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101.
Klaus Albert Markus Dachtler Tobias Glaser Heidi Hndel Tanja Lacker Gtz Schlotterbeck Sabine Strohschein Li-Hong Tseng Ulrich Braumann 《Journal of separation science》1999,22(3):135-143
The hyphenation of chromatographic separation techniques with NMR spectroscopy is one of the most powerful and time-saving methods for the separation and structural elucidation of unknown compounds and molecular compositions of mixtures. Most of the routinely used NMR flow-cells have detection volumes between 40–180 μL for conventional separations with analytical columns, and the newest designs employ detection volumes in the order of 200 nL for capillary separations. The low flow rates used in capillary chromatography permit the use of deuterated solvents. Unequivocal structural assignment of unknown chromatographic peaks is possible by two-dimensional stopped-flow capillary HPLC-NMR experiments. 相似文献
102.
Tobat P.I. Saragi Christoph Schmidt Tanja Weis Arno Ehresmann 《Journal of magnetism and magnetic materials》2009,321(14):2204-2209
The surface and interface morphology and magnetization characteristics of Co70Fe30 thin films deposited on bare glass and p-Si/SiO2 substrates and on conjugated polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films on such substrates have been studied by atomic force microscopy and magneto-optic Kerr effect. It was found that the average absolute magnitude of the coercive field of Co70Fe30 correlates with the roughness of the underlayer prior to Co70Fe30 deposition. P3HT deposited on p-Si/SiO2 substrates possesses an increased surface roughness as compared to the p-Si/SiO2 surface, but displays a decreased surface roughness as compared to the one of a bare glass substrate. 相似文献
103.
Tanja Soldatović Predrag Čanović Radivoje Nikolić Ratomir Jelić Živadin D. Bugarčić 《Journal of solution chemistry》2009,38(1):57-71
The formation equilibria of the [Pt(SMC)(H2O)2]+ complex with some biologically relevant ligands such as L-methionine (L-met) and glutathione (GSH) were studied. The stoichiometry
and stability constants of the formed complexes are reported, and the concentration distribution of the various complex species
has been evaluated as a function of pH. The reaction between [PtCl2(SMC)] and guanosine-5′-monophosphate (5′-GMP) was studied by 1H NMR spectroscopy. The NMR spectra indicated that first step is the hydrolysis of the [PtCl2(SMC)] complex and second step is the substitution of an aqua ligand, either in the cis or trans position with guanosine-5′-monophosphate in molar ratio 1:1. The values of rate constant showed faster substitution of coordinated
H2O in the trans position to the S donor atom of S-methyl-L-cysteine, whereas the slower reaction was assigned to the displacement of the
cis coordinated aqua molecule. This is due to the strong trans labilization effect of coordinated sulfur.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
104.
Tanja Grkovic 《Tetrahedron》2009,65(32):6335-207
A survey of the secondary metabolite chemistry profiles of New Zealand sponges of the genus Latrunculia has yielded new members of the discorhabdin A- and B-type families. The structure elucidation of (+)-(6R,8S)-1-thiomethyldiscorhabdin G∗/I (5) and both enantiomers of 16a,17a-dehydrodiscorhabdin W (6) are reported. Absolute configurations were assigned by comparison with a dataset of recently reported electronic circular dichroism spectra of discorhabdin alkaloids. A stereochemical correction of the recently reported natural product (+)-3-dihydrodiscorhabdin A from (3S,5R,6S,8S)-(7) to the C3-epimeric (+)-(3R,5R,6S,8S)-(8) and assignment of absolute configuration is also presented. Semi-synthesis of (+)-(3S,5R,6S,8S)-(7) from (+)-discorhabdin A provided further evidence for this structure revision. Cytotoxicity data is reported for 5-8. 相似文献
105.
Bringmann G Kajahn I Reichert M Pedersen SE Faber JH Gulder T Brun R Christensen SB Ponte-Sucre A Moll H Heubl G Mudogo V 《The Journal of organic chemistry》2006,71(25):9348-9356
The isolation and structural elucidation of three novel-type naphthylisoquinoline alkaloids, ancistrocladinium A and B (the latter along with its atropisomer), from a Congolese Ancistrocladus species collected in the habitat Yeteto is reported. Their structures, including all stereochemical features, were elucidated by spectroscopic, chemical, and chiroptical methods. Ancistrocladinium A and B are the first N,C-coupled naphthyldihydroisoquinoline alkaloids found in nature, i.e., with an iminium-aryl axis. Although ancistrocladinium A, which is N,8'-coupled, is configurationally stable at this axis, ancistrocladinum B and its rotational isomer are based on a hitherto unprecedented N,6'-coupling type, with a slow rotation about the hetero biaryl axis at room temperature; they thus occur as a 46:54 mixture of two configurationally semistable atropo-diastereomers. For the isomerization of (P)-ancistrocladinium B to its (M)-diastereomer and for the opposite direction, the Gibbs free energies of activation were determined to be DeltaG double dagger1 = 105.8 kJ mol-1 and DeltaG double dagger2 = 105.7 kJ mol-1, respectively. In addition, the compounds were shown to have promising antileishmanial activities. 相似文献
106.
Dr. Yuzhou Wu Prof. Dr. Fedor Jelezko Prof. Dr. Martin B Plenio Prof. Dr. Tanja Weil 《Angewandte Chemie (International ed. in English)》2016,55(23):6586-6598
The currently available techniques for molecular imaging capable of reaching atomic resolution are limited to low temperatures, vacuum conditions, or large amounts of sample. Quantum sensors based on the spin‐dependent photoluminescence of nitrogen‐vacancy (NV) centers in diamond offer great potential to achieve single‐molecule detection with atomic resolution under ambient conditions. Diamond nanoparticles could also be prepared with implanted NV centers, thereby generating unique nanosensors that are able to traffic into living biological systems. Therefore, this technique might provide unprecedented access and insight into the structure and function of individual biomolecules under physiological conditions as well as observation of biological processes down to the quantum level with atomic resolution. The theory of diamond quantum sensors and the current developments from their preparation to sensing techniques have been critically discussed in this Minireview. 相似文献
107.
A stereospecific photochemical ring contraction was used as the key step in the first total synthesis of the marine pseudopteranyl diterpene 11-gorgiacerol and its 11-epimer. The synthesis allowed the correction of the configurations that had been misassigned in the literature. In addition, some novel pseudopteranyl derivatives have been made. 相似文献
108.
Chia PW Livesey MR Slawin AM van Mourik T Wyllie DJ O'Hagan D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(28):8813-8819
N-Methyl-D-aspartate (NMDA) is the prototypical agonist of the NMDA receptor subtype of ionotropic glutamate receptors. Stereogenic placement of a C-F bond at the 3-position of (S)-NMDA generates either the (2S,3S)- or (2S,3R)- diastereoisomers of 3F-NMDA. The individual diastereoisomers were prepared by synthesis in enantiomerically pure forms and it was found that (2S,3S)-3F-NMDA is an agonist with a comparable potency to NMDA itself, whereas the (2S,3R)-diastereoisomer has negligible potency. The difference in potency of these stereoisomers is attributed to a preference of the C-F bond (2S,3S)-3F-NMDA to adopt a gauche conformation to the C-N(+) bond in the binding conformation, whereas the (2S,3R)-3F-NMDA forces these bonds anti, losing electrostatic stabilisation, to achieve the required binding conformation. These observations illustrate the utility of stereoselective fluorination in influencing the molecular conformation of β-fluorinated amino acids and thus probing the active conformations of bioactive compounds at receptors. 相似文献
109.
Schulz-Gasch T Schärfer C Guba W Rarey M 《Journal of chemical information and modeling》2012,52(6):1499-1512
Advantages like intuitive interpretation, objectivity, general applicability, and its easy, automated calculation make the rmsd (root-mean-squared deviation) the measure of choice for the investigation of the accuracy of conformational model generators. For comparing conformations of a single molecule this is a clearly superior method. Single molecule analysis is, however, a rare scenario. Typically, conformations are generated for huge corporate or external vendor databases of high diversity which are then further investigated with high-throughput computational methods like docking or pharmacophore searching, in virtual screening campaigns. Representative subsets for accuracy investigations of computational methods need to mimic this diversity. Averaged rmsd values over these data sets are frequently used to assess the accuracy of the methods. There are, however, significant weaknesses in rmsd comparisons for such kind of data sets. The interpretation is for example no longer intuitive because what can be expected in terms of good or bad rmsd values crucially depends on the data set composition like size or number of rotatable bonds of the underlying molecules. Further, rmsd lacks normalization which might result in very high averaged rmsd values for highly flexible molecules and thus might completely skew results. We have developed a novel measure to compare conformations of molecules called Torsion Fingerprint Deviation (TFD). It extracts, weights, and compares Torsion Fingerprints from a query molecule and generated conformations under consideration of acyclic bonds as well as ring systems. TFD is alignment-free and overcomes major limitations of rmsd while retaining its advantages. 相似文献
110.