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Aqueous Biphasic Systems with Ionic Liquids _________________________________________________________________________ changing either the concentration of salt and IL; (iii) introduction of additional co-solvents, anti-solvents or amphiphilic structures to the overall system. As shown in Table 9, the partition coefficients of L-tryptophan (KTrp) in IL-based ABS are substantially higher than in usual PEG-polysaccharide systems (with KTrp 1) 85 or PEG- inorganic salts systems (with KTrp 1 to 7) 86 . The IL-based ABS are thus far more efficient for L-tryptophan separation than conventional ABS. Table 9 also shows the composition of the ternary system employed for the L-tryptophan partition studies as well as the corresponding TLs and TLLs. Table 9. Weight fraction composition and partition coefficients of L-tryptophan in ILs-ABS systems. 52 IL Weight fraction composition / % TL equation IL (wt %) = a + b·K3PO4 (wt %) TLL KTrp IL K3PO4 a b [amim][Cl] 26.91 15.91 47.20 -1.275 52.53 124 ± 5 [C7H7mim][Cl] 25.11 18.30 56.62 -1.722 57.62 78.4 ± 0.5 [OHC2mim][Cl] 40.57 16.05 87.17 -2.904 68.38 73.1 ± 0.8 [C2mim][Cl] 25.90 14.90 42.36 -1.105 45.73 59.2 ± 0.4 [C4mim][Cl] 25.35 15.97 43.46 -1.149 50.03 36.6 ± 0.6 [C1im][Cl] 15.36 30.53 --- --- --- 21.3 ± 0.3 [im][Cl] 15.24 32.80 --- --- --- 14.2 ± 0.4 [C2mim][CH3CO2] 24.94 14.96 38.31 -0.8940 49.18 16.4 ± 0.8 [C2mim][MeSO4] 24.98 14.94 49.80 -1.661 28.89 4.5 ± 0.9 [C2mim][EtSO4] 24.97 15.06 48.90 -1.589 39.86 6.0 ± 0.5 [C2mim][CF3SO3] 24.87 16.35 75.49 -3.095 70.66 17.5 ± 0.8 [C4mim][Br] 25.82 15.17 51.60 -1.699 48.36 35.6 ± 0.8 [C4mim][CH3SO3] 25.03 14.96 43.66 -1.245 38.91 10.4 ± 0.4 [C4mim][N(CN)2] 24.40 16.82 67.35 -2.553 64.90 45.1 ± 0.9 [C4mim][TFA] 25.13 15.22 57.90 -2.154 56.16 36.1 ± 0.7 [C4mim][CF3SO3] 25.08 16.18 76.12 -3.154 75.39 16.6 ± 0.6
ILs + H2O + K3PO4 Ternary Systems _________________________________________________________________________ During the partitioning of L-tryptophan between the two phases there are several competing interactions between the IL, the inorganic salt, the L-tryptophan and water. There may occur hydrogen-bonding interactions, ··· interactions, as well as electrostatic interactions. In general, the results indicate that KTrp increases with the IL cation hydrophilic nature and thus the main interactions between the IL cation and the aminoacid determining the L-tryptophan partitioning are hydrophobic and hydrogen-bonding type interactions. The cation influence of the ILs studied in L-tryptophan partition coefficient follows the rank [amim][Cl] > [OHC2mim][Cl] > [C2mim][Cl] > [C4mim][Cl] > [C7H7mim][Cl] > [C1im][Cl] > [im][Cl]. The highest partition coefficient occurs for the [amim][Cl] followed by [OHC2mim][Cl] due to the presence of a double bound and a hydroxyl group at one of the alkyl side chains, respectively. Increasing the IL cation alkyl chain decreases the L-tryptophan partitioning in the di-substituted imidazolium-based ILs. The mono- and un-substituted imidazolium-based ILs present the lower partition coefficients for the L-tryptophan that could result from the decrease of the hydrophobic interactions existence between them. Evaluating the anion capability to extract L- tryptophan, the KTrp follow the rank: [C2mim][Cl] > [C2mim][CF3SO3] [C2mim][CH3CO2] > [C2mim][EtSO4] [C2mim][MeSO4] and [C4mim][N(CN)2] > [C4mim][Cl] [C4mim][TFA] [C4mim][Br] > [C4mim][CF3SO3] > [C4mim][CH3SO3]. L-tryptophan partitions preferentially for IL-rich phases composed by halogenated ions such as [Cl] or [Br] or to the most hydrophobic anions, i.e., anions with higher hydrogen bonding accepting strength (), such as [N(CN)2] and fluoride-based anions. Indeed, these partition coefficients seem to closely follow the Hofmeister series 87 . Salting-in inducing IL ions tend to increase the solute partition coefficient while the salting-out inducing IL ions tend to decrease it. Comparing the cation and the anion influence on partition coefficients of L-tryptophan, the influence of the IL imidazolium-based cation on the extraction capacity of ABS seems to be more important than the influence of the anion. Indeed, in the study of the cation influence the KTrp was found to vary between 10 and 120 (at approximately the same compositions of IL plus inorganic salt). The presence of benzyl groups and double bounds at the imidazolium side alkyl chain substantially increased such partition coefficients. Besides the ··· stacking, the possibility of solute-IL hydrogen-bonding seems to rule the partition behaviour. 53
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Catarina Maia Seco Seiça Neves Uni
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Ao meu Pai e ao meu Avô…
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agradecimentos Gostaria de começar
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keywords abstract Ionic liquids, wa
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4.2.3. Partitioning of L-tryptophan
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List of Abbreviations ABS Aqueous B
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List of Tables Table 1. Experimenta
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List of Figures Figure 1. Example o
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[C4mim][TFA]; ×, [C4mim][Br]; ○,
Page 27: 1. 1. General Introduction
Page 30 and 31: Aqueous Biphasic Systems with Ionic
Page 35 and 36: ILs + H2O Binary Systems __________
Page 41 and 42: Table 2. Experimental mole fraction
Page 49: 3. 3. QSPR Modelling of ILs + H2O B
Page 61 and 62: ILs + H2O + K3PO4 Ternary Systems _
Page 77: ILs + H2O + K3PO4 Ternary Systems _
Page 83: 5. 5. Final Remarks
Page 89 and 90: References ________________________
Page 95: 7. 7. List of Publications
Page 101 and 102: Appendix A ________________________
Page 111: Appendix B
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Aqueous Biphasic Systems with Ionic
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