News
Buckyballs separate Using SIMS to control peptide calixarenes synthesis Move over ODS, here come the buckyballs! Kiyokatsu Jinno and colleagues at Toyohashi University of Technology Japan), Nagoya University (Japan), the University of Western Australia, and the National University of Singapore separated 4-tert-butylcalix[4]arene, 4-fert-butylcalix[6] arene, and 4-fetf-butylcalix[8]arene with microcolumn LC using a chemically bonded C60 silica stationary phase, which has already been shown to have a selectivity different from octadecylsilane (ODS)-bonded stationary phases in the separation of isomeric polycyclic 3.1*0" matic hydrocarbons. The differences be explained by the interaction of the C stationary phase with molecules that have a similar curvature The researchers confirmed the mechanism of the inclusion complex formation between the calixarenes and the C The retention and separation factors for the calixarenes using a 40/60 toluene/acetonitrile mobile phase were larger for the C60 stationary phase than for the ODS stationary phase. The cavity of thefert-butylcalix[8]areneis approximately 10 A in diameter; and the C60, including the van der Waals radius of the carbon atoms, has a diameter less than 10 A, so the two can strongly interact. Because the cavities of the other two calixarenes are smaller the interactions are not as strong. The authors believe that the C bonded phase has a strong molecular shape recognition capability fortert-butylcalix[8]arenebased on inclusion complex formation (/ Hish Resolut Chromatogr 1996 19 475-77)
Structure of calixarenes used as sample probes, n = 1: 4-tert-butylcalix[4]arene; n = 2:4-terl-butylcalix[6]arene; n = 3: 4-terl-butylcaiix[8]arene. (Adapted with permission from Huthig.) 712 A
that the product be separated from the solid support To avoid this problem, J-L Aubagnac and colleagues at the Universite de Montpellier I et II (France) and the Ecole des Mines de Paris (France) described using Synthesis on solid supports has become a method of choice for preparing biomolecules static secondary ion TOFMS (SIMS)tofolsuch as peptides and ollgonucleottdes, and ii low the step by step synthesis of a peptide eo a solid support without cleavage of the moleis used extensively in combinatorial synthecule from the support. sis. The solid-phase technique has several advantages over the solution-phase techThe Merrifield strategy was usedtosynnique, including the abillty to drrve the syn- thesize a three-arnino-acid peptide on a polythesis to completion by using large excesses styrene support functionalized with benzylof reagents that can then be removed from oxy "handles"; the acid labile fert-butoxycarthe insoluble support-product conjugate by bonyl (Boc) group was used as temporary extensive washings. It is difficult, however, to N-terminal protection. In positive-ion mode, identify the product of these reactions, bethe secondary ions are characteristic of the cause standard spectroscopic techniques terminal groups of the step being studied. .n such as NMR and MS necessitate thar the negative-ion mode, secondary ions result compounds be in solution and thus require from the cleavage of the benzyl ester llnk between the polymer support and the first amino acid, providing direct identification of the growing sequence. The authors are currently working to identify other urethane-protecting groups and resins and to apply the method the synthesis of larger peptides (Rabid Commun Mass Sbertrom Positive-ion SIMS spectrum of Resin-Ala-Phe-Pro-Boc. 1996 10 lTO-ll) (Adapted with permission from John Wiley & Sons.)
Anionic CDs separate enantiomers Cyclodextrins (CDs) are among the most successfully used chiral selectors, but it is difficult to predict which ones have the highest resolving power for a given racemate. Several CE methods are available for separating chiral molecules, including CZE (with Separation of 0.1 mg/mL primaquine racemate spiked chiral selectors added to the in human plasma in a 5-mM $-CD-Phos/50-mM running buffer) and micellar phosphate buffer running solution. (Adapted with electrokinetic chromatography permission from Huthig.) (MEKC). Yoshihide Tanaka of Nippon Boehringer Ingelheim Qapan) phosphate sodium salt, sulfobutyl ether and co-workers at Himeji Institute of fJ-CD sodium salt, carboxymethylated Technology Qapan) tested five anionic •y-CD, and y-CD phosphate sodium salt. CDs in cyclodextrin electrokinetic chroThe researchers explored the range of matography (CDEKC) comparing the use enantiomers that can be separated by of anionic CD derivatives with that of neu- CDEKC and the potential use of CDEKC tral CD derivatives for enantiomeric separation in biological matrices. Benzoin racemates were sepaThe CD derivatives used in the study rated in both types of capillaries, and meswere carboxymethylated (5-CD, [3-CD
Analytical Chemistry News & Features, December 1, 1996
