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141.
Appel R Atoyan GS Bassalleck B Bergman DR Cheung N Dhawan S Do H Egger J Eilerts S Fischer H Herold W Issakov VV Kaspar H Kraus DE Lazarus DM Lichard P Lowe J Lozano J Ma H Majid W Menzel W Pislak S Poblaguev AA Rehak P Sher A Thompson JA Truöl P Zeller ME 《Physical review letters》2000,85(14):2877-2880
A search for lepton flavor violating decays, K+ --> mu+ mu+ pi-, K+ --> e+ e+ pi-, K+ --> pi+ e+ mu-, K+ --> mu+ e+ pi-, and pi0 --> e+ mu-, was performed using the data collected in Experiment E865 at the Brookhaven Alternating Gradient Synchrotron. No signal was found in any of the decay modes. At the 90% confidence level, the branching ratios are less than 3.0x10(-9), 6.4x10(-10), 5. 2x10(-10), 5.0x10(-10), and 3.4x10(-9), respectively. 相似文献
142.
Wenz G Strassnig C Thiele C Engelke A Morgenstern B Hegetschweiler K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(24):7202-7211
Inclusion compounds of cationic, anionic, and neutral p-substituted derivatives of tert-butylbenzene complexed in beta-cyclodextrin and its ionic 6-mono and 6-hepta derivatives were systematically investigated by isothermal titration calorimetry (ITC). All inclusion compounds showed 1:1 stoichiometry with binding constants ranging from 10 to 3 x 10(6) M(-1). The binding free energies could be subdivided into apolar and electrostatic contributions. The electrostatic interactions could be quantitatively described by Coulomb's law by taking into account the degree of protonation of hosts and guests, the orientations of the guests within the hosts, and ion shielding as described by the Debye-Hückel-Onsager theory. The orientations of the guests within the cyclodextrin cavities were determined by ROESY NMR spectroscopy. 相似文献
143.
Dr. Felix Kaspar Felix Brandt Sarah Westarp Lea Eilert Dr. Sebastian Kemper Dr. Anke Kurreck Prof. Dr. Peter Neubauer Prof. Dr. Christoph R. Jacob Prof. Dr. Anett Schallmey 《Angewandte Chemie (International ed. in English)》2023,62(20):e202218492
Biocatalytic nucleoside (trans-)glycosylations catalyzed by nucleoside phosphorylases have evolved into a practical and convenient approach to the preparation of modified nucleosides, which are important pharmaceuticals for the treatment of various cancers and viral infections. However, the obtained yields in these reactions are generally determined exclusively by the innate thermodynamic properties of the nucleosides involved, hampering the biocatalytic access to many sought-after target nucleosides. We herein report an additional means for reaction engineering of these systems. We show how apparent equilibrium shifts in phosphorolysis and glycosylation reactions can be effected through entropically driven, biased esterification of nucleosides and ribosyl phosphates with inorganic borate. Our multifaceted analysis further describes the kinetic implications of this in situ reactant esterification for a model phosphorylase. 相似文献
144.
145.
Inducing Axial Chirality in a “Geländer” Oligomer by Length Mismatch of the Oligomer Strands
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Michel Rickhaus Linda Maria Bannwart Dr. Markus Neuburger Heiko Gsellinger Kaspar Zimmermann Dr. Daniel Häussinger Prof. Dr. Marcel Mayor 《Angewandte Chemie (International ed. in English)》2014,53(52):14587-14591
Helical molecules are not only esthetically appealing due to their structural beauty, they also display unique physical properties as a result of their chirality. We describe herein a new approach to “Geländer” oligomers by interlinking two oligomer strands of different length. To compensate for the dimensional mismatch, the longer oligo(benzyl ether) oligomer wraps around the oligophenyl backbone. The new “Geländer” oligomer 1 was assembled in a sequence of functional‐group transformations and cross‐coupling steps followed by final cyclizations based on nucleophilic substitution reactions, and was fully characterized, including X‐ray diffraction analysis. The isolation of pure enantiomers enabled the racemization process to be studied by circular dichroism spectroscopy. 相似文献
146.
Christian Neis Kaspar Hegetschweiler 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(4):396-399
In the title monohydrated cocrystal, namely 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol iodide–1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol–water (1/1/1), C6H16N3O3+·I−·C6H15N3O3·H2O, the neutral 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol (taci) molecule and the monoprotonated 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol cation (Htaci+) both adopt a chair conformation, with the three O atoms in axial and the three N atoms in equatorial positions. The cation, but not the neutral taci unit, exhibits intramolecular O—H...O hydrogen bonding. The entire structure is stabilized by a complex three‐dimensional network of intermolecular hydrogen bonds. The neutral taci entities and the Htaci+ cations are each aligned into chains along [001]. In these chains, two O—H...N interactions generate a ten‐membered ring as the predominant structural motif. The rings consist of vicinal 2‐amino‐1‐hydroxyethylene units of neighbouring molecules, which are paired via centres of inversion. The chains are interconnected into undulating layers parallel to the ac plane, and the layers are further held together by O—H...N hydrogen bonds and additional interactions with the iodide counter‐anions and solvent water molecules. 相似文献
147.
Kaspar Hegetschweiler Andr Egli Eberhardt Herdtweck WolfgangA. Herrmann Roger Alberto Volker Gramlich 《Helvetica chimica acta》2005,88(3):426-434
The two neutral complexes [Re(CO)3(H−1taci)] ( 1 ) and [ReO3(H−1taci)] ( 2 ) (taci=1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol) were synthesized from the conventional ReI and ReVII precursors (Et4N)2[ReBr3(CO)3] and [ReO3(OSnMe3)]. The crystal structures of 1 and 2 , which were determined by single crystal X‐ray analysis, are virtually isomorphous. Both compounds crystallize in the orthorhombic space group Pnma, Z=4; 1 : a=14.806(3), b=8.466(2), c=9.781(2) Å, 2 : a=13.050(2), b=8.732(1), c=9.061(1) Å. In both complexes, the monodeprotonated H−1taci ligand is bonded to the Re center in an N,O,N‐coordination mode. The resulting molecular Cs symmetry is retained in the crystal structure and confirmed by IR spectroscopy of solid‐state samples. The observed binding mode of the ligand is discussed in terms of steric and electronic effects. 相似文献
148.
Christian Neis Bernd Morgenstern Kaspar Hegetschweiler 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(1):28-34
A first preliminary report on the crystal structure of a hydrated salt formulated as [Ge(taci)2]Cl4·13H2O (taci is 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol) appeared more than 20 years ago [Ghisletta (1994). PhD thesis, ETH Zürich. Switzerland]. At that time it was not possible to discriminate unambiguously between the positions of some of the chloride ions and water O atoms, and disorder was thus postulated. In a new determination, a conclusive scheme of hydrogen bonding proves to be a particularly appealing aspect of the structure. Single crystals of the title compound, C12H30GeN6O64+·4Cl−·6H2O or [Ge(taci)2]2Cl8·12H2O, were grown from an aqueous solution by slow evaporation of the solvent. The two [Ge(taci)2]4+ cations exhibit a double‐adamantane‐type structure with exclusive O‐atom coordination and approximate D3d symmetry. The taci ligands adopt a zwitterionic form with deprotonated hydroxy groups and protonated amino groups. Both cations are hydrogen bonded to six water molecules. The structure of the hydration shell of the two cations is, however, slightly different. The {[Ge(taci)2]·6H2O}4+ aggregates are interlinked in all three dimensions by further hydrogen bonds of the types N—H...Cl...H—N, N—H...O(H)2...H—N, (Ge)O...H—O(H)...H—N, N—H...O(H)—H...Cl...H—N, (Ge)O...H—O—H...Cl...H—N, N—H...O(H)—H...Cl...H—(H)O...H—N, (Ge)O...H—O—H...Cl...H—(H)O...H—N and Ge(O)...H—O—H...Cl...H—O—H...O(Ge). 相似文献
149.
150.
Dialdehydes Lead to Exceptionally Fast Bioconjugations at Neutral pH by Virtue of a Cyclic Intermediate
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Pascal Schmidt Dr. Linna Zhou Kiril Tishinov Kaspar Zimmermann Prof. Dr. Dennis Gillingham 《Angewandte Chemie (International ed. in English)》2014,53(41):10928-10931
One of the open challenges in chemical biology is to identify reactions that proceed with large rate constants at neutral pH values. As shown here, dialdehydes react with O‐alkylhydroxylamines at rates of 500 M ?1 s?1 at neutral pH values in the absence of catalysts. The key to these conjugations is an unusually stable cyclic intermediate, which ultimately undergoes dehydration to yield an oxime. The scope and limitations of the method are outlined, as well as its application in bioconjugation and a mechanistic interpretation that will facilitate further developments of reactions with alkylhydroxylamines at low substrate concentrations. 相似文献