Novel Inorganic Mesoporous Material with Chiral Nematic Structure

Article pubs.acs.org/ac

Novel Inorganic Mesoporous Material with Chiral Nematic Structure Derived from Nanocrystalline Cellulose for High-Resolution Gas Chromatographic Separations Jun-Hui Zhang,† Sheng-Ming Xie,‡ Mei Zhang,§ Min Zi,‡ Pin-Gang He,† and Li-Ming Yuan*,†,‡ †

Department of Chemistry, East China Normal University, Shanghai 200241, People’s Republic of China Department of Chemistry, Yunnan Normal University, Kunming 650500, People’s Republic of China § Department of Pharmacy, Yunnan University of Traditional Chinese Medicine, Kunming 650500, People’s Republic of China ‡

S Supporting Information *

ABSTRACT: Chiral nematic mesoporous silica (CNMS) has attracted widespread attention due to some unique features, such as its nematic structure, chirality, large pore size, high temperature resistance, low cost, and ease of preparation. We first reported the use of CNMS as a stationary phase for capillary gas chromatography (GC). The CNMS-coated capillary column not only gives good selectivity for the separation of linear alkanes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and isomers but also offers excellent enantioselectivity for chiral compounds. Compared with enantioseparations on commercial β-DEX 120 and Chirasil-L-Val columns, a CNMS-coated capillary column offers excellent enantioselectivity, chiral recognition complementarity, and the separation of analytes within short elution times. It can also be potentially applied in high-temperature GC at more than 350 °C. This work indicates that CNMS could soon become very attractive for separations.

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ince the discovery of M41S materials in 1992,1,2 such mesoporous materials have attracted much research attention, owing to their potential applications in catalysis,3−6 adsorption,7−9 separation,10,11 sensors,12 drug delivery,13−15 etc. They offer new opportunities as separation media in chromatography because of their high surface areas, narrow pore size distributions, and adjustable pore diameters.16−21 It is wellknown that inorganic mesoporous silicas with ordered mesostructures can be synthesized by coassembling silica precursors with surfactants or polymeric templates.1,2,22−27 Introducing chirality into inorganic mesoporous materials could be useful for chiral separation, asymmetric catalysis, and chiral sensing.28−30 However, chirality is harder to impose on inorganic materials; the preparation of such materials with enantiomerically pure chirality poses a considerable challenge.31,32 Most approaches for obtaining chirality in inorganic mesoporous materials involve the use of organic chiral elements and the subsequent chemical modification of these materials. The chirality of the inorganic−organic hybrid materials is due to the grafting of chiral molecules rather than their porosity or the backbone structure. Cellulose, consisting of repeating D-glucose units, is the most abundant organic polymer, and is considered to be an almost inexhaustible raw material. Nanocrystalline cellulose (NCC) is a nanomaterial obtained by acid hydrolysis of cellulosic materials.33−35 NCC has many advantages over cellulose, such © XXXX American Chemical Society

as nanometer dimensions, high surface area, high specific strength and modulus, and unique optical properties. Template synthesis based on the self-assembly of liquid crystals is a powerful method for constructing novel porous materials with highly specific surface areas and periodic structures.22,36−38 In water, suspensions of rod-like NCC organize into a chiral nematic liquid crystalline phase that can form periodic lefthanded helical structures and iridescent films during slow evaporation of the solvent.33,34,39 The unique properties of NCC make it an attractive potential template for preparing novel ordered porous materials. Recently, MacLachlan and coworkers prepared several materials with chiral nematic structures using NCC templates.40−53 Chiral nematic mesoporous silica (CNMS) is a novel inorganic mesoporous material that can be obtained by high-temperature calcination of the chiral nematic composite films synthesized by the spontaneous self-assembly of NCC with tetramethoxysilane (TMOS).40 The synthesis of inorganic mesoporous materials exhibiting both mesoporous structures and inherent chirality is challenging, as their combination usually results in the loss of one of these properties, such as destruction of the local chirality during the removal of chiral templates.54,55 Interestingly, CNMS does not Received: June 5, 2014 Accepted: September 4, 2014

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dx.doi.org/10.1021/ac502073g | Anal. Chem. XXXX, XXX, XXX−XXX

Analytical Chemistry

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lose enantioselectivity during removal of the template by calcination. The chiral nematic organization of NCC has been replicated in CNMS. It not only shows a left-handed helical structure but also a chiral nanoporous structure generated by the imprinting of cellulose at multiple levels. Moreover, CNMS shows some properties of liquid crystalline materials. We report herein the fabrication of a CNMS-coated open tubular column for high-resolution gas chromatography (GC) separations, taking advantage of the excellent chemical and thermal stability, large pore size, unique chiral nanoporous structure, low cost, and ease of preparation of CNMS. Some racemates, isomers, linear alkanes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and Grob’s test mixture have been used as the targets for separations.

Figure 1. (a) Suspension of CNMS powder dispersed in ethanol: (1) ethanol; (2) the supernatant of CNMS suspension; (3) the supernatant after set aside for 1 h. (b) TEM image of CNMS powder (scale bars = 100 nm).

Chirasil-L-Val capillary column (25 m × 0.25 mm i.d. × 0.12 μm film, Agilent Technologies, USA), a β-DEX 120 (30 m × 0.25 mm i.d. × 0.25 μm film, Supelco Inc., USA), and a SUPELCOWAX 10 (30 m × 0.25 mm i.d. × 0.25 μm film, Supelco Inc., USA) were employed as commercial columns for comparison. Preparation of CNMS. CNMS was prepared by the addition of TMOS to an aqueous suspension of NCC according to the method of MacLachlan et al.40 At pH = 2.4, TMOS could be hydrolyzed in the presence of NCC to give a homogeneous mixture without disrupting the ability of NCC to form a chiral nematic phase. Therefore, the NCC suspension had to be adjusted to pH = 2.4 before the addition of TMOS. TMOS is compatible with NCC self-assembly for several reasons: (1) the isoelectric point of colloidal silica (pH ≈ 2) is near the pH of the as-prepared acidic NCC suspension; (2) hydrolysis of TMOS generates the corresponding alcohol, which does not perturb evaporation-induced self-assembly (EISA); (3) operating close to the isoelectric point of colloidal silica and the slight acidity and high water ratio of the NCC suspensions suppress silica polymerization until the later stages of evaporation.51,56 Typically, the suspensions of NCC were prepared first, which organized into a left-handed chiral nematic liquid crystalline phase in water due to the anisotropic rod-like shape and intrinsic chirality of this material. TMOS was then added to the suspension at pH = 2.4, and the chiral nematic phase was formed during evaporation. After drying, NCC− silica composite films with a chiral nematic structure were obtained. To remove the NCC, the composite films were heated at a rate of 2 °C min−1 to 100 °C, held at 100 °C for 2 h, then heated to 540 °C at 2 °C min−1 and held at 540 °C for 6 h. After slowly cooling to room temperature, free-standing CNMS films were recovered (see the Supporting Information for further details). Preparation of the CNMS-coated Capillary Column. An untreated fused silica capillary column (15 m long × 0.25 mm i.d.) was pretreated according to the following method before dynamic coating: it was washed with 1 M NaOH for 2 h, ultrapure water for 1 h, 0.1 M HCl for 2 h, and again with ultrapure water until the washings were neutral. Finally, it was dried by a nitrogen purge at 120 °C for 6 h. CNMS was coated onto the pretreated capillary column by a dynamic coating method according to previous literature reports.57−59 CNMS films were milled to a powder and dispersed in ethanol with the aid of ultrasound for 15 min before dynamic coating. The suspension was set aside for 30 min and the supernatant was collected. The CNMS powder was well dispersed in ethanol and no obvious deposition was observed after 1 h (Figure 1a). A TEM image revealed that the size of the suspended CNMS particles was about 50 nm (Figure 1b). A 2 mL aliquot of the supernatant containing CNMS (ca. 2 mg mL−1)

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EXPERIMENTAL SECTION Chemicals and Reagents. All chemicals and reagents used were at least of analytical grade. Benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, isopropylbenzene, 1,3,5-trimethylbenzene, isomeric chloroanilines, bromoanilines, iodoanilines, nitroanilines, dinitrobenzenes, α- and β-ionones, 1-naphthol, and 2-naphthol were purchased from Aladdin Chemistry Co. Ltd. (Shanghai, China). The analytes used for evaluation of chromatographic performance, namely n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, 2,6-dimethylphenol, 2,6-dimethylaniline, nonanal, methyl decanoate, methyl undecanoate, methyl dodecanoate, and dicyclohexylamine were purchased from Beijing Chemical Reagent Company (Beijing, China). Acenaphthene, chrysene, and benzo[a]pyrene were procured from Acros Organics (New Jersey, USA). Naphthalene, biphenyl, fluorene, phenanthrene, fluoranthene, pyrene, 1-phenylethanol, citronellal, 2-amino-1-butanol, menthol, methionine, tryptophan, glutamic acid, isoleucine, valine, and serine were purchased from Sigma-Aldrich (St. Louis, MO, USA). TMOS (Adamas-beta, Shanghai, China), filter paper (Whatman-Xinhua Filter Paper Co. Ltd., Hangzhou, China), and sulfuric acid (Fengchuan Chemical Reagent Technology Co. Ltd., Tianjin, China) were used for the preparation of CNMS. Untreated fused-silica capillary column was purchased from Yongnian Ruifeng Chromatogram Apparatus Co. Ltd. (Hebei, China). Instrumentation. GC measurements were performed on a Shimadzu GC-2014C system (Kyoto, Japan) with a flame ionization detector. Nitrogen (99.999%) was used as the carrier gas. Data acquisition and processing were controlled by an N2000 chromatography data system. Powder X-ray diffraction (PXRD) patterns were collected on a D/max-3B diffractometer (Rigaku, Japan) using Cu Kα radiation. Scanning electron microscopy (SEM) images were recorded on an XL30ESEMTMP scanning electron microscope (Philips, The Netherlands). Polarized optical microscopy was performed on a Sunny XY-P microscope (Ningbo, China) with perpendicular polarizers. Transmission electron microscopy (TEM) micrographs were recorded on a JEM-2100 transmission electron microscope (Tokyo, Japan) operating at an accelerating voltage of 200 kV. The thermogravimetric analysis (TGA) experiment was carried out under air atmosphere at a heating rate of 10 °C min−1 on a ZRY-1P simultaneous thermal analyzer (Shanghai, China). N2 adsorption isotherms were measured at 77 K on a Micromeritics ASAP 2020 M+C system (Micromeritics, USA). Pore volumes were estimated based on the Barrett−Joyner− Halenda (BJH) method. A DB-17 capillary column (30 m × 0.25 mm i.d. × 0.25 μm film, Agilent Technologies, USA), a B



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Figure 2. PXRD patterns and SEM images of NCC−silica composite films and CNMS films. (a) PXRD of NCC−silica composite film shows two peaks characteristic of crystalline cellulose at 2θ ≈ 16° and 24°. (b, c) Cross-section SEM images of NCC−silica composite film at different magnifications (scale bars = 3 μm in panel b; scale bar = 0.5 μm in panel c). (d) PXRD of CNMS after NCC removal by calcination shows only abroad peak characteristic of amorphous silica and no peaks associated with the NCC. (e, f) Cross-section SEM images of CNMS film at different magnifications (scale bar = 20 μm in panel e; scale bar = 3 μm in panel f).

540 °C in air to obtain CNMS, the PXRD pattern (Figure 2d) and SEM images (Figure 2e,f) were similar to those reported in the literature.40 Looking at cross sections of the CNMS films at low magnification (Figure 2e), a repeating layered morphology is observed, due to replication of the chiral nematic phase of NCC. At a higher magnification, a twisted fibrous texture is apparent (Figure 2f). Thermal gravimetric analysis (TGA) curves showed that CNMS does not lose weight at 700 °C (Figure S1, Supporting Information), further indicating it is suitable for high-temperature GC usage. The CNMS-coated capillary column was characterized by scanning electron microscopy (SEM). Figure 3 shows SEM images of a cross-section of the fabricated capillary column and the coated CNMS films on the inner wall of the capillary column. The fabricated capillary column had an approximately 2 μm thick CNMS coating on the inner wall. The column efficiency of the prepared CNMS column was measured by using n-dodecane as a test compound at 120 °C, and the number of theoretical plates was 2060 plates m−1. To evaluate the polarity of the novel stationary phase, McReynolds constants were determined on the prepared column using benzene, 1-butanol, 2-pentanone, 1-nitropropane, and pyridine

was introduced into the capillary column under gas pressure, giving about a 7 m long plug in the capillary, and then forced through the column at a rate of 50 cm min−1 to leave a wet coating layer on the inner wall of the capillary column. To avoid acceleration of the solution plug near the end of the column, a 1 m long buffer tube was attached to the capillary column end as a restrictor. Finally, the coated capillary column was flushed for 4 h with nitrogen and then conditioned from 25 to 300 °C at a rate of 1 °C min−1, and at 300 °C for 3 h.

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RESULTS AND DISCUSSION Characterization of the Synthesized CNMS and the CNMS-coated Capillary Column. PXRD patterns (Figure 2a) and SEM images (Figure 2b,c) showed that the NCC−silica composite films were similar to pure NCC films, with the properties of NCC remaining unchanged,40 and that a chiral nematic layered structure had been formed. When the NCC template was removed by calcination of the composite films at

Table 2. Separation Factor (α) and Resolution (Rs) of Isomers on the CNMS-coated Capillary Column separation factor (α) isomers

Figure 3. SEM images of (a) the thickness of CNMS coating in part of the capillary column (scale bar =10 μm). (b) CNMS deposited on the inner wall of the capillary column (scale bar = 20 μm).

chloroaniline bromoaniline iodoaniline nitroaniline dinitrobenzene isopropylbenzene, n-propylbenzene, 1,3,5-trimethylbenzene naphthol ionone

Table 1. McReynolds Constants of the CNMS-coated Capillary Column at 120 °C benzene

1-nitropropane

2-pentanone

1-butanol

pyridine

average

22

472

335

288

573

338 C

resolution (Rs)

T (°C)

α1

α2

Rs1

Rs2

145 155 150 170 193 80

1.55 1.53 1.84 1.27 1.11 1.20

1.15 1.12 1.13 1.58 1.13 1.31

4.66 4.91 5.68 1.52 0.91 1.56

1.44 1.36 1.30 2.39 1.06 2.46

150 170

1.14 1.35

0.58 2.27



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Figure 4. GC chromatograms on the CNMS-coated open tubular column (15 m long × 0.25 mm i.d.) using a temperature program for the separation of (a) Grob’s test mixture (first peak, solvent n-hexane; 1, n-decane; 2, n-undecane; 3, 2,6-dimethylphenol; 4, 2,6-dimethylaniline; 5, nonanal; 6, methyl decanoate; 7, methyl undecanoate; 8, methyl dodecanoate; 9, dicyclohexylamine): 140 °C for 1 min, then 50 °C min−1 to 250 °C under a N2 linear velocity of 16.5 cm s−1, 0.2 μL injection volume. (b) n-Alkanes: 110 °C for 0.7 min, then 60 °C min−1 to 240 °C under a N2 linear velocity of 16.5 cm s−1, 0.02 μL injection volume. (c) Aromatic hydrocarbon mixture (1, benzene; 2, toluene; 3, ethylbenzene; 4, n-propylbenzene; 5, n-butylbenzene): 80 °C for 0.7 min, then 55 °C min−1 to 200 °C under a N2 linear velocity of 13.8 cm s−1, 0.03 μL injection volume. The split ratio is 40:1.

Table 3. Separations of Racemates on the CNMS-coated Column, β-DEX 120 Column, and Chirasil-L-Val Column β-DEX 120

CNMS

a

Chirasil-L-Val

racemates

T (°C)

α

Rs

T (°C)

α

Rs

T (°C)

α

Rs

1-phenylethanol citronellal 2-amino-1-butanola menthol methionineb tryptophanb glutamic acidb isoleucineb valineb serineb

160 150 165 95 160 155 150 150 130 140

1.10 1.21 1.20 1.68 1.44 2.04 2.01 2.28 1.90 1.79

0.96 1.03 2.45 2.50 1.56 2.34 2.56 3.28 2.36 3.13

130 110 125 130 130 160 140 95 95 125

1.05 1.00 1.03 1.05 1.00 1.00 1.00 1.02 1.00 1.06

2.62 /c 2.19 2.66 /c /c /c 1.03 /c 2.00

90 95 100 90 150 170 155 115 100 125

1.00 1.00 1.03 1.00 1.14 1.03 1.11 1.16 1.20 1.12

/c /c 1.36 /c 6.29 1.30 4.83 6.49 6.93 5.00

Trifluoroacetyl derivative. bTrifluoroacetyl isopropyl ester derivative. cCould not be separated.

as analytes.60,61 The polarity of the stationary phase is an important factor affecting the selectivity in GC separation. Squalane was used as a standard nonpolar stationary phase, and the McReynolds constants of the CNMS-coated column were compared to those of squalane. The McReynolds constants of the five reference analytes on the CNMS-coated column are summarized in Table 1. The average of the five McReynolds constants is 338, indicating a moderate polarity of the CNMS. The elution sequence of the probes was benzene, 1-nitropropane, 2-pentanone, 1-butanol, and pyridine. Separation Performance of the CNMS-coated Capillary Column. To investigate the overall chromatographic properties of the capillary column, we chose Grob’s test mixture, linear alkanes, and aromatic hydrocarbons as test solutes. The retention factor (k′), resolution (Rs), asymmetry factor (As), and column efficiency (N) for each analyte are listed in Table S1 (Supporting Information). Grob’s test mixture contains n-decane, n-undecane, 2,6-dimethylphenol, 2,6-dimethylaniline, nonanal, methyl decanoate, methyl undecanoate, methyl dodecanoate, and dicyclohexylamine, providing a variety of functional groups and a wide range of polarities. Figure 4a shows that baseline separation of this complicated mixture was obtained on the column within 5.2 min. Linear alkanes and aromatic hydrocarbons are nonpolar compounds. As can be observed in Figure 4b,c, all of the components of the normal

alkane mixture (n-C10 to n-C16) and aromatic hydrocarbon mixture (benzene, toluene, ethylbenzene, n-propylbenzene, nbutylbenzene) were baseline resolved with nice peak shapes and in a short time on the CNMS-coated column. The CNMS-coated capillary column also offered good selectivity for the separation of isomers. As shown in Figure 5a−h and Table 2, all of the isomers were separated in a short time on the column. Commercial DB-17 and SUPELCOWAX 10 columns were employed for comparison. The comparability of the chromatographic data is indicated in Table S2 (Supporting Infomation). In general, it is relatively difficult to separate m- and p-isomers. Both the resolution values (Rs) and the separation factors (α) for the m- and p-isomers on the CNMScoated column were clearly better for the five isomeric analytes (isomeric chloroanilines, bromoanilines, iodoanilines, nitroanilines, and dinitrobenzenes) than those on the SUPELCOWAX 10 column (Table S2, Supporting Infomation), which was also better than those on the DB-17 column for isomeric chloroanilines, bromoanilines, and iodoanilines. Moreover, although the N2 linear velocities were the similar, the analysis times of the five isomeric analytes on the CNMS-coated column were distinctly shorter than those on the two commercial columns. PAHs are a group of persistent organic pollutants that can form during the incomplete combustion of fossil fuels, garbage, and other organic substances such as tobacco and charbroiled meat.62,63 Monitoring D



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Figure 5. GC chromatograms on the CNMS-coated open tubular column (15 m long × 0.25 mm i.d.) for the separation of (a) o-, m-, and p-chloroaniline at a N2 flow rate of 11.9 cm s−1 under 145 °C; (b) o-, m-, and p-bromoaniline at a N2 flow rate of 13.9 cm s−1 under 155 °C; (c) o-, m-, and p-iodoaniline at a N2 flow rate of 16.6 cm s−1 under 150 °C; (d) o-, m-, and p- nitroaniline at a N2 flow rate of 13.9 cm s−1 under 170 °C; (e) o-, m-, and p-dinitrobenzene at a N2 flow rate of 14.0 cm s−1 under 193 °C; (f) 1-naphthol and 2-naphthol at a N2 flow rate of 14.0 cm s−1 under 150 °C; (g) isopropylbenzene, n-propylbenzene, and 1,3,5-trimethylbenzene at a N2 flow rate of 14.1 cm s−1 under 80 °C; (h) α-, β-ionone isomers at a N2 flow rate of 14.0 cm s−1 under 170 °C; (i) PAHs (first peak, solvent toluene; 1, naphthalene; 2, biphenyl; 3, acenaphthene; 4, fluorene; 5, phenanthrene; 6, fluoranthene; 7, pyrene, 8, chrysene; 9, benzo[a]pyrene) at a N2 flow rate of 14.5 cm s−1 using a temperature program (160 °C for 1 min, then 60 °C min−1 to 350 °C).

GC. However, we did not test the separation performance at higher temperatures because the polyimide coating on the silica capillary would have decomposed above 300 °C. The most important advantage of this stationary phase is its enantioselectivity and resolving ability. The following ten

and detection of PAHs is very important because of they are highly carcinogenic at relatively low levels. We chose a mixture of nine PAHs and set a maximum separation temperature of 350 °C. The chromatogram obtained is shown in Figure 5i. The resolution indicates that CNMS has potential application in high-temperature E



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Figure 6. GC chromatograms on the CNMS-coated open tubular column (15 m long × 0.25 mm i.d.) for the separation of racemates. (a) 1-Phenylethanol derivative at 160 °C under a N2 linear velocity of 16.6 cm s−1; (b) citronellal at 150 °C under a N2 linear velocity of 16.5 cm s−1; (c) 2-amino-1-butanol derivative at 165 °C under a N2 linear velocity of 16.5 cm s−1; (d) menthol at 95 °C under a N2 linear velocity of 12.0 cm s−1; (e) methionine derivative at 160 °C under a N2 linear velocity of 13.9 cm s−1; (f) tryptophan derivative at 155 °C under a N2 linear velocity of 11.9 cm s−1; (g) glutamic acid derivative at 150 °C under a N2 linear velocity of 13.9 cm s−1; (h) isoleucine derivative at 150 °C under a N2 linear velocity of 11.9 cm s−1; (i) valine derivative at 130 °C under a N2 linear velocity of 13.9 cm s−1; (j) serine derivative at 140 °C under a N2 linear velocity of 12.2 cm s−1.

separations of 2-amino-1-butanol, isoleucine, and serine were not as good as those on the CNMS-coated column. Moreover, citronellal, methionine, tryptophan, glutamic acid, and valine could not be separated on the β-DEX 120 column but could be separated on the CNMS-coated column. The Chirasil-L-Val column proved to be very effective for the separation of amino acid derivatives. The resolution (Rs) values of methionine, glutamic acid, isoleucine, valine, and serine were higher on the Chirasil-L-Val column than on the CNMS-coated column. However, 1-phenylethanol, citronellal, and menthol were not separated on the Chirasil-L-Val column but could be separated

racemates were separated on the column: 1-phenylethanol, citronellal, 2-amino-1-butanol, menthol, methionine, tryptophan, glutamic acid, isoleucine, valine, and serine. The separation factors (α) and resolutions (Rs) are given in Table 3. The chromatograms are shown in Figure 6. All enantiomer pairs have reached baseline separation, except 1-phenylethanol and citronellal. Comparing the chiral recognition ability of the CNMS-coated column with those of commercial β-DEX 120 and Chirasil-L-Val columns, some advantages are evident. The β-DEX 120 column showed superior recognition ability for the separation of 1-phenylethanol and menthol; however, the F



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Figure 7. Reproducible chromatograms on the CNMS-coated open tubular column (15 m long × 0.25 mm i.d.) for the separation of (a) o-, m-, and p-chloroaniline at a N2 flow rate of 11.9 cm s−1 under 145 °C; (b) methionine derivative at 160 °C under a N2 linear velocity of 13.9 cm s−1. (1) Chromatogram obtained before the column was used for the separations by rapid temperature programming. (2, 3) Chromatograms obtained after the column had been subjected to more than 100 injections by rapid temperature programming.

clear that the chiral nanoporous structure exists in CNMS. Further studies on these aspects will be reported in due course. The column also showed good stability and reproducibility for the separations after more than 100 injections by rapid temperature programming (at 60 °C min−1). Figure 7 shows the reproducible chromatograms of chloroaniline isomers and methionine derivative separated before and after repeated use by rapid temperature programming. No significant changes in retention time, selectivity, or recognition ability were observed, thus indicating that the stationary phase is extremely stable and not damaged by thermal shock.

on the CNMS-coated column, and the separation of 2-amino-1butanol and tryptophan were not as good as those on the CNMS-coated column. Notably, separation factors (α) were higher on the CNMS-coated column than on both the β-DEX 120 and Chirasil-L-Val commercial columns. The chromatographic data are presented in Table 3. The experimental results demonstrate that the novel stationary phase of CNMS has excellent chiral recognition ability in GC. The Brunauer−Emmett−Teller (BET) surface area and pore volume of CNMS were determined as 571 m2 g−1 and 0.56 cm3 g−1 (Figure S2a, Supporting Information), respectively. The calculated BJH pore diameter is about 5.1 nm (Figure S2b, Supporting Information). The large pore size of CNMS allows easy access of analytes. Cellulose is a leading material for chiral separation, which has a one-handed helical conformation, and the glucose units are regularly arranged along the helical axis. A chiral helical groove runs to the main chain and will be imprinted in the pores of CNMS. CNMS possesses numerous chiral nanoporous and left-handed chiral nematic structures imprinted by cellulose at multiple levels.40,49,64 In Figure 6, all L- or (+)isomers were first eluted. The discrimination of enantiomers in the presence of the CNMS-based chiral stationary phase depends on the one-handed helical porous structure of CNMS, in which the chiral steric fit between the nanoporous structure and conformation of the solute molecule is the main interactive force. The cellulose chiral groove always plays a major role in chiral recognition because enantiomers interact differently with the framework in view of the difference in the structures and shapes of these molecules.65,66 Because the chiral nematic organization and high surface area of nanocrystalline cellulose is accurately replicated in the inorganic solid, the long-range chiral nematic ordering phase properties of CNMS is also important for efficient recognition of isomers and enantiomers.65 In addition, the dispersion forces, hydrogen bonding, dipole−dipole interactions, and van der Waals forces may also play some role in the chiral recognition. Unfortunately, it is difficult to obtain the size of the chiral groove because CNMS does not possess a single-crystal structure measured by the single-crystal X-ray diffraction method. The influence of the chiral microenvironment on the chiral properties of chromatographic systems is far from being understood, although it is

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CONCLUSIONS In summary, we have reported the first example of the utilization of CNMS as a stationary phase for high-resolution GC. The fabricated CNMS-coated capillary column not only showed excellent recognition ability for the separation of linear alkanes, aromatic hydrocarbons, PAHs, and isomers but also for the resolution of racemates. The results show that CNMS is very attractive for exploration as a novel stationary phase in GC. Further research is focusing on the potential applications of CNMS in high-temperature GC.

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ASSOCIATED CONTENT

S 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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AUTHOR INFORMATION

Corresponding Author

*L.-M. Yuan. E-mail: [email protected]. Fax: 86-87165941088. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Nature Science Foundation of China (No. 21275126, No. 21127012). REFERENCES

(1) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992, 359, 710−712.

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(38) Yang, H.; Coombs, N.; Sokolov, I.; Ozin, G. A. Nature 1996, 381, 589−592. (39) Habibi, Y.; Lucia, L. A.; Rojas, O. J. Chem. Rev. 2010, 110, 3479−3500. (40) Shopsowitz, K. E.; Qi, H.; Hamad, W. Y.; MacLachlan, M. J. Nature 2010, 468, 422−425. (41) Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. Angew. Chem., Int. Ed. 2011, 50, 10991−10995. (42) Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. J. Am. Chem. Soc. 2012, 134, 867−870. (43) Kelly, J. A.; Shopsowitz, K. E.; Ahn, J. M.; Hamad, W. Y.; MacLachlan, M. J. Langmuir 2012, 28, 17256−17262. (44) Kelly, J. A.; Yu, M.; Hamad, W. Y.; MacLachlan, M. J. Adv. Opt. Mater. 2013, 1, 295−299. (45) Kelly, J. A.; Shukaliak, A. M.; Cheung, C. C. Y.; Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. Angew. Chem., Int. Ed. 2013, 52, 8912−8916. (46) Khan, M. K.; Giese, M.; Yu, M.; Kelly, J. A.; Ham, W. Y.; MacLachlan, M. J. Angew. Chem., Int. Ed. 2013, 52, 8921−8924. (47) Qi, H.; Roy, X.; Shopsowitz, K. E.; Hui, J. K. H.; MacLachlan, M. J. Angew. Chem., Int. Ed. 2010, 49, 9740−9743. (48) Shopsowitz, K. E.; Stahl, A.; Hamad, W. Y.; MacLachlan, M. J. Angew. Chem., Int. Ed. 2012, 51, 6886−6890. (49) Qi, H.; Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. J. Am. Chem. Soc. 2011, 133, 3728−3731. (50) Nguyen, T.-D.; Hamadb, W. Y.; MacLachlan, M. J. Chem. Commun. 2013, 49, 11296−11298. (51) Shopsowitz, K. E.; Kelly, J. A.; Hamad, W. Y.; MacLachlan, M. J. Adv. Funct. Mater. 2014, 24, 327−338. (52) Khan, M. K.; Hamad, W. Y.; MacLachlan, M. J. Adv. Mater. 2014, 26, 2323−2328. (53) Nguyen, T.-D.; Hamad, W. Y.; MacLachlan, M. J. Adv. Funct. Mater. 2014, 24, 777−783. (54) Thomas, A.; Antonietti, M. Adv. Funct. Mater. 2003, 13, 763− 766. (55) Dujardin, E.; Blaseby, M.; Mann, S. J. Mater. Chem. 2003, 13, 696−699. (56) Kelly, J. A.; Giese, M.; Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. Acc. Chem. Res. 2014, 47, 1088−1096. (57) Gu, Z.-Y.; Yan, X.-P. Angew. Chem., Int. Ed. 2010, 49, 1477− 1480. (58) Chang, N.; Gu, Z.-Y.; Yan, X.-P. J. Am. Chem. Soc. 2010, 132, 13645−13647. (59) Xie, S.-M.; Zhang, Z.-J.; Wang, Z.-Y.; Yuan, L.-M. J. Am. Chem. Soc. 2011, 133, 11892−11895. (60) McReynolds, W. O. J. Chromatogr. Sci. 1970, 8, 685−691. (61) Berthod, A.; Zhou, E. Y.; Le, K.; Armstrong, D. W. Anal. Chem. 1995, 67, 849−857. (62) Wenzl, T.; Simon, R.; Kleiner, J.; Anklam, E. Trends Anal. Chem. 2006, 25, 716−725. (63) Keyte, I. J.; Harrisonz, R. M.; Lammel, G. Chem. Soc. Rev. 2013, 42, 9333−9391. (64) Asefa, T. Angew. Chem., Int. Ed. 2012, 51, 2008−2010. (65) Okamoto, Y.; Yashima, E. Angew. Chem., Int. Ed. 1998, 37, 1021−1043. (66) Ikai, T.; Okamoto, Y. Chem. Rev. 2009, 109, 6077−6101.

(2) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T-W.; Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834−10843. (3) Corma, A. Chem. Rev. 1997, 97, 2373−2419. (4) Taguchi, A.; Schuth, F. Microporous Mesoporous Mater. 2005, 77, 1−45. (5) Sharma, K. K.; Asefa, T. Angew. Chem., Int. Ed. 2007, 46, 2879− 2882. (6) Ivanova, I. I.; Knyazeva, E. E. Chem. Soc. Rev. 2013, 42, 3671− 3688. (7) Wu, Z. X.; Zhao, D. Y. Chem. Commun. 2011, 47, 3332−3338. (8) Hartmann, M. Chem. Mater. 2005, 17, 4577−4593. (9) Coasne, B.; Galarneau, A.; Pellenq, R. J. M.; Renzo, F. D. Chem. Soc. Rev. 2013, 42, 4141−4171. (10) Karger, J.; Valiullin, R. Chem. Soc. Rev. 2013, 42, 4172−4197. (11) Grün, M.; Kurganov, A. A.; Schacht, S.; Schüth, F.; Unger, K. K. J. Chromatogr. A 1996, 740, 1−9. (12) Wagner, T.; Haffer, S.; Weinberger, C.; Klaus, D.; Tiemann, M. Chem. Soc. Rev. 2013, 42, 4036−4053. (13) Lai, C. Y.; Trewyn, B. G.; Jeftinija, D. M.; Jeftinija, K.; Xu, S.; Jeftinija, S.; Lin, V. S. Y. J. Am. Chem. Soc. 2003, 125, 4451−4459. (14) Vallet-Regi, M.; Balas, F.; Arcos, D. Angew. Chem., Int. Ed. 2007, 46, 7548−7558. (15) Yang, P.; Gai, S.; Lin, J. Chem. Soc. Rev. 2012, 41, 3679−3698. (16) Rebbin, V.; Schmidt, R.; Fröba, M. Angew. Chem., Int. Ed. 2006, 45, 5210−5214. (17) Salesch, T.; Bachmann, S.; Brugger, S.; Rabelo-Schaefer, R.; Albert, K.; Steinbrecher, S.; Plies, E.; Mehdi, A.; Reyé, C.; Corriu, R. J. P.; Lindner, E. Adv. Funct. Mater. 2002, 12, 134−142. (18) Gallis, K. W.; Araujo, J. T.; Duff, K. J.; Moore, J. G.; Landry, C. C. Adv. Mater. 1999, 11, 1452−1455. (19) Boissière, C.; Kümmel, M.; Persin, M.; Larbot, A.; Prouzet, E. Adv. Funct. Mater. 2001, 11, 129−135. (20) Martin, T.; Galarneau, A.; Renzo, F. D.; Brunel, D.; Fajula, F.; Heinisch, S.; Crétier, G.; Rocca, J.-L. Chem. Mater. 2004, 16, 1725− 1731. (21) Zhao, J. W.; Gao, F.; Fu, Y. L.; Jin, W.; Yang, P. Y.; Zhao, D. Y. Chem. Commun. 2002, 752−753. (22) Yang, P.; Zhao, D.; Margolese, D. I.; Chmelka, B. F.; Stucky, G. D. Nature 1998, 396, 152−155. (23) Wan, Y.; Zhao, D. Chem. Rev. 2007, 107, 2821−2860. (24) Kresge, C. T.; Roth, W. J. Chem. Soc. Rev. 2013, 42, 3663−3670. (25) Wu, S. H.; Moua, C. Y.; Lin, H. P. Chem. Soc. Rev. 2013, 42, 3862−3875. (26) Han, L.; Che, S. Chem. Soc. Rev. 2013, 42, 3740−3752. (27) Deng, Y.; Wei, J.; Sun, Z.; Zhao, D. Chem. Soc. Rev. 2013, 42, 4054−4070. (28) Gabashvili, A.; Medina, D. D.; Gedanken, A.; Mastai, Y. J. Phys. Chem. B 2007, 111, 11105−11110. (29) Johnson, B. F. G.; Raynor, S. A.; Shephard, D. S.; Mashmeyer, T.; Mashmeyer, T.; Thomas, J. M.; Sankar, G.; Bromley, S.; Oldroyd, R.; Gladden, L.; Mantle, M. D. Chem. Commun. 1999, 1167−1168. (30) Fireman-Shoresh, S.; Popov, I.; Avnir, D.; Marx, S. J. Am. Chem. Soc. 2005, 127, 2650−2655. (31) Che, S.; Liu, Z.; Ohsuna, T.; Sakamoto, K.; Tersarki, O.; Tatsumi, T. Nature 2004, 429, 281−284. (32) Qiu, H. B.; Che, S. Chem. Soc. Rev. 2011, 40, 1259−1268. (33) Revol, J. F.; Bradford, H.; Giasson, J.; Marchessault, R. H.; Gray, D. G. Int. J. Biol. Macromol. 1992, 14, 170−172. (34) Revol, J. F.; Godbout, L.; Dong, X. M.; Gray, D. G.; Chanzy, H.; Maret, G. Liq. Cryst. 1994, 16, 127−134. (35) Klemm, D.; Kramer, F.; Moritz, S.; Lindstrom, T.; Ankerfors, M.; Gray, D. G.; Dorris, A. Angew. Chem., Int. Ed. 2011, 50, 5438− 5466. (36) Attard, G. S.; Glyde, J. C.; Göltner, C. G. Nature 1995, 378, 366−368. (37) Göltner, C. G.; Antonietti, M. Adv. Mater. 1997, 9, 431−436. H


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