VANCOMYCIN AS A CHIRAL SELECTOR IN CAPILLARY ELECTROPHORESIS - AN APPRAISAL OF ADVANTAGES AND LIMITATIONS

The properties of the macrocyclic antibiotic vancomycin, used as a chi ral selector, were studied with aminoquinolycarbamate derivatives of a mino acids, containing sulfur and selenium, as well as with other orga nic ions. Vancomycin combines the ability to resolve fully ionized ani onic enantiomers, typical of proteins, with excellent separation effic iency, exceeding that of cyclodextrins. It allows better than baseline chiral separations of several anionic analytes within 3-5 min. The re solving power of vancomycin results from its great skill in discrimina ting enantiomers rather than from high affinities to the separated ena ntiomers. The association constants of vancomycin are of the same orde r of magnitude, 10(2) L/mol, as that found for beta-cyclodextrin (beta -CD). The difference in association constants of separated cystine ena ntiomers with vancomycin, 2 x 10(2) L/mol, is one order of magnitude h igher than that of enantiomers separated with beta-CD Analytically con venient mobility differences up to 1-2 x 10(9) m(2)V(-1)s(-1), with on ly one of the enantiomers appreciably decelerated, are obtained at sub millimolar vancomycin concentrations. Typical separation efficiencies are close to 250 000 theoretical plates per meter of capillary. Decele ration of various organic ions by millimolar vancomycin implies that c hiral separations with vancomycin need not be restricted to carboxylic acids. The vancomycin-analyte interactions are strongly affected by t he chemical composition and concentration of the buffer. An additional experimental variable, highly effective in manipulating the separatio n selectivity of analytes, is the buffer pH.