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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

Diffusion behaviors of xylene isomers in the hierarchical porous crystal.a–c. Moving trajectories (orange sticks, with the starting and ending points highlighted in green and red spheres) of xylene isomers in 1 within 450 ps. The host frameworks are shown in the stick mode in gray (hydrogen atoms are omitted for clarity) with the aperture passed by the guest highlighted in blue. d–f. The self-diffusion rates of xylene isomers in 1 (pristine), 1a (pX-blocked), and 1b (rigid).
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f4: Diffusion behaviors of xylene isomers in the hierarchical porous crystal.a–c. Moving trajectories (orange sticks, with the starting and ending points highlighted in green and red spheres) of xylene isomers in 1 within 450 ps. The host frameworks are shown in the stick mode in gray (hydrogen atoms are omitted for clarity) with the aperture passed by the guest highlighted in blue. d–f. The self-diffusion rates of xylene isomers in 1 (pristine), 1a (pX-blocked), and 1b (rigid).

Mentions: To visualize the overall adsorption and diffusion behaviors of the xylene isomers in the hierarchical pore system of 1, we carried out molecular dynamics (MD) simulations with the same temperature (453 K) for the GC experiments. As shown by the obtained guest moving trajectories (Fig. 4a–c), all three isomer molecules mainly hop around the entrance of the small aperture and travel fast along the large 1D channel, confirming that the small aperture is the primary adsorption site and the large 1D channel is the transportation path for the fast guest diffusion. Interestingly, the pX molecule can occasionally past through the small aperture and diffuse to the adjacent 1D channels. In contrast, oX and mX molecules only appear in the original 1D channel. These phenomena show that although pX and oX can both completely insert into the small aperture, only the one with the smallest cross-section area can easily pass through, which can be attributed to their very different steric hindrances and structure transformation energies of the host framework. It should be noted that, without the MD simulation, one cannot judge the difficulty for mX to pass through the small aperture, because the crystal structure and GCMC/PDFT simulation cannot capture the high-energy transient states.


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)

Diffusion behaviors of xylene isomers in the hierarchical porous crystal.a–c. Moving trajectories (orange sticks, with the starting and ending points highlighted in green and red spheres) of xylene isomers in 1 within 450 ps. The host frameworks are shown in the stick mode in gray (hydrogen atoms are omitted for clarity) with the aperture passed by the guest highlighted in blue. d–f. The self-diffusion rates of xylene isomers in 1 (pristine), 1a (pX-blocked), and 1b (rigid).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Diffusion behaviors of xylene isomers in the hierarchical porous crystal.a–c. Moving trajectories (orange sticks, with the starting and ending points highlighted in green and red spheres) of xylene isomers in 1 within 450 ps. The host frameworks are shown in the stick mode in gray (hydrogen atoms are omitted for clarity) with the aperture passed by the guest highlighted in blue. d–f. The self-diffusion rates of xylene isomers in 1 (pristine), 1a (pX-blocked), and 1b (rigid).
Mentions: To visualize the overall adsorption and diffusion behaviors of the xylene isomers in the hierarchical pore system of 1, we carried out molecular dynamics (MD) simulations with the same temperature (453 K) for the GC experiments. As shown by the obtained guest moving trajectories (Fig. 4a–c), all three isomer molecules mainly hop around the entrance of the small aperture and travel fast along the large 1D channel, confirming that the small aperture is the primary adsorption site and the large 1D channel is the transportation path for the fast guest diffusion. Interestingly, the pX molecule can occasionally past through the small aperture and diffuse to the adjacent 1D channels. In contrast, oX and mX molecules only appear in the original 1D channel. These phenomena show that although pX and oX can both completely insert into the small aperture, only the one with the smallest cross-section area can easily pass through, which can be attributed to their very different steric hindrances and structure transformation energies of the host framework. It should be noted that, without the MD simulation, one cannot judge the difficulty for mX to pass through the small aperture, because the crystal structure and GCMC/PDFT simulation cannot capture the high-energy transient states.

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