Homochiral Metal-Organic Cage for Gas Chromatographic

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Homochiral Metal-Organic Cage for Gas Chromatographic Separations Sheng-Ming Xie, Nan Fu, Li Li, Bao-Yan Yuan, Jun-Hui Zhang, Yan-Xia Li, and Li-Ming Yuan Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b01670 • Publication Date (Web): 10 Jul 2018 Downloaded from http://pubs.acs.org on July 10, 2018

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Analytical Chemistry

Homochiral Metaletal-Organic Cage for Gas Chromatographic Separations eparations Sheng-Ming Xie*, Nan Fu, Li Li, Bao-Yan Yuan, Jun-Hui Zhang, Yan-Xia Li, Li-Ming Yuan* Department of Chemistry, Yunnan Normal University, Kunming 650500, People’s Republic of China ABSTRACT: Metal-organic cages (MOCs) as a new type of porous materials with well-defined cavities have been extensively pursued because of their relative ease of synthesis and their potential applications in host-guest chemistry, molecular recognition, separation, catalysis, gas storage and drug delivery. Here we first reported that a homochiral MOC [Zn3L2] is explored to fabricate [Zn3L2] coated capillary column for high-resolution gas chromatographic separation of a wide range of analytes, including nalkanes, polycyclic aromatic hydrocarbons (PAHs) and positional isomers, especially for racemates. Various kinds of racemates such as alcohols, diols, epoxides, ethers, halohydrocarbons and esters colud be separated with good enantioselectivity and reproducibility on the [Zn3L2] coated capillary column. The fabricated [Zn3L2] coated capillary column exhibited significant chiral recognition complementarity to a commercial β-DEX 120 column and our recently reported homochiral porous organic cage CC3R coated column. The results show that the homochrial MOCs will be very attractive as a new type of chiral selectors in separation science.

Supramolecular materials (e.g., macrocyclic, crypt and cage-like molecules) with well-defined shapes, sizes and cavities have attracted considerable interest because of their fascinating structres and potential applications such as molecular recognition, separation, catalysis, gas storage, sensing and drug delivery, etc.1-4 Self-assembly is an essential feature of supramolecular chemistry and plays a vital role in the creation of various supramolecules.5 Metal-organic cages (MOCs) are a class of discrete coordination assemblies built from the spontaneous coordination-driven assembly of suitable metal ions or metal clusters and polydentate ligands.2,6-8 Chirality at a molecular and supramolecular level is very important because it is strongly related to chemistry, physics, biology, materials, and nanoscience.9 Over the past few decades, chiral MOCs have evolved to be one of the most attractive topics within supramolecular chemistry and materials science.7 To date, a great deal of complicated and novel structures of chiral MOCs have been reported. In general, the chiral MOCs can be constructed from optically pure chiral building blocks (a “hard” approach) and achiral building blocks (a “soft” approach) in a self-assembled system. Based on the unique chiral functionalities and welldefined cavities of chiral MOCs, many chiral MOCs have been extensively used for chiral molecular recognition10-19 and asymmetric catalysis.20-25 In recent years, a large number of chiral porous materials such as metal-organic frameworks (MOFs),26-27 covalent organic frameworks (COFs),28-30 hydrogen-bonded organic frameworks (HOFs)31 and porous organic cages (POCs)32 have been reported. Some of them have been successfully applied for enantioselective separation of various racemic compounds.29-45 Compared with other chromatographic methods, capillary gas chromatography (GC) is an excellent chromatographic technique for the separation and analysis of some volatile organic compounds (VOCs). It is well known that a thin and uniform coating of stationary phases on the

inner wall of the capillary column is of great importance for the performance of a coated capillary column in GC. Traditional cyclodextrin derivatives (CDs) and newly reported chiral POCs as GC stationary phases exhibited excellent chiral resolution ability toward enantiomers.40-43,45-46 In constrast to MOFs and COFs, chiral MOCs with similar properties of CDs and POCs are well-defined discrete cage-like molecular entities, which can be dissolved in some common organic solvents. Therefore, some chiral MOCs are easily processable and can be coated on the inner wall of capillary to form membranes by a static coating method. All these characteristics make chiral MOCs attractive candidate as new chromatographic separation medias to prepare chiral MOCcoated capillary columns for high-resolution gas chromatography. To the best of our knowledge, no work on the utilization of chiral MOCs as stationary phases for highresolution capillary GC separation of enantiomers has been reported so far. Herein we report the first exploration of a homochiral MOC [Zn3L2] as the stationary phase for high-resolution GC separation of various analytes, including normal alkanes, polycyclic aromatic hydrocarbons (PAHs), positional isomers and enantiomers with excellent selectivity and good reproducibility. EXPERIMENTAL SECTION Chemicals and Reagents. All chemicals and reagents used were at least of analytical grade. Zn(CH3COO)2·2H2O, 4-tertbutyl-2,6-diformylphenol and (1R, 2R)-diaminocyclohexane were purchased from Sigma-Aldrich (USA). All racemates were obtained from Sigma-Aldrich. The normal alkanes (n-C10 to n-C16) were from Beijing Chemical Reagent Company (China). Xylene, dinitrobenzene and nitrotoluene, α,β-ionones and cis,trans-citrals were purchased from Aladdin Chemistry Co. Ltd. (China). Naphthalene, acenaphthene, fluorine,

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phenanthrene, fluoranthene, pyrene, chrysene and benzo[a]pyrene were purchased from Acros Organics (USA) and Sigma-Aldrich (USA). Dichloromethane (DCM), ethanol and acetonitrile were from Tianjin Guangfu Fine Chemical Research Institute (China). Untreated fused-silica capillary column was purchased from Yongnian Ruifeng Chromatogram Apparatus Co. Ltd. (China). Instrumentation. All GC separations were performed on a Shimadzu GC-2014C system (Japan) with a flame ionization detector. The instrument control and data acquisition were carried out by N-2000 software. 1H and 13C NMR spectra were recorded on a Bruker DRX 500 NMR ultrashield spectrometer (Germany). The thermogravimetric analysis (TGA) experiment was performed on a NETZSCH STA 449F3 simultaneous thermal analyzer (Germany) from room temperature to 800 °C at a heating rate of 10 °C min−1. Scanning electron microscopy (SEM) images were recorded on a FEI Quanta FEG 650 scanning electron microscope (USA). Commercial β-DEX 120 capillary column (30 m × 0.25 mm i.d. × 0.25 µm film thickness, Supelco Inc., USA) was employed for comparison. Synthesis of Enantiopure [3+3] Macrocycle (L) and Homochiral MOC [Zn3L2]. The L was synthesized according to the method of Lisowski et al.47 Typically, a 20 mL acetonitrile of 4-tert-butyl-2,6-diformylphenol (2.062 g, 10 mmol) was added into a 15 mL acetonitrile of (1R, 2R)diaminocyclohexane (1.142 g, 10 mmol) at room temperature. Then, the resulted yellow suspensions was stirred at 50 °C for 12 h. A yellow product (2.26g, 76%) was obtained by filtration and washed with acetonitrile. Scheme S1 (Supporting Information) is the synthesis diagram of L. The homochiral MOC [Zn3L2] was synthesized according to the method of Lisowski et al.47,48 Typically, a solution of Zn(CH3COO)2·2H2O (0.1098 g, 0.50 mmol) in methanol (10 mL) was added to the stirred suspension of the enantiopure [3+3] macrocycle L (0.2840 g, 0.334 mmol) in methanol (30 mL). The mixture was refluxed for 2h, cooled down and then placed in the fridge overnight. A light yellow product (0.194g, 62%) was obtained. Finally, the product was recrystallized from chloroform and dried under vacuum. Scheme S2 (Supporting Information) is the synthesis diagram of [Zn3L2]. Capillary Pretreatment and Preparation of the Homochiral Capillary Columns. Fused-silica capillary column (15 m long × 0.25 mm i.d.) was pretreated according to the following method prior to coating: the column was washed with 1 M NaOH for 3 h, ultrapure water for 1 h, 0.1 M HCl for 1 h and again using ultrapure water until the washings were neutral. Finally, the capillary was dried via a nitrogen purge at 120 °C for 6 h. The homochiral capillary columns were prepared by using the static coating method. The static coating process as follows: one end of the capillary column was sealed when the solution of stationary phase was introduced into the pretreated capillary column and the other end was connected to a vacuum system to gradually remove the solvent under vacuum at 36 °C. Column A was statically coated with a mixture by mixing 1 mL solution of homochiral MOC [Zn3L2] (3 mg mL−1) in dichloromethane (DCM) and 1 mL solution of polysiloxane OV-1701 (4.5 mg mL−1) in DCM. The preparation of column B was the same as that of column A except for the use enantiopure [3+3] macrocycle as stationary phase. Finally, the

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coated capillary columns were conditioned under nitrogen flow from 30 °C to 200 °C (2 °C min−1) and held at 200 °C for 3 h before use. RESULTS AND DISCUSSION Characterization of the Synthesized Homochiral MOC [Zn3L2] and the MOC [Zn3L2] coated Capillary Column. The preparation of homochiral MOC [Zn3L2] was based on coordination-driven self-assembly of Zn2+ ions with enantiopure [3+3] triphenolic Schiff-base macrocycle derived from trans-1,2-diaminocyclohexane and aromatic dialdehyde. Figures S1 and S2 (Supporting Information) showed that the successful synthesis of enantiopure [3+3] triphenolic Schiffbase macrocycle (Scheme S1, Supporting Information). As can be seen from Scheme S2 (Supporting Information), two enantiopure deprotonated [3+3] macrocyclic units are connected by three Zn2+ ions to form the cage-like molecule [Zn3L2]. The successful synthesis of [Zn3L2] was confirmed by NMR data (Figures S3 and S4, Supporting Information). The experimental PXRD pattern matches well with the simulated pattern, further demonstrating the successful synthesis of [Zn3L2] (Figure 1a). The thermal gravimetric analysis (TGA) curve shows that the [Zn3L2] is stable up to 400 °C (Figure 1b). The weight loss at 100°C arose from the escape of solvent molecules inside the pores of [Zn3L2]. A distinguishing feature of [Zn3L2] and other porous frameworks (eg., MOFs and COFs) is that they are soluble in some organic solution such as dichloromethane and chloroform. The good thermal stability and solubility of [Zn3L2] make it particularly suitable for GC usage. Column A coated with homochiral MOC [Zn3L2] diluted with OV-1701 was fabricated by a static method. The MOC [Zn3L2] coated capillary columns were characterized by scanning electron microscopy (SEM). The capillaries were cut to expose the inner wall for SEM measurement. As can be seen from Figure 1c, an approximately 300 nm thick [Zn3L2] coating was deposited on the inner wall of column A. The column efficiency of column A was measured by using n-dodecane as analyte at 120 °C, and the number of theoretical plates was 2300 plates m−1.

Figure 1. (a) Comparison of the experimental and simulated XRD patterns of homochiral MOC [Zn3L2]; (b) TGA of homochiral MOC [Zn3L2]; (c) SEM image of the cross section view of the inlet of homochiral MOC [Zn3L2] coated capillary column.


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coherent boiling points (eg. xylene: p-xylene, 138.4 °C; mxylene, 139 °C). In this work, column A also offered good selectivity for the separation of some positional isomers, including ionone, citral, xylene, dinitrobenzene and nitrotoluene. Citral and ionone are basic raw material of perfume and medical industry, while xylene, dinitrobenzene and nitrotoluene are useful intermediates for the production of important chemical products such as polymers, insecticides and dyes etc. The chromatograms of five isomers on column A are shown in Figure 4, and the chromatographic data is listed in Table 1. The elution sequence of all these substituted aromatics isomers followed the order of boiling points on column A as observed on some commercial capillary columns in GC.

Separation of Normal Alkanes, PAHs and Positional Isomers. To test the overall chromatographic properties of column A, many different types of compounds were selected as targets, including normal alkanes, PAHs and positional isomers. Alkanes are important constituents of raw chemicals in the petroleum and chemical industry.49 The separation of normal alkanes is a very important process in petroleum refining. As can be seen from Figure 2, all the seven n-alkanes (n-C10 to nC16) with a wide range of boiling points were baseline separated with sharp peak shapes on column A and eluted in the order of their boiling points. The high-resolution separation of n-alkanes on column A mainly arises from the van der Waals interaction between n-alkane molecules and MOC [Zn3L2] stationary phase.

Figure 2. GC chromatograms on the column A (15 m long × 0.25 mm i.d.) for the separation of n-Alkanes at a N2 flow rate of 15.2 cm s−1 using a temperature program: 100 °C for 0.5 min, then 35 °C min−1 to 220 °C, and finally 220 °C for the remainder of the measurement.

Figure 4. GC chromatograms on the column A (15 m long × 0.25 mm i.d.) for the separation of (a) α-, β-ionone isomers at a N2 flow rate of 12.5 cm s−1 under 137 °C; (b) cis-, trans-citral isomers at a N2 flow rate of 13.5 cm s−1 under 122 °C; (c) o-, m-, p-xylene at a N2 flow rate of 14.2 cm s−1 under 85 °C; (d) o-, m-, p-dinitrobenzene at a N2 flow rate of 13.3 cm s−1 under 180 °C; (e) o-, m-, p-nitrotoluene at a N2 flow rate of 13.8 cm s−1 under 130 °C. Table 1. Separation factor (α) and resolution (Rs) of isomers on column A separation resolution (Rs) factor (α) isomers T (°C) Rs1 Rs2 α1 α2 ionone 137 1.37 7.60 citral 122 1.24 2.57 xylene 85 1.09 1.25 0.53 1.47 dinitrobenzene 180 1.23 1.62 1.55 3.21 nitrotoluene 130 1.27 1.10 2.41 1.36

Polycyclic aromatic hydrocarbons (PAHs) are a type of persistent organic pollutants (POPs) with highly carcinogenic at relatively low levels. Therefore, it is of vital importance for the detection and analysis of PAHs in the environment. In this work, we chose a mixture of eight PAHs as analytes. Figure 3 shows that eight PAH molecules were baseline separated with good peak shapes on column A using a temperature program. The result indicates that MOC [Zn3L2] coated capillary column has potential application for GC separation of some environmentally important POPs.

Separation of Racemates. The most striking feature of homochiral MOC [Zn3L2] is its chiral cavity, which makes it attractive as a new media to prepare chiral stationary phase for separation of racemates. To evaluate the resolving ability and enantioselectivity of the homochiral MOC [Zn3L2], various kinds of racemates were selected as analytes. The following twelve racemates were separated on column A: 2-butanol, 1methoxy-2-butanol, 2-pentanol, 4-methyl-2-pentanol, 1,2butanediol, 1,2-epoxypropane, 1-methoxy-2-hydroxypropane, epichlorohydrin, epibromohydrin, methyl 3-hydroxybutyrate, ethyl 3-hydroxybutyrate and mandelic acid. Those racemates include alcohols, diols, epoxides, ethers, halohydrocarbons

Figure 3. GC chromatograms on the column A (15 m long × 0.25 mm i.d.) for the separation of PAHs (first peak: solvent toluene; 1: naphthalene; 2: acenaphthene; 3: fluorene; 4: phenanthrene; 5: fluoranthene; 6: pyrene; 7: chrysene; 8: benzo[a]pyrene) at a N2 flow rate of 16.6 cm s−1 using a temperature program: 120 °C for 0.5 min, then 40 °C min−1 to 320 °C, and finally 320 °C for the remainder of the measurement.

Selective separation of some positional isomers is of great importance in industry and also a challenging task because of their similar chemical and physical properties, and their



and esters. The separation factors (α), resolutions (Rs) and column temperatures (T) are given in Table 2. The chromatograms are exhibited in Figure 5. As can be seen from Figure 5 and Table 2, a majority of racemates obtained baseline separation with sharp peaks, indicating that the excellent enantioselectivity and resolving ability of homochiral MOC [Zn3L2]. Comparing the chiral recognition ability of column A with those of commercially available βDEX 120 column and previously reported homochiral porous organic cage (POC) CC3-R column, the separation results obtained on the β-DEX 120 column and CC3-R column under the optimum chromatographic conditions are listed in Table 2. Although the length of column A is half of the β-DEX 120 column, the resolution ability of column A were higher than the β-DEX 120 column. Half of twelve enantiomers including 1,2-epoxypropane, 1-methoxy-2-hydroxypropane, epichlorohydrin, epibromohydrin, methyl 3-hydroxybutyrate and ethyl 3-hydroxybutyrate could not be separated on the βDEX 120 column but were baseline separated on the column A except for ethyl 3-hydroxybutyrate. In addition, the resolution (Rs) values of 2-butanol and 1-methoxy-2-butanol on column A are higher than on the β-DEX 120 column. Recently, a new class of chiral functional material POCs used as GC chiral stationary phases were reported by our group.4043,45 Especially for POC CC3-R column, it exhibited excellent chrial recognition ability toward a wide range of chiral compounds, including alcohols, diols, amines, alcohol amines, esters, ketones, ethers, halohydrocarbons, organic acids, amino acid methyl esters and sulfoxides, and has useful commercial value.40 From Table 2, the POC CC3-R column showed more excellent separation ability for alcohols and diols than column A. However, column A gave higher resolutions for 1,2epoxypropane, epichlorohydrin and epibromohydrin than CC3-R column, and some enantiomers (methyl 3hydroxybutyrate, ethyl 3-hydroxybutyrate and mandelic acid) were separated on the column A but could not be resolved on the CC3-R column. The experimental results demonstrate that the novel stationary phase of homochiral MOC [Zn3L2] with excellent enantioselectivity can be complementary to those of the β-DEX 120 column and CC3-R column. As we all known, the influence of the chiral microenvironment on the chiral properties of chromatographic systems is complicated.40,50 In this work, the homochiral MOC [Zn3L2] offered the good enantioselectivity and resolution for the separation of several different types of racemates. Different elution order of their enantiomers were observed on column A (Figure 5). For instance, the (S)-enantiomers of some racemates such as alcohols and esters eluted after their (R)-enantiomers, while the (R)-enantiomers of epoxides eluted after their (S)-enantiomers. Therefore, it is very difficult to completely explain the enantioselectivity of homochiral MOC [Zn3L2] by only one chiral recognition mechanism. The cagelike [Zn3L2] molecule was synthesized by two enantiopure deprotonated [3+3] macrocyclic units and three Zn2+ ions via self assembly method (Figures 6a and 6b). We think that the chiral recognition process was derived from the host-guest interaction between the cage of [Zn3L2] and enantiomers. The retention time of (S)-enantiomer for 2-butanol was longer than its (R)-enantiomer, indicating that the interaction between host molecule [Zn3L2] and guest molecule (S)-enantiomer was stronger than that with the (R)-enantiomer. The

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enantioselective binding of chiral alcohols such as 2-butanol in the same homochiral MOC [Zn3L2] has previously been investigated by J. Lisowski et al.48 The experimental results showed that the cavity of [Zn3L2] molecules is occupied by the (S)-enantiomer of 2-butanol. In the [Zn3L2{(S)CH3CH(OH)CH2CH3}] complex, the alcohol molecule is held by a weak coordination bond. Thus, it can be seen that the (S)enantiomer of 2-butanol exhibited preferential binding to the [Zn3L2] molecules, which is similar to the separation performance of 2-butanol on column A. On the contrary, there is a preferential binding ability existing between (R)enantiomer and [Zn3L2] molecules for the 1-methoxy-2hydroxypropane and epoxides (1,2-epoxypropane, epichlorohydrin and epibromohydrin). To demonstrate that the cavity of [Zn3L2] molecules is very important for the separation of enantiomers, we use enantiopure [3+3] macrocyclic L as GC stationary phase for comparison. Here, we fabricated another chiral capillary column (column B) using enantiopure [3+3] macrocyclic L as stationary phase for separation of all above-mentioned twelve racemates. Unfortunately, all twelve racemates could not be separated on column B (Figure S5, Supporting Information). The results further indicated that the chiral microenvironment of cavity is vital for the chiral recognition of racemates. The reproducibility and stability of column A was investigated. Figure 7 is the reproducible chromatograms for the replicate separations of α-, β-ionone isomers and 1methoxy-2-butanol on column A. No significant changes in retention time, selectivity and separation ability were observed, indicating the good reproducibility and stability of column A for GC separations. These features of the homochiral MOC [Zn3L2] column are favourable for its practical applications as a novel chiral stationary phase in GC.

CONCLUSIONS In conclusion, we have reported the first example of the utilization of homochiral MOC as a novel chiral stationary phase for GC separation of various organic compounds. The fabricated homochiral MOC [Zn3L2] coated capillary column showed high-resolution separation of n-alkanes, PAHs and positional isomers, expecially for the racemates with good selectivity and reproducibility. Compared with commercial βDEX 120 and homochiral POC CC3-R capillary columns, the MOC [Zn3L2] coated capillary column can be complementary to the chiral recognition ability of them. The results show that homochiral MOCs are very attractive for exploration as novel chiral stationary phases for GC enantioseparation. We believe that this work may also bring a bright future for broad applications of homochiral metal organic cages in chiral separation science.


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Figure 5. GC chromatograms on the column A (15 m long × 0.25 mm i.d.) for the separation of racemates: (a) 2-butanol, (b) 1-methoxy-2butanol, (c) 2-pentanol, (d) 4-methyl-2-pentanol, (e) 1,2-butanediol, (f) 1,2-epoxypropane, (g) 1-methoxy-2-hydroxypropane, (h) epichlorohydrin, (i) epibromohydrin, (j) methyl 3-hydroxybutyrate, (k) ethyl 3-hydroxybutyrate and (l) mandelic acid. Separation conditions as shown in Table 2.



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Table 2 Separations of racemates on homochiral MOC [Zn3L2] coated column A, β-DEX 120 column and POC CC3-R coated column. column A β-DEX 120 CC3-R[32,37] racemates

T(°C)

α

va (cm s-1)

Rs

T(°C)

α

Rs

va (cm s-1)

T(°C)

α

Rs

va (cm s1 )

2-butanol

70

1.15

1.43

16.0

50

1.04

1.35

12.8

110

1.71

16.09

16.5

1-methoxy-2-butanol

120

1.30

2.41

14.7

70

1.04

2.06

14.3

160

1.77

17.60

16.6

2-pentanol

75

1.10

0.83

16.2

63

1.03

1.23

14.3

145

1.32

6.14

14.8

4-methyl-2-pentanol

80

1.12

0.96

13.8

80

1.04

1.51

14.2

145

1.24

3.16

14.7

1,2-butanediol

125

1.04

0.75

13.2

110

1.04

1.51

13.1

165

1.11

2.60

14.7

b

14.3

85

1.06

1.59

14.7

12.5

150

1.13

3.21

13.2

1,2-epoxypropane

55

1.24

1.62

16.6

40

1.00

—

1-methoxy-2hydroxypropane

115

1.17

1.60

14.7

55

1.00

—b

epichlorohydrin

85

1.18

1.69

14.7

65

1.00

—b

14.3

125

1.04

1.51

14.7

epibromohydrin

90

1.25

2.26

14.7

70

1.00

—b

14.3

138

1.05

1.63

14.7

methyl 3-hydroxybutyrate

112

1.29

1.74

14.3

90

1.00

—b

13.5

150

1.00

—b

14.8

1.00

b

1.00

—

b

15.2

—

b

15.8

ethyl 3-hydroxybutyrate

118

1.11

0.89

14.3

100

—

13.5

c

158

mandelic acid 130 1.20 1.53 15.1 145 1.05 3.32 16.0 190 v is the linear velocity of carrier gas of N2. bCould not be separated. cTrifluoroacetyl isopropyl ester derivative.

1.00

a

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Li-Ming Yuan); [email protected] (Sheng-Ming Xie). Fax: 86-87165941088.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

Figure 6. The side (a) and top (b) views of homochiral MOC [Zn3L2] molecule. The hydrogen atoms of [Zn3L2] molecule have been omitted.

This work was supported by the National Natural Science Foundation of China (Nos. 21765025, 21675141) and the Yunnan Province’s Basic Research Program of China (No. 2017FB013).

REFERENCES (1) Shahgaldian, P.; Pieles, U. Sensors. 2006, 6, 593-615. (2) Chen, L.; Chen, Q. H.; Wu, M. Y.; Jiang, F. L.; Hong, M. C. Acc. Chem. Res. 2015, 48, 201-210. (3) Cook, T. R.; Stang, P. J. Chem. Rev. 2015, 115, 7001-7045. (4) Zarra, S.; Wood, D. M.; Roberts, D. A.; Nitschke, J. R. Chem. Soc. Rev. 2015, 44, 419-432. (5) Luo, D.; Wang, X. Z.; Yang, C.; Zhou, X. P.; Li, D. J. Am. Chem. Soc. 2018, 140, 118-121. (6) Schmidta, A.; Casinib, A.; Kuhna, F. E. Coord. Chem. Rev. 2014, 275, 19-36. (7) Chen, L. J.; Yang, H. B.; Shionoya, M. Chem. Soc. Rev. 2017, 46, 2555-2576. (8) Pan, M.; Wu, K.; Zhang, J. H.; Su, C.Y. Coord. Chem. Rev. 2017, in press. (9) Liu, M. H.; Zhang, L.; Wang, T. Y. Chem. Rev. 2015, 115, 7304-7397. (10) Fiedler, D.; Leung, D. H.; Bergman, R. G.; Raymond, K. N. J. Am. Chem. Soc. 2004, 126, 3674-3675. (11) Fiedler, D.; Pagliero, D.; Brumaghim, J. L.; Bergman, R. G.; Raymond, K. N. Inorg. Chem. 2004, 43, 846-848. (12) Frantz, R.; Grange, C. S.; Al-Rasbi, N. K.; Ward, M. D.; Lacour, J. Chem. Commun. 2007, 14, 1459-1461.

Figure 7. GC chromatograms on the column A (15 m long × 0.25 mm i.d.) for five replicate separations: (a) α-, β-ionone isomers at a N2 flow rate of 12.5 cm s−1 under 137 °C; (b) 1-methoxy-2butanol at a N2 flow rate of 14.7 cm s−1 under 120 °C.

ASSOCIATED CONTENT Supporting Information Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.


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For TOC only

Coating

Homochiral MOC

Racemates

Capillary column


Page 8 of 8

Homochiral Metal-Organic Cage for Gas Chromatographic

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