A Flexible Solution to Anion Transport: Powerful Anionophores Based on a Cyclohexane Scaffold

Transmembrane anion carriers (anionophores) have potential for biological activity, including the treatment of channelopathies such as cystic fibrosis. A new family of anionophores has been synthesized, in which three thiourea groups are mounted on a cyclohexane‐based scaffold. Though conceptually related to earlier polycyclic systems, these molecules are simpler and far more accessible. Preorganization is somewhat reduced compared to earlier systems, and anion affinities are correspondingly lower. However, transport activities set new records. This surprising performance suggests a role for controlled flexibility in the design of transmembrane anion carriers.     

Transport of Ca^2＋ Ion through a Bubbling Pseudo—emulsion Liquid Membrane with Calixarenes and Calixcrowns as Carriers

ＩｎｔｒｏｄｕｃｔｉｏｎＣａｌｉｘａｒｅｎｅｓｃｏｎｓｔｉｔｕｔｅａｖｅｒｓａｔｉｌｅｃｌａｓｓｏｆｍａｃｒｏｃｙｃｌｉｃｃｏｍｐｏｕｎｄｓｔｈａｔｃａｎｂｅｅａｓｉｌｙｆｕｎｃｔｉｏｎａｌｉｚｅｄ ,ｔｈｕｓａｆｆｏｒｄ ｉｎｇａｌａｒｇｅｖａｒｉｅｔｙｏｆｎｅｗｍｕｌｔｉｆｕｎｃｔｉｏｎａｌｒｅｃｅｐｔｏｒｓ .1Ｉｎｔｈｅｐａｓｔｔｗｏｄｅｃａｄｅｓ ,ｔｈｅｙｈａｖｅｐｌａｙｅｄａｎｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｓｕｐｒａｍｏｌｅｃｕｌａｒｃｈｅｍｉｓｔｒｙａｓｕｓｅｆｕｌｂｕｉｌｄｉｎｇｂｌｏ…     

Influence of the Insertion Method of Aryl-Extended Calix[4]pyrroles into Liposomal Membranes on Their Properties as Anion Carriers

We disclose the results of our investigations on the influence that the insertion method of aryl-extended calix[4]pyrrole into liposomal membranes exerts on their properties as anion carriers. We use the standard HPTS assay to assess the transport properties of the carriers. We show that the post-insertion of the carrier, as DMSO solution, assigns better transport activities to the “two-wall” α,α-aryl-extended calix[4]pyrrole 1 compared to the “four-wall” α,α,α,α-counterpart 2 . Notably, opposite results were obtained when the carriers were pre-inserted into the liposomal membranes. We assign this difference to an improved incorporation of carrier 2 into the membrane when delivered by the pre-insertion method. On the other hand, carrier 1 shows comparable levels of transport independently of the method used for its incorporation. Thus, an accurate comparison of the chloride transport activities featured by these two carriers demands their pre-incorporation in the liposomal membranes. In contrast, using the lucigenin assay with the pre-insertion method both carriers displayed similar transport efficiencies.     

冠醚配合物的研究(ⅩⅠⅤ)——2,3-苯并-11-甲基-18-冠-6液膜模拟细胞膜传输钾离子的研究

以2,3-苯并-11-甲基-18-冠-6(BCl-18C6)为液膜载体研究其对钾离子的传输,金属离子可以逆其浓度梯度进行跨膜传输。当源相金属离子浓度和膜相载体浓度相近时,传输为串联一级反应,传输速率正比于源相及受相阴、阳离子浓度乘积之差。同时讨论了搅拌速度对传输的影响,探讨了传输机理。     

Electrochemical Elucidation of the Facilitated Ion Transport Across a Bilayer Lipid Membrane in the Presence of Neutral Carrier Compounds

The ion transport facilitated by neutral carrier compounds (valinomycin, nonactin) has been investigated by cyclic voltammetry in the several electrolyte solutions (KF, KCl, KBr, KNO₃, KSCN, KClO₄), and we demonstrated the effect of the counter anions on the facilitated transport of K⁺ from the viewpoint of electroneutrality. Voltammograms for the ion transport were generated at steady state and the current density between W1 and W2, j_W1–W2, increased with the absolute value of the applied membrane potential, E_W1–W2. Then, the magnitude of j_W1–W2 at a certain E_W1–W2 increased with the hydrophobicity of the counter anion. It was proved that the logarithm of |j_W1–W2|at a certain E_W1–W2 is almost proportional to the hydration energy of the counter anion. This indicates that not only K⁺ but also the counter anion distributes into the BLM. Therefore, the magnitude of j_W1–W2 at a certain E_W1–W2 increased with an increase of pH, because the hydroxide ion was served as a counter anion. Based on the variation of the zero‐current potential in case of various asymmetrical ionic compositions, it is found that the amount of cation transport is much larger than that of anion transport.     

Development of a Library of Thiophene-Based Drug-Like Lego Molecules: Evaluation of Their Anion Binding,Transport Properties,and Cytotoxicity

The anion-binding and transport properties of an extensive library of thiophene-based molecules are reported. Seventeen bis-urea positional isomers, with different binding conformations and lipophilicities, have been synthesized by appending α- or β-thiophene or α-, β-, or γ-benzo[b]thiophene moieties to an ortho-phenylenediamine central core, yielding six subsets of positional isomers. Through ¹H NMR, X-ray crystallography, molecular modelling, and anion efflux studies, it is demonstrated that the most active transporters adopt a pre-organized binding conformation capable of promoting the recognition of chloride, using urea and C−H binding groups in a cooperative fashion. Additional large unilamellar vesicle-based assays, carried out under electroneutral and electrogenic conditions, together with N-methyl-d -glucamine chloride assays, have indicated that anion efflux occurs mainly through an H⁺/Cl⁻ symport mechanism. On the other hand, the most efficient anion transporter displays cytotoxicity against tumor cell lines, while having no effects on a cystic fibrosis cell line.     

杯芳烃的超分子化学研究(Ⅰ)-对-叔丁基杯[n]芳烃对K+和Na+离子的液膜传输规律

杯芳烃的液膜传输作用是其典型的超分子化学特征之一［１］．在探索杯芳烃及其衍生物作为流动载体传输金属离子的能力及传输作用的规律性,以及模仿细胞壁两边金属离子的传递过程及其控制方式方面有潜在应用前景．Ｉｚａｔ［２］等认为,只有当源相处于强碱性条件（ｐＨ＞...     

Permselectivity between two anions in anion exchange membranes crosslinked with various diamines in electrodialysis

A membranous copolymer crosslinked with divinylbenzene reacted with N,N,N′,N′-tetra-methylethylenediamine, N,N,N′,N′-tetramethyl-1,3-propanediamine, and N,N,N′,N′-tetramethyl-1,6-hexanediamine to prepare highly crosslinked anion exchange membranes. More than 80% of both tertiary amino groups of the diamines reacted with chloromethyl groups of the membrane to form crosslinkage. After formation of the high crosslinkage of the membrane was confirmed with dialysis of a neutral molecule, electrochemical properties of the obtained membranes (mainly, relative transport number between two anions in electrodialysis) were evaluated: nitrate ions to chloride ions, sulfate ions to chloride ions, fluoride ions to chloride ions, and bromide ions to chloride ions. Though larger anions, in general, were difficult to permeate through the membranes due to high crosslinkage, the number of methylene groups of the diamines (which means the increase in hydrophobicity of anion exchange groups) also affected the relative transport number between two anions. The lower the hydration of anions, the higher the relative transport number of the anions through the membranes with the hydrophobic anion exchange groups. © 1996 John Wiley & Sons, Inc.     

The effect of MWS polarisation on the morphology and electro-optical behaviour of normal-mode polymer-stabilised cholesteric textures

We investigate the process and the resulting properties of the curing electric-field-induced segregation of reactive monomers (containing polar groups) in a host liquid crystal. The obtained dielectric spectrum of these cholesteric liquid crystals (CLCs) reveals polarisation at low frequencies. This is a strong indication that charge carriers accumulate at the interface between the sample and the electrodes in these compounds and consistent with Maxwell–Wagner–Sillars (MWS) polarisation. A polymer film forms on the substrate with its thickness determined by the MWS polarisation strength. The SEM images show that the polymer network becomes less dense when MWS polarisation increases. The results are a higher operating voltage and faster response time.     

Anion–π Slides for Transmembrane Transport

The recognition and transport of anions is usually accomplished by hydrogen bonding, ion pairing, metal coordination, and anion–dipole interactions. Here, we elaborate on the concept to use anion–π interactions for this purpose. Different to the popular cation–π interactions, applications of the complementary π‐acidic surfaces do not exist. This is understandable because the inversion of the aromatic quadrupole moment to produce π‐acidity is a rare phenomenon. Here, we suggest that π‐acidic aromatics can be linked together to produce an unbendable scaffold with multiple binding sites for anions to move along across a lipid bilayer membrane. The alignment of multiple anion–π sites is needed to introduce a cooperative multi‐ion hopping mechanism. Experimental support for the validity of the concept comes from preliminary results with oligonaphthalenediimide (O‐NDI) rods. Predicted by strongly positive facial quadrupole moments, the cooperativity and chloride selectivity found for anion transport by O‐NDI rods were consistent with the existence of anion–π slides. The proposed mechanism for anion transport is supported by DFT results for model systems, as well as MD simulations of rigid O‐NDI rods. Applicability of anion–π slides to achieve electroneutral photosynthesis is elaborated with the readily colorizable oligoperylenediimide (O‐PDI) rods. To clarify validity, scope and limitations of these concepts, a collaborative research effort will be needed to address by computer modeling and experimental observations the basic questions in simple model systems and to design advanced multifunctional anion–π architectures.     

Mechanism of facilitated saccharide transport through plasticized cellulose triacetate membranes

Mechanistic insight is gained for saccharide transport through plasticized cellulose triacetate (CTA) membranes containing lipophilic ion-pair transport carriers. The molecular structures of the different membrane components are systematically varied and diagnostic transport characteristics such as saccharide–carrier diffusion constant and saccharide extraction constant are determined. The observed percolation thresholds support a jumping mechanism, however, the diffusion constants are found to decrease as the size of the saccharide, carrier cation, and carrier anion increase, indicating that the rate-limiting step in the transport process involves diffusion of a complex comprised of all three components. The data is reconciled in terms of mobile-site jumping mechanism where the saccharide is relayed along a sequence of ion-pair carriers that are locally mobile. In an attempt to improve saccharide selectivity, calix-[4]-arene dicarboxylates were evaluated as potential ditopic transport carriers. This produced no major change in saccharide extraction constants.     

Transmembrane Transport of Bicarbonate Unravelled**

Anion receptors can be used to transport ions across lipid bilayers, which has potential for therapeutic applications. Synthetic bicarbonate transporters are of particular interest, as defects in transmembrane transport of bicarbonate are associated with various diseases. However, no convenient method exists to directly observe bicarbonate transport and study the mechanisms involved. Here, an assay is presented that allows the kinetics of bicarbonate transport into liposomes to be monitored directly and with great sensitivity. The assay utilises an encapsulated europium(III) complex, which exhibits a large increase in emission intensity upon binding bicarbonate. Mechanisms involving CO₂ diffusion and the dissipation of a pH gradient are shown to be able to lead to an increase in bicarbonate concentration within liposomes, without transport of the anion occurring at all. By distinguishing these alternative mechanisms from actual bicarbonate transport, this assay will inform the future development of bicarbonate transporters.     

Anion influence on extraction and transport of amino acid methyl esters by functionalised calix[4]arene

The liquid–liquid extraction of a series of amino acid methyl esters has been carried out with functionalised calix[4]arene (5,11,17,23-tetrakis(N-methylpiperazino)-25,26,27,28-tetrahydroxycalix[4]arene) from an aqueous phase into a chloroform phase as ion pairs in the presence of picrate ion or tropaeolin 00 as counter ion in order to study the molecular recognition properties of this receptor. The active transport assisted by pH gradient of amino acids as ion pairs through liquid membrane employing the functionalised calix[4]arene as carrier has been investigated. The results showed that the receptor exhibits good extractability towards amino acids and it can also act as carrier through liquid membrane aiming to the separation of amino acids. It was highlighted that the anion nature used as counter ion, the structure of calix[4]arene, and the structure of amino acids are responsible for the experimental results obtained. High yields in both amino acids extraction and transport were obtained for picrate ion used as counter ion.     

杯芳烃衍生物对K＋和电子的耦合液膜传输

在文献的基础上设计了一套电子/阳离子同向耦合传输的新体系,以多硫1,2-二硫醇烯镍的配合物为电子载体,杯芳烃的酯类衍生物为阳离子载体,采用连二亚硫酸钠和铁氰化钾作为还原剂和氧化剂,成功地实现了电子/钾离子同向耦合传输.研究了电子载体和离子载体对耦合传输的影响,并对电子耦合传输的传输机理做了初步的研究.     

Low‐Energy‐Barrier Proton Transfer Induced by Electron Attachment to the Guanine⋅⋅⋅Cytosine Base Pair

The photoelectron spectrum of the anion of the guanine ??? cytosine base apair (GC)^.? is recorded for the first time. The observed variation in the spectral peak‐height ratios with the source conditions suggests the presence of two or more anionic isomers. Two maxima of the broad bands in the photoelectron spectrum were measured at about 1.9 and about 2.6 eV. These values are very well reproduced by the vertical detachment energies of the B3LYP/6‐31++G(d,p) calculated low‐energy anionic structures, which are 1) the Watson–Crick base‐pair anion with proton transferred from N1 of guanine to N3 of cytosine, 2) its analogue in which the proton is transferred from N9 of guanine to N7 of guanine, and 3) the global minimum geometry, which is formed from the latter anion by rotation of guanine about the axis approximately defined by C2 of guanine and C4 of cytosine. Furthermore, a minor difference in the stabilities of the two lowest energy anions explains the experimentally observed source (temperature) dependence of the PES spectrum. A rational procedure, based on the chemistry involved in the formation of anionic dimers, which enables the low‐energy anions populated in the photoelectron spectrum to be identified is proposed. In contrast to the alternative combinatorial approach, which in the studied case would lead to carrying out quantum chemical calculations for 2000–2500 structures, the procedure described here reduces the computational problem to only 15 geometries.     

Membrane extraction of alkaline earth metal by phosphorylated azapodands

ABSTRACT

Membrane transport properties of the new lipophilic phosphorylated azapodands toward Сa(II), Ва (II), Mg(II), and Sr(II) were studied. The investigation of the processes of passive membrane ion transport showed the high values of the transfer flow of the alkaline earth metals’ ions with all carriers. It was found that N,N’-bis(di-p-tolylphosphorylmethyl)-1,8-diamino-3,6-dioxaoctane (I) is the most effective carrier among all compounds studied.     

Membrane-active calixarenes: toward ‘gating’ transmembrane anion transport

This paper describes on-going efforts to develop calixarene amides as transmembrane anion transporters. We report on the transport of Cl⁻ anions across phospholipid membranes as mediated by some lipophilic calixarenes, all fixed in the cone conformation. We present significant findings regarding use of these calixarenes as transmembrane Cl⁻ transporters: (1) the cone conformer cone-H 2a, like its 1,3-alt and paco isomers, transports Cl⁻ across liposomal membranes; (2) the conformation of the calixarene (paco-H 1 vs cone-H 2a) is important for modulating Cl⁻ transport rates; (3) the substitution pattern on the calixarene's upper rim is crucial for Cl⁻ transport function; and (4) at least one of the four arms of the calixarene can be left unmodified without loss of function, enabling development of a pH-sensitive anion transporter (TAC-OH 3). This last finding is useful given the interest in gating the activity of synthetic ion transporters with external stimuli.     

A new conduction phenomenon observed in polyethylene and epoxy resin: Ultra‐fast soliton conduction

A new conduction mechanism in polyethylene and epoxy resin is presented and discussed in this article. This mechanism is based on the presence of charge pulses that can be seen as solitons (solitary waves) crossing dielectrics with mobility 4–5 orders of magnitude larger than that of conventional charge carriers. The nature of this new process that is characterized by charge pulses with such high mobility requires a completely different mechanism for transport to be theorized with respect to that, mediated by trap sites, of conventional charge carriers. It is speculated in this article that injection and transport of positive and negative solitons occurs through the coupling of space charge and relaxation processes involving molecular chains, but of different nature for negative or positive solitons. Observation of space charge shows the existence of such solitons for at least two families of materials, polyethylene, and epoxy resin. In addition, it has been observed that nanostructuration, which is able to modify mechanical properties, affects also the presence and size of the solitons. In this article, we not only seek to demonstrate the existence of this new phenomenon, but attempt to provide an explanation and a kind of qualitative–quantitative model, which shows that the assumption of a pulsive conduction mechanism mediated by chain relaxation processes, transport in free volume (for negative solitons), and reverse‐tunneling between macromolecular chains (positive solitons) seems to fit quite well with the experimental observations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Proton-ionizable crown compounds. 12. Proton-Coupled selective membrane transport of Li+ using a proton-ionizable pyridono macrocycle

The macrocycle-mediated fluxes of several alkali metal cations have been determined in a H₂O-CH₂Cl₂-H₂O liquid membrane system. Water-insoluble proton-ionizable macrocycles of the pyridono type were used. The proton-ionizable feature allows the coupling of cation transport to reverse H⁺ transport. This feature offers promise for the effective separation and/or concentration of alkali metal ions with the metal transport being driven by a pH gradient. A counter anion in the source phase is not co-transported. The desired separation of a particular metal ion involves its selective complexation with the macrocycle, subsequent extraction from the aqueous phase to the organic phase, and exchange for H⁺ at the organic phase-receiving phase interface. Factors affecting transport which were studied include ring size, source phase pH, and receiving phase pH. Lithium was transported at a rate higher than that of the other alkali metals in both single and competitive systems using a 15-crown-5 pyridono carrier.