نتایج جستجو برای: Enantiomeric Excess
تعداد نتایج: 75059 فیلتر نتایج به سال:
an important property of electromagnetic fields, which arises from the interaction between fields and chiral molecules, is called optical chirality. by enhancing this field property, while maintaining constant input power, we are able to increase absorption of circularly polarized light by chiral molecules of a certain handedness. this enhancement is achieved through the use of achiral plasmoni...
Many apparently achiral organic molecules on Earth may be chiral because of random substitution of the 1.11% naturally abundant 13C for 12C in an enantiotopic moiety within the structure. However, chirality from this source is experimentally difficult to discern because of the very small difference between 13C and 12C. We have demonstrated that this small difference can be amplified to an easil...
Enantiomeric excess of chiral compounds is a key parameter that determines their activity or therapeutic action. The current paradigm for rapid measurement of enantiomeric excess using NMR is based on the formation of diastereomeric complexes between the chiral analyte and a chiral resolving agent, leading to (at least) two species with no symmetry relationship. Here we report an effective meth...
Different strategies for the resolution of racemates in lipase catalyzed hydrolyses, esterifications, and transesterifications are presented. The importance of the equilibrium conversion for the optimization of the enantiomeric excess is emphasized. Investigations have been carried out on esters of 1-phenylethanol and 2methylalkanoic acids. Results are presented, which provide general informati...
A colour indicator for the full range of enantiomeric excess (-100%-->100% ee) is presented which is based on visual colour inspection of a liquid crystal doped with the analyte, i.e. the methyl ester of amino acid phenylglycine, providing the enantiomeric excess and allowing the assignment of the major enantiomer.
Simple methods for determining the enantiomeric purity of mevalonolactone and linalool by NMR using the chiral shift reagent Eu(hfc)3 are reported. These methods are more reliable than polarimetry and require only a few milligrams of sample to detect as little as 2% of the minor enantiomer. The accuracy of these methods is limited primarily by spectral resolution for samples of high enantiomeri...
We present differential optical reflectivity and null transmission ellipsometry data from several mixtures of MHPBC enantiomers. From this data, we have determined the chiral smectic phase sequence as a function of enantiomeric excess. The data suggest a change in the structure of the smectic-C(*)(alpha) phase and the surface tilt state as the enantiomeric excess is reduced. The results also sh...
A general enantioselective route to functionalized first generation molecular motors is described. An enantioselective protonation of the silyl enol ethers of indanones by a Au(I)BINAP complex sets the stage for a highly diastereoselective McMurry coupling as a second enhancement step for enantiomeric excess. In this way various functionalized overcrowded alkenes could be synthesized in good yi...
The ability to photoinduce enantiomeric excess from the chirality of circularly polarized light (CPL) is pertinent to the study of the origin of homochirality in biomolecules. Such CPL-induced reactions, including both chirality generation and formation of partial enantiomeric imbalance, from nonchiral starting compounds have been known, however, only for the conversion of diarylolefins into ch...
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