Phase behavior and physicochemical properties of thermoreversible aqueous biphasic systems composed of ionic liquids and deep eutectic solvents

doi:10.11949/0438-1157.20201412

Abstract

Abstract:

Compared with the polymer-based aqueous biphasic systems (ABSs), the ionic liquid (IL)-based ABSs exhibited higher phase separation efficiency and stronger selectivity, and have attracted increasing attention in separation and purification. However, the kosmotropic components in the IL-based ABSs were inorganic salts or organic salts, which were adverse to maintain the stability and biological activity of the biomolecules in a strong alkaline solution. In this study, deep eutectic solvents (DESs) were used as alternative kosmotropic components to form novel ABSs with ILs (chaotropic components). The law of phase behavior at different temperature was investigated to screen out thermoreversible systems showing upper critical solution temperature (UCST) and lower critical solution temperature (LCST). Moreover, the physicochemical properties, such as the viscosity, density, conductivity, and pH of the IL-DES-water ternary systems as function of temperature were explored. Furthermore, quantum chemical calculations were used to analyze the interaction between the IL and water or DES and water. The research aims to reveal the mechanism of the thermoreversible IL-DES ABS and provide essential data for the desigin of a new ideal extraction system for the extraction of thermo-sensitive biomolecules.

Key words: thermoreversible, ionic liquid, deep eutectic solvent, aqueous biphasic system, phase behavior, physicochemical properties

摘要：

与聚合物双水相体系相比，离子液体双水相体系具有相分离效率高和选择性强的特点，在萃取领域得到了广泛关注。然而，离子液体双水相体系中常见的kosmotropic组分为无机盐或有机盐，溶液环境通常呈现强碱性，不利于保持萃取分子的稳定性和生物活性。以低共熔溶剂替代盐类作为kosmotropic组分、以离子液体为chaotropic组分构建新型离子液体-低共熔溶剂双水相体系，考察了不同温度下的相行为规律，筛选出具有高临界共熔温度（UCST）和低临界共熔温度（LCST）两种截然相反的热可逆相转变行为的萃取体系，从宏观角度探索了离子液体-低共熔溶剂-水三元体系的黏度、密度、电导率以及pH等理化特性随温度变化的规律，利用量子化学计算从微观角度分析离子液体、低共熔溶剂与水分子之间的相互作用。研究旨在揭示热可逆离子液体-低共熔溶剂双水相体系的成相机理，为萃取温敏性生物分子设计新的理想萃取体系提供基础数据。

关键词: 热可逆, 离子液体, 低共熔溶剂, 双水相, 相行为, 理化特性

CLC Number:

TQ 013

ZHANG Lili, LI Yan, GAO Jing. Phase behavior and physicochemical properties of thermoreversible aqueous biphasic systems composed of ionic liquids and deep eutectic solvents[J]. CIESC Journal, 2021, 72(5): 2493-2505.

张莉莉, 李艳, 高静. 热可逆离子液体-低共熔溶剂双水相体系的相行为及理化特性研究[J]. 化工学报, 2021, 72(5): 2493-2505.

Figures/Tables 12

Fig.1 Chemical structure of ionic liquid sand deep eutectic solvents

Table 1 Properties of ionic liquids and deep eutectic solvents

ILs/DESs	W_c/%	η×10^-3/(mPa·s)(298.15 K)	α (298.15 K)	β (298.15 K)	π^* (298.15 K)	$E T N$ (298.15 K)	T_i/K	T_peak/K	T_f/K	W_lost/%	W_973.15/%
[C₄mim]BF₄	0.52±0.01	0.10±0.00	0.69±0.02	0.32±0.01	1.05±0.03	0.70±0.02	644.45	691.05	701.75	370.71	1.12
[C₄mim]Br	0.27±0.02	ND	ND	ND	ND	ND	556.75	587.15	595.25	362.91	3.61
[C₄mim]Cl	0.13±0.02	ND	ND	ND	ND	ND	538.95	560.75	569.85	360.51	4.33
[C₄mim]CF₃COO	1.49±0.02	0.08±0.00	0.61±0.03	0.71±0.03	0.96±0.02	0.64±0.01	454.05	471.45/551.45	519.25	353.05	7.16
[P₄₄₄₄]BF₄	0.29±0.01	ND	ND	ND	ND	ND	719.45	741.35	753.45	364.74	3.19
[P₄₄₄₄]Br	0.52±0.02	ND	ND	ND	ND	ND	645.55	675.45	691.05	369.57	1.88
[P₄₄₄₄]Cl	0.02±0.01	ND	ND	ND	ND	ND	640.25	669.95	685.65	364.47	3.72
[P₄₄₄₄]CF₃COO	0.15±0.01	ND	ND	ND	ND	ND	462.15	476.65/499.15/518.35	512.05	350.60	3.91
[P₄₄₄₈]BF₄	1.25±0.45	0.89±0.00	ND	0.68±0.01	0.87±0.02	ND	703.95	743.95	751.35	366.02	5.31
[P₄₄₄₈]Br	2.69±0.30	ND	ND	ND	ND	ND	639.85	665.45	685.05	364.95	6.31
[P₄₄₄₈]Cl	3.11±0.11	1.26±0.02	ND	1.30±0.01	0.04±0.01	ND	635.25	664.55	680.65	357.40	5.80
[P₄₄₄₈]CF₃COO	0.27±0.01	0.24±0.00	ND	1.07±0.04	0.87±0.02	ND	480.95	472.85/548.55	569.85	359.71	6.17
[N₄₄₄₄]BF₄	0.94±0.06	ND	ND	ND	ND	ND	469.75	492.25/664.75	676.65	367.82	3.65
[N₄₄₄₄]Br	0.94±0.00	ND	ND	ND	ND	ND	473.35	492.85/536.15	506.35	349.57	4.14
[N₄₄₄₄]Cl	8.51±0.08	ND	ND	ND	ND	ND	464.95	485.25	497.35	361.95	4.76
[N₄₄₄₄]CF₃COO	0.16±0.03	ND	ND	ND	ND	ND	480.25	504.25	513.75	365.62	6.35
[ChCl][Rib]	0.06±0.04	23.40±0.25	ND	ND	ND	ND	520.55	545.05	557.75	342.81	18.29
[ChCl][Glu]	0.01±0.00	654.05±39.65	ND	ND	ND	ND	494.35	520.85	563.25	341.91	19.06
[ChCl][Fru]	12.93±0.12	54.06±0.48	ND	ND	ND	ND	432.75	448.85/514.55/564.35	563.75	347.21	16.17
[ChCl][Sur]	7.87±0.08	>2201.00±83.00	ND	ND	ND	ND	509.05	543.85	559.65	338.53	20.83

Table 1 Properties of ionic liquids and deep eutectic solvents

ILs/DESs	W_c/%	η×10^-3/(mPa·s)(298.15 K)	α (298.15 K)	β (298.15 K)	π^* (298.15 K)	$E T N$ (298.15 K)	T_i/K	T_peak/K	T_f/K	W_lost/%	W_973.15/%
[C₄mim]BF₄	0.52±0.01	0.10±0.00	0.69±0.02	0.32±0.01	1.05±0.03	0.70±0.02	644.45	691.05	701.75	370.71	1.12
[C₄mim]Br	0.27±0.02	ND	ND	ND	ND	ND	556.75	587.15	595.25	362.91	3.61
[C₄mim]Cl	0.13±0.02	ND	ND	ND	ND	ND	538.95	560.75	569.85	360.51	4.33
[C₄mim]CF₃COO	1.49±0.02	0.08±0.00	0.61±0.03	0.71±0.03	0.96±0.02	0.64±0.01	454.05	471.45/551.45	519.25	353.05	7.16
[P₄₄₄₄]BF₄	0.29±0.01	ND	ND	ND	ND	ND	719.45	741.35	753.45	364.74	3.19
[P₄₄₄₄]Br	0.52±0.02	ND	ND	ND	ND	ND	645.55	675.45	691.05	369.57	1.88
[P₄₄₄₄]Cl	0.02±0.01	ND	ND	ND	ND	ND	640.25	669.95	685.65	364.47	3.72
[P₄₄₄₄]CF₃COO	0.15±0.01	ND	ND	ND	ND	ND	462.15	476.65/499.15/518.35	512.05	350.60	3.91
[P₄₄₄₈]BF₄	1.25±0.45	0.89±0.00	ND	0.68±0.01	0.87±0.02	ND	703.95	743.95	751.35	366.02	5.31
[P₄₄₄₈]Br	2.69±0.30	ND	ND	ND	ND	ND	639.85	665.45	685.05	364.95	6.31
[P₄₄₄₈]Cl	3.11±0.11	1.26±0.02	ND	1.30±0.01	0.04±0.01	ND	635.25	664.55	680.65	357.40	5.80
[P₄₄₄₈]CF₃COO	0.27±0.01	0.24±0.00	ND	1.07±0.04	0.87±0.02	ND	480.95	472.85/548.55	569.85	359.71	6.17
[N₄₄₄₄]BF₄	0.94±0.06	ND	ND	ND	ND	ND	469.75	492.25/664.75	676.65	367.82	3.65
[N₄₄₄₄]Br	0.94±0.00	ND	ND	ND	ND	ND	473.35	492.85/536.15	506.35	349.57	4.14
[N₄₄₄₄]Cl	8.51±0.08	ND	ND	ND	ND	ND	464.95	485.25	497.35	361.95	4.76
[N₄₄₄₄]CF₃COO	0.16±0.03	ND	ND	ND	ND	ND	480.25	504.25	513.75	365.62	6.35
[ChCl][Rib]	0.06±0.04	23.40±0.25	ND	ND	ND	ND	520.55	545.05	557.75	342.81	18.29
[ChCl][Glu]	0.01±0.00	654.05±39.65	ND	ND	ND	ND	494.35	520.85	563.25	341.91	19.06
[ChCl][Fru]	12.93±0.12	54.06±0.48	ND	ND	ND	ND	432.75	448.85/514.55/564.35	563.75	347.21	16.17
[ChCl][Sur]	7.87±0.08	>2201.00±83.00	ND	ND	ND	ND	509.05	543.85	559.65	338.53	20.83

Table 2 Construction of thermo reversible ILs-DESs-H2O system

ILs	[ChCl][Rib]	[ChCl][Glu]	[ChCl][Fru]	[ChCl][Sur]
[C₄mim]BF₄	?	UCST	UCST	UCST
[C₄mim]Br	?	?	?	?
[C₄mim]Cl	?	?	?	?
[C₄mim]CF₃COO	?	?	?	?
[P₄₄₄₄]BF₄	×	×	×	×
[P₄₄₄₄]Br	LCST	LCST	LCST	LCST
[P₄₄₄₄]Cl	LCST	?	LCST	LCST
[P₄₄₄₄]CF₃COO	?	?	?	?
[P₄₄₄₈]BF₄	×	×	×	×
[P₄₄₄₈]Br	LCST	LCST	LCST	LCST
[P₄₄₄₈]Cl	LCST	LCST	LCST	LCST
[P₄₄₄₈]CF₃COO	×	×	×	×
[N₄₄₄₄]BF₄	×	×	×	×
[N₄₄₄₄]Br	?	?	?	?
[N₄₄₄₄]Cl	?	?	?	?
[N₄₄₄₄]CF₃COO	LCST	LCST	LCST	LCST

Fig.2 Phase diagrams of UCST (a) and LCST (b) of IL-DES-H2O

Fig.3 Phase diagrams of ILs-[ChCl][Fru]-H2O and ILs-[ChCl][Sur]-H2O at 308.15 K

Fig.4 Phase diagrams of DESs-[P4444]Br-H2O (a) and DESs-[N4444]CF3COO-H2O (b) at 308.15 K

Table 3 Phase diagram of ILs-DESs-H2O with the corresponding fitting of the experimental data

ILs	DESs	T/K	A	B	C	R²
[C₄mim]BF₄	[ChCl][Fru]	298.15	1.00	-1.02	9.75	0.9999
	[ChCl][Glu]	298.15	1.19	-2.05	8.86	0.9941
	[ChCl][Glu]	328.15	1.23	-1.67	0.31	0.9982
	[ChCl][Sur]	308.15	1.21	-1.99	1.08	0.9929
[P₄₄₄₄]Br	[ChCl][Rib]	308.15	1.48	-1.70	4.17	1.0000
	[ChCl][Glu]	308.15	2.10	-2.54	3.44	0.9994
	[ChCl][Fru]	308.15	1.58	-1.81	4.30	0.9998
	[ChCl][Sur]	308.15	1.04	-0.91	11.69	0.9983
[P₄₄₄₄]Cl	[ChCl][Fru]	308.15	0.07	3.83	8.64	0.9996
[P₄₄₄₄]Cl	[ChCl][Sur]	308.15	0.62×10^-17	59.49	65.87	0.9928
[P₄₄₄₈]Br	[ChCl][Fru]	308.15	0.58	-4.97	24.29	0.9976
[P₄₄₄₈]Br	[ChCl][Sur]	308.15	0.10	-2.04	133.00	0.9912
[P₄₄₄₈]Cl	[ChCl][Fru]	308.15	0.72	-0.61	63.26	0.9890
[P₄₄₄₈]Cl	[ChCl][Sur]	308.15	1.47	-2.31	51.95	0.9971
[N₄₄₄₄]CF₃COO	[ChCl][Rib]	308.15	8.05	-5.90	2.34	0.9916
	[ChCl][Glu]	308.15	2.66	-4.36	9.64	0.9978
	[ChCl][Fru]	298.15	3.65	-4.23	5.02	0.9961
	[ChCl][Fru]	308.15	28.17	-8.74	-3.85	0.9976
	[ChCl][Fru]	328.15	3.57	-5.40	-1.52	0.9976
	[ChCl][Sur]	308.15	3696.29	-19.26	-23.64	0.9782

Fig.5 Phase diagram of [P4444]Br-[ChCl][Fru]-H2O with the corresponding fitting of the experimental data at 308.15 K

Fig.6 Viscosities, densities, conductivities, pH for ILs-DESs-H2O as a function of temperature

Fig.7 Molar volume (Vm), standard molar entropy (S?) and lattice energy (UPOT) for ILs-DESs-H2O as a function of temperature

Fig.8 Geometric equilibrium configuration of ILs-DESs-H2O ternary system

Table 4 Interaction energy of ILs-DESs-H2O ternary system

System	E_complex/(kJ·mol^-1)	E_[ChCl][Fru]/(kJ·mol^-1)	$E [P 4448] C l$ /(kJ·mol^-1)	$E H 2 O$ /(kJ·mol^-1)	E_BSSE/(kJ·mol^-1)	ΔG/(kJ·mol^-1)
[P₄₄₄₈]⁺-Cl^-	-998.19×10³	-709.25×10³	-288.84×10³	—	4.79	-91.01
[P₄₄₄₈]Cl-H₂O	-1046.19×10³	-998.19×10³	-47.98×10³	—	1.36	-16.39
[Ch]⁺-Cl^-	-495.19×10³	-206.35×10³	-288.84×10³	—	4.05	-110.71
[ChCl][Fru]	-926.74×10³	-495.29×10³	-431.41×10³	—	2.10	-43.25
[ChCl][Fru]-H₂O	-974.74×10³	-926.73×10³	-47.98×10³	—	1.68	-20.95
[P₄₄₄₈]Cl-[ChCl][Fru]-H₂O	-1972.96×10³	-926.73×10³	-998.18×10³	-47.98×10³	3.70	-60.43

Table 4 Interaction energy of ILs-DESs-H2O ternary system

System	E_complex/(kJ·mol^-1)	E_[ChCl][Fru]/(kJ·mol^-1)	$E [P 4448] C l$ /(kJ·mol^-1)	$E H 2 O$ /(kJ·mol^-1)	E_BSSE/(kJ·mol^-1)	ΔG/(kJ·mol^-1)
[P₄₄₄₈]⁺-Cl^-	-998.19×10³	-709.25×10³	-288.84×10³	—	4.79	-91.01
[P₄₄₄₈]Cl-H₂O	-1046.19×10³	-998.19×10³	-47.98×10³	—	1.36	-16.39
[Ch]⁺-Cl^-	-495.19×10³	-206.35×10³	-288.84×10³	—	4.05	-110.71
[ChCl][Fru]	-926.74×10³	-495.29×10³	-431.41×10³	—	2.10	-43.25
[ChCl][Fru]-H₂O	-974.74×10³	-926.73×10³	-47.98×10³	—	1.68	-20.95
[P₄₄₄₈]Cl-[ChCl][Fru]-H₂O	-1972.96×10³	-926.73×10³	-998.18×10³	-47.98×10³	3.70	-60.43

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