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Junker J Reif B Steinhagen H Junker B Felli IC Reggelin M Griesinger C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(17):3281-3286
The structure of a catalytic intermediate with important implications for the interpretation of the stereochemical outcome of the palladium complex catalyzed allylic substitution with phosphino-oxazoline (PHOX) ligands is determined by liquid state NMR. The complex displays a novel structure that is highly distorted compared with other palladium eta2-olefin complexes known so far. The structure has been determined from nuclear overhauser data (NOE), scalar coupling constants, and long range projection angle restraints derived from dipole dipole cross-correlated relaxation of multiple quantum coherence. The latter restraints have been implemented into a distance geometry protocol. The projection angle restraints yield a higher precision in the determination of the relative orientation of the two molecular moieties and are essential to provide an exact structural definition of the olefinic part of the catalytic intermediate with respect to the ligand. 相似文献
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Bernd Reif Valentin Wittmann Harald Schwalbe Christian Griesinger Karlheinz Wrner Kerstin Jahn-Hofmann Joachim W. Engels Wolfgang Bermel 《Helvetica chimica acta》1997,80(6):1952-1971
1-(2′-Deoxy-2′-fluororibofuranosyl)pyrimidines were synthesized and incorporated into an RNA oligonucleotide to give 5′-r[CfGCf(UfUfCfG)GCfG]-3′ (Cf: short form of C = 2′-deoxy-2′-fluorocytidine; Uf: short form of U = 2′-deoxy-2′-fluorouridine). The oligomer was investigated by means of UV, CD, and NMR spectroscopy to address the question of how F-labels can substitute 13C-labels in the ribose ring. Through-space (NOE) and through-bond (scalar couplings) experiments were performed that make use of the ameliorated chemical-shift dispersion induced by 19F as an alternative heteronucleus. A comparison of the structures of fluorinated vs. unmodified oligomer is given. It turns out that the fluorinated oligonucleotide exists in a 14:3 equilibrium between a hairpin and a duplex conformation, in contrast to the unmodified oligonucleotide which predominantly adopts the hairpin conformation. Furthermore, the fluorinated hairpin structure adopts two distinct conformations that differ in the sugar conformation of the U and C nucleoside units, as detected by the 19F-NMR chemical shifts. The role of the 2′-OH group as stabilizing element in RNA secondary structure is discussed. 相似文献
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Zhenhui Qi Dr. Changzhu Wu Dr. Paula Malo de Molina Han Sun Andrea Schulz Prof. Christian Griesinger Prof. Michael Gradzielski Prof. Rainer Haag Prof. Marion B. Ansorge‐Schumacher Prof. Christoph A. Schalley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10150-10159
A new and versatile, crown ether appended, chiral supergelator has been designed and synthesized based on the bis‐urea motif. The introduction of a stereogenic center improved its gelation ability significantly relative to its achiral analogue. This low‐molecular‐weight gelator forms supramolecular gels in a variety of organic solvents. It is sensitive to multiple chemical stimuli and the sol–gel phase transitions can be reversibly triggered by host–guest interactions. The gel can be used to trap enzymes and release them on demand by chemical stimuli. It stabilizes the microparticles in Pickering emulsions so that enzyme‐catalyzed organic reactions can take place in the polar phase inside the microparticles, the organic reactants diffusing through the biphasic interface from the surrounding organic phase. Because of the higher interface area between the organic and polar phases, enzyme activity is enhanced in comparison with simple biphasic systems. 相似文献
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Dr. Lukas Kaltschnee Dr. Anil P. Jagtap Dr. Jeffrey McCormick Dr. Shawn Wagner Prof. Dr. Louis-S. Bouchard Prof. Dr. Marcel Utz Prof. Dr. Christian Griesinger Dr. Stefan Glöggler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(47):11031-11035
NMR offers many possibilities in chemical analysis, structural investigations, and medical diagnostics. Although it is broadly used, one of NMR spectroscopies main drawbacks is low sensitivity. Hyperpolarization techniques enhance NMR signals by more than four orders of magnitude allowing the design of new contrast agents. Parahydrogen induced polarization that utilizes the para-hydrogen's singlet state to create enhanced signals is of particular interest since it allows to produce molecular imaging agents within seconds. Herein, we present a strategy for signal enhancement of the carbonyl 13C in amino acids by using parahydrogen, as demonstrated for glycine and alanine. Importantly, the hyperpolarization step is carried out in water and chemically unmodified canonical amino acids are obtained. Our approach thus offers a high degree of biocompatibility, which is crucial for further application. The rapid sample hyperpolarization (within seconds) may enable the continuous production of biologically useful probes, such as metabolic contrast agents or probes for structural biology. 相似文献