The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Takanori Fukushima - One of the best experts on this subject based on the ideXlab platform.
-
Discotic Ionic liquid crystals of triphenylene as dispersants for orienting single-walled carbon nanotubes
Angewandte Chemie - International Edition, 2012Co-Authors: Jeongho Jay Lee, Norifumi Fujita, Akihisa Yamaguchi, Md Akhtarul Alam, Takanori Fukushima, Kenichi Kato, Masaki Takata, Yohei Yamamoto, Takuzo AidaAbstract:Orient and conduct: Triphenylene-based discotic Ionic liquid crystals (ILCs) with six Imidazolium Ion pendants can disperse pristine single-walled carbon nanotubes (SWNTs). When the ILC is columnarly assembled, doping with SWNTs results in macroscopic homeotropic columnar orientatIon. CombinatIon of shear and annealing treatments gives rise to three different orientatIon states, which determine the anisotropy of electrical conductIon.
-
Bicontinuous Cubic Liquid Crystalline Materials from Discotic Molecules: A Special Effect of Paraffinic Side Chains with Ionic Liquid Pendants
Journal of the American Chemical Society, 2009Co-Authors: Akhtarul Alam, Takanori Fukushima, Kenichi Kato, Masaki Takata, Yohei Yamamoto, Jin Motoyanagi, Jungeun Kim, Akinori Saeki, Shu Seki, Seiichi TagawaAbstract:Triphenylene (TP) derivatives bearing appropriate paraffinic side chains with Imidazolium Ion-based Ionic liquid (IL) pendants were unveiled to display a phase diagram with liquid crystalline (LC) mesophases of bicontinuous cubic (Cubbi) and hexagonal columnar (Colh) geometries. While their phase transitIon behaviors are highly dependent on the length of the side chains and the size of the Ionic liquid pendants, TPs with hexadecyl side chains exclusively form a Cubbi LC assembly over an extremely wide temperature range of ∼200 °C from room temperature when the anIons of the IL pendants are relatively small. Wide-angle X-ray diffractIon analysis suggested that the Cubbi LC mesophase contains π-stacked columnar TP arrays with a plane-to-plane separatIon of ∼3.5 A. Consistently, upon laser flash photolysis, it showed a transient microwave conductivity comparable to that of a Colh LC reference.
-
Ionic liquids for soft functIonal materials with carbon nanotubes.
Chemistry (Weinheim an der Bergstrasse Germany), 2007Co-Authors: Takanori Fukushima, Takuzo AidaAbstract:A serendipitous finding that Ionic liquids gel with carbon nanotubes has opened a new possibility of Ionic liquids as modifiers for carbon nanotubes. Upon being ground into Ionic liquids, carbon nanotube bundles are untangled, and the resultant fine bundles form a network structure. This is due to the possible specific interactIon between the Imidazolium Ion component and the pi-electronic nanotube surface. The resultant gelatinous materials, consisting of highly electroconductive nanowires and fluid electrolytes, can be utilized for a wide variety of electrochemical applicatIons, such as sensors, capacitors, and actuators. Ionic liquids allow for noncovalent and covalent modificatIons of carbon nanotubes and fabricatIon of polymer composites with enhanced physical properties. The processing of carbon nanotubes with Ionic liquids is not accompanied by the disruptIon of the pi-conjugated nanotube structure and does not require solvents; therefore it can readily be scaled up. This article focuses on new aspects of Ionic liquids for designer soft materials based on carbon nanotubes.
-
π-Electronic Soft Materials Based on Graphitic Nanostructures
Polymer Journal, 2006Co-Authors: Takanori FukushimaAbstract:This review focuses on our recent studies on the development of soft materials consisting of graphitic nanostructures. We found that single-walled carbon nanotubes, when suspended in Imidazolium Ion-based Ionic liquids and ground in an agate mortar, form physical gels (bucky gels), where entangled nanotube bundles are exfoliated to give highly dispersed, much finer bundles. The use of polymerizable Ionic liquids as the gelling media leads to the formatIon of highly electroconductive polymer/nanotube composites, which show a dramatic enhancement in mechanical properties. Bucky gels allow the fabricatIon of the first printable actuator that operates for a long time in air at low applied voltages. We also succeeded in the development of a new family of nanotubular graphite through self-assembly of amphiphilic hexabenzocoronene derivatives. The nanotube consists of a graphitic wall formed from a great number of π-stacked hexabenzocoronene units, which provide a charge carrier transport pathway. Suitable chemical modificatIons of the amphiphile resulted in the formatIon of nanotubes with various interesting properties. Details of the design, properties, and scope of such π-electronic soft nanomaterials are described herein.
-
Novel soft composite materials composed of Ionic liquids and single-walled carbon nanotubes
2005Co-Authors: Takanori Fukushima, Takuzo AidaAbstract:Pristine single-walled carbon nanotubes form gels when ground with Imidazolium Ion-based room-temperature Ionic liquids. In the gels, the heavily entangled nanotube bundles are exfoliated to give much finer bundles. Phase-transitIon and rheological properties suggest that the gels are formed by physical crosslinking of nanotube bundles mediated by local molecular ordering of Ionic liquids, rather than entanglement of nanotubes. Single-walled carbon nanotube gels of Ionic liquids, thus obtained, are thermally stable and do not shrivel even under reduced pressure, because of the non-volatility of the Ionic liquids, but readily undergo gel-to-solid transitIon on absorbent materials. The use of a polymerizable Ionic liquid as the gelling medium allowed for the fabricatIon of a novel electroconductive polymer/nanotube composite material, which showed a significant enhancement in dynamic hardness due to a strong connectivity at the polymer/nanotube interface.
Yixiang Cheng - One of the best experts on this subject based on the ideXlab platform.
-
Imidazolium Ion tagged proline organocatalyst for α aminoxylatIon of aldehydes and ketones in Ionic liquids
Advanced Synthesis & Catalysis, 2010Co-Authors: Xiong Ding, Wenming Tang, Chengjian Zhu, Yixiang ChengAbstract:A novel Imidazolium Ion-tagged L -proline catalyst has been developed. The asymmetric α-aminoxylatIon of aldehydes and ketones with excellent enantioselectivities, up to 99% ee, and high yields in Ionic liquids has been achieved. The system can be easily recycled and reused for at least six times without significant loss of yields and enantioselectivity.
-
Direct asymmetric α-aminatIon of aldehydes with azodicarboxylates in Ionic liquids catalyzed by Imidazolium Ion-tagged proline organocatalyst
Tetrahedron Letters, 2010Co-Authors: Xiong Ding, Chengjian Zhu, Honglai Jiang, Yixiang ChengAbstract:Abstract Direct asymmetric α-aminatIon of unmodified aldehydes with azodicarboxylates in Ionic liquids in the presence of Imidazolium Ion-tagged l -proline organocatalyst 1 gives excellent enantioselectivities (up to 98% ee) and high chemical yields. The system can be easily recycled and reused for at least four times without significant loss of yields and enantioselectivity.
László Polgár - One of the best experts on this subject based on the ideXlab platform.
-
The unusual catalytic triad of poliovirus protease 3C.
Biochemistry, 2003Co-Authors: Zsuzsa Sárkány, László PolgárAbstract:Picornaviruses are small pathogen RNA viruses, like poliovirus, hepatitis A virus, rhinovirus, and others. They produce a large polyprotein, which is cleaved by virally encoded cysteine peptidases, picornains 2A and 3C. Picornain 3C represents an intermediate between the serine peptidase chymotrypsin and the cysteine peptidase papain. Its steric structure resembles chymotrypsin, but its nucleophile is a thiol instead of the hydroxyl group. The histidine is a general base catalyst in chymotrypsin but forms a thiolate-Imidazolium Ion pair in papain. The third member of the catalytic triad is an acid (Glu71) as in chymotrypsin rather than an amide found in papain. TransformatIon of poliovirus 3C peptidase into a serine peptidase results in lower activity by a factor of 430, but the activity extends toward higher pH with the more basic hydroxyl group. The decrease in activity is caused by the less ordered active site, as supported by the unfavorable entropy of activatIon. At 25 degrees C the specificity rate constant for the thiol enzyme approaches k(1), the rate constant for the formatIon of the enzyme-substrate complex, but k(2), the acylatIon constant, becomes predominant with the increase in temperature. In contrast, for the serine peptidase the specificity constant is less than k(1) over the entire temperature range, and the transitIon state is controlled by both k(1) and k(2). The acidic component of the catalytic triad is essential for activity, but its negative charge does not influence the IonizatIon of the thiol group.
-
Thiolate-Imidazolium Ion pair is not an obligatory catalytic entity of cysteine peptidases: the active site of picornain 3C.
Biochemistry, 2001Co-Authors: Zsuzsa Sárkány, Zoltán Szeltner, László PolgárAbstract:Cysteine peptidases are thought to attack the substrate by a thiolate-Imidazolium Ion-pair, as demonstrated with the most extensively studied papain. Picornavirus proteinases (picornains), a different family of cysteine peptidases, are structurally related to the trypsin family of serine peptidases, whose catalytically competent histidine operates as a general base catalyst. Measuring the absorbance change upon alkylatIon of picornains at 250 nm, where the nondissociated thiol group has a negligible absorbance relative to the Ionized form, one can test the IonizatIon state of the catalytic cysteine. For such studies, we have prepared and used a mutated variant of the poliovirus proteinase 3C, which contains a single thiol group. The pH dependence of the molar extinctIon coefficient has undoubtedly shown that picornain 3C contains an ordinary thiol group rather than the usual Ion-pair. Therefore, the imidazole assistance, demonstrated in alkylatIon reactIons, is presumably general base catalysis, as found with serine peptidases. Kinetic studies on k(cat)/K(m) gave large inverse deuterium isotope effects, which may overcompensate the reverse values characteristic of the potential general base catalysis. The inverse effects is associated with the stabilizatIon of the protein structure in heavy water.
-
CharacterizatIon of the active site thiol group of rhinovirus 2A proteinase
FEBS letters, 2000Co-Authors: Z. Sárkány, Tim Skern, László PolgárAbstract:Picornains 2A are cysteine proteases of picornaviruses, a virus family containing several human and animal pathogens. The pH dependencies of the alkylatIons of picornain 2A of rhinovirus type 2 with iodoacetamide and iodoacetate show two reactive thiol forms, namely the free thiolate Ion at high pH and an imidazole assisted thiol group at low pH. Kinetic deuterium isotope effects do not support general base catalysis by the imidazole group, but rather the existence of a catalytically competent thiolate-Imidazolium Ion-pair. The nature of the Ion-pair differs from that of papain, the paradigm of cysteine proteases. The Ion-pair is confined to the same, unusually narrow pH range in which the enzyme exhibits catalytic activity.
Avelino Corma - One of the best experts on this subject based on the ideXlab platform.
-
chiral vanadyl salen complex anchored on supports as recoverable catalysts for the enantioselective cyanosilylatIon of aldehydes comparison among silica single wall carbon nanotube activated carbon and Imidazolium Ion as support
Tetrahedron, 2004Co-Authors: Carlos Baleizao, Barbara Gigante, Hermenegildo Garcia, Avelino CormaAbstract:Abstract The activity and enantiomeric excess (ee) (in some cases >85%) obtained for the asymmetric additIon of trimethylsilyl cyanide to aldehydes using different heterogeneous chiral catalysts are compared. A library of recoverable catalysts was developed by immobilizatIon of a chiral vanadyl salen complex having a terminal carbon–carbon double bond onto a series of scaffolds including silica, single-wall carbon nanotubes, activated carbon and room-temperature Ionic liquids. The covalent linkage has been achieved by radical initiated additIon of mercapto groups to C C. The highest enantiomeric excesses, similar to those obtained in the homogeneous phase, were achieved using silica as support or with the homogeneous tetra- tert -butyl salen catalyst dissolved in an Imidazolium Ionic liquid. The use of silica as support permits an easier separatIon and reuse of the catalyst from the reactIon media.
-
vanadyl salen complexes covalently anchored to an Imidazolium Ion as catalysts for the cyanosilylatIon of aldehydes in Ionic liquids
Tetrahedron Letters, 2003Co-Authors: Carlos Baleizao, Barbara Gigante, Hermenegildo Garcia, Avelino CormaAbstract:Two vanadyl salen complexes having peripheral styryl substituents have been reacted with 1-methyl-3-(3-mercaptopropyl)-Imidazolium chloride using azoisobutyronitrile as radical initiator. The resulting compounds contain at the same time a vanadyl salen complex and one Imidazolium catIon. In agreement with the expectatIons in view of their structure, these compounds were insoluble in conventIonal organic solvents, but completely miscible in Imidazolium Ionic liquids. These vanadyl salen complexes bonded to an Imidazolium catIon are highly active and reusable catalysts for the cyanosilylatIon of aldehydes. Moderate enantiomeric excesses were obtained using the chiral versIon of this complex.
Takuzo Aida - One of the best experts on this subject based on the ideXlab platform.
-
Discotic Ionic liquid crystals of triphenylene as dispersants for orienting single-walled carbon nanotubes
Angewandte Chemie - International Edition, 2012Co-Authors: Jeongho Jay Lee, Norifumi Fujita, Akihisa Yamaguchi, Md Akhtarul Alam, Takanori Fukushima, Kenichi Kato, Masaki Takata, Yohei Yamamoto, Takuzo AidaAbstract:Orient and conduct: Triphenylene-based discotic Ionic liquid crystals (ILCs) with six Imidazolium Ion pendants can disperse pristine single-walled carbon nanotubes (SWNTs). When the ILC is columnarly assembled, doping with SWNTs results in macroscopic homeotropic columnar orientatIon. CombinatIon of shear and annealing treatments gives rise to three different orientatIon states, which determine the anisotropy of electrical conductIon.
-
Ionic liquids for soft functIonal materials with carbon nanotubes.
Chemistry (Weinheim an der Bergstrasse Germany), 2007Co-Authors: Takanori Fukushima, Takuzo AidaAbstract:A serendipitous finding that Ionic liquids gel with carbon nanotubes has opened a new possibility of Ionic liquids as modifiers for carbon nanotubes. Upon being ground into Ionic liquids, carbon nanotube bundles are untangled, and the resultant fine bundles form a network structure. This is due to the possible specific interactIon between the Imidazolium Ion component and the pi-electronic nanotube surface. The resultant gelatinous materials, consisting of highly electroconductive nanowires and fluid electrolytes, can be utilized for a wide variety of electrochemical applicatIons, such as sensors, capacitors, and actuators. Ionic liquids allow for noncovalent and covalent modificatIons of carbon nanotubes and fabricatIon of polymer composites with enhanced physical properties. The processing of carbon nanotubes with Ionic liquids is not accompanied by the disruptIon of the pi-conjugated nanotube structure and does not require solvents; therefore it can readily be scaled up. This article focuses on new aspects of Ionic liquids for designer soft materials based on carbon nanotubes.
-
Novel soft composite materials composed of Ionic liquids and single-walled carbon nanotubes
2005Co-Authors: Takanori Fukushima, Takuzo AidaAbstract:Pristine single-walled carbon nanotubes form gels when ground with Imidazolium Ion-based room-temperature Ionic liquids. In the gels, the heavily entangled nanotube bundles are exfoliated to give much finer bundles. Phase-transitIon and rheological properties suggest that the gels are formed by physical crosslinking of nanotube bundles mediated by local molecular ordering of Ionic liquids, rather than entanglement of nanotubes. Single-walled carbon nanotube gels of Ionic liquids, thus obtained, are thermally stable and do not shrivel even under reduced pressure, because of the non-volatility of the Ionic liquids, but readily undergo gel-to-solid transitIon on absorbent materials. The use of a polymerizable Ionic liquid as the gelling medium allowed for the fabricatIon of a novel electroconductive polymer/nanotube composite material, which showed a significant enhancement in dynamic hardness due to a strong connectivity at the polymer/nanotube interface.
-
Discotic liquid crystals stabilized by interIonic interactIons: Imidazolium Ion-anchored paraffinic triphenylene
Chemical communications (Cambridge England), 2004Co-Authors: Jin Motoyanagi, Takanori Fukushima, Takuzo AidaAbstract:IncorporatIon of Imidazolium Ion functIonalities into the paraffinic side-chain termini of a triphenylene derivative resulted in stabilizatIon of a columnar mesophase of its liquid crystalline assembly, which was retained over a wider temperature range down to 4 °C by an externally added Imidazolium-based Ionic liquid.
-
Molecular ordering of organic molten salts triggered by single-walled carbon nanotubes
Science, 2003Co-Authors: Takanori Fukushima, Atsuko Kosaka, Yasuko Ishimura, Toshikazu Takigawa, Noriyuki Ishii, Takashi Yamamoto, Takuzo AidaAbstract:When mixed with Imidazolium Ion-based room-temperature Ionic liquid, pristine single-walled carbon nanotubes formed gels after being ground. The heavily entangled nanotube bundles were found to untangle within the gel to form much finer bundles. Phase transitIon and rheological properties suggest that the gels are formed by physical cross-linking of the nanotube bundles, mediated by local molecular ordering of the Ionic liquids rather than by entanglement of the nanotubes. The gels were thermally stable and did not shrivel, even under reduced pressure resulting from the nonvolatility of the Ionic liquids, but they would readily undergo a gel-to-solid transitIon on absorbent materials. The use of a polymerizable Ionic liquid as the gelling medium allows for the fabricatIon of a highly electroconductive polymer/nanotube composite material, which showed a substantial enhancement in dynamic hardness.