| 1. |
- Tan, Tianwei, et al.
(författare)
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Cross-linked agarose for separation of low molecular weight natural products in hydrophilic interaction liquid chromatography
- 2010
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Ingår i: Biotechnology Journal. - : Wiley. - 1860-6768. ; 5:5, s. 505-510
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Forskningsöversikt (refereegranskat)abstract
- Following its market introduction in 1982, the cross-linked 12% agarose gel media Superose 12 has become widely known as a tool for size exclusion chromatography of proteins and other biological macromolecules. In this review it is shown that, when appropriate mobile phases are used, Superose possesses adsorption properties similar to that of traditional media for hydrophilic interaction liquid chromatography (HILIC). This is illustrated by the separation and purification of low molecular weight compounds such as polyphenols including active components of traditional Chinese medicinal herbs and green tea. Structural features of the cross-linked agarose that likely cause the observed adsorption effects are discussed aswell. These are identified as being primarily ether bonds acting as strong hydrogen bond acceptors as well as hydrophobic residues originating from the cross-linking reagents.
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| 2. |
- Xu, Jun, et al.
(författare)
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Mixed-mode retention mechanism for (-)-epigallocatechin gallate on a 12% cross-linked agarose gel media
- 2006
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1137:1, s. 49-55
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption behaviour of (−)-epigallocatechin gallate (EGCG), the major polyphenolic substance in green tea extracts, on the cross-linked agarose gel Superose 12 HR 10/30, has been studied using a variety of solvent systems and shown to be based on a mixture of hydrogen bonding and hydrophobic interaction. The hydrogen bonding was studied in acetonitrile in the presence of different co-solvents possessing varying hydrogen bond donor (HBD) and/or hydrogen bond acceptor (HBA) characteristics. The HBA-value of the co-solvent had the highest effect whereas the HBD-value played a subordinate role. Retention due to hydrophobic interaction could be demonstrated when mobile phases containing high water content were applied. The retention of EGCG, and its analogues (−)-epigallocatechin (EGC) and (−)-catechin (C) were thus shown to be dependent on the polarity of the organic modifiers added. However, the elution order of EGC and C, was inversed to that observed in reversed phase chromatography, indicating that some hydrogen bonding was still in effect. The retardation of EGCG in the presence of a wide concentration range of acetonitrile in water confirmed the interpretation that the retention mechanism is of mixed-mode character based on both hydrogen bonding and hydrophobic interaction.
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| 3. |
- Xu, Jun, et al.
(författare)
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NMR Studies on the interaction between (−)-epigallocatechin gallate and cyclodextrins, free and bonded to silica gels
- 2007
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 342:6, s. 843-850
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between (−)-epigallocatechin-3-gallate (EGCG) and β- or γ-cyclodextrin (CD), in free solution and bonded to silica beads, has been studied by 1H HR-MAS NMR spectroscopy. The chromatographic retardation of EGCG on columns packed with CD-silica beads was shown to be due to the interaction of EGCG with the CD ligands because no nonspecific interaction with the silica gel could be observed. EGCG forms a tighter complex with β-CD than with γ-CD and NMR data obtained from hydroxy protons together with mm2 calculations suggest that for β-CD intermolecular hydrogen bonding, in addition to hydrophobic interaction, stabilizes the complex.
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| 4. |
- Xu, Jun, et al.
(författare)
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One-step purification of epigallocatechin gallate from crude green tea extracts by isocratic hydrogen bond adsorption chromatography on β-cyclodextrin substituted agarose gel media
- 2005
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Ingår i: Journal of Chromatography B. ; 824:1-2, s. 323-326
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Tidskriftsartikel (refereegranskat)abstract
- An oligomerized β-cyclodextrin ligand coupled to brominated allyl-group substituted Sepharose HP has been used for the one-step purification of polyphenolic epigallocatechin gallate (EGCG), an important antioxidant, by isocratic hydrogen bond adsorption chromatography. With a sample load of 1.33 mg crude green tea polyphenolic extract per ml column packing and with water/ethanol/acetonitrile (57/30/13, v/v) as the optimum mobile phase, an EGCG purity of about 98% with a recovery of approximate 73% could be achieved by proper peak cutting. After about 10 sample applications, the column performance started to deteriorate but could be regenerated to its original function by cleaning with 0.35 M NaOH.
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| 5. |
- Xu, Jun, et al.
(författare)
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One-step purification of epigallocatechin gallate from crude green tea extracts by mixed-mode adsorption chromatography on highly cross-linked agarose media
- 2007
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1169:1-2, s. 235-238
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Tidskriftsartikel (refereegranskat)abstract
- (−)-Epigallocatechin gallate (EGCG) was purified in one step from a green tea polyphenol (GTP) crude extract by adsorption chromatography on a Superose 12 HR 10/30 column. The mobile phase used was a mixture of acetonitrile and water with an optimum mobile phase compositions regarding purity, recovery and separation time of 78/22 (v/v). Maximum practical sample loading was 100 mg GTP per run (corresponding to 4.2 mg/ml Superose). An EGCG purity of 99% with recoveries in the range 60–65% was achieved in one step directly from the crude GTP extract. Full column regeneration was obtained using solvents in the following order: 0.5 M NaOH, distilled water and 30% acetic acid.
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| 6. |
- Xu, Jun, et al.
(författare)
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One-step simultaneous purification of three water-soluble constituents in crude extracts from Danshen by adsorption chromatography on oligo-β-cyclodextrin substituted agarose gel media
- 2007
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Ingår i: Process Biochemistry. - : Elsevier BV. - 1359-5113 .- 1873-3298. ; 42:3, s. 480-485
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Tidskriftsartikel (refereegranskat)abstract
- A new adsorption chromatographic method for the simultaneous purification of Danshensu, Protocatechuic aldehyde and Salvianolic acid B (Lithospermic acid B) from a crude extract from radix of Danshen (Salviae miltiorrhiza) has been developed using oligo-β-cyclodextrin immobilized to Sepharose HP agarose gel media. Sample loads of up to 2.3 mg crude extracts/ml gel gave satisfactory results. The target components were eluted using step-wise isocratic elution with increasing concentrations of acetic acid. The separated fractions were identified by LC–MS. The recoveries of Danshensu, Protocatechuic aldehyde and Salvianolic acid B were 88.3%, 90.2% and 73.6% with purities of 99%, 99%, and 98%, respectively. Isocratic elution in 6% acetic acid gave baseline separation of Danshensu and Protocatechuic aldehyde, whereas 40% acetic acid was required for purification of Salvianolic acid B. Full separation efficiency could be restored by cleaning the column with 0.5 M NaOH followed by distilled water and 30% acetic acid.
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