Gram negative bacterial species, including Escherichia coli. Here we study the effect of indole on the electrical properties of lipid membranes. Using electrophysiology, we show that two indole molecules act cooperatively to transport charge across the hydrophobic core of the lipid membrane. To enhance charge transport, induced by indole across the lipid membrane, we use an indole derivative, 4 fluoro‐indole. We demonstrate parallels between charge transport through artificial lipid membranes and the function of complex eukaryotic membrane systems by showing that physiological indole concentrations increase the rate of mitochondrial oxygen consumption. Our data provide a biophysical explanation for how indole may link the metabolism of bacterial and eukaryotic cells.     

Functional Tethered Bilayer Lipid Membranes on Aluminum Oxide

Tethered bilayer lipid membranes are established as well‐suited model membrane systems adaptable to different surfaces, for example, gold and silicon. These solid supported membranes are highly flexible in their tethering and lipid parts and can thus be optimized for functional incorporation of membrane proteins. The excellent sealing properties of the tethered membranes allow incorporated ion‐channel proteins to be investigated. Preparation of ultrasmooth aluminum oxide by sputtering and synthesis of new tethering lipids with phosphonic acid anchor groups enable formation of an electrically sealing membrane on this surface. This process is monitored by electrochemical impedance spectroscopy and by surface plasmon resonance spectroscopy. High sealing performance of the membrane and functional incorporation of the ion carrier valinomycin are demonstrated.     

Dendritic Domains with Hexagonal Symmetry Formed by X‐Shaped Bolapolyphiles in Lipid Membranes

A novel class of bolapolyphile (BP) molecules are shown to integrate into phospholipid bilayers and self‐assemble into unique sixfold symmetric domains of snowflake‐like dendritic shapes. The BPs comprise three philicities: a lipophilic, rigid, π–π stacking core; two flexible lipophilic side chains; and two hydrophilic, hydrogen‐bonding head groups. Confocal microscopy, differential scanning calorimetry, XRD, and solid‐state NMR spectroscopy confirm BP‐rich domains with transmembrane‐oriented BPs and three to four lipid molecules per BP. Both species remain well organized even above the main 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine transition. The BP molecules only dissolve in the fluid membrane above 70 °C. Structural variations of the BP demonstrate that head‐group hydrogen bonding is a prerequisite for domain formation. Independent of the head group, the BPs reduce membrane corrugation. In conclusion, the BPs form nanofilaments by π stacking of aromatic cores, which reduce membrane corrugation and possibly fuse into a hexagonal network in the dendritic domains.     

平板双分子层脂膜的制备及锌离子跨该膜的输运过程

制备了氧化胆固醇 卵磷脂(脑磷脂)平板双分子层脂膜,研究了膜配方对双分子层脂膜的稳定性和离子通透性的影响,得到了最佳制膜工艺,建立了锌离子跨卵 (脑 )磷脂膜的吸附 -扩散模型,其计算值与实验值基本吻合.     

Bio‐Inspired Fabrication of Lotus Leaf Like Membranes as Fluorescent Sensing Materials

A fluorescent organic small molecule, hexaphenylsilole (HPS), has been used as a sensing material, while a HPS/polymethyl methacrylate composite film with a lotus leaf like structure is prepared by a simple electrospin method. The film shows high stability and excellent sensitivity for the metal ions Fe³⁺ and Hg²⁺, respectively. The special surface morphology containing micro‐/nanocomposite structure is attributed to the exhibition of these unusual properties.     

自组装ITO/双层磷脂膜的制备及其光电行为研究

在ITO(Indium-tin-oxide)导电玻璃电极上制备上自组装双层磷脂膜和经C60修饰的双层磷脂膜,研究了这种自组装双层磷脂膜的光电行为,考察了偏压、溶液中的给体和受体的浓度对自组装膜光电流强度的影响,讨论了C60分子对光电子跨膜传递过程的促进作用。     

平板双层磷脂膜中伏安行为的研究

未经修饰的双层类脂膜（BLM）是很好的绝缘体，不能进行离子和电子传导。但是，经过适当的修饰，如嵌入碘分子或者富含π-电子的有机化合物（四氰代二甲基苯醌TCNQ，四硫富瓦烯TTF），BLM显示出双偶电极的行为，也就是BLM一侧是进行氧化还原反应的阴极，另一侧是进行氧化还原反     

Bio‐Inspired Formal Synthesis of Hirsutellones A–C Featuring an Electrophilic Cyclization Triggered by Remote Lewis Acid‐Activation

A bio‐inspired strategy was used to complete the formal synthesis of the antitubercular hirsutellone B and congeners A and C, through construction of its decahydrofluorene core from a linear polyene strand activated at both ends by a silyl enol ether and an allyl acetate. Our synthesis features a key electrophilic cyclization, starting with the remote activation (by [Yb(OTf)₃] or BF₃ ? OEt₂) of the allyl acetate and stereoselectively affording the C ring. This was followed by an intramolecular Diels–Alder reaction to get the tricyclic core of the natural product. The stereoselective reduction of the resulting ketone towards the formal intermediate was critical to the success of this strategy.     

冠醚修饰的固体支撑双层类脂膜的形成及性能研究

用饱和了胆固醇和饰用冠醚的角鲨烷／氯仿溶液作成膜液，制备了冠醚修饰的固体支撑双层类脂分子膜。重点考察了成膜物种及技术对膜稳定性及电特生影响。其膜电势随接触水相中的变化呈现Ｎｅｒｎｓｔ响应，线性范围１０＾－４－１０＾－１ｍｏｌ／Ｌ。     

Label‐Free Measurements of the Diffusivity of Molecules in Lipid Membranes

An important and characteristic property of a cell membrane is the lateral mobility of protein molecules in the lipid bilayer. This has conventionally been measured by labeling the molecules with fluorescent markers and monitoring their mobility by different fluorescence‐based techniques. However, adding the label to the studied molecule may affect the system, so it is an assumption in almost all experiments that the measured mobility of the biomolecule with its label is the same as that of the unlabeled molecule. However, this assumption is rarely tested due to a lack of suitable methods. In this work, a new technique to perform label‐free diffusivity measurements is developed and used to measure the effect of the label for two common protein–lipid systems: 1) streptavidin (SA) coupled to a supported lipid bilayer (SLB) through biotinylated lipids and 2) the extracellular part of the T‐cell adhesion protein CD2, coupled to an SLB through histidine tags to nickel‐chelating lipids. A measurable (≈12 %) decrease in diffusivity is found for both labeled proteins, even though the molecular mass of the label is almost 100 times smaller than those of the proteins (≈50 kDa). The results illustrate the importance of being able to study different biophysical properties of cell membranes and their mimics without relying on fluorescent labels, especially if fluorescent labeling is difficult or is expected to affect the nature of the intermolecular interactions being studied.