[雙語(yǔ)翻譯]--外文翻譯--氨基酸離子液體（原文）

1、Amino Acid Ionic LiquidsHIROYUKI OHNO* AND KENTA FUKUMOTODepartment of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, JapanReceived March 6, 2007ABSTRACT The preparation of ionic

2、liquids derived from amino acids, and their properties, are outlined. Since amino acids have both a carboxylic acid residue and an amino group in a single molecule, they can be used as either anions or cations. These gro

3、ups are also useful in their ability to introduce functional group(s). Twenty different natural amino acids were used as anions, to couple with the 1-ethyl-3-methylimidazolium cation. The salts obtained were all liquid a

4、t room temperature. The properties of the resulting ionic liquids (AAILs) depend on the side groups of the amino acids involved. These AAILs, composed of an amino acid with some functional groups such as a hydrogen bondi

5、ng group, a charged group, or an aromatic ring, had an increased glass transition (or melting) temperature and/or higher viscosity as a result of ad- ditional interactions among the ions. Viscosity is reduced and the dec

6、omposition temperature of imidazolium-type salts is improved by using the tetrabutylphosphonium cation. The chirality of AAILs was maintained even upon heating to 150 °C after acetylation of the free amino group. Th

7、e amino group was also modified to introduce a strong acid group so as to form hydrophobic and chiral ionic liquids. Unique phase behavior of the resulting hydrophobic ionic liquids and water mixture is found; the mixtur

8、e is clearly phase separated at room temperature, but the solubility of water in this IL increases upon cooling, to give a homogeneous solution. This phase change is reversible, and separation occurs again by raising the

9、 temperature a few degrees. It is extraordinary for an IL/water mixture to display such behavior with a lower critical solution temperature. Some likely applications are proposed for these amino acid derived ionic liquid

10、s.1. IntroductionMolten salts at ambient temperature containing only ions and no solvent are referred to as “ionic liquids”.1 Ionic liquids have very different properties from molecular liquids, making them promising sub

11、stances for use in a variety of fields. Variation of the ion species is a great advantage in organic salts. However, in spite of the enormous number of combinations of cation and anion, based on the diversity of organic

12、ions, there are limited types of effective ions for ionic liquids (ILs), havingphysicochemical properties suitable for applications. It is almost impossible to synthesize perfect ILs, which com- bine all desirable proper

13、ties, such as nonvolatility,2 ther- mal stability, low melting temperature, high decomposi- tion temperature, low viscosity,3 and zero toxicity.4 It is therefore necessary to prepare “object-oriented” or “task- specific”

14、 ionic liquids.5 This involves the design of ions to minimum specifications which depend on the purpose or field of application. A relatively straightforward way to prepare functional IL systems is to mix functional mole

15、cules with ILs. This is a convenient and effective method of preparing ILs for certain applications.6 However, these additives will bring their own properties. For example, ILs containing volatile organic compounds would

16、 have considerable vapor pres- sure, which can be a serious drawback in spite of their otherwise excellent properties. It is important to find a general method for the design of various functional or task-specific ILs, a

17、nd to this end, we have been studying amino acid-based ILs. We first reported ILs composed of imidazolium cations and amino acid (AA) anions.7 Since the AA contains both an amino group and a carboxylic acid residue in a

18、single molecule, with various side groups and a chiral carbon atom, AAs are candidates to act as a platform for functional ILs (Figure 1).8 One great merit of the AAs is their low cost. It is easy to obtain pure AAs in l

19、arge quantities at low cost. There are further advantages of AAs, including biodegradability9 and biological acti- vity.10 The availability of AAs as both anions and cations is another advantage. Below, a summary is pres

20、ented of the preparation and properties of ionic liquids composed of amino acids (AAILs). Chemical modifications of the carboxylic acid residue or amino group, for functional design of the ILs, is included.2. Amino Acid-

21、Based Ionic Liquids: A Prototype2.1. Imidazolium Cation-Based AAILs. There are fewer papers on the structural design of anions for forming useful ILs than for cations. We expect there to be a limited number of anion spec

22、ies for ILs with low melting tem- perature (Tm) or easier modification of a series of onium cations. A series of AAs are, however, expected to provide liquid salts with the potential for chemical modification. Since AAs

23、are zwitterionic and are stabilized by electro- static interaction between the carboxylate anion and the protonated amino group, there have been no challengesHiroyuki Ohno graduated from Waseda University in 1976. He rec

24、eived his masters degree in 1978 and his Ph.D. in 1981, both from Waseda University. He worked at Waseda University and Case Western Reserve University from 1981 to 1988. In August 1988 he moved to Tokyo University of Ag

25、riculture and Technology (TUAT) as an associate professor. He was promoted to professor in the Department of Biotechnology in TUAT in 1997. His research interests include molecular assembly, conductive polymers, and ion

26、conductive matrixes. His recent research activities have concentrated on the science and technology of ionic liquids, especially the applications of ionic liquids as solvents, electrolyte solutions, and starting material

27、s for conductive and functional materials in biochemical and bioelectrochemical fields.Kenta Fukumoto obtained his B.A. (2002), M.Sc. (2004), and Ph.D. (2007) degrees from TUAT, specializing in amino acid ionic liquids.

28、In 2006 he was awarded a Research Fellowship for Young Scientists from the Japan Society for the Promotion of Science. Since the beginning of 2007, he has been working as a postdoctoral research fellow in Professor Hiroy

29、uki Ohno’s laboratory in TUAT.FIGURE 1. Design of amino acids for functional ionic liquids.Acc. Chem. Res. XXXX, xxx, 000–00010.1021/ar700053z CCC: $37.00 ? XXXX American Chemical Society VOL. xxx, NO. xx, XXXX / ACCOUNT

30、S OF CHEMICAL RESEARCH APAGE EST: 7.2 Published on Web 10/31/2007used to prepare ILs, with alanine (Ala) as a typical amino acid. Salts 5 and 7 prepared from symmetric ammonium and pyrrolidinium cations are solid, with a

31、 melting point above 70 °C. On the other hand, the asymmetric am- monium salt 6 has only a glass transition temperature, at -40 °C, and is a highly viscous liquid (Table 1). Though some quaternary ammonium salt

32、s become liquid at room temperature, their thermal decomposition temperatures of 150–170 °C were about 50 °C lower than that of the imidazolium cation-based AAIL, 4. These results indicate that adequate thermal

33、 stability and lowered melting point were scarcely attained with ammonium cations. On the other hand, the tetrabutylphosphonium cation-based AAIL 8 exhibited higher thermal stability and lower glass transition temperatur

34、e than those of the imidazolium- based AAIL, 4. Taking these preliminary results into account, all 20 distinct amino acids were neutralized by [P4444][OH]. These [P4444][AA] salts were obtained as liquids at room tempera

35、ture, except for [P4444][Glu] (Tm ) 101.7 °C), [P4444][His] (Tm ) 85.9 °C), and [P4444][Asn] (Tm ) 83.0 °C).15 A total of 16 salts out of the 20 had a lower Tg than that of the corresponding [emim] salt. V

36、iscosity follows a similar pattern. For example, [emim][Gly] had the lowest viscosity (486 cP at 25 °C) of the [emim][AA] salts. In fact, five amino acids (Ala, Met, Leu, Gly, and Val) formed less viscous ILs by cou

37、pling with the [P4444] cation than [emim][Gly]. These [P4444] salts were even less viscous than the [P66614][Tf2N] salt (450 cP at 25 °C). These data show that the amino acids combine with the phosphonium cation to

38、give compounds with desirable properties. This was not predicted from any previous database. 2.3. Polarity of Amino Acid Ionic Liquids. Polarity is a further important property of ILs, because the solubility of the solut

39、e, the reaction efficiency as solvent, and the miscibility with other solvents are influenced by the IL properties.16 To determine the polarity of the ILs, severalsuitable probes, mainly solvatochromic dyes, have been re

40、ported.17 The Kamlet–Taft parameters, determined with the three probes N,N-diethyl-4-nitroaniline, 4-nitroaniline, and Reichardt’s dye, are useful parameters in considering the hydrogen bond acidity, hydrogen bond basici

41、ty, and dipolarity/polarizability, respectively.18 From the maxi- mum absorption wavelength of these dyes in ILs, the hydrogen bond acidity (R), hydrogen bond basicity (?), and dipolarity/polarizability (π*) were calcula

42、ted.AAILs exhibited strong hydrogen bond basicity (? between 0.88 and 1.38). These ? values are larger than those of ILs reported previously (Table 2). ILs exhibiting strong hydrogen bond basicity were expected to dissol

43、ve cellulose and other biopolymers effectively.19 Since hy- drogen bond basicity is due mainly to the anion of ILs, [bmim][Cl] is frequently used as the IL, since it has the greatest hydrogen bond basicity (? ) 0.95). Ho

44、wever, almost all ILs containing Cl– have melting points above room temperature, because the strong hydrogen bond basicity induced an increase of hydrogen bonding with the cation, as well as a strong electrostatic intera

45、ction force involving the relatively small anion. These chloride salts required heating for use as solvents for target compounds. As well as exhibiting stronger hydrogen bond basicity than chloride salts, these AAILs are

46、 liquid at room temperature. They are expected to be polar solvents for scarcely soluble compounds (due mainly to intermolecular hydrogen bonding).AAILs composed of AAs having hydrogen donating properties, such as the ca

47、rboxylic acid residue and the hydroxyl group, displayed relatively low hydrogen bond basicity. This can be explained by the weakened interac- tion between the dye and the carboxylic acid residue, through the interaction

48、of these hydrogen bonding groups with the anion. The cation species also influences the ? value. The value of ? for [emim][Ala] was 1.036, but that for [P4444][Ala] it is 1.308.The cation species is known to affect the h

49、ydrogen bond acidity (R). The hydrogen bond acidity (R value) was around 0.5 for imidazolium salts, as a result of the extensive contribution of a proton at the 2 position of the imidazolium ring. On the other hand, the

50、R value of phosphonium salts was influenced by the anion species because there was no specific interaction between this cation and the dye molecule. From analysis of the phos- phonium salts, the hydrogen bond acidity of

51、AAILs wasTable 1. Thermal Properties of Various Alanine Saltsaa ND: not detected.Table 2. Kamlet–Taft Parameters for a Series of Amino Acid Ionic Liquids[emim] [P4444]π* R ? π* R ?[Ala] 1.10 0.479 1.036 1.029 0.914 1.308

52、 [Asp] 1.137 0.523 0.882 1.052 0.103 1.077 [Gln] 1.135 0.57 1.031 solid solid solid [Glu] 1.132 0.563 0.957 solid solid solid [Gly] 1.201 * 1.199 1.039 0.183 1.302 [His] 1.239 0.462 0.917 solid solid solid [Lys] 1.056 *

53、1.212 1.011 0.295 1.317 [Met] 1.071 0.408 1.14 0.997 0.925 1.34 [Ser] 1.10 0.514 1.032 1.106 0.042 1.099 [Val] 1.044 0.519 1.069 0.926 0.919 1.381Amino Acid Ionic Liquids Ohno and FukumotoVOL. xxx, NO. xx, XXXX / ACCOUNT