Dissolution and resourcfulization of biopolymers in ionic liquids

    Dissolution and resourcfulization of biopolymers in ionic liquids Xiaodeng Yang, Congde Qiao, Yan Li, Tianduo Li PII: DOI: Reference:

S1381-5148(16)30015-3 doi: 10.1016/j.reactfunctpolym.2016.01.017 REACT 3625

To appear in: Received date: Revised date: Accepted date:

21 August 2015 7 December 2015 28 January 2016

Please cite this article as: Xiaodeng Yang, Congde Qiao, Yan Li, Tianduo Li, Dissolution and resourcfulization of biopolymers in ionic liquids, (2016), doi: 10.1016/j.reactfunctpolym.2016.01.017

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ACCEPTED MANUSCRIPT Dissolution and resourcfulization of biopolymers in ionic liquids

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Xiaodeng Yang1, Congde Qiao, Yan Li, Tianduo Li Shandong Provincial Key Laboratory of Fine Chemicals, Qilu University of Technology, Jinan

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250353, P. R. China

Abstract

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Cellulose, starch, chitosan, β-cyclodextrin, lignin and proteins are the most abundant elements in the universe with excellent properties, such as good

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biodegradability and biocompatibility, thus have gained tremendous interest in many fields. Unfortunately, these biopolymers suffer greatly from the solubility in neutral or

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basic solutions, insufficient mechanical properties, brittleness, and also have other

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drawbacks. Ionic liquids (ILs) are a kind of greener solvents for biopolymers, owning

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to their excellent physical-chemical properties. ILs also provide a premise condition for the homogeneous reaction of biopolymers; improve the utilization value of biopolymer. In this paper, the dissolution, regeneration and modification of cellulose, starch, chitosan, lignin and protein in ionic liquids are reviewed. Keywords: biopolymer, ionic liquid, dissolution, regeneration, resourcfulization Introduction With the development of industry, the consumption of non-renewable resources such as petroleum, coal and natural gas is increasing. Apart from exhaustion of fossil fuels, the resulting synthetic polymers are difficult to be degraded, leading to serious environmental pollutions[1]. Therefore, studies on the development and utilization of renewable biopolymers, such as cellulose, starch, chitosan, β-cyclodextrin, lignin and 1

To whom correspondence should be addressed. Email: [email protected]; Tel: +86-531-89631208 1

ACCEPTED MANUSCRIPT proteins, have attracted much attention for decades. Renewable biopolymers possess various functional groups, through which different functions are imparted.

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Unfortunately, the studies suffered greatly from poor solubility in neutral or basic solutions, insufficient mechanical properties, brittleness, and other drawbacks of

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biopolymers[2]. Exploring the environmental friendly processing technologies for

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biopolymers has become a great challenge for scientists[3].

Ionic liquids (ILs) are regarded as an attractive replacement for ordinary

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environment-unfriendly organic solvents, owing to their excellent physical-chemical

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properties, such as low vapor pressure, satisfactory solvability, designability and biodegradability[4-8]. The utilization of ILs in dissolution, regeneration and modification of biopolymers has drawn growing attention. In this paper, the

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dissolution, regeneration and modification (or degradation) of cellulose, chitosan, starch, β-cyclodextrin, lignin and protein in various ILs are reviewed. Specifically, the

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influencing factors on the dissolution of biopolymers in ILs, such as the kind and volume of cation or anion of IL, temperature, heating method and the source of biopolymers are summarized. The mechanisms that ILs dissolve biopolymers are enumerated. The physicochemical properties of the regenerated biopolymers are compared with those of native ones. The reactions of biopolymers in ILs as well as the physicochemical properties of biopolymer derivatives are introduced.

1. Dissolution and modification of biopolysaccharides in ionic liquids Biopolysaccharides, namely carbohydrate polymers, are the most abundant and widely distributed in nature[9]. About 200 billion tons of renewable resources are produced in the world per year, among which 65-85% are biopolysaccharides. The biopolysaccharides are mainly used as food, besides the utilization in papermaking, 2

ACCEPTED MANUSCRIPT textile, and other light industries. To improve the utilization efficiency of biopolysaccharides, scientists are trying to decompose them into small molecule

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organic compounds. Various methods of dealing with biopolysaccharides are investigated[10-18]. In this section, the dissolution and modification of cellulose,

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chitosan, starch and β-cyclodextrin in ionic liquids are reviewed.

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1.1 Dissolution and precipitation of cellulose in ionic liquids

Cellulose is one of the most abundant biopolysaccharides, widely used in fiber,

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paper, membrane, and coating making. Raw cellulose has high degree of crystallinity

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due to numerous hydrogen bonds among intra- and inter-molecules, resulting in its insolubility in neutral water as well as organic solvents, thus limited their application severely. To expand the application of cellulose, the chemical modification is

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proposed, during which the selection of homogeneous reaction solvent is a key problem to be addressed.

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In 1934, Graenacher[19] found that organic molten salt N-ethylpyridinium chloride could dissolve cellulose. However, the high melting temperature requied (118-120 oC) restricted the broad investigation and utilization of the organic salt. Until 1990s, the presence of ionic liquid(IL), namely, organic molten salt at room temperature provides a prerequisite for the dissolution of cellulose under neutral conditions. It has been revealed that ILs composed of quaternary ammonium groups, pyridine cation and imidazole cation could dissolve cellulose[20, 21]. The commonly used ILs and the solubility of cellulose in these ILs are listed in Table 1. In 2002, Swatloski

and

coworkers[4]

found

that

ILs

containing

1-butyl

(or

octyl)-3-methylimidazolium cations (C4mim+ or C8mim+) could dissolve cellulose without any pretreatment. This work opened up a new system for dissolving cellulose. The anions of ILs affected the dissolution of cellulose significantly. The ILs 3

ACCEPTED MANUSCRIPT composed of BF4- and PF6- could not dissolve cellulose, while those composed of Cl-, Br- and SCN- could. It ascribes to, on the one hand, the stronger ability of accepting

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hydrogen atoms and destroying the hydrogen bonds among inter- or intra-cellulose molecules for Cl-, Br- and SCN-. On the other hand, the concentration of Cl- in

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BmimCl is much higher than that in traditional solvents. Xu and coworkers[22]

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studied the dissolving ability of ILs that are composed of Bmim+ and different anions for cellulose. They found that the order of the dissolving ability is [Bmim][CH3COO]>

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[Bmim][HSCH2COO]>[Bmim][HCOO]>[Bmim][(C6H5)COO]>

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[Bmim][H2NCH2COO] >[Bmim][HOCH2COO]>[Bmim][CH3CHOHCOO]>[Bmim][ N(CN)2]. Namely, the stronger the ability of accepting hydrogen atoms for the anion of IL is, the easier the IL dissolves cellulose. This result is consistent with that

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Swatloski and coworkers[4] obtained. Data obtained from molecular dynamics simulation and theoretical calculation

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have demonstrated the hydrogen bonding and Van der Waals interactions between C2 in imidazole ring and biopolysaccharides[23, 24], indicating that the solubility of cellulose in ILs is influenced by not only anion ions, but also cation ions. The formation of C2-H···Cl bond and the ionic pair requires an energy of 90.35 kcal/mol, indicating that the effective hydrogen bond and the strong Coulomb interaction between the cation and anion are key factors for the dissolution of cellulose in IL. The mean energies for Coulomb interaction are -483.58, -802.76 and -1154.41 kJ/mol for cellulose oligomers with a degree of polymerization (DP) 2, 4 and 6, respectively, which are almost twice greater than those for van der Waals interaction (-204.23 kJ/mol for DP=2, -308.41 kJ/mol for DP=4 and -514.32 kJ/mol for DP=6)[24]. Liu et al. found that the total interaction energy between C2mim+ and cellulose with DP of 10 is ca. -23 kcal/mol (-6 kcal/mol is from electrostatic interaction and -17.3 kcal/mol 4

ACCEPTED MANUSCRIPT from van de Waals interaction energy between C2mim+ and cellulose). Meanwhile, the total interaction energy between cellulose and OAc- is -52.4 kcal/mol (-52.6

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kcal/mol is from electrostatic interaction and +0.56 kcal/mol from van der Waals interaction). That is, the anions form strong hydrogen bonds with strong electrostatic

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interactions with cellulose, while the cations with strong van der Waals

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interactions[25].

Data from 13C and 35/37Cl relaxation illustrate the hydrogen bond between Cl- and

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cellulose, whereas, it is absent between Bmim+ and cellulose[6]. The side chain of IL

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also shows significant impact on the solubility of cellulose. The solubility of cellulose decreases as the side chain of an IL contains hydroxyl, double bond and alkyl groups, respectively [21, 26, 27]. That is, an IL composed of a cation with small volume but

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large polarity shows high dissolving capacity for cellulose, due to the strong interaction between cation and cellulose unit[4, 26]. The longer the alkyl chain, the

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weaker the dissolving capacity of an IL is. It ascribes to the decrease of effective concentration of anion (e.g. Cl-)[4]. The dissolving capacity of ILs with alkyl chain homologues

shows

“odd

and

even”

effect.

Namely,

the

solubility

of

biopolysaccharides in ILs with an even number of carbon chains is larger than that with an odd number of carbon chains[28]. A small amount of water in ILs will decrease the solubility of biopolysaccharides, for the destruction and formation of hydrogen bonds are competitive processes. It is found that an IL cannot dissolve any cellulose while the content of water in it is more than 1.0 wt%[4]. The dissolution rate and solubility of cellulose in ILs could be improved by microwave heating method. The dissolution rate and solubility of cellulose are also influenced by temperature. For instance, cellulose with polymerization degree of 650 can only swell in AmimCl at room temperature, while it can dissolve in AmimCl totally within 30 5

ACCEPTED MANUSCRIPT min at 80 oC, forming 8 wt% “solution”[26]. Zhang and coworkers[26] revealed that the conductivity of AmimCl varies abrupt while the temperature was higher than 43 C, which was caused by completely ionization. At 80 oC, the free Amim+ and Cl-

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o

ions interact with the oxygen and hydrogen atoms, respectively, destroying the

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hydrogen bonds in cellulose, thus dissolving the cellulose in AmimCl (Fig. 2).

cellulose/BmimCl solution through

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Moulthrop and coworkers[29] found that the absence of hydrogen bonds in C NMR method, illustrating the destruction of

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inter- and intra-molecular hydrogen bonds as well as the dissolution mechanism

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proposed by Zhang et al.[26].

The dissolved cellulose could be precipitated when deionized water, ethanol, methanol or acetone is added into cellulose/IL solution[4, 30, 31]. The precipitated

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cellulose is called regenerated cellulose, whose morphology becomes rougher than that of native cellulose [32]. The thermal stability and crystallinity of the regenerated

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cellulose are decreased, while the chemical structure remains almost unchanged[4, 33]. The crystal form of regenerated cellulose is transformed into cellulose II from cellulose I of native cellulose[32]. If the cellulose/BmimCl solution is frozen, followed by solvent exchange and drying at room temperature, porous celluloses (PCs) with densities of 44-88 mg/cm3 and oil adsorption capacities ranging from 9.70-22.40 g/g (oil/PC) could be obtained[34]. 1.2 Modification of cellulose in ionic liquids The formation of homogeneous cellulose/IL solution provides an expedient method for the preparation of cellulose-based materials by homogeneous reaction[35], e.g. cellulose acetate butyrate[4], cellulose lauric acid ester[36] and methyl phenyl amino acids[36]. The cellulose acetate butyrate (CAB) prepared in AmimCl could dissolve in 2-methyl ethyl ketone, 1,2-dichloroethane, ethyl acetate and butyl acetate, 6

ACCEPTED MANUSCRIPT and the solubility increases with the increase of butyryl content in CAB[37]. The thermal decomposition temperature of CAB (334-348 oC) is lower than that of

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cellulose (376 oC). The larger the content of butyryl in CAB is, the lower the thermal decomposition temperature is. It ascribes to the weakened hydrogen bonds among

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inter- or intra-molecules[38].

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Water soluble cellulose derivatives could be prepared through reactions between cellulose and urea, phthalic anhydride, maleic anhydride or butyloxirane propyl ether

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in BmimCl[39]. The reactions are approved by data of FTIR, 1H NMR and TGA. The

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solubility of these derivatives in water could be up to 25 wt%. Cellulose macromolecular initiator could be prepared through reaction between cellulose and 2-bromopropiomyl bromide in AmimCl, providing the precondition for the

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preparation of cellulose derivates through atom transfer radical polymerization method[5].

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In addition, cellulose derivatives could be prepared in ILs through homogenous reaction under the assistance of organic catalyst (including ILs themselves). Sun and coworkers

found

that

both

4-dimethylaminopyridine

(DMAP)[40]

and

N-bromosuccinimide (NBS)[41] could catalyze the modification of succinic anhydride on cellulose in BmimCl under homogeneous reaction system, and obtained succinylated cellulose with degree of substitution (DS) in the range of 0.24-2.31. The DS is higher than that without catalyst under the same reaction conditions. The

13

C

NMR chemical shifts at 67.8 (C2 and C3), 61.1 and 59.8 (C6) ppm disappeared, indicating that the modifying reaction takes place at C2, C3 and C6 sites. An IL can also be used as a catalyst for their special advantages, such as less corrosion, special capability of swelling cellulose and breaking the inter- and intramolecular hydrogen bonds[42].

Zhang et al.[43] synthesized cellulose acetate by environment friendly 7

ACCEPTED MANUSCRIPT solvent-free method using small amount of 1-vinyl-3-(3-sulfopropyl) imidazolium hydrogensulfate (SO3H-functionalized acidic IL, abbreviated as VSimHSO4),

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N-methyl-imidazolium chloride (HmimCl) or N-methyl-imidazolium bisulfate (HmimHSO4) as catalysts. The DS values of resulting cellulose acetate are

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controllable, ranging from 1.13 to 2.95, by changing the reaction time and the amount

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of ILs. It is considered that the dual-function of swelling and catalyzing of acidic ILs play an important role in producing “quasi-homogeneous” acetylation system as well

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as controlling the DS of cellulose acetate. The structure and acidity of ILs play key

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roles on their catalytic activity. The catalytic activities are in the order of CF3SO3- > HSO4-> OAc-, which is in good agreement with their acidity order [13]. Functionalized cellulose derivatives could also be prepared in ILs. For instance,

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cellulose-based amphiphilic surfactant has been prepared in BmimCl by esterification and graft polymerization of the ε-caprolactone monomer onto the hydroxyl group of

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cellulose as well as sulphonation with sulfamic acid[44]. The cellulose-based amphiphilic surfactant (cellulose-g-poly-caprolactone) lowers surface tension of aqueous solution to 48.62 mN/m, and its critical micelle concentration is 0.65 wt% ata grafting ratio of 25.40%. The membrane induced by alcohol shows excellent hydrophobic property. The contact angle between a droplet of water and the surface of membrane is up to 90.84o. This study may promote the utilization of natural and biodegradable surface active materials with improved properties as surfactants. Cellulose-g-2-(dimethylamino)

ethylmethacrylate

(cellulose-g-DMAEMA)

is

prepared by grafting polymerization of DMAEMA on cellulose in BmimCl under the assistance of microwave irradiation[45]. The cellulose-g-DMAEMA copolymer presents dual pH and salinity-responsive properties. It ascribes to the protonation of DMAEMA at low pH and deprotonation at high pH, resulting in the transformation of 8

ACCEPTED MANUSCRIPT hydrophilic polymer chains into hydrophobic ones as well as the variation of electrostatic repulsion among ionized DMAEMA.

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1.3 Dissolution and precipitation of chitosan in ionic liquids Chitosan (CS), fully or partically deacetylated product of chitin, is the second

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most abundant polysaccharide after cellulose, and the second most abundant natural

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nitrogen-containing biopolymer after proteins. It has gained tremendous interest in many fields, such as pharmaceutical, food, textile, daily chemical and papermaking

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for its biocompatibility, biodegradability, hygroscopicity, antimicrobial activity and

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fiber-film forming properties[46, 47]. Being different from the structure of cellulose, the group in C2 of chitosan skeleton is –NH2, forming more hydrogen bonds, thereore

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broad utilization of chitosan.

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making chitosan insoluble in water and basic solution. The insolubility restricts the

Inspired by the dissolution and modification of cellulose in ILs, those of chitosan

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in ILs have been explored, and the commonly used ILs are shown in table 1. In 2006, Xie et al.[48] found that chitosan could dissolve in BmimCl with concentration up to 10 wt% at 110 oC. They considered that BmimCl destroys the hydrogen bonds of inter- or intra-molecules of chitosan, forming the chitosan dissolution. As the first document studied the dissolution of chitosan in ILs, it had important theoretical significance.

The

following

1-ethyl-3-methylimidazolium

researches

acetate

showed

(EmimAc),

that

ILs,

such

as

1-butyl-3-methylimidazolium

acetate (BmimAc), and 1-allyl-3-methylimidazolium chloride (AmimCl) all show excellent dissolving capacity for chitosan, and the concentration of chitosan in EmimAc could be up to 15 wt%. The order of the dissolving capacity is EmimAc>BmimAc>AmimCl>BmimCl[17].

The

dissolving

capacity

of

1-butyl-3-methylimidazolium bromide (BmimBr) for chitosan is smaller than that of 9

ACCEPTED MANUSCRIPT BmimCl[49]. The influencing regularity of carboxylic acid anions with different structure of ILs on the dissolving capacity for chitosan is similar to that for cellulose.

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The dissolving capacity of an IL for biopolymers is closely related to the ability of accepting hydrogen atoms to form hydrogen bonds of anion[26, 27]. The Ac- is more

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prone to form hydrogen bond with –OH or –NH2 than Cl-. Therefore, the dissolving

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capacity of EmimAc and BmimAc are larger than that of AmimCl and BmimCl for chitosan. The dissolving capacity of carboxylic acid anion based ILs is also

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influenced by the branched group on carboxylic acid anion, for the interaction

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between carboxylic acid anion and hydrogen is weak. The influencing regularity of cation in IL on the dissolving capacity for chitosan is also similar to that for cellulose. The amino groups in chitosan are more prone to forming hydrogen bonds than

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the hydroxyls; therefore, the network structure in chitosan/IL solution is more complex than that in cellulose/IL solution[50]. Zhu and coworkers[17] considered that

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the anions of IL could interact with hydrogen atoms in both hydroxyl and amine groups; meanwhile, the cations could interact with oxygen atom in hydroxyl group and nitrogen atom in –NH2 group, destroying the hydrogen bonds in chitosan and making it dissolve in IL. The molecular structure of EmimAc and proposed dissolution mechanism of chitosan in EmimAc are presented in Fig. 3. The mechanism is validated by 13C NMR data[51]. The 13C NMR chemical shift of C12 in BmimAc moves to the low field due to the interaction between oxygen in carboxylic acid ion and hydrogen atoms in –OH and –NH2 of chitosan. On the contrary, the 13C NMR chemical shift of C2 in Bmim+ moves to the high field due to the interaction between Bmim+ and oxygen or nitrogen atoms in –OH and –NH2 of chitosan. The maximum concentration of chitosan solubilized in 1,3-dimethyl imidazole chloride (DmimCl)/1,3-methyl hydrogen imidazole chiloride (HmimCl) mixed ILs at 10

ACCEPTED MANUSCRIPT a weight ratio of 9/1 is up to 15 wt%[17]. The concentration is larger than that solubilized in AmimCl/HmimCl mixed ILs. However, it is difficult to separate the

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two ILs for their high boiling points and non-volatility, namely, the utilization of mixed ILs is limited. The dissolving capacity of Glycine based IL for chitosan is

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weaker than that of imidazole based IL, and Glycine based IL degrades chitosan

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severely[52].

The dissolved chitosan could be precipitated by adding large amount of water

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into chitosan/IL solution. The precipitated chitosan is called regenerated chitosan.

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During the dissolution of chitosan in IL, there is no derivatization reaction and ammonium salt. α-Typed chitosan is dissolved in IL However, β-typed one is regenerated, indicating the destruction of hydrogen bonds in chitosan molecules

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during their dissolution[17, 51]. The decomposition temperature (td) of regenerated chitosan is lower than that of raw chitosan, and the td of chitosan regenerated from Ac-

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based IL is much lower than that of regenerated from Cl- based IL, illustrating that the destructing degree of hydrogen bonds for Ac- is severer than that for Cl-[17, 51]. 1.4 Modification of chitosan in ionic liquids Along with the research of the ionic liquid dissolving chitosan, the modification of chitosan in an IL through homogenous reaction has attracted much attention. Wei and

coworkers[53]

prepared

chitosan-IL

1-carboxymethyl-butyl-3-methylimidazolium

grafted chloride

polymer

(CS-IL)

(CmimCl)

in

through

homogenous reaction between carboxyl and –NH2 at 100 oC. The CS-IL has excellent adsorption capacity for Cr2O72- (0.422 mmol/g) and PF6- (0.840 mmol/g) anions. The adsorption capacity increases with the grafted degree of CmimCl, as well as the decreases of aqueous pH. It ascribes to the protonation of –NH2 at low pH, which is inclined to interact with anions through electrostatic force. The CS-IL adsorbed anion 11

ACCEPTED MANUSCRIPT aggregates in aqueous solution and precipitates from bulk solution, in favor of being separated. Wang and coworkers[54] prepared polycaprolactone grafted chitosan

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(CS-g-PCL) in EmimCl through the reaction between polycaprolactone and –NH2 in chitosan with stannous octoate as catalyst at 100 oC. The structure and grafting degree

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of CS-g-PCL could be modulated by changing the reaction conditions and reactant

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materials ratio. The glass transition temperature (Tg) of CS-g-PCL is lower than that of CS, due to the change of polymer crystallinity and polymer composition. The Tg of

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PCL is about -60 oC. It provides a novel method for the preparation of CS-g-PCL that

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could be used in tissue engineering, drug and gene transfer. Wang and coworkers[55] prepared two kinds of monomethyl fumaric acid (MFA) modified chitosan (MF-chitosan) with different chemical structures in ILs. One is an MF-chitosan salt

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that composes chitosan cation and MFA anion, synthesized in a mixture of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide.

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In MF-chitosan molecules, MFA and chitosan are covalently attached. The other is an MF-chitosan amide that synthesized in EDC. The antioxidant activity of the two chitosan derivatives is improved due to the introduction of MFA. In our previous work[56], N-[(2-hydroxyl)-propyl-3-trimethyl ammonium] chitosan chloride (HTCC) is synthesized through nucleophilic substitution of 2,3-epoxypropyltrimethyl ammonium

chloride

(EPTAC)

onto

chitosan,

using

ionic

liquid

of

1-allyl-3-methylimidazole chloride (AmimCl) as a homogeneous and green reaction media. Data of quantum chemistry calculations revealed that the C atom with less steric hindrance in EPTAC can be attacked by –NH2 (assigned as path I), -CH2OH (path II) and –OH (path III) groups in chitosan, and the barriers are 30.08 kcal/mol, 31.99 kcal/mol and 41.87 kcal/mol, respectively. The overall reactions are exothermic by 59.48 kcal/mol for path I, 49.72 kcal/mol for path II and 56.05 kcal/mol for path III. 12

ACCEPTED MANUSCRIPT That is, path I is more favorable, which is consistent with the results of the experiments. The crystalline degree, decomposition temperature, decomposition

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enthalpy and glass transition temperature (Tg) decrease due to the introduction of EPTAC, as well as the destruction of inter- and intra-molecular hydrogen bonds

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between and within chitosan molecules. The higher the degree of substitution, the

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lower decomposition temperature, decomposition enthalpy and Tg are. 1.5 Dissolution and modification of starch in ionic liquids

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Starch could also dissolve in many kinds of ILs, which is affected significantly

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by the structure and temperature of ILs[57]. For instance, the concentrations of starch can be up to15 wt% in BmimCl and 20 wt% in AmimCl at 80 oC, 50 wt% in AmimCl at 100 oC, 20 wt% in AmimCl, 10 wt in 1-buty-3-methyl imidazolium dicyanamide

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(BmimDCD), 30 mg/L in 1-methoxy-ethyl-3-imidazole bromide salt (MemimBr) and 0 in 1-methyl imidazole tetrafluoroborate (MimPF4) at 60 oC (table 1) [27, 58-61],

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respectively. The interaction between IL and starch from various sources is different. For example, the molecular weight of cereal amylopectin decreases after being dissolved in IL, whereas, that of potato starch increases slightly. It ascribes to the interaction between phosphate anion in potato starch and cation of IL, resulting in the increase of molecular weight[62]. The dissolution rate of starch in ILs is affected significantly by heating method. For instance, the starch of wheat, barley, potatoes, rice, corn and waxy can be completely dissolved in IL at 100 oC under ordinary oil bath heating, whereas, they are completely dissolved at 80 oC under microwave heating[63]. Modification of starch in IL possesses several advantages, such as low toxicity, easy recycle and high degree of substitution (DS), compared to traditional solvent (e.g. dimethyl

sulfoxide)[64].

Xie

and

coworkers[64] 13

prepared

starch-phosphate

ACCEPTED MANUSCRIPT derivatives with DS up to 55% in BmimCl through reaction between sodium dihydrogen phosphate (and disodium hydrogen phosphate) and starch, which is much

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higher than that modified in traditional solvent (20%). Fatty acid esters with DS of 28-37% have been prepared by reaction between starch and lauric acid or stearic acid

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using basic catalyst[65]. Acetylated starch with DS of 30-260% and benzoate ester

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have been prepared by reaction between starch dissolved in BmimCl and acetic anhydride, and benzoyl anhydride under catalysis of pyrimidine, respectively[66].

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Starch-g-PS with grafting percentage up to 114% was prepared by homogeneous

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grafting copolymerization in EmimAc[67]. The crystalline structure and morphology of starch are effectively disrupted during the dissolution and modification processes, resulting in amorphous starch with numerous cavities. The starch-g-PS shows thermal

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stability of both the starch and PS. Lehmann and Wolkert[68] demonstrated that the reactivity of hydroxyl at C6 of starch unit is the maximum and that at C3 is the

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minimum in BmimCl. However, Shogren and coworkers[69] considered that the reactivity of hydroxyl in starch depends on the type of IL; for instance, the hydroxyl at C2 is the maximum in 1-butyl-3-methylimidazolium dicyanamide acetylated (BmimDCA).

1.6 Dissolution and modification of β-cyclodextrin in ionic liquids, and the application of modified-β-cyclodextrin Cyclodextrins (CD) are cone-shaped macrocycles (Fig. 4A) composed of 6 (α-CD), 7 (β-CD), 8 (γ-CD) or more D-glucopyranoside units linked by α-(1→4)-glucosidic bonds[70, 71]. The CDs have a hydrophobic inner cavity and hydrophilic outside surface (Fig. 4B). A high electrodensity of the inner CD cavity lends it some Lewis base characters[72]. The 2- and 3-hydroxy groups of glucopyranoside units are involved in hydrogen bondings. In the molecule of β-CD, 14

ACCEPTED MANUSCRIPT these H-bonds form the complete integrated belt providing rather rigid structure (Table 2).

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The dissolving capacity of dimethylacetamide (DMAC)/IL mixed system for β-CD is larger than that of LiCl/DMAC mixed system (as shown in table 1). The

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dissolving capacity of DMAC/IL for β-CD increases with the rising of temperature.

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However, an opposite trend is observed in LiCl/DMAC systems. At the same temperature, the dissolving capacity for β-CD of DMAC/ILs composed of Cl- or Br- is

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larger than that of DMAC/ILs composed of BF4- or PF6-[73].

β-CD

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Solutions of β-CD/IL have important applications. For example, solutions of and 1,11-bis(3-methyl-imidazole) 3,6,9-trioxane

bis (trifluoromethane)

sulfonimide (Mim2PEG3-2NTf2), 1,12-bis (3- methylimidazole) 3,6,9-trioxane bis

D

imide

(TPP2C12-2NTf2)

of

six

ILs

dissolved

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(trifluoromethanesulfonyl)

permethylated single-6-butylimidazolium cyclodextrin (BIM-BPM) and methylated

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single-6-propyl phosphorus cyclodextrin (TPP-BPM) can be used as a kind of novel gas chromatography chiral stationary phases[74].

2 Dissolution and separation of lignin in ionic liquids 2.1 Dissolution of lignin in ionic liquids Lignin, with amphetamine skeleton and content accounts for 50 wt%, is the only biopolymer containing aromatics. Lignin is an integral part of the cell walls and fills the spaces between cells, conferring the strength to the cell wall and sticking fibers in the plant tissues. Lignin contains three monomers, i.e. guaiacyl (R1=H, R2=OMe, G-lignin), syringyl (R1=R2=OMe, S-lignin), and 4-hydroxyphenyl (R1=R2=H, H-lignin) lignin subunits (Fig. 5), which provide lignin with complex structure and stable physico-chemical properties through inter-linkages of C-C or C-O bonds[47]. 15

ACCEPTED MANUSCRIPT Given the increasing shortage of petroleum resources, it is of great significance to make full use of aromatic functional groups in lignin molecule in the preparation of

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aromatic compounds. The fuel derived from lignin is known as the third generation biofuels, which has received much attention in recent years[75].

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To improve the lignin quality, pretreatment is one of the most important

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operation units in biorefinery process[76], among which ILs are used to pretreat lignin. Pu and coworkers[77] revealed that ILs, such as [Hmim][CF3SO3], [Mmim][MeSO4]

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and [Bmim][MeSO4] could dissolve lignin with concentration of up to 20 wt%. IL

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composed of Cl- or Br- also show strong dissolving capacity for lignin. For instance, BmimCl and AmimCl have good solubility for Norway spruce wood fiber, southern pine fiber and Eucalyptus[78, 79]. The anion of IL has significant effect on the

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dissolving capacity. The order of the dissolving capacity for ILs with different anions is [MeSO4] >Cl->Br->> [PF6][77]. The smaller the wood density and particle size are,

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the larger the solubility of the lignin in ILs is (table 1). 2.2 Degradation and extraction of lignin in ionic liquids Sun and coworkers[80] extracted and separated lignin within a mixture of IL and organic solvent. The extraction efficiency of lignin from IL/toluene mixture yields up to 15.4 wt%, and the recycling utilization rate of used IL is up to 94.6%. Microwave assisted heating method could shorten the lignin extracting time and increase the yield of aromatic ring in the product[81]. Results of FTIR, 1H NMR and

13

C NMR show

that the structures of lignin extracted within EmimAc[82] and EmimCl[83] are the same to that of untreated lignin. Data of GPC indicate that the content of G-lignin increases when the lignin is extracted within ILs. Semi cellulose and lignin could be extracted from oak tree using MimCl as a catalyst and an extractant under mild conditions, after it is dissolved in EmimAc[84]. During the dissolving and extracting 16

ACCEPTED MANUSCRIPT processes, some amount of lignin is degraded. A 50 % and 45 % reduction of methoxy groups are observed after lignin regeneration from BmimCl and EmimOAc,

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respectively[85]. It is found that acidic ILs with Hammett acidity of 1.48-2.08, such as 1-H-3-methylimidazolium hydrogen chloride (MimCl), 1-H-3-methylimidazolium

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bromide (MimBr), 1-butyl-3-methylimidzaolium hydrogen sulfate (BmimHSO4), hydrogen

bisulfate

1-H-3-methylimidazolium

tetrafluoroborate

(MimBF4)

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1-H-3-methylimidazolium

(MimHSO4)

would

catalyze

and lignin

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degradation. The anions of ILs show significant influence on the degradation of lignin,

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and the order of anions degrading lignin molecules is sulfates > lactate > acetate > chlorides > phosphates, while cations are held constant. It ascribes to the destruction of hydrogen bonds of inter-lignin molecules via either the catalytic function of anion

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or through the nucleophilic attack of β-O-4 ether bonds. Different anions could cause breakage of different linkages with lignin [86, 87]. Casas and coworkers[88] revealed

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that hydrogen bonds play a key role in the dissolution of cellulose and lignin in ILs through model of Cosmo-Rs, while the van der Waals force shows little impact. This result is consistent with that Blair and coworkers deduced.

3 Dissolution and modification of protein in ionic liquids 3.1 Dissolution and regeneration of protein in ionic liquids Under a certain temperature, leather waste can also be dissolved in ILs while the collagen remains undamaged, which provides a promising method in dealing with leather waste[89]. The dissolution rate and solubility of collagen and elastin in EmimCl are small, which is due to the super helical structure formed by the three strands[90]. Meng and coworkers[91] revealed that the crystal structure and triple helix structure of the collagen fibers could be completely destroyed during dissolution 17

ACCEPTED MANUSCRIPT in BmimCl and regeneration. The regeneration method affected the film-forming property and thermal stability of collagen significantly, based on which the utilization

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field of collagen could be expanded. Silk protein, a kind of natural protein, is a major component of silk and

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accounted for about 75 wt% of the total weight. It has been attracting great interest in

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the field of biology and medicine in recent years for its good biocompatibility, excellent physical and chemical properties[92]. Silk protein is easy to dissolve in ILs

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such as BmimCl, DmbimCl and EmimCl at 100 oC and the maximum concentration in

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EmimCl is up to 23.3 wt% (table 1). Although both the anions and cations of ILs show notable influence on the solubility of silk protein, more influence of anions is boserved[73, 93]. XRD results showed that the IL could destroy the hydrogen bond in

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the crystalline region of silk; and Raman spectra showed that acetonitrile and methanol can be used as coagulants for silk protein regeneration, whereas water is

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inappropriate[93]. The solubilized silk fibroin in AmimCl or HemimCl at 80-100 oC could be regenerated by adding ethanol or butanol. The conformation of the regenerated silk fibroin is mainly β-sheet structure. The thermal stability of regenerated silk fibroin is slightly lower than that of the natural one, but the thermal decomposition residue is more than that of natural one. Keratin solution can be used not only for spinning, but also as a finishing agent for textile. Therefore, the keratin solution is of broad application prospect. There are plenty of –s–s– bonds in keratin, which combine each other among keratin protein macromolecules to form a stable three-dimensional (3D) network structure. The unique structure makes natural keratin insoluble in a variety of solvents. BmimCl could destroy the 3D network structure of wool keratin and dissolve it, during which

18

ACCEPTED MANUSCRIPT process the α-helix structure is destroyed. The thermal stability of the regenerated wool keratin is better than that of the native one[66].

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3.2 Modification of silk fibroin in ionic liquids Homogeneous chemical modification of silk fibroin by chlorosulfonic acid has

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been processed in BmimCl under mild condition[94]. The new adsorption peaks at

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1046, 866 and 620 cm-1 belong to the characteristic peaks of sulfate groups. The significantly changed peaks at 4.40 and 3.89 ppm in 1H NMR spectra indicate that the

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reaction sites occurred mainly at the tyrosine and serine residues. The sulfation

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efficiency is up to 95.8% while the modification is processed at 0-5 oC for 4 h. ILs have also been widely used in enzymatic catalysis to provide enzymes with excellent activity and stability. More chaotropic cation and kosmotropic anion result in a higher

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modification degree (MD), for the activated cation will be easy to graft onto the enzyme with a more kosmotropic anion by preferential hydration. The hydrolytic

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activity of the grafted lipase is improved, as well as the thermal stability and enantioselectivity because of the protection of active conformations after high degree modification[95]. Doumèche revealed that the lower steric hindrances induced by the cations, as well as the alkyl chain flexibility play a key role in the modification[96, 97].

4 Conclusions and prospects In this review, the dissolution, regeneration and modification or degradation of cellulose, chitosan, starch, β-CD, lignin and protein are summarized. The influencing factors on the dissolution of biopolymer are introduced, such as the kinds, volume and the ability to accept hydrogen atom of cation and anion of ILs, the temperature, the heating method, and the source of biopolymers. Based on the analysis of data 19

ACCEPTED MANUSCRIPT obtained from different methods, the dissolution mechanisms of cellulose and chitosan are proposed. The physicochemical properties including conformation,

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thermal decomposition temperature, glass-transition temperature and morphology of the regenerated biopolymers are compared with natural ones, and the possible reasons

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are proposed. The modification of cellulose, chitosan, starch, β-CD and protein are

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summarized. The influencing factors, such as kinds of ILs, temperature, time and heating method on the degree of substitution are introduced, as well as the properties

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and potential utilization of modified biopolymers. Based on the data obtained from

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various methods, the reactivities of functional groups (eg. -OH and -NH2) are compared. The influencing factors on degradation of lignin in ILs are also introduced. ILs, as a new generation solvent for natural polymers, provide a new platform for

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the efficient use and transformation of high value derivative products of biopolymers. However, there are also several problems to be solved, such as (i) the toxicity,

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biodegradability and the effect on health of human beings is unclear, (iii) The dissolving mechanisms of starch, β-CD, lignin and protein, as well as the reaction mechanisms of biopolymers in ILs are to be further illustrated, (iv) the physico-chemical properties of biopolymer/IL solution, the relationship between the properties and the structure of biopolymer, as well as physico-chemical properties of biopolymer derivatives are to be studied in detail. Nevertheless, with the booming of studies on the generation and utilization of high quality derivatives, the problems mentioned above will be solved. The theoretical knowledge of biopolymers in ILs will be established, building the foundation for their application in fields of material, life, information, and environment sciences.

20

ACCEPTED MANUSCRIPT Acknowledgements The authors acknowledge the financial support from National Natural Science Foundation of China (21306092 and 21376125), Science and Technology Plan Project for Universities of Shandong Province (J12LA02) and the support of Program for Scientific Research

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Innovation Team in Colleges and Universities of Shandong Province.

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References

[1] J.M. Raquez, M. Deléglise, M.F. Lacrampe, P. Krawczak, Prog. Polym. Sci. 35 (2010)

SC

487-509.

[2] A.S. Amarasekara, L.D. Williams, C.C. Ebede, Carbohyd. Res. 343 (2008) 3021-3024.

NU

[3] M.C. Gómez-Guillén, M. Pérez-Mateos, J. Gómez-Estaca, E. López-Caballero, B. Giménez, P. Montero, Trends Food Sci. Technol. 20 (2009) 3-16.

MA

[4] R.P. Swatloski, S.K. Spear, J.D. Holbrey, R.D. Rogers, J. Am. Chem. Soc. 124 (2002) 4974-4975.

D

[5] X. Sui, J. Yuan, M. Zhou, J. Zhang, H. Yang, W. Yuan, Y. Wei, C. Pan, Biomacromol. 9

TE

(2008) 2615-2620.

[6] R.C. Remsing, G. Hernandez, R.P. Swatloski, W.W. Massefski, R.D. Rogers, G. Moyna, The J.

AC CE P

Phys. Chem. B, 112 (2008) 11071-11078. [7] A. Ibn Yaich, U. Edlund, A.-C. Albertsson, Biomacromol. 13 (2012) 466-473. [8] H. Geng, Z. Yuan, Q. Fan, X. Dai, Y. Zhao, Z. Wang, M. Qin, Carbohyd. Polym. 102 (2014) 438-444.

[9] R.M. West, M.H. Tucker, D.J. Braden, J.A. Dumesic, Catal. Commun. 10 (2009) 1743-1746. [10] F. Tao , H. Song, L. Chou, ChemSusChem, 3 (2010) 1298-1303. [11] F. Tao, H. Song, J. Yang, L. Chou, Carbohyd. Polym. 85 (2011) 363-368. [12] F. Tao, H. Song, L. Chou, Bioresour. Technol. 102 (2011) 9000-9006. [13] Y. Shen, J.K. Sun, Y.X. Yi, B. Wang, F. Xu, R.C. Sun, Bioresour Technol, (2015) 10.1016/j.biortech.2015.1005.1080. [14] R.d.C.L.B. Rodrigues, G.J.M. Rocha, D. Rodrigues Jr, H.J.I. Filho, M.d.G.A. Felipe, A. Pessoa Jr, Bioresour. Technol. 101 (2010) 1247-1253. [15] S. Saka, T. Ueno, Cellulose, 6 (1999) 177-191. 21

ACCEPTED MANUSCRIPT [16] B. Ma, M. Zhang, C. He, J. Sun, Carbohyd. Polym. 88 (2012) 347-351. [17] W. Xiao, Q. Chen, Y. Wu, T. Wu, L. Dai, Carbohyd. Polym. 83 (2011) 233-238. [18] C. Stefanescu, W.H. Daly, I.I. Negulescu, Carbohyd. Polym. 87 (2012) 435-443.

PT

[19] C. Graenacher, in: U.S. Patent (Ed.), 1943, 19431761934.

RI

[20] O.A. El Seoud, A. Koschella, L.C. Fidale, S. Dorn, T. Heinze, Biomacromol. 8 (2007) 2629-2647.

SC

[21] S. Zhu, Y. Wu, Q. Chen, Z. Yu, C. Wang, S. Jin, Y. Ding, G. Wu, Green Chem. 8 (2006) 325-327.

NU

[22] A. Xu, J. Wang, H. Wang, Green Chem. 12 (2010) 268-275.

[23] T.G.A. Youngs, C. Hardacre, J.D. Holbrey, J. Phys. Chem. B, 111 (2007) 13765-13774.

MA

[24] H. Xu, W. Pan, R. Wang, D. Zhang, C. Liu, J. Comput. Aided Mol. Des. 26 (2012) 329-337. [25] Hanbin Liu, Kenneth L. Sale, Bradley M. Holmes, Blake A. Simmons, S. Singh, J. Phys.

D

Chem. B, 114 (2010) 4293-4301.

TE

[26] H. Zhang, J. Wu, J. Zhang, J. He, Macromol. 38 (2005) 8272-8277. [27] Y. Fukaya, A. Sugimoto, H. Ohno, Biomacromol. 7 (2006) 3295-3297.

AC CE P

[28] T. Erdmenger, C. Haensch, R. Hoogenboom, U.S. Schubert, Macromol. Biosci. 7 (2007) 440-445.

[29] J.S. Moulthrop, R.P. Swatloski, G. Moyna, R.D. Rogers, Chem. Commun. (2005) 1557-1559. [30] C. Michels, B. Kosan, Lenzinger Berichte, 84 (2005) 62-70. [31] B. Kosan, C. Michels, F. Meister, Cellulose, 15 (2008) 59-66. [32] Z. Liu, X. Sun, M. Hao, C. Huang, Z. Xue, T. Mu, Carbohyd. Polym. 117 (2015) 99-105. [33] R. Vanholme, K. Morreel, J. Ralph, W. Boerjan, Curr. Opin. Plant Biol. 11 (2008) 278-285. [34] X. Liu, P.R. Chang, P. Zheng, D.P. Anderson, X. Ma, Cellulose, 22 (2014) 709-715. [35] L. Feng, Z.-l. Chen, J. Mol. Liq. 142 (2008) 1-5. [36] S. Barthel, T. Heinze, Green Chem. 8 (2006) 301-306. [37] Y. Cao, H. Li, J. Zhang, Ind. Eng. Chem. Res. 50 (2011) 7808-7814. [38] K.J. Edgar, K.M. Arnold, W.W. Blount, J.E. Lawniczak, D.W. Lowman, Macromol. 28 (1995) 4122-4128. 22

ACCEPTED MANUSCRIPT [39] Y. Zhang, H. Li, X. Li, M.E. Gibril, M. Yu, Carbohyd. Polym. 99 (2014) 126-131. [40] W.Y. Li, A.X. Jin, C.F. Liu, R.C. Sun, A.P. Zhang, J.F. Kennedy, Carbohyd. Polym. 78 (2009) 389-395.

PT

[41] C. Liu;, A. Zhang;, W. Li;, F. Yue;, R. Sun, J. Agr. Food Chem. 57 (2009) 1814-1820.

RI

[42] D. Groff, A. George, N. Sun, N. Sathitsuksanoh, G. Bokinsky, B.A. Simmons, B.M. Holmes, J.D. Keasling, Green Chem. 15 (2013) 1264-1267.

SC

[43] D. Tian, Y. Han, C. Lu, X. Zhang, G. Yuan, Carbohyd. Polym. 113 (2014) 83-90. [44] F. Yang, Y.-n. Liu, J.-l. Yu, H.-p. Li, G. Li, Appl. Surf. Sci. 345 (2015) 187-193.

NU

[45] X. Wei, G. Chang, J. Li, F. Wang, L. Cui, T. Fu, L. Kong, J. Polym. Res. 21 (2014). [46] A. Wang, Chitin Chemistry, Chemical Industry Press, Beijing, 2008.

MA

[47] J. Tingda, Chitosan, Chemical Industry Press, 2001.

[48] H. Xie, S. Zhang, S. Li, Green Chem. 8 (2006) 630-633.

D

[49] Z. Zhang, C. Li, Q. Wang, Z.K. Zhao, Carbohyd. Polym. 78 (2009) 685-689.

TE

[50] Y. Wu, T. Sasaki, S. Irie, K. Sakurai, Polymer, 49 (2008) 2321-2327. [51] Q. Chen, A. Xu, Z. Li, J. Wang, S. Zhang, Green Chem. 13 (2011) 3446-3452.

AC CE P

[52] Liang Sheng, Ji Huanhuan, Li Lu, Yu Shitao, Liu Fusheng, X. Congxia, Polym. Mater. Sci. Eng. 26 (2010) 70-72.

[53] Y. Wei, W. Huang, Y. Zhou, S. Zhang, D. Hua, X. Zhu, Int. J. Biolog. Macromol. 62 (2013) 365-369.

[54] Z. Wang, L. Zheng, C. Li, D. Zhang, Y. Xiao, G. Guan, W. Zhu, Carbohyd. Polym. 94 (2013) 505-510. [55] G. Xu, L. Deng, X. Wen, P. Pi, D. Zheng, J. Cheng, Z. Yang, J. Coat Technol. Res. 8 (2011) 401-407. [56] X. Yang, C. Zhang, C. Qiao, X. Mu, T. Li, J. Xu, L. Shi, D. Zhang, Carbohyd. Polym. 130 (2015) 325-332. [57] K. Wilpiszewska, T. Spychaj, Carbohyd. Polym. 86 (2011) 424-428. [58] A. Biswas, R.L. Shogren, D.G. Stevenson, J.L. Willett, P.K. Bhowmik, Carbohyd. Polym. 66 (2006) 546-550. 23

ACCEPTED MANUSCRIPT [59] Q. Xu, J.F. Kennedy, L. Liu, Carbohyd. Polym. 72 (2008) 113-121. [60] Q. Xu, Q. Wang, L. Liu, J. Appl. Polym. Sci. 107 (2008) 2704-2713. [61] N. Kimizuka, T. Nakashima, Langmuir, 17 (2001) 6759-6761.

PT

[62] D.G. Stevenson, A. Biswas, J.-l. Jane, G.E. Inglett, Carbohyd. Polym. 67 (2007) 21-31.

509-516.

SC

[64] W. Xie, L. Shao, Starch - Stärke, 61 (2009) 702-708.

RI

[63] J. Kärkkäinen, K. Lappalainen, P. Joensuu, M. Lajunen, Carbohyd. Polym. 84 (2011)

[65] W. Xie, Y. Wang, Starch - Stärke, 63 (2011) 190-197.

NU

[66] H. Xie, S. Li, S. Zhang, Green Chem. 7 (2005) 606-608.

[67] Y. Men, X. Du, J. Shen, L. Wang, Z. Liu, Carbohyd. Polym. 121 (2015) 348-354.

MA

[68] A. Lehmann, B. Volkert, J. Appl. Polym. Sci. 114 (2009) 369-376. [69] R.L. Shogren, A. Biswas, Carbohyd. Polym. 81 (2010) 149-151.

D

[70] J. Szejtli, Chem. Rev. 98 (1998) 1743-1754.

TE

[71] T. Linhui, Cyclodextrin chemistry: basic and applied, Science press, Beijing, 2001. [72] X. Yang, Q. Wang, H. Yu, Russ. Chem. Bull. 63 (2014) 555-560.

AC CE P

[73] Y. Yu, J. Li, Y. Sun, Q. Liang, X. Peng, Y. Liu, Y. Hu, Pet. Sci., 5 (2008) 263-268. [74] K. Huang, X. Zhang, D.W. Armstrong, J. Chromatogr. A, 1217 (2010) 5261-5273. [75] Y. Li, S. Sarkanen, Macromol. 38 (2005) 2296-2306. [76] A.T.W.M. Hendriks, G. Zeeman, Biores. Technol. 100 (2009) 10-18. [77] Y. Pu, N. Jiang, A.J. Ragauskas, J. Wood Chem. Technol. 27 (2007) 23-33. [78] I. Kilpeläinen, H. Xie, A. King, M. Granstrom, S. Heikkinen, D.S. Argyropoulos, J. Agr. Food Chem. 55 (2007) 9142-9148. [79] B. Li, J. Asikkala, I. Filpponen, D.S. Argyropoulos, Ind. Eng. Chem. Res. 49 (2010) 2477-2484. [80] Y.-C. Sun, J.-K. Xu, F. Xu, R.-C. Sun, Ind. Crop. Prod. 47 (2013) 277-285. [81] A. Casas, M. Oliet, M.V. Alonso, F. Rodríguez, Sep. Purif. Technol. 97 (2012) 115-122. [82] J.-Y. Kim, E.-J. Shin, I.-Y. Eom, K. Won, Y.H. Kim, D. Choi, I.-G. Choi, J.W. Choi, Biores. Technol. 102 (2011) 9020-9025. 24

ACCEPTED MANUSCRIPT [83] D. Yang, L.-X. Zhong, T.-Q. Yuan, X.-W. Peng, R.-C. Sun, Ind. Crop. Prod. 43 (2013) 141-149.

[85] Y. Qu, H. Luo, H. Li, J. Xu, Biotechnol. Rep. 6 (2015) 1-7.

PT

[84] B.J. Cox, J.G. Ekerdt, Biores. Technol. 118 (2012) 584-588.

RI

[86] B.J. Cox, S. Jia, Z.C. Zhang, J.G. Ekerdt, Polym. Degrad. Stabil. 96 (2011) 426-431. [87] A. George, K. Tran, T.J. Morgan, P.I. Benke, C. Berrueco, E. Lorente, B.C. Wu, J.D.

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Keasling, B.A. Simmons, B.M. Holmes, Green Chem. 13 (2011) 3375.

[88] A. Casas, J. Palomar, M.V. Alonso, M. Oliet, S. Omar, F. Rodriguez, Ind. Crop. Prod. 37

NU

(2012) 155-163.

[89] Y. Zhou, B. Cheng, Y. Deng, H. Shang, China Leather, 39 (2010) 22-25.

MA

[90] A. Mantz Robert, M. Fox Douglas, J.M. Green, A. Fylstra Paul, C. De Long Hugh, C. Trulove Paul, in: Zeitschrift für Naturforschung A, 2007, pp. 275.

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[91] Z. Meng, X. Zheng, K. Tang, J. Liu, Z. Ma, Q. Zhao, Int. J. biolog. Macromol. 51 (2012)

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440-448.

[92] H. Zhu, X. Feng, J. Chen, Y. Guo, H. Zhang, Funct. Mater. 39 (2008) 1710-1713.

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[93] D.M. Phillips, L.F. Drummy, D.G. Conrady, D.M. Fox, R.R. Naik, M.O. Stone, P.C. Trulove, H.C. De Long, R.A. Mantz, J. Am. Chem. Soc. 126 (2004) 14350-14351. [94] X. Liu, W. Xu, C. Zhang, H. Liu, J. Fang, Mater. Lett. 143 (2015) 302-304. [95] R. Jia, Y. Hu, L. Liu, L. Jiang, B. Zou, H. Huang, ACS Cat. 3 (2013) 1976-1983. [96] M. Bekhouche, B. Doumèche, L.J. Blum, J. Mol. Cat. B, 65 (2010) 73-78. [97] M. Bekhouche, L.J. Blum, B. Doumèche, ChemCatChem, 3 (2011) 875-882.

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Figure Captions

Fig.1 The linear relationship between the solubility of microcrystalline cellulose in

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RTILs and β values at 70 oC[22].

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Fig. 2 Schematic diagram for dissolution mechanism of cellulose in AmimCl[25].

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mechanism of chitosan in EmimAc[17].

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Fig. 3 Molecular structure of BmimAc[50] and schematic diagram for dissolution

Fig. 4 Schematic diagram of α-CD (A), and Corey-Pauling-Koltun (CPK) models of

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α-, β- and γ-CD (B)[69].

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Fig. 5 Arylpropane fragments of lignin molecule (A) and lignin(B) [46].

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Fig. 1

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Fig. 2

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Fig. 3

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Fig. 4(A)

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Fig. 4(B)

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B

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Fig. 5(A)

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Fig. 5(B)

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ACCEPTED MANUSCRIPT Table Caption

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Table 2 The basic properties of α-, β- and γ-CD[69].

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Table 1 The solubility of biopolymers in ionic liquids under different conditions.

34

Table 1

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ACCEPTED MANUSCRIPT

methoda

solubilityb

Ref.

cellulose

100 oC

10.0

[4]

cellulose

70 oC

3.0

[4]

cellulose

sonication(80 o C)

5.0

[4]

C4mimCl

cellulose

microwave

25.0

[4]

C4mimCl

cellulose

3-5 s pulses

viscous solution

[4]

C4mimBr

cellulose

microwave

7

[4]

C4mimSCN

cellulose

microwave

7

[4]

C4mimBF4

cellulose

microwave

insoluble

[4]

C4mimPF6

cellulose

microwave

insoluble

[4]

C6mimBr

cellulose

100 oC

5

[4]

C8mimBr

cellulose

100 oC

slightly soluble

[4]

biopolymers

C4mimCl C4mimCl

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C4mimCl

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Ionic liquid

35

ACCEPTED MANUSCRIPT cellulose

70 oC

15.5

[22]

C4mimHSCH2COO

cellulose

70 oC

13.5

[22]

C4mimHCHOO

cellulose

70 oC

12.5

[22]

C4mim(C6H5)COO

cellulose

70 oC

12.0

[22]

C4mimH2NCH2COO

cellulose

70 oC

12.0

[22]

C4mimHOCH2COO

cellulose

70 oC

10.5

[22]

C4mimCH3CHOHCOO

cellulose

70 oC

9.5

[22]

C4mimN(CN)2

cellulose

70 oC

insoluble

[22]

AmimCl

Cellulose (DP=650)

80 oC

8 (in30 min)

[26]

cotton linter

80 oC

8

[26]

AmimCl

cellulose

100 oC

10

[27]

AmimFc

cellulose

60 oC

10

[27]

AmimFc

cellulose

85 oC

22

[27]

AmimFc

dextrin

40 oC

25

[27]

AmimFc

inulin

50 oC

25

[27]

AmimFc

amylose

60 oC

20

[27]

AmimFc

xylan

95 oC

20

[27]

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AmimCl

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C4mimCH3COO

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80 oC

4

[27]

C4mimCl

cellulose

100 oC

20

[28]

C7mimCl

cellulose

100 oC

DmimCld

cellulose

110 oC

DmimCl/HmimCle

chitosan

AmimCl/HmimCl

chitosan

BmimCl

chitosan

GlyClg

[28]

22

[17]

110 oC

17

[17]

110 oC

12

[17]

110 oC

10

[48]

chitosan

25 oC

5.00

[52]

25 oC

3.66

[52]

chitosan

25 oC

insoluble

[52]

ProClg

chitosan

25 oC

3.29

[52]

ProNO3g

chitosan

25 oC

3.10

[52]

ProHSO4g

chitosan

25 oC

insoluble

[52]

LysCl2g

chitosan

25 oC

2.53

[52]

Lys(NO3)2g

chitosan

25 oC

2.34

[52]

Lys(HSO4)2g

chitosan

25 oC

insoluble

[52]

BmimCl

starch

80 oC

15

[58]

SC NU

MA

GlyNO3g

TE

chitosan

AC CE P

GlyHSO4g

RI

5

D

PT

AmimFc

37

starch

90 oC

10

[58]

BmimBF4

starch

90 oC

insoluble

[58]

AmimCl

starch

80 oC

20

[59]

AmimCl

starch

100 oC

50

[62]

AmimCOO

amylose

60 oC

20

[27]

MmimBrf

amylose

60 oC

30 mg/L

[61]

BmimCl/DMACh

beta-CD

80 oC

3.9 g/100mL

[73]

LiCl/DMACh

beta-CD

50 oC

3.0 g/100mL

[73]

BmimBr/DMACh

beta-CD

80 oC

3.86 g/100mL

[73]

beta-CD

80 oC

2.68 g/100mL

[73]

BmimPF6/DMACh

beta-CD

80 oC

2.65 g/100mL

[73]

AmimCl

Norway spruce sawdust

110 oC(8h)

8

[78]

BmimCl

Norway spruce sawdust

110 oC(8h)

8

[78]

MmimMeSO4

softwood lignin

50 oC

344 g/L

[77]

HmimCF3SO3

softwood lignin

70 oC

275 g/L

[77]

BmimMeSO4

softwood lignin

50 oC

312 g/L

[77]

BmimCl

softwood lignin

75 oC

13.9 g/L

[77]

RI

SC NU

MA

TE

AC CE P

BmimBF4/DMACh

PT

Bmim dicyanamide

D

ACCEPTED MANUSCRIPT

38

ACCEPTED MANUSCRIPT Bm2imBF4

softwood lignin

70-100 oC

14.5 g/L

[77]

EmimCl

protein

100 oC

23.3

[86]

-the temperature is heated unless special notification;

b

-the solubility is in wt % unless special notification;

d

e

RI

-1-H-3-methylimidazolium chloride;

-1-methoxymethyl-3-methylimidazolium bromide;

MA

f

-1,3-dimethylimidazolium chloride;

SC

-1-allyl-3-methylimidazolium formate;

NU

c

PT

a

-the concentration of the ionic liquids in aqueous is 2 wt%;

h

-the molarity of ionic liquids in DMAC is 0.43 mol/kg.

AC CE P

TE

D

g

39

SC

RI

PT

ACCEPTED MANUSCRIPT

NU

Table 2

β-CD

γ-CD

6

7

8

972

1135

1297

14.5

1.85

23.2

0.47-0.53

0.60-0.65

0.75-0.83

Height of cavity (nm)

0.79±0.01

0.79±0.01

0.79±0.01

Outside diameter of cavity (nm)

1.46±0.04

1.54±0.04

1.75±0.04

Volume of cavity (nm3)

0.174

0.262

0.427

Unit numbers of Glucose Molecular weight

D

Solubility in water

MA

α-CD

AC CE P

TE

Diameter of cavity (nm)

40