One-dimensional ion transport in self-organized columnar ionic liquids

New fan-shaped ionic liquids forming columnar liquid crystalline phases have been prepared to obtain one-dimensional ion-transporting materials. The ionic liquids consist of two incompatible parts: an imidazolium-based ionic part as an ion-conducting part and tris(alkyloxy)phenyl parts as insulating parts. Two compounds having octyl and dodecyl chains have been synthesized. Self-assembly of these materials leads to the formation of thermotropic hexagonal columnar liquid crystalline states at room temperature. Anisotropic one-dimensional ionic conductivities have been successfully measured by the cells having comb-shaped gold electrodes. The self-organized columns have been aligned macroscopically in two directions by shearing perpendicular and parallel to the electrodes. The ionic conductivities parallel to the column axis are higher than those perpendicular to the axis. The incorporation of lithium salts in these columnar materials leads to the enhancement of the ionic conductivities and their anisotropy. These materials would be useful for anisotropic transportation of ions at the nanometer level.     

Various columnar phases formed by bent-core mesogens

Two new compounds containing bent-core mesogens are presented in which a flexible central methyleneoxycarbonyl unit acts as the bent fragment. The compounds form different two-dimensional columnar (‘B₁’) phases both with a rectangular lattice but different in the angle of the director of the molecules with respect to the a-axis of the lattice. Based on X-ray diffraction measurements structural models are proposed which cannot be described with the common model of p2mg symmetry for B₁ phases of bent-shaped molecules. The new models are of layer group symmetry (p11n and pm2₁ n) and are discussed as a new common model for two-dimensional columnar phases of bent-shaped mesogens.     

In‐Situ Spin Labeling of His‐Tagged Proteins: Distance Measurements under In‐Cell Conditions

New spin labeling strategies have immense potential in studying protein structure and dynamics under physiological conditions with electron paramagnetic resonance (EPR) spectroscopy. Here, a new spin‐labeled chemical recognition unit for switchable and concomitantly high affinity binding to His‐tagged proteins was synthesized. In combination with an orthogonal site‐directed spin label, this novel spin probe, Proxyl‐trisNTA (P‐trisNTA) allows the extraction of structural constraints within proteins and macromolecular complexes by EPR. By using the multisubunit maltose import system of E. coli: 1) the topology of the substrate‐binding protein, 2) its substrate‐dependent conformational change, and 3) the formation of the membrane multiprotein complex can be extracted. Notably, the same distance information was retrieved both in vitro and in situ allowing for site‐specific spin labeling in cell lysates under in‐cell conditions. This approach will open new avenues towards in‐cell EPR.     

Columnar nanostructured polymer films containing ionic liquids in supramolecular one-dimensional nanochannels

Ionic liquids have attracted a considerable attention as the next generation electrolytes for energy devices. We have developed new free-standing and nanostructured polymer films in which ionic liquids are confined into one-dimensionally ordered nanochannels. These polymer films have been obtained by photopolymerization of hydrogen-bonded supramolecular columnar liquid-crystalline self-assemblies of an imidazolium-based ionic liquid and a wedge-shaped diol compound containing polymerizable groups. The macroscopically parallel alignment of the columnar structures on a glass substrate has been achieved by the application of mechanical shearing, and subsequently fixed into polymer films by UV irradiation. This ionic liquid-containing polymer film exhibits higher ionic conductivity than that of the previously reported one-dimensional polymer film obtained by in situ photopolymerization of a covalent-type columnar liquid-crystalline imidazolium salt. The noncovalent supramolecular approach to one-dimensionally ion-conductive polymer films has led to improvement on conductive properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 366–371     

Pyrrolidinium Ionic Liquid Crystals

N‐Alkyl‐N‐methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium‐containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2‐ thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group C_nH_2n+1 was varied from eight to twenty carbon atoms (n=8, 10–20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X‐ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self‐assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium‐containing mesogens, luminescence can be induced by dissolving them in an ionic liquid matrix. The europium‐containing compound shows intense red photoluminescence with high colour purity.     

Enantioseparation and thermodynamic study of naphthalene derivatives,new melatoninergic agonists,on coated amylose [tris(S)‐1‐phenylethylcarbamate] stationary phase. Transposition to preparative scale

This work reports a high‐performance liquid chromatography normal‐phase methodology to elucidate enantiomers of naphthalene derivatives, evaluated as melatoninergic agonists. For this purpose four different polysaccharide based chiral stationary phases were evaluated, namely Chiralcel OD‐H (cellulose tris‐3,5‐dimethylphenylcarbamate), Chiralcel OJ (cellulose tris‐methylbenzoate), Chiralpak AD (amylose tris‐3,5‐dimethylphenylcarbamate) and Chiralpak AS (amylose tris‐(S)‐1‐phenylethylcarbamate) with different alcoholic modifiers on different amounts in n‐heptane. A temperature study was carried out, between 20 and 40 °C and the apparent thermodynamic parameters were calculated thanks to the Van't Hoff linearization. For all compounds (except 3), ΔΔH° and ΔΔS° exhibited positive values ranging from 791.2 to 9999.3 J/mol and from 3.9 to 37.8 J/K/mol respectively, indicating entropically driven separations. Optimized conditions led to goof resolution of 2.37 for compound 1 on Chiralpak AS, with heptane–2‐propanol 90:10 (v/v), at a temperature of 30 °C. Then they were transposed to the preparative scale for compound 1, generating 22 mg of each enantiomer with an 80% yield. The limits of detection and of quantification were determined to allow the calculation of the enantiomeric excess. They were found with very low values, equal to 0.32 and 1.05 µ m and 0.33 and 1.11 µ m, respectively, for peaks 1 and 2 of compound 1. Copyright © 2014 John Wiley & Sons, Ltd.     

Mesomorphic properties of some 1,4,8,11,15,18,22,25-octa-alkoxymethylphthalocyanines

Abstract

The mesophase behaviour of a number of non-peripherally octa-substituted phthalocyanine derivatives has been studied by optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction. A homologous series of straight chain alkoxymethyl derivatives has exhibited both rectangular and hexagonal columnar mesophases, with the rectangular phases being favoured by the shorter chains. Two branched chain derivatives were found to give rectangular columnar phases at room temperature. A detailed analysis of the X-ray data has shown some differences from the analogous n-alkyl compounds. It has been deduced that the increased polarizability and flexibility of the ether linkage allows the disc-like molecules to approach more closely face to face with correspondingly thicker columns.     

Reversed-Phase Liquid Chromatographic Separation, on Cellulose Chiral Stationary Phases, of the Stereoisomers of Methoxytetra-hydronaphthalene Derivatives, New Agonist and Antagonist Ligands for Melatonin Receptors

A stereoselective high-performance liquid chromatographic method has been established for chiral separation of melatoninergic derivatives with one or two chiral centers, new agonist and antagonist ligands for melatonin receptors. Reversed-phase separations were performed on cellulose-based chiral stationary phases—tris-3,5-dimethylphenylcarbamate (Chiralcel OD-RH) or tris-methylbenzoate (Chiralcel OJ-R). Water–modifier (methanol or acetonitrile) mixtures in different proportions were used as mobile phases. The effects of organic mobile-phase modifier concentration, temperature, and compound structure were examined. Baseline separation (R_S > 1.5) was readily obtained for many of the compounds.     

High‐performance liquid chromatographic enantioseparation of amino alcohol analogues possessing 1,2,3,4‐tetrahydroisoquinoline skeleton on polysaccharide‐based chiral stationary phases

The stereoisomers of 1,2,3,4‐tetrahydroisoquinoline amino alcohol analogues and derivatives thereof were separated in normal‐phase mode on chiral stationary phases based on preprepared silica coated with cellulose tris‐(3,5‐dimethylphenyl carbamate), cellulose tris‐(3‐chloro‐4‐methylphenyl carbamate), cellulose tris‐(4‐methylbenzoate) or cellulose tris‐(4‐chloro‐3‐methylphenyl carbamate). On all the investigated chiral columns, the retention and the enantioseparation were influenced by the nature and the concentrations of the mobile phase components and additives, and also the temperature. Experiments were performed in the temperature range 10–50°C. Thermodynamic parameters were calculated from plots of lnα vs 1/T. On these polysaccharide‐based chiral columns, both enthalpy‐driven separations and entropy‐controlled enantioseparations were observed. The latter was advantageous with regard to the shorter retention and greater selectivity at high temperature. The sequence of elution of the stereoisomers was determined in all cases. Copyright © 2014 John Wiley & Sons, Ltd.     

Columnar liquid crystalline tris-(ether)triazines with pendant 1,3,4-thiadiazole groups: synthesis,mesomorphic, luminescence,solvatofluorochromic and electrochemical properties

Novel columnar liquid crystals whose molecular structures consist of a C₃ star-shaped 1,3,5-triazine unit as a central core, and three pendant 2-phenyl-5-(di-, and/or tri-n-alkoxyphenyl)-1,3,4-thiadiazole arms, containing ether connecting groups, variable number and positions of linear alkoxy chains were synthesised and their mesomorphic properties were studied by differential scanning calorimetry, polarised optical microscopy and X-ray diffraction. The mesomorphic properties were found to be dependent on the length, position and number of the peripheral alkoxy chains. Most compounds form enantiotropic hexagonal columnar phases. These compounds also show photoluminescent properties in the visible region with good quantum yields. Photophysical studies were realised in solution and in solid state. Also, solvatofluorochromism and cyclic voltammetry studies were performed.     

Syntheses and Properties of meso‐Substituted Porphyrin Mesogens with Triazole Linkages and Peripheral Alkyl Chains

Discotic mesogens P/n‐M (n=12, 16, 18, M=2 H, Zn and Cu) bearing a porphyrin core, triazole linkages and peripheral 3,4,5‐trialkoxybenzyl units have been synthesized by a click‐chemistry approach. The thermal behavior, photophysical properties and morphologies of these compounds were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), XRD, UV and PL, SEM and TEM. These compounds can self‐assemble into hexagonal columnar phases in their pure states and form organogels in 1,4‐dioxane with unusually flower‐like sphere morphology. The supramolecular complexes of P/18‐Zn with C₇₀ or 4,7‐di‐4‐pydriyl‐2,1,3‐benzothadiazole can display hexagonal columnar phases too. Additionally, zinc porphyrin compounds P/n‐Zn show binding selectivity to Cu²⁺ among a series of cations in THF/H₂O.     

T-shaped ionic liquid crystals based on the imidazolium motif: exploring substitution of the C-2 imidazolium carbon atom

In this contribution the first examples of so‐called rigid‐core, T‐shaped imidazolium ionic liquid crystals, in which the C‐2 atom of the imidazolium ring is substituted with an aryl moiety decorated with one or two alkoxy chains, are described. The length of the alkoxy chain(s) was varied from six to eighteen carbon atoms (n=6, 10, 14–18). Whereas the compounds with one long alkoxy chain display only smectic A phases, the salts containing two alkoxy chains exhibit smectic A, multicontinuous cubic, as well as hexagonal columnar phases, as evidenced by polarising optical microscopy, differential scanning calorimetry, and powder X‐ray diffraction. Structural models are proposed for the self‐assembly of the molecules within the mesophases. The imidazolium head groups and the iodide counterions were found to adopt a peculiar orientation in the central part of the columns of the hexagonal columnar phases. The enantiotropic cubic phase shown by the 1,3‐dimethyl‐2‐[3,4‐bis(pentadecyloxy)phenyl]imidazolium iodide salt has a multicontinuous Pm$\bar 3In this contribution the first examples of so-called rigid-core, T-shaped imidazolium ionic liquid crystals, in which the C-2 atom of the imidazolium ring is substituted with an aryl moiety decorated with one or two alkoxy chains, are described. The length of the alkoxy chain(s) was varied from six to eighteen carbon atoms (n=6, 10, 14-18). Whereas the compounds with one long alkoxy chain display only smectic A phases, the salts containing two alkoxy chains exhibit smectic A, multicontinuous cubic, as well as hexagonal columnar phases, as evidenced by polarising optical microscopy, differential scanning calorimetry, and powder X-ray diffraction. Structural models are proposed for the self-assembly of the molecules within the mesophases. The imidazolium head groups and the iodide counterions were found to adopt a peculiar orientation in the central part of the columns of the hexagonal columnar phases. The enantiotropic cubic phase shown by the 1,3-dimethyl-2-[3,4-bis(pentadecyloxy)phenyl]imidazolium iodide salt has a multicontinuous Pm ?3m structure. To the best of our knowledge, this is the first example of a thermotropic cubic mesophase of this symmetry.     

High‐performance liquid chromatographic enantioseparation of fluorinated cyclic β3‐amino acid derivatives on polysaccharide‐based chiral stationary phases. Comparison with nonfluorinated counterparts

The stereoisomers of five fluorinated cyclic β³‐amino acid derivatives and their nonfluorinated counterparts were separated on chiral stationary phases containing as chiral selectors cellulose tris‐(3,5‐dimethylphenyl carbamate), cellulose tris‐(3‐chloro‐4‐methylphenyl carbamate), cellulose tris‐(4‐methylbenzoate), cellulose tris‐(4‐chloro‐3‐methylphenyl carbamate), amylose tris‐(3,5‐dimethylphenyl carbamate) or amylose tris‐(5‐chloro‐2‐methylphenyl carbamate). The enantioseparations were carried out in normal‐phase mode with n‐hexane/alcohol/alkylamine mobile phases in the temperature range 5–40 °C. The effects of the mobile phase composition, the nature and concentration of the alcohol and alkylamine additives, the structures of the analytes and temperature on the separations were investigated. Thermodynamic parameters were calculated from plots of ln α vs. 1/T. The Δ(ΔH°) values ranged between ?5.0 and +1.6 kJ/mol, while Δ(ΔS°) varied between ?12.6 and +5.7 J/mol/K. The enantioseparation was enthalpically controlled, the retention factor and the separation factor decreasing with increasing temperature, but entropically controlled separation was also observed. The elution sequence was determined for all of the investigated analytes. Copyright © 2016 John Wiley & Sons, Ltd.     

Steric effect on the formation of columnar phases in β-diketonate copper(II) complexes

A systematic study of the mesomorphic properties of three series of copper(II) complexes based on β-diketonate ligands containing branched side chains is reported. These disc-like compounds have four, six and eight flexible alkoxy side chains appended to the central core, in which two or four side chains were substituted by bulkier secondary alkoxy groups: 1-methylbutyloxy R ' = C₅(2°) or 1-methylheptyloxy R ' = C₈(2°). The mesomorphic results indicated that at least eight side chains are required to form stable columnar mesophases; other compounds with four or six side chains are not mesogenic regardless of the combination of the carbon length on the alkoxy or secondary alkoxy groups of the side chains. The compounds 3 with shorter R ' = C₅(2°) side chains were all non-mesogenic regardless of the carbon length of three alkoxy side chains (R = C₈, C₁₀, C₁₂) used. However, when the longer 1-methylheptyloxy side chain R ' = C₈(2°) was substituted, the compounds 3b-3e with various alkoxy groups (R = C₆, C₇, C₈, C₁₀, C₁₂) exhibited columnar phases. The mesophases were characterized and identified as columnar hexagonal phases (Col_h), as expected, by thermal analysis and optical polarized microscopy. The presence of the introduced secondary alkoxy groups apparently appeared to influence the formation of columnar phases. The clearing points were relatively lower than other similar copper(II) compounds not substituted by secondary alkoxy side chains.     

Self‐Assembly in Helical Columnar Mesophases and Luminescence of Chiral 1H‐Pyrazoles

Chiral polycatenar 1H‐pyrazoles self‐assemble to form columnar mesophases that are stable at room temperature. X‐ray diffraction and CD studies in the mesophase indicate a supramolecular helical organization consisting of stacked H‐bonded dimers. The liquid‐crystalline compounds reported are 3,5‐bis(dialkoxyphenyl)‐1H‐pyrazoles that incorporate two or four dihydrocitronellyl chiral tails. It can be observed that the grafting of these branched chiral substituents onto the 3,5‐diphenyl‐1H‐pyrazole core has a beneficial role in inducing mesomorphism, because isomeric linear‐chain compounds are not liquid crystalline; this is not the usual scheme of behavior. Furthermore, the molecular chirality is transferred to the columnar mesophase, because preferential helical arrangements are observed. Films of the compounds are luminescent at room temperature and constitute an example of the self‐organization of nondiscoid units into columnar liquid‐crystalline assemblies in which the functional molecular unit transfers its properties to a hierarchically built superstructure.     

Self‐Assembly of Imidazolium‐Based Rodlike Ionic Liquid Crystals: Transition from Lamellar to Micellar Organization

By using aryl‐amination chemistry, a series of rodlike 1‐phenyl‐1H‐imidazole‐based liquid crystals (LCs) and related imidazolium‐based ionic liquid crystals (ILCs) has been prepared. The number and length of the C‐terminal chains (at the noncharged end of the rodlike core) and the length of the N‐terminal chain (on the imidazolium unit in the ILCs) were modified and the influence of these structural parameters on the mode of self‐assembly in LC phases was investigated by polarizing microscopy, differential scanning calorimetry, and X‐ray diffraction. For the single‐chain imidazole derivatives nematic phases (N) and bilayer SmA₂ phases were found, but upon increasing the number of alkyl chains the LC phases were lost. For the related imidazolium salts LC phases were preserved upon increasing the number and length of the C‐terminal chains and in this series it leads to the phase sequence SmA–columnar (Col)–micellar cubic (Cub_I/Pm3n). Elongation of the N‐terminal chain gives the reversed sequence. Short N‐terminal chains prefer an end‐to‐end packing of the mesogens in which these chains are separated from the C‐terminal chains. Elongation of the N‐terminal chain leads to a mixing of N‐ and C‐terminal chains, which is accompanied by complete intercalation of the aromatic cores. In the smectic phases this gives rise to a transition from bilayer (SmA₂) to monolayer smectic (SmA) phases. For the columnar and cubic phases the segregated end‐to‐end packing leads to core–shell aggregates. In this case, elongation of the N‐terminal chains distorts core–shell formation and removes Cub_I and Col phases in favor of single‐layer SmA phases. Hence, by tailoring the length of the N‐terminal chain, a crossover from taper‐shaped to polycatenar LC tectons was achieved, which provides a powerful tool for control of self‐assembly in ILCs.     

SLAP: Small Labeling Pair for Single‐Molecule Super‐Resolution Imaging

Protein labeling with synthetic fluorescent probes is a key technology in chemical biology and biomedical research. A sensitive and efficient modular labeling approach (SLAP) was developed on the basis of a synthetic small‐molecule recognition unit (Ni‐trisNTA) and the genetically encoded minimal protein His_6‐10‐tag. High‐density protein tracing by SLAP was demonstrated. This technique allows super‐resolution fluorescence imaging and fulfills the necessary sampling criteria for single‐molecule localization‐based imaging techniques. It avoids masking by large probes, for example, antibodies, and supplies sensitive, precise, and robust size analysis of protein clusters (nanodomains).     

Ionic hexagonal columnar metallomesogens derived from tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine

A series of transition metal (Ni, Cu, Pd) complexes derived from macrocyclic tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine (TAAB) was synthesized and their mesomorphic properties studied by differential scanning calorimetry, polarized optical microscopy and X-ray powder diffraction (XRD). These compounds have eight alkoxy side chains attached around the central molecular core and form disc-like molecules. All the derivatives exhibited columnar mesophases over a wide range of temperature. The mesomorphic behaviour was found to be dependent on the incorporated metal and the carbon length of the alkoxy side chains. The clearing temperatures decreased in the order M = Ni > Pd > Cu; this decrease was probably due to the size of the metal ions. Some derivatives with shorter side chains (n = 10, 12) were room temperature liquid crystals. All compounds were found to exhibit hexagonal columnar (Col_h) phases which were confirmed by powder XRD.     

Supramolecular main-chain liquid crystalline polymers and networks with competitive hydrogen bonding: networks and linear polymers created from tris- and bis-functionalised pyridyl networking agents

A series of supramolecular polymers and networks with variable liquid crystalline characteristics have been created. These species are formed through the benzoic acid/pyridine hydrogen bonding of a flexible bis-acid and a mixture of a rigid bis-pyridyl and non-mesogenic tris- and bis-pyridyl molecules. The tris networked systems displayed liquid crystalline characteristics up to and including 31.0% netpoint inclusion. Above this concentration, only crystalline and melting behaviours were observed. The bis-containing polymer system displayed liquid crystalline characteristics up to and including 22.5% inclusion. The phenomenon observed in the tris system would seem to be linked to a statistical correlation of hydrogen bond acceptors and donors. The elimination of liquid crystallinity at lower concentrations of the bis-pyridyl dopant could be attributed to the lower melting nature of that species. Smectic phases were found in both series of complexes in loadings up to 10% of the non-liquid crystalline component. There was also no observed phase segregation of the species after multiple heat/cool cycles and extended periods of time in the isotropic state. This would indicate that the thermodynamically more stable mesogenic phase cannot out-compete the non-liquid crystalline network.     

Supramolecular Metallacycles and Their Binding of Fullerenes

The synthesis of a new triaminoguanidinium-based ligand with three tris-chelating [NNO]-binding pockets and C₃ symmetry is described. The reaction of tris-(2-pyridinylene-N-oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C₆₀ can be observed by NMR spectroscopy and single-crystal X-ray diffraction and is verified using computation.