The Experts below are selected from a list of 141 Experts worldwide ranked by ideXlab platform
Fosong Wang - One of the best experts on this subject based on the ideXlab platform.
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length dependence of electron conduction for Oligo 1 4 phenylene ethynylene s a conductive probe atomic force microscopy investigation
Journal of Physical Chemistry C, 2008Co-Authors: Ke Liu, Xianhong Wang, Fosong WangAbstract:The dependence of electron conduction of Oligo(1,4-phenylene ethynylene)s (OPEs) on length, terminal group, and main chain structure was examined by conductive probe-atomic force microscopy (CP-AFM) via a metal substrate-molecular wire monolayer-conductive probe junction. The electron transport in the molecular junction was a highest occupied molecule orbital (HOMO)-mediated process following a coherent, non-resonant tunneling mechanism represented by the Simmons equation.
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rapid solution and solid phase synthesis of monodisperse Oligo 1 4 phenyleneethynylene alt 2 5 thiopheneethynylene s
Tetrahedron, 2006Co-Authors: Xianhong Wang, Xiaojiang Zhao, Fosong WangAbstract:Monodisperse Oligo[(1,4-phenyleneethynylene)-alt-(2,5-thiopheneethynylene)]s, new candidates for molecular wires, were rapidly synthesized via an iterative divergent/convergent doubling strategy in solution as well as on Merrifield's resin.
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column chromatographic purification free synthesis of long chain monodisperse Oligo 1 4 phenyleneethynylene s towards large scale automatic synthesis of molecular wires
Tetrahedron Letters, 2006Co-Authors: Xianhong Wang, Fosong WangAbstract:A facile, mild and rapid solid phase synthetic route free of column chromatographic purification to the synthesis of soluble monodisperse long-chain Oligo(1,4-phenyleneethynylene)s is presented.
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a novel in situ deprotection coupling and iterative divergent convergent strategy for the synthesis of Oligo 1 4 phenyleneethynylene s
Tetrahedron Letters, 2005Co-Authors: Xianhong Wang, Fosong WangAbstract:Abstract A novel in situ deprotection/coupling and iterative divergent/convergent strategy for the synthesis of Oligo(1,4-phenyleneethynylene)s is described.
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synthesis of monodisperse Oligo 1 4 phenyleneethynylene alt 2 5 thiopheneethynylene s
Synthetic Communications, 2005Co-Authors: Xianhong Wang, Xiaojiang Zhao, Fosong WangAbstract:Abstract The synthesis of monodisperse Oligo[(1,4‐phenyleneethynylene)‐alt‐(2,5‐thioph‐eneethynylene)]s using an iterative divergent/convergent doubling strategy based on Sonogashira coupling reaction was presented.
Xianhong Wang - One of the best experts on this subject based on the ideXlab platform.
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length dependence of electron conduction for Oligo 1 4 phenylene ethynylene s a conductive probe atomic force microscopy investigation
Journal of Physical Chemistry C, 2008Co-Authors: Ke Liu, Xianhong Wang, Fosong WangAbstract:The dependence of electron conduction of Oligo(1,4-phenylene ethynylene)s (OPEs) on length, terminal group, and main chain structure was examined by conductive probe-atomic force microscopy (CP-AFM) via a metal substrate-molecular wire monolayer-conductive probe junction. The electron transport in the molecular junction was a highest occupied molecule orbital (HOMO)-mediated process following a coherent, non-resonant tunneling mechanism represented by the Simmons equation.
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rapid solution and solid phase synthesis of monodisperse Oligo 1 4 phenyleneethynylene alt 2 5 thiopheneethynylene s
Tetrahedron, 2006Co-Authors: Xianhong Wang, Xiaojiang Zhao, Fosong WangAbstract:Monodisperse Oligo[(1,4-phenyleneethynylene)-alt-(2,5-thiopheneethynylene)]s, new candidates for molecular wires, were rapidly synthesized via an iterative divergent/convergent doubling strategy in solution as well as on Merrifield's resin.
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column chromatographic purification free synthesis of long chain monodisperse Oligo 1 4 phenyleneethynylene s towards large scale automatic synthesis of molecular wires
Tetrahedron Letters, 2006Co-Authors: Xianhong Wang, Fosong WangAbstract:A facile, mild and rapid solid phase synthetic route free of column chromatographic purification to the synthesis of soluble monodisperse long-chain Oligo(1,4-phenyleneethynylene)s is presented.
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a novel in situ deprotection coupling and iterative divergent convergent strategy for the synthesis of Oligo 1 4 phenyleneethynylene s
Tetrahedron Letters, 2005Co-Authors: Xianhong Wang, Fosong WangAbstract:Abstract A novel in situ deprotection/coupling and iterative divergent/convergent strategy for the synthesis of Oligo(1,4-phenyleneethynylene)s is described.
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synthesis of monodisperse Oligo 1 4 phenyleneethynylene alt 2 5 thiopheneethynylene s
Synthetic Communications, 2005Co-Authors: Xianhong Wang, Xiaojiang Zhao, Fosong WangAbstract:Abstract The synthesis of monodisperse Oligo[(1,4‐phenyleneethynylene)‐alt‐(2,5‐thioph‐eneethynylene)]s using an iterative divergent/convergent doubling strategy based on Sonogashira coupling reaction was presented.
Nikolay E Nifantiev - One of the best experts on this subject based on the ideXlab platform.
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trimodal control of ion transport activity on cyclo Oligo 1 6 β d glucosamine based artificial ion transport systems
Chemistry: A European Journal, 2015Co-Authors: Arundhati Roy, Tanmoy Saha, Marina L Gening, Denis V Titov, Alexey G Gerbst, Yury E Tsvetkov, Nikolay E Nifantiev, Pinaki TalukdarAbstract:Cyclo-Oligo-(1→6)-β-D-glucosamines functionalized with hydrophobic tails are reported as a new class of transmembrane ion-transport system. These macrocycles with hydrophilic cavities were introduced as an alternative to cyclodextrins, which are supramolecular systems with hydrophobic cavities. The transport activities of these glycoconjugates were manipulated by altering the Oligomericity of the macrocycles, as well as the length and number of attached tails. Hydrophobic tails of 3 different sizes were synthesized and coupled with each glucosamine scaffold through the amide linkage to obtain 18 derivatives. The ion-transport activity increased from di- to tetrameric glucosamine macrocycles, but decreased further when flexible pentameric glucosamine was introduced. The ion-transport activity also increased with increasing length of attached linkers. For a fixed length of linkers, the transport activity decreased when the number of such tails was reduced. All glycoconjugates displayed a uniform anion-selectivity sequence: Cl(-) >Br(-) >I(-) . From theoretical studies, hydrogen bonding between the macrocycle backbone and the anion bridged through water molecules was observed.
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cyclo Oligo 1 6 β d glucosamine based artificial channels for tunable transmembrane ion transport
Chemical Communications, 2014Co-Authors: Tanmoy Saha, Arundhati Roy, Marina L Gening, Denis V Titov, Alexey G Gerbst, Yury E Tsvetkov, Nikolay E Nifantiev, Pinaki TalukdarAbstract:Unimolecular ion channels were designed by functionalization of a new type of cyclic Oligosaccharides, cyclo-Oligo-(1 → 6)-β-D-glucosamines, with pentabutylene glycol chains. Their ion transporting activity was tuned by varying Oligomericity. A halide selectivity sequence, Cl− > Br− > I− was observed.
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nmr and conformational studies of linear and cyclic Oligo 1 6 β d glucosamines
Carbohydrate Research, 2011Co-Authors: Alexey A Grachev, Marina L Gening, Denis V Titov, Alexey G Gerbst, Yury E Tsvetkov, Olga N Yudina, Alexander S Shashkov, Gerald B Pier, Nikolay E NifantievAbstract:Abstract The conformational behavior of a series of linear and cyclic Oligo-(1→6)-β- d -glucosamines and their N-acetylated derivatives, which are related to fragments of natural poly- N -acetylglucosamine, was studied by theoretical molecular modeling and experimental determination of transglycosidic vicinal coupling constants 3 J C,H and 3 J H,H . Molecular dynamics simulations were performed under several types of conditions varying in the consideration of ionization of amino groups, solvent effect, and temperature. Neural network clustering and asphericity calculations were performed on the basis of molecular dynamics data. It was shown that disaccharide fragments in the studied linear Oligosaccharides were not rigid, and tended to have several conformers, thus determining the overall twisted shape with helical elements. In addition, it was found that the behavior of C5–C6 bond depended significantly upon the simulation conditions. The cyclic di-, tri-, and tetrasaccharides mostly had symmetrical ring-shaped conformations. The larger cycles tended to adopt more complicated shapes, and the conformational behavior of their disaccharide fragments was close to that in the linear Oligosaccharides.
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synthesis nmr and conformational studies of cyclic Oligo 1 6 β d glucosamines
European Journal of Organic Chemistry, 2010Co-Authors: Marina L Gening, Denis V Titov, Alexey G Gerbst, Yury E Tsvetkov, Alexey A Grachev, Olga N Yudina, Alexander S Shashkov, A O Chizhov, Nikolay E NifantievAbstract:The first synthesis of a series of homologous cyclic Oligo-(1→6)-β-D-glucosamines consisting of two to seven residues and representing a new type of functionalized cyclic Oligosaccharides is reported. Remarkably high yields of the studied macrocyclization reaction irrespective of the length of the acyclic precursors were observed. In the case of compounds constituted of four to seven glucosamine units α-stereoisomers formed as side products despite the presence of a strongly participating 2-N-phthaloyl group to control β-glycosylation. Both phenomena may be accounted for by conformational features of the linear bifunctional precursors. According to computer modeling and NMR conformational studies, the described linear (1→6)-β-linked Oligoglucosamines exist in a right-handed helix-like conformation, in which the glycosyl donor and acceptor moieties are prearranged in a way that facilitates intramolecular glycosylation from the α-side. Prepared cyclo-Oligoglucosamines differ in their conformational flexibilities, as illustrated by their spectral characteristics and calculated asphericity distributions. Moreover, the obtained compounds do not possess a distinct hydrophobic cavity, which is in contrast to the well-known cyclodextrins. All these characteristics provide an excellent basis for the use of these novel cyclic Oligosaccharides as scaffolds for the construction of biomolecular conjugates.
Kunihiko Watanabe - One of the best experts on this subject based on the ideXlab platform.
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the refined crystal structure of bacillus cereus Oligo 1 6 glucosidase at 2 0 a resolution structural characterization of proline substitution sites for protein thermostabilization
Journal of Molecular Biology, 1997Co-Authors: Kunihiko Watanabe, Yasuo Hata, Hidekazu Kizaki, Yukiteru Katsube, Yuzuru SuzukiAbstract:The crystal structure of Oligo-1,6-glucosidase (dextrin 6-alpha-glucanohydrolase, EC 3.2.1.10) from Bacillus cereus ATCC7064 has been refined to 2.0 A resolution with an R-factor of 19.6% for 43,328 reflections. The final model contains 4646 protein atoms and 221 ordered water molecules with respective root-mean-square deviations of 0.015 A for bond lengths and of 3.166 degrees for bond angles from the ideal values. The structure consists of three domains: the N-terminal domain (residues 1 to 104 and 175 to 480), the subdomain (residues 105 to 174) and the C-terminal domain (residues 481 to 558). The N-terminal domain takes a (beta/alpha)8-barrel structure with additions of an alpha-helix (N alpha6') between the sixth strand Nbeta6 and the sixth helix N alpha6, an alpha-helix (N alpha7') between the seventh strand Nbeta7 and the seventh helix N alpha7 and three alpha-helices (N alpha8', N alpha8" and N alpha8'" between the eighth strand Nbeta8 and the eighth helix N alpha8. The subdomain is composed of an alpha-helix, a three-stranded antiparallel beta-sheet, and long intervening loops. The C-terminal domain has a beta-barrel structure of eight antiparallel beta-strands folded in double Greek key motifs, which is distorted in the sixth strand Cbeta6. Three catalytic residues, Asp199, Glu255 and Asp329, are located at the bottom of a deep cleft formed by the subdomain and a cluster of the two additional alpha-helices N alpha8' and N alpha8" in the (beta/alpha)8-barrel. The refined structure reveals the locations of 21 proline-substitution sites that are expected to be critical to protein thermostabilization from a sequence comparison among three Bacillus Oligo-1,6-glucosidases with different thermostability. These sites lie in loops, beta-turns and alpha-helices, in order of frequency, except for Cys515 in the fourth beta-strand Cbeta4 of the C-terminal domain. The residues in beta-turns (Lys121, Glu208, Pro257, Glu290, Pro443, Lys457 and Glu487) are all found at their second positions, and those in alpha-helices (Asn109, Glu175, Thr261 and Ile403) are present at their N1 positions of the first helical turns. Those residues in both secondary structures adopt phi and phi values favorable for proline substitution. Residues preceding the 21 sites are mostly conserved upon proline occurrence at these 21 sites in more thermostable Bacillus Oligo-1,6-glucosidases. These structural features with respect to the 21 sites indicate that the sites in beta-turns and alpha-helices have more essential prerequisites for proline substitution to thermostabilize the protein than those in loops. This well supports the previous finding that the replacement at the appropriate positions in beta-turns or alpha-helices is the most effective for protein thermostabilization by proline substitution.
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multiple proline substitutions cumulatively thermostabilize bacillus cereus atcc7064 Oligo 1 6 glucosidase irrefragable proof supporting the proline rule
FEBS Journal, 1994Co-Authors: Kunihiko Watanabe, Tomoko Masuda, Hiroyuki Ohashi, Hisaaki Mihara, Yuzuru SuzukiAbstract:Nine residues of Bacillus cereus ATCC7064 Oligo-1,6-glucosidase were replaced stepwise with proline residues. Of the nine residues, Lys121, Glu208 and Glu290 were at second sites of β turns; Asn109, Glu175 and Thr261 were at N-caps of α helices; Glu216, Glu270 and Glu378 were in coils within loops. The replacements were carried out in the order, Lys121Pro, Glu175Pro, Glu290–Pro, Glu208Pro, Glu270Pro, Glu378Pro, Thr261Pro, Glu216Pro and Asn109 Pro. The resultant nine active mutant enzymes contained 1–9 more proline residues than B. cereus Oligo-1,6-glucosidase. The thermostability of these mutants was additively enhanced with the increase in the number of proline residues introduced. The increase in the thermostability was most remarkable when proline residues were introduced at second sites of β turns or at N-caps of α helices. The above results afforded irrefragable proof for the proline rule as an effective principle for increasing protein thermostability [Suzuki, Y., Oishi, K., Nakano, H. & Nagayama, T. (1987) Appl. Microbiol Biotechnol. 26, 546–551].
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proline residues responsible for thermostability occur with high frequency in the loop regions of an extremely thermostable Oligo 1 6 glucosidase from bacillus thermoglucosidasius kp1006
Journal of Biological Chemistry, 1991Co-Authors: Kunihiko Watanabe, K Chishiro, K Kitamura, Y SuzukiAbstract:The gene encoding for an extremely thermostable Oligo-1,6-glucosidase from Bacillus thermoglucosidasius KP1006 (DSM2542, obligate thermophile) was sequenced. The amino acid sequence deduced from the nucleotide sequence of the gene (1686 base pairs) corresponded to a protein of 562 amino acid residues with a Mr of 66,502. Its predicted amino acid composition, Mr, and N-terminal sequence of 12 residues were consistent with those determined for B. thermoglucosidasius Oligo-1,6-glucosidase. The deduced sequence of the enzyme was 72% homologous to that of a thermolabile Oligo-1,6-glucosidase (558 residues) from Bacillus cereus ATCC7064 (mesophile). B. cereus Oligo-1,6-glucosidase contained 19 prolines. Eighteen of these were conserved at the equivalent positions of B. thermoglucosidasius Oligo-1,6-glucosidase. This enzyme contained 14 extra prolines besides the conservative prolines. The majority of extra prolines was replaced by polar or charged residues (Glu, Thr, or Lys) in B. cereus Oligo-1,6-glucosidase. The extra prolines were responsible for the difference in thermostability between these two enzymes. We suggested that 11 of the extra prolines in B. thermoglucosidasius Oligo-1,6-glucosidase occur in beta-turns or in coils within the loops binding adjacent secondary structures.
Yuzuru Suzuki - One of the best experts on this subject based on the ideXlab platform.
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the refined crystal structure of bacillus cereus Oligo 1 6 glucosidase at 2 0 a resolution structural characterization of proline substitution sites for protein thermostabilization
Journal of Molecular Biology, 1997Co-Authors: Kunihiko Watanabe, Yasuo Hata, Hidekazu Kizaki, Yukiteru Katsube, Yuzuru SuzukiAbstract:The crystal structure of Oligo-1,6-glucosidase (dextrin 6-alpha-glucanohydrolase, EC 3.2.1.10) from Bacillus cereus ATCC7064 has been refined to 2.0 A resolution with an R-factor of 19.6% for 43,328 reflections. The final model contains 4646 protein atoms and 221 ordered water molecules with respective root-mean-square deviations of 0.015 A for bond lengths and of 3.166 degrees for bond angles from the ideal values. The structure consists of three domains: the N-terminal domain (residues 1 to 104 and 175 to 480), the subdomain (residues 105 to 174) and the C-terminal domain (residues 481 to 558). The N-terminal domain takes a (beta/alpha)8-barrel structure with additions of an alpha-helix (N alpha6') between the sixth strand Nbeta6 and the sixth helix N alpha6, an alpha-helix (N alpha7') between the seventh strand Nbeta7 and the seventh helix N alpha7 and three alpha-helices (N alpha8', N alpha8" and N alpha8'" between the eighth strand Nbeta8 and the eighth helix N alpha8. The subdomain is composed of an alpha-helix, a three-stranded antiparallel beta-sheet, and long intervening loops. The C-terminal domain has a beta-barrel structure of eight antiparallel beta-strands folded in double Greek key motifs, which is distorted in the sixth strand Cbeta6. Three catalytic residues, Asp199, Glu255 and Asp329, are located at the bottom of a deep cleft formed by the subdomain and a cluster of the two additional alpha-helices N alpha8' and N alpha8" in the (beta/alpha)8-barrel. The refined structure reveals the locations of 21 proline-substitution sites that are expected to be critical to protein thermostabilization from a sequence comparison among three Bacillus Oligo-1,6-glucosidases with different thermostability. These sites lie in loops, beta-turns and alpha-helices, in order of frequency, except for Cys515 in the fourth beta-strand Cbeta4 of the C-terminal domain. The residues in beta-turns (Lys121, Glu208, Pro257, Glu290, Pro443, Lys457 and Glu487) are all found at their second positions, and those in alpha-helices (Asn109, Glu175, Thr261 and Ile403) are present at their N1 positions of the first helical turns. Those residues in both secondary structures adopt phi and phi values favorable for proline substitution. Residues preceding the 21 sites are mostly conserved upon proline occurrence at these 21 sites in more thermostable Bacillus Oligo-1,6-glucosidases. These structural features with respect to the 21 sites indicate that the sites in beta-turns and alpha-helices have more essential prerequisites for proline substitution to thermostabilize the protein than those in loops. This well supports the previous finding that the replacement at the appropriate positions in beta-turns or alpha-helices is the most effective for protein thermostabilization by proline substitution.
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multiple proline substitutions cumulatively thermostabilize bacillus cereus atcc7064 Oligo 1 6 glucosidase irrefragable proof supporting the proline rule
FEBS Journal, 1994Co-Authors: Kunihiko Watanabe, Tomoko Masuda, Hiroyuki Ohashi, Hisaaki Mihara, Yuzuru SuzukiAbstract:Nine residues of Bacillus cereus ATCC7064 Oligo-1,6-glucosidase were replaced stepwise with proline residues. Of the nine residues, Lys121, Glu208 and Glu290 were at second sites of β turns; Asn109, Glu175 and Thr261 were at N-caps of α helices; Glu216, Glu270 and Glu378 were in coils within loops. The replacements were carried out in the order, Lys121Pro, Glu175Pro, Glu290–Pro, Glu208Pro, Glu270Pro, Glu378Pro, Thr261Pro, Glu216Pro and Asn109 Pro. The resultant nine active mutant enzymes contained 1–9 more proline residues than B. cereus Oligo-1,6-glucosidase. The thermostability of these mutants was additively enhanced with the increase in the number of proline residues introduced. The increase in the thermostability was most remarkable when proline residues were introduced at second sites of β turns or at N-caps of α helices. The above results afforded irrefragable proof for the proline rule as an effective principle for increasing protein thermostability [Suzuki, Y., Oishi, K., Nakano, H. & Nagayama, T. (1987) Appl. Microbiol Biotechnol. 26, 546–551].
