Synthesis Of Novel Positively Charged β-cyclodextrins And Their Application For Enantiomeric Separation In Capillary Electrophoresis

Enantioseparation, especially the separation of chiral drugs has become one of the most important topics in the field of analytical chemistry in recent years. As a critical technique for enantiomers analysis and separation, capillary electrophoresis (CE) has the advantages such as high separation efficiency, rapid analysis, and small injection volume of sample. At present, the study of chiral capillary electrophoresis has been focused on the development of various chiral selectors and the optimization of separation experiment conditions. It has been reported thatβ-cyclodextrin and its derivates are a class of commonly used chiral selectors in chiral capillary electrophoresis.This thesis mainly describes three types of positively chargedβ-cyclodextrins (CDs) and their application as chiral selectors in chiral separation of dansyl (Dns) amino acids,α-hydroxy acids and carboxylic acids in CE, and it contains four parts:(1) The first type is mono-substituted positively charged 6A-(3-methoxypropyl-ammonium)-6A-deoxy-β-cyclodextrin chloride having one positively charged center. By introducing the methoxy group (-OCH3) to the common alkyl chain, the methoxy group of this new positively charged ammoniumβ-cyclodextrin can form hydrogen bonds with analytes to enhance the chiral separation process. Such enhancement is elucidated by 1HNMR spectroscopic study on the synergistic effect of CD's complexation and hydrogen bonding on the chiral separation.(2) The second series of CDs are four mono-substituted CDs,6A-ammonium-alkyl imidazolium-6A-deoxy-β-cyclodextrins chlorides possessing two positively charged centers and an alkyl chain length of two to six carbons. The preparation of 6A-ammonium-alkylimidazolium-6A-deoxy-β-cyclodextrins chlorides were achieved with a first Gabriel reaction, and followed treatement with hydrochloride to afford the positively charged ammonium. Consequently, these P-cyclodextrins derivatives possessed two positively charged centers, i.e. imidazolium and ammonium. The chiral recognition ability of such cyclodextrins was further investigated with 1H NMR technnique.(3) The third series of CDs are four disubstituted positively charged CDs, 6A-ammonium-6c-alkylimidazolium-β-cyclodextrins chlorides possessing two positively charged centers and and an alkyl chain length of one to four carbons. These cyclodextrins possessed not only the features of ammonium P-cyclodextrins but also the merits of imidazoliumβ-cyclodextrins, so they could be able to achieve good chiral separation towards both amino acids and other acidic racemates.(4) Chiral separation experiments of Dns-amino acids,α-hydroxylic acids and carboxy- lic acids were carried out using the above three types of positively chargedβ-cyclodextrins as chiral selectors. Herein, we chose 6A-ammonium-butylimidazolium-6A-deoxy-β-cyclodex-trin chlorides (AMBuIMCD) and 6A-ammonium-6c-butylimidazolium-β-cyclodextrin chlorides (DAMBuIMCD) as model chiral selectors of the second and the third series of cyclodextrins. Three series of positively chargedβ-cyclodextrins all showed good chiral separation ability, and their concentrations and buffer pHs for the optimum resolutions of selected analytes were secured via CE experiments.In summary, altogether nine positively chargedβ-cyclodextrins in three catagories have been prepared with high yields via facile synthetic procedures in this thesis. All compounds were characterized with melting point,1H NMR,13C NMR,IR and ESI-MS techniques. More importantly, these as-prepared CDs were successfully explored in for chiral separation of Dns-aminos, a-hydroxy acids and carboxylic acids in CE has been explored. The results show that these newly-designed CDs have exhibited wide-spectrum enantioselectivities towards both ampholytic and acidic racemates, which offers their potential applications as powerful chiral selectors in chiral chromatography techniques. Chiral separation via CE features fast analysis and small sample consumption. It is mostly carried out in aqueous solutions, which fits well with the current appeal for eco-friendly and green chemistry.