title: Isolation and purification of acid-labile carotenoid 5,6-epoxides on modified silica gels.
abstract: BACKGROUND
  The acid-labile carotenoid 5,6-epoxides occur in all green plants and in most fruits, but their isolation or purification is complicated and expensive because they decompose on normal silica gels. Alkaline stationary phases in open column chromatography (OCC) have low capacities, which makes them unsuitable for preparative scale.
  
  
  OBJECTIVE
  To find a simple high-capacity stationary phase for OCC that does not induce transformations of acid-labile compounds.
  
  
  METHODS
  Commercially available silica gel was treated with aqueous sodium bicarbonate solution to neutralise its slightly acidic character, and was then washed and dried. The effect of the treated gel (named silica-9) on violaxanthin was studied. The modified gel was also applied to the OCC of different complex natural extracts (maple leaves and fruits of yellow paprika). Carotenoids were examined by HPLC-PAD both before and after chromatography on the modified gel.
  
  
  RESULTS
  Violaxanthin decomposed rapidly on normal silica gels but not on the modified gel. Chromatography of plant extracts showed that the modified gel had a similar capacity to the untreated gel but did not effect epoxy-carotenoids, which could be separated or enriched readily on a large scale.
  
  
  CONCLUSIONS
  The modified gel does not induce any transformation or decomposition of epoxy-carotenoids but still exhibits a high capacity, suggesting that it can be used in preparative organic chemistry as an additional and convenient tool in the OCC for the separation of other acid-labile compounds.
authors.affiliation: Department of Biochemistry and Medical Chemistry, University of Pécs, Medical School, Szigeti út 12, Pécs, Hungary. vera.nagy@aok.pte.hu
authors.forename: Veronika
authors.initials: V
authors.lastname: Nagy
authors.forename: Attila
authors.initials: A
authors.lastname: Agócs
authors.forename: Erika
authors.initials: E
authors.lastname: Turcsi
authors.forename: József
authors.initials: J
authors.lastname: Deli
mesh_terms: D000143:Acids / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry / Q000302:isolation & purification*; D002851:Chromatography, High Pressure Liquid; D004852:Epoxy Compounds / Q000737:chemistry / Q000302:isolation & purification*; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification; D058428:Silica Gel; D012822:Silicon Dioxide
chemical_list: D000143:Acids; D004852:Epoxy Compounds; D010936:Plant Extracts; D002338:Carotenoids; D058428:Silica Gel; D012822:Silicon Dioxide