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Structural, energetic, and dynamic insights into the abnormal xylene separation behavior of hierarchical porous crystal.

Lin JM, He CT, Liao PQ, Lin RB, Zhang JP - Sci Rep (2015)

Bottom Line: Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked.Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms.More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

View Article: PubMed Central - PubMed

Affiliation: MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P.R. China.

ABSTRACT
Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked. Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms. More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

No MeSH data available.


Related in: MedlinePlus

Chromatograms of GC separation of structural isomers of disubsituted benzene derivatives.a. Separation of xylene isomers (1.2 μg each isomer) using a temperature program of 180 to 200 °C with a rate of 5 °C min−1, under a N2 flow rate of 14 mL min−1. b. Separation of ethyltoluene isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1. c. Separation of chlorotoluene isomers (4 μg each isomer) at 215 °C under a N2 flow rate of 14 mL min−1. d. Separation of methylanisole isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1.
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f2: Chromatograms of GC separation of structural isomers of disubsituted benzene derivatives.a. Separation of xylene isomers (1.2 μg each isomer) using a temperature program of 180 to 200 °C with a rate of 5 °C min−1, under a N2 flow rate of 14 mL min−1. b. Separation of ethyltoluene isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1. c. Separation of chlorotoluene isomers (4 μg each isomer) at 215 °C under a N2 flow rate of 14 mL min−1. d. Separation of methylanisole isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1.

Mentions: Considering the hierarchical pore structure and good thermal stability, 1 may be suitable as a stationary material for gas chromatography (GC) separation of highly similar molecules such as isomers of xylene and similar disubstituted benzene derivatives. A capillary column with microcrystalline 1 coated on its inner surface was fabricated by a dynamic coating method (Figure S7)8. As shown in Fig. 2a and Table S2, the three xylene isomers are well separated from each other with good precision for retention time, half peak width, and peak area. It is noteworthy that the column can efficiently separate mX and pX with large resolutions of 1.54–1.65 (Figure S8), which are higher than for similar materials such as MIL-101 (0.9–1.0)8. More interestingly, the GC elution times follow oX < mX < pX, an order that has not been reported for other materials. For common stationary phases84950, the elution times usually follow pX < mX < oX, being the same as the orders of their boiling points and polarities (dipole moment and polarizability, 0 D and 13.7 cm3 for pX, 0.36 D and 14.2 cm3 for mX, and 0.44 D and 14.9 cm3 for oX, respectively). Comparison of the molecular sizes (Figure S9) and the observed retention times shows that 1 tends to retain the smaller molecules, which is similar to that of molecular sieving effect. However, molecular sieves can only divide the mixture into two groups (smaller/larger than the aperture size), indicating that there should be a distinctive separation mechanism for 1.


Structural, energetic, and dynamic insights into the abnormal xylene separation behavior of hierarchical porous crystal.

Lin JM, He CT, Liao PQ, Lin RB, Zhang JP - Sci Rep (2015)

Chromatograms of GC separation of structural isomers of disubsituted benzene derivatives.a. Separation of xylene isomers (1.2 μg each isomer) using a temperature program of 180 to 200 °C with a rate of 5 °C min−1, under a N2 flow rate of 14 mL min−1. b. Separation of ethyltoluene isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1. c. Separation of chlorotoluene isomers (4 μg each isomer) at 215 °C under a N2 flow rate of 14 mL min−1. d. Separation of methylanisole isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4481377&req=5

f2: Chromatograms of GC separation of structural isomers of disubsituted benzene derivatives.a. Separation of xylene isomers (1.2 μg each isomer) using a temperature program of 180 to 200 °C with a rate of 5 °C min−1, under a N2 flow rate of 14 mL min−1. b. Separation of ethyltoluene isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1. c. Separation of chlorotoluene isomers (4 μg each isomer) at 215 °C under a N2 flow rate of 14 mL min−1. d. Separation of methylanisole isomers (2 μg each isomer) at 230 °C under a N2 flow rate of 14 mL min−1.
Mentions: Considering the hierarchical pore structure and good thermal stability, 1 may be suitable as a stationary material for gas chromatography (GC) separation of highly similar molecules such as isomers of xylene and similar disubstituted benzene derivatives. A capillary column with microcrystalline 1 coated on its inner surface was fabricated by a dynamic coating method (Figure S7)8. As shown in Fig. 2a and Table S2, the three xylene isomers are well separated from each other with good precision for retention time, half peak width, and peak area. It is noteworthy that the column can efficiently separate mX and pX with large resolutions of 1.54–1.65 (Figure S8), which are higher than for similar materials such as MIL-101 (0.9–1.0)8. More interestingly, the GC elution times follow oX < mX < pX, an order that has not been reported for other materials. For common stationary phases84950, the elution times usually follow pX < mX < oX, being the same as the orders of their boiling points and polarities (dipole moment and polarizability, 0 D and 13.7 cm3 for pX, 0.36 D and 14.2 cm3 for mX, and 0.44 D and 14.9 cm3 for oX, respectively). Comparison of the molecular sizes (Figure S9) and the observed retention times shows that 1 tends to retain the smaller molecules, which is similar to that of molecular sieving effect. However, molecular sieves can only divide the mixture into two groups (smaller/larger than the aperture size), indicating that there should be a distinctive separation mechanism for 1.

Bottom Line: Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked.Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms.More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

View Article: PubMed Central - PubMed

Affiliation: MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P.R. China.

ABSTRACT
Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked. Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms. More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

No MeSH data available.


Related in: MedlinePlus