title: Extraction and enrichment of n-3 polyunsaturated fatty acids and ethyl esters through reversible π-π complexation with aromatic rings containing ionic liquids.
abstract: The present study investigated the potentials of ionic liquids (ILs) containing aromatic rings in extracting and enriching n-3 polyunsaturated compounds. The relationship between extraction efficiency, selectivity, and structure of ILs was studied and elucidated. Ionic liquids containing aromatic rings such as the N,N'-dialkylimidazolium and N-alkylpyridinium are found to selectively extract and enrich n-3 polyunsaturated compounds. The IL extraction process reached equilibrium relatively quickly (<30 min), and the extraction efficiency can be further enhanced by increasing the volume ratio of IL to solvent, addition of silver tetrafluoroborate, and usage of double bond containing solvents such as 1-hexene as stripping solvent. At optimal conditions, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim]PF(6) and 1-butyl-3-methylpyridinium dicyanamide [BuMePyr]DCN had increased extraction capabilities of n-3 polyunsaturated fatty acids (PUFA) (16.19%) and n-3 polyunsaturated fatty acid ethyl esters (PUFAEE) (144.54%), respectively. Multiple-step reverse extraction whereby n-3 PUFAs were first enriched through IL/hexane extraction followed by addition of fresh hexane repeatedly up to three times to the IL phase to desorb the saturated FAs resulted in a higher purity of n-3 PUFAs. Following this reverse extraction operation, the purity of n-3 PUFA and n-3 PUFAEE in the IL phase increased from the initial 15.88 to 38% (step 1) and further to 45% (step 3) and from the initial 72.56 to 82% (step 1) and further to 89% (step 3), respectively. The results from this study strongly suggested the correlation of n-3 PUFA extraction with aromatic/delocalized cation structure of ILs, which provides the basis for future research in designing novel ILs task-specified for efficient long-chain PUFA concentration.
authors.affiliation: Department of Molecular Biology, Aarhus University, Aarhus, Denmark.
authors.forename: Ling-Zhi
authors.initials: LZ
authors.lastname: Cheong
authors.forename: Zheng
authors.initials: Z
authors.lastname: Guo
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Yang
authors.forename: Seong-Chea
authors.initials: SC
authors.lastname: Chua
authors.forename: Xuebing
authors.initials: X
authors.lastname: Xu
mesh_terms: D004952:Esters / Q000737:chemistry / Q000302:isolation & purification; D005230:Fatty Acids, Nonesterified / Q000302:isolation & purification; D015525:Fatty Acids, Omega-3 / Q000737:chemistry / Q000302:isolation & purification*; D005395:Fish Oils / Q000737:chemistry / Q000378:metabolism; D052578:Ionic Liquids / Q000737:chemistry*
chemical_list: D004952:Esters; D005230:Fatty Acids, Nonesterified; D015525:Fatty Acids, Omega-3; D005395:Fish Oils; D052578:Ionic Liquids; C030341:salmon oil