title: Enantioseparation of (DL)-tryptophan by spiral tube assembly counter-current chromatography and evaluation of mass transfer rate for enantiomers.
abstract: Spiral tube assembly counter-current chromatography was successfully applied in enantioseparation of dl-tryptophan using bovine serum albumin as chiral selector. An improved biphasic aqueous-aqueous solvent system 12.0% (w/w) polyethyleneglycol 8000-9.0% (w/w) dibasic potassium phosphate-0.1% ammonia-78.9% water was used as the solvent system for counter-current chromatography, in which bovine serum albumin was predominantly distributed in the lower phase of the two-phase aqueous system. The aqueous-aqueous solvent system gave a very high enantioselectivity for d- and l-tryptophan at α=2.605 along with distribution ratio DD=1.200 and DL=0.461. High peak resolution was obtained for enantioseparation of 2.0mg of dl-tryptophan by spiral tube assembly counter-current chromatography under room temperature. It was found that 0.1% ammonia added in the aqueous-aqueous solvent system greatly improved the enantioseparations. An unusual extremely broad peak for l-tryptophan was observed during enantioseparations. In order to give an explanation, mass transfer rates of d- and l-enantiomers through the interface between the two phases were measured. It was found that l-tryptophan showed lower mass transfer rate than d-tryptophan. Further discussions were proposed for possible reasons for mass transfer rate difference between the enantiomers.
authors.affiliation: College of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou, 310032, China; Laboratory of Bioseparation Technologies, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Shengqiang
authors.initials: S
authors.lastname: Tong
authors.affiliation: Laboratory of Bioseparation Technologies, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address: itoy@nhlbi.nih.gov.
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Ito
authors.affiliation: Laboratory of Molecular Imaging and Nanomedicine, National Institutes of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Ma
mesh_terms: D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003377:Countercurrent Distribution / Q000379:methods*; D059625:Liquid-Liquid Extraction; D012710:Serum Albumin, Bovine; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism; D014364:Tryptophan / Q000737:chemistry / Q000302:isolation & purification*
chemical_list: D012997:Solvents; D012710:Serum Albumin, Bovine; D014364:Tryptophan
keywords: Aqueous–aqueous solvent system; Bovine serum albumin; Counter-current chromatography; Enantioseparation; Mass transfer rate; dl-Tryptophan