Cyclodextrin concentration

Lin et al. [95] used capillary electrophoresis with dual cyclodextrin systems for the enantiomer separation of miconazole. A cyclodextrin-modified micellar capillary electrophoretic method was developed using mixture of /i-cyclodextrins and mono-3-0-phenylcarbamoyl-/j-cyclodextrin as chiral additives for the chiral separation of miconazole with the dual cyclodextrins systems. The enantiomers were resolved using a running buffer of 50 mmol/L borate pH 9.5 containing 15 mmol/L jS-cyclodextrin and 15 mmol/L mono-3-<9-phcnylcarbamoyl-/j-cyclodextrin containing 50 mmol/L sodium dodecyl sulfate and 1 mol/L urea. A study of the respective influence of the /i-cyclodcxtrin and the mono-3-(9-phenylcarbamoyl-/i-cyclodextrin concentration was performed to determine the optical conditions with respect to the resolution. Good repeatability of the method was obtained. 

Rawjee, YY, Williams, R.L., Buckingham, L.A., Vigh, G Effects of pH and hydroxypropyl fS-cyclodextrin concentration on peak resolution in the capillary electrophoretic separation of the enantiomers of weak bases. J. Chromatogr. 1994, 688, 273-282. 

Almost no influence of the methylated /i-cyclodextrin on the yield can be observed if no additional organic solvent (except for butadiene or the product) is used as the non-polar phase. With hydroxypropyl-jd-cyclodextrin a decreased yield is obtained and the phase separation is more difficult. If cyclohexane or n-octane is added as the non-polar solvent the conversion and the yield increase with increasing cyclodextrin concentration up to a concentration of about 2 mol % cyclodextrin based on butadiene. Because of the high viscosity of the solution no further improvement can be achieved using higher cyclodextrin concentrations. Lower yields are obtained by use of a-cyclodextrin as compared with the methylated j8-cyclodextrin. 

With increasing concentration of methylated /1-cyclodextrin the selectivity to n-nonanal increases from 64% to 72%, while the conversion of the olefin is constantly as high as 97%. Obviously the addition of the methylated /i-cyclodextrin has only a moderate influence on the isomerizing hydroformylation of trans-4-octene to n-nonanal. The addition of only 0.2 mol.-% of methylated /3-cyclodextrin lowers the isomerization rate which results in the formation of slightly more branched aldehydes. In pharmacy j6-cyclodextrins are established as solvation mediators between polar and less polar solvents. This is one possible explanation for the rise in selectivity to n-nonanal with an increasing j6-cyclodextrin concentration. At higher con-... 

Until 1984, all of the stopped-flow and temperature-jump kinetic studies of alpha cyclodextrin inclusion-complex formation were explainable in terms of a single-step, binding mechanism. According to this mechanism, the observed rate constant, kobs, (for stopped-flow) and the reciprocal relaxation time, 1/t, (for temperature-jump) should show a linear dependence on the edpha cyclodextrin concentration. Sano and coworkers, however, in the case of the iodide-alpha cyclodextrin interaction, and Hersey and Robinson,in the case of various azo dye-alpha cyclodextrin interactions (see Fig. 7), found that certain guest species exhibit a limiting value of kobs and 1/t at high concentrations of alpha cyclodextrin. This behavior can most simply be explained in terms of a mechanism of the type,... 

A study similar to that of Hersey and Robinson has been reported by Seiyama and coworkers.From a stopped-flow, kinetic study of the interaction of various azo dyes and some azo dye-metal complexes with alpha cyclodextrin, they observed two kinetic processes. The dependence of the observed rate-constants for these two processes on the alpha cyclodextrin concentration was found to be explainable in terms of a mechanism identical to that proposed earlier by Hersey and Robinson. In the case of the guests used by Seiyama and coworkers, however, values for the rate constants of the binding step could be determined from the concentration dependence of kobs for the faster process thus,... 

Further support for the presence of a conformational change has come from the work of Orstan and Wojcik, who also studied azo dye-alpha cyclodextrin complexes by using the temperature-jump technique. The dyes that they investigated showed three different types of behavior. Certain dyes showed a limiting value of 1/t at high alpha cyclodextrin concentrations, others showed a linear dependence of 1/t on alpha cyclo-... 

TH Seals, C Sheng, JM Davis. Influence of neutral cyclodextrin concentration on plate numbers in capillary electrophoresis. Electrophoresis 22 1957-1973, 2001. 

The host-guest p-cyclodextrin-C522 complex formation was determined based on fluorescence blue shift as a function of the increasing p-cyclodextrin concentration from 10 6 to 10 2 M. Similar result was observed for coumarin C6 [4] and this blue shift was considered along with anisotropy results as a proof of the host-guest formation. Time-resolved fluorescence spectroscopy was utilized to differentiate between fluorescence dynamics of... 

Figure 9.2 Effect of HS-y-cyclodextrin concentration on the chiral separation of (1) norephedrine, (2) amphetamine, and (3) methamphetamine on S-folded separation channel (160 mm length) using 50 mM phosphate buffer (pH 7.35) with 5 mM SDS at 8 kV/cm potential, (a) 5 mM, (b) 10 mM, (c) 15 mM, and (d) 20 mM HS-y-cyclodextrins [18].

The utility of the highly soluble 6-cyclodextrin derivatives (soluble polymer and dimethyl-6-cyclodextrin) in RPTLC is illustrated in the separation of barbiturates. The lipophilicity of a barbiturate or any guest decreases when included in a cyclodextrin-cavity. Therefore its mobility is modified in reversed phase thin layer chromatography. With this simple and rapid method, the stability of a complex can be estimated empirically (Table II). The "b" value of the following equation is characteristic for the complex stability (in water ethanol =4 1 solution, R determined at 5 different cyclodextrin concentrations for 21 barbiturates) ... 

The use of cyclodextrins as the mobile phase components which impart stereoselectivity to reversed phase high performance liquid chromatography (RP-HPLC) systems are surveyed. The exemplary separations of structural and geometrical isomers are presented as well as the resolution of some enantiomeric compounds. A simplified scheme of the separation process occurring in RP-HPLC system modified by cyclodextrin is discussed and equations which relate the capacity factors of solutes to cyclodextrin concentration are given. The results are considered in the light of two phenomena influencing separation processes adsorption of inclusion complexes on stationary phase and complexation of solutes in the bulk mobile phase solution. 

Fig. 7. l/(ife b5 — A ) for p-nitrophenyl acetate decomposition is plotted vs. the reciprocal of the jS-cyclodextrin concentration (data from Fig. 6). From VanEtten, R.L., Sebastian, J.F., Clowes, G.A. and Bender, M.L. (1967) J. Am. Chem. Soc. 89, 3242, reprinted by permission.

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