To firmly immobilize enzyme on carrier surface without covalent attachment as well as improve enzyme stability, an effective method of enzyme immobilization was developed by encapsulating enzyme into nano-molecular cages on the surface of magnetic microspheres. Compared with physical adsorption, molecular cage encapsulation could fix lipase much more firmly and make lipase more active. Then, this study focused on investigating the effects of cage hydrophobicity and cage size on lipase encapsulation respectively by adjusting the log P value (from −0.85 to 1.28) and chain length (from 2.93 to 5.41 nm) of crosslinkers. It showed that lipase activity was dependent on the hydrophobicity of cage. Moreover, the size of cage had important effect on lipase loading amount, and a big cage was conducive to house lipase molecule. The structural analysis indicated that molecular cages could retain the active conformation of lipase and increase its structural rigidity. Molecular dynamics simulation revealed the interaction between the lid domain of lipase and molecular cage, leading to the higher activity of encapsulated lipase (63.6 U/mg) than that of free lipase (50.6 U/mg). Besides, the encapsulated lipase showed more than twice higher thermal stability and almost 8 times higher tolerance to denaturant than the adsorbed lipase.
In this work, ZIF-300 and ZIF-301 derivatives with tunable ellipsoidal cage sizes were synthesized by adjusting the ratio between the small-sized mIm and large-sized bbIm/cbIm ligands. During ZIFs synthesis, when the amount of the fixed ligand is equimolar to Zn²⁺, adjusting the content of the other ligand does not yield a continuously tunable structure. In contrast, maintaining an excess of one ligand relative to Zn²⁺ and varying the content of the other ligand enables the formation of ZIF derivatives with continuously tunable chemical compositions and ellipsoidal cage sizes. This tunability is likely due to the increased concentration of the fixed ligand, which enhances its competitive coordination ability within the ZIF framework. Consequently, ZIF-300 and ZIF-301 derivatives with adjustable long-axis cage sizes ranging from 6.5 Å to 9.6 Å were successfully prepared. Notably, the small cage-sized ZIF-300-S1 (6.5 × 6.1 Å2) and ZIF-301-S1 (6.5 × 6.6 Å2) exhibited exceptional molecular length separation of acetone (6.4 × 5.8 Å2) and butanol (8.4 × 5.5 Å2). Liquid-phase adsorption and breakthrough experiments confirmed their separation performance, and GCMC simulations provided further insights into the separation mechanism.
Zixing Guo,Wenji Zheng,Xiaoming Yan,Yan Dai,Xuehua Ruan,Xiaochen Yang,Xiangcun Li,Ning Zhang,Gaohong He
Cage-type MOFs based Mixed-matrix membranes (MMMs) hardly exhibit screening effect of gas molecules due to the flexible aperture. Regulation of nanocages of MOFs by Ionic Liquid (IL) has been proved to be effective. Therefore, in this work, an IL adsorption/infiltration two-step strategy is proposed to confine IL into the nanocages of MOFs, achieving fine tuning of effective cage size for screening gas pair with similar size. [Bmim][PF 6 ] are first adsorbed on the outer-surface of ZIF-8, then through heat treatment, the aperture of ZIF-8 is dilated, and the bigger [Bmim][PF 6 ] molecules infiltrate through the dilated aperture into the nanocage driven by thermodynamics and differential concentration. When the temperature is down to room temperature, the aperture is narrowed to 3.4 Å, thus [Bmim][PF6] are confined into nanocages, which are confirmed by PXRD , TGA and FT-IR characteristics. By controlling IL content in the cage, the effective cage size of ZIF-8 is tuned to specific slope among dynamic diameters of CO 2 over N 2 , which is perfectly reflected in the CO 2 /N 2 separation. Compared with ZIF-8/Pebax MMMs, the IL@ZIF-8/Pebax MMMs exhibit improved CO 2 /N 2 selectivity but decreased CO 2 permeability, demonstrating effectiveness of cage size adjustment. Furthermore, with the IL molecules inside ZIF-8 cage increasing, the CO 2 /N 2 selectivity of the MMMs continues to rise, indicating cage size screening effect of ZIF-8 by IL infiltration . Especially, the IL 8 @ZIF-8/Pebax MMMs exhibit the best gas separation performances with CO 2 permeability of 117 Barrer and CO 2 /N 2 selectivity of 84.5, beyond the 2008 Robinson upper bound. The proposed strategy provides an effective but facile way to confine IL into the cages of MOFs to precisely screen gas pairs with similar size and can be easily expanded to other IL and MOFs system.
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