Electrolyte salts chiral

No racemization was observed when the electrode potential was scanned only to a value where the dianion is formed. Upon formation of the tetraanion, subsequent chemical reactions were found. With a slightly different electrolyte salt (Mc4NBF4 instead of BU4NF6), reversibility without racemization was found even up to the tetraanion formation. Further examples include the spectroelectrochemistry of vitamin D2 [139], which has been studied with a long pathlength cell similar to the design described by Zak et al. [44]. Optical rotary dispersion and CD of optically active polybithiophene that has been electropolymerized in a cholesteric electrolyte have been studied [140]. The optical rotation of this chiral polymer could be controlled via the electrode potential. 

CE has been applied extensively for the separation of chiral compounds in chemical and pharmaceutical analysis.First chiral separations were reported by Gozel et al. who separated the enantiomers of some dansylated amino acids by using diastereomeric complex formation with Cu " -aspartame. Later, Tran et al. demonstrated that such a separation was also possible by derivatization of amino acids with L-Marfey s reagent. Nishi et al. were able to separate some chiral pharmaceutical compounds by using bile salts as chiral selectors and as micellar surfactants. However, it was not until Fanali first showed the utilization of cyclodextrins as chiral selectors that a boom in the number of applications was noted. Cyclodextrins are added to the buffer electrolyte and a chiral recognition may... 

In these examples it was not possible to visualise any chiral structure with a microscope, but when PANI was prepared using poly(acrylic acid) as an in situ template, helical microwires were visualised [65]. In an even more general sense, helical fibres of PANI, poly(ethylenedioxythiophene) (PEDOT), and poly(pyrrole) were prepared using synthetic lipids as templates [66,67]. The synthetic lipid molecules used are shown in Fig. 6 along with some of the helical fibres of PEDOT that are formed when the sulphonate salt is used to shape the fibres during the polymerisation. The procedure involves growing the fibres by electrochemical polymerisation onto an ITO electrode with the lipid molecules in the electrolyte. 

Neutral cyclodextrins are also used in micellar electrokinetic chromatography with achiral surfactants to modify their enantioselectivity, particularly for the separation of hydrophobic analytes [53,55,185-187]. Enantioselectivity in this case results from differences in the distribution of enantiomers between the micellar pseudostation-ary phase and the cyclodextrin, as well as from the different migration velocities of the cyclodextrin and micelles. Neutral enantiomers can be separated based on differences in their equilibrium constants between the electrolyte solution and a charged chiral surfactant micellar phase, if the micelle has a different electrophoretic mobility to the free enantiomers. Suitable chiral surfactants include the bile salts (section 8.3.3), long alkyl-chain amino acid derivatives (e.g. sodium N-dodecanoyl-... 

The separation of PCB congeners has been addressed by SDS/neutral CD containing electrolytes, modified by organic solvents or urea and mixtures of bile salts. CD-EKC and CDCD-EKC modes with a large assortment of ionic CDs and modifiers are often employed for the chiral discrimination of PCB racemates. The use of polymeric surfactants such as polysodium undecyl sulfate (poly-SUS), in acetonitrile and its valinate form (poly-D-SUV) in combination with hydroxypropyl-y-CD, methanol, and urea has also been reported. 

Mobility and selectivity in CZE are most profoundly affected by analyte charge, and selection of the electrolyte pH is the most effective method of controlling a CZE separation. A wide variety of buffers have been employed in CZE, and a buffer is selected to provide good buffering capacity at the desired pH, low UV absorbance, and low conductivity. In addition to the buffer, other components may be added to the electrolyte to control EOF, reduce solute-wall interactions, or to modulate the mobility or solubility of an analyte. Additives for CZE include neutral salts, organic amines, surfactants, organic solvents, and chiral selectors. Secondary equilibria introduced by additive-analyte interactions are very important for achieving resolution in CZE. 

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