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Mohammed A E Sallam - One of the best experts on this subject based on the ideXlab platform.
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chiroptical assignment of the anomeric configuration of 4 α β d lyxopyranosyl and 4 α β d lyxofuranosyl 2 phenyl 2h 1 2 3 triazole c nucleoside anomeric pairs extension of the cd triazole rule
Journal of Carbohydrate Chemistry, 2009Co-Authors: Mohammed A E SallamAbstract:The circular dichroism of the anomeric 4-(α,β-D-lyxopyranosyl)- and 4-(α,β-D-lyxofuranosyl)-2-phenyl-2H-1,2,3-triazole C-nucleoside analogs obtained by acid-catalyzed dehydrative cyclization of 4-(D-galacto-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole analog was studied. A correlation between the sign of the Cotton Effect at the maximal UV absorption and the absolute configuration of the anomeric carbon atom was obtained and used for their anomeric configuration assignment. This correlation supports the CD triazole rule for anomeric assignment and is in accord with the assignment obtained by NMR spectral studies.
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circular dichroism as a reliable tool for anomeric assignment of glycosyl 2 phenyl 2h 1 2 3 triazole c nucleoside analogs a rule for prediction of their anomeric configuration
Chirality, 2006Co-Authors: Mohammed A E SallamAbstract:The circular dichroism (CD) of a series of acyclic C-nucleoside analogs; 4-(pentahydroxypentyl-1-yl)-2-phenyl-2H-1,2,3-triazoles [1–5] and 4-(D-glycero-D-gulo)-2-phenyl-2H-1,2,3-triazole 6, are reported. A correlation between the sign of the Cotton Effect at the maximal UV absorption and the absolute configuration of the carbon atom α- to the triazole base moiety is reported. The CD of anomeric 4-(α,β-D-arabinofuranosyl)- and 4-(α,β-D-arabinopyranosyl)-2-phenyl-2H-1,2,3-triazole C-nucleosides are reported. The assignment of the anomeric configuration of C-glycosyl-2-phenyl-2H-1,2,3-triazoles from their CD spectra was found to be a simple method that relies on comparison of the sign of the Cotton Effect at the maximal UV absorption and the absolute configuration of the anomeric carbon atom. A correlation between the anomeric configuration and the sign of the Cotton Effect at the maximal UV absorption is deduced and generalized as a rule for prediction of the anomeric configuration of C-glycosyl-2-phenyl-2H-1,2,3-triazoles. Nuclear Overhauser Effect and 13C NMR spectra supported the CD assignment rule. Chirality, 2006. © 2006 Wiley-Liss, Inc
Eiji Yashima - One of the best experts on this subject based on the ideXlab platform.
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synthesis of complementary double stranded helical oligomers through chiral and achiral amidinium carboxylate salt bridges and chiral amplification in their double helix formation
Journal of the American Chemical Society, 2011Co-Authors: Masato Ikeda, Takashi Hasegawa, Yoshio Furusho, Eiji YashimaAbstract:A series of complementary molecular strands from 2-mer to 5-mer that are composed of m-terphenyl units bearing chiral/achiral amidine or achiral carboxyl groups linked via Pt(II) acetylide complexes were synthesized by sequential stepwise reactions, and their chiroptical properties on the double-helix formation were investigated by circular dichroism (CD) and 1H NMR spectroscopies. In CHCl3, the “all-chiral” amidine strands consisting of (R)- or (S)-amidine units formed preferred-handed double helices with the complementary achiral carboxylic acid strands through the amidinium−carboxylate salt bridges, resulting in characteristic induced CDs in the Pt(II) acetylide complex regions, indicating that the chiral substituents on the amidine units biased a helical sense preference. The Cotton Effect patterns and intensities were highly dependent on the molecular lengths. The complementary double-helix formation was also explored using the chiral/achiral amidine strands with different sequences in which a chiral...
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cu ii assisted helicity induction on a poly phenylacetylene derivative bearing an achiral glycine residue with amino acids in water
Chemistry Letters, 2003Co-Authors: Hiroaki Kawamura, Miki Ishikawa, Katsuhiro Maeda, Eiji YashimaAbstract:Poly(phenylacetylene) bearing an achiral glycine residue exhibits an induced circular dichroism in the UV–vis region upon complexation with free amino acids in water due to a predominantly one-handed helix formation and the Cotton Effect intensity is amplified in the presence of a Cu(II) ion.
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detection and amplification of a small enantiomeric imbalance in α amino acids by a helical poly phenylacetylene with crown ether pendants
Journal of the American Chemical Society, 2003Co-Authors: Ryuji Nonokawa, Eiji YashimaAbstract:We have designed a novel stereoregular poly(phenylacetylene) bearing the bulky crown ether as the pendant (poly-1) for the amino acid binding site. The polymer forms a one-handed helix upon complexation with l-amino acid perchlorates, and the complexes exhibit an induced circular dichroism (ICD) with the same Cotton Effect signs in the polymer backbone region through a significant cooperative interaction. Poly-1 is highly sensitive to the amino acid chirality and can detect an extremely small enantiomeric imbalance in α-amino acids (less than 0.005% enantiomeric excess of alanine, for example).
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chiral stimuli responsive gels helicity induction in poly phenylacetylene gels bearing a carboxyl group with chiral amines
Journal of the American Chemical Society, 2003Co-Authors: Hidetoshi Goto, Hao Qian Zhang, Eiji YashimaAbstract:Poly(phenylacetylene) gels (gel-1-H and gel-2-H) bearing a carboxy pendant were synthesized either by the copolymerization of (4-carboxyphenyl)acetylene (gel-1-H) with a bis(phenylacetylene) derivative as the cross-linking reagent using a rhodium complex ([Rh(cod)2]BF4: cod = 1,5-cyclooctadiene) as the catalyst or by the cross-linking of poly[(4-carboxyphenyl)acetylene] with diamines (gel-2-H). The obtained gels were found to swell in DMSO and exhibited an induced circular dichroism (ICD) in the long absorption region of the main chain in the presence of optically active amines. These results indicate that a predominantly one-handed helix can be induced in the polymer network of the gels through chiral acid−base interactions. The swelling properties and the Cotton Effect intensities of the gels depend on the cross-linking ratio and the chiral amines. Gel-1-Na and gel-2-Na prepared from gel-1-H and gel-2-H, respectively, also significantly swelled in water and showed ICDs characteristic of chiral amino al...
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chirality assignment of amines and amino alcohols based on circular dichroism induced by helix formation of a stereoregular poly 4 carboxyphenyl acetylene through acid base complexation
Journal of the American Chemical Society, 1997Co-Authors: Eiji Yashima, Teruyuki Matsushima, Yoshio OkamotoAbstract:An optically inactive polyacetylene, poly((4-carboxyphenyl)acetylene) (poly-1), exhibits an induced circular dichroism (ICD) in the UV−visible region upon complexation with chiral amines and amino alcohols in DMSO and in the film, the sign of which reflects the stereochemistry including bulkiness, type (primary, secondary, or tertiary), and absolute configuration of the amines. Therefore, the polyacetylene can be used as a novel probe for determining the chirality of amines. Most primary amines and amino alcohols of the same configuration gave the same sign for the induced Cotton Effect; however, secondary and/or tertiary amines used in the present study tended to show Cotton Effect signs opposite to those of the primary amines and amino alcohols of the same configuration. The magnitude of the ICD likely increases with an increase in the bulkiness of the chiral amines. The complexation dynamics during the formation of the helical structure of poly-1 with chiral amines were investigated on the basis of the...
Huangtianzhi Zhu - One of the best experts on this subject based on the ideXlab platform.
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formation of planar chiral platinum triangles via pillar 5 arene for circularly polarized luminescence
Journal of the American Chemical Society, 2020Co-Authors: Huangtianzhi Zhu, Bingbing Shi, Hao Xing, Yan Sun, Liqing Shangguan, Feihe Huang, Peter J StangAbstract:Chiral metal-organic complexes hold great promise as new functional materials that exhibit unique stereochemical and optical properties. Here, we report the formation of optically pure pillar[5]arene-based platinum chiral metallacycles. By coordination with 60° and 90° Pt(II) acceptors, planar chiral platinum triangles were self-assembled efficiently and characterized by multiple spectroscopic techniques. Optical studies indicated that these metallacycles had chiral properties: pS enantiomers showed a negative Cotton Effect, and pR enantiomers exhibited a positive Cotton Effect. In addition, these metallacycles also exhibited circularly polarized luminescence.
Kazuo Akagi - One of the best experts on this subject based on the ideXlab platform.
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helically π stacked thiophene based copolymers with circularly polarized fluorescence high dissymmetry factors enhanced by self ordering in chiral nematic liquid crystal phase
Chemistry of Materials, 2012Co-Authors: Kazuyoshi Watanabe, Itaru Osaka, Shinichi Yorozuya, Kazuo AkagiAbstract:Novel derivatives of polythiophenes and their phenylene copolymers were synthesized by introducing chiral alkoxy carbonyl substituents into their side chains. Most of these polymers showed enantiotropic main-chain liquid crystallinity at high temperatures and across a wide range of elevated temperatures. They exhibited fluorescence that ranged in color from blue to orange in chloroform solutions and from blue to red in films. The bisignate Cotton Effect was observed in the π–π* transition region of the circular dichroism (CD) spectra of the polymers consisting of three aromatic rings in the repeating unit, which was attributed to the formation of a polymer assembly with an interchain helically π-stacked structure. The dependence of UV–vis absorption and CD spectra on the concentration and temperature of the solution indicated that the polymer assembly exists, even in dilute concentration at room temperature, but it dissociated into single polymers at high temperatures. Additionally, the polymer films exhi...
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Helically π-Stacked Thiophene-Based Copolymers with Circularly Polarized Fluorescence: High Dissymmetry Factors Enhanced by Self-Ordering in Chiral Nematic Liquid Crystal Phase
2012Co-Authors: Kazuyoshi Watanabe, Itaru Osaka, Shinichi Yorozuya, Kazuo AkagiAbstract:Novel derivatives of polythiophenes and their phenylene copolymers were synthesized by introducing chiral alkoxy carbonyl substituents into their side chains. Most of these polymers showed enantiotropic main-chain liquid crystallinity at high temperatures and across a wide range of elevated temperatures. They exhibited fluorescence that ranged in color from blue to orange in chloroform solutions and from blue to red in films. The bisignate Cotton Effect was observed in the π–π* transition region of the circular dichroism (CD) spectra of the polymers consisting of three aromatic rings in the repeating unit, which was attributed to the formation of a polymer assembly with an interchain helically π-stacked structure. The dependence of UV–vis absorption and CD spectra on the concentration and temperature of the solution indicated that the polymer assembly exists, even in dilute concentration at room temperature, but it dissociated into single polymers at high temperatures. Additionally, the polymer films exhibited an enhanced Cotton Effect caused by the strengthening of the helical π-stacking in the polymer assembly. Both the polymer solutions and films generated circularly polarized fluorescence with values for gem, the dissymmetry factor, on the order of 10–3 and 10–2, respectively. Values for gem as high as 10–1 were obtained by annealing the polymer films at temperatures corresponding to the liquid crystalline region and were due to the self-ordering of their chiral nematic phases. Furthermore, a mixture of red, green, and blue fluorescent polymers generated a unique, circularly polarized white luminescence not only in solution but also in the cast film prepared by dispersing the mixture in an excess of polystyrene
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advanced conjugated polymer helical polyacetylene
Polymers for Advanced Technologies, 2000Co-Authors: G Piao, Kazuo Akagi, Naoya Kawamura, H Shirakawa, Mutsumasa KyotaniAbstract:Helical polyacetylene [(CH)x] thin films were synthesized in chiral nematic (N*) liquid crystal (LC) solvents. The N*LC was prepared by adding a chiral titanium complex as a chiral dopant to a mixture of two nematic LCs. The titanium complexes induced the N* phase when dissolved in nematic LCs and they were catalytically active for acetylene polymerization. Positive or negative Cotton Effect was observed in the region of π π* transition of polyene chain in circular dichroism (CD) spectra for the (CH)x thin films synthesized under the N* LC. Spiral fibrillar morphology was observed through SEM measurement of the helical (CH)x film. Copyright © 2000 John Wiley & Sons, Ltd.
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helical polyacetylene synthesized with a chiral nematic reaction field
Science, 1998Co-Authors: Kazuo Akagi, G Piao, H Shirakawa, S Kaneko, K Sakamaki, Mutsumasa KyotaniAbstract:Helical polyacetylene was synthesized under an asymmetric reaction field consisting of chiral nematic (N*) liquid crystals (LCs). The chiral nematic LC was prepared by adding a chiroptical binaphthol derivative as a chiral dopant to a mixture of two nematic LCs. Acetylene polymerizations were carried out using the catalyst titanium tetra- n -butoxide–triethylaluminum dissolved in the chiral nematic LC solvent. The polyacetylene film was shown by scanning electron microscopy to consist of clockwise or counterclockwise helical structure of fibrils. A Cotton Effect was observed in the region of the π → π* transition of the polyacetylene chain in circular dichroism spectra. The high electrical conductivities of ∼1500 to 1800 siemens per centimeter after iodine doping and the chiral helicity of these films may be exploited in electromagnetic and optical applications.
Ivan I Stoikov - One of the best experts on this subject based on the ideXlab platform.
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synthesis and properties of chiral nanoparticles based on ps and pr decasubstituted pillar 5 arenes containing secondary amide fragments
RSC Advances, 2016Co-Authors: D N Shurpik, Pavel L Padnya, Vladimir G Evtugyn, Timur A Mukhametzyanov, Arthur A Khannanov, M P Kutyreva, Ivan I StoikovAbstract:Employing induced asymmetric synthesis, new decasubstituted pillar[5]arenes containing (R)-(+)- or (S)-(−)-1-phenylethane-1-acetamide fragments have been obtained and characterized. Using NTA and TEM, and circular dichroism spectroscopy, it was shown that the amidopillar[5]arenes synthesized form spherical chiral nanoscale aggregates in CHCl3. During heating, both positive and negative Cotton Effects corresponding to nanoparticles in CHCl3 reversibly decrease. Keeping the nanoparticles at room temperature results in a decrease in their size and intensification of the Cotton Effect.
