Chiral phases metal chelates

The effects of pH on electrokinetic velocities in micellar electrokinetic chromatography was studied by using sodium dodecyl sulfate solutions [179]. Micellar electrokinetic capillary chromatography with a sodium dodecyl sulfate pseudostationary phase has been used to determine the partition constants for nitrophenols, thiazolylazo dyes, and metal chelate compounds [180]. A similar technique was used to separate hydroquinone and some of its ether derivatives. This analysis is suitable for the determination of hydroquinone in skin-toning creams [181]. The ingredients of antipyretic analgesic preparations have also been determined by this technique [182], The addition of sodium dodecyl sulfate improves the peak shapes and resolution in chiral separations by micellar electrokinetic chromatography [183]. 

Even more generally applicable are GC columns with chiral metal chelates as stationary phases (complexation gas chromatography)26 (Table 6). Quite recently, chiral GC methods have been developed on the basis of cyclodextrin derived stationary phases27. 

A limiting factor of complexation gas chromatography is the low temperature range (25-120°C). Therefore, improved thermostable polymeric stationary phases, e.g., Chirasil-Metal, in which the chiral metal chelates are chemically anchored to a polysiloxane backbone, have been prepared155 156. 

Y. Tapuhi, M. Miller, and B. L. Kanger, Practical considerations in the chiral separation of D,L-amino acids by reversed-phase liquid chromatography using metal chelate additives, J. Chromatogr., 205 325 (1981). 

A number of enantiomers have been resolved by forming diastereomeric complexes with a chiral selector which had been added to the mobile phase. These complexes can be resolved on conventional achiral sorbents. Metal chelates, ion-pairing agents, and proteins have been used as chiral selectors. 

Determination of the degree and indeed the sense of enantioselection in these reactions is now easily achieved using complexation capillary gas chromatography20. Several chiral liquid phases based on metallic chelates of (1 / )-8-(ethylidene)-3-(heptafluorobutanoyl)camphorate 4 have been developed20 that serve admirably to separate the enantiomers of a wide variety of volatile epoxides, ketals and acetals. 

Chiral catalysis using zeolites has been considered, however, intercalation of chiral metal chelates or the use of asymmetric organic pillaring agents may be a new way of introducing such selectivity. Iwai and coworkers have used asymmetric organic pillars, (R)- or (S)- phenylethylammonium cations in several layered phases and have observed some molecidar recognition Certainly further work is needed in this rather different definition of selective catalysis. 

Liquid chromatographic resolutions based on highly selective host-guest, metal chelate and charge-transfer com-plexations have been described (1,2). Recently, a chiral diamide-bonded stationary phase (I) has been prepared, which relies entirely on hydrogen bond associations for the material to be resolved. Despite the weak and flexible interaction in this system, direct resolution of enantiomeric N-acyl-fl-amino acid esters (II) was accomplished with the advent of a highly efficient column technology (2- ). 

Capillary Electrophoresis Mobile phase Cyclodextrin Derivatives Chiral Surfactants (MEKC) Poly(saccharides) Glycopeptides Proteins Metal Chelates... 

Chiral Stationary Phases for Gas Chromatography Small Molecule Stationary Phases Chiral Polysiloxane Stationary Phases Chiral Metal Chelating Stationary Phases Cyclodextrin Chiral Stationary Phases... 

W. Lindner, J. N. LePage, G. Davies and B. L. Karger, Reversed-phase separation of optical isomers of Dns-amino acids and peptides using chiral metal chelate additives,/. Chromatogr, 1979, 185, 323-344. 

The direct resolution of underivatised enantiomers has been effected with the aid of some metal-containing chiral stationary phases. Particular attention has been paid to the resolution of chiral alkenes and epoxides using stationary phases derived from chiral metal chelate complexes. The rhodium dicarbonyl P-diketonate complex (5), when dissolved in squalene and coated onto a capillary column, permitted the quantitative enantiomer resolution of 3-methylcyclopentene while methyl oxirane was similarly resolved... 

Retention of Rohrschneider-McReynolds standards of selected chiral alcohols and ketones was measured to determine the thermodynamic selectivity parameters of stationary phases containing (- -)-61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in poly(dimethylsiloxane) . Separation of selected racemic alcohols and ketones was achieved and the determined values of thermodynamic enantioselectivity were correlated with the molecular structure of the solutes studied. The decrease of the ionic radius of lanthanides induces greater increase of complexation efficiency for the alcohols than for the ketone coordination complexes. The selectivity of the studied stationary phases follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis acid-base interactions between the selected alcohols, ketones and lanthanide chelates. The retention of over fifty solutes on five stationary phases containing 61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in polydimethylsiloxane were later measured ". The initial motivation for this work was to explore the utility of a solvation parameter model proposed and developed by Abraham and coworkers for complexing stationary phases containing metal coordination centers. Linear solvation... 

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