Kinetic discrimination

This equilibrium value is the same as that found for the chelated acid (Kk = 1.0) (17) so it is likely that the dipeptide carbanion, like 15 (Scheme 15), shows less kinetic discrimination for reprotonation (k-i/ k-2) than does the ester carbanion 18. In D20 H-exchange and epi-merization occur at the same rate, kohs = 6.4 X 10 4 s 1 (pD = 8.4, 34°C), to give the same equilibrium distribution of A-S-S and A-R-S products (24). 

SCHEME 18. Kinetic discrimination in the BINAL-H reduction of the 9-keto function. 

Scheme 18 shows interesting kinetic discrimination in the reduction of a chiral cyclopentanone 10b). Although (S)-BINAL-H is almost inert to the PGE derivative, reduction with the enantiomeric R reagent... 

In their studies the authors consider two possible scenarios for the formation of linear and branched aldehydes assuming an irreversible olefin insertion step. In the first scenario, the olefin insertion proceeds through a single intermediate, and the lineanbranched product distribution is determined by the partitioning between the two forms (linear or branched) of the transition state (kinetic discrimination). In the second scenario, the linear... 

The parameter estimation and the kinetic discrimination studies obtained from the numerical simulations are tedious, complex, and time-consuming. Complex softwares are required, and lengthy strategies are used to fit to the data. Moreover. the number of parameters describing the model complicates the interpretation of the experimental results. Simplifying approaches are recommended to make easier the analysis of the chromatographic profiles [371. 

A QUANTITATIVE COMPARISON OF THE KINETIC DISCRIMINATION OF COMMON ELECTRODE GEOMETRIES AT STEADY STATE... 

The recent availability of working curves and surfaces for a range of conunon mechanisms at a number of electrode geometries (Alden and Compton, 1997a) allows a broad quantitative comparison of the kinetic discrimination of conunon electrode geometries for both first- and second-order homogeneous processes. 

The conventional channel using a macroelectrode and fast-flow channel both operate in the limit of negligible axial diffusion. The enhanced kinetic discrimination of the channel microband electrode arises from using a small microband at slow flow rates thus incurring a significant amount of axial diffusion. 

A comparison of voltammetric techniques 96 A quantitative comparison of the kinetic discrimination of common electrode geometries at steady state 97 Steady-state vs. transient experiments 102 Current and future directions of voltammetry 104 Instrumentation 104 Electrodes 105 Voltammetric simulations 108... 

One may vary the concentration of any reagent that is not included in route and y are constants). This dependence could be used for kinetic discrimination if the number of key reagents coincides with the number of routes (or, in other words, if the route basis is also their stoichiometric basis ). 

Kinetic discrimination and kinetic enhancement are two procedures that can be used in conjunction with wet chemical FIA. Kinetic discrimination works well when it is known that there are differences in the rate of reaction between the reagent and the analyte of interest and the rates of reaction between the reagent and the interferents in the sample. If, for example, the analyte reacts more quickly with the reagent than the interferents, then the timing for measuring of the signal by the detector can be set so as to exploit this. Kinetic enhancement is when the direction of the reaction is manipulated to favour measurement of the analyte of interest with improved signal-to-noise. 

Use of peak area or peak width at continuous flow has not yet been reported, although it is potentially useful. Most frequent applications of kinetic assays (cf. Chapter 7) are aimed at the enhancement of sensitivity of measurement or at the blank correction offered by the kinetic discrimination between analyte-nonrelated initial response of sample material and the analyte-related reaction rate response due to formation of the measurable product. 

By combining the FIA gradient techniques, dedicated separation techniques, and kinetic discrimination, novel selective methods will be introduced in the future. Some of them will be improved versions of existing methods, while others might be based on rediscovery of old chemical... 

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