Discrimination mechanism

Sakai K, Sakurai R, Nohira H (2007) New Resolution Technologies Controlled by Chiral Discrimination Mechanisms. 269 199-231... 

The influence of the mobile phase composition was also studied on the enanti-oseparation of several cycloaliphatic -substituted a-quaternary a-amino acids on a teicoplanin CSP [88,89] the study revealed two distinct enantiomeric and diastereo-meric discrimination mechanisms based on different interactions with the stationary phase. 

Bonadonna, F., Villafane, M., Bajzak, C., and Jouventin, P. (2004). Recognition of burrow s olfactoiy signature in blue petrels, Halobaena caerulea an efficient discrimination mechanism in the dark. Animal Behaviour67,893. 

Yashima, E., Yamada, M., Kaida, Y., and Okamoto, Y. Computational studies on chiral discrimination mechanism of cellulose trisphenylcarbamate, J. Chromatogr. A 694, 347-354. 

As briefly mentioned above, Takeshita et al. reported the first enantiodifferentiat-ing photoisomerization of tropolone derivatives to the optically active bicyclo[3,-2.0]heptadienones in 1980 [99], but the product ee and detailed chiral discrimination mechanism have not been determined until recently. Ramamurthy and coworkers reinvestigated the photobehavior of tropolone alkyl ethers in a-, (3-, and y-CDx cavities [102]. 

Although the basic principle and procedure of diastereomeric resolution are not difficult to understand, the chiral discrimination mechanism involved in the selective crystallization of one diastereomer from the mixture is very complicated. The chiral discrimination mechanism for diastereomeric resolution changes in accord with the resolving system, since not only the properties of diastereomeric crystals but also the conditions for crystallization strongly influence the chiral discrimination mechanism. In particular, the polymorphism of crystal, the severe solvent effect on solubility, and the kinetic factor for crystal growth are still not perfectly understood regarding this chiral discrimination phenomenon. The study is therefore limited in its investigation of the chiral discrimination mechanism for the diastereomeric resolution, as the mechanism involves both the crystal and solution properties of diastereomers.7... 

As described in this chapter, it is useful to study the crystal structures of diastereomeric salt crystals, which precipitate upon resolution, for understanding the chiral discrimination mechanism of the diastereomeric resolution in a molecular level. The authors studies on the crystal structures described... 

Yashima, E.,Yamada,Y., Kaida,Y., Okamoto, Y, Computational Studies on Chiral Discrimination Mechanism on Cellulose Trisphenylcarbamate,... 

Photochemical asymmetric synthesis with native and modified CDx s is certainly one of the most potentially successful examples of supramolecular photochirogen-esis, which is applicable in principle to most photoreactive substrates of appropriate size and shape. Despite this wide applicability, the enantiodifferentiating ability of CDx and hence the product ee obtained are not sufficiently high in many cases. Furthermore, the elucidation of the chiral discrimination mechanism and the rationalization of the product chirality and ee are generally more difficult in photochemical asymmetric induction. For more simple and well-defined host-guest interactions (in the ground as well as excited states), several approaches to photochemical asymmetric induction with newly designed synthetic chiral hosts have been reported. 

These malonate and nitroalkane reactions gave the adducts with the predicted absolute configurations (i )-adducts were obtained from cyclic (Z)-enones and (S)-adducts from acyclic ( )-enones when (S)-21 was employed. The stereochemical outcome can be summarized as M(a)-attack. The involvement of the a-enantioface-discriminating mechanism suggests that the chiral catalysts are located in the vicinity of the enone carbonyl group at the transition state. The reaction of the primary nitroalkane mentioned above also supports this explanation. 

The results are shown in Table II. As seen from these figures, the separation factor decreases with increasing number of 3-ala ligands. This trend is just the reverse to the trend in the case of d-tart. Therefore, the discrimination mechanism for Sb d-tart is presumed to be quite different from that for d-tart. 

Persaud, K.C. and Dodd, G.H., Analysis of discrimination mechanisms in the mammalian olfactory system using a model nose. Nature, 299, 352, 1982. 

The uncoated responses of the inlet sensor also show some differential response that is stimulus dependent, which is most likely due to the kinetics of the ligand/sensor interaction rather than the mucosa properties - an example of the second discrimination mechanism discussed in Section 1 due to differential ligand/sensor temporal interactions. 

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