The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Seiji Shinkai - One of the best experts on this subject based on the ideXlab platform.
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polysaccharide polynucleotide complexes 2 complementary polynucleotide mimic behavior of the natural polysaccharide schizophyllan in the macromolecular complex with single stranded rna and dna
Biomacromolecules, 2001Co-Authors: Kazuo Sakurai, Masami Mizu, Seiji ShinkaiAbstract:Schizophyllan is an extracellular polysaccharide consisting of a β-1,3-d-glucan main chain and exists as a triple helix in water and as a single chain in dimethyl sulfoxide (DMSO). When the single chain of schizophyllan (s-SPG) was mixed with poly(C), poly(A), poly(dA), or poly(dT), they form a macromolecular complex. On the other hand, poly(G), poly(U), poly(I), poly(dG), and poly(dC) do not. This nucleotide specificity evidences that the hydrogen bonds are essential to form the complex, because the former nucleotides have an unoccupied hydrogen-Bonding Site and the latter ones use the hydrogen-Bonding Sites in the intramolecular aggregation (i.e., such as the G quartet for poly(G) and poly(dG) and the U hairpin for poly(U)). The hypochromic effect and the increment in the circular dichroism (CD) intensity are observed in accordance with the complex formation. These facts indicate that the base stacking is enhanced in the complex. The solvent−composition (DMSO/water) dependence demonstrates that the hydr...
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polysaccharide polynucleotide complexes 2 complementary polynucleotide mimic behavior of the natural polysaccharide schizophyllan in the macromolecular complex with single stranded rna and dna
Biomacromolecules, 2001Co-Authors: Kazuo Sakurai, Masami Mizu, Seiji ShinkaiAbstract:Schizophyllan is an extracellular polysaccharide consisting of a beta-1,3-D-glucan main chain and exists as a triple helix in water and as a single chain in dimethyl sulfoxide (DMSO). When the single chain of schizophyllan (s-SPG) was mixed with poly(C), poly(A), poly(dA), or poly(dT), they form a macromolecular complex. On the other hand, poly(G), poly(U), poly(I), poly(dG), and poly(dC) do not. This nucleotide specificity evidences that the hydrogen bonds are essential to form the complex, because the former nucleotides have an unoccupied hydrogen-Bonding Site and the latter ones use the hydrogen-Bonding Sites in the intramolecular aggregation (i.e., such as the G quartet for poly(G) and poly(dG) and the U hairpin for poly(U)). The hypochromic effect and the increment in the circular dichroism (CD) intensity are observed in accordance with the complex formation. These facts indicate that the base stacking is enhanced in the complex. The solvent-composition (DMSO/water) dependence demonstrates that the hydrophobic interaction is important to form the complex as well as the hydrogen-Bonding interaction. With increasing temperature the complex dissociates cooperatively and the melting curve enables the thermodynamic parameters to be evaluated (delta H = -60 to 70 kcal mol-1 and delta S = -150 to 200 cal mol-1 K-1). These values are comparable with those for double helix DNA. Namely, the complex can be characterized by enhancement of the base stacking, cooperative dissociation, the similar thermodynamic parameters to DNA, and combination of the hydrogen-Bonding and hydrophobic interactions to form the higher-order structure. These facts surprisingly coincide with characters of the double helix of DNA. In other words, the s-SPG molecule behaves as if it were a complementary polynucleotide chain for the corresponding polynucleotide. Furthermore, stoichiometric study suggested that the complex structure is a triple helix consisting of two s-SPG and one poly(C) or poly(A) chains.
Kazuo Sakurai - One of the best experts on this subject based on the ideXlab platform.
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polysaccharide polynucleotide complexes 2 complementary polynucleotide mimic behavior of the natural polysaccharide schizophyllan in the macromolecular complex with single stranded rna and dna
Biomacromolecules, 2001Co-Authors: Kazuo Sakurai, Masami Mizu, Seiji ShinkaiAbstract:Schizophyllan is an extracellular polysaccharide consisting of a β-1,3-d-glucan main chain and exists as a triple helix in water and as a single chain in dimethyl sulfoxide (DMSO). When the single chain of schizophyllan (s-SPG) was mixed with poly(C), poly(A), poly(dA), or poly(dT), they form a macromolecular complex. On the other hand, poly(G), poly(U), poly(I), poly(dG), and poly(dC) do not. This nucleotide specificity evidences that the hydrogen bonds are essential to form the complex, because the former nucleotides have an unoccupied hydrogen-Bonding Site and the latter ones use the hydrogen-Bonding Sites in the intramolecular aggregation (i.e., such as the G quartet for poly(G) and poly(dG) and the U hairpin for poly(U)). The hypochromic effect and the increment in the circular dichroism (CD) intensity are observed in accordance with the complex formation. These facts indicate that the base stacking is enhanced in the complex. The solvent−composition (DMSO/water) dependence demonstrates that the hydr...
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polysaccharide polynucleotide complexes 2 complementary polynucleotide mimic behavior of the natural polysaccharide schizophyllan in the macromolecular complex with single stranded rna and dna
Biomacromolecules, 2001Co-Authors: Kazuo Sakurai, Masami Mizu, Seiji ShinkaiAbstract:Schizophyllan is an extracellular polysaccharide consisting of a beta-1,3-D-glucan main chain and exists as a triple helix in water and as a single chain in dimethyl sulfoxide (DMSO). When the single chain of schizophyllan (s-SPG) was mixed with poly(C), poly(A), poly(dA), or poly(dT), they form a macromolecular complex. On the other hand, poly(G), poly(U), poly(I), poly(dG), and poly(dC) do not. This nucleotide specificity evidences that the hydrogen bonds are essential to form the complex, because the former nucleotides have an unoccupied hydrogen-Bonding Site and the latter ones use the hydrogen-Bonding Sites in the intramolecular aggregation (i.e., such as the G quartet for poly(G) and poly(dG) and the U hairpin for poly(U)). The hypochromic effect and the increment in the circular dichroism (CD) intensity are observed in accordance with the complex formation. These facts indicate that the base stacking is enhanced in the complex. The solvent-composition (DMSO/water) dependence demonstrates that the hydrophobic interaction is important to form the complex as well as the hydrogen-Bonding interaction. With increasing temperature the complex dissociates cooperatively and the melting curve enables the thermodynamic parameters to be evaluated (delta H = -60 to 70 kcal mol-1 and delta S = -150 to 200 cal mol-1 K-1). These values are comparable with those for double helix DNA. Namely, the complex can be characterized by enhancement of the base stacking, cooperative dissociation, the similar thermodynamic parameters to DNA, and combination of the hydrogen-Bonding and hydrophobic interactions to form the higher-order structure. These facts surprisingly coincide with characters of the double helix of DNA. In other words, the s-SPG molecule behaves as if it were a complementary polynucleotide chain for the corresponding polynucleotide. Furthermore, stoichiometric study suggested that the complex structure is a triple helix consisting of two s-SPG and one poly(C) or poly(A) chains.
Thorsten Bach - One of the best experts on this subject based on the ideXlab platform.
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a chiral phenanthroline ligand with a hydrogen Bonding Site application to the enantioselective amination of methylene groups
Journal of the American Chemical Society, 2020Co-Authors: Rajasekar Reddy Annapureddy, Christian Jandl, Thorsten BachAbstract:A silver-catalyzed amination is reported that occurs at the aliphatic C3-substituent of various quinolones and pyridones. The C–H amination reaction proceeded with high Site- and enantioselectivity...
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enantio and regioselective epoxidation of olefinic double bonds in quinolones pyridones and amides catalyzed by a ruthenium porphyrin catalyst with a hydrogen Bonding Site
Journal of the American Chemical Society, 2012Co-Authors: Philipp Fackler, Stefan M Huber, Thorsten BachAbstract:An array of differently substituted 3-alkenylquinolones was synthesized, and the enantio- and regioselectivity of their Ru-catalyzed epoxidation were studied. A precursor ruthenium(II) complex with a chiral tricyclic γ-lactam skeleton (octahydro-1H-4,7-methanoisoindol-1-one) was available by Sonogashira cross-coupling with a monobromo-substituted ruthenium(II) porphyrin. Enantioselective epoxidation reactions (60–83% yield, 85–98% ee) were achieved with this catalyst, and it was shown that the enantioselectivity depends critically on the presence of a two-point hydrogen bond interaction between the γ-lactam Site of the catalyst and the δ-lactam (quinolone) Site of the substrate. DFT calculations support the hypothesis that the reaction occurs via a hydrogen-bound transition state, in which the 3-alkenylquinolone adopts an s-trans conformation. The calculations further revealed that this transition state is preferred over a competing s-cis transition state because it exerts less strain in the rigid backbon...
Tsong-song Hwang - One of the best experts on this subject based on the ideXlab platform.
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Remote Communication between Charge Centers and Hydrogen‐Bonding Sites: Possibility for a Signal Transducer?
Angewandte Chemie (International ed. in English), 2001Co-Authors: Ito Chao, Tsong-song HwangAbstract:Signal enhancement from a reaction center to a hydogen-Bonding Site occurs when they are separated by an azo linker. A computational study has shown that the binding of ammonia to a pyrrole unit in an iminium compound increases as the length of the azo group between the two Sites increases. This surprising result is explained in terms of resonance effects and the larger electron-withdrawing power of longer azo linkers.
Eric S Simon - One of the best experts on this subject based on the ideXlab platform.
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the use of hydrolytic enzymes and multi stage tandem mass spectrometry to analyze pyridoxal phosphate modified peptides
Analytical Biochemistry, 2019Co-Authors: Eric S Simon, Phil AndrewsAbstract:Abstract A previous approach was established that allowed direct identification of pyridoxal-5ˊ-phosphate (PLP) Bonding Sites in proteins using mass spectrometry after tryptic proteolysis. The approach required peptide mass fingerprinting owing to suppressed amide backbone fragmentation in favor of side-chain elimination of diagnostic product ions from PLP-derivatized lysyl residues. While sufficient for purified proteins, unambiguous sequence determination is needed to assign PLP Bonding Sites in unknown proteins in complex mixtures. Here, we describe the use of hydrolytic enzymes and multi-stage tandem mass spectrometry to elucidate the amino acid sequence and PLP Bonding Site in PLP-modified peptides.
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determination of pyridoxal 5 phosphate plp Bonding Sites in proteins a peptide mass fingerprinting approach based on diagnostic tandem mass spectral features of plp modified peptides
Rapid Communications in Mass Spectrometry, 2009Co-Authors: Eric S Simon, John AllisonAbstract:Peptides modified by pyridoxal-5'-phosphate (PLP), linked to a lysine residue via reductive amination, exhibit distinct spectral characteristics in the collision-induced dissociation (CID) tandem mass (MS/MS) spectra that are described here. The MS/MS spectra typically display two dominant peaks whose m/z values correspond to neutral losses of [H3PO4] (-98 Da) and the PLP moiety as [C8H10NO5P] (-231 Da) from the precursor peptide ion, respectively. Few other peaks are observed. Recognition of this distinct fragmentation behavior is imperative since determining sequences and Sites of modifications relies on the formation of amide backbone cleavage products for subsequent interpretation via proteome database searching. Additionally, PLP-modified peptides exhibit suppressed precursor ionization efficiency which diminishes their detection in complex mixtures. Presented here is a protocol which describes an enrichment strategy for PLP-modified peptides combined with neutral loss screening and peptide mass fingerprinting to map the PLP-Bonding Site in a known PLP-dependent protein. This approach represents an efficient alternative to Site-directed mutagenesis which has been the traditional method used for PLP-Bonding Site localization in proteins.