Search results for "stereo"
showing 10 items of 6147 documents
Syntheses, Structures and Reactivity of New Intramolecularly Coordinated Tin Alkoxides Based on an Enantiopure Ephedrine Derivative
2011
The syntheses of the tin compounds [LSn]2 (2), spiro-L2Sn (3), [LSnW(CO)5]2 (4), [LSnBr2]2 (5), spiro-L2Sn·SnBr4 (6) and LSn[OC(O)Ph]2 (8), where L = MeN(CH2CMe2O)[(S)-CH(Me)-(R)-CH(Ph)O], and (Ph4P)2SnBr6 (7) are reported. The compounds were characterized by elemental analysis, multinuclear NMR spectroscopy including 119Sn cross polarisation–magic angle spinning NMR (CP–MAS) (2, 3–6), electrospray ionization mass spectrometry (2–4) and single crystal X-ray diffraction analysis (2, 2·C7H8, 3a, 3b, 4·C7H8, 5, 6·C7H8, 7).
Unravelling the mechanism of the ketene-imine Staudinger reaction. An ELF quantum topological analysis
2015
The mechanism of the ketene-imine Staudinger (KI-S) reaction between t-butyl-cyano ketene and N-phenyl phenylimine has been studied using DFT methods at the MPWB1K/6-311G(d) computational level. The reaction takes place through a two-step mechanism: (i) the first step is the nucleophilic attack of the imine nitrogen lone pair on the central carbon of the ketene yielding a zwitterionic (ZW) intermediate; (ii) the second step, which is the rate- and stereoselectivity-determining step, is a ring-closure process achieved by a nucleophilic attack of the terminal carbon atom of the ketene on the imine carbon atom. Due to the unfeasibility of a cis/trans and an E/Z stereoisomerisation at the ZW in…
Bipolar membranes under forward and reverse bias conditions. Theory vs. experiment
1994
Abstract Bipolar membranes are layered structures composed of one cation-and one anion-exchange membrane joined together in series. The current—voltage curves of two recently developed bipolar membranes have been analysed theoretically and experimentally under both forward and reverse bias conditions. The experimental trends observed are high conductivity under forward bias conditions and high impedance first, and then electric field enhanced (EFE) water dissociation for high enough applied voltages, under reverse bias conditions. The forward bias measurements can contribute to a better knowledge of some of the transport parameters entering also in the reverse biased membrane. Comparison of…
Methode zur enzymatischen Bestimmung vond(+)-Malat
1982
Zur Bestimmung des unnaturlichen Enantiomers von Apfelsaure wird eine enzymatische Methode zur quantitativen Analyse vond(+)-Malat beschrieben. Mit einem ausPseudomonas luorescens isoliertend-Malat-Enzym (d(+)-Malat: NAD Oxidoreduktase, decarboxylierend), dasd-Malat spezifisch zu Pyruvat decarboxyliert, wobei NADH entsteht, wurde eine Analysenmethode entwickelt, die es ermoglicht, 20 bis 200 mgd-Malat je Liter in Fruchtsaften zu bestimmen. Mit dem optischen Test wurden bei der Untersuchung verschiedener Fruchtsafte keine Storungen beobachtet.
On the Formation of Droperidol Solvates: Characterization of Structure and Properties
2014
A solvate screening and characterization of the obtained solvates was performed to rationalize and understand the solvate formation of active pharamaceutical ingredient droperidol. The solvate screening revealed that droperidol can form 11 different solvates. The analysis of the crystal structures and molecular properties revealed that droperidol solvate formation is mainly driven by the inability of droperidol molecules to pack efficiently. The obtained droperidol solvates were characterized by X-ray diffraction and thermal analysis. It was found that droperidol forms seven nonstoichiometric isostructural solvates, and the crystal structures were determined for five of these solvates. To b…
1H,13C and17O NMR study of substituted nitropyridines
1991
1H, 13C and 17O NMR spectra for 22 substituted nitropyridines were measured and their 1H NMR spectra were analysed. The most significant variations in the NMR parameters are found for isomeric hydroxy derivatives, owing to the possibility of keto–enol tautomerism. The prevalence of the keto form is observed in 2- and 4-hydroxy derivatives, while the 3-hydroxy derivative exists in its enol form. Among the three nuclei studied, 17O seems to be the best nucleus for probing the keto–enol tautomerism. No correlation is observed between the torsion angle of the nitro group and its 17O NMR chemical shift. Molecular mechanics calculations were performed to clarify the torsional energetics of the ni…
Über den thermischen Abbau von Polyamiden der Nylon-Reihe
1978
Eine Reihe von aliphatischen Polyamiden (Nylon-7, Nylon-12, Nylon-4, Nylon-6,6, Nylon-6,10, Nylon-4,10, Nylon-11,6, Nylon-12,12) wurde im Massenspektrometer untersucht. In allen genannten Polyamiden lassen sich cyclische Oligomere ohne vorherige Isolierung nachweisen, die im Hochvakuum der Ionenquelle bei Temperaturen unterhalb 200°C verdampfen. Das Einsetzen eines thermischen Abbaus last sich bei Temperaturen oberhalb 350°C uber den Totalionenstrom beobachten. Die Polylactame werden unter diesen Bedingungen vor allem durch Verschiebung des Ring-Kettengleichgewichtes zu cyclischen Oligomeren, die Polyamide aus Dicarbonsauren und Diaminen bevorzugt durch cis-Eliminierung und Spaltung der Ami…
Innentitelbild: Die stark wachsende chemische Vielfalt der RNA-Modifikationen enthält eine Thioacetalstruktur (Angew. Chem. 26/2018)
2018
Sulfatierte und nicht sulfatierte Glycopeptid-Erkennungsdomänen des P-Selektin-Glycoprotein-Liganden 1 und ihre Bindung an P- und E-Selektin
2009
Totalsynthese via Blockglycosylierung und selektive chemische O-Sulfatierung von Tyrosinresten ergaben die Glycopeptid-Erkennungsregion A (X=SO3−) des P-Selektin-Glycoprotein-Liganden 1, in dem die terminale Sialinsaure der komplexen Hexasaccharid-Seitenkette durch (S)-Cyclohexylmilchsaure als Mimetikum ersetzt ist. In Bindungsassays zeigt die O-sulfatierte Form A hohe Affinitat zu P-Selektin, die nicht sulfatierte Form zu E-Selektin.