Siylated and acetylated β-cyclodextrins for gas chromatographic stationary phases

,8N.4De.2001J. CENT. SOUTH UNIV. TECHNOLAtcD:10059784(001)04029405Silylated and acetylated B-cyclodextrins forgas chromatographic stationary phases06 ATANG Ke-wen"2, YI Jian-ming, ZHOU Chun-shan, ZHONG Shi-an(1. College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China2. College of Chemistr: and Chemical Engineering, Yueyang Nomal University, Yueyang 414000, ChinaAbstract: Two new chiral stationary phases, 2, 3-di-0-acetyl-6-0-trimethylsilyl-B-cyclodextrin( DATBCD)nd 2, 6-di-O-trimethylsilyl-3-0-acetyl-B-cyelodextrin( DTABCD)), were synthesized, their structures wereidentified by means of infrared and NMR spectra. Capillary columns were coated with the two stationary phasesby dynamic method. The chromatographic properties, and enantiomers separation, such as ketone, esters, al-cools and olefines, were investigated on the silylated and acetylated B-cyclodextrin stationary phases. Theexperimental results show tiat the silylated and acetylated B-cyclodextrins are suitable to be used as capillary gashrumatographic stationar; phases, the relative polarity of DAT'BCD and ITABCD stationary phases is respetively 4143 and 3928, the column efficiencies are respectively 3084 and 4198, and DA'TBCD is of stronger rrantioselectivity than DTABCD, capacity factor of the first eluted enantiomer(h, )and separation factor(a)ofaphenylethanol on DATBC )stationary phase are respectively 8.2.3 and 1.019Key words: capillary Fas chromatography: silylated and acetylated B-cvelodextnins; enantionenieDocument code: ASeparation of enantiomers of chiral com- abilities of CDs, CD derivatives are used in cappounds for both analytical and preparative purposes lary gas chromatography(GC), instead of CDs diis an attractive topic, espec ally in the fields of or- rectly. The unique separation properties of (d de-ganic and pharmaceutical =hemistry. Direct gas rivatives are attributed to their cavity size,theromatographic enantiomer separation using chiral volume and electron effects of the. derivatizationstationar phases( CSPs)is a simple and effective groups. Modification of CDs at their wicprocess, and is one of the most suitable methods ow rim may change their conformational mobilityfor the purpose. As B-cyclodextrin(3-CD)has size of the inclusion cavity and steric interactionsmany chiral carbon atoms and a special cavity with guest molecules. If the hydroxyl groups withstructure.it can separate not only aromatic com. different activities at the side of the-3-CD cavitypounds. but also enantio rs. Since 1988, the are modified by different methods, the stationayuse of cyclodextrins(CDs)and their derivatives phases with dierent properties and enantioselecttfor the separation of enantiomers has been deve- vities, may be obtained. Up to the present, manyloped. and the application f these materials as CD derivatives have been synthesized by the methohy ods of alkylation and acetylation, and some ofhas become increasingly popular. The tremen- them have been proved to be versatile GC stationdous potential of cyclodextrins and their derivatives ary phases+71for enantiomeric separation was described in re-However, as far as we know, there is neviews by Schurig and Nowoty. Because of the port on the中国煤化工ianhigh melting point and the bad film formming acetyl asCNMHG IPauthor: TAN Ke-wen, doctoral studen. bom in 1970, majoring in applemistryMarch 5, 2000Joumal CSUT2. 3-di-0-acet l-6-0-trimethylsilyl-3-CD and 2, 6- dextrin(5.0 g)was dissolved in 100 ml. drieddi-O-trimethylsilyI-3-O-acetyl-B-CD were prepared pyridine. 4. 2 mL acetyl anhy dride was addedand studied as chiral stationary phases( CSPs )in dropwise and heated in reflux for 10 h. The solvent was removed, and then the raw material wascooled below 20C and dissolved in 100 ml. meth1 Experimentalylene dichloride. The solution was washed untilneutral respectively with saturated NaHCO, solu1. 1 Apparatus and chemicalstion and ice-water mixture, and dried with anAll chromatographic separations were per- hydrous Na SO,. After evaporating the solvent offormed with a HP-5890A gas chromatograph methylene dichloride, the pale solid (7.2 g)equipped with a flame ionization detector. The 2.3di-0-acely1-6-0-trinmethylsilyl-F3-cyelodcxtrinfused silica capillary columns( 15 mx0. 25 mm was obtained. Infrared and NMR spectra data of it1. D )were purchased from the Hebei Yongmian are as followsptical fiber manufacter in China. Nitmgen was IR( KBr)(cm)I: 2 960(CH, s):1842(C=Oused as camier gas wi h an inlet pressure of 50kPa. The injector and detector temperatures rema- (Si-CH. s); 1 200-1000(C-O. Si-O), vs)ined at 250 C. IR sectra were recorded on iNMR(CDC1)(pm):170.2,169Shimadzu ir-460 spectmmeter with kBr disks forsamples. NMR spectra were measured on a Bruker(C=0);%6.8(C-1);75.4(C-4);71.9DRY-400 spectrometer with CDCl, as intemal(C-2);71.6(C-3);71.3(C-5):61.9(C-6);21.0,20.8(COCH3);-5.13-Cvelodextrin wa; purified by twice recrys-((CH,)3Si)tallization, and dried at 80 C in vacuum. 1. 2. 2 Synthesis of 2, 6-di-0-trimetht sil\ 1-3-0-Hydroxyl groups of all s amples of enantiomers were acetyl-B-cyelodextrinacetylated. All comme cial reagents were of anaThe synthetic scheme of DTABCd is theIytical gradesame as that of DatBCD. DTABCD was also pre-of B-cyclodextrin chiral sta- pared in two steps. First, the intermediattionary phasesproduct, 2, 6-di-0-trimethysilyl-P-cyclodextrirSynthesis of 2, 3-di-0-acet; 1-6-0-irn- was obtained by the reaction of 4 g?)with9.6methylsilyl-3-cvclodextr in483-cvclodextrin and 40 mL pyridine were mixture of a solution of 6.0 g the intennediateadded to a 250 mL three-necked flask, and stirred product in 120 mL anhydrous pyridine, 3 mlace-for 0. 5 h at room teInperature to be dissolved. tic anhydride was added dropwise and he led in4.8 mL trimethylchlor-silicane was added dropreflux for 10 h. The obtained product is pale sol-wise and stirred for 2 h at mom temperature in ni- id. Infrared and NMR spectra data of it are as fol-trogen. The reaction m xture was refluxed for 2 hloand cooled below 201. Ice-water was added loIR( KBr)(cm): 2960(CH, s);the reaction mixture, and precipitate was ob- 1 840(C=0. s): 1 360(C-CH,, m):1260tained. The raw product was dissolved in methenyl (Si-CH3, s); 1 160-1 000(C-0. St-0chloride. The methen I chloride solution was vswashed respectively with 50 mL of 3 %(mass fracC-MR(CDCl4)(pm):170.6,169.5tion)chlorhydric acid HCI), 50 ml of saturated (C=0),97. 3(C-1),75.6(C-4).72sodium bicarbonate(\aHCO,)solution and ice-(C中国煤化工C-5).62water mixture until ne atral. Then. the metheny (C(CH:):Si)hloride solution was died with anhydrous sodium 1.3CNMHal capillarulfate( \a S(2 ). Afte r evaporating the solventcolumnsthe obtained material 6-0-trimethylsilyl-B-cyclo-15% dilutent stationary liquids were prTANG Kowen, ef al: Silylated und acetylated 3-CD for GC -taint ary phasesby mixing 0.75 g s lyiated and acetylated 3- described with adsorption isotherm, and then most0.75 g diluent of silicone oil I, and two of chromatogramsvmmetric, The silylateddrops of the tailing reduce r of Tween-80 in 10 mL and acetylated stationary phases diluted withmethlene dichloridecone oil l which were used as the CC stationaryAt first, fused silica capillary columns were phases are of the properties of gas solid chmmatogheated at 250 t with nitrogen for 4 h, then coat- raphy anded by dynamic method wi h the stationary liquids time, tailing reducer of Tween-80 is added to thetioned, for I h at 60 C, heated to 200 C by of the capillary columns and symmetry. rof the solution, the coated columns were condi- stationary phases to improve the column efficittemperature programming at 2 C/min and thisAccording to Ref. [8, the relative polaritytemperature was kept for 8 hof the columns was evaluated by measuring thetention indices of benzene, butanol. 2-pentanone2 Results and discussionnitropropane and pyridine. If the total of the re-tention indices of the five compounds in the2.1 Chromatographic Froperties of the chiral column is less than 3 000, the relative polarity ofcapillary columnsthe column is non-polar. If it is beyond 5 (00.itColumn efficiency sho as kinetic characteriza- is strongly polar. If it is between 3 00andtion of chromatography and reflects thickness and 5000, it is moderately polar. From Table 1. i isevenness of liquid film on columns. Column effi- clear that after B-cyclodextrin is modified withciencies for both columns were determined at Iacetyl and silyl, its film formicC with n-dodecane which gave plate number vimproved. It ean be seen from Table 2 that ace:yues of above 3 000 plate/m for the two columnlated and sily lated B-CD stationary phases arePeak asymmetry factor was measured with naphmoderately polar, the polarity of which is near thatof the diluent of silicone oil I, so both of ththalene. As shown in table 1. when column 1 andcolumn 2 were coated respe ctively with DATBCDre of better compatibility and the capillary columns WTand DtABCD stationary phaseith them as stationary phases are of highercolumn efficiency. As expected, the polaritytry factor on the two columns are all close to 1. 3-di- 0-acety1-6-0)-trimethylsilvl-B-CD is higherwhich shows that the chiral capillary columns arthan that of 2, 6-d i-0-trimethylsilyl-3-0-acetyl-3-inert.and two capillary col umns are of excellent CDchromatographic propertiesTable 2 Relative polaranty ol stationary phase>Table 1 Chromalorapliic oroperties of the twochiral columCompOuNds Bruene Butene.Pen\itrAncine TamIr preyingColumnCapacity Colurm cffirirncy! PrakDATEC:)75881179083351414factor kale.m:) asymmetry factor polarity1.103928The relations of theoretical plate height( H)with temperature(t )for n-dodecane on column IIt is found that the colur ins are of low column and 2 were measured. As silylated and acetylatedficiency, prepared directly with silylated and B-CD derivatives are of high melting points,thacety lated 3-CD stationary phases, instead uf us- temperatures of optimum column efficiency aning the diluent of silicone oil I in the stationary high. As shown in Fig. I, the column e y ofphacolumn 2 is always higher than that of column I atseparated on the columns. trailed seriouslythe same temperature. This is because the meltingis probably because silylated and acetylated 3-CD point of silylater R. n decreasesderivatives are solid at separating temperature in with the ind中国煤化工 timur ntsGC. In general. the separating mechanism inat the catieCNMHGmeltingsolid chromatography is adsorption one. The ad- point of DTaBCd is lower than that of DATBCDsorption phenomena on the s ationary phases areThe mass transfer resistanee on theJoumal CSUTVol 6phases was investigated by measuring the relations clodextrin CSPs included ketone, esters, alcoholsof theoretical plate height( H)with velocity(u)for and olefines. As shown in Table 3, almost all then-dodecane on columns 1 and 2 with nitrogen as chiral compounds separated on 2, 6-di-0-inimethcarrier gas( see Fig. . ) From Fig 2, the opti- ylsilyl-3-0-acetyl-B-CD CSP can be: separated onmum gas velocities of columns I and 2 are about9 2, 3-di-0-acetyl-6-0-trimethylsilyl-3-CD CSP. Itcm/s like common stationary phases, which coin- can be concluded that DATBCD-CSP is of strongercides with Van Deemter equation and indicates and wider enantioselectvities than DTABCD-CSPthat the two silylated and acetylated 3-CD station. DATBCD-CSP can separate not only enantiomersary phases are of low Inass transfer resistance and such as ketone, esters, alcohols and olefines, butsuitable to be used as capillary gas chromatograpalso the underivatized lactate acid. which isIc stationaryTable 3 Enantioselectivity of tw o silylated andacetylated B-cyclodextrinsEanaticoer(U tII三0.4901.611.140161.IM902.301.118241.1OC0.3phenylethanol1508231.019811.0lI-o 11. 2-prrpunediol203.871.1623.911.068Q-lonone506.841.1786.91.09rthnl-a-chrupurupiun901.361.0101.31.000t/℃y-valerolaclone1404.281.126421.I81401151,2561.|1.000I-column 1: 2-column 23-butanediol1303.901.1523.951.061g. 1 Plot of H with t for n-dodecane onNote: k, stands for capacity factor of thr first eluted enantiomer: astands for separation factorFig. 3 shows the chromatograms of a-Phenylethanol separated on DATBCD and DTABCD stationary phases. From Fig. 3, it can be seen thatboth of them reach baseline separation(b)1015202/(cms-1)LI-column I; 2-column 2t/mint/ minFig. 2 Plot of H with t for n-dodecane onFig. 3on DATBCD-CSP(a)and I)TARCD-(SP(b)2.2 Separation of enantiomers on the twocolumnsahC国煤化工 Imn life spanThe separation results of enantiomers investicnns was investi-gated on the two silylated and acetylated B-CD gateN MHGne drift by tem-chiral stationary phases( CSPs)are listed in perature programming and bled temperatune. BothTable 3. The enantiomers separated on the two cy. of them relate to not only the characteristics ofTANG Kewn, e a: Silylated and acetylated B-CDs for GC stationary phasesstationary phases, but also the aging degree ofand strong enantioselectivity for such enantiomerscolumns. If the aging temperature is harsh and ag. as ketone, esters, alcohols and olefines etc. It ising time is long, the baseline drift is small and the found that DATBCD stationary phase shows stronbled temperature rises. In this experiment, the ger enantioselectivity than DrTABCDthermal stability of the chiral capillary columnswas investigated with the degree of the baseline Referencesdrift by temperature progr amming at the rate of 6C/min. It is found that there is no baseline drift [1] Schurig V, Nowotny H P,Angew.Gas-chromatopaphicat200℃, and it is beloy3.6×10-3Aat240separation of enantiomers on stationary phase without metalicity factors for n-dode- [2] Schurig v, Nowoermy H P, Angew. Separation of enantiomerscane and separalion facto s for some enantiomersdiluted permcthylated p-cyclodextrin ly high-resolutionon the two columns hard y chaomatography[ J].Chromatogr,1988, 441:155-163columns have worked for 2.0 h. It can be conclud- [3: YI Jian-ming, TANG Kuo-wen. Insoluble 3-cyclodextrinpolymer for capillary gas chromatographic separation of enaned that the columns are o: good thermal stabilitytiomers and isomer J. Chromatogr A, 2000. 883: 137.The life span of the columns was investigated bymeasuring the separation factors and capacity fac- [4] WANG Hong, ZHOU Xin, oU Qing-yu. Gas chromatographlors for a-phenylethanol cn them after they haveic separation of amino acid enantiomers and their nrognitiunmechanism on a 2, 6-di-0-butvl-3-0-trifluoroacetvlated-y-cvbeen used for 3, 12 and 18 months respectivelyclodextrin capillary column.]. Chromatogr.1994.67It is found that the separa. ion factors and capacity107-l1lfactors change a little, which indicates that the [5] WANG Hong, WANG Yi, OU Qing-yu, et al. Improved entwo stationary phases have long life span of chiralantiomeric separation with a 2. 6-di-0-pentyl-30-trifluoro-acetylated-p-cyclodextrin and oV-7 mixed stationary chiralcapillary column[ J.Chromatog,1993. 644:202.?[6]Shitangkoon A, Vigh G. Systematic modification of the sepa-Conclusionration selectivity of cyclodextrin-hased gas chromatog aphistationary phases by varying the size of the 6-0-substiluents[J]. Chromatog A, 1996, 738: 31-42After derivatization with silyl and acetyl, the 7 NIE Meng-yan. ZHOU Liang-mo.WANGHong.(hronato-film forming ability of B-crclodextrin derivativesgraphic enatiomer separation on long-chain alkylated p-tyclo-improved, and they are su itable for being usedextrin chiral stationary phase [J]. Anal Chim Acta. 2000capillary stationary phase: in GC. At the same48:2792863] YU Thong- jian, LONG Yi-chen. LUO Zong-jnan. Investigatime, the capillary column s prepared with silicontion on a new model porous polvmer bead[J.Acta Chimicaoil l as diluent, are of high column efficiencySimca,l990,48:287-294.中国煤化工CNMHG