Selectivity factor, chiral selectors

The chiral recognition of enantiomers can be of three types (i) desionoselective, (ii) ionoselective, or (iii) duoselective, in which only the non-dissociated, the dissociated or both forms (charged and uncharged), respectively, of the enantiomers selectively interact with the chiral selector. In the case of ionoselective and duoselective interactions, a reversal of the migration order of the enantiomers is theoretically possible by the appropriate selection of CD concentration and the pH of the BGE. The addition of organic modifier to the BGE can also change selectivity by modifying the solubility of the chiral selector and/or of the solute, the complex equilibrium, the conductivity of the BGE and the electroendos-motic flow (EOE) level. Several other factors, such as the temperature, the type and the concentration of the BGE, and the level of the EOE can influence the separation. 

The KR of esters of various amino acids, phosphonate esters and lactams were also described through a two-phase hydrolysis process, using the chiral selector (S)-25. Hydrolysis of racemic 27 was performed with an apparent selectivity factor s of 80. It was indicated that among the various factors that may influence the stereoselectivity of this hydrolytic process, the extent of differential complexation between (S)-25 and the enantiomers of 27 is predominant. 

CCD provides data which are sufficient for the fitting of a linear polynomial model to a set of data. Regression analysis can be used for such a model which enables one to predict the response at levels of the variables within the factor space not investigated in the design. The response in the case of CE can be resolution or selectivity and factors can be the concentration of the chiral selector, the pH value, or the ionic strength of the buffer. 

Abstract Target-specific chiral selectors, which are characterized by a predictable elution order depending on the target enantiomer empioyed for the selection of the chirai selector, have recently received much attention in the enantioselective analysis fieid. In this context, bioaffinity-based molecular recognition toois such as nucleic acid aptamers have notabiy demonstrated very attractive features for the chiral discrimination of active moiecuies. In this chapter, the enantioseiective properties of aptamer chiral selectors and the major factors that control and modulate the liquid chromatography and capillary electrophoresis enantiomer separation are addressed. 

As indicated by these equations, both retention factor and separation factor are controlled by an enthalpic contribution, which decreases with the elevation of temperature, and an entropic contribution, which is independent of the temperature. The selectivity is a compromise between differences in enantiomeric binding enthalpy and disruptive entropic effects. The enthalpy term is a function of overall interactions between each enantiomer and the chiral selector. By plotting ln(o ) vs. 1 /T, all processes that do not contribute to the enantiomeric discrimination cancel out and the plot is linear, the slope being the difference between the enthalpy of association of the enantiomers with the stationary phase. The linear inverse relationship between In a and temperature demonstrates the enhancement of selectivity with a decrease in temperature. There exists a Tiso where - (AG ) = 0 owing... 

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